Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
. . . _
Field of the Invention
The present invention relates to latently curable binder
compositions for bonding a network of solids including:
refractory materials such as in the manufacture of foundry molds
and cores and the like; lignocellulosic materials such as in the
manufacture of plywood, hardboard, particleboard, fiberboard,
waferboard, oriented strandboard and the like; and other solids,
including glass fibers, metal filings, ceramic powders and the
10 ; like. The invention is slso directed to processes for producing
these binder compositions and processes which put these binder
compositions to use. More particularly, the latently curable
binder composition contains a curing agent with ester
functionality for enhancing the cure speed of phenolic resins
conventionally used in bonding solid materials. The curing
agent is incorporated into the resin in small, effective quantities
with rapid agitation. The stable binder compositions of the
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present invention permit the bonding of high moisture
llgnocellulosic starting materials.
Background of the Invention
Phenolic resins are widely used as adhesives and binders in
many products, including foundry molds, frictional elements
(brake shoes), filter paper, ceramics, fiber mats and structur~l
wood products such as plywood, particleboard, fiberboard,
hardboard, waferboard and oriented strand board. The
production of most manufacturing processes utilizing liquid
phenol-formaldehyde resole tPF) binders is often limited by the
cure speed of the binder. This is true because of the
inherently slow thermal cure of these products, compared to
other commonly used binders, and because of the need to
eliminate moisture from the system during curing. It is known
that phenolic resin cure can be accelerated by adding
formaldehyde dcinors, hexamethylene tetraamine or various
organic and inorganic acids. These methods are not well suited
to the current purposes, however, because hexamethylene
tetraamine is relatively ineffectual with resoles and acids cause
problems with corrosion of processing equipment and metal
fasteners .
In i957, Orth et al. disclosed that lactone curing agents
could be used to harden PF binders suitable for wood gluing
(DAS 1,065,605). The use of lactones as curing agents to
harden PF binders suitable for use in foundry molds was
disclosed by Quist et al. in U. S . Patent No. 4,4~6,467.
In these processes, the lactone and PF binders are
maintained as two separate components just prior to use since
these lactones provide cure (or gelation) of the PF binder at
3 o ambient temperature* Such a two component system is
disadvantageous to the end user of the binder compositions in
that he must provide for adequate mixing by processes and
equipment which are separate from the manufacturing procedure.
*Hereina~ter rererring to a temperature
~, approximate ly 2 0 ~ 2 5 C .
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The art describes a process for
combining curing agents with phenolic resins in-line with the
manufacturing process, thus a~oiding separate process steps.
This invention provides binder compositions wherein the
curing agent is added to the phenolic resin solution well in
advance of use. Therefore, the end user need not admix the
two components. Prior to the present invention, the addition of
curing agents to phenolic resins without immediate cure was
difficult. Adding highly reactive curing agents, such as
alkylene carbonates, was particularly difffcult in that colloid
particles often formed in the binder composition, as disclosed by
Cherubim et al. in U . S . Patent 3, 949 ,149 . The process of the
present invention provides for rapid distribution of the curing
agent without formstion of colloids. The distribution of curing
agent obtained is sufficient to provide a binder composition of
high stability.
Phenolic resin solutions modified with ester curing agents
are known to be useful in the manufacture of plywood,
composition board, particleboard, hardboard, fiberboard,
waferboard, oriented strand board and the like.
Plywood is a glued-wood panel that is composed of relatively
thin layers, or plies, with the grain of adjacent layers at an odd
number of plies to provide a balanced construction. If thick
layers of wood are used as plies, often two corresponding layers
with the grain directions parallel to each other are used;
plywood that is so con~tructed often is called ~our ply or six
ply. The outer pieces are faces or face and back plies, the
inner plies are core~ or centers and the plies between the inner
and outer plies are crossbands. The core may be veneer,
lumber or particleboard, with total panel thickness typically
being less than one-eighth inch and no more than two inches.
In general, the plywoffd panels are dried to remove moisture
to a level which i~ compatible for gluing. The panels are coated
with a liquid glue, front and/or back as appropriate, with a glue
spreader. }leat and pressure are applied in a hot press to cure
the glue and bond the panels together to form the plywood .
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The process of the present invention provides for the use of
veneers wi.h higher moisture levels, permitting the manufacturer
to prepare higher volumes of veneer from existing dryers.
SUMMARY OF THE INVENTION
The invention provides a latently curable binder composiffon
which contains a curing agent having ester functionality and
which is sufficiently stable to permit storage for periods in
excess of 24 hours. The term "latently curable", aæ used
herein, is intended to mean curable after a sufficient time for
storage, transportation and application to solids.
These stable binder composiffons comprise a phenolic resin
solution capable of binding a network of fibers upon cure. This
phenolic resin solution is sufficiently stable to permit storage in
e~cess of 24 hours.
The latently curable binder composition also contains a
curing agent having ester functionality. This curing agent is
soluble in the phenolic resin solution. The quantity of curing
agent used is sufficiently high to enhance the cure speed of the
alkaline condensed phenolic resin yet sufffciently low to prevent
gelation within the binder composition for a period in excess of
24 hours so as to remain in a liquid form.
Also provided by the present invention is a method for
- making a latently curable binder composition containing a curing
agent with ester functionality. By this process, the curing
agent i8 introduced to an alkali-condensed phenol-formaldehyde
resin solution having a viscosity below about 500 cps and at a
temperature below about 40C at a region of rapid agitation.
The curing agent is charged into the resin solution at a rate
sufficiently high to prevent the formation of gels or colloids
upon addition.
Another embodiment of the present invention is a method
for the bonding of lignocellulosic materials in the manufacture of
structural wood products which can use high moisture starting
materials .
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a latently curable binder
composition which comprises an alkaline condensed phenolic resin
solution capable of binding a network of solids. The solids
which can be bound upon gelation (or cure) of the resin include
those in the form of granules, fibers, strands, wafers, flakes,
veneers and powders. The solids may be refractory materials,
such as alumina, magnesia, zircon, silica sand, quartz, chromite
sand, zircon sand or olivine sand. In addition, lignocellulosic
materials such as wood may also be used either in wood fiber,
wood flake, wood chip, wood shaving, wood wafer, or wood
particle form or as a veneer. Other solids may include glass
ffbers, carbon fibers, nylon fibers, rayon ffbers, ceramics such
as calcium oxide and metal filings such as iron or copper used in
frictional elements.
The alkaline phenolic resin solution must also be sufficiently
stable to remain liquid at ambient temperature for periods in
excess of 24 hours from synthesis and be sufficiently reactive to
gel upon heating to a temperature above about 100C, and
preferably above about 150C. A majority of the commonly used
alkaline condensed phenolic resins satisfy these criteria.
Alkaline conden ed phenolic resin solutions are often not
completely stable at ambient temperatures in that polymerization
continues resulting in an increase in the soluffon vi~cosity.
Reaction is slow under ambient conditions and, often, the
vi~cosity will increa~e about 30 to 40 centipoise per day.
Although the viscosity of these phenolic resin solutions may
increase, they remain liquids and do not experience gelation for
a period in excess of 24 hours from synthesis. For most alkaline
phenolic resins, gelation does not occur until well beyond the 24
hour period and for some, irreversible gelation at ambient
~l conditions may never occur until desired, permitting the additionof solvent to reduce viscosity after prolonged storage.
The alkaline condensed phenolic resin must also be
sufficiently reactive to gel upon heating to a temperature of at
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least about 100C. The major~ty of the common alkaline
condensed phenolic resins may gel at temperatures significantly
below 100C, as well as at temperatures above 100C.
A large number of alkaline condensed phenolic resins
provide adequate bond strengths to bind solids in a network.
Those which are most commonly used have a weight average
molecular weight preferably greater than 700, more preferably
greater than 1,000 and most preferably within the range of about
1,000 to 2,200, as determined by a solution method.
Suitable alkaline materials used to condense the phenolic
resins include sodium, potassium, calcium and magnesium
hydroxides, with potassium and sodium hydroxides being most
preferred. The phenolic re ins may be obt~~ned by the reaction
of phenoi, cresols, resorcinol, 3,5-xylenol, bisphenol A, other
substituted phenols, or mixtures thereof with aldehydes such as
formaldehyde, acetaldehyde, or furfuraldehyde. The preferred
reactants are phenol and formaldehyde utilized in a molar ratio of
phenol to formaldehyde in the range of 1:1 to 1: 3 .1, and more
preferably 1:2.1 to 1:2.8 for bonding lignocellulosic material.
The phenolic resin solutions have an alkalinity content,
i. e ., contain a base, in the range of about 1% to about 15%,
preferably 2.5% to 7%, based on the weight of the resin solution,
when the base is sodium hydroxide. When a different base is
utili~ed, the alkalinity content i8 proportionately equivalent. As
used herein, "alXalinity content" will mean percent of solution
according to equivalent sodium hydroxide weight unless
expressly stated according to base. For example, an alkalinity
content of 6 . 4% potassium hydroxide would be equivalent to an
alkalinity content of about 9%, based on the equivalent weight of
sodium hydroxide. Additional base can be added to a commercial
resin to bring it to the desired concentration. The base may be
an alkali metal or alkaline earth metal compound such as a
hydroxide .
The more commonly used phenolic resins which satisfy the
criteria given above have a solids content of about 40 to 7596 by
weight, preferably about 40 to 60% by weight. Such
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compositions are typically sufficiently low in viscosity to permit amore simplified addition of the curing agent. The viscosity of
these phenolic resin solutions generally range from about 200 to
1, 500 centipoise, as determined by an LVF Brookfield
Viscometer, using number 2 spindle, at 30 rpm, at 25C.
Preferably, the viscosity is below about 500 centipoise and most
preferably about 200 to 400 centipoise.
The curing agent for the phenol-formaldehyde resin hac an
ester functional group and must be dispersible in the phenolic
resin solution. By "dispersible" i5 meant either soluble, miscible
or otherwise distributable. Preferably, the curing agent i8
soluble in the resin solution. The curing agent may be selected
from the group consisting of lactones, organic carbonates,
carboxylic acid esters or mixtures thereof. Generally, it is
preferred to use curing agent~ with from 4 to 12 carbon atoms.
It is most preferable to use a curing agent with a reactivity less
than or equal to that of propylene carbonate to simplify its
addition into the resin solution. Although a curing agent may
be dispersible in the resin solution, special equipment may be
required to prevent the formation of gel and colloids upon
addition. Curing agents with a higher molecular weight than
propylene carbonate often have lower reactivities.
Examples of lactones which accelerate the cure of phenolic
resins include, but are not limited to, gamma-butyrolactone,
valerolactone, caprolactone, beta-propiolactone, beta-
butyrolactone, beta-isobutyrolactone, beta-isopentylactone,
gamma-isopentylactone and delta-pentylactone. Where a lactone
is used, it is preferable to use gamma-butyrolactone, which is
lower in reactivity than propylene carbonate.
~, Examples of organic carbonates which accelerate the cure of
phenolic resins include, but are not limited to, propylene
carbonate, ethylene glycol carbonate, glycerol carbonate,
1, 2-butanediol carbonate, 1, 3-butanediol carbonate,
1,2-pentanediol carbonate and 1,3-pentanediol carbonate. If an
organic carbonate is utilized, it is preferable to use propylene
carbonate. Carboxylic acid esterA which accelerate the cure of
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phenolic resin~ include, but are not limited to, n-butyl acetate,
ethylene glycol diacetate and triacetin (glycerol triacetate). If a
carboxylic acid ester is u~ed, triacetin is preferred. Triacetin
ha~ a lower reactivity than propylene carbonate.
Other aliphatic monoesters may be suitable, such as
propionates, butyrates or pentanates, and the like. Additional
aliphatic multiesters which may be suitable include diformate,
diacetate, or higher diester~ of ethylene glycol, diethylene
glycol, propylene glycol, butylene glycol, glycerol,
1, 3-propanediol, 1, 3-butanediol, and 1, 4- butanediol.
Furthermore, diesters of dicarboxylic acids, such as dimethyl
malonate, dimethyl glutarate, dimethyl adipate, and dimethyl
succinate, are suitable.
The quantity of curing agent within the latently curable
binder composition is sufficiently high to accelerate the cure of
the alkaline condensed phenolic resin. Very small quantities of
curing agents are effective in enhancing the cure of such
resins . Quantities as low as 0. 01 wt. % of a highly reactive
curing agent based on total solids of the binder composition will
provide detectable results. Actually, the larger the quantity of
curing agent, the greater the enhancement of cure speed.
However, the quantity of curing agent must be sufficiently low
to maintain the binder compo~ition in a liquid form at ambient
temperature for at least 24 hours, and preferably at least a
week. By "liquid" is meant that the composition is fluid or
flowable, and is sub~tantially free of gel or colloids. In such a
condition, the binder composition of the present invention has a
pot life of at least 24 hours, and preferably at least a week.
Quantities of propylene carbonate curing agent equal to
about ~ wt. % of the total binder composition (about 11% ba~ed
on solids) have been found to provide an unstable binder
composition which cures within minutes at ambient temperature.
- It is preferable to maintain the concentration of curing
agent below about 5% by weight ba~ed on solids. Most
preferably, the quantity of curing agent is selected to fall within
the range of about 0 .1 wt . % to 1. 0 wt . % based on total solids
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of the binder composiffon. Such compositions will be relatively
stable and will remain in a liquid form for a period in excess of
three weeks without gelation.
The viscosity of the binder composition does increase where
these quantities are introduced to a phenolic resin solution and,
in fact, increases at a faster rate than resin ~olutions which do
not contain curing agent. However, the rate of viscosity
increase is sufficiently low to permit short term storage,
transportation and application of the binder compositions.
Preferred binder compositions of the present invention will
exhibit a viscosity below about 1, 000 centipoise at 25C even
after one week from production.
It is important to note that the binder composiffons of the
present inventis~n may contain other components, modifiers,
extenders, etc. For example, cornstarch extenders may be
added without deleterious effect of the present invention and
urea may also be added without effecting the cure rate of the
phenolic resole resin.
The addition of curing agent to the phenolic res<-le resin
will not inhibit cure and upon the application of heat,
particularly at temperatures well above ambient temperature, the
binder composition will cure rapidly. Gelation times oP about 10
to 20 minutes are common for binder compositions of the present
invention which are maintained at 100C.
Also provided by the present invention i8 a process for
preparing a latently curable binder composition described sbove.
The binder compositions prepared by this process exhibit
stability at ambient temperature and reactivity upon heating.
The initial step of the process incorporates conventional
techniques for the manufacture of phenol-formaldehyde resin
~t condensed by alkaline materials. The resin obtained must be
capable of binding a network of solids upon gelation and the
resin solution must have a viscosity below about 500 centipoise at
25C. The phenol-formaldehyde resin solution is cooled to a
temperature below about 40 C to retard the activity of the
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curing agent when introduced. Preerably, the temperature ofthe resin solution is maintained below about 30C.
The phenol-formaldehyde resin solution i8 agitated rapidly
prior to the addition of the curing agent. Agitation is necessary
to prevent the formation of colloids or gel upon the addition of
curing agent . An impeller operating at about 80 to I00 r . p . m .
within a baffled vessel has been found to provide adequate
agitation for the addition of propylene carbonate curing agent.
The curing agent is added to the phenol-formaldehyde resin
solution in a region of rapid afitation to obtain rapid, uniform
dispersion. In a conventional reactor, the curing agent is
intrsduced at the bottom, in close proximity to a high speed
impeller.
The curing agent is introduced at a rate sufffciently high
to prevent the formation of gel or colloids upon addition. This
can generally be accomplished by injecting the charge of curing
agent with air pressure of about 30 to 40 psi. It is preferable
for the entire charge of curing agent to be introduced within
about 20 to 45 seconds, even where a charge of as much as
1 wt. 96 of curing agent based on the weight of the resin
solution i8 required.
The curing agents used contain at least one ester functional
group and are soluble in the phenol-formaldehyde resin solution.
Preferred curing agents are selected from propylene carbonate,
gamma-butyrolactone and triacetin. The quantity of curing
agent introduced to the resin sol~tion must be sufficiently high
to accelerate the cure of the alkaline condensed phenol-
formaldehyde resin and at the same time~ must be sufficiently
low to maintain the binder composition in liquid form at ambient
temperature. As discussed previously, quantities which provide
these results fall below about 5 wt. % based on the weight of
total solids of said binder composiffon. The preferred range is
about 0 . 01 wt . % to 1 wt . % based on the weight of total solids
of said binder composition.
To obtain a binder composiffon of adequate stability, it is
preferable that the phenol-formaldehyde resin solution have a
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visc06ity of from about 200 to 400 centipoise at 25C for a resin
having a phenol-formaldehyde mole ratio of 1:1 to 1: 3 .1. To
further insure stability, it is preferable to maintain the
phenol-formaldehyde resin at a temperature below about 30C.
To provide the rapid afitation necessary, it is helpful to use
equipment such as baffled vessels, high speed impellers and
subsurface feedlines.
It is recognized the process of the present invention may
comprise additional steps, such as those which provide for the
addition of cornstarch or other extenders.
The latently curable binder composition of the present
invention can be applied to solids with any form of conventional
equipment currently in use. Such equipment includes spray
nozzles, atomizing wheels, roll coaters, curtain coaters, foam
applicators, mixers, roll mills, dip tanks, and the like.
Also provided by this invention is a method for bonding
lignocellulosic material (wood) with an adhesive mixture
containing binder compositions of the present invention. The
process comprises applying the adhesive mixture to a
lignocellulosic material, consolidating the lignocellulosic material
and curing the lbinder composition within the adhesive mixture.
The preferred binder compoæitions utilize propylene carbonate,
gamma butyrolactone or triacetin curing agents.
Boards made from homogeneous lignocellulose material or
from mixtures of different kinds of such material can be
produced by this process. A board may be made, for example,
completely from wood particles, or completely from wood flakes,
or from wood fibers, shavings or the like, or from mixtures of
these. Similarly, a board may be formed with multiple layers,
with fine surface flakes and a core of coarse flakes, or it may
have a coarse-flaked core with an overlay of fibers on each of
its surfaces. Other combinations may also be produced.
It is preferable to manufacture plywood from the process of
this invention for bonding lignocellulosic materials, Plywood i8 a
board composed of multiple layers of wood veneers. The veneers
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are usually arranged so that the wood grain direction is
perpendicular in adjacent veneers.
The plywGod process requires straight logs cut to length,
and conditioned in heated vats containing water and surfactants
to increase the heating efficiency of the vats. The heated logs
are then "peeled" wherein a veneer of predetermined thickness is
removed continuously until the log diameter is reduced to a
certain point, usually 3 to 6 inches. The veneer is then clipped
into strips, sorted and dried. In conventional bonding
processes, the moisture content of the veneer is reduced to 10%
or less. Higher moisture contents are permitted by this
invention.
After drying, the veneers are graded and assembled into
plywood panels. The adhesive is applied to the veneers st this
stage of manufacture. The adhesive is usually composed of
phenol-formaldehyde resin, water, a basic material such as
sodium hydroxide, and fillers that include inorgulic and organic
flours, such as wheat flours, wood flours, and clays. The
adhesives are specially formulated for individual user mills
depending on manufacturing equipment, type of wood to be
glued, type of product to be made, and ambient environment
conditions at the time of panel manufacture. The adhesive is
usually applied to the veneers by roll coater, curtain coater,
sprayline or foam extruder. The adhesive usually contains
phenol-formaldehyde resin at a level of 20 to 40% resin solids by
weight. The adhesive is normally u~ed with spread levels of 50
to 110 lbs. of adhesive per 1000 square feet of gluelines, when
the veneer is spread on both sides , or 25 to 55 lbs ., when
spread on one side.
After the adhesive is applied to the wood veneers and the
panels are assembled, they are consolidated under heat and
pressure. This is usually done in a steam hot-press using
platen temperatures of about 240 to 350F and pressures of
about 75 to 250 psi.
In producing plywood, the most critical glueline for cure is
the innermost one. This glueline i8 the most difficult to cure
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under present conditions. That is, often the innermost glueline
is not fully cured when the other glUelines are. It is
necessary, then, to apply additional hot pressing to the board to
cure this glueline. One additional use of the binder composition
of the present invention is that they can be applied to the
innermost glueline and a conventional resin applied at the other
gluelines. The accelerated resin is then able to provide a
complete cure at the innermost glueline in the same time period
as it takes to cure the other gluelines.
It has been discovered that several advantages are obtained
by utilizing the binder compositions of the present invention,
i . e ., a resin containing the curing agent , in the manufacture of
structural wood products. One advantage is that cure time can
be decreased. For example, in the preparation of ~ ply-1/2"
thick plywood by conventional processes, a 3.5 minute cycle cure
time (press and heat) is utilized when the resin does not contain
a curing agent . The time can be reduced to a 2 . 5 minute cycle
with binder composition having a propylene carbonate curing
agent in a quantity of about O . 35 to 1 wt . 96, based on the
weight of solids, without loss in durability and other important
properties. A second, significant advantage is that the addition
of the curing agent increases the tolerance to moisture in the
system. Thus, where plywood formed by conventional processes
has a moisture content for the face sheets of 1 to 9 wt. % and a
moisture content of O to 6 wt. % for the core sheets, if a curing
agent is used, the moisture content for the core can be up to 12
wt. % and up to 25 wt. % moisture for the face sheets.
Even when a higher moisture content is used, a minimal
number of blows result, and board properties such as thickness,
swell and durability are good with no effect on the test for wood
failure. After pressing and heatirig, i.e., curing the resin, the
moisture content of the product i8 also generally higher. Since
the system can withstand more moisture when the binder
compositions of the present invention are used, it is possible to
produce more on-grade panels. It has been found that the
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thicker the board, the more effective this invention, and the
more signiffcant the advantages.
It is recognized that the compositions of the present
invention may be used in preparing products requiring an
adhesive or binder other than structural wood products. For
example, the compositions may be used as binder~ for foundry
molds or cores.
The invention will be demonstrated by the following
examples. In these examples and elsewhere throughout the
specification, pa~ts and percentages are by weight and
temperatures are in degrees Celsius unles~ expressly indicated
otherwise. The term "molar ratio" refers to the molar ratio of
formaldehyde to phenol unless indicated otherwise. All
Brookfield viscoæity values recited hereinabove and in the
appended claims are made with reference to an LVF Brooklleld
Viscometer using a #2 spindle at 30 rpm and at 25C, unless
otherwise specified.
A Method for Making Binder Compositions of High Stability
With a Curing A~ent Therein
Example 1
To a 5 gal. reactor equipped with baffles and an impeller
powered by a motor were added about 4680 gms of phenol and
about 3285 gms of formaldehyde (50% aqueous solution), with
stirring at about 80 up to 100 r.p.m.
The refractive index of the mixture was determined in order
to confirm molar ratios. The valu8 was found to fall within the
range of about 1.4840 to 1.~860.
About 3240 gms of wster were subsequently added and the
refractive index redetermined to confirm the molar ratio, which
was found to fall within the range of about 1.4350 to 1.4360.
Thereafter, about 540 gms of a 50% sodium hydroxide
solution were added with stirring and the temperature of the
mixture was allowed to increase to about 95C by exotherm. The
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viscosity during reaction of the solution was monitored by
comparison to Gardner-Holt bubble standards. About 20 minutes
after the addition of NaOH, the mixture had an A-1 rating,
corresponding to about 30 centipoise.
About 1 hour after the addition of NaOH, the viscosity
increased to an A-rating (40 centipoise), at which time the
mixture was cooled to about 80C and a second charge of about
1080 gms a 50% NaOH solution was added. The temperature was
maintained at about 80C during the exothermic reacffon.
Immediately after the addition of NaOH, about 3285 gms of
formaldehyde (50% solution) were added over about 30 minutes.
The refractive index was again measured and found to fall in the
3 range of 1.4700 to 1.4730.
`, The temperature of the mixture was allowed to rise by the
heat of exothermic reaction to about 90C near the end of the
formaldehyde addition. Upon completing the addition of
formaldehyde, the temperature of the reaction was maintained at
90C, providing an increase in viscosity which corresponded to
an F-rating (140 centipoise). The mixture wa~ then cooled to
about 85C and the reaction proceeded at that temperature until
a viscosity corresponding to an M-rating (320 centipoise) was
attained.
The addition of about 990 gms of water followed and the
mixture was allowed to cool to about 72C. The reaction
proceeded at 72C providing an increase in viscosity to a
P-rating (400 centipoise).
The mixture was then further cooled to 67C and an
additional charge of about 540 gms of 50% NaOH solution was
~ , added. The reaction proceeded at about 67C. The viscosity
-~ decreased with the addition of NaOH to an H-rating (240
3 centipoise) with reaction.
When a J-rating was obtained, the mixture was cooled to
about 50C and about 90 gms of cornstarch extender and about
- 90 gms of urea were added.
Upon cooling to about 30C, about 180 gms of propylene
3 carbonate were injected through the bottom of the 5 gallon
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reactor, under vacuum, in close proximity to the impeller. The
mixture was allowed to cool to 25 C and the batch was
characterized as having a refractive index of about 1. 4693, a
specific gravity of about 1. 204 and a Brookfield viscosity of
about 450 centipoise at 25C, and as determined by a RVF
Brookfield Viscometer with a #3 spindle at 20 rpm. A sample of
the batch was cured at 100C and gelled to a solid in about 13.2
minutes.
After about 40 minutes, about 156 gms of urea (1% solution)
were added. The refractive index was redetermined to be 1.4700
and the viscosity was about 450 centipoise as determined above,
A sample of this composition was cured at 100C and gelled in
about 13 . 6 minutes to form a solid.
The remaining portion of the composiffon stayed in liquid
form for over several hours.
The second addition of urea in this example demonstrated
that it is not urea which enhances cure speed.
Urea Does Not Enhance Cure Speed
Example 2
This example demonstrates that when urea is present, cure
speeds are not affected. The procedure of Example 1 was
repeated except that the initisl mixture of phenol, formaldehyde
and water was found to have a refractive index of 1. 43~4. The
mixture after addition of the second charge of formadehyde had
a refractive index of about 1.4734.
The process of Example 1 was modified by cooling the
mixture to 50C after a Gardner-Holt viscosity rating of "I" was
obtained (220 centipoise). After cooling to 50C, the quantities
of cornstarch, urea and propylene carbonate added were the
same.
The batch was characterized as having a refractive index of
about 1. 4695, a specific gravity of 1. 204 and a Brookfield
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viscosity of 440 at 25C, as measured in Example 1. A sample of
the batch gelled to a solid in 13.1 minutes at 100C.
An additional charge of urea (about 1% by weight or about
156 gms) was added to the batch with mixing. A sample of this
composition was gelled to a solid in about 13.4 minutes at 100C.
The composition remained liquid after several hours.
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The Presence of Ester-Functionalized Curing Agents
Enhances Cure Speeds
Example 3
This example demonstrates the effectiveness of the curing
agents having ester functionality in enhancing cure speed.
The procedure of Example 1 was repeated utilizing the same
equipment except that about 4320 gms of phenol were used with
3240 gms of formaldehyde to make the initial mixture followed by
addition of about 3420 gms of wster. The first charge of NaOH
was 558 gms (50% solution) and the second charge was about
1260 gms. The second charge of formaldehyde (about 3076 gms
of a 50% solution) was added over 20 minutes as in Example 1.
The second charge of water was about 1566 gms and the third
charge of NaOH, 540 gms.
After the desired viscosity of fibout 240 centipoise was
obtained (J-rating), the mixture was cooled to about 30C and
propylene carbonate (about 54 gms, 0.36 wt. % based on total
resin) was added. A speciffc gravity of 1.198, a refractive
index of 1. 4610 and a Brookfield viscosity of 250 centipoise at
25C were noted. A sample was found to gel in 22.1 minutes at
- 100C~
Additional propylene carbonate was added to this mixture
(about 54 gms) to double the concentration of the original
mixture (about O . 73 wt . percent based on the total mixture, or
about 1. 2 wt . percent based on solids) . The Brookfield
viscosity was 410 centipoise at 25C aB measured in Example 1.
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The speciffc gravity was 1.196 and the refractive index 1.4635.
A sample was gelled in 17.1 minutes at 100C.
This demonstrates that the ester-functionalized species i8 an
effective curing agent for enhancing cure speeds.
Production of Binder Compositions on a Commercial Scale
Example 4
The following components were added through the top of an
11, 000 gallon reactor equipped with baffles, cooling coils for
temperdture control and an impeller powered by a 25 h.p. motor,
with stirring at about 100 r . p . m .: phenol - about 2684 gallons ;
formaldehyde (50% aqueous solution) - about 1817 gallons. The
refractive index of the mixture was determined in order to
confirm molar ratios. Recycled water (about 2154 gallons) was
then added through the top and the refractive index
redetermined.
Thereafter, about 2928 lbs. of NaOH (50% solution) were
added through the top and an exothermic reaction continued.
The temperature was maintained at about 93 to 95C by the
cooling coils. A Gardner-Holt viscosity rating of about "A" was
obtained (about 40 centipoise) for the mixture after about 1.5
hours. The reactor contents were cooled to 80C and a second
charge of about 6614 lbs. of NaOH (50% aqueous solution~ was
added. Immediately following the addition of NaOH, 1737 gallons
of formaldehyde (50% solution) were added. The refractive index
was measured for quality control. The temperature was allowed
to rise to about 90 C with exothermic reaction until a vlscosity
rating of "D" was obtained (about 100 cenffpoise). The mixture
was cooled to about 85C and the reaction continued. When a
viscosity rating of "L" (about 300 centipoise) was obtained, an
additional charge of 987 gallons of water was added and the
mixture was cooled further to about 80C. Reaction continued
within the mixture to provide a P-rating for the viscosity (about
400 centipoise), after which the mixture was cooled to about
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70C and additional NaOH (50% ~olution) was addéd (about 2832
lbs. ) . The viscosity decreased to less than an H-rating on the
addition of NaOH and, after about 1 hour, the visco ity
approached an I-rating (220 centipoise). The mixture was cooled
to about 30C and cornstarch was added (about 700 lbs. )
followed by propylene carbonate (about 700 lbs. ) . The
propylene carbonate was injected through the bottom of the
11,000 gallon reactor near the impeller with the aid of air
pressure (30-40 psi). The entire charging time was less than 30
seconds .
The mixture waq then cooled to about 25C and the batch
characterized as having a refractive index of about 1.4590, a
specific gravity of about 1.194 and a Brookfield viscosity of 345
centipoise at 25C, as determined by an LVF Brookfield
Viscometer with a #2 spindle at 30 rpm. A sample of the batch
was cured by heating to 100C and gelled to a solid in about
17.1 minutes.
The remaining batch was transported to a storage tank and
remained in liquid form for over 72 hours.
Uniformity of Product
Example 5
This example is a repeat of the process used for the
production OI the stable binder compositions of the present
invention on a large scale, and illustrates the uniformity of
product .
The quantities of reactants and the equipment used in this
example are the same as in Example 4 except that about 2724
gallons of phenol were used instead of the 2684 gallons of
Example 4, and the phenol:formaldehyde mixture had a refractive
index of about 1.4850. In addition, the 2154 gallons of water
comprised 50% recycled water and 50% fresh water and the
refractive index for this mixture was 1.4455.
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The procedural variations from Example 4 were as follows.
After the first addition of NaOH, the viscosity was allowed to
reach slightly higher than an A-rating (Gardner-Holt) and after
the second addition of NaOH, formaldehyde was added over a 20
minute period (Refractive Index = 1.4704) and reacted at 90C
unffl an F-rating for viscoeity (about 140 centipoise) was
attained.
The mixture was then cooled to about 87C and the reaction
proceeded to maintain a viscosity corresponding to an M-rating
(320 centipoise). The second charge of water was added (about
987 gallons), the mixture cooled to about 75C and the reaction
proceeded to attain a viscosity slightly higher than an O-rating.
The mixture was about 80C when a P-rating was attained (400
centipoise).
The mixture was then cooled to 67C followed by addiffon of
the third charge of NaOH (50% solution). The reaction then
proceeded until a viscosity slightly above an l-rating (220
centipoise) was attained.
This mixture was then cooled to 30C, at which time 700
lbs. of propylene carbonate were added as described in Example
4.
After cooling to 25C the batch was characterized as having
a refractive index of about 1.4595, a specific gravity of about
1.194 and a Brookffeld viscosity of 400 centipoise at 25C, as
measured in Example 4. A sample of the composition was cured
and found to gel to a solid in about 17.6 minutes at about
10QC. The remaining batch was transferred to a storage tank
and remained liquid for over 24 hours.
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Effective and Excessive Quantities of Curing Agent
Examples 6-9
The following examples illustrate that excess quantities of
curing agent sre unsuitable.
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In these example~ a resin was prepared in large scale in
accordance ~nth the procedures described in Example 4. A
portion of the mixture was removed from the 11, 000 gallon
reactor and transferred to a 5 gallon reactor equipped as
described in Example 1.
For Examples 6 and 7, 18, 000 gm samples (about 45 wt. 96
solids ) were removed after the third charge of NaOH . These
samples were cooled to about 70C and the viscosity increased to
above an N-rating (about 340 centipoise). The mixtures were
cooled to 30C and 63 gm~ (about 0. 35% based on the total
weight of resin) of propylene carbonate were added to each
mixture in the manner described in Example 1.
For Example 6, the mixture had a Brookfield viscosity of
395 centipoise at 25C, as determined by an RVF Brookfield
Viscometer with a #3 spindle at 20 rpm. A specific gravity of
1.198 and a refractive index OI about 1.470 were determined . A
sample gelled in about 21.4 minutes at 100C.
For Example 7, the mixture had a Brookfield viscosity of
370 centipoise at 25C, as determined in Example 6, a specific
gravity of 1. 200 and a refractive index of 1. 4701. A sample
gelled to a solid in 22.0 minutes at 100C.
About 9, 000 gms of the batch from Example 7 was added to
a 5 gallon reactor and a second charge of propylene carbonate
(about 16 gms) was added, as described in Example 1, to
provide about 0.53 wt. % curing agent based on the total weight
of resin (about 1. 78 wt. % solids) . This mixture had a
refractive index of 1.4697, a Brookfield viscosity of 550
centipoise at 25C, as determined in Example 6, and a speciffc
gravity of 1.153. A sample gelled to a solid in 19 . 6 minutes at
100C.
A portion of the mixture (about 250 gms) in the 11, 000
gallon reactor was removed just after the addition of the third
charge of NaOH and prior to the addition of propylene
carbonate. A 95 gm sample was taken from this 250 gm portion
for Example 8 and a second, 99 gm ~ample was obtained from the
250 gm portion for Example 9. Each sample was placed within a
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250 ml beaker and was cooled to about 30C. Propylene
carbonate was added to each with rapid hand-stirring using a
wooden spatula. In Example 8, about 5 gms. of propylene
carbonate (about 5% by weight based on total resin) was added
to the sample of resin and, in Example 9, about 1 gm of
propylene carbonate (about 1% by wt. based on total resin) was
added to the sample of resin. After about 30 to 60 sec~ of
stirring, each sample was allowed to stand at ambient
temperature (about 25C). The sample of Example 8 had gelled
to a solid within less than 3 minutes. At the same time, the
sample of Example 9 remained a viscous liquid for several hours.
Long Term Stability
Examples 10-12
These examples demonstrate the long term stability of the
binder compositions of the present invention.
The equipment described in Example 4 was used to make the
large volumes of binder composition for Examples 10, 11, and 12.
In each of Examples 10-12, about 2898 gallons of phenol
were used and about 1867 gallons of formaldehyde (50% aqueous
solution). The refractive index was checked to be between
1.4865 and 1.4855. About 2074 gallons of fresh water were used
in Examples 10 and 11 while the same volume of recycled water
was used in Example 12. The refractive index was checked
again and about 2880 lbs . of NaOH (50% solution) were added .
The reaction proceeded at from 73 to 95C to obtain an A-rating
for viscosity (Gardner-Holt), after which the reaction mixture
was cooled to 80C and a second charge of 5760 lbs. NaOH,
followed by 1987 gallons of formaldehyde, were added to the
mixture for each example. The refractive index was checked at
about 1.4700 to 1.4750. The reaction was allowed to proceed at
90C. A D-rating for viscosity was attained for Example 10, a
G-rating for Example 11 and an F-rating for Example 12. The
reaction mixture was then cooled to about 85C and the viscosity
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increased tc 8 K-rating for Example 10, an L-rating for Example
11 and a G-rating for Example 12. About 621 gallons of water
were added to each reaction mixture. Each mixture was cooled
to 80C and each obtained a P-rating for viscosity. Additional
NaOH (50% solution) was added (about 2880 lbs. ) after a
temperature of 70C was obtained. Reaction proceeded in each
mixture to a J-rating for viscosity, after which about 240 lbs. of
cornstarch and 720 lbs. of urea were added at about 50C.
Each mixture was then cooled to 30C and about 700 lbs. of
propylene carbonate were added to each of Examples 10, 11 and
12.
Upon cooling to 25C, each mixture was characterized.
Example 10 showed about a 1.4678 refractive index, a 1.202
specific gravity and an initial sample showed a Brookfield
viscosity of 430 centipoise at 25C, as determined by an LVF
Brookfield Viscometer with a #2 spindle at 30 rpm. A sample
gelled in 16 minutes at 100C. Another sample was retained
(about 100 ml). After 8 days, this retained sample was found to
have a Brookfield viscosity of about 750 centipoise at 25C, as
determined by an RVF Brookfield Viscometer with a #4 spindle at
20 rpm. A portion of this sample was cured at 100C and found
to gel in about 14.4 minutes.
Example 11 showed a 1.4670 refractive index, a 1.200
specific gravity and a Brookfield viscosity of about 345
centipoise at 25C, as determined for the initial sample of
Example 10. A sample was cured at 100C and found to gel in
16.6 minutes . Another sample waQ retained (about 100 ml) for 2
days. This retained sample had a Brookfield viscosity of about
440 centipoise at 25C on the second day, as determined for the
retained sample of Example 10.
Example 12 showed a value of 1.4663 for the refractive
index, a 1.200 specific gravity and a Brookffeld viscosity of 340
centipoise at 25C, as determined for the initial sample of
Example 10. A sample was cured at 100C and found to gel in
about 17.5 minutes. Another sample was retained (about 100 ml)
for 5 days. This retained sample had a Brookfield viscosity of
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--24--
about 560 centipoise at 25C on the fifth day, as determined for
the retained sample of Example 10.
These examples demonstrate there is a slight increase in
viscosity during storage; however, the liquids had not gelled
and were still useful. The viscosity of these mixtures remains
sufficiently low to permit easy handling within conventional
equipment, even after storage beyond 24 hours.
High Strength Cure for High ~loisture Solids
Example 13
This example demonstrates that the binder compositions of
the present invention provide suitable strength for binding high
moisture solids.
An adhesive mix for plywood was made from the binder
formulation prepared in accordance with Example 3 by adding the
following ingredients to a high shear (speed) mixer:
Binder composition 1400 gms. 58.8 wt %
(based on the total
weight of adhesive)
Furafil (at 5% m.c.) extender 200 gms. 8.4 wt. %
Wheat Flour (at 11% m.c. )150 gms. 6.3 wt. %
extender
Sodium Hydroxide 80 gms . 3 . 3 wt. %
(50% solution)
Water 550 gms .23 . 2 wt . %
2380 gms.100 wt. %
Board ManuIacturing
Veneers of about 1/8" were cut into 12" by 12" panels and
their moisture content was checked. Faces generally have about
a 14% average moisture and cores generally have an 8% average
moisture. The adhesive was applied with a roller coater using a
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--25--
standard glue spread commonly used in the manufacture of
plywood. A glue spread of about 58 to 60 lbs . /1000 ft2 of
double glue line is generally used.
The panels were laid-up and prepressed for about 4-6
minutes followed by hot-pressing or a time period of from 2 1/2
to 3 1/2 minutes. The following gluing conditions were used
Thickness 1/2 inch
No. of Plie~ 4
Press Temperature 315F (157C)
Glue Spread 58 to 60 lbs/1000 ft2 of double
glue line (M . D . G . L . )
Assembly Time 1 û to 60 minutes
Mix Solids 58.3% by weight
Resin Solids
in Mix 26.5 wt. %
Mix Viscosity 3000 to 7000 cps
Applicator Roll Coater
Veneer Moisture
Content:
Faces 14% average moisture, 9-22% range
Cores 8% average moisture, 5-12% range
After the boards were hot pressed, they were cooled to
ambient temperature. Adhesion was tested by separating the
glued panels with a square knife at the corners of the plys and
at the middle of an edge. All glueline separations of veneer
plies contained at least 85% wood failure.
Plywood boards were made from the large scale batches of
Examples ~ and 5 and all boards tested passed commercial
standards and approval by the American Plywood Association.
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--26--
Other Effective Curing Agents
Examples 14 and 15
These examples are presented to demonstrste the efficacy of
curing a~ents other than propylene carbonate.
The procedure of Example 1 is substantially repeated,
except that 180 gms of gamma-butyrolactone and of triacetin
(glycerol triacetate) (Examples 14 and 15, respectively) are used
in lieu of propylene carbona~e. Acceptable results are expected
for each parameter measured in Example 1 and the binder
composition is expected to have acceptable stability.
Potassium Phenol-~ormaldehyde Resins
Example 16
This example demonstrates that potassium hydroxide-
condensed resins may be used in connection with this invention.
The procedure of Example 1 is again substantially followed
except that three potassium hydroxide charges are employed in
lieu of the sodium hydroxide charges. In each case,
approximately 50% more of the potassium hydroxide is used
relative to the sodium hydroxide. Propylene carbonate is again
used. Acceptable values for each parameter measured in
Example 1 and acceptable stability of the binder composiffon are
again expected.
While the invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modiffcations. This application is intended to
cover any variations, uses or adaptation~ of the invention
following, in general, the principles of the invention, and
including such departures from the present disclosure as come
within known and customary practice within the art to which the
invention pertains.
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