PRESSURE-SENSITIVE ADHESIVE COMPOSITIONS AND RELATED AQUEOUS POLYMER DISPERSIONS

Abstract

The invention relates to a pressure sensitive adhesive comprising an aqueous polymer dispersion which comprises at least one polymer with monomeric units from a monomeric composition comprising (by weight): a) 60 to 95% of 2-ethylhexyl acrylate; b) 0.1 to 15% of butyl (meth)acrylate; c) 0.5 to 5% of a vinyl aromatic monomer; d) 0.1 to 4% of at least one ethylenically unsaturated acid; e) 0 to 20% of a vinylic ester of C2-C8 carboxylic acid; f) optionally, a monomer different from a), b), c), d) and e); g) at least 0.005% with respect to the total weight of monomers a)+b)+c)+d)+e)+f) of at least one chain transfer agent; the sum of a)+b)+c)+d)+e)+f) being equal to 100%, wherein said monomeric composition does not comprise any C1-C2 alkyl (meth)acrylate.

Claims

1. A pressure sensitive adhesive composition, comprising an aqueous polymer dispersion with said polymer comprising monomeric units from the polymerization of a monomeric composition comprising: a) 60 to 95% by weight of 2-ethylhexyl acrylate, b) 0.1 to 15% by weight of butyl (meth)acrylate, c) 0.5 to 5% by weight of a vinyl aromatic monomer, d) 0.1 to 4% by weight of at least one ethylenically unsaturated acid, e) 0 to 20% by weight of a vinylic ester of C2-C8 carboxylic acid, f) optionally, a monomer different from a), b), c), d) and e) as defined above, g) at least 0.005% by weight with respect to the total weight of monomers a)+b)+c)+d)+e)+f) of at least one chain transfer agent, the sum of a)+b)+c)+d)+e)+f) being equal to 100% and with the proviso that said monomeric composition does not comprise any C1-C2 alkyl (meth)acrylate or any monomer containing sulfonic groups or any polymerizable surfactant or any diester of an unsaturated dicarboxylic acid.

2. The pressure sensitive adhesive composition according to claim 1, wherein said butyl (meth)acrylate is n-butyl methacrylate.

3. The pressure sensitive adhesive composition according to claim 1, wherein said vinyl aromatic monomer is styrene.

4. The pressure sensitive adhesive composition according to claim 1, wherein said ethylenically unsaturated acid is (meth)acrylic acid.

5. The pressure sensitive adhesive composition according to claim 1, wherein said vinylic ester e) is vinyl acetate.

6. The pressure sensitive adhesive composition according to claim 1, wherein said transfer agent g) is selected from mercaptans.

7. The pressure sensitive adhesive composition according to claim 1, wherein said transfer agent g) is n-dodecyl mercaptan.

8. The pressure sensitive adhesive composition according to claim 1, wherein said transfer agent g) is present at a content of from 0.005 to 0.2% by weight.

9. The pressure-sensitive adhesive composition according to claim 1, wherein said composition comprises: A) 60-95 parts by weight of said aqueous polymer dispersion as defined according to claim 1, and B) 5-40 parts by weight of at least one tackifier resin, and optionally C) 0-10 parts by weight per 100 parts of A)+B) of additives selected from the group consisting of wetting agents, thickeners, preferably associative thickeners, defoamers, crosslinkers fillers, colorants, leveling agents, plasticizers, and pigments.

10. An aqueous polymer dispersion as defined in claim 1.

11. (canceled)

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. A pressure sensitive self-adhesive article comprising the pressure-sensitive adhesive composition as defined according to claim 1.

18. The pressure sensitive self-adhesive article according to claim 17, which is an adhesive label, adhesive tape or adhesive film.

19. The pressure sensitive self-adhesive article according to claim 18, wherein said adhesive label is a paper adhesive label.

Description

EXPERIMENTAL PART

1) Raw Materials Used for the Aqueous Dispersions and Resulting PSA

[0065]

TABLE-US-00001 TABLE 1 raw materials used in the examples Raw material Supplier Symbols used sodium metabisulfite Brentagg tert-butyl hydroperoxide Arkema sodium persulphate Peroxitalia CALFAX ® DB45 Pilot Aerosol ® GPG Solvay Rhodapex ® LA 120S Solvay vinyl acetate Lyondell VA ethyl acrylate Arkema EA 2-ethylhexyl acrylate Arkema EHA methyl methacrylate Arkema MMA butyl methacrylate Evonik BMA styrene Versalis S 2-hydroxyethyl methacrylate Evonik HEMA acrylic acid Arkema AA N-dodecylmercaptan Arkema n-DM Takolyn ® 3519 Eastmann Tackifier resin

2) Aqueous Polymer Dispersions Examined and Preparation

Example 1 (Comparative)

[0066] 1800 g of deionized water are added in a glass reactor fitted with a condenser, a stirrer, a temperature control system and inlets for nitrogen, the initiator solutions and the pre-emulsion feed, respectively. A monomer pre-emulsion composed of 811 g of deionized water, of 48 g of Rhodapex® LA 120S, 50 g of CALFAX® DB45, 33 g of Aerosol® GPG and 4472 g of the monomeric mixture of the composition of row 1 in table 2, is prepared in another container fitted with a stirrer (pre-emulsifier). When the contents of the reactor have reached a temperature of 81° C., 6.22 g of a 36% solids polystyrene seed with 30 nm particle size and then 60 g of a 7% sodium persulfate solution are added.

[0067] About two minutes after having added the initiators, the portion of the monomer pre-emulsion and 230 g of a 7% sodium persulfate solution, 107 g of a sodium acetate 6% solution, are fed into the reactor at a constant feed rate, over a period of 3 hours, taking care to keep the contents of the reactor at a temperature of 84-86° C. throughout all the introduction.

[0068] Then, the reaction mass is maintained at 84-86° C. for a further 30 minutes, then 133 g of 13% tert-butyl hydroperoxide solution and 100 g of a 20% sodium metabisulfite solution are feed separately into the reactor at 66° C. over a period of 60 minutes at constant rate.

[0069] Ten minutes after the end of the above addition, the product obtained is cooled to 35° C., the pH is corrected with sodium hydroxide up to pH 4.0-5.0. Then, the mixture is filtered through a screen of 36 mesh. The solids content of the dispersion is set between 55-57%.

Example 2 (Comparative)

[0070] The polymerization of example 1 is repeated but preparing the pre-emulsion by replacing the monomeric composition with that of row 2 in table 2.

Example 3 (Invention)

[0071] The polymerization of example 1 is repeated but preparing the pre-emulsion replacing the monomeric composition with that of row 3 in table 2.

Example 4 (Invention)

[0072] The polymerization of example 1 is repeated but preparing the pre-emulsion replacing the monomeric composition with that of row 4 in table 2.

Example 5 (Invention)

[0073] The polymerization of example 1 is repeated but preparing the pre-emulsion replacing the monomeric composition with that of row 5 in table 2.

Example 6 (Invention)

[0074] The polymerization of example 1 is repeated but preparing the pre-emulsion replacing the monomeric composition with that of row 6 in table 2.

Example 7 (Invention)

[0075] The polymerization of example 1 is repeated but preparing the pre-emulsion replacing the monomeric composition with that of row 7 in table 2.

[0076] The monomeric composition of each examined aqueous polymer dispersion as prepared according to the above disclosed examples, is shown comparatively in the below table 2.

TABLE-US-00002 TABLE 2 monomeric compositions of the aqueous polymer dispersions as prepared according to the above examples EHA MMA AE BMA VA S HEMA AA n-DM Ex-1 89.0 4.3 0 0 5.3 0 0.8 0.6 0.11 (comparative) Ex-2 89.0 0 4.3 0 4.6 1.0 0.8 0.6 0.11 (comparative) Ex-3 88.7 0 0 4.3 4.6 1.0 0.8 0.6 0.11 (invention) Ex-4 88.4 0 0 4.3 4.0 1.8 0.8 0.6 0.06 (invention) Ex-5 88.7 0 0 2.3 6.6 1.0 0.8 0.6 0.11 (invention) Ex-6 88.3 0 0 4.3 4.0 2.0 0.8 0.6 0.06 (invention) Ex-7 87.3 0 0 2.3 6.5 2.5 0.8 0.6 0.11 (invention)

3) Applicative Adhesive Performances

3.1) Applicative Tests and Conditions Used

[0077] The polymer dispersions produced in the above examples have been characterized for their PSA adhesive properties without further formulation (dispersions used as such), for test of peel adhesion, of loop tack and of cohesion, while for cold temperature loop tack test a combination with a tackifier resin (see conditions below) is used.

Peel Adhesion and Loop Tack Test

[0078] The polymer dispersions are applied on a PET film and dried at 80° C. for a few minutes in order to obtain the same dry weight per unit area of about 20 g/m.sup.2. Once dried, the PET foils are laminated with a siliconized paper (liner). After storing the test strip for 24 hours at 23° C. and 50% Relative Humidity (RH), they were applied on a stainless steel plate and the 180° peel adhesion was tested according to FINAT FTM1 method.

[0079] The tack of the applied PSA (loop tack) were tested according to FINAT FTM9 method.

Cohesion Test

[0080] On the test strip prepared in the same way as for the peel adhesion test, is also measured the shear strength as a measure of cohesion according to test FINAT FTM 7 method.

Cold Temperature Loop Tack Test on Paper Strips

[0081] 84 weight parts on solids of the aqueous polymer dispersions of the above examples are compounded with 16 weight parts of solids of Takolyn 3519 (tackifier resin). Then, these compounds were applied on siliconized paper film (liner) and dried at 80° C. for few minutes, once the adhesives films were completely dry on the liner, they have been laminated with a sheet of paper. Then, some strips 1-inch-wide have been casted from this foils. After storing, these test paper strips for 24 h at 23° C. and 50% RH, the loop tack has been carried out by using a dynamometer with a cold box set at −10° C., after conditioning the strips for at least 10′ in the box before starting the test.

3.2) Applicative Results

[0082] The results of the above tests are shown in point 3.2) and tables 3 and 4 below.

TABLE-US-00003 TABLE 3 applicative results of the aqueous polymer dispersion of the examples applied on PET without any tackifier addition Peel Peel Loop Tack Loop Tack Tg (24 h SS) (24 h PE) (24 h SS) (24 h PE) Shear in ° C. in N/25 mm in N/25 mm in N in N in h Ex-1 −54 11.0 A/C 11.3 A/C 10.0 9.0 30 (comparative) Ex-2 −53 11.9 C 10.6 C 13.4 9.3 6 (comparative) Ex-3 −56 11.1 A/C 10.9 A/C 9.7 9.8 140 (invention) Ex-4 −55 10.6 A/C 10.2 A/C 9.7 7.3 400 (invention) Ex-5 −54 10.6 A/C 10.2 A/C 9.7 7.3 94 (invention) Ex-6 −55 12.9 A/C 12.2 A/C 10.8 9.8 63 (invention) Ex-7 −53 11.1 C 11.4 A/C 13.3 9.9 14 (invention) A = adhesive separation C = cohesive separation

TABLE-US-00004 TABLE 4 Loop tack results on PE at low temperature, with PSA compositions obtained from the aqueous polymer dispersion of the examples, compounded with tackifier resin and applied on paper Loop Tack Cold PE (−10° C.) in N Ex-1 (comparative) 0.5 Ex-2 (comparative) 1.0 Ex-3 1.1 Ex-4 1.5 Ex-5 2.0 Ex-6 1.6 Ex-7 1.7