FUNCTIONALIZED (CO)POLYMERS FOR ADHESIVE SYSTEMS

Abstract

The invention relates to a polymer obtainable by the radical polymerization of at least one monomer, namely one or more (meth)acrylate monomers and optionally, in addition, vinylic comonomers, wherein the polymer has a molar mass M.sub.W of at least 5,000 g/mol and at most 200,000 g/mol and at least one of the monomers is functionalized with at least one epoxy group, wherein the proportion of the epoxide-functionalized monomer(s) (a) is more than 30 wt %.

Claims

1. A polymer formed from the free-radical polymerization of at least one monomer, namely one or more (meth)acrylate monomers and optionally additionally one or more vinylic comonomers, where the formed polymer has a molar mass M.sub.W of at least 5000 g/mol and at most 200 000 g/mol and at least one of the monomers has been functionalized with at least one epoxy group, wherein: the proportion of the epoxy-functionalized monomer(s) is more than 30% by weight.

2. The polymer of claim 1, wherein: the molar mass M.sub.W is at least 10 000 g/mol.

3. The polymer of claim 2, wherein: the molar mass M.sub.W is at most 150 000 g/mol.

4. The polymer of claim 1, wherein: all or some of the oxygen atoms in the epoxy groups bridge an aliphatic C—C bond (aliphatic epoxy group) in at least some of the epoxy-functionalized monomers.

5. The polymer of claim 1, wherein: all or some of the oxygen atoms in the epoxy groups in at least some of the epoxy-functionalized monomers bridge a C—C bond that is part of an optionally hetero-substituted aliphatic hydrocarbon ring (cycloaliphatic epoxy group).

6. The polymer of claim 1, wherein: its glass transition temperature in the uncrosslinked state is above 0° C.

7. The polymer of claim 1, wherein the polymer's glass transition temperature in the uncrosslinked state is below 120° C.

8. The polymer of claim 1, wherein: at least one of the monomers is a hard monomer in that the homopolymer formed from this monomer, in the molecular weight-independent range, has a glass transition temperature of at least 25° C.

9. The polymer of claim 1, wherein: at least one of the monomers is a soft monomer in that the homopolymer formed from this monomer, in the molecular weight-independent range, has a glass transition temperature of less than 25° C.

10. The polymer of claim 1, wherein: at least one of the monomers bears one or more other functionalities which is not an epoxy group.

11. The polymer of claim 10, wherein: at least one of the other functionalities is a silicon-containing group.

12. The polymer of claim 10, wherein: the proportion of monomers having other functionalities is up to 10% by weight.

13. The polymer of claim 2, wherein: the glass transition temperature of the polymer in the cured state is at least 40° C. higher than that of the polymer in the uncrosslinked state.

14. A reactive adhesive composition, comprising a polymer of claim 1, and at least one initiator for a curing reaction involving the polymer.

15. The reactive adhesive composition of claim 14, wherein: the glass transition temperature of the adhesive composition in the cured state is at least 40° C. higher that of the adhesive composition in the uncrosslinked state.

16. The polymer claim 2, wherein: the molar mass M.sub.W is at least 20 000 g/mol.

17. The polymer of claim 3, wherein: the molar mass M.sub.W is at most 100 000 g/mol.

18. The polymer of claim 6, wherein: its glass transition temperature in the uncrosslinked state is above 25° C.

19. The polymer of claim 7, wherein the polymer's glass transition temperature in the uncrosslinked state is below 100° C.

20. The polymer of claim 8, wherein: at least one of the monomers is a hard monomer in that the homopolymer formed from this monomer, in the molecular weight-independent range, has a glass transition temperature of at least 50° C.

Description

EXAMPLES

[0197] Raw Materials Used:

TABLE-US-00001 Vazo ® 52 2,2-azobis(2,4-dimethylvaleronitrile) from DuPont TTA15 3,4-epoxycyclohexylmethyl methacrylate from Tetrachem K-Pure ® CXC 1614 thermal activator based on a quaternary ammonium salt of trifluoromethanesulfonic acid from King Industries Desmomelt ® 530 polyurethane from Covestro Uvacure 1500 (3′,4′-epoxycyclohexane)methyl (3,4-epoxy- from Allnex cyclohexyl)carboxylatc

[0198] Production of the adhesive compositions and reactive adhesive tape specimens:

Example A

[0199] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 100 g of 3,4-epoxycyclohexylmethyl methacrylate and 396 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 70° C. and evacuated to boiling. Subsequently, 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. The reaction is conducted at a constant product temperature of 70° C. under evaporative cooling. After a reaction time of 1 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70° C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. After a reaction time of 2 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70° C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. After a reaction time of 3 h, 100 g of 3,4-epoxycyclohexylmethyl methacrylate that had been preheated to 70° C. and through which nitrogen had been passed for 45 minutes were added, and 2.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 4.0 g of methyl ethyl ketone were added. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0200] The molar mass of the resulting polymer was 15 900 g/mol.

[0201] The glass transition temperature of the uncured polymer was 32° C., determined from the first heating curve by test C. The material produced by self-curing during the heating phase in the DSC experiment had a glass transition temperature of 72° C. in the second heating curve.

Example B

[0202] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 400 g of 3,4-epoxycyclohexylmethyl methacrylate, 420 g of isopropanol and 726 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 65° C. and evacuated to boiling. Subsequently, 4.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 8.0 g of methyl ethyl ketone were added. The reaction is conducted at a constant product temperature of 65° C. under evaporative cooling. After a reaction time of 7 h, 4.0 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 8.0 g of methyl ethyl ketone were added. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0203] The molar mass of the resulting polymer was 25 900 g/mol.

[0204] The glass transition temperature of the uncured polymer was 34° C., determined from the first heating curve by test C. The material produced by self-curing during the heating phase in the DSC experiment had a glass transition temperature of 68° C. in the second heating curve.

Example C

[0205] A pressure-resistant 2 L polymerization reactor of a conventional type for free-radical polymerizations was charged with 400 g of 3,4-epoxycyclohexylmethyl methacrylate, 420 g of isopropanol and 150 g of methyl ethyl ketone. After passing nitrogen gas through while stirring for 45 minutes, the reactor was heated up to product temperature 65° C. and evacuated to boiling. Subsequently, 1.6 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 30.4 g of isopropanol were added. The reaction is conducted at a constant product temperature of 65° C. under evaporative cooling. After a reaction time of 7 h, 1.6 g of 2,2-azobis(2,4-dimethylvaleronitrile) dissolved in 30.4 g of isopropanol were added. After a reaction time of 14 hours, the mixture was diluted with 100 g of methyl ethyl ketone. The reaction was terminated after 24 h reaction time and cooled to room temperature.

[0206] The molar mass of the resulting polymer was 30 600 g/mol.

[0207] The glass transition temperature of the uncured polymer was 38° C., determined from the first heating curve by test C. The material produced by self-curing during the heating phase in the DSC experiment had a glass transition temperature of 70° C. in the second heating curve.

Examples I

[0208] For the production of reactive adhesive tape specimens (examples I1 and I2, comparative example C1), all the formulation constituents required were dissolved in solvent and any insoluble constituents such as inorganic fillers were suspended with a dispersion disk and coated as a solution or suspension. The solvent content in the solutions was 80% by weight. The solvent used was methyl ethyl ketone. The coating was effected on a siliconized release paper. Coated and dried specimens were dried at 50° C. for 30 min. After drying, the adhesive layer thickness of the coats was 100 μm (within the customary error tolerances). After 24 h, the reactive adhesive tape specimens were processed to give test specimens and these were then analyzed after a further 48 h. Details of the test specimens can be found in the respective test methods.

Example I1—Reactive Adhesive Tape Thermally Curable

[0209] 9.7% by weight of polymer from example A were admixed with 90% by weight of Desmomelt 530 as film former (B) and 0.3% by weight of K-Pure CXC 1614 as curing agent (A). For the resulting reactive adhesive tapes, bond strength (push-out resistance by test E) and squeeze-out propensity in the pressing step (test A) were examined. The push-out resistance was 5.5 N/mm.sup.2 and the squeeze-out propensity 0 mm.

Example I2—Reactive Adhesive Tape Thermally Curable

[0210] 49.7% by weight of polymer from example A were admixed with 50% by weight of Desmomelt 530 as film former (B) and 0.3% by weight of K-Pure CXC 1614 as curing agent (A). For the resulting reactive adhesive tapes, bond strength (push-out resistance by test E) and squeeze-out propensity in the pressing step (test A) were examined. The push-out resistance was 2.2 N/mm.sup.2 and the squeeze-out propensity 1.4 mm.

Comparative Example C1—Reactive Adhesive Tape Thermally Curable

[0211] 9.7% by weight of Uvacure 1500 (low molecular weight cycloaliphatic diepoxide) were admixed with 90% by weight of Desmomelt 530 as film former (B) and 0.3% by weight of K-Pure CXC 1614 as curing agent (A). The formulation did not contain any (co)polymer of the invention. For the resulting reactive adhesive tapes, bond strength (push-out resistance by test E) and squeeze-out propensity in the pressing step (test A) were examined. The push-out resistance was 2.5 N/mm.sup.2 and the squeeze-out propensity >1.5 mm.

[0212] It is clear from the examples and comparative example that epoxy-functionalized (co)polymers of the invention can be utilized advantageously in curable adhesive compositions. These (co)polymers achieve bond strengths in accordance with the stated object. Squeeze-out propensity is within a favorable range. If a low molecular weight reactive resin according to the prior art (Uvacure 1500) is used in place of the epoxy-functionalized (co)polymer of the invention, the demands on low squeeze-out propensity are not met.