GB2140017A - Phenolic resin binder compositions exhibiting low fume evolution in use - Google Patents

Abstract

Binder compositions comprise a liquid, aqueous alkaline phenol-formaldehyde resole resin and from 10-150% by weight of a curing agent comprising a major proportion of at least one formate and/or acetate ester of a mono- or polyhydric phenol reactive with formaldehyde. The binder compositions are useful in the manufacture of bonded granular refractory materials such as foundry moulds and cores. The binder compositions are capable of curing rapidly under alkaline conditions and they exhibit a reduced tendency to evolve noxious fumes during use.

Description

SPECIFICATION Phenolic resin binder compositions exhibiting low fume evolution in use This invention relates to compositions particularly intended for the manufacture of bonded granular refractory materials, such as foundry moulds and cores. More particularly, the invention relates to binder compositions capable of curing rapidly under alkaline conditions which exhibit a reduced tendency to evolve noxious fumes during use.

Highly condensed alkaline phenolic resoles have found application as binders for particulate refractory materials, for example, in the bonding of sand to make moulds and cores for foundry use. It is also known, for example, from Japanese Patent No. 130627/1975, UK Patent Application 2059972 and UK Patent Application 8201668 to employ esters as a means of crosslinking alkaline phenolic resins for such applications.

Such compositions offer many advantages in use including the ability to set rapidly at moderate temperatures, the absence of objectionable elements such as sulphur, the ability to set in the presence of materials having an alkaline reaction and, when employed for metal casting, the ability to provide castings of superior surface finish.

Potassium hydroxide catalysed phenol formaldehyde polymers having a molecular weight of 700-2000 and an F: P ratio of 1.5-2.6:1-give the best performance as foundry binders in terms of speed to set with esters and the resultant strength of the core or mould setting at room temperature. However, they tend to evolve formaldehyde on contact with molten metal upon casting, particularly at intermediate temperatures from 350-600'C, where evolved formaldehyde is not ignited and particularly when the F: P ratio is above 1.7:1.

We have now found that compositions which exhibit a greatly reduced level of fume evolution on casting, while preserving the several advantages recited, can be produced by employing, as the ester component or as part of the ester component, certain esters of compounds which are capable of undergoing reaction with formaldehyde.

Esters which are suitable for the purposes of the present invention are the formates and acetates of phenol and its homologues and of polyhydric phenols and their homologues, chosen for their ability to react with formaldehyde as it is released at intermediate casting temperatures.

Moreover, they have the advantage that on saponification with the alkali metal from the phenolic resin, the phenol released will react with methylol groups on the resin molecule and be absorbed within the resin structure. This ester type is thus unique in that the alcohol (phenol) 'no longer remains as a diluent in the crosslinked product, resulting in higher crosslinked density, higher heat distortion temperature and better chemical resistance.

Accordingly, the present invention comprises a binder composition comprising a liquid, aqueous alkaline phenol-formaldehyde resole resin and, as curing agent therefor, from 10 to 1 50 percent by weight of a composition comprising a major proportion of at least one formate and/or acetate ester of a mono- or polyhydric phenol reactive with formaldehyde.

The types of esters claimed in the present invention are the formates and acetates of o-cresol, m-cresol, p-cresol and their mixtures, all isomers of xylenol, particularly 3,5-xylenol, meta ethyl phenol, resorcinol, catechol, hydroquinone, pyrogallol, phloroglucinol, chlorophenol, o-hydroxy diphenyl, para hydroxy diphenyl, diphyhenylol methane, phenol formaldehyde novolacs, diphenylol propane, mimsoa, quebracho, tannins, lignins, vinsol and related products.

It is not necessary for the dihydric and polyhydric phenols to be completely esterified by reaction with formic or acetic acid. The mono ester will cause crosslinking of the phenolic resin to occur and release the phenol to absorb formaldehyde, although it may be necessary to use higher proportions of the mono ester to achieve setting speed.

the present invention also envisages the use of a mixture of esters which may include esters of components not reactive towards formaldehyde. such mixtures may be used to achieve specific setting rates or other properties.

The proportion used on the liquid resole resin will depend upon the composition of the resin (its F:P ratio and KOH : P ratio) and the composition of the ester.

It is usual to use from 15-40% of most esters on the phenolic resole resin. However, in this case, because of the higher molecular weight of the ester and the fact that only one ester grouping may be present, proportions of up to 150% may be used under the same circumstances. However, it will be normal to use from 20-60% of the esters of the present invention on the alkaline phenolic resole.

Although the the compositions of this invention find particular application in the foundry industry to provide a cold setting binder, they need not be confined to this use, but will find applications in many industries, e.g. for casting, laminating, moulding, impregnating, and the like.

The following examples are quoted in order to illustrate but not limit the invention.

Manufacture of phenol formaldehyde resin solution: 100% phenol was dissolved in 50% aqueous KOH in an amount corresponding to the desired KOH : phenol molar ratio (from 0.5 to 1.2). The solution was heated to reflux and 50% aqueous formaldehyde was added slowly, whilst maintaining reflux, in an amount corresponding to the desired formaldehyde: phenol molar ratio (1.6 to 2.0). The reaction mixture was maintained under reflux until it attained a predetermined viscosity corresponding to the desired value of the weight average molecular weight. If desired, the solids content may be adjusted, for example, by distillation, but this is not usually necessary and constitutes a further advantage of the invention. In some cases, minor amounts of KOH may be added to adjust the KOH : phenol ratio, but this would not be necessary in full scale production.The resin solution is cooled to 40"C and 0.4% by weight on the weight of the resin solution of gamma-aminopropyl triethoxy silane added.

General methods of preparation of hydroxyaryl acetates 1 gramme mole of the appropriate phenol was dissolved in an equivalent weight of pyridine and reacted with 200 mi of acetic anhydride per gramme -OH group at 100"C for 1 hour.

Excess acetic anhydride and pyridine were distilled off under vacuum. The resultant liquid was dissolved in excess petroleum ether and washed thoroughly with a 5m aqueous solution of HCI to remove any residual pyridine. The extract was dried over anhydrous sodium sulphate and the petroleum ether distilled off.

In some preparations, it was found necessary to employ chloroform in place of petroleum ether, to improve solubility.

Using the above method, mono- (and, if appropriate, di- and tri-) acetates were made of the following compounds: PHENOLIC COMPOUND PHASE OF ACETATE catechol solid pyrogallol solid 4-methyl catechol liquid o-cresol liquid p-cresol liquid quinol solid phloroglucinol solid phenol liquid 4,4-diphenolol propane solid resorcinol acetate 1:1 liquid resorcinol acetate 1:0.4 liquid resorcinol acetate 1:0.25 liquid Use of hydroxyaryl acetates as cross-linking agents.

Use of hydroxyaryl acetates as crosslinking agents for the phenolic resins made as above in the binding of sand for foundry moulds and cores.

1,000 g of Chelford 50 sand was mixed with 4.5 9 of the appropriate hydroxyaryl acetate for 30 seconds, then 1 5 9 of the resin made as above were added and mixed for a further 1 minute 30 seconds in a heavy-duty laboratory core sand mixer.

The sand was immediately discharged, core samples made and compression strengths measured at cure time intervals.

Small sample cores were fired into a hot zone at 400 C, nitrogen gas passed over the core for 20 minutes. Any formaldehyde released was absorbed into 0.2% acetyl acetone solution heated for 1 5 minutes at 60"C and the absorption measured on an IR spectrophometer. Formaldehyde released was expressed as ug/g of sand.

The results are summarized in the following table.

TABLE 1 SAND Chelford 50 % RESIN ON SAND 1.5% (P: F = 1: 2.0, P: KOH = 1: 0.87) % CATALYST ON RESIN 30% CATALYST COMPOSITION triacetin 9 6 7.5 8.25 4.5 butyrolactone - - - - 4.5 resorcinol diacetate - 3 1.5 0.75 COMPRESSION STRENGTH kN/m2 after 1 hour 1675 1135 1675 1825 after 2 hours 2615 1825 2565 2660 after 4 hours 3400 2760 3500 3400 after 24 hours 4500 5000 5000 5100 4500 Formaldehyde evolved at 400 C in ug/g sand 120 51 87 95 116.4 TABLE 2 SAND . . .100 PARTS BY WEIGHT RESIN .. . . 1.5 PARTS BY WEIGHT ESTER .. 0.45 PARTS BY WEIGHT BENCH SET FORMAL COMPO- SAND LIFE TIME DEHYDE RESIN SITION TEMP.MIN- MIN- EVOLUTION HYDROXYARYL ESTER P: F KOI ì: P C UTES UTES ug/g of sand Resorcinol diacetate R:A=1:2.0 1:1.5 1:0.78 25 3 5 5.7 Resorcinol diacetate R:A=1:0.8 1:1.5 1:0.78 25 6 9 6.1 Resorcinol diacetate R:A=1:0.5 1:1.5 1:0.78 25 14 20 4.6 30% Catechol diacetate in 1:1.5 1:0.78 24 4 6 14.0 10% Pyrogallol diacetate inBL* 1:1.5 1:0.78 24 4 6 12.0 30% 4-Methylcatechol DA in 1:1.5 1:0.78 24 4 6 13.0 30% o-Cresol diacetate in BLv 1:1.5 78 24 4.5 6 15% Quinol diacetate in BL* 1::1.5 78 26 3 5 15.0 15% Phloroglucinol TA in BL 1:1.5 1:0.78 26 3 5 15.0 15% 4,4 -Diphenylolpropane diacetateinBL* 1:1.5 1:078 26 4.5 6 - 30% Phenyl acetate in BU 1:1.5 1:0.78 26 3.5 5.5 Butyrolactone 1:1.5 1:0.78 24 4 7 14.6 Triacetin 1:1.5 1:078 24 15 19 20.0 30% Catechol diacetate inBL* 1:2.0 1:0.64 26 2.5 3.5 17.0 10% Pyrogallol diacetate in BL" 1:2.0 1:0.64 26 2.5 3.5 17.0 30% 4-Methylcatechol DAinBL* 1:2.0 1:0.64 26 3 5 30% o-Cresol diacetate in BL* 1:2.0 1:0.64 26 3 4 10.7 15% Quinol diacetate in BL 1:2.0 1: :0.64 26 2.5 3.5 15% Phloroglucinol TA in BL* 1:2.0 1:0.64 26 2.5 3.5 15% 4,4 -Diphenylolpropane diacetate in BL* 1:2.0 1:0.64 26 3 5 30% Phenyl acetate in BL* 1:2.0 1:0.64 26 2.5 3.5 Butyrolactone 1:2.0 1:0.64 26 3 5 22.0 Triacetin 1:2.0 1:0.64 26 14 18 30.0 * DA = diacetate BL = butyrolactone

Claims (8)

1. A binder composition comprising a liquid, aqueous alkaline phenol-formaldehyde resole resin and from 10 to 150% by weight of the composition of a curing agent comprising a major proportion of at least one formate and/or acetate ester of a mono- or polyhydric phenol reactive with formaldehyde.

2. A binder composition according to claim 1, wherein the curing agent comprises at least a major proportion of one or more formate and/or acetate esters of a mono- or polyhydric phenol selected from o-cresol, m-cresol, p-cresol, all isomers of xylenol, m-ethylphenol, resorcinol, catechol, hydroquinone, pyrogallol, phloroglucinol, chlorophenol, o-hydroxydiphenyl, p-hydroxydiphenyl, diphenylol methane, phenol-formaldehyde novolacs, diphenylol propane, mimsoa, quebracho, tannins, lignins, vinsol and mixtures thereof.

3. A binder composition according to claim 2, wherein the curing agent comprises an acetate selected from resorcinol diacetate, o-cresol diacetate, phloroglucinol triacetate, 4,4'diphenylolpropane diacetate, phenyl acetate, 4-methylcatechol diacetate and quinol diacetate.

4. A binder composition according to any one of claims 1 to 3, wherein the curing agent additionally contains one or more esters of a compound not reactive with formaldehyde.

5. A binder composition according to claim 4, wherein, the ester of a compound not reactive with formaldehyde is triacetin or butyrolactone.

6. A binder composition according to any one of claims 1 to 5, wherein the liquid, aqueous alkaline phenol-formaldehyde resole resin is a KOH-catalysed phenol-formaldehyde resin having a molecular weight of from 700 to 2000 and a formaldehyde to phenol molar ratio of from 1.5 to 2.6:1.

7. A binder composition according to any one of claims 1 to 6, wherein the curing agent is present in an amount of from 20 to 60% by weight of the composition.

8. A foundary moulding composition comprising a granular refractory material and from 1 to 5% by weight of the composition of a binder according to any one of claims 1 to 7.