The present invention relates to unsaturated polyester resin or vinyl ester resin compositions that are curable with a peroxide component, comprise - while being cured - a transition metal compound, a polymer containing reactive unsaturations, optionally a reactive diluent, and a dioxo-component; and that are showing a reduced gel-time drift tendency. Such resin compositions are so-called pre- accelerated resin compositions, if the dioxo-component is already present in the resin composition before the addition of the peroxide. In case the dioxo-component is added for the curing together with or after the addition of the peroxide, then the resin compositions are called accelerated resin compositions.

The present invention further also relates to objects and structural parts prepared from such unsaturated polyester or vinyl ester resin compositions by curing with a peroxide. The present invention finally also relates to methods of peroxide curing of unsaturated polyester resin or vinyl ester resin compositions.

As meant herein, objects and structural parts are considered to have a thickness of at least 0,5 mm and appropriate mechanical properties. The term "objects and structural parts" as meant herein also includes cured resin compositions as are used in the field of chemical anchoring, construction, roofing, flooring, windmill blades, containers, tanks, pipes, automotive parts, boats, etc.

As meant herein the term gel-time drift (for a specifically selected period of time, for instance 30 or 60 days) reflects the phenomenon, that - when curing is performed at another point of time than at the reference standard moment for curing, for instance 24 hours after preparation of the resin - the gel time observed is different from that at the point of reference. For unsaturated polyester resins and vinyl ester resins, as can generally be cured under the influence of peroxides, gel time represents the time lapsed in the curing phase of the resin to increase in temperature from 25 ⁰ C to 35 ⁰ C. Normally this corresponds to the time the fluidity (or viscosity) of the resin is still in a range where the resin can be handled easily. In closed mould operations, for instance, this time period is very important to be known. The lower the gel-time drift is, the better predictable the behavior of the resin (and the resulting properties of the cured material) will be.

W. D. Cook et a/, in Polym. Int. Vol.50, 2001 , at pages 129-134 describe in an interesting article various aspects of control of gel time and exotherm behavior during cure of unsaturated polyester resins. They also demonstrate how the

exotherm behavior during cure of such resins can be followed. Figures 2 and 3 of this article show the gel times in the bottom parts of the exotherms measured. Because these authors focus on the exotherms as a whole, they also introduced some correction of the exotherms for heat loss. As can be seen from the figures, however, such correction for heat loss is not relevant for gel times below 100 minutes.

Gel time drift (hereinafter: "Gtd") can be expressed in a formula as follows:

Gtd = (T25->35°C at x-days " T25-35°C after mixing) / T ₂ 5->35°C after mixing X1 OO% (formula 1 )

In this formula T _2S- ^= _C (which also might be represented by T _ge |) represents, as mentioned above, the time lapsed in the curing phase of the resin to increase in temperature from 25 ⁰ C to 35 ⁰ C. The additional reference to "at x days" shows after how many days of preparing the resin the curing is effected. All polyester resins, by their nature, undergo some changes over time from their production till their actual curing. One of the characteristics where such changes become visible is the gel-time drift. The state of the art unsaturated polyester or vinyl ester resin systems generally are being cured by means of initiation systems. In general, such unsaturated polyester or vinyl ester resin systems are cured under the influence of peroxides and are accelerated (often even pre-accelerated) by the presence of metal compounds, especially cobalt salts as accelerators. Cobalt naphthenate and cobalt octanoate are the most widely used accelerators. In addition to accelerators, the polyester resins usually also contain inhibitors for ensuring that the resin systems do not gellify prematurely (i.e. that they have a good storage stability). Furthermore, inhibitors are being used to ensure that the resin systems have an appropriate gel time and/or for adjusting the gel-time value of the resin system to an even more suitable value.

Most commonly, in the state of the art, polymerization initiation of unsaturated polyester resins, etc. by redox reactions involving peroxides, is accelerated or pre-accelerated by a cobalt compound in combination with another accelerator. Reference, for instance, can be made to US-A-3,584,076, wherein dioxo-compounds chosen from the group of enolisable ketones are used as co- accelerators. Although this reference, in only one of the Examples, also discloses curing of a cobalt containing resin in the presence of a vicinal diketone (namely 2,3-butanedione, hereinafter also simply referred to as butanedione), there is no

indication in this reference, that acceleration can also be achieved with butanedione in the absence of cobalt.

In this context it is to be noted, that Kolczynski et al. have shown interesting results in the proceedings of the 24 ^th Annual Technical Conference SPI (The Society of the Plastics Industry, Inc.), 1969, Reinforced Plastics/Composites Division, at Section 16-A pages'! -8. Namely, it can be seen from table 2 at page 5 of Section A-16, that curing in the presence of cobalt and 2,4-pentanedione is much (i.e. about 10 times) faster than in the presence of cobalt and 2,3-pentanedione. 2,4-Pentanedione is also known as acetylacetone. It is also to be noted that this reference does not give any indication as to effect on gel-time drift, nor to effects of any other metal than cobalt to such gel-time drift.

It is further to be noted, that there are some vicinal diketones that are often used in photo-curing applications. The mechanism in photo-curing, however, is completely different from that in peroxide curing. Experience in photo-curing can not be used for the decomposition of peroxides as in peroxide curing.

An excellent review article of M. Malik et al. in J. M. S. - Rev. Macromol. Chem. Phys., C40(2&3), p.139-165 (2000) gives a good overview of the current status of resin systems. Curing is addressed in chapter 9. For discussion of control of gel time reference can be made to the article of Cook et al. as has been mentioned above. Said article, however, does not present any hint as to the problems of gel-time drift as are being solved according to the present invention.

The phenomenon of gel-time drift, indeed, so far got quite little attention in the literature. Most attention so far has been given in literature to aspects of acceleration of gel time in general, and to improving of pot-life or shelf life of resins. The latter aspects, however, are not necessarily correlated to aspects of gel-time drift, and so, the literature until now gives very little suggestions as to possible solutions for improvement of (i.e. lowering of) gel-time drift. For instance, reference can be made to a paper presented by M. Belford et al., at the Fire Retardant Chemicals Association Spring Conference, March 10-13, 2002 where the gel-time reducing effect of a new antimony pentoxide dispersion (NYACOL APE 3040) has been addressed in fire retardant polyester resins promoted with cobalt.

Accordingly, for the unsaturated polyester resins and vinyl ester resins as are part of the current state of the art there is still need for finding resin systems showing reduced gel-time drift, or in other words, resin systems having only slight gel-time drift when cured with a peroxide. Moreover, there is need for providing

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the skilled man with appropriate means for better tuning of the gel-time. Preferably the properties of the resin composition after curing with a peroxide (e.g. the color) are unaffected (or improved) as a result of the changes in the resin composition for achieving the reduced gel-time drift. The present inventors now, surprisingly, have provided an unsaturated polyester resin or vinyl ester resin composition a) comprising a transition metal compound, a polymer containing reactive unsaturations, optionally a reactive diluent; and a dioxo-component; and b) being curable with a peroxide component; wherein c) the resin composition is essentially free of cobalt; and d) the dioxo-component consists of one or more dioxo-compounds having a calculated reduction energy (CRE), being the energy difference in kcal/mole between the lowest energy conformations of the radical anion and the corresponding neutral molecule as calculated by means of the Turbomole

Version 5 program, in the range of from -5 to -30 kcal/mole.

The resin compositions according to the invention are, although being essentially free of cobalt, nevertheless and most surprisingly accelerated (and, in case the dioxo-component is added before the addition of the peroxide: pre- accelerated) by the presence of a dioxo-component having a CRE in the said range of from -5 to -30 kcal/mole. The term "essentially free of cobalt" as meant herein indicates that the content of cobalt is lower than about 0,015 mmol/kg, preferably even lower than about 0,005 mmol/kg, of the basic resin system (as is being defined hereinbelow), and most preferably the basic resin system is completely free of cobalt. According to the present invention the aforementioned problems of the prior art have been overcome and resin compositions having reduced gel-time drift are obtained.

The present inventors now have found, that excellent tunability of the gel-time of the resin compositions according to the invention can be achieved by means of using other transition metals than cobalt, in amounts that are not very critical.

Taking into account that curing in the presence of cobalt and 2,4-pentanedione (= acetylacetone, having a CRE-value of +4,16 kcal/mole), as mentioned above, is much faster than in the presence of cobalt and 2,3-pentanedione, it is really very surprising that such excellent results are being achieved with dioxo- compounds having CRE-values in the abovementioned range in combination with

transition metals other than cobalt and without the presence of cobalt.

The polymer containing reactive unsaturations as is comprised in the unsaturated polyester resin or vinyl ester resin compositions according to the present invention, may suitably be selected from the unsaturated polyester resins or vinyl ester resins as are known to the skilled man. Examples of suitable unsaturated polyester or vinyl ester resins to be used as basic resin systems in the resins of the present invention are, subdivided in the categories as classified by Malik et al., cited above.

(1) Ortho-resins: these are based on phthalic anhydride, maleic anhydride, or fumaric acid and glycols, such as 1,2-propylene glycol, ethylene glycol, diethylene glycol, Methylene glycol, 1 ,3-propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol or hydrogenated bisphenol-A. Commonly the ones derived from 1 ,2-propylene glycol are used in combination with a reactive diluent such as styrene.

(2) Iso-resins: these are prepared from isophthalic acid, maleic anhydride or fumaric acid, and glycols. These resins may contain higher proportions of reactive diluent than the ortho resins.

(3) Bisphenol-A-fumarates: these are based on ethoxylated bisphenol-A and fumaric acid.

(4) Chlorendics: are resins prepared from chlorine/bromine containing anhydrides or phenols in the preparation of the UP resins.

(5) Vinyl ester resins: these are resins, which are mostly used because of their because of their hydrolytic resistance and excellent mechanical properties, as well as for their low styrene emission, are having unsaturated sites only in the terminal position, introduced by reaction of epoxy resins (e.g. diglycidyl ether of bisphenol-A, epoxies of the phenol-novolac type, or epoxies based on tetrabromobisphenol-A) with (meth)acrylic acid. Instead of (meth)acrylic acid also (meth)acrylamide may be used.

Besides these classes of resins also so-called dicyclopentadiene (DCPD) resins can be distinguished. All of these resins, as can suitably used in the context of the present invention, may be modified according to methods known to the skilled man, e.g. for achieving lower acid number, hydroxyl number or anhydride number, or for becoming more flexible due to insertion of flexible units in the backbone, etc. The class of DCPD- resins is obtained either by modification of any of the above resin types by Diels-Alder reaction with cyclopentadiene, or they are obtained alternatively by first reacting maleic

acid with dicyclopentadiene, followed by the resin manufacture as shown above. Of course, also other reactive groups curable by reaction with peroxides may be present in the resins, for instance reactive groups derived from itaconic acid, citraconic acid and allylic groups, etc. Accordingly, the - basic - unsaturated polyester resins or vinyl ester resins used in the present invention may contain solvents. The solvents may be inert to the - basic - resin system or may be reactive therewith during the curing step. Reactive solvents are particularly preferred. Examples of suitable reactive solvents are styrene, α-methylstyrene, (meth) acrylates, N-vinylpyrrolidone and N-vinylcaprolactam. Preferably the - basic - unsaturated polyester resins or vinyl ester resins contain at least 5 wt.% of a reactive solvent.

The unsaturated polyester resins and vinyl ester resins as are being used in the context of the present invention may be any type of such resins, but preferably are chosen from the group of DCPD-resins, iso-phthalic resins, ortho- phthalic resins and vinyl ester resins. More detailed examples of resins belonging to such groups of resins have been shown in the foregoing part of the specification.

According to the present invention, the resin compositions are essentially free of cobalt; and contain one or more transition metals not being cobalt. It is preferred that at least one of the transition metals of the transition metal compound is selected from the metals having any of the atomic numbers 21-26, 28-30 and 39-48. The metal having atomic number 27 (cobalt) is excluded from said list.

It is particularly preferred that at least one of the transition metals is selected from the group of Ti, V, Mn, Fe, Ni, Zn and Cu.

For better understanding of the invention, and for proper assessment of the amounts of transition metal compound, dioxo-component and/or other components of the unsaturated polyester resin or vinyl ester resin compositions according to the invention, the term "basic resin system" is introduced here. As used herein, the term "basic resin system" is understood to mean the total weight of the resin, but excluding any fillers as may be used when applying the resin system for its intended uses. The basic resin system therefore consists of the polymer containing reactive unsaturations, and any reactive diluent and any additives present therein (i.e. except for the peroxide component that is to be added shortly before the curing) for making it suitable for being cured, for instance all kinds of compounds soluble in the resin, such as initiators, accelerators, inhibitors, colorants (dyes), release agents etc., as well as styrene and/or other solvents as may usually be present therein. The amount of additives soluble in the resin usually may be as from 1 to 25 wt.% of the

basic resin system; the amount of styrene and/or other solvent may be as large as, for instance, up to 75 wt.% of the basic resin system. The basic resin system, however, explicitly does not include compounds not being soluble therein, such as fillers (e.g. glass or carbon fibers), talc, clay, solid pigments, low-profile agents, thixotropic agents, flame retardants, e.g. aluminium hydrates (e.g. aluminium trihydrate (AI(OH) ₃ ), etc.

According to the present invention, already the basic resin system as such is excellently curable.

Calculating the total weight of the basic resin system of a resin composition while excluding the weight of fillers, low-profile agents, thixotropic agents, enforcement materials, etc. which do not form part of the resin composition (i.e. in the present case the polymer containing reactive unsaturations, the optionally present reactive diluent and the dioxo-compound(s)) is standard practice in the field of unsaturated polyester and vinyl ester resins.

The amount of transition metal other than cobalt in the resin composition may vary within wide ranges. It is preferably at least 0,015 mmol per kg of resin and at most about 20 mmol per kg of resin. More preferably, the amount of transition metal is in the range of from 0,05 to 15 mmol/kg of resin, and most preferably in the range of from 0,1 to 10 mmol/kg of resin.

These resin compositions according to the invention all can be cured by means of peroxide curing. According to the present invention, in addition to the peroxide specific dioxo-components are applied as accelerator, but also other (co-)accelerators can be applied. The peroxides used for the initiation can be any peroxide known to the skilled man for being used in curing of unsaturated polyester resins and vinyl ester resins. Such peroxides include organic and inorganic peroxides, whether solid or liquid; also hydrogen peroxide may be applied. Examples of suitable peroxides are, for instance, peroxy carbonates (of the formula -OC(O)O-), peroxyesters (of the formula -C(O)OO-), diacylperoxides (of the formula -C(O)OOC(O)-), dialkylperoxides (of the formula -00-), etc. They can also be oligomeric or polymeric in nature. An extensive series of examples of suitable peroxides can be found, for instance, in US 2002/0091214-A1 , paragraph [0018]. The skilled man can easily obtain information about the peroxides and the precautions to be taken in handling the peroxides in the instructions as given by the peroxide producers.

Preferably, the peroxide is chosen from the group of organic peroxides. Examples of suitable organic peroxides are: tertiary alkyl hydroperoxides (such as, for instance, t-butyl hydroperoxide), and other hydroperoxides (such as, for

instance, cumene hydroperoxide), the special class of hydroperoxides formed by the group of ketone peroxides (such as, for instance, methyl ethyl ketone peroxide and acetylacetone peroxide), peroxyesters or peracids (such as, for instance, t-butyl peresters, benzoyl peroxide, peracetates and perbenzoates, lauryl peroxide, including (di)peroxyesters), perethers (such as, for instance, peroxy diethyl ether). Often the organic peroxides used as curing agent are tertiary peresters or tertiary hydroperoxides, i.e. peroxy compounds having tertiary carbon atoms directly united to a -O-O-acyl or -OOH group. Clearly also mixtures of these peroxides with other peroxides may be used in the context of the present invention. The peroxides may also be mixed peroxides, i.e. peroxides containing any two of different peroxygen-bearing moieties in one molecule). In case a solid peroxide is being used for the curing, the peroxide is preferably benzoyl peroxide (BPO).

Most preferably, however, the peroxide is a liquid hydroperoxide. The liquid hydroperoxide, of course, also may be a mixture of hydroperoxides. Handling of liquid hydroperoxides when curing the resins for their final use is generally easier: they have better mixing properties and dissolve more quickly in the resin to be cured.

In particular it is preferred that the peroxide is selected from the group of ketone peroxides, a special class of hydroperoxides. The peroxide being most preferred in terms of handling properties and economics is methyl ethyl ketone peroxide (MEK peroxide).

The dioxo-component in the resin compositions according to the invention of one or more dioxo-compounds having a calculated reduction energy (CRE), being the energy difference in kcal/mole between the lowest energy conformations of the radical anion and the corresponding neutral molecule as calculated by means of the Turbomole Version 5 program, in the range of from -5 to - 30 kcal/mole. Preferably, the one or more dioxo-compounds used in the resin compositions according to the invention each have a calculated reduction energy (CRE) between -10 and -20 kcal/mole, and more preferably between -13 and -17 kcal/mole. A detailed description of the assessment of CRE-values for different dioxo- compounds is presented hereinbelow in the experimental part.

Many dioxo-compounds are falling within the said range of CRE- values. Suitable examples of such dioxo-compounds are the ones shown in table 1 of the experimental part, namely, for instance, pyruvic aldehyde, camphorquinone, 2,3-hexanedione, 3,4-hexanedione, 2,3-pentanedione, and butanedione, but many other dioxo-compounds will have CRE-values in the said range. Other dioxo-

compounds, for instance 3,5-di-£-butyl-1 ,2-benzoquinone, benzil, oxalic acid, diethyl oxalate, acetylacetone, methylacetoacetate and dimethylacetoacetamide, have CRE- values well outside the said range. For instance, acetylacetone, a substance often used in combination with cobalt for achieving curing according to the state of the art (e.g. see the Kolczynski et al. reference cited above) has a CRE-value of +4,16 kcal/mole.

Preferably, the dioxo-component comprises at least one vicinal dioxo- compound having a CRE in the range of from -5 to -30 kcal/mole

The above presented list of dioxo-compounds having a CRE in the range of from -5 to -30 kcal/mole, is at the same time a list of examples of suitable vicinal dioxo-compounds to be used in the present invention. More preferably, the one or more vicinal dioxo-compounds preferably used in the resin compositions according to the invention each have a calculated reduction energy (CRE) between -10 and -20 kcal/mole, and even more preferably between -13 and -17 kcal/mole. Accordingly, from the above list of dioxo-compounds, 2,3-hexanedione, 3,4-hexanedione, 2,3-pentanedione and butanedione are most preferred.

The present invention therefore also relates to a pre-accelerated unsaturated polyester resin or vinyl ester resin composition a) comprising a transition metal compound, a polymer containing reactive unsaturations, optionally a reactive diluent; and a dioxo-component; and b) being curable with a peroxide component; wherein c) the resin composition is essentially free of cobalt; and d) the dioxo-component consists of one or more dioxo-compounds selected from pyruvic aldehyde, camphorquinone, 2,3-hexanedione, 3,4-hexanedione,

2,3-pentanedione, and butanedione.

Advantageously, in the resin compositions according to the invention, at least one of the oxo-groups in the one or more dioxo-compounds is a ketone group.

More preferably at least one of the dioxo-compounds in the resin compositions according to the invention is a diketone. Even more preferably at least one of the dioxo-compounds in the resin compositions according to the invention is a vicinal diketone.

It is especially advantageous if, in the resin compositions according to the invention, at least one of the ketone groups is a methyl ketone. The methyl ketones provide best results as to gel-time drift improvement.

Accordingly, from the above list of dioxo-compounds, 2,3-hexanedione, 2,3-pentanedione and butanedione are most preferred.

The amount of dioxo-compound(s) in the resin compositions according to the invention is not very critical and may vary between wide ranges. For understanding of the invention, and for proper assessment of the amounts of dioxo-component and/or other components of the unsaturated polyester resin or vinyl ester resin compositions according to the invention, the term "basic resin system" is introduced here. As used herein, the term "basic resin system" is understood to mean the total weight of the resin composition, but excluding any fillers as may be used when applying the resin system for its intended uses. The basic resin system therefore consists of the polymer containing reactive unsaturations, and any reactive diluent and any additives present therein (i.e. except for the peroxide component that is to be added shortly before the curing) which are soluble in the resin, such as initiators, accelerators, inhibitors, colorants (dyes), release agents etc., as well as styrene and/or other solvents as may usually be present therein. The amount of additives soluble in the resin usually may be as from 1 to 25 wt.% of the basic resin system; the amount of styrene and/or other solvent may be as large as, for instance, up to 75 wt.% of the basic resin system. The basic resin system, however, explicitly does not include compounds not being soluble therein, such as fillers (e.g. glass or carbon fibers), talc, clay, solid pigments (such as, for instance, titanium dioxide (titanium white)), low-profile agents, thixotropic agents, flame retardants, e.g. aluminium hydrates (e.g. aluminium trihydrate, AI(OH) ₃ ), etc.

Preferably, however, the amount of the one or more dioxo- compounds is between 0,001 and 10 % by weight, calculated on the total weight of the basic resin system of the resin composition, which total weight is determined excluding fillers and the like.

More preferably, this amount of the one or more dioxo-compounds is between 0,01 and 5 % by weight, and most preferably it is between 0,1 and 3 % by weight. In a preferred embodiment of the present invention, the resin composition has an acid value in the range of from 0-300 mg KOH/g of resin and wherein the molecular weight of the polymer containing reactive unsaturations is in the range of from 500 to 200.000 g/mole. Advantageously, the molecular weight of the polymer containing reactive unsaturations is in the range of from 750 to 75.000 g/mole, and more preferably of from 1.000 to 10.000 g/mole.

In even more preferred embodiments of the invention, the resin composition according to the invention also contains one or more reactive diluents. Such reactive diluents are especially relevant for reducing the viscosity of the resin in order to improve the resin handling properties, particularly for being used in techniques like vacuum injection, etc. However, the amount of such reactive diluent in the resin composition according to the invention is not critical. Preferably, the reactive diluent is a methacrylate and/or styrene.

Advantageously, the resin compositions according to the invention also contain one or more inhibitors. Preferably the inhibitors are selected from the groups of: (i) phenolic inhibitors; (ii) N-oxyl based inhibitors; (iii) phenothiazine inhibitors; or (iv) any combination of phenolic and/or -oxyl based and/or phenothiazine inhibitors. More preferably the one or more inhibitors selected from the groups of phenolic and/or N-oxyl based inhibitors.

The amount of inhibitor, preferably phenolic and/or N-oxyl based inhibitor, as used in the context of the present invention, may, however, vary within rather wide ranges, and may be chosen as a first indication of the gel time as is desired to be achieved. Preferably, the amount of phenolic inhibitor is from about 0,001 to 35 mmol per kg of basic resin system, and more preferably it amounts to more than 0,01 , most preferably more than 0,1 mmol per kg of basic resin system. The skilled man quite easily can assess, in dependence of the type of inhibitor selected, which amount thereof leads to good results according to the invention.

Suitable examples of inhibitors that can be used in the resin compositions according to the invention are, for instance, 2-methoxyphenol, 4-methoxyphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, 2,4,6-trimethyl- phenol, 2,4,6-tris-dimethylaminomethyl phenol, 4,4'-thio-bis(3-methyl-6-t-butylphenol), 4,4'-isopropylidene diphenol, 2,4-di-t-butylphenol, 6,6'-di-t-butyl-2,2'-methylene di-p-cresol, hydroquinone, 2-methylhydroquinone, 2-t-butylhydroquinone, 2,5-di-t-butylhydroquinone, 2,6-di-t-butylhydroquinone, 2,6-dimethylhydroquinone , 2,3,5-trimethylhydroquinone, catechol, 4-t-butylcatechol, 4,6-di-t-butylcatechol, benzoquinone, 2,3,5,6-tetrachloro-1 ,4-benzoquinone, methylbenzoquinone,

2,6-dimethylbenzoquinone, napthoquinone, 1-oxyl-2,2,6,6-tetramethylpiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidine-4-ol (a compound also referred to as TEMPOL), 1-oxyl-2,2,6,6-tetramethylpiperidine-4-one (a compound also referred to as TEMPON), 1-oxyl-2,2,6,6-tetramethyl-4-carboxyl-piperidine (a compound also referred to as 4-carboxy-TEMPO), 1-oxyl-2,2,5,5-tetramethylpyrrolidine, 1-oxyl-2,2,5,5-tetramethyl-3-

carboxylpyrrolidine (also called 3-carboxy-PROXYL), aluminium-N-nitrosophenyl hydroxylamine, diethylhydroxylamine, phenothiazine and/or derivatives or combinations of any of these compounds.

It is advantageous, if the resin composition according to the invention is curable with a liquid or dissolved peroxide component. The peroxide is most preferably a liquid or dissolved hydroperoxide.

The present invention also relates to cured objects obtained from a resin composition according to the above described invention by curing with a peroxide. Moreover, the present invention also relates to a method for curing, in the presence of a dioxo-component, of unsaturated polyester resin or vinyl ester resin compositions comprising a transition metal compound, a polymer containing reactive unsaturations, optionally a reactive diluent; and; and being curable with a peroxide component; wherein the resin composition is essentially free of cobalt; and wherein the dioxo-component is added to the resin composition before or immediately after the addition of the peroxide component, and the dioxo-component consists of one or more dioxo-compounds having a calculated reduction energy (CRE), being the energy difference in kcal/mole between the lowest energy conformations of the radical anion and the corresponding neutral molecule as calculated by means of the Turbomole Version 5 program, in the range of from -5 to -30 kcal/mole.

If the dioxo-component is added to the resin composition as an accelerator for the curing after the peroxide has been added thereto for curing, the skilled man in peroxide curing of resin compositions can easily assess within which period of time, or at which moment after the addition of the peroxide, the dioxo- component is most advantageously added. If said period would be too long (i.e. more than 10 to 20 hours), than increase in viscosity of the resin composition and/or gelation thereof will occur. Handling of the resin composition then becomes unnecessarily difficult. Preferably, in such method for curing, the dioxo-component is present in the resin composition before the peroxide is being added for curing. Preferred embodiments of these methods for curing have the narrower characteristics of the dioxo-component, resin composition and amount of dioxo-component as can be found in the abovementioned paragraphs dealing with the resin compositions.

Calculated Reduction Energy (CRE)

For each dioxo-compound, for which the Calculated Reduction Energy needs to be assessed, the following procedure is to be followed: In a first step, for any of such dioxo-compounds, the neutral molecule and its corresponding radical anion are constructed by means of the builder facilities of the Spartan Pro package (version 1.03; January 2000) from Wavefunction Inc. (18401 Von Karman Ave., Suite 370, Irvine, CA 92612, United States of America).

The package used in said first step, then subsequently is used for performing initial geometry optimizations and conformational analyses at the so-called AM1 level.

Next, for each dioxo-compound studied, except for the AM1 structures containing internal hydrogen bonds, all AM1 structures having a relative energy of 0 - about 4 kcal/mole with respect to the AM1 global minimum, are used as input for carrying out density functional calculations by means of the Turbomole program (Turbomole Version 5, January 2002 from the Theoretical Chemistry Group of the University of Karlsruhe, Germany, as developed by R. Ahlrichs et a/.). These Density Functional Turbomole (DFT) optimizations are performed with the Becke Perdewδδ functional "BP86" as is described in the combined papers of A. Becke (Phys. Rev. A, 1988, 38, p.3098-3100) and J. Perdew (Phys. Rev. B, 1986, 33, p.8822-3824), in combination with the standard SV(P) basis set (as described by A. Schafer et a/., J. Chem. Phys., 1992, 97, p.2571-2577) and the so-called Rl (Resolution of Identity) algorithm (as described by K. Eichkorn et a/., Theor. Chem. Ace. 1997, 97, p.119-124) employing default convergence criteria of 10 ^"6 a.u. (atomic units) for the maximum energy change and of 10 ^"3 a.u. for the maximum gradient. Accordingly, all calculations relating to the radical anions, involve the unrestricted open-shell spin wavefunctions. The BP86/SV(P) method used here, in combination with the RI algorithm in the Turbomole program, is unambiguously defined for the skilled user of the Turbomole program. From the BP86/SV(P) global minima so obtained, subsequently the electron affinity (EA) is determined for each of individual dioxo-compound X studied, by means of formula (2):

EA(X) (kcal/mole) = (E _tot ai(radical anion of X) - E _tota i(X) )*627.51 formula (2)

with E _tota i denoting the BP86/SV(P) global minima total energies in a.u., respectively for the radical anion and for the neutral molecule of the dioxo-compound X.

The electron affinity so determined is, in the context of the present application, referred to as Calculated Reduction Energy (CRE), in kcal/mole. Most of the resins used for curing are commercially available products, as indicated in the Examples and Comparative Examples. In addition thereto, also an ortho-resin (which hereinafter will be referred to as Resin A) was specifically prepared on behalf of the inventors for being used in the tests. Resin A was made as follows:

Preparation of Resin A

184,8 g of propylene glycol (PG), 135,8 g of diethylene glycol (DEG), 216,1 g of phthalic anhydride (PAN), 172,8 g of maleic anhydride (MAN), and standard inhibitors were charged in a vessel equipped with a reflux condenser, a temperature measurement device and inert gas inlet. The mixture was heated slowly by usual methods to 205 ⁰ C. At 205 ⁰ C the mixture was kept under reduced pressure until the acid value reached a value below 16 mg KOH/g resin and the falling ball viscosity at 100 ⁰ C was below 50 dPa.s. Then the vacuum was relieved with inert gas, and the mixture was cooled down to 130 ⁰ C, and thereafter the solid UP resin so obtained was transferred to a mixture of 355 g of styrene and 0,07 g of mono-t-butyl-hydroquinone and was dissolved at a temperature below 80 ⁰ C. The final resin viscosity reached at 23 ⁰ C was 640 mPa.s, and the Non Volatile Matter content was 64,5 wt.%.

In the following Examples and Comparative Examples amounts of the components are being indicated either in weight units, or in weight percentages, respectively in mmol. The percentages and mmol values at each occurrence should be read as having been calculated per kg of resin in the so-called "basic resin system".

Monitoring of curing

In most of the Examples and Comparative Examples presented hereinafter it is mentioned, that curing was monitored by means of standard gel time equipment. This is intended to mean that both the gel time (T _ge ι or T ₂₅ ^ ₃₅ - _C ) and peak time (Tpeak or T _25- >p _ea k) were determined by exotherm measurements according to the method of DIN 16945 when curing the resin with the peroxides as indicated in the Examples and Comparative Examples. The equipment used therefore was a Soform gel timer, with a Peakpro software package and National Instruments hardware; the

waterbath and thermostat used were respectively Haake W26, and Haake DL30.

For some of the Examples and Comparative Examples also the gel- time drift (Gtd) was calculated. This was done on the basis of the gel times determined at different dates of curing according to formula 1 :

Gtd = (T ₂ 5->35°C at y-days"T25->35°C after mixing)/ T ₂ 5->35°C after mixing X100% (form Ula 1 )

with "y" indicating the number of days after mixing.

Example 1 and Comparative Example A

90 g of resin A was mixed with 10 g styrene and 0,25 g of a 31% solution Of ZnCI ₂ in ethanol (= 6 mmol/kg of resin), followed by addition of 1 wt.% of dioxo-compound as indicated in table 1 below. After stirring for about 5 min, 3 g of peroxide (Butanox M50; a methyl ethyl ketone peroxide solution of Akzo Nobel, the Netherlands) was added and the resin was allowed to cure. Effect of curing was evaluated qualitatively by assessing whether a solid resin material was obtained after 24 hr, or whether the resin still remained liquid after 24 hr, as shown in Table 1.

Table 1

+ means solid material obtained after 24hr, - means remains liquid after 24 hr

Example 2

Examples 2.1-2.12 (for Resin A)

In each of the Examples 2.1-2.12 90 g of Resin A was mixed with 10 g styrene, followed by 1 g of butanedione. After stirring for 5 min an amount of a metal compound (in the form of one of its salts: Ti-tetrabutoxide; Cu-, Fe- and V-naphthenate; Mn-ethylhexanoate; ZnCI ₂ ), as indicated in table 2, was added. After stirring for another 30 min, 3 g of Butanox M50 was added and the curing was monitored by means of standard gel time equipment as described above. The results are shown in Table 2.

Table 2

From the above results it can be seen, that the curing characteristics of the resins according to the invention can be adjusted easily by means of adding specific transition metals, in a properly selected amount, to the resin, whereas this kind of tuning of curing characteristics is not feasible with resins containing a cobalt curing system according to the state of the art.

It can be seen, for instance, that acceleration of curing is achieved by addition of Ti, Fe, or V, whereas addition of Mn, for instance, tends to increase the gel time. Hardly any effect at all is being seen by the addition of Cu or Zn. Adding of Zn is considered to be particularly advantageous because the cured resins are completely colorless, whereas otherwise the cured resins are clearly colored.

Example 3 In each of the Examples 3.1-3.3 270 g of a resin (as indicated in table

8) was mixed with 30 g of styrene, and 0,75 g of a 31% solution of ZnCI ₂ in ethanol (= 6 mmol/kg of resin); and 3 g of butanedione was added together with 0,5 mmol of t-butylcatechol per kg of resin. This sample was split into portions of 100 g each. 3 g of Butanox M50 was added with stirring to one portion of the resin and curing was

monitored by means of standard gel time equipment as described above. This was repeated after 36 days for the other portion of the resin after it had been stored for 36 days at room temperature, approximately 25 ⁰ C. For the third portion the same procedure was repeated after 150 days. The gel-time drift over 36 days, resp. 150 days, then was determined according to formula 1 , with y being 36 (resp. 150). The results are shown in Table 3. No differences were found in the results after 36 and 150 days.

Table 3

It is to be noticed that the above type of resins, when being cobalt pre-accelerated, tend to show gel-time drift values in the order of magnitude of at least 35% after 36 days.

Example 4 and Comparative Example B

To 900 g of a resin (as indicated in table 4 below) mixed with 100 g of styrene, 10 g of butanedione (in all Examples, except in 4.2 and 4.6, where 20 g of butanedione was used for obtaining acceptable gel times), respectively 10 g of acetylacetone (in the Comparative Examples), was added with mixing. After stirring for about 5 min 1 mmol per kg of resin of t-butylcatechol was added, and subsequently a metal compound (3 mmol of metal/kg of resin in the form of one of its salts: Ti- tetrabutoxide; Cu-, Fe- and V-naphthenate; Mn-ethylhexanoate) was added, as indicated in table 4, and stirring was continued for some minutes. After stirring for about 30 min, the resin then was split into portions of 100 g each. Then, to such 100 g portion, 3 g of Butanox M50 was added and curing was monitored by means of standard gel time equipment as described above. This was repeated after 36 days for

another portion of 100 g of the resin after it had been stored for 36 days at room temperature, approximately 25 ⁰ C. The gel-time drift over 36 days then was determined according to formula 1 , with y being 36. The results are shown in Table 4.

Table 4

These Examples and Comparative Examples clearly demonstrate that use of dioxo-components according to the invention results in more stable curing characteristics as compared to use of other dioxo-components, like acetylacetone. Moreover, gel-time drift is much lower for the Examples than for the Comparative Examples. In Comparative Examples B.2 and B.6 very low peak exotherms are observed, and thus curing is poor.

It is to be noticed that the above type of resins, when being cobalt pre-accelerated, tend to show even much higher gel-time drift values. For instance (and for further comparison) such Gtd for Palatal P4-01 , pre-accelerated with cobalt and acetylacetone is in the order of magnitude of about 105%.

Example 5 and Comparative Example C

90 g of resin A was mixed with 10 g of styrene and 0,25 g of a 31 % solution Of ZnCI ₂ in ethanol (= 6 mmol/kg of resin), followed by addition of the amount of dioxo-compound (either 1 wt.%, or 116 mmol/kg, or at varying wt.%) as indicated in tables 5.1 - 5.3 below. After stirring for about 5 min, 3 g of peroxide (Butanox M50) was added and curing was monitored by means of standard gel time equipment as described above. The results are shown in table 5.1

Table 5.1

Table 5.3

The experiments of Examples 5.1-5.10 show that methyl ketones are preferred as dioxo-compounds. Comparative Examples C.1-C.3 demonstrate that no curing occurs outside the CRE-range if no cobalt is present.

The experiments of Examples 5.11-5.15 clearly demonstrate that the gel time can be adjusted easily by varying the amount of dioxo-component in the composition.

Example 6 and Comparative Example D

Most of the peroxides used in this Example (Butanox M50, Butanox LPT, Trigonox 44B and Trigonox 239) are available from Akzo Nobel, the Netherlands.

Example 6.1

90 g of resin A was mixed with 10 g styrene and 0,25 g of a 31% solution of ZnCI ₂ in ethanol (= 6 mmol/kg of resin), followed by addition of 1 g of butanedione . After stirring for about 5 min, 3 g of peroxide (as indicated in the table) was added and curing was monitored by means of standard gel time equipment as described above. The results are shown in table 6.1.

Table 6.1 (butanedione)

The results show that gel time and other gelation properties can be tuned within wide ranges by proper choice of peroxide.

Example 6.2

90 g Palatal P4-01 , an unsaturated polyester resin from the Palatal ester resins series commercially available from DSM Composite Resins, Schaffhausen, Switzerland) was mixed with 10 g of styrene, 0,25 g of a 31% solution Of ZnCI ₂ in ethanol (= 6 mmol/kg of resin) and with 0,5 g of 2,3-hexanedione. After stirring for about 5 min, 2 g of a peroxide (as indicated in table 6.2) was added and curing was monitored by means of standard gel time equipment as described above. The results are shown in table 6.2a.

Table 6.2a (2,3-hexanedione)

Additionally, curing experiments according to the invention also were carried out with 1 wt.% of butanedione instead of 2,3-hexanedione as used above (at 3 wt.% of Butanox M50 for each experiment), for mutual comparison purposes, with some more resin types as are commercially available from DSM Composite Resins, Schaffhausen, Switzerland. The results are summarized in table 6.2b. Of these resins all Palatal type resins are ortho-type unsaturated polyester resins (in styrene) and Synolite type resins are DCPD-type unsaturated polyester resins (in styrene); and Daron XP-45 is a methacrylate resin (in styrene). For these experiments, except for the Example using Diacryl 121 (a resin product obtainable from Akzo, the Netherlands; where no styrene was added), the weight ratio resin vs. styrene was in each case set at 90 : 10.

Examples 6.1 and 6.2 demonstrate that, according to the invention, various kinds of resins can be cured with a broad range of peroxides and in varying amounts thereof.

It is to be noticed, moreover, that for none of the Examples from the set of 6.2a to 6.2m foaming problems were observed when curing in the presence of a dioxo-compound according to the invention. On the other hand, in otherwise identical Comparative curing experiments, that are not shown here (but for convenience are correspondingly being referred to as Comparative Examples D.d, D.h, D.j, D.k, D.I and D.m, respectively) foam formation was observed, if - instead of the dioxo-compound - 3 mmol of cobalt per kg of resin was used as accelerator for the curing.

Example 6.3 To 90 g of resin A, respectively of Palatal P5-01, mixed with 10 g of styrene and 0,25 g of a 31% solution of ZnCI ₂ in ethanol (= 6 mmol/kg of resin), was added 1 g of butanedione, followed by stirring for about 5 min. Then an amount of Butanox M50 was added, as indicated in Table 6.3, and curing was monitored by means of standard gel time equipment as described above. The results are shown in table 6.3.

Table 6.3 (butanedione)

These results clearly show, that gel time and other gelation properties can be tuned within wide ranges by proper choice of the amount of peroxide.

Example 7

To a mixture of 90 g of Resin A and 10 g of styrene, and 0,25 g of a 31 % solution of ZnCI ₂ in ethanol (= 6 mmol/kg of resin), first 3 g of Butanox M50 was added and then the mixture was stirred for 1 min. Subsequently, at a predetermined point of time (5 min; 8 hours; or 24 hours) an amount of 1 g of butanedione was added, and then the mixture stirred for 30 sec and and curing was monitored by means of standard gel time equipment as described above. The results are shown in Table 7.

Table 7

Moreover, in none of the Examples presented here, foaming problems occurred during the preparation of the castings. Foaming problems, however, are frequently observed in curing of resins that are pre-accelerated with cobalt.