JP2001055549A - Masking tape for coating and composition used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tackifier composition useful for obtaining a masking tape that can exhibit excellent adhesiveness at high temperatures and exhibit high cohesive force when heated and then cooled again by mixing an acrylic copolymer having covalently crosslinkable groups and ionically crosslinkable groups with a covalently crosslinking agent and an ionically crosslinking agent. SOLUTION: The masking tape is one composed of a support and a layer formed thereon and made of an acrylic pressure-sensitive adhesive containing a covalently crosslinked acrylic copolymer having ionically crosslinkable groups and an ionically crosslinking agent, one composed of a support and a layer formed thereon and made of an acrylic pressure-sensitive adhesive containing a covalently crosslinked and ionically crosslinked acrylic copolymer, or one composed of a support and a layer formed thereon and made of an acrylic pressure-sensitive adhesive having an ordinary-state holding force of 0-1.0 mm/15×20 mm.kg.hr, a holding force after heating of 0-0.4 mm/15×20 mm.kg.hr, a high-temperature adhesiveness of 0.6-2.0 N/15 mm, and an adhesiveness after heating of 1.0-6.0 N/15 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure-sensitive adhesive composition for a masking tape for coating, which has excellent tackiness at high temperatures and high cohesion when cooled again after heating. Related to masking tape for painting.

[0002]

2. Description of the Related Art In painting a vehicle such as an automobile, a masking tape is used to protect an unpainted portion when different colors are applied. This masking tape generally includes
Rubber-based and acrylic-based adhesives are used. However, when high-temperature baking and drying at 120 to 180 ° C. is required as in the case of new car painting, various problems occur, and improvements are required.

For example, when a rubber-based pressure-sensitive adhesive is used, a low-molecular-weight substance such as a tackifying resin or a decomposed substance due to heat remains on the surface to be adhered, and contaminates the product. It may be necessary to wash with a solvent or the like. Further, depending on conditions such as a high baking temperature and a long baking time, the adhesive may remain due to a decrease in cohesive strength of the adhesive.

Acrylic pressure-sensitive adhesives generally have better heat resistance, weather resistance, aging resistance, and transparency than rubber-based pressure-sensitive adhesives. When used as a masking tape, they are subjected to high-temperature baking and drying. Also, it is unlikely to cause contamination by a low molecular weight substance or decrease in cohesive strength. However, the acrylic pressure-sensitive adhesive tends to have an increased adhesive strength after heating such as baking and drying, and requires extremely high cohesive strength after heating and cooling in order to peel off without leaving the adhesive.

[0005] Meanwhile, in order to improve the cohesive force of the acrylic pressure-sensitive adhesive after heating and cooling, there is also a conventional technique in which a crosslinking agent is added to form a covalent bond crosslink. But,
Such an adhesive has extremely low adhesiveness at high temperatures, and peels or floats when baked.
In some cases, this may cause a problem in that a color-separated portion cannot be obtained sharply.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a masking tape for coating which does not cause contamination or adhesive residue on an adherend and which does not easily peel off or float at high temperatures. With the goal.

[0007]

SUMMARY OF THE INVENTION The present invention provides an acrylic copolymer having a covalent crosslinkable group and an ionic bond crosslinkable group; a covalent crosslinker; and an ionic crosslinker for a masking tape for coating. The present invention relates to a pressure-sensitive adhesive composition.

[0008] The present invention also provides a covalently crosslinked
The present invention relates to a coating masking tape in which an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer having an ion-bonding crosslinkable group and an ion crosslinking agent is provided on a support.

Further, the present invention relates to a masking tape for coating, in which an acrylic pressure-sensitive adhesive layer containing a covalently crosslinked and ionically crosslinked acrylic copolymer is provided on a support.

[0010] The present invention also provides a normal state holding power of 0 to 1.0.
mm / 15 × 20mm · kg · hr, holding force after heating is 0
0.4 mm / 15 × 20 mm · kg · hr, high temperature adhesive strength is 0.6 to 2.0 N / 15 mm, and adhesive strength after heating is 1.
The present invention relates to a masking tape for coating, wherein an acrylic pressure-sensitive adhesive layer having a thickness of 0 to 6.0 N / 15 mm is provided on a support.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the acrylic pressure-sensitive adhesive composition for a masking tape for coating according to the present invention will be described.

The acrylic copolymer in the composition according to the present invention is preferably a copolymer of an alkyl (meth) acrylate monomer and a monomer having a crosslinkable group. here,
In the case of a monomer having both an ionic crosslinkable group and a covalent crosslinkable group, the crosslinkable group-containing monomer may be used alone, or a monomer having either an ionic crosslinkable group or a covalent crosslinkable group is used. In this case, the ion-crosslinkable group-containing monomer and the covalent crosslinkable group-containing monomer are used in combination.

Suitable alkyl (meth) acrylate monomers include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate, acrylic C1-C14 alkyl acrylate such as cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, lauryl methacrylate And alkyl methacrylates having 1 to 14 carbon atoms in an alkyl group such as cyclohexyl methacrylate. These may be used in combination of one or more. However, in order to impart high adhesiveness, it is preferable to use, as main monomers, alkyl acrylate having an alkyl group having 2 to 14 carbon atoms and alkyl methacrylate having an alkyl group having 4 to 14 carbon atoms. In order to add cohesion, it is preferable to use alkyl acrylate having an alkyl group having 1 carbon atom and alkyl methacrylate having an alkyl group having 1 to 3 carbon atoms as secondary monomers.

The ionic crosslinkable group in the monomer having a crosslinkable group is not particularly limited as long as it is a group that can be ionically crosslinked by an ionic crosslinker. The covalent crosslinkable group in the crosslinkable group-containing monomer is not particularly limited as long as it is a group that can be covalently bonded by a covalent crosslinker. The following table shows examples of crosslinkable groups and combinations of crosslinkers suitable for crosslinking the groups.

[0015]

[Table 1]

The ionic bond crosslinking group and the covalent bond crosslinking group are:
They may be the same or different. For example, both -OH and -COOH can function as an ionic bond crosslinking group and a covalent bond crosslinking group (see Table 1).

As such a crosslinkable group-containing monomer,
For example, monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, polycarboxylic acids such as maleic acid, fumaric acid, citraconic acid, itaconic acid and anhydrides thereof, hydroxyl groups such as hydroxyethyl acrylate, hydroxypropyl methacrylate A carboxylic acid derivative having dimethylaminoethyl methacrylate,
Acrylamide, methylol acrylamide, glycidyl methacrylate and the like can be mentioned. These may be used in combination of one or more.

The monomers constituting the acrylic copolymer include, in addition to the above-mentioned alkyl (meth) acrylate and a monomer having a crosslinkable group, vinyl acetate, acrylonitrile, acrylamide, styrene, etc., if necessary.
One or more types may be used.

The acrylic copolymer preferably has a molecular weight in the range of 100,000 to 800,000 in weight average molecular weight (Mw). Further, it may be a block copolymer or a random copolymer. The ratio (weight ratio) between the alkyl (meth) acrylate monomer and the crosslinkable group-containing monomer is preferably from 99/1 to 90/10. When a monomer having a low glass transition temperature is used as the crosslinkable group-containing monomer (Tg <0), the amount of the crosslinkable group-containing monomer may be increased (for example, from 99/1 to 99% by weight). 50/5
0). Further, the acrylic copolymer is preferably a substantially linear random copolymer. Here, the term “substantially” is a concept including, for example, some branching that occurs during solution polymerization. Further, it is preferable that the acrylic copolymer used has no three-dimensional network structure.

The acrylic copolymer can be synthesized by a generally used known polymerization method such as a solution polymerization method, an emulsion polymerization method, and a suspension polymerization method, and preferably contains a small amount of unnecessary additives. A solution polymerization method is used.

The covalent crosslinking agent in the composition according to the present invention is appropriately selected so as to be adapted to the type of the covalent crosslinking group in the acrylic copolymer (see Table 1).

The amount of the covalent crosslinking agent added to the composition according to the present invention varies depending on the molecular weight and the number of functional groups, but is 0.01 to 100 parts by weight of the acrylic copolymer.
The range of -5.0 parts by weight is preferred.

The ionic bonding crosslinking agent in the composition according to the present invention is appropriately selected, for example, according to the type of the ionic bonding crosslinking group in the crosslinking group-containing monomer to be used (see Table 1). For example, if the ionic bond crosslinkable group is -OH or -C
When OOH, a suitable crosslinking agent is a polyvalent metal. Others, for example, aluminum oxide, metal oxides such as zinc oxide, metal alkoxides, acetylacetone metal salts,
Organometallic compounds such as metal soaps (aliphatic metal salts) are exemplified.

In particular, when the ion-bonding cross-linking agent is a divalent or higher valent metal ion such as aluminum, titanium, zinc, calcium and barium, the source is a fatty acid salt such as metal soap and has 12 to 22 carbon atoms. It is preferable to use a saturated fatty acid salt of Specifically, myristic acid,
The above metal salts with palmitic acid and stearic acid are available. Particularly, barium stearate and calcium stearate are preferable.

In the composition according to the present invention, the addition amount of the ionic bonding crosslinking agent is preferably in the range of 0.1 to 10.0 parts by weight based on 100 parts by weight of the acrylic copolymer.

The composition of the present invention further comprises a tackifying resin,
It may contain a plasticizer, a filler, a coloring pigment, an antioxidant, an ultraviolet absorber and the like.

The acrylic pressure-sensitive adhesive composition for a masking tape for coating according to the present invention is prepared, for example, by first dissolving an acrylic monomer, a polymerization initiator and the like in an organic solvent, and then heating the composition at a temperature of 50 to 100 ° C. For a predetermined time, preferably about 8 hours to obtain a solution of the acrylic copolymer in ethyl acetate. After adjusting the solution concentration, the solution can be obtained by adding a crosslinking agent and other additives.

Next, the coating masking tape according to the present invention will be described. The “masking tape” in the present invention is a concept including a masking sheet.

By appropriately changing the kind and amount of the cross-linking group, the normal state holding force is 0 to 1.0 mm / 15 × 20 mm · kg ·
hr, holding force after heating is 0 to 0.4 mm / 15 × 20 mm
・ Kg ・ hr, high temperature adhesive strength 0.6 ~ 2.0N / 15m
m, and an acrylic pressure-sensitive adhesive layer having an adhesive force after heating of 1.0 to 5.0 N / 15 mm is provided on a support, so that a coating masking tape can be obtained. The “normal holding power” in the present specification refers to JIS-Z-0237.
(However, the test plate is glass, the bonding area is width 15
mm, a length of 20 mm, a load of 1 kg was applied, and the amount of displacement after 1 hour was measured). The “holding force after heating” refers to a value measured after heating at 160 ° C. for 30 minutes in a 23 ° C., 65% RH atmosphere in the same manner as the normal holding force. The “high temperature adhesive strength” refers to the value of 120
It refers to a value measured in the same manner as the normal adhesive force in an atmosphere of ° C.
The “adhesive strength after heating” was obtained by attaching a test piece to a panel,
After heating at 60 ° C. for 30 minutes, it refers to a value measured in the same manner as the normal adhesive strength in an atmosphere of 23 ° C. and 65% RH.

Examples of the support substrate used in the coating masking tape of the present invention include plastic films such as vinyl chloride, polyester, polyolefin, and nylon, composite films thereof, metal foil, paper, cloth, nonwoven fabric, and the like. A composite film with the plastic or the like can be given. If necessary, a surface treatment such as a corona treatment or a plasma treatment, a coating with a primer or a release agent, a printing, or the like may be performed.

The masking tape for coating of the present invention is prepared by coating the acrylic pressure-sensitive adhesive composition for a masking tape for coating of the present invention on the primer-primed surface of a supporting substrate which has been subjected to necessary treatments such as peeling treatment and primer treatment. It is obtained by applying an object, winding it around a paper tube, cutting it into a desired width to form a tape, or laminating release paper and cutting it into a desired shape to form a sheet. At this time, after application of the pressure-sensitive adhesive, aging is carried out to advance necessary crosslinking. The aging condition is preferably at a temperature of 20 to 100 ° C. for 1 hour to 3 hours.
The period is 0 days, more preferably 1 to 5 days at a temperature of 40 to 80 ° C. The thickness of the support varies depending on the material, but is preferably in the range of 10 to 300 μm, and more preferably in the range of 20 to 200 μm. The thickness of the pressure-sensitive adhesive layer is preferably 5 to 200 μm.
m, more preferably 10 to 50 μm.

[0032]

The present invention will be specifically described below with reference to examples.

Example 1 98 parts by weight of 2-ethylhexyl acrylate, 2 parts by weight of acrylic acid, and 0.5 part by weight of lauroyl peroxide as a polymerization initiator were dissolved in ethyl acetate, and the mixture was refluxed under a nitrogen atmosphere at a reflux temperature of ethyl acetate. For 8 hours to obtain an acrylic copolymer. To a 35% ethyl acetate solution containing 100 parts by weight of the obtained acrylic copolymer, 0.05 part by weight of an epoxy-based crosslinking agent (pentaerythritol polyglycidyl ether, Denacol EX-411, manufactured by Nagase Kasei Kogyo Co., Ltd.), and stearic acid 1. Barium (SB, manufactured by Sakai Chemical Co.)
0 parts by weight of the pressure-sensitive adhesive composition was mixed with 70 μm thick C
A primer (unstretched polypropylene film) substrate was coated on the primer undercoat surface to obtain a masking tape sample. At this time, the thickness of the pressure-sensitive adhesive was 30 μm.

Example 2 A masking tape sample was obtained in the same manner as in Example 1 except that 2.0 parts by weight of a metal soap-based crosslinking agent (mixture 593 of zinc stearate and calcium stearate, manufactured by Asahi Denka Co., Ltd.) was added. Was.

Comparative Example 1 A masking tape sample was obtained in the same manner as in Example 1 except that no ionic bonding crosslinking agent was added.

[0036] Comparative Example 2 epoxy-based crosslinking agent (pentaerythritol polyglycidyl ether, Denacol EX-411, Nagase Kasei Kogyo Co., Ltd.) except for using 0.15 parts by weight amount of Comparative Example 1
A sample of the masking tape was obtained in the same manner as described above.

Comparative Example 3 A masking tape sample was obtained in the same manner as in Comparative Example 1 except that 3.0 parts by weight of barium stearate (SB, manufactured by Sakai Chemical Co.) was added without adding a covalent crosslinking agent. Was.

The weight average molecular weight is measured by using a gel permeation chromatography (GPC). The polystyrene equivalent weight average molecular weight of the acrylic copolymer obtained in Example 1 was 700,000.

With respect to the obtained masking tape sample, at normal temperature (23 ° C.), at high temperature (120 ° C.), 160 ° C. ×
The adhesive strength after heating for 30 minutes was measured (180-degree peeling method according to JIS Z 0237), a paint peeling test and a folded part floating test were performed, and the results are shown in Table 2.

In the paint peeling test, a melamine-based paint was applied to a cationic electrodeposition coated steel sheet, baked and dried at 160 ° C. for 30 minutes, and the sample was stuck on the coated plate.
A melamine-based paint is further applied from above,
It is baked and dried for 0 minutes, left standing in an atmosphere of 23 ° C. for about 1 hour, cooled, rapidly peeled off, and the adhesive residue is observed.

In the folded part floating test, the sample was folded back onto the painted plate, attached to the back side, a cut was made in parallel with the painted plate end at 1 mm from the end portion, and heated at 160 ° C. for 30 minutes to float the folded portion. Observe.

[0042]

[Table 2]

[0043]

According to the present invention, both a covalent cross-link and an ionic cross-link are introduced into an adhesive for a masking tape for coating. This covalent cross-linking provides constant cohesion over all temperature ranges, and ionic cross-linking results in high cohesion at high temperatures and high cohesion at low temperatures (dissociate at high temperatures and re- Therefore, the adhesive for coating masking tapes according to the present invention has an unprecedented breakthrough property of high cohesive strength at low temperatures and high adhesive strength at high temperatures. It has.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D073 AA01 BB03 DB03 DB14 DB15 DB50 4J004 AA10 AA17 AB01 CA02 CA04 CA05 CA06 CA08 CB01 CB02 CC02 CC03 DB02 FA04 4J040 DF041 DF051 GA05 GA07 GA11 GA14 GA15 GA22 HA136 HB07 HB J20 LA01 LA06

Claims (4)

[Claims] An acrylic pressure-sensitive adhesive composition for a masking tape for coating, comprising an acrylic copolymer having a covalent crosslinkable group and an ionic crosslinkable group; a covalent crosslinker; and an ionic crosslinker. 2. An application for coating, wherein an acrylic pressure-sensitive adhesive layer containing a covalently cross-linked acrylic copolymer having an ionic bond crosslinkable group and an ionic crosslinker is provided on a support. Masking tape. 3. A masking tape for coating, wherein an acrylic pressure-sensitive adhesive layer containing a covalently crosslinked and ionically crosslinked acrylic copolymer is provided on a support. 4. A normal holding force of 0 to 1.0 mm / 15 × 20.
mm · kg · hr, holding force after heating is 0 to 0.4 mm / 15
× 20mm ・ kg ・ hr, high temperature adhesive strength is 0.6 ~ 2.0
N / 15mm, adhesive strength after heating is 1.0-6.0N / 1
A masking tape for painting, wherein an acrylic pressure-sensitive adhesive layer of 5 mm is provided on a support.