PLASTICIZER MIGRATION-RESISTANT, UV-CURABLE HOTMELT ADHESIVE FOR GRAPHICS FILMS AND LABELS MADE OF PLASTICIZED PVC

Abstract

Plasticizer migration-resistant, UV-curable hotmelt adhesive for graphics films and labels made of plasticized PVC

Described here is a UV-curable hotmelt adhesive largely resistant to plasticizer migration and comprising a UV-crosslinkable poly(meth)acrylate formed from methyl acrylate, C4-18 alkyl (meth)acrylate, monomer with acid groups, copolymerized photoinitiator and optionally further monomers. The hotmelt adhesive further comprises an aliphatic polyester polymer. The use of the hotmelt adhesive on graphics films and self-adhesive labels made of plasticized PVC is also described.

Claims

1. A UV-curable hotmelt adhesive, comprising: (a) at least one UV-crosslinkable poly(meth)acrylate formed from (i) at least 20% by weight of methyl acrylate, (ii) at least one alkyl (meth)acrylate comprising 4 to 18 carbon atoms in the alkyl group, (iii) at least one ethylenically unsaturated monomer comprising at least one acid group, (iv) at least one ethylenically unsaturated copolymerizable photoinitiator monomer and (v) optionally at least one further monomer distinct from (i) to (iv); and (b) at least one aliphatic polyester polymer which at 20 C. has a dynamic viscosity of 500 to 20,000 mPas.

2. The UV-curable hotmelt adhesive of claim 1, wherein before crosslinking the at least one UV-crosslinkable poly(meth)acrylate has a glass transition temperature of not more than 10 C.

3. The UV-curable hotmelt adhesive of claim 1, wherein before crosslinking the at least one UV-crosslinkable poly(meth)acrylate has a K value of at least 20.

4. The UV-curable hotmelt adhesive of claim 1, wherein the at least one aliphatic polyester polymer is employed in an amount of 1% to 20% by weight based on the at least one UV-crosslinkable poly(meth)acrylate.

5. The UV-curable hotmelt adhesive of claim 1, wherein the at least one aliphatic polyester polymer is formed from at least one aliphatic dicarboxylic acid comprising 3 to 10, carbon atoms and at least one alkanediol comprising 2 to 10, carbon atoms.

6. The UV-curable hotmelt adhesive of claim 5, wherein the at least one aliphatic polyester polymer is formed from adipic acid and at least one alkanediol comprising 4 to 8 carbon atoms.

7. The UV-curable hotmelt adhesive of claim 1, wherein the at least one UV-crosslinkable poly(meth)acrylate is formed to an extent of 25% to 60% by weight from methyl acrylate.

8. The UV-curable hotmelt adhesive of claim 1, wherein the at least one UV-crosslinkable poly(meth)acrylate is formed to an extent of least 30% by weight from C4- to C10-alkyl (meth)acrylates.

9. The UV-curable hotmelt adhesive of claim 1, wherein the at least one UV-crosslinkable poly(meth)acrylate is formed to an extent of 0.1% to 30% by weight from the at least one ethylenically unsaturated monomer (iii) comprising the at least one acid group.

10. The UV-curable hotmelt adhesive of claim 1, wherein the at least one ethylenically unsaturated copolymerizable photoinitiator monomer (iv) is copolymerized into the at least one UV-crosslinkable poly(meth)acrylate in an amount of not less than 0.1% by weight.

11. The UV-curable hotmelt adhesive of claim 1, wherein the at least one UV-crosslinkable poly(meth)acrylate is formed to an extent of 0% to 25% by weight from the at least one further monomer (v) distinct from (i) to (iv).

12. The UV-curable hotmelt adhesive of claim 1, wherein the at least one further monomer (v) comprises no N-containing monomers and no aromatic monomers.

13. The UV-curable hotmelt adhesive of claim 1, wherein the at least one UV-crosslinkable poly(meth)acrylate (a) is formed from (i) 25% to 60% by weight of methyl acrylate, (ii) 35% to 60% by weight of at least one alkyl (meth)acrylate selected from the group consisting of n-butyl acrylate, n-n-hexyl acrylate, 2-ethylhexyl acrylate, propylheptyl acrylate and mixtures thereof, (iii) 1% to 10% by weight of acrylic acid, methacrylic acid or a mixture thereof, (iv) 0.2% to 5% by weight of the at least one ethylenically unsaturated copolymerizable photoinitiator monomer and (v) 0% to 25% of the at least one further monomer distinct from (i) to (iv), and the at least one aliphatic polyester polymer (b) is used in an amount of 1% to 20% by weight and is formed from at least one aliphatic dicarboxylic acid comprising 4 to 8 carbon atoms and at least one alkanediol comprising 4 to 8 carbon atoms.

14. The UV-curable hotmelt adhesive of claim 1, wherein at least one tackifier is present.

15. A method of producing a graphics film made of plasticized PVC or a label made of plasticized PVC, the method comprising contacting the graphics film or the label with the UV-curable hotmelt adhesive of claim 1.

16. The method of claim 15, wherein the plasticized PVC comprises PVC-compatible plasticizers in an amount of 10% to 70% by weight and the PVC-compatible plasticizers are selected from phthalate esters, esters of trimellitic acid and linear or predominantly linear C.sub.6- to C.sub.11-alcohols; acyclic and aliphatic dicarboxylate esters, alicyclic dicarboxylate esters, phosphate esters, citrate esters, lactate esters, epoxy plasticizers, benzenesulfonamides, methylbenzenesulfonamides; and polymeric plasticizers obtainable by reaction of dihydric alcohols with dibasic carboxylic acids, optionally with co-use of monofunctional alcohols.

17. A self-adhesive graphics film made of plasticized PVC or a self-adhesive label made of plasticized PVC, each comprising an adhesive layer formed from the UV-curable hotmelt adhesive of claim 1.

18. The self-adhesive graphics film or the self-adhesive label of claim 17 wherein an application rate of the UV-curable hotmelt adhesive is 5 to 50 g/m.sup.2.

Description

EXAMPLES

[0085] Input materials: [0086] nBA n-butyl acrylate [0087] 2-EHA 2-ethylhexyl acrylate [0088] MA methyl acrylate [0089] AA acrylic acid [0090] F1 photoinitiator monomer: polymerizable photoinitiator (35% solution in MEK) of formula F-1. [0091] MEK methyl ethyl ketone [0092] t-BPPiv tert-butyl perpivalate (75% solution in mineral oil) [0093] Palamoll 632: polyester made of adipic acid and 1,2-propanediol, polymeric adipate dynamic viscosity 2000-3500 mPas [0094] Plastomoll DOA: di-i-octyl adipate; monomeric adipate; dynamic viscosity 13-15 mPas (mixture of di-n-octyl adipate and diethylhexyl adipate) [0095] Lutonal M 40: polyvinyl methyl ether [0096] Foral 85-E: glyceryl ester of hydrogenated colophony resin [0097] acResin A 260 UV: MA-free polyacrylate, UV-crosslinkable [0098] acResin A 204 UV: polyacrylate, UV-crosslinkable having MA content of more than 15% and less than 20% by weight [0099] Polymer 1: UV-crosslinkable poly(meth)acrylate made of 44% by weight of 2-EHA, 40% by weight of MA, 5% by weight of AA, 10% by weight of MMA, 1% by weight of F1

[0100] Production of polymer 1 (V7)

[0101] In a polymerization apparatus consisting of a glass reactor, a reflux condenser, a stirrer and a nitrogen inlet 210 g of MEK are initially charged under a light nitrogen stream and heated to 80 C. 25 g of altogether 920 g of a monomer mixture composed of 2-EHA, MA, AA, MMA and F1 and having the abovementioned composition are added. Upon reattaining 80 C. 1.9 g of a starter solution of 3.6 g of tert-butyl perpivalate and 42.3 g of MEK are added and the mixture is polymerized for 3 min. Then the remaining 895 g of monomer mixture and 44 g of starter solution are added over 3 h. The temperature is then increased to 90 C. and a solution of 3 g of tert-butyl perpivalate in 28 g of MEK is added over 30 min. A vacuum is then applied and the solvent is distilled off at not more than 135 C. and less than 50 mbar. The mixture is then degassed with slow stirring for 1 h at 135 C. and the maximum achievable vacuum. The melt is drained into a PP cup.

[0102] K value (1% in THF): 42

[0103] Zero-shear viscosity at 130 C.: 51 Pas

[0104] Production of the mixtures:

[0105] V2: 50 g of acResin A 260 UV are heated to 80 C. and 3.5 g Palamoll 632 are added with stirring, then the mixture is cooled.

[0106] K value of acResin A 260 UV (1% in THF): 48-52

[0107] Zero-shear viscosity of acResin A 260 UV at 130 C.: 30-70 Pas

[0108] V4: 50 g of acResin A 204 UV are heated to 80 C. and 2 g of Palamoll 632 are added with stirring, then the mixture is cooled.

[0109] K value (1% in THF): 49

[0110] Zero-shear viscosity at 130 C.: 37 Pas

[0111] V5: 50 g of acResin A 204 UV are heated to 80 C. and 10 g of Lutonal M40 are added with stirring, then the mixture is cooled.

[0112] K value of acResin A 204 UV (1% in THF): 48-52

[0113] Zero-shear viscosity of acResin A 204 UV at 130 C.: 20-55 Pas

[0114] V6: The polymer is synthesized as described for polymer 1 (V7) but before application of the vacuum the solution is cooled in MEK and 64.5 g of Palamoll 632 are added. The mixture is subsequently worked up as for polymer 1.

[0115] K value (1% in THF): 42

[0116] Zero-shear viscosity at 130 C.: 40 Pas

[0117] B1: The polymer is synthesized and worked up as described in V6. In contrast to V6 the coated film is crosslinked through UV curing.

[0118] B2: The polymer is synthesized as described for polymer 1 but before application of the vacuum the solution is cooled in MEK and 64.5 g of Palamoll 632 and 69 g of Foral 85-E are added. The mixture is subsequently worked up as for polymer 1.

[0119] K value (1% in THF): 42

[0120] Zero-shear viscosity at 130 C.: 45 Pas

[0121] V8: 50 g of polymer 1 (V7) are heated to 80 C. and 3.5 g of Plastomoll DOA are added with stirring, then the mixture is cooled.

[0122] K value (1% in THF): 40

[0123] Zero-shear viscosity at 130 C.: 24 Pas

[0124] Measurement of Zero-Shear Viscosity:

[0125] The zero-shear viscosity is the threshold value of the viscosity function at infinitely low shear rates. It is measured with an Anton Paar MCR 100 rheometer (US 200 evaluation software) in plate/plate geometry. The samples are measured under oscillatory shear at a small shear amplitude of 10%. Temperature 130 C. (or as stated), angular frequency ramp log 100-0.1 1/s, measuing gap 0.5 mm, evaluation according to Carreau-Gahleitner I, piston diameter 25 mm.

[0126] Performance Tests:

[0127] The measurements are carried out at room temperature (20 C.) unless explicitly stated otherwise.

[0128] The pressure-sensitive adhesives were heated to 120 C. and doctor coated from the melt onto siliconized PET film at an application rate of 25 g/m.sup.2 or 15 g/m.sup.2 (only V7) and irradiated with UVC light or not irradiated (V6). The film is then transferred to a commercially available 100 m plasticized PVC film (SK-S-P Transparent from Renolit) as a carrier. The carrier coated with pressure-sensitive adhesive was cut into 25 mm wide test strips. The tests were either continued immediately or the test strips were stored for 3 days at 70 C. and 50% rel. humidity before testing to determine plasticizer resistance.

[0129] a) peel strength

[0130] To determine peel strength the 25 mm wide test strips were bonded to the test surface made of steel (AFERA steel) and rolled on once with a 1 kg roller. One end of the test strips is then clamped in the upper jaws of a tensile strain tester. The adhesive strip was removed from the test surface at 300 mm/min and an angle of 180 , i.e. the adhesive strip was bent and removed parallel to the steel test sheet and the force required therefor was measured. The measure for peel strength is the force in N/25 mm obtained as the average value from five measurements. The peel strength was determined 24 hours after bonding. The adhesive strength has fully developed after this time.

[0131] b) shear strength

[0132] To determine shear strength the test strips were bonded to steel sheet (AFERA steel) with a bonded area of 2525 mm, rolled on once with a 1 kg roller and then loaded with a 1 kg hanging weight. The shear strength (cohesion) was determined under standard climatic conditions (23 C.; 50% relative atmospheric humidity). The measure for shear strength is the time in hours until the weight drops off. An average was formed from five measurements in each case.

TABLE-US-00001 TABLE 1 UV-curable hotmelt adhesives UV-crosslinkable Example poly(meth)acrylate Additive V1 acResin A 260 UV V2 acResin A 260 UV 7% by weight Palamoll 632 V3 acResin A 204 UV V4 acResin A 204 UV 4% by weight Palamoll 632 V5 acResin A 204 UV 20% by weight Lutonal M 40 V6 polymer 1 7% by weight Palamoll 632 V7 polymer 1 B1 polymer 1 7% by weight Palamoll 632 B2 polymer 1 7% by weight Palamoll 632 7.5% by weight Foral 85E V8 polymer 1 7% by weight Plastomoll DOA

TABLE-US-00002 TABLE 2 Test results 24 h Peel steel Shear 1 h steel; [N/25 mm] 25 25 mm, 1 kg [h] Irradiation, Before After Before After Example UVC dose storage 3 d/70 C. storage 3 d/70 C. V1 20 mJ/cm.sup.2 16 10 28 5 V2 20 mJ/cm.sup.2 14 10 13 4 V3 20 mJ/cm.sup.2 12 6 >50 11 V4 20 mJ/cm.sup.2 12 6 35 10 V5 10 mJ/cm.sup.2 24 9 38 4 V6 27 24 1 0.2 V7 10 mJ/cm.sup.2, 23 13 >50 23 (15 g/m.sup.2) B1 20 mJ/cm.sup.2 20 18 >50 >50 B2 20 mJ/cm.sup.2 25 18 >50 38 V8 20 mJ/cm.sup.2 15 9 >50 31 V1 to V8: Comparative tests; B1 to B2: inventive

[0133] The following adhesion values are preferred:

TABLE-US-00003 24 h Peel after 3 d/70 C. less than 50% drop and >10N/25 mm 1 h Shear after 3 d/70 C. less than 50% drop and >15 h

[0134] The results show:

TABLE-US-00004 V1 cohesion value too low, cohesion drop (shear) > 50% V2 cohesion value too low, cohesion drop (shear) > 50% V3 peel value falls to too low a value, cohesion drop (shear) > 50% V4 peel value falls to too low a value, cohesion drop (shear) > 50% V5 peel value drop (peel) and cohesion drop (shear) > 50% V6 no cohesion V7 cohesion drop (shear) > 50% B1 inventive B2 inventive V8 peel values too low

[0135] The results show that an MA-free polymer (V1 and V2), both with and without the addition of plasticizer, has too little plasticizer resistance as reflected in a more than 50% drop in cohesion values. A polymer having an MA content of less than 20% (V3) shows excessively low peel values after storage. The addition of plasticizer (V4) does not increase the peel values as desired. Furthermore both samples show too pronounced a drop in cohesion after storage (too little plasticizer resistance). The addition of polyvinyl ethers (V5) does not improve plasticizer resistance either. A composition according to the invention but without crosslinking by means of UV curing (V6) results in very low cohesion values even before storage. However, with crosslinking it is possible to achieve a pressure-sensitive adhesive system that meets the required demands on adhesion values and plasticizer resistance both with additional tackifier (B2) and without additional tackifier (B1). The pure, plasticizer-free polymer (V7) only just fails to meet the demands on plasticizer resistance in respect of shear values after storage. Replacing the polymeric plasticizer with a monomeric plasticizer (V8) results in excessively low peel values.