METHOD OF IMPROVING SHEAR STABILITY OF HIGHLY CONCENTRATED AQUEOUS ADHESIVE POLYMER COMPOSITIONS

Abstract

Method of improving shear stability of highly concentrated aqueous adhesive polymer compositions comprising a specific adhesive polymer which has been prepared by emulsion polymerization and which is dispersed in the aqueous adhesive composition. Said method comprises treating the aqueous adhesive polymer composition with at least one anion exchange resin.

Claims

1.-16. (canceled)

17. Method of improving shear stability of highly concentrated aqueous adhesive polymer compositions, wherein the aqueous adhesive polymer composition comprises more than 50% by weight of at least one adhesive polymer which has been prepared by emulsion polymerization and which is dispersed in the aqueous adhesive composition, wherein the adhesive polymer has been made by free-radical emulsion polymerization of a monomer mixture comprising a) at least 60 wt. %, based on the total amount of monomers, of at least one monomer selected from the group consisting of C1 to C20 alkyl acrylates, C1 to C20 alkyl methacrylates, vinyl esters of carboxylic acids containing up to 20 carbons, vinylaromatics having up to 20 carbons, vinyl halides, vinyl ethers of alcohols containing 1 to 10 carbons, ethylenically unsaturated nitriles, aliphatic hydrocarbons having 2 to 8 carbons and one or two double bonds, and mixtures thereof, b) from 0.1 to 10 wt. %, based on the total amount of monomers, of at least one monomer having at least one acid group; c) optionally at least one further monomer, different from the monomers a) and b); said method comprises treating the aqueous adhesive polymer composition with at least one anion exchange resin and not treating the aqueous adhesive polymer composition with a cation exchange resin or with a mixed bed ion exchange resin.

18. The method according to claim 17, wherein the adhesive polymer is a pressure-sensitive adhesive polymer and has a glass transition temperature of less than 10° C. measured by differential scanning calorimetry according to ASTM D 3418-08 as the midpoint temperature when evaluating the second heating curve at a heating rate of 20° C./min.

19. The method according to claim 17, wherein the adhesive polymer has a bimodal or a multimodal particle size distribution.

20. The method according to claim 19, wherein a first particle mode has a weight average particle diameter in the range of 50 to 200 nm, a second particle mode has a weight average particle diameter in the range of 250 to 1200 nm and the weight average particle diameters of the first and second mode differ by at least 50 nm.

21. The method according to claim 17, wherein the anion exchange resin has a total anion exchange capacity of at least 0.9 eq/L and is used in an amount of more than 1 wt.-%, based on the amount of adhesive polymer.

22. The method according to claim 17, wherein the anion exchange resin is selected from the group consisting of copolymers of styrene and divinyl benzene with quaternary ammonium functional groups, copolymers of styrene and divinyl benzene with tertiary amine functional groups, crosslinked acrylic polymers with quaternary ammonium functional groups and crosslinked acrylic polymers with tertiary amine functional groups.

23. The method according to claim 17, wherein the monomers a) are selected from the group consisting of C1 to C10 alkyl acrylates, C1 to C10 alkyl methacrylates, styrene, and mixtures thereof.

24. The method according to claim 17, wherein the monomers b) having at least one acid group are selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, vinylacetic acid, vinyllactic acid, vinylsulfonic acid, styrenesulfonic acid, acrylamidoglycolic acid, acrylamidomethylpropane sulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, anhydrides thereof and mixtures thereof.

25. The method according to claim 17, wherein the monomers a) are used in an amount of at least 80 wt. %, based on the total amount of the monomers, and are selected from the group consisting of C1 to C10 alkyl acrylates, C1 to C10 alkyl methacrylates, styrene, and a mixture thereof; and the monomers b) are used in an amount of 0.5 to 7 wt. %, based on the total amount of the monomers, and are selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, and a mixture thereof.

26. The method according to claim 17, wherein monomer a) comprises no ethyl acrylate or less than 10 wt.-% ethyl acrylate, based on the total amount of the monomers.

27. The method according to claim 17, wherein the monomers c) are used in an amount of 0.1 to 10 wt. %, based on the total amount of the monomers, and are selected from the group consisting of amides of ethylenically unsaturated carboxylic acids, N-alkylolamides of ethylenically unsaturated carboxylic acids, phenyloxyethyl glycol mono(meth)acrylate, hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, monomers containing amino groups, nitriles of unsaturated C3 to C8 carboxylic acids, bifunctional monomers which as well as an ethylenically unsaturated double bond have at least one glycidyl group, oxazoline group, ureido group, ureido-analogous group or carbonyl group, and crosslinking monomers which have more than one radically polymerizable group.

28. The method according to claim 17, wherein the aqueous adhesive polymer composition comprises at least one additive selected from the group consisting of crosslinkers, wetting agents, fillers, dyes, flow agents, thickeners, light stabilizers, biocides, defoamers, tackifiers and mixtures thereof.

29. Aqueous adhesive polymer compositions obtained by a method according to claim 17.

30. A method comprising utilizing the aqueous adhesive polymer composition according to claim 29 for making self-adhesive articles or for bonding substrates wherein the substrate of the self-adhesive article or at least one of the substrates to be bonded is a transparent substrate.

31. The method according to claim 30, wherein the transparent substrate comprises is polymer film comprising a film of PVC, polyethylene terephthalate, polyethylene or polypropylene.

32. A self-adhesive article obtained by the method of claim 30.

Description

EXAMPLES

[0079] Abbreviations [0080] pphm parts by weight per hundred parts by weight of monomer [0081] EHA 2-ethylhexyl acrylate [0082] MMA methyl methacrylate [0083] MA methyl acrylate [0084] S styrene [0085] HPA hydroxypropyl acrylate [0086] AS acrylic acid [0087] BDA-2 butanediol diacrylate [0088] IRA 402 OH Amberlite® IRA402 OH; strong base anion exchanger, matrix polystyrene divinylbenzene copolymer with quaternary ammonium functional groups; total exchange capacity≥1.60 eq/I (free base form) [0089] IRA67 Amberlite® IRA67; weak base anion exchanger, matrix crosslinked acrylic gel with tertiary amine functional groups; total exchange capacity 0.95 meq/ml minimum (OH.sup.−form) Lewatit® adsorber VP 1064 macroporous adsorber resin without functional groups [0090] IRI20H Amberlite® IRI20H, strong acid cation exchange resin; matrix styrene divinylbenzene copolymer with sulfonic acid functional groups; total exchange capacity≥1.80 eq/I (H.sup.+form) [0091] MB20 Amberlite® MB20 mixed bed cation and anion exchange resin, mixture of a strongly acidic cation exchanger with a strongly basic anion exchanger

[0092] Acrylic Polymer Dispersions

Example 1

[0093] Acrylic polymer dispersion made by emulsion polymerization of (amounts in pphm):

[0094] 78.5 EHA, 8 MMA, 8 MA, 2 S, 2HPA, 1.5 AS

[0095] monomodal particle size distribution

[0096] solids content: 53%

[0097] viscosity: 30-150 mPa s (23° C.; 250 1/s; according to DIN EN ISO 3219)

[0098] Tg: −40° C.

[0099] A polymer film made from this polymer dispersion after removal of the water and after storage of the polymer film in water for 6 hours and for 20 hours remained crystal clear.

Example 2

[0100] Acrylic polymer dispersion made by emulsion polymerization of (amounts in pphm):

[0101] 48 EHA, 41 EA, 5 VAc, 3 S, 3 AS, 0.1 BDA-2

[0102] monomodal particle size distribution

[0103] solids content: 51%

[0104] viscosity: 40-80 mPa s (23° C.; 250 1/s; according to DIN EN ISO 3219)

[0105] Tg: −30° C.

[0106] A polymer film made from this polymer dispersion after removal of the water and after storage of the polymer film in water for 6 hours turned slightly turbid.

Example 3

[0107] Acrylic polymer dispersion made by emulsion polymerization of

[0108] 85 parts by weight n-butyl acrylate, 10 parts by weight styrene and 5 parts by weight of methacrylic acid

[0109] bi-modal particle size distribution: 60 wt. % 140 nm; 40 wt. % 510 nm

[0110] solids content: 61%

[0111] viscosity: 100-200 mPa s)23° C.)

[0112] Tg: −27° C.

Example 4

[0113] Acrylic polymer dispersion made by emulsion polymerization of (amounts in pphm)

[0114] 86.65 n-butyl acrylate, 3.75 methyl methacrylate, 1.25 ureido methacrylate, 3.9 ethyl acrylate, 1 styrene and 1.5 acrylic acid

[0115] trimodal particle size distribution

[0116] particle size maxima at about 150 nm, 350 nm, 900 nm

[0117] solids content: 60%

[0118] viscosity: about 500 mPa s (23° C.; 100 1/s; according to DIN EN ISO 3219)

[0119] Tg: −35° C.

Example 5

[0120] Acrylic polymer dispersion made by emulsion polymerization of (amounts in pphm)

[0121] 78.8 2-ethylhexyl acrylate, 7.9 MMA, 8 methyl acrylate, 2 S, 2 HPA and 0.5 acrylic acid

[0122] bimodal particle size distribution,

[0123] particle size maxima at about 150 nm and 600 nm

[0124] solids content: 60%

[0125] viscosity: 30-150 mPa s (23° C.; 250 1/s; according to DIN EN ISO 3219)

[0126] Tg: −45° C.

Example 6

[0127] Acrylic polymer dispersion made by emulsion polymerization of (amounts in pphm)

[0128] 79 EHA, 9 MMA, 8 MA, 1 S, 2 HPA, 1 AS

[0129] bimodal particle size distribution; particle size maxima at about 120 nm and 330 nm

[0130] solids content: 50%

[0131] viscosity: about 100 mPa s (23° C.; 100 1/s; according to DIN EN ISO 3219)

[0132] Tg: −43° C.

[0133] Particle Size Measurement by Light Scattering

[0134] Measurement of particle sizes and particle size distributions is done by quasi-elastic light scattering The particle diameter of polymer particles and of coagulates is measured at a 0.01 to 0.1 wt.-% aqueous polymer dispersion at 23°.

[0135] Method of Ion Exchange:

[0136] Polymer dispersion samples are mixed with anion exchange resins for 1 hour. Types and amounts of ion exchange resins are listed in tables 1 to 6. Anion exchange resin is removed from the polymer dispersions by filtration.

[0137] Measurement of Shear Stability

[0138] 12 g of polymer dispersion sample is placed in a beaker and sheared. Shearing time and shearing rate is listed in tables 1 to 6. 1 g of the samples is diluted with 1.5 kg of water. Particle size distribution is measured by the light scattering method. Production of coagulates with a particle size of 10 μm and more is an indication of shear instability.

[0139] The results of the shear stability tests are summarized in tables 1 to 6.

TABLE-US-00001 TABLE 1 Shear stability test results of example 1; coagulate particles in μg/g Example 1 Example 1 Anion Example 1 Anion exchange.sup.2) Particle size Example 1 exchange.sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 1648 1630 7774 4337 10-250 μm 4132 4214 10953 6794 >10 μm 4132 4214 11168 6802 .sup.1) shearing rate 5000 1/s for 5 minutes .sup.2)5 pphm IRA67

TABLE-US-00002 TABLE 2 Shear stability test results of example 2; coagulate particles in μg/g Example 2 Example 2 Anion Example 2 Anion exchange.sup.2) Particle size Example 2 exchange.sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 111 108 1205 79 10-250 μm 139 130 1235 139 >10 μm 139 130 1282 162 .sup.1) shearing rate 3000 1/s for 5 minutes .sup.2)5 pphm IRA67

TABLE-US-00003 TABLE 3 Shear stability test results of example 3; coagulate particles in μg/g Example 3 Example 3 Anion Example 3 Anion exchange.sup.2) Particle size Example 3 exchange.sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 599 343 28857 428 10-250 μm 1147 1162 51391 1236 >10 μm 1232 1178 51529 1236 .sup.1) shearing rate 5000 1/s for 5 minutes .sup.2)10 pphm IRA67

TABLE-US-00004 TABLE 4 Shear stability test results of example 4; coagulate particles in μg/g Example 4 Example 4 Anion Example 4 Anion exchange .sup.2) Particle size Example 4 exchange .sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 13713 13290 30827 13651 10-250 μm 17274 17619 35293 18052 >10 μm 17274 17619 35293 18386 .sup.1) shearing rate 5000 1/s for 5 minutes .sup.2) 10 pphm IRA67

TABLE-US-00005 TABLE 5 Shear stability test results of example 5; coagulate particles in μg/g Example 5 Example 5 Anion Example 5 Anion exchange .sup.2) Particle size Example 5 exchange .sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 5281 5320 17515 10182 10-250 μm 9096 9117 22868 14374 >10 μm 9112 9117 22868 14374 .sup.1) shearing rate 3000 1/s for 5 minutes .sup.2) 10 pphm IRA67

TABLE-US-00006 TABLE 6 Shear stability test results of example 6; coagulate particles in μg/g Example 6 Example 6 Anion Example 6 Anion exchange .sup.2) Particle size Example 6 exchange .sup.2) Sheared .sup.1) Sheared .sup.1) 10-25 μm 2981 3198 10060 5752 10-250 μm 3710 4106 11381 6576 >10 μm 3710 4106 11381 6576 .sup.1) shearing rate 3000 1/s for 5 minutes .sup.2) 10 pphm IRA67

[0140] Measurement of Water Whitening Resistance

[0141] The adhesive polymer dispersion to be tested is coated on a transparent siliconized PETP film (polyethylene terephthalate polyester) and dried at 90° C. for 3 minutes. coating weight: 20 g/m.sup.2

[0142] The coated adhesive film is immersed in water for 6 hours by inserting it in a UV standard cuvette (1 cm) filled with water (⅔ volume).

[0143] The color white is composed of all visible colors from red (700 nm) to blue (350 nm). By using UV-Vis Spectroscopy it is possible to screen all absorptions from 350 nm to 700 nm and to measure the average absorption in this wavelength range as a function of time that the adhesive film was immersed in water. This average absorption is converted into opacity (whitening). The average absorption from 350 nm to 700 nm are recorded as a function of time and normalized with the opacity of a white film having an absorption of 3.5:

opacity %=average absorption.sub.(350-700 nm)/3.5×100

[0144] The results of the water whitening measurements for examples 1 and 2 are summarized in table 7.

TABLE-US-00007 TABLE 7 Water whitening test results Opacity [%] Example 1 0.75 Example 1 0.2 anion exchange with 5 pphm IRA 402 OH Example 1 0.3 anion exchange with 5 pphm IRA67 Example 2 3.7 Example 2 2.0 anion exchange with 5 pphm IRA 402 OH Example 2 2.0 anion exchange with 5 pphm IRA67

Example 7

[0145] Acrylic polymer dispersion made by emulsion polymerization of

[0146] 95 parts by weight n-butyl acrylate, 5 parts by weight of methacrylic acid 0.15 pphm tert.-dodecyl mercaptan

[0147] 1.5 pphm seed latex

[0148] monomodal particle size, average 150 nm

[0149] solids content: 50%

[0150] viscosity: 100 mPa s

[0151] The results of the water whitening measurements are summarized in table 8.

TABLE-US-00008 TABLE 8 Water whitening test results Opacity [%] Example 7 29.8 Example 7 + 168 Lewatit ® adsorber VP 1064 Example 7 96.2 cation exchange with IR120H Example 7 70.7 Ion exchange with MB20 (mixed bed) Example 7 2.8 anion exchange with IRA67

Example 8

[0152] Acrylic polymer dispersion made by emulsion polymerization of

[0153] 85 parts by weight n-butyl acrylate, 10 parts by weight styrene, 5 parts by weight of methacrylic acid

[0154] 0.26 pphm NaPS

[0155] 0.2 pphm seed latex

[0156] monomodal, particle size 240 nm

[0157] solids content: 56%

[0158] viscosity: 150 mPa s

[0159] Tg: −27° C.

Example 9

[0160] same as example 8 with addition of 0.75 pphm aluminum acetylacetonate

Example 10

[0161] same as example 8 except 84.5 parts by weight n-butyl acrylate, 10 parts by weight styrene, 5 parts by weight of methacrylic acid, 0.5 parts by weight diacetone acrylamide (DAAM), 0.25 pphm adipic acid dihydrazide (ADDH)

[0162] The results of the water whitening measurements of examples 8 to 10 are summarized in table 9.

TABLE-US-00009 TABLE 9 Water whitening test results Opacity [%] Example 8 15.5 Example 8 1.57 anion exchange with IRA67 Example 9 16.33 Example 9 0.58 anion exchange with IRA67 Example 10 19.5 Example 10 2.53 anion exchange with IRA67

[0163] The results of the water whitening measurements of examples 3 and 8 are summarized in table 10.

TABLE-US-00010 TABLE 10 Water whitening test results Opacity [%] Example 3 (bimodal) 35.7 Example 3 (bimodal) 1.72 anion exchange .sup.1) Example 8 (monomodal) 15.5 Example 8 (monomodal) 1.57 anion exchange .sup.1) .sup.1) anion exchange with 10 pphm Amberlite ® IRA67 for 1 hour

Example 11

[0164] Acrylic polymer dispersion made by emulsion polymerization of

[0165] 79.5 parts by weight 2-ethylhexyl acrylate, 8 parts by weight methyl methacrylate, 8 parts by weight vinyl acetate, 2 parts by weight styrene, 2 parts by weight hydroxypropyl acrylate, 0.5 parts by weight of acrylic acid

[0166] solid content: 69% by weight

[0167] Ion exchange resin Amberlite® IRA67 is washed with deionized water and activated, using a 120 μm filter. 10 weight % of ion exchange resin (based on the solid content of the polymer dispersion) is added to the polymer dispersion, stirred for 1 h at room temperature and filtered over a 120 μm filter.

[0168] Test for migratable components (soluble in ethanol; based on ISEGA test method): 0.275 g±0.025 g of the polymer dispersion are applied and levelled on a 20 cm.sup.2 aluminum surface dried at 90° C. for 120 min. The dried sample is weighed. Then the dried sample is extracted in 145 g Ethanol (95%) for 3 days at room temperature. The extracted sample is dried an weighed again. The test is repeated a second time.

[0169] The migratable components are calculated according to the following formula:

[00002]$m_{\mathrm{migratable}\mathrm{components}}=100\%-\left(\frac{m_{\mathrm{before}\mathrm{extraction}}}{m_{\mathrm{after}\mathrm{extraction}}}\right)*100\%$

[0170] The results are summarized in table 11.

TABLE-US-00011 TABLE 11 Results of Test for migratable components migration test Migratable components Example 11 10.6% Without ion exchange treatment Example 11 9.8% With ion exchange treatment