EP1181120A2

EP1181120A2 - Urethane foundry binders

Info

Publication number: EP1181120A2
Application number: EP00935373A
Authority: EP
Inventors: Richard David Lewis Simmons; Andrew Michael Penson
Original assignee: Borden Chemical UK Ltd
Current assignee: Hexion UK Ltd
Priority date: 1999-06-03
Filing date: 2000-06-01
Publication date: 2002-02-27
Also published as: WO2000074873A2; NO20015866L; NO20015866D0; AU5091900A; WO2000074873A3; GB9912812D0

Abstract

A two-component foundry binder system which has use in the manufacture of foundry moulds and cores comprises, as a first component, a solution in a solvent of a phenolic resin having free hydroxyl group and, as a second component, a liquid polyisocyanate or a solution of a polyisocyanate which is capable of reacting with the phenolic resin of the first component, when the first and second components are mixed together, to produce a polyurethane. The solvent in the first component comprises at least one 1-4C alkenoic acid ester of a glycol or of a glycol ether.

Description

URETHANE FOUNDRY BINDERS

The present invention relates to urethane foundry binders. More particularly, it relates to binder systems, based on urethane polymers, for use in the production of foundry moulds and cores.

Urethane foundry binder systems are conventionally employed in the form of two components, a resin component, such as a phenolic resin, and a polyisocyanate hardener component which, when mixed together, react to produce a polyurethane. In use, the two components may be mixed together before being mixed with a foundry aggregate, such as sand, or may be mixed with the foundry aggregates sequentially. The resin component, and usually the polyisocyanate component, are employed in the form of solutions in order to keep the viscosities of the components at a reasonably low level so that they can be uniformly distributed throughout the foundry aggregate during mixing. Also, the use of solvents makes it possible for other materials, which can influence or modify the properties of the binder system, those of the moulding mixture, (i.e., the mixture of the binder and the foundry aggregate prior to moulding) or those of the final moulds or cores, to be incorporated.

Conventionally, the resin component and the hardener component require different types of solvents. The isocyanate component is traditionally employed as a solution in a non-polar solvent, typically a high boiling aromatic hydrocarbon, and the phenolic resin component is traditionally employed as a solution in a mixed solvent system comprising a polar solvent, for compatibility with the phenolic resin, and a non-polar solvent, typically a high boiling aromatic hydrocarbon, to provide compatibility with the polyisocyanate. However, since the solvents used for the two components of the binder system need to be compatible with one another so that the complete reaction of the reactive components can take place, care has to be exercised in choosing the solvents to be used. Furthermore, a major problem in the use of traditional urethane binder systems arises because of the continued employment of high boiling aromatic hydrocarbons in the solvent system. It is well known that such materials have strong odours which create an unpleasant working environment. Continued exposure to such materials may be hazardous to human health.

One solution to this problem is offered by EP-A-0771599. According to this, the use of a fatty acid methyl ester as the solvent or solvent component for one or both components of the urethane binder system makes the use of problematical high-boiling aromatic hydrocarbons completely superfluous. Unfortunately, the use of such fatty acid methyl esters appears to have disadvantages in that certain properties, such as the flexural strengths of the cured binder systems, are lower than those obtained when conventional high boiling aromatic solvents are used.

The present invention is based on a discovery of the inventors that these and other disadvantages of the prior art binder systems may be overcome by using a novel solvent system in a two-part urethane binder.

The present invention provides a two-component foundry binder system for use in the manufacture of foundry moulds and cores comprising, as first component, a solution in a solvent of a phenolic resin having free hydroxyl groups and, as second component, a liquid polyisocyanate or a solution in a solvent of a polyisocyanate, which polyisocyanate is capable of reacting with the phenolic resin of the first component, when the first and second components are mixed together, to produce a polyurethane characterised in that the solvent in the first component comprises butyl diglycol acetate.

Where the words "comprising" and "comprises" are used herein it is to be understood that these shall be taken to mean "including" and "includes", respectively, such that the presence of other substances, in the case of a composition, or the presence of other process steps, in the case of a process, are not excluded.

The phenolic resin of the first component of the two-component binder system is preferably a non-aqueous condensation product obtained by the reaction of a phenol, preferably the compound phenol itself, with an aldehyde which typically will be formaldehyde. The phenolic resin will have free hydroxyl groups available for reaction with the isocyanate groups in the polyisocyanate. Typically, the phenolic resin is a predominantly ortholinked benzylic ether phenol-formaldehyde resole resin which is either uncapped or capped with alkoxy groups, such as methoxy, ethoxy, propoxy, isopropoxy, butoxy and isobutoxy groups. Such resins may be prepared by the condensation reaction of phenol and formaldehyde (50% aqueous solution) and/or paraformaldehyde at a temperature of 95 to 105°C in the presence of an ortho-directing catalyst, such as an acetate or naphthenate of zinc, tin, manganese, cobalt or lead. Once the polymer has been condensed to the desired level it is dehydrated under reduced pressure to a specified viscosity and free phenol content. Such phenolic resins are well known in art of two- component urethane foundry binders and suitable resins are described in GB- A-1190644, US-A-4546124 and US-A-5189079.

The second component of the two-component urethane foundry binder system of the present invention comprises an aliphatic, cycloaliphatic or aromatic polyisocyanate preferably having from 2 to 5 isocyanate groups and mixtures of these. Isocyanate prepolymers formed by reacting excess polyisocyanate with a polyhydric alcohol, e.g., a prepolymer of toluene diisocyanate and ethylene glycol, can also be employed. Suitable polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate, and aromatic polyisocyanates such as 2,4- and 2,6-toluene diisocyanate, diphenylmethyl diisocyanate, and the dimethyl derivatives thereof. Further examples of suitable polyisocyanates are 1 ,5-naphthalene diisocyanate, triphenyl methane triisocyanate, xylylene diisocyanate, and the methyl derivatives thereof, polymethylenepolyphenol isocyanates and chlorophenylene-2,4-diisocyanate. Although all polyisocyanates react with the phenolic resin to form a cross-linked polymer structure, the preferred polyisocyanates are aromatic polyisocyanates and particularly diphenylmethane diisocyanate and triphenylmethane triisocyanate.

The polyisocyanate will be employed in sufficient concentrations to cause the curing of the phenolic resin. In general, the polyisocyanate will be employed in a range of 10 to 500 weight percent of polyisocyanate based on the weight of the phenolic resin. Preferably, from 20 to 300 weight percent of polyisocyanate on the same basis is employed.

The polyisocyanate, if liquid, may be used without a solvent although it may also be used in the form of a solution in a solvent in order to ensure thorough and uniform mixing with the other components and with a granular refractory material. Solid or viscous polyisocyanates will have to be employed as solutions in a solvent.

According to a particularly preferred embodiment of the invention, the polyisocyanate will be employed as a solution in a solvent comprising at least one di-isobutyl ester of a dibasic acid, typically a 4-8C alkanedioic acid, since the use of such a solvent system improves the humidity resistance of moulds and cores obtained. Di-isobutyl esters of dibasic acids are polar and, despite the teaching in the art that the use of polar solvents may be detrimental to urethane systems, do not cause any problems of compatibility with the polyisocyanate. Preferably, the di-isobutyl ester will be a di-isobutyl ester of a saturated dicarboxylic acid of general formula HOOC(CH₂)_xCOOH, wherein x is an integer of from 2 to 4, for example di-isobutyl succinate, di-isobutyl glutarate and di-isobutyl adipate and mixtures of two or more of these. Furthermore, these esters have low odour and their use does not create unpleasant conditions in the workplace unlike high-boiling aromatic hydrocarbons such as naphthalene and alkyl-substituted benzenes which are conventionally used as the solvent for the polyisocyanate component in the prior art binder systems.

The di-isobutyl ester of a dibasic acid, or mixtures thereof, may be used as the sole solvent for the polyisocyanate or may be used together with one or more esters selected from 2 to 8C alkyl esters of a 12 to 18C fatty acid. The use of at least one such fatty acid ester, as cosolvent, is found to improve the strength performance of moulds and cores formed from moulding mixtures comprising a binder system containing such cosolvents. Preferably, the esters will be ethyl, butyl or 2-ethylhexyl esters of 12-18C fatty acids and examples of such esters include ethyl oleate, ethyl rapeate, ethyl palmitate (also known as ethyl palmeate), butyl oleate, 2-ethylhexyl palmitate and 2- ethylhexyl cocoate. Where we describe the fatty acid esters as "ethyl rapeate" and "2-ethylhexyl cocoate" what is meant is the ethyl esters and 2- ethylhexyl esters of the fatty acids derived from rapeseed oil and coconut oil, respectively. These may be mixtures of two or more ester compounds such as ethyl oleate, ethyl palmitate, ethyl laurate and the like. We have found that the best strength improvements are obtained in this invention by using ethyl rapeate or ethyl palmitate as the cosolvent for the polyisocyanate component of the binder system. Preferably, the fatty acid ester cosolvent and the di- isobutyl ester of a dibasic acid are used in approximately equal amounts, on a % by weight basis, as the solvent for the polyisocyanate component. Typically this will mean that the total solvent comprises from 20 to 30% by weight of the second component of the binder system.

The first component of the two-component binder system comprises a solution of the phenolic resin in one or more of 1 to 4C alkanoic acid esters of glycols or glycol ethers, i.e., 1 to 4C alkanoic acid esters of lower alkylene diols, such as formates, acetates, propionates and butyrates of ethylene glycol, propylene glycols and butylene glycols and ethers of these. The use of certain types of esters, as solvent for the phenolic resin, has been proposed in the prior art, as mentioned above. The ester solvents used in the prior art, however, have a disagreeable odour or have a detrimental effect on the final properties of moulds and cores obtained from moulding mixtures containing them. We have found that the esters used in the present invention are not only less odorous than the ester solvents proposed in the prior art but that their use as solvents for the phenolic resin gives final products having properties at least as good as those of products obtained using prior art ester solvent systems. Examples of 1 to 4C alkanoic acid esters of"glycols and glycol ethers that can be used include butylene glycol diacetate and butyl diglycol acetate. We particularly prefer butyl diglycol acetate as the solvent for the phenolic resin in view of the good results obtained using it.

As is the case with the polyisocyanate component, the use of one or more fatty acid esters as cosolvent for the phenolic resin component is preferred since these esters enhance the performance of the final products. As mentioned above, these esters are 2 to 8C alkyl esters of 12 to 18C fatty acids, for example ethyl oleate, ethyl rapeate, ethyl palmitate, butyl oleate, 2-ethylhexyl palmitate and 2-ethylhexyl cocoate.

According to a preferred embodiment of the present invention the two- component binder system includes a first component which comprises a solution of a phenolic resin in a solvent system which is a mixture of butyl diglycol acetate (as major solvent component) and a fatty acid ethyl ester (as minor solvent component) and a second component which comprises a solution of a polyisocyanate in a solvent system which is a mixture of 50% by weight of at least one di-isobutyl ester of a dibasic acid with 50% by weight of a fatty acid ethyl ester. Preferably, the fatty acid ethyl ester used as a cosolvent in each of the first and second components of the binder system is selected from ethyl rapeate and ethyl palmitate, with ethyl palmitate being most preferred. It is also preferred that the same fatty acid ethyl ester will be used as cosolvent in both the first and second components of the binder system.

One or both components of the binder system of the present invention may contain one or more other additives to modify the properties of the binder system or products obtained using the binder system. For instance, a silane adhesion promoter such as 3-glycidylpropyl trimethoxysilane may be incorporated in either or both components to improve adhesion between the binder and the foundry aggregate used. Phenylphosphonic chloride, which is known to improve bench life characteristics of moulding mixtures, may also be incorporated.

The present invention also provides a method of making a foundry mould or core which comprises the steps of mixing the two-component binder system as described herein with a foundry aggregate, moulding the resultant mixture into the desired shape and allowing the binder system to harden and cure. The two components of the binder system may be premixed before being added to and being mixed with the foundry aggregate. Alternatively, one of the components of the binder system may be added to and mixed with a granular refractory material and then the other component may be added to and mixed with the existing mixture of the refractory material and binder component.

Curing of the binder will typically be carried out according to techniques known in the art, such as by the use of a gaseous amine, such as triethylamine or dimethylisopropylamine or by the use of a liquid tertiary amine, such as phenyl propyl pyridine, which is incorporated into the mixture of components.

The foundry aggregate, typically sand, will form the major constituent of the mixture with the binder system. The amount of binder used will typically be less than 10% by weight of foundry aggregate and more typically will be in the range of from 0.2 to 5% by weight of the foundry aggregate.

The following examples illustrate the principles and the benefits of the present invention. In the Examples, UCB 150 Base PF is a benzylic ether resole resin prepared as follows:

Pure phenol (1.0 mol) was charged into a reaction vessel, followed by zinc acetate crystals (0.0035 mol) and methanol (0.66 mol). The mixture was held at a specified temperature (60°C) with vigorous stirring and 50% formaldehyde solution added rapidly (1.50 mol). Once addition of 50% formaldehyde solution was complete the reaction mixture was heated to a specified temperature (94-96°C) and held at the temperature range for 60 minutes, the reaction mixture was then subjected to atmospheric distillation followed by distillation under reduced pressure. The distillation was continued until a specified moisture content (3.5-4.5%) was attained, at which point further methanol was added (0.24 mol) and the reaction mixture heated and held at reflux for a period of 4 hours until a specified free formaldehyde (1.5- 2.5%) was attained. Once the free formaldehyde was within specification, lactic acid was added and the reaction mixture distilled under pressure until a specified melt viscosity (4-6 poise) was attained. The phenol-formaldehyde benzylic ether resole thus formed was partially cooled and the solvents added. The mixture was then subjected to centrifugation to remove residual catalyst, after which the silane adhesion promoter was added. EXAMPLES 1 to 6

2kg of HST 60 silica sand was weighed into the mixing bowl of a Kenwood Major mixer and the temperature of the sand was measured. The required amount of hardener (COMPONENT TWO) was weighed into a paper cup and then transferred to the sand. The cup was rinsed out with three portions of sand to ensure that all of the hardener was transferred into the bowl.

The sand and hardener were mixed together for 1 minute to ensure an even sand/hardener mixture (setting 3 on the mixer speed control was used).

The required amount of the part 1 resin (COMPONENT ONE) was weighed into a paper cup and then transferred to the sand. The sand/hardener mixture and the resin were then mixed together to ensure thorough and even mixing.

Immediately after preparing the mixture of the sand, hardener and part 1 resin above the mixture was distributed evenly between longitudinally split moulds. For this, a flexural/transverse box containing six longitudinally split moulds of cross section 22.4 x 22.4 mm and minimum length of 170 mm was used. The sand mixture was packed into the corners of each mould by hand and then rammed into the moulds using a wooden strickling bar. Excess sand mixture was removed by drawing a steel ruler across the top of the box. A small quantity of sand was then placed along the middle of each box and carefully pressed using the steel ruler to ensure a consistent smooth surface across the middle of each bar.

A gassing lid, specially made to fit, was placed onto the top of the flexural box and clamped to the top of the box. Gaseous triethylamine was passed into the box for a period of 5 minutes at a flow rate of 15 cm³/S to cure the samples in the moulds.

The flexural pieces so prepared were then tested as follows.

The first three flexural pieces were tested immediately after the curing procedure was terminated and the fourth, fifth and six pieces were tested one hour after termination of the curing procedure. The seventh, eighth and ninth pieces were tested 24 hours after curing and the tenth, eleventh and twelfth pieces, immediately after termination of the curing procedure, were placed in a humidity cabinet where they remained for 24 hours. They were then removed from the humidity cabinet and tested immediately after removal. The conditions of the humidity cabinet (HL 4033 Heraeus Vosch) were set at 20°C and 100% relative humidity. The results of the flexural testing are shown below in TABLE 4. All flexural strengths are expressed as kg/cm^"2.

TABLE 1 - COMPONENT ONE

^* RPDE-9 (Rhone Poulenc) is a mixture of ~ 15% dimethyl adipate, ~

62% dimethyl glutarate and ~ 23% dimethyl succinate.

^** Glymo Silane is 3-glycidylpropyl trimethoxysilane

The physical properties of the Component One resins are shown below in Table 2.

TABLE 2

TABLE 3 - COMPONENT TWO

Lupranat M20S Isocyanate (BASF) based on diphenylmethane diisocyanate.

Coasol is a trademark of Chemoxy International pic and comprises di-isobutyl glutarate 55-65% di-isobutyl adipate 12-23% di-isobutyl succinate 15-25%

Glymo Silane is 3-glycidylpropyl trimethoxysilane

TABLE 4 - FLEXURAL STRENGTHS (Kg/cm²)

As can be seen from the results shown in TABLE 4 the combinations D/l, E/K, F/L and G/M give particularly good results compared to the prior art systems, showing much improved overall strength performance and humidity resistance. A flexural bench life evaluation was conducted on samples as follows:

A sand/hardener/part 1 mixture was prepared as described above and the mixture was stored in a 2.5 I metal tin. Flexural transverse pieces were prepared as described above.

Two pieces were made immediately and tested after 24 hours (following termination of the curing procedure).

Two pieces were made 30 minutes after commencement of mixing the sand/hardener/part 1 resin together and tested after 24 hours.

Two pieces were made 90 minutes after commencing the mixing of the components and tested after 24 hours.

Two pieces were made 120 minutes after commencing the mixing of the components and tested after 24 hours.

Two pieces were made 180 minutes after commencing the mixing of the components and tested after 24 hours.

The results of the flexural bench life evaluation are shown below in TABLE 5.

All flexural strengths are expressed as kg/cm^"2.

TABLE 5 - FLEXURAL STRENGTH BENCH LIFE EVALUATION (Kg/cm²)

As can be seen from the results shown above in TABLE 5, the combinations C/H and D/J show good bench life characteristics compared to the prior art systems. EXAMPLES 7 - 9

Using the formulations of COMPONENT ONE and COMPONENT TWO, set out in TABLES 6 and 7, respectively, below flexural pieces were prepared as described in Examples 1 to 6 with the exception that a liquid catalyst was incorporated into the binder mixture, as shown, instead of the samples being cured by gassing (as in the case of Examples 1 to 6). Some flexural pieces so prepared were tested as described in Examples 1 to 6, 1 hour after the introduction of the catalyst, others were tested 2 hours after the introduction of the catalyst and others were tested 24 hours after the introduction of the catalyst into the binder mixture. Further samples were kept in a humidity cabinet for 24 hours at 50% relative humidity before being tested.

The results are shown below in TABLE 8.

TABLE 6 - COMPOSITION OF COMPONENT ONE

26.6% mixed aliphatic/aromatic hydrocarbons comprising 7% naphthalene,

18% methyl naphthalene, 7% dimethyl naphthalene and 8% other aromatics

13.0% DBE-9 (Mixture of dimethyl glutarate/dimethyl succinate/dimethyl adipate) TABLE 7 - COMPOSITION OF COMPONENT TWO

Mixed aliphatic/aromatic hydrocarbons comprising 5% naphthalene, 14% methyl naphthalene and 8% dimethyl naphthalene.

TABLE 8 - PERFORMANCE EVALUATION

Phenyl Propyl Pyridine - catalyst addition adjusted to give same strip time

Claims

1. A two-component foundry binder system for use in the manufacture of foundry moulds or cores comprising, as first component, a solution in a solvent of a phenolic resin having free hydroxyl groups and, as second component, a liquid polyisocyanate or a solution in a solvent of a polyisocyanate, which polyisocyanate is capable of reacting with the phenolic resin of the first component, when the first and second components are mixed together, to produce a polyurethane characterised in that the solvent in the first component comprises at least one 1-4C alkanoic acid ester of a glycol or of a glycol ether.

2. A two-component foundry binder system according to claim 1 , wherein the solvent in the first component is butyl diglycol acetate.

3. A two-component foundry binder system according to either claim 1 or claim 2, wherein the solvent in the first component additionally comprises at least one 2 to 8C alkyl ester of a 12 to 18C fatty acid.

4. A two-component foundry binder system according to claim 3, wherein the 2 to 8C alkyl ester of a 12 to 18C fatty acid is ethyl oleate, ethyl rapeate, ethyl palmitate, butyl oleate, 2-ethylhexyl palmitate or 2- ethylhexyl cocoate.

5. A two-component foundry binder system according to claim 4, wherein the solvent in the first component is a mixture of butyl diglycol acetate and ethyl rapeate.

6. A two-component foundry binder system according to claim 4, wherein the solvent in the first component is a mixture of butyl diglycol acetate and ethyl palmitate.

. A two-component foundry binder system according to claim 4, wherein the solvent in the first component is a mixture of butyl diglycol acetate and butyl oleate.

8. A two-component foundry binder system according to claim 4, wherein the solvent in the first component is a mixture of butyl diglycol acetate and 2-ethylhexyl palmitate.

9. A two-component foundry binder system according to any one of claims 1 to 8, wherein the second component comprises a solution of the polyisocyanate in, as solvent, a di-isobutyl ester of a dibasic acid.

10. A two-component foundry binder system according to claim 9, wherein the di-isobutyl ester of a dibasic acid is a di-isobutyl ester of an alkanedioic acid containing 4 to 8 carbon atoms.

11. A two-component foundry binder system according to claim 10, wherein the alkanedioic acid has the general formula HOOC(CH₂)_xCOOH, wherein x is an integer having a value of from 2 to 4.

12. A two-component foundry binder system according to claim 11 , wherein the di-isobutyl ester is selected from di-isobutyl succinate, di- isobutyl glutarate, di-isobutyl adipate and mixtures of two or more of these.

13. A two-component system according to any one of claims 9 to 12, wherein the solvent in the second component additionally comprises at least one 2 to 8C alkyl ester of a 12 to 18C fatty acid.

14. A two-component system according to claim 13, wherein the solvent in the second component comprises a mixture of equal amounts, % by weight basis, of the di-isobutyl ester of the dibasic acid and the 2-8C alkyl ester of a 12-18C fatty acid.

15. A two-component foundry binder system according to claim 13 or claim 14, wherein the 2-8C alkyl ester of a 12-18C fatty acid is ethyl oleate, ethyl rapeate, ethyl palmitate, butyl oleate, 2-ethylhexyl palmitate or 2- ethylhexyl cocoate.

16. A two-component foundry binder system according to claim 13 or claim 14, wherein the solvent in the second component is a mixture of at least one di-isobutyl ester of a dibasic acid with ethyl rapeate.

17. A two-component foundry binder system according to claim 13 or claim 14, wherein the solvent in the second component is a mixture of at least one di-isobutyl ester of a dibasic acid with ethyl palmitate.

18. A two-component foundry binder system according to claim 13 or claim 14, wherein the solvent in the second component is a mixture of at least one di-isobutyl ester of a dibasic acid with butyl oleate.

19. A two-component foundry binder system according to claim 13 or claim 14, wherein the solvent in the second component is a mixture of at least one di-isobutyl ester of a dibasic acid with 2-ethylhexyl palmitate.

20. A two-component foundry binder system according to any one of claims 1 to 19, wherein the polyisocyanate is diphenylmethanediisocyanate.

21. A two-component foundry binder system according to any one of claims 1 to 20, wherein the second component is a solution of polyisocyanate in a solvent which solution additionally contains phenylphosphonic dichloride in an amount not greater than 1% by weight.

22. A method of making a foundry mould or core which comprises mixing the two-component binder system of any one of claims 1 to 21 with a foundry aggregate, moulding the mixture into the desired shape and allowing the binder system to harden and cure.

23. A method according to claim 22, wherein the two components of the foundry binder system are premixed prior to being mixed with the foundry aggregate.

24. A method according to claim 22, wherein the foundry aggregate is mixed with one component of the two-component binder system and then the resulting mixture is further mixed with the other component of the two-component binder system.