AQUEOUS BINDERS FOR HEAT-SEALING APPLICATIONS

Abstract

The present invention relates to aqueous binders and to heat-sealing lacquers produced therefrom for heat-sealable coatings which adhere on aluminium without use of any primer, permit good sealability of the coated aluminium foil with respect to PS and/or PVC, and moreover feature good blocking resistance even at temperatures above 40 C.

Claims

1. A process, comprising applying a heat-sealing lacquer in a single layer to an aluminum surface prior to performing a sealing process, wherein the heat-sealing lacquer comprises at least 50% by weight of an aqueous dispersion comprising: a first polymer phase having a glass transition temperature of from 20 to 30 C.; and a second polymer phase having a glass transition temperature of from 20 to less than 50 C. and comprising from 2 to 10% by weight of at least one acid copolymerizable with methacrylates, based on a total weight of the first polymer phase and the second polymer phase.

2. The process of claim 1, wherein the aqueous dispersion comprises from 15 to 64% by weight of polymers comprising: from 25 to 78% by weight of an alkyl ester of methacrylic acid; from 4 to 40% by weight of an alkyl ester of acrylic acid; from 2 to 9% by weight of the at least one acid copolymerizable with methacrylates; and up to 20% by weight of at least one other monomer copolymerizable with (meth)acrylates, but which is not a (meth)acrylate.

3. The process of claim 1, wherein polymers in the aqueous dispersion comprise from 49 to 65% by weight of an alkyl ester of methacrylic acid; from 17 to 30% by weight of an alkyl ester of acrylic acid; from 3 to 8% by weight of (meth)acrylic acid; and from 8 to 15% by weight of styrene.

4. The process of claim 1, wherein: the first polymer phase has a glass transition temperature of from 10 to 25 C.; and the second polymer phase has a glass transition temperature of from 30 to 45 C.

5. The process of claim 1, wherein polymers in the aqueous dispersion further comprise from 2 to 12% by weight of an alkyl ester of (meth)acrylic acid having at least one other functional group.

6. The process of claim 5, wherein the alkyl ester of (meth)acrylic acid having at least one other functional group comprises hydroxyethyl (meth)acrylate, and an amount of the hydroxyethyl (meth)acrylate in the polymers is from 3 to 7% by weight.

7. The process of claim 1, wherein polymers of the aqueous dispersion comprise: from 37 to 70% by weight of methyl methacrylate, butyl methacrylate, or both, from 12 to 35% by weight of a C.sub.1-C.sub.4-alkyl ester of acrylic acid; from 3 to 7% by weight of a hydroxy-functional (meth)acrylate; from 2 to 9% by weight of (meth)acrylic acid; and from 4 to 20% by weight of styrene.

8. The process of claim 7, wherein the polymers comprise: from 49 to 65% by weight of the methyl methacrylate, the butyl methacrylate, or both; from 20 to 30% by weight of the C.sub.1-C.sub.4-alkyl ester of acrylic acid; from 4 to 6% by weight of the hydroxy-functional (meth)acrylate; from 5 to 7% by weight of the (meth)acrylic acid; and from 8 to 15% by weight of the styrene.

9. The process of claim 1, wherein the aqueous dispersion is formed by emulsion polymerization, such that: a first monomer mixture, which forms a polymer having a glass transition temperature of from 20 to 30 C., is initially charged; and after polymerization of the first monomer mixture a second monomer mixture, which forms a polymer having a glass transition temperature of from 20 to less than 50 C. is added, and polymerized, to form a core-shell particle comprising the first polymer phase and the second polymer phase.

10. The process of claim 9, wherein: the first monomer mixture comprises one or more hydroxy-functional (meth)acrylates; the second monomer mixture comprises a carboxylic acid copolymerizable with (meth)acrylates; and a ratio by weight of the first monomer mixture to the second monomer mixture ranges from 1:9 to 8:2.

11. The process of claim 9, wherein the second monomer mixture is polymerized in the presence of a chain-transfer agent.

12. The process of claim 1, wherein the heat-sealing lacquer is effective to seal aluminum surfaces with respect to styrene, PET, PLA or PVC.

13. The process of claim 1, wherein: the first polymer phase has a glass transition temperature of from 5 to 5 C.; and the second polymer phase has a glass transition temperature of from 30 to 45 C.

14. The process of claim 5, wherein the alkyl ester of (meth)acrylic acid having at least one other functional group comprises hydroxyethyl (meth)acrylate, and an amount of the hydroxyethyl (meth)acrylate in the polymers is from 4 to 6% by weight.

15. The process of claim 9, wherein the second monomer mixture is polymerized in the presence of 0.2% by weight of n-DDM as a chain-transfer agent.

Description

EXAMPLES

[0036] Production specifications for Inventive Examples 1-11 and Comparative Examples 1 and 3.

[0037] Inventive Example 9 provides a detailed description of the synthesis method and of the nature of the starting materials used. Inventive Example 9 differs from Inventive Examples 1-8, inventive Examples 10 and 11, and also Comparative Examples 1 and 3, in monomer composition of the first and second stage, which can be found in table 1, and also in the distribution of some of the starting materials, amounts of which can be calculated as follows: all of the polymerization processes were conducted in two stages, in each case distributing 520 g of monomer over the two stages. Emulsifier content is 0.52%, of which 52.4% are used in the first stage and 47.6% in the second stage. 10% of the emulsifier for the first stage here are used in the initial charge in the reactor, and 90% are used in the emuision. The emulsions are in each case mixed with 34% by weight water content. The amount of initiator used is 0.09505 mol % of ammonium persulphate (APS), based on the monomers of the first stage. A further amount of 0.1062 mol % of initiator, based on the monomers of the second stage, is added to the second-stage emulsion.

Production Specification for Inventive Example 9

[0038] 224 g of deionized water and 0.19 g of Rewopol SBDO 75 emulsifier are weighed into a 1 litre round-bottomed Quickfit flask with Quickfit lid, thermometer and stirrer, and are heated to an internal temperature of about 80 C. in a water bath, with stirring (150 rpm). The first-stage emulsion was produced by, weighing 1.70 g of Rewopol SBDO 75, 36.40 g of hydroxyethyl acrylate, 162.0 g of MMA, 165.6 g of n-butyl acrylate and 188.0 g of deionized water into a Woulff bottle and stirring this mixture for 5 min, leaving it to stand for 1 min and then stirring for a further 15 min.

[0039] The initial charge in the reactor is heated to an internal temperature of 80 C. and then 7.0 mL of APS (10% by weight) are added and incorporated by stirring for 5 min. The emulsion is metered at a metering rate of 3.3 g/min for three minutes. A slight temperature rise occurs here. and the metering is interrupted for 4 min. The rest of the emulsion is now metered at a metering rate of 3.3 g/min, and on completion stirring continued for 20 min.

[0040] The second-stage em ion is produced by weighing 1.72 g of Rewopol 5800 75 emulsifier, 15.6 g of acrylic acid, 31.2 g of styrene, 109.2 g of n-butyl methacrylate and 81 g of deionized water into a Woulff bottle, stirring the mixture for 5 min, leaving it to stand min and then again stirring for 15 min. 3.1 g of ammonium persulphate are added to this mixture and incorporated by vigorous stirring.

[0041] Once the reaction time for the first stage has expired, the second stage is metered into ;.a mixture at a metering rate of 3.3 g/min, and this is followed by 60 minutes of continued-reaction time. The dispersion is cooled and then filtered through a 150 m sieve.

Production Specification for Comparative Example CE2

[0042] Comparative Example CE 2 was produced in accordance with the prior art of WO2011017388. Example 2.

[0043] Foil Material Used

[0044] High-flexibility aluminium foils of thickness 38 m and PS and PVC foils of thickness 500 m were used.

[0045] Laboratory Application of Heat-Sealing Dispersion

[0046] A K Hand coater No. 3 was used to apply the aqueous binder.

[0047] Laboratory Drying of Coated Foils

[0048] Directly after application of the aqueous binder, the foils were dried at 180 C. in convection oven for 15 seconds.

[0049] Heat-Sealing and Determination of Seal Seam Strength

[0050] Heat sealing equipment from LOWA GmbH was used to produce the seals.

[0051] Sealing condition

[0052] Temperature: 180 C.

[0053] Pressure: 3 bar

[0054] Time: 1 sec.

[0055] Sealing area: 10100 mm

[0056] Seal seam strength was determined by cutting specimens into strips of width 15 mm and subjecting these t tension at a velocity of 100 mm/min., in an Instron 1195 or Zwick 1454 tensile tester. During tensile testing, care as taken to ensure that the angle between the separated parts of the foils and the remainder not yet subjected to stress was 90.

[0057] Exposure to Water

[0058] The water resistance of the lacquer was determined by placing the sealed strips in mains water for 48 h, and then drying them and determining heat sealing strength as described above.

[0059] Determination of Blocking Point

[0060] Blocking point was determined by using the heat-sealing equipment described above, but after replacement of one of the heated jaws by an unheated rubber jaw. The lacquered sides of two lacquered aluminium strips (prepared as described above) were pressed against one another at a defined temperature under a pressure of one bar for 30 seconds in the equipment. The blocking point is the temperature at which the aluminium strips remain adhering to one another when only one of the strips is held. At lower the weight of the aluminium strips is sufficient to separate these from one another. Measurements were made at intervals of 5 C.

TABLE-US-00001 TABLE 1 Compositions and production process for Inventive Examples 1-9 Proportion of Stage 1 Stage 2 Specimen Stage 1 in % MMA n-BA HEA BMA AA Styrene n-DDM TGA Inv. Ex. 1 50 57 33 10 70 10 20 Inv. Ex. 2 60 44.5 45.5 10 69.8 10 20 0.2 Inv. Ex. 3 50 44.5 45.5 10 70 10 20 Inv. Ex. 4 60 44.5 45.5 10 80 10 10 Inv. Ex. 5 60 44.5 45.5 10 69.8 10 20 0.2 Inv. Ex. 6 50 48 52 70 10 20 Inv. Ex. 7 50 48 42 10 70 10 20 Inv. Ex. 8 30 44.5 45.5 10 70 10 20 Inv. Ex. 9 70 44.5 45.5 10 70 10 20 MMA: Methyl methacrylate; n-BA: n-butyl acrylate; HEA: 2-hydroxyethyl acrylate; BMA: n-butyl methacrylate; AA: acrylic acid; n-DDM: n-dodecyl mercaptan; TGA: thioglycolic acid

TABLE-US-00002 TABLE 2 Composition and production process for Comparative Examples 1-3 and Inventive Examples 10-11 Proportion of Stage 1 Stage 2 Specimen Stage 1 in % MMA BMA EA AA BA HEA MMA BMA Styrene EHMA AA CE1 50 44.5 45.5 10 70 10 10 10 CE2 see WO2011017388, Example 2 CE3 30 70 20 10 70 10 20 IE10 60 24 66 10 70 10 20 IE11 15 44.5 0 45.5 10 0 70 20 0 10 MMA: methyl methacrylate; EA: ethyl acrylate; BA: n-butyl acrylate; HEA: 2-hydroxyethyl acrylate; BMA: n-butyl methacrylate; AA: acrylic acid; n-DDM: n-dodecyl mercaptan; TGA: thioglycolic acid; EHMA: ethylhexyl methacrylate

TABLE-US-00003 TABLE 3 Properties of binders produced in Inventive Examples 1-11 and Comparative Examples 1-3 HSF v PS [N/15 mm] HSF v PVC [N/15 mm] H.sub.2O H.sub.2O Blocking Tg Tg Fracture Fracture Fracture Fracture point Ps Stage 1 Stage 2 Specimen site site site site [ C.] [nm] [ C.] [ C.] IE 1 6 PS nd nd <1 partial nd nd 50 146 20 41 IE 2 8 PS 8 PS 7 Al 8 partial 45 161 0 41 IE 3 7 PS nd nd 6 Al nd nd 45 172 0 41 IE 4 7 PS nd nd 6 Al nd nd 40 145 0 34 IE 5 8 PS 8 partial 6 Al 5 partial 45 143 0 41 IE 6 2 PS nd nd 5 Al nd nd 45 150 0 41 IE 7 7 PS nd nd 5 partial nd nd 45 124 5 41 IE 8 7 PS 7 PS 2 partial 6 partial 50-55 181 0 41 IE 9 8 PS 7 PS 6 Al 4 Al 45 153 0 41 IE 10 9 PS 6 Al 6 Al 5 Al 40 141 1 41 IE 11 4 PS 5 PS 1 nd 1 nd 55 263 0 41 CE1 1 PS nd nd 1 PVC nd nd 55-60 158 0 79 CE2 6 Both 7 partial 5 partial 6 partial <35 78 15* 56* sides CE3 3 Al 1 partial 60 155 43 41

[0061] Glass transition temperatures indicated by * have been taken from WO2011017388. The HSF column in the table states the heat sealing strength values measured with respect to polystyrene (PS) and polyvinyl chloride (PVC). The column headed H.sub.2O describes the heat sealing strength values after exposure to water. The Blocking point column indicates the blocking points measured. Ps describes the particle size (determined with Beckmann Coulter LS 13320 equipment, the stated values being the d50 from the numerical distribution), and T.sub.g (stage 1) and T.sub.g (stage 2) are the calculated glass transition temperatures of the respective stages. T.sub.g is calculated by using the Fox equation.

[0062] Inventive Examples 1-9 and 11 comprise dispersions with identical monomer units but markedly different compositions within the individual stages, and in particular with markedly different stage 1: stage 2 ratios. Nevertheless, despite these wide variations good heat sealing strengths and good blocking resistance values are obtained throughout. In the case of inventive Example 11with only a small proportion of stage 1strength values observed with respect to PS after exposure to water are still surprisingly good. Inventive Example 10 shows that it is not essential to use butyl acrylate and that this monomer can be replaced for example by ethyl acrylate, as long as the necessary alterations, which will be understood by the person skilled in the art, are made in the ratios of the individual monomers. However, use of monomers with longer side chains, e.g. n-butyl acrylate or ethylhexyl acrylate, can be expected to give inter aim better water resistance values for the lacquers.

[0063] Comparative Example 1 corresponds to the systems of the prior art in accordance with EP 0 574 803, and does not exhibit any significant heat sealing strength values.

[0064] Comparative Examples 2 corresponds to Example 2 from WO2011017388. Blocking resistance is inadequate.

[0065] Comparative Example 3 exhibits inadequate heat sealing strength values. The glass transition temperature of the first stage is too high.