One-component pressure-sensitive adhesive composition having gel content based on reversible crosslinking via metal salts

Abstract

A description is given of a one-component pressure-sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one pressure-sensitive adhesive polymer which is formed by emulsion polymerization of soft (meth)acrylic ester monomers, methacrylic acid, and optionally further monomers, where the polymerization takes place in the presence of chain transfer agents or styrene. The pressure-sensitive adhesive polymer has a gel content which is based at least partly on a reversible crosslinking via metal salts. The one-component pressure-sensitive adhesive composition can be used for producing adhesive labels, adhesive tapes or adhesive foils.

Claims

1. A one-component pressure-sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one pressure-sensitive adhesive polymer formed by emulsion polymerization of (i) at least 60 wt %, based on the sum of the monomers, of at least one soft (meth)acrylic ester monomer which when polymerized as a homopolymer has a glass transition temperature of less than 0° C., (ii) 0.1 to 10 wt %, based on the sum of the monomers, of methacrylic acid, (iii) 10 to 25 wt %, based on the sum of the monomers, of styrene, (iv) optionally one or more further monomers, different from (i) to (iii), where the polymerization takes place in the presence of 0 to 1 parts by weight of chain transfer agent per 100 parts by weight of monomers, where the pressure-sensitive adhesive polymer has a gel content of at least 40 wt %, based on a polymer film produced from the pressure-sensitive adhesive polymer, where the gel content is based at least partly on a reversible crosslinking by metal salts, and the gel content of the pressure-sensitive adhesive polymer that is based on reversible crosslinking by metal salts is at least 10 wt %, where the metal salts which bring about the reversible crosslinking are used in uncoated form, where the gel content may also be based partly on covalent, irreversible crosslinking, and the gel content of the pressure-sensitive adhesive polymer that is based on covalent, irreversible crosslinking is 0 to 50 wt %, and where the glass transition temperature of the polymer is less than 0° C.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the soft (meth)acrylic ester monomer is selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive polymer is formed from 65 to 99.5 wt %, based on the sum of the monomers, of at least one soft (meth)acrylic ester monomer selected from the group consisting of n-butyl acrylate and 2-ethylhexyl acrylate.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive polymer is formed from 0.5 to 6 wt %, based on the sum of the monomers, of methacrylic acid.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the one or more optional monomers (iv) are used in amounts of 0 to 10 wt %, based on the sum of the monomers, and are selected from the group consisting of C1 to C20 alkyl (meth)acrylates, monomers comprising hydroxyl groups, vinyl esters of carboxylic acids, comprising up to 20 carbon atoms, vinylaromatics having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols comprising 1 to 10 carbon atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds, which are different from the monomers (i) to (iii).

6. The pressure-sensitive adhesive composition according to claim 1, wherein the crosslinking via metal salts takes place by addition of at least one metal salt after the polymerization, where the molar ratio of metal cations to carboxylate groups of the polymer is 1 to 300 mol % or wherein the crosslinking via metal salts takes place by copolymerization with at least one metal salt monomer having an at least divalent metal cation.

7. The pressure-sensitive adhesive composition according to claim 1, wherein the polymerization takes place in the presence of 0.01 to 0.75 part by weight of chain transfer agent per 100 parts by weight of monomers.

8. The pressure-sensitive adhesive composition according to claim 1, wherein the gel content of the pressure-sensitive adhesive polymer that is based on reversible crosslinking by metal salts is at least 40 wt %, and the gel content of the pressure-sensitive adhesive polymer that is based on covalent, irreversible crosslinking is greater than 0 and up to 30 wt %.

9. The pressure-sensitive adhesive composition according to claim 1, wherein the metal cations of the metal salts are selected from the group consisting of Al.sup.3+, Zn.sup.2+, Ti.sup.4+, Ca.sup.2+, Fe.sup.3+ and Ze.sup.4+.

10. The pressure-sensitive adhesive composition according to claim 1, wherein the crosslinking via metal salts takes place by addition of at least one metal salt after the polymerization, and the metal salt is selected from the group consisting of zinc salts and aluminum salts, or wherein the crosslinking via metal salts takes place by copolymerization with zinc (meth)acrylate or aluminum (meth)acrylate.

11. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition comprises at least one tackifier.

12. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive polymer is formed from (i) at least 65 wt %, based on the sum of the monomers, of at least one acrylic ester monomer selected from the group consisting of n-butyl acrylate and 2-ethylhexyl acrylate, (ii) 0.5 to 8 wt %, based on the sum of the monomers, of methacrylic acid, (iii) 10 to 25 wt %, based on the sum of the monomers, of styrene, (iv) 0 to 10 wt %, based on the sum of the monomers, of monomers selected from the group consisting of C1 to C20 alkyl (meth)acrylates, monomers comprising hydroxyl groups, vinyl esters of carboxylic acids comprising up to 20 carbon atoms, vinylaromatics having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols comprising 1 to 10 carbon atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double bonds, which are different from the monomers (i) to (iii), where the pressure-sensitive adhesive polymer has a gel content of at least 50 wt %, based on the polymer film, where the gel content of the pressure-sensitive adhesive polymer that is based on reversible crosslinking by metal salts is at least 40 wt %, where the gel content of the pressure-sensitive adhesive polymer that is based on covalent, irreversible crosslinking is greater than 0 and up to 30 wt %, where the metal cations of the metal salts are selected from the group consisting of Al.sup.3+, Zn.sup.2+, Ti.sup.4+, Ca.sup.2+, Fe.sup.3+ and Zr.sup.4+, and where the glass transition temperature of the polymer is less than −20° C.

13. A self-adhesive article coated with the one-component pressure-sensitive adhesive composition according to claim 1.

14. A method for producing a self-adhesive article by coating a substrate with the one-component pressure-sensitive adhesive composition according to claim 1.

15. A one-component pressure-sensitive adhesive composition in the form of an aqueous polymer dispersion comprising at least one pressure-sensitive adhesive polymer formed by emulsion polymerization of (i) at least 60 wt %, based on the sum of the monomers, of at least one soft (meth)acrylic ester monomer which when polymerized as a homopolymer has a glass transition temperature of less than 0° C., (ii) 0.1 to 10 wt %, based on the sum of the monomers, of methacrylic acid, (iii) 0 to 30 wt %, based on the sum of the monomers, of styrene, (iv) optionally one or more further monomers, different from (i) to (iii), where the polymerization takes place in the presence of 0 to 1 parts by weight of chain transfer agent per 100 parts by weight of monomers, where if no chain transfer agent is used, the amount of styrene (iii) is at least 5 wt %, where the pressure-sensitive adhesive polymer has a gel content of at least 40 wt %, based on a polymer film produced from the pressure-sensitive adhesive polymer, where the gel content is based at least partly on a reversible crosslinking by metal salts, and the gel content of the pressure-sensitive adhesive polymer that is based on reversible crosslinking by metal salts is at least 10 wt %, where the metal salts which bring about the reversible crosslinking are used in uncoated form, where the gel content may also be based partly on covalent, irreversible crosslinking, and the gel content of the pressure-sensitive adhesive polymer that is based on covalent, irreversible crosslinking is 0 to 50 wt %, where the glass transition temperature of the polymer is less than 0° C., and wherein the crosslinking via metal salts takes place by copolymerization with at least one metal salt monomer having an at least divalent metal cation.

Description

EXAMPLES

(1) Starting materials and abbreviations used are as follows: EHA: 2-Ethylhexyl acrylate BA: n-Butyl acrylate EA: Ethyl acrylate MA Methyl acrylate MMA Methyl methacrylate VAc: Vinyl acetate S: Styrene HPA Hydroxypropyl acrylate AA: Acrylic acid MAA Methacrylic acid BDA-2 Butanediol diacrylate (crosslinker for covalent, irreversible crosslinking) tDMC tert-Dodecyl mercaptan EHTG 2-ethylhexyl thioglycolate Al(acac).sub.3 Aluminum acetylacetonate Rongalit® Sodium hydroxymethylsulfinate Acronal® 310 S Acrylate copolymer of (meth)acrylic esters and acrylic acid with a gel content of 67.5% Acronal® 4D Acrylate copolymer of (meth)acrylic esters and acrylic acid with a gel content of 65% Acronal® 50D Acrylate copolymer of (meth)acrylic esters, acrylonitrile and acrylic acid having a gel content of 79%

(2) Room temperature refers to 20° C. unless otherwise indicated.

(3) The examples denoted by C . . . are comparative examples; the examples denoted by I . . . are inventive examples.

(4) Performance Tests

(5) Determination of Total Gel Content

(6) Polymer films are produced from the polymer dispersion under investigation. The polymer films are dried for 1 day at room temperature (20° C.) and then for 4 days at 50° C. The dried film is admixed with 99 times the mass of methyl ethyl ketone. The inserted film is stored at room temperature for 4 days. Then the swollen or dissolved film is filtered off over tared 125 μm Perlon filters. The filter is dried at room temperature until it is free of solvent. This is followed by further drying at 50° C. for an hour, and the gel fraction (solids fraction insoluble in methyl ethyl ketone and remaining in the filter) is determined by reweighing.

(7) The total gel content (gel.sub.total) is 1 determined after the addition of metal crosslinker. The gel content based on covalent, irreversible crosslinking (gel.sub.irreversible) is determined before the addition of metal crosslinker. The gel content based on reversible crosslinking via metal salts (gel.sub.reversible) is the difference between total gel content and irreversible gel content:
gel.sub.reversible=gel.sub.total−gel.sub.irreversible

(8) Testing of Adhesive Properties

(9) To test the adhesive properties, the PSAs are coated with a coatweight of around 60 g/m.sup.2 onto Hostaphan® RN 36 (biaxially oriented polyethylene terephthalate film, 36 μm in thickness) as carrier and dried at 90° C. for 3 minutes. Dispersion films with metal salt crosslinked are stored for 5 days under standard conditions (23° C., 50% relative humidity); dispersion films without metal salt added are stored under standard conditions of temperature and humidity for 24 hours and then the adhesive properties are determined under standard conditions of temperature and humidity, unless otherwise indicated.

(10) Quickstick

(11) In the determination of the quickstick (surface tack, also called loop tack), generally, a determination is made of the force with which an adhesive applied to a carrier material by bonding without pressure onto a substrate opposes removal from the substrate at a defined removal speed. Test substrates are steel or polyethylene. From the carrier coated with adhesive, a test strip 25 mm in width and 250 mm in length is cut and is stored under standard conditions of temperature and humidity (23° C., 50% relative humidity) for at least 16 hours. The two ends of the test strip are folded over for a length of around 1 cm with the adhesive side inward. A loop is formed from the adhesive strip, with the adhesive side outward, and the two ends are brought together and clamped into the upper jaw of a tensile testing machine. The test substrate mount is clamped into the lower jaw. The loop of adhesive strip is run downward through the tensile testing machine at a speed of 300 mm/minute, causing the adhesive side of the test strip to bond to the substrate without additional pressure. The tensile testing machine is halted and is immediately moved upward again when the bottom edge of the upper jaw is 40 mm above the substrate. The test result is reported in N/25 mm width. The maximum value on the display (Fmax) is read off as the measure of the surface tack. An average is formed from three individual results.

(12) Peel Strength

(13) For the determination of the peel strength (adhesion), a test strip 25 mm wide is adhered in each case to a test element composed of polyethylene or steel, and is rolled down once with a roller weighing 1 kg. The strip was then clamped by one end into the upper jaws of a tensile strain testing apparatus. The adhesive strip was peeled from the test surface at an angle of 180° and at 300 mm/min—that is, the adhesive strip was bent around and pulled off parallel to the test element, and the expenditure of force required to achieve this was measured. The measure of the peel strength was the force in N/25 mm which resulted as the average value from five measurements. The peel strength was determined 24 hours after bonding. After this time, the bonding force has fully developed. The test methods correspond essentially to Finat test methods (FTM) 1 and 8.

(14) Shear Strength

(15) The shear strength is a measure of the cohesion. The PSA-coated carrier is cut into test strips 25 mm and 12.5 mm wide, respectively. For determination of the shear strength, the test strips are adhered to steel, with a bonded area 25×25 mm (measurements at 70° C.) or 12.5×12.5 mm (measurements under standard conditions of temperature and humidity) and rolled down once with a roller weighing 1 kg, and, after storage for 10 minutes (under standard conditions of temperature and humidity, 50% relative humidity, 1 bar, 23° C.) they are loaded in suspension with a 1 kg weight (under standard conditions of temperature and humidity, 12.5×12.5 mm) or with a 2 kg weight (at 70° C., 25×25 mm). The measure of the shear strength is the time taken, in minutes, for the weight drop; the average is calculated in each case from five measurements.

(16) The shear strength 3 d/70° C. [h] is the shear strength after storage of the test strips at 70° C. for 3 days.

(17) S.A.F.T. Test (Heat Stability)

(18) The test strips are adhered to AFERA steel, with a bonded area of 25×25 mm, rolled down four times using a roller weighing 2 kg, and, after a contact time of at least 16 hours, loaded in suspension with a 1 kg weight. During loading, heating takes place continuously, starting from 23° C., at a rate of 0.5° C./min. The heating temperature achieved when the weight drops off is a measure of the heat stability of the adhesive.

(19) The average was calculated in each case from three measurements.

(20) Test Protocol: Plasticizer Resistance, Cross-Cut

(21) Plasticizer resistance is the capacity of an adhesive to counter any possible migration of plasticizer particles from a plasticized PVC foil into the adhesive. The loss in volume resulting from the migration of plasticizer causes the plasticized PVC film to shrink. The adhesive under test is drawn down with a coatweight of around 22 g/m.sup.2 (dry), using a laboratory coating table, onto an auxiliary carrier material (NSA 1370 white silicone paper from Laufenberg) and dried in a forced-air drying cabinet at 90° C. for 3 minutes. After the drying process, the adhesive is transferred from the auxiliary carrier material onto the final carrier material (H935693 monomer-plasticized PVC foil, white, from Renolit) and then again lined with silicone paper. After 5 days of storage under standard conditions of temperature and humidity (23° C., 50% relative humidity), the silicone paper is removed and the coated carrier material is adhered without bubbles to a glass plate (250 mm×250 mm×4 mm) and rolled down. Here, the running direction of the foil should be noted and marked. The foil edges protruding from the glass plate are cut off flush using a carton knife. The bonded foil is then divided with one cut each, using a razor blade 0.043 mm thick, in the middle in the longitudinal direction (running direction of the foil, machine direction) and in the cross direction (transverse to the machine direction), thus forming four squares of equal size. The bonded glass plate is subsequently stored at 70° C. for 5 days. Following storage, the glass plate is taken from the drying cabinet and cooled at room temperature for about 1 hour. Using a magnifier with 10-times magnification and a scaling of 10 sd/mm, a measurement is made of the width of the horizontal and vertical cut gap at at least two different locations in each case. The test results reported are the average values of the individual values for each direction in mm.

(22) Test Protocol: Laminate Shrinkage

(23) A laminate sheet (25×25 cm) is prepared and is conditioned under standard conditions of temperature and humidity (23° C., 50% relative humidity) for 5 days. The laminate sheet consists of an auxiliary silicone paper carrier, the layer of adhesive, and the carrier material (monomer-plasticized PVC foil, Renolit). The adhesive coatweight is around 22 g/m.sup.2 (dry).

(24) After hot storage (3 days at 70° C.), a magnifier is used to measure the shrinkage in length (=machine direction) and width (=cross direction), and the result is reported in %.

(25) Test Procedure, Blushing Stability

(26) Coating of an OPP foil (biaxially oriented polypropylene, foil thickness 45 μm) with a target coatweight (dry) of around 20 g/m.sup.2.

(27) Drying of the film at 90° C. for 3 min.

(28) Lining of the coating with silicone paper, storage of the coating for 24 h.

(29) Taking of a sample approximately 8 mm wide and 30 mm long.

(30) Transfer of the sample to a PS cell filled with fully demineralized water, cell path length 1 cm. Immediate measurement of the absorption relative to uncoated comparison sample, OPP foil in fully demineralized water, in the 300-700 nm wavelength range. This is followed by further measurements every 5 minutes over a period of 6 hours. Conversion of the absorption into haze.

Examples C1 to C4 and I1 to I4b—One-Component Adhesives

(31) Comparative samples C1 to C3: only covalent, irreversible crosslinking Inventive samples I1 to I4b: covalent crosslinking less than 50%, with subsequent metal salt crosslinking

(32) Emulsion polymers are used that are prepared from the monomers identified in Table 1 and are admixed with Snowtack® 933 tackifier (rosin ester dispersion) in a weight ratio of 75:25 (solid:solid, polymer to tackifier). The quantities are parts by weight. The examples designated by C . . . are comparative examples; the examples designated by I . . . are inventive examples.

(33) TABLE-US-00001 TABLE 1a Emulsion polymers Al(acac).sub.3 Example EHA BA S MA MAA BDA-2 [pphm] tDMC C1 59 15 20 5 1 0.07 — — I1 59 15 20 5 1 — 0.25 — C2 59 15 20 5 1 0.1  — — I2 59 15 20 5 1 — 0.375 — C3 59 15 20 5 1 0.25 — — I3 59 15 20 5 1 — 1 — C4.sup.1) 97.5 — — — 2.5 — — — I4a.sup.2) 97.5 — — — 2.5 — 0.5 0.15 I4b.sup.2) 97.5 — — — 2.5 — 1 0.15 .sup.1)Initiator: sodium persulfate .sup.2)Redox initiator: tert-butyl hydroperoxide/Rongalit ®

(34) TABLE-US-00002 TABLE 1b Gel contents and glass transition temperature Gel.sub.irreversible Gel.sub.total Tg Example [%] [%] [° C.] C1 55.9 55.9 about −30 I1 <5 45.1 about −30 C2 68.8 68.8 about −30 I2 <5 67.2 about −30 C3 85.6 85.6 about −30 I3 <5 87.7 about −30 C4 75 75 about −55 I4a 29 nd about −55 I4b 29 62.5 about −55

(35) Adhesive foils were produced and the adhesive values were measured (quickstick, peel strength, shear strength, heat stability S.A.F.T. test). The results are set out in Table 1c.

(36) TABLE-US-00003 TABLE 1c Performance results Quickstick Peel strength Shear strength [N/25 mm] [N/25 mm] [h] S.A.F.T. Example Steel PE Steel PE SC 70° C. [° C.] C1 14.9 12.6 15.6 7.3 0.9 0.07 68 I1 15.0 14.9 15.1 7.3 1.4 0.1 81 C2 15.5 12.8 14.2 7.1 0.8 0.1 71 I2 16.2 13.5 14.9 8.0 1.4 0.2 92 C3 11.3 9.2 10.6 5.3 0.8 0.1 93 I3 13.7 11.7 14.5 6.7 0.8 1.2 162 C4 10.0 6.6 9.2 2.6 0.03 0.03 46 I4a 15.7 15.0 14.7 11.3 0.1 0.05 51 I4b 13.8 8.7 13.3 4.1 0.2 0.05 65

(37) The examples show that for comparable total gel contents, the samples with metal salt crosslinking achieve better adhesion and cohesion values and/or heat stabilities (SAFT).

Examples C5 to C6 and I5 to I6—One-Component Adhesives

(38) Comparative samples C5 to C6: only covalent, irreversible crosslinking Inventive samples I1 to I5: covalent crosslinking less than 50%, with subsequent metal salt crosslinking

(39) Emulsion polymers are used that are prepared from the monomers identified in Table 2a. Examples C5 and I5 are without tackifier. Examples C6 and I6 are admixed with Snowtack® 933 tackifier in a weight ratio of 75:25 (solid:solid, polymer to tackifier). The quantities are parts by weight.

(40) TABLE-US-00004 TABLE 2a Emulsion polymers Al(acac).sub.3 Gel.sub.irreversible Gel.sub.total Tg Example BA S MAA [pphm] [%] [%] [° C.] C5 75 20 5 — 20.6 20.6 −17 I5 75 20 5 1 20.6 91.8 −17 C6 75 20 5 — 20.6 20.6 −17 I6 75 20 5 1 20.6 91.8 −17

(41) Adhesive foils were produced and the adhesive values were measured (quickstick, peel strength, shear strength, heat stability S.A.F.T. test). The results are set out in Table 2b.

(42) TABLE-US-00005 TABLE 2b Performance results Quickstick Peel strength Shear strength [N/25 mm] [N/25 mm] [h] S.A.F.T. Example Steel PE Steel PE SC 70° C. [° C.] C5 11.4 10.9 2.7 85.3 20.0 128 I5 10.6 8.6 2.0 191.0 >141 >180 C6 2.1 16.8 10.0 10.4 0.5 109 I6 3.0 17.6 10.0 24.5 8.3 142

(43) The examples show, when using a metal salt crosslinking, a sharp increase in the cohesion and heat stability, with little or no drop in the adhesion.

Examples C7 to C8 and I7 to I8c—One-Component Adhesives

(44) Emulsion polymers are used that are prepared from the monomers identified in Table 3a. Examples I7a, I8a-c, C7 and C8 are admixed with Snowtack® 933 tackifier in a weight ratio of 75:25 (solid: solid, polymer to tackifier). In Example I7b the weight ratio polymer:tackifier is 87.5:12.5. The quantities are parts by weight. In the case of Examples C7 and I7a-b, 0.26 pphm sodium persulfate was used. In Examples C8 and I8a-c, 0.52 pphm sodium persulfate was used.

(45) TABLE-US-00006 TABLE 3a Emulsion polymers with Tg around −38° C. Al(acac).sub.3 Gel.sub.irreversible Gel.sub.total Example EHA S VAc HPA MAA [pphm] [%] [%] C7 77.5 10 8 2 2.5 0 17.3 17.3 I7a 77.5 10 8 2 2.5 1 17.3 82.4 I7b 77.5 10 8 2 2.5 1 17.3 82.4 C8 77.5 10 8 2 2.5 0 21.6 21.6 I8a 77.5 10 8 2 2.5 1 21.6 86 I8b 77.5 10 8 2 2.5 1.5 21.6 90 I8c 77.5 10 8 2 2.5 2 21.6 91

(46) TABLE-US-00007 TABLE 3b Performance results Quickstick Peel strength Shear strength [N/25 mm] [N/25 mm] [h] S.A.F.T. Example Steel PE Steel PE SC 70° C. [° C.] C7 13.7 9.0 16.5 3.7 0.6 0.08 88 I7a 12.8 6.9 13.2 3.0 5.0 16.1 >180 I7b 9.1 4.2 10.9 0.9 5.6 >100 >180 C8 12.6 6.9 15.9 3.6 2.2 0.3 110 I8a 11.7 6.2 11.6 2.5 10.1 21.2 >180 I8b 9.5 5.8 11.4 2.5 9.3 38.8 >180 I8c 9.3 5.7 10.6 2.4 9.6 37.3 >180

(47) The examples show that by the addition of metal salt, the cohesion and the heat stability are increased very greatly, with no significant deterioration in the adhesion.

Examples I9 to I10b

(48) One-Component Adhesives with Synthetic Tackifiers

(49) Emulsion polymers are used that are prepared from the monomers stated in Table 4a, and are admixed with tackifiers A or B in a weight ratio of 75:25 (solid:solid, polymer to tackifier).

(50) Tackifier polymer dispersion A: prepared from 65 parts by weight EHA/30 parts by weight MMA/5 parts by weight MAA and 5 parts by weight EHTG as CTA with Tg of −35° C.

(51) Tackifier polymer dispersion B: prepared from 65 parts by weight EHA/30 parts by weight MMA/5 parts by weight MAA and 0.95 part by weight EHTG as CTA with Tg of −18.5° C.

(52) TABLE-US-00008 TABLE 4a Emulsion polymers without tackifier or with 25 parts by weight of tackifier to 75 parts by weight of adhesive polymer Al(acac).sub.3 Example EHA BA S MA VAc HPA MAA [pphm] Tackifier I9 59 25 10 3.5 — — 2.5 1 — I9a 59 25 10 3.5 — — 2.5 1 A I9b 59 25 10 3.5 — — 2.5 1 B I10 77.5 — 10 — 8 2 2.5 1 — I10a 77.5 — 10 — 8 2 2.5 1 A I10b 77.5 — 10 — 8 2 2.5 1 B

(53) TABLE-US-00009 TABLE 4b Gel contents and glass transition temperature Gel.sub.irreversible Gel.sub.total Tg Example [%] [%] [° C.] I9 10 89 −39 I9a 10 89 −39 I9b 10 89 −39 I10 20 87 −38 I10a 20 87 −38 I10b 20 87 −38

(54) Adhesive foils were produced and the adhesive values were measured (quickstick, peel strength, shear strength, heat stability S.A.F.T. test). The results are set out in Table 4c.

(55) TABLE-US-00010 TABLE 4c Performance results Quickstick Peel strength Shear strength [N/25 mm] [N/25 mm] [h] S.A.F.T. Example Steel PE Steel PE SC 70° C. [° C.] I9 5.5 2.7 10.5 1.0 1.3 >100 >180 I9a 7.2 6.0 11.5 2.5 0.4 24.1 171 I9b 5.3 3.9 10.3 1.8 1.9 36.3 169 I10 5.5 2.7 10.5 1.0 1.3 >100 >180 I10a 7.1 5.9 13.8 2.2 1.0 6.3 >180 I10b 5.1 4.2 12.6 1.7 12.0 3.4 135

(56) The examples show that by using tackifiers it is possible to boost the adhesion, especially to PE, without a sharp drop in the heat stability (SAFT).

Examples I11 and C11 One-Component Adhesives

(57) Emulsion polymers are used that are prepared from the monomers stated in Table 5a, and are admixed with tackifiers A or B in a weight ratio of 75:25 (solid:solid, polymer to tackifier).

(58) Tackifier: Tackifier polymer of 65 parts by weight EHA/30 parts by weight MMA/5 parts by weight MAA and 0.95 part by weight EHTG as CTA

(59) TABLE-US-00011 TABLE 5a Emulsion polymers with 25 parts by weight of tackifier to 75 parts by weight of adhesive polymer Al(acac).sub.3 Gel.sub.irreversible Gel.sub.total Example EHA S VAc MAA HPA BDA2 [pphm] [%] [%] I11 77.5 10 8 2.5 2 — 0.75 30 88 C11 77 10 8 2.5 2 0.5 — 88 88

(60) The results of the blushing stability test are set out in Table 5b.

(61) TABLE-US-00012 TABLE 5b Blushing stability Example 120 min 180 min 240 min 300 min 360 min I11  0.7% 0.7% 0.8% 0.9% 1.3% C11 1.00% 1.5% 2.0% 2.4% 3.0%

(62) The examples show that the sample crosslinked with metal salts, in comparison to a covalently irreversible crosslinked sample, with comparable total gel content, becomes cloudy less quickly during water storage—that is, exhibits better blushing resistance.

Examples I12a-c and C12

(63) Polymer dispersions were prepared from the following monomers:

(64) 77.5 parts by weight EHA/10 parts by weight styrene/8 parts by weight VAc/2 parts by weight HPA/2.5 parts by weight MAA

(65) Comparative example C12 was prepared additionally with 0.07 part by weight BDA-2. In the case of Examples I12a-c, the ongoing polymerization, i.e., the time after the end of the monomer feed and initiator feed, at reaction temperature was carried out for different lengths of time. The samples were admixed with 0.75 pphm Al(acac).sub.3.

(66) The polymer dispersions were blended with 25 parts by weight of Snowtack 933 to 75 parts by weight of adhesive polymer.

(67) TABLE-US-00013 TABLE 6a Gel contents Ongoing polymer- ization time after Ex- emulsion feed Al(acac).sub.3 Gel.sub.irreversible Gel.sub.total Tg ample [min] [pphm] [%] [%] [° C.] C12 30 — 83 83 about −38 I12a 10 0.75 20 82.4 about −38 I12b 30 0.75 33 81.6 about −38 I12c 60 0.75 49 83.7 about −38

(68) Adhesive foils were produced and the adhesive values were measured (quickstick, peel strength, shear strength, heat stability S.A.F.T. test). The results are set out in Table 6b.

(69) TABLE-US-00014 TABLE 6b Performance results Quickstick Peel strength Shear strength [N/25 mm] [N/25 mm] [h] S.A.F.T. Example Steel PE Steel SC 70° C. [° C.] C12 11.7 8.1 11.5 0.9 0.1 98 E12a 11.8 8.3 12.2 2.6 15 128 E12b 12.1 8.3 12.4 1.6 7.6 125 E12c 11.6 8.4 13.4 3.1 21.7 130

(70) The examples show that the samples crosslinked with metal salt, in comparison to a purely covalently irreversible crosslinked sample, with comparative total gel content, exhibit better adhesion and cohesion values and also better heat stability (SAFT).

Examples C13, I13-I19 with Different Metal Salts

(71) Polymer dispersions were prepared from the following monomers: 59 parts by weight EHA/15 parts by weight BA/20 parts by weight styrene/5 parts by weight MA/1 part by weight MAA

(72) and admixed with varying amounts of different metal salts (see Table 7).

(73) TABLE-US-00015 TABLE 7 Effect of different metal salts on the gel content Gel.sub.irreversible Gel.sub.total Tg Example Metal salt [%] [%] [° C.] C13 — <5 0 about −30 I13 1 pphm <5 87.9 about −30 Al(acac).sub.3 I14 1.12 pphm <5 77.1 about −30 Ti(acac).sub.2 (IPA).sub.2 I15 0.88 pphm <5 30.6 about −30 Zr(IV) (OH/CO.sub.3) .sup.1) I16 0.83 pphm <5 28.7 about −30 Fe(II)ox I17 0.55 pphm <5 28.4 about −30 Fe(II)ox I18 1 pphm <5 22.4 about −30 Zr(IV) (OH/CO.sub.3) .sup.1) I19 0.23 pphm <5 15.2 about −30 C19? Ca(OH).sub.2 .sup.1) Bacote ® 20

(74) Preferred metal cations are aluminum and titanium, since they bring about the greatest increase in gel.sub.total. Other metal cations such as zirconium, iron or calcium can also be used, since they likewise produce an increase in gel.sub.total. They are used preferably in combination with polymers which exhibit a sufficiently high gel content gel.sub.irreversible, so that gel.sub.total is at least 40%.

Examples C20-21, I22-I25 with Copolymerized Zn(MAA).SUB.2

(75) Polymer dispersions were prepared from the following monomers:

(76) 59 parts by weight EHA/15 parts by weight BA/20 parts by weight styrene/4 to 5 parts by weight MA/0.5 part by weight MAA, and different amounts of Zn(MAA).sub.2 (see Table 8).

(77) TABLE-US-00016 TABLE 8 Gel contents Zn(MAA).sub.2 Gel.sub.irreversible Gel.sub.total Tg Example [pphm] [%] [%] [° C.] C20 0 0 0 about −30 C21 0.36 0 14.4 about −30 I22 0.73 0 40.2 about −30 I23 1.09 0 79.6 about −30 I24 1.45 0 90.2 about −30 I25 ½(0.73 + 1.45) 0 77 about −30 (1:1 blend E22 + E24)

Examples I26-I28, C26-C28—Acrylic/Methacrylic Acid Comparison

(78) Emulsion polymers are prepared from the monomers identified in Table 9a and are admixed with 1 pphm Al(acac).sub.3. The quantities are parts by weight.

(79) TABLE-US-00017 TABLE 9a Emulsion polymers - composition Al(acac).sub.3 Example EHA BA S VAc HPA MA AA MAA [pphm] I26 77.5 — 10 8 2 — — 2.5 1 C26 77.5 — 10 8 2 — 2.5 — 1 I27 — 85 10 — — — — 5   1 C27 — 85 10 — — — 5   — 1 I28 59 15 20 — — 3.5 — 2.5 1 C28 59 15 20 — — 3.5 2.5 — 1

(80) TABLE-US-00018 TABLE 9b Emulsion polymers - Properties Fine Fine coagulum .sup.1) coagulum .sup.2) Blushing Gel.sub.irreversible Gel.sub.total 125 μm 125 μm after 6 h Example [%] [%] [g/100 g] [g/100 g] Viscosity [%] E26 12.7 87.3 0.010 0.019 Flowable 2.05 C26 76.6 88.3 0.035 0.034 Pasty 3.99 Not flowable I27 10.6 90.1 0.005 0.003 3.5 C27 56.9 89.5 0.008 0.003 13.04 I28 0 91.4 0.005 0.004 6.28 C28 55.4 87.5 0.019 0.011 6.49 .sup.1) before addition of Al(acac).sub.3 .sup.2) after addition of Al(acac).sub.3

(81) The examples show that methacrylic acid relative to acrylic acid is advantageous as an acid monomer, since the gel content based on irreversible, covalent crosslinking can be adjusted below 50% only with methacrylic acid, the values for fine coagulum before and after addition of Al(acac).sub.3 tend to be lower, the viscosity tends to be lower, and the blushing stability is improved.

Examples I29-I35, C29-C30

(82) Emulsion polymers were prepared from the amounts of monomers identified in Table 10a and Al(acac).sub.3 and were admixed with 2 wt % of Rheovis® 1420 (thickener). The amount of thickener was 1 wt % for I30 and I31 and 2.5 wt % for I32. The quantities are parts by weight.

(83) TABLE-US-00019 TABLE 10a Emulsion polymers (quantities in parts by weight) Al(acac).sub.3 Gel-.sub.irreversible Gel-.sub.total Example EHA BA S VAc EA MA MAA [pphm] [%] [%] I29 57 0 10 5 25 3 1 <5 83 C29 57 0 10 5 25 3 — <5 <5 I30 52 10 35 3 1 <5 80.5 C30 52 10 35 3 — <5 <5 I31 57 20 5 15 3 1 <5 84 I32 45.5 30 10 12 2.5 1 <5 84.4 I33 64.5 8 15 10 2.5 1 <5 83.5 I34 58.25 10 5 25 1.75 1 <5 81.5 I35 59 15 20 5 1 1 <5 81.7

(84) Adhesive foils were produced from plasticized PVC. The performance properties are set out in Table 10b.

(85) TABLE-US-00020 TABLE 10b Performance properties Shear strength Shear strength Gap width .sup.1) Shrinkage .sup.2) Example [h] 3 d/70° C. [h] 5 d/70° C. [mm] 3 d/70° C. [%] I29 >100 >100 0.1 vert. 0.1 width 0.1 horiz. 0.2 length C29 33.1 26.4 2.0 vert. 0.7 width 2.4 horiz. 0.9 length I30 >100 >100 0.1 vert. 0.1 width 0.1 horiz. 0.2 length C30 69.8 58.9 1.3 vert. 0.5 width 1.5 horiz. 0.6 length I31 >100 >100 0.1 vert. 0.2 width 0.1 horiz. 0.3 length I32 >100 >100 0.1 vert. 0.2 width 0.1 horiz. 0.2 length I33 >100 >100 0.1 vert. 0.1 width 0.1 horiz. 0.2 length I34 86 >100 0.1 vert. 0.2-0.3 width >100 0.1 horiz. 0.3-0.4 length I35 >100 >100 0.1 vert. 0.4 width 0.1 horiz. 0.5 length .sup.1) Measurement method: plasticizer resistance, cross-cut .sup.2) Measurement method: laminate shrinkage