Note: Descriptions are shown in the official language in which they were submitted.
Applicant's copending Canadian applica~ion Serial No. 415~6~6,
filed November 16, 1982, relates to the preparation of flame-retardant, rigid,
thermosetting foam products, by reacting, in the presence of a blowing agent~
a catalyst, a furfural-alcohol polymer, a phenol-formalde]lyde or benzylic-
ether formaIdehyde resin, a melamine resin and a methylene diphenyl isocyanate.
The reaction provides for a rigid foam characterized by low friability and good
heat and flame-retardant properties.
Typically, thermosetting foam products are prepared by the use of
a phenol-formaldehyde resin, a blowing agent and a strong acid catalyst. Such
thermosetting foam products Qre often characterized by having a fairly brittle
foam structure, with low compression strength and exhibiting high friability
and brittleness properties. Such phenolic foams, usually have an open-cell
foam structure and very little, if any, strength at low densities; for example,
below about 2.5 pounds per cubic foot. These phenolic foams, are difficult to
burn, melt or smoke, in that they are characterized substantially by methylene
linkages. However, such phenolic foams are not generally commercially accept-
able, because of low compression strength, poor insula-tion value and the
corrosive characteristics of the foam.
Modified phenolic foams have been prepared employing polyisocyanates,
to produce a phenolic urethane foam product. ~or example, United States
Patent 3,948,324, issued April 6, 1976, describes a modified urethane benzylic-
ether phenolic foam product. The cellular polymeric reaction product is pro-
duced by the reaction of a benzylic-ether phenolic foam in the presence of a
liquid methylene diisocyanate-type isocyanate, a blowing agent and amine
catalysts, to form a ben~ylic-ether phenolic urethane foam product. The reac-
tion mixture foams and cures spontaneously in an exotherm into a tough, non-
friable foam. The resulting foam product is closed-cell and has good insula-~ion
-- 1--
55~
properties; however, the foam product, because it ~urns arld smokes in a
manner very similar to a ure-thane foam product made from aromatic polyols, does
not have commercially acceptable flame-retardallt properties, probably due in
part to the presence o-f urethane linkages in the resulting foam mass.
Another difficulty associated with benzylic-ether phenolic urethane
foams is that the resul-ting material is quite reactive, and, therefo-re, it is
difficult to control the nature and extent of the reaction and is difficult
to produce the thermosetting foam in a consistently high-quality manner in
standard production foaming equipmen-t, due to the very high reactivity of
the ingredients.
It would be desirable ~o prepare a phenolic foam material which pro-
vides for a substantially closed-cell ultra low density foam s-tructure of low
friability and which exhibits nonburning and nonsmoking characteris-tics.
~his inven-tion relates to an improved, modified, phenolic thermo-
setting foam product and to the method of preparing and using the foam product.
In particular, the invention concerns a thermosetting foam product prepared by
the reaction of a benzylic-ether phenol-formaldehyde resin and reacting the pre-
polymer in the presence of a weak acid catalyst, to produce a prepolymer with
a diisocyanate to provide a modified benzylic-e-ther pehnolic foam product.
More particularly, the invention relates to a method of preparing
a nonEriable, closed-cell, benzylic-e-ther phenol-formaldehyde modified
thermosetting foam product characterized by a low flame spread and smoke
properties, which method comprises:
a~ reacting, under substantially anhydrous conditions, 100 parts
of a benzylic-ether phenol-formaldehyde resill, having a hydroxyl number of
greater than about 200, wi-th from about 50 to 150 parts by weight per 100 parts
of the benzylic-ether phenol-formaldehyde resin of a weak acid catalys-t at a
-- 2
pH of from about ~.0 -to 6.5, -to form a benzylic-ether phenol resin
prepolymer; and
b) reacting the prepolymer, in the presence of a blowin$ amount o-f
a blowing agent to form a Eoamable mass, and acatalytic amount of an organo-
metallic catalyst, which i.s not affected by the pH o:E the prepolymer, with from
about 50 to 200 parts by weight per 100 parts of the benzylic-e-ther phenol
resin prepolymer of a methylene diphenyl polyisocyanate in an exothermic reac-
tion, to provide for the further heat and acid condensation of -the phenol
resin prepolymer and the reaction of the isocyana-te wi-th the prepolymer, to
produce a low-friability, substantially closed-cell, phenolic modified
thermosetting foam product composed substantially of acid methylene linkages.
It has been discovered that a modified benzylic-ether phenolic
aldehyde foam product may be prepared containillg substantially methylene
linkages and few, if any, urethane linkages in a controlled reaction, by the
employment of a weak acid catalyst compound, to prepare a prepolymer, and the
subsequent reaction of the weak acid-containing benzylic-ether phenol resin
prepolymer with a methylene diphenyl isocyana-te compound in the presence of
a blowing agent and a catalyst, to produce a phenol modified product. The
thermosetting foam product of the invention is not friable or has low
2() friability characteristics,
;~
- 2a -
is composed of closed cells or subs-tantially closed cells, and has comparable
strength to unmodified urethane foam, without the burning and smoking character-
istics and properties of such urethane foam. The resulting foam product, for
example, is substantially nonburning and nonsmoking foam with a low density of
generally less than 3.0 pounds per cubic foot. The foam product has a flame
spread under AST~I E-84 of lO or less and a smoke value of ~0 or less.
The benzylic-ether phenol-formaldehyde modified foam product of *he
invention is prepared by reacting 100 parts of a substantially anhydrous
benzylic-ether formaldehyde resin, typically having a hydroxyl number of greater
than 200; for example, ~00 to 600, with about 50 to 150 parts by weight per 100
parts of the benzylic-ether resin of a ~eak acid catalyst, to form a benzylic-
ether resin prepolymer. Typically, the reaction is carried out without the use
of external heating at a tempera-ture of less than 100F; that is, at room
temperature 60-80F. The resulting prepolymer then is reacted in the presence
of a blowing agent and in the presence of a catalyst, to eE:Eect the reaction
with the isocyanate, typically an organometal catalyst not affected by the
acid pH of the prepolymer, with Erom about 50 to 200 parts by weight of a methy-
lene diphenyl isocyanate (MDI) per 100 parts of the benzylic-ether phenolic
resin. The prepolymer MDI reaction produces an exothermic reaction, with the
exothermic reaction providing and generating heat to complete further the heat
and acid condensation of the benzylic-ether phenol-formaldehyde resin, to pro-
duce a thermosetting :Eoam product which comprises substantially methylene
linkages and, therefore, having desirable flame spread and smoke properties, but
having desirable friability and compression strength properties of a typical
phenolic foam.
In one preferred embodiment, it has been found that the reaction to
form the weak acid-catalyst benzylic-ether formaldeh~de prepolymer should be
;t~
carried out with mixing of the components of the reaction for at least 6 hours
and preferably 8 to 12 hours, e.g., 12 to 24 hours, to provide :Eor a substantial-
ly condensed prepolymer with methy]ene linkages.
Further, the formaldehyde odor of the prepolymer is often quite
powerful so that prior to the reaction of the prepolymer with the polyisocyanate
to form the modified foam of the invention a sufficient amount oE melamine
or other amine reactive with formaldehyde should be added to and mixed with
the phenolic resin or the prepolymer reaction components to react with all or
substantially all of the free formaldehyde of the prepolymer reaction mixture.
One mole of melamine is added to about every six moles of free formaldehyde to
react the free formaldehyde stoichiometrically and provide a substantially
formaldehyde-odor-free foam product. Commercially available benzylic-ether
phenol-formaldehyde has about two percent free formaldehyde so that about 2.5
parts of melamine is added to the resin prior to or with the addition of the
weak acid catalyst. The amount of melamine to be used often ranges from about
1 to 5 parts per 100 parts of the resin.
In operation, the melamine is added and mixed with the free formal-
dehyde containing benzylic-ether phenol-formaldehyde resin to react the free
formaldehyde, then the weak acid catalyst is added with the blowing agent and
other fillers and additives 9 and the mixture reacted with continuous mixing and
blending for 6 to 24 hours to provide a condensed prepolymer. The prepolymer
is then reacted with the ~1DI typically in a foam mixing head wherein the ~IDI
containing the tin catalysts in one stream is intimately admixed with the pre-
polymer in another separate stream to provide an exothermic foam mixture dis-
charged from the mixing head on a production line.
The method of the invention overcomes the difficulties associated
with the preparation of the cellular polymeric masses, as disclosed in the
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\~
abovementioned United States Patent NQ. 3,9~8,824, in that the reaction is a
controlled reaction) by the employment of a weak acid catalyst and the avoidance
of the typically strong acid catalyst employed phenolic foams, such as the
sulfonic acid catalyst, such as methane sulfonic acid and paratoluene sulfonic
acid and similar strong acids which are far too reactive in curing the benzylic-
ether phenol-formaldehyde resin. Purther, the benzylic-e~her phenol-formaldehyde
resin comprises a novola~c resin which is substantially anhydrous; that is,
having less than about 1% by weight water, in order to avoid the intentional
creation of urethane linkages, which leads to unacceptable flame and smoke
properties in the foam.
The benzylic-ether phenolic resins employed in the present invention
are characterized by containing one or more units having the formula:
Oll R' R'
~ CH - 0 -lH
A ~ B
_,
wherein A, B and C are hydrogen, hydrocarbon radicals, oxyhydrocarbon radicals
or halogen and R' is individually a hydrogen or a hydrocarbon radical of 1 to
8 carbon atoms. The resins have average degrees of polymerization, as measured
by the number of repeating aromatic rings, of 3 to 100, and preferably about
to 10. Although higher molecular weight resins are operable in the curing
reactions above described, such resins are difficult to handle from the stand-
point of viscosity.
The described benzylic-ether resins are condensation polymers of a
phenol having the general formula:
OH
A ~ B
- 5 --
S5 L)
wherein A, B and C are hydrogen, hydrocarbon radicals, oxyhydrocarbon radicals
or halogen, with an aldehyde having the general formula R'CHO, wherein R' is a
hydrogen or a hydrocarbon radi.cal of 1 to 8 carbon atoms, prepared in the liquid
phase in the substantial absence of water a~ temperatures below about 130C in
the presence of catalytic concentrations of a metal ion dissolved in the reac-
tion medium. The molar ratio of aldehyde to phenol generally can be varied from
3:1 to 1:1, although some resin is also formed outside these ratios. ~he pre-
paration and characterization of these resins is disclosed in greater detail in
United States Patent 3,485,797. In the preferred form, these resins have the
general formula:
nH n~l m
X ~ CH2-0-CH2 ~ CH2 [~
wherein R is a hydrogen or a phenolic substituent meta to the phenolic hydroxyl
group, the sum of m and n is at least 2 and the ratio of m to n is at least l,
and X is an end group selected from the group consisting of hydrogen and methyl-
ol, the molar ratio of said methylol-to-hydrogen end groups being at least 1.
The most preferred benzylic-ether resins employed in the resin com-
positions of the present invention are -those in which R is hydrogen. The phenols
employed in the formation of the benzylic-ether resins are generally all phenols
which have heretofore been employed in the formation of phenolic resins general-
ly, and which are not substituted at either of the carbon atoms ortho to the
hydroxyl group. Any one, all or none of the remaini.ng carbon atoms of the
phenol ring can be substituted. The nature of the substituent can vary widely,
and it isonly necessary that the substituent not interfere in the polymerization
of the aldehyde with the phenol at the ortho position. Substituted phenols
-- 6 --
3 ~ r~ r ~
,, ~;9 ~
employed in the formation o:E the phenolic resins include: alkyl-substituted
phenols; aryl-substituted phenols; cycloalkyl-substituted phenols; alkenyl-
substituted phenols; alkoxy-substituted phenols; aryloxy-substituted phenols;
and halogen-substituted phenols, the foregoing substituents containing from 1 to
26 and preferably from 1 to 6 carbon atoms. Specific examples of suitable
phenols, aside from tlle preferred unsubstituted phenol, include: m-cresol; p-
cresol; 3,5-xylenol; 3,4-xylenol; 3,4,5-trimethyl phenol; 3-ethyl phenol; 3,5-
diethyl phenol; p-butyl phenol; 3,5-dibutyl phenol; p-amyl phenol; p-cyclohexyl
phenol; p-octyl phenol; 3,5-dicyclohexyl phenol; p-phenyl phenol; p-crotyl
phenol; 3,5-dimethoxy phenol; 3,4,5-trimethoxy phenol; p-ethoxy phenol; p-
butoxy phenol; 3-methyl-4-methoxy phenol; and p-phenoxy phenol.
A prepolymer of the ben~ylic-ether phenol-formaldehyde resin is pre-
pared employing at least 50 parts by weight to 100 parts by weight of the resin
of a weak acid catalyst, and often from 50 to 150 parts may be employed. The
weak acid catalyst may, for example, be an organic or inorganic weak acid cata-
lyst and should be anhydrous or substantially anhydrous, and typically in pow-
dered form. Representative weak acid catalysts, which may be useful in the
practice of the invention, would include, but are not limi~ed to: oxalic acid;
citric acid, tartaric acid; and boric acid, and combinations thereof. The
preferred weak acid catalyst comprises an anhydrous or substantially anhydrous
powdered boric acid catalyst.
The boric acid catalyst, in a l/~Oth normal solution, provides for a
pil of about 5.2 and, in addition to initiating effectively polymeri~ation of the
phenolic resin as a prepolymer, also provides and incorporates excellent flame-
retardant properties and increases the dimensional s-tability o the resulting
foam product, and raises the upper temperature range of the Eoam from about
250F to 350F. In the preferred embodiment, the boric acid is employed in an
-- 7 --
amount ranging from about 50 to 120 per lO0 parts of the benzylic-ether resin.
It has been found that sodium tetra borate, substituted for a boric acid in
the reaction of the inven-tion, is not effective, indicating clearly that the
improved flammability and flame-spread properties of the resulting foam are not
the result of the borate acting as a flame-retardant agent, but rather in-
dicates the controlled reaction provided by the boric acid and the preparation
of foam with substantially methylene, rather than urethane, linkages. The use
of the borate resulted in a phenolic foam which burned and smoked and had high
friability and an unacceptable K factor, due to the open-cell nature of the
resulting foam.
The preparation of the thermosetting foam product is carried out in
thepresence of a catalyst, which catalyst should n~t be affected by the acid
environment of a low pH, that is, one which is not hydrolyzed in an acid environ-
ment. The catalyst employed is in an amount suf-ficient to effect the complete
cure, cross-linking or condensation of the reactant, to provide for the rigid
urethane modified foam product. The catalyst should provide for the condensa-
tion of the resulting phenolic resin, as well as reaction of the diisocyanate
with the hydroxyl groups of the prepolymer. It has been found that organo-
metallic catalysts, such as cadmium, tin and the like; for example, those
catalysts, or accelerators, used as urethane foam-type catalysts, particularly
catalysts used as trimerization catalysts for polyisocyanurate foams~ may be
employed in the practice of the invention. For example, a suitable organo-
metallic catalyst may comprise alkyl fatty acid, metal catalyst, such as a tin
catalyst, such as stannous octoate, dibutyl ti.n dilaureate and similar type
catalysts. The catalysts may be employed in an amoun~ sufficient to effect the
condensation reaction and typically ranges from about 0.05 to 10 parts per 100
parts of the benzylic-ether resin; for example, 0.5 to 5 parts.
-- 8 --
~ ~ r ~
The reaction is carrled out in the presence of a blowing agent, and
typical blowing agents which may be employed include physical and chemical blow-
ing agents, as well as mechanical blowing techniques. Ilowever, the preferred
blowing agent and technique comprise the employment of liquid physical blowing
agents which are volatile liquids introduced into the reaction mixture, and
which produce a blowing gas, through vapori.~.ation of the blowing agent or thro-
ugh decomposition of the blowing agent during the exotherm of the reaction.
Suitable blowing agents are short-chain aliphatic hydrocarbons; for example, in
the C3-C7 range, and their chlorinated and fluorinated analogs~ such as the
fluoro and chloro alkanes known as Freon (a registered trademark of E.I. du Pont
de Nemours ~ Co.~, methylene chloride and similar blowing agents. The blowing
agents may be employed in amounts ranging from 0.5 to 50 parts; for example, 1
to 10 parts, per 100 parts by weight of the phenol resin employed in the
reaction mixture.
It is usually also desirable to provide a small, but ef-fective,
amount of surfactant to act as a cell-control or nucleating agent, to produce
a lmiform, fine cellular structure to the resulting rigid foam. Typical sur-
factants employed would include, but not be limited to, silicone surfactants in
an amount generally of Erom about 0.15 to 5 parts by weight; for example, 0.1
to 2 parts by weight, of the suractant to 100 parts by weight of the phenol
resin in the reaction mixture. Typical silicone surfactants which may be employ-
ed include those nonhydrolyzable silicone surfactants, such as those described
in United States Patents 3,772,224 and 33849~156J and those polyalkylene glycol
silicones and dimethyl silicone surfactant and block copolymers commonly employ-
ed in foam preparation.
Optionally, if desi.red, a wide variety of other chemicals, additives,
fillers, property enhancers and reinforcers may be incorporated ;n the resinous
9 _
r-- F~ ~
reaction mixture, such as, for example, antioxidants, stabilizers, antistatic
agents, biocides, dyes, fibers, ~illers, particles, clays, flame re-tardants,
fungicides, heat stabili.zers, lubricants, plasticizers, viscosity-control agents,
ultraviolet absorbers and other addltives.
The polyisocyanate useful in the invention comprises polyisocyanates
having 2 to 5 isocyanate groups and typically a methylene diphenyl isocyanate,
such as toluene diisocyanate, or mixtures of isocyanates, such as those of the
abovementioned ~nited States Patent ~o. 3,9~,824. The isocyanates may be
employed alone or in combination or as prepolymers with excess isocyanate, such
as in the abovementioned IJnited States Patent. Typically, the average func-
tionality of the isocyanate would range from 2.~ to 3.2. The isocyanates are
employed typically in a range of from about 50 to 200 parts by weight of the
isocyanate per 100 parts of benzylic-ether phenolic resin; for example, 70 to
120 parts per 100 parts of the benzylic-ether resin.
The modified thermosetting foam of the invention is prepared by,
firstly, reacting the substantially anhydrous benzylic-ether phenol-formaldehyde
resin with melamine and with the weak acid, such as the anhydrous boric acid
powder, to institute prepolymerization at a pH range of from ~.5 to about 6.5
and typically from about 5 to 5.6. The reaction mixture is then mixed with a
silicone surfactant as a cell-control agent, the liquid blowing agent, such as
~reon, and the tin catalyst which is not affected by the low pH employed in the
reaction mixture. The reaction mixture is then reacted with mixing to provide
the prepolymer which is reacted with the methylene diisocyanate, to cause an
exotherm and to produce a closed-cell, low-friability, low-density foam with
good smoke and burning characteristics.
It has been ~ound that if the same procedure is repeated with a
resole resin; that is, one containing water, no reacti.on takes place, since the
- 10 -
MWI in the water and the resole resin react. The employment of the weak cata-
lyst, such as boric acid, provides for a controlled reaction, and strong acids,
which would lead to a lower pil and a very vigorous, uncontrolled reactive
product, such as sulfonic acid, should be avoided. ~ecause of the lower pH of
the resin mixed, after the addition of the boric acid, the reactivity of the
benæylic-ether resin prepolymer is slowed down, so that it is much easier to
handle on a continuous foam machine, unlike the modified urethane foam resin
system of the abovementioned United States Patent No. 3,948,824, wherein the
presence of low pHs and formic acid leads to a very reactive system, which is
difficult to handle with conventional foam equipment.
The invention will be illustrated with reference to certain specific
examples and embodiments; however, it is recognized that various changes and
modifications may be made in the formulations and practice of my invention,
as described hereinafter, all within the spirit and scope of the invention.
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i3S
Example 1.
A thermosetting phenolic foam product was prepared by mixing to-
gether the following ingredients as shown:
Ingredients Parts by Weight
1. Benzylic-ether phenol-formaldehyde
resin #220-000 (Ashland Chemical
Co~) - hydroxyl number 525
ratio phenol/formaldehyde
1/1.5
water less than 0.5% 100
2. Blowing agent - trichlorofluoro
methane (Freon-ll (du Pont)) 25
3. Catalyst - triethanol amine (TEA) 0.3
4. Silicone surfactant - DC-193
(Dow Corning Co.) 2
5. Flame retardant - chlori.nated
(Thermolin 101 (Olin Corp.)) 10
6. Methylene diphenyl diisocyanate
(MDI) (Rubicon XI-171) 125
Cream Time 6 seconds
Tack free time 30 seconds
Cure time 90 seconds
Flame spread (E-84) 25
Smoke 250
Density 2.0 psi
Compressive strength 30 psi
K factor .125
The resulti.ng foam prepared in accordance with the disclosure of
United States Patent 3,948,824 is surface-friable.
- 12 -
S~
Example 2.
A thermosetting phenolic foam product was prepared by mi.xing to-
gether the following ingredients as shown:
Ingredient Parts by Weight
1. Ben~ylic-ether phenol-formaldehyde
resin #220-000 100
2. Boric acid (anhydrous powder) 75
3. Blowing agent - Freon 11 25
. Silicone surfactant DC-193 2
5. Organo metallic catalyst -
stannous octoate 2
6. DMI (Rubicon XI-171) 100
Cream time 20 seconds
Tack free time 60 seconds
Cure time 90 seconds
Density 1.6 pcf
Compressive strength 20 psi
K factor .125
E-84 flame spread 5
Smoke 15
The thermosetting modified foam of the invention provided a closed-
cell foam with good compressive strength and low smoke and flame-spread
properties (as measured by ASTM E-84 tunnel test). The same formulation used
with a water-containing phenol-formaldehyde resole resin provides a friable
foam of very low or no strength and with a density of 4.0 pcf. The use of an
alkaline catalyst, such as an amine catalyst, will not be effective, since the
acid of the resin mixture will render the catalyst ineffective. An exotherm
occurs on -the addition of the isocyanate, which increases the acid reacti.vi.ty
of the phenolic resin, so that both condensation and polymeri~ation occur in
- 13 -
?t~
~ 3~
the reaction mixture, providing a Eoam with substantially methylene bridges
connected with other methylene bridges, which provides excellent flame and smoke
properties to the foam.
It has also been found that the above formulation, when mixed for
a short period of time, provides mixture having a white, creamy texture; how-
ever~ on continuous mixing for long periods of time, such as 12 hours, -the
mixture has a bluish coat or color with condensed water on the wall of the
mixing vessel, providing a substantially reacted prepolymer with methylene link-
ages. The use of melamine, either to the phenolic ether or to the reacted
prepolymer, removes the free formaldehyde odor. The long-mixed prepolymer
reacted with MDr on the formulation produces a low-density foam with low smoke
and flame spread values, yet with good compressive strength and good friability.
The foam is suitable for use as insulation and other uses for closed-cell low-
density foam products.
