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(11) | EP 0 000 096 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for the manufacture of amino-formaldehyde resins |
| (57) A method for the manufacture of an amino- formaldehyde resin. An amino compound is
reacted with formaldehyde or paraformaldehyde in the liquid phase, the latter being
ensured by the presence of a reactive modifier in the reaction mixture. The reactive modifier comprises an amino- formaldehyde resin which is capable of reaction with further monomers and capable of rendering the mixture of reactants liquid at least at the temperature at which the reaction is to be carried out. An amino-formaldehyde resin obtained by this method. |
TECHNICAL FIELD
[0001] This invention relates to the manufacture of resins, and in particular the manufacture of aminoformaldehyde resins,
[0002] 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.
BACKGOUND ART
[0003] The usual commercial method for the manufacture of aminoformaldehyde 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.
[0004] The product in such cases will inevitably contain a large amount of water which for many uses has to be removed.
[0005] Thus the manufacture of moulding powders from such resins requires a lengthy process in which a large volume of water has to be removed.
[0006] We have also found that in the production of foam from urea-formaldehyde resin, as used, for example, for insulation purposes, foams of superior resilience may be produced from resins of low water content as described in our UK Patent Application No.51269/77.
[0007] It has been disclosed (US Patent No.1,985,937) that polyhydric alcohols can be reacted with methylol ureas, methyl ethers thereof, or dimethyl thiourea to give a clear viscous solution.
[0008] It has been disclosed (US Patent No.1,986,067) that urea can be reacted with a glycol and the product condensed with formaldehyde to give a resinous product. Finally it has been disclosed (UK Patent 1,107,245) that a polyetherurea can be obtained by reacting formaldehyde with glycol to produce a hemiformal, and then reacting the hemiformal with urea or thiourea.
[0009] However, in each of these three prior art disclosures the end product is a material containing a high proportion of glycol which has totally unsatisfactory properties when considered as replacement for modern urea-formaldehyde or melamine-formaldehyde resins.
[0010] It 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.
[0011] 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.
[0012] We propose a solution to this problem in the specification of our co-pending UK Patent Application No 21751/77 in which we describe a method for the manufacture of an amino-formaldehyde resin which comprises reacting an amino compound with formaldehyde or paraformaldehyde at a temperature above 60°C in the liquid phase, the liquid phase being ensured by the presence of a minor proportion of a reactive modifier being a compound capable of taking part in said reaction and also capable of modifying the mixture of reactarts to be liquid at the temperature at which the reaction is to be carried out. Examples are given in that specification of the production of low-water content resins using various different compounds as reactive modifiers. The products so made are useful resins, but the reactive modifiers described are compounds which not only modify the reaction system to the liquid phase at the reaction temperature, but also modify the properties of the resulting resin from those of a simple urea-or melamine-formaldehyde resin.
[0013] The present invention has as its primary objective the preparation of amino-formaldehyde resin of lower water content than those obtained by the conventional aqueous system, whilst avoiding the need to use compounds which will modify the properties of the resin produced.
DESCRIPTION OF THE INVENTION
[0014] According to the present invention a method for the manufacture of an aminoformaldehyde resin comprises reacting an amino compound with formaldehyde or paraformaldehyd in the liquid phase characterized in that said compounds are reacted in the presence of a reactive modifier to ensure said liquid phase, said modifier comprising an aminoformaldehyde resin capable of reaction with further monomers, and which is capable of rendering the mixture of reactants liquid at least at the temperature at which the reaction is to be carried out.
[0015] The reaction is preferably carried out at a temperature above 60°C and more preferably in the range 70 C to 115°C.
[0016] 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.
[0017] 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. 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.
[0018] The reactive modifier, i.e. the initial aminoformaldehyde 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.
[0019] The aminoformaldehyde 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 resin may contain different proportions of monomers, and/or additional or different monomers as desired, provided that it remains capable of carrying out its function as reactive modifier.
[0020] Thus the present invention provides a method for manufacturing mixed resins, as well as a means of making aminoformaldehyde resins of low water content.
[0021] For example, a urea formaldehyde resin may be produced, using a melamine-formaldehyde resin as the reactive solvent, or vice-versa.
[0022] 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 capabde of liquifying the reaction 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.
[0023] 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.
[0024] 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. ThepH 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 neutralized or made alkaline before storage.
[0025] Other ingredients may be added to the reaction mixture in the normal manner, a particularly useful ingredient when making a urea/formaldehyde resin to be foamed being low molecular weight, partly reacted melamine/formaldehyde resin which improves the film- forming properties of the resin produced.
[0026] The invention may be used in conjunction with the method for manufacturing an aminoformaldehyde resin described in our co-pending UK Patent Application No. 21751/77.
EMBODIMENTS OF THE INVENTION
Example 1
[0028] This example illustrates the preparation of a resin from urea, paraformaldehyde and urea-formaldehyde resin.
[0030] This formulation gives a theoretical solids content of 93.0% and an overall urea:formaldehyde molar ratio of 1:1.33.
[0031] The preparation of the resin was carried out in a 5 litre split reactor fitted with a stainless steel agitator, a thermometer pocket a reflux condenser and a heating mantle.
[0032] 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.
[0033] After standing for 8 days an 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 boilding water yielding a faintly opalescent solution containing traces of a gelatinous suspension.
Example 2
[0034] This example illustrates the preparation of a resin from urea, paraformaldehyde, urea-formaldehyde resin and melamine formaldehyde resin.
[0035] 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.
[0037] 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.
[0038] 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 780C 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.
[0039] 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.
[0040] 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 5i to 7 by periodic additions of Ammonium Sulphamate. After the 45 minutes the pH was raised to 8½ by adding 3 ml of NaOH and forced cooling of the reaction vessel was begun.
[0041] A hazy resin solution was obtained having a viscosity of 13,360 poise at 24½°C and a low water content.,
Example 3
[0042] 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.
[0043] The reagents used are tabulated below in Table IV.
(Its usual use is in impregnation of print and overlay papers in laminating)
[0045] The procedure followed in preparing the resin is expressed in tabular form below in Table V.
The resin produced had a viscosity of 22, 560 poise at 24°C and an SRY solids content of 77.7%.
Example 4
[0046] 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.
[0048] 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 maintain 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 7½ and the resin was opaque. Heating was stopped and the liquid resin gradual cleared.
Example 5
[0050] This example illustrates the preparation of a mixed resin usi a methylated melamine-formaldehyde resin as reactive modifier and urea and paraform as the other reactants.
[0052] *BC 309 is a liquid resin commercially available from British Industrial Plastics Limited and has a solids content of 90% (SRY solids content 80%).
[0055] 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.
1. A method for the manufacture of an amino-formaldehyde resin which comprises reacting
an amino compound with formaldehyde or paraformaldehyde in the liquid phase characterised
in that said compounds are reacted in the presence of a reactive modifier to ensure
said liquid phase, said modifier compri.- an amino-formaldehyde resin capable of reaction
with further monomers and capable of rendering the mixture of reactants liquid at
least at the temperature at which the reaction is to be carried out.
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 Claim 1, 2 or 3 in which the reactive modifier is an aminoformaldehyde
resin capable of reacting with further monomers and in solution in water, the solution
having a solids content of at least 50% by weight.
6. 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.
7. A method according to any one of the preceding claims in which the amino compound
to be reacted with formaldehyde or paraformaldehyde is melamine or urea.
8. 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.
9. 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.
10. A method for the manufacture of an amino-formaldehyde resin substantially as described
herein in example 1 or 2.
11. A method for the manufacture of an amino-formaldehyde resin substantially as described
herein in example 3, 4 or 5.
12. An amino-formaldehyde resin manufactured by a method as claimed in any one of
the preceding claims.