GB2045151A

GB2045151A - Process for the manufacture of polyamide tubes

Info

Publication number: GB2045151A
Application number: GB8009404A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-30
Filing date: 1980-03-20
Publication date: 1980-10-29
Also published as: IT8020933A0; BE882502A; DE2912846C2; IT1131071B; FR2452369A1; NL8001875A; DE2912846A1

Abstract

A process for the manufacture of polyamide tubes by a centrifuging operation in a heated rotary mould is disclosed in which at least two different liquid starting material quantities are metered successively into the rotary mould at a certain temperature, for example 398 DEG K (125 DEG C). The mould is rotatingly driven to provide uniform distribution of the material under the effect of the polymerisation temperature and subsequently stopped for the shrinking process, The different starting materials may be, for example, caprolactam for polyamide 6 and laurinlactam for polyamide 12. <IMAGE>

Description

SPECIFICATION Process for the manufacture of polyamide tubes The present invention relates to a process for the manufacture of polyamide tubes.

There is known a polyamide tube manufacturing process in which liquid starting material is metered into a heated rotary mould at a certain material temperature, for example 398 K (1 25#C), and the rotary mould is temporarily rotatingly driven to effect uniform distribution of the material under the effect of the polymerisation temperature and subsequently stopped for the shrinking process.

Polyamide tubes with different wall thicknesses and for different uses can be manufactured in simple manner by this process. It is also possible to produce polyamide tubes with different properties by introducing an appropriately different starting material into the rotary mould. Thus, tubes of polyamide 6 can be manufactured by feeding caprolactam as starting material into the rotating mould. Tubes of polyamide 12, on the other hand, can be formed simply by introducing laurinlactam as starting material into the mould.

Tubes of mixed polymerisates can be produced in the same manner when different starting materials, for example caprolactam and laurinlactam, are intensively intermixed before introduction into the mould.

Tubes of polyamide 12 are distinguished by toughness and low water absorption and at the same time they are safe for foodstuffs and drinking water. On the other hand, there are relatively high production costs for the starting material laurinlactam.

Although the starting material caprolactam for polyamide 6 can be manufactured more economically, polyamide 6 has properties substantially different from polyamide 12. Thus, although it displays a higher strength, buta lower toughness than polyamide 12, it is not compatible with foodstuffs and drinking water.

Although tubes can be produced from nonpolymerisates by a centrifuging process to have a strength and toughness between tubes of polyamide 12 and 6, full compatibility with foodstuffs and drinking water, which is essential for many uses of such tubes, is not achieved by mixed polymerisation.

There is therefore a need for a process for manufacturing, in a simple manner, tubes with properties which can be optimally matched to different requirements within the scope of the available starting materials.

According to the present invention there is provided a process for the manufacture of a polyamide tube, comprising the steps of introducing metered quantities of at least two different polymerisable polyamide starting materials in liquid form one after the other into a heated rotary mould, rotating the mould to centrifugally distribute each material quantity uniformly in a layer under the influence of a polymerisation temperature, and causing or permitting the distributed material quantities to shrink whilst the mould is stationary.

Preferably, the individual material charges are allowed to start polymerisation before the next material change is added. This prevents intermixing of the different starting materials in the centrifuging process, yet on the other hand the boundary between the polyamide layers, for example polyamide 6 and polyamide 12, resulting from the different starting materials is not readily discernible.

For preference, the wall thickness and the thickness of the different wall layers of the tubes can be determined by quantity regulation of the different starting materials.

With a process exemplifying the invention, a layered build-up for the walls of the tube can be provided, so that the tube can be optimally matched to the particular use requirements and produced in an economic manner.

Examples of the invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a cross-section of a two layer polyamide tube produced by a process according to one example of the invention, Figure 2 is a cross-section of a three layer polyamide tube produced by a process according to another example of the invention.

Referring now to the drawings, Figure 1 shows a polyamide tube manufactured from liquid starting material by a centrifuging process in a heated rotary mould, the tube being formed with two layers 2 and 3 of different polyamides. For the manufacture of the outer and thicker wall layer 2, caprolactam with the addition of catalysts was metered as liquid starting material into the rotary mould, exposed to the centrifuging process and initially polymerised after uniform distribution around the wall of the rotary mould. Then, for the formation of the inner and thinner layer 3 of the tube wall, laurinlactam with the addition of catalysts was metered as liquid starting material for polyamide 12 into the rotating rotary mould.Under the effect of the polymerisation temperature prevailing in the rotary mould, the two different material layers 2 and 3 were finally polymerised together and the two-layered wall build-up of the polymeride tube 1 obtained thereby. The different starting materials were os united with one another by the centrifuging process in the rotary mould that the boundary layer between the two material layers 2 and 3 can no longer be readily determined.

The polyamide tube 4 illustrated in Figure 2 has a build-up of three layers 5, 6 and 7, wherein the outer layer 5 and the inner layer 7 have a small thickness, while the middle layer 6 has a larger thickness. The outer layer 5 and the inner layer 7 were centrifuged by the centrifuging process from the same starting material, for example laurinlactam to provide polyamide 12, while the middle layer, for example, was centrifuged from caprolactam to provide polyamide 6.

The introduction of the metered different starting materials into the rotating rotary mould takes place after the preceding material layer, already distributed evenly in the rotary mould by the centrifuging process, has begun polymerisation so that intermixing of the different starting materials cannot occur.

All of the layers of the polyamide tube 4 are then finally polymerised together while continuing the centrifuging process until they have solidified sufficiently.

Subsequently, the usual shrinking process of the polyamide takes place with the rotary mould stationary so that the finished polyamide tube 1 or 4 can be axially withdrawn from the rotary mould after a certain time.

Claims

1. A process for the manufacture of a polyamide tube, comprising the steps of introducing metered quantities of at least two different polymerisable polyamide starting materials in liquid form one after the other into a heated rotary mould, rotating the mould to centrifugally distribute each material quantity uniformly in a layer under the influence of a polymersiation temperature, and causing or permitting the distributed material quantities to shrink whilst the mould is stationary.

2. A process as claimed in claim 1, wherein the starting material quantities are each introduced into the mould at a temperature of substantially 1 25 C.

3. A process as claimed in either claim 1 or claim 2, wherein one of the starting materials is caprolactam.

4. A process as claimed in any one of the preceding claims, wherein one of the starting materials is laurinlactam.

5. A process as claimed in any one of the preceding claims, wherein each of the material quantities is centrifugally distributed in the mould and caused to commence polymerisation before introduction of the succeeding material quantity.

6. A process as claimed in any one of the preceding claims, further comprising the preliminary step of so metering each of the material quantities as to provide a predetermined layer thickness of that material in the finished tube.

7. A process for the manufacture of a polyamide tube, the process being substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

8. A process for the manufacture of a polyamide tube, the process being substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.