Paint Masking Tape

Abstract

To provide a coating masking tape having a high adhesive force, secured in adhesiveness even in high-temperature heating, and causing less contamination by the residue of an adhesive after high-temperature heating.SOLUTION: A coating masking tape has an adhesive layer and a resin substrate. The coating masking tape is such that: the adhesive layer is formed from an adhesive composition containing an acrylic copolymer, a non-block type crosslinking agent, and a block type isocyanate crosslinking agent; and the acrylic copolymer is obtained by copolymerizing a monomer mixture which contains (A)-(B) as follows: (A) 100 pts.mass of an alkyl (meth) acrylate; and (B) 0.1-15 pts.mass of a carboxyl group-containing vinyl monomer of a carboxylic acid anhydride group-containing vinyl monomer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a paint masking tape. [Background technology]

[0002] Paint masking tape is generally used to mask areas (masking areas) on a substrate that should not be painted during painting. Masking tape is usually composed of a tape base material, an adhesive layer, and a release liner, and when used, the release liner is peeled off and the adhesive strength of the exposed adhesive layer is used to attach the masking area of ​​the substrate (substrate). After painting, the paint masking tape is peeled off from the substrate and discarded.

[0003] During painting, drying at about 150 to 200°C is performed to harden the coating. Therefore, the paint masking tape is exposed to high temperatures. When exposed to such high temperatures, the cohesive strength of the adhesive used in the adhesive layer is reduced, and as a result, when the paint masking tape is peeled off from the masked object, there is a problem of adhesive residue, in which a trace of the paint masking tape remains on the masked object.

[0004] Silicone adhesives are known as adhesives that leave relatively little adhesive residue (see, for example, Patent Documents 1 and 2). However, when a paint masking tape having a silicone adhesive layer is used, outgassing derived from siloxane can occur, and this outgassing can cause painting defects in painted areas.

[0005] As an adhesive other than a silicone adhesive, an acrylic emulsion type adhesive containing a cyclic compound having a double bond in the ring is used in Patent Document 3. Patent Document 3 states that such a composition can prevent the adhesive layer from leaving adhesive residue even when exposed to a high temperature environment (190°C in the embodiment). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 47-22936 [Patent Document 2] JP 2014-148646 A [Patent Document 3] JP 2010-163484 A Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, after the paint masking tape is applied to the object to be masked, it is transported on the production line and moved to the painting process. During movement on the production line or during painting, it is necessary to ensure that the paint masking tape adheres to the object to be masked so that the paint masking tape does not peel off. As described above, during painting, the masking tape is exposed to high temperatures of 150 to 200°C. Therefore, it is important that the paint masking tape maintains a certain level of adhesion from application until removal.

[0008] Therefore, an object of the present invention is to provide a paint masking tape that has high adhesive strength, maintains its adhesiveness even when heated at high temperatures, and is less susceptible to contamination by adhesive residue after high-temperature heating. [Means for solving the problem]

[0009] The present invention is a paint masking tape having a pressure-sensitive adhesive layer and a resin substrate, wherein the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer, a non-blocked crosslinking agent, and a blocked isocyanate crosslinking agent, and the acrylic copolymer is obtained by copolymerizing a monomer mixture containing the following (A) to (B): (A) 100 parts by mass of an alkyl (meth)acrylate; and (B) 0.1 to 15 parts by mass of a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer. Effect of the Invention

[0010] The paint masking tape of the present invention has high adhesive strength, and its adhesion to the object to be masked is guaranteed even when heated to high temperatures. Furthermore, even if the paint masking tape is peeled off after being exposed to high temperatures during painting, there is little contamination of the masked object due to adhesive residue. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing one embodiment of a paint masking tape. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] This embodiment will be described in detail below.

[0013] In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and physical properties are measured under the conditions of room temperature (20 to 25°C) and relative humidity of 45 to 55% RH. In this specification, "(meth)acrylate" refers to "acrylate or methacrylate," and "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid."

[0014] A first embodiment of the present invention is a paint masking tape having a pressure-sensitive adhesive layer and a resin substrate (also simply referred to as substrate), in which the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer, a non-blocked crosslinking agent, and a blocked isocyanate crosslinking agent, and the acrylic copolymer is obtained by copolymerizing a monomer mixture containing the following (A) to (B): (A) 100 parts by mass of an alkyl (meth)acrylate; and (B) 0.1 to 15 parts by mass of a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer.

[0015] The paint masking tape of the first embodiment has high adhesive strength, and its adhesion to the object to be masked is guaranteed even when heated to high temperatures. Furthermore, even if the paint masking tape is peeled off after being exposed to high temperatures during painting, there is little contamination of the masked object due to residual adhesive.

[0016] The paint masking tape of the first embodiment is characterized in that two types of crosslinking agents are added to an acrylic copolymer formed from a monomer mixture containing 100 parts by mass of alkyl (meth)acrylate; and (B) 0.1 to 15 parts by mass of a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer. First, under normal conditions, the non-blocked crosslinking agent exerts adhesiveness by forming a crosslink with the acrylic copolymer. However, when an adhesive having such a composition is exposed to a high temperature of about 200°C, the adhesive becomes soft, and as a result, when the paint masking tape is peeled off after heating, a large amount of adhesive residue remains on the masked object (see Comparative Example 1 described later). The present inventors thought that if the adhesive is prevented from softening when heated, the amount of adhesive residue when peeled off can be reduced, and they found the use of a blocked isocyanate crosslinking agent that exerts crosslinking ability when heated, and completed the present invention. The blocked isocyanate crosslinking agent exerts its crosslinking ability by heating during drying of the coating film, crosslinking the crosslinkable groups in the acrylic copolymer and hardening the adhesive. Therefore, even after high-temperature drying, adhesive residue is reduced and removability is improved.

[0017] Fig. 1 is a schematic cross-sectional view showing one embodiment of a paint masking tape. In Fig. 1, the paint masking tape 10 is composed of a resin substrate 11, an adhesive layer 12, and a release liner 13. The resin substrate 11 is disposed adjacent to the adhesive layer 12. When applying, the release liner 13 is removed from the paint masking tape 10, and the paint masking tape is applied to the object to be masked by the exposed adhesive layer 12.

[0018] 1 shows a laminate having a resin substrate, an adhesive layer, and a release liner in that order, but other intermediate layers may be present on the resin substrate and / or between the resin substrate and the adhesive layer as long as the adhesive layer is exposed when applied to an object to be masked. However, from the viewpoint of processability, it is preferable that the thickness of the paint masking tape is thin, and the paint masking tape is preferably composed of a resin substrate and an adhesive layer (and optionally a release liner).

[0019] The concept of tape includes what are called films, labels, sheets, and the like.

[0020] The adhesive strength of the paint masking tape is preferably 1N / 25mm or more, more preferably 3N / 25mm or more, even more preferably 5N / 25mm or more, even more preferably 8N / 25mm or more, and particularly preferably 10N / 25mm or more. In large-scale production lines, a pre-treatment process may be performed between the application of the paint masking tape and the transfer to the painting line, and the paint masking tape must remain applied until painting is completed and the worker peels it off. It is preferable for the adhesive strength of the paint masking tape to be equal to or greater than the above lower limit, since the paint masking tape is less likely to peel off until after the painting process.

[0021] Considering removability, the adhesive strength of the paint masking tape is preferably 20 N / 25 mm or less, and more preferably 15 N / 25 mm or less. The adhesive strength is measured by the method described in the following examples.

[0022] The adhesive strength can be controlled, for example, by the type and composition of monomers in the acrylic copolymer that constitutes the adhesive composition used to form the adhesive layer, and the type and amount of crosslinking agent in the adhesive composition.

[0023] The adhesive strength of the paint masking tape after heating at 200°C for 20 minutes and cooling (hereinafter also referred to as post-heating adhesive strength) is preferably 25N / 25mm or less, more preferably 10N / 25mm or less. Heating at 200°C is a temperature range far exceeding the Tg of the acrylic adhesive, and the adhesive is in a very soft state. This may result in higher adhesive strength to the masked object than before heating, and significant adhesive residue may be left after peeling the paint masking tape from the masked object. By having the post-heating adhesive strength be equal to or less than the above upper limit, less adhesive residue will be left after peeling the paint masking tape from the masked object.

[0024] The adhesive strength of the paint masking tape after heating is preferably 1 N / 25 mm or more, more preferably 2 N / 25 mm or more, and even more preferably 3 N / 25 mm or more. By having the adhesive strength after heating be equal to or greater than the above lower limit, the adhesiveness of the paint masking tape to the object to be masked after heating is ensured.

[0025] In a preferred embodiment, the paint masking tape has an adhesive strength after heating of 1 to 25 N / 25 mm.

[0026] The post-heating adhesive strength is a value measured by the method described in the Examples below. Furthermore, if the paint masking tape is not immediately after production, the paint masking tape can be left to stand for one day under standard conditions (23°C, 50% RH), the release liner can be peeled off, the adhesive layer surface can be attached to a SUS plate, heated at 200°C for 20 minutes, and then left to cool under standard conditions (23°C, 50% RH) for 24 hours, and the post-heating adhesive strength can be measured by the method described in the Examples below.

[0027] The adhesive strength after heating can be controlled, for example, by the type and composition of monomers in the acrylic copolymer constituting the adhesive composition used in forming the adhesive layer, the type of blocking agent, the amount of crosslinking agent in the adhesive composition, etc.

[0028] Each of the components constituting the paint masking tape will be described below.

[0029] <Adhesive layer> The pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition contains an acrylic copolymer, a non-blocked crosslinking agent, and a blocked isocyanate crosslinking agent.

[0030] (Acrylic copolymer) The acrylic copolymer is obtained by copolymerizing a monomer mixture containing (A) and (B): (A) 100 parts by mass of an alkyl (meth)acrylate; and (B) 0.1 to 15 parts by mass of a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer. Hereinafter, the carboxyl group-containing vinyl monomer or the carboxylic anhydride group-containing vinyl monomer will also be simply referred to as component (B).

[0031] The acrylic copolymer is formed by using alkyl (meth)acrylate as the main monomer component and, if necessary, a monomer copolymerizable with alkyl (meth)acrylate (copolymerizable monomer). Here, the main component refers to 50% by mass or more of the monomer, preferably 65% ​​by mass or more, and more preferably 85% by mass or more.

[0032] The alkyl group of the alkyl (meth)acrylate may be any of a linear, branched, or cyclic alkyl group. The alkyl group is preferably an alkyl group having 1 to 24 carbon atoms, and more preferably an alkyl group having 1 to 18 carbon atoms.

[0033] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more. Among them, as the alkyl (meth)acrylate, in consideration of adhesive residue after high-temperature drying, the alkyl group constituting the alkyl ester is preferably an alkyl (meth)acrylate having 1 to 4 carbon atoms, more preferably n-butyl (meth)acrylate, and even more preferably n-butyl acrylate (n-butyl acrylate).

[0034] In the present embodiment, in order to ensure the hardness of the adhesive and to improve the adhesiveness, a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer is used. Preferably, a carboxyl group-containing vinyl monomer is used.

[0035] The carboxyl group-containing vinyl monomer may be a compound having an ethylenic double bond and a carboxyl group in the same molecule.Specific examples of the carboxyl group-containing vinyl monomer include (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, myristoleic acid, palmitoleic acid, and oleic acid.Among them, from the viewpoint of adhesion, cohesive strength, and tack, the carboxyl group-containing vinyl monomer is preferably (meth)acrylic acid, and more preferably acrylic acid.

[0036] Examples of the vinyl monomer containing a carboxylic acid anhydride group include compounds having an ethylenic double bond and a carboxylic acid anhydride group in the same molecule. Specific examples of the vinyl monomer containing a carboxylic acid anhydride group include maleic anhydride and itaconic anhydride.

[0037] The carboxyl group-containing vinyl monomer or the carboxylic anhydride group-containing vinyl monomer may be used alone or in combination of two or more. A carboxyl group-containing monomer and a carboxylic anhydride group-containing vinyl monomer may be used in combination.

[0038] The content of component (B) in the monomer mixture is 0.1 to 15 parts by mass relative to 100 parts by mass of alkyl (meth)acrylate. If the content of component (B) is less than 0.1 parts by mass, crosslinking with the crosslinking agent does not proceed sufficiently, and appropriate cohesive strength is not obtained, so that removability is not expressed. If the content of component (B) exceeds 15 parts by mass, the crosslinking density increases, and the adhesive strength immediately after application becomes too low, so that peeling may occur. The content of component (B) in the monomer mixture is preferably 5 to 15 parts by mass relative to 100 parts by mass of alkyl (meth)acrylate.

[0039] The monomer mixture may also contain other copolymerizable monomers that are copolymerizable with alkyl (meth)acrylates. Examples of copolymerizable monomers that are copolymerizable with alkyl (meth)acrylates include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and hydroxyl group-containing monomers such as glycerin dimethacrylate; amide group-containing monomers such as acrylamide, methacrylamide, N-vinylpyrrolidone, and N,N-dimethylacrylamide; amino group-containing monomers such as aminoethyl (meth)acrylate and (meth)acryloylmorpholine; aromatic vinyl compounds such as styrene and substituted styrene; cyano group-containing monomers such as acrylonitrile; and vinyl esters such as vinyl acetate. These may be used alone or in combination of two or more.

[0040] When other copolymerizable monomers are used, the amount thereof is preferably 10 parts by mass or less (lower limit: 0 parts by mass), and more preferably 5 parts by mass or less, per 100 parts by mass of the alkyl (meth)acrylate.

[0041] The molecular weight of the acrylic copolymer is not particularly limited, but the weight average molecular weight (Mw) is preferably 400,000 to 2,000,000, and more preferably 450,000 to 1,500,000. In this specification, the weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC) as a standard polystyrene equivalent molecular weight. Specifically, the value measured under the following measurement conditions is used.

[0042] <Measurement conditions> GPC measuring device: Tosoh HLC-8220 GPC GPC columns (passed in the following order): Tosoh Corporation TSK guard column HXL-H TSK gel GMHXL (×2) TSK gel G2000HXL Measurement solvent: Tetrahydrofuran ·Measurement temperature: 40℃ The method for producing the acrylic copolymer is not particularly limited, and conventionally known methods such as solution polymerization, emulsion polymerization, suspension polymerization, reversed-phase suspension polymerization, thin film polymerization, and spray polymerization using a polymerization initiator can be used. In addition to the method of initiating polymerization using a polymerization initiator, a method of initiating polymerization by irradiation with radiation, electron beams, ultraviolet rays, etc. can also be adopted. Among them, the solution polymerization method using a polymerization initiator is preferred because it is easy to adjust the molecular weight and can reduce impurities. For example, the copolymer can be obtained by using a solvent, adding preferably 0.01 to 0.50 parts by mass of a polymerization initiator to a monomer mixture with respect to 100 parts by mass of the total amount of monomers, and reacting in a nitrogen atmosphere at a reaction temperature of, for example, 60 to 90° C. for 3 to 10 hours.

[0043] Here, the solvent used in the solution polymerization method is preferably an organic solvent having a boiling point of 80° C. or less, since the solvent can be removed at a low temperature and the boiling point is away from the preferred dissociation initiation temperature of the blocked isocyanate crosslinking agent.

[0044] Examples of organic solvents having a boiling point of 80° C. or less include hydrocarbon solvents such as n-hexane (67° C.), alcohol solvents such as methanol (65° C.), ester solvents such as methyl acetate (54° C.) and ethyl acetate (77° C.), ketone solvents such as acetone (56° C.), diethyl ether (35° C.), methylene chloride (40° C.), and tetrahydrofuran (66° C.). Among these, acetone and ethyl acetate are preferred from the viewpoint of versatility and safety, and ethyl acetate is particularly preferred. The numbers in parentheses following the names of the above organic solvents are boiling points.

[0045] (Non-blocking crosslinking agent) In this embodiment, the pressure-sensitive adhesive composition essentially contains a non-blocked crosslinking agent. The crosslinking agent forms a crosslinked structure with the acrylic acid in the acrylic copolymer. The formation of the crosslinked structure allows the pressure-sensitive adhesive to exhibit high adhesion before heating (before the blocking agent of the blocked isocyanate crosslinking agent is dissociated).

[0046] As the non-blocking type crosslinking agent, a known crosslinking agent can be used, for example, but not limited to, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, a metal chelate-based crosslinking agent, etc.

[0047] Examples of the polyisocyanate constituting the isocyanate-based crosslinking agent include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0048] Examples of aromatic polyisocyanates include 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4',4"-triphenylmethane triisocyanate, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

[0049] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0050] Examples of alicyclic polyisocyanates include 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-bis(isocyanatemethyl)cyclohexane, and 1,4-bis(isocyanatemethyl)cyclohexane.

[0051] These polyisocyanates may be trimethylolpropane adduct-type modified products of the above polyisocyanates, biuret-type modified products obtained by reacting with water (e.g., HDI biuret), or isocyanurate-type modified products containing an isocyanurate ring (e.g., HDI trimer).

[0052] The polyisocyanate may be a polymer polyisocyanate obtained by reacting the above polyisocyanate with a polyol compound and polymerizing the polyisocyanate so that one molecule has two or more isocyanate groups. Alternatively, the above polyisocyanate may be polymerized to obtain a polymer polyisocyanate having two or more isocyanate groups per molecule.

[0053] The polyisocyanates may be used alone or in combination of two or more kinds.

[0054] Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0055] Examples of the metal chelate crosslinking agent include acetylacetonate complexes of metals such as aluminum, titanium, nickel, chromium, iron, zinc, cobalt, manganese, and zirconium.

[0056] Among them, the non-blocked crosslinking agent is preferably an isocyanate-based crosslinking agent, since it is easy to obtain a pressure-sensitive adhesive layer having the desired physical properties of the present invention. The non-blocked isocyanate-based crosslinking agents may be used alone or in combination of two or more.

[0057] It is preferable to add the non-blocked crosslinking agent in such an amount that the carboxyl groups of the acrylic copolymer are not completely blocked by the crosslinking reactive groups of the non-blocked crosslinking agent (isocyanate groups in the case of an isocyanate crosslinking agent). The presence of unblocked carboxyl groups in the acrylic copolymer allows the blocked isocyanate crosslinking agent to react efficiently with the carboxyl groups in the acrylic copolymer. The blocking ratio (functional group blocking rate) can be calculated as the mol % of the crosslinking reactive groups of the non-blocked crosslinking agent (isocyanate groups in the case of an isocyanate crosslinking agent) relative to the carboxyl groups of the acrylic copolymer. In this case, it is preferable that 0.1 to 30 mol % of the carboxyl groups are blocked by the crosslinking reactive groups of the non-blocked crosslinking agent. Blocking within this range ensures adhesion before heating and allows the blocked isocyanate crosslinking agent to react efficiently with the carboxyl groups in the acrylic copolymer.

[0058] The amount of the non-blocking crosslinking agent added may be designed in consideration of the content of the functional group-containing unsaturated monomer so as to achieve the above-mentioned functional group blocking rate. For example, the amount of the non-blocking crosslinking agent added is 0.01 to 3.0 parts by mass relative to 100 parts by mass of the acrylic copolymer.

[0059] The mass ratio of the unblocked crosslinking agent to the blocked isocyanate crosslinking agent added is preferably unblocked crosslinking agent:blocked isocyanate crosslinking agent=1:0.05-10, and more preferably 1:0.1-3.

[0060] (Blocked isocyanate crosslinking agent) In this embodiment, the pressure-sensitive adhesive composition essentially contains a blocked isocyanate crosslinking agent.

[0061] Blocked isocyanate crosslinking agents are compounds that are inactive at room temperature (25°C), but when heated, the blocking agent bonded to the polyisocyanate reversibly dissociates to regenerate the isocyanate group.

[0062] When the compound is heated during painting, the blocking agent dissociates, and the exposed isocyanate group and the acrylic acid in the acrylic copolymer form a crosslinked structure. The formation of the crosslinked structure suppresses the increase in the cohesive strength of the adhesive, and after painting, the coated masking tape is peeled off, and there is little or no adhesive residue on the masked object.

[0063] The dissociation initiation temperature of the blocking agent is preferably 100° C. or higher, more preferably 110° C. or higher, even more preferably 120° C. or higher, and even more preferably 140° C. or higher, since the adhesiveness is likely to be maintained even when heated during coating. The upper limit of the dissociation initiation temperature of the blocking agent is not particularly limited, but may be, for example, 200° C. or lower and less than 190° C. In this specification, the dissociation initiation temperature of a blocked isocyanate group means the minimum value of the temperatures required to regenerate an isocyanate group from a blocked isocyanate group.

[0064] The blocked isocyanate crosslinking agent is an isocyanate crosslinking agent in which the terminal isocyanate group is blocked by a blocking agent. Specifically, a compound in which the terminal isocyanate group of a polyisocyanate is blocked by a blocking agent can be mentioned. Here, as the polyisocyanate, the same one as the above-mentioned isocyanate crosslinking agent can be used. The blocked isocyanate crosslinking agent can be used alone or in combination of two or more kinds.

[0065] In the blocked isocyanate crosslinking agent, examples of the blocking agent that bonds to the isocyanate group include amine-based, phenol-based, lactam-based, oxime-based, active methylene-based, alcohol-based, benzotriazole-based, mercaptan-based, acid amide-based, imide-based, imidazole-based, urea-based, and imine-based blocking agents.

[0066] Examples of the amine blocking agent include ethylisopropylamine, di-n-propylamine, diisopropylamine, diphenylamine, isopropyl-tert-butylamine, di-n-butylamine, diisobutylamine, dicyclohexylamine, di-(3,5,5-trimethylcyclohexyl)amine, piperidine, 2,6-dimethylpiperidine, pyrrolidine, 2,5-dimethylpyrrolidine, 2,2,6,6-tetramethylpiperidine, morpholine, 2,6-dimethylmorpholine, isopropylcyclohexylamine, and 3,5-dimethylpyrazole.

[0067] Examples of the phenol-based blocking agent include phenol, cresol, xylenol, and ethylphenol.

[0068] Examples of lactam blocking agents include caprolactam, valerolactam, butyrolactam, and propionolactam.

[0069] Examples of the oxime-based blocking agent include formamide oxime, acetoamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime.

[0070] Examples of active methylene-based blocking agents include diethyl malonate, dimethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, etc. Examples of alcohol-based blocking agents include methanol, ethanol, propanol, isopropanol, butanol, 2-ethylhexanol, ethylene glycol monomethyl ether, etc.

[0071] The blocking agents may be used alone or in combination of two or more.

[0072] Among these, the blocking agent of the blocked isocyanate-based crosslinking agent is preferably at least one selected from the group consisting of active methylene-based blocking agents, amine-based blocking agents, lactam-based blocking agents, and oxime-based blocking agents, and more preferably an amine-based blocking agent and / or an oxime-based blocking agent, because of its good reactivity and the ease with which the effects of the present invention can be obtained.

[0073] As the blocked isocyanate-based crosslinking agent, a commercially available product may be used.

[0074] The amount of the blocked isocyanate crosslinking agent added is appropriately set in consideration of the type of acrylic copolymer, the amount of the unblocked isocyanate crosslinking agent added, etc., and is preferably 0.001 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the acrylic copolymer.

[0075] The pressure-sensitive adhesive composition may also contain a blocking agent dissociation catalyst such as an organotin compound such as dibutyltin dilaurate.

[0076] The adhesive layer is formed using the adhesive composition.

[0077] The thickness of the adhesive layer is not particularly limited, but from the viewpoints of adhesiveness and thinning, it is preferably in the range of 10 to 100 μm.

[0078] If necessary, a colorant, a filler, an antistatic agent, a wetting agent, a leveling agent, a thickener, an antifoaming agent, a preservative, and the like may be appropriately added to the adhesive layer.

[0079] The method of forming the adhesive layer is not particularly limited, but usually, the adhesive composition is applied to a substrate or a release liner. The application method is not particularly limited, and can be applied using a known application device such as a roll coater, a knife coater, an air knife coater, a bar coater, a blade coater, a slot die coater, a lip coater, or a gravure coater. After the adhesive is applied to the substrate, a drying process is performed to form the adhesive layer. The drying conditions at this time are not particularly limited as long as they are lower than the dissociation start temperature of the blocking agent of the blocked isocyanate crosslinking agent, and are appropriately set.

[0080] Alternatively, the adhesive layer may be formed by printing the adhesive using various known printing machines such as a letterpress printer, a gravure printer (an intaglio printer), a screen printer, or an offset printer.

[0081] <Resin Substrate (hereinafter also simply referred to as substrate)> In this embodiment, a resin substrate is used in consideration of solvent resistance and the like.

[0082] The resin substrate is not particularly limited, but since it is exposed to heat due to painting, it is preferably a heat-resistant substrate.

[0083] As the heat-resistant substrate, polyethylene terephthalate film, polyethylene naphthalate film, polyimide film, polyetherimide film, polyaramid film, polyether ketone film, polyether ether ketone film, polyphenylene sulfide film, poly(4-methylpentene-1) film, etc. are used. As the material forming the heat-resistant substrate, polyethylene naphthalate or polyethylene terephthalate is preferable from the viewpoint of excellent balance of mechanical properties, heat resistance, chemical resistance, economical efficiency, etc., and as the material forming the heat-resistant substrate, polyethylene terephthalate is more preferable. Polyethylene terephthalate is preferably biaxially stretched in order to reduce the heat shrinkage rate. In addition, polyethylene terephthalate can be used that is produced by producing an unstretched resin film by a known method such as T-die extrusion molding, and then using a known method such as sequential biaxial stretching or simultaneous biaxial stretching. The substrate may be transparent or opaque.

[0084] One or both sides of the substrate may be subjected to a surface treatment such as a primer treatment, a corona discharge treatment, etc., for the purpose of improving the adhesion of adjacent layers. The liquid agent that can be used for the primer treatment is not particularly limited, and may be any of the conventionally known liquid agents such as acrylic, polyester, polyurethane, silicone, and rubber liquid agents.

[0085] The substrate may contain, as necessary, a lubricant, an antistatic agent, a colorant, and the like.

[0086] There are no particular limitations on the thickness of the substrate, but taking into consideration the above-mentioned total thickness of the substrate and the adhesive layer, as well as from the viewpoint of ensuring the mechanical properties of the paint masking tape and ease of application, it is preferable that the thickness be 50 to 200 μm.

[0087] <Release liner> The paint masking tape may contain a release liner, which is used before the adhesive film is applied to an adherend and has the function of protecting the adhesive layer and preventing a decrease in adhesiveness before use.

[0088] The release liner is not particularly limited, but examples thereof include plastic films such as polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene; and papers such as fine paper, glassine paper, kraft paper, and clay-coated paper.

[0089] There are no particular limitations on the thickness of the release liner, but it is usually 10 to 400 μm.

[0090] <Painting masking method, painting method> The heat-resistant paint masking tape of the present invention is suitable for use as a masking tape in painting various articles that are subjected to high-temperature drying treatment.

[0091] Therefore, another embodiment of the present invention is a paint masking method in which the paint masking tape of the first embodiment is applied to an object to be masked.

[0092] Another embodiment of the present invention is a coating method in which the paint masking tape of the first embodiment is applied to an object to be masked, a coating film is formed on the object to be masked by a paint, and the coating film is heated to a temperature exceeding the dissociation start temperature of the blocked isocyanate-based crosslinking agent. Furthermore, this coating method usually includes peeling the paint masking tape from the object to be masked. The drying temperature of the coating film may be 10°C or higher than the dissociation start temperature of the blocked isocyanate-based crosslinking agent. Specifically, the drying temperature of the coating film is, for example, 190°C or higher.

[0093] The coating method is not particularly limited, and examples thereof include dip coating, spray coating, hand coating, baking coating, electrodeposition coating, electrostatic coating, and electrostatic powder coating. In addition, when depositing the components of the paint on the surface of the coated body, the coated body immersed in the paint may be subjected to a surface treatment by an electrolytic method. In this embodiment, the term "paint" refers to a liquid composition used in the coating treatment, and may contain a coloring material consisting of a dye and / or a pigment, or may not contain a coloring pigment. Therefore, the coating treatment according to this embodiment also includes a surface treatment by an electrolytic method in which the components of the electrodeposition liquid that serves as the undercoat of the color coating are deposited on the coated body, and a treatment for depositing a clear coat formed on the colored coating film. Furthermore, in this embodiment, a surface conditioning treatment performed as necessary to improve the adhesion between the coating film and the coated body (masked body), specifically, a treatment liquid composition used in an etching treatment, a phosphate treatment, etc., is also included in the concept of "paint" in this embodiment, and a surface conditioning treatment performed using such a treatment liquid composition is also included in the concept of the coating treatment in this embodiment.

[0094] The object to be masked is not particularly limited, and examples thereof include the housings and frames of electrical appliances such as mobile devices, LCD televisions, refrigerators, and lighting fixtures; building materials such as doors and window frames; furniture such as chairs and tables; and structural members (main bodies, bonnets, etc.) and components (carriers, etc.) of transportation equipment. EXAMPLES

[0095] The effects of the present invention will be described using the following examples and comparative examples. In the examples, the terms "parts" and "%" may be used, but unless otherwise specified, they represent "parts by mass" or "% by mass". Furthermore, unless otherwise specified, each operation is carried out at room temperature (25°C).

[0096] Example 1 A monomer mixture consisting of 100 parts by mass of butyl acrylate and 10 parts by mass of acrylic acid, azobisisobutyronitrile (polymerization initiator), and ethyl acetate (solvent) were added to a flask equipped with a reflux condenser and a stirrer, and the mixture was heated to 65°C while replacing with nitrogen, and polymerization was carried out for 7 hours to obtain an acrylic copolymer (weight average molecular weight: 500,000).

[0097] A pressure-sensitive adhesive composition was prepared by adding and mixing 2.0 parts by mass of an isocyanate crosslinking agent, Coronate L (manufactured by Tosoh Corporation), and 1.0 part by mass of a blocked isocyanate crosslinking agent (diethyl malonate, TRIXENE (registered trademark) BI 7963, manufactured by Baxenden Chemicals) to 100 parts by mass of the acrylic copolymer. The obtained pressure-sensitive adhesive composition was applied to a release agent-coated surface of a release liner, which was a 38-μm-thick polyethylene terephthalate film coated with a silicone release agent at 0.1 μm, using a knife coater to give a dry film thickness of 50 μm, and then dried at 90° C. to obtain a laminate of a release liner and a pressure-sensitive adhesive layer.

[0098] A polyethylene terephthalate film having a thickness of 100 μm was attached as a resin substrate (heat-resistant substrate) to the pressure-sensitive adhesive layer surface of the laminate, and then allowed to stand at 23° C. for one week to obtain a paint masking tape.

[0099] Example 2 A painted masking tape was obtained in the same manner as in Example 1, except that a blocked isocyanate crosslinking agent in which the blocking agent is 3,5-dimethylpyrazole (TRIXENE (registered trademark) BI 7982, manufactured by Baxenden Chemicals) was used as the blocked isocyanate crosslinking agent in Example 1.

[0100] Example 3 A painted masking tape was obtained in the same manner as in Example 1, except that a blocked isocyanate crosslinking agent in which the blocking agent is methyl ethyl ketoxime (TRIXENE (registered trademark) BI 7984, manufactured by Baxenden Chemicals) was used as the blocked isocyanate crosslinking agent in Example 1.

[0101] Example 4 A painted masking tape was obtained in the same manner as in Example 1, except that a blocked isocyanate crosslinking agent in which the blocking agent is caprolactam (TRIXENE (registered trademark) BI 7981, manufactured by Baxenden Chemicals) was used as the blocked isocyanate crosslinking agent in Example 1.

[0102] Comparative Example 1 A paint masking tape was obtained in the same manner as in Example 1, except that the blocked isocyanate crosslinking agent was not added.

[0103] (Measurement method 1: Adhesive strength) The paint masking tapes obtained in the examples and comparative examples were left to stand for one day under standard conditions (23°C, 50% RH), the release liner was peeled off, and the adhesive layer surface was attached to a SUS plate (SUS304 steel plate), and the adhesive strength was then measured. Specifically, the sheet was peeled off in a 180° direction at a test speed of 300 mm / min using a tensile tester, and the adhesive strength was measured. The numerical value was converted to the peeling force per 25 mm of sheet width (N / 25 mm). The results are shown in Table 1.

[0104] (Measurement method 2: Adhesion test after heating) The release liner of the paint masking tape obtained in the examples and comparative examples was peeled off, and the adhesive layer surface was attached to a SUS plate (SUS304 steel plate). After leaving it to stand for 1 hour under standard conditions (23°C, 50% RH), it was heated at 200°C for 20 minutes, and then left to stand for 24 hours under standard conditions (23°C, 50% RH) to cool. Thereafter, the adhesive strength was measured in the same manner as in the above adhesive strength measurement. The results are shown in Table 1.

[0105] (Evaluation method 1: Removability (adhesive residue)) The release liner was peeled off from the paint masking tapes obtained in the examples and comparative examples, and the adhesive layer surface was attached to a SUS plate (SUS304 steel plate). After standing for 1 hour under standard conditions (23°C, 50% RH), the attached paint masking tape was heated at 200°C for 20 minutes, and then left for 24 hours under standard conditions (23°C, 50% RH) to cool. The paint masking tape was then peeled off from the SUS plate. At this time, whether or not adhesive residue was left on the SUS plate was visually judged according to the following criteria.

[0106] ◎: No adhesive residue on the surface of the substrate 〇: The area of ​​adhesive residue is 10% or less of the unit area of ​​the masked surface ×: The area of ​​residual glue is more than 10% of the unit area of ​​the masked surface.

[0107] The results are shown in Table 1.

[0108] [Table 1]

[0109] As can be seen from the above results, although the paint masking tapes of Examples 1 to 4 had relatively high adhesive strength, the adhesive strength did not increase even when heated, and even when the paint masking tapes were peeled off from the object to be painted, no adhesive glue or only a small amount of adhesive residue remained on the masked object, and the paint masking tapes had excellent removability. [Explanation of symbols]

[0110] 10 Paint masking tape, 11 Resin substrate, 12 adhesive layer, 13 Release liner.

Claims

1. A paint masking tape having a pressure-sensitive adhesive layer and a resin substrate, the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing an acrylic copolymer, a non-blocked crosslinking agent, and a blocked isocyanate crosslinking agent; The acrylic copolymer is The following (A) to (B): (A) 100 parts by mass of alkyl (meth)acrylate; and (B) 0.1 to 15 parts by mass of a carboxyl group-containing vinyl monomer or a carboxylic anhydride group-containing vinyl monomer; A copolymer of the monomer mixture A paint masking tape, wherein the non-blocking type crosslinking agent is an isocyanate-based crosslinking agent.

2. 2. The paint masking tape according to claim 1, wherein the blocking agent of the blocked isocyanate crosslinking agent has a dissociation initiation temperature of 100°C or higher.

3. 3. The paint masking tape according to claim 1, having an adhesive strength of 1 N / 25 mm or more.

4. The paint masking tape according to claim 3, which has an adhesive strength of 1 to 25 N / 25 mm after heating at 200° C. for 20 minutes and cooling.

5. The paint masking tape according to any one of claims 1 to 4, wherein the alkyl (meth)acrylate is butyl acrylate.

6. A paint masking method comprising applying the paint masking tape according to any one of claims 1 to 5 to an object to be masked.

7. A paint masking tape according to any one of claims 1 to 5 is applied to an object to be masked, A coating film is formed on the masked object using paint, The coating film is heated to a temperature exceeding the dissociation initiation temperature of the blocked isocyanate-based crosslinking agent.

Images