Process for the preparation of radiation curable compositions

Abstract

The present invention relates to a process for the preparation of a radiation curable composition comprising at least one (meth)acrylic copolymer A and at least one radiation curable compound B, said process comprising a first copolymerization step, and a subsequent ring opening step.

Claims

1. Process for the preparation of a radiation curable composition comprising at least one (meth)acrylic copolymer A and at least one radiation curable compound B, said process comprising: (a) in a first copolymerization step, the preparation of a (meth)acrylic copolymer in the presence of at least one non-copolymerizable cyclic compound (b1) containing at least one ##STR00003## group in the cycle where XO or NH, by copolymerization of a monomer mixture M comprising: (i) from 40 to 95 wt % of at least one (meth)acrylic monomer (a1), (ii) from 5 to 60 wt % of at least one other copolymerizable monomer (a2) different from (meth)acrylic monomer (a1), with the proviso that said monomers (a1) and (a2) contain no functional group that can react with the cyclic compound (b1) during copolymerization, (iii) optionally from 0 to 20 wt % of at least one copolymerizable monomer (a3) containing at least one functional group that can react with the cyclic compound (b1), (iv) optionally from 0 to 5 wt % of at least one copolymerizable monomer (a4) containing at least one cyclic anhydride, (b) in a subsequent ring opening step, the preparation of the radiation curable compound B by the ring opening of the cyclic compound (b1) with at least one radiation curable compound (a5) that contains at least one hydroxyl, carboxylic acid, amine, or thiol functional group, wherein the percentages by weight are herein relative to the total weight of the monomer mixture M and the composition after radiation curing is a viscoelastic material which remains permanently tacky.

2. Process according to claim 1 wherein the cyclic compound (b1) is a lactone or a mixture of lactones.

3. Process according to claim 1 wherein the (meth)acrylic monomer (a1) is selected from alkyl(meth)acrylates whose homopolymers have a Tg of at most 30 C.

4. Process according to claim 1 wherein the (meth)acrylic monomer (a1) is selected from butylacrylate, iso-octylacrylate, 2-ethyl hexylacrylate and mixtures thereof.

5. Process according to claim 1 wherein the copolymerizable monomer (a2) is selected from monomers whose homopolymers have a Tg of more than 30 C.

6. Process according to claim 1 wherein the copolymerizable monomer (a2) is selected from methyl(meth)acrylate, ethyl(meth)acrylate, tertbutyl(meth)acrylate, vinyl acetate, styrene and mixtures thereof.

7. Process according to claim 1 wherein the copolymerizable monomer (a3) is selected from hydroxyalkyl(meth)acrylates, the ethoxylated and/or propoxylated derivatives thereof, the adducts thereof with lactones, polyalkoxy monohydroxy mono(meth)acrylates, (meth)acrylic acid, -carboxyethyl(meth)acrylate, crotonic acid, maleic acid, fumaric acid, itaconic acid, and mixtures of any of them.

8. Process according to claim 1 wherein the copolymerizable monomer (a4) is selected from maleic anhydride, itaconic anhydride, 4-methacryloyloxyethyl trimellitate anhydride and mixtures thereof.

9. Process according to claim 1 wherein in the copolymerization step: (i) from 5 to 60 wt % of cyclic compound (b1), and (ii) from 40 to 95 wt % of the monomer mixture M are used, the wt % are herein relative to the total weight of cyclic compound (b1) and monomer mixture M.

10. Process according to claim 1 wherein the radiation curable compound (a5) is selected from hydroxyalkyl(meth)acrylates, the ethoxylated and/or propoxylated derivatives thereof, the adducts thereof with lactones, polyalkoxy monohydroxy (meth)acrylates, (meth)acrylic acid, -carboxyethyl(meth)acrylate, crotonic acid, maleic acid, fumaric acid, itaconic acid, and mixtures of any of them.

11. Process according to claim 1 wherein the equivalent ratio of cyclic compound (b 1) to functional groups of radiation curable compound (a5) is from 1:1 to 6:1.

12. Process according to claim 1 wherein the monomer mixture M of step (a) comprises: (i) from 40 to 94.5 wt % of (meth)acrylic monomer (a1), (ii) from 5 to 59.5 wt % of copolymerizable monomer (a2), (iii) from 0.5 to 20 wt % of copolymerizable monomer (a3), (iv) optionally from 0 to 5 wt % of copolymerizable monomer (a4), in order to prepare a (meth)acrylic copolymer comprising functional groups originating from copolymerizable monomer (a3) that can react with the cyclic compound (b1), and where the process further comprises a grafting step (c) wherein at least part of said functional groups are reacted with a part of the cyclic compound (b1).

13. Process according to claim 12 wherein the equivalent ratio of cyclic compound (b1) to the sum of the functional groups of copolymerizable monomer (a3) and radiation curable compound (a5) is from 1:1 to 6:1.

14. Process according to claim 12 wherein the grafting step (c) is conducted after the copolymerization step (a).

15. Process according to claim 1 wherein the monomer mixture M of step (a) comprises: (i) from 40 to 94.5 wt % of monomer (a1), (ii) from 5 to 59.5 wt % of copolymerizable monomer (a2), (iii) optionally from 0 to 20 wt % of copolymerizable monomer (a3), (iv) from 0.5 to 5 wt % of copolymerizable monomer (a4), in order to prepare a (meth)acrylic copolymer comprising cyclic anhydride groups originating from copolymerizable monomer (a4), and where the process comprises an adduct formation step (d) wherein at least part of the cyclic anhydride groups is reacted with at least one radiation curable compound (a6).

16. Process according to claim 15 wherein the radiation curable compound (a6) is selected from hydroxyalkyl(meth)acrylates, the ethoxylated and/or propoxylated derivatives thereof, the adducts thereof with lactones, polyalkoxy monohydroxy (meth)acrylates.

17. Process according to claim 15 wherein the equivalent ratio of functional groups of radiation curable compound (a6) to cyclic anhydride groups of monomer (a4) is from 0.5:1 to 2:1.

18. Process according to claim 1 wherein the process further comprises a capping step (e) wherein a functional end group W that is formed by the ring opening of the cyclic compound (b1) at the ring opening step (b), or both at the ring opening step (b) and grafting step (c), is capped with at least one capping compound containing at least one functional group Y capable of reacting with the functional end group W.

19. Process according to claim 18 wherein the functional end group W is a hydroxyl or a primary amine and wherein the capping compound is a mono-, a di- or a polyisocyanate.

20. Process according to claim 1 wherein the process comprises an adduct formation step (d) and a capping step (e).

21. The process according to claim 1, further comprising including a tackifier in said composition.

Description

EXAMPLE 1

(1) Following the above procedure and using the composition given in the table as Example 1, a colourless hazy resin is produced which has the following properties when cured in a 50 m film.

(2) TABLE-US-00002 Adhesive properties Peel 2 N/25 mm Shear 10 min Optical properties Haze 2% Transmission 98.88 L 99.65 a 0.114 b 0.562

(3) Peel is low around 2N/25 mm and the shear is less than 10 min for a 25 mm square strip and a weight of 1 kg. The viscosity of the resin is 10.000 mPa.Math.s at 100 C.

EXAMPLE 2

(4) The above procedure is again followed this time using the composition given in the table as Example 2, in this case however there is a delay of 20 min between addition of the DBTL catalyst and addition the HBA. This allowed time for some -caprolactone to react with the OH functionality on the polymer chain improving compatibility with the -caprolactone, HBA reacted compound B. This product is haze free and has improved optical and adhesive properties compared to example 1.

(5) TABLE-US-00003 Adhesive properties Peel 11 N/25 mm Shear 200 min Optical properties Haze 0.5% Transmission 99.5 L 99.7 a 0.05 b 0.35

(6) The viscosity of the resin is 4500 mPa.Math.s at 100 C.

(7) The PSA films are then aged in an oven at 85 C. for 312 hours and the optical properties are re-measured. This shows that here is no change in haze or transmission and only a very small increase in color.

(8) TABLE-US-00004 Optical properties Haze 0.5% Transmission 99.5 L 99.7 a 0.13 b 0.57

EXAMPLE 3

(9) The above procedure is again followed this time using the composition given in the table as Example 3 with MMA incorporated into the polymer chain, DBTL catalyst is then added followed immediately with 232 g of HBA. This product is haze free with good optical properties. In this case the peel is seen to improve.

(10) TABLE-US-00005 Adhesive properties Peel 15 N/25 mm Shear 30 min

EXAMPLE 4

(11) The above procedure is again followed this time using the composition given in the table as Example 4 with all of the MA replaced by MMA in the polymer chain, DBTL catalyst is then added followed immediately with 232 g of HBA. This product is haze free with good optical properties. In this case we see that the peel adhesion has increased to around 20N/25 mm. Various formulations of this material give us a range of different adhesive and shear properties (examples 5 to 8).

(12) TABLE-US-00006 Adhesive properties Peel 18 N/25 mm Shear 45 min

EXAMPLES 5 to 8

(13) The resin from Example 4 is formulated with TMPTA as shown in the table below in order to give examples 5 to 8. All of these examples were optically clear and haze free.

(14) TABLE-US-00007 Example 5 6 7 8 TMPTA % 1.5 3 4.5 6 Results Peel (N/25 mm) 23 16 15 13 Shear (min) 2780 6420 10060 >12700

EXAMPLE 9

(15) The above general procedure is again followed this time using the composition given in the table as Example 4 with all of the 2EHA replaced by butyl acrylate in the polymer chain, DBTL catalyst is then added followed immediately with 232 g of HBA. This product is haze free with good optical properties. In this case the peel adhesion and shear are those listed in the table below. Various formulations of this material give us a range of different adhesive and shear properties (examples 10 to 14).

(16) TABLE-US-00008 Adhesive properties Peel 17 N/25 mm Shear 460 min

EXAMPLES 10 TO 14

(17) The resin from Example 9 is formulated with TMPTA as shown in the table below in order to give improved shear performance, examples 10 to 14.

(18) TABLE-US-00009 Example 10 11 12 13 14 TMPTA % 1 1.5 3 4.5 6 Results Peel (N/25 mm) 15 17 16 11 10 Shear (min) 2360 1940 2980 >11700 >11700

EXAMPLE 15

(19) The composition given in example 4 is cast onto PET substrate at a thickness of 2 mm (2000 m). This is cured by passing it one time under the UV curing lamp at 5 m/min. The sample is completely cured after one pass. This particular system allows the in depth curing of a very thick composition layer and gives high peel values and moderate shear.

(20) TABLE-US-00010 Adhesive properties Peel 32 N/25 mm Shear 4 min