of its polymers, such as trioxane or paraformaldehyde, the use of paraformaldehyde being preferred according to the invention. 

Additionally, apart from formaldehyde, other aldehydes can also be used. Suitable aldehydes are for example acet- aldehyde, propionaldehyde, butyraldehyde, acrolein, croton› aldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes. 

Particularly preferred organic acids with a pKa value in the range from 3 to 5 at 25° C. are selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid and salicylic acid, wherein benzoic acid, lactic acid, and citric acid are more preferred, and benzoic acid is most preferred. 

In step (S-1 ), a pH value is preferably established in the range from 2.8 to 5, preferably in the range from 3.5 to 4.5, in each case measured at 20° C. 

In a preferred method according to the invention, step (S-1) takes place at a temperature in the range from 90 to 20 160° C., preferably at a temperature in the range from 100 to 150° C. 

A preferred method according to the invention comprises the following further steps: 

(S-2) preheating of the (first) reaction mixture resulting from step (S-1) to a temperature in the range from 40 to 90° C., preferably in the range from 50 to 80° C., (S-3) optionally adjustment of the desired pH value with an inorganic base, preferably with an alkali metal hydroxide, preferably NaOH and/or KOH, (S-4) addition of one or a plurality of compounds that can react with any formaldehyde still present ( or addition of one or a plurality of compounds for reaction with any formaldehyde still present), wherein these compounds are preferably selected from the group of organic compounds with one or a plurality of H$_{2}$N and/or HN groups and/or the group of phenolic compounds, (S-5) preheating of the reaction mixture resulting from the preceding steps to a temperature in the range from 10 to 50° C., preferably in the range from 15 to 40° C., (S-6) optionally addition of further constituents, preferably one, a plurality of or all of the constituents ( e ), (f), (g), (h), G), (k), (m) and (n) as defined above for a mixture according to the invention, preferably in one of the embodiments characterised as preferable. 

In a preferred method according to the invention the total amount of furfuryl alcohol used is at least 50 wt. %, preferably at least 55 wt. %, and is preferably in the range from 60 to 75 wt.%, more preferably in the range from 62 to 72 wt. %, wherein the percentages by weight are relative to the total weight of the resultant mixture according to the invention. 

A preferred mixture according to the invention ( as defined above), preferably in one of the embodiments characterised as preferable, is a mixture that is producible by a method according to the invention, preferably in one of the embodi› ments characterised as preferable. 

The invention also relates to a method of production of a mould or a core, preferably a no-bake mould or a no-bake core for producing metal objects, comprising the step: 

curing, preferably acid-catalysed curing, of a mixture or according to the invention, preferably in one of the embodiments characterised as preferable, curing of a reaction mixture according to the invention, preferably in one of the embodiments characterised as preferable, 

wherein curing preferably takes place at a temperature below 60° C., preferably in the range from 0 to 50° C., more preferably in the range from 10 to 40° C., particu› larly preferably in the range from 15 to 30° C. 

In a preferred embodiment for carrying out the no-bake process, the refractory moulding base material according to the invention ( constituent (iii) of a reaction mixture accord› ing to the invention) is first coated with the acid hardener ( constituent (ii) of a reaction mixture according to the invention). Then the binder (i.e. a mixture according to the invention; constituent (i) of a reaction mixture according to the invention) is added and, by mixing, is uniformly dis› tributed on the grains of the refractory moulding base material already coated with the catalyst. The moulding mixture can then be formed into a moulded article. Because the binder and the acid hardener are uniformly distributed in the moulding mixture, curing takes place substantially uni› formly even with large moulded articles. 

In a preferred method according to the invention, curing preferably takes place in the absence of sulphur dioxide. Preferably, for curing a mixture according to the invention, a reaction mixture according to the invention is produced, which then hardens directly. The statements regarding the reaction mixture according to the invention apply corre› spondingly to the method according to the invention. 

In the method according to the invention for producing cores and moulds for the foundry industry, preferably a moulding mixture is used that is suitable in particular for producing large moulds and cores, wherein these moulds and cores display reduced emission of harmful compounds during casting. 

The invention also relates to a mould or a core for producing metal objects, obtainable by curing a reaction mixture according to the invention, preferably in one of the embodiments characterised as preferable. 

In another aspect, the invention relates to the use of a mixture according to the invention, preferably in one of the embodiments characterised as preferable, as a cold-setting binder, preferably as a no-bake binder in foundry practice, in particular in the production of metal objects by a casting process, wherein the curing of the binder preferably takes place without the use of gaseous sulphur dioxide. 

In another aspect, the invention relates to the use of a mixture according to the invention or of a reaction mixture, preferably in each case in one of the embodiments charac› terised as preferable, in a no-bake process for producing metal objects, preferably in a no-bake process in which no gaseous sulphur dioxide is used for curing, preferably in a no-bake process without a gassing step. 

The invention further relates to a kit, comprising as a first component, a mixture according to the invention, preferably in one of the embodiments characterised as preferable, as a second component, an aqueous solution of an acid, wherein the acid has a pKa value below 2 at 25° C. The invention is explained in more detail below with examples. 

Unless stated otherwise, all figures given refer to weight. Abbreviations used: FA=furfuryl alcohol, AI=assessment index. 

The chemical and physical parameters of the resins are compared in Table 1 below. The values given correspond to average values, which are typical for the respective binder. 

## EXAMPLES 

