Polymerization catalyst for polyesters, polyester produced with the same, and process for production of polyester

This invention provides a novel polycondensation catalyst using no antimony compound, polyester produced by using the same, and a process for producing polyester. A novel catalyst comprising an aluminum compound and a phosphorus compound is used as the polycondensation catalyst in producing polyester. The polyester of this invention can be applied to fibers for clothes, fibers for industrial materials, various films, sheets and molded articles such as bottles and engineering plastics, as well as coatings and adhesives.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a polyester polymerization catalyst, polyester produced by using the same and a process for producing polyester and in particular to an antimony compound-free novel polyester polymerization catalyst, polyester produced by using the same and a process for producing polyester.

2. Prior Art

Polyester, particularly polyethylene terephthalate (abbreviated hereinafter into PET), is superior in mechanical and chemical properties and applied to various uses such as fibers for clothes and industrial materials, various films such as packaging films and magnetic tapes and sheets, and molded articles such as bottles and engineering plastics.

PET is obtained industrially by esterification or transesterification of terephthalic acid or dimethyl terephthalate with ethylene glycol thereof to produce bis(2-hydroxyethyl) terephthalate and subsequent polycondensation thereof with a catalyst at high temperature in vacuo. As the catalyst used in this polycondensation, antimony trioxide is widely used. Antimony trioxide is a catalyst which is inexpensive and superior in the catalytic activity, but since an antimony metal is precipitated during polycondensation, there is the problem of gray discoloration and formation of insoluble particles in PET. Further, a problem with the safety of antimony is recently noted from an environmental viewpoint. Under these circumstances, there is demand for polyester containing no or little antimony.

While using antimony trioxide as the polycondensation catalyst, an attempt at inhibiting occurrence of gray discoloration and formation of insoluble particles in PET has been made. In Japanese Patent No. 2666502, for example, antimony trioxide and bismuth and selenium compounds are used as the polycondensation catalyst, whereby formation of gray insoluble particles in PET is inhibited. Further, Japanese Unexamined Patent Publication No. 291141/1997 describes that when antimony trioxide containing sodium and iron oxides is used as the polycondensation catalyst, precipitation of an antimony metal is inhibited. However, these polycondensation catalysts cannot achieve the object of obtaining polyester containing no or little antimony.

A polycondensation catalyst substituted for antimony trioxide has also been investigated. In particular, a titanium compound represented by tetraalkoxy titanate has already been proposed, but there is the problem that PET produced using this compound is significantly discolored and easily thermally degraded.

As an attempt to overcome such problem when tetraalkoxy titanate is used as the polycondensation catalyst, for example Japanese Unexamined Patent Publication No. 116722/1980 has proposed a method of using tetraalkoxy titanate with a cobalt salt and a calcium salt. Further, Japanese Unexamined Patent Publication No. 73581/1996 has proposed a method of using tetraalkoxy titanate simultaneously with a cobalt compound as the polycondensation catalyst and simultaneously using a optical brightener. By these proposes, the discoloration of PET is reduced when tetraalkoxy titanate is used as the polycondensation catalyst, but effective inhibition of thermal degradation of PET has not been achieved.

As a polycondensation catalyst which is substituted for antimony trioxide and overcomes such problem when tetraalkoxy titanate is used, a germanium compound has been practically used, but this catalyst has the problem that it is very expensive and that the catalyst easily evaporates from the reaction system to the outside so that the concentration of the catalyst in the reaction system is changed thus making control of polymerization difficult.

It is known that aluminum compounds are generally inferior in the catalytic activity. Among the aluminum compounds, aluminum chelate compounds are reported to have a higher catalytic activity as a polycondensation catalyst than other aluminum compounds, but the catalytic activity is not practically sufficient as compared with the antimony compounds and titanium compounds described above.

This invention provides a novel polycondensation catalyst other than antimony compounds, polyester produced by using the same and a process for producing polyester.

SUMMARY OF THE INVENTION

The present inventors made extensive examination for solving the problems described above, and as a result, they surprisingly found that as a polycondensation catalyst, an aluminum compound, though being originally inferior in the catalytic activity, came to have a sufficient activity by allowing a phosphorus compound to be coexistent therewith, thus arriving at this invention. When the polycondensation catalyst of this invention is used, polyester superior in qualities can be obtained without using the antimony compound.

That is, this invention provides a polyester polymerization catalyst, which comprises an aluminum compound and a phosphorus compound, polyester produced by using the same and a process for producing polyester, as a method of solving the problems above.

This invention provides a novel polycondensation catalyst other than antimony compounds, polyester produced by using the same, and a process for producing polyester. The polycondensation catalyst of this invention is a polyester polymerization catalyst, which comprises an aluminum compound and a phosphorus compound, as follows:

{circle around (1)} a polyester polymerization catalyst, which comprises an aluminum compound and a phosphorus compound;

{circle around (2)} the polyester polymerization catalyst according to the above-described {circle around (1)}, wherein the phosphorus compound is at least one compound selected from the group consisting of a phosphonic acid based compound, a phosphinic acid based compound, a phosphine oxide based compound, a phosphonous acid based compound, a phosphinous acid based compound, and a phosphine based compound;
{circle around (3)} the polyester polymerization catalyst according to the above-described {circle around (1)}, wherein the phosphorus compound is at least one phosphonic acid based compound;
{circle around (4)} the polyester polymerization catalyst according to any one of the above-described {circle around (1)} to {circle around (3)}, wherein the phosphorus compound is a compound having an aromatic ring structure;
{circle around (5)} the polyester polymerization catalyst according to the above-described {circle around (1)}, wherein the phosphorus compound is at least one compound selected from the group consisting of the compounds represented by the following Formulae (1) to (3):
P(═O)R1(OR2)(OR3)  (Formula 1)
P(═O)R1R4(OR2)  (Formula 2)
P(═O)R1R5R6(Formula 3)
(wherein R1, R4, R5and R6independently represent hydrogen, a C1-50hydrocarbon group, and a C1-50hydrocarbon group containing a hydroxyl group, a halogen group, an alkoxy group or an amino group, and R2and R3independently represent hydrogen and a C1-10hydrocarbon group, provided that the hydrocarbon group may contain an alicyclic structure or an aromatic ring structure);
{circle around (6)} the polyester polymerization catalyst according to the above-described {circle around (5)}, wherein each of R1, R4, R5and R6is a group having an aromatic ring structure;
{circle around (7)} the polyester polymerization catalyst according to any one of the above-described {circle around (1)} to {circle around (6)}, characterized in that one or more metals and/or metal compounds selected from the group consisting of alkali metals or compounds thereof and alkaline earth metals or compounds thereof are coexistent therewith;
{circle around (8)} polyester produced by using a catalyst described in any one of the above-described {circle around (1)} to {circle around (7)}; and
{circle around (9)} a process for producing polyester which comprises using a catalyst described in any one of the above-described {circle around (1)} to {circle around (7)} in producing polyester.

DETAILED DESCRIPTION

The aluminum compound constituting the polycondensation catalyst of this invention includes, but is not limited to, e.g. carboxylates such as aluminum formate, aluminum acetate, aluminum propionate, aluminum oxalate, aluminum acrylate, aluminum laurate, aluminum stearate, aluminum benzoate, aluminum trichloroacetate, aluminum lactate, aluminum citrate and aluminum salicylate, inorganic acid salts such as aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, aluminum carbonate, aluminum phosphate and aluminum phosphonate, aluminum alkoxides such as aluminum methoxide, aluminum ethoxide, aluminum n-propoxide, aluminum iso-propoxide, aluminum n-butoxide and aluminum t-butoxide, aluminum chelate compounds such as aluminum acetylacetonate, aluminum acetylacetate, aluminum ethyl acetoacetate, and aluminum ethyl acetoacetate di-iso-propoxide, organoaluminum compounds such as trimethyl aluminum and triethyl aluminum and partially hydrolyzates thereof, as well as aluminum oxides, metal aluminum, etc. Among these, the carboxylates, inorganic acid salts and chelate compounds are preferable, among which aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are particularly preferable.

The amount of the aluminum compound used in the invention is preferably 5×10−7to 0.01 mole, more preferably 1×10−6to 0.005 mole, relative to the number of moles of all constitutive units of carboxylic acid components such as dicarboxylic acid and polyfunctional carboxylic acid components in the resulting polyester.

The phosphorus compound constituting the polycondensation catalyst of the invention is not particularly limited, but at least one compound selected from the group consisting of a phosphonic acid based compound, a phosphinic acid based compound, a phosphine oxide based compound, a phosphonous acid based compound, a phosphinous acid based compound, and a phosphine based compound is preferably used for a significant effect of improving the catalytic activity. Among these, at least one phosphonic acid based compound is preferably used for a particularly significant effect of improving the catalytic activity.

The phosphonic acid based compound, phosphinic acid based compound, phosphine oxide based compound, phosphonous acid based compound, phosphinous acid based compound and phosphine based compound mentioned in the invention refer respectively to compounds having the structures shown in the following Formulae (4) to (9):

The phosphine oxide based compound in this invention includes e.g. diphenyl phosphine oxide, methyl diphenyl phosphine oxide and triphenyl phosphine oxide.

Among the phosphorus compounds described above, those compounds having an aromatic ring structure are preferably used for a significant effect of improving the catalytic activity.

As the phosphorus compound constituting the polycondensation catalyst of the invention, a compound represented by the following Formulae (1) to (3) is preferably used for a particularly significant effect of improving the catalytic activity.
P(═O)R1(OR2)(OR3)  (Formula 1)
P(═O)R1R4(OR2)  (Formula 2)
P(═O)R1R5R6(Formula 3)
(wherein R1, R4, R5and R6independently represent hydrogen, a C1-50hydrocarbon group, and a C1-50hydrocarbon group containing a hydroxyl group, a halogen group, an alkoxy group or an amino group, and R2and R3independently represent hydrogen and a C1-10hydrocarbon group, provided that the hydrocarbon group may contain an alicyclic structure such as cyclohexyl or an aromatic ring structure such as phenyl and naphthyl.)

The phosphorus compound constituting the polycondensation catalyst of the invention is particularly preferably a compound of Formulae (1) to (3) above wherein each of R1, R4, R5and R6is a group having an aromatic ring structure.

The amount of the phosphorus compound used in the invention is preferably 5×10−7to 0.01 mole, more preferably 1×10−6to 0.005 mole, relative to the number of moles of all constitutive units of carboxylic acid components such as dicarboxylic acid and polyfunctional carboxylic acid components in the resulting polyester.

For a further effect of improving the catalytic activity, it is preferable that one or more metal compounds selected from the group consisting of alkali metals or compounds thereof and alkaline earth metals or compounds thereof are coexistent with the polycondensation catalyst of this invention comprising the aluminum compound and the phosphorus compound.

The alkali metals or compounds thereof or the alkaline earth metal or compounds thereof in this invention are not particularly limited insofar as they are alkali metals or alkaline earth metals or one or more compounds selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba compounds; for example, these metal compounds include saturated aliphatic carboxylates such as formate, acetate, propionate, butyrate and oxalate, unsaturated aliphatic carboxylates such as acrylate and methacrylate, aromatic carboxylates such as benzoate, halogen-containing carboxylates such as trichloroacetate, hydroxycarbonates such as lactate, citrate and salicylate, inorganic acid salts such as carbonate, sulfate, nitrate, phosphate, phosphonate, hydrogen carbonate, hydrogen phosphate, hydrogen sulfate, sulfite, thiosulfate, hydrochloride, hydrobromate, chlorate and bromate, organic sulfonates such as 1-propane sulfonate, 1-pentane sulfonate and naphthalene sulfonate, organic sulfates such as lauryl sulfate, alkoxides such as methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy and t-butoxy, chelate compounds such as acetylacetonate, oxides and hydroxides, among which saturated aliphatic carboxylates are preferable and acetate is most preferable.

The amount of these alkali metal or compounds thereof or alkaline earth metals or compounds thereof used is preferably in the range of 1×10−6to 0.1 mole, more preferably in the range of 5×10−6 to 0.05 mole, relative to the number of moles of all constitutive units of carboxylic acid components such as dicarboxylic acid and poly functional carboxylic acid components in the resulting polyester.

Production of polyester according to this invention can be conducted by a method known in the art. For example, PET can be produced by a method of esterifying terephthalic acid with ethylene glycol and subsequent polycondensation reaction, or a method of transesterification reaction between alkyl terephthalate such as dimethyl terephthalate and ethylene glycol and subsequent polycondensation reaction. Further, the polymerization apparatus may be a batch type or continuous reaction type.

The catalyst of this invention has a catalytic activity not only in polycondensation reaction but also in esterification reaction and transesterification reaction. The transesterification reaction between alkyl dicarboxylate such as dimethyl terephthalate and glycol such as ethylene glycol is conducted usually in the presence of a transesterification catalyst such as zinc, and in place of such catalyst or in coexistence of such catalyst, the catalyst of this invention can also be used. Further, the catalyst of this invention has a catalytic activity not only in melt state polymerization but also in solid state polymerization and solution polymerization.

The polycondensation catalyst of this invention is added desirably before polycondensation reaction, but the catalyst can also be added to the reaction system in an arbitrary stage before or during esterification reaction or transesterification reaction.

The polycondensation catalyst of this invention may be added in any form such as powder, neat, or a slurry or solution in a solvent such as ethylene glycol. Alternatively, a mixture prepared by previously mixing the aluminum compound with the phosphorus compound may be added, or the compounds comprising the catalyst may be separately added. Further, a mixture prepared by previously mixing the two or more compounds with alkali metals or compounds thereof or alkaline earth metals or compounds thereof may be added, or these compounds may be added separately.

For polymerization of polyester by use of the polymerization catalyst of the invention, an antimony compound and a germanium compound may be used in combination with the catalyst. In this case, the antimony compound is preferably added in an amount of 50 ppm or less (in terms of antimony atom) relative to the polyester obtained by polymerization. The antimony compound is added more preferably in an amount of 30 ppm or less. Addition of antimony in an amount of more than 50 ppm is not preferable because an antimony metal is precipitated resulting in the gray discoloration and formation of insoluble particles in the polyester. The germanium compound is added preferably in an amount of 20 ppm or less (in terms of germanium atom) in the polyester obtained by polymerization. The germanium compound is added more preferably in an amount of 10 ppm or less. Addition of germanium in an amount of more than 20 ppm is economically disadvantageous and thus not preferable.

The antimony compound used in this invention includes antimony trioxide, antimony pentaoxide, antimony acetate and antimony glycoxide, among which antimony trioxide is preferable. The germanium compound includes germanium dioxide and germanium tetrachloride, among which germanium dioxide is preferable.

With the polymerization catalyst of this invention, other polymerization catalysts such as titanium compound, tin compound and cobalt compound can be coexistent in such amount as not to deteriorate the thermal stability and color tone of polyester.

The polyester mentioned in the invention refers to polyester comprising at least one component selected from polyfunctional carboxylic acids including dicarboxylic acids and ester-forming derivatives thereof and at least one component selected from polyfunctional alcohols including glycols, to polyester comprising hydroxycarboxylic acids and ester-forming derivatives thereof, or to polyester comprising cyclic esters.

Further, the polyester of this invention can contain a known phosphorus compound as a copolymerizable component. The phosphorus compound is preferably a bifunctional phosphorus compound, and examples thereof include dimethyl phenylphosphonate, diphenyl phenylphosphonate, (2-carboxylethyl) methylphosphinic acid, (2-carboxylethyl) phenylphosphinic acid, methyl(2-methoxycarboxylethyl) phenylphosphinate, methyl (4-methoxycarbonylphenyl) phenylphosphinate, [2-(β-hydroxyethoxycarbonyl)ethyl]methylphosphinic acid ethylene glycol ester, (1,2-dicarboxyethyl) dimethyl phosphine oxide, 9,10-dihydro-10-oxa-(2,3-carboxypropyl)-10-phosphaphenanthrene-10-oxide, etc. By incorporating these phosphorus based compounds as copolymerizable components, the resulting polyester can improve flame retardancy etc.

The ester-forming derivatives of polyfunctional carboxylic acids or hydroxycarboxylic acids include alkyl esters, acid chlorides and acid anhydrides of such acids.

The polyester of this invention is preferably polyester whose main acid component is terephthalic acid or an ester-forming derivative thereof or naphthalene dicarboxylic acid or an ester-forming derivative thereof and whose main glycol component is alkylene glycol. The polyester whose main acid component is terephthalic acid or an ester-forming derivative thereof or naphthalene dicarboxylic acid or an ester-forming derivative thereof is polyester wherein the total of terephthalic acid or an ester-forming derivative thereof or naphthalene dicarboxylic acid or an ester-forming derivative thereof is preferably 70 mole % or more, more preferably 80 mole % or more, and most preferably 90 mole % or more, to the total acid components. The polyester whose main glycol component is alkylene glycol is polyester wherein the total of alkylene glycol is preferably 70 mole % or more, more preferably 80 mole % or more, and most preferably 90 mole % or more, to the total glycol components. As used herein, the alkylene glycol may contain a substituent group or an alicyclic structure in the molecular chain thereof.

The polyester of this invention can contain a known phosphorus based compound as a copolymerizable component. The phosphorus based compound is preferably a bifunctional phosphorus based compound, and examples thereof include dimethyl phenylphosphonate, diphenyl phenylphosphonate, (2-carboxylethyl) methylphosphinic acid, (2-carboxylethyl) phenylphosphinic acid, methyl(2-methoxycarboxylethyl) phenylphosphinate, methyl(4-methoxycarbonylphenyl) phenylphosphinate, [2-(β-hydroxyethoxycarbonyl)ethyl]methylphosphinate ethylene glycol, (1,2-dicarboxyethyl) dimethyl phosphine oxide, 9,10-dihydro-10-oxa-(2,3-carboxypropyl)-10-phosphaphenanthrene-10-oxide, etc. By incorporating these phosphorus based compounds as copolymerizable components, the resulting polyester can improve flame retardancy etc.

The polyester of the invention is preferably polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, poly(1,4-cyclohexanedimethyleneterephthalate), polyethylene naphthalate, polybutylene naphthalate, polypropylene naphthalate and a copolymer thereof, among which polyethylene terephthalate and a copolymer thereof are particularly preferable.

The polyester of this invention can contain antioxidants such as phenolic or aromatic amines, and by containing one or more of these antioxidants, the resultant polyester can improve e.g. thermal stability. The phenolic antioxidants include tetrakis-[methyl-3-(3′,5′-di-tert-butyl-4-hydroxyphenyl)propionate]methane, 4,4′-butylidene bis-(3-methyl-6-tert-butylphenol), and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene.

EXAMPLES

Hereinafter, this invention is described in more detail by reference to the Examples, which however are not intended to limit this invention. The intrinsic viscosity (IV) of polyester in each of the Examples and Comparative Examples was measured at a temperature of 30° C. in a 6/4 mixed solvent (ratio by weight) of phenol/1,1,2,2-tetrachloroethane.

As the catalyst, 3 g/l aluminum chloride in ethylene glycol was added, in an amount of 0.015 mole % in terms of aluminum relative to the acid component in polyester, to bis(2-hydroxyethyl) terephthalate, and then dimethyl phenylphosphonate was added in an amount of 0.02 mole % relative to the acid component in polyester, and the mixture was stirred at 245° C. for 10 minutes at atmospheric pressure. Then, the mixture was heated over 50 minutes to 275° C., during which the pressure in the reaction system was gradually reduced to 0.1 mmHg, and further polycondensation reaction was conducted for 3 hours at the same temperature and at the same pressure. The intrinsic viscosity of the resulting polymer is shown in Table 1.

Examples 2 to 7 and Comparative Examples 1 to 2

Polyester was polymerized in the same manner as in Example 1 except that the catalyst was changed. The intrinsic viscosity of the resulting polymer is shown in Table 1.

According to this invention, there is provided a novel polycondensation catalyst other than antimony compounds as well as polyester produced by using the same. The polyester of this invention can be applied to fibers for clothes, fibers for industrial materials, various films, sheets and molded articles such as bottles and engineering plastics, as well as coatings and adhesives.