GB1590527A - Copolyamides - Google Patents

Description

(54) COPOLYAMIDES (71) We, BAYER AKTIÈNGESELLSCHAFT, 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 partlcuiarly described in and by the following statement: This invention relates to a process for the production of copolyamides.

More particularly, this invention relates to a process for the production of copolyamides of isophthalic acid, hexamethylene diamine and lbis-(4-aminocyclohexyl)-al- kanes.

Copolyamides consisting of bis-(4-aminocyclohexyl)-alkanes, further diamines and dicarboxylic acids and their production by polycondensing the monomers respectively the corresponding salts at a temperature of from'150--300"C are known from Gernian Offenlegungsschriften No. 1933395 and No.

1595354.

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 2300 C, is condensed at a temperature of from 2600C to 300"C, whereby the pressure is gradually reduced to atmospheric pressure.'This process has the disadvantage that the salt has td be -produced from the acid and diamine and isolated before the condensation in 'a separate stage in order to obtain high molecular 'weight products 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 to prevent discoloured products which are for many applications worthless.

We have now surprisingly found that transparent polyamides of isophthalic acid, hexamethylene diamine and bis-(4-aminocyclohexyl)-alkanes with excellent mechanical, electrical and thermal properties can be obtained by using the isophthalic acid'in the impure form, containing up to 1.6% by weight of impurities, in which it is obtained from its production and without isolating and purifying the salt formed from the acid and diamine before polycondensation.

Thus the present invention provides a process for the production of a transparent, thermoplastic polyamide which comprises polycondensing a 50% to 85% by - weight aqueous solution of a salt formed from hexamethylene diamine, a bis-(4-aminocyåo- hexyl)-alkane and an isophthalic aåd in the impure form containing up to 1;6% by -weight of impurities, in which it is obtained from its production, the polycondensing being carried out without isolation and purification of the salt other than an - optional treatment with a reducing agent and -flItra- tion.

In the process, according to the invention the mixture of diamines used preferably consists of 70 - 95 mol %, more preferably 75 - 90 mol %, of hexamethylene diamine and of 5-80 mol: SO more preferably 10- 25 mol %, of .bis(4-aminocyclohexyl)-alkanes wfth I - 4 carbon atoms in the alkyl radi 'cal. -The cyclohexyl-ring optionally, can be substituted with C1-C4 alkyl radicals.

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). Preferably the bis-(4-aminocyclohexyl)-alkane is bis (4-aminocyclohexyl)-methane, 2,2-(bis-(4aminocyclohexyl)-propane or bis-(4-amino3 -methyl-cyclohexyl)-methane.

The isophthalic acid used is preferably one 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 or tetrabromoethane, and which in addition to up to 1% by weight of terephthalic acid which does not effect 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 mono carboxylic 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 tri carboxylic 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.

In order to produce the salts of isophthalic acid, hexamethylene diamine and the bis-(4 àminocyclohexyl)-alkanes which are used without isolation and purification apart from - an optional treatment with a reducing agent and a filtration step- in the process according to the invention, the diamines are, for example,' introduced at 100C to 300C 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%, preferably from 60 to 80%, and the equivalent quantity of isophthalic acid is introduced into the solution of the diamine whereby an increase of the temperature is observed. The temperature of the aqueous solution should not exceed 80"C to 900 C. The salt solution having a temperature of 80oC 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 large quantities of a reducing agent, although in that case there is no longer any evidence of a colour-improving effect. Suit- able 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, potassium 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.

In order to obtain high molecular weight products, the diamines and dicarboxylic acid should be used in equivalent quantities.

The equivalence of acid and amine may easily be checked by controlling the pHvalue of the salt solution formed and may if necessary be corrected. A 5% by weight aqueous solution of the salts has a pH-value of from 6.9 to 7.4 (as measured with a glass electrode at 230 C.

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. High molecular weight polyamides are only obtained when the pHvalue of the aqueous salt solution is between'6.0 and 9.0.

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 2300 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 2603000 C- and preferably to 270-, 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 a conventional method, for example under pure nitrogen, from a singlehole die to form a strand which is cooled by being passed through a -water bath and is subsequently- delivered to a granulating machine.

The polyamides should have a relative viscosity Wrel of at least 2.2 (as measured on a 1 % by weight solution in m-cresol at 25"C).

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 oi, 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 can be expected during precondensation, although they may be compensated by adding an excess of diamine at the beginning of the polycondensation process. The losses of hexamethylene 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 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 thermal stability of more than 125"C are obtained by the process according to this invention.

These transparent polyamides may be process 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.

The polyamides may contain conventional additives such as fillers, especially glass fibres, mould release agents, lubricants, fire retardants, stabilisers, pigments or other dyes.

The invention is illustrated by the following Examples.

EXAMPLES 1. 2.57 kg of hexamethylene diamine were dissolved under nitrogen in 2.57 kg of water in a storage vessel. 4.32 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 700C. After the addition of 0.82 kg of bis- (4-aminocyclohexyl)-methane having a melting point of 42--44"C the mixture was heated to 900C for a short time. The salt solution was diluted with water to a solid content of 5%, by weight. Its pH-value was 7.25.

In addition to 0.5% by weight of terephthalic acid, the isophthalic acid used contained 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; and 30 ppm of bromine; and 0.3% by weight of other unknown impurities.

The solution was introduced under pressure into a nitrogen-filled autoclave which was heated to 2250C. 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 2.7, as measured on a 1 % solution of the polyamide in m-cresol in an Ubbelohde viscosimeter at 25"C.

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

Impact strength (according to DIN 53 453): unbroken Second order transition temperature (DTA): 1450C EXAMPLE 2 Following the procedure of Example 1, polyamides were obtained from salt solutions which has been produced using the isophthalic acid characterised in Example 1 and various molar ratios of the diamine.

The resulting polyamides were transparent and colourless.

Molar ratio of hexa methylene diamine: second order transibis-(4-aminocyclohexyl)- tion methane temperature "C 70 : 30 165 95 : 5 136 WHAT WE CLAIM IS: 1. A process for the production of a transparent, thermoplastic polyamide which comprises polycondensing a 50% to 85% by weight aqueous solution of a salt formed from hexamethylene diamine, a bis-(4aminocyclohexyl)-alkane and an isophthalic acid in the impure form, containing up to 1.6% by weight of impurities in which it is obtained from its production, the polycondensing being carried out without isolation and purification of the salt other than an optional treatment with a reducing agent and filtration.

2. A process as claimed in claim 1, wherein the isophthalic acid used contains in addition to up to 1 % by weight of terephthaiic acid; from 0.01 to 0.15% by weight of one or more monocarboxylic acids; from 0.01 to 0.1% by weight of one or more aldehyde carboxylic acids; from 0.01 to 0.5% 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 or 2, wherein the isophthalic acid used is

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. the aqueous salt solution may also be carried out without use of excess pressure. In this case, losses of hexamethylene diamine can be expected during precondensation, although they may be compensated by adding an excess of diamine at the beginning of the polycondensation process. The losses of hexamethylene 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 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 thermal stability of more than 125"C are obtained by the process according to this invention. These transparent polyamides may be process 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. The polyamides may contain conventional additives such as fillers, especially glass fibres, mould release agents, lubricants, fire retardants, stabilisers, pigments or other dyes. The invention is illustrated by the following Examples. EXAMPLES 1. 2.57 kg of hexamethylene diamine were dissolved under nitrogen in 2.57 kg of water in a storage vessel. 4.32 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 700C. After the addition of 0.82 kg of bis- (4-aminocyclohexyl)-methane having a melting point of 42--44"C the mixture was heated to 900C for a short time. The salt solution was diluted with water to a solid content of 5%, by weight. Its pH-value was 7.25. In addition to 0.5% by weight of terephthalic acid, the isophthalic acid used contained 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; and 30 ppm of bromine; and 0.3% by weight of other unknown impurities. The solution was introduced under pressure into a nitrogen-filled autoclave which was heated to 2250C. 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 2.7, as measured on a 1 % solution of the polyamide in m-cresol in an Ubbelohde viscosimeter at 25"C. The resulting product can be processed into almost colourless transparent mouldings. Impact strength (according to DIN 53 453): unbroken Second order transition temperature (DTA): 1450C EXAMPLE 2 Following the procedure of Example 1, polyamides were obtained from salt solutions which has been produced using the isophthalic acid characterised in Example 1 and various molar ratios of the diamine. The resulting polyamides were transparent and colourless. Molar ratio of hexa methylene diamine: second order transibis-(4-aminocyclohexyl)- tion methane temperature "C 70 : 30 165 95 : 5 136 WHAT WE CLAIM IS:

1. A process for the production of a transparent, thermoplastic polyamide which comprises polycondensing a 50% to 85% by weight aqueous solution of a salt formed from hexamethylene diamine, a bis-(4aminocyclohexyl)-alkane and an isophthalic acid in the impure form, containing up to 1.6% by weight of impurities in which it is obtained from its production, the polycondensing being carried out without isolation and purification of the salt other than an optional treatment with a reducing agent and filtration.

2. A process as claimed in claim 1, wherein the isophthalic acid used contains in addition to up to 1 % by weight of terephthaiic acid; from 0.01 to 0.15% by weight of one or more monocarboxylic acids; from 0.01 to 0.1% by weight of one or more aldehyde carboxylic acids; from 0.01 to 0.5% 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 or 2, wherein the isophthalic acid used is

obtained by oxidising 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.

4. A process as claimed in any of claims 1 to 3, wherein bis-((4-aminocyclohexyl)methane, 2,2-bis-(4-aminocydohexyl)-pro pane or bis-(4-amino-3-methyl-cyclohexyl)methane are used as the bis-(4-aminocyclohexyl)-alkanes.

5. A process as claimed in any of claims 1 to 4, wherein the aqueous solution of the salt has a concentration of 60% to 80% by weight.

6. A process as claimed in any of claims 1 to 5, wherein the aqueous solution of the salt is polycondensed at a temperature of from 80"C to 900C.

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

8. A transparent, thermoplastic polyamide when prepared by a process claimed in any of claims 1 to 7.