AU600601B2 - Latently curable binder compositions which contain cure enhancing agents - Google Patents

Description

6'S Re 5885 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: 1'1 Related Art: trar I rt r i t Name and Address of Applicant: Borden, Inc.

180 East Broad Street Columbus Ohio 43215 UNITED STATES OF AMERICA Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia S Complete Specification for the invention entitled: Latently Curable Binder Compositions Which Contain Cure Enhancing Agents The following statement is a full description of this invention, including the 'best method of performing it known to me/us 5845/3 "Ile o ABSTRACT OF THE DISCLOSURE The present invention provides a binder composition which is stable at room temperature for extended periods of time ranging up to 3 weeks.

The composition is stable although a curing agent is present. The composition will provide an accelerated gelation rate upon exposure to heat. This binder composition is a one component system which does not require a premix step prior to use. A novel process for producing the binder composition is provided wherein conditions favor rapid agitation and uniform dispersion of the added curing agent. The binder composition obtained by the process of this invention is used in other embodiments to produce products from high moisture starting materials.

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S I S I IS JTA:1373P i BACKGROUND OF THE 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 like. The invention is also 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 present invention permit the bonding of high moisture lignocellulosic 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 structural wood products such as plywood, particleboard, fiberboard, hardboard, waferboard and oriented strand board. The production of most manufacturing processes utilizing liquid phenol-formaldehyde resole (PF) 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

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because of the need to eliminate moisture from the system during curing.

SIt is known that phenolic resin cure can be accelerated by adding formaldehyde donors, hexamethylene tetramine or various organic and inorganic acids. These methods are not well suited to the current ?1 purposes, however, because hexamethylene tetramine is relatively ineffectual with resoles and acids cause problems with corrosion of processing equipment and metal fasteners.

In 1957, 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. 4,426,467.

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 ambient temperature. Such a two component 4 -3- JTA:1373P \Le 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.

1 opendn application s.al N _--L1e--lp±embe----la- -a describes a process for combining curing agents with phenolic resins in-line with the manufacturing process, thus avoiding 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 difficult 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 formation 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 constructed often is called four ply or six ply. The outer pieces are faces or face and back plies, the inner plies are cores 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 plywood panels are dried to remove moisture to a S' level which is compatible for gluing. The panels are coated with a liquid glue, front and/or back as appropriate, with a glue spreader. Heat and pressure are applied in a hot press to cure the glue and bond the panels together to form the plywood. The process of the present invention provides for the use of veneers with higher moisture levels, permitting the manufacturer to prepare higher volumes of veneer from existing dryers.

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y^-n II SUMMARY OF THE INVENTION The invention provides a latently curable binder composition 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", as used herein, is intended to mean curable after a sufficient time for storage, transportation and application to solids.

These stable binder compositions 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 excess 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 sufficiently 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 I functionality. By this process, the curing agent is introduced to an alkali-condensed phenol-formaldehyde resin solution having a viscosity below about 500 cps and at a temperature below about 40 0 C 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODMENTS 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 fibers, carbon fibers, nylon fibers, rayon fibers, ceramics such as calcium oxide and metal JTA:1373P

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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 1001C, and preferably above about 150 0 C. A majority of the commonly used alkaline condensed phenolic resins satisfy these criteria. Alkaline condensed phenolic resin solutions are often not completely stable at ambient temperatures in that polymerization continues resulting in an increase in the solution viscosity. Reaction is slow under ambient conditions and, often, the viscosity will increase about 30 to centipoise per day. Although the viscosity of these phenolic resin solutions may increase, they remain liquids and do not experience gelation I 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 conditions may never occur until desired, permitting the addition of 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 least about 1000C.

The majority of the common alkaline condensed phenoiic resins may gel at temperatures significantly below 1000C, as well as at temperatures above Sl100 0

C.

i 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 wieght 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 resins may be obtained by the reaction of phenol, cresols, resorcinol, 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 based on the weight of the resin solution, when the base is sodium -6- JTA:1373P

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iilll i j hydroxide. When a different base is utilized, the alkalinity content is proportionately equivalent. As used herein, "alkalinity content" will means 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 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 75% by weight, preferably about 40 to 60% by weight. Such compositions are typically sufficiently low in viscosity to permit a more 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 25 0 C. Preferably, the viscosity is below about 500 centipoise and most preferably about 200 to 400 centipoise.

The curing agent for the phenol-formaldehyde resin has an ester functional group and must be dispersible in the phenolic resin solution.

By "dispersible" is meant either soluble, miscible or otherwise distributable. Preferably, the curing agent is 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 agents 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 preferably 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, -7- JTA:1373P

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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 esters which accelerate the cure of phenolic resins include, but are not limited to, n-butyl acetate, ethylene glycol diacetate and triacetin (glycerol triacetate). If a carboxylic acid ester is used, triacetin is preferred. Triacetin has a lower reactivity than propylene carbonate.

I Other aliphatic monoesters may be suitable, such as propionates, butyrates or pentanates, and the like. Additional aliphatic multiesters j which may be suitable include diformate, diacetate, or higher diesters 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, j 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 composition 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 substantially 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 5 wt. of the total binder composition (about 11% based 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 based on solids. Most preferably, the quantity of curing agent is selected to fall within the range of about 0.1 wt. to wt. based on total solids of the binder composition. Such compositions will be relatively stable and will remain in a liquid form for a period in excess of three weeks without gelation.

-8- JTA:1373P 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 solutions which do not contain curing agent. However, the rater 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 25 0 C even after one week from production.

It is important to note that the binder compositions of the present invention *;uy 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 resole 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 of about 10 to 20 minutes are common for binder compositions of the present invention which are maintained at 1000C.

Also provided by the present invention is a process for preparing a latently curable binder composition described above. 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 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 250C. The phenol-formaldehyde resin solution is cooled to a temperature below about 400C to retard the activity of the curing agent when introduced. Preferably, the temperature of the resin solution is maintained below about 300C.

The phenol-formaldehyde resin solution is 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 100 r.m.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 agitation to obtain rapid, uniform dispersion. In a conventional reactor, the curing agent is introduced at the bottom, in -9- JTA:1373P close proximity to a high speed impeller.

The curing agent is introduced at a rate sufficiently 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. of curing agent based on the weight of the resin solution is 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 solution 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 composition. 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 composition of adequate stability, it is preferable that the phenol-formaldehyde resin solution have a viscosity of from about 200 to 400 centipoise at 25°C 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 30°C. To provide the rapid agitation 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 JTA:1373P lignocellulosic material and curing the binder composition within the adhesive mixture. The preferred binder compositions 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 it surfaces. Other combinations may also be produced.

It is preferable to manufacture plywood from the process of this invention for bonding lignocellulosic materials. Plywood is a board composed of multiple layers of wood veneers. The veneers are usually arranged so that the wood grain direction is perpendicular in adjacent veneers.

The plywood 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 at 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 inorganic 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 used 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.

-11- JTA:1373P After the adhesive is applied to the wcod 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 2400 to 350°F and pressures of about 75 to 250 psi.

In producing plywood, the most critical glueline for cure is the innermost one. This glueline is the most difficult to cure 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, 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 4 ply-1/2" thick plywood by conventional processes, a .iinute 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 0.35 to 1 wt. 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 0 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 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 heating, curing the resin, the moisture content of the product is 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 thicker the board, the more effective this invention, and the more significant the advantages.

-12- JTA:1373P li 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 binders for foundry molds or cores.

The invention will be demonstrated by the following examples. In these examples and elsewhere throughout the specification, parts and percentages are by weight and temperatures are in degrees Celsius unless expressly indicated otherwise. The term "molar ratio" refers to the molar ratio of formaldehyde to phenol unless indicated otherwise. All Brookfield viscosity values recited hereinabove and in the appended claims are made Swith reference to an LVF Brookfield Viscometer using a #2 spindle at 30 rpm and at 250°C, unless otherwise specified.

SA Method for Making Binder Compositions of High Stability Nith a Curing Agent 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 reflective index of the mixture was determined in order to confirm molar ratios. The value was found to fall within the range of about 1.4840 to 1.4860.

About 3240 gms of water 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 95°C by exotherm. The 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-I rating, corresponding to about 20 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 and a second charge of about 1080 gms a 50% NaOH solution was added. The temperature was maintained at about 80 0 C during the exothermic reaction. 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 range of 1.4700 to 1.4730.

-13- JTA:1373P The temperature of the mixture was allowed to rise by the heat of exothermic reaction to about 900°C near the end of the formaldehyde addition. Upon completing the addition of formaldehyde, the temperature of the reaction was maintained at 90°C. providing an increase in viscosity which corresponded to an F-rating (140 centipoise). The mixture was then cooled to about 850°C and the reaction proceeded at that temperature until a viscosity corresponding to an M-rating (320 centipoise) was attained.

i The addition of about 990 gms of water followed and the mixture was allowed to cool to about 72 0 C. The reaction proceeded at 72 0

C

providing an increase in viscosity to a P-rating (400 centipoise).

The mixture was then further cooled to 670°C and an additional 1i charge of about 540 gms of 50% NaOH solution was added. The reaction proceeded at about 67 0 C. The viscosity decreased with the addition of |i NaOH to an H-rating (240 centipoise) with reaction.

When a J-rating was obtained, the mixture was cooled to about 500°C t and about 90 gms of cornstarch extender and about 90 gms of urea were added.

Upon cooling to about 300°C, about 180 gms of propylene carbonate were injected through the bottom of the 5 gallon reactor, under vacuum, in close proximity to the impeller. The mixture was allowed to cool to 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 250°C, and as determined by a RVF Brookfield ii Viscometer with a #3 spindle at 20 rpm. A sample of the batch was cured at 100 0 C and gelled to solid in about 13.2 minutes.

'I After about 40 minutes, about 156 gms of urea 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 100°C and gelled in about 13.6 minutes to form a i~ solid.

A The remaining portion of the composition 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 initial mixture of phenol, formaldehyde and water was found to have a refractive index of 1.4394. The mixture after addition of the second -14- JTA:1373P :1

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charge of formaldehyde had a refractive index of about 1.4734.

The process of Example 1 was modified by cooling the mixture to 50 0 C after a Gardner-Holt viscosity rating of was obtained (220 centipoise). After cooling to 50 0 C, 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 viscosity of 440 at 0 C, as measured in Example 1. A sample of the batch gelled to a solid in 13.1 minutes at 100 0

C.

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 1000C.

The composition remained liquid after several hours.

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 water. 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 about 240 centipoise was obtained (J-rating), the mixture was cooled to about 30°C and propylene carbonate (about 54 gms, 0.36 wt. based on total resin) was added. A specific gravity of 1.198, a refractive index of 1.4610 and a Brookfield viscosity of 250 centipoise at 250°C were noted. A sample was found to gel in 22.1 minutes at 1000C.

Additional propylene carbonate was added to this mixture (about 54 gms) to double the concentration of the original mixture (about 0.73 wt.

percent based on the total mixture, or about 1.2 wt. percent based on solids). The Brookfield viscosity was 410 centipoise at 25°C as measured in Example 1. The specific gravity was 1.196 and the refractive index 1.4635. A sample was gelled in 17.1 minutes at 100°C.

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This demonstrates that the ester-functionalized species is 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 temperature control and an impeller powered by a 25 h.p. motor, with stirring at about 100 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 Ibs. of NaOH (50% solution) were added through the top and an exothermic reaction continued. The temperature was maintained at about 930 to 95 0 C by the cooling coils. A Gardner-Holt viscosity rating of about was obtained (about 40 centipoise) for the mixture after about 1.5 hours. The reactor contents were cooled to and a second charge of about 6614 Ibs. 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 0

C

with exothermic reaction until a viscosity rating of was obtained (about 100 centipoise). The mixture was cooled to about 85°C and the reaction continued. When a viscosity rating of (about 300 centipoise) was obtained, an additional charge of 987 gallons of water was added and the mixture was cooled further to about 80 0 C. Reaction continued within the mixture to provide a P-rating for the viscosity (about 400 centipoise), after which the mixture was cooled to about 70 0 C and additional NaOH solution) was added (about 2832 Ibs.). The viscosity decreased to less than an H-rating on the addition of NaOH and, after about 1 hour, the i viscosity approached an I-rating (220 centipoise). The mixture was cooled about 30 0 C 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 seconds.

The mixture was then cooled to about 25 0 C 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 0 C, as determined by an LVF Brookfield Viscometer with #2 spindle at -16- JTA:1373P -e rpm. A sample of the batch was cured by heating to 100°C 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 This example is a repeat of the process used for the production of 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.

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 90 0 C until an F-rating for viscosity (about 140 centipoise) was attained.

The mixture was then cooled to about 87 0 C 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 75 0 C and the reaction proceeded to attain a viscosity slightly higher than an O-rating. The mixture was about 800°C when a P-rating was attained (400 centipoise).

The mixture was then cooled to 67°C followed by addition of the third charge of NaOH (50% solution). The reaction then proceeded until a Sviscosity slightly above an I-rating (220 centipoise) was attained.

SThis mixture was then cooled to 30 0 C, at which time 700 Ibs. of propylene carbonate were added as described in Example 4.

After cooling to 25°C the batch was characterized as having a refractive index of about 1.4595, a specific gravity of about 1.194 and a Brookfield viscosity of 400 centipoise at 250°C, as measured in Example 4. A samp;e of the composition was cured and found to gel to a solid in about 17.6 minutes at about 1000°C. The remaining batch was transferred to a storage tank and remained liquid for over 24 hours.

-17- JTA:1373P L "ar~o-r~ Effective and Excessive Quantities of Curing Agent Examples 6 to 9 The following examples illustrate that excess quantities of curing agent are unsuitable.

In these examples a resin was prepared in large scale in accordance with 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. solids) were removed after the third charge of NaOH. These samples were cooled to about 700°C and the viscosity increased to above an N-rating (about 340 centipoise). The mixtures were cooled to 300°C and 63 gms (about 0.35% b1sd on the total weight of resin) of propylene carbonate were added to each mixture in the manner described in Example 1.

For Ex,-mple 6, the mixture had a Brookfield viscosity of 395 centipoise at 25°C, as determined by an RVF Brookfield Viscometer with a #3 spindle at 20 rpm. A specific gravity of 1.198 and a refractive index of about 1.470 were determined. A sample gelled in about 21.4 minutes at 100°C.

For Example 7, the mixture had a Brookfield viscosity of 370 centipoise at 250°C, 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 100 0

C.

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 25 0 C, as determined in Example 6, and a specific gravity of 1.153. A sample gelled to a solid in 19.6 minutes at 100°C.

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 sample was obtained from the 250 gm portion for Example 9. Each sample was placed within a 250 ml beaker and was cooled to about 300°C. Propylene carbonate was added to each with rapid hand-stirring, using a wooden spatula. In Example 8, about 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 -18- JTA:1373P 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 250C). 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 to 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 to 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 r, reaction proceeded at from 730 to 950C to obtain an A-rating for viscosity (Gardner-Holt), after which the reaction mixture was cooled to 800C 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 90 0 C. 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 85 0 C and the viscosity increased to a K-rating for Example 10, and 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 80 0 C and each obtained a P-rating for viscosity. Additional NaOH (50% solution) was added (about 2880 lbs.) i after a temperature of 700C was obtained. Reaction proceeded in each Smixture to a J-rating for viscosity, after which about 240 lbs. of cornstarch and 720 lbs. of urea were added at about 500C. Each mixture was then cooled to 300C and about 700 lbs. of propylene carbonate were added to each of Examples 10, 11 and 12.

Upon cooling to 250C, 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 250C, as determined by an LVF Brookfield Viscometer with a #2 spindle at 30 rpm. A sample gelled in 16 minutes at 1030C. Another -19- JTA:1373P -I sample was retained (about 100 ml). After 8 days, this retained sample was found to have a Brookfield viscosity of about 750 centipoise at 250°C, as determined by an RVF Brookfield Viscometer with a #4 spindle at 20 rpm. A portion of this sample was cured at 100°C 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 250°C, as determined for the initial sample of Example 10. A sample was cured at 100 0 C and found to gel in 16.6 minutes. Another sample was retained (about 100 ml) for 2 days. This retained sample had a Brookfield viscosity of about 440 centipoise at 25 0 C on the second day, as determined for the retained sample of Example Example 12 showed a value of 1.4663 for the refractive index, a 1.200 specific gravity and a Brookfield viscosity of 340 centipoise at 250°C, as determined for the initial sample of Example 10. A sample was cured at 100°C 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 about 560 centipoise at 250°C on the fifth day, as determined for the retained sample of Example 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 Moisture 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 (based on 1400 gms. 58.8 wt. the total weight of adhesive) Furafil (at 5% extender 200 gms. 3.4 wt. Wheat Flour (at 11% 150 gms. 6.3 wt. extender Sodium Hydroxide (50% solution) 80 gms. 3.3 wt. Water 550 gms. 23.2 wt. 2380 gms. 100 wt. JTA:1373P Board Manufacturing 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 standard glue spread commonly used in the manufacture of plywood. A glue spread of about 58 to 60 lbs./1000 ft 2 of double glue line is generally used.

The panels were laid-up and prepressed for about 4 to 6 minutes followed by hot-pressing for 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 Plies 4 Press Temperature 315 0 F (1570C) Glue Spread 58 to 60 ibs/1000 ft 2 of double glue line Assembly Time 10 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 to 22% range Cores 8% average moisture, 5 to 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 4 and 5 and all boards tested passed commercial standards and approval by the American Plywood Association.

Other Effective Curing Agents Examples 14 and These examples are presented to demonstrate the efficacy of curing agents 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 carbonate.

Acceptable results are expected for each parameter measured in Example 1 -21- JTA:1373P

__C

i and the binder composition is expected to have accept~fle stability.

Potassium Phenol-Formaldehyde 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, appruximately 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 composition 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 modifications. This application is intended to cover any variations, uses or adaptations 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.

-22- JTA:1373P

Claims (33)

1. 2. A binder composition as in claim 1 wherein the alkaline condensed phenolic resin is the reaction product of a phenol and formaldehyde.
2. 3. A binder composition as in claim 2 wherein said resin is the condensation product of a phenol and formaldehyde and the phenol:formaldehyde molar ratio falls within the range of 1:1 to 1:3.1.
3. 4. A binder composition as in claim 3 wherein the solids content of the phenolic resin solution is from about 40 to 75% by weight and the viscosity of said phenolic resin solution is less than about 1500 centipoise at 25 0 C. A binder composition as in claim 1 wherein the phenolic re.in is condensed with an alkali selected from the group consisting of potassium hydroxide, sodium hydroxide and mixtures thereof, and the alkalinity content, based on sodium hydroxide, is from 1% to 15 by weight of said resin solution
4. 6. A binder composition as in claim 5 wherein the alkaline condensed phenolic resin has a weight average molecular weight of from about 700 to about 2200.
5. 7. A binder composition as in claim 1 wherein the alkaline condensed phenolic resin is capable of bonding solids selected from the group consisting of granular refractory material and lignocellulosic material.
6. 8. A binder composition as in claim 7 wherein the granular refractory material is selected from the group consisting of alumina, magnesia, zircon, silica sand, quartz, chromite sand, zircon sand and olivine sand, and the lignocellulosic material is selected from the group -23- JTA:1373P -i consisting of wood veneer, wood fibers, wood wafers, wood shavings, wood chips, wood flakes, and wood particles.
7. 9. A latently curable binder composition comprising in admixture an alkaline condensed phenol-formaldehyde resin solution having a phenol:formaldehyde molar ratio within the range of 1:1 to 1:3.1, a solids content of from about 40 to 75% by weight, a viscosity of less than about 1500 centipoise at 25 0 C, an alkalinity content, based on sodium hydroxide, of from about 1% to 15% by weight of said resin solution, wherein said alkali is selected from the group consisting of potassium hydroxide, sodium hydroxide and mixtures thereof, and a curing agent, having at least one ester functional group which is dispersible in said alkaline condensed phenol-formaldehyde resin solution, wherein said quantity of curing agent is sufficiently high to accelerate the cure of the alkaline condensed phenol-formaldehyde resin and said quantity of curing agent is sufficiently low to maintain the binder composition in a liquid form at ambient temperature for a period in excess of 24 hours. A binder composition as in claim 1 wherein the curing agent is selected from the group consisting of lactones, carboxylic acid esters, organic carbonates and mixtures thereof.
8. 11. A binder composition as in claim 10 wherein the curing agent has from 4 to 12 carbon atoms. i 12. A binder composition as in claim 9 wherein the curing agent has from 4 to 12 carbon atoms.
9. 13. A binder composition as in claim 11 wherein the reactivity of the curing agent is equal to or less than the reactivity of propylene carbonate.
10. 14. A binder composition as in claim 12 wherein the reactivity of the curing agent is equal to or less than the reactivity of propylene carbonate. A binder composition as in claim 1 wherein the curing agent is selected from the group consisting of propylene carbonate, triacetin and gamma-butyrolactone.
11. 16. A binder composition as in claim 9 wherein the curing agent is selected from the group consisting of propylene carbonate, triacetin and gamma-butyrolactone.
12. 17. A binder composition as in claim 1 wherein the quantity of curing agent in said composition falls below about 5 wt. percent, based on the total solids of the binder composition.
13. 18. A binder composition as in claim 9 wherein the quantity of -24- JTA:1373P curing agent in said composition falls below about 5 wt. percent, based on the total solids of the binder composition.
14. 19. A latently curable binder composition comprising in admixture an alkaline condensed phenol-formaldehyde resin solution having a phenol:formaldehyde molar vatio in the range of 1:1 to 1:3.1, a solids content in the range of about 40% to 75% by weight, an alkalinity content, based on sodium hydroxide, of about 1% to 15%, by weight of resin solution, a viscosity of less than about 1500 centipoise at 250C wherein said alkali is selected from the group consisting of sodium hydroxide, potassium hydroxide and mixtures thereof, a curing agent with a reactivity less than or equal to propylene carbonate, having from 4 to 12 carbon atoms, wherein said curing agent is selected from the group consisting of lactones, carboxylic acid esters, organic carbonates and mixtures thereof, the quantity of said curing agent falling below about 5 wt. percent, based on total solids of the binder composition. A composition as in claim 19 wherein the curing agent is selected from the group consisting of butyrolactone, triacetin and propylene carbonate, in a quantity falling in the range of about 0.1 wt. percent to 1.0 wt. percent, based on total solids of the binder composition.
15. 21. A composition as in claim 1 which remains in a liquid form for at least 72 hours, at a viscosity less than 1000 centipoise.
16. 22. A composition as in claim 19 which additionally comprises cornstarch and urea.
17. 23. A process for preparing a latently curable binder composition which is sufficiently stable to remain in a liquid form at ambient temperature for at least 24 hours and which is sufficiently reactive to gel upon heating to a temperature above about 100 0 C, comprising the steps of reacting phenol and formaidehyde in the presence of aqueous alkali to form a resin in solution, the resin solution having a viscosity below about 500 cps at 250C; cooling said resin solution to a temperature of below about 400C; agitating the resin solution rapidly; and (d) adding to said resin solution, in a region of rapid agitation, a curing agent for the resin solution at a rate of addition which is sufficiently high to prevent the formation of gel or colloids upon addition, wherein the quantity of curing agent added is sufficiently high to accelerate the cure of the alkaline condensed phenol-formaldehyde resin and is sufficiently low to maintain the binder composition in a liquid form at ambient temperature, wherein said curing agent has at least one ester functional group and is dispersible in the resin solution. JTA:1373P
18. 24. The process of claim 23 wherein the curing agent is injected into the resin solution a pressure of about 30 to 40 psi. The process of claim 23 wherein rapid agitation is provided by an impeller means within a baffled reactor.
19. 26. The process of claim 25 wherein the curing agent is added below the surface of the resin solution to a region of rapid agitation.
20. 27. The process of claim 26 wherein the curing agent is added in close proximity to the impeller means.
21. 28. The process of claim 23 wherein the curing agent is added over a period of about 20 to 45 seconds.
22. 29. The process of claim 23 wherein the resin solution is cooled to a temperature of below about 30 0 C. The process of claim 23 wherein phenol and formaldehyde are reacted in the presence of an aqueous alka.i to form a resin in solution, the solution having a viscosity in range of about 200 to about 400 cps at 0 C.
23. 31. The process according to claim 23 comprising the additional step of adding cornstarch prior to the addition of curing agent.
24. 32. A process as in claim 23 wherein the phenol and formaldehyde are reacted to provide a resin having a phenol:formaldehyde molar ratio of from about 1:1 to 1:3.1, and said solution comprises from about 40% to 75% by weight solids, has a Brookfield viscosity of from about 200 to 400 centipoise at 25 0 C and has an alkalinity content, based on sodium hydroxide, of from about 2.5% to based on the weight of resin solution, and said alkali is selected from potassium hydroxide and sodium hydroxide.
25. 33. A process as in claim 23 wherein the curing agent is selected from propylene carbonate, gamma butyrolactone and triacetin.
26. 34. A process for preparing a latently curable binder composition which is sufficiently stable to remain in a liquid form at ambient temperature for at least 24 hours and which is sufficiently reactive to gel upon heating to a temperature above about 100 0 C, comprising the steps of: reacting phenol and formaldehyde in the presence of aqueous alkali selected from potassium hydroxide and sodium hydroxide to form a resin in solution, said resin having a phenol:formaldehyde molar ratio of from about 1:2.1 to 1:2.8, said resin solution having an alkalinity content, based on sodium hydroxide, of about 2.5 to based on the weight of resin solution, a solids content in the range of 40 to 60% by weight and a viscosity of from 250 to 400 centipoise at 25 0 cooling said resin so'ution to a temperature of below about 300°C, agitating the resin -26- JTA:1373P solution rapidly, and adding to the resin solution a curing agent selected from the group consisting of propylene carbonate, triacetin and gamma butyrolactone in a quantity of from about 0.1 wt. percent to 1 wt. percent, based on the weight of solids in said binder composition, said addition of curing agent being completed within about 20 to 45 seconds. A method for bonding lignocellulosic material under heat and pressure which comprises applying an adhesive to said lignocellulosic material wherein said adhesive comprises in admixture an alkaline condensed phenol-formaldehyde resin solution, the resin having a phenol:formaldehyde molar ratio of about 1:1 to 1:3.1, the solution having a viscosity of less than about 1500 centipoise at 250°C, a solids content of from about 40% to 75% by weight, and an alkalinity content based on sodium hydroxide, of from about 1% to 15% by weight of the resin solution of an alkali selected from sodium hydroxide, potassium hydroxide, and mixtures thereof, and (ii) a curing agent selected from the group consisting of gamma butyrolactone, triacetin and propylene carbonate in a quantity below about 5% by weight based on the solids content of said resin solution; and consolidating said lignocellulosic material and curing the alkaline condensed phenol-formaldehyde resin.
27. 36. A method as in claim 35 wherein the lignocellulosic material is selected from the group consisting of wood flakes, wood particles, wood fibers, wood shavings, wood veneers and mixtures thereof, and said lignocellulosic material is consolidated into boards. *i 37. A method as in claim 35 wherein said lignocellulosic material comprises at least 3 wood veneers which are consolidated into plywood boards of at least 3 plies, the core ply having a moisture content up to 12% by weight and the face plies having a moisture content up to 25% by weight.
28. 38. A method as in claim 37 wherein the lignocellulosic material comprises wood veneers consolidated to 1/2" plywood and the alkaline condensed phenol-formaldehyde is cured within about 2.5 minutes.
29. 39. A method for bonding granular refractory material under heat and pressure which comprises applying an adhesive to said granular refractory material wherein said adhesive comprises in admixture an alkaline condensed phenol-formaldehyde resin solution, the resin having a phenol:formaldehyde molar ratio of about 1:1 to 1:3.1, the solution having a viscosity of less than about 1500 centipoise at 250°C, a solids content of from about 40% to 75% by weight, and an alkalinity content based on sodium hydroxide, of from about 1% to 15% by weight of the resin solution -27- JTA:1373P V of an alkali selected from sodium hydroxide, potassium hydroxide, and mixtures thereof, (ii) a curing agent selected from the group consisting of gamma butyrolactone, triacetin and propylene carbonate in a quantty from about 0.05% to 5% by weight based on the solids content of said resin solution; and consolidating said granular refractory material and curing the alkaline condensed phenol-formaldehyde resin. A method as in claim 39 wherein the granular refractory material is selected from the group consisting of alumina, magnesia, zircon, silica sand, quartz, chromite sand, zircon sand, olivine sand, and mixtures thereof.
30. 41. A process for preparing a latently curable binder composition which is sufficiently stable to remain in a liquid form at ambient temperature for at least 24 hours and which is sufficiently reactive to gel upon heating to a temperature above about 100 0 C substantially as hereinbefore described with reference to any one of the Examples.
31. 42. The product of the process of any one of claims 23 to 34 or 41.
32. 43. A latently curable binder composition substantially as hereinbefore described with reference to any one of the Examples.
33. 44. A method for bonding lignocellulosic material under heat and pressure substantially as hereinbefore described with reference to any one of the Examples. A method for bonding granular refractory material under heat and pressure substantially as hereinbefore described with reference to any one of the Examples. DATED this TNENTY-EIGHTH day of SEPTEMBER 1988 Borden, Inc. Patent Attorneys for the Applicant SPRUSON FERGUSON -28- JTA:1373P