IL28802A - Manufacture of high molecular weight synthetic linear polyamides - Google Patents

Description

PATENTS FORM NO. 3.

PATENTS AND DESIGNS ORDINANCE SPECIFICATION IMPROVEMENTS IN OR RELATING TO THE MANUFACTURE OF HIGH MOLECULAR WEIGHT SYNTHETIC LINEAR POL YA MIDES mm '-ικ' ρ^ιο p zi -> >y2 We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, a British Company of Imperial Chemical House, Millbank, London, S. W.1. , England, DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed, to be particularly ascertained in and by the following The present invention relates to the manufacture of high molecular weight synthetic linear polyamides containing pigments by the polycondensation of diammonium salts of dibasic acids or of omega-amino aliphatic carboxylic acids, and more particularly to a continuous process for carrying out said polymerisation in an elongate reaction zone.

The term "polyamides" as used in this specification and its claims includes interpolyamides .

The expression "high molecular weight linear polyamides" signifies that the degree of polymerisation of the polyamides is great enough for them to be melt-spun into filaments, this degree of polymerisation corresponding to the elimination from the monomers of circa 0 - 95<> of the total theoretically available water of condensation. The term "pignent" includes colourless pigments otherwise referred to as "delustrants" .

The manufacture of such polyamides, particularly polyhexamethylene adipamide, for example, is commercially important. Moreover most of the manufactured polymer is put to uses which entail the incorporation thei in of a delustrant. For this purpose titania is employed in proportions usually varying from about l/3 - 3 depending on the nature of the textile articles to be made of the polyamide. Sometimes coloured pigments are introduced so that filaments of various shades can be directly melt-spun without any subsequent dyeing process; for example black polyamides are obtained by the incorporation of carbon black.

Processes for carrying out such polyamide polymerisations in a tube or elongate reaction zone are known including the incorporation of a pigment as an aqueous dispersion as described in lixamples and 13 of British Patent Specification No. 9 630. The molten polymerising mass is understood to flow along the tube as an annulus on the inner surface thereof whilst gas (steam) passes down the centre, the process thus constituting a case of two phase annular flow.

The efficiency of the melt-spinning process and the properties of the resulting polyamide filaments depend however very much on the success which is achieved in maintaining the pigment particles in a state of fine dispersion. The term "fine" must be understood as indicating a sort of average fineness because normally the dispersion is not uniform since the particles (and aggregates thereof) are present in a range of sizes. Should the dispersion become insufficiently fine, the filters employed in melt-spinning get clogged and require unduly frequent renewal. In addition the so-called covering power of the pigment decreases. Thus in the case of titania (for a given concentration) the opacity of the filament diminishes. This can readily be seen on inspection of a fabric with the naked eye, although it is not easy to assign numerical values to measure the degree of opacity.

Whilst as already mentioned, the pigment dispersion can be added to the starting materials for the polyamide polymerisation, it has now been found that better dispersions of pigment in the polyamide are obtainable when the aqueous dispersion is not introduced until polymerisation has commenced. The theoretical reasons are not thoroughly understood, one hypothesis being to the effect that the dispersion is sensitive to carboxyl ions the concentration of which is known to decrease during the course of the polymerisation. Be this as it may, it has proved advantageous not to add the pigment dispersion until after lower oligomers have been formed with the almost complete disappearance of the original monomer. Experiments show that this state of affairs is reached when the temperature of the reaction mass has attained or nearly attained that of the wall of the reaction vessel, which may take the form of a tube or series of tubes to contain the elongate reaction zone. On the other hand the pigment dispersion must not be added too late for the following reason. The further the polymerisation proceeds, and the lower the pressure falls in the elongate reaction zone, the more the polyamide tends to freeze if a fall in the temperature is caused by the introduction of cold water (pigment dispersion) . The tendency to freeze is however less where relatively lower degrees of polymerisation, corresponding to higher pressures, are present. In practice it has been found satisfactory to introduce the dispersion at any point in the elongate reaction zone (l) a ter the reaction mass has attained the temperature of the vessel wall but (2) before the pressure has fallen to a value less than 7 atmospheres above the pressure at the end of the reaction zone.

Accordingly the invention consists of a continuous process for the manufacture of pigmented high molecular weight linear polyamides by the condensation polymerisation of one or more monomers selected from the group comprising a diammoniura salt of a diamine HHg ~ x ~ with a dibasic acid HOOC - Y- COOH, or an amino acid NH^ - Z - COOH wherein X, Y and Z denote chains of methylene groups, X & Y together containing at least 6 methylene groups and Z at least 3, each methylene chain containing, not joined directly to an amino group, 0, 1 or 2 meta- or para-phenylene groups, and X, Y and Z optionally bearing alkyl or aryl substituents and optionally containing -0- links in the chain, providing the groupings -0-0-, -O-CHg-N- and -O-CHg-CHg-CO-be absent, comprising pumping an aqueous solution of said monomer or monomers through an elongate reaction zone heated to polymerisation temperatures wherein the reaction mass flows in two phases from a pressure of at least 14 atmospheres at the inlet to the zone to a pressure not over 1 atmosphere at the outlet to the zone, and injecting a dispersion of the pigment into the elongate reaction zone at a point along its length where the temperature of the reaction mass is less than 5°C below that of the wall of the vessel containing the elongate reaction zone and the pressure is not less than atmospheres above the pressure at the outlet to the reaction zone.

The monomers, mixtures of which can be used, should be chosen so as to yield a polyamide or interpolyamide which melts, if necessary in admixture with a plasticiser, below 350°C and preferably below 300°C. As is well known interpolyamides usually melt at lower temperatures than the constituent polyamides.

Indeed a minor proportion of a second monomer to lower the melting point of the resulting polymer is frequently termed an internal plasticiser.

Examples of suitable monomers for carrying out the process of the present invention are:- hexamethylene diammonium adipate hexamethylene diammonium sebacate octamethylene diammonium adipate decamethylene diaiamonium adipate pentameth lene diammonium sebacate dodecamethylene diammonium adipate omega-aminocaproic acid omega-aminoundecanoic acid hexamethylene diammonium azelaate hexamethylene diammonium suberate p-(gamma-amino-n-propyl) phenoxyacetic acid l-p-( amma-carboxy-n-pro y1) phenyl-2-aminoethane also the diammonium salts from the following pairs of amines and acids: m-xylylene diamine adipic acid hexamethylene diamine isophthalic acid 2,5 di-(beta-aininoethyl)-p-xylene pimelic acid di-(beta-aminoethyl)durene 1,16-hexadecane dicarboxylic acid m-di-(beta-aminoethyl)benzene adipic acid di-(aminomethyl)mesitylene azelaic acid dodecamethylene diamine terephthalic acid decamethylene diamine p-di-( eta-carboxyethy1) benzene The following mixtures of monomers yield, for example, interpolyamides: (1) hexamethylene diammonium adipate and omega-amino caproic acid. (2) hexamethylene d ammonium adipate and hexamethylene diammonium sebacate. (3) hexamethylene diammonium adipate and hexamethylene diammonium isophthalate. (4) dodecamethylene diammonium suberate and dodecamethylene diammonium laurate. (5) dodecamethylene diammonium terephthalate and hexamethylene diammonium terephthalate. (6) the salts from hexamethylene diamine, p-di-(beta-carboxyethyl) benzene and beta-(p-carboxymethylphenyl) propionic acid. (7) the salts from hexamethylene diamine, adipic acid and 1,4- diphenyladi ic acid.

Small amounts of the order of a few per cent of other polyamide-forming monomers, e.g. N,N^-piperazine-di-(gamma)-n-propylammonium adipate or hexamethylene diammonium fluorene-Z-sodio-sulphonate-bis-9,9-propionate, may also be employed in conjunction with the above monomers.

There may also be added to the reaction mixture bifunctional or monofunotional compounds in small quantity, notably monoamines or monobasic acids, e.g. acetic acid in order to prevent polymerisation proceeding beyond the desired degree at elevated temperatures, for example, when the polyamide is held molten for the purpose of melt-spinning. Such monofunctional compounds are known as viscosity stabilisers. Other adjuvants may also be added, for instance, dyes, dyestuff formers, heat stabilisers, light stabilisers, and polyamide and other resins. t is advisable to include with the aqueous monomer salt starting material a little of the amine constituent of the salt e.g. hexamethylene diamine, in order to compensate for the loss of amine in the gas phase (steam) which tends to occur. This is one of the reasons for stipulating a minimum pressure of 14 atmospheres (based upon experiments) at the inlet to the elongate reaction zone.

Another reason is that with lower pressures the process is apt to run unsteadily yielding unsatisfactory results.

If desired, the gas phase which is mainly steam, can be replaced to a greater or less extent by an inert gas, for instance by injecting nitrogen, but the inert gas must be free of oxygen, since very small quantities thereof degrade the polymer.

Suitable plasticisers, which should be devoid of halogen and ester groups, are phenols, medium and high boiling glycols and sulphonamides, for instance: - 1,12-di-(p-hydrox henyl)-octadecane hexamethylene glycol 2-ethylhexane diol-1,3 N-ethyl -o-toluene sulphonamide N-butyl-p-toluene sulphonamide N-phenylcyclohexane sulphonamide For making a given polyainide it is found in practice that a temperature at least 10°C above the melting point of the polyamide can be regarded as a suitable polymerisation temperature i.e. a temperature at which amide formation proceeds at a useful rate, provided it be not too high otherwise degradation of the polyamide is likely ot occur. The temperature of the polymerising material is preferably not allowed to fall ae it passes through the elongate reaction zone. It is convenient that the whole zone be at one uniform temperature. The temperature is advantageously from 2?5°C to 300°C.

The mixture of monomer and water should constitute a strong solution or suspension and contains preferably at least /*<> by weight of monomer. Furthermore suspensions of monomer are desirably heated so as to bring about solution} in any case sufficient water should be present to dissolve the monomer at polymerisation temperatures. Of course all materials entering the elongate reaction zone should be as free as possible of impurities which lead to undesirable deposits forming on the inside walls of said zone.

The elongate reaction zone, conveniently contained by a tube, may possess any feasible shape, e.g. a helix positioned vertically or horizontally. The vertical helix can be traversed by the polymerising mass in an upward or downward direction. The material of which the tube is constructed is preferably one not subject to corrosion by the polymerising mass and may be, for instance, stainless steel.

The tube must be capable of withstanding a high pressure which may, for example reach 26 atmospheres at the inlet end and in some oases considerably higher valuee.

The invention includes melt-spinning the above polyamides into filaments, films, ribbons and like lengthy extruded objects and the said objects when so melt-spun. In su¾n case the viscosity V of the melted polymer prior to extrusion is of importance and may be measured by, for instance, the pressure drop across an orifice in the polymer path .

The pigment e.g. titania is injected, i.e. pumped in under pressure in the form of a fine dispersion, preferably aqueous.

The dispersion is conventionally made by milling the titania, say, with water, advantageously in the presence of ¾ - sodium hexametaphosphate or sodium pyrophosphate. To minimise abrasion and wear the piston and other parts of the pump used for the aqueous dispersion or slurry of the pigment may be made of polyhexamethylene adipamide (nylon) or other plastic resistant to abrasion. The concentration of the pigment dispersion should be adjusted to e.g. 1-lOfo so that the desired rate of injection corresponds to a conveniently pumpable volume rate. Thus difficulties may be experienced in accurately pumping- the dispersion at a lower rate than 10 cc. per minute, unless pumps specially designed for the purpose are employed. For instance a pump of refined construction, unable itself to handle the pigment dispersion, but capable of pumping water very accurately, can be employed to pass water into a suitable pump where it actuates a floating piston, on the other side of which is the pigment dispersion. The latter is thus impelled at the same accurate volume rate as the water. The water pump may consist of a diaphragm pump or may comprise a reciprocating plunger in place of the diaphragm. Instead of the floating piston pump, the flexible chamber pump described in British patent specification No. 635,920 can be used.

Examples of pigments besides titania and carbon black which may be incorporated in the polyamide are:- barium sulphate, zinc titanate, zinc oxide, zinc sulphide, lithopone, zirconium dioxide, calcium sulphate, copper phthalocyanine, chromium oxide, lead chromate, magnesium oxide, iron oxide and cadmium sulphide.

Such pigments may, if desirable, be used as mixtures one with another. Furthermore other insoluble compounds may conveniently be incorporated in the pigment dispersion, as may other compounds soluble in the · dispersing- medium. Such other compounds may, if necessary, be pre-coated onto the insoluble particles.

Other dispersing agents may be used in the dispersion and indeed, the dispersing- agent may have to be chosen in accordance with the materials comprising the dispersion as well as taking into account ®· any effects in the finally produced polymer.

The following Examples are intendedto illustrate not limit the invention. The parts and percentages are calculated by weight.

Example 1 The elongate reaction zone is contained in a coiled steel » tube jacketted with the vapours of the eutectic mixture of diphenyl and diphenyloxide which condense at 290°C. The tube comprises 203 metres of internal diameter 17 mm. starting from the inlet followed by 70 metres of internal diameter 57 mm* An aqueous solution containing 0 of hexamethylene diamnwndum . adipate, 0.24 of hexamethylene diamine and 0.0028 of acetic acid is pumped at a rate of 3 · 28 kg./min. into the inlet of the above tube where the pressure is 28.6 atmospheres and the temperature of the reaction mass 289°C. Titania (anatase form) is milled with water and the resulting slurry diluted to a 10J¼ dispersion. The latter . is injected at a rate of 272 gm/min. into the above tube at a point 122 metres from the inlet where the pressure is 23 atmospheres.

The polyhexamethylene adipamide obtained is melt-spun into delustred filaments in which the titania is finely dispersed.

Example 2.

. Example 1 is repeated with the following reagents and conditions f substituted for the ones given: - Monomer solution 47 hexamethylene diammonium adipate, 0.026$ hexamethylene diamine, 0.0103?» acetic acid.

Rate of pumping .96 kg/min.

· Pigment dispersion 10?» aqueous carbon black.

Rate of injection 245 gms./min.

The polyamide is melt-spun into a black yam of 20 filaments which is drawn down to 7 denier.

Example 3.

. A tube of austenitic steel comprising (starting with the inlet end) 137 metres of internal diameter 14 mm. followed by 52 metres of internal diameter 45 nun. is made into a coil. The tube is maintained at 290°C.

An aqueous monomer solution containing 47 hexamethylene diammonium adipate and Ο.445 hexamethylene diamine is pumped into the · inlet end of the above tube (pressure 30.6 atmospheres) at a rate of L64 kgm./min. 82 metres down the tube where the pressure is 29 atmospheres and the temperature of the reaotion mass 289°C there ie injected at a rate of 134 gms/min. by means of a pump w th a nylon plunger a titania dispersion made as follows . Titania dispersion .4 kgm. of finely divided titania (anatase form) together with Ο gm. finely divided commercial manganese pyrophosphate are added to a solution of 224 gm. sodium pyrophosphate decahydrate in 38.1 kgm. filtered deionised water. The dispersion is milled until . an average particle size of 0.2Θ microns has been attained, and then diluted by adding it to a solution of 224 m. sodium pyrophosphate deoahydrate in 190. kgm. of filtered deionised water. This diluted dispersion is injected into the coil.

The resulting polyamide is melt-spun into a yarn of 13 filaments . having a total denier of 130. The titania delustrant is well dispersed in the filaments.

Example 4 A narrow coiled polymerisation tube of stainless steel com rising 73 metres of internal diameter 8 mm. followed by 32 metres of internal diameter 25· 4 mm. is maintained at 291°C The outlet end of the tube leads into a cylindrical reservoir 30 cms. in diameter and 60 cirs. high with a conical bottom enclosing an angle of 80° carrying s t its apex a pump for forwarding the polyamide which collects as a pee l in the reservoir, to spinnerets, where it is melt-spun into fil aments.

Two different solutions of monomer are pumped into the inl; t, where the pressure is 23 atmospheres, namely: - Solution Mo . 1 44· 17° hexamethylene di ammonium adipate 0.3 hexamethylene diamine 55.0 water Solution Mo . 2 30«6 hexamethylene diammonium adipate 0.3 hexamethylene diamine 60. $ water The output of polyamide is regulated by alternating the monomer supply between these solutions. The alternation is effected b conventional electronic means actuated by the intermittent interruption (when the level of polyamide rises in the reservoir) of a collrlnated beam of gamma rays from a caesium 137 source . When the beam pisses, Solution No . 1 is pumped at 313*5 cc/min. } when the beam is interrupted by the polymer in the vessel Solution No. 2 is pumped at 290 cc/i;;.n.

An aqueous titania dispersion, prepared as in Example 3 is injected into the coil at a point 48.7 metres from the inlet an Example 5» Example 4 is repeated except that the titania dispersion i s · injected at a point 24· 3 metres from the inlet, where the temperature of the reaction mass is 290°C, ahd the pressure 17 atmospheres, and the alternation of the solutions of monomer is controlled by an electrically conducting probe which makes contact with the eurf&oe of the molten polyamide in the reservoir (so completing an elec trical . circuit) when the pool rises to the desired level.

Example 6.

A coiled steel tube comprising (starting with the inlet end) 45·7 metres of internal diameter 6.3 mm. followed by 15.2 metre of internal diameter 22.2 mm. is maintained at 290°C . An aqueous monomer . solution containing 47$ of hexamethylene dianunoniura adipate, 0. of hexamethylene diamine and 0.028^o of acetic acid is pumped into the inlet of the tube where the pressure is 22 atmospheres at a rate of 155 gm./min. A aqueous dispersion of titania is injected into the tube 29.8 metres from the inlet where the reaction mass is at . 289°C , against a pressure of 14 atmospheres at a rate of 25 gms o-in.

A well delustred polyamide results.

Example 7 » Example 6 is repeated except that the titania is replaced 0,7 channel blaok, and the polyamide is melt-spun into filaments.

' The latter possess a lustrous dense black colour.

Example 8.

Example is repeated except that the channel black is replaced by cadmium sulphide, yellow filaments are obtained.

Example 9» Example 6 is repeated save that the monomer solution is replaced by an aqueous solution containing 40'<> omega-aminocaproic acid, and 0.1$ acetic acid. A similar delustred polyamide is obtained.

Claims (12)

Having now particularly of our said invention and in what we declare that what we claim is XXXXXXXXXXX JOCXX

1. A process for the manufacture of pigmented high molecular weight linear polyamides by the condensation polymerisation of one or more monomers, selected from the group comprising a diammonium * salt of a diamine KH2 - X - NHg with a dibasic acid HOOC - Y - COOH, or an amino acid HHg - Z - COOH wherein X, Y and Z denote chains of methylene groups, X & Y together containing at least 6 methylene groups and Z at least 3, each methylene chain containing, not joined directly to an amino group, 0, 1 or 2 raeta- or para-phenylene groups, and X, Y and Z optionally bearing alkyl or aryl substituents and optionally containing -0- links in the chain, providing the groupings -0-0-, -O-CHg-N- and -O-CHg-CHg-CO- be absent, comprising pumping an aqueous solution of said monomer or monomers through an elongate reaction zone heated to polymerisation temperatures wherein the reaction mass flows in two phases from a pressure o at least I4 atmospheres at the inlet to the zone to a pressure not over 1 atmosphere at the outlet to the zone, and injecting a dispersion of the pigment into the elongate reaction zone at a point along its length where the temperature of the reaction mass is less than 5°C below that of the wall of the vessel containing the elongate reaction zone and the pressure is not less than 7 atmospheres above the pressure at the outlet to the reaction zone.

2. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in claim 1 wherein the reaction zone inlet pressure is between 20 and 50 atmospheres and the pressure at the dispersion injection point is below the inlet pressure and between 10 and 40 atmospheres.

3. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in claims 1 or 2, wherein the polyamide forming components comprise one or more salts of the following combinations: hexamethylene diamine and sebacic ac d, hexamethylene diamine or and suberic acidj omega-amiho caproic acidr or omega-amino undecanoic acid.

4. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in claims 1 or 2 wherein the polyamide forming components comprise one or more salts of the following combinations: m-xylylene diamine and adipic acid, dodecamethylene diamine and terephthalic acid, nonamethylene diamine and terephthalic acid, hexamethylene diamine and terephthalic acid, hexamethylene diamine and isophthaiic acid.

5. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in claims 1 or 2 wherein the polyamide forming components comprises the salt of hexamethylene diamine and adipic acid.

6. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in any preceding claims wherein the pigment dispersion is aqueous.

7. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in any preceding claims wherein the pigment comprises titanium dioxide.

8. A continuous process for the manufacture of pigmented high molecular weight polyamides as claimed in any of claims 1 to 6 wherein the pigment comprises carbon black.

9. · A continuous process for the manufacture of pigmented high molecular weight polyamides substantially as described with reference to the examples in the description. 1

10. Pigmented high molecular weight polyamides manufactured by a continuous process as claimed in any of the preceding claims.

11. A continuous process for the manufacture of filaments, films, ribbons and similar elongated shaped articles comprising making a pigmented high molecular weight polyamide by the process claimed in any preceding claim and melt extruding said polyamide to form said shaped articles.

12. Filaments, films ribbons and the like produced by the process as claimed in claim 11. DATED the 22nd October, 1967