CA1141099A - Thermosetting resin glues foamable to high density - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A glue foamable to high density comprises an aqueous alkaline thermosetting resin and a surfactant comprising (1) a fatty acid amide of the alkanol-amines or (2) a tertiary amine oxide used in amount sufficient to render the glue foamable to a stable foam having a density of at least 0.5 and a viscosity of from 1,000 to 20,000 centipoises upon being beaten with air. The glue is useful particu-larly in the manufacture of plywood.

Description

THERMOSETTING RESIN GLUES FOAMABLE TO HI&~ DENSITY

BACKGROUND OF THE INVENTION
This invention relates to glues of the class useful in the manu~acture o~ plywood. It pertains particularly to glues which are foflmable to produce stable, high density foams.
The use of ~oflmed glues in the manufacture of plywood is advan-tageous for many reasons, including, particularly, uniformity of plywood product and economy of glue use. Their application is ill-ustrated in a number of U. S. Patents, of which U. S. 2,323,831 and 3,905~921 are illustrative.
It is characteristic of the prior art foamed plywood glues that they are of low density, i.e. a density of less than 0.5 grams/
cc., usually less than 0.3 grams/cc. . The low density inherently results from the foaming operation by which the glues are produced.
The prior art foamed glues are difficult to convey because of their high viscosity and low density. This in turn makes them un-suitable for application in conventional plywood glue application equipment such as spreaders, curtain coaters~ and sprayers. Special-ized equipment, accordingly, is required to convey the glues and to spread them in the uniform spreads required to achieve a manufactured plywood product o~ uniform properties.
It is the general object of this invention to provide thermo-setting resin glues which are foamable to high density, i.e. a den-sity above 0.5 grams/cc., and to viscosities in the broad range of from 1,000 to 20,000 centipoises.
Further objects of the present invention are the provision of thermosetting resin glues which are foamable to produce adhesive foams which are stable in density and viscosity, which can be readily conveyed, and which can be applied without difficulty by the spread-ers, curtain coaters and spray applicators which are standard equip-ment in the conventional plywood mill.
Still another object of the present inven~ion is the provision of foamable glues having the above mentioned properties which in addition are highly adhesive, having bonding properties superior to conventional glues on an equal welght basis, or equal thereto when used at lower spreads of foamed glue.
Broadly considered, the foamable glues of our invention com-prise at least one aqueous alkaline thermosetting resin of the group consisting of tlle phenol-formaldehyde-, the resorcinol-formaldehyde-, the urea-formaldehyde-, and the urea-melamine-formaldehyde- thermo-setting resins, and at least one surfactant of the class consisting of:
(1) the fatty acid amides of the alkanol amines having the following structure RlC$ - N ~ 2 ~R30H

wherein RlC~ - is a fatty acid radical of 8 to 1~ carbon atoms, and R2 and R3 are lower alkyl radicals, and

(2) the tertiary amine oxides having the following structure Rl wherein Rl is an alkyl radical of 8 to 18 carbon atoms and R2 and R3 are lower alkyl radicals. The surfactant is used in amount suf-ficient to render the glue foamable with a non-reactive gas to a stable foam having a density of more than 0.5 and a Brookfield vis-cosity of from 1,000 to 20,000 centipoises at 25C;' Further included in the glues in amount appropriate to develop the desired properties a-re clay, a bodying agen~ an alkaline mater-ial and water.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
As indicated above, the concept of the invention is applicable to the production of plywood and other glues foamable to high density using as base resins the thermosetting phenol-formaldehyde-, resor-cinol-formaldehyde-, urea formaldehyde-, and urea-melamine- formal-dehyde- thermosetting resins.
Tllese may be employed in the forms in which they are conven-tionally used for the manu:Eacture of plywood glues, i.e. in aqueous allcaline solution containing 4 to 8% caustic at viscosities oE from ; 100 to 1,000 cen~ipoises, and a resin solids content of from 40 to 56% by weight. They are formulated into the foamable glues of the invention by admixture with surfactant, clay, bodying agent, alkaline material and water in the general and specific proportions indicated below, in "1 in o/o by weight, solids basis".

The Resin is a Broad Range Phenol Urea- ~~ Resorcinol-(all resins) Formaldehyde Formaldehyde- Formaldehyde Resin or Urea- Resin Melamine-Formaldehyde Resin Thermosetting Resin (Solids basis) 10 to 50 20 - 35 15 - 30 30 - 45 `
Surfactant0.1 to 5.15 - .60 .15 - .60 .15 - 5 Clay 0 to 10 1 - 3 1 - 5 0 10 Bodying Agent 0 to 40 5 - 12 20 - 40 0 - 10 Alkaline Material 0 to 4 0 - 3 --- ---Water 0 to 55 10 - 30 25 - 40 Investigation of a large number of suractants has revealed only two classes of the same the use of which in the above formu-lation achieves the desired purpose of producing a glue foamable to ; a stable, high density foam of the desired viscosity.
One such surfactant class comprises the fatty acid amides of the alkanol-amines having the following structure ~ ,,~R20H
Rl C

.~ ^~
o wherein RlC - is a fatty acid radical of 8 to 18 carbon atoms, and R2 and R3 are lower alkyl radicals.
These surfactants may be prepared by condensing the fatty acids, or fatty acid esters containing fatty acid radicals, or acyl groups, of 8 to 18 carbon atoms with a lower alkylol, i.e. one havi~ 4 carbon atoms in the alkyl group.
A particularly suitable surfactant of this class is produced by condensing coconut oil fatty acids or fatty acid esters with diethanol amine. Coconut oil contains acid groupings comprising about 7% capric, 49% lauric, 17% myristic, 9% palmitic and 6% oleic acid radicals. The surfactant derived therefrom accordingly will have a corresponding composition.
Such fatty acid amides are referred to in the surfactant trade as "superamides". One such product which is available commercially is that sold under the brand name *"VARAMIDE", a product of Ashland Chemicals of Columbus, Ohio.
Although coconut oil offers a convenient and readily available source of suitable fatty acid components, other naturally occurring fats and oils may be employed as source materials provided their fatty acid content conforms to thP above requirements.
As also indicated above, another class of surfactant suitable for the present purposes comprises the tertiary amide oxides having the follo~ing structure:

Rl~
2 / N = 0 wherein Rl is an alkyl radical of 8 to 18 carbon atoms and R2 and R3 are lower alkyl radicals.
These compounds are prepared by the oxidation of a tertiary amine by an oxidizing agent such as hydrogen peroxide. Again, coconut oil is a suitable source material for the high molecular weight fatty component of the tertiary amine oxides. Alcohols hav-ing alkyl radicals containing from 8 to 18 carbon atoms, as required * Trademaxk fox Rl, are produced industrially by the reduction of coconut oil derivatives. The other substituent groups of the amine oxide, i.e.
R2 and R3, are lower alkyl radicals such as methyl, ethyl and propyl obtainable ~rom a variety of sources.
Whatever its identlty, tlle surfactant is employed in amount su~flclent to render ~he glue foamable with a non-reactive gas such as air or nitrogen to a stabl.e foam having a density of more than 0.5. More specifically, the surfactant is employed within the range of from 0.1 to 5% by weight of the total glue composition.
A ~hird component which may be included to advantage in the hereindescribed foamable glues comprises clay. The clay serves the function of imparting static stability to the foam. With the clay present, at least 2~ hours foam static stability is obtained.
Without the clay, the static stability is reduced to a few hours, which is sufficient for some purposes. The clay thus serves as a supplementary foam stabilizer which extends the foam life of the glue.
As shown hereinafter in the Examples, a particularly suitable clay for use in the glues of the invention comprises attapulgus clay. This material, which is commonly called attapulgite, is a crystalline, hydrated magnesium aluminum silicate. It is particular-ly effective in imparting foam stability to the glue compositions.
The clay is used in varying amount depending upon the identity of the other constituents of the glue. However, in general, from 0 to 10% by weight of clay may be employed to advantage.
The bodying or thickening agent, which is another important component of the hereindescribed glue, serves the function of im-proving the bonding quality of the glue by reducing penetration of the glue into the wood veneer substrate. It also raises the glue viscosity. This, in turn, improves the bonding quality for the same reason.
A variety of conventional bodying or thickening agents, both proteinaceous and amylaceous, may be used for this purpose. Illus-trative of suitable ones include wheat flour, rye flour, potato flour,soya flour, the various natural gums, and methocel.
A further component of the hereindescribed glues comprises a ca~lstic or alkaline material sucll as caustic soda, sodi~tm carbonate, or other allcaline, basic acting compound, such as a basic acting compound o~ an allcali metal, o~ the class conventionally employed for adjust~ng the pH of plywood gl-les. This is used in amount sufficient to maintain the pH of the glue above 9. It serves the function of ; solvating the other components of the glue and improving the glue penetration into the wood, thereby improving the bonding properties of the glue.
Although the phenolic and other thermosetting resins of the classes used herein are available commercially and used in the form of their aqueous alkaline solutions, it may be desirable or necess-ary to incorporate a proportion of water as another constituent of the glue mix. In this evenk, su:~icient water is employed to adjust the solids content and viscosity to desired levels.
In formulating the glues of the invention the resin component is compounded with the cited ingredients in the following preferred order, which may be changed as desirable or necessary:
The resin first is mixed with the surfactant, then with the clay, then with the bodying agent, then with the water. The resulting composition is mixed in a conventional high shear or paddle mixer until fully dispersed Caustic next is introduced and the mixing continued to a predetermined viscosity. If desired the resin may be added in two stages; part at the beginning and the remainder after the other constituents have been mixed in.
The resulting mixed, unfoamed glue is subjected to mechanical foaming by any suitable means which introduces air, nitrogen, or other inert (to the glue) gas into the composition. The apparatus employed may be a conventional beater, or apparatus for introducing air into a constricted chamber in which the glue is repeatedly rotated between shear blades.

The resulting glues in their foamed condition are ready for stor-age or immediate use. They will be characterized by densities of more than 0.5, prefera~ly between 0.6 and 0.75 grams/cc.at 25C.
Typical densities,for g:lues prepared by the procedure of Example lA, infra, are shown in the single figure of the drawings. The visco9ities of the glues will ~e from 1,000 to 20,000,preferably betweetl S,000 ancl 10,000 celltipoises as measured by a Brookfield viscometer at 25 RPM and 25F.
Characterized by these qualities, the foamed glues of the in-vention can be readily pumped and conveyed in the glue lines of theconventional mill. They also can be applied without difficulty in conventional spreaders, curtain coaters and spray coaters.
Furthermore, the foams are stable both as to dentify and vis-cosity, enabling their storage for periods of as much as one week.
They also are resistant to substantial viscosity change with temper-ature.
Comparative tests indicate that the bonding qualities of thehereindescribed high density foamed glues are superior to conven-tional glues on an equal weight basis, or equal thereto at lower weights of the foamed glues. The validity of these observations is indicated in the ~ollowing examples, wherein the amou~ts o~ the glue components are given in percent by weight, solids basis.
EXAMPLE lA
This example illustrates the formulation of the glues of the in vention incorporating a phenol formaldehyde thermosetting resin and a surfactant comprising the condensation product of di-ethanol amine with coconut oil fatty acids ("Varamide"; Ashland Chemical Co.) at various resin solids content.
This example illustrates a glue containing 31.2% resin solids /O B~ Weight Water 12.23 Wh~at Flour 7.22 Resin ~41% N.V.) 24.07 Attapulgus ~lay Mix 10 minutes 1.40 .. .~ ,~
~. -7-50% Caustic Soda Mix 15 minutes2.61 Resln (41% N.V.)52.15 Surfactant ("Varamide") Mix 5 minutes.32 Un~oamed viscosity 3500 cpsDensity 1.10 - 1.15 g/cc Foflmed viscosity 6500 cpsDensity .60 - .70 g/cc EXAMPLE lB
This example illustrates the formulation of a glue containing 26.0% resin solids.
% By Wei~ht Water 23.33 Wheat Flour 9.03 Resin (41% N.V.)11.26 Attapulgus Clay Mix 10 minutes1.31 50~/O Caustic Soda Mix 15 minutes2.60 Resin (41% N.V.)52.15 Surfactant Mix 5 minutes.32 `:~ Unfoamed viscosity 3500 cps~ensity 1.10 - 1.15 g/cc Foamed viscosity 6500cps~ensity .60 - .70 g/cc This example illus~rates the formulation of a glue utilizing 31.5% resin solids.
% By Wei~ht Water 29.13 Wheat Flour 10.00 Resin (56% N.V.)10.25 Attapulgus Clay Mix 10 minutes1.50 50% Caustic Soda Mix 15 minutes2.63 Resin (56% N.V.)46.17 Surfactant Mix 5 minutes.32 Unfoamed viscosity 2500 cpsDensity 1.10 - 1.15 g/cc Foamed viscosity 5600 cpsDensity .60 - .70 g/cc ` `~

The glues of Examples lA, lB and lC were tested for foam stability and viscosity stability by the following tests:
Test 1: The foamed glue composition after introduction in a measuring cylinder retains at least 90% of its original volume for at least 24 hours.
Test 2: 2,000 grams of the foamed glue is introduced between a cooperating rubber roll and doctor roll, rotating in opposite directions and having a nip space ~etween them of approximately 0.050 inches. The rolls are rotated at approximately 59 rpm. The viscosity and density of the glue are measured prior to introduction of the glue to the spreader.
The spreader is operated for 30 minutes. The viscosity and density of the glue then are re-measured. To be suitable, these properties of the glue should not deviate by more than 10% from their original value.
All three of the glues f~rmulated as above successfully passed the foregoing tests. Where the hereindescribed critical surfactants are employed, not only is the desired high glue density obtained, but this density is retained when the glue is subjected to the shear test outlined above. If the glue is adequately foamed by simple mechanical means, additional mechanical foaming does not change the density. The constancy of foam density under these conditions is a primary advantage characteristic of the glues of the invention.

This example indicates the unique character of the surfac~ants employed in the glues of the invention.
The properties of the glue of Example lA were compared with the properties of glues prepared in an identical manner, but using a variety of surfactants of other standard classes ~iz:
Trade NameManufacturer Chemical Class & Structure *Sipex - BOSAlcolac Sodium 2-ethylhexyl sulfate *Zonyl FSCDuPont Fluoro alkyl dimethyl sulfate quaternary amine (Alkyl = C7 or C8) *Trademark ~ _g_ *Zonyl FSB DuPont Fluoro alkyl sulfonated betaine (Alkyl = C7 or C8) *Dow Corning 193 Dow Corning Silicone ~lycol copolymer *Dupanol EP DuPont Alkyl alkylol dimethylamine sulfate (Alkyl = C12) *Areosol OT American Cyan- Sulfosuccinate diester ÇH2-COOR
amid (R = C8) NaO35~HCOOR

*Tween 40 ICI ~nericas Polyoxyethylene (20) sorbitan monopalmitate *Crufax DA (3) Crucible Chem- Alkanolethoxylate ical (Alkyl = C8 C16) *Crufax 3.5 Crucible Chem- Alkanolethoxyiate ical (~lkyl + C8 - C16) *Varamide A2 Ashland Chem- (2:1) Alkanolamide (Refined coconut ical oil Diethanolamide) AlkYl = Cg ~ C18 The resultiny foamed glues were tested by the stability tests outlined above. ~11 of them failed the tests in that the volume of each foamed glue diminished by more than 10% after standing 24 hours.
Also, the viscosity and density of each glue deviated by more than 10% from its original value after being subjected to the shear test.
_ AMPLE 3 This example illustrates the application of the high density foamed glues of the invention to the manufacture of plywood.
The glues of Examples lA, lB and lC were applied to both sides of 12" x 12" Douglas Fir, 1/8" thick veneers, so that the amount deposited on each veneer was equivalent to 65 lbs of glue per 1,000 square feet of veneer. Each coated veneer was overlaid by a top and bottom layer of the same kind of 1/8" veneer to form a plywood laminate. This was placed in a steam heated press kept of 285F.

and pressed under 175 lbs. per square inch for 5 mlnutes.
The cooled plywood was subjected to a shear test under conditions specified by the vacuum pressure test in PS 1-74 of the American Plywood Association. The sheaxed specimens were then examined for percent wood failure. This represents the 'iStandard"
conditions.
In the "Dry~Out" test a similar procedure was used, but the *Trademark ~ . .. .

veneers were dried to essentially 0% moisture content and glued in this condition with a 45 lb. spread. This test defines glue prop-erties under highly adverse conditions.
The table below ill~lstrates the results, compared with percent wood ~flil~lre of plywood macle using a conventional, commercial phenol-~ormaldehyde control glue containing 31% resin solids, 9% furafil extender, 5% wheat flour and 2.5% caustic soda, applied using the same spreads and conditions.
Conventional Composition lA lB lC Glue % Wood failure under "Standard Conditions" 100% 98% 100% 98%
% Wood failure under '~ry-Out Conditions" 99% 85% 98% 65%
The test results show that under "Standard Conditions" the glue of this invention is equal to the conventional glue and is superior under "Dry-Out Conditions".
EXA~PLE 4 This example illustrates a urea type high density foam glue of the invention.
The glue had the following composition:
% By Wei~ht Urea-formaldehyde resin (60-65% by weight solids) 35 Water 31 Wheat flour 28.5 Catalyst (Ammonium Chloride, 4 25% solution in water) Attapulgus Clay 1.3 Surfactant ("Superamide") 0.2 The glue was foamed to a density of 0.62 grams/cc. in the man-ner described in Example 1. The resulting foam was stable under shear conditions and maintained its density for over 24 hours.
The performance of this glue was compared with ~hat of a con-~entional urea glue having the following composition:
% By ~eight Urea-foxmaldehyde resin (60-65% by weight solids) 35 -~.1-Water 31 Wheat flour 30 Catalyst (~mmonium Chloride, 4 25% solution in water) Both the foamed glue o~ ~he irlvention and the control liquid glue were applied to wood veneers in the manner described in Ex-ample 2, utillzing in each case a 65 pound spread Eor l,000 square feet of glue line. Tlle assemblies were pressed into plywood for 3 minutes at 260F. The resulting plywood samples were tested with results as follows:
The samples were tested as specified in PS 1~74 of the american Plywood Association, involvîng a water soak test. Both the co~ven-tional and glue o Example 4 showed no visible delamination, con-stituting passing performance.
; EX~MPLE 5 This example illustrates a foamed resorcinol phenol ~ormalde-hyde glue of the invention.
Typical resorcinol glues contain a resin which has as the phen-olic component a mixture o~ 10-50% resorcinol and 20-60% of phenol.
The typical 50% solids resorcinol resin used in this example as a control was prepared in the conventional manner ~rom ~5 parts by weight phenol, 10 parts formaldehyde, 15 parts resorcinol and 1.5 ; parts caustic soda.
The resorcinol glue o~ the invention was prepared from this re-sorcinol glue composition as ~ollows:
Parts by Wei~ht Resorcinol Resin 100 Paraformaldehyde 10 Wood Flour 10 Attapulgus Clay 2 Surfactant ("Superamide") 4 The glue of the invention was prepared and foamed as described in Example 1 to a density of 0.65 gramsJcc.

The ~oamed test glue and liquid control glue were applied to wood veneers in the manner described in Example 1, utilizing a sp-read o 100 pounds per 1,000 square feet of glue line. The assem-blies were pressed into plywood for seven hours at 77F. The re-sultirlg plywood samples were then tested witll results as follows:
The resulting plywood samples were then tested in accordance wlth MIL-.A-397B for dry and wet shear. The specimens passed the test by exceeding a strength of 400 p.s.i.

Claims (19)

I claim:

1. A glue foamable to high density comprising:
a) at least one aqueous alkaline thermosetting resin of the group consisting of the phenol-formaldehyde-, the resorcinol-formal-dehyde-, the urea-formaldehyde- and the urea-melamine-formalde-hyde- thermosetting resins and b) at least one surfactant of the group consisting of 1) the fatty acid amides of the alkanol-amines having the following structure wherein - is a fatty acid radical of 8 to 18 carbon atoms, and R2 and R3 are lower alkyl radicals, and 2) the tertiary amine oxides having the following structure wherein R1 is an alkyl radical of 8 to 18 carbon atoms and R2 and R3 are lower alkyl radicals the surfactant being used in amount sufficient to render the glue foamable with a non reactive gas to a stable foam having a density of more than 0.5 and a Brookfield viscosity of from 1,000 to 20,000 centipoises at 25°C. and 20 rpm.

2. The glue of claim 1 wherein the resin comprises a resinous con-densation product of phenol and formaldehyde.

3. The glue of claim 1 wherein the resin comprises a resinous con-densation product of resorcinol and formaldehyde.

4. The glue of claim 1 wherein the resin comprises a resinous con-densation product of urea and formaldehyde.

5. The glue of claim 1 wherein the resin comprises a resinous con-densation product of urea, melamine and formaldehyde.

6. The glue of claim l wherein the surfactant comprises a fatty acid amide of the alkanol-amines having the following structure wherein - is a fatty acid radical of 8 to 18 carbon atoms, and R2 and R3 are lower alkyl radicals.

7. The glue of claim 6 wherein - is the mixture of fatty acid radicals of the mixture of fatty acids of coconut oil and wherein R2 and R3 are ethyl.

8. The glue of claim 1 wherein the surfactant comprises a tertiary amine oxide having the following structure = 0 wherein R1 is an alkyl radical of 8 to 18 carbon atoms and R2 and R3 are lower alkyl radicals.

9. The glue of claim 8 wherein R1 is the mixture of alkyl radical of the hydrogenated fatty acids of coconut oil and R2 and R3 are ethyl.

10. The glue of claim 1 wherein the components are used in the following proportions, expressed in percent by weight solids basis:
Thermosetting Resin 10 to 50 Surfactant 0.1 to 5 Clay 0 to 10 Bodying Agent 0 to 40 Alkaline glue pH
adjusting agent 0 to 6 Water 0 to 55

11. The glue of claim 1 wherein the thermosetting resin is a resin-ous condensation product of phenol and formaldehyde and wherein the glue components are employed in the following proportions, expressed as percent by weight, solids basis:

Thermosetting Resin 20 to 35 Surfactant .15 to .60 Clay 1 to 3 Bodying Agent 5 to 12 Alkaline glue pH
adjusting agent 0 to 6 Water 10 to 30

12. The glue of claim 1 wherein the thermosetting resin is a resin-ous condensation product of urea and formaldehyde and wherein the glue constituents are employed in the following proportions, exp-ressed in percent by weight, solids basis:
Thermosetting resin 15-30 Surfactant .15-.60 Clay 1-5 Bodying Agent 20-40 Water 25-40

13. The glue of claim 12 wherein the thermosetting resin comprises a resinous condensation product of urea, melamine and formaldehyde.

14. The glue of claim 1 wherein the thermosetting resin comprises a resinous condensation product of resorcinol, phenol and formalde-hyde and wherein the glue constituents are used in the following proportions, expressed as percent by weight, solids basis:
Thermosetting Resin 30 - 45 Surfactant .15 - 5 Clay 0 - 10 Bodying Agent 0 - 10

15. The glue of claim 10 wherein the clay comprises attapulgus clay.

16. The glue of claim 10 wherein the bodying agent comprises an amylaceous bodying agent.

17. The glue of claim 16 wherein the bodying agent comprises wheat flour.

18. The glue of claim 10 wherein the bodying agent comprises a pro-teinaceous bodying agent.

19. The glue of claim 18 wherein the bodying agent comprises soya flour.