WO2000009586A1

WO2000009586A1 - Process for obtaining a polyamide product from the smelt at a high production rate

Info

Publication number: WO2000009586A1
Application number: PCT/NL1999/000505
Authority: WO
Inventors: Gerardus Johannes Maria De Koning; Cornelis Eme Koning; Lilian Marie Jeanne Teuwen
Original assignee: Dsm N.V.
Priority date: 1998-08-12
Filing date: 1999-08-09
Publication date: 2000-02-24
Also published as: AU5387899A; NL1009846C2

Abstract

The invention relates to a process for obtaining a polyamide product from the smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4-butanediamine, as well as to polyamide products obtainable from the smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4-butanediamine. Such a process exhibits a high production rate, the polyamide crystallises rapidly and the polyamide has a higher melting point than the polyamides used in a process according to the state of the art. The polyamide objects have mechanical properties that are comparable with those of polyamide products with which the polyamide consists essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,6-hexanediamine. Preferably 1,10-decanedioic acid or 1,12-dodecanedioic acid is chosen as the dicarboxylic acid. The invention also relates to a process for the preparation of a polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4-butanediamine in which, successively, a first polymerisation of the diacarboxylic acid with 8-14 C-atoms and 1,4-butanediamine is effected in the fluid phase, resulting in a low-molecular polymer, followed by a post-polymerisation of the low-molecular polymer thus obtained in the solid phase, and to a polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4-butanediamine, the number average molar mass being at least 15,000 g/m.

Description

PROCESS FOR OBTAINING A POLYAMIDE PRODUCT FROM THE SMELT AT A HIGH PRODUCTION RATE

The invention relates to a process for obtaining a polyamide product from the smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and an aliphatic diamine.

In the context of this application, Essentially' is understood to be at least 50 % by weight, preferably at least 75 % by weight, more preferably at least 85 % by weight, most preferably at least 90 % by weight.

In the context of this application, a 'product' is understood to be an object extending in 1, 2 or 3 dimensions, for example a fibre, a monofilament, a foil, a film, a plate or a moulded part. As a fibre, such a polyamide product can be used in applications demanding a high wear resistance, for example in carpets, textile fibres or technical yarns. A well- known monofilament application is for example the application as fishing yarn or as toothbrush bristles. As a foil, such a polyamide product can be used for example as packaging material for foodstuffs, for example sausage or cheese. As a moulded part, such a polyamide product can be used for example in the automotive industry, in particular to replace metal parts, in order to lower a car's weight, or for applications 'under the bonnet' . A polyamide moulded part can also often be used in the E&E industry, for example as housing for electric or electronic components and for components of surface-mounted devices . A prerequisite for the aforementioned polyamide products is that said products have excellent mechanical properties, in particular a high degree of stiffness, in particular a high degree of stiffness in a conditioned state, a high degree of toughness and a high impact resistance and little creep. The polyamide product must have a high heat distortion temperature, it must be chemically resistant to all kinds of chemicals, such as de-icing salt, oil and grease, and it must absorb little moisture, so that a good dimensional stability can be obtained.

The polyamides that are used most often for such a polyamide product are polyamides with which 1,6- diaminohexane is chosen as the aliphatic diamine, more in particular the polyamides with which 1,6- diaminohexane is chosen as the aliphatic diamine and 1, 10-decanedioic acid (Nylon 6,10) or 1,12 dodecanedioic acid (Nylon 6,12) as the dicarboxylic acid with 8-14 C-atoms. Such a polyamide product can be prepared using a process in which a melt of the polyamide is cooled in a particular shape. Fibres and monofilaments can be prepared for example via the melt-spinning method; foils can be prepared via the extrusion method and moulded parts can be prepared for example using the injection-moulding method. One of the features that said methods for the preparation of polyamide products from the smelt have in common is that the method's production rate, for example the number of products that can be made per unit of time or for example the length of the spun fibre or extruded foil per unit of time, cannot be increased limitlessly with the current technical means and seems to have reached the limit inherent to the polyamide employed. In particular this relates to a process for preparing a thick moulded part, i.e. a moulded part with a wall thickness of more than 2 mm, and a process for preparing a fibre that is spun at a speed of more than 5,000 m/min (the so-called high-speed spinning fibre) .

The process according to the state of the art presents the disadvantage that the production rate of the process in which a melt of the polyamide is cooled in a particular shape is relatively slow. A low production rate is not desirable and there is hence a need to prepare the product at a higher production rate .

The inventors have now found that the production rate is to a great extent dependent on the crystallisation rate of the polyamide used to prepare the polyamide product . A conventional means that is used to raise the crystallisation rate of polymers in general is adding heterogeneous additives to the melt, for example talk and metal salts, for example sodium benzoate. This however presents the disadvantage that an extra processing step will in may cases be required.

The aim of the invention is to provide a process for obtaining a polyamide product from a smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and an aliphatic diamine, the process having an improved production rate.

This aim was achieved by choosing 1,4- butanediamine as the aliphatic diamine. Surprisingly, it was found that the crystallisation rate of the polyamide product was increased by choosing 1,4-butanediamine as the aliphatic diamine in the process according to the invention, as a result of which the polyamide product could be prepared at a high production rate.

Another advantage of the polyamide process according to the invention is the higher melting temperature of the polyamide product, in comparison with a polyamide product with which the polyamide consists essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,6- hexanediamine, as a result of which the polyamide product according to the invention can be used in high- temperature applications.

The product according to the invention also shows comparable mechanical properties, a comparable wear resistance in a conditioned state and a comparable absorption of moisture, in comparison with a polyamide product with which the polyamide consists essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1, 6-hexanediamine, so that the product according to the invention is in principle suitable for the same applications. A product is known from DE-A- 1669657 which consists of 95 % by weight polypropylene and 5 % by weight of a polyamide prepared from 1,4-butanediamine and decamethylene dicarboxylic acid. Such a product shows a greater elongation, in comparison with a product that consists exclusively of polypropylene.

As the aliphatic dicarboxylic acid with 8- 14 C-atoms is chosen a dicarboxylic acid from the group comprising 1 , 8-octanedioic acid, 1, 9-nonanedioic acid, 1, 10-decanedioic acid, 1 , 11-undecanedioic acid, 1,12- dodecanedioic acid, 1, 13-tridecanedioic acid and 1,14- tetradecanedioic acid. Preferably, 1, 10-decanedioic acid and 1 , 12 -dodecanedioic acid is chosen.

The polyamide product may also contain other polymers, or conventional additives, for example flame retardants, nucleating agents, fillers, for example glass fibres, pigments and processing aids.

The process is suitable for obtaining polyamide products in all applications in which the polyamide products according to the state of the art are used, for example as a fibre, monofilament, foil, film, plate or moulded part .

The polyamide products obtained by the process according to the invention may also contain other polymers. Then, the product contain 6 - 100 % by weight of the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4, preferably 50 - 100 % by weight, more preferably 60 - 100 % by weight, most preferably 70 - 100 % by weight.

The product can also be used in all current applications according to the state of the art in which polyamide products are used that consist essentially of units derived from caprolactam (Nylon 6) or of units derived from 1, 6-hexanedioic acid and 1, 6-hexanediamine

(Nylon 6,6) .

In particular, the product is used as a thick moulded part with a wall thickness of more than 2 mm and as a fibre, in particular as a high-speed- spinning fibre.

The product is obtained from the smelt by any process in which a product is formed from a smelt, for example by casting, moulding, extrusion, spinning or any equivalent process, known to a skilled person. The invention also relates to a process for the preparation of a polyamide consisting essentially of units derived from a dicarboxylic acid with 8-14 C- atoms and 1,4-butanediamine.

Such a process is known from Dreyfuss, Journal of Polymer Science. Vol 11(2), 201-216 (1973), in which is described a process in which the polymerisation is carried out in a mixture of two non- miscible solvents (water and perchloroethylene) with the aid of the dicarboxylic acid chloride of 1,12- dodecanedioic acid and 1,4-butanediamine.

The disadvantage of said method is that it does not result in a high yield, it does not yield a polymer with a number average molar mass of more than 15,000, it is very corrosive and it is hence neither environmentally nor commercially attractive for use on a large scale.

The inventors have now found that a polyamide consisting essentially of units derived from a dicarboxylic acid with 8-14 C-atoms and 1,4- butanediamine can be prepared by successively carrying out a first polymerisation of the dicarboxylic acid with 8-14 C-atoms and 1,4-butanediamine in the fluid phase, resulting in a low-molecular polymer (M_n = 1,000 - 4,000 g/mol) , followed by an post-polymerisation of the low-molecular polymer thus obtained in the solid phase until a polymer with the desired molar weight is obtained.

In particular, a polyamide is prepared which consists essentially of units derived from a dicarboxylic acid with 8-14 C-atoms and 1,4- butanediamine having a number average molar mass of at least 15,000 g/mol. An product prepared with such a polyamide from the smelt presents the advantage that it can be prepared at an elevated production rate.

In a preferred embodiment a prepolymer is prepared in an aqueous mixture of about 85-90 % by weight salt of the dicarboxylic acid and the diamine, at a temperature of 180-240°C and at a pressure of 10- 15xl0⁵ Pa. The aftercondensation of this prepolymer subsequently takes place while a N₂/water vapour mixture is passed over it, at a temperature that lies about 10- 50°C below the polymer's melting point, for as long as it takes to obtain the desired molar mass (M_n is typically 15,000-30,000 g/mol).

The invention will now be further elucidated with reference to the following examples, without being limited thereto.

Examples

Example I : Preparation of Nylon 4.10 a. Prepolymerisation 350 grams of 1 , 10-decanedioic acid (Acros

Organics) , 235 grams of 1,4-butanediamine solution (67 % by weight in water) (DSM N.V.) and 338 grams of water are stirred in a 1.4-litre autoclave for 30 minutes at 90°C such that a 55 % by weight salt solution is obtained. Then water is removed through distillation by first raising the temperature in 10 minutes to 180°C, removing half of the amount of water through distillation and then raising the temperature to 200°C and removing an amount of water through distillation such as to obtain a 90 % by weight aqueous salt solution. Then the reactor is completely closed, the distillation is stopped and the temperature is raised to 227°C and the prepolymerisation begins. The water present and the high temperature cause the pressure to rise slowly. The pressure at the end of the prepolymerisation is about 12xl0⁵ Pa. The prepolymerisation is performed during 1/2 hour at a constant temperature, after which the content of the autoclave is flashed in a nitrogen atmosphere. The prepolymer is cooled in a nitrogen atmosphere.

b. Postcondensation

The prepolymer granules obtained according to step a) are sieved so that the fraction having a diameter of between 1 and 2 mm is obtained. This fraction is introduced into either a static bed (capacity approximately 50 g of solid substance) or a tumble dryer (capacity approximately 10 litres) and postcondensed at an elevated temperature (about 25 °C below the polymer's melting point) in a nitrogen/water vapour (75/25 % by volume) atmosphere for 24 hours. Then the polymer granules were cooled to room temperature. From the polymer thus prepared a number of rods and plates were injection-moulded.

Example II : Preparation of Nylon 4.12

In the same way as in Example I, an analogous amount of Nylon 4,12 was prepared, using as starting materials 1,4 -butanediamine (DSM N.V.) and 1, 12 -dodecanedioic acid (Acros Organics) in the same molar ratio. From the polymer thus prepared a number of rods and plates were injection-moulded.

Example III : Preparation of Nylon 4.8

In the same way as in Example I, an analogous amount of Nylon 4,8 was prepared, using as starting materials 1,4 -butanediamine (DSM N.V.) and 1, 8-octanedioic acid (Acros Organics) in the same molar ratio. From the polymer thus prepared a number of rods and plates were injection-moulded. Comparative Example A : Preparation of Nylon 6.10.

In the same way as in Example I , an amount of Nylon 6,10 was prepared, using as starting materials 1, 6-hexanediamine (Acros Organics) and 1, 10-decanedioic acid (Acros Organics) in the same molar ratio. From the polymer thus prepared a number of rods and plates were inj ection-moulded.

Nylon 6,10 is also commercially available from for example the company Nyltech (France) .

Comparative Example B : Preparation of Nylon 6.12.

In the same way as in Example 1, an amount of Nylon 6,12 was prepared, using as starting materials 1, 6-hexanediamine (Acros Organics) and 1,12- dodecanedioic acid (Acros Organics) in the same molar ratio. From the polymer thus prepared a number of rods and plates were injection-moulded.

Nylon 6,12 is also commercially available from for example the company DuPont (USA) .

Molecular characterisation of the polyamides of Examples I-III and Comparative Examples A-B.

The molecular characteristics of the polyamides of Examples I-III and Comparative Examples A-B were determined as follows.

The viscosity number was determined in formic acid (c = 0.005 g/ml) at 25°C with the aid of an Ubbelohde (Schott type 530-10/1) .

The relative viscosity was determined in H₂S0₄ at 25°C with the aid of an Ubbelohde (Schott type 530-10/1) .

The carboxyl end groups were potentiometrically determined in o-cresol by means of a titration with tetrabutyl ammonium hydroxide. The amino end groups were potentiometrically determined in phenol by means of a titration with hydrochloric acid.

The total concentration of pyrrolidine end groups of the polyamides based on 1,4-butanediamine was determined with a through-flow fluorimeter via detection of a fluorescent compound formed in a reaction of pyrrolidine with NBD-chloride (4-chloro-7- nitrobenzo-2-oxa-l, 3-diazole) . The molecular characteristics of the polyamides are summarised in Table 1. From Table 1 it is evident that all the polyamides in Table 1 have approximately comparable molar masses.

Table 1 : Molecular characterisation of the polyamides of Examples I-III and Comparative Examples A-B.

Determination of the crystallisation properties The thermal characterisation of the polyamides was carried out using a Perkin Elmer DSC-7. The measurements were carried out in an N₂ atmosphere at a block temperature of the DSC apparatus of -10°C.

Dynamic measurements

The melting (T_m) and crystallisation temperature (T_c) were determined by means of dynamic measurements using a heating and cooling rate of

20°C/min. A polyamide was successively heated to above its melting temperature, cooled to below the crystallisation temperature and heated a second time. The difference between the melting temperature inferred from the second heating curve and the crystallisation temperature, the subcooling (T_m2-T_c = ΔT) , is a measure of a polyamide's crystallisation rate. The results are summarised in Table 2. From Table 2 it is evident that less subcooling is required to effect the crystallisation of Nylon 4,10 and Nylon 4,12 in comparison with Nylon 6,10 and Nylon 6,12, respectively. By way of comparison: the degree of subcooling required for Nylon 6 at a cooling rate of 20°C/min is 47°C, while it is 43°C for Nylon 6,6. It will be clear that with the process according to the invention less subcooling is needed and hence faster crystallisation results. Table 2 : Dynamic crystallisation of the polyamides of Examples I-III and Comparative Examples A-B.

Kinetic measurements

The half-life period for crystallisation (tι_/2) , which is the amount of time required to realise half of the total degree of crystallisation realisable, was determined via isothermal crystallisation. A sample of polyamide was heated in an N₂-atmosphere to approximately 40°C above its melting point. The polyamide was kept at this temperature for half an hour, to enable all the remains of the crystalline phase to disappear, after which the temperature was quickly returned to a temperature between the glass transition temperature and the melting temperature. The sample was kept at this temperature, the crystallisation temperature, for an hour, to enable it to crystallise, while the flow of heat was measured with a DSC. This experiment was repeated four times at four different crystallisation temperatures. The half- life period for crystallisation (tι_/2) was calculated from the measurements thus obtained. This parameter characterises the polymer's ability to crystallise. A lower value implies a greater ability to crystallise. The results are summarised in Table 3. From Table 3 it is evident that Nylon 4,10 and Nylon 4,12 crystallise faster at comparable subcooling values than Nylon 6,10 and Nylon 6,12, respectively.

Table 3 : Kinetic crystallisation of the polyamides of Examples I-III and Comparative Examples A-B.

Determination of the mechanical properties

To determine the mechanical properties of the polymer products, the polymer was first dried at 105°C in an N₂-atmosphere at reduced pressure for 16 hours. Specimens for tensile and IZOD testing were injection-moulded using an Arburg 5, at an injection- moulding temperature of between 245 and 290°C. The mould temperature was 80°C.

The mechanical properties were determined using dry or conditioned (conditioning conditions: 50% relative humidity at 23°C to equilibrium) tensile test specimens. The results are summarised in Table 4. By way of comparison (Comparative Example C) , the properties of Nylon 6, determined using the commercial grade Akulon 123 (DSM N.V. , the Netherlands) are also indicated. From Table 4 it is evident that the polyamide tensile test specimens according to the invention show mechanical properties that are at least comparable with those according to the state of the art.

Table 4 : Mechanical properties of the polyamides of Examples I-III and Comparative Examples A-B.

n.d. = not determined.

Determination of the resistance to stress cracking

The resistance to stress cracking of polyamide products was determined by subjecting a polyamide compressed plate with a thickness of 1 mm to a pressure of 3 N/mm2 at 75°C, while the compressed plate was submerged in an aqueous ZnCl₂ solution (50 % by weight) . The amount of time required for the plate to crack (cracking time) is measured.

Before the test, the polyamide compressed plate was first dried for 24 hours in a vacuum at 90°C. The test showed that a compressed plate of Nylon 4,12 showed a resistance to stress cracking that is at least the same as a that of a compressed plate of Nylon 6,12. By way of comparison: the cracking time of a compressed plate of Nylon 6 was substantially lower than that of both Nylon 4,12 and Nylon 6,12.

Claims

C L A I M S

1. Process for obtaining a polyamide product from the smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and an aliphatic diamine, characterised in that the diamine is 1,4- butanediamine .

2. Process according to Claim 1, characterised in that the polyamide product consists of 6 - 100 % by weight of polyamide.

3. Process according to Claim 1, characterised in that the polyamide product consists of 50 - 100 % by weight of polyamide.

4. Process according to Claim 1, characterised in that the polyamide product consists of 70 - 100 % by weight of polyamide .

5. Process according to any one of Claims 1-4, characterised in that as the aliphatic dicarboxylic acid with 8-14 C-atoms is chosen a dicarboxylic acid from the group comprising 1,8- octanedioic acid, 1, 9-nonanedioic acid, 1, 10- decanedioic acid, 1, 11-undecanedioic acid, 1,12- dodecanedioic acid, 1, 13-tridecanedioic acid and 1 , 14-tetradecanedioic acid.

6. Process according to Claim 5, characterised in that as the aliphatic dicarboxylic acid with 8-14 C-atoms is chosen 1, 10-decanedioic acid or 1,12- dodecanedoic acid.

7. Process according to any one of Claims 1-6, characterised in that the product obtained is a fibre, monofilament, foil, film, plate or moulded part .

8. Process according to any one of Claims 1-7, characterised in that the process comprises a step in which the product is obtained by cooling a polyamide melt .

9. Polyamide product, obtainable from the smelt, the polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C- atoms and 1,4-butanediamine.

10. Process for the preparation of a polyamide that consists essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C-atoms and 1,4 butanediamine, characterised in that, successively, a first polymerisation of the dicarboxylic acid with 8-14 C-atoms and 1,4- butanediamine is effected in the fluid phase, resulting in a low-molecular polymer, followed by an post-polymerisation of the low-molecular polymer thus obtained in the solid phase.

11. Process according to Claim 10, characterised in that a polyamide with a number average molar mass of at least 15,000 g/mol is prepared.

12. Polyamide consisting essentially of units derived from an aliphatic dicarboxylic acid with 8-14 C- atoms and 1,4 butanediamine, characterised in that the number average molar mass is at least 15,000 g/mol .

13. Processes for obtaining a polyamide product and polyamide products as described and elucidated in the examples.