CA1134989A - Cold hardening binder for material mixtures for the production of casting moulds and cores - Google Patents
Cold hardening binder for material mixtures for the production of casting moulds and coresInfo
- Publication number
- CA1134989A CA1134989A CA000318783A CA318783A CA1134989A CA 1134989 A CA1134989 A CA 1134989A CA 000318783 A CA000318783 A CA 000318783A CA 318783 A CA318783 A CA 318783A CA 1134989 A CA1134989 A CA 1134989A
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- Canada
- Prior art keywords
- groups
- polyol
- amino
- molecule
- binder
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/30—Low-molecular-weight compounds
- C08G18/32—Polyhydroxy compounds; Polyamines; Hydroxyamines
- C08G18/3271—Hydroxyamines
- C08G18/3278—Hydroxyamines containing at least three hydroxy groups
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
- B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
- B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/30—Low-molecular-weight compounds
- C08G18/32—Polyhydroxy compounds; Polyamines; Hydroxyamines
- C08G18/3271—Hydroxyamines
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/48—Polyethers
- C08G18/50—Polyethers having heteroatoms other than oxygen
- C08G18/5021—Polyethers having heteroatoms other than oxygen having nitrogen
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Mold Materials And Core Materials (AREA)
- Polyurethanes Or Polyureas (AREA)
Abstract
ABSTRACT
A cold-hardening polyurethane-based binder for material mixtures used in the production of casting moulds and cores of the type including polyisocyanate with at least two NCO-groups in the molecule and a polyol with at least two OH-groups in the molecule. The polyol 18 an amino polyol, containing in the molecule at least one.
tertiary amino group, effective as an accelerator.
A cold-hardening polyurethane-based binder for material mixtures used in the production of casting moulds and cores of the type including polyisocyanate with at least two NCO-groups in the molecule and a polyol with at least two OH-groups in the molecule. The polyol 18 an amino polyol, containing in the molecule at least one.
tertiary amino group, effective as an accelerator.
Description
.3~
In casting technology, material mixtures are frequently used for the production of casting moulds and cores, wherein a granular base materiaJ (e.g. quartz or olivine sand) is mixed with a binder, which binder hardens after the mixture has been introduced into a casting box.
For many reasons - not least for reasons of energy economy and in the interests of a simple production method requiring little complicated apparatus - cold-hardening binders are preferred to warm-hardening or hot-hardening binders.
Various types of cold-hardening binders are already in practical use. These include the group of resins of condensation, in particular those based upon furfuryl alcohol, phenol, urea and/or melamine with aldehydes, which can be cold-hardened by strong acids such as sulphuric acid, phos-phoric acid or p-toluene sulphonic acid. Another group includes polyurethane resins, which are reaction products of polyisocyanates with at least two ~CO-groups in the molecule and of polyols with at least two OH-groups in the molecule, to which tertiary amines or chelate compounds are added as accelerators. In this connection also, oil-modified poly-ester resins and corresponding alkyd resins, which are hardened by isocyanates and metallic siccatives, may also be mentioned.
One possible way of working these cold-hardening binders consists in mixing the base materiaL - normally in several successive steps - with all the other constituents of the binder system (including any hardeners, accelerators ;
or catalysts necessary), of then introducing the thus pro-duced material mixture into the casting box, further com-pacting the mixture there if necessary, and leaving it in the casting box until it can be removed as a cast object, ~'t~ '~
.. ~ .
o i.e. a mould or core. The hardening of the binder takes place so slowly, however, that the cast object MUS't be stored for hours after removal from the casting box until it reaches its maximum strength or at least a sufficient degree of strength for the production of good quality castings.
This long waiting period necessary before the cast object can be used, which can amount to more than 24 hours depending upon the type of binder employed, is an important and notable disadvantage in casting practice of the cold~
hardening binders hitherto used. It is indeed possible, with some types of binders, to increase the rate of hardening by substantially increasing -the amount of accelerator added, but this is accompanied by considerable loss of strength and is therefore not acceptable in practice. In addition, the use ~of very large quantities of accelerators with correspondingly high hardening rates can reduce excessively the time available for working the mixture!(i.e. the time within which the mixture must be introduced into the casting box and compacted).
For polyurethane-based binders/ the material may also be worked by the so-called "gas-hardening process". In this process, the binder system is first worked into the mould material mixture without the accelerator and the accelerator is not added until the mixture has been placed in the casting ' box and compacted, the mixture being briefly exposed to a ~
gaseous tertiary amine such as triethylamine in the casting ;
box. This process is poorly suited for the production of larger mouldings, but has gained acceptanc0 in practice for the production of smaller cores and moulds. It possesses also certain advantages, however, for example because the removal of the moulding from the mould is possible within a shorter time, and because a material mixture which does not yet con- ' tain the accelerator has a very long working time. On the
In casting technology, material mixtures are frequently used for the production of casting moulds and cores, wherein a granular base materiaJ (e.g. quartz or olivine sand) is mixed with a binder, which binder hardens after the mixture has been introduced into a casting box.
For many reasons - not least for reasons of energy economy and in the interests of a simple production method requiring little complicated apparatus - cold-hardening binders are preferred to warm-hardening or hot-hardening binders.
Various types of cold-hardening binders are already in practical use. These include the group of resins of condensation, in particular those based upon furfuryl alcohol, phenol, urea and/or melamine with aldehydes, which can be cold-hardened by strong acids such as sulphuric acid, phos-phoric acid or p-toluene sulphonic acid. Another group includes polyurethane resins, which are reaction products of polyisocyanates with at least two ~CO-groups in the molecule and of polyols with at least two OH-groups in the molecule, to which tertiary amines or chelate compounds are added as accelerators. In this connection also, oil-modified poly-ester resins and corresponding alkyd resins, which are hardened by isocyanates and metallic siccatives, may also be mentioned.
One possible way of working these cold-hardening binders consists in mixing the base materiaL - normally in several successive steps - with all the other constituents of the binder system (including any hardeners, accelerators ;
or catalysts necessary), of then introducing the thus pro-duced material mixture into the casting box, further com-pacting the mixture there if necessary, and leaving it in the casting box until it can be removed as a cast object, ~'t~ '~
.. ~ .
o i.e. a mould or core. The hardening of the binder takes place so slowly, however, that the cast object MUS't be stored for hours after removal from the casting box until it reaches its maximum strength or at least a sufficient degree of strength for the production of good quality castings.
This long waiting period necessary before the cast object can be used, which can amount to more than 24 hours depending upon the type of binder employed, is an important and notable disadvantage in casting practice of the cold~
hardening binders hitherto used. It is indeed possible, with some types of binders, to increase the rate of hardening by substantially increasing -the amount of accelerator added, but this is accompanied by considerable loss of strength and is therefore not acceptable in practice. In addition, the use ~of very large quantities of accelerators with correspondingly high hardening rates can reduce excessively the time available for working the mixture!(i.e. the time within which the mixture must be introduced into the casting box and compacted).
For polyurethane-based binders/ the material may also be worked by the so-called "gas-hardening process". In this process, the binder system is first worked into the mould material mixture without the accelerator and the accelerator is not added until the mixture has been placed in the casting ' box and compacted, the mixture being briefly exposed to a ~
gaseous tertiary amine such as triethylamine in the casting ;
box. This process is poorly suited for the production of larger mouldings, but has gained acceptanc0 in practice for the production of smaller cores and moulds. It possesses also certain advantages, however, for example because the removal of the moulding from the mould is possible within a shorter time, and because a material mixture which does not yet con- ' tain the accelerator has a very long working time. On the
- 2 -.
~ ~3~ 3 other hand, an additional process step must be accepted, involving also complicated apparatus, in order that the working area shall not be exposed to the very poisonous and extremely evil-smelling amines. Above all, however, the gas-hardening process does not overcome the chief disadvantage of the hitherto used cold-hardening binders, namely the excessively long storage time required before the moulding can be used.
In connection with the gas-hardening process, German Paten~ DT-OS 2,3~8,226 has proposed a special polyurethane-based binder, which consists of a polyisocyanate and a polyetherpolyol and also an aromatic compound comprising at least two OEI groups as initiator and which can be hardened by a tertiary amine. The polyetherpolyol may contain also tertiary amino groups, and hardening is effected either by gas treatment or by making up two separate batches of sand, of which the one contains the polyisocyanate and the other the remaining constituents of the binder (including the tertiary amine), and mixing these two together shortly before use. This binder is said to counteract the occurrence of certain casting defects, to `
decompose easily after casting and also to result in useful initial strength levels, thus giving a moulding which can be removed from -the casting box in a short time. However, with regard to the storage time necessary before the moulding is usable, this binder is alsonot satisfactory, i.e.
it takes as long to reach its maximum strength as the other familiar systems.
The objective of the present invention is to create -a cold-hardening binder for material mixtures for the pro-duction of casting moulds and cores, which combines suffi-ciently long working times with good values of initial ~ ~ 3~ 4~
strength in the moulding and in particular leads to very much reduced storage times for the moulding, which does not give off any toxic or evil-smelling vapours, and which requires no gas treatment or other involved measures for hardening.
The invention achieves this objective wi-th a poly-urethane-based mould material binder, which consists of a polyisocyanate comprising at least two NCO groups in the molecule and of a polyol comprising at least two OH groups in the molecule, and which according to this invention is characterised in that the polyol is an amino polyol, which contains at least one tertiary amino group in the molecule acting as accelerator.
The invention is based upon the insight that the impractical slow rise in strength with the previously used polyurethane-based cold-hardening binders can be attributed to the fact that the accelerator (that is normally the tertiary amine) is always present in the form of a separate component, and indeed also in only a relatively small quantity, by comparison with the reactive NCO and OH groups.
An accelerator of this type naturally requires a fairly long ~ ;
time to act upon all the NCO/OH pairs. An additional factor ~ ;
is that the accelerator can be incorporated into the end ~ -product in the course of hardening, either chemically or mechanically (in the sense of a steric blockage), which also reduces its activity. Since the rate of hardening depends ~ ~-upon the quantity of accelerators, this inevitably means that the hardening rate steadily decreases in the course of harden- -ing. This can be regarded as one of the reasons -for the need for extraordinarily long storage times before mouldings become usable. A similar situation obtains for the other known binder ! `
systems which are cold-hardening.
_ ~ _ ~.3~
As a logical use of this insight, the invention no longer makes use of a separate accelerator, but instead pro-vides that one of the reaction partners of the system can function simultaneously as a reaction accelerator on the basis of its molecular structure. This resul-ts in a much higher amount of the accelerator being available to the reaction partners, this amount being many times higher than that hitherto usual for the acceleration and possibly being equal to or greater than the stoichiometric quantity, referred to the reactive NCO and OH groups. Thus, in a sense, every NCO/O~I pair now has its own accelerator and this leads to a very constant acceleration, which occurs largely uniformly and simultaneously for all the NCO/OH pairs and leads -to the result that a moulding absolutely ready for use is produced extraordinarily quickly. Correspondingly, it has also been found in practice that the initial strength of a moulding produced with the binder according to this invention is many times higher than the initial values attainable with the hitherto used cold-hardening binders, and that there is no significant increase in strength, even aEter long s-torage.
One fact is especially surprising and not yet explained, namely that, in spite of the very large amount of accelerating tertiary amino groups in the binder accord-ing to this invention, the working time remains, as previously, within a range that is quite acceptable in practice, and that the absolute values of strength achieved are also quite excellent. This is clearly in contradiction to the earlier claim that an increase in the quantity of accelerator, while leading to a more rapid course of the reaction, nevertheless also leads to a substantial reduction in the working time and also reduces considerably the strength values attained.
~ ~! 3 ~
~ he binder according to this invention is also extraordinarily simple to work. It is only necessary to mix the amino polyols (preferably in the form of a solution) and the isocyanates (also preferably in the form of a solution) in approximately equal quantities with the base material, without the addition of any other substances being necessary.
After that, the usual procedure for working can be used, namely the mould material mixture is introduced into the casting box, if necessary further compacted there, and then left in the casting box until removal. In general, the moulding can be removed from the box and handled after only 15 minutes, and after a further 15 minutes (that is 30 minutes in total) it can, if needed, be supplied to the casting process. Besides this simplicity of use and the previously unattained speed of curing, the binder according to this invention also has the advantage that it makes for much better working conditions, because the amino polyols are not harmful to health, nor can they release harmful substances during hardening. Moreover, the finished cores and moulds do not give off any evil smell, an unavoidable consequence up to now in the use not only of amine hardened polyurethane systems, but also (due for example to the splitting off of formaldehyde~
in certain types o~ condensation resins.
In the simplest case, the amino polyols suitable for the binder according to this invention have a tertiary amino group in the molecule, that is they have the structure R
"
/ \ .: ."~
R R ~
where R is any alkyl, cycloalkyl and/or aryl substituent and -where all three R-substituents to~ether contain at least two reactive O~I groups. However, amino polyols compri.sing more than one tertiary amino group are preferred, for which the following general formula is a typical example:
_ _ Rl \ IR5 / R3 N R6- X - R7 - \ R
In this formula:
X is an N or O atom, Rl to R5 are like or different alkyl, cycloalkyl, arylalkyl and/or aryl substituents, including such compounds with heterostructure, which comprise at least two OH groups and which can contain also further functional groups in particular ether bridges, where Rl, R3 and/or R5 can also be H atoms, and R5 does not appear when X is an O atom.
R6 and R7 are like or different alkylene, cyclo-alkylene, arylalkylene and/or arylene substituents, including such compounds with heterostructure, which also may contain OH groups as well as side chains with ether bridges and/or ;
further tertiary amino groups, ~
n is either zero or a positive integer. : :;
m e number of C atoms in the various R-substitue}lts as well as the magnitude of n are not particularly critical, these values are limited in principle only by the requirement that the amino polyol must still be soluble in customary :~
solutions. Molecular weights of up to about 10,000 are possible for the amino polyol. ~ -~^3~
Production o~ the amino polyols can be carried out in accordance with various known processes. It is especially effective to react alkylene oxides, such as ethylene oxide, propylene oxide and the like, with multivalent amines which possess primary and/or secondary amino groups capable of reacting with alkylene oxides and which may additionally contain tertiary amino groups.
Examples of such amines are ethylene diamine, 1,2-propylene diamine, 1,3-diaminopropane, 3-amino-L-methyl-aminopropane' 4,9-dioxadodecane-1,12-diamine, 6,6-dimethyl-4,8-dioxaundecarle-1,11-diamine, dipropylene triamine' N,N'-bis-(3-aminopropyl)-ethylene diamine, bis-(3-aminopropyl)-methylamine, N,N'-dimethyl-~,N' -bis-(3-aminopropyl)-ethylene diamine, bis-(6-aminohexyl)-amine, tripropylene tetramine tetrapropylene pentamine' 2-(aminomethyl)-cyclopentylamine, 1,1-bis-(4-aminophenyl~-cyclohexane, bis-(4-aminocyclohexyl)-methane, bis-(3-methyl-4-aminocyclohexyl)-methane; 2,2-bis-(4-aminocyclohexyl)-propane, bis-(4-aminophenyl)-methane, bis-(4-methylaminophenyl)-methane, bis-(3-methyl-4-aminophenyl)-methane, 3-cyclohexylamino-propylamine, 1,4-diaminobutane, hexamethylene diamine, and 2,5-dimethyl-2,5-diaminohexane.
As can be seen from the general formula given above, individual amino groups of the amino polyols can also be secondary amino groups, although it is more favourable for the ~ .
effect aimed at if as many as possible of all the amino groups :
of the amino polyols have a tertiary structure. The reaction between the alkylene oxides and the amines is therefore pre-ferably carried out in such a manner that the amino polyols which come into being contain primarily or exclusively tertiary amino groups.
::
_ ~ -.. .. :. ~ . .. :. ,: . : . , : . . .-. : -.3L~
The polyisocyana-te.s used in the binder accordiny to this invention can be chosen from any of the common aliphatic, cycloaliphatic, arylaliphatic, aromatic or heterocyclic polyisocyanates used for the production of polyurethane resins, provided they have at least two ~C0 groups.
Examples are diphenylmethane-4,4'-diisocyanate;
2,4-toluol-diisocyanate; phenylene diisocyanate-(1,4), 2,2',6,6'-tetramethyl-diphenylmethane-4,4'-diisocyanate;
diphenyldimethylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate; 2,6-toluoldiisocyanate or isomeric mixtures thereof; diphenyl-4,4'-diisocyanate; triphenyl-4,4',4"-triisocyanate; hexane-1,6-diisocyanate, cyclohexylphenyl-methane-4,4'-diisocyanate; n-xyloldiisocyanate, p-xyloldi-isocyanate; cyclohexane-1,4-diisocyanate, diphenylether-4,4-diisocyanate; or derivatives of these compounds having halogens substituted.
Whereas the amino polyols are used in the form of solutions, as is usually the case in practice, any polar and non-polar solvents as well as protic or aprotic solvents may be used. It is effective to dissolve the amino polyols in the same solvent (or the same mixture of solvents) as is used for the polyisocyanates.
Examples of suitable solvents are benzene, xylol, cymol, solvent naphtha (e.g. Supersol M, made by British Petroleum), tetrahydronaphthaline, diacetone alcohol, methylethylketone, cyclohexamone, isophoron, ethylene glycolmonopropylether, dioxane, dimethylformamide, methyl-glycolacetate, and ethylglycolacetate.
The rate of hardening of the binder according to this invention can moreover be controlled through the solvent, the rule being that the higher the degree of polarity of the _ g _ ~,3 ~ d~
solvent, the higher will be the rate o-f hardening. A further possible way o~ in-fluencing the rate of hardening consists of selecting the molecular structure in such a way that either more or less strongly reactive polyisocyanates and amino polyols come in-to use, according to -the immediate need.
The invention is explained below by means of an example of embodiment thereof and is compared with two reference examples.
Illustrative Example:
From 1,3-diaminopropane and propylene oxide in molar ratio 1,4, N,N,N', N'-tetrakis-(2-hydroxypropyl)-1,3-diamino-propane was produced. 50 g of a 50% solution of this amino-polyol in solvent naphtha (Supersol M, manufactured by British Petroleum) were added to 5 kg of washed and dried quartz sand, together with 50 g of an 80% solution of 4,4'-diphenylmethane diisocyanate-prepolymer (the commercial product Baymidur 83 made by Bayer AG) in the same solvent.
The mixture was agitated for 30 seconds. Finally, the mixture was used to make test pieces according to German Industrial Standard 52401 (DIN 52401), and the bending strength of the forms was measured. The results are summarized in the following table. -Compa ison Example 1:
Using 5 kg of quartz sand of the same type as in the illustrative example of the invention, a material mixture was made with the addition of 70 g of a cold-hardening con-densation resin containing 70% furfuryl alcohol and about 5% nitrogen and also 30 g of a 65% aqueous solution of p-toluol sulfonic acid. The sand was first mixed with the acid for 15 seconds, then the resin was added, and then the whole was mixed for a further 30 seconds. Test pieces were then made and examined in the same way as in the example of ~; -' 10 -- . . . . ., , ~ . . . ~ , . - . . .
~l3~
the invenkion. The results are a]so given in the table below.
Comparison Exam~e_2:
Using again 5 kg of the same type of ~uartz sand and 80 g of an oil-modi-fied alkyd resin, which was treated with cobalt siccatives, and also 20 g of 4,4'-diphenylmethane diisocyanate prepolymer (saymidur 88), a material mixture was produced. The mixture was made using the same procedure as in the example of the invention. Test pieces were then made and examined in the same manner as in the example of this invention. The results obtained here also are given in the table below.
T A B L E: bending strength in N/cm - , after min. min. min. min. min. min. hrs.
__________________________________ ____________________________ Invention 40 270 320 520 600 670 720 Comparison 1 - - - 90 110 200 470 Comparison 2 - - - - 20 100 330 The superiority of the binder according to this invention over kno~n cold-hardening binder systems is clearly evident from this table. The test pieces made with the binder according to this invention reach within lS minutes a strength ~-level which, in practice, is ~uite sufficient for the mouldings to be removed from the casting boxes, and after only 20 or 30 minutes they reach strength levels which are suitable for casting in practice. After 60 minutes, the maximum strength has substantially been reached, i.e. the rise in strength in the period 60 minutes - 24 hours is only slight.
By constrast, the known binders according to the two comparison examples harden only very slowly, and in particular they take a lorlg time to reach a usable degree of strength. Mouldings made from them cannot in practice be removed until 45 to 60 minutes have passed, and they cannot ..
be used until 6 to 24 hours have elapsed and they have reached the.ir maximum strengths. At the same time, the absolute values of the final strength reached in the two comparison examples are clearly lower than the absolute value of the fina]. strength reached in the example illustrating this invention. If, in the two comparison examples, the amount of accelerator were to be increased in order to increase the rate of hardening, the resultant strength values would be still worse and, in fact, would no longer be acceptable.
, ' :
~ ~3~ 3 other hand, an additional process step must be accepted, involving also complicated apparatus, in order that the working area shall not be exposed to the very poisonous and extremely evil-smelling amines. Above all, however, the gas-hardening process does not overcome the chief disadvantage of the hitherto used cold-hardening binders, namely the excessively long storage time required before the moulding can be used.
In connection with the gas-hardening process, German Paten~ DT-OS 2,3~8,226 has proposed a special polyurethane-based binder, which consists of a polyisocyanate and a polyetherpolyol and also an aromatic compound comprising at least two OEI groups as initiator and which can be hardened by a tertiary amine. The polyetherpolyol may contain also tertiary amino groups, and hardening is effected either by gas treatment or by making up two separate batches of sand, of which the one contains the polyisocyanate and the other the remaining constituents of the binder (including the tertiary amine), and mixing these two together shortly before use. This binder is said to counteract the occurrence of certain casting defects, to `
decompose easily after casting and also to result in useful initial strength levels, thus giving a moulding which can be removed from -the casting box in a short time. However, with regard to the storage time necessary before the moulding is usable, this binder is alsonot satisfactory, i.e.
it takes as long to reach its maximum strength as the other familiar systems.
The objective of the present invention is to create -a cold-hardening binder for material mixtures for the pro-duction of casting moulds and cores, which combines suffi-ciently long working times with good values of initial ~ ~ 3~ 4~
strength in the moulding and in particular leads to very much reduced storage times for the moulding, which does not give off any toxic or evil-smelling vapours, and which requires no gas treatment or other involved measures for hardening.
The invention achieves this objective wi-th a poly-urethane-based mould material binder, which consists of a polyisocyanate comprising at least two NCO groups in the molecule and of a polyol comprising at least two OH groups in the molecule, and which according to this invention is characterised in that the polyol is an amino polyol, which contains at least one tertiary amino group in the molecule acting as accelerator.
The invention is based upon the insight that the impractical slow rise in strength with the previously used polyurethane-based cold-hardening binders can be attributed to the fact that the accelerator (that is normally the tertiary amine) is always present in the form of a separate component, and indeed also in only a relatively small quantity, by comparison with the reactive NCO and OH groups.
An accelerator of this type naturally requires a fairly long ~ ;
time to act upon all the NCO/OH pairs. An additional factor ~ ;
is that the accelerator can be incorporated into the end ~ -product in the course of hardening, either chemically or mechanically (in the sense of a steric blockage), which also reduces its activity. Since the rate of hardening depends ~ ~-upon the quantity of accelerators, this inevitably means that the hardening rate steadily decreases in the course of harden- -ing. This can be regarded as one of the reasons -for the need for extraordinarily long storage times before mouldings become usable. A similar situation obtains for the other known binder ! `
systems which are cold-hardening.
_ ~ _ ~.3~
As a logical use of this insight, the invention no longer makes use of a separate accelerator, but instead pro-vides that one of the reaction partners of the system can function simultaneously as a reaction accelerator on the basis of its molecular structure. This resul-ts in a much higher amount of the accelerator being available to the reaction partners, this amount being many times higher than that hitherto usual for the acceleration and possibly being equal to or greater than the stoichiometric quantity, referred to the reactive NCO and OH groups. Thus, in a sense, every NCO/O~I pair now has its own accelerator and this leads to a very constant acceleration, which occurs largely uniformly and simultaneously for all the NCO/OH pairs and leads -to the result that a moulding absolutely ready for use is produced extraordinarily quickly. Correspondingly, it has also been found in practice that the initial strength of a moulding produced with the binder according to this invention is many times higher than the initial values attainable with the hitherto used cold-hardening binders, and that there is no significant increase in strength, even aEter long s-torage.
One fact is especially surprising and not yet explained, namely that, in spite of the very large amount of accelerating tertiary amino groups in the binder accord-ing to this invention, the working time remains, as previously, within a range that is quite acceptable in practice, and that the absolute values of strength achieved are also quite excellent. This is clearly in contradiction to the earlier claim that an increase in the quantity of accelerator, while leading to a more rapid course of the reaction, nevertheless also leads to a substantial reduction in the working time and also reduces considerably the strength values attained.
~ ~! 3 ~
~ he binder according to this invention is also extraordinarily simple to work. It is only necessary to mix the amino polyols (preferably in the form of a solution) and the isocyanates (also preferably in the form of a solution) in approximately equal quantities with the base material, without the addition of any other substances being necessary.
After that, the usual procedure for working can be used, namely the mould material mixture is introduced into the casting box, if necessary further compacted there, and then left in the casting box until removal. In general, the moulding can be removed from the box and handled after only 15 minutes, and after a further 15 minutes (that is 30 minutes in total) it can, if needed, be supplied to the casting process. Besides this simplicity of use and the previously unattained speed of curing, the binder according to this invention also has the advantage that it makes for much better working conditions, because the amino polyols are not harmful to health, nor can they release harmful substances during hardening. Moreover, the finished cores and moulds do not give off any evil smell, an unavoidable consequence up to now in the use not only of amine hardened polyurethane systems, but also (due for example to the splitting off of formaldehyde~
in certain types o~ condensation resins.
In the simplest case, the amino polyols suitable for the binder according to this invention have a tertiary amino group in the molecule, that is they have the structure R
"
/ \ .: ."~
R R ~
where R is any alkyl, cycloalkyl and/or aryl substituent and -where all three R-substituents to~ether contain at least two reactive O~I groups. However, amino polyols compri.sing more than one tertiary amino group are preferred, for which the following general formula is a typical example:
_ _ Rl \ IR5 / R3 N R6- X - R7 - \ R
In this formula:
X is an N or O atom, Rl to R5 are like or different alkyl, cycloalkyl, arylalkyl and/or aryl substituents, including such compounds with heterostructure, which comprise at least two OH groups and which can contain also further functional groups in particular ether bridges, where Rl, R3 and/or R5 can also be H atoms, and R5 does not appear when X is an O atom.
R6 and R7 are like or different alkylene, cyclo-alkylene, arylalkylene and/or arylene substituents, including such compounds with heterostructure, which also may contain OH groups as well as side chains with ether bridges and/or ;
further tertiary amino groups, ~
n is either zero or a positive integer. : :;
m e number of C atoms in the various R-substitue}lts as well as the magnitude of n are not particularly critical, these values are limited in principle only by the requirement that the amino polyol must still be soluble in customary :~
solutions. Molecular weights of up to about 10,000 are possible for the amino polyol. ~ -~^3~
Production o~ the amino polyols can be carried out in accordance with various known processes. It is especially effective to react alkylene oxides, such as ethylene oxide, propylene oxide and the like, with multivalent amines which possess primary and/or secondary amino groups capable of reacting with alkylene oxides and which may additionally contain tertiary amino groups.
Examples of such amines are ethylene diamine, 1,2-propylene diamine, 1,3-diaminopropane, 3-amino-L-methyl-aminopropane' 4,9-dioxadodecane-1,12-diamine, 6,6-dimethyl-4,8-dioxaundecarle-1,11-diamine, dipropylene triamine' N,N'-bis-(3-aminopropyl)-ethylene diamine, bis-(3-aminopropyl)-methylamine, N,N'-dimethyl-~,N' -bis-(3-aminopropyl)-ethylene diamine, bis-(6-aminohexyl)-amine, tripropylene tetramine tetrapropylene pentamine' 2-(aminomethyl)-cyclopentylamine, 1,1-bis-(4-aminophenyl~-cyclohexane, bis-(4-aminocyclohexyl)-methane, bis-(3-methyl-4-aminocyclohexyl)-methane; 2,2-bis-(4-aminocyclohexyl)-propane, bis-(4-aminophenyl)-methane, bis-(4-methylaminophenyl)-methane, bis-(3-methyl-4-aminophenyl)-methane, 3-cyclohexylamino-propylamine, 1,4-diaminobutane, hexamethylene diamine, and 2,5-dimethyl-2,5-diaminohexane.
As can be seen from the general formula given above, individual amino groups of the amino polyols can also be secondary amino groups, although it is more favourable for the ~ .
effect aimed at if as many as possible of all the amino groups :
of the amino polyols have a tertiary structure. The reaction between the alkylene oxides and the amines is therefore pre-ferably carried out in such a manner that the amino polyols which come into being contain primarily or exclusively tertiary amino groups.
::
_ ~ -.. .. :. ~ . .. :. ,: . : . , : . . .-. : -.3L~
The polyisocyana-te.s used in the binder accordiny to this invention can be chosen from any of the common aliphatic, cycloaliphatic, arylaliphatic, aromatic or heterocyclic polyisocyanates used for the production of polyurethane resins, provided they have at least two ~C0 groups.
Examples are diphenylmethane-4,4'-diisocyanate;
2,4-toluol-diisocyanate; phenylene diisocyanate-(1,4), 2,2',6,6'-tetramethyl-diphenylmethane-4,4'-diisocyanate;
diphenyldimethylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate; 2,6-toluoldiisocyanate or isomeric mixtures thereof; diphenyl-4,4'-diisocyanate; triphenyl-4,4',4"-triisocyanate; hexane-1,6-diisocyanate, cyclohexylphenyl-methane-4,4'-diisocyanate; n-xyloldiisocyanate, p-xyloldi-isocyanate; cyclohexane-1,4-diisocyanate, diphenylether-4,4-diisocyanate; or derivatives of these compounds having halogens substituted.
Whereas the amino polyols are used in the form of solutions, as is usually the case in practice, any polar and non-polar solvents as well as protic or aprotic solvents may be used. It is effective to dissolve the amino polyols in the same solvent (or the same mixture of solvents) as is used for the polyisocyanates.
Examples of suitable solvents are benzene, xylol, cymol, solvent naphtha (e.g. Supersol M, made by British Petroleum), tetrahydronaphthaline, diacetone alcohol, methylethylketone, cyclohexamone, isophoron, ethylene glycolmonopropylether, dioxane, dimethylformamide, methyl-glycolacetate, and ethylglycolacetate.
The rate of hardening of the binder according to this invention can moreover be controlled through the solvent, the rule being that the higher the degree of polarity of the _ g _ ~,3 ~ d~
solvent, the higher will be the rate o-f hardening. A further possible way o~ in-fluencing the rate of hardening consists of selecting the molecular structure in such a way that either more or less strongly reactive polyisocyanates and amino polyols come in-to use, according to -the immediate need.
The invention is explained below by means of an example of embodiment thereof and is compared with two reference examples.
Illustrative Example:
From 1,3-diaminopropane and propylene oxide in molar ratio 1,4, N,N,N', N'-tetrakis-(2-hydroxypropyl)-1,3-diamino-propane was produced. 50 g of a 50% solution of this amino-polyol in solvent naphtha (Supersol M, manufactured by British Petroleum) were added to 5 kg of washed and dried quartz sand, together with 50 g of an 80% solution of 4,4'-diphenylmethane diisocyanate-prepolymer (the commercial product Baymidur 83 made by Bayer AG) in the same solvent.
The mixture was agitated for 30 seconds. Finally, the mixture was used to make test pieces according to German Industrial Standard 52401 (DIN 52401), and the bending strength of the forms was measured. The results are summarized in the following table. -Compa ison Example 1:
Using 5 kg of quartz sand of the same type as in the illustrative example of the invention, a material mixture was made with the addition of 70 g of a cold-hardening con-densation resin containing 70% furfuryl alcohol and about 5% nitrogen and also 30 g of a 65% aqueous solution of p-toluol sulfonic acid. The sand was first mixed with the acid for 15 seconds, then the resin was added, and then the whole was mixed for a further 30 seconds. Test pieces were then made and examined in the same way as in the example of ~; -' 10 -- . . . . ., , ~ . . . ~ , . - . . .
~l3~
the invenkion. The results are a]so given in the table below.
Comparison Exam~e_2:
Using again 5 kg of the same type of ~uartz sand and 80 g of an oil-modi-fied alkyd resin, which was treated with cobalt siccatives, and also 20 g of 4,4'-diphenylmethane diisocyanate prepolymer (saymidur 88), a material mixture was produced. The mixture was made using the same procedure as in the example of the invention. Test pieces were then made and examined in the same manner as in the example of this invention. The results obtained here also are given in the table below.
T A B L E: bending strength in N/cm - , after min. min. min. min. min. min. hrs.
__________________________________ ____________________________ Invention 40 270 320 520 600 670 720 Comparison 1 - - - 90 110 200 470 Comparison 2 - - - - 20 100 330 The superiority of the binder according to this invention over kno~n cold-hardening binder systems is clearly evident from this table. The test pieces made with the binder according to this invention reach within lS minutes a strength ~-level which, in practice, is ~uite sufficient for the mouldings to be removed from the casting boxes, and after only 20 or 30 minutes they reach strength levels which are suitable for casting in practice. After 60 minutes, the maximum strength has substantially been reached, i.e. the rise in strength in the period 60 minutes - 24 hours is only slight.
By constrast, the known binders according to the two comparison examples harden only very slowly, and in particular they take a lorlg time to reach a usable degree of strength. Mouldings made from them cannot in practice be removed until 45 to 60 minutes have passed, and they cannot ..
be used until 6 to 24 hours have elapsed and they have reached the.ir maximum strengths. At the same time, the absolute values of the final strength reached in the two comparison examples are clearly lower than the absolute value of the fina]. strength reached in the example illustrating this invention. If, in the two comparison examples, the amount of accelerator were to be increased in order to increase the rate of hardening, the resultant strength values would be still worse and, in fact, would no longer be acceptable.
, ' :
Claims (4)
1. A cold-hardening polyurethane-based binder for material mixtures used in the production of casting moulds and cores, consisting of a polyisocyanate with at least two NCO-groups in the molecule and a polyol with at least two OH-groups in the molecule, characterised by the fact that the polyol is an amino polyol, containing in the molecule at least one tertiary amino group, effective as an accelerator.
2. Binder according to claim 1, characterised in that the amino polyol contains at least two tertiary amino groups in the molecule.
3. Binder according to claim 2, characterised in that the amino polyol has the general formula in which X is an N- or O-atom;
R1 to R5 are like or different alkyl, cycloalkyl, arylalkyl and/or aryl substituents, including such compounds with heterostructure, which possess a total of at least two OH-groups and may also contain further functional groups, in particular ether bridges, where R1, R3 and/or R5 can also be H-atoms and R5 does not appear, if X is an O atom;
R6 and R7 are like or different alkylene, cyclo-alkylene, arylalkylene, and/or arylene substituents, including such compounds with heterostructure, which also may contain OH-groups as well as side chains with ether bridges and/or further tertiary amino groups, n is either zero or a whole number from 1 upwards.
R1 to R5 are like or different alkyl, cycloalkyl, arylalkyl and/or aryl substituents, including such compounds with heterostructure, which possess a total of at least two OH-groups and may also contain further functional groups, in particular ether bridges, where R1, R3 and/or R5 can also be H-atoms and R5 does not appear, if X is an O atom;
R6 and R7 are like or different alkylene, cyclo-alkylene, arylalkylene, and/or arylene substituents, including such compounds with heterostructure, which also may contain OH-groups as well as side chains with ether bridges and/or further tertiary amino groups, n is either zero or a whole number from 1 upwards.
4. Binder according to claim 3, characterised in that the amino polyol is obtained by the reaction of alkylene oxides with multivalent amines possessing primary and/or secondary amino groups, which can react with alkylene oxides, and also in some cases tertiary amino groups.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19772759258 DE2759258A1 (en) | 1977-12-30 | 1977-12-30 | Cold curing binder for molding compounds for the production of molds and cores |
| DEP2759258.1 | 1977-12-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134989A true CA1134989A (en) | 1982-11-02 |
Family
ID=6027935
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000318783A Expired CA1134989A (en) | 1977-12-30 | 1978-12-28 | Cold hardening binder for material mixtures for the production of casting moulds and cores |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS5496426A (en) |
| AR (1) | AR220366A1 (en) |
| AU (1) | AU4293878A (en) |
| BE (1) | BE865741A (en) |
| BR (1) | BR7808389A (en) |
| CA (1) | CA1134989A (en) |
| DE (1) | DE2759258A1 (en) |
| ES (1) | ES476072A1 (en) |
| FR (1) | FR2413453A1 (en) |
| GR (1) | GR66462B (en) |
| IT (1) | IT1102406B (en) |
| NL (1) | NL7812549A (en) |
| ZA (1) | ZA783393B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4370463A (en) * | 1978-06-14 | 1983-01-25 | Ashland Oil, Inc. | Process for no-bake foundry application utilizing polyurethanes based on amine polyols |
| DE2855391A1 (en) * | 1978-12-21 | 1980-06-26 | Woellner Werke | COLD-HARDENING BINDING AGENT FOR PARTICULATE SOLIDS, IN PARTICULAR FOUNDRY SAND |
| DE2925733A1 (en) * | 1979-06-23 | 1981-01-15 | Huettenes Albertus | POLYURETHANE-BASED BINDERS AND THE PRODUCTION THEREOF |
| JPS5736115A (en) * | 1980-08-12 | 1982-02-26 | Mitsui Tekisako Chem Kk | Curing agent composition for polyurethane |
| US4448907A (en) * | 1981-03-30 | 1984-05-15 | Ashland Oil, Inc. | Process for casting lightweight metals |
| DE3329452A1 (en) * | 1983-08-16 | 1985-03-07 | Bayer Ag, 5090 Leverkusen | METHOD FOR PRODUCING CELL-SHAPED POLYURETHANES, IF ANY |
-
1977
- 1977-12-30 DE DE19772759258 patent/DE2759258A1/en not_active Withdrawn
-
1978
- 1978-04-06 BE BE186603A patent/BE865741A/en unknown
- 1978-06-13 ZA ZA00783393A patent/ZA783393B/en unknown
- 1978-12-16 ES ES476072A patent/ES476072A1/en not_active Expired
- 1978-12-20 IT IT31040/78A patent/IT1102406B/en active
- 1978-12-21 FR FR7836602A patent/FR2413453A1/en active Granted
- 1978-12-21 BR BR7808389A patent/BR7808389A/en unknown
- 1978-12-22 GR GR57979A patent/GR66462B/el unknown
- 1978-12-27 NL NL7812549A patent/NL7812549A/en not_active Application Discontinuation
- 1978-12-27 JP JP16023878A patent/JPS5496426A/en active Pending
- 1978-12-28 AU AU42938/78A patent/AU4293878A/en active Pending
- 1978-12-28 CA CA000318783A patent/CA1134989A/en not_active Expired
- 1978-12-28 AR AR275018A patent/AR220366A1/en active
Also Published As
| Publication number | Publication date |
|---|---|
| NL7812549A (en) | 1979-07-03 |
| BR7808389A (en) | 1979-08-07 |
| IT1102406B (en) | 1985-10-07 |
| FR2413453A1 (en) | 1979-07-27 |
| JPS5496426A (en) | 1979-07-30 |
| AU4293878A (en) | 1979-07-05 |
| DE2759258A1 (en) | 1979-07-12 |
| ZA783393B (en) | 1979-06-27 |
| FR2413453B1 (en) | 1983-03-18 |
| ES476072A1 (en) | 1979-05-16 |
| BE865741A (en) | 1978-07-31 |
| IT7831040A0 (en) | 1978-12-20 |
| GR66462B (en) | 1981-03-23 |
| AR220366A1 (en) | 1980-10-31 |
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