Compositions, preparation thereof and use thereof for production of cast polyamides

1. A composition comprising

a) N-acetylcaprolactam

 and

b) at least one, optionally caprolactam-blocked, polyisocyanate based on hexamethylene diisocyanate (HDI) wherein the polyisocyanate is selected from the group consisting of:

HDI biuret of the formula (I)

HDI uretdione of the formula (II)

HDI isocyanurate of the formula (III)

 and

HDI allophanate of the formula (IV)

where R IV is —(CH 2 ) 6 — and R V is C 1 -C 6 -alkyl.

2. The composition according to claim 1 , wherein the polyisocyanate based on hexamethylene diisocyanate (HDI) is caprolactam-blocked.

3. The composition according to claim 1 , further comprising at least one acid scavenger.

4. The composition according to claim 3 , wherein the acid scavenger comprises epoxides and/or carbodiimides.

5. The composition according to claim 4 , wherein the carbodiimides are compounds of the formula (V)

R 1 —(—N═C═N—R 2 —) m -R 3

in which

m is an integer from 1 to 10,

R 1 =—R 2 —NCO, —R 2 —NHCONHR 4 , —R 2 —NHCONR 4 R 5 or —R 2 —NHCOOR 6 ,

R 2 =C 1 -C 18 -alkylene, C 5 -C 18 -cycloalkylene, arylene and/or C 7 -C 18 -aralkylene, and

R 3 =—NCO, —NHCONHR 4 , —NHCONR 4 R 5 or —NHCOOR 6 ,

where R 4 and R 5 are the same or different and are each independently a C 1 -C 6 -alkyl, C 6 -C 10 -cycloalkyl or C 7 -C 18 -aralkyl radical, R 6 has one of the meanings of R 2 or is —(CH 2 ) l —(O—(CH 2 ) k —O) g —R 7 , with l=1-3, k=1-3, g=0-12, and R 7 =H or C 1 -C 4 -alkyl.

6. The composition according to claim 1 , wherein a ratio of N-acetylcaprolactam to polyisocyanate based on hexamethylenediamine (HDI) is 1:1 to 1:4.

7. The composition according to claim 3 , wherein a proportion of acid scavenger in the composition is 0.1-2% by weight based on the composition.

8. A process for preparing a composition according to claim 1 , the process comprising mixing the N-acetylcaprolactam with the at least one, optionally caprolactam-blocked, polyisocyanate based on hexamethylene diisocyanate (HDI), at a temperature of 20° C. to 60° C., and optionally in the presence of at least one acid scavenger.

9. The process for preparing a composition according to claim 8 , wherein the polyisocyanate is caprolactam blocked and the process further comprises preparing the caprolactam-blocked HDI polyisocyanate in situ in N-acetylcaprolactam.

10. The composition according to claim 3 , wherein a proportion of acid scavenger in the composition is 0.5-1% by weight, based on the composition.