GB1579521A

GB1579521A - Phenolic resin binder compositions

Info

Publication number: GB1579521A
Application number: GB91478A
Authority: GB
Original assignee: Ruetgerswerke AG
Current assignee: Rain Carbon Germany GmbH
Priority date: 1977-01-10
Filing date: 1978-01-10
Publication date: 1980-11-19
Also published as: DE2700763A1; BE862203A; YU265377A; IT1090652B; LU78698A1; DE2700763C3; FR2400977B1; FR2400977A1; DE2700763B2; YU39404B

Description

(54) PHENOLIC RESIN BINDER COMPOSITIONS (71) We, RUTGERSWERKE AKTIENGESELLSCHAFT, of Mainzer Landstrasse 217, D 6000 Frankfurt/Main 1, Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to phenolic resin binder compositions. More particularly it relates to binder compositions based on phenol-formaldehyde or other resins for use as thermosetting binders in free-flowing moulding compositions with sand or other inert fillers, which binder compositions are easy to use and give a uniform wall thickness in the moulded article.

From German Offenlegungsschrift 1808673 it is known to use novolac phenolformaldehyde resins in combination with resol phenol resins, synthetic waxes and aromatic monocarboxylic acids as binders for sand in the shell mould process.

German Patent Specification 1 095 516 describes a mixture of novolac phenol resins with hexamethylenetetramine (hexamine), as well as a specific proportion of salicylic acid and sand, in the presence of a water-ethanol mixture as a moistening agent. It is known from German Patent Specification 1 520 069 that these phenol resins, dissolved while still molten in the organic-aqueous solvent, can be used to coat sand.

However, difficulties arise when processing these pourable resin-coated sands on mould blowing machines and heated moulds with raised contours. These difficulties arise because the moulded parts thereby produced do not have uniform wall thicknesses.

Even if after initial deposition it does not already cover the mould in a non-uniform layer, the sand that has been coated on the mould usually falls off in the areas of horizontal-vertical transitions during the curing stage. Curing, which is effected at 150-3500C, causes falling off because of the shock and shaking during the necessary further transportation of the mould.

German Patent Specification 1 962 356 proposes that mixtures of ground phenol-novolac.

hexamine and fillers wetted with mineral oils can be processed to form moulds after mixing with sand. However, compared with pure phenol resins these binders have the disadvantage that they have to be added in fairly large amounts and are therefore qualitatively and commercially less suitable.

German Offenlegungsschrift 2 419 229 describes binders for foundry sand moulds that consist of bentonite, wood flour and polyurethane resins and that are treated, after mixing with sand, with a water-oil emulsion. This moist mixture is then compacted physically into moulds. It is also known to impregnate wood flour with castor-oil in order to be able to reduce the binder proportion, in accordance with German Offenlengungsschrift 2 165 519. The wood flour treated in this manner is processed as an additive, mainly in moist mixtures of sand with phenol-resin solutions, diisocyanates and tertiary amine, the binding system curing at room temperature.

German Offenlegungsschrift 2 424 936 discloses the addition of castor-oil as a stabiliser for a plastic, blast-furnace tap-hole ramming mixture which may contain phenol resin as binder.

In these compositions the castor-oil adopts the function of a drying and curing retardant and the plastic mixtures are used to seal tapped blast furnaces.

The subsequent addition of oils or similar acting substances to the resin-coated sand, which could obviate the disadvantage of a pourable, resin-coated sand, is not possible in practice.

Such a treated material would no longer be screenable or sievable on the existing equipment and could not be transported on the usual air-bed. Furthermore, for qualitative reasons, only small amounts of oil should be added to resin-coated sand and these cannot be distributed sufficiently homogeneously in the sand.

The objective therefore arose of providing a binder that does not have the described disadvantages. It has now surprisingly been found that the addition of vegetable oils of the castor-oil type containing hydroxyl groups, or similar synthetically prepared esters and/or fatty acids having a chain length of C12 - C22 and containing free hydroxyl groups, to an organic-aqueous phenol resin solution can eliminate the described disadvantages.

According to the present invention there is therefore provided a binder composition comprising a solution of a resin formed by condensation of a phenol with an aldehyde or a ketone and a fatty acid and/or ester thereof which acid contains at least one free hydroxyl group and has a C12 to C22 chain.

In practice, we have found that such compositions can not only eliminate the abovedescribed disadvantages but also have further advantages compared with the pure phenol resin solutions. Sand coated using the present compostions has only a slight tendency to shed the resin film during transportation, has less tendency to form lumps in storage vessels, and the sand does trickle back from the head of the mould blowing machine.

Certain of the present compositions do not require the addition of a curing agent to give a thermosetting binder, whereas others will; such considerations are not specific to the present composition but are general to the art of phenol resins.

The fatty acid or ester thereof can be contained in a vegetable, hydroxyl group-containing oil such as castor or the like oil preferably with a hydroxyl group number of 120 to 190. The oil is preferably castor-oil containing 80 to 85% by weight of the triglyceride of ricinoleic acid.

Such oils typically have an iodine number of 82 to 90, a saponification number of 176 to 190, and a density of 0.961 to 0.963.

The fatty acid or ester when a synthetically prepared ester is preferably a triglyceride of ricinoleic acid having a hydroxyl group number of 120 to 190, and when a fatty acid is preferably ricinoleic acid having a hydroxyl group number of 120 to 190.

The fatty acid or fatty acid ester content in the phenol resin solution is preferably 0.5 to 10% by weight.

The phenol resins can be novolacs, resols or a mixture thereof and are conveniently employed in the form of an organic aqueous solution with a solid resin content of 50 - 75 wt %.

The resins can be prepared using on the one hand phenol, substituted phenols, for example cresols, xylols and longer chain alkyl-phenols, as well as dihydroxyphenols, for example resorcinol and their substituted homologues, and on the other hand aldehydes, for example formaldehyde, acetaldehyde, acrolein, benzaldehyde or furfurylaldehyde, or ketones. The molar ratio of the particular phenol to aldehyde or ketone is typically in the range 1:0.5 to 1:2.5. The phenol resins may also be employed in modified form obtained by chemical conversion of the methylol or phenolic hydroxyl groups thereof, and/or by physical dispersion with a modifying additive. The chemical conversion of the phenol resins may for example be carried out with aminoplast-forming compounds, such as urea, melamine, dicyandiamide and/or epichlorhydrin.Modifying additives for the phenol resin in the form of appropriate thermoplasts, for example a polyvinyl acetal; natural resins, for example a vinsol (Vinsol being a Registered Trade Mark); and hydrocarbon resin, for example a coumarone-indene resin; in an amount of up to 20% by weight are possible, as also are additions of aromatic monocarboxylic acids, for example salicylic acid, and/or metal soaps or their free acids, for example stearic acid. These additives are largely only physically distributed in the phenol resin.

To prepare novolac phenol resins, a phenol to aldehyde or ketone molar ratio of 1:0.5 to 1:0.9 is used with an inorganic or organic acid catalyst. Examples of suitable catalysts are hydrochloric acid, sulphuric acid, phosphoric acid, sulphonic acids of organic compounds, oxalic acid, maleic acid, acetic acid, as well as phthalic anhydride and acid salts of an organic acid with a divalent or trivalent cation e.g. zinc acetate.

To prepare resol phenol resins, a phenol to aldehyde or ketone molar ratio of 1:1 to 1:2.5 is used with a base or basically reacting substance as catalyst. Suitable catalyst include for example alkali metal and alkaline earth metal hydroxides, carbonates and sulphites, and also nitrogen-containing inorganic or organic compounds, for example ammonia, hexamine, triethanolamine, or other secondary or tertiary amines.

Other components of the solvent mixture of the resins in addition to water are generally C1 to C5 monohydric or polyhydric alcohols, for example methyl alcohol, ethyl alcohol, n- and isopropyl alcohol or butyl alcohol, and also furfuryl alcohol, and/or ketones, for example dimethyl ketone or diethyl ketone. In these phenol resin solutions the proportion of phenol resin is usually 50 to 75%by weight with the solvent mixture normally containing 10 to 40% by weight of water.

Thermosetting of novolac-based binder compositions is preferably carried out after adding a formaldehyde donor, for example hexamine or paraformaldehyde. Hexamine for example is typically added in an amount of 1 to 20% by weight referred to the binder solution.

Resol-based binder compositions do not require such curing agents.

Thermosetting binders derived from binder compositions do not require such curing agents.

Thermosetting binders derived from binder compositions of the invention can be used to coat granular inorganic fillers whereby a moulding composition is obtained.

A lubricant and/or mould release agent, for example a metal soap such as calcium stearate or an acid amide, may be added. An amount of 1 to 4%by weight referred to the phenol resin solution is usually added during coating of the filler with the binder.

Inert fillers which can be coated using the present phenol resin binders include quartz sand, chrome ore sand, zirconium sand, corundum and/or other inorganic granular materials.

Quartz sand having a grain size range of up to 1.0 mm is preferably used.

Quartz sand coated using the present phenol resin binders can be used to produce foundry cores and moulds, finished structural elements, abrasive tools, and other moulded articles.

Coated quartz sand or other inert filler of similar grain distribution may be prepared using 1 to 6% by weight of resin solution, referred to the filler, and also advantageously hexamine (if the resin is a novolac) and calcium stearate in the already mentioned amounts. The amount of binder used depends on the specific surface of the filler.

The coating with the phenol resin binder is advantageously effected by premixing the filler, which may be preheated to a temperature of for example up to 1200 C, with any hexamine and then adding the phenol resin solution. In this respect, the solvent is driven off by air (if necessary heated air) blown into the mixture. The resulting resin-coated filler is free-flowing and can be passed at a pressure of 2 to 6 atmospheres excess pressure to a heated mould, compressed, and compacted, with the addition of heat, into moulded parts of uniform wall thickness.

The degree of uniformity of the mould wall thickness can be expressed by means of a so-called formability index. The core size is determined by means of a test apparatus specifically developed for this purpose. The apparatus consists of a glass or plastics powder funnel having an upper width of 150 mm and a lower outlet of 20 mm diameter. A DIN test screen (DIN 4188) with a mesh width of 1.25 mm is arranged at a distance of 50 mm below the funnel outlet. The powder funnel, closed at the bottom with a stop, is filled with 300 g of the free-flowing, resin-coated filler. The powder funnel stop is then opened so that the contents fall from the funnel on to the screen and largely remain on the latter.The filler remaining on the screen, expressed as a fraction of the amount initially weighed and multiplied by 100, is referred to, in percent by weight, as the formability index for evaluating the uniformity of the wall thickness.

The processing properties of the phenol resin-coated filler are optimised when the formability index is greater than 80% and less than 95%.

The following Examples illustrate embodiments of the invention in detail. Comparison Examples are included, together with preparations of the resins used.

Preparation 1: A double-walled vessel of the type which can be heated and cooled and of a corrosionresistant material (for example copper or a stainless steel such as one containing 18% chromium, 8% nickel, 2% molybdenum and up to 0.7% carbon) is fitted with a stirrer, thermometer and reflux condenser.

A phenol resin of the novolac type is prepared by adding 660 kg of 37% formaldehyde solution to 1020 of phenol (100 O/o) and 20 of crystalline oxalic acid in the reaction vessel at 90-100 C. The reaction mixture is reacted for a total of 5 hours at 1000C with reflux cooling. Water is then removed from the reaction mixture. at first under the normal pressure and then under reduced pressure of 80-120 mm Hg, until the phenol resin has a melting point of 75-85"C as measured by the capillary method. The phenol resin melt is then dissolved to form a clear solution in a solvent mixture consisting of 420 kg of 95 % technical ethyl alcohol and 125 kg of water.

Preparation 2: The preparation of a phenol resin of the resol type was carried out in the type of apparatus described in Preparation 1. 400kg of phenol (100%) and 10kg of sodium carbonate were heated to 60 - 65"C and 655kg of 37% formaldehyde solution was then added. After 2 hours the reaction temperature was raised to 75 - 80"C and maintained at this temperature for 2 to 22 hours until the specified reactivity (at 1300C) was obtained. The reaction mixture was then dried in vacuo until the solid resin exhibited a softening point of 45 - 50"C. The solid resin was dissolved in a solvent mixture consisting of 158kg of 95 % technical ethyl alcohol and 42kg of water. The solids content was then approximately 72 % by weight.The pH value was adjusted to 5 - 6 by dissolving 2 - 4% by weight of salicylic acid in the mixture.

Preparation 3: 50% by weight of a novolac solution prepared according to Preparation 1 was homogeneously mixed with 50% by weight of a phenol-resol solution prepared according to Preparation 2.

Example 1: 3% by weight of castor-oil was dissolved in a phenol-novolac solution prepared according to Preparation 1.

Comparison Example 1 3 % by weight of linseed oil was dissolved in a phenol-novolac solution prepared according to Preparation 1.

Comparison Example 2 3 % by weight of mineral oil was mixed with a phenol-novolac solution prepared according to Preparation 1.

Example 2: 3% by weight of a synthetically prepared ester of ricinoleic acid was dissoved in a phenol-resol solution prepared according to Preparation 2.

Comparison Example 3 3 % by weight of linseed oil was dissolved in a phenol-resol solution prepared according to Preparation 2.

Comparison Example 4 3 % by weight of mineral oil was mixed with a phenol-resol solution prepared according to Preparation 2.

Example 3: 8% by weight of ricinoleic acid was dissolved in a phenol-novolac-resol solution prepared according to Preparation 3.

Comparison Example 5 3% by weight of wood oil was mixed with a phenol-novolac-resol solution prepared according to Preparation 3.

Comparison Example 6 3% by weight of paraffin oil was mixed with a phenol-novolac-resol solution prepared according to Preparation 3.

The resin solutions prepared according to Preparation 1, Example 1, and Comparison Examples 1 and 2 were processed according to the following formulation into phenol resin-coated quartz sand: 1000 parts by weight of quartz sand having a grain size of 0.1 - 0.315 mm were heated to 60 - 65"C, mixed dry with 3.4 parts by weight of hexamine and then mixed with 34g of the particular phenol resin solution for about 4 minutes, air being blown through the mixture in order to evaporate the solvent.

The sintering temperature was determined on a Kofler bench, and the cold bending strength of GF standard test bodies (cured at 4 atmospheres excess pressure and 3 minutes at 230"C) and the formability index were measured according to the method described at the beginning. The resin of Preparation 1 is imparted a formability index of about zero to the resin-coated quartz sand. The resin according to Example 1 satisfied all the required properties. The resin according to Comparison Example 1 was much too moist, resulting in too low a sintering temperature and a too high formability index. The resin according to Comparison Example 2 immediately exhibited demixing or separation phenomena and produced a large quantity of fumes. Moreover, the mechanical cold bending strength was 10% less than in the case of Example 1.

In addition, quartz sand coated with resins according to Examples 2 and 3 was substantially less free-flowing than that of Example 1. The actual values obtained and those for the subsequent tests are summarised in the accompanying table.

The phenol resin solutions prepared according to the Preparation 2, Examples 2 and Comparison Examples 2 and 3 were processed in accordance with the following formulation into phenol resin-coated quartz sand 1000.0 parts by weight of sand (as used above) 0.5 parts by weight of hexamine 34.0 parts by weight of phenol resin solution The tests on the phenol resin-coated sand were carried out as above: Resin prepared according to Preparation 2 imparted a formability index approximately equal to zero to the resin-coated sand. The resin according to Example 2 satisfied the quality requirements. The resin according to Comparison Example 3 produced a moist, resin-coated moulding sand and tended to result in lump formation of the latter. The resin according to Comparison Example 4 immediately exhibited demixing or separation phenomena and produced copious fumes on thermosetting.

The phenol resin solutions prepared according to Preparation 3, Example 3 and Comparison Examples 5 and 6 were processed in accordance with the following formulation into phenol resin-coated quartz sand.

1000.0 parts by weight of sand (as used above) 2.0 parts by weight of hexamine 34.0 parts by weight of phenol resin solution The phenol resin-coated sands were tested as described above.

The sand coated with resin solution according to Preparation 3 gave a formability index approximately equal to zero. The resin-coated sand prepared according to Example 3 corresponded in all its properties to the specified requirements. The resin-coated sand prepared with resin according to Comparison Example 5 resulted in too moist a sand and thus gave too high a formability index. In addition, the free-flowing property was too low and the tendency of the sand to form lumps was too great. Resin according to Comparison Example 6 immediately exhibited demixing phenomena and fumed excessively on heat curing the resin-coated sand.

Phenol Resin Solution* P1 P2 P3 E1 C1 C2 E2 C3 C4 E3 C5 C6 A. Miscibility of additive with the phenol resin - - YES YES NO YES YES NO YES YES NO solution B. Coating time in minutes 7 8 7.6 7.1 7.6 7.8 8.3 8.9 9.4 7.6 8.6 9.0 Formability index in % 5 9 8 92 98 96 94 99 98 95 98 98 Sintering temperature in C 102 80 97 96 78 86 90 75 80 92 80 84 Lump formation tendency NO NO NO NO YES NO NO YES NO NO YES NO Cold bending strength in N/cm2 700 680 695 730 600 620 720 625 640 700 600 610 * P Preparation Number E Example Number C Comparison Example Number

Claims

WHAT WE CLAIM IS:

1. A binder composition comprising a solution of a resin formed by condensation of a phenol with an aldehyde or a ketone, and a fatty acid and/or ester thereof which acid contains at least one free hydroxyl group and has a C12 to C22 chain.

2. A composition according to Claim 1 wherein the acid and/or ester is contained in castor-oil or a like vegetable oil.

3. A composition according to Claim 2 wherein the oil has a hydroxyl group number of 120 to 190.

4. A composition according to Claim 3 wherein the oil is castor-oil containing 80 to 85% by weight of the triglyceride of ricinoleic acid.

5. A composition according to Claim 1 wherein the fatty acid and/or ester is synthetically prepared.

6. A composition according to Claim 5 wherein the acid and/or ester is an ester.

7. A composition according to Claim 6 wherein the ester is a triglyceride of ricinoleic acid.

8. A composition according to any one preceding claim wherein the fatty acid and/or ester thereof constitutes 0.5 to 10% by weight of the composition.

9. A composition according to any one preceding claim wherein the solution has a dissolved solid content of the resin of 50 to 75% by weight.

10. A composition according to any one preceding claim wherein the resin is a novolac resin.

11. A composition according to any one of Claims 1 to 9 wherein the resin is a resol resin or a novolac-resol resin mixture.

12. A composition according to any one preceding claim which contains a formaldehyde donor.

13. A composition according to Claim 12 wherein the donor is hexamethylenetetramine.

14. A binder composition substantially as hereinbefore described in any one of Examples 1 to 3.

15. A moulding composition comprising an inorganic granular filler coated with a thermosetting binder derived from a binder composition according to any one preceding claim.

16. A composition according to Claim 15 wherein a filler is quartz sand.

17. A moulded article made from a moulding composition according to Claim 15 or 16.

18. A moulded article according to Claim 17 which is a foundry case or mould.

19. A method for preparing a moulding composition wherein a heated filler and a solution of a binder are mixed together and air is blown through the mixture, the binder solution comprising a resin formed by condensation of a phenol with an aldehyde or ketone, a fatty acid or ester thereof which acid contains at least one free hydroxyl group and has a C12 to C22 chain, and if appropriate a curing agent.

20. A method according to Claim 19 wherein 1 to 6 % by weight of the binder solution is employed, based on the weight of the filler.

21. A method according to Claim 19 or 20 wherein 1 to 20% by weight of curing agent is included in the binder solution.

22. A moulding composition when prepared by a method according to any one of Claims 19 to 21.