GB1590526A - Thermoplastic copolyamides - Google Patents

Description

(54) THERMOPLASTIC COPOLYAMIDES (71) We, BAYER AKTIENGELLSCHAFT a body corporate organised under the laws of the Federal Republic of Germany of 509 Leverkusen, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the production of copolyamides of isophthalic acid, hexamethylene diamine and 3-(amino-methyl)-3,5,5-trimethyl-cyclohexylamine, hereinafter called isophorone diamine.

British Patent No. 1,096,908 described copolyamides of isophorone diamine further diamines and dicarboxylic acids and their preparation by polycondensing the monomers consisting of the corresponding salts.

It is also known that polyamides of diamines and dicarboxylic acids can be produced by polycondensing the corresponding neutral salts in the presence of sufficient water to maintain the fluidity of the reaction mixture before the condensation temperature is reached.

According to this process the polycondensation is carried out in an autoclave to an extent such that most of the salt is converted into the amide. In the second stage, the precondensate formed, which is still soluble in water at 2000C to 2300C, is condensed at a temperature of from 260"C to 3000C, whereby the pressure is gradually reduced to atmospheric pressure. This process has the disadvantage that the salt has to be produced from the acid and diamine and isolated in a separate reaction stage before the condensation in order- to obtain high- molecular weight produets with a high degree of- purity --and good properties. Although high molecular weight polyamides of diamines and dicarboxylic acids can also be produced by condensation in aqueous solution, even without isolating the intermediate salt, by using equivalent quantities of diamine and dicarboxylic acid, the starting components have to be particularly pure in order to prevent discoloured products which are for many applications worthless.

It has now surprisingly been found that transparent copolyamides of isophthalic acid, hexamethylene diamine and isophorone diamine with excellent mechanical, electrical and thermal properties can be obtained by using the isophthalic acid in the impure form in which it is obtained from its production and without isolating and purifying the salts formed from the acid and diamines before polycondensation.

The mixture of diamines used preferably consists of 70-95 mol%, more preferably 75-90 mol %, of hexamethylene diamine and of 5-30 mol%, more preferably 10-25 mol%, of isophorone diamine Preferably an isophthalic acid is used which has been obtained by the liquid-phase oxidation of commercial-grade m-xylene in glacial acetic acid solution with air or oxygen in the presence of heavy metal catalysts and bromine or a bromine-containing compound, for example NaBr of tetrabromoethane, and which, in addition to up to 1% by weight of terephthalic acid which does not affect the polycondensation reaction, generally contains up to 0.6% by weight of further impurities such as: 0.01 to 0.15% by weight of aromatic monocarboxylic acids, e.g.

3-methyl benzoic acid; 0.01 to 0.1% by weight of aromatic aldehyde carboxylic acids, e.g. 3-formyl benzoic acid; 0.01 to 0.05% by weight of aromatic tricarboxylic acids, e.g.

trimesic acid and trimellitic acid; 1 to 50 ppm of heavy metal ions, e.g. cobalt and/or manganese; 1 to 50 ppm of bromine ions; and 0.1 to 0.3% by weight of other unknown impurities.

Accordingly, the present invention proves a process for the production of transparent, thermoplastic copolyamides which comprises polycondensing the salt of an isophthalic acid in the impure form in which it is obtained from its production and containing up to 1.6% by weight of impurities hexamethylene diamine and isophorone diamine without isolation and purification of the salt except for an optical treatment with a reducing agent and filtration.

In order to produce the salts which are used without isolation and purification apart from an optional treatment with a reducing agent and a filtration in the process according to the invention, the hexamethylene diamine and isophorone diamine are, for example, introduced at 100C to 30"C in the absence of oxygen into a quantity of water such that the salt solution obtained after reaction with isophthalic acid has a concentration of from 50 to 85% by weight, preferably from 60 to 80% by weight, and the equivalent quantity of isophthalic acid is introduced into the solution of the diamines whereby an increase of the temperature is observed. The temperature of the aqueous solution should not exceed 80 to 90"C. The salt solution having a temperature of 80"C to 900C is then introduced into the autoclave under pressure either through a filter or through an adsorbent.

Particularly light-coloured polyamides can be obtained by adding from 0.01 to 1% by weight (based on salts) of a reducing agent during the production of the salts. It is of course also possible to add larger quantities of a reducing agent, although in that case there is no longer any evidence of a colour-improving effect. Suitable reducing agents are, for example, sulphites, dithionites, phosphites, hypophosphites, hydrides and hydrazine hydrate. Particularly suitable reducing agents are hypophosphorous acid and its salts, for example, sodium, potassum or ammonium hypophosphite, and also hydrides such as sodium or potassium borohydride.

The salts may also be produced by initially introducing a suspension of isophthalic acid in water and then adding the equivalent quantity of diamines in portions.

The salt to be polycondensed may be a salt as described and claimed in our copending United Kingdom patent application No.31543/77. (Serial No. 1590528).

In order to obtain high molecular weight products and to avoid the expensive isolation of the salts, the diamines and dicarboxylic acid have to be used in equivalent quantities. The equivalence of acid and amine may easily be checked by controlling the pH-value of the salt solution formed and may if necessary be corrected. A 5% by weight aqueous salt solution has depending on the composition of the mixture a pH-value of 6.8 - 7.3 (as measured with a glass electrode at 23"C).

Sometimes it is advantageous to carry out the polycondensation at pH values up to 8.5, in order to compensate losses of diamine.

Higher or lower pH-values correspond to a definite excess of amine or acid which may be directly read off and readily compensated by a corresponding addition of the deficient component.

The salt solution obtained in this way is then condensed by a conventional method.

Preferably, the salt solution may be transferred through a filter to the condensation autoclave and heated under pressure to a temperature of from 200"C to 230"C. A pressure of from 10 to 30 bars is observed depending upon the temperature and filling level of the autoclave. After a reaction time of 1 to 2 hours, the temperature is increased to 2600C 300"C and preferably to 2700C - 290"C and, simultaneously, the pressure in the autoclave is slowly reduced to atmospheric pressure. Polycondensation is continued under nitrogen until the required degree of polymerisation is obtained. The water-clear, viscous melt of the polymer is then extruded by the usual method, for example under pure nitrogen, from a single-hole die to form a strand which, is cooled by being passed through a water bath and is subsequently delivered to a granulating machine.

Preferably the polyamides have a relative viscosity Tirel of at least 2.2. (as measured on a 1% by weight in m-cresol at 250C).

The polyamides show excellent properties when their relative viscosity is adjusted to values of from 2.2 to 3.5, preferably from 2.5 to 3.0. In order to adjust the required, molecular weight, chain terminators, for example, acetic acid, propionic acid, stearic acid or, preferably, aromatic monocarboxylic acids, such as benzoic acid, may also be used in the known way in the process according to the invention. The molecular weight may also be limited by using a small excess of isophthalic acid or hexamethylene diamine.

The above described polycondensation of the aqueous salt solution may also be carried out without use of excess pressure. In this case, losses of hexamethylene diamine and isophorone diamine can be expected during precondensation, although they may be made up by adding an excess of diamine at the beginning of the polycondensation process. The losses of diamine are governed by a large number of parameters, for example by the polycondensation temperature, by the intensity of the inert gas stream and by the dimensions of the apparatus. Under adverse conditions, the loss of diamine may be as much as 6% by weight, based on the amine used.

Non-crystalline, completely transparent, colourless polyamides with a high impact strength and a dimensional - stability under heat of more than 125"C are obtained by the process according to the invention.

These transparent polyamides may be processed by injection moulding or extrusion in standard machines to form shaped articles, films, sheets, fibres, bristles or hollow bodies.

By virtue of their electrical properties, they may be used as electrical insulating materials.

In addition, they may contain fillers, especially glass fibres, mould release agents, lubricants, fire retardants, stabilisers, pigments or other dyes.

Examples 1. 2.63 kg of hexymethylene diamine were dissolved under nitrogen in 2.57 kg of water of storage vessel. 4.42 kg of isophthalic acid were then added in portions with cooling to this solution so that the temperature of the reaction mixture did not exceed 70"C.

In addition to 0.5% by weight of terephthalic acid, the isophthalic acid used contains the following substances: 0.08% by weight of aromatic monocarboxylic acids; 0.08% by weight of aromatic aldehyde carboxylic acids; 0.03% by weight of aromatic tricarboxylic acids; 3 ppm of cobalt; 5 ppm of manganese; 30 ppm of bromine; and 0.3% by weight of other unknown impurities.

Following the addition of 0.685 kg of isophorone diamine, the mixture was briefly heated to 900C. The pH-value of the salt solution which was diluted with water to a solids content of 5% by weight, was 7.9. After the addition of 0.0039 kg hypophosphorous acid the solution was introduced under pressure into a nitrogen-filled autoclave which was heated to 225"C. The salt solution was precondensed for 2 hours at an internal temperature of 220"C.

By this time a pressure of 18 bars prevailed. The temperature was increased to 2700C and simultaneously the pressure was carefully reduced. Polycondensation under nitrogen ceased after another 4 hours. The polyamide was then run off in the form of a bristle through a waterbath, granulated and dried. The product had a relative viscosity of 2.6, as measured on a 1% by weight solution of the polyamide in m-cresol in an Ubbelohde viscosimeter at 25"C.

The product can be processed into almost colourless, transparent mouldings.

Impact strength (according to DIN 53 453): unbroken Dimensinal stability under heat according to Vicat, Method B (DIN 53 460): 144"C Elongation at break: 22% Flexural strength: 163 MPa E-modulus (tensile test): 3110 MPa Example 2 Following the procedure of Example 1, polyamides with the same properties, apart from their dimensional stability under heat, as in Example 1 were obtained from salt solutions which have been produced using the isopthalic acid characterised in Example 1 and hexamethylene diamine and isophoronic diamine in different molar ratios molar ratio of dimensional stability hexamethylene diamine: under heat according isophorone diamine to Vicat, meth. B.

90 10 137"C 80 : 20 1500C WHAT WE CLAIM IS: 1. A process for the production of a transparent, thermoplastic copolyamide which comprises polycondensing a salt of an isophthalic acid in the impure form in which it is obtained from its production and containing up to 1.6% by weight of impurities, hexamethylene diamine and isophorone diamine without isolation and purification of the sat except for an optional treatment with a reducing agent and filtration.

2. A process as claimed in claim 1, wherein the isophthalic acid used contains up to 1% by weight of terephthalic acid; from 0.01 to 0.15% by weight of one or more monocarboxylic acids; from 0.01 to 0.1 by wieght of one or more aldehyde carboxylic acids; from 0.01 to 0.05% by weight of one or more tricarboxylic acids; from 1 to 50 ppm of one or more heavy metal ions; from 1 to 50 ppm of bromine ions; and from 0.1 to 0.3% by weight of other unknown impurities.

3. A process as claimed in claim 1 to 2, wherein the isophthalic acid used is one obtained by oxidising commercial-grade m-xylene in glacial acetic acid solution with air or oxygen in the presence of a heavy metal catalyst and bromine or a bromine-containing compound.

4. Transparent thermoplastic polyamides obtained by a process as claimed in claim 1.

5. A process as claimed in any of claims 1 to 3, wherein the salt is polycondensed in the form of a 50 to 85% by weight aqueous solution.

6. A process as claimed in claim 4, wherein the salt is polycondensed in the form of a 60 to 80% by weight aqueous solution.

7. A process as claimed in any of claims 1 to 5 wherein the salt is prepared by introducting hexamethylene diamine and isophorone diamine at a temperature of 10 C to 30"C in the absence of oxygen into water and by introducing isophthalic acid into the solution.

8. A process for the production of a transparent thermoplastic copolyamide substantially as herein described with reference to either of the specific Examples.

9. A transparent thermoplastic copolyamide when prepared by a process as claimed in any of claims 1 to 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Example 2 Following the procedure of Example 1, polyamides with the same properties, apart from their dimensional stability under heat, as in Example 1 were obtained from salt solutions which have been produced using the isopthalic acid characterised in Example 1 and hexamethylene diamine and isophoronic diamine in different molar ratios molar ratio of dimensional stability hexamethylene diamine: under heat according isophorone diamine to Vicat, meth. B.

   90 10 137"C 80 : 20 1500C WHAT WE CLAIM IS: 1. A process for the production of a transparent, thermoplastic copolyamide which comprises polycondensing a salt of an isophthalic acid in the impure form in which it is obtained from its production and containing up to 1.6% by weight of impurities, hexamethylene diamine and isophorone diamine without isolation and purification of the sat except for an optional treatment with a reducing agent and filtration.
2. 2. A process as claimed in claim 1, wherein the isophthalic acid used contains up to 1% by weight of terephthalic acid; from 0.01 to 0.15% by weight of one or more monocarboxylic acids; from 0.01 to 0.1 by wieght of one or more aldehyde carboxylic acids; from 0.01 to 0.05% by weight of one or more tricarboxylic acids; from 1 to 50 ppm of one or more heavy metal ions; from 1 to 50 ppm of bromine ions; and from 0.1 to 0.3% by weight of other unknown impurities.
3. 3. A process as claimed in claim 1 to 2, wherein the isophthalic acid used is one obtained by oxidising commercial-grade m-xylene in glacial acetic acid solution with air or oxygen in the presence of a heavy metal catalyst and bromine or a bromine-containing compound.
4. 4. Transparent thermoplastic polyamides obtained by a process as claimed in claim 1.
5. 5. A process as claimed in any of claims 1 to 3, wherein the salt is polycondensed in the form of a 50 to 85% by weight aqueous solution.
6. 6. A process as claimed in claim 4, wherein the salt is polycondensed in the form of a 60 to 80% by weight aqueous solution.
7. 7. A process as claimed in any of claims 1 to 5 wherein the salt is prepared by introducting hexamethylene diamine and isophorone diamine at a temperature of 10 C to 30"C in the absence of oxygen into water and by introducing isophthalic acid into the solution.
8. 8. A process for the production of a transparent thermoplastic copolyamide substantially as herein described with reference to either of the specific Examples.
9. 9. A transparent thermoplastic copolyamide when prepared by a process as claimed in any of claims 1 to 7.