PRODUCTION OF POLYAMIDES BY HYDROLYTIC POLYMERIZATION AND SUBSEQUENT TREATMENT IN A KNEADER

Abstract

The present invention provides a process for producing polyamides, which comprises a) providing a monomer composition comprising at least one lactam or at least one aminocarbonitrile and/or oligomers of these monomers, b) reacting the monomer composition provided in step a) in a hydrolytic polymerization at elevated temperature in the presence of water to obtain a reaction product comprising polyamide, water, unconverted monomers and oligomers, c) the reaction product obtained in step b) being fed into at least one kneader (3) and subjected to a postpolymerization, d) optionally forming the reaction product obtained in step c) to obtain polyamide particles, e) optionally treating the reaction product obtained in step c) or the polyamide particles obtained in step d) with at least one extractant.

Claims

1. A process for producing a polyamide, the process comprising: a) reacting a monomer composition by hydrolytic polymerization at elevated temperature in the presence of water to obtain a reaction product comprising a polyamide, water, unconverted monomers and oligomers; and b) postpolymerizing the reaction product a) in at least one kneader, to obtain a reaction product b), wherein: the monomer composition comprises at least one lactam, at least one aminocarbonitrile, an oligomer of at least one lactam, an oligomer of at least one aminocarbonitrile, an oligomer of at least one lactam and at least one aminocarbonitrile, or a mixture thereof; the kneader includes at least two screws; at least one reaction zone and a discharge zone are arranged in a direction of a longitudinal axes of the at least two screws; in the at least one reaction zone there are kneading elements arranged consecutively on each of the at least two screws; and, inside the kneader a head space zone is provided above the at least two screws with a head space volume ranging from 10 to 70%, based on an overall volume of the at least one reaction zone.

2. The process according to claim 1, further comprising: c) forming the reaction product b) to obtain polyamide particles.

3. The process according to claim 1, further comprising: d) treating the reaction product b) with an extractant, to obtain an extracted polvamide.

4. The process according to claim 3, further comprising: e) drying the extracted polyamide.

5. The process according to claim 1, wherein the monomer composition comprises -caprolactam,. 6-aminocapronitrile, an oligomer of -caprolactam, an oligomer of 6-aminocapronitrile, an oligomer of -caprolactam and 6-aminocapronitile, or a mixture thereof.

6. The process according to claim 1, wherein the head space zone has a head space volume ranging from 15 to 60%, based on the overall volume of the at least one reaction zone.

7. The process according to claim 1, wherein the kneader has an inert gas flowing through it.

8. The process according to claim 4, wherein the drying is conducted at a temperature ranging from 70 to 220 C.

9. A polyamide obtainable by the process of claim 1.

10. A method, comprising forming an article with the polyamide of claim 9, wherein the article is selected from the group consisting of a pellet, a film, a sheet, a fiber and a molding.

11. The process according to claim 2, further comprising: d) treating the polyamide particles with an extractant.

Description

[0119] The process will now be more particularly elucidated by FIG. 1 and the examples.

[0120] FIG. 1 shows a schematic of one mode to carry out the process of the present invention.

[0121] The following reference signs are used in FIG. 1:

TABLE-US-00001 1 pressure prereactor 2 VK tube 3 kneader 4 pelletizer 5 extraction 6 drying

[0122] A monomer composition provided in process step a) is fed, optionally via a pressure reactor 1, to a VK tube 2. Process step b) takes place in optionally said pressure reactor 1 and/or said VK tube 2. The reaction product obtained in process step b) is supplied in process step c) to a kneader 3 and subjected to a postpolymerization. Optionally, the reaction product obtained in process step c) is subjected to forming in a pelletizer 4 to obtain polyamide particles. Optionally, the reaction product obtained in process step c) or the polyamide particles obtained in process step d) are treated with at least one extractant in an extraction 5. Optionally, the extracted polyamide obtained in process step e) is additionally subjected to a drying step 6.

WORKING EXAMPLES

Working Example 1

[0123] A nylon-6 pellet material produced on an industrial scale with a viscosity number of 143 ml/g and a caprolactam content of 9.96% was melted and the melt was fed under nitrogen (80 l(s.t.p.)/h) to a KRC type kneader from Kurimoto having a head space volume of 21% for postpolymerization. The residence time in the kneader was 16 min at a temperature of 290 C. The kneader output was pelletized by underwater pelletization and subsequently dried. The end product had a viscosity number of 156 ml/g and a caprolactam content of 3.986%.

Working Example 2

[0124] Working example 2 was carried out similarly to working example 1 except that, unlike working example 1, the residence time in the kneader was 60 min.

[0125] The end product had a viscosity number of 225 ml/g and a caprolactam content of 0.39%.

Working Example 3

[0126] Working example 3 was carried out similarly to working example 1 except that, unlike working example 1, the residence time in the kneader was 100 min.

[0127] The end product had a viscosity number of 254 ml/g and a caprolactam content of 0.264%.