Method for welding two polyamide plastics

Abstract

The present invention relates to a method for welding two polyamide plastics using a primer, the primer containing at least one polymer synthesized from at least one maleic anhydride or maleic anhydride derivative. The invention also relates to correspondingly welded products.

Claims

1. A method for welding two polyamide plastics using a primer, comprising: providing a first polyamide substrate including a surface and a second polyamide substrate including a surface; providing a primer containing at least one polymer synthesized from at least one maleic anhydride or maleic anhydride derivative; applying the primer to at least one of the substrate surfaces; disposing the substrate surfaces in contact with each other; and welding the substrate surfaces to join the first polyamide substrate to the second polyamide substrate.

2. The welding method according to claim 1, characterized in that the each polyamide substrate is independently selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.10, polyamide 6.12, polyamide 10.10, polyamide 11, polyamide 12, polyamide 10.12, polyphthalamides, and optically transparent polyamides.

3. The welding method according to claim 1, characterized in that the at least one polymer is a copolymer consisting of at least one styrene or styrene derivative and at least one maleic anhydride or maleic anhydride derivative.

4. The welding method according to claim 3, characterized in that the copolymer has a molar ratio of styrene to maleic anhydride of from 1:0.01 to 1:2.

5. The welding method according to claim 1, characterized in that the at least one polymer has a maleic anhydride content of 0.1-50 wt. % based on the polymer.

6. The welding method according to claim 1, characterized in that the at least one polymer of the primer has a glass transition temperature Tg of more than 30 C.

7. The welding method according to claim 1, characterized in that the at least one polymer has a weight-average molecular weight Mw in the range of from 5000-2000000 g/mol.

8. The welding method according to claim 1, characterized in that the primer contains, in addition to the at least one polymer, at least one further polymer that is compatible with at least one of the polyamide substrates.

9. The welding method according to claim 1, characterized in that the primer has a solvent content of 10-90 wt. % based on the total weight of the primer.

10. The welding method according to claim 9, characterized in that the solvent has a vapor pressure at 20 C. of from 1 to 600 hPa.

11. The welding method according to claim 1, wherein the first polyamide substrate is selected from the group consisting of polyamide 6, polyamide 6.6, polyamide 6.10, polyamide 6.12 and the second polyamide substrate is selected from the polyamide plastics from the group consisting of polyamide 10.10, polyamide 11, polyamide 12.

12. The welding method according to claim 1, wherein the primer comprises an organic solvent.

13. The welding method according to claim 1, wherein the primer comprises 60-80 wt. % of solvent based on the total weight of the primer and the solvent is selected from tetrahydrofuran, methyl isobutyl ketone (MIBK), cyclohexanone and mixtures thereof.

14. The welding method according to claim 1, wherein the primer is a liquid.

15. The welding method according to claim 1, wherein after the step of applying the primer forms a layer on the substrate surface.

16. An object produced according to a welding method according to claim 1.

Description

EMBODIMENTS

(1) PA=polyamide

(2) PA 6=Polycaprolactam

(3) PA12=Polylauryl lactam

(4) MAH=maleic anhydride

(5) MIBK=methyl isobutyl ketone

(6) CH=cyclohexanone

(7) PS=polystyrene having Mw=192000 g/mol

(8) Copolymer SM1=styrene-maleic anhydride copolymer having 15 wt. % MAH and Mw=170000 g/mol

(9) Copolymer SM2=styrene-maleic anhydride copolymer having 8 wt. % MAH and Mw=250000 g/mol

(10) Copolymer SM3=poly(styrene-co-maleic acid) partially isobutyl/methyl esterified having

(11) Mw=180000 g/mol

(12) US=Ultrasonic welding

(13) Preparation of primer 1-4:

(14) In order to prepare the primers, the polymer components were dissolved in solvent at 90 C., by mechanical stirring, and left to cool to 20 C. The composition of the primers in g can be found in the following table.

(15) TABLE-US-00001 Primer 1 2 3 4 PS 30 SM1 30 SM2 30 SM3 32.5 MIBK 50 50 50 CH 20 20 20 67.5

(16) General test execution:

(17) An AWS (American Welding Society) test specimen without an energy director. The lower half of the test specimen consists of a base plate of 50 mm12.4 mm2.8 mm having a centrally arranged, perpendicular web 9.4 mm high and 2.5 mm wide (T-shape). The upper half of the test specimen consists of a base plate of 50 mm12.4 mm2.8 mm having a centrally arranged, perpendicular web 3 mm high and 2.5 mm wide (T-shape). A double T-shape is achieved by welding the surfaces of the central webs.

(18) The primers were applied, at room temperature, to the surface (50 mm2.5 mm) of the lower half of the test specimen of an AWS (American Welding Society) test specimen, without an energy director, of the PA12 plastics material to be welded. Subsequently, the primer was dried of solvent for 24 hours at room temperature. After drying, the thickness of the primer was approximately 0.2 mm. Subsequently, the upper half of the test specimen, having a geometry of 50 mm2.5 mm, was welded edge-to-edge to the 50 mm2.5 mm surface of the lower half of the test specimen. The tensile strength was determined after 24 hours and at a traction speed of 5 mm/s. The following table in each case shows the tensile strength (in MPa) that was able to be achieved, at room temperature, for the welded test specimens, for the combination of the primer with the plastics materials used:

(19) Ultrasonic weldina:

(20) TABLE-US-00002 Tensile strength Primer Polymer 1 Polymer 2 MPa (US) No primer PA12 Grilamid PA6 Grilamid 4.06 TRS 90 TR30LS 1 PA12 Grilamid PA6 Grilamid 3.91 TRS 90 TR30LS 2 PA12 Grilamid PAG Grilamid 6.43 TRS 90 TR30LS 3 PA12 Grilamid PA6 Grilamid 7.73 TRS 90 TR30LS 4 PA12 Grilamid PA6 Grilamid 15.26 TRS 90 TR30LS

(21) The results show that the samples welded using a primer containing MAH exhibit excellent tensile strength. The tests with no primer or with a polystyrene as the primer do not have sufficient strength. It can also be seen that the primer layer comprising cyclohexanone as the solvent does not have any bubbles after the solvent has evaporated. However, the time required for the solvent to evaporate increases as the cyclohexanone content in the formulation increases.