DK141877B - Cold-curing phenolic resin blend, especially for use in the manufacture of sand molds. - Google Patents

Description

1A18 7 7

The invention relates to a cold-hardening phenolic resin composition, particularly for use in the preparation of sand molds, consisting of a phenolaldehyde-soluble phenolaldehyde resin-containing organic benzyl ether or methylol group, liquid or dissolved polyisocyanate base containing at least 2 isocyanate moiety and

In the foundry, cores for use in the manufacture of metal castings are usually prepared from 10 mixtures of a basic substance, such as sand, which have been combined with a bonding amount of a polymerizable or curable binder. Often, minor amounts of other materials are incorporated into these mixtures, e.g. iron oxide and ground flax fibers. The binder allows such a molding composition to be formed in the desired shape and then cured to form a self-supporting structure.

Usually, sand is used as the basic substance.

After the sand and binder have been blended, the resulting cast sand blend is stamped or blown into a model or otherwise introduced herein, the blend assuming the shape determined by the adjacent surfaces of the model. Then, the polymerizable binder is polymerized using catalysts, e.g. chlorine and carbon dioxide, or the use of heat or both, thereby transferring the molded, uncured cast sand mixture to a hard, solid, hardened state. This curing can be done in the original model, in a gas treatment chamber or in the support model. Reference is made to the disclosures of U.S. Patents Nos. 3,154,438 and 3,121,268, illustrating the prior art.

Phenolic resins are one of the well-known classes of curable resins used as binding agents in foundry. Both the novo-lactype of the phenolaldehyde resin and the "resol" or "A-stage" resins have been used for this purpose. Novolach resins are soluble, fusible resins in which the polymer chains have phenol end groups. They are usually prepared by condensing phenols with aldehydes using acidic catalysts and using a molar excess of phenol relative to aldehyde. Novolach resins can be cured to insoluble, indigestible products by the addition of a formaldehyde source such as hexamethylenetetramine or paraformaldehyde. Resol and resin resins, the latter being the more highly polymerized form of a resol resin, are usually prepared using an alkaline catalyst with excess aldehyde. Thus, polymers having a highly branched structure and therefore a high concentration of alkylene end groups are formed. Since any alkylol group constitutes a potential crosslinking site, the resol and resitol resins are readily converted to the crosslinked, non-fusible polymer upon heating. The most commonly used monomers are phenol, ie. hydroxybenzene, and formaldehyde for both the resole type and the novolact type.

Both the novolach resins and the resole resins have, by their known use as a casting binder, advantages and disadvantages characteristic of their different polymeric structure, but both suffer from the lack of heating to obtain the cured mold. It is often necessary to keep the "wet" 25 cores in the original molds or models during this heating period, as many heat-curable binders do not provide sufficient strength in the wet state for "wet" cores to retain their desired shape without external support until the time at which a final cure can be effected.

The lack of novolach resins and resole resins that they cannot cure at room temperature also applies in other areas where these resins are used. In particular, such areas are the preparation of 35 blends for forming, wherein the phenolic resin is blended with inert, organic and inorganic fillers, preparation of coating materials and adhesives.

3 1A1877

Danish Patent Specification No. 133,182 discloses a process for making molds and cast cores, in which a cold-hardening phenolic resin mixture of the kind specified in the first paragraph of the specification is used as a binder for the mold sand. It is proposed that a filler containing molding sand as the main constituent be distributed a binder based on a phenolaldehyde resin and an organic polyisocyanate containing at least two isocyanate groups, after which molding is formed in a mold and then cures the shaped mass by contacting it with a tertiary amine in gaseous state or suspended in an inert gas stream. Examples of tertiary amines are disclosed in the present disclosure trimethylamine, triethylamine and dimethylethanolamine and, more generally, tertiary amines containing functional groups such as hydroxyl groups, alkoxy groups, amino groups, alkylamino groups, ketoxy groups and thio groups.

This process is stated to be extremely suitable for the rapid, continuous production of many mold bodies, with the curing of the molded mold mass proceeding exceedingly rapidly, e.g. over a time period of less than 1 minute, possibly as much as 25 down to 15 seconds.

It has now surprisingly been found, according to the present invention, that certain bases, namely heterocyclic compounds having at least one nitrogen atom in the ring structure and having a pK 2 value in the range 7-11, in addition to having the catalyst effect that they cause rapid cure at room temperature gives the phenolic resin mixtures an extremely surprising and desirable property. Most cold-hardening resin blends combine long holding times, ie. the time after the mixing of the resin components where there is no reaction whereby the mixtures can be worked, e.g. perform forming work, with long curing times or short curing times with short holding times. Mixtures containing as the curing catalyst contain said bases, for reasons that are not clearly understood, combine long shelf life with short cure times, resulting in superior mechanical properties of the cured product.

The cold-curing phenolic resin composition of the invention, based on this disclosure, is of the kind set forth in the preamble of the specification, and is characterized in that the curing catalyst is a heterocyclic compound having at least one nitrogen atom in the ring structure and having a pK value in the range 7-11 measured in yand at 25 ° C.

The present resin mixtures are generally marketed as a 2-pack system comprising the phenolic resin in one package and the polyisocyanate hardener component in the other package, both components being in liquid form and therefore generally present as solutions in organic solvents. In general, although the catalyst is not essential, the catalyst is incorporated into the resin component. At the time of use, the contents of the two packages are combined and used for the purpose in question. Furthermore, for applications in the foundry, it is possible to first mix one component with the molding substance such as sand, and then add the other component and mix it with the resultant mixture. After uniform distribution of the binder on the sand grains, when used in the foundry, the resulting molding mass is formed into the desired shape. The molded product can be immediately removed from the mold and will form a cured product upon standing at room temperature. The time required for the curing varies with the nature of the base catalyst and especially with the pK ^ value of the catalyst. Although the phenolic resin compositions of the invention are especially intended to achieve cure at room temperature, it will be clear that these mixtures can also be cured by firing at elevated temperatures.

The benzyl ether resins used in mixtures of the invention as phenolic resins are characteristic in that they contain repeating units of formula 1 -

OH

Ar 'r'

i

_CH-O-CH-- A-kJ * -B 1 C _ 10 wherein A, B and C represent hydrogen, hydrocarbon groups, oxycarbohydride groups or halogen, and R * represents hydrogen or a hydrocarbon group having 1-8 carbon atoms. They have average polymerization rates, measured by the number of repeated aromatic rings, of at least 3 and 15, generally not more than 100. Although resins of higher molecular weight can be used in the curing reactions described above, such resins are difficult to handle due to their viscosity as they require very large amounts of solvents to bring down the viscosity of the resin component to a size normally desirable in coatings and bonding applications.

The benzyl ether resins described are condensation polymers of a phenol of the general formula II 25 OH

Λ

A-K> <- B

30 C

wherein A, B and C represent hydrogen, hydrocarbon groups, oxycarboxylic groups or halogen, with an aldehyde of the general formula R'CHO, wherein R 'represents hydrogen or a hydrocarbon group of 1-8 carbon atoms, produced in the liquid phase substantially in the absence of water at temperatures below ca. 130 ° C in the presence of catalytic concentrations of a metal ion dissolved in the reaction medium. The molar ratio of 141877 6

aldehyde and phenol can generally be varied from 3: 1 to 1: 3, although some resin is also formed outside these ratios. In the preferred form, these resins have the general formula III

5 Γ

OH OH OH

X __-! # Ii ^ \ ^ _ CH_-0-CHo__CH0- _X

. I I! Γ

^ S

wherein R represents hydrogen or a substituent in the meta position of the phenol hydroxyl group, wherein the sum of m and 15 n is at least 2 and ratio m: n is at least 1 and X is an end group consisting of hydrogen or methylol; the molar ratio of methylol to hydrogen end groups being at least 1.

The most preferred benzyl ether resins used in the compositions of the invention are those in which R represents hydrogen.

The phenols used in the formation of the benzyl ether resins are generally all phenols which have heretofore been used in the formation of phenol resins in general and which are not substituted by any of the carbon atoms in ortho position to the hydroxyl group. Any, all or none of the remaining carbon atoms in the phenol ring may be substituted. The nature of the substituent can vary greatly, and it is only necessary that the substituent does not interfere with the polymerization of the aldehyde with the phenol in the ortho position. Substituted phenols used in the formation of the phenolic resins include, inter alia: alkyl-substituted phenols, aryl-substituted phenols, cycloalkyl-substituted phenols, alkenyl-substituted phenols, alkoxy-substituted phenols, aryloxy-substituted phenols and aryloxy-substituted phenols. Said substituents contain from 1 to 14 267 and preferably from 1 to 6 carbon atoms. Particular examples of suitable phenols, other than the preferred unsubstituted phenol, are: m-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethylphenol, 3-ethyl-5-phenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol, p-cyclohexylphenol, p-octylphenol, 3,5-dicyclohexylphenol, p-phenylphenol, p-crotylphenol, 3, 5-dimethoxyphenol, 3,4,5-trimethoxyphenol, p-ethoxyphenol, p-butoxyphenyl, 3-methyl-4-methoxyphenol and p-phenoxyphenol.

The aldehydes reacted with phenol may be any of the aldehydes used heretofore in the formation of phenolic resins such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde and benzaldehyde. In general, the aldehydes used are of the formula R'CHO wherein R 'is hydrogen or a hydrocarbon group having 1-8 carbon atoms. The most preferred aldehyde is formaldehyde.

The methylene groups terminated with methylol groups which may be used in the composition of the invention are resoln resins which are soluble in organic solvents. This severely limits the class of usable Resol resins and generally only those Resol resins made from alkyl substituted phenols useful Resol Resins soluble in organic solvents are a well known class of resins whose preparation is known.

The phenolic resin component is generally used as a solution in an organic solvent, although it is also possible to use the low molecular weight liquid resins without dilution. The desirability and effect of solvents will be described in more detail below. The optimum solvent concentrations for the phenolic resins vary according to the type of resin used and its molecular weight. Generally, the solvent concentration is in the range of up to 80% by weight of the resin solution and preferably in the range of 20-80%. It is preferred to maintain the viscosity of the resin component at less than X-l on the Gardner-Holt scale.

As mentioned, the catalyst used in the present mixtures is a heterocyclic compound having at least one nitrogen atom in the ring structure and having a pK 2 value in the range 7-11. The pK ^ value is the negative logarithm of the dissociation constant of the base and is a well-known measure of the basicity of a basic material. The higher this value, the weaker the base. Specific examples of 10 heterocyclic compounds of the kind having pK ^ values within the required range are 4-alkyl pyridines wherein the alkyl group has 1-4 carbon atoms, isoquinoline, arylpyridines such as phenylpyridine, pyridine, acridine, 2-methoxypyridine, pyridazine, 4-cyano-pyridine, pyrimidine, pyrazine, N-ethyl-morpholine, 4,4'-dipyridine, phenylpropylpyridine, 5-methylpyrimidine and pyridine-N-oxide.

Due to the different catalytic activities and different catalytic effects desired, catalyst concentrations will vary greatly. In general, the retention time of the mixture will be shorter the lower the pK ^ value and the faster and more complete the cure will be. Solvents and any acidity present in the added materials such as sand can affect the catalyst activity. In general, however, the catalyst concentrations will be in the range of 0.01 to 10% by weight based on the phenolic resin.

The second component of the novel binder composition contains an aliphatic, cycloaliphatic or aromatic polyisocyanate, preferably having 2-5 isocyanate groups. If desired, mixtures of polyisocyanates may be used. Also, although less preferred, isocyanate prepolymers formed by the reaction of excess polyisocyanate with a polyhydric alcohol, e.g. a prepolymer of toluene diisocyanate and ethylene glycol. Suitable polyisocyanates include the aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate, and aromatic polyisocyanates such as 3,4- and 2,6-toluene diisocyanate, diphenylmethane . Additional examples of suitable polyisocyanates are 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate, and the methyl derivatives thereof, polymethylene polyphenol isocyanates, chlorophenylene-2,4-diisocyanate and the like. Although all polyisocyanates react with the described phenolic resin to form a crosslinked polymer structure, the preferred polyisocyanates are aromatic polyisocyanates and especially diphenylmethane diisocyanate, triphenylmethane triisocyanate and mixtures thereof.

The polyisocyanate is used in sufficient concentrations to effect curing of the phenolic resin. In general, the polyisocyanate is used in a range of 10-500% by weight polyisocyanate based on the weight of the benzyl ether resin. Preferably, from 20-300% by weight of polyisocyanate is used on the same basis. The polyisocyanate is used in liquid form. Liquid polyisocyanates can be used in undiluted form. Low or viscous polyisocyanates are used in the form of solutions in organic solvents, the solvent being present in the range of up to 80% by weight of the solution.

Although the solvent used in combination with either the phenolic resin or the polyisocyanate or both components does not significantly interfere with the reaction between the isocyanate and the phenolic resin, it can affect the reaction. Thus, the difference in polarity between the polyisocyanate and the benzyl ether resins limits the choice of solvents in which both components are compatible. Such compatibility is necessary to achieve complete reaction and cure of the resin mixtures. Further, by decreasing the viscosity of the binder, the solvent, 35, facilitates the uniform distribution of the resin mixture on a substrate or particulate solid. Polar solvents of either the protic or aprotic type are good solvents for the phenolic resin, but have limited compatibility with the polyisocyanates. Aromatic solvents are compatible with the polyisocyanates but are less compatible with the phenolic resins. It is therefore preferred to use combinations of solvents and especially combinations of aromatic and polar solvents. Suitable aromatic solvents are benzene, toluene, xylene, ethylbenzene, naphthalene and mixtures thereof. Preferred aromatic solvents are mixed solvents having an aromatic content of at least 90% and a boiling range between 140 and 230 ° C.

The polar solvents should not be extremely polar so as to be incompatible with the aromatic solvent. Suitable slightly polar solvents which are compatible with aromatic solvents, especially ester and ether solvents. Suitable more polar but less expensive solvents are generally those solvents classified in the art as coupling solvents, and they include furfural, furfuryl alcohol, cellosolvacetate, butylcellosolve, butylcarbitol, diacetone alcohol and "Texanol".

After combining the two components of the resin mixture of the invention, the resulting mixture is capable of crosslinking at room temperature to form a coating or binder for particulate solids. In the foundry, the binder or its components are mixed with sand or a similar mold foundation substance to form the molding material.

Methods for distributing the binder or its components on the base substance particles are well known to those skilled in the art. The molding compound may optionally contain other ingredients such as iron oxide, ground flax fiber, wood shavings, beech, refractory flour and the like.

A valuable additive to the binder compositions of the invention is a silane of the general formula R

R'O -SiR

R 'represents a hydrocarbon group and preferably an alkyl group of 1-6 carbon atoms, and R represents an alkyl group, an alkoxy-substituted alkyl group or an alkylamino-substituted alkyl group wherein the alkyl groups have from 1-6 carbon atoms. Said silane, when used at concentrations of 0.1-2% based on the phenolic binder and the hardener, adheres to the phenolic binder to the mold substrate particles.

The basic substance, e.g. sand is usually the main constituent, and the binder portion is a relatively smaller amount, generally less than 10%, and frequently within the range of 0.25 to about 2.5%. 5%, these figures being based on the weight of the basic substance. The sand used is preferably dry sand, but moisture of up to approx. 1% by weight based on the weight of the sand can be tolerated. This is especially true if the solvent used is not miscible with water or if an excess of the polyisocyanate necessary for curing is used, as such polyisocyanate will react with the water, thereby reducing the toxic effect of the water on the metal ion. The resulting farm mass is then formed into the desired core or other form, upon which it can be cured either slowly or rapidly upon standing at room temperature.

The invention is further illustrated by the following examples in which all parts are parts by weight and all percentages are weight percent unless otherwise indicated.

Example 1 In a closed boiler, 28.3 kg of phenol, 21.1 kg of paraformaldehyde, 0.43 kg of a 24% solution of lead naphthenate in toluene and 1.8 kg of toluene were introduced. The vessel was closed and heated to temperatures of 100 ° C to 125 ° C for a period of 3 hours. During this heating period, the pressure was maintained at 0.14-0.28 kp / cm and steam was released from the container as the pressure increased. Some toluene distilled out with the steam. A total of 10.9 kg of water was removed. After 3 hours, the reaction mixture was set in vacuo to remove all initially added toluene. The resin was of the benzyl ether type as defined in formula III.

5% 4,4'-dipyridine (pK ^ value 9, Ι- ΙΟ, 8) was added to the resin solution. 50 Parts of the resin solution were mixed with 5000 parts of Wedron silica sand until uniform distribution was obtained. A liquid polyisocyanate curing solution was prepared 10 of 80 parts of a commercially available polyisocyanate "Mondur MR", a mixture of di- and triphenylmethane, di- and triisocyanate, and 20 parts of an aromatic solvent ("Hi-Sol 96C"). as described below). 50 Parts of the liquid polyisicyanate were added to the mixture of sand 15 and resin and uniformly distributed.

The resulting molding mass was formed into standard AES tensile test specimens using the standard procedure. The tensile strength of the test bars • 2 2 was 1.40 Kp / cm after 2 hours, 7.7 Kp / cm after 4 hours, 2 2 20 14 Kp / cm after 24 hours and 15.4 Kp / cm after 16 hours at 52 ° C.

Example 2

Using only the resin of Example 1, the following resin and hardener solutions were prepared:

Resin solution: 52% resin according to Example 1 22% cellosolvacetate 25% aromatic solvent 30 1% 1,3-bis (4-pyridyl) propane (pK, value between 8.5 and 9.5) Curing solution: 80% polyisocyanate % aromatic solvent

The aromatic solvent used in the preparation of the solutions was the commercial Bronoco Hi-Sol 96 having a boiling range of 157-181 ° C and a mixed aniline point of 13.9 ° C. The Polyisocya night was in the commercial "Mondur MR". 50 parts of the resin mixture and 50 parts of the curing solution were then mixed with 5000 parts of Wedron silica sand. The resulting mold mass was then formed into standard AFS tensile test specimens using the standard method.

The test bodies were tested for compressive strength to determine when these samples could be removed from the mold. In general, a compressive strength of 0.70 2 is considered

Kp / cm as a minimum for removal from the sand mold. The following results were obtained:

Compressive strength in Kp / cm 15 After 7 minutes 0.014 "9" 0.042 "13" 4.27 "16" 6.23 "18 6.93 20 As can be seen, curing in the mold could be reduced to about 10 minutes.

2

The test bars had tensile strengths of 2.80 Kp / cm 2 after 30 minutes, 4.55 Kp / cm after 1 hour, 11.20 2 Kp / cm after 2 hours, 16.8 Kp / cm after 4 hours and 22, 4 Kp / cm2 after approx. 16 hours at 52 ° C.

Example 3

Resin and curing solutions were prepared as set forth in Example 2 except that 1% 4-phenylpropylpyridine (pK

8) instead of the dipyridyl propane and a molding mass was prepared from these solutions as described in Example 2. The resulting molding mass was found to have a holding time of 13 minutes and could be removed from the mold with sufficient strength for free curing. - 35 in 10 1/2 minutes. After 4 hours, the tensile strength of the test bars was 15.4 Kp / cm and after 16 hours 18.9 Kp / cm 2 at 52 ° C.

U1877 14

Examples 4-10

Resin solutions containing 52 parts of resin of Example 1, 22 parts of cellosolvacetate, 25 parts of the 5 aromatic solvent used in Example 2 and the indicated amounts (Table 1) of 1,3-bis (4-pyridyl) propane were prepared.

Molds were prepared using 5000 parts of Wedron silica sand, 50 parts of the resin solution and 50 parts of the hardener solution of Example 2. The holding time and time of these molds were found in the mold. Tensile specimens made according to AFS methods were air cured and their tensile strength was measured. The following results were obtained.

Table 1 15 Tensile strength (Kp / cm2)

Example% Cat- Hold-Time in cure- 12 4 night lysator time form time over ___ (min) (min) (hours) __ 4 0.7 7 10 8.4 12.6 16.8 24.5 5 0 6 8 11.5 5.6 9.8 14.7 20.3 20 6 0.5 8.5 12 5.6 9.8 15.4 22.4 7 0.4 13 17 4.5 9.1 17.5 23.1 8 0.3 15 21 3.8 8.4 15.1 23.1 9 0.2 34 54 0.7 2.1 9.8 22.4 10 0.1 100 - 0, Example 11

34 kg of phenol, 17 kg of paraform aldehyde (91%), 45 g of lead naphthenate and 23 g of lead oxide were introduced into a closed boiler. The vessel was closed and heated to a temperature of 116-124 ° C. 30 water began to distill over. After one hour, 5.4 kg of water was removed and the percentage of free formaldehyde was less than 1%. Full vacuum was then applied for 10 minutes and the resin cooled to 93 ° C and removed.

The average molecular weight was 150-200 determined by gel chromatography and the molar ratio of formaldehyde: phenol was 1.3 calculated from the residual material. The resin was a mixture of the resins defined by formulas I, II and III.

A resin solution was prepared containing 52% by weight of the above resin, 22% cellulose acetate, 25% of the aromatic solvent of Example 2 and 0.2% 1,3-bis (4-pyridyl) propane. 50 parts of this resin solution and 50 parts of the curing solution of Example 2 were then mixed with 5000 10 parts of Wedron silica sand. The resulting mold mass was then formed into standard AFS tensile test specimens using the standard method.

The test bodies were tested for compressive strength to determine at what time they could be removed from the mold. Generally, a compressive strength of 0.7 o is required

Kp / cm before removal. The following results were obtained.

2

Compressive strength (Kp / cm)

After 16 minutes 0.5 20 After 27 minutes 1.4

After 50 minutes 6.0

Example 12 56 Parts of phenol, 58 parts of formalin (37% µg) and 2 parts of soda liquor (50% µg) were introduced into a container 25 and heated to ca. 60 ° C - After the exothermic reaction started, the mixture was cooled to keep the temperature at ca. 77 ° C for approx. 2 hours while the reaction was taking place. Then 6 parts of p-toluene sulfonic acid (50% aqueous) were introduced, and vacuum was continuously applied to release the reaction mixture for water until the temperature reached 88 ° C.

Then the obtained resole resin was cooled and taken out of the container.

A resin solution containing 59% by weight of the above resole resin, 50% cyclohexanone and 1% 4-phenylpropylpyridine was prepared. 50 parts of the above solution and 50 parts of solution contain