GB2224509A

GB2224509A - Colour reduction of phenol formaldehyde resins

Info

Publication number: GB2224509A
Application number: GB8924667A
Authority: GB
Inventors: Julie Reeves
Original assignee: Scott Bader Co Ltd
Current assignee: Scott Bader Co Ltd
Priority date: 1988-11-03
Filing date: 1989-11-02
Publication date: 1990-05-09
Anticipated expiration: 2009-11-02
Also published as: GB2224509B; GB8924667D0; GB8825741D0

Abstract

Discolouration of a phenol formaldehyde resin composition is reduced or inhibited by adding to the uncured PF resin 1 to 40 parts by weight (based on solid content), per 100 parts by weight of solid phenol formaldehyde resin, of an additive derived from a compound of the formula <IMAGE> or a conjugated isomer thereof, in which formula (I): Y is NH2, in which case X is O, S or a group providing N, adjacent the C-NH2, the N being capable of forming part of a conjugated bond system, or (a) X and Y are each an individual group and each group provides an N adjacent the CH2, or (b) X and Y or together form a single group, providing at least two Ns, each adjacent the C-NH2, the said Ns, in either of cases (a) and (b) being capable of forming part of the same conjugated bond system. Certain of the additives derived from compound (I) are reaction products of the compound (I) with a hemiformal, optionally in solution in an alkylene glycol, and a source of formaldehyde. Such products have film forming products in their own right.

Description

COLOUR REDUCTION OF PHENOL FORMALDEHYDE RESINS This invention relates to colour reduction in phenol formaldehyde (PF) resins.

It is well known that phenol formaldehyde resins tend to darken upon ageing, and this is especially pronounced if the resins are in contact with metal or air, exposed to light or heat, or any combination thereof. Resins that have only a slight reddish tint on manufacture can develop a dark red-brown colouration after several months' storage.

JP 46/2897 teaches that yellow, i.e. bleached, phenolic resins may be prepared by adding compounds capable of forming ammonia on decomposition to the reaction system of phenol formaldehyde resin. Examples given include urea, ethylideneurea and phenylurea.

Bleaching is effected by adding the degradable compound at 1700C after the main reaction has been completed.

It was therefore both unexpected and surprising to find that, at ambient temperature, with mere physical mixing, addition of certain urea-related compounds, resins and adducts effectively bleaches phenol formaldehyde resins, in particular resole (A-stage) resins.

The invention thereby provides a method of achieving significant colour reduction in alreadyprepared phenol formaldehyde resins, and in particular resins darkened by storage, without the need for applying heat in the process.

For a given resin and additive, it has been found that age-darkened material may be reduced to a similarly pale colouration as when treated directly after manufacture.

The invention therefore may reduce the problems associated with the reproducible pigmentation of phenol formaldehyde resins in either bright or pastel colour shades. Such resins may be formulated into e.g.

gelcoats, flowcoats, hot or cold cured in-mould coating or laminating resins. These have wide applications in the construction and transport industries particularly where superior fire resistance is desired.

The urea-related colour-reducing additive materials which are used may be derived from compounds of the following formula:

or a conjugated isomer thereof, in which formula (I) Y may be -NH2, in which case X may be O, S, or a group providing N, adjacent the C-NH2, the N being capable of forming part of a conjugated bond system or (a) X and Y may each be an individual group each of which groups X and Y provides an N adjacent the C-NH2, or (b) X and Y together may form a single group, providing at least two Ns, each adjacent the C-NH2, the said Ns in either of cases (a) and (b) being capable of forming part of the same conjugated bond system.

Thus X and Y may be separate respective groups (which may be the same as or different from one another) providing respective Ns each adjacent the C-NH2 so that the groups X and Y together form a conjugated chain system (case (a) above). Alternatively X and Y, together with one another and with the carbon atom between them, may form a single group providing at least respective Ns, each adjacent the C-NH2, which group comprises a conjugated ring structure (case (b) above).

As is evident from the above the conjugated system may comprise an open ended chain or a ring structure.

Examples of such compounds of the formula (I) include urea, thiourea, dicyandiamide, melamine and benzoguanamine, and especially suitable are urea and melamine.

To make the colour-reducing additive, all or some of the hydrogen atoms on the -NH2 group(s) of the formula (I) compound may be reacted with a mono- or poly- hydroxy compound such as an alcohol or glycol, or a formaldehyde source, or any combination thereof. The compounds, adducts or resins so formed are blended, at ambient temperature, to reduce the colour of the phenol formaldehyde resin, and/or inhibit its discolouration.

Thus the invention provides a method of reducing or inhibiting the discolouration of a curable phenol formaldehyde resin, which method comprises admixing therewith a colour reducing additive derived from a compound or the formula (I), given above.

The methods of manufacture of urea formaldehyde (UF) and melamine formaldehyde (MF) resins and adducts, which are preferred additives used in a method of the invention, are well known. Hence the methods of reacting (I) with formaldehyde may follow normal industrial practice and procedure for similar reactions; for example, in the use of paraform as the source of formaldehyde, and in the relative molar ratios and catalysts employed.

Linear or branched aliphatic alcohols (containing 1-6 carbon atoms) are often reacted into MF and UF resins; the most commonly used alcohols are methanol, nbutanol and iso-butanol and may be included in such a resin used as an additive in accordance with a method embodying the invention. Either the alcohol is reacted onto the "completed" resin or it is reacted with the formaldehyde before reaction with the -NH2 group(s). In processing (I), formaldehyde and alcohol, methods, molar ratios and degree of conversion may be as in normal industrial practice.

Preferred additives are the reaction products of a compound (I), especially urea or melamine, with a glycol and formaldehyde. Suitable methods for their preparation are disclosed in US 1,986,067; GB 1,107,245; and GB 1,603,431. Linear aliphatic glycols, or mixtures thereof containing 2-6 carbon atoms, may be used in the reaction. They include e.g. ethylene, 1,2-propylene, diethylene, 1,4-butane, and 1,6-hexane glycols.

Preferred are those that contain 3-4 carbon atoms of which diethylene glycol is especially preferred.

A particularly preferred additive is the reaction product of a hemiformal with a compound of the formula (I) and formaldehyde. In an especially preferred additive, the hemiformal is the reaction product of formaldehyde with a glycol which may be any of those given above, especially diethylene glycol.

In a particularly preferred method of preparing such an additive, a glycol is firstly reacted with a source of formaldehyde, of which paraformaldehyde is especially preferred, under alkaline conditions to form a hemiformal. The glycol should be present in an amount which is at least equimolar with that of the formaldehyde, but may be present to excess to provide a solution of the formaldehyde source and the resultant hemiformal in the glycol. The compound (I) is then added while maintaining alkaline conditions and allowed to react, after which reaction an additional amount of the formaldehyde source is added. At that stage the pH may be allowed to decrease to a roughly neutral pH.

The molar proportions the glycol, urea and source of formaldehyde and the time period over which the reactants are added may be adjusted to achieve the following desirable results (a) a concentrated source of formaldehyde, such as paraformaldehyde, is provided so as to reduce the amount of added water and thus avoid the requirement for vacuum stripping, (b) the reaction mixture remains liquid throughout the entire method of producing the colour reducing additive, the reaction product of each successive step serving as a solvent for any reactant added in a subsequent step; this enables the reaction to be carried out simply and efficiently to provide a concentrated liquid resin, (c) a sufficient amount of the formaldehyde is present to render the final resin compatible with the phenol formaldehyde resin so that it does not adversely affect the film forming properties or moulding properties of the final film forming or moulding composition, and (d) a sufficient amount of the compound (I) is present to confer upon the additive the excellent colour reducing properties attainable, without the final product becoming solid.

Bearing this in mind, a typical molar ratio of compound (I) : formaldehyde in the final colour reducing additive is from 0.45 : 1 to 0.55 : 1, especially 0.5 : 1.

A typical molar ratio of compound (I) glycol is from 1.5 : 1 to 2.5 : 1, especially 2 : 1.

For example, when the compound (I) is urea, the source of formaldehyde is paraformaldehyde and the glycol is diethylene glycol, a preferred molar ratio of diethylene glycol : urea : formaldehyde is 1 : 2 : 4.

The resinous products of such a method are believed to be novel and, especially when the molar proportions of the reactants are adjusted as described above, provide excellent film forming properties in their own right, such films being free from cracks or crazing.

However, as later illustrated with reference to the Examples, irrespective of whether or not the resinous product is, of itself, capable of forming films free of cracking or crazing, it may still be effective as an excellent colour reducing additive.

The colour reducing additive may be incorporated into the PF resin composition as a 100% liquid additive, the preferred method, or as a solution of the additive in a suitable solvent or mixture of solvents. Levels of addition may be 1-40, preferably 5-30 and most preferably 10-25 p.b.w. additive (based on solids content thereof) per 100 p.b.w. of phenol formaldehyde resin solids.

Although mixtures of PF and MF or UF resins are known, it is believed that a resin composition comprising a PF resin and an additive derived from a compound of the formula (I) given above, and present in an amount of from 1-40 p.b.w. per 100 p.b.w. of PF resin solids, are novel compositions.

Methods and compositions embodying the invention are illustrated by the following Examples.

Example 1 is a variation on the hemiformal method described in Example 1 of GB 1,603,431 and differs from this method at least in the following respects (i) in the initial, hemiformal producing step, a large excess of the glycol is employed; compare the large excess of formaldehyde used in the hemiformal producing process of the prior document, (ii) the pH is maintained alkaline throughout the process until the final addition of the formaldehyde source; in the process of the prior document the conditions alternate between alkaline and acidic, and (iii) in the final step of adding the formaldehyde source, the pH is allowed merely to become neutral; in the corresponding step of the process of the prior document the pH is rendered acidic.

Example 2 is a less preferred, "acetal" method, but this can still be used to provide excellent colour reducing additives; however the film forming properties of the resin product are inferior to the product of Example 1.

Examples 3-6 illustrate the colour reducing properties of the resin products of Examples 1 and 2.

Colour was assessed according to ASTM D2244-85, using the illuminant D65 and an IBM Colour Computer.

The measurement compares the surface reflectance of 2 samples, from which the computer calculates a colour difference, expressed as a tE value. This value is calculated from the colour difference formula given in item 6.2.2 of the ASTM D2244-85 namely: Eab = t ( dL)2 + ( lea2 ) + ( dub)2 ] Note: 1. The smallest difference that the human eye can detect is approximately 1/4 of a unit.

2. Two samples having the same aE value, relative to a common standard, need not necessarily be of the same colour.

All viscosities were measured on an ICI Cone and Plate Viscometer.

In each example the resin or resin blend was catalysed by the addition of 10 p.b.w. of catalyst per 100 p.b.w. of solid resin, using a p.toluene sulphonic/phosphoric acid mixture as the catalyst, followed by post cure for 3 hours at 80"C.

Example 1 Diethylene Glycol modified UF resin: Resin A Total additions: Diethylene Glycol 4 moles Urea 8 moles Formaldehyde (in the form of paraformaldehyde) 16 moles formaldehyde All the diethylene glycol and 0.4 moles of formaldeyhde were charged into the reaction vessel, stirred and the p.H. adjusted to 10 by the addition of sodium hydroxide.

Regular sampling and testing occurred throughout the entire reaction, and when required, further additions of sodium hydroxide were made to maintain the p.H. within the range 8-10.

0-30 minutes The vessel and contents were steadily heated reaching a maximum temperature of 100 C by which time a clear solution had formed.

30-90 minutes All the urea was gradually added and reacted in.

Reaction was controlled between 95-100 C.

90-180 minutes The remaining paraformaldehyde was added in aliquots, care being taken on each addition to keep a fluid mixture. At this stage, the pH was allowed to drift down to a final value of about pH7. Within the 180 minutes the reaction (at 95-100 C) was completed.

Resin properties were determined as being; p.H. 7, solids 85% and viscosity l9ps at 30"C.

On cooling, a sample of the resin was catalysed and spread as a thin layer. On curing a continuous noncrazing film was formed.

Example 2 Diethylene glycol modified UF resin: Resin B Total additions: Diethylene Glycol 4 moles Urea 8 moles Formaldehyde (Paraformaldehyde) 16 moles formaldehyde 0-7 hours All the glycol and 1 mole of formaldehyde were charged into the reaction vessel, stirred, and heated. Reaction temperature was 137-140"C and the p.H. 0.6-1.2.

7-8.5 hours All the remaining formaldehyde was added, the clear solution became white and opaque; the temperature fell to 1120 C. As the reaction was reheated to 1300C a clear solution was formed.

8.5-10 hours Sodium hydroxide was added to adjust the p.H. to 8.0 prior to the addition of urea in aliquots. An exotherm followed each addition.

Resin properties were determined as being; solids 86.5%, p.H.=7, and viscosity 22ps at 30"C. After vacuum stripping, the properties were; solids 95%, p.H.=7 and viscosity 25ps at 500 C.

On curing, a continuous film was formed but this cracked and crazed on ageing.

Example 3 Bleaching effect of uncured Resins A and B on a Resole Resin Resin compositions given below were catalysed, then impregnated and consolidated into 2 layers of 450g/sq m chopped strand glass mat to form a laminate. When fully cured the colour differences were compared.

aE Crestophen 905 100 p.b.w. 0.0 + 11.1 p.b.w. Resin B 16.92 + 17.6 p.b.w. Resin B 25.12 + 22.0 p.b.w. Resin B 27.21 + 25.0 p.b.w. Resin B 26.22 + 25.0 p.b.w. Resin A 28.70 Crestophen 905 is a commercially available (Scott Bader Co Ltd) phenolic resole resin of 69% solids, p.H. 6.06.5, and viscosity 4.5-5.5ps at 250 C.

All the mixtures produced a lightening of colour from the unblended red to pale yellow at the 25% addition level. Considering the differences in the manufacturing processes, and in the film forming properties of the cured additive resins, Resins A and B had a remarkably similar colour reducing effect.

Thus, irrespective of whether or not the UF additive resin is or is not, of itself, capable of forming a film which is not subject to crazing or cracking, the additive UF resin can be incorporated in a PF resin to give a curable PF resin composition having at most only a pale colour.

Example 4 The effect of ageing on the bleaching of a Resole Resin A sample of Crestophen 905, that for several months had been kept in a clear glass bottle on the laboratory shelf, was used as the aged resin colour standard.

The resins below were catalysed, and cast as films, which when fully cured were measured for colour difference.

hE Crestophen 905 (aged) 100 p.b.w. 0.0 Crestophen 905 (new) 100 p.b.w. 15.2 Crestophen 905 (aged) 100 + 25 p.b.w. Resin A 41.7 Crestophen 905 (new) 100 + 25 p.b.w. Resin A 41.2 All numbers indicated a lightening of colour. The difference between the bleached aged and new samples was visually minimal - the presence of filler and pigment would reduce this further.

Example 5 Urea derived compounds/resins and the bleaching of Resoles To 100 p.b.w. of the aged Crestophen 905 was added 25 parts of modifying material. Each blend was catalysed, cast as a film and allowed to fully cure before colours were compared.

Additive None 0.0 Resin A 41.7 Beetle BE 655 (an isobutylated UF resin of 71% solids, available from BIP Ltd) 44.1 Beetle BE 610 (a butylated UF resin of 74% solids, available from BIP Ltd) 47.1 Dynomin UM-15 (a partially methylated urea of 96% solids, available from Dyno Industriar AS) 33.4 Aqueous UF resin (obtained from Hepworth Minerals & Chemicals Ltd) 45.7 Dimethylol Urea 44.7 Sobral P138X (a butylated UF resin of 60% solids, available from Scott Bader Ltd) 45.3 All additives tested bleached the phenolic resin; those that gave the highest numerical values were the most effective.

Example 6 Melamine derived resins and the bleaching of Resoles.

These were blended, cured and evaluated as in Example 5.

Additive Dynomin MM-9 (a partially methylated melamine of 74% solids, available from Dyno Industriar AS) 50.9 Cymel 303 (a hexamethoxymethylmelamine of 98% solids, available from Charles Tennant Ltd) 59.1 Both materials were effective bleaches.

Claims

1. A phenol formaldehyde resin composition comprising an uncured phenol formaldehyde resin and from 1 to 40 parts by weight (based on solid content), per 100 parts by weight of solid phenol formaldehyde resin, of an additive derived from a compound of the formula

or a conjugated isomer thereof, in which formula (I): Y is NH2, in which case X is 0, S or a group providing N, adjacent the C-NH2, the N being capable of forming part of a conjugated bond system, or (a) X and Y are each an individual group and each group provides an N adjacent the C-NH2, or (b) X and Y or together form a single group, providing at least two Ns, each adjacent the C NH2, the said Ns, in either of cases (a) and (b) being capable of forming part of the same conjugated bond system.

2. A phenol formaldehyde resin composition according to Claim 1, wherein in the compound of the formula (I), defined in claim 1, Y is NH2.

3. A phenol formaldehyde resin composition according to claim 2, wherein the compound of the formula (I) is urea.

4. A phenol formaldehyde resin composition according to claim 1, wherein in the compound of the formula (I), defined in claim 1, X and Y together form a group providing at least two Ns, each adjacent the C-NH2, which Ns are capable of forming part of the same conjugated bond system and which group comprises a ring structure.

5. A phenol formaldehyde resin composition according to claim 4, wherein the compound of the formula I is melamine

6. A phenol formaldehyde resin composition according to any preceding claim, wherein the additive is the reaction product of a compound of the formula (I), defined in claim 1, with a hydroxyl-containing compound.

7. A phenol formaldehyde resin composition according to claim 6, wherein the hydroxyl-containing compound is a monohydric alcohol.

8. A phenol formaldehyde resin composition according to claim 7, wherein the monohydric alcohol is methanol, n butanol or isobutanol.

9. A phenol formaldehyde resin composition according to claim 6, wherein the hydroxyl-containing compound is a dihydric alcohol.

10. A phenol formaldehyde resin composition according to claim 9, wherein the dihydric alcohol is a C26 linear aliphatic glycol.

11. A phenol formaldehyde resin composition according to claim 10, wherein the C26 linear aliphatic glycol is diethylene glycol.

12. A phenol formaldehyde resin composition according to any one of claims 1 to 5, wherein the additive is the reaction product of a compound of the formula (I) defined in claim 1, with a source of formaldehyde.

13. A phenol formaldehyde resin composition according to claim 12, wherein the source of formaldehyde is paraformaldehyde.

14. A phenol formaldehyde resin composition according to claim 12 and claim 13, wherein the compound of the formula I is urea or melamine and the said reaction product is an uncured urea-formaldehyde or melamine formaldehyde resin.

15. A phenol formaldeyhyde resin composition according to claim 14, wherein the said urea-formaldehyde or melamine-formaldehyde resin is modified with a mono- or polyhydric alcohol.

16. A phenol formaldehyde resin composition according to claim 1, wherein the colour reducing additive is a resinous product derived from (a) a C26 alkylene glycol, (b) a compound of the formula (I), defined in claim 1, and (c) a source of formaldehyde.

17. A phenol formaldehyde resin composition according to claim 16, wherein the resinous product is the reaction product of (a) a hemiformal derived from the C26 alkylene glycol and formaldehyde, optionally in the presence of an excess of the C26 alkylene glycol, (b) the compound of the formula (I) and (c) the source of formaldehyde.

18. A phenol formaldehyde resin composition according to claim 16 or 17, wherein the compound of the formula (I) is urea.

19. A phenol formaldehyde resin composition according to claim 16, 17 or 18, wherein the C26 alkylene glycol is diethylene glycol.

20. A phenol formaldehyde resin composition according to any preceding claim, wherein the said additive is present in an amount, per 100 parts by weight of the solid phenol formaldehyde resin, of from 5-30 parts by weight.

21. A phenol formaldehyde resin composition according to claim 20, wherein the said additive is present in an amount, per 100 parts by weight of the solid phenol formaldehyde resin, of from 10-25 parts by weight.

22. A phenol formaldehyde resin composition according to any preceding claim, wherein the said additive is in liquid form.

23. A phenol of formaldehyde resin composition according to any preceding claim, wherein the phenol formaldehyde resin is a resole.

24. A phenol formaldehyde resin composition according to any preceding claim substantially as hereinbefore described and exemplified.

25. A method of reducing or inhibiting discolouration of a curable phenol formaldehyde resin, which method comprises admixing therewith a colour reducing additive derived from a compound of the formula I, defined in claim 1.

26. A method according to claim 25, wherein the colour reducing additive is a resinous product derived from (a) a C2 -6 alkylene glycol (b) a compound of the formula (I), defined in claim 1, and (c) a source of formaldehyde.

27. A method according to claim 26, wherein the resinous product is the reaction product of (a) a hemiformal derived from the C26 alkylene glycol and a source of formaldehyde, optionally in the present of an excess of the C26 alkylene glycol, (b) the compound of the formula (I), and (c) the source of formaldehyde

28. A method according to claim 26 or 27, wherein the compound of the formula (I) is urea.

29. A method according to claim 26, 27 or 28, wherein the Q-6 alkylene glycol is diethylene glycol.

30. A method of reducing or inhibiting discolouration of a curable phenol formaldehyde resin, which method comprises the steps of (1) reacting a C2 -6 alkylene glycol with a source of formaldehyde, optionally in solution in an excess of the Q-6 alkylene glycol,in alkaline conditions to form a hemiformal, (2) reacting the hemiformal with a compound of the formula (I), defined in claim 1, while maintaining the alkaline conditions, (3) reacting the product of step (2) with a source of formaldehyde to form an amine-formaldehyde resin, and (4) admixing the amine-formaldehyde resin with a phenol formaldehyde resin.

31. A method according to any one of claims 23 to 30 substantially as herein described and exemplified.

32. A phenol formaldehyde composition resin whenever prepared by a method according to any one of claims 25 to 31.

33. A film comprising a cured phenol formaldehyde resin according to any one of claims 1 to 24.

34. A moulded product comprising a cured phenol formaldehyde resin according to any one of claims 1 to 24.

35. A method of preparing a curable amine-formaldehyde resin, which method comprises the steps of (1) reacting a C2 6 alkylene glycol with a source of formaldehyde, optionally in solution in an excess of the C26 alkylene glycol, in alkaline conditions to form a hemiformal (2) reacting the hemiformal with a compound of the formula (I), defined in claim 1, while maintaining the alkaline conditions, and (3) reacting the product of step (2) with a source of formaldehyde to form the amine-formaldehyde resin.

36. A method according to claim 35, wherein the compound of the formula (I) is urea.

37. A method according to claim 34 or 35, wherein the C26 alkylene glycol is diethylene glycol.

38. A method according to any one of claims 35 to 37 substantially as herein described and exemplified.

39. An amine-formaldehyde resin prepared by the method of any one of claims 35 to 38.

40. A film comprising a cured amine-formaldehyde resin according to claim 39.