Method for the production of cross-linkable acrylate contact adhesive materials
View Patent ↗Process for preparing crosslinked pressure ensitive adhesives, in which a plyacrylate is prepared by the free radical copolymericzation of a monomer mixture , the polyacrylate is then concentrated and the concentrated polyacrylate is reacted with further monomers having functional groups and subsequently crosslinking.
1. A process for preparing crosslinked acrylic pressure sensitive adhesives which comprises
first preparing polyacrylates by free-radical (co)polymerization in water, organic solvent or solvents or a mixture thereof from a monomer mixture comprising:
(a) 45-95% by weight of acrylic acid monomers, methacrylic acid monomers, or both, of the following structure:
where R 1 =H or CH 3
and R 2 =an alkyl chain with 2-20 carbon atoms,
(b) 0.5 to 25% by weight of one or more carboxylic anhydrides containing olefinic double bonds,
(c) 0-30% by weight of further olefinically unsaturated monomers possessing functional groups A,
concentrating the polymers thus prepared to form a concentrated polyacrylate composition having a water, solvent or water and solvent concentration of ≦2% by weight,
adding to the concentrated polyacrylate composition further monomers which have at least two functional groups B and C, the groups B being groups which are capable of entering into polymer-analogous reactions with the carboxylic anhydrides, and the groups C being crosslinkable groups,
reacting the functional groups B with the carboxylic anhydride, to attach the monomers containing functional groups B as side chains to the polymers,
after the reaction between the functional groups B and the carboxylic anhydride, crosslinking the polymers with high-energy radiation to form a cross-linked acrylic pressure sensitive adhesive.
2. The process of claim 1 , wherein after reaction of the functional groups B with the carboxylic anhydride and before the crosslinking step, the composition is applied from the melt to a backing.
3. The process of claim 1 , wherein the addition of the monomers possessing the functional groups B and C and the reaction of the functional groups B with the carboxylic anhydride take place directly after the concentration step.
4. The process of claim 1 , wherein the solvent, water or solvent and water content after the concentration step is ≦0.5% by weight.
5. The process of claim 1 , wherein the functional groups B of the monomers are selected from the group consisting of hydroxyl groups, alkoxy groups, mercapto groups, thioether groups, unsubstituted and substituted amino groups, oxalines, unsubstituted or substituted amido groups and combinations thereof.
6. The process of claim 1 , wherein the functional groups C of the monomers are selected from the group consisting of vinyl groups, acrylate groups, methacrylate groups and combinations thereof.
7. The process of claim 1 , wherein the monomers containing functional groups B and C are selected from the group consisting of 2-hydroxyethyl acrylate (2-HEA, acrylic acid 2-hydroxyethyl ester), hydroxypropyl acrylate (acrylic acid 3-hydroxypropyl ester), 2-hydroxyethyl methacrylate (2-HEMA, methacrylic acid 2-hydroxyethyl ester), hydroxypropyl methacrylate (methacrylic acid 3-hydroxypropyl ester) and combinations thereof.
8. The process of claim 1 , wherein the molar ratio of the number n s of the functional groups B of the added monomers to the number n CSA of the copolymerized carboxylic anhydride units, n B /n CSA , is between 0.8 and 1.2.
9. The process of claim 1 , wherein a catalyst is added to the polyacrylate composition.
10. The process of claim 1 , wherein the polymer-analogous reaction is conducted at a temperature of between 60° C. and 180° C.
11. The process of claim 1 , wherein resins or additives selected from the group consisting of aging inhibitors, light stabilizers, ozone protectants, fatty acids, plasticizers, nucleators, blowing agents, accelerators, fillers and combinations thereof are added to the monomer mixture or to the acrylic pressure sensitive adhesive.
12. The process of claim 1 , wherein crosslinkers, photoinitiators or both are added to the polymeric composition to be crosslinked.
13. The process of claim 1 , wherein electron beams or UV radiation are used as high-energy radiation for the crosslinking.
14. An adhesive tape comprising the acrylic pressure sensitive adhesive prepared by the process of claim 1 on one or both sides of a backing.
15. The process of claim 3 , wherein said reaction is conducted in an extruder.
16. The process of claim 8 , wherein said ratio is between 0.8 and 1.
17. The process of claim 9 , wherein said catalyst is a Lewis acid or a Lewis base.
18. The process of claim 17 , wherein said Lewis acid is p-toluenesulfonic acid and said Lewis base is 4-vinylaniline.
19. The process of claim 10 wherein said temperature is between 110°and 160° C.
20. The process of claim 12 , wherein said crosslinkers are selected from the group consisting of difunctional acrylates, difunctional methacrylates, polyfunctional acrylates, polyfunctional methacrylates and combinations thereof.