Removal pressure sensitive adhesive of aqueous emulsion and method for preparing the same

Abstract

Disclosed are a removal aqueous emulsion adhesive, as an aqueous adhesive, which is environmental-friendly, exhibits superior adhesive strength and heat resistance, and low removal noise and is free of ghosts, as compared to rubber-soluble adhesives, and is thus applicable to a variety of commercial labels including labels for cosmetics, medicine, foods, chemical products and promotion, as well as to adhesive sheets such as adhesive labels used for electric and electrical products that require heat resistance and absence of ghosts, and a method for preparing the same.

Claims

1. A method for preparing a removal adhesive comprising: preparing a neutralized acrylic adhesive solution of a resin (A), prepared by: adding an anionic emulsifier and 0.1 to 3 parts by weight of an ammonium persulfate polymerization initiator to 100 parts by weight of a monomer mixture comprising (i) greater than 90 to 99.9% by weight of a (meth)acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms, (ii) 0.1 to less than 2% by weight of a monomer having a carboxyl group or a hydroxyl group, or a mixture thereof; and (iii) less than 0.1% by weight of a cross-linking agent having an acrylate group or vinyl group, and neutralizing the solution of resin (A); adding 0.3 to 1.9 parts by weight of a compound having a structure of below Formula 1 (B), relative to 100 parts by weight of resin (A), adding 15 to 25 parts by weight of a rubber based resin (C), relative to 100 parts by weight of resin (A), and adding 1.65 to 2.75 parts by weight of plasticizer (D), relative to 100 parts by weight of resin (A), wherein the plasticizer is acetyl tributyl citrate, wherein the prepared removal adhesive is free of ghosts, ##STR00003## wherein R.sub.1 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms and R.sub.2 is a hydroxyl group or an alkyl group having 1 to 12 carbon atoms.

2. The method according to claim 1, comprising neutralizing the solution of resin (A) to a pH of 8.0.

3. An adhesive sheet formed by coating one side of a surface paper with an adhesive prepared by the method of claim 1.

4. The adhesive sheet according to claim 3, wherein the surface paper is a paper sheet.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Now, the present invention will be described in more detail with reference to the following Examples. These examples are only provided to illustrate the present invention and should not be construed as limiting the scope and spirit of the present invention.

EXAMPLES

Example 1

(2) <Preparation of Acrylic Adhesive Agent>

(3) 200 g of distilled water and 1.2 g of sodium alkylaryl naphthalene sulfonate as an emulsifier were added to a 2 L glass reactor equipped with a stirring blade, a thermometer, a nitrogen gas feed pipe and a reflux condenser, the atmosphere of the reactor was replaced with nitrogen gas with stirring, and the mixture was heated to 70 C. under the nitrogen atmosphere.

(4) 8 g of 5% ammonium persulfate (APS) solution was added to the reactor, a solution of 312 g of butyl acrylate (BA), 481 g of 2-ethylhexyl acrylate (2-EHA) and 8 g of acrylic acid (AA) was mixed with a solution of 0.8 g of allyl methacrylate (AMA), 6.8 g of sodium alkylaryl naphthalene sulfonate, 360 g of distilled water and 1.6 g of sodium carbonate, the mixture was reacted for 4 hours while a free emulsion was added dropwise thereto. At this time, 68.8 g of the 5% ammonium persulfate solution and the free emulsion were simultaneously added dropwise over the course of 4 hours.

(5) After the dropwise addition, 5.2 g of the 5% ammonium persulfate solution was added at a time and allowed to stand at 80 C., unreacted monomers were completely reacted and cooled to room temperature, and 28% by weight of an aqueous ammonia solution was added thereto to neutralize the reaction mixture to pH 8 and thereby prepare an acrylic adhesive agent (about 55% solid).

(6) <Preparation of Plasticizer Solution>

(7) As a plasticizer, acetyl tributyl citrate (ATBC) was used. A solution of 0.55 g of sodium alkylaryl naphthalene sulfonate in 45 g of distilled water, as an emulsifier to disperse the plasticizer was added to 55 g of acetyl tributyl citrate. Then, the mixture was dispersed at a rate of 2,500 rpm/min for 5 minutes using a homogenizer to prepare a 55% plasticizer solution.

(8) <Incorporation of Additive>

(9) 0.275 g of trimethylolpropane tris[()-N-2-methyl-1-aziridineyl]propionate (0.5 parts by weight, based on 100 parts by weight of the total amount of the monomers and cross-linking agent), as a cross-linking agent, 47.8 g of a styrene-butadiene rubber (SBR) solution (20 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent, solid content: 23%) and 5 g of the 55% plasticizer solution thus prepared (5 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) were added to 100 g of the neutralized acrylic adhesive agent, followed by mixing for 10 minutes to prepare a removal adhesive.

(10) <Production of Adhesive Sheet>

(11) The removal adhesive was uniformly applied to a release paper with a thickness of 1305 m, dried at 120 C. for 2 minutes and laminated on one side of art paper to produce a sheet for adhesive labels with a thickness of 202 m including a release paper, an adhesive layer and art paper which are laminated from top to bottom in this order.

Example 2

(12) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 0.55 g (1 part by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) of trimethylolpropane tris[()-N-2-methyl-1-aziridineyl]propionate was added as the aziridine cross-linking agent.

Example 3

(13) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 35.9 g of a styrene-butadiene rubber (SBR) solution (15 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent, solid content of 23%) was added.

Example 4

(14) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 59.8 g of a styrene-butadiene rubber (SBR) solution (25 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent, solid content of 25%) was added.

Example 6

(15) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 3 g of the plasticizer solution (5 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Example 6

(16) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of preparing the acrylic adhesive agent, polymerization was carried out without using 0.8 g of allyl methacrylate (AMA) and, in the process of incorporating an additive, 35.9 g of a styrene-butadiene rubber (SBR) solution (15 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent, solid content of 23%) was added.

Comparative Example 1

(17) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 0.11 g of the aziridine cross-linking agent (0.2 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 2

(18) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 1.1 g of the aziridine cross-linking agent (2 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 8

(19) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, a styrene-butadiene rubber (SBR) solution having a (solid content of 23%) was not added.

Comparative Example 4

(20) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 23.9 g of the styrene-butadiene rubber (SBR) solution having a solid content of 23% (to parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 5

(21) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 71.7 g of the styrene-butadiene rubber (SBR) solution having a solid content of 23% (30 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 6

(22) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, no plasticizer solution was used.

Comparative Example 7

(23) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 1 g of the plasticizer solution (1 part by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 8

(24) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, in the process of incorporating an additive, 10 g of the plasticizer solution (10 parts by weight, based on 100 parts by weight of the total amount of monomers and cross-linking agent) was added.

Comparative Example 9

(25) A sheet for adhesive labels was produced in the same manner as in Example 1, except that, the aziridine cross-linking agent, the styrene-butadiene rubber (SBR) solution and the plasticizer solution were not added.

Comparative Example 10

(26) A sheet for adhesive labels was produced in the same manner as in Example 1, except that the styrene-butadiene rubber (SBR) solution and the plasticizer solution were not added.

EXPERIMENTAL EXAMPLE

(27) The physical properties of sheets for adhesive labels produced in Examples 1 to 6 and Comparative Examples 1 to 10 were measured in accordance with the following method. The results are shown in Table 1 below.

(28) 1) Measurement Method of Room Temperature Adhesive Strength (90 Peel):

(29) The sheet for adhesive labels thus produced was evaluated in accordance with a KS A 1107 adhesive strength measurement method. Specifically, five specimens with a size of 2.5 cm20 cm were prepared, attached to a glass surface, and rolled out back and forth 5 times at a rate of 300 mm/min using a 2 kg roller. After 20 minutes, the specimens were peeled out at 90 degrees at a rate of 5 mm/sec under conditions of 23 C. and 50% humidity and the adhesive strength thereof was measured. The target adhesive strength level was 300 to 500 gf/in.

(30) 2) Measurement Method of Initial Adhesive Strength (Ball Tack)

(31) The sheet for adhesive labels was evaluated in accordance with the KS A 1107 initial adhesive strength measurement method. Specifically, a ball was rolled on adhesive specimens with a length of 10 cm arranged on a 30 sloped surface and was then stood for 5 seconds or longer. At this time, the size of the ball was measured. The target ball size level was No. 5 or more.

(32) 3) Measurement method of heat resistance:

(33) Three specimens with a size of 2.5 cm15 cm were prepared from the sheet for adhesive labels and attached to an outer wall of a 500 ml PE bottle. The specimens were stored in an oven at 50 C. for one hour and allowed to stand at room temperature for 3 days. Then, a state in which the sheet is attached to the outer wall of the bottle was qualitatively evaluated. The target state was that the adhesive sheet was closely attached to the wall surface of PE without causing air tunnel or separation.

(34) : Neither separation nor air tunnel

(35) : No separation, but slight air tunnel

(36) : Slight separation and air tunnel

(37) X: Serious separation

(38) 4) Measurement Method of Removal Noise:

(39) Specimens with a size of 2.5 cm15 cm of the sheet for adhesive labels were prepared. Then, the specimens were attached to a glass surface and immediately peeled therefrom, this attachment/peel process was repeated 10 or more times and removal noise generated during this process was evaluated. The removal noise was graded from 0 to 4.0 means little or no noise and 4 means the most noise. The target level of removal noise was 1 or less.

(40) 0: Little or no noise

(41) 1: Very slight noise

(42) 2: Slight noise

(43) 3: Serious noise

(44) 4: Very serious noise

(45) 5) Ghost Measurement Method:

(46) Three specimens with a size of 2.5 cm15 cm of the sheet for adhesive labels were prepared and then attached to a mirror surface. These specimens were stored in an oven at 50 C. for one hour and allowed to stand at room temperature for 3 days, the adhered sheets were peeled from the mirror surface and residues generated on the mirror surface was qualitatively evaluated. The intended state was that the sheets did not leave any ghost on the mirror surface after being peeled therefrom and the mirror surface was kept clean.

(47) TABLE-US-00001 TABLE 1 Room- temperature Initial adhesive adhesive strength strength Heat Removal Ex. No. (kgf/in) (Ball No.) resistance noise Ghost Ex. 1 380 6 1 No Ex. 2 320 5 1 No Ex. 3 340 5 1 No Ex. 4 450 7 1 No Ex. 5 470 9 1 No Ex. 6 380 6 1 No Comp. Ex. 1 430 8 2 No Comp. Ex. 2 280 3 1 No Comp. Ex. 3 120 1 X 0 No Comp. Ex. 4 320 3 1 No Comp. Ex. 5 560 8 2 No Comp. Ex. 6 670 14 3 No Comp. Ex. 7 590 11 2 No Comp. Ex. 8 270 4 0 Slight Comp. Ex. 9 Transferred 6 X 4 Bad Comp. 250 3 1 No Ex. 10

(48) As shown in the above Table 1, Examples 1 to 6 using the aziridine cross-linking agent exhibited improved cohesive strength of resin prior to use, were free of ghosts and considerably reduced removal noise, as compared to Comparative Example 9. It can be seen that the amount of aziridine cross-linking agent used was preferably 0.5 to 1.9 parts by weight in terms of room temperature adhesive strength, initial adhesive strength (tack) and removal noise (See Comparative Examples 1 and 2). In particular, Comparative Example 1 exhibited bad removal noise, the most essential physical property of the removable adhesive.

(49) In addition, Examples 1 to 6 using a rubber based resin as a resin exhibited considerably improved room temperature, initial adhesive strength (tack) and heat resistance, as compared to Comparative Example 3 using no rubber resin. When the content of rubber based resin was higher than so parts by weight (Comparative Example 5), removal noise increased and when the content was lower than 15 parts by weight (Comparative Example 4), initial adhesive strength (tack) was bad. Accordingly, it can be seen that the content of rubber based resin is preferably 15 to 25 parts by weight in terms of room temperature and initial adhesive strength (tack), heat resistance and removal noise.

(50) Meanwhile, Examples 1 to 6 in which a plasticizer was applied to the resin, exhibited improved removal noise, but considerable deterioration in room temperature and initial adhesive strength (tack) as the amount of plasticizer increased, as compared to Comparative Example 6 in which a plasticizer was not used. Comparative Example 8, in which the plasticizer was present in an amount of 10 parts by weight, exhibited ghosts. Accordingly, it can be seen that the content of plasticizer is preferably 1.1 to 9.9 parts by weight in terms of room temperature adhesive strength, initial adhesive strength (tack), removal noise and ghosts.

(51) Furthermore, it can be seen that Examples 1 to 5, in which all of interior cross-linking agent, exterior cross-linking agent, rubber based resin and plasticizer solution were applied to the resin, exhibited improved room temperature and initial adhesive strength (tack) and heat resistance, as compared to Comparative Example 10 in which only an exterior cross-linking agent is applied to the resin.

(52) In addition, Example 6 in which the exterior cross-linking agent, rubber based resin and plasticizer solution were applied to the resin, despite absence of any interior cross-linking agent (such as AMA), exhibited only slight increase in room temperature and initial adhesive strength (tack) and had no great effect on physical properties such as removal noise or ghosts, as compared to Example 3 in which only interior cross-linking agent was applied.