EP1507823A1

EP1507823A1 - A food approved accelerator solution for curing unsaturated polyester resins

Info

Publication number: EP1507823A1
Application number: EP03722536A
Authority: EP
Inventors: Anna Gerdine Van De Bovenkamp-Bouwman; Johannes Martinus Gerardus Maria Reijnders
Original assignee: Akzo Nobel NV
Current assignee: Akzo Nobel NV
Priority date: 2002-05-30
Filing date: 2003-04-22
Publication date: 2005-02-23
Also published as: JP2005528496A; WO2003102067A1; AU2003229721A1

Abstract

The invention relates to an accelerator solution for curing an unsaturated polyester resin which consists essentially of one or more solvents, one or more cobalt-containing salts, and, optionally, one or more stabilizers. The solvent, the salt, and the stabilizer are food-approved compounds. The solution itself is used for hardening unsaturated polyester resins which are suitable for foodrelated applications.

Description

A FOOD APPROVED ACCELERATOR SOLUTION FOR CURING UNSATURATED POLYESTER RESINS

The invention relates to an accelerator solution for curing an unsaturated polyester resin comprising a solvent and a cobalt-containing salt.

The curing process to which the present invention relates is a conventional hardening process of unsaturated polyester-based formulations, wherein the curing is effected by means of peroxides. An accelerator solution is added to promote and accelerate said curing process. More particularly, it serves to specifically increase the activity of the peroxide at lower temperatures and consequently to speed up the rate of hardening of the polyester resin, resulting in a reduced hardening time.

Such an accelerator solution is known from JP-A-57 147509, wherein the solution contains a solvent, an organic cobalt compound, an organic copper salt, and an alkali metal carboxylate. The mixture of metal salts poses a problem with respect to suitability for food-related applications. Also aromatic compounds, e.g., the aromatic solvents that are listed, are undesired.

It is an object of the present invention to provide an accelerator solution which is suitable for food-related applications and preferably has a good storage stability.

We have now found that by employing one or more suitable solvents and optionally by adding one or more suitable stabilizers the object of the invention can be achieved. The invention consists of an accelerator solution suitable for peroxide curing of an unsaturated polyester resin which consists essentially of said solvent or solvents, one or more cobalt-containing salts, and, optionally, one or more stabilizers. Addition of a stabilizer to the accelerator solution generally improves its stability.

Solvents used in the present invention should fulfill the requirement of being non-toxic and thus applicable in food-related applications. Furthermore, the solvent should not or should not be suspected to significantly burden the environment. Aromatic solvents generally do not meet these requirements and are less preferred. The one or more accelerators present in the accelerator solution according to the invention, viz. the cobalt-containing salt or salts, must further be sufficiently soluble in the solvent, for which the solvent preferably comprises one or more polar groups, for example a hydroxyl or a carboxylate group. The cobalt-containing salt or salts are considered to be sufficiently soluble in the solvent if at least 1%w/w of said salt or salts can be dissolved in 99%w/w of solvent. The solvent preferably does not adversely affect the accelerating properties of the cobalt-containing salt(s). it is also contemplated that the solvent is already present during the preparation of the cobalt salt(s). Accordingly, it is preferred that the solvent is inert in this reaction mixture, after which the solution is used for curing of unsaturated polyester resins (UP resins). Preferably, the solvent has a melting point below 0°C. Moreover, the solvent employed in the present invention preferably is a non-hygroscopic solvent.

Examples of suitable solvents are alkanes such as pentane, isopentane, and hexane; glycols such as diethyleneglycol, dipropyleneglycol, and ethyleneglycol; isobutanol; pentanol; phosphor-containing compounds such as triethylphosphate and triethylphosphite; and esters such as dibutylmaleate, dibutylsuccinate, and ethylacetate. Preferred solvents are triethylphosphate, triethylphosphite, isopentane, ethyleneglycol, diethyleneglycol, and ethylacetate. More preferred are ethyleneglycol, diethyleneglycol, triethylphosphate, and triethylphosphite. It is also contemplated to use a mixture of at least two of the aforementioned solvents. However, it is preferred to use only one.

The accelerator solution comprises at least 20 percent by weight (%w/w), preferably at least 25%w/w, and most preferably at least 30%w/w, and at most 99%w/w, preferably at most 98%w/w, and most preferably at most 95%w/w of the solvent, all based on the weight of the total accelerator solution.

Advantageously, the one or more accelerators of the present invention are chosen such that they generally are soluble in the unsaturated polyester resin. Suitable accelerators are cobalt-containing salts selected from 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. The most preferred accelerator solutions essentially contain cobalt octoate, cobalt 2- ethylhexanoate and/or cobalt naphthenate as metal salts. Although mixtures of the above-mentioned cobalt-containing salts may be employed, it is preferred to use only one of them. Although this is less preferred, the cobalt-containing salt can be combined with another metal-containing accelerator. Such a metal-containing accelerator can be selected from the group consisting of conventional salts of one or more carboxylic acids with one or more of the metals and complexes of metals selected from the group consisting of lithium, copper, potassium, manganese, magnesium, vanadium, and iron. The accelerator solution can comprise at least 1%w/w, preferably at least 2%w/w, and most preferably at least 5%w/w, and at most 80%w/w, preferably at most 75%w/w, and most preferably at most 70%w/w of the accelerator or combined accelerators, all based on the weight of the total accelerator solution. Preferably, the accelerator solution consists essentially of accelerator and solvent. However, optionally, one or more stabilizers may be added to improve the stability of the accelerator solution.

Stabilizers suitable for the present invention are compounds that typically prevent crystallization of the cobalt salt or salts in the solution, for example tertiary amines such as triethanol amine and dimethylamino ethanol, and secondary amines such as diethanol amine. These stabilizers preferably are non-toxic and suitable for food-related applications. For this reason, aromatic amines are not preferred. These stabilizers are added to the solution in at least 0.1%w/w, preferably at least 0.2%w/w, and most preferably at least 0.5%w/w, and at most 8%w/w, preferably at most 6%w/w, and most preferably at most 4%w/w of the stabilizer, all based on the weight of the total accelerator solution.

The curing process of the present invention comprises the addition of an accelerator solution according to the invention to one or more conventional resins and/or pre-polymers and preferably at least one peroxide, followed by mixing and dispersing. The curing process is preferably carried out at ambient temperatures commonly used in applications such as hand lay-up, spray-up, filament winding, resin transfer moulding, coating (e.g. gel-coat and standard coatings), button production, centrifugal casting, corrugated sheets or flat panels, relining systems, kitchen sinks via pouring compounds, etc. However, it can also be used in SMC, BMC, pulltrusion techniques, and the like, for which temperatures up to 180°C, more preferably up to 150°C, most preferably up to 100°C are used.

The resin or pre-polymer can be selected from any conventional resin. Preferably, it is chosen from the group consisting of conventional unsaturated polyesters, including so-called ortho resins, iso-resins, iso-npg resins, vinyl ester resins, acrylic resins, and dicyclopentadiene resins. Examples of such resins are maleic, allylic, vinylic, and epoxy-type materials, combined with at least one ethylenically unsaturated reactive monomer. Preferred ethylenically unsaturated reactive monomers include styrene and styrene derivatives such as α-methylstyrene, vinyltoluene, indene, divinyl benzene, stilbene, but also diallylphtalate, dibenzylideneacetone, allyl benzene; triallyl cyanurate, triallyl isocyanurate, and mixtures thereof. The amount of ethylenically unsaturated reactive monomer is at least 0.1%w/w, based on the weight of the resin, preferably at least 1%w/w, and most preferably at least 5%w/w, and at most 50%w/w, preferably at most 40%w/w, and most preferably at most 35%w/w.

In the process of the present invention, the accelerator solution is generally employed in a conventional amount. Amounts of at least 0.1%w/w, preferably at least 0.25%w/w, and at most 5%w/w, preferably at most 2%w/w of the accelerator solution, based on the weight of the resin, are typically used.

Peroxides suitable for the curing of UP resins include organic peroxides, such as conventionally used ketone peroxide, perester, and peroxydicarbonate. The skilled person will understand that these peroxides can be combined with conventional additives, for instance phlegmatizers, such as hydrophilic esters and hydrocarbon solvents.

The amount of peroxide formulation to be used in the curing process is at least 0.1 %w/w, preferably at least 0.5%w/w, and most preferably at least 1%w/w, and at most 8%w/w, preferably at most 5%w/w, most preferably at most 2%w/w, all based on the weight of the resin.

Other optional additives may be employed in the curing process according to the invention, such as fillers, glass fibres, pigments, inhibitors, and promoters. In the curing process of the present invention, typically the UP resin is first mixed with the ethylenically unsaturated reactive monomer. The accelerator composition can be added in several different manners and may have been pre-mixed with the monomer or resin. The peroxide formulation can be added directly to the mixture. However, it can also be first mixed with the monomer or resin. Care is to be taken that the peroxide formulation and the accelerator solution are not pre-mixed, since this will be hazardous.

By using the accelerator solution of the present invention, the cured UP resin may be applied in food-related applications. These resins can be employed in glass reinforced and non-glass reinforced products which come into contact with potable liquids, such as wine, water, whiskey, cognac, milk etc., and food articles such as vegetables or meat. The UP resin may also be used in for example pipes, boxes or truck panels. The invention is elucidated in the following examples.

Examples

An example of an accelerator solution according to the invention is a solution in triethylphosphate containing 35%w/w cobalt 2-ethylhexanoate. Also a composition further containing 2%w/w of triethanolamine was prepared. Both solutions show a good storage stability. The solvent triethylphosphate as well as the stabilizer triethanolamine is food-approved. The curing of a UP resin with Butanox M50^® in which these accelerator formulations are used was identical to the curing with conventional accelerator compositions which are not food- approved. The UP resin resulting from the curing process in the presence of the accelerator solution is suitable for food-related applications.

Claims

1. An accelerator solution suitable for peroxide curing of an unsaturated polyester resin which consists essentially of one or more cobalt- containing salts, one or more solvents, and, optionally, one or more stabilizers, wherein the solvents are selected from the group consisting of alkanes, glycols, phosphor-containing compounds, and esters.

2. An accelerator solution according to claim 1 wherein the solvent is selected from the group consisting of pentane, isopentane, hexane, diethyleneglycol, dipropyleneglycol, ethyleneglycol, isobutanol, pentanol, triethylphosphate, triethylphosphite, dibutylmaleate, dibutylsuccinate, and ethylacetate.

3. A solution according to claim 1 or 2 comprising 20 to 99%w/w of solvent(s), and 1 to 80%w/w of cobalt-containing salt(s), and optionally 0.1 - 8%w/w of stabilizer(s), up to a total of 100%w/w.

4. A solution according to any one of the preceding claims wherein the cobalt-containing salt is selected from the group consisting of cobalt octoate, cobalt 2-ethylhexanoate, and cobalt naphtenate.

5. A solution according to any one of the preceding claims further comprising 0.1 to 4%w/w of the stabilizer.

A solution according to any one of the preceding claims wherein the stabilizer is an aliphatic amine selected from the group consisting of triethanolamine, dimethylaminoethanol, and diethanolamine.

7. A solution according to any one of the preceding claims wherein the solvent is triethylphosphate and the cobalt-containing salt is cobalt 2- ethylhexanoate.

8. A process for curing an unsaturated polyester resin wherein the polyester resin is hardened with an organic peroxide and an accelerator solution according to any one of claims 1 to 7.

9. A hardened unsaturated polyester resin as obtained in the process of claim 8.

10. An article suitable for storing or transporting potable liquids or food articles made of a cured unsaturated polyester resin of claim 9.