CA2226274A1 - Phenol-formaldehyde resins modified with guanidine salts - Google Patents

Abstract

A guanidine-modified phenol-formaldehyde resole resin by reacting formaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1.5:1 in the presence of an effective amount of an alkaline catalyst and in the presence of a catalytic amount of a guanidine salt. The resin is suitable for use in adhesives for high moisture content substrates.

Description

. CA 02226274 1998-01-06 P~ENO~FORMALDEErYDE RESINS MODIFIED
WlT~ GUANII)INE SALTS

Field of the ~nvention The present invention is directed to phenol-formaldehyde resins modified with guanidine salts for use as adhesives which exhibit high moisture content substrate bonding abilities over a wide range of conditions without sacrificing glue line dry out re~ist~nce.
s Ba~ kpround of the Invention There are several types of adhesives which have been used, with varied success, to bind higher than average moisture content substrates (8% to 20% average moisture content), for example wood veneer. Such adhesives include AF/PF adhesives and foamed adhesives.
10 Foamed adhesives are believed to have a slight advantage by their better ability to bond higher than average moisture content veneer at lower glue spread rates, thus limiting excess water in the glue line. The lesser amount of water at the glue line tr~nQ~tes to less steam produced during hot l)re~ulg. This reduces the problem of veneer d~l~min~tions, or "blows," when the hot press opens due to the force of the steam pressure being greater than the cured adhesive 15 strength of the glue. The AFIPF system acts as a catalyzed system and is designed to bond quicldy before the steam pressure builds to a level at which the adhesive strength will not bind the veneer. These systems have ~ccori~ted disadvantages. The AF/PF system is prone to dry out on the glue line, re.lu.l~,s the h~n-lling of two components, and has a finite shelf life following mucing ofthe two ~ ,one,lts. Foam glues are equipment specific resins and are not 20 widely used c.~ tl~ in the plywood industry.
Recently, ~lo~ are d~ e adhesives which will bond both normal and higher moisture content ~I.~s, in order to increase throllehput in their dryers and e;~n~llt~neo~ y reduce plant ~nissir~n~ The sought-after adhesives must ~.Ai~A;.~ several physical p,opti,lies inherent to those currently used. These include a specific viscosity range, low free 25 fonnAItlehyde, etc. For exarnple, proper application of the adhesive is dependent on viscos;ly, and ~ngeS to the adhesive which shi~ the viscosity range beyond the çapability of the mill equipment is undesirable.
Further requile.ll.,nls for developing a superior adhesive which has the ability to bind varying, especially high moisture content substrates, include the ability to resist glue line dry 30 out under varied con-lition~ Dry out is defined as the loss of moisture from the glue line which subsequently results in an ineffective adhesive. During the m~nllf~cture of wood products, there is a variable period of time between the lay up of the construction and the final thermal curing in the hot press. Du~ing this time the veneer often is subjected to conditions which tend to starve the glue line of moisture. Lower moisture content veneer and high temperature 5 veneer can aggravate this ph~nomçnon. The desired adhesive must be able to withstand the factors which contribute to dry out.
Past approaches to prepa~ing a PF resin adhesive which can bond high moisture substrates have included increasing the resin molecular weight and/or the mole ratio in order to increase the cure speed or reduce the cure time of the PF adhesive. Both of these 10 approaches reduce the dry out resiet~nce ofthe resin and in the case ofthe higher mole ratio resins, increased formaldehyde emissions become a concern.
Therefore, there is a contin-lin~ need for a one-component resin with excellent storage stability, fast cure speeds to handle high moisture conditions, and low molecular weight to give dry out resistance, especially from t,.ll~,.,e thermal conditions during prepress assembly.
Summary of the ~nvention The present invention is directed to the use of ~ ni~ine salts in plepali,-g phenol-fc~ d~hyde resin adhesives. Adhesives prepared from resins modified with gll~ni~line salts are suitable for bonding high moisture content substrates, such as veneer and wood strands, and 20 for rO.,..ing quality bonds at shorter prese times. Such adhesives also exhibit improved dry-out resiet~nce.
An embodiment of the present invention is directed to a method for pl~palillg a ~ nitline-modified phenol-formaldehyde resole resin composition by r.acting formaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1.5 :1 in the presence of an 25 effective amount of an ~Ik~line catalyst and introducing a catalytic amount of a ~ni~ine salt during the resin preparation.
The present invention is also directed to a guanidine-modified phenol-forrn~lrle.hyde resin useful for prepalh,g an adhesive, ~I,ere.., the resin is prepared by reacting formaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1.5:1, in the presence of an 30 effective amount of an alkaline catalyst and introducing a catalytic amount of a gl~ni-line salt during the resin prep~lion.

The present invention is also directed to a method for gluing high moisture content substrates by applying to the substrates an adhesive made from a guanidine-modified, phenol-formaldehyde resole resin.
The present invention is also directed to bonded wood products, such as plywood and OSB, prepared by applying to high moisture content substrates such as veneer or wood strands an adhesive made from a guanidine-modified, phenol-formaldehyde resole resin.

Brief Desc~ ;~)lion of the D.~. in&.c Fig. 1 depicts wood failure results for normal moisture content veneer press time study.
Fig. 2 depicts high moisture content veneer press time study results.
Fig. 3 depicts dry out study results.
Fig. 4 depicts high moisture content veneer press time study results.
Fig. S depicts dry out study results.

Detailed Descl ;plion of the Invention In accordance with the present invention, a guanidine salt is added during a phenol-formaldehyde resole resin cook to produce a guanidine-modified phenol-formaldehyde resole resin. Guanidine itself is an unstable material that readily hydrolyzes to urea. However, ~l~ni~1ine is stable as a salt, such as a salt of carbonic acid, e.g. ~l~ni~line carbonate.
It was discovered that phenol-formaldehyde resole resins modified with gll~ni~line salts during the yreparalion of the resin are s~bsl ~ y less advanced at a given viscosity than similarly prepared unrnodified phenol-formaldehyde resole resins and therefore the modified resins have good ability to resist dry out when the resin, applied to the glue line, is aged prior to hot pr~s~.g. In addi~ion, these ~l~n ~ine salt-modified resins bond (cure) quickly and thus have good press speed characteristics. In addition, gu~ni-line salts react with excess formaldehyde in the resin during the resin plepa-alion, redllçing formaldehyde emissions.
As a result of its ability to enh~nce press speed, a gLI~ni~ine-modified phenol-formaldehyde resole resin plel)al ed accordil-g to the present invention is particularly suitable for use in pl~p~ing an adhesive for bonding high moisture content veneer (generally between 8% and 20% average moisture content). For example, adhesives made with phenol-fo~naldehyde resole resins mor~ified with ~l~nitline carbonate exhibited excellent press speeds even though the resins were cooked to a lower resin adv~nc~m~nt than is norrnal for phenol-forrnaldehyde resole resins used for veneer and wood strand bonding applications. The resins . CA 02226274 1998-01-06 of the present invention are suitable for bonding all types of lignocellulosic materials such as veneer, flakes, particles, strands, fibers, etc.
Suitable methods for preparing phenol-formaldehyde resole resins for use with the present invention may be found in, inter alia, U.S. Patent 5,079,332 which is hereby incorporated by reference in its entirety. There are a variety of techniques known in the art for reacting phenol and formaldehyde in the presence of an alkaline catalyst. Typically, the resin is reacted in stages with separate partial additions of either one or both of the react~nt~ and alkaline catalyst. For eY~mrle, one conl,non procedure is to react phenol with a portion of the formaldehyde, in the presence of a portion of the alkaline catalyst. After a brief, initial exothermic reaction, a~ tio~l amounts of alk~line catalyst and formaldehyde are added to the reacting mixture and the reaction is contim~e~ with careful control of the reaction temperature.
Once all of the react~nt.c and catalyst have been added, the reaction is allowed to proceed to a suitable endpoint, which may be determined by measuring the refractive index of the reacting mixture or by measuring the viscosity of the reacting mixture or by some combin~tion thereof as recognized by those sldlled in the art. Once the selected end point is achieved, the reaction mixture is cooled and the resin is ready for plep~i. g an adhesive mixture.
In accordance with the invention, an alkaline catalyzed resole resin composition is ~lepal~d by co.~ i"p formaldehyde and phenol at a formaldehyde to phenol mole ratio of at least 1.5:1 and possibly up to 3:1, pr~ bly in a range of about 2.0:1 to 2.5:1, and more preferably about 2.0:1 to 2.3 :1, in an aqueous reaction media in the presence of an effective amount of a alkaIine catalyst using known procedures. The pH during the reaction is preferably adapted to a value b~ about 9 and 12, and more preferably between about 10.5 and 11.5 using the alkaline catalyst.
Once the phenol and formaldehyde has been combined, the resin is heated to a tel,~e~ Jre ~her~l)on controllable viscosity adv~ncem~nt is achieved. The resin is heated to advance the resin to the desired viscosity, typically between about 500 and 1100 cps and then cooled to room te."l)e,~lule. The viscosity is typically measured by a Brookfield viscometer such as Model LVF spindle 2 or 3, speed 30.
In accordance with the present invention, a ~nidine salt is added as an additional catalyst to the resin at any time during the resin prepal~lion. However, it is prerelable to add the guanidine salt at a point between the time after subst~nti~lly all of the formaldehyde has been added during the synthesis and the end of the resin cook just prior to cooling the resin . CA 02226274 1998-01-06 composition. More preferably, the guanidine salt is added immediately after all of the formaldehyde has been added to the reaction mixture.
The guanidine salt is added in a catalytic amount s~ffiei~nt to obtain the desired final resin viscosity and degree of resin adv~nc~ment Typically the ~nidine salt is added to the resin S in an arnount b~lwe~n about 0.02 and 12 wt%, preferably between about 0.2 and 5 wt%, more preferably between about 1 and 2.5 wt%, based on the total weight ofthe resin solids.
The guanidine salt may be any suitable salt inclllding guPnidine carbonate, guanidine hydrochloride, guanidine sulfate, etc and low molecular weight ~l~nidine adducts with formaldehyde. Other sources of guanidine salts inclllde, but are not lirnited to, methyl gu~ni(~ine and ethyl ~l~ni~ine derivatives. Fl~r~l~bly, the gll~ni~line salt is g~l~ni~ine carbonate.
As used herein, phenol-fom~ lehyde resole resin includes reaction products of a phenol and formaldehyde having reactive methylol groups. The solids level of the final resin is preferably about 30 to 75% by wt and depends on the ~lltim~te use of the resin. For example, resins for use in preparing an adhesive for making plywood, preferably have a solids level of about 40 to 50% by wt, whereas resins for use in preparing an adhesive for making oriented strand board preferably have a solids level of about 50 to 60 % by wt.
As well known to those of skill in the art, a suitable alkaline catalyst is added during the resin cook. Preferably, part of the catalyst is added at the be~ of the cook, and the rest is added during the cook. The catalyst promotes the reaction of the form~ld~hyde with phenol to form a resole resin. The catalyst is prefe-~bly one of the inorganic or organic alkaline catalysts known to be useful in prepa ~lg phenol-formaltlehyde resole resins. The catalyst is present in an amount effective to catalyze the reaction between the phenol and forrn~ld~hyde.
The catalyst generally provides 1 to 15 wt%, often about 4 to 8 wt%, more usually about 6 wt%, of the final weight of the resin. Typical catalysts include alkali metal hydroxides, such as sodium hydroxide, lithium hydroxide, potassium hydroxide, or l~lu~es thereof, generally sodium hydroxide is pl~fe.~ed for cost and availability. Other catalysts include allcali metal carbonates such as sodium carbonate and potassium carbonate, alkaline earth hydroxides such as magnesil~m hydroxide, cP~ m hydroxide and barium hydroxide, aqueo~s ammonia and amines.
In a preferred embodiment ofthe present invention, ~lanidine carbonate is added during the cook of a 2.0:1 to 2.3:1 molar ratio formaldehyde-phenol resole resin after all of the formaldehyde has been added during the ~.-tl.e~;s. The resin is catalyzed by sodium hydroxide and heated to a temperature whereupon controllable viscosity advancement is achieved. The cook is ended by cooling when the desired application viscosity has been reached.
Urea also may be added during the resin cook. Typically, urea is used as a formaldehyde scavenger. However, urea may not be desirable because it counteracts the desired lower 5 molecular weight of the resin and reduces the dry out resist~nce. That is, urea has a thinning effect and to achieve a given viscosity requires a relatively higher molecular weight resin. Urea is available in many forms such as solid urea, for c.,alll~le prill, and urea solutions, typically aqueous solutions. Any form of urea is suitable for use in the practice of the invention. The urea is generally added between about 0 and 3 wt%, preferably above about 0.5 wt%.
Forrnaldehyde is also available in many forms. Paraform (a solid, polyrnerized formaldehyde) and formalin solutions (aqueous solutions of formaldehyde, sometimeS with methanol, in 37%, 44%, or 50% formaldehyde concentrations) are commonly used forms.
Fonn~l~ehyde also is available as a gas. Any of these forms is suitable for use in the practice of the invention. Further, the formaldehyde may be partially or totally replaced with any 15 suitable aldehyde as known in the art. Typically, formalin solutions low in meth~nt)l are prere,led as the formaldehyde source.
The phenol compollelll ofthe resole resin inrllldçs any phenol typically used in preparing phenolic resole resins, which are not substituted at either the two ortho positions or at one ortho and the para position, such un~ubstituted positions being necessal~ for the desired 20 polyTn~ri7~tion reaction to occur. Phenols s.~bs~ ed in these positions may be used in lesser qu~ntiti~c (e.g., up to about 30 weight % of the phenol component) as it is known in the art to control molecular weight by a chain t~llnil~alion reaction. Any one, all, or none of the re~n~ carbon atoms of the phenol ring can be s~lbstit.lted in a conventional f~hion The nature of these s~lbstit~lents can vary widely, and it is only necessary that the substituent not 25 interfere in the polymerization of the aldehyde with the phenol at the ortho andJor para positions thereo~ FullLe.lllore, at least a portion of the phenol component must include a phenol not blocked at the ortho and para positions so that the resin is thermosettable.
Plerelably~ at least 10% by weight of the phenol component should include such tri-functional phenol and usually the phenol component consists ess~nti~lly entirely of such tri-functional 30 phenol.
Substituted phenols which optionally can be employed in the forrnation of the phenolic resins include alkyl s ~ ed ph-onnlc, aryl s ~ lled phenols, cycloalkyl substituted phenols, alkenyl-substituted phenols, alkoxy substituted phenols, aryloxy substituted phenols, and halogen-substituted phenols, the foregoing substituents possibly cont~ining from 1 to 26, and usually from 1 to 9~ carbon atoms.
Specific examples of suitable phenols for preparing the resole resin composition of the present invention include: hydroxy benzene (phenol), o-cresol, m-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 3,4,5-trimethylphenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, p-phenoxy phenol, naphthol, anthranol and substituted derivatives thereof. Oldhlaly phenol (hydroxy benzene) normally is preÇelled for most applications based on cost and availability.
During the process of pl ~?aling the resole resins of the present invention, a variety of other modifiers can be added into the resole resin in order to improve tollghness and other cured resin properties. These modifiers include, for example, chain termin~ting phenols, glycols, with or without halogen substitution for additional fire retardancy, polyester polyols, alkyl phenol~, hydroxy-containing acrylates, and the like and mixtures thereo~ The proportion of such modifiers incorporated into the resole resin typically ranges from S to 3 5 weight percent (based on the phenol component.) Other modifiers such as fire retardants, lubricants, defoamers, plasticizers, softening agents, pigments and fillers also can be added to the resole resin composition. Reactive modifiers such as di- and higher polyols, e.g., di- or polyhydric phenols, resorcinol, phloroglucinol, and the like, can be added to the resole resin after it has been forrnul~ted.
Finally, modifiers to achieve special effects in particular applications may be appropriate, e.g., polyvinyl butyrals, or epoxies for better impact strength in composites.
The present invention is also directed to processes of bonding high moisture content substrates using a gll~nirline-modified phenol-formaldehyde resin in a suitable adhesive composition, and the resl-lting bonded products. The adhesive is applied to the substrate materials by any suitable method and then the substrate materials are hot pressed to form a bonded wood product or composite. Suitable substrate materials include, but are not limited to, wood plies, composite panels, veneer, particles, flakes, sawdust, meal, flour, and fibers.
The present invention is particularly useful for bonding high moisture content substrates for example having an overall average moisture content of about 5 to 20 wt%. The present invention may also be used with wood stock having an average moisture content of about 8 to 20 wt%, but cont~ining a substantial amount of stock having a moisture content below about 3% by wt. The moisture content is determined by means known in the art such as taking an average value of a number of sample readings. ASTM D2016-74 provides a preferred method for determining the moisture content of a substrate. Determining average moisture is within the skill of the art.
An adhesive cont~inine a resin in accordance with the present invention may be applied to a substrate in any suitable manner such as with spray nozzles, ~tomi7.ing wheels, roll coaters, curtain coaters, and foam applicators. Typically the adhesive is applied to the substrate ;, ."-ledi~l~ly or fairly shortly before hot ples~ing. An advantage of the present invention is that the adhesive may be applied even up to about 60 minutes prior to hot pressing with signiffcantly less dry out problems than prior art adhesives. Descriptions of how to make bonded wood products or composites such as ply-wood, particleboard, hardboard, fiberboard, oriented strand board and the like may be found in U.S. Patent 4,758,478 U.S Patent 5,079,332, incorporated by reference above, provides a description of making plywood.
The amount of adhesive applied to the substrate depends on the nature of the substrate, and the desired quality of the final product, and is usually belweell 3 and 8 wt% dry resin solids based on the fini~hed product. Suitable amounts are also provided in U.S. Patent 4,748,478 and U.S. Patent 5,079,332.

Examples The invention will be further descnbed by reference to the following examples. These -- ~rl-~ should not be construed in anyway as limiting the invention to a"yll~ing less than that which is disclosed or which would have been obvious to anyone skilled in the art.

Example 1 Due to the ~",oll,el,llic nature of the reaction used to produce resoles, reagents are added to initiate and fuel the poly",e,iLalion in quantities which allow the reaction to remain under control. Therefore, with the exception of phenol and water, fractional proportions of the [~.-"~ g reagents generally are added stepwise to ensure the safety of the person preparing the resin and the equirlnPnt The following ingredients were combined in the following order.

. CA 02226274 1998-01-06 Resin Ingredients Component Weight %
Phenol 24 50% CH2O 12 Water 27 50% NaOH 6 50% CH2O 23 Guanidine Carbonate 2 50% NaOH 6 Phenol, formaldehyde and water were charged to a reactor and the temperature wasadjusted to 37~C. Sodiurr. hydroxide solution was added and the temperature was allowed to increase to 82~C. The second charge of formaldehyde was added incrementally, in order to ;n control of the reaction. The reaction contents were then heated to 96~C and held at that temperature for 30 minutes. The contents were cooled to 82~C and reacted to 1020 cps as measured on a Brookfield viscometer (model LVF). During the viscosity hold to 1020 cps the ren-~ining ingredients, inçlllding ~l~ni~ine carbonate, were added increment~lly. The res~ltin~ product contained 43% solids.

20 Example 2 A gl~ni~ine carbonate resin was prepared and ~Y~mined for its ability to bond both normal moisture content veneer and high moisture content veneer, and for its resistance to drying out during varying open ~sseml,ly times. Resin A (control) was a commercially available IMC (int~.~nedi~te moisture content) veneer bonding adhesive sold as GP RPPY 5777. Resin 25 B was a 2.3 mole ratio resin cooked with 2% guanidine carbonate added after all the formaldehyde was added in accordance with Example 1.

Table 1 - Properties for the Resins Resin % Caustic Visco~;ty RI % NVS FreeFormaldehyde (cps) A 6.66 650 1.4618 42.7 negli~ihle B 6.60 1020 1.4663 42.9 *
*Unable to do this test due to test method interference from methylolated guanidine carbonate. There was no noticeable formaldehyde odor.

Table 2 10Resin Mn M~, M~

Surprisingly, Resin B had a lower molecular weight at a higher resin viscosity.
The resins were il.col~,o,~led into a RESI-MIX~ (mixed adhesive) formulation listed in Table 3.

Table 3 - RESI-M~l~) Formulation 20 Component Amount, %
Water 14.3 CO-COB~ filler 6.8 SPRAY-X~ e rtçntl~r 6.9 50% NaOH 3.1 25Soda Ash 0 Resin 68.9 Target Total Dry Solids 43.5 Target Resin Solids 29.6 Target Viscosity 2200 30Filler/Extender Ratio The rnixes were aged overnight and used in a press speed and high moisture study. An open asselllbly time study was run the following day. Details of the conditions used for these 5 studies are listed in Table 4.

Table 4 - Condition for the Panel Studies Press Speed StudyDry Out Study High r' ~ l ~ Study Veneer 1/8" thick southern yellow 1/8" thick southern yellow 1/8" thick southern yellow pine 12" x 12"pine 12" x 12" pine 12" x 12"
Face/13ack Average 8-10% 6-8% 1 1-13%
Moisture Content Core Average 6-8% 6-8% 9-11%
Moistute Content Panel Construction 3-ply, 3/8" thick, 3-ply, 3/8" thick, 3-ply, 3/8" thick, 12" x 12" 12" x 12" 12" x 12"
Glue Spreads 31-33 g/ft2, 73 Ibs.31-33 g/ft2, 73 Ibs. 31-33 g/ft2, 73 Ibs.
MDGL EquivalentMDGL Equivalent MDGL Equivalent Lay-up 4 panels per each 2 min., 4 4 panels per each 2 tnin., 4 4 panels per each 2 min., 4 panels per condition panels per condition panels per condition Open Assernbly 15 rninutes Variable 15 minutes Tirne 60,90,120,150,180 rninutes (in open racks) Prepress 4 rninutes at 150 psi None 4 minutes at 150 psi Closed Assembly NeL,'i"i~'- Negligible N~,"lig-' '-Titne Hot Press Variable 3 minutes Vatiable 1.9, 2.2, 2.5, 2.8 minutes 1.9, 2.2, 2.5, 2.8 minutes Hot Stack Overnight O~retnight Overnight Test APA VacuurnlPtessureAPA Vacuum/Pressure APA VacuuTn/Pr~sure 8 chips per panel8 chips per panel 8 chips per panel Results for the press time study are listed in Table 5 and detailed in Figure 1.
Table 5 - Results for the Press Time Study - Press Time Average Wood Failure Results 95% Interval Range Resin 1.9 2.2 2.5 2.8Average Lower Upper Limit Limit The high moisture veneer study results are shown in Table 6 and Figure 2.

Table 6 - Results for the ~igh Moisture Study Press Time Average Wood Failure Results 95% Interval Range Resin 1.9 2.2 2.5 2.8Average Lower Upper Limit Limit Press times were idçntic~l to the time used for the press speed study to intlic~te the adhesives ability to bond veneer with a wide moisture profile. The 2.3 mole ratio resin (Resin B) performed significantly better at bonding the higher moisture profile veneer than Resin A
as detPnninYi by wood failure values. At the lowest press time, Resin B showed wood failure 25 on the glue line whereas Resin A failed to deliver any bonding. There is a wider tolerance for veneer moisture content differences for Resin B.

. CA 02226274 1998-01-06 Dry out resistance for the two resins was determined by an open assembly time study and the results from this study are listed in Table 7 and shown in Figure 3.

Table 7 - Results for the Open Assembly Time Study Open Assembly Times (min) Average Wood Failure Results 95% Interval Range Resin 180 150 120 90 60Average Lower Upper Limit Limit The two resins were found to be statistically dirrelen l from each other by ~- A~ AI ;~n of wood failure results over all five open assembly times used. Resin B was statistically superior to Resin A.
The high moisture veneer study clearly demonstrates the ability ofthe 2.3 mole ratio guanidine-modified resin (Resin B) to bind veneer surfaces faster than the commercially available resin (Resin A) despite the additive which enhances the speed of Resin A. The better dry out reci~nce of the gl~ni-line carbonate-modified 2.3 mole ratio resins vs. Resin A was not expected.
Example 3 Two ~l~n~ ne carbonate co~ --in~ resins were prepared using 2.0:1 and 2.2:1 formaldehyde to phenol mole ratios. A summary ofthe plepar~lion for the 2.2 mole ratio resin is shown below. The 2.0 mole ration version was prepared similarly.

. CA 02226274 1998-01-06 Resin Ingredients Component Weight %
Phenol 25 50% CH2O 13 Water 27 Pearl Starch 0.4 50% NaOH 6 50% CH2O 22 Gll~ni~1ine Carbonate 50% NaOH 6 Phenol, formaldehyde, water and starch were charged to a reactor and the temperature was ~ ted to 37~C. Sodium hydroxide solution was added and the temperature was allowed to increase to 82~C. The second charge of formaldehyde was added incr~ment~lly, keeping the reaction from getting too exothermic. Guanidine carbonate was then charged to the reactor.
The reaction contents were then heated to 96~C and held at that temperature for 10 minlltes The contents were cooled to 82~C and reacted to 700-800 cps as measured on a Brookfield viscon~ler (model LV~i~). During the viscosity hold to 700-800 cps the r~m~ining caustic was added incrementally. The res--lting product contained 42.6% solids.
Example 4 Two ~l~nidine carbonate modified resins were prepared and P.Y~mined for their ability to bond high moisture content veneer, and for their resi~t~n~.e to drying out during varying open assembly times. Resin E (control) is a col,lll,erc;ally available interm~li~te moisture content adhesive G-P RPPY 5763 with a 2.2: 1 F/P mole ratio. Resin F (control) was a resin prepared similarly to 5763 with a 2.0: 1 F/P mole ratio. Resin G was the 2.2: 1 F/P mole ratio resin pl~al~d as described in ry;1~llple 3. Resin H was the 2.0: 1 F/P mole ratio resin prepared similarly to Resin G. Resins G and H were modified with 1.0 wt% of ~l~nitline carbonate.

Table 8 - Properties for the Resins Resin% Caustic Viscosity RI % NVSFreeFormaldehyde (cps) E 6.00 736 1.462 43.49 0.06 F 6.06 772 1.4621 42.99 0 G 6.21 800 1.4593 42.62 0 H 6.41 680 1.461 42.36 0 Table 9 - GPC RPS~ ItC for the Resins Resin Mn M~, Mz lS
The advantages of adv~n~mPnt and viscosity noted in Example 2 were not evident when this lower level of ~ni~1inP carbonate (1%) was used.
The resins were incorporated into the same RESI-M~) formulation listed in Table 3 from Example 2. The mixes were aged ovt;l.~h~ and used in a high moisture and dry out study 20 similar to those dPS~, ibed in Table 4, Example 2 with the following exceptions. For the dry out study the open assembly times eY~mined were 0, 10, 30, 60 and 120 minlltes For the high moisture study the face/back average moisture content of the veneer was 9-11% and the hot press times were 2.4, 2.8, 3.2 and 3.6 minutes Results for the high moisture study are listed in Table 10 and detailed in Figure 4.

Table 10 - Results of the High Moisture Study Press Time Average Wood Failure Results 95% Interval Range Resin 2.4 2.8 3.2 3.6Average Lower Upper Limit Limit Both gll~nitline carbonate modified resins bonded the 10% MC veneer sigl~Lficantly better than both commercially available resin E and the F/P mole ratio adjusted resin F as determined 15 by wood failure values. Remarkably, resin H ...~ in~d APA acceptable wood failure values of >80% over all con~litionc used, inc~ ling the two lowest press times where the commercially available adhesive had several panels "blow" apart.
Dry out rP-cict~nr~ for the four resins was determined using an open assembly time study and the results can be found in Table 11 and are shown graphically in Figure 5.

Table 11 - Results for the Open Assembly Time Study Open Assembly Times (min) Resin 120 ¦ 60 ¦ 30 ¦ 10 ¦ 0 Resin H was found to be st~tictir~lly superior to the other resins at resisting glue line dry 30 out in addition to its superior performance for bonding high moisture content veneer.
Therefore, the advantage shown by the guanidine carbonate modified resins in the high moisture study did not come at the expense of glue line dry out when varying assembly times were eY~mlned.

It will be appa ~llt to those sl~lled in the art that various modifications and variations can 5 be made in the compositions and methods of the present invention without departing from the spirit or scope of the invention. Thus, it is intçnfled that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (25)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for preparing a phenol-formaldehyde resole resin wherein formaldehyde and phenol are reacted at a formaldehyde to phenol mole ratio above about 1.5:1, in the presence of an effective amount of an alkaline catalyst, the improvement comprising introducing a catalytic amount of a guanidine salt during the preparation of the resin.

2. The method of claim 1 wherein the guanidine salt is selected from the group consisting of guanidine carbonate, guanidine hydrochloride, guanidine sulfate, and low molecular weight guanidine adducts with formaldehyde.

3. The method of claim 3 wherein the guanidine salt is guanidine carbonate.

4. The method of claim 1 further comprising introducing the guanidine salt in anamount of 0.02 to 12 wt % based on the total weight of the resin solids.

5. The method of claim 1 wherein the formaldehyde to phenol ratio is between about 1.5:1 and 2.5:1.

6. The method of claim 1 wherein the effective amount of alkaline catalyst establishes a pH between about 9 and 12.

7. The method of claim 1 wherein the guanidine salt is introduced after substantially all of the formaldehyde has reacted with the phenol.

8. An improved phenol-formaldehyde resole resin composition prepared by reactingformaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1.5:1, in the presence of an effective amount of an alkaline catalyst, wherein the improvement comprises introducing a catalytic amount of a guanidine salt into the composition during the preparation of the resin.

9. The resin of claim 8 wherein the guanidine salt is selected from the group consisting of guanidine carbonate, guanidine hydrochloride, guanidine sulfate, and low molecular weight guanidine adducts with formaldehyde.

10. The resin of claim 9 the guanidine salt is guanidine carbonate.

11. The resin of claim 8 wherein the guanidine salt is introduced in an amount of 0.02 to 12 wt % based on the total weight of the resin solids.

12. The resin of claim 8 wherein the formaldehyde to phenol ratio is between about 1.5:1 and 2.5:1.

13 . The resin of claim 8 wherein the guanidine salt is introduced after substantially all of the formaldehyde has reacted with the phenol.

14. In a method for making a bonded wood product comprising (i) applying to a substrate an adhesive and (ii) hot pressing the substrate, whereby the adhesive comprises a resin prepared by reacting formaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1. 5 :1, in the presence of an effective amount of an alkaline catalyst, the improvement comprising introducing a catalytic amount of a guanidine salt during the preparation of the resin.

15. The method of claim 14, wherein the substrate is veneer or wood strand.

16. The method of claim 14, wherein the bonded wood product is plywood or OSB.

17. The method of claim 14 wherein the guanidine salt is selected from the groupconsisting of guanidine carbonate, guanidine hydrochloride, guanidine sulfate, and low molecular weight guanidine adducts with formaldehyde.

18. The method of claim 18 wherein the guanidine salt is guanidine carbonate.

19. The method of claim 14 further comprising introducing the guanidine salt in an amount of 0.02 to 12 wt % based on the total weight of the resin solids.

20. A bonded wood product prepared by (i) applying to a substrate an adhesive and (ii) hot pressing the substrate, wherein the adhesive comprises a resin prepared by reacting formaldehyde and phenol at a formaldehyde to phenol mole ratio above about 1.5:1, in the presence of an effective amount of an alkaline catalyst, the improvement comprising introducing a catalytic amount of a guanidine salt during the preparation of the resin.

21. The product of claim 20, wherein the substrate is veneer or wood strand.

22. The product of claim 20, wherein the bonded wood product is plywood or OSB.

23. The product of claim 20 wherein the guanidine salt is selected from the group consisting of guanidine carbonate, guanidine hydrochloride, guanidine sulfate, and low molecular weight guanidine adducts with formaldehyde.

24. The product of claim 23 wherein the guanidine salt is guanidine carbonate.

25. The product of claim 20 further comprising introducing the guanidine salt in an amount of 0.02 to 12 wt % based on the total weight of the resin solids.