Title of Invention	PROCESSS FOR MANUFACTURING POLYAMIDE''
Abstract	Process for manufacturing polyamides by polymerization in a manner such as herein described, characterized in that the polymerization is catalysed by solid particles based on titanium dioxide with a diameter of less than 100 nm wherein the polyamide optionally contains a matt-effect agent such as herein described.

Full Text

Process for manufacturing polyamides The invention relates to a process for manufacturing polyamide. The process is carried out in the presence of a catalyst. The manufacture of polymers of polyamide type is mainly carried out by polycondensation starting with dicarboxylic acid monomers and diamine monomers or starting with compounds of lactam or amino acid type. These polycondensations can be accelerated by using a catalyst. Many studies have been carried out on active catalysts and on their method of introduction. Among the known catalysts, catalysts containing phosphorus have been the subject of many studies. US patent 3 944 5118 teaches the use of phosphoric acid as a polycondensation catalyst for the manufacture of polyamide 66, this phosphoric acid being introduced with hexamethylenediamine into the polymerization medium. US patent 4 912 175 teaches the use of phosphonic catalysts such as, for example, 2-(2'-pyridyl)ethylphosphonic acid or diethyl 2-(2'-pyridyl)ethylphosphonate. The use of these catalysts makes it possible to increase the polyamide polycondensation kinetics. However, for catalysts containing phosphorus, their effect is generally almost entirely inhibited in the presence of matt-effect agents, for example coated titanium dioxide. Such agents are used in particular for textile applications in order to reduce the translucency of fibres, for example for the manufacture of women's footwear. They are generally composed of micrometre-sized titanium dioxide compounds in proportions ranging from 0.3% to 2% by weight. Micrometric titanium dioxide is chosen for its ease of use and its whiteness. It is generally incorporated into the polymerization medium at the start of the process. It is advantageously passivated, for example using a protective layer, so as to limit the photochemical degradation of the polymer in its presence. The protective layers used are generally based on silica and can contain alumina. The presence of matt-effect agents and particularly of passivated matt-effect agents greatly reduces the catalytic efficacy of the compounds used to accelerate the polymerizations. The catalyst according to the invention is composed of solid particles based on nanometre-sized titanium dioxide. The term "nanometre-sized" means that the average diameter of the particles or their average size is less than about 100 nm. The catalyst can be used for the manufacture of all types of polyamides or of copolymers based on polyamide. It is effective, for example, for the manufacture of polyamides derived from the polymerization of lactams or amino acids, such as caprolactam or 6-aminohexanoic acid, or for the manufacture of polyamides derived from copolymerization between dicarboxylic acid monomers and diamine monomers. It is effective in particular for catalysis of the condensation of adipic acid and hexamethylenediamine. It is adapted to the manufacture of any composition based on polyamide and of any copolymer based on polyamide. According to one embodiment of the invention, the surface of the catalyst based on titanium dioxide is coated with a compound other than titanium dioxide, for example silica. The coating at the surface of the catalyst is possibly not continuous and is possibly present at the surface of the particles, for example in the form of accumulations. The catalyst concentrations used can depend on the surface state of the particles and on their method of preparation. They are advantageously greater than 100 ppm by weight relative to the weight of monomers. Polymerizations starting with dicarboxylic acid monomers and diamine monomers generally comprise three steps. The first step is the concentration of a carboxylate-ammonium di-salt in water, known as "salt N". This step is followed by an amidation (condensation of the acid and amine functions), in particular under pressure. The condensation is then continued under atmospheric pressure up to the desired degree of polymerization. This final step is known as finishing. For this type of polymerization, the catalyst can be introduced into the salt N, for example during the amidation phase at high pressure. Polymerizations starting with lactams and amino acids are generally carried out in the following way: polyaddition of the monomers at a temperature of between 200°C and 300°C starting with a mixture of monomer and water, granulation of the product obtained, washing of the granules with water to extract the monomer units of low molecular mass, and drying. The catalyst can be introduced, for example, into the mixture of monomer and water. The nanoparticulate titanium dioxide can be introduced into the condensation reactor either directly in powder form or in the form of a suspension or dispersion in a liquid medium. The said liquid medium can be water or a molten polyamide composition. The nanoparticulate titanium dioxide catalyses the polymerization of all polyamide-based compositions. Its use is particularly advantageous when the product manufactured is a composition containing a matt-effect agent. Inhibition of the catalytic effect with the said agent is less pronounced than with a phosphorus-based catalyst. This property is confirmed in particular in the presence of a matt-effect agent based on titanium dioxide with a particle size of the order of a micrometre. For example, the catalyst which is the subject of the invention is effective in the presence of titanium dioxide coated or partially coated with a silica-based compound, in the form of particles with a diameter of greater than 1 µm. The use of the catalyst described in the present document is particularly advantageous compared with the use of other catalysts when the content of matt-effect agent in the compositions is greater than 0.5% by weight. Other details and advantages of the invention will emerge more clearly in the light of the examples below, given purely as a guide. Example 1 A suspension at a concentration of 20% in water of titanium dioxide particles with a diameter of about 50 nm, prepared according to the first two steps described in Example 1 of the published patent FR 2 744 914, is introduced into a polyamide 66 condensation reactor during the amidation phase under pressure, so as to obtain in the reactor a proportion of catalyst of 500 ppm by weight relative to the polymer. The condensation is carried out at a temperature of 275°C. After finishing for 45 minutes, the viscosity index of the polymer obtained is 145 ml/g. An identical process carried out in the absence of catalyst leads to a viscosity index of 135 ml/g after finishing for 45 minutes. The viscosity indices (Vis) are measured at 25°C using a Ubbelohde-type viscometer for a solution containing 5 g/1 of polymer dissolved in a mixture composed of 90% by weight of formic acid and 10% of water. Example 2 The catalytic efficacy of a catalyst is defined by the difference in the amidation kinetic constants k1 after finishing in the presence and absence of catalyst relative to the kinetic constant k1 in the absence of catalyst. (Equation Removed) The constant k1 is defined by the following system: (Formula Removed) The kinetic equations are as follows: d/[NH2]/dt = [- k, [COOH] [NH2O]][k, [CONH] [H20]] [COOH] -k, [COOH] d/[NH2]/dt = [. k, [COOH] [NH2 ]+k2 [CONH] [H2O]][COOH] +k3 [COOH] d/[NH2]/dt = [k, [COOH] [NH2]-k2 [CONH] [H2O]] [COOH] -k, [COOH] in which [COOH] is the concentration of acid end groups, [NH2] is the concentration of amine end groups, [NHCO] is the concentration of amide units and [H20] is the concentration of water. [COOH] and [NH2] are measured by potentiometric assay, [H20] is determined by measuring the partial pressure of water PH2O in the condensation reactor: log ([H2O] / PH2O) = 1800/T - 1.2214, in which T is the temperature in kelvins, PH2O is the partial pressure of water in bar and [H20] is the concentration of water in meq/kg. [CONH] is determined by a material balance. A polyamide 66 is prepared according to a usual process without matt-effect agent, in the presence either of a usual catalyst comprising phosphorus, or of catalyst according to the invention. A polyamide 66 in the absence of catalyst is prepared according to the same process. A polyamide 66 composition is prepared comprising microparticulate titanium dioxide coated with silica (matt-effect agent) in a proportion of 1.6% by weight. The catalytic effect obtained is measured using the same catalysts. Relative to the catalytic effect observed in the absence of matt-effect agent, a 95% reduction in the catalytic efficacy of a phosphoric acid in a proportion of 8.4 ppm is observed in the presence of the matt-effect agent. For a catalyst composed of titanium dioxide particles with a diameter of about 50 nm, partly coated with silica and concentrated to 2000 ppm, prepared according to the four steps of Example 1 of the published patent FR 2 744 914, a 69% reduction in the catalytic efficacy is observed. The activity of the catalyst according to the present invention is thus less inhibited than that of a phosphorus-containing catalyst in the presence of a matt-effect agent. Example 3 A polyamide 6 is prepared in the presence and absence of catalyst. The catalyst used is nanoparticulate titanium dioxide treated with silica, prepared according to the four steps of Example 1 of the published patent FR 2 744 914. The polymerization process is as follows: a mixture of 7 0% by weight of caprolactam and 3 0% by weight of water is concentrated by heating to 80% by weight of caprolactam. The concentrated mixture is brought to a pressure of 17.5 bar and distilled at this pressure. The product obtained is returned to atmospheric pressure and subjected to finishing at 270°C. The catalyst is introduced, in a proportion of 2000 ppm by weight relative to the polymer, into the initial mixture of caprolactam and water. In the absence of catalyst, the viscosity index after finishing is 130 ml/g. In the presence of the catalyst, the viscosity index after finishing is 145 ml/g.

Documents:

in-pct-2001-00638-del-abstract.pdf

in-pct-2001-00638-del-claims.pdf

in-pct-2001-00638-del-complete specification (granted).pdf

in-pct-2001-00638-del-correspondence-others.pdf

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in-pct-2001-00638-del-description (complete).pdf

in-pct-2001-00638-del-form-1.pdf

in-pct-2001-00638-del-form-13.pdf

in-pct-2001-00638-del-form-19.pdf

in-pct-2001-00638-del-form-2.pdf

in-pct-2001-00638-del-form-3.pdf

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in-pct-2001-00638-del-gpa.pdf

in-pct-2001-00638-del-pct-210.pdf

in-pct-2001-00638-del-pct-409.pdf

in-pct-2001-00638-del-pct-416.pdf

in-pct-2001-00638-del-petition-137.pdf

in-pct-2001-00638-del-petition-138.pdf