EP1682601A1

EP1682601A1 - Pre-accelerated unsaturated polyester or vinyl ester resin compositions

Info

Publication number: EP1682601A1
Application number: EP04765936A
Authority: EP
Inventors: Johan Franz Gradus Antonius Jansen; Ivo Ronald Kraeger; Franciscus Johannes Marie Derks
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2003-10-31
Filing date: 2004-10-06
Publication date: 2006-07-26
Also published as: WO2005047364A1

Abstract

The present invention relates to pre-accelerated unsaturated polyester resin or vinyl ester resin compositions, curable with liquid peroxides. They contain (a) an ascorbic acid compound, and (b) a soluble complex containing iron with oxidation state 2 or 3, not being ferrocene or a derivative of ferrocene, and are essentially free of cobalt. The ascorbic acid compound and the soluble complex each are present in an amount of, respectively at least 0.1 mmol and at least 0.05 mmol per kg of primary resin system. These resin compositions show good curing properties and have a strongly reduced content of cobalt as compared to the state of the art preaccelerated unsaturated polyester resin or vinyl ester resin compositions. The present invention further also relates to objects and structural parts prepared from such unsaturated polyester or vinyl ester resins.

Description

PRE-ACCELERATED UNSATURATED POLYESTER OR VINYL ESTER RESIN COMPOSITIONS

The present invention relates to pre-accelerated unsaturated polyester resin or vinyl ester resin compositions, curable with liquid peroxides. The resin compositions show good curing properties and have a strongly reduced content of cobalt as compared to the state of the art pre-accelerated unsaturated polyester resin or vinyl ester resin compositions. The present invention further also relates to objects and structural parts prepared from such unsaturated polyester or vinyl ester resins. In the curing of unsaturated polyester resins and vinyl ester resins, classes of resins that can generally be cured under the influence of peroxides, gel time is a very important characteristic of the curing properties. In addition also the time from reaching the gel time to reaching peak temperature, and the level of the peak temperature (higher peak temperature generally results in better curing) are important. Apart from that, of course, also the mechanical properties of the objects and/or structural parts obtained in the curing process are important. As meant herein gel time represents the time lapsed in the curing phase of the resin to increase in temperature from 25 °C to 35 °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. Accordingly, the term good curing properties reflects, amongst other things, that the rein composition has suitable gel-time properties: i.e. the resin to be cured should remain sufficiently fluid for an acceptable time in the first stage of curing. For good curing properties it is important, that the gel time is rather short, i.e. in the order of some minutes to few tens of minutes. For reasons of process efficiency and results to be achieved, the skilled man accordingly will always try to find options to achieve a minimal gel time, while retaining good mechanical properties of the ultimately cured products. In addition, the skilled man also will try to find curable resin compositions having good storage stability, i.e. being stable (i.e. remain their handling properties without gellification) before being subjected to curing for at least one week after manufacture of the resin composition. W. D. Cook et al., in Polym. Int. Vol.50, 2001 , at pages 129-134 describe in an interesting article various aspects of control of gel time and exotherm behaviour during cure of unsaturated polyester resins. They also demonstrate how the exotherm behaviour 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. 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 stability in the curable state of the resin after its manufacture. The state of the art unsaturated polyester or vinyl ester resin systems generally are being cured under the influence of peroxides and are pre-accelerated by the presence of metal compounds, especially cobalt salts, tertiary amines and mercaptans. As can be seen from the article of W. D. Cook et al., as has been cited above, cobalt accelerators are the most common accelerators being used. Cobalt naphthenate and cobalt octanoate are the most widely use accelerators in the resins of the state of the art. In the standard unsaturated polyester and vinyl ester resins of the prior art they are usually present in an amount of from 0.1 to 10 mmol/kg. 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 these resin systems. Curing is addressed in chapter 9. The presence of cobalt in resin systems, however, generally is undesirable for environmental reasons because of the suspect carcinogenity (toxicity) of cobalt. This is the more so, inasmuch the cobalt content of the resin systems is higher. Attempts to find resin compositions pre-accelerated by other metals than cobalt have been made in the past. Reference can, for instance, be made to US- A-3,830,876 wherein polyester resin compositions are described that are pre- accelerated by the presence of a ferrocene compound and another compound, amongst which can be chosen for ascorbic acid. These resin systems, however, can only be cured in the presence of a solid peroxide, such as benzoyl peroxide. Moreover, emphasis of the invention of US-A-3,830,876 is on color reduction of the resins. The use of ferrocene compounds in curing of unsaturated polyesters, by the way, also has been described in the prior art (see SU-443876-A). In said document, however, no other additional component was used and curing, again, occurred using a solid peroxide, namely benzoyl peroxide. The present inventors have shown (see Comparative Examples E and F hereinafter), that these resin systems from US-A- 3,830,876 and SU-443876-A are unsuitable for being cured with liquid peroxides, so their applicability is quite restricted. Accordingly, there is a substantial need in the unsaturated polyester resin business, and in particular in the field of production of structural materials (i.e. of materials to be used for the production of all kinds of structural parts having a thickness of at least 0.5 mm), for finding pre-accelerated unsaturated polyester resin and vinyl ester resin compositions showing good curing properties and having a strongly reduced content of cobalt. In particular, there is need for providing such pre-accelerated resin compositions that are curable with liquid peroxides. In particular such curing should preferably also be possible at relatively low temperatures. As meant herein, structural materials are being used in closed and open mould applications, and for end segments where the unsaturated polyester resins and vinyl ester resins according to the present invention can be applied are also marine applications, chemical anchoring, roofing, construction, relining, pipes & tanks, flooring, windmill blades, etc. The present inventors now surprisingly have found that the above problems can be overcome, and that pre-accelerated unsaturated polyester resin and vinyl ester resin compositions showing good curing properties and having a strongly reduced content of cobalt can be obtained by providing pre-accelerated unsaturated polyester resin or vinyl ester resin compositions, curable with a liquid peroxide, containing: a) an ascorbic acid compound, in an amount of at least 0.1 mmol per kg of primary resin system; and b) a soluble complex containing iron with oxidation state 2 or 3, not being ferrocene or a derivative of ferrocene, in an amount of at least 0.05 mmol/kg of primary resin system, while being essentially free of cobalt. As meant herein "essentially free of cobalt" means that the content of cobalt is lower than about 0.05 mmol/kg of primary resin system. For understanding of the invention, and for proper assessment of the amounts of ascorbic acid compound and iron compound to be present in the pre-accelerated resin composition, the term "primary resin system" as used herein 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 primary resin system therefore consists of the unsaturated polyester resin or vinyl ester resin, any additives present therein (except for the liquid 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, low-profile agents, colorants (dyes), thixotropic agents, 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 primary resin system; the amount of styrene and/or other solvent may be as large as up to 50 wt.% of the primary resin system. The primary 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)), flame retardants, e.g. aluminium oxide hydrates, etc. The unsaturated polyester resin or vinyl ester resin may be any such resin as is known to the skilled man. Examples thereof can be found in the aforementioned review article by M. Malik et al., who descibe a classification of such resins - on the basis of their structure - in five groups: (1) ortho resins; (2) iso-resins; (3) bisphenol-A-fumarates; (4) chlorendics, and (5) vinyl ester resins. Besides these classes of resins also so-called dicyclopentadiene (DCPD) resins can be distinguished. More detailed examples thereof will be given below in some of the following paragraphs, as well as in the experimental part. Examples of suitable unsaturated polyester or vinyl ester resins to be used as primary 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, triethylene 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) Isoresins: these are prepared from isophtalic 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 hydrolytic resistance and excellent mechanical properties, 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. The DCPD-resins can either be obtained by modification of any of the above types of resins by Diels-Alder reaction with cyclopentadiene, or by first reacting maleic acid with dicyclopentadiene, followed by resin manufacture as shown above. 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. 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. According to the invention the pre-accelerated unsaturated polyester resin or vinyl ester resin compositions are containing an ascorbic acid compound, in a certain amount (at least 0.1 mmol per kg of primary resin system), a soluble complex containing iron with oxidation state 2 or 3 (not being ferrocene or a derivative of ferrocene; at least 0.05 mmol per kg of primary resin system), while being essentially free of cobalt. The amounts of and molar ratio between the ascorbic acid compound and the soluble complex (not being ferrocene or a derivative thereof) can be chosen within wide ranges. Of course, exceptionally high amounts of the soluble complex, for instance in the range of 100 mmol per kg of primary resin (or even higher) do not bring any further advantage (and even may influence the color of the resin composition negatively). The molar ratio between the ascorbic acid compound and the soluble complex can suitably be chosen in the range of from 20:1 to 1:20, most preferably in the range of from 10:1 to 1:10. The inventors surprisingly have found that such pre- accelerated resin compositions, being essentially free of cobalt, have excellent curing properties in curing with liquid peroxides. If the content of the ascorbic acid compound is lower than that of the lower limit of 0.1 mmol per kg of primary resin indicated, then the effect on the curing properties is too small. If, on the other hand, the amount of the ascorbic acid compound, in combination with a (too) high amount of soluble complex, is too high, than the combination of ascorbic acid compound and soluble complex starts to act as a softening agent and curing properties of the resin again will be poor, even though curing might become very fast. The skilled man will easily be capable of finding suitable ranges of the required content of ascorbic acid compound and soluble complex. It is remarkable that excellent results in curing with liquid peroxides can be obtained in resin compositions essentially free of cobalt and already at very low levels of the ascorbic acid and/or iron compound used. Preferably, the ascorbic acid compound is present in the resin compositions according to the invention in an amount of from 0.1 to 60 mmol per kg of primary resin system, most preferably in the range of from 0.5 to 20 mmol per kg. The ascorbic acid compound as used in the present invention can suitably be chosen from the group of ascorbic acid, ascorbic acid salts, ascorbic acid esters and other derivatives of ascorbic acid. The ascorbic acid salts, for instance, can be its salts with alkali or alkaline earth metals, ammonia and or amine compounds. The ascorbic acid esters, most preferably, are chosen from the group of Cι_-12 alkyl or alkenyl esters, and also may contain aromatic or (hetero)cyclic groups. Other derivatives of ascorbic acid, for instance ascorbic acid amide or N-substituted derivatives thereof, can also be used. Most preferably, the ascorbic acid compound is ascorbic acid, an ascorbic acid alkali salt or a Cι_-12 alkyl ester of ascorbic acid. However, also mixtures of acorbic acid compounds can be used. The soluble complexes to be used, can be chosen from the group of iron salts and complexes, but will not be ferrocene or a derivative of ferrocene. The valence of the iron atom in these compounds is 2 or 3. It is assumed that the effectiveness of the soluble complexes in the present invention is due to the possible transition between these valence states. Preferably the soluble complex is an iron salt that is soluble in the primary resin. Of course, also mixtures of soluble complexes can be used. The soluble complex, as used in the context of the present invention, is most preferably used in combination with a solvent that ensures the proper solution of the soluble complex and/or of the ascorbic acid compound in the primary resin system. The valence of the iron in the soluble complex as is used in the context of the present invention preferably will be such that the iron in the soluble complex resin system will be capable of undergoing transition from Fe" to Fe'", and vice versa. Most preferably, the iron in the soluble complex has the valence state of Fe" when the iron compound is being added to the primary resin. Generally, the soluble complexes used most suitably will be organo- iron compounds. The complexes, however, also can be formed in situ in the primary resin, for instance from reaction of an inorganic iron compound (e.g. a salt like FeCI₂ or FeCI₃) with an organic compound while forming HCI. The skilled man will easily be able to find suitable iron compounds to be used, taking into account considerations as to required solubility in the primary resin, resistance against hydrolysis, etc. Suitable solvents for ensuring the dissolution of the complex and/or of the ascorbic acid compound in the primary resin can be chosen from the group consisting of, but not limited to, C_5-16 hydrocarbons, that may be aliphatic, or ethylenically unsaturated, or containing aromatic groups; C_1-8 alkyl esters derived from C_4-20 alkyl and/or alkenyl carboxylic acids; C_1-12 alcohols; C_1-16 alkyl phosphates; and substituted lactams. Excellent results are being achieved with C5-₁6 aliphatic hydrocarbons; C_1-8 alkyl esters from C_6-14, alkyl carboxylic acids, for instance ethyl octanoate and 2-ethylhexyl octanoate; or with substituted lactams like N-methyl pyrrolidone or N-vinylcaprolactam. Of course, also mixtures of such solvents are possible. Most preferably the solvents for ensuring the dissolution of the complex and/or of the ascorbic acid compound in the primary resin is a reactive solvent. Examples of suitable reactive solvents are styrene, (meth)acrylates, and N-vinyl pyrrolidone or N-vinyl caprolactam. In the resin systems according to the invention the content of cobalt is extremely reduced as compared with standard curable resin systems: the resin compositions according to the invention are essentially free of cobalt. The content of cobalt is lower than about 0.05 mmol/kg of primary resin system. It is to be noticed here, that the present inventors have observed that unsaturated polyester and vinyl ester resins containing cobalt as a pre-accelerator for the curing show poor stability upon storage in case they also contain ascorbic acid. In such case the cobalt- accelerated resin often already within one day is gellified and becomes difficult to handle in curing. It is particularly advantageous if the soluble complex is present in an amount of from 0.05 to 50 mmol per kg of primary resin system, preferably of from 0.1 to 20 mmol per kg. 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-phtalic 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. The present invention also relates to all such objects or structural parts as are being obtained when curing the unsaturated polyester or vinyl ester resin compositions according to the invention. These objects and structural parts have excellent mechanical properties. These resins all can be cured by means of radical curing. Most advantageously, the curing is being initiated with a liquid peroxide. Of course, in addition to the peroxide further accelerators (of course, because the resins should be essentially free of cobalt, cobalt is not included in such list of accelerators) can be applied. Although in principle all peroxides known to the skilled man for being used in curing of unsaturated polyester resins and vinyl ester resins can be used, including organic and inorganic peroxides, whether solid or liquid; liquid peroxides are being preferred. Accordingly also also hydrogen peroxide may be applied. Examples of suitable peroxides in general 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 -OO-), 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 liquid peroxide is chosen from the group of organic peroxides and hydrogen peroxide. Examples of suitable liquid organic peroxides are: tertiary alkyl hydroperoxides (such as, for instance, t-butyl hydroperoxide), and other hydroperoxides (such as, for instance, cumene hydroperoxide), peroxyesters or peracids (such as, for instance, t-butyl peresters, peracetates, lauryl peroxide, and also including (di) peroxyesters), perethers (such as, for instance, peroxy diethyl ether), perketones (such as, for instance, methyl ethyl ketone peroxide, acetylacetone peroxide). 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). Preferably the peroxide, as mentioned above, is a liquid peroxide. Handling of liquid peroxides when curing the resins for their final use is generally more easy: 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 perethers and perketones. The peroxide being most preferred in terms of handling properties and economics is methyl ethyl ketone peroxide (MEK peroxide). As mentioned before, the resins according to the invention also may contain an inhibitor. Inhibitors are compounds that prevent initiation of the curing reactions in the resin during storage of the resin. Especially the inhibitors increase the pot-life (i.e. shelf-life) of the resin. In the context of the invention, inhibitors that are most preferred to be used, are preferably chosen from the group of phenolic inhibitors, for instance t-butylcatechol; N-oxyl free radical inhibitors, for instance hydroxytempo (i.e. 2,2,6,6-tetramethyl-4-hydroxy-piperidine-N-oxyl), and carboxyproxyl (i.e. 3- carboxy-2,2,5,5-tetramethyl-1-piperidinyl-oxy); or phenothiazine. In addition to the iron containing soluble complex in the resins according to the invention, also compounds derived from other metals, with the exception of metal oxides (as they are considered to be inert materials in the context of the present invention), may be present in the resin. Such other metal compounds, preferably organometal compounds, in particular such compounds containing copper, nickel, vanadium or manganese, and thereby can be used to lower the (environmentally undesirable) cobalt content of the resins. As has been mentioned above for the dissolving of the complex and/or the ascorbic acid compound into the primary resin various solvents are particularly suitable. Such solvents already also may be present in the primary resin before the complex and/or ascorbic acid compound are being added thereto. Accordingly, the unsaturated polyester resins used in the present invention may contain solvents. The solvents either can be inert towards the resin system during curing, or may be reactive therewith. Reactive solvents are most preferred. Examples of suitable reactive solvents are styrene, (meth)acrylates, N-vinylpyrrolidone and N-vinylcaprolactam. Styrene is the most preferred solvent. Preferably the unsaturated polyester resin or vinyl ester resin compositions according to the invention contains at least 5 wt.% of a reactive solvent. The skilled man, however, easily can find out which solvent (or combination of solvents), in combination with the choice of soluble complex, ascorbic acid compound and amounts thereof, leads to good results in terms of curing properties of the resin compositions according to the invention. The unsaturated polyester resins and vinyl ester resins according to the present invention can be applied in all applications as are usual for such types of resins. In particular they can suitably used in closed mould applications, but they also can be applied in open mould applications. For closed mould applications it is especially important that the manufacturer of the closed mould products reliably can use the favorable properties of the resins acording to the invention. End segments where the unsaturated polyester resins and vinyl ester resins according to the present invention can be applied are also marine applications, chemical anchoring, roofing, construction, relining, pipes & tanks, flooring, windmill blades, etc. That is to say, the resins according to the invention can be used in all known uses of unsaturated polyester resins and vinyl ester resins.

The invention is now demonstrated by means of a series of examples and comparative examples. All examples are supportive of the scope of claims. The invention, however, is not restricted to the specific embodiments as shown in the examples.

Experimental part - Gel time (Tgel_25-35«c) and peak time (Tpeak_25-pea ) were determined by exotherm measurements according to the method of DIN 16945 when curing the resin with 2% of methylethylketone (MEK) peroxide. The equipment used therefor 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.

All experiments described below were performed using a resin that may be considered to be representative for unsaturated polyester and vinyl ester resin compositions, namely Palatal P69-02 (a resin from DSM Composite Resins AG, Schaffhausen, Switzerland). The resin is based on propylene glycol (PG), dipropylene glycol (DPG), phthalic anhydride (PAN), maleic anhydride (MAN) and contains standard inhibitors. The acid value is lower than 20 mg KOH/g resin and the viscosity at 23 °C is in the range of 650-750 mPa.s. Palatal P69-02 is being sold (and used in the experiments) as a solution in styrene. It contains a small amount of methylhydroquinone for stabilization. The solids content (i.e. the non-volatile matter content) is about 66 %. It is to be noticed, that comparable results were achieved with other types of unsaturated polyester and vinyl ester resin compositions.

Example 1

To 100 g of Palatal P69-02 was added 0.0784 g (0.843 mmol Fe/kg of primary resin) of Nuodex Fe (a 6 wt.% of iron product from Servo, Delden, the Netherlands; the iron is present in the form of its 2-ethylhexyl carboxylic acid salt), and 0.175 g (0.994 mmol/kg of primary resin) of ascorbic acid (added as a 10 wt.% solution in N-methylpyrrolidone). After stirring for 1 minute the resin was cured with 2 % of Butanox M-50 (MEK peroxide; Akzo, the Netherlands), resulting in a solidified material. The gel time was determined, according to the method of DIN 16945 as:

Example 2

Example 1 was repeated, though with different amounts of Nuodex Fe (now 0.0784 g; = 0.843 mmol Fe/kg of primary resin) and of ascorbic acid (now 0.3312 g (1.881 mmol/kg of primary resin) of ascorbic acid, added as a 10 wt.% solution in N-methylpyrrolidone). The gel time was determined as:

Example 3

To 100 g of Palatal P69-02 was added 0.3922 g (4.213 mmol Fe/kg of primary resin) of Nuodex Fe, and 0.873 g (4.957 mmol/kg of primary resin) of ascorbic acid (added as a 10 wt.% solution in N-methylpyrrolidone). After stirring for 1 minute the resin was cured with 2 % of Butanox M-50, resulting in a solidified material. The gel time, as well as the peak time and peak temperature were determined, according to the method of DIN 16945 as: Tpeak₂₅-p_eaκ = 15.7 min; peak temp = 161 °C. Example 4

To 100 g of Palatal P69-02 0.0732 g (0.786 mmol Fe/kg of primary resin) of Nuodex Fe and 0.8896 g (5.051 mmol/kg of primary resin) of ascorbic acid (10% N-methyl pyrrolidone) was added. To this mixture 2.00 g of Butanox M-50 was added. Tpeak _25-peak = 12.3 min; peak temp = 157 °C.

Each of the Examples clearly shows the good curing properties of the resins according to the invention. Moreover, it can be seen, that gel time and peak time can be controlled in a proper way, according to the desired curing properties for the resin, by proper choice of the amounts of iron compound and ascorbic acid compound. This offers excellent opportunities in fine-tuning of the curing behavior of unsaturated polyester and vinyl ester resins. The Comparative Examples A-N, presented below, respectively show the level of gel time usual for cobalt accelerated resins (Comp. Ex. A) can be easily reached, or even outperformed (Comp. Ex. N) by the resins according to the invention; the negative effect as to gel times in case of addition of solely ascorbic acid (Comp. Ex. B and C); the absence of curing in case ferrocene (with or without ascorbic acid) is present (Comp. Ex. D, E and F); - the absence of curing in case only a soluble iron containing complex is added (Comp. Ex. D and G); the absence of curing in case the soluble complex is being used in combination with any of a large range of other chemicals (Comp. Ex. H to M).

Comparative Examples A-N

Comparative Examples A-M were carried out similar to Example 1 , but for the changes as shown in Table 1 below. Comparative Example N was carried out similar to Example 3, but for the changes as shown below. The results of the comparative Examples are shown in Table 2. Table 1

White spirit is a mixture of aliphatic compounds Table 2: Results

It is to be noticed that the storage stability of the resins of Comp. Ex. B and C is very poor in comparison to that of the resins of Examples 1-3; already after 1 day these resins (comprising a cobalt component and an ascorbic acid component) have gellified, whereas the resins according to the invention show a much longer storage stability, at least for one or two weeks before gellification becomes observable. With the use of the combination of a soluble iron containing complex (not being ferrocene or a derivative thereof) and an ascorbic acid compound (as described in the specification) the inventors have been able to show that unsaturated polyester and vinyl ester resin compositions can be cured at low temperature. Apparently the curing (and, in fact, also the energy released by the cure system) is far better than could be obtained in curing with any of the current cure systems, in particular cobalt-ketone peroxides or aromatic amine-benzoyl peroxides. This curing efficiency could be demonstrated by peak exotherms that are higher than with the current systems. The known disadvantage of cobalt based cure systems, namely poor curing at low temperatures (i.e. temperatures below 15 °C), is not observed when using the resin compositions according to the present invention.

Claims

1. Pre-accelerated unsaturated polyester resin and vinyl ester resin compositions, curable with a liquid peroxide, characterized in that they are containing: a) an ascorbic acid compound, in an amount of at least 0.1 mmol per kg of primary resin system; and b) a soluble complex containing iron with oxidation state 2 or 3, not being ferrocene or a derivative of ferrocene, in an amount of at least 0.05 mmol/kg of primary resin system, while being essentially free of cobalt.

2. Resin composition according to claim 1 , characterized in that the molar ratio between the ascorbic acid compound and the soluble complex is chosen in the range of from 20:1 to 1 :20, most preferably in the range of from 10:1 to 1 :10.

3. Resin composition according to claim 1 or 2, characterized in that the ascorbic acid compound is present in the resin composition in an amount of from 0.1 to 60 mmol per kg of primary resin system, most preferably in the range of from 0.5 to 20 mmol per kg.

4. Resin composition according to any of claims 1 to 3, characterized in that the ascorbic acid compound is ascorbic acid, an ascorbic acid alkali salt or a Cι_ι₂ alkyl ester of ascorbic acid.

5. Resin composition according to any of claims 1 to 4, characterized in that the soluble complex to be used is chosen from the group of iron salts and complexes, excluding ferrocene and derivatives of ferrocene.

6. Resin composition according to claim 5, characterized in that the soluble complex is an iron salt that is soluble in the primary resin.

7. Resin composition according to claim 5 or 6, characterized in that the soluble complex is used in combination with a solvent that ensures the proper solution of the complex and/or of the ascorbic acid compound in the primary resin system.

8. Resin composition according to claim 7, characterized in that the solvent for dissolution of the soluble complex and/or of the ascorbic acid compound is chosen from the group of C_5-16 hydrocarbons; C_1-8 alkyl esters derived from C _-20 alkyl and/or alkenyl carboxylic acids; C_1-12 alcohols; C_1-16 alkyl phosphates; and substituted lactams.

9. Resin composition according to claim 8, characterized in that the solvent for dissolution of the complex and/or of the ascorbic acid compound is chosen from the group of C_5-16 aliphatic hydrocarbons; C_1-8 alkyl esters from C_6-14, alkyl carboxylic acids; or N-methyl pyrrolidone or N-vinylcaprolactam.

10. Resin composition according to any of claims 7 to 9, characterized in that the solvent for dissolution of the complex and/or of the ascorbic acid is a reactive solvent.

11. Resin composition according to claim 10, characterized in that the solvent for dissolution of the complex and/or of the ascorbic acid is chosen from the group of styrene, (meth)acrylates, and N-vinyl pyrrolidone or N-vinyl caprolactam.

12. Resin composition according to any of claims 1 to 11 , characterized in that the soluble complex is present in an amount of from 0.05 to 50 mmol per kg of primary resin system, preferably of from 0.1 to 20 mmol per kg.

13. Resin composition according to any of claims 1 to 12, characterized in that the unsaturated polyester resins and vinyl ester resins are chosen from the group of DCPD-resins, iso-phthalic resins, ortho-phtalic resins and vinyl ester resins.

14. Objects or structural parts as are being obtained when curing the unsaturated polyester or vinyl ester resin compositions according to any of claims 1 to 13, or 17 to 21.

15. Objects or structural parts according to claim 14, characterized in that they are obtained by curing with a liquid peroxide chosen from the group of organic peroxides and hydrogen peroxide.

16. Objects or structural parts according to claim 15, characterized in that they are obtained by curing with a liquid peroxide selected from the group of perethers and perketones, preferably with methyl ethyl ketone peroxide.

17. Resin composition according to any of claims 1 to 12, characterized in that it also contain an inhibitor, which is preferably chosen from the group of phenolic inhibitors, N-oxyl free radical inhibitors, or phenothiazine.

18. Resin composition according to claim 17, characterized in that it also contains a compound derived from other metals than iron, with the exception of metal oxide compounds, preferably an organometal compound, in particular such compounds where the metal is selected from the group of copper, nickel, vanadium or manganese.

19. Resin composition according to any of claims 1 to 12, and 17 or 18, characterized in that the resin composition contains a solvents, preferably a solvent reactive with the resin.

20. Resin composition according to claim 19, characterized in that the reactive solvents is selected from the group of styrene, (meth)acrylates N-vinylpyrrolidone and N-vinylcaprolactam.

21. Resin composition according to claim 20, characterized in that the resin composition contains at least 5 wt.% of a reactive solvent.