GB2065685A

GB2065685A - Improved colour unsaturated polyester resins containing bromine

Info

Publication number: GB2065685A
Application number: GB8040514A
Authority: GB
Original assignee: Scott Bader Co Ltd
Current assignee: Scott Bader Co Ltd
Priority date: 1979-12-21
Filing date: 1980-12-18
Publication date: 1981-07-01
Also published as: GB2065685B

Abstract

Discolouration of an unsaturated polyester resin derived from dibromoneopentyl glycol can be suppressed by conducting the esterification reaction in the presence of a colour suppressant comprising at least one tri- or pentavalent compound of Group V element. Only small quantities need be used and typical compounds are triphenyl stibine and tri-(chloroethyl) phosphate.

Description

SPECIFICATION Improved colour polyester resins containing bromine This invention relates to a method of manufacturing dibromoneopentyl glycol based polyester resins which results in a product having an acceptable colour.

Unsaturated polyester resins containing halogen atoms in the chains are frequentiy used where some degree of fire retardancy is required from the cured resin either in cast or laminate form.

Typically halogenated saturated diacids have been used for this purpose e.g. tetrabromophthalic anhydride, tetrachlorophthalic anhydride or chlorendic acid.

Resins based on tetrachlorophthaiic anhydride do not allow sufficient halogen to be incorporated and laminates made from such resins do not pass a number of fire retardancy tests. This can be overcome by the use of chlorendic acid and resins containing up to 30% chlorine can readily be obtained. However even these resins are not capable of giving clear laminates which meet some of the highest fire retardancy requirements.

As bromine is a more efficient fire retardant than chlorine means of incorporating high amounts of bromine have been investigated and the use of tetrabromophthalic anhydride has been studied. Whilst the necessary fire retardancy has been obtained such resins yielded laminates which darkened considerably on weathering due to the ease with which the aromatic C - Br bond can be broken by U. V. light.

In more recent times aliphatic bromine constituents have been available e.g. dibromoneopentyl glycol and resins based on this compound have been shown to be more stable to weathering than those based on aromatic bromo compounds. Unfortunately during polyesterifications using dibromoneopentyl glycol small quantities of hydrogen bromide are evolved and this attacks the stainless steel equipment commonly used to manufacture unsaturated polyester resins, causing discolouration of the resin.

We have now found that dibromoneopentyl glycol based resins can be processed in normal stainless steel equipment by the presence during the ester formation of small quantities of colour suppressants which can either be one or more tri- or pentavalent compounds of Group V elements. Typical compounds are triphenyl stibine (C6H5)3Sb and tri-(chloroethyl) phosphate 0 = P (OC2 H4 Cl)3 used at concentrations of 0.02 - 0.1% (200 - 1000 ppm).

The compounds are applicable whenever dibromoneopentyl glycol is the major glycol component, say greater than 0.5 molar proportion of the glycol constituents which are present.

Processes embodying the invention (Examples II and Ill) and for comparison a known process (Example I) are illustrated in more detail with reference to the following Examples, which also illustrate the improved colouration achieved by the processes embodying the invention.

Example I An unsaturated polyester resin was made from 4.4 moles dibromoneopentyl glycol, 3 moles maleic anhydride and 1.0 mole phthalic an hydride. The reactants were heated together at 1700C in a stream of nitrogen gas in a glass reactor. The reactor was equipped with a stainless steel stirrer and the overhead separating column was packed with stainless steel saddles.

Reaction was continued until the acid value reached 38mgKOH/g. The resin was cooled to 140"C and blended with styrene monomer containing a mixture of hydroquinone and toluhydroquinone as inhibitors so that the final solution contained 50ppm of each. The resin solution was adjusted to 34% styrene and the colour measured. Results are shown in Table Example II The same procedure was followed as in Example I except that 1000ppm of triphenyl stibine were added to the reactants. Colour results are shown in Table I.

Example III The same procedure was followed as in Example I except that 200ppm of tri-(chloroethyl) phosphate were added to the reactants. Colour results are shown in Table I.

TABLE I Lovibond tintometer colours 2" cell Addn ppm Red Yellow Blue Example I Control - 2.1 26.0 Example II Triphenylstibine 1000 1.3 7.9 Example III Tri(chloroethyl)phosphate 200 1.0 5.5

Claims

1. A process for preparing an unsaturated polyester resin which includes esterifying at least one unsaturated acid or anhydride with at least one glycol, the or one said glycol being dibromoneopentyl glycol, which process is carried out in the presence of at least one tri- or pentavalent compound of a Group V element as colour suppressant.

2. A process according to claim 1, wherein the esterification is carried out in a stainless steel vessel.

3. A process according to claim 1 or claim 2, wherein the or one said tri- or pentalvalent compound of a Group V element is triphenyl stibene.

4. A process according to claim 1 or claim 2, wherein the or one said tri- or pentavalent compound of a Group V element is tri-(chloroethyl) phosphate.

5. A process according to claim 3 or claim 4, wherein the concentration of the said tri- or pentavalent compound of the Group V element is from 0.02 to 0.1% inclusive based on the weight of the reactants.

6. A process according to any one of the preceding claims substantially as herein described and exemplified.

7. An unsaturated polyester resin whenever prepared by a process according to any one of claims 1 to 6.

8. An unsaturated polyester resin according to claim 1, which contains more than one glycol component and wherein, of the glycol components which are present, more than a 0.5 molar proportion thereof is the dibromoneopentyl glycol.