EP0000096B1

EP0000096B1 - Method for the manufacture of amino-formaldehyde resins

Info

Publication number: EP0000096B1
Application number: EP78300026A
Authority: EP
Inventors: Georges Inverarity; Dennis Henry Ogden
Original assignee: British Industrial Plastics Ltd
Current assignee: British Industrial Plastics Ltd
Priority date: 1977-06-11
Filing date: 1978-06-08
Publication date: 1982-09-01
Also published as: CA1142683A; ES470680A1; IT1156815B; JPS544987A; MX147709A; IT7849800A0; GB1603088A; ZA783136B; US4224423A; DE2862011D1; EP0000096A1; YU137278A

Description

Technical field

This invention relates to the manufacture of resins, and in particular the manufacture of amino-formaldehyde resins.
Amino-formaldehyde resins are manufactured on a large scale and used in moulding powders, foams for cavity wall insulation etc, for adhesives and in textile finishing. The most commonly used amino compounds are urea and melamine and their derivatives.

Background art

The usual commercial method for the manufacture of amino-formaldehyde resins such as urea-formaldehyde or melamine-formaldehyde resins is to react the amino compound and formaldehyde in an aqueous system at a temperature of 60 to 90°C.
The product in such cases will inevitably contain a large amount of water which for many uses has to be removed.
Thus the manufacture of moulding powders from such resins requires a lengthy process in which a large volume of water has to be removed.
It has been proposed (French Patent No. 2,062,186) to make resin solutions of good storage stability by reacting amino compound and formaldehyde in the presence of a highly condensed melamine-formaldehyde resin. However, in this case the reaction system is conventional apart from the presence of the pre-formed resin and the usual 30% formaldehyde solution in water is used.
In US Patent No. 3,308,098 there is disclosed a stage by stage process for making a high solids syrup containing a urea-formaldehyde condensate and a thiourea-formaldehyde condensate but to achieve the high solids the process described requires a concentration step.
It has been disclosed (French Patent No. 1,484,507) that an alkanolamine can be reacted with paraformaldehyde in substantially water-free conditions, and the product reacted with a triazine such as melamine to give a resin of low water content.
Similarly it has been disclosed (UK Patent No. 1,317,774) that formaldehyde can be reacted with aliphatic hydroxylated monoamine as defined in UK Patent No. 1,012,319 and the product condensed with melamine to give a resinous product, the reaction stages being carried out at high solids contents. The formaldehyde can alternatively be reacted first with the melamine and then with the hydroxylated monoamine.
However, in each of these latter two prior art patent disclosures a major ingredient of the reaction system is an alkanolamine which is a modifier for melamine-formaldehyde resins and simple urea-formaldehyde or melamine-formaldehyde resins cannot be produced using these techniques.
tt has been proposed (UK Patent No. 1,390,370) to make amino-formaldehyde resins by reaction, in the absence of solvent, of urea or thiourea, paraformaldehyde, and hexamethylene tetramine in a molar ratio in the range from 1:1.1:0.01 to 1:25:0.2. This proposal, however, suffers from the difficulty that in the solid phase, reaction control is virtually impossible and a consistently satisfactory end product is not obtained.
The present invention is thus concerned with the problem of providing a process for the preparation of amino-formaldehyde resins of lower water content than by the conventional aqueous system, yet avoiding the difficulties of solid phase reaction, and not requiring the presence of compounds which will modify the properties of the resin.

Description of the invention

According to the present invention a method for the manufacture of an amino-formaldehyde resin comprises reacting in the liquid phase an amino compound, selected from urea and melamine, with formaldehyde in a reaction system including, as reactive modifier, an amino-formaldehyde resin, characterised in that said reactive modifier resin is itself a urea-formaldehyde or melamine-formaldehyde resin which reacts with further amino-compound and/or formaldehyde and is in the form of a liquid resin or an aqueous solution of at least 50% solids content, and renders the mixture of reactants liquid at least at the temperature at which the reaction is to be carried out, the amino-compound and the formaldehyde being introduced into said reactive modifier in a solid form neither dissolved nor dispersed in water.
The reaction is preferably carried out at a temperature above 60°C and more preferably in the range 70°C to 115°C.
In carrying out the method of this invention water may be omitted, or if added, the amount of water present in the reaction mixture (excluding water formed in the condensation reaction) is preferably less than 6% by weight of the total mixture.
A preferred reactive modifier is thus a low molecular weight liquid amino-formaldehyde resin having a water content of less than 10% by weight.
Although these low water contents in the initial reaction mixture are preferred, low molecular weight liquid resins of low water content are not freely available to use as starting materials at the present time. Thus, we find that a high solids content aqueous solution of a reactant resin (i.e. one capable of reacting with further monomers) can be used successfully as a reactive modifier i.e. a solution having a solids content of at least 50% by weight. The end product when using such a modifier is of lower water content than the products of the usual method of producing such resins. Clearly if desired these products could be used as reactive modifiers in turn, with a correspondingly lower water content in the reaction mixture.
The reactive modifier, i.e. the initial amino-formaldehyde resin; will, when the reaction is completed, form part of the resin produced. The function of the reactive modifier in the method of this invention is to render the reactant mixture a liquid at the temperature of reaction so that the reaction can be carried out in a liquid phase.
The amino-formaldehyde resin used as reactive modifier may be a resin containing the same monomers in the same ratio as the resin being manufactured. However, this need not necessarily be the case and the reactive modifier resins may contain different proportions of monomers, and/or additional monomers as desired, provided that it remains capable of carrying out its function as reactive modifier.
Thus the present invention provides a method for manufacturing mixed resins, as well as a means of making amino-formaldehyde resins of low water content.
For example, a urea formaldehyde resin may be produced, using a melamine-formaldehyde resin as the reactive modifier or vice-versa.
The proportion of the resin used as reactive modifier in the reaction mixture will depend upon the proportion desired, particularly when making a mixed resin, but also will be limited by the extent to which it is capable of liquifying the reactive system. For instance if the reactive modifier is a liquid resin in which the other reactants are highly soluble it need be used in a proportion lower than would be the case if the other reactants were less soluble in it.
In general, however, the molar proportion of the resin used as reactive modifier to the total reactants will not be greater than 40% and will preferably be substantially less.
The formaldehyde, e.g. paraformaldehyde and the amino compound are generally added to the reactive modifier separately, whilst warming the mixture, to form the reaction mixture in the desired liquid phase. The pH of the system during this stage is alkaline. When the three reactants are in the liquid phase the final condensation may be accelerated by acidifying the reaction mixture if this is desirable, but in many cases, particularly when melamine is the amino compound, there is no need to accelerate the reaction in this way.
If the reaction mixture is acidified, the final product is subsequently neutralised or made alkaline before storage.
Other ingredients may be added to the reaction mixture in the normal manner, a particularly useful ingredient when making a urea/formaidehyde resin to be foamed being low molecular weight, partly reacted melamine/formaldehyde resin which improves the film-forming properties of the resin produced.

Embodiments of the invention

The invention will now be particularly described by means of the following Examples.

Example 1

This example illustrates the preparation of a resin from urea, paraformaldehyde and urea-formaldehyde resin. The reagent quantities used are detailed in Table 1.
This formulation gives a theoretical solids content of 93.0% and an overall urea:formaldehyde molar ratio of 1:1.33.
The preparation of the resin was carried out in a 5 litre split reactor fitted with a stainless steel agitator, and thermometer pocket a reflux condenser and a heating mantle.
The procedure followed in preparing the resin is expressed below in tabular form in Table II.
The resin was soluble in water, yielding a cloudy solution. After standing for 8 days at ambient temperature the resin had set to a firm white paste. This could be dispersed in cold water to yield a milky dispersion of pH 9. It was almost completely soluble in boiling water yielding a faintly opalescent solution containing traces of a gelatinous suspension.

Example 2

This example illustrates the preparation of a resin from urea, paraformaldehyde, urea-formaldehyde resin and melamine formaldehyde resin.
In this case the melamine-formaldehyde resin, paraformaldehyde and urea are dissolved in turn in the U.F. resin under alkaline conditions and then allowed to react under acid conditions.
The reagent quantities used are detailed below in Table III.
The U.F. resin was charged to a reaction vessel provided with a heating/cooling jacket and fitted with a stirrer, thermometer and reflux condenser. The pH of the resin was adjusted to 10 with 40% NaOH and heating and stirring commenced.
When the temperature in the vessel had reached 35°C gradual addition of the BL35 M.F. resin was commenced, the total addition taking 15 minutes and the temperature rising to 56°C during that period. The temperature was then increased gradually to 78°C when gradual addition of the paraformaldehyde was commenced. During addition of the paraform, which took 55 minutes, the pH was maintained above 8 by addition of 40% NaOH as necessary (2ml NaOH added together) and the temperature was held at 85 to 90°C.
Gradual addition of urea was then commenced with the heating off, the temperature and pH being held as for the paraform addition, heating and adding 40% NaOH as necessary.
When the urea addition was complete the pH of the mixture was allowed to fall to 6 and 2 ml of Ammonium Sulphamate added, the reaction being continued over the following 45 minutes. During the reaction the temperature was held in the range 85° to 90°C and the pH in the range 5.5 to 7 by periodic additions of Ammonium Sulphamate. After the 45 minutes the pH was raised to 8.5 by adding 3 ml of NaOH and forced cooling of the reaction vessel was begun.
A hazy resin solution was obtained having a viscosity of 13,360 poise (1336 PaS) at 24.5°C and a low water content.

Example 3

This example illustrates the use of an aqueous solution of a melamine-formaldehyde resin as reactive modifier in the preparation of a-melamine formaldehyde resin.
The reagents used are tabulated below in Table IV
^*BL 34 resin is a spray-dried Melamine-Formaldehyde resin of M:F ratio 1:2.0, containing 2% free moisture and an SRY solids content of 93%.
(lts usual use is in impregnation of print and overlay papers in laminating)
This formulation gives a total water content of 17% by weight in the reaction mixture.
The procedure followed in preparing the resin is expressed in tabular form below in Table V.
The resin produced had a visocisty of 22,560 poise at 24°C and an SRY solids content of 77.7%.

Example 4

This example illustrates the preparation of a mixed resin using a Uron resin as reactive modifier and urea and paraform as the other reactants. The reagents used are detailed in Table VI.

The bis (methoxymethyl) uron resin is a liquid with a solids content of 95% to 100%.

The procedure followed was as follows. The uron resin was charged to a reaction vessel, stirred and heated. The pH of the resin was 8.5. When the temperature reached 62°C paraform addition was commenced, the temperature being kept in the range 60 to 65°C and the pH at 8.5. The paraform addition was complete after 30 mins, and the mix was maintained at 62 to 64°C for a further 75 mins. The paraform was not completely dissolved. Urea addition was then begun, maintaining the same temperature and pH, and was completed in 60 mins during which time the solids were dissolving giving a white opaque resin. After a further 28 mins the solids were totally dissolved, the pH was 7.5 and the resin was opaque. Heating was stopped and the liquid resin gradually cleared.
When cold the resin slowly became a white paste.

Example 5

This example illustrates the preparation of a mixed resin using a methylated melamine- formaldehyde resin as reactive modifier, and urea and paraform as the othe reactants.
The reagents used are detailed below in Table VII.
^*BC 309 is a liquid resin commercially available from British Industrial Plastics Limited and has a solids content of 90% (SRY solids content 80%).
The procedure followed is given below in tabular form in Table VIII.
The resin produced was a pasty solid when cold, and had an SRY solids content of 79.8%.
It should be noted that the SRY solids content quoted in the above Examples were measured by heating weighed samples of the resins for 3 hours, at 120°C to drive off water of reaction, the residue being regarded as the solids content of the resin. These values should therefore not be confused with the frequently quoted value of resin solids in aqueous solution, in which the non-aqueous content is all taken to be solids, and therefore is generally a very much higher percentage figure.

Claims

1. A method for the manufacture of an amino-formaldehyde resin which comprises reacting in-the liquid phase an amino compound, selected from urea and melamine, with formaldehyde in a reaction system including, as reactive modifier an amino-formaldehyde resin, characterised in that said reactive modifier resin is itself a urea-formaldehyde or melamine-formaldehyde resin which reacts with further amino-compound and/or formaldehyde and is in the form of a liquid resin or an aqueous solution of at least 50% solids content, and renders the mixture of reactants liquid at least at the temperature at which the reaction is to be carried out, the amino-compound and the formaldehyde being introduced into said reactive modifier in a solid form neither dissolved nor dispersed in water.

2. A method according to Claim 1 in which the reaction is carried out at a temperature above 60°C.

3. A method according to Claim 2 in which the reaction is carried out between 70°C and 115°C.

4. A method according to Claim 1, or 2 or 3 in which the reactive modifier is a low molecular weight liquid amino-formaldehyde resin having a water content of less than 10% by weight.

5. A method according to any one of the preceding claims in which the reactive modifier is a resin containing the same monomers in the same ratio as the resin being manufactured.

6. A method according to any one of the preceding claims in which the reactive modifier is selected from urea formaldehyde resins, melamine formaldehyde resins and methylated melamine formaldehyde resins.

7. A method according to any one of the preceding claims in which the amount of water present in the reaction mixture is less than 6% by weight of the total mixture.

8. A method according to any one of the preceding claims in which the amino-compound and the formaldehyde are added, in solid form, to the reactive modifier separately under alkaline conditions, the reaction mixture when all three ingredients are present being reacted under alkaline or acidic conditions as appropriate to achieve a desired reaction rate.