WO2006034981A1

WO2006034981A1 - Curing of water-containing unsaturated polyester resins involving a cobalt accelerator and a complexing compound

Info

Publication number: WO2006034981A1
Application number: PCT/EP2005/054717
Authority: WO
Inventors: Anna Gerdine Van De Bovenkamp-Bouwman; Frederik Willem Karel Koers
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 2004-09-28
Filing date: 2005-09-21
Publication date: 2006-04-06
Anticipated expiration: 2007-03-28

Abstract

The present invention relates to a process for curing an unsaturated polyester resin wherein the unsaturatedpolyester resin comprises at least 0.15 percent by weight of water, and 0.02 to 5.0 percent by weight of one or more conventional radical initiators comprising a -OOH moiety, at least 5 ppm of a cobalt accelerator, and at least one complexing compound, all percentages being based on the weight of the polyester resin. Furthermore it relates to the cured articles obtained using such a process.

Description

CURING OF WATER-CONTAINING UNSATURATED POLYESTER RESINS INVOLVING A COBALT ACCELERATOR AND A COMPLEXING COMPOUND

The present invention relates to cobalt-accelerated curing processes of unsaturated polyester resins, such as maleic, allylic, vinylic and epoxide-type polyester resins, and to cured items obtainable with the process.

British patent 2,085,464 suggests the use of cobalt, manganese or lithium naphthenate or cobalt or tin octanoate as hardening accelerators for the peroxide curing of unsaturated polyesters.

Similarly, GB 1336804 mentions, in a generic fashion, that cobalt naphthenate can be used as a promotor for various catalyst systems for the curing of various compositions comprising unsaturated polyester resins.

Zei Saito et al., Kenkyu Hokoku - Kanagawa-ken Kogyo Shikensho, vol. 38 (1973) pp. 71-73, disclose that more than 0.5% of water in a polyester resin prolongs the gelation time in the cobalt-accelerated curing of said resins. Furthermore, it was show that the addition of dimethyl aniline did not accelerate the gelation.

JP 2004-010715 deals with the problem of curing unsaturated polyester resins containing 1 to 70% by weight of water. It proposes the use of cobalt- accelerated ketone peroxide-based curing systems wherein the amount of cobalt that is used, based on the total formulation, is increased from normal levels of up to about 300 ppm (mg/kg) to a level of 600-3000 ppm and the amount of ketone peroxide is 500 to 5000 ppm. It is further suggested to introduce 1% of water and a surfactant in the case a resin is used with low water content in order to reduce the difference in curing characteristics. As is confirmed in the examples below, there is a negative influence of water on the performance of a conventional cobalt accelerator. Nevertheless, cobalt, especially when it can be used at the low conventional levels, is the accelerator of choice because of its excellent cost-efficiency and because it can also be used to catalyse the condensation reaction to form a polyester compound. Therefore, a lot of conventional polyester resins are standard already pre- catalysed, meaning that they contain residual cobalt and/or added cobalt. It is preferred not to have to remove residual cobalt from a polyester compound and it is also preferred to limit the number of polyester grades that are marketed and handled for a variety of reasons, such as, economics, storage space, error/risk reduction, and etcetera. For the same reasons it is also undesired to have resins which have been pre-catalysed with varying levels of cobalt. Also it is undesired, as suggested by JP 2004-010715, to add water and surfactant to a system with low water content, since surfactants are typically undesired and because difficult mixing into the viscous resin would be needed. Furthermore, it is undesired to have to catalyse unsaturated polyester resins with more than accepted amounts of cobalt for environmental reasons. Also for these reasons the solution as presented by JP 2004-010715 is not practical.

US 3,743,686 discloses the use of a dehydromonomer, which reacts with the water to generate an acrylate comonomer, which can be incorporated in the resin. Hence, this method involves the addition of an additive to consume the water. A disadvantage of this method is the formation of the acrylate comonomer and hydrolysis products.

In the mean time it is observed that present polyester resins tend to have great fluctuations in the amount of water contained therein. This is in contrast to traditional polyester resins wherein the amount of water was narrowly specified and well controlled. More specifically, more recently introduced resins showed water levels that varied from close to zero to as high as 5% by weight. It appears that during the process of polyester production less stringent water specifications are applied and/or that a number of present day polyester resins are blended with other streams comprising a high amount of water, or that more hygroscopic polyester resins are produced which absorb various amounts of water, depending on the storage conditions.

As explained above, the varying water levels cause a number of problems in the curing process of cobalt-accelerated polyester resins. Therefore, there is a need for a process for cobalt-accelerated curing of water-containing polyester resins, which process is less sensitive to the amount of water present in the system and which allows the use of conventional amounts of cobalt accelerator and does not require the use of additives that consume the water.

The present invention provides such a process. According to this process, a polyester resin comprising from 0.15 to 5 percent by weight of water is cured using

■ 0.02 to 5.0 percent by weight of one or more conventional radical initiators comprising a -OOH moiety,

■ at least 5 ppm of a cobalt accelerator, and

■ at least one complexing compound, all based on the weight of the polyester resin.

The polyester resins used herein can be of any type. As is known in the art, the unsaturated polyester resins include an unsaturated polyester compound and an unsaturated monomeric compound. Suitable polyester compounds include those prepared in conventional ways by reaction between one or more polyhydric alcohols and one or more polycarboxylic acids whereby one or more of the polyhydric alcohols and/or one or more of the polycarboxylic acids is ethylenically unsaturated. In practice, the preferred polymerizable unsaturated polyhydric alcohol-polycarboxylic acid polyesters are the so-called "linear" or "substantially linear" polyesters, i e, those which have no, or very little crosslinking in the polyester molecules, as evidenced by the fact that such polyesters are soluble in solvents such as acetone These are typically formed mainly by esterification of a dihydric alcohol and a dibasic acid. However, it is also possible to additionally employ polyhydric alcohols with more than two hydroxy groups and polycarboxylic acids with more than two carboxy groups in polyester preparation. The esterification reaction is carried out substantially to completion (i e, to an acid number of less than about 80) without permitting substantial (addition) polymerization to take place. Although the esterification reaction is usually carried out under an inert gas atmosphere so as to exclude oxygen, various inhibitors may be used to prevent appreciable addition polymerization of the polyester during the esterification reaction. Since the curing system as proposed in this invention is not sensitive to water, the condensation reaction to form the polyester compound can be conducted in a number of ways, wherein it is not a prerequisite that all water has been removed.

A typical example of a polyester compound useful in this invention is a product prepared by the reaction of (1 ) an ethylenically unsaturated dicarboxylic acid, for instance fumaric, maleic, itaconic, citraconic, mesaconic or chloromaleic acid or anhydride or mixtures of these acids, with (2) a dihydric alcohol, for instance any polymethylene glycol in the series from ethylene glycol to decamethylene glycol, propylene glycol, any butylene glycol, any polyethylene glycol in the series from diethylene glycol to decaethylene glycol, dipropylene glycol and its higher dialkylene homologues, neopentyl glycol, any glycerol monobasic acid monoester, any monoether of glycerol with a monohydric alcohol, or any dihydroxy alkane, in which the hydroxy radicals are attached to carbon atoms which are primary or secondary or both, in the series from dihydroxy butane through dihydroxy decane. As is known to those skilled in the art, part of the unsaturated dicarboxylic acid may be replaced by a saturated dicarboxylic acid, e g, oxalic, malonic, sebacic, phthalic, isophthalic, terephthalic or tetra- hydrophthalic acids, among others. Of course, other components which can be used in the esterification reaction will suggest themselves to those skilled in the art. Further, any of the usual modifiers can be comprised in order to provide certain properties to the polyester product, e g, solubility in various solvents, rheology, shrinkage, etc; and to the product resulting from subsequent curing of the polyester resin, e g, degree of cross-linking, hardness, residual volatiles, water-repulsion, inertness, etc.

Preferred polyesters include those derived from 0.8-1.2 moles of the polyhydric component, most preferably ethylene glycol, diethylene glycol, propylene glycol, preferably isopropylene glycol, dipropylene glycol and neopentyl glycol, for each 1.0 mole of unsaturated polycarboxylic acid or mixture thereof, most preferably maleic and/or fumaric, orthophthalic, isophthalic, tetrahydrophthalic and adipic acids or their anhydrides Modified diethylene, dipropylene, ethylene, propylene or neopentyl maleates or fumarates also may be employed as well as bisphenol-modified and/or halogenated or phosphorus-containing acids or glycols which yield chemical and flame-resistant polyesters These compounds are preferred from a standpoint of economics and the desirable properties that they produce in the end product.

The process according to the invention preferably does not involve the use of polyisocyanate.

The unsaturated monomeric component of the polyester resin used in the process of the invention desirably contains at least one CH=C moiety to crosslink with the unsaturated polyester during curing operations. Any monomer of this type which has been used in polyester systems may be suitably employed in the present invention. Specific monomers which are at present preferred because of their availability, reactivity and other desirable properties are styrene, styrene derivatives such as α-methylstyrene, chlorostyrene, t-butyl- styrene, vinyl toluene, diallyl phthalate, vinyl acetate, methyl methacrylate, diacetone acrylamide, indene, divinyl benzene, stilbene, dibenzal acetone, propenyl benzene and isopropenyl benzene; triallyl cyanurate, triallyl isocyanurate and mixtures thereof. Other vinyl-type monomers may also be employed, either alone or in combination with those of the aforementioned group. The preferred proportion of monomer employed ranges from 0.05 to 1.6 parts per part of polyester, more preferably from 0.1 to 1.0 parts per part of polyester, all on a weight basis, to ensure the most efficient crosslinking/thermosetting reaction.

The cobalt-catalysed curing process of the water-containing polyester resins according to the invention involves the use of conventional radical or ionio radical initiators wherein the radical initiator comprises at least one -OOH moiety, in conventional quantities. More particularly, typically between 0.02 and 5.0 percent by weight of one or more of said -OOH moiety-containing peroxide initiators, based on the weight of the polyester resin, is employed.

The radical initiator comprising at least one -OOH moiety is preferably selected from the group consisting of conventional hydroperoxides of the formula ROOH and so-called ketone peroxides. The ketone peroxides are typically prepared by reacting a ketone and hydrogen peroxide and typically comprise compounds of formula

R¹

HOO-C-OOH

I ₂ ^R

(type-4 ketone peroxide), and/or compounds of the formula

(type-3 ketone peroxides), and water. All R groups in these formulae are independently selected from substituted or unsubstituted hydrocarbons, preferably substituted or unsubstituted alkyls or arylalkyls, more preferably linear or branched alkyls. Substituents, if present, are preferably selected from one or more halide, hydroxy, acid, alkylester, alkylcarbonate, and alkylether groups. Any alkyl moiety is preferably selected from d-Cs linear or branched alkyls, more preferably C1-C4 linear or branched alkyls. Preferably R¹ and R³ are methyl, while R² and R⁴ are preferably selected from ethyl, n-propyl, isopropyl, isobutyl, and n-butyl.

Conventional accelerators, promotors, such as dimethyl aniline, or inhibitors may also be present during the curing procedure of the present invention in addition to the accelerators of the present invention in order to further adjust the curing rate, as is well known to the person skilled in the art.

As said, the present invention relates to the cobalt-accelerated curing of water- containing polyester resins. More specifically, it relates to the curing of a polyester resins comprising at least 0.15%, preferably at least 0.18%, more preferably at least 0.2%, more preferably at least 0.22%, even more preferably at least 0.25%, and most preferably more than 0.30% by weight of water. Preferably the amount of water in the polyester resin is below 5%, more preferably below 3%, even more preferably less than 1%, even more preferably less than 0.99%, and most preferably less than 0.95% by weight of water. All percentages given are based on the weight of the polyester resin.

In the curing process at least 5, 10, preferably 20 ppm (mg/kg) of cobalt accelerator is used, calculated as Co metal and based on the weight of the polyester resin. Preferably, the maximum amount of cobalt accelerator that is used is the maximum conventional amount of cobalt accelerator, being 300 ppm. However, if so desired, amounts of up to 600 ppm can be used. Most preferably, the amount of cobalt accelerator in the process according to the invention is 200 ppm, based on the weight of the polyester resin. Suitably, the cobalt accelerator present in the curing mixture has the form of a cobalt salt, such as cobalt acetate, cobalt proprionate, cobalt butyrate, cobalt 2- ethylhexanoate, cobalt hexanoate, cobalt octoate, cobalt laurate, cobalt oleate, cobalt linoleate, cobalt palmitate, cobalt stearate, cobalt acetylacetonate, and cobalt naphthenate. Most preferred cobalt accelerators are cobalt octoate, cobalt 2-ethylhexanoate and/or cobalt acetate.

Surprisingly, it has now been found that complexing compounds for cobalt can reduce the adverse effects of water on a cobalt accelerator, meaning that the cobalt still remains an effective catalyst.

The complexing compound is capable of forming complexes with cobalt. More preferably, the complexing compound is selected from compounds comprising one or more aldehyde, ketone, alcohol, substituted or unsubstituted alkyl ether and/or substituted or unsubstituted alkyl ester moieties. It should be noted that unsaturated anhydrides, mixed anhydrides, mixed anhydrides of carboxylic acids and boron or silicon acids, and borate esters are not suitable as complexing agents, as they react with rapidly water to form acrylate comonomers.

Preferred complexing compounds are selected from the group consisting of keto- and aldo-esters, ethers, and alcohols, in particular methylacetoacetate; ethyl acetoacetate; mono- and diesters of ketoglutaric acid; pyruvates; sugars such as glucose and fructose; esters of ascorbic acid such as ascorbic palmitate; 1 , 3-d i ketones and aldehydes, in particular acetylacetone, benzoylacetone, and dibenzoylmethane; mono- and diesters such as diethylmalonate and succinates; 1 ,2-diketones, in particular diacetyl and glyoxal; and certain polyalcohols and other alcohols such as butyldioxytol (also known as diethyleneglycol monobutyl ether, formula nBuOChfeChfeOChhChhOH), diethylene glycol (DEG), benzyl alcohol, monoethanolamine, diethanolamine (DETA), triethanolamine, and fatty alcohols.

More preferred are complexing compounds selected from the group consisting of methylacetoacetate, ethylacetoacetate, Cr₄ alkyl monoesters of ketoglutaric acid, Cr₄ alkyl diesters of ketoglutaric acid, esters of ascorbic acid, Cr₄ alkyl malonate esters, Cr₄ alkyl succinate esters, diacetyl, glyoxal, butyldioxytol, diethylene glycol, benzyl alcohol, monoethanolamine, diethanolamine, triethanolamine, and C12-C26 fatty alcohols.

Even more preferred are complexing compounds selected from the group consisting of butyldioxytol, diethylene glycol, benzyl alcohol, monoethanolamine, diethanolamine, triethanolamine, and C12-C26 fatty alcohols. Most preferred complexing agents are butyldioxytol, monoethanolamine, diethanolamine, and triethanolamine.

The complexing compound is typically employed in an amount such that the water-sensitivity of the cobalt accelerator is reduced. Preferably, the complexing compound is used in an amount such that the increase in gel time of a resin containing 014 wt% water upon addition of 0.4 wt% water (based on the weight of resin) is reduced with at least 25%, more preferably at least 50%, and most preferably at least 60%. In other words: addition of 0.4 wt% of water to a resin already containing 0.14 wt% of water causes the gel time to increase. The complexing agent is preferably employed in such an amount that - compared to the situation without complexing agent - this increase, i.e. the difference in gel time of the resin with and without added water divided by the gel time without added water, is reduced by at least 25%, more preferably at least 50%, and most preferably at least 60%.

In the process of the present invention, the complexing compound was found to be suitably used in an amount of 0.002% to 2.0%, more preferably 0.01%-1.0% by weight, based on the weight of the polyester resin, in order to achieve this effect. Specific materials, such as ethylene glycol, diethylene glycol, and diethanolamine, are preferably employed in amounts of 0.01% to 0.5% by weight while other compounds, such as ascorbic palmitate, are used in an amount of 0.02% to 1% by weight, based on the weight of the polyester resin. Some of the other complexing compounds may need to be used in higher quantities, as the skilled person will be able to detect by a conventional curing test.

As disclosed in WO 90/12825, mixed complexes of copper, lithium, magnesium, manganese, vanadium, cobalt and iron can be used in the curing process of traditional polyester resins. The additional metal functions as a co-accelerator.

Also in the process of the present invention, such a co-accelerator may have a beneficial effect. Accordingly, in a preferred embodiment one or more further metals are present which are preferably selected from the group consisting of lithium, copper, magnesium, manganese, vanadium, and iron.

The total amount of metal that is used ranges typically from between 5 to 500 ppm. More preferably a total amount of from 10 ppm to 300 ppm of metal is used, based on the weight of the polyester resin. More preferred concentrations of the further metals, if used, based on the weight of the polyester resin, are as follows: Li from 1 to 100 ppm, Cu from 0.1 to 300 ppm, Fe from 5 to 150 ppm, Mg from 3 to 200 ppm, V from 1 to 200 ppm, and Mn from 1 to 200 ppm. Preferably Cu is used as the co-accelerator. The amount of Cu is preferably in the range of from 1 to 200 ppm.

In the curing process of the present invention, it is common practice to first prepare the polyester compound and to combine this compound with the ethylenically unsaturated monomeric compound. Such mixtures are commercially available. To such polyester resins the accelerator may be added in several different manners. For example, the one or more metal accelerators may be pre-mixed with complexing compound to form a metal salt complex prior to it being added to the unsaturated polyester resin composition. Another possibility is to add the individual one or more metals and the complexing compound to the resin and form the metal complex in situ. Which of these methods is preferred will depend on the specific curing process being carried out. The peroxide initiator, and optional further compounds to adapt the curing rate, may be added directly to the resin without first mixing them with the accelerator composition. However, in some cases it may be desirable to premix the compounds to adapt the curing rate with one or more of the initiator or accelerator components prior to introduction to the resin composition. However, care is to be taken that radical initiator and metal or destabilizing compounds to adapt the curing rate are not mixed with one another since this can result in hazardous mixtures.

The curing process of the present invention may be carried out at any temperature from -5⁰C up to 25O⁰C, depending on the initiator system, accelerator system, compounds to adapt the curing rate, and the resin composition being cured.

Another embodiment of the present invention relates to the cured product obtained by any of the above-identified processes.

EXAMPLES

Materials used:

The curing of the unsaturated polyester resins was analysed by determining the gel time (Gt) using standard method of analysis F/72.1. The water content was analyzed using standard method of analysis Amp/87.2. These standard methods of analysis are available from Akzo Nobel Polymer Chemicals.

Comparative Examples A-F

In the following examples two resins were cured using a conventional cobalt accelerator. Clearly the effect of water on the curing rate is observed.

Examples 1-5 and Comparative Example G

The previous examples were repeated. However, this time an accelerator was used comprising a complex of cobalt and copper.

Comparing the influence of water in Comparative examples A, and C, wherein the relative increase in gel time is 41.7-21.5/21.5*100% = 94% and G, and 2, wherein the relative increase in gel time = 10.7-9.7/9.7 = 10% then it is shown that in G, and 2, the influence of water is reduced by a factor of (94- 10)/94*100% = 89%. Also it is shown that the use of the complex leads to shorter gel times. Hence, it is clearly shown that the retardation effect of the water is greatly reduced when a complexing compound is used. In examples 3 to 5 the gel time is essentially the same over the experiments (since the error in the gel time analysis is about 10%). Examples G, 2, 3, and 5 were repeated using 0.25 parts of accelerator 383 and also in this case the use of the complexing compound resulted in a decrease of the effect of water addition of 89%.

Examples 6-9 and Comparative Example H The amount of Co and Cu as added separately in examples 7 and 8 is the same as the amount of Co and Cu being added as a complex in example 6.

These examples show that simply adding the complexing compound to the unsaturated polyester resin suffices to counter the effect of the water on the cobalt accelerator. However, it is also clear that a pre-formed complex is more efficient.

Claims

1. A process for curing a polyester resin comprising from 0.15 to 5 percent by weight of water, using ■ 0.02 to 5.0 percent by weight of one or more conventional radical initiators comprising a -OOH moiety,

■ at least 5 ppm of a cobalt accelerator, and

2. A process according to claim 1 wherein a co-accelerator metal is used, selected from the group consisting of lithium, magnesium, manganese, copper, cobalt, vanadium and iron.

3. A process according to claim 1 or 2 wherein the complexing compound is comprises at least one functional moiety selected from the group consisting of aldehyde, ketone, alcohol, alkylether, and alkylester.

4. A process of claim 3 wherein the complexing compound is selected from the group consisting of methylacetoacetate, ethylacetoacetate, monoesters of ketoglutaric acid, diesters of ketoglutaric acid, pyruvates, sugars, esters of ascorbic acid, acetylacetone, benzoylacetone, dibenzoylmethane, malonate esters, succinate esters, diacetyl, glyoxal, butyldioxytol, diethylene glycol, benzyl alcohol, monoethanolamine, diethanolamine, triethanolamine, and fatty alcohols.

5. A process of claim 4 wherein said complexing compound is selected from the group consisting of methylacetoacetate, ethylacetoacetate, C1-4 alkyl monoesters of ketoglutaric acid, Cr₄ alkyl diesters of ketoglutaric acid, esters of ascorbic acid, Cr₄ alkyl malonate esters, Cr₄ alkyl succinate esters, diacetyl, glyoxal, butyldioxytol, diethylene glycol, benzyl alcohol, monoethanolamine, diethanolamine, triethanolamine, and C12-C26 fatty alcohols.

6. A process of claim 5 wherein the complexing compound is selected from the group consisting of butyldioxytol, diethylene glycol, benzyl alcohol, monoethanolamine, diethanolamine, triethanolamine, and C12-C26 fatty alcohols, preferably from butyldioxytol, monoethanolamine, diethanolamine, and triethanolamine.

7. A process according to any one of the preceding claims wherein the polyester resin comprises from 0.2 to 5 percent by weight of water.

8. A process according to any one of the preceding claims wherein the amount of complexing compound is chosen such that the increase in gel time of a resin containing 014 wt% water upon addition of 0.4 wt% water, is reduced with at least 25%, more preferably at least 50%, and most preferably at least 60%.

9. A process according to any one of the preceding claims wherein the amount of complexing compound is from 0.002% to 2.0% by weight, based on the weight of the polyester resin.

10. Articles obtained by a process according to any one of the preceding claims.