CA2199463C - Composites prepared with ready-to-use resin/wax emulsion adhesives - Google Patents

Abstract

A single package, ready-to-use (RTU) resin/wax emulsion adhesive and a metho d ofpreparing the same by heating a thermosetting resin and adjusting the pH of the wax emulsion prior to combining the resin and wax emulsion. The use of the adhesive in m aking bonded composites such as wood products, including oriented strand board (OSB), par allel strand lumber, wafer board and particle board composites.

Description

5242 . ,04628 COMPOSlTES PREPARED WlTH READY-TO-USE
RESIN/WAX EMULSION AD~IESIVES
2199~63 Field of the Invention The invention is d~c~ed to a single Fa,~ge, ready-to-use (RTU) adhesive co~ a thermosetting resin and a wax em~ ion si2ing agent, a process for prep~mg the adhesive composition and the use of the adhesive in making bonded composites such as wood products, d; ..~, parallel strand lumber, G~ ed strand board (OSB), wafer board and particle board, and textile products, inr.1~ldin~ ceiling tiles.

Barkground of the Invention There are avariety of adhe.~ csfor con ro~itr~s such as particle boards, fiber boards, and textile composites. Generally these adhesives are made from urea resins, urea-m.ol~mine resins, ph~nr~1ic, resins, and the li'ke. In orderto impart sllffiri~tt water-resistant p,ope,lies to the constructions made with these resins, attempts have been made to co~ e a wax emulsion sizing agent with the resin.
However, it has been very protl~-n~tie to obtain a stable blend of resin and wax ~nllQion Wax solids may not remain homogeneously suspended in ~l~lu~es with water-borne resins, particularly during LI~ , tlansfer, and use. Thus, the resin-wax blend needs to be used ;~ ed;~ely or else separation occurs restllting in non-ul.i~olll,ily in the water-repellency and bond quality imparted to the composite by the adhesive. Further, since wood sh[inks and swells as its moisture content varies, if the composite is not properly treated with a sizing agent and resin, the composite will have less integrity or debond on c~yos~lre to llloi~lure.
Often the wax emulsion is col,lb,ned with the resin at the time of use. Of course this complicsttp~s h~ntllin~ and mixing at the site of use. It would be much more convenient to provide the user with a ready-to-use adhesive that r~u~es no mixing prior to application.
U.S. Patent 4,407,999 attempts to provide a single component, ready-to-use ~RTIJ), water repellant adhesive composition for wooden m~teri~l purportedly having good blPn-1~bility and storage stability. The adhesive consists e~ nti~lly of a paraffin emulsion cont~ininf~ oxidi~ed paraffin and a resin such as a phenolic resole resin. This patent suggests that by using an o~rirli7ed parafflll having an acid value offrom 10 to 70 and a melting point of from 30 to 90~C, with the co~e~l;on~l paraffin wax component, one can s~lcce-e~fi~lly prepare a pre-blended adhesive from the resin and wax el".~l~;on. Too low an acid value makes çm~ ification ofthe wax difficult; too high a value reduces the water rlo-ci~t~nr~ ofthe composite. The wax emulsion is prepared in the presence of a sl~ r~t~nt and/or a water-soluble allcali metal compound such as sodium hydroxide. Blending of wax em~ ;on and resin is carried out from ambient temperature to 60~C.

Summary of the Invention 21 9 9 ~ 6 3 A~plic~ have dis~vt;led that adjusting the pH ofthe wax emulsion to closely match that of the resin and heating the resin prior to ~d~ition of the wax emulsion greatly il~ uved resin/wax co...~ and h~n~1;~ Applic~lLs further discuv~;;led that the resllltAnt resin/wax adhesive blend provided ~....po~ c having IIl~F ~ P.~ly ",~p,~ved thi~l~npcc swell and water absorption prope,Lies over composites made with prior art technology, i.e. resin-wax blends not treated with the co...l.;~ n of pH adj..~ l and hP~tir~ The adhesive also provided good storage life and low odor. The resiïl/wax emulsion adhesive of the present invention ~l;...;-.~les the need to handle mllhirle raw m~teri~l~ at the site of use.
The present invention is directed to a composite prep~ed by cG",bining a furnish and a ready-to-use, single package, adhesive composition. The adhesive composition comprises a cG...bil-AIilnn of a thermosetting resin and a wax emlll~ion p,~paled by:
(a) heating the thermosettir~ resin to an initial temperature of above 40~C, wherein the resin has a pH of about 9 to 12;
(b) adjusting the pH of a wax emulsion to within about 1 pH unit of the resin; and (c) co...h ~. .p the wax P.mlll~;on with the resin and rnixing while ll.~illlA;~ g the temperature ofthe resin above 40~C.

Brief Derc- ;~"ion of the Drawin~
Figures 1, 2, and 3 depict data from a strand board study using the RTU resin/wax system of the present invention.
Figure 1 shows Internal Bond ~l,el1gL}l results.
Figure 2 shows % Thic~n~ss Swell pe~ro",~allce.
Figure 3 shows % Water Absorption performance.
Figures 4, 5, and 6 depict data from a strand board study using two dirre-e,ll wax emulsions in the RTU resin/wax system using a 25~C or a 75~C resin-wax blending temperature.
Figure 4 shows Internal Bond ~LIenglh results Figure S shows % Th~ n~ss Swell pe~ro"llance.
Figure 6 shows % Water Absorption pelrolmance.

Detailed Desw iplion of the Invention The present invention comhines a resin and a wax ~m~ on sizing agent into a single-component or ready-to-use ~RTU) adhesive. The RTU adhesive is then provided to the cohSu~
in a single p~i-'L ;~e The wax emlllcion sizing agent (hereinarlel "wax emulsion") is used pl ;,~ lly to impart water-res:~tsll~re to the final c~ o~ ~ e construction. The RTU adhesive has increased wax comp~atihility, sul~sl~ lly no ~o~lli~l~, problems, and provides ul~ e~iled pt;l~llllance improvelllents in thir~n~pcs swell and water absorption plopellies of the final product without degradation of other properties.
- The resin may he any lht;. ~ ~ ~os~ l ;. ¢ (formal~e.hyde-based) resin used in prep~ing adhesives for bonding composite wood products such as phenol-form-aklPhyde resins, phenol-lesolcinol-formal~Phyde resins, urea-ll~el~n~ e-form~ldehyde resins, ..~ -formaldehyde resins, phenol-mPl~mine-form~ldPhyde resins, mPl~minp~-urea-rt;sc~r~ih~ol-form~ldehyde resins, and co...h;n~ion.c thereo~ Preferably the resin is a phenol-form~1dPhyde resole resin (phPn~lic resin).
The resins may be plep~ed by any suitable method to provide an adhesive resin having a final pH of between about 9 and 12 and a suffi~iently high fi)rm~klPhyde mole ratio to make the resin thP.rmosP~tting For example, a phPnolic resole resin is prepaled to provide a form~ldehyde to phenol mole ratio of about 1:1 to 3:1, preferably, about 1.8:1 to 2.7:1. The present invention is not limited to any particular process of plep~,l-g the resin and methods are well known to those skilled in the art.
Skilled practitioners recognize that the react~ntC used to prepare the resin are co,...~ ;ially available in many forms. Any form which can react with the other re~ct~nts and which does not introduce extraneous moieties deleterious to the desired reaction and reaction product can also be used in the plepa,a~ion of the resins used in the adhesives of the present invention.
Formaldehyde, for inct~nce, is available in many forms. Pal~ullll (solid, polymP.ri7e~1 fonn~l-lPhyde) and rn....~ s~ tions (aqueous solutions of form~ phyde~ sometimes with mPth~ns)l in 37 percent, 44 percent, or 50 percent form~ Phyde concentrations) are common. Instead of form~l~Phyde, other aldehydes may be used such as ~cet~ldPhyde, and propionaldehyde. Typically, formalin solutions are plerelled as the aldehyde source.
The phenol component ofthe resin incllldes any phenol typically used in plepaling phenolic resole resins. Typically, oldil ~y phenol is used, but the phenol may be partly or completely b~ P~ with xylenols, cresols, catechol, resorcil~ol, alkyl resorcinols, other naturally occurring or synthetic phenols or alkyl phenols such as cresylic acids, urea, mel~mine, or con~bil alions thereof.

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Urea is available in many forms. Solid urea, such as prill, and urea solutions, typically aqueous ssl lfir~nc~ are co -- l- Urea is also a~ ~lc in co~ -A1iol~ with form~ldPhyde as a UF conc~ ale.
MP~ P, is also CQ.. ~. c;ally available and the ,~ .. ;ne may be totally or partially repl~eçd with other ~minol~ e col.lpounds. Other suitable a-m-inotriazine compounds include s~liluled mPl~ -es, or cycloaliphatic ~l~n~minps~ or n~lul~s thereo~
Any suitable catalyst may be used to form the ~ ns~ , resin. Phenolic resins, for il-~n~
typically use allcali metal hydroxides, alkaline earth hydroxides, ~mmonillm hydroxide, metal ~ubol~es, and amines. Preferably the catalyst for prepa~illg a phenolic resin is sodium hydroxide.
- The wax PmlllQ~on (also l~own as paraffln emillcio~c) may be formed from natural waxes such as slack wax, whale wax, pappy wax, honey wax, and chinese wax, or from synthetic waxes such as esters of fatty acids, for eY~mple, n-octadecyl p~lmit~te and cetyl stearate. Slack wax, a solid at ambient tellll.el~lu~s, is a by-product of oil refining processes, is sold as a commodity product, and is a ~ler~lled wax for reasons of econol,l~ and its high melting lempelalul~. The present invention is not limited to any particular wax so long as the wax provides the desired sizing or water-repella properties in the end product.
The wax em~ on iS a wax-in-water emulsion and is typically formed by, for eAampl~, stirring molten wax into water in the plt;sel~ce of a d;s~ , emulsifier or surf~ct~nt Most commPrcial wax Pm.llcionc may be used. Prer~ , no additional s.~ r~ , other than what was needed to produce a stable wax ~",.,l~:ol~, are added to the colllbined resin and emulsion. Some sllrf~ct~ntc can lead to foaming problems re.clllting in poor h~ntlling problems. Further, any dispersant, emlllcifier, or s~rfi~ nt used in the emulsion, must not a~fect the final resin/wax emulsion adhesive qualities. For Px~mplP~, lignosulfonate-based di~yel~l~s provide suitable wax-in-water emulsions whereas our experience inrlic~tes that fatty-acid based disper~&--Ls are less desired.
Typically, a sufficient amount of the wax emulsion is blended with the resin to impart the desired level of water-resistant properties to the final composite. Generally, the amount will not exceed 50 wt% of the total adhesive used. The pr~relled amount will depend on the composites intended use and target properties. In most cases, the wax emulsion will be used in an amount between about 4 wt% and 33 wt% based on solids of the resin/wax emulsion adhesive.
Prior to ~dtlition ofthe aqueous wax emlll~ic)n to the aqueous resin, the pH of the wax em~ ;on is adjusted to closely match the pH of the resin. ~ltern~tively~ the pH of the resin may be adjusted to closely match that ofthe wax ~ si~m Either way, the pH of ~e resin and the wax emulsion need not be i~.o.ntir~l but should be within about 1 pH unit. For example, if the pH of the resin is 10, the pH ofthe wax should be a~ ed to between about 9 and 11 prior to mixing with the resin. The pH

2199q6~
of a phennlir resole resin prior to c~...ll ,;..;~g with the wax emlllcirln is preferably about 9 to 12, more preferably about 11.5.
The pH of the wax emulsion is adjusted by adding an effective amount of a suitable alkaline m~t~ l or base. The base must be sPl~cted so it does not, for . ~ i....pl~" negate the dispersing effect ofthe wax solids in the ~ .cl- or d~t~hili7e the resin or the emulsion. Suitable bases inrlllde, but are not limited to sodium hydroxide (caustic), amines, ammonium hydroxide, and carbonates. Any effect the base may have on the resin or f~mlllr;on del~n~ on the particular resin and wax being used.
Further, prior to colllb.nil.g the resin with the wax emlll~ion~ the resin is heated to an initial t~ )clalure above about 40~C, pleftlably, about 60 to 85~C, more preferably, about 60 to 75~C.
The le...l)cl~lulc ofthe resin depends on the particular wax and its s~çnin,~ and melting pl-)pellies, and also the col-~ ;1,;1ity ofthe wax and the resin. Adding the wax ~.mlllcion at higher tempelalurcs generally increases the co~p~ibility of the ph~nolic resole resin and wax em.~lcion and app~,lt water-soak p-opc-lies of composites made using the blend.
After aAjll~ti~ the pH and heating the resin, the wax emlll~ion is combined with the resin with mixing while the resin is still hot. The te..lpela~u~e of the combined resin and wax emulsion is preferably n~A~ Ail~ed within 5~C ofthe initial temperature during addition ofthe wax çmlll~ion The resin and wax emulsion co..ll,h-alion of the present invention can be used to impruve the water absorption properties of any composite product that is prepared using a furnish, a sizing agent and a thermosetting resin. The furnish may be wood, textile, or wood/textile combin~tion~. Wood furnish include fibers, particles, scrim, flakes, veneer, and the like, and co---t,illations thereof. Textile furnish include fibers of polyester, nylon, and the l~ce. F.Y~mples of composites in~ lde, but are not limited to, oriented strand board (OSB), wafer board, particle board, hardboard, meAillm density fiberboard (MDF), SCRIMBFR~, 1~ PA veneer lumber (LVL), plywood, oriented strand lumber, parallel strand lumber, and textile fiber mats (e.g. for ceiling tiles and sound insulation.) The resin and wax co...binalion may be applied to the furnish in any suitable manner, for PY.~mple, as atomi7eA. drops using a sprayer or s~ disk or by a roll coater. The recin~ted furnish may then be formed into a mat and placed into a hot press at 3 50 to 450 ~F for consolidation into a unitary composite. Those skilled in the art appreciate that other types of plessing equipment or heating equipment such as radio-frequency devices and steam injection presses can be used.
Appropriate pressure is applied to the mat to compress to the desired final thickness for a time sufficient to allow the resin to cure and bond the furnish or consolidate the composite.

E~amples The invention will be further d~ ed by ler~ellce to the following eY~mrles These eY~mr!es should not be construed in any way as limiting the invention to ~l~lLillg less than that which is disclosed or which could have been obvious to anyone skilled in the art.

Example 1 A ready-to-use adhesive can be prep~ed by the following procedure. The mole ratios, t~,llpe,~l~es, etc. may be modified as necesc~ to obtain approp,iale product pe requirements.
FIrst a pl~ ~ resin is pl~d using known procedures from the following ingredients (parts by weight):
28 parts phenol 13 parts water 36 parts 50% form~l~ehyde 11 parts 50% caustic 4 parts urea The temperature of the resin is adjusted to 60~C. The pH of a wax em.lleion is ndj~leted to within 1 pH unit ofthe pH ofthe ph~nnlic resin, for instance with caustic, and then 8 parts by weight of the pH adjusted wax emulsion is added to 92 parts by weight of the resin and mixed. The telll~ ure ofthe resin is ~ ined at a temperature of at least 60~C during the mixing and then the mixture is cooled.

Example 2 Adhesive system C was prepared by collvt;~ll;o~lly cold blending a wax emulsion with a PF
resin made in accordance with the process of F.Y~mple 1 (~xclll(1in~ pH adj~lctmP.nt of the wax emulsion and the hot blending of the resin and wax). Adhesives A and B were prep~ed in accordance with the process of Example 1 incl~lrlin~ pH adj~lstmt-nt of the wax ~mllleion and the hot blending of the resin and wax emulsion. Emulsion A used wax emulsion BW-048 obtained from Dominion Chemical Corl~p~l~. Emulsions B and C used wax emulsion 2057B obtained from ~11 ~Iopton Technologies, Inc.) Panels were m~n~f~ red using the below-listed parameters:

Furnish Southern Yellow Pine Flakes produced from ~imPn~ion~l lumber FurnishMoi~lre Content 2.4%
Board Th~ ness 7/16"
Resin Solids in Board 6%
Board Density 40 PCF
Final Mat Moi~hlre 7.2%
Hot Press 400~F/600 psi initial, 60 psi final P,es~ure released on mat over final two .. ;~.--les of press time Time in Hot Press 4 min.

Two panels were used for each contlitiQn Two samples were taken from each panel to determine th;cl~ness swell and water absorption. Four s~...rles were taken from each panel to deL~ c TntPrn~l Bond ~B). The median results are reported below.

AD~ESIVE
Measurement (rle~i~n) A B C

Th ~nP.sc Swell(%) 16.5 16.3 18.1 Water absorption(%) 50.2 52.0 54.9 Figures 1, 2, and 3 depict the average ofthe samples and the 95% confidPrlr-e interval ofthe average for the samples from strand board studies using the RTU resin/wax system.
Figure 1 shows that TntPrn~l Bond strength was not significantly affected by the hot blend procedure of the present invention.
Figure 2 shows that the % Thickness Swell pelro"nallce i",proved using the RTU adhesive of the present invention.
Figure 3 shows that the % Water Absorption performance improved using the RTU adhesive of the present invention.

Example 3 A study was made using two diLre,elll wax emulsions previously pH adjusted to within 1 pH
unit of the resin, at both a 25~C and a 75~C bl~on~ing temperature. The resin was prepaled in accordance with Example 1 and the wax emulsion was added at either cold (25 ~C) or hot (75 ~C) 219946~
temper~lures. Panels were prepared and used in acco.dal~ce with EAan,ple 2. The wax ~m~lQion~
used were Dominion Chemical Col"p~,~'s BW-048 and Polypro's Pr~waA 45. Both of the wax PmlllciOn~ p~l r." 1ll~ equivalently in this study and the data were collll);l-ed for pres~nt~tion in Figures 4, 5, and 6.
Figure 4 shows that wax ~ lition tt;",pe,a~ure has no si~ifir2r~t effect on Tntem~l Bond. That is the RTU ad~ e ofthe present invention pe. rOI 1~ as well as or better than tr~ition~lly prepaled cold blentle~ resin and wax ~nnlllcion Figure 5 shows that the nd~litiQn of the wax emlllQion at an elevated temperature provided uvt;d % Thir~n-oss Swell p. . r~.. ",~ ~ in the composites.
Figure 6 shows that the addition of the wax eml~l~ion at an elevated tellli)elalure provided i"~proved % Water Absorption pe- ~l Ill~nce in the composites.

Example 4 A phenol-formaldehyde resin having a mole ratio of about 2.0 was coll~hi~-ed with a wax emulsion in the following four ways:
(1) resin at 25~C and wax rmlll~ion as received at pH 6.5.

(2) resin heated to 60~C and wax .omlll~ion as received at pH 6.5.

(3) resin at 25~C and wax emulsion adjusted to pH 11.5.

(4) resin heated to 60~C and wax emulsion adjusted to pH 11.5.

Panels were m~nllf~e~lred using the below-listed parameters:

Furnish Southern Yellow Pine Flakes produced from dimensional lumber FurnishMoisture Content 3.2%
Board Thickness 7/16"
Resin Solids in Board 6%
Board Density 42 PCF
Final Mat Moisture 8.8%
Hot Press 400~F/600 psi initial, 60 psi final, pressure stepped down after 1 min.
Time in Hot Press 2.8 min.
Hot Stack overnight Tests Tntern~l Bond - 4 samples Thir~n~ss swell - 3 s~mples Water absorption - 3 s~mples 2199g6~
Two panels were used for each condition. Two samples were taken from each panel to determine thi~l~ness swell and water abso.l lion. Four samples were taken from each panel to determinç Tntern~l Bond (~3).
Results: The diagrams below s~ ;,e the average of results of internal bond, water absorption, and thi~l~ness swell tests for the resin/wax adhesives (1) - (4).

Tntern~l Bond (psi) 1 1.5 194.9 90.5 pH
6.5l91.8 96.4 Temp ~C
Water Absorption (%) 11.5 l82.8 81.5 pH
6.5l82.4 77.9 Temp ~C

Thickness Swell (%) 1 1.5 l27.2 26.2 pH
6.5 l28.6 27.1 Temp ~C
The above data demonstrates that internal bond and water absorption ofthe panels were not si nific~ntly affected by the conditions for prep~ing the adhesive blend. However, there was an pr~v~ ll (reduction) in % thickness swell if either the pH of the wax emulsion was adjusted or the wax to.m~ ion was added to a hot resin but the largest improvement in % thickness swell occurred when both the pH of the wax emulsion was adjusted and the emulsion was added to a hot resin.
It will be appafel l to those skilled in the art that various modifications and variations can be made in the compositions and methods of the present invention without departing from the spirit or scope ofthe invention. Thus, it is int~n~ed 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 (20)

WHAT IS CLAIMED IS:

1. A composite prepared by bonding a furnish with a ready-to-use, single package, adhesive composition wherein the composition comprises a combination of a thermosetting resin and a wax emulsion prepared by:
(a) heating the resin to an initial temperature of above 40°C, wherein the resin has a pH of about 9 to 12;
(b) adjusting the pH of a wax emulsion to within about 1 pH unit of the pH of the resin; and (c) combining the wax emulsion with the resin and mixing while maintaining the temperature of the resin above 40°C.

2. The composite of claim 1 wherein the furnish is wood furnish.

3. The composite of claim 2 wherein the wood furnish is selected from the group consisting of wood fiber, particles, scrim, flakes, veneer, strand, or combinations thereof.

4. The composite of claim 1 wherein the resin is a phenol-formaldehyde resole resin.

5. The composite of claim 4 wherein the formaldehyde to phenol ratio is between about 1:1 to 3:1.

6. The composite of claim 1 wherein the initial temperature is between about 60°C and 85°C.

7. The composite of claim 6 wherein the initial temperature is between about 60°C and 75°C.

8. The composite of claim 6 wherein the temperature is maintained within 5°C of the initial temperature.

9. The composite of claim 1 wherein the pH of the wax emulsion is adjusted with an effective amount of a base.

10. The composite of claim 9 wherein the base is sodium hydroxide.

11. A process of making a composite comprising applying a ready-to-use, single package, adhesive composition to a furnish and then pressing and heating;
wherein the composition comprises a combination of a thermosetting resin and a wax emulsion prepared by:
(a) heating the resin to an initial temperature of above 40°C, wherein the resin has a pH of about 9 to 12;
(b) adjusting the pH of a wax emulsion to within about 1 pH unit of the pH of the resin; and (c) combining the wax emulsion with the resin and mixing while maintaining the temperature of the resin above 40°C.

12. The process of claim 11 wherein a hot press is used for the pressing and heating.

13. The process of claim 11 wherein the furnish is wood furnish.

14. The process of claim 13 wherein the wood furnish is selected from the group consisting of wood fiber, particles, scrim, flakes, veneer, strand, or combinations thereof.

15. The process of claim 11 wherein the resin is a phenol-formaldehyde resole resin.

16. The process of claim 11 wherein the initial temperature is between about 60°C and 85°C.

17. The process of claim 16 wherein the initial temperature is between about 60°C and 75°C.

18. The process of claim 16 wherein the temperature is maintained within 5°C of the initial temperature.

19. The process of claim 1 wherein the pH of the wax emulsion is adjusted with an effective amount of a base.

20. The process of claim 19 wherein the base is sodium hydroxide.