AQUEOUS COATING COMPOSITIONS CONTAINING POLYMER DISPERSION WITH LOW ELECTRICAL CONDUCTIVITY AND PHYLLOSILICATES FOR OXYGEN BARRIER COATINGS

Abstract

Described is an aqueous coating composition comprising an aqueous dispersion of a radically polymerized addition polymer and phyllosilicate. The aqueous polymer dispersion has a particularly low electrical conductivity. The composition can be used for providing oxygen barrier properties to polymer films.

Claims

1. An aqueous coating composition, comprising: (a) at least one aqueous dispersion of a radically polymerized addition polymer, and (b) at least one phyllosilicate, wherein the at least one aqueous dispersion has an electrical conductivity below 0.6 mS/cm, measured at a concentration of 2.5 wt.-% of solids and at 20? C.

2. The aqueous coating composition of claim 1, comprising: (a) the radically polymerized addition polymer in a range of 10 to 90 wt. %, with respect to a solids content of the aqueous coating composition, and (b) the at least one phyllosilicate in a range of 5 to 75 wt. %, with respect the solids content.

3. The aqueous coating composition of claim 1, wherein the aqueous coating composition is a one-component composition which comprises no crosslinker for the radically polymerized addition polymer.

4. The aqueous coating composition of claim 1, wherein the at least one aqueous dispersion is a secondary polymer dispersion, polymerized in an organic solvent or in bulk and then dispersed in water; or wherein the at least one aqueous dispersion is a primary polymer dispersion, polymerized in water by emulsion or suspension polymerization and then reduced in terms of an amount of an ionic component.

5. The aqueous coating composition of claim 1, wherein the radically polymerized addition polymer is at least one polymer selected from the group consisting of an acrylic copolymer, a styrene-acrylic copolymer, a vinyl-acrylic copolymer, a styrene-butadiene copolymer, a vinyl acetate copolymer, a vinyl chloride copolymer and a vinylidene chloride copolymer.

6. The aqueous coating composition of claim 1, wherein the radically polymerized addition polymer is obtained via free-radically initiated polymerization of one or more ethylenically unsaturated, free-radically polymerizable monomers selected from the group consisting of a vinylaromatic compound, a conjugated aliphatic diene, an ethylenically unsaturated acid, an ethylenically unsaturated carboxamide, an ethylenically unsaturated carbonitrile, a vinyl ester of a saturated C.sub.1 to C.sub.20 carboxylic acid, an ester of acrylic acid or methacrylic acid with a monohydric C.sub.1 to C.sub.20 alcohol, an allyl ester of a saturated carboxylic acid, a vinyl ether, a vinyl ketone, a dialkyl ester of an ethylenically unsaturated dicarboxylic acid, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, an N,N-dialkylaminoalkyl acrylamide, an N,N-dialkylaminoalkyl methacrylamide, an N,N-dialkylaminoalkyl acrylate, an N,N-dialkylaminoalkyl methacrylate, a vinyl halide, an aliphatic hydrocarbon having 2 to 8 carbon atoms and one or two double bonds, and a mixture thereof.

7. The aqueous coating composition of claim 1, wherein the radically polymerized addition polymer is selected from the group consisting of: (i) a copolymer comprising 19.8 to 80 parts by weight of at least one vinylaromatic compound, 19.8 to 80 parts by weight of at least one conjugated aliphatic diene, 0.1 to 10 parts by weight of at least one ethylenically unsaturated acid, and 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, wherein the parts by weight sum to 100; (ii) a copolymer comprising 19.8 to 80 parts by weight of at least one vinylaromatic compound, 19.8 to 80 parts by weight of at least one (meth)acrylate monomer comprising a C.sub.1 to C.sub.20 alkyl group, 0.1 to 10 parts by weight of at least one ethylenically unsaturated acid, and 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, wherein the parts by weight sum to 100; (iii) a copolymer comprising vinyl acetate and at least one (meth)acrylate monomer comprising a C.sub.1 to C.sub.20 alkyl group; (iv) an ethylene-vinyl acetate copolymer; and (v) a (meth)acrylate copolymer comprising at least 80 parts by weight of at least one (meth)acrylate monomer comprising a C.sub.1 to C.sub.20 alkyl group, and 0 to 15 parts by weight of at least one further monomer, different from the at least one (meth)acrylate monomer.

8. The aqueous coating composition of claim 1, wherein at least 60% by weight of the radically polymerized addition polymer is polymerized from butadiene, a mixture comprising butadiene and styrene, a C.sub.1 to C.sub.20 alkyl (meth)acrylate or a mixture comprising a C.sub.1 to C.sub.20 alkyl (meth)acrylate and styrene.

9. The aqueous coating composition of claim 7, comprising (i), wherein the vinylaromatic compound is selected from the group consisting of styrene, methylstyrene and a mixture thereof, the conjugated aliphatic diene is selected from the group consisting of 1,3-butadiene, isoprene and a mixture thereof, and the ethylenically unsaturated acid comprises a compound 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, acrylamidomethylpropanesulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, vinylphosphonic acid and a salt thereof.

10. The aqueous coating composition of claim 1, wherein a weight ratio of the radically polymerized addition polymer to the at least one phyllosilicate is in a range of 95:5 to 50:50.

11. The aqueous coating composition of claim 1, wherein the at least one phyllosilicate is an exfoliated organically modified smectite.

12. The aqueous coating composition of claim 1, wherein the at least one phyllosilicate is a natural or synthetic phyllosilicate with an aspect ratio greater than 400.

13. The aqueous coating composition of claim 1, wherein the at least one phyllosilicate is a synthetic smectite of formula [M.sub.n/valency].sup.inter[M.sup.I.sub.mM.sup.II.sub.o].sup.oct[Si.sub.4].sup.tetO.sub.10Y.sub.2, wherein M is H.sup.+ or a metal cation with an oxidation state of 1 to 3, M.sup.I is a metal cation with an oxidation state of 2 or 3, M.sup.II is a metal cation with an oxidation state of 1 or 2, O is oxygen, Y is a mono-anion m is ?2.0 for each M.sup.I metal cation with an oxidation state of 3, and ?3.0 for each M.sup.I metal cations with an oxidation state of 2, o is ?1.0, and n, the layer charge, is in a range of 0.01 to 2.0.

14. The aqueous coating composition of claim 1, wherein a surface of the at least one phyllosilicate comprises at least one organic compound comprising at least one group selected from the group consisting of an amino group and an ammonium group.

15. A polymer film, coated with the aqueous coating composition of claim 1, wherein the polymer film can be comprised by a laminate.

16. The polymer film of claim 15, wherein an oxygen transmission rate of the polymer film after coating is less than 70% of an oxygen transmission rate of the polymer film before coating, both rates being measured at 25? C. and 90% relative humidity.

17. The polymer film of claim 16, wherein the polymer film comprises at least one material selected from the group consisting of a polyethylene terephthalate, an oriented polypropylene, a polyethylene, a casted polypropylene, a biodegradable aliphatic-aromatic copolyester, a metalized polyethylene terephthalate, a metalized oriented polypropylene and a polyamide, and wherein a thickness of a coating layer is in a range of 0.2 to 50 ?m after drying.

18. A package, comprising the polymer film of claim 16.

19. A method of coating a polymeric film with the aqueous coating composition of claim 1, the method comprising: (a) contacting of at least one side of the polymeric film with the aqueous coating composition and (b) drying said aqueous coating composition to form a barrier coating on the polymeric film.

20. A method of providing oxygen barrier properties to an article, the method comprising contacting a surface of the article with the aqueous coating composition of claim 1.

Description

EXAMPLES

Determination of Particle Size

[0119] The particle size is determined by hydrodynamic fractionation (HDC) using a CHDF-3000 High Resolution Particle Sizer from Matec Instrument Companies. The Cartridge PL0850-1020 column type, filled with polystyrene beads, is used and is operated with a flow rate of about 1 ml/min. The filtered samples are diluted to an absorption of about 0.5 AU/?l with the eluent solution. The sample is eluted, through the size exclusion principle, in dependence of the hydrodynamic diameter. The eluent contains 0.2 g/L of dodecyl poly(ethylene glycol ether)23 (Brij? 35), 0.5 g/L of sodium dodecyl sulfate, 0.24 g/L of sodium dihydrogenphosphate, and 0.2 g/L by weight of sodium azide in deionized water. The pH is about 5.5 to 6. The elution time is calibrated using polystyrene calibration latices. Measurement takes place in the 20 nm to 1200 nm range. Detection is carried out using a UV detector at a wavelength of 254 nm.

Determination of Glass Transition Temperature:

[0120] The glass transition temperature is measured by means of differential scanning calorimetry in accordance with ASTM D 3418-08. For conditioning, the polymers are poured out, dried overnight, then dried at 120? C. in a vacuum drying cabinet for 1 hour. At measurement, the sample is heated to 150? C., cooled rapidly, and then measured on heating at 20? C./min up to 150? C. The value reported is the mid point temperature.

Measurement of Oxygen-Barrier Action:

[0121] The determination method is based on ASTM D3985-05, using a coulometric sensor. Each sample is measured twice and the mean result is calculated. Oxygen transmission rate (OTR) is determined on coatings on polymer films at a relative humidity (RH) level of 75% or 90%, respectively, and at a temperature of 25? C. Measurements are done with synthetic air (21% oxygen); results are extrapolated for 100% oxygen. OTR are obtained on a Mocon OX-TRAN 2/21 XL instrument with a lower detection limit of 0.0005 cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1.

Carrier Material:

[0122] Polymer film of PET (polyethylene terephthalate) from Bleher Folientechnik (Ditzingen, Germany) with a thickness of 36 ?m, one side corona treated.

[0123] OTR of the uncoated plastic film: 33 cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1.

Measurement of Conductivity of Polymer Dispersions:

[0124] In order to determine the conductivity and, thus, salt content of the polymer emulsions employed within these investigations, each dispersion was diluted with distilled water down to a solids content of 2.5% of the respective polymer dispersion. Then, at a temperature of 20? C. the sample was gently stirred with the sensor probe until the reading remained constant. Measurements were performed on an electrical measuring transducer, model Cond 330i from WTW GmbH (Weilheim, Germany) utilizing a TetraCon? 325 sensor probe (cell constant: 0.475 cm.sup.?1, working range: 1 ?S/cm to 2 S/cm) from WTW GmbH. Before recording conductivity values, the device was calibrated against KCl standards (0.01 M and 0.1 M) and air. Each sample was measured twice and the mean result is calculated.

Aqueous Dispersions of a Radically Polymerized Addition Polymers:

[0125]

TABLE-US-00001 Joncryl? anionically stabilized acrylic copolymer, DFC 3030 neutralized with NH.sub.3, 47% solids content commercially available from BASF SE (Ludwigshafen, Germany) described in Example 1 from WO 2006/115729 Joncryl? anionically stabilized styrene-acrylic copolymer, DFC 3040 neutralized with NH.sub.3, 45% solids content commercially available from BASF SE (Ludwigshafen, Germany) described in Example 2 from WO 2006/115729 Vinyl-A anionically stabilized styrene-acrylic copolymer, neutralized with NaOH, 53% solids content detailed manufacture procedure given below Vinyl-B anionically stabilized styrene-acrylic copolymer, neutralized with NaOH, 52% solids content detailed manufacture procedure given below Vinyl-C anionically stabilized styrene-butadiene copolymer, neutralized with NaOH, 56% solids content detailed manufacture procedure given below

Vinyl-A

[0126] A monomer emulsion is prepared which is composed of 188.35 parts of water, 13.28 parts of a sulfuric-acid hemiester of an ethoxylated fatty-alcohol (32% aqueous solution, sodium salt), 5.00 parts of an ethoxylated fatty alcohol (20% aqueous solution), 21.11 parts of sulfonated phenoxy dodecylbenzene (45% aqueous solution, disodium salt), 7.50 parts of acrylic acid, 7.50 parts of styrene, 485.00 parts of n-butyl acrylate and 8.00 parts of sodium hydroxide (25% aqueous solution). To prepare the initiator solution, 2.0 parts of sodium persulfate were dissolved in 38.00 parts of water. A 1.5-liter glass reactor was charged with 138.70 parts of water and 8.33 parts of a polystyrene seed-latex (d ?23 nm, 33% solids), flooded with nitrogen and heated to 85? C. When the polymerization temperature had been reached, 25% of the initiator solution was added within 5 min and stirred for another 2 min at 150 rpm. Thereafter the monomer emulsion and the remainder of the initiator solution were each metered in at a uniform rate over 3 hours, followed by a post-polymerization hold-time of 30 min. For further depletion of residual monomers, a chemical deodorization was carried out by supplying the reaction mixture with 15.70 parts of 9.55% aqueous tert-butyl hydroperoxide solution and 40.23 g of a 6.21% aqueous acetone bisulfite solution simultaneously over a period of 2 hours. After the reaction mixture had cooled to room temperature, 50.00 parts of sodium hydroxide (5% aqueous solution) were added for neutralization.

Vinyl-B

[0127] Similarly to dispersion Vinyl A, a higher-T.sub.g emulsion polymer differing in co-monomer composition was prepared. The respective monomer emulsion is composed of 188.35 parts of water, 13.28 parts of a sulfuric-acid hemiester of an ethoxylated fatty-alcohol (32% aqueous solution, sodium salt), 5.00 parts of an ethoxylated fatty alcohol (20% aqueous solution), 21.11 parts of sulfonated phenoxy dodecylbenzene (45% aqueous solution, disodium salt), 7.50 parts of acrylic acid, 60.00 parts of styrene, 432.50 parts of n-butyl acrylate and 8.00 parts of sodium hydroxide (25% aqueous solution).

Vinyl-C

[0128] A first monomer solution is prepared which is composed of 281.44 parts of water, 220.00 parts of a ethoxylated tridecyl-alcohol (20% aqueous solution), 88.00 parts sodium pyrophosphate (3% aqueous solution) and 110.00 parts acrylamide (50% aqueous solution). A second monomer solution is prepared which is composed of 1379.40 parts of styrene and 17.60 parts of tertdodecyl mecaptane. A 6.0-liter metal reactor with a 3-stage MIG stirrer was charged with 1034.80 parts of water and 42.07 parts of a polystyrene seed-latex (d ?23 nm, 33% solids), flooded with nitrogen and heated to 95? C.; at 90? C., 18.07 parts of sodium persulfate (7% aqueous solution) was slowly added and stirred at 200 rpm. When the polymerization temperature had been reached, at the same time several feeds were started being pre-mixed before entering the polymerization vessel: The first monomer solution was metered in over 2.5 hours, the second monomer solution as well as 765.560 parts of butadiene were metered in over 4.5 hours and 343.36 parts of sodium persulfate (7% aqueous solution) was added over 5.5 hours. When the last feed has ended, the reactor was kept for another hour at 95? C. for post-polymerization. Thereafter, the mixture was neutralized with 22.00 parts of sodium hydroxide (5% aqueous solution) and cooled down to 85? C. For further depletion of residual monomers, a chemical deodorization was carried out by supplying the reaction mixture with 66.00 parts of 10% aqueous tert.-butyl hydroperoxide solution and 47.02 g of a 13.1% aqueous acetone bisulfite solution simultaneously over a period of 1.5 hours. The reaction mixture was cooled to room temperature.

Phyllosilicates:

[0129] Na-hect synthetic sodium fluorohectorite [0130] L-hect hectorite modified with L-lysine

Modification Agents:

[0131] L-lysine: (S)-2,6-Diaminohexanoic acid monohydrochloride C.sub.6H.sub.14N.sub.2O.sub.2.HCl, reagent grade 98%, Sigma-Aldrich GmbH, Germany.

##STR00001##

[0132] The type of phyllosilicate used in the examples is exfoliated smectite type with layer charge of 0.5 per formula unit (p.f.u.). The synthesis procedure of the used phyllosilicate is described in M. Stoter, D. A. Kunz, M. Schmidt, D. Hirsemann, H. Kalo, B. Putz, J. Senker, J. Breu, Langmuir 2013, 29, 1280-1285. The phyllosilicate is a synthetic sodium fluorohectorite (Na-hect) and has a cation exchange capacity of 127 meq/100 g. The chemical formula is:

[Na.sub.0.5.xH.sub.2O].sup.int[Mg.sub.2.5Li.sub.0.5].sup.oct[Si.sub.4].sup.tetO.sub.10F.sub.2

Modification of the Sodium Fluorohectorite:

[0133] Cationic modification was used to replace sodium cations from the surface of the delaminated layered silicate. Modification provides stabilization of the delaminated layered silicates and compatibilization of the layered silicate with the polymer matrix within the suspension and in the drying step of film-formation.

Example 1: Modification of Delaminated Na-Hect (L-Hect)

[0134] In a 50 ml centrifuge tube 0.25 g of Na-hect was suspended in 30 ml of distillate water. For the surface modification of the Na-hect a 125% of CEC (cation exchange capacity) of the modification agent L-Lysin (dissolved in 5 ml distillate water) was added and placed into an overhead shaker for 12 h. Afterward the modified Na-hect was centrifuged at 10000 rpm, the separated supernatant was discarded and the modified Na-hect was re-suspended in distillate water and again a 125% of CEC of the modification agent L-Lysin (dissolved in 5 ml distillate water) was added and placed into an overhead shaker for 12 h to ensure complete surface modification of Na-hect. Again the modified Na-hect was centrifuged at 10000 rpm and the separated supernatant was discarded and the resulting, completely modified clay (=L-hect) was washed with distilled water washed until the conductivity of the separated supernatant was below 25 ?s/cm.

Example 2: General Procedure

Manufacture of Coating Formulation by Suspension of Modified Phyllosilicate Na-Hect in Polymer Dispersions and Preparation of Barrier Films

[0135] Under stirring, the lysine-modified clay (=L-hect) synthesized in Example 1 was added to the required amount of polymer dispersion to produce a suspension with 20 wt. % (based on inorganic material, i.e. without modification agent) of phyllosilicate in the final solid material (the amount of modification agent was calculated on the side of polymer). The final solids content was adjusted to 2.5 wt. % by addition of respective amounts of distilled water yielding a ready-to-use formulation which was applied on the corona-treated side of a pre-heated PET substrate (70? C.) via doctor-blading (18 mm/s, 60 ?m slit width). The resulting coating film was dried first at ambient conditions, then at 80? C. for 48 h and had a dry-film thickness of 1-2 ?m (approx. 1.6 ?m). Subsequently, the coating was analyzed for its oxygen barrier properties. The results are found in Table 1.

Examples 3 to 7

Manufacture of Coating Formulations by Suspension of Modified Phyllosilicate Na-Hect in Low Conductivity Polymer Emulsions and Preparation of Barrier Films

[0136] In a first step, Joncryl? 3030, Joncryl? 3040 as well as vinyl emulsion polymers Vinyl-A to Vinyl-C were post-processed via dialysis to remove excess background salt. For this purpose, the samples were diluted to a solids content of ca. 20% and dialyzed against distilled water (K=0.01 mS/cm) employing an 350 ml Amicon? Stirred Cell from Merck Millipore (Darmstadt, Germany) with a Whatman? Nuclepore? Track-Etched filter membrane (#111503, diam. 76 mm, pore size 0.05 ?m) until electrical conductivity K of the eluent kept at constant low levels. Afterwards, the general procedure outlined in Example 2 was followed employing the respective dialyzed emulsion polymers.

Comparative Examples C2

Barrier Films Based on Clay-Free Polymer Emulsions

[0137] The as-received vinyl emulsion polymers Joncryl? 3030, 3040 and Vinyl-A to Vinyl-C were diluted with distilled water to such an extent that respective drawdowns via doctor-blading (18 mm/s, 60 ?m slit width) yielded a dry-film thickness comparable to Examples 3 to 7 (approx 1.6 ?m).

Comparative Examples C3-C7

Manufacture of Coating Formulations by Suspension of Modified Phyllosilicate Na-Hect in High Conductivity Polymer Emulsions and Preparation of Barrier Films

[0138] The general procedure outlined in Example 2 was followed employing Joncryl? 3030, Joncryl? 3040 as well as vinyl emulsion polymers Vinyl-A to Vinyl-C as received, i.e. without additional post-treatment at their pristine level of background salt.

TABLE-US-00002 TABLE 1 Oxygen barrier properties of polymer-emulsion based coatings OTR of uncoated polymer film = 33.0 [cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1] Particle Polymer Size Post- Conductivity OTR (75% r.h.) OTR (90% r.h. Example Emulsion [nm] treatment [mS/cm] [cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1] [cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1] Joncryl? Joncryl? 3030 071 none 1.29 33.0 3030 .sup.1) C-3 Joncryl? 3030 071 none 1.29 27.0 3 Joncryl? 3030 071 dialyzed 0.08 21.6 Joncryl? Joncryl? 3040 059 None 1.36 33.0 3040 .sup.1) C-4 Joncryl? 3040 059 None 1.36 21.7 4 Joncryl? 3040 059 dialyzed 0.06 10.6 C-5 Vinyl-A 161 None 0.72 34.5 5 Vinyl-A 161 dialyzed 0.04 21.8 C-6 Vinyl-B 164 None 0.63 34.0 6 Vinyl-B 164 dialyzed 0.04 17.0 Vinyl-C .sup.1) Vinyl-C 164 none 0.47 33.0 C-7 Vinyl-C 164 none 0.47 17.5 7 Vinyl-C 164 dialyzed 0.02 8.5 .sup.1) neat polymer dispersion without clay

[0139] As can be seen from the data in Table 1, the neat polymer films of any chemistry under evaluation exhibit no barrier performance at all with OTR values in the range of the uncoated PET substrate. By incorporation of 20 wt. % high-aspect ratio clay filler, barrier properties are improved as demonstrated by a substantial reduction in oxygen transmission rates (OTR) compared to the respective clay-free polymer films. For each pair of samples, i.e. Example C-3 vs. 3, there is a clear trend to be observed in that barrier properties of the final nanocomposite film correlate with the conductivity of the corresponding polymer dispersion, i.e. if conductivity of a 2.5% dispersion is high, OTR values are also high. Thus, both Joncryl? grades described in the Experimental section of WO 2006/115729 as suitable binder resins for clay-filled barrier coatings exhibit high conductivities of >1.0 mS/cm and show only moderate oxygen barrier properties in our test setup. OTR (75% r.h.) values at 20 wt.-% clay loading remain at a 65-80% level, i.e. OTR (75% r.h.) >20 cm.sup.3 m.sup.?2 day.sup.?1 bar.sup.?1. When their conductivity is brought below a certain threshold of ?0.6 mS/cm, preferably ?0.5 mS/cm, O.sub.2 barrier is significantly improved. The same is true for emulsion polymers Vinyl-A to -C where in each case the dialyzed, low conductivity sample exhibits a lower OTR value than its pristine counterpart, even at harsher test conditions of 90% r.h. vs. 75% r.h. Due to the hydrophilic groups of the dispersed polymers water uptake and lower OTR values would be expected at higher humidity (90% r.h.) compared to measurements at lower humidity (75% r.h.). Surprisingly, the OTR values of all low conductivity samples 3 to 7 show lower OTR values than their high conductivity counterparts C.sub.3 to C.sub.7, even at humidity levels as high as 90% r.h.