CA1078084A - Aminoplast resin moulding composition - Google Patents

Abstract

ABSTRACT

A thermosetting moulding composition comprising an aminoplastic resin, and a filler which is constituted at least in part by a cured aminoplast material produced by a process comprising mixing a urea- or melamine, formaldehyde resin or precursors for producing same with an acid catalyst at a pH of less than 4 and agitating the system to produce a slurry containing cured aminoplast material in precipitated particulate form, the constant of the precipitated aminoplast in the slurry being controlled at less than 20% by weight; fillers produced in this fashion have -NH- groups capable of reacting with the resin during curing of the latter.

Description

1078~8~

This invention concerns improvements in or relating to aminoplast moulding materials.
In U.K. Patent Specification No. 904954, it is proposed that synthetic resin compositions be provided with a fire-retardant filler capable of forming foam layers at elevated temperatures, the filler being based on an essentially uncured urea formaldehyde material; in U.K. Patent Specificat-ion No. 1,136,260 it is proposed to provide a curable resin mixture that can be cured without giving off volatile substances, comprising a curable resin component that can be cured to give a non-elastomeric cured product, and a filler which comprises a cured comminuted aminoplast resin which is insoluble in the curable resin component.
According to the present invention, a thermosetting moulding composition comprises a curable aminoplastic resin and a filler, wherein the filler comprises at least in part a cured cellulose-free, particulate urea-formaldehyde or melamine-formaldehyde material having -NH- groups capable of reacting with the resin during curing of the latter.
Preferably the curable aminoplastic resin is a urea-formaldehyde resin, preferably one having a urea:
formaldehyde ratio prior to curing of from 1:1.2 to 1:1.8.
Preferably the particulate urea- or melamine- formaldehyde material has a B.E.T. surface area of less than 10 square meters per gram, more preferably less than 1 square meter per gram, and a water absorbency of from 1.0 to 6.0 ml/g, although more preferred absorbencies are from 1.5 to 2.5 ml1g.

1078~84 The preferred fillermaterial is a urea-formaldehyde material having a urea:formaldehyde molar ratio after curing of from 1:1.0 to less than 1:2.0 (it is by having a urea:formaldehyde ratio less than 1:2.0 that the filler has reactive -NH-groups).
S The particulate urea- or melamine-formaldehyde material may constitute the whole of the filler for the moulding composition, or may constitute one component of a multi-component filler, and finds excellent application as a partial or complete substitute for the normal content of cellulosic, e.g., cellulose, filler in standard cellulose-filled aminoplast moulding materials.
The filler may constitute from 15 to 80% by weight of the moulding composition, and may comprise from 1 to 100%
preferably 30 to 100% by weight (based on the total weight of the filler~ of the particulate urea- or melamine-formaldehyde material.
It is preferred to produce the particulate urea- or melamine-formaldehyde material by a process which comprises providing an aqueous system which has a pH of less than 4, is free of surface active agent, and contains:-(i) an urea- or melamine-formaldehyde resin or the precursors for producing same and (ii) an acid catalyst, agitating the system gently to produce a slurry containing cured aminoplast material in precipitated form as aggregates of microspherical particles and controlling the content of precipitated urea- or melamine-formaldehye resin in the system at less than 20% by weight, and 1(~78084 drying and neutralizing the precipitated urea- or melamine-formaldehyde resin whilst maintaining a water ab~sorbency for said precipitated resin of l to 6 millilitres/gram.
The present invention further provides a thermosetting moulding composition comprising a curable aminoplastic resin and a filler, wherein the filler comprises at least in part a cured precipitated aminoplast produced by the process aforesaid.
The aminoplast resin used to produce the precipitate may be any adduct or condensate of urea or melamine ('amino compound') and formaldehyde, produced outside of the aqueous system.
Alternatively, the resin may be formed in situ in the aqueous system by providing in a reaction vessel an aqueous ; solution of the amino compound or of formaldehyde and addingthereto formaldehyde or amino compound, respectively, optionally also as an aqueous solution, or may be formed in situ by combining separate foodstocks comprising amino compound and formaldehyde fed to a reaction vessel.
By additional reaction of an adjunct such as ethylene glycol, glycerol or caprolactam, it is possible to produce modified forms of aminoplast precipitate; alternatively, it is possible to modify the precipitate by subsequent treatment with a modifier, for example epichlorohydrin. The precipitated aminoplast will usually be unfilled.
The precipitated aminoplast solids content of the aqueous system is preferably within the range from 5 to 20% by weight of the total, more preferably from 6.0 to 18% by weight and still more preferably from 9 to 12% by weight.

1078~84 The urea:formaldehyde molar ratio at the initiation of the curing reaction is preferably at least 1:1.1 and more preferably is within the range from 1:1.3 to 1:2.2 even more preferably from 1:1.3 to 1:1.6; when melamine is used, these ratios will preferably be altered proportionately.
The aqueous system is preferably maintained at a temperature within the range from 20 to 80C during precipitation of the aminoplast. The temperature, the degree of agitation to which the system is subjected, the amino compound:
formaldehyde molar ratio, the acidity and the dilution of the system all play a part in the nature of the resultant precipitate, at least in respect of its 'hydrophilicity' i.e. its capability to absorb water~
To obtain a particulate precipitate rather than a gel or solid block of the urea- or melamine-formaldehyde, it is necessary to control the precipitated solids content of the system. This is temperature dependant; it will usually be necessary to use lower temperatures at higher reactive solids contents to maintain the system fluid or it may be necessary to use higher temperatures at lower reactive solids contents, within the temperature range quoted above, to obtain the desired absorbency for the precipitate. At solids contents of about 19%, for example, it may be necessary to reduce the temperature to about or below 0C, to prevent formation of a solid (or at least 'unstirrable') mass.
The process preferably is operated on a batch basis but it 1(~78~)84 may be operated continuously, when the precipitated aminoplast solids content may be controlled at less than 20% by weight by controlling the temperature, by stripping precipitate from the system as it is formed or by controlling the reactive component solids content of the system.
~y the term "reactive component solids content" is meant the content in the system of the components which are chemically reacted together to form the cured product, and hence this term excludes the acid catalyst content and the content of any other chemically inactive materials which may be present.
The precipitate may be separated from the 'mother liquor' by a dewatering process, such as by simple filtration or by centrifuging and the mother liquor may be recycled, amino compound and/or formaldehyde and/or amino-formaldehyde resin being added as necessary to bring the reactive components solids content back to the desired level. The precipitate need not, and in fact rarely will, have the same amino compound:formaldehyde molar ratio as the aqueous system from which it originates. The precipitate can be washed and dried and used directly; alternatively, the precipitate (optionally pre-washed, or washed and dried) can be neutralised with a base, for example by dispersing the precipitate in water and adding a calculated quantity of base. The neutralised precipitate may then be re-filtered, washed and dried, before use.
T~e precipitate will be produced, if the conditions given above are observed, as loose agglomerates of particulate, lQ78084 approximately spherical, non-porous, cured, unfilled particles of average diameter approximately 0.5-5 microns and a surface area of less than 1 square meter per gram, consisting of substantially fully cross-linked aminoplast resin with a methylol content of less than 2% (i.e. the resin is, in fact, about 98% cross-linked).
In a preferred process for manufacturing the filler material, urea is dissolved in aqueous formaldehyde and reacted at a temperature of 30 to 40 C at pH 7 to 9 for 1 hour. These conditions are not critical to the subsequent production of filler, and the presence of other compound in the resin does not usually affect the process.
The resin is diluted with water and acid is added to precipitate the filler. After the reaction period, the slurry is centrifuged and the filtrate is returned to dilute more resin. The damp filler is mixed with a base to neutralise the residual acidity and then dried.
Values of the various parameters involved are:
U:F molar ratio of resin 1:1.33 Cured solids content of about 9% by weight precipitation tank Addition of acid 1% by weight of 65%

pH in reaction tank 2 to 2.5 Reaction time 45 mins Reaction temperature 45C
It should be noted that the process described above provides a particulate urea-formaldehyde material which, when dried, is suitable for direct incorporation as a filler in a curable aminoplast resin system, without any need for 1C~78084 comminution as by ball-milling or other grinding process.
Furthermore, we consider it surprising that such a material being non-fibrous, should be capable of use as a replacement for cellulose as a filler in moulding materials without significant loss of any beneficial property of the moulding material or articles moulded therefrom.
The following examples illustrate preferred embodiments of the present invention, parts and percentages being by weight unless otherwise stated. Examples 1 to 7 illustrate the production of the materials used as fillers in the present invention as illustrated by the succeeding Examples.

A series of cured, cellulose-free particulate urea-formaldehyde resins were made by first providing stock solutions of various urea:formaldehyde ratios, as follows:-Table I
U:F Molar Parts Parts 36%
Stock Solution Rat~o Urea Formaldehyde (reactive Solution _ solids) _ A 1:1.3 600 1083 B 1:1.4 600 1167 C 1:1.5 600 1250 D 1:1.6 600 1330 E 1:1.9 600 1580 F 1:2.2 600 ¦ 1834 These solutions may be diluted as desired. Thus for solutions of, for example 6% reactive solids content, the quantity of stock solution taken for dilution to 4.0 litres is:-1~78084 Stock Solution Quantity taken (grams) Each reaction mixture (or 'aqueous system') of 4.0 litres also contained 40 mls of 65% phosphoric acid solution. In each case, the system was stirred for two hours at the desired temperature to form a slurry and then the slurry was filtered to remove the cured urea formaldehyde material formed as particulate precipitate. A sample of each precipitate was dried in an oven at 110C, then was tested for water absorbency by mastication on a glass plate whilst adding water dropwise, the "absorbency" being defined as the maximum volume of water absorbed by one gram of the material without separation of the water being visually noticeable.
A1BO neutralisation of some of the precipitates was effected by re-dispersing the precipitate in water at 85C, with stirring for 3 hours, and during this time adding calcium carbonate to bring the pH of the new slurry to about 7Ø
The neutralised precipitates were refiltered and dried, and the water-absorbency of each was determined as described above. The results are shown in Tables II and III hereafter, absorbencies in brackets being those of the neutralised materials. The term "precondensation" means the condensation effected from the immediate precursors in concentrated - 9 _ 107808~

solution at reflux, before acidifying the system to precipitate cured particulate material. The urea:formaldehyde ratio of each of the neutralised fillers was within the range from 1:1.25 to 1:4.0; the B.E.T. surface areas of these materials were difficult to determine but were less than 1 square metre per gram.

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EXAMPLES 2 to 4 Urea was dissolved in water and mixed with aqueous formaldehyde to produce aqeuous reaction s-ystems at room temperature as identified in Table IV, the reactive solids content in each case being maintained at 10% to control the precipitated solids content at less than 10%, 1% v/v of 65%
phosphoric acid (S.G. 1.5) was immediately added as catalyst and a precipitate of cured urea formaldehyde was allowed to form over a period of 2 hours, with stirring under the conditions indicated at Table IV. Neutralisation was effected as described above and the neutralised precipitate was dried at 90C for 16 hours in an oven set at 110C.
TABLE IV

Water Content Absorbency Urea:formal- Stirring Example of dried of dried dehyde molar Conditions 15ppt. (%) ppt. (ml/g) ratio

2 13.4 3.0 1:1.3 50 r.p.m.

3 10.0 4.5 1:1.6 50 r.p.m.

4 10.0 1.7 1:1.3 Silverson high speed shear mixer EXAMPLES 5 and 6 The procedure was the same as for Examples 2 and 3, except that the aqueous reaction system was allowed to stand unmixed for two hours to form a resin precondensate, before addition of the acid catalyst. Table V shows the results obtained for the products, neutralised as described above.

3n 1~78~)84 TABLE V

Water Content Absorbency Urea:formal-Example of dried ppt. of dried ppt. d-ehyde molar (%) (ml/g) ratiO

3.5 3.2 1:1.9 6 8.0 2.2 1:1.2 A commerical urea formaldehyde resin having a urea:
formaldehyde molar ratio of 1:1.6 (BU700 (trademark) - produced by British Industrial Plastics Limited, Chemicals Division) was diluted with water to provide an aqueous system having a reactive components solids content of 10%, and 1% v/v of 65%
phosphoric acid (S.G.1.5) as catalyst was added. A slurry of solids content less than 10% by weight was obtained as in the preceding Examples. The dried precipitate had a water content of 16.5% and an absorbency of 3.0 ml H20/g, after neutralisation as described above.
In each of Examples 2 to 7, the B.E.T. surface area of the product was less than 1 square metre per gram and the average diameter was about 2 microns.
EXAMPLES 8 to 21 Moulding powders were made, a number based on urea formaldehyde resin, and a number based on melamine formaldehyde resin, by mixing the ingredients (specified 107808~

below) in a Z-blade mixer at 60C for 35 minutes. The resultant mix in each case was dried at 80C in a Mitchell oven to a free water content of about 1% and the dry chips obtained were comminuted in an Apex mill and ground to a fine powder. 0.25% zinc stearate was added before granulation on a PR46 Buss Ko-Kneader (reg. Trade Mark and final comminution on the Apex mill.
Urea formaldehyde resin-based powder Urea formaldehyde resin (urea:formaldehyde ratio 1:1.33, solids content 62.5%) 3480 parts Filler (cellulose + material produced by the invention) 896 parts Catalyst 45 parts Hexamethylenetetramine 45 parts Zinc Stearate 15 parts Plasticizer 8 parts Barium Sulphate 59 parts Melamine formaldehyde resin-based powder Melamine formaldehyde resin (melamine:formaldehyde molar ratio 1:2, solids content 57%) 3600 parts Filler (cellulose + material produced by the invention) 896 parts Plasticizer 10 parts The actual compositions and properties are further detailed in Table VI.

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1078~8~

Notes (a) UF Example = urea formaldehyde material produced by Example, number in brackets.
(b) UF = urea formaldehyde; MF = melamine formaldehyde i.e. resin used as binder.
(c) Disc flow - in inches (Standard Test) (d) Cure = minimum time of press closure in seconds, to produce blister-free moulding.
(e) Free water, in ~ by weight, of finished moulding powder.
(f) In mg. after 0.5 hour immersion in boiling water or 24 hours in cold water.
(g) In percent.
(h) Electric Strength in volts per mil.
(i), (j) Surf. = surface resistivity in log 1 ohm;
Vol - volume resistivity in log 10 ohm cm.
(k), (1) St = Flexural Strength in MN/m ;
Mod = Flexural Modulus in GN/m2.

In (e) to (1), the methods used are those set out in B.S. Text 1322.

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermosetting moulding composition, comprising a curable aminoplast resin and from 15 to 80% by weight (based on the total weight of the composition) of a filler, wherein the filler comprises at least in part a cured, precipitated, cellulose-free, urea-formaldehyde or melamine-formaldehyde material having -NH- groups capable of reacting with the curable aminoplast resin during curing of the latter, produced by a process which comprises (a) providing an aqueous system which has a pH of less than 4, is free of surface active agent, and contains:
(i) a urea- or melamine-formaldehyde resin or the precursors for producing same, and (ii) an acid catalyst, (b) agitating the system gently to produce a slurry containing cured aminoplast material in precipitated form as aggregates of microspherical particles and controlling the content of precipitated urea- or melamine-formaldehyde resin in the system at less than 20% by weight and (c) drying and neutralizing the precipitated urea- or melamine-formaldehyde resin whilst maintaining a water absorbency for said precipitated resin of 1 to 6 millilitres/gram.

2. A thermosetting moulding composition according to Claim 1, wherein the precipitated aminoplast is one produced by a process as defined wherein the solids content of the precipitated aminoplast has been controlled in the aqueous system by controlling the temperature during precipitation.

3. A thermosetting moulding material according to Claim 1, wherein the precipitated aminoplast is one produced by a process as defined wherein the solids content of the pre-cipitated aminoplast has been controlled in the aqeuous system by controlling the content in the system of the components which are chemically reacted together to form the cured product excluding the acid catalyst content.

4. A thermosetting moulding composition according to Claim 1, wherein the particulate urea- or melamine-formaldehye material has a B.E.T. surface area of less than 10 square metres per gram.

5. A thermosetting moulding composition according to Claim 4, wherein the particulate urea- or melamine-formaldehyde material has a B.E.T. surface area less than 1.0 square metre per gram.

6. A thermosetting moulding composition according to Claim 1, wherein the particulate urea- or melamine-formaldehyde material has a water absorbency of from 1.5 to 2.5 millilitres per gram.

7. A thermosetting moulding composition according to Claim 1, wherein the particulate urea- or melamine-formaldehyde material is one produced in the form of aggregates of microspherical particles having an average particle diameter of from 0.5 to 5 microns.

8. A thermosetting moulding composition according to Claim 1, wherein the particulate urea- or melamine-formaldehyde material has not been ground or comminuted prior to its incorporation in aminoplast resin.

9. A thermosetting moulding composition according to Claim 1, wherein the particulate urea- or melamine-formaldehyde material has been neutralised prior to its incorporation in the resin.

10. A thermosetting moulding composition according to Claim 1, wherein the filler comprises from 30 to 100%
by weight (based on the weight of the filler) of the particulate urea- or melamine-formaldehyde material.

11. A thermosetting moulding composition according to Claim 1, wherein the filler comprises two components, one being the cured, precipitated, cellulose-free particulate aminoplast material and the other being .alpha. - cellulose.

12. A thermosetting moulding composition according to Claim 1, wherein the aminoplast resin is a urea-formaldehyde resin having a urea:formaldehyde molar ratio prior to curing of from 1:1.2 to 1:1.7.

13. Articles whenever produced by curing a thermo-setting moulding composition as defined in Claim l.