Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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.
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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
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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.
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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
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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,
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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%
H3P04
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
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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.
EXAMPLE 1
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:-
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1~78084
Stock Solution Quantity taken (grams)
A 407
B 416
C 423
D 425
E 447
F 463
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
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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.
-- 10 --
1078084
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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.
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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
EXAMPLE 7
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.
- 15 -
1~78084
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-- 16 --
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.
