NO147110B - LIQUID CATALYST FOR CURING RESIN BINDING AGENTS - Google Patents

Description

The present invention relates to liquid catalysts for curing resin binders, especially

spikes used in the manufacture of moulds.

It is common to make molds from it

sand bound with a hardenable resin system, e.g. co-

polymers of phenol, resorcinol and/or urea with formaldehyde

hyd and/or furphyryl alcohol. As examples, resins based on phenol/formaldehyde, urea/formaldehyde, phenyl/formaldehyde/furfuryl alcohol, urea/formaldehyde/furfuryl alcohol, phenol/urea/formaldehyde/furfuryl alcohol or resorcinol/furfuryl alcohol can be mentioned. The present invention can be applied to all of the aforementioned curable resins

systems. The mold will harden when the resin hardens.

a .

Up until now, it has been common practice to use toluenesulfonic acid or xylene, cumene or benzenesulfonic acid in concentrations of 65 - 70% in the form of solutions in water. However, the curing rate for such solutions is

very slow for certain purposes.

The presence of water reduces the rate of curing

for the sulfonic acid catalyst. Addition of sulfuric acid increases the hardening rate, but on the other hand lowers the mechanical properties of the finished form.

In addition to satisfactory curing activity, a satisfactory and acceptable curing catalyst for molds should have sufficient fluidity so that it can be pumped and remain liquid during storage. Preferably, it should not crystallize during storage, even at the low temperatures obtained in winter conditions.

If one lowers the water content in the hitherto known sulphonic acid catalysts in order to thereby increase their activity, this will however result in an increase in the viscosity to too high a level, and in most cases make the catalyst easily crystallisable. The use of thinners such as methanol and acetone to avoid such problems will slow the cure rate, increase the price of the catalyst and may give rise to toxic fumes.

In general, it will be the case that the most effective curing agents are those with the lowest molecular weight. These will also cause the greatest problems at high concentrations. Anhydrous benzenesulfonic acid will e.g. crystallize out at temperatures below 45°C, and aqueous solutions of benzenesulfonic acid can only be used in practice at concentrations below approx. 75%. Toluenesulfonic acid is similarly easily crystallized at high concentrations. Xylene and cumenesulfonic acids, which are less active than benzene or toluenesulfonic acids, are less prone to crystallization, but their viscosities at a concentration of 90% or more are so high (ie between 1000 and 2000 est for 96% cumenesulfonic acid at 20°C ), that they cannot be used in practice at such high concentrations. Furthermore, it is the case that high molecular weight sulphonic acids will usually have too little activity.

It has been discovered that by using mixtures of arylsulfonic acids, the good curing properties of low molecular acids can be achieved, combined to a certain extent with the lower melting points of high molecular acids. However, most such mixtures will be too highly viscous and are often unstable, tending to crystallize, especially at low temperatures.

Very surprisingly, certain compositions have now been discovered which combine high activity with unexpectedly high fluidity, and in most cases with good stability.

According to the present invention, a liquid catalyst for curing resin binders is thus provided, comprising a mixture of arylsulfonic acids, characterized in that it comprises a mixture of 20-80% by weight, preferably 30-70% by weight, benzenesulfonic acid, 80-20% by weight, preferably 70-30% by weight, alkylbenzenesulfonic acids with 8-

9 carbon atoms, such as xylene and/or cumenesulfonic acid, and optionally up to 50% by weight toluenesulfonic acid, as well as optionally up to 5% by weight water and optionally up to 10% by weight sulfuric acid.

Present catalyst mixtures are preferably substantially anhydrous, as water tends to lower their stability. In practice, however, the commercially available sulphonic acid will normally contain up to approx. 2% water. The new catalyst will usually be capable of sufficient stability in the presence of up to 5% water, although less than 4% is preferred and less than 3% is most preferred.

Sulfuric acid provides good stability in the present catalysts, while a larger amount of sulfuric acid will result in weak castings. For this reason, the sulfuric acid content must be less than 10%, most preferably 0.5 - 5%, e.g. 1-3%.

Benzenesulfonic acid is an essential component of the new catalyst. This compound is found to exhibit a special synergism in connection with C 8 - and C 8 -sulfonic acids (such as xylene or cumenesulfonic acids), which has not been observed so far with any other known mixture of sulfonic acids, and this results in unexpectedly high fluidity, and in most cases also satisfactory stability.

Amounts of benzenesulfonic acid of less than 20 percent by weight of the two "sulfonic acids" tend to give poor stability, especially when the water content is high, while obtaining a relatively high viscosity, and they are less active than the preferred compositions. Preferably, the amount of benzenesulfonic acid exceed 30%.

Amounts of more than 80% give relatively poor stability at low temperatures. For most purposes, the amount will usually be below 70%, especially where the remaining part of the active mixture consists of a single xylene isomer. It is therefore preferred that the present mix-

ing should contain at least 30%, but preferably at least 40% benzenesulfonic acid per weight of the total sulphonic acids, typically 40 - 60%, e.g. 45 - 55%.

Cg and Cg -sulfonic acids all have a specific synergism with benzenesulfonic acid. If the mixture of sulphonic acids contains less than a total of 20 percent by weight of Cg and Cg sulphonic acids, then the stability of the catalyst at low temperatures will be insufficient. Concentrations of Cg and Cg-sulfonic acids above 80% result in poor stability in the presence of high water concentrations, and also give high viscosity and relatively low activity. The present mixture should preferably contain a total of 30 - 70%

of Cg and/or Cg sulphonic acids in relation to the weight of the total sulphonic acid mixture. Preferably, the amount of Cg and/or Cg sulphonic acids is 40 - 60%, and preferably

and preferably the amount of benzenesulfonic acid is at least 8 times,

and preferably at least 10 times greater than the amount of water.

The preferred Cg and Cg sulfonic acids are respectively a commercial mixture of Cg isomers sold under the names "xylene sulfonic acid" and cumenesulfonic acid (isopropylbenzene sulfonic acid). Commercial xylene sulphonic acid will normally include, in addition to sulphonated ortho-, meta- and para-xylene, a smaller amount (e.g. 20%) of ethylbenzene sulphonic acid. Ethylbenzenesulfonic acid alone is a special, effective synergist, with benzenesulfonic acid, but is less readily available commercially than the so-called "xylenesulfonic acid". Generally, mixtures of -of..;-Cg -isomers will be preferred over pure xyleniso-Iftierejfc' both because of efficiency and cost. The xylene isomer -~■ clines give rise to problems with premature crystallization when the amount of benzenesulfonic acid exceeds approx. 65 percent by weight.

The presence in the mixture of sulphonic acids in smaller quantities, e.g. less than 50% in total, preferably less than approx. 30%, of toluenesulfonic acid, However, toluenesulfonic acid will tend to lower the stability of the composition, and in quantities of more than 30% can cause crystallization. It is therefore pre-

concluded that the compositions are essentially free of toluenesulfonic acid. ciq~oc3 higher arylsulphonic acids tend to have high melting points and will not be easily processed into liquid compositions according to the present invention. Catalysts according to the present invention will normally contain a smaller amount, i.e. up to 4%, of sulphones

and sulfonated sulfones, which are normally and commonly present as impurities in commercial sulfonic acids and which have not been found to be harmful in the present catalysts. Compositions according to the present invention can be prepared by mixing commercial benzenesulfonic acid, with e.g. commercial xylene and/or cumenesulfonic acids, or alternatively by sulfonating a suitable mixture of Cg - Cg aromatic hydrocarbons, e.g. with sulfuric acid, oleum or sulfur trioxide using commonly known sulphonation techniques. Thereby, it will be preferred that the compositions are prepared by reacting benzene with an excess of the sulfonating agent and then adding the alkyl benzene together with any additional sulfonating agent that is necessary to obtain a complete reaction.

Present catalysts can be used for curing a variety of resin binders, e.g. the curable resin systems mentioned earlier, as in particular polymers of phenols with aldehydes, such as formaldehyde, e.g. resins of the resol type. They are particularly well suited for use during fast casting processes, e.g. of the type described in British Patent No. 1,441,572. Typically, the catalyst will be added in amounts of 10 - 80%, preferably 20 - 60%, e.g. 30 - 50% by weight based on the weight of the resin. The resin can typically be mixed with sand in proportions of 0.25 - 10% by weight, preferably 0.5 - 5%, e.g. 1 - 2%.

The following examples illustrate the invention. A series of catalyst compositions were prepared by mixing benzenesulfonic acid with commercial cumenesulfonic acid in the amounts indicated in Table I.

The preceding viscosity figures can be compared with benzenesulfonic acid which is crystalline below 45°C and cumenesulfonic acid which has a viscosity of between 1000 and 2000 cSt at a concentration of 96% and at 20°C.

The stability of the present catalyst mixtures at various temperatures in the presence of added water was determined and is set forth in the following Table II.

The activity of the compounds was determined

by mixing 3 kg of sand with the catalyst (40% based on the weight of the resin) for 1 minute, and then continuing the mixing for another 1 minute with a resol resin (viscosity is 300 eps, pH is 6-6.4,

solids content = 76-78%) in an amount of 1.2 percent by weight in relation to sand. The processing time (i.e. the time period during which the mixture remains workable) and withdrawal time (i.e.

when the mold or core is self-supporting) was determined and is given in Table 3 compared to the results obtained when aqueous toluenesulfonic acid and benzenesulfonic acid were used.

Mixtures of benzenesulfonic acid with commercial xylenesulfonic acid were prepared. Their properties are listed in the table

To demonstrate the stability and properties of mixtures of benzenesulfonic acid and individual Cg isomers, mixtures were prepared from the acids listed in Table V.

The following examples 13 to 32 were prepared by mixing benzenesulfonic acid in ratios of 70/30, 60/40, 50/50, 40/60 and 30/70 with each of the four Cg acids. The viscosities and amount of water in Examples 13 - 32 are given in Table VI.

The stated results clearly show that man

in all examples obtained a significant synergistic improvement with respect to viscosity.

All examples 13 - 32 were tested for stability at 20 and -16°C. At 20°C, the catalysts from examples 18, 23, 28 and 29 crystallized out in less than 4 days, but the remaining ones were liquid even after 2 months. The samples that crystallized were those containing 70% benzenesulfonic acid with 30% ortho- meta- or para-xylenesulfonic acid and 60% benzenesulfonic acid and 40% metaxylenesulfonic acid. This shows that in a mixture with pure xylene isomers the amount of benzenesulfonic acid must not exceed

60% of the active mixture, preferably not exceeding 50%. Mixtures with ethylbenzenesulfonic acid were stable at room temperatures in all the proportions tested. The results of the tests at -16°C are given in Table VII.

To test the effect of toluenesulfonic acid, samples were prepared by adding toluenesulfonic acid in amounts of 5, 10, 15, 20 and 50% of the total active mixture to benzenesulfonic acid, to 50/50 mixtures of benzenesulfonic acid and commercial xylenesulfonic acid, and with cumenesulfonic acid, respectively, and to a 1:1:1 mixture of benzene, commercial xylene and cumenesulfonic acid.

Mixing with benzenesulfonic acid to toluenesulfonic acid gives rapid crystallization. In the presence of other acids in addition to toluenesulfonic acid, this raised the viscosity somewhat, and gave certain indications of instability at a content of 50%.

In comparison, sulfonic acid mixtures of toluene/benzenesulfonic acid were found to be unstable, while mixtures of xylene/cumene, toluene/xylene, toluene/cumene, and toluene/xylene/cumenesulfonic were all too viscous for commercial use in an absence of organic thinners.

Claims (1)

Liquid catalyst for curing resin binders, comprising a mixture of arylsulfonic acids, characterized in that it comprises a mixture of 20-80% by weight, preferably 30-70% by weight, benzenesulfonic acid, 80-20% by weight, preferably 70- 30% by weight, alkylbenzenesulfonic acids with 8-9 carbon atoms, such as xylene and/or cumenesulfonic acids, and optionally up to 50% by weight toluenesulfonic acid, as well as optionally up to 5% by weight water and optionally up to 10% by weight sulfuric acid.