WO2004069896A1

WO2004069896A1 - Process for producing neopentyl-glycol based polyesters

Info

Publication number: WO2004069896A1
Application number: PCT/EP2004/000179
Authority: WO
Inventors: Luc Moens; Nele Knoops; Daniel Maetens; Filip Vanacker
Original assignee: Surface Specialties, S.A.
Priority date: 2003-02-06
Filing date: 2004-01-14
Publication date: 2004-08-19
Also published as: TW200420603A

Abstract

The invention relates to a process for producing neopentyl-gycol based polyesters in the presence of an organotitanium catalyst whereby a polyol component comprising neopentyl gycol and a polyacid component comprising isophthalic and/ or terephthalic acid are added gradually to a reactor maintained at a temperature of 230 to 330 0C.

Description

PROCESS FOR PRODUCING NEOPENTYL-GLYCOL BASED POLYESTERS

The present invention relates to a process for producing neopentyl-glycol based polyesters. Powder coating compositions for use in painting are extremely desirable since they greatly reduce and can even eliminate organic solvents used in liquid paints. The best known powder coating compositions contain as binder either a mixture of carboxyl group containing polymers, such as a carboxyl group containing polyester, and epoxy compounds, such as triglycidyl isocyanurate, glycidyl group containing acrylic copolymers or β-hydroxyalkylamides or a mixture of hydroxyl group containing polymers, most often a hydroxyl group containing polyester, with blocked or non- blocked isocyanates, mela-mine resins, and the like, or (meth)acrylic group containing polymers, such as (meth) acrylic group containing polyester or polyacrylate. These carboxyl, hydroxyl or (meth) acrylic group containing polyesters suitable for use in the preparation of powdered varnishes and paints have already been described in numerous publications.

These polyesters are usually prepared from aromatic dicarboxylic acids, mainly terephthalic acid and/or isophthalic acid and optionally a minor proportion of aliphatic or cycloaliphatic dicarboxylic acids and from various polyols, mainly neopentyl glycol, from which minor parts may be replaced by other polyols such as ethylene glycol, diethylene glycol, neopentyl glycol hydroxypivalate, 1,4- cyclohexanedimethanol and the like. Instead of polycarboxylic acids, the esters of these polycarboxylic acids can be used. These polyesters are normally prepared accordingly a solvent-free process involving usual esterifLcation and/or transesterlfication catalysts such as tin-based catalysts. Though this process is generally considered as ecological, in recent years the use of these tin-based catalysts tends towards coming under increased environmental pressure. Otherwise, organic titanates such as tetraisobutyl and tetra-n-butyl titanates are known to be effective polycondensation catalysts for producing polyalkyleneterephthalates in general. However these catalysts tend to hydrolyse on contact with water forming glycol-insoluble oligomeric species which lose catalytic activity. As the starting materials for the neopentyl glycol based polyesters preferably include carboxylic acids and polyhydric alcohols, which under the influence of heat upon reaction release water, these organic titanates can not be used. Till now, because of this restriction, all commercial resins are obtained from a tin-catalysed polyesterification process.

Recently, titanium containing catalysts with high catalytic activity, whereby the catalytic activity is not reduced by the water formed during esteriflcation, have been proposed in e.g. US 5,656,716, US 5,866,710, US 6, 166, 170, US 6,372,929. However, all these catalysts only prove catalytic activity at reaction temperatures from about 250°C. In the production of polyethyleneterephthalate these high reaction temperatures are obtained for an esterification reaction under pressure using a substantial excess of ethylene glycol on terephthalic acid. This ethylene glycol excess is subsequently removed in a second transesterification polycondensation step. However, when neopentyl glycol is used, the elevated temperature necessary for effectively using these new types of catalysts can not be used in classical preparation processes. Due to its physical properties (melting point = 127°C; boiling point = 208°C), the continuous evaporation/ condensation of neopentyl glycol from and to the reactor prevents the reaction temperature from rising to a set point where the catalytic activity of these titanium containing catalysts will achieve an optimum. Moreover, uncontrolled evaporation and/or sublimation losses cause an undesirable change in the prescribed molar ratio of acid to alcohol groups. These two phenomena have until now prevented the preparation of neopentyl glycol based polyesters and copolyesters by using titanium based catalysts.

The present invention overcomes these problems by providing a process for the preparation of neopentyl-glycol based polyesters using titanium containing catalysts. The present invention therefore concerns a process for the preparation of neopentyl-glycol based polyesters in the presence of an organotitanium catalyst, which comprises a controlled addition step wherein (i) a polyol component comprising from 30 to 100 mole % of neopentyl glycol and (ii) a polyacid component comprising from 70 to 100 mole % of isophthalic and/or terephthalic acid, are gradually added to a reactor containing a polyester (A) while maintaining the reaction mixture in the reactor at a temperature of from 230 to 330 °C.

In the process according to the present invention, the polyol component (i) and the polyacid component (ii) are preferably present in a molar ratio of (0.7 to 1.4) : 1. By molar ratio of polyol to polyacid is understood the ratio of acid groups present in the polyacid component to hydroxyl groups present in the polyol component. In the process according to the invention, the polyol component (i) and the polyacid component (ii) may be added to the reactor separately. Preferably, they are mixed together, at least partly, before adding the resulting mixture to the reactor containing the polyester (A). If necessary, water can be added to the mixture in order to decrease its viscosity and/or to improve the miscibility of its constituents. The mixture of the polyol and the polyacid component, and optionally water, is preferably effectuated and/or is pre-heated at a temperature of from 30 to 90 °C, before adding it to the reactor. The addition of the polyol component (i) and the polyacid component (ii) to the reactor is done gradually, preferably in such a way that the temperature in the reactor is almost unaffected.

When a mixture of the polyol component (i) and the polyacid component (ii) is added to the reactor containing the polyester (A) and the titanium catalyst, the addition rate of the mixture is preferably adapted such that the whitish mixture is almost immediately reacted and becomes completely transparent.

In the process according to the invention, the temperature of the reaction mixture during the controlled addition step is preferably maintained from 250 to 290 °C. During the controlled addition step, the pressure in the reactor is in general maintained in the range of atmospheric pressure to 10 bar. Preferably, the controlled addition step is conducted at atmospheric pressure.

The controlled addition step is in general conducted under inert atmosphere, preferably under a nitrogen atmosphere. The controlled addition step is preferably conducted in such a way as to obtain after the controlled addition step, a polyester having a number average molecular weight of between 500 and 10000, more preferably of between 500 and 8500.

In the process according to the present invention, the polyacid component (ii) is preferably composed of from 70 to 100 mole % of isophthalic and/or terephthalic acid and from 0 to 30 mole % of another aliphatic, cycloaliphatic and/or aromatic polyacid or the anhydrides resulting in such polyacids by ringopening. The other polyacid is preferably selected from fumaric acid, maleic acid, phthalic acid, 1,4- cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2- cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azealic acid, sebacic acid, 1, 12-dodecanedioic acid, trimellitic acid or pyromellitic acid, or the corresponding anhydrides.

Most preferably, the polyacid component (ii) consist essentially of isophthalic and/or terephthalic acid.

In the process according to the present invention, the polyol component (i) is preferably composed of from 30 to 100 mole % of neopentyl glycol and from 0 to 70 mole % of another aliphatic or cycloaliphatic polyol. The other polyol is preferably selected from ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4- cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methyl-l,3-proρanediol, 2-butyl-2- ethyl-l,3-propanediol, hydrogenated Bisphenol A, hydroxypivalate of neopentyl glycol, trimethylolpropane, ditrimethylolpropane and pentaerythrytol.

More preferably, the polyol component (ii) is composed of from 50 to 100 mole % of neopentyl glycol and from 50 to 100 mole % of the other ahphatic or cycloaliphatic polyol. Most preferably, the polyol component (i) consist essentially of neopentyl glycol. According to a first embodiment of the process according to the invention, the molar ratio of the polyol component (i) to polyacid component (ii) is at most 1 and the polyacid component is substantially free of terephthalic acid. By substantially free of terephthalic acid is meant to designate that the polyacid component contains less than 1 % by weight of terephthalic acid.

In this first embodiment, the process generally comprises a further step wherein the reaction πiixture obtained after the controlled addition step is submitted to a treatment under reduced pressure, hereafter referenced to as vacuum step. The pressure at which the vacuum step is performed is usually lower than atmospheric pressure, preferably lower than 0.1 bar. Most preferably a pressure of 0.01 to 0.07 bar is used.

During the vacuum step, the reaction mixture is usually maintained at a temperature of 230 to 330 °C, preferably of 250 to 290 °C. The vacuum step is usually applied until the desired polyester characteristics (i.e. acid number, hydroxyl number and viscosity) are obtained. Usually, the vacuum step is applied for a period of about 0.5 to 10 hours. If required, possible corrections in polyol component or polyacid component can be done by introducing small amounts, usually less than 10 % of the amount of polyol or polyacid component introduced during the controlled addition step, into the reactor before or during the vacuum step. The vacuum step can be performed in the same reactor as the controlled addition step or in a separate reactor, especially designed to this end.

According to a second embodiment of the process according to the invention, the molar ratio of polyol component (i) to polyacid component (ii) is higher than 1.

According to a first variant of this second embodiment of the process according to the invention, the process comprises a further vacuum step such as described here above in relation with the first embodiment of the process according to the invention.

According to a second variant of this second embodiment of the process according to the invention, the process comprises a supplementary addition step wherein a polyacid different from terephthalic acid or an anhydride thereof is added to the reaction mixture obtained from the controlled addition step. This polyacid and/or anhydride thereof is preferably chosen amongst adipic acid, isophthalic acid, 1,4- cyclohexane dicarboxylic acid, succinic anhydride, hexahydrophthalic anhydride and/or trimellitic anhydride. Most preferred is isophthalic acid. The supplementary addition step is preferably performed at a temperature ranging from 230 to 300°C. It is generally done under atmospheric pressure.

The supplementary addition step is preferably followed by a further vacuum step such as described here above. According to a third variant of this second embodiment of the process according to the invention, the process comprises an additional addition step wherein a polyanhydride is added to the reaction mixture obtained from the controlled addition step in such conditions that anhydride ring opening takes place. The polyanhydride is preferably chosen from succinic anhydride, hexahydrophthalic anhydride, trimellitic anhydride and their mixtures.

This additional addition step is preferably performed at a temperature of at least 150 °C. It is generally done under atmospheric pressure. It is preferably not followed by a further vacuum step. During the process according to the present invention, one or more stabilising agents, preferably chosen from phosphorous type stabilising agents, most preferably selected from the phosphite or phosphonite type stabilising agents, can be introduced, generally in order to prevent discoloration and/or decomposition of the polyester. These stabilising agents are generally used in an amount of from 0 to 1% by weight on the total amount of polyol component and polyacid component. It is preferred to add the stabilising agent to reactor containing the polyester (A). Alternatively the stabilising agent may be added just before the vacuum step. Preferably part of the stabilising agent is added to the reactor containing the polyester (A) and another part of the stabilising agent is added just before the vacuum step. The polyester (A) used in the process of the present invention generally has a delta hydroxyl or delta carboxyl of from 10 to 150 mg KOH/g, preferably from 10 to 100 mg KOH/g. In the present invention delta hydroxyl is defined as the difference of hydroxyl number minus acid number and delta carboxyl is defined as the difference of acid number minus hydroxyl number. The polyester (A) used in the process according to the present invention preferably presents a number average molecular weight ranging from 500 to 15000, more preferably from 500 to 8500.

The polyester (A) used in the process according to the present invention generally presents an ICI cone/plate viscosity from 0.5 to 15000 mPa.s, preferably from 5 to 15000 mPa.s, as measured at 200°C according to ASTM D4287.

The polyester (A) used in the process according to the present invention generally presents a glass transition temperature (Tg) from 25 to 85°C, preferably from 40 to 85°C, as measured by differential scanning calorimetry (DSC) according to ASTM D3418 with a heating gradient of 20°C/min.. The polyester (A) can be a hydroxyl functional polyester. In this case, the polyester

(A) preferably has a delta hydroxyl number ranging from 10 to 150 mg KOH/g, more preferably from 10 to 100 mg KOH/g and most preferably from 30 to 70 mg KOH/g. The polyester (A) can be a carboxyl functional polyester. In this case, the polyester (A) preferably has a delta acid number ranging from 10 to 150 mg KOH/g, more preferably from 10 to 100 mg KOH/g and most preferably from 30 to 70 mg KOH/g. The polyester (A) used in the process according to the invention is preferably obtained by reacting a polyol component comprising at least 30 mole % of neopentyl glycol and a polyacid component comprising at least 70 mole % of isophthalic and/or terephthalic acid, in a molar ratio of (0.7 to 1.4) : 1. The polyester (A) can have the same, constitution as the mixture of the polyol component and the polyacid component added to the reactor. By same constitution is meant to designate that the polyester (A) comprises the same polyol(s) and polyacid(s) as the polyol component and the polyacid component added to the reactor, in the same molar ratio. Alternatively, the polyester (A) can have another constitution as this mixture.

Most preferably, the polyester (A) is obtained accordingly the process of the present invention. The quantity of polyester (A) initially present in the reactor is preferably at least

10 % by weight of the total content of the reactor after the controlled addition of the polyol component and the polyacid component.

The organotitanium catalyst used in the process according to the invention is usually chosen from titanium alcoholates and titanium chelates. Preferably the catalyst is chosen from titanium tetra-isopropylate, titanium tetra-n-butanoate, titanate (2-) dihydroxy bis(2-hydropropanato(2-)01,02), lactic acid titanate chelate and their mixtures.

It now has been surprisingly found that by using the process of the present invention, the direct esterification of free polycarboxylic acids, principally terephthalic acid and/or isophthalic acid, with free polyols, principally neopentyl glycol, can be performed not only in the presence of these titanium catalysts particularly developed for their resistance to hydrolysis, such as for example the hydroxy carboxylic acid complexes of titanium, as described in e.g. US 5,866,710, US 6,372,929 or US 6, 166, 170, among others, but also when using the conventional titanium alcoholates such as titanium tetra-isopropylate or titanium tetra-n-butanoate.

In the process according to the invention, the amount of catalyst is generally from 5 to 1000 ppm of Ti, preferably from 5 to 500 ppm of Η, and more preferably from 20 to 100 ppm of Ti, on the weight of the overall weight of polyester (A), polyol component (i) and polyacid component (ii). The process according to the invention can be operated as a batch process.

The process according to the invention is advantageously operated as a continuous process by continuously adding the polyol component (i) and polyacid component (ii), preferably as a mixture, to the reactor containing the polyester (A) while maintaining the temperature between 230 and 330°C, allowing the polyacid and polyol component to react and continuously withdrawing an amount of polymer approximately equal to the sum of polyol component (i) and polyacid component (ii) added. In this case, the polyol component and polyacid component are preferably fed to the reactor containing the polyester (A) at such a rate that the heterogeneous whitish mixture is immediately converted into polyester which is completely transparent. The polyester is then withdrawn from the reactor in such a way that the quantity of polyester in the reactor stays unaffected. Hence, the quantity of polyester A in the reactor varies from 10 to almost 100% weight of the total reactor quantity.

For the process of the present invention, operated as a continuous process the different process steps, as mentioned before, are preferably executed in separate, interconnected reactors. For the process of the present invention, operated as a continuous process, each process steps can be executed in one or more interconnected reactors. According to a preferred variant of the process, and especially when a polyol different from neopentyl glycol and/or a polyacid different from isophthalic and terephthalic acid is/are used, the controlled addition step is operated in at least two interconnected reactors. In the first reactor, a mixture of neopentyl glycol and isophthalic and/or terephthalic acid is added to a polyester (A) based on neopentyl glycol and isophthalic and/or terephthalic acid, the resulting mixture is continuously withdrawn from this first reactor and introduced into a subsequent reactor wherein the polyol different from neopentyl glycol and/or the polyacid different from isophthalic and terephthalic acid is added. For the process of the present invention, operated as a continuous process , a separate, usually continuous, feeding of the organotitanium catalyst and optionally of the stabilising agent can be used for preserving an almost unaffected level of catalyst and/or stabilising agent in the reactor. Alternatively, the organotitanium catalyst and/or stabilising agent can be added together with the polyol component (i), with the polyacid component (ii) or with their mixture.

The process according to the invention permits to obtain neopentyl glycol based polyesters, especially intended for powder coating compositions, which generally present a number average molecular weight ranging from 1500 to 8500. Hydroxyl functional polyesters can be prepared accordingly a one-step polyesteriflcation process whereby an excess of polyols is put into reaction with polycarboxylic acids. Carboxyl functional polyesters can be prepared accordingly a one-step polyesteriflcation process whereby an excess of polycarboxylic acids, not including terephthalic acid, is put into reaction with polyols. If terephthalic acid is present among the polyacids, the acid functional polyester may be prepared accordingly a two-step procedure where the first step consists of the synthesis of a hydroxyl functional polymer , which is afterwards carboxylated in a second step by means of the reaction with a polyacid, different from terephthalic acid and/or with a polyanhydride.

The hydroxyl or carboxyl functional polyesters obtainable accordingly the process of the present invention are generally characterised by: a hydroxyl number ranging from 10 to 150 mg KOH/g, preferably from 10 to 100 mg KOH/g and more preferably from 30 to 70 mg KOH/g for hydroxyl functional polyesters; an acid number ranging from 10 to 150 mg KOH/g, preferably from 10 to 100 mg KOH/g and more preferably from 30 to 70 mg KOH/g for carboxyl functional polyesters; an average molecular weight ranging from 750 to 15000 and preferably from 1500 to 8500; a glass transition temperature (Tg) from 40 to 85°C; an ICI cone/plate viscosity from 5 to 15000 mPa.s, measured at 200°C. The hydroxyl or carboxyl functional polyesters prepared accordingly the process of the present invention can be further converted into (methjacryloyl group containing polyesters. Therefore the polyester is allowed to cool down to a temperature between 100 and 160°C and a radical polymerisation inhibitor, such as phenothiazine, or an inhibitor of the hydroquinone type is added in a proportion of e.g. 0.01 to 1.00% with respect to the weight of the polyester, meanwhile oxygen is added to the polyester. When started from a hydroxyl group containing polyester, a substantially equivalent amount of hydroxyalkyl(meth)acrylate is added thereto. When all the hydroxyalkyl(meth)acrylate is added, an equivalent amount of diisocyanate is slowly added to the mixture. A catalyst for the hydroxyl/isocyanate reaction can optionally be used in an amount of 0 to 1% with respect to the weight of the polyester. Otherwise, when started from a polyester containing carboxyl groups, a substantially equivalent amount of glycidyl(meth)acιylate is added thereto. A catalyst for the acid/epoxy reaction can optionally be used in an amount of 0.05 to 1.00% with respect to the weight of the polyester.

The polyesters as prepared accordingly the process of the present invention can be used in thermosetting and radiation curable powder coatings. When intended for use in powder coatings, to the polyesters, on completion, optionally cross-linking catalysts such as amines, phosphines, ammonium or phosphonium salts, anti-oxidants such as Irganox 1010 (Ciba) and stabilisers from the phosphonite or phosphite type can be added in amounts from 0 to 5% with respect to the weight of the polyester while it is still in the molten state.

The hydroxyl and carboxyl functional polyesters can be used as part of the binder system along with a hardener in the preparation of thermosetting paints or clear lacquers.

Typical hardeners for this use are ε-caprolactam blocked isocyanates, adducts of the l,3-diazetidine-2,4-dione dimer of isophorone diisocyanate, among others when hydroxyl functional polyesters are considered and polyepoxy compounds, such as triglycidyl isocyanurate, mixtures of diglycidyl terephthalate and triglycidyl terephthalate, glycidyl group containing acrylic copolymers or β-hydroxyalkylamides when carboxyl functional polyesters are concerned.

When the (meth)acryloyl group containing polyesters are formulated in radiation curable coatings, photo-initiators can be added, depending on the type of radiation used for curing. The following examples are submitted for a better understanding of the invention without being restricted thereto. EXAMPLES

Example 1 : Synthesis of a terephthalic acid-neopentyl glycol-isophthalic acid based carboxyl functional polyester according a two-step procedure. 608.9 parts of terephthalic acid, 423.5 parts of neopentyl glycol and 100 parts of water were homogeneously mixed by agitation at a temperature of 90°C (= "the mixture") in a conventional four-neck round-bottom flask equipped with a stirrer, a water-cooled condenser, a thermocouple attached to a thermoregulator and a tube connecting through a peristaltic pump this flask to an esterifϊcation reactor, which is equipped with a stirrer, a distillation column connected to a water-cooled condenser, an inlet for nitrogen and a thermocouple attached to a thermoregulator. The esterification reactor was filled with 250 parts of the hydroxyl functional polyester (= "the prepolymer A"), with a hydroxyl number of 56 mg KOH/g, an acid number of 7 mg KOH/g, as obtained from previous batch, and as catalyst 0.1% by weight (on mixture and prepolymer A) of titanate (2-)dihydroxy bis[2-hydropropanato(2-)01,02] (Tyzor LA from Dupont) and heated at a temperature of 270°C. The mixture is then pumped to the esterification reactor containing the prepolymer A in a period of about 4 hours while maintaining the reaction temperature in the reactor unaffected at a temperature of 270 °C. A transparent first-step prepolymer, with characteristics as reproduced in table 1 below, is obtained immediately after completion of the addition. In the same table 1 the quantities of distillate (expressed in % of distillate relative to the theoretical amount of water to be collected during the esterification reaction), distilled of from the esterification reactor as a function of time, are reproduced.

The first-step prepolymer is then cooled down to a temperature of 230 °C. While maintaining the temperature at 230°C, 141.7 parts of isophthalic acid are then added. Thereupon the reactor is gradually heated up to 270°C. After about 1 hour at 270°C the reaction mixture is transparent. Then, a vacuum of 50 mm Hg is gradually applied. After 2 hours at 270°C and 50 mm Hg a resin with characteristics as given in table 1 is obtained.

Examples 2 to 4 : Example 1 was repeated, except that the nature of the titanium catalyst was modified.

In Example 2, 0.1 % by weight of tetra-n-butyltitanate (Tyzor TNBT from Dupont) was used.

In Example 3, 0.25 % by weight of lactic acid titanate chelate (Vertec AC220 from Synetix) was used.

In Example 4, 0.25 % by weight of lactic acid titanate chelate (Vertec AC220 from Synetix) was used as catalyst and 0.02 % by weight of tributyl phosphite (on mixture and prepolymer) was added to the reaction mixture.

The results obtained are presented in table 1.

Table 1

The colour of the obtained polyesters was measured by use of a Dr Lange Micro Color II which uses filters that approximate spectrally the standard observer functions as defined in the CIEL*a*b* specifications. The b*-value is an indication of the yellowness of the polyester and is determined by the equation:

b * = 7.0 (y -0.847 z)

The lower the value of b* the less yellow is the polyester. A positive b*-value indicates that some yellow exists while a negative indicates that some blue exists. The polyesters prepared with the different titanium catalysts present b*-values of less than 10. Example 5: Synthesis of an isophthalic acid-neopentyl glycol based carboxyl functional polyester accordingly an one-step procedure.

Using the same equipment as in example 1 , a homogeneous mixture containing 722.1 parts of isophthalic acid, 424.9 parts of neopentyl glycol and 150.0 parts of water, agitated at a temperature of 90°C, is pumped in 4 hours into an esterification reactor containing 300 parts of a carboxyl functional polyester with acid number of 35 mg KOH/g and hydroxyl number of 4 mg KOH/g containing 1.5 parts of Tyzor LA, standing at 260°C. All through the addition of the mixture to the prepolymer, the temperature remains unaffected, and the mixture brought in the esterification reactor immediately is converted in a transparent prepolymer. The distillate distilled from the reactor as a function of time is reproduced in table 2. Once the addition of the mixture is completed, a vacuum of 50 mm Hg is gradually applied. After 1 hour at 260°C and 50 mm Hg, a resin with characteristics as reproduced in table 2, is obtained. Table 2

Comparative examples 6R to 8R: Synthesis of a hydroxyl functional prepolymer from direct esterification of terephthalic acid and neopentyl glycol accordingly a conventional procedure.

423.5 parts of neopentyl glycol is placed in a conventional four-neck round- bottom flask equipped with a stirrer, a distillation column connected to a water-cooled condenser, an inlet for nitrogen and a thermocouple attached to a thermoregulator. The flask contents are heated while stirring under nitrogen, to a temperature of circa 140°C, at which point 608.9 parts of terephthalic acid and x parts of catalyst are added. The reaction set-point is then increased to 250°C. In table 3 here below the % of distillate as a function of time, as well as the bulk temperature is represented for 2.6 parts (0.25%) of n-butyltintrioctoate (= comparative example 6R), for 2.6 parts (0.25%) of Vertec AC220 (= comparative example 7R) and for 10.3 parts (1.0%) of Vertec AC220 (= comparative example 8R).

Table 3

(*) analysis showed that the distillate contained large amount of decomposition products and neopentyl glycol. As appears from table 3, 5 hours are needed for a conventional tin catalyst to successfully convert the terephthalic acid/neopentyl glycol mixture into a hydroxyl functional prepolymer.

The polyester of comparative example 6R is then further converted in a second reaction step into a carboxyl functional polyester through reaction with isophthalic acid such as in example 1.

On the contrary, when titanium containing catalysts are used for the preparation of polyesters accordingly a conventional procedure as generally applied for neopentyl glycol containing polyesters with a molecular weight between 1000 and 15000 and which can be used in powder coating compositions, it is impossible to get far enough conversion of the terephthalic acid/neopentyl glycol mixture in order to get a transparent hydroxyl functional prepolymer. Even with a temperature of 350°C at the rim of the round-bottom flask, it is very difficult to get a high enough temperature in the reactor. Important neopentyl glycol losses are observed through the distillation. Even using 200 ppm of titanium (comparative example 8R) does not allow to get a transparent hydroxyl functional prepolymer, when using the conventional esterification procedure.

Examples 9 to 11

Using the same equipment and procedure as in example 1, the polyesters of examples 9 to 11 were prepared with the monomers as indicated in table 4. Example 11 further differs from example 1 in that no final vacuum step is used. The polyesters of examples 9 and 10 were prepared accordingly the second variant of the second embodiment of this invention. The polyester of example 11 was prepared accordingly the third variant of the second embodiment of this invention. The "prepolymer A" is a hydroxyl functional polyester based on terephthalic acid and neopentyl glycol only with a hydroxyl number of 56 mg KOH/g and an acid number of 7 mg KOH/g.

The resin characteristics are reproduced in table 5. table 4

table 5

The polyesters of example 1, formulated into a white (RAL9010) or medium dark brown (RAL8014) powder formulation with triglycidyl isocyanurate (TGIC) as hardener (polyester /TGIC = 93/7% weight), upon application and curing result in finished coatings proving properties, such as flexibility (reverse and direct impact), accelerated weathering (UV-A), among others, which are equal to those as obtained for similar powders derived from comparative example 6R, a conventional commercial polyester resin.

Claims

CLAIMS:

1. Process for the preparation of neopentyl-glycol based polyesters in the presence of an organotitanium catalyst, which comprises a controlled addition step wherein (i) a polyol component comprising from 30 to 100 mole % of neopentyl glycol and (ii) a polyacid component comprising from 70 to 100 mole % of isophthalic and/or terephthalic acid, are gradually added to a reactor containing a polyester (A) while maintaining the reaction mixture in the reactor at a temperature of from 230 to 330 °C.

2. Process according to claim 1, wherein said polyol component (i) and said polyacid component (ii) are present in a molar ratio of (0.7 to 1.4) : 1.

3. Process according to any of claims 1 or 2, wherein the polyacid component is composed of from 70 to 100 mole % of isophthalic and/or terephthalic acid and from 0 to 30 mole % of a polyacid selected from fumaric acid, maleic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2- cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azealic acid, sebacic acid, 1, 12-dodecanedioic acid, trimellitic acid or pyromellitic acid, or the corresponding anhydrides.

4. Process according to any of claims 1 to 3, wherein the polyol component is composed of from 30 to 100 mole % of neopentyl glycol and from 0 to 70 mole % of a polyol selected from ethylene glycol, propylene glycol, 1,4-butanediol, 1,6- hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methyl-l,3- propanediol, 2-bύtyl-2-ethyl-l,3-propanediol, hydrogenated Bisphenol A, hydroxypivalate of neopentyl glycol, trimethylolpropane, ditrimethylolpropane and pentaeiythrytol.

5. Process according to any of claims 1 to 4, wherein the molar ratio of polyol component (i) to polyacid component (ii) is at most 1 and wherein the polyacid component is substantially free of terephthalic acid.

6. Process according to any of claims 1 to 4, wherein the molar ratio of polyol component (i) to polyacid component (ii) is higher than 1.

7. Process according to claim 6, wherein the reaction mixture obtained after the controlled addition step is submitted to a supplementary addition step wherein a polyacid component different from terephthalic acid or an anhydride is added to the reaction mixture.

8. Process according to any of claims 1 to 7, wherein the reaction mixture obtained after the addition step is submitted to a treatment under reduced pressure.

9. Process according to claim 6, wherein the reaction mixture obtained after the controlled addition step is submitted to an additional addition step wherein a polyanhydride is added to the reaction mixture obtained from the controlled addition step in such conditions that anhydride ring opening takes place.

10. Process according to any of claims 1 to 9, wherein the polyester (A) presents a cone/plate viscosity at 200 °C of 0.5 to 15000 mPa.s, a delta hydroxyl or delta carboxyl of from 10 to 150 mg KOH/g, a glass transition temperature from 25 to

85°C and/or number average molecular weight of 500 to 15000.

11. Process according to any of claims 1 to 10, wherein the polyester (A) is obtained by reacting a polyol component comprising at least 30 mole % of neopentyl glycol and a polyacid component comprising at least 70 mole % of isophthalic and/or terephthalic acid, in a molar ratio of (0.7 to 1.4) : 1.

12. Process according to any of claims 1 to 11, wherein the quantity of polyester (A) initially present in the reactor is at least 10 % by weight of the total content of the reactor after the controlled addition of the polyol component and the polyacid component.

13. Process according to any of claims 1 to 12, wherein the titanium containing catalyst is chosen from titanium alcoholates and titanium chelates.

14. Process according to any of claims 1 to 13, wherein the amount of catalyst is from 5 to 1000 ppm of Ti on the overall weight of polyester (A), polyol component (i) and polyacid component (ii).

15. Process according to any of claims 1 to 14, wherein a stabilising agent is added.

16. Process according to any of claims 1 to 15, wherein the neopentyl-glycol based polyesters obtained from previous reaction steps are further converted into (meth)acιyloyl group containing polyesters.

17. Process according to any of claims 1 to 16, wherein the polyol component (i) and polyacid component (ii) are added continuously to the reactor containing the polyester (A), allowing the polyacid and polyol component to react and wherein an amount of polymer approximately equal to the sum of polyol component (i) and polyacid component (ii) is withdrawn continuously from the reactor.