Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
l~r:TllOD I~OR ~NUl~/~CTUI~] NG PrlJ~NOLIC r~rSIl~S
ABSTRACT OF THE I)ISCLOSURE
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A method of making phcnolic resins from the conden-
sation of phenol with formaldehyde in the pres0nce of a basic
S catalyst is disclosed. After the condensation reac~ion has pro-
ceeded to a desired point, the reaction mass is acidified to a
pl~ between 3 and 4. This facilitates removal of water from the
phenolic resin. As a result, the viscosity of the resin obtained
is sufficiently high so that when the resin is used in combination
1 10 with blowing agents, surfactants, and catalysts to form rigid
j foams,-such foams have uniform cellularization.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the manufacture of
phenolic resins and particularly to phenolic resins that
S are useful for making rigid foams.
Prior Developments
Canadian Patent Application, S~rial No. 139,727,
. . ,
. filed April 14, 1972, in the name of Daniel Hanton, dis- :
.:~ closes a method of making phenolic resin by the condensa~ 10 tion of phenol and formaldehyde, in which quantities of
both the formaldehyde and a basic catalyst are added to
the phenol in at least two successive steps. According
. to the process disclosed in the above-identified applica-
. tions, after the last stage of the condensation reaction
has proceeded to a desired point, the
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rc~ction en~iroluncnt i~ ncutralizc~ by thc adc1ition oE
an acid. Sufficient ncid is a(tdc~ to bring the pll of
the reaction cnvironmcnt to betwccn ~ and 7.5. Then thc
reaction mass is allowed to rest an(l thc resin phasc and
the aqueous phase separate. The resin is then decantcd
from the reaction mass. After this decantationJ ~he resin
is ~ubjected to at least one additional water r~moval step,
for example, vacuum distillation, to increase its viscosity.
According to the above-idcntified applications,
the phenolic resin thus obtained can be used to manufacture
rigid phenolic foams, by mixing a blowing agent, a surfactant,
and a hardening catalyst with the resin,
The resins obtained according to the method just
outlined above, i.e., in whicn the reaction environ-,nent is
?i 15 neutralized to a pH ranging between 7 and 7.5, have dry
extracts of 64 to 66 per cent, and have viscosities ranging
between 700 and 900 centipoises ~cp).
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- It has been found that when using resins having
viscosities in this ~range, the vapor bubbles formed by the
blowing agent during its evaporatio~ under the influence of
heat at the outset of the hardening reaction can have a
tendency to coalesce and to rise in the resin-bubble disper-
sion. This can result in a non-homogcnous cellularization
throughout the thickness of the foam. Where there is coa-
lescence of the bubbles,}eterogeneous cellularization occurs,
with tlle largest and greatest number of cells being found
on the side of the panel that is uppcrmost during produ~tion.
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This rcsults in a foam lulving a non-uniforln dcnsity ~nd
poor mcchanical properties, especially in thc rcgions
whcrc rclativcly lar~c cclls are located.
,
It sllould be ~ointed out that thc blowing a~ents,
' 5 surfactants, and hardening catalys~s that are commonly
', uscd have a tcn~ency to a~gravate this problem as they
' ' tend to reduce the viscosity'of the expansible mixturc and
-, thus increase tlle likelihood that a heterogeneous cellulari-
zation will occur.
It has been determined that, in order to obtain
; -foams having small cells and a homogeneous cellularization
'' 5 ,, throughout their thickness, it is necessary to use a resin
~; having a viscosity high enough to prevent migration and
' coalescence of the bubbles in the foam prior to the harder.-
,',~ 15 ing of the resin. ' '
, One effort that was made to increase the viscosity
of the resin involved removing water from the resin by means
,' of a relatively long duration vacuum distillation step. It
was found to be extremely difficult, even when distilling
at low temperatures under reduced pressure, to avoid the
continuing condensation of the resin. Under, these conditions, '~
,~, viscosities of the resins reached 4,000 to 8,000 cp at 20C, '
,i~ with dry extracts of 70 and 75 per cent, respectively. When -
,~ ' resins having such und,uly high vis,cosities are used, the foam
~ 25 manufacturing process is adversely affected, especially fro~
"' an economic standpoint. This is so because, i'n order to mix ',
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the higll viscosity rcsin, so that a low density foam having
a homogencous cellularization of small bubbles is produced,
the mixin~ device requires more power and the duration of
the mixing step must be increased. This increases the
total energy required by the process and thus increases the
cost.
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Another effort to increase the viscosity of the
resin involved centrifuging of the resin to eliminate water.
However, the resin retained a significant amount of water,
even after very high-speed centrifuging, and it was not
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,~ possible to obtain resins having a dry extract of above
70 per cent.
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. It has now been found that these disadvantages
can be avoided, particularly the loss of time and energy
involved in concentration by distillation or centrifugation. -
Further, it has been found possible to regulate the dry
b", extract of the phenolic resin, thus its viscosity, more
easily and more precisely. This considerably facilitates
the manufacture of phenolic foams having desired densities
;:, .
- 20 and cell distribution.
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SUM~RY OF THE INVENTION
The invention concerns a method for the manufacture
of phenolic resins, notably useful for manufacturing foams,
from phenol and formaldehyde, by condensation in at least
two successive stages in the presence of an alkaline catalyst.
After the reacting mixture has been cooled at the end of the
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l~st sta~c o~ condcl1sntion, a ~ua11tity oE an acid su~ficient
to ob~ain a pll rangi11g bctwccn about 3 to ~, and preferably
betwecn about 3.4 and 3.6, is added to thc phenol-formalde11yde
mixturc. Un~cr thcsc conditions, the resin is separated from
: 5 its aqueous environmcnt so that it can be used to form ex-
.pansible dispcrsions.
.
- According to one fcature of the invention, thc
reacting mixture is cooled to a temperature ranging between
30 and 35C before the addition of acid.
. lO DESCRIPTION OF THE INVENTION
.
According to the.method described in the above-
. idçntified Canadian patent application for making phenolic
resins identified as Resole II bis, mixtures of phenol and ~ :
formaldehyde are.reacted in the presence of an alkaline
. 15 catalyst. The mole ratio of formaldehyde to phenol in these
reactions is between about l and 1.6 and does not exceed ~
~: l.7. The formaldehyde and a portion of the catalyst are
. added to the phenol in successive steps and sometime after
. the last addition of formaldehyde and catalyst to the reaction
. 2~ mixture, the mixture is cooled. This mixt.ure contains an
.~ excess of the basic catalyst tfor example, sodium hydroxide).
According to. this previous method, an acid, for example,
hydrochloric acid, at 35 per cent concentration, is added
to the mixture in order to neutralize the sodium hydroxide
and to bring the pH of the mixture to about 7.
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~ccording to the invention l1erein disclosed,
instead of stopping th~ addition of the acid when the
pH reaches about 7, an additional qu~lntity of acid is
added to bring the pH to between about 3 and 4. It has
been found that if a stoichiometric quantity of hydro-
chloric acid is added in relation to the total quantity
of sodium hydroxide used, a p~1 of about 3.5 is obtained.
~; This indicates that, at this pH value, all the phenolic-OH
groups present in the resin, which were previously found
` l0 to be water soluble in the sodium phenate state, are free.
The acid added to the reaction can be dilute or
concentrated. For the purposes herein disclosed, hydro-
chloric acid has been found to be especially useful.
' ' .
It has be~n foun~l that whe~ ~he pH of the reaction
environment is between 3 and 4, a higher propor1ion of
water separates from the resin and the dry extract of the
separated resin is higher than in the case of neutraliza-
; tion of the reaction environment to a pH of only 7 to 7.5.
,
The range of acidification of t~e reaction mix-
ture to a pH between 3 and 4 is considered to be optimal.
If the reaction mixture is acidified to values lower than
about 3, the resins obtained after separation of water
have much higher viscosities. It is believed that the
excess acid introduced catalyzes the reactants, even at
2S - low temperatures, and thereby increases the v;scosity of
~ the resin.
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Convcrs~ly, i the pl-l value is higher t]~an about
1 4, resins having viscosities sufficiently high to ensure
l the attainment of fine, homogenous cellularization through-
out the thickness of the foam are not obtained. For example
¦ 5 in one phenol-formaldehyde reaction, the quantity of hydro-
chloric acid added to the reaction mixture to bring the
~ pH to about 7, corresponds to only about 58 percent of
¦ the total quantity of sodium hydroxide used as a catalyst.
Under these conditions, the sodium phenate groups retain
j ]0 water and the desired resin viscosities after decantation,
~ and even after centrifuging, are not obtained.
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For purposes of further illustrating the invention,
the following specific examples are g~iven.
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EXAMPLE l
A reaction mixture was prepared, according to ~ -
the method for preparing Resole II bis resins disclosed
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in Canadian patent application, Serial No. 139,727, having a ~ .
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; total mole ratio of formaldehyde to phenol of 1.4 and using
an amount of sodium hydroxide catalyst equal to 2 per cent
by weight of phenol. The following corresponding values
~ for the dry extract and the viscosity were obtained:
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pH of
the resin 3.0 3.4 3.6 4.0
dry extract of
the resin decanted
S and drawn o f f in
~ by w~ight 74.0 72.5 71.5 70.0
viscosity of
the resin decanted
~ drawn off, in
cp, at 20C 4000 2000 1500 1100
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EXAMPLE 2
63.45 kg (675 moles) of phenol were placed in a
; 150 liter stainless steel reactor, having double wall con-
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struction for the passage of a heating or cooling medium
and having a means for agitating the contents of the reactor.
67.50 kg of formaldehyde in aqueous solution, having a con-
centration of 36 per cent by weight (810 moles) were added
to the phenol. The temperature of the mix was brought to
50C and at this temperature, 1268g of an aqueous solution
of sodium hydroxide, having a concentration of 50 per cent
by weight, was added to the reactor.
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The mix was heated to about 70C to start the
reaction. Because the reaction is exothermic the tempera-
ture of the mix rose to 100C, and this temperature was
maintained for one hour by circulating a coola~t between
the walls of the reactor.
The mixture was then cooled to about 80C and
11.25 kg of an aqueous formaldehyde solution having a
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107~439
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concentration of 36 per cent by weight ti.e., 135 moles
of formaldehyde) were added to the ~eactor. The tempera-
ture of the mixture was maintained at 80C and 1268g of
an aqueous solution of sodium hydroxide having a concen-
tration of 50 per cent by weight was added to the reactor,
and the 80C temperature was maint~ined for 30 minutes.
:
The mixture was then cooled to 30C and divided
into eight equal parts. These eight parts of the mixture
were separately acidified by dilute hydrochloric acid
having a concentration of 18 per cent by weight, under
- agitation, to pH values ranging from 2.0 to 7.4.
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'After acidification, all eight parts were left
at rest for 6 hours so that in each of them, a resin laycr
and an aqueous layer formed. Resin was obtained by
decantation from each of the eight parts.
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` The dry extract and viscosity of the resin from
- each of the eight parts were measured. Then, the resin
taken from the parts in which the pH had been adjusted
to 5.0, 7.0 and 7.4 were concentrated under vacuum to a
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dry extract of 72 per cent and the viscosity was measured
~! again.
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