Polyurethane Adhesive with Semi-Crystalline and Highly Crystalline Polyesters

Abstract

The present invention refers to polyurethane adhesives with semi-crystalline and highly crystalline polyesters, a method for the production of the same as well as the use of the polyurethane adhesive in the production of electronic devices.

Claims

1. A polyurethane adhesive that is the reaction product of a mixture comprising at least one semi-crystalline polyester and at least one highly crystalline polyester, wherein the melting point of the highly crystalline polyester is higher than the melting point of the semi-crystalline polyester.

2. The polyurethane adhesive according to claim 1, wherein the at least one semi-crystalline polyester and the at least one highly crystallized polyester are employed in a weight ratio of 15:1 to 1.5:1 in the reaction mixture.

3. The polyurethane adhesive according to claim 1, wherein the at least one semi-crystalline polyester and the at least one highly crystallized polyester are employed in a weight ratio of 7:1 to 3:1 in the reaction mixture.

4. The polyurethane adhesive according to claim 1 wherein the reaction mixture comprises the at least one semi-crystalline polyester in an amount of 10 to 30 wt.-%, based on the total weight of the reaction mixture.

5. The polyurethane adhesive according to claim 1 wherein the reaction mixture comprises the at least one highly crystalline polyester in an amount of 2 to 15 wt.-%, based on the total weight of the reaction mixture.

6. The polyurethane adhesive according to claim 1 wherein the at least one semi-crystalline polyester has a hydroxyl value (OH value) of 10 to 50 mg KOH/g, determined according to DIN ISO 4629-2.

7. The polyurethane adhesive according to claim 1 wherein the at least one highly crystalline polyester has a hydroxyl value (OH value) of 20 to 100 mg KOH/g, determined according to DIN ISO 4629-2.

8. The polyurethane adhesive according to claim 1 wherein the at least one semi-crystalline polyester has a hydroxyl value (OH value) of 25 to 40 mg KOH/g and the at least one highly crystalline polyester has a hydroxyl value (OH value) of 35 to 60 mg KOH/g, each determined according to DIN ISO 4629-2.

9. The polyurethane adhesive according to claim 1 wherein the average molecular weight Mn of the semi-crystalline polyester and/or the highly crystalline polyester is 1000 to 5000 g/mol, determined according to DIN 55672-1:2007-08.

10. The polyurethane adhesive according to claim 1 wherein the average molecular weight Mn of the semi-crystalline polyester and/or the highly crystalline polyester is 1500 to 4000 g/mol, determined according to DIN 55672-1:2007-08.

11. The polyurethane adhesive according to claim 1 wherein the at least one semi-crystalline polyester has a melting point of 30 to 105° C., determined with DSC.

12. The polyurethane adhesive according to claim 1 wherein the at least one highly crystalline polyester has a melting point of 60 to 130° C., determined with DSC.

13. The polyurethane adhesive according to claim 1 wherein the at least one semi-crystalline polyester has a melting point of 50 to 100° C. and/or the at least one highly crystalline polyester has a melting point of 65 to 120° C., each determined with DSC.

14. The polyurethane adhesive according to claim 1 wherein the reaction mixture further comprises at least one of the following components: polyol; amorphous polyester; acrylate; NCO-terminated compound.

15. The polyurethane adhesive according to claim 1 wherein the reaction mixture further comprises at least one of the following components: 10 to 30 wt.-% polyol; 10 to 30 wt.-% amorphous polyester; 10 to 30 wt.-% acrylate; 5 to 25 wt.-% NCO-terminated compound; the wt.-% being based on the total weight of the reaction mixture, respectively.

16. The polyurethane adhesive according to claim 1 being a solid at room temperature.

17. Cured reaction products of the polyurethane adhesive according to claim 1.

18. A device comprising cured reaction products of the polyurethane adhesive according to claim 1.

19. The polyurethane adhesive according to claim 1 being a hot-melt adhesive.

20. The polyurethane adhesive according to claim 1 being a hot-melt adhesive that is free of water and solvent.

Description

EXAMPLES

[0029] Different polyurethane adhesives were prepared from reaction mixtures containing highly crystalline polyesters and semi-crystalline polyesters. As a comparative example, a reaction mixture was used containing only semi-crystalline polyester. The obtained adhesives were tested with regard to their green strength and compared with commonly used products which contain a semi-crystalline polyester and a high molecular weight polyacrylate. The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Comp.-1 Comp.-2 highly 25 wt.-% 25 wt.-% — — crystalline (mp*: 70° C.) (mp: 115° C.) semi- 25 wt.-% 25 wt.-% 25 wt.-% — crystalline (mp: 55° C.) (mp: 55° C.) (mp: 96° C.) green 0.72 0.42 0.03 0.31 strength [Mpa] *mp: melting point determined with DSC

[0030] Green strength was determined by applying two parallel lines of adhesive to the center of the surface of a lap-shear specimen which has been previously cleaned with ethanol and allowed to dry. After the dispensing the adhesive, the lap-shear specimen is assembled and a 2 kg weight block is placed on top of the mating lap-shear specimen for 15 seconds. The samples were cured at 23° C. and 50% relative humidity and the green strength determined after 3 minutes of assembling the lap-shear specimen.

[0031] As can be seen from the experimental data as summarized in Table 1, the inventive adhesive obtained from a reaction mixture comprising both, semi-crystalline and highly crystalline polyester, showed a superior green strength than compared to an adhesive obtained from a reaction mixture comprising just a semi crystalline polyester. The green strength of the polyurethane adhesives according to the invention also surpassed the green strength observed using commonly used polyurethane adhesives containing a semi-crystalline polyester and high molecular weight polyacrylate which was first thought to be suitable to improve green strength. Further, it was found that all inventive polyurethane adhesives meet the requirement of a minimum open time of two minutes.