CA1225763A - Moisture-resistant corrugated board adhesive having extended pot life - Google Patents

Abstract

Abstract A moisture resistant emulsion corrugated board adhesive composition having an extended pot life which comprises a major portion of water starch, a crosslinking polymeric agent, a boric acid compound, strong base, wax and an emulsifier wherein the pH of the emulsion is greater than about 8.

Description

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M&G 219.396-~S-01 MOISTURE-RESISTANT CORR~GATED BOARD ADHESIVE
HAVING EXTENDED POT LIFE

Field of the Invention The invention relates to an adhesive composition that can be used to form a moisture-resistant bond for corrugated board construction.
Bac~ground of the Invention The sensitivity of corrugated board structural adhe-sives to moisture continues to be a difficult problem for those using shipping or storage containers made of corru-gated board. Corrugated board is made by gluing papermembers with starch based adhesive compositions. The resulting corrugated board product can lose strength in the presence of high humidity, mist, rain or standing water since both the starch and the paper members are hydrophilic or water sensitive.
Starch-based adhesives are generally applied by coating starch or a starch suspension on corrugated board and heating the starch, resulting in a hydrophilic partly hydrolyzed film of starch. The starch molecules bond the paper members through hydrogen bonds between the starch polysaccharides and the polysaccharides in the paper mem-bers. However, the adhesive remains hydrophilic and can absorb substantial amounts of water. The starch in the presence of such water can become a gummy suspension or emulsion of starch in water and can rapidly lose bond strength.
The paper used in making corrugated board is generally formed from a water slurry of cellulose derived from wood or other plant sources which is made into a sheet by removing water from the sheeted slurry. The sheet is commonly rolled and dried to remove residual water resulting in finished paper. The resulting paper remains water sensitive since its component parts are hydrophilic and can tend to revert partly, in the presence of water, to the dispersion of ~3g .. . _,_ . . .

~5~3 cellulose particles in water from which it was prepared.
The degree of water resistance engineered into corru-- gated board varies according to the functional use of a container made from the corrugated board. The lowest degree of rnoisture resistance can be found in containers made from paper members and unmodified starch adhesives.
In comparison, waterproofed boards that must survive immer-sion in water without delamination are V board or "top iced poltry board" where components having exceedingly high levels of wet strength are made by fully impregnating the board with microcrystalline/paraffin wax on the corrugator and later curtain coated with a hard wax/polymer blend. In these instances and all variations between them it is important to note that water resistance requirements vary depending on the amount of water resistance required.
Many adhesives for preparing corrugated board have been proposed in the past including starch-based adhesives, thermoplastic adhesives, string-like adhesives, adhesives comprising emulsions of synthetic polymers, and others in both acidic and basic media. Starch based adhesives have been made in a variety of formulations including high amylose starch adhesives, resorcinol-formaldehyde adhesives~
calcium cyanamide-formaldehyde resins, urea-formaldehyde resins, and ketone-formaldehyde resins.
One type of starch adhesive can contain ketone-form-aldehyde resins. These resins are useful in starch based adhesives but are generally so chemically reactive that only limited amounts have been used in the past in corrugating adhesives. Starch-based ketone-formaldehyde resins can prematurely insolubilize raw starch and can prevent or interfere with starch gelatinization. Addition levels of 25 to 50 lbs. (12-23 kilograms) of dry resin solids (2.5 to 4~
of resin based on the starch) to a 700 gallon batch of standard adhesive are common. Further, it is believed that the ketone formaldehyde resin can only provide limited moisture resistance on non-wet strength components and the effective pot life of such adhesives is limited to a .,. . _ .

~;~25~63 ' few hours. Accordingly, a substantial need exists to provide a corrugated board adhesive that can provide water resistance to both the adhesive liner and the paper members, long pot life and effective corrugated board construction.
Brief Description of the Invention We have found that a starch based carrier, no carrier, or carrier/no carrier adhesive composition comprising a suspension or emulsion of either or both gelatinized or hydrated and ungelatinized or nonhydrated starch, a cross-linking resin, a wax, a strong alkali metal hydroxide and a boric acid compound can have a useful pot life in the range of 4 to 48 hours, and can be used in the manufacture of corrugated board providing strong, water-resistant bonds. The starch in the starch composition can combine with water upon heating in the corrugator after application to the corrugated board components, can swell to form gelatinized or partly hydrated starch particles which can react with the crosslinking resin, forming a more insoluble crosslinked polysaccharide mass. The cross]inked starch in combination with the corrugating board paper forms the adhesive bond. Upon further heating the starch can be dehydrated to form the fully cured bond line. The basic reacting ketone-aldehyde resin crosslinks the starch molecules of the adhesive, rendering them more water resist-ant.
The wax emulsion particles included in the adhesiveperform a number of functions. First the wax particles can migrate from the adhesive composition into the paper fibers in contact with the adhesive. The wax particles interact with the paper fibers changing the fibers from substantially hydrophilic to substantially hydrophobic, reducing the sensitivity of the fibers to the presence of moisture. Secondly the wax blooms to ~he surface of the cured and noncured glue line. Before curing the wax tends to prevent evaporation of water from the adhesive which makes the adhesive very convenient to use. The control of moisture evaporation or release insures latent curing of .... ... . . . .. .. .. .

~L~2~ 3 corrugated board. The corrugated board having cured glue line made from the adhesive of this invention can withstand the effects of temporary contact with substantial amounts of liquid water. The wax layer which forms during application on the surface of the glue line repels water from the surface of the glue line over ~he short term. The wax prevents water from rehydrating starch and weakening the bonds. Further the starch prevents ~ater from soaking through ~he paper fibers to weaken the bond line. The utility of the starch is very sensitive to wax content.
Below a certain quantity of wax insufficient water repel-lency is present in the uncured and cured bond line.
More than~a certain amount of wax results in wax particles interfering in curing of the adhesive.
The starch based adhesives of this invention are commonly characterized as being either a carrier adhesive, a no carrier adhesive, or a carrier/no carrier adhesive. The term carrier adhesive implies the presence of a thin base of gelatinized starch in which ungelatinized or nonhydrated starch particles are emulsified or suspended. The term no carrier adhesive implies the substantial absence of gelatin-ized or hydrated starch in the adhesive emulsion. The term carrier/no carrier adhesive implies that the distinction between gelatinized starch and ungelatinized starch is not distinct in the adhesive composition. Generally carrier/no carrier adhesives are prepared in a way that a substantial amount of partly hydrated or partly gelatinized starch is formed. These terms are inprecise since during the prepara-tion of the starch based adhesives some starch inherently becomes gelatinized during processing at any temperature and some starch remains ungelatinized and nonhydrated during preparation and use. The important characteristics of the invention are that the starch is crosslinked and dehydrated during curing, the wax particles in the adhesive emulsion provide moisture resistance to corrugated board material, and the glue line, the strong base and boric acid compound provide low cure temperatures and strong high quality bonds ~%25~63 after curing.
Surprisingly, we have found that the components of the novel adhesive composition of the invention cooperate to produce a useful pot life of greater tha~ about 4 hours and can have a pot life up to 48 h~urs. Pot life is generally considered to be the time durins which the adhesive can be maintained in the co~rugating machine at an elevated appli-cation temperaturel can maintain viscosity and can form useful bonds. During the time the adhesive is maintained at elevated temperature, both mechanical agitation, chemical action and heat can degrade starch molecules substantially reducing molecular weight, resulting solution viscosity, applicability, and potential bond strength. As ~he adhesive nears the end of its pot life, viscosity, applicability, curing time, and resulting bond strength between corrugated board paper members drops rapidly.
A first aspect of this invention is the novel corru-gated board adhesiv~. A second aspect of the invention is a process for making corrugated board which comprises forming a glue line between corrugated board paper members using the novel adhesive composition of the invention. A third aspect of the invention comprises a method for the manufacture of the novel adhesive of the invention. A fourth aspect is the corrugated board product.
Thus the present invention provides an aqueous adhesive composition for assembling corrugated board by adhesively bonding a corrugated medium to at least one liner, that when cured is resistant to water, which comprises in an aqueous emulsion having a pH
of greater than about 8, a major proportion of water, about 5 to 75 parts starch, about 0.1 to 5 parts of a basically reacting polymeric ketonealdehyde resin cross-linking agent, about 0.1 to 10 parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts wax, and an effective amount of an emulsifier each per 100 parts of the water, wherein the '~1 i ~,h: ' - 5a -adhesiYe composition can ~aintain a viscosity of at least 8 ~5 zahn cup seconds for at least 24 hours at a temperature greater than about 32C. (90F.).
In another aspect the invention provides a method for forming an aqueous adhesive composi-tion for assembling corrugated board by adhesively bonding a corrugated medium to at least one liner, which comprises forming an aqueous emulsion of a major proportion of watex, about lO to 75 parts of starch, about 0.1 to 5 parts of a basically reacting polymeric ketone-aldehyde resin cross-linking agent, about 0.1 to lO parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts of wax and an effective amount of an emulsifier, each per lO0 parts of the water, wherein the adhesive composition has a pH of greater than about 8 andwherein the adhesive composition can maintain a viscosity of at least 8 #5 zahn cup seconds for at least 24 hours at a temperature greater than about 32C. (90F.).
In still a further aspect, the invention provides a method of forming a substantially water resistant corrugated product which comprises applying to the flutes of a corrugated medium an aqueous adhesive composition, comprising in an aqueous emulsion having a pH of greater than about 8, a major proportion of water, about 6 to 75 parts starch, about 0.1 to 5 parts of a basically reacting polymeric resin crosslinking agent, about 0.1 to lO parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts wax, and an effective amount of an emulsifier each per 100 parts of water, wherein the adhesive com-position prior to application can maintain a viscosity of at least 8 #5 zahn cup seconds for at least 24 hours at a temperature greater than about 32C., to form a glue line on each flute, and contacting the glue line with a liner sheet.

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~2~63 - 5b -Detailed Descri tion of the Invention p Briefly, the novel water-resistant corrugated board adhesives of this invention are prepared by forming an aqueous emulsion, having a pH greater than about 8, of starch in the form of an ungelatinized starch or gelatinized starch, a basically reacting crosslinking resin, a wax, a strong alkali metal hydroxide base and a boric acid com-pound. The corrugated paper board adhesive of this inven-tion is preferably formed from a suspension of ungelatinized starch particles in a thin paste of gelatinized starch, called the carrier phase. The viscosity and solids content of the paste are important factors influencing the speed with which the pa~er board machine can be operated and also ,~, 1~

3L2~57~i3 effects the quality of the finished paper board. The suspending paste or carrier medium must be sufficiently viscous to maintain a smooth suspension of the nongelatin-ized starch particles, but not so viscous as to interfere with the application of the adhesive to the paper board.
The nature and proportion of dissolved solids in the carrier medium influences both pot life and the speed with which a given paper stock absorbs water from the applied adhesive. The water content of the adhesive efects adhesive propertieS. A small degree of water absorption from the adhesive to the paper is desirable in forming strong bonds between the paper plies. Absorption of water beyond that required to give good bonding is undesirable slnce it robs the adhesive of water needed to complete the gelatini-zation of the suspended starch upon heating in the corruga-tor and leads to inferior bonding.
Starch The starch used in both the carrier phase and suspend-ed starch phase is a commodity chemical produced from a number of plant root, stem or fruit sources. Starch is a high molecular weight polymeric carbohydrate polysaccharide, most commonly composed of six carbon monosaccharide units joined by alpha-glycan linkages having an approximate molecular formula of (C6Hloos)nt wherein n equals 102 to 106. Starch occurs naturally in the form of white granules and comprise linear and branched polysaccha-ride polyrners. Starch is commonly manufactured by first soaking and grinding the plant starch source, and separating the starch from waste matter. The starch is commonly reslurried and processed into a finished dried starch product. Commercial starch often has the form of a pearl starch, powdered starch, high amylose starch, precooked or gelatinized starch, etc. Preferably pearl starch is used in making both the carrier phase and the particulate starch suspended in the carrier.
Crosslinking Resins Resins that can be used in the novel adhesive composi-~L2Z5~763 -- 7 --tions of this invention include resins that upon heating in basic media generate crosslinking species that react with and crosslink the hydroxyls in adjacent starch molecules.
The crosslinking reagent tends to reduce the hydrophilic nature and the water solubility of the starch molecules by effectively removing the availability of hydroxyl groups to water and by introducing aliphatic alkylene-type crosslink-ing moieties.
A preferred class of crosslinking resins comprise well known condensation products of the reaction of a ketone and an aldehyde compound. These resins are characterized as a polyether polymer but can contain a variety of other monomers such as urea, melamine, etc. In the presence of heat and base, they commonly decompose to produce species that effectively crosslink the starch molecules. Preferred resins are acetone-formaldehyde resins, acetone-urea-form-aldehyde resins, acetone-melamine-formaldehyde resins comprising 15 to 30 wt-~ acetone, about 5 to 50 wt-% form-aldehyde and 0 to 15 wt-% of third monomer. One example of the preferred crosslinking resin embodiment of this inven-tion comprises the Ketack*series of resins manufacture~ by American Cyanamide.
Wax The term wax is used very broadly and is applied to a wide variety of materials. The materials can have proper-ties resembling certain well known waxes or can be used to provide physical properties similar to those associated with well known properties of wax such as sealing, polishing, candle making, etc. Many waxy substances have been found in nature and have been known to be useful for many years.
Historically waxes include substances that are natural products. Chemically natural waxes are esters of fatty acids and monohydric fatty alcohols. Physicall~ waxes are water repellant solids having a useful degree of plastic character. However, modern waxes include various synthetic substances that can replace natural waxes in many prepara-tions. The composition of natural waxes generally comprise -i *Trade Mark - 8 - ~2~5~
an ester of a saturated fatty acid and a long chain mono-hydric alcohol. Long chain fatty acids often include acids having greater than 16 carbon atoms and most commonly about 26 carbon atoms. The aliphatic monohydric alcohol commonly has at least 14 and can range as high as 36 carbon atoms. Petroleum, mineral or other synthetic waxes often consist of saturated hydrocarbons having aliphatic or open chain structures with relatively low branching or side chains.
Particularly preferable waxes for the water resistant corrugated board adhesive are waxes such as petroleum waxes, candelilla wax, beeswax, etc. Particularly preferred waxes are the petroleum waxes such as microcrystalline waxes, slack waxes and paraffin waxes.
Base The novel adhesive composi-tions of the invention con-tain a strong base which promotes the production of cross-linking species from the resin and acts to cure the adhe-sive. Essentially any strong base can be used, however preferred bases are alkali metal hydroxides. The most preferred strong bases include sodium and potassium hydrox-ide. The strong base also lowers the gel point of the starch, which increases the rate of hydration of the starch during curing of the glue line.
Boric Acid Compound The novel adhesive compositions of the invention include a boric acid compound which cooperates with the gelatinized and nongelatinized starch during heating and curing by reacting with available hydroxyl groups of the starch, forming a starch borax complex which aids in gelling the carrier starch molecules and the suspended starch molecules. The cooperative reaction increases the tack of the adhesive and produces strong bonds. Any boric acid compound having free hydroxyl groups attached to the boron atom can be used, however commercial boric acid (orthoboric acid, H3BO3 and its hydrated forms) and borax (sodium tetraborate decahydrate, Na2B4O7 10H2O and other hydrate 9 ~225~3 and anhydrous forms) are commonly used. For a discussion of boric acid compounds such as boron oxides, boric acicls and borates, see Kirk-Othmer Encyclopedia of Chemical Technolo-gy, 2nd Edition, Vol. 3, pp. 608-652. The boric acid compound increases the tackiness, viscosity, and cohesive strength of the adhesive. As the adhesive cures in the glue line, a gel structure forms between the boric acid compound hydroxyl group and the hydroxyl groups of the polysaccha-ride. The exact mechanism of the reaction between the boric acid compound and the starch is unknown. Further7 the borax buffers the caustic nature of the base used in the adhesive stabilizing the adhesive to the hydrolytic effect of the base.
In somewhat greater detail, the novel adhesives of this invention are made by first combining water and starch and then adding the balance of the components. PreEerably the adhesive is made by first forming the carrier phase compris-ing water, gelatinized starch and strong base. The carrier phase is made by mixing water with about 1 to about 25 parts Of starch and about 0.1 to about 10 parts of strong base.
The mixture is blended until uniform and heated to gelatinize or hydrate the starch particles. The carrier phase is then combined with additional particulate starch, the boric acid compound, the crosslinking resin, and addi-tional amounts of water or strong base if needed. About 5to 50 parts of additional starch per 100 parts of water, about 0.1 to 5.0 parts of boric acid compound per 100 parts of water, about 0.1 to about 5 parts of basically reacting resin per 100 parts of water and about 0.1 to 5 parts of wax ~ 30 per 100 parts of water are added. The mixture can be heated to partly hydrate or gelatinize the starch.
The wax is preferably added in the form of an emulsion of the wax in water. The wax emulsions preferred in the invention are commonly made by suspending wax in water using commonly available emulsifying agents. A particu-larly advantageous wax emu]sion is prepared by adding about 10 to 40 parts of nonionic slack wax to about 10 parts of hot water in the presence of a nonionic surfactant. The mixture is blended until uniform and abo~t 40 parts of warm water is added along with about 3.3 parts of urea. The mixture is blended until uniform and an antifoam agent is added and additional water is provided until the proper wax concentration is reached.
The final adhesive composition of the invention con-tains about 10 to 80 wt-%, preferably 10 to 40 wt-%, and most preferably 20 to ~0 wt-% solids for reasons of vis-cosity control and application speed. The pH of theadhesive is greater than about 8, preferably in the range of 9 to 13, and most preferably for reasons of low gel point and rapid cure of the glue line, about 11 to 12.
The following Examples describe the preparation of the novel adhesives of this invention and contain a best mode.
Example I
Into a two-liter container maintained at 100 F. (36 F~) was placed 6.1 parts of water. Into the water is mixed 1.6 parts of cornstarch and a sodium hydroxide solution prepared by mixing 0.8 parts of sodium hydroxide and 1.3 parts water. The mixture was stirred until blended and maintained at a temperature of about 35 C. ~100 F.) until the sta~ch was ~ully gelatinized forming the carrier phase, a period of about 15 minutes. Once gelatinized the mixture was placed in a dipping funnel.
In a separate two-liter vessel was mixed 51 parts of water and 29 parts of pearl corn starch maintained at 32 C. (88 F.)~ Into this suspension of pearl starch and water was slowly added drop-wise the contents of the dropping funnel containi~g the carrier phase. After the addition was complete the r~s~lting mixture of carrier phase and raw starch was heated until the raw starch had a viscosity of 22 #4 Zahn cup viscosity units. At that point 0.2 parts of boric acid were added to the mixture and the mixture was agitated until uniform. Into the mixture was placed a~out 1.2B parts of a premixed emulsion containing a ketone-J~-, 25i~3 aldehyde resin and wax. The emulsion is formed by combining equal parts of KETAC 1156, a water solution containing 65 wt-% of the resin and the emulsion of wax of Example III.
Example II
Into a two-liter container immersed in a water bath maintained at 130 F~, was added 30 parts of water, 6.2 parts of Vinamyl*II (a modified high amylose starch made by National Starch and Chemical). Into the suspension, at 130 F., was added a premix of 1.0 part of sodium hydroxide and 0.5 part of water and the mixure was stirred until uniform. The mixture was agitated for 15 minutes at 130 F. until the Vinamyl II was fully hydrated and gelatin-ized. The container was removed to a 100 F. water bath and into the mixture was added 0.1 part borax (Na2B4O7~5H2O) and 38.6 parts of water. The mixture was stirred until uniform and into the mixture was added 23.4 parts of corn-starch. The mixture was stirred until the suspension was uniform and an additional 0.2 parts of borax was added. The mixture was again stirred until uniform and into the uniform mixture was placed about 1.4 parts of the emulsion of Example III.
Example III
Into a suitable container was placed 39.35 parts of plasticrude LMPF*wax (a slack wax), 2.15 parts TWEEN*60, a polysorbate 60 emulsifier, and 2.15 parts of SPAN 60, a sorbitan monooleate emulsifier. The mixture was heated with agitation to 210 F. and into the mixture was added 5.0 parts of water at 185 F. and 0.5 parts urea. The mixture was stirred until uniform and a solution of 39.25 parts of warm water and 2.8 parts of urea are added to the mixture.
The mixture was stirred until uniform and 7.0 parts of cold water and a foam control agent were added to the mixture along with 0.15 parts formaldehyde as a preservative.
~sing the procedure of Example I the following Tables set forth the preparation of Examples IV through XXIX.

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~2~763 The corr~gated board whose properties and manufacture are summarized in Table III were prepared by cutting "C"
flute into 5" x 6" rectangles wherein the flutes are paral-lel with the 5" side. The facing medium (wet strength sized liner board) is cut into 6" x 8" rectangles wherein the grain of the board is parallel with the lengthwise direc-tion. After the adhesive has aged in the pot for a period of from about 1/2 to 23 hours after the resin wax is added, the corrugated b~ard is assembled by first aspirating 20 milliliters of adhesive into a syringe, releasing 10 milli-liters of the adhesive onto a glass plate and drawing the adhesive into a 12 mil (0.012 inch) film with a Gardene knife. Onto the 12 mil film is placed a S" x 6" flute, flute side down on the adhesive. A smooth application of the adhesive to the flute was insured by pressing the flute back with fingertips into the adhesive film~ The coated flutes are then contacted with the grain side of the liner board. The combined liner board and flute board are placed on a platen heated at 350 F. The adhesive is cured by pressing the board with a glass plate as the glue line is heated by the platen, commonly for 10 seconds or more. The glass plate, equipped with a handle, weighed 7.3 pounds.
The board was removed from the platen and allowed to cool and tested for bond strensth using the "Pin Adhesion Test of Corrugated Fiber ~oard", established by TAPPI (Technical Association Paper and Pulp Industry). In this test, the force required to separate the liner from the flute of the corrugated board is measured and the mechanism of separa-tion, whether fiber failure or glue line failure is noted.
In the test a rigid templ~e 4" x 4" square is placed on the bonded si~e of the board so the liner board is on the top.
Two 2" x 4" corrugated board pieces are cut from the board with a razor knife and are labeled. The pieces are cut so that the flutes are parallel with the 2" side. After aging the board a minimum of 24 hours at ambient temperatures, the bonded samples are immersed in water at ambient temperature and allowed to soak for 3 + 1/2 hour. The soaXed sample .~ ,~,i ~, ~2S763 is inserted onto the pin testing jig making sure that the pins are inserted between a single face side and the bonded liner board and not through the single face side alone. The soaked samples are debonded in an Instron device at a cross set speed of 2" per minute by using compression to separate the liner board from the bonded medium. The debonding strength is noted in pounds per area of the specimen and the type and percent of failure (fiber failure or glue line failure) are also recorded.

~LZ25~

Table III
Test Properties of Corrugated Board Using Adhesive Adhe- Bond sive strength Film Cur- #4 Hours of Finished Adhesive Thick- ing Press Zahn Gel Aged Corrugated of ness Temp. time Visc. Temp. at Board Example (Mils) (F.) (Sec.) (Sec.) (F.) Ambient lb/8in_) 10 XXIII 12 350 10 28 142 1/2 17.6 23 1-1/2 22.0

2-1/2 17.5

3-1/2 14.8 18 153 22 10.5 15 XXXIV 12 350 10 28 142 1/2 20.6 23 1-1/2 19.9 2-1/2 17.3 3-1/2 16.2 18 153 22 8.5 20 XXXV 12 350 10 28 145 1/2 18.4 1-1/2 15.85 27 2-1/2 14.5 3-1/2 14.0 23 4-1/2 13.7 150 23 7.5 XXXVI 12 350 10 28 145 1/2 19.1 1-1/2 16.2 27 2-1/2 18.5 3-1/2 13.8 23 4-1/2 15.2 - 30 150 23 6.9 XXXVII 12 350 10 25 142 1/2 18.57 1-1/2 18.2 23 3 15.3

4 16.2 15.5 6 13.3 22 152 23 6.26 ... .. . .. .

~2~57~

Adhe- Bond sive strength Film Cur- #4 Hours of Finished Adhesive Thick- ing Press Zahn Gel Aged Corrugated

5 of ness Temp. time Visc. Temp. at Board Example (Mils) (F.) (Sec.) (Sec.) (F._ Ambient lb/8in2) XXXVIII 12 350 10 25 142 1/2 18.9 1-1/2 16u9 23 3 17.0 4 19.1 15.97

6 16.1 22 152 23 8.7 .

~2~

Adhe-- Bond sive strength Film Cur- ~5 Hours of Finished Adhesive Thick- ing Press Zahn Gel Aged Corrugated 5 of ness Temp. time Visc. Temp. at Board Example (Mils) (F.) (Sec.) (Sec.) (F.l Ambient lb/8in_) XXXIX 12 350 10 20 141 1/2 19.77 1-1/2 18.47 3-1/2 18.10 4-1/2 15.35 6-1/2 12.00 IV 12 350 10 23 148 1/2 18.75 6 17 1-1/2 9.93 8 1-1/2 13.45 12 1 1/2 18.9 12 18 3-1/2 18.37 8 4-1/2 5.4 12 4-1/2 12.67 12 19 148 5-1/2 10.2 V 12 350 10 23 148 1/2 17.3 6 17 1-1/2 9.5 8 1-1/2 12.8 12 1-1/2 18.5 12 18 3-1/2 14.95 6 18 4-1/2 4.0 8 4-1/2 6.2 12 4-1/2 10.4 12 19 148 5-1/2 6.2 XL 12 350 10 13 145 1 27.5 13 2 24.7 3 22.2 9 4 19.8 9 145 5 21.2 6 15.9 i7~

Adhe- Boncl sive strength Film Cur- #5 Hours of Finished Adhesive Thick- inq Press Zahn Gel Aged Corrugated 5 of ness Temp. time Visc. Temp. at Board Example (~lils) (F.) (Sec.l (Sec.) (F.) Ambient lb/8in_) XLI 12 350 10 9 145 1 25.9 9 2 15.1 8 3 22.1 8 4 17.3 8 14~ 5 15 8 6 16.6 XLII 12 350 10 10 145 1/2 25.1 1~1/2 23.5 2-1/2 17.0 3-1/2 18.1 5-1/2 9.8 9 21 7.4 XLIII 12 350 10 11 144 1/2 23.4 9 1-1/2 22.1 9 2-1/2 18.2 9 3-1/2 12.4 - 5-1/2 11.2 21 4.0 An examination of the Tables set out above shows that the gel temperature, pot life viscosity, and bond strength are much improved when compared to o-ther starch based adhesives. The No. 4 and 5 Zahn cup viscosity of the adhesive over a 22 or 23 hour period remains suffi-cient for satisfactory machine application of the adhesive to corrugated board members and sufficient to provide adequate bond strengths as shown. The gel temperatures range from 142 to 153 F. which will provide an efficient, rapid, energy conserving corrugated board manufacture.
While the above description, Examples and data provide a basis for understanding the invention, since many embodi-:~25~76~

ments can be made without departing from the spirit and scope of the invention, the invention resides wholly in the claims hereinafter appended.

Claims (30)

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

1. An aqueous adhesive composition for assembling corrugated board by adhesively bonding a corrugated medium to at least one liner, that when cured is resistant to water, which comprises in an aqueous emulsion having a pH
of greater than about 8, a major proportion of water, about 5 to 75 parts starch, about 0.1 to 5 parts of a basically reacting polymeric ketonealdehyde resin cross-linking agent, about 0.1 to 10 parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts wax, and an effective amount of an emulsifier each per 100 parts of the water, wherein the adhesive composition can maintain a viscosity of at least 8 #5 zahn cup seconds for at least 24 hours at a temperature greater than about 32°C. (90°F.).

2. The aqueous adhesive composition of claim 1 wherein the starch is present in the form of ungelatinized starch particles suspended in a carrier phase of gelatin-ized starch in the aqueous emulsion wherein there are about 1.0 to 25 parts of the gelatinized starch and about 5 to 50 parts of ungelatinized starch particles per 100 parts of water.

3. The aqueous adhesive composition of claim 1 wherein the pH of the emulsion is between 9 and 13.

4. The aqueous adhesive composition of claim 1 wherein the pH of the emulsion is between about 11 and 12.

5. The aqueous adhesive composition of claim 1 wherein there are about 50 to 85 parts of starch in both the carrier and solid particulate starch phases per 100 parts of the water and the ratio of starch in the carrier phase to starch in the solid suspended phase is about 1:5 to 1:25.

6. The aqueous adhesive composition of claim 1 wherein the basically reacting polymeric ketonealdehyde resin crosslinking agent comprises a ketone-urea-formalde-hyde resin which is present at concentration of about 0.2 to 2 parts per 100 parts of the water.

7. The aqueous adhesive composition of claim 1 wherein the alkali metal hydroxide is sodium hydroxide and is present at a concentration of about 0.002 to 0.75 parts of sodium hydroxide per 100 parts of adhesive composition.

8. The aqueous adhesive composition of claim 1 wherein the boric acid compound is H3BO4.XH2O or Na2B4O7.
XH2O wherein X is a number from 1 to 10, and is present in a concentration of about 0.1 to about 5 parts per 100 parts of the water.

9. The composition of claim 1 wherein the wax comprises a slack wax and is present at a concentration of about 0.1 to 1 part of wax per 100 parts of the water.

10. A method for forming an aqueous adhesive composi-tion for assembling corrugated board by adhesively bonding a corrugated medium to at least one liner, which comprises forming an aqueous emulsion of a major proportion of water, about 10 to 75 parts of starch, about 0.1 to 5 parts of a basically reacting polymeric ketone-aldehyde resin cross-linking agent, about 0.1 to 10 parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts of wax and an effective amount of an emulsifier, each per 100 parts of the water, wherein the adhesive composition has a pH of greater than about 8 and wherein the adhesive composition can maintain a viscosity of at least 8 #5 zahn cup seconds for at least 24 hours at a temperature greater than about 32°C. (90°F.).

11. The method of claim 10 wherein the starch is in the form of ungelatinized starch particles suspended in an emulsion containing gelatinized starch particles wherein there are about 1.0 to 25 parts of gelatinized starch and 5 to 50 parts of ungelatinized starch particles per 100 parts of water.

12. The method of claim 10 wherein the pH of the emulsion is between 9 and 13.

13. The method of claim 10 wherein the pH of the emulsion is between 11 and 12.

14. The method of claim 11 wherein there is a total of about 50 to 85 parts of starch in the carrier and solid particulate starch phases and wherein the ratio of starch in the carrier phase to starch in the solid suspended phase is about 1:5 to 1:25.

15. The method of claim 10 wherein the basically reacting polymeric ketone-aldehyde crosslinking agent comprises a ketone-urea-formaldehyde resin which is present at a concentration of about 0.2 to 2 parts per 100 parts of the water.

16. The method of claim 10 wherein the alkali metal hydroxide is sodium hydroxide and is present at a concentra-tion of about 0.002 to 0.75 parts of sodium hydroxide to 100 parts of adhesive composition.

17. The method of claim 10 wherein the boric acid compound is H3BO4.XH2O or Na2B4O7.XH2O wherein X is a number between 1 and 10 and is present in a concentration of about 0.1 to about 2.5 parts per 100 parts of the composition.

18. A method for forming corrugated board which comprises forming a glue line between the flutes of a corrugated board member and a liner with the adhesive of claim 1 and curing the adhesive.

19. The method of claim 18 wherein the adhesive is applied at a thickness of about 1 to 50 mils.

20. The method of claim 18 wherein the adhesive is cured at a temperature greater than about 100°C.

21. The product of claim 18.

22. A method of forming a substantially water resistant corrugated product which comprises applying to the flutes of a corrugated medium an aqueous adhesive composition, comprising in an aqueous emulsion having a pH of greater than about 8, a major proportion of water, about 6 to 75 parts starch, about 0.1 to 5 parts of a basically reacting polymeric resin crosslinking agent, about 0.1 to 10 parts of an alkali metal hydroxide, about 0.1 to 5 parts of a boric acid compound, about 0.1 to 5 parts wax, and an effective amount of an emulsifier each per 100 parts of water, wherein the adhesive com-position prior to application can maintain a viscosity of at least 8 #5 zahn cup seconds for at least 24 hours at a temperature greater than about 32°C., to form a glue line on each flute, and contacting the glue line with a liner sheet.

23. The method of claim 22 wherein the starch is present in the form of ungelatinized starch particles suspended in a carrier phase of gelatinized starch in the aqueous emulsion wherein there are about 1.0 to 25 parts of the gelatinized starch and about 5 to 50 parts of ungelatinized starch particles per 100 parts of water.

24. The method of claim 22 wherein the pH of the emulsion is between 9 and 13.

25. The method of claim 22 wherein the pH of the emulsion is between about 11 and 12.

26. The method of claim 22 wherein the ratio of starch in the carrier phase to starch in the solid sus-pended phase is about 1.5 to 1:25.

27. The method of claim 22 wherein the basically reacting polymeric resin which is present at a concentra-tion of about 0.2 to 2 parts per 100 parts water.

28. The method of claim 22 wherein the alkali metal hydroxide is sodium hydroxide and is present at a concen-tration of about 0.002 to 0.75 parts of sodium hydroxide per 100 parts of adhesive composition.

29. The method of claim 22 wherein the boric acid compund is H3BO4.XH2O or Na2B4O7XH2O wherein X is a number from 1 to 10, and is present in a concentration of about 0.1 to about 5 parts per 100 parts water.

30. The method of claim 22 wherein the wax comprises a slack wax and is present at a concentration of about 0.1 to 1 part of wax per 100 parts water.