CA1063752A - In situ method for preparing high speed corrugating adhesives - Google Patents

Abstract

ABSTRACT

High speed corrugating adhesives are provided based upon the use of certain saponifiable starch ester materials. These are prepared in situ by introducing a carboxylic acid anhydride into an aqueous slurry of granular starch, and saponifying with alkali the ester formed. The specific formu-lations described have superior properties that permit higher corrugating machine speeds.

Description

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This invention relates to starch-based corrugating adhesives and more particularly to an ln situ method for their preparation.
sy means of such adhesives it is possible to unite articles, particularly laminated articles of fibrous, cellulosic ;
webs, and more particularly, to produce paperboard for use in the production of corrugated containers. There are disclosed articles produced through the use of the new adhesive composi-tions.
One usual method of making corrugated board consists of corrugating a strip of paper by means of a corrugated roller, applying an adhesive to the tips of the flutes of the corruga~
tions on one side and adhering another strip of paper called a "liner", to the flute tips by use of heat and under high pressure.
This product, called "single face" corrugated board may be used as is. However, it is usual to make "double face", also called "double back" board by sending the single face board into -~
the second stage of the corrugating machine called the "double .~ .
backer" stage. The term "single facer" genexally refers to the first stage of the machine. An adhesive is applied to the opposite flute tips, and a second liner of paper is adhered to said opposite side by the use o-f heat and under a relatively small amount of pressure. The fact that the use of a great amount of pressure in the adherence of the second strip of paper ; would tend to crush the corrugations makes the adhesive problem in the second step quite difficult.
starch-based corrugating adhesive formulations have been in wide use since the advent of the Stein-Hall technology, as disclosed in U.S. Patent `
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No. 2,051,025, granted August 18, 1936, to J. V. Bauer, and U.S. Patent No.
2,102,937, granted December 21, 1937, also to J. V. Bauer.

A Stein-Hall type adhesive is a two component aqueous system. One ;
component in this system is generally formed fro~ a cooked, or gelatinized starch material, which serves as a carrier phase. Other materials which can form relatively viscous aqueous slurries, such as carboxymethyl cellulose, may also be used as a carrier phase.

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The second component or phase is formed from a raw, ungelatinized starch material. This second phase is a latent or potential adhesive phase.
That is, the'adhesive characteristics of such a formulation are not fully developed until after the adhesive has been applied to the tips of the flutes of the corrugated web, the liner has been pressed against the adhesive-coated flutes, and heat and pressure haYe been applied; the heat causing the ~-granular starch material to gelatinize and develop structure.

15The swelling and gelatini2ation of the latent adhesive phase takes .
place as the newly assembled corrugated board is passed through a hot plate-dryer system that is associated wlth a corrugating machine. This system also -~
partially dries the corrugated board and sets the adhesive sufficiently so that it can be subjected to subsequent operations, such as trimming, slitting, and sheeting without delamination.
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The initial degree of cohesiveness in the bond of the corrugated `, board is referred to as the green bond strength. This characteristic determines the ability of the newly formed corrugated board to resist the instantaneous ,

-3-- . ,-, high shear forces that are developed during subsequent process-ing op~rations, such as the trimming, slitting, and sheeting operations, and is not necessarily an indication of the final bond strength.
Greenbondstrength, or for brevity, green strength, is a major limiting factor which controls the operating speed at which corrugated board may be manufactured on a given machine.
An experienced machine operator often will operate a machine at the maximum speed of which it is capable without having the board delaminate during the trimming, slitting, and sheeting operations.
Since the resistance to delamination is a characteristic that is directly dependent on green strength, the characteristics of the ~ ;
corrugating adhesive play a direct role in machine efficiency, which in turn determines the rate of return on the fixed invest-ment represented by the machine.
After corrugated board has been trimmed, slit, and sheeted, it is stacked and sent to storage, where the adhesive cures to a full strength. Until thebond is dry and fully cured, the corrugated board may be delaminated by slowly and firmly pulling the liner away from the corrugated sheet.
Since the middle thirties, one of the major advances in corrugating adhesive technology is that disclosed in U.S. Patent 3,355,307, granted ~ovember 28, 1967, to John J. Schoenberger and Raymond P. Citko. Th1s patent discloses a single phase corrugating adhesive referred to as a "non-carrier" system, in which partially swollen starch granules are present as a homo-geneous phase, suspended in an aqueous, alkaline vehicle. The -~
elimination of the carrier phase permitted substantial operating economies. The no-carrier type corrugating adhesive disclosed and claimed in the Schoenberger-Citko patent was applied and cured in the same manner as the ~tein-Hall type adhesive ~-formulations.

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O~her advances in the corrugating adhesive field related primarily to building in moisture resistance, generally through the addition of synthetic resins, such as urea-formaldehyde, phenol-formaldehyde, and re-sorcinol-formaldehyde resins.

The Bauer patents represented a significant advance in the art, for their time. Bauer reported that the use of his adhesive systems permitted corrugated board machines to be operated up to 20~ faster than would have been possible utilizing prior art adhesive compositions. The prior art compositions included preparations based on sodium silicate and adhesive io preparations based on the use of gelatinized starches or modified starches -such as dext~ins.
j In the Stein-Hall type syste~, according to the teachings of ~
Bauer, the time required to form an adhesive bond between the corrugated `~ -interliner and a liner or facer sheet is substantially independent of the rate at which the moisture in the adhesive is driven off by heat or absorbed by the paper. According to Bauer, the time required to form the adhesive bond depended mainly on the time required to cause gelatinization of the granular starch particles suspended in the gelatinized starch carrier phase. As this granular starch gelatinized, water was taken up, and the viscosity of the adhesive was raised rapidly, to form an immediate green bond. Bauer considered that tapioca, rye and potato starches were inherently superior to corn, wheat, and rice starches for making corrugating adhesives in accordance with his developments.
' Bauer described four principal factors that he considered to ; 25 determine the suitability of the starch for use as the latent adhesive component in his system. These four factors were:
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1. the time required for complete gelatinization of the granular starch by means of the heat input on the corrugating machine.
2. the temperature at which the starch gelatinizes.
3. the ViSCClSity developed after gelatinization.

4. the degree of tackiness developed after gelatiniza-tion.
However, subsequent developments indicate that the greenbondstrength depends significantly on the evaporation of moisture from the bond site; Thayer & ~homas, Analysis Of the ~-~
Glue Lines in Corrugated Board, TAPPI, 22nd Corrugated Containers Conference, May 1971.
It has now been discovered that a select clas~ of starch materials, when used as the adhesive component in a corrugating adhesive composition, demonstrate superior proper~
ties. One way to take advantage of these properties is by the use of machine speeds that are ordinarily from 5~/O to 10~/o higher ~ ;~
than had been considered possible with conventional Stein-Hall type corrugating adhesive compositions, or with the more recently introduced no-carrier corrugating adhesive compositions, at generally the same levels of adhesive usage.
Stated in another way, superior results have been obtained when the primary active adhesive component in a corru-gating adhesive formulation is a saponifiable starch ester mater-.
ial which exhibits at least about a 3~O greater area under an Instron force-time heating curve and at least about a 3~/O greater `
area under an Instron force-time cooling curve, compared with un~
modlfied corn starch under the same test conditions.

Accorcling to the invention there is providecl a method for the in situ preparation of a composition suitable for use in a corrugating machine, that permits operation of the corru-gating machine at speeds of operation at least about 2~o higher than those obtainable using unmodified corn starch as the~rimary active component in the composition, comprising, form-ing under alkaline conditions an aqueous slurry of unmodified, granular starch material, a carrier material, a reagent capable of forming a saponi~iable ester with said starch material, and a quantity of alkali sufficient to substantially completely saponify said saponifiable ester, to destroy any unreacted re-agent and to neutralize any acid formed.
In accordance with one embodiment of the invention the method comprises a) forming an aqueous slurry of an unmodified ,~
granular starch material; b) introducing under alkaline condi-tions, into said slurry, i) a reagent capable of forming a saponifiable ester with said starch material, and ii) a quantity of alkali sufficient to substantially completely saponify said `~ ~;
saponifiable ester, to destroy any unreacted reagent and to neutralize any acid formed, to form a reaction mixture, and, c) admixing the reaction mixture with an aqueous slurry of a carrier màterial.
Preferred adhesive compositions within the invention are based on the use of primary adhesive components which are saponifiable starch esters having a saponifiable degree of `
substitution (D.S.) of at least about 0.015. As used herein, "saponifiable degree of substitution" means the total D.S. of all saponifiable ester groups on the starch molecule. Particular-ly preferred starch ester materials are starch acetate, starch succinate and starch acetate succinate. One or more of these active adhesive components can ~e used to advantage either in a Stein-Hall type formulation or in a no-carrier type formulation, with equally superior improvernents over the prior art.

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The most preferred adhesive component is a starch ace-tate succinate having a saponifiable degree of substitution (D.S.) in the range from about 0.025 to about 0.045. These D.S.
levels represent ranges that are applicable to starch acetate succinate. Other derivatives that are useful in accordance with the invention will have their own preferred D.S. ranges. General-ly, if the D.S. level is too low, the derivatized material will not exhibit significant improvement over unmodified corn starch when used in a corrugating adhesive formulation. If the D.S.

level is too high, the gelatinization temperature may be unworkable.
~ he specific materials that have been identified, f~r use in accordance wlth the invention, are starch derivatives identi~ied ahove. These starch derivatives are, in accordance with the present invention, prepared immediately prior to use, i.e., in situ at the corrugating machine; they may also be prepared in ~;

advance, and may be formulated into corrugating adhesive com-positions as with other starch materials that are to be used for such purposes in accordance with prior art practices.
It is also possible to utilize modi~ied starch materials which may be produced from the aforementioned starch esters.
These modified starch materials are produced by substantially ~ :
comple~ely saponifying the starch esters and removing the salts formed thereby. The resulting modified starch material may then be dried. Although the derivative has been substantially com-pletely removed from the starch material, the modified starch -retains the beneficial properties of the ester matexial.

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While we do not fully understand the reason why the special materials identified by our invention are superior for use in corrugating adhesives in particular, it can be theorized that they not only develop unusually high viscosity upon gelatinization, but in addition, provide a high green strength without the necessity of solvent evaporation.

While the final form of the useful starch materials of this ~ ;
invention is not known, it is known that the esters materials saponify ~ ~-substantially completely in a short period of time in the environ~ent present in the mixing apparatus on the corrugating machine.
:", - The invention will be better understood by a more detailed explanation of several specific embodiments thereof. All parts and percentages are by weight, on a commercial basis, unless expressly stated to be otherwise. The commercial basis for the starch materials includes about 12% moisture.

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DETAILED DESCRIPTIO~ OF THE PREFERRED EM~ODIMENTS

The proper selection of the primary active adhesive component is of great importance for the proper practice of the present invention.
In preparing saponifiable starch esters for use as the primary active adhesive components, the starting starch material may be derived from ;
any vegetable source. Starches derived from non-waxy grain sources, such as, for example, corn, wheat, rice, and grain sorghum are preferred.
The term "starch" is used broadly herein and encompasses flour, un-modified starch and tailings. Corn starch is a preferred starting starch material.

The initial starch is esterified, as will be described presently, `~
to produce the primary active adhesive component that has the desired characteristics in accordance with the invention.

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In a typical corrugating adhesive formulation, it is usual to add borax and caustic to increase the adhesive strength and tack, and to ad-just the gelatinization temperature. When using either a carrier-type or a no-carrier type adhesive formulation, the Stein-Hall viscosity of -the formulation must be within the conventional range to permit an adequate amount of adhesive to be applied to the flute tips at all machine speeds. Generally, to be tractable on a corrugating machine, an adhesive formulation should ha~e a Stein-Hall viscosity in the range of about 20 sec. to about 100 sec. The optimum Stein-Hall viscoslty of the formu-lation will depend on the particular corrugating machine.

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Unless otherwise specified, the materials described and claimed llerein are those which are to be added to form the adhesive formulation. In the particular environment of the adhesive formula-tion, the form of certain materials may be altered. For example, the starch ester will saponify in a typical corrugating adhesive formulation.
This will reduce the actual amount of alkali present. The borax may be present in any of several species, or as an equilibrium mixture of these species, depending primarily on the pH of the formulation.

~s previously described, it is standard practice in the corrugating industry to add alkali and borax to the adhesive formulations.
~hile formula`tions which do not include these materials may be used as corrugating adhesives, it is preferred to include both of these materials to the formulations of this invention.

The borax is generally utilized to increase the gel structure of the adhesive paste. However, an excess of borax may have an adverse -effect on the cured bond strength. In addition, borax has the tendency to increase the gel temperature of the formulation. Generally, up to about 5% borax ~10 mol) may be incorporated into the formulations.
A more usual quantity would be about 2% to about 3%. The percentages are based on the total starch material present in the formulation, including both the primary active adhesive material and the carrier material. If 5 mol borax is to be used instead of 10 mol, it is necessary to compensate for the reduced water of hydration. In no-carrier systems, boric acid may be utilized as a reaction stopper. The boric acid will ' --11-- .

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quickly be converted to a borate and is then able to serve as a substi-tute for added borax. ~s used herein, the term "borc~" will include those borates which are present due to the additlon of boric acid.

~ny standard alkali may be used. However, for economic reasons, sodium hydroxide is most commonly utilized. The alkali serves to reduce the gel temperature of the adhesive formulation to a readily tractable point. Generally this will be in the range of from about 145F to about 150F, but may in some applications range from about 140F to about 160F.
It is important that large amounts of alkali not be used in any corru-gating adhesive formulation, whether conventional or in accordance withthis invention, as alkali tends to reduce gel structure formation.
Generally up to about 5% alkali (calculated as sodium hydroxide) may be used, based on total starch material in the system. More usual amounts would be from about 3% to about 3.5%.

It is of critical importance to the practice of this invention that at least enough alkali to substantially completely saponify the starch ester be used. The amounts of alkali referred to above are the quantity of alkali in excess of this minimum amount.
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The particular starch ester to be used in the practice of this invention is not critical, as long as it will saponify in the environ-ment of a corrugating adhesive formulation, Consequently, inexpensive and simple starch esters, such as starch acetate are preferred. Particularly preferred is the mixed ester, starch acetate succinate.

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The starch esters may be obtainecl commercially, or may be made by any conventional method, such as by reacting unmodified starch with acid anhydrides, acid halides, vinyl esters and the like. The ~ame reagents may be used when u~ilizing the in situ method of this invention.
It is necessary however that the esterification be carried out at a temperature which is below the actual gelatinization temperature of both ~he unmodified starch and the starch ester.

In addition, the water content of an adhesive formulation should be adjusted so that an extremely tacky adhesive characteristic is obtained immediately after gelatinization. This implies that suEEicient water is present for oomplete gelatinization. It is most desirable that rapid development of tack is obtained upon the application of heat in the corrugating equipment.
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The amounts of starch materials utilized in the adhesive formula-15 tions of this invention are similar to those utilized in conventional formulations. Generally, the granular starch component of a Stein-Hall type formulation will contain from about 10% to about 25% starch. The final adhesive mixture generally has from about 12% to about 25% of its -total starch in the form of the gelatinized carrier.
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The starch esters of this invention may also be used as the car~ier portion of a Stein-Hall type adhesive. In such instances, it may be possible to reduce the quantity of carrier somewhat due to the greater thickness of these starch esters. i : :`
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The desirable de~ree of substitution depends upon the particular initial search material selected. However, in general, it has been found desirable to utilize a saponifiable D.S. of at least about 0.015. Starch esters having a saponiEiable D.S. of at least about 0.015 have been found to-~satlsfy the Instron test criteria, discussed infra, and therby permit ~'machine speeds at least about 20% greater than those attainable utilizing unmodified corn starch as the primary active adhesive component.

Generally D~S. levels greater than 0.015 will produce even faster machine speeds. It has been found preferable to utilize saponifiable starch esters having a saponifiable D.S. in the range of from about 0.02S
-to about 0.04~5. The utilization of such materials will generally permit operation of a corrugating machine at speeds of up to about 1O0~D higher than those attainable using conventional adhesives.

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The green strength, and the viscosity of the gelatinized corrugating adhesive that produces the green strength, cannot conveniently ;~
be subjected to direct quantitative measurement at the exact site of the bond. However, it appears that the inherent ability of a corrugating adhesive to form higher green strength, which permits improved corru-gating speeds, may be predicted by a measurement of the area under an 2Q Instron force-time curve of a paste made in a particular manner from the primary active adhesive component that is selected for use in accordance with the présent invention.

~,, The Instron force-time curve of a paste of a primary active adhesive component may be determined in accordance with the following ~5 procedure.

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ST~NDARD INSTRON MET~IOD
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An Instron Tensile Tester Model TT is fitted with compression load cell "CM". A culture tube approximately 22 rnm in diameter and 175 mm high is fitted into a constant temperature chamber. This chamber is a metal sleeve approximately 23 mm in diameter and 116 mm high, wrapped with about 4 feet of 3/16 inch copper tubing and covered wlth asbestos wrap. The copper tubing is connècted to constant temperature baths through appropriate inlets.

The starch slurry to be tested is placed into the culture tuhe to a depth of 2.75 inches.

- " :' The culture tube is lowered into the sleeve, which has been preheated by circulating water at a temperat~re of 210F through the copper tubing. ~ thermocouple probe having a diameter of 0.184 inch -is inserted about 1 inch deep into the top surface of the slurry. Simul-- 15 taneously the machine and recorder are turned on, with the probe being driven into the slurry at a speed of 0.02 in/min. This heating cycle is continued for 14 min. and then the hot water circulation is stopped.
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After another minute, ice water is circulated through the tubing and continued for 15 minutes.

' The curve generated on the recorder is called a force-time curve. The first 15 minute segment will be referred to as the heating cycle and the second 15 minute segment as the cooling cycle.

The test slurries for use on the Instron are made as follows.

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~ predetermined quantity of unmodified corn starch i~ ~Lurried in 110 ml ~ater. A predetermined amolmt of a 4% w/v borax (10 mol) solution and a predetermined amount of a 20% w/v NaO~ solution are added. Suficient water i5 added to produce a total additional volume of 60 ml. The re- -sulting slurry is heated at a temperature of 212F, with agitation for 5 minutes, and then allowed to stand for 5 minutes. It is then immediately added to the second slurry which has been previously prepared.

The second slurry is prepared by slurrying 50 gm of the test starch in 165 ml of water. The first slurry is then mixed with this slurry and the admixture stirred for 15 min. It is then immediately tested on thè Instron tester. ;

A sample of unmodified corn starch is run as the test starch ;~
under these standard test conditions. The force-time heating and cooling curves are generated as described above and the area ùnder each of these segments is independently determined.
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The identical procedure is then followed for the starch material to be tested. The areas under the heating curve for the test starch is compared with the area for unmodified corn starch. The same is done for the areas under the cooling curve. It must be stressed that the areas under each of the segments of the curves are treated independently of each other.

The absolute areas determined in this manner are arbitrary values largely determined by the test pr~ocedure. The crucial feature of the test is not these absolute values, but the ratio:of the areas - . .

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for the test starch to the are~s for the unmodified corn starch, when performed under the samc test conditions. This means that the pre-determined amounts of carrier starch, borax and sodium hydroxide are identical.

While the Instron test does not duplicate exactly the viscosity and gel structure on the glue line, it does give a relative measurement of the ability of a particular primary adhesive component to develop high green strength in a corrugating bonding environment.
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It has been found that to produce the desired 20% improvement in machine speed, the ester material must exhibit at least about a 30%
greater area under both the Instron heating and cooling curves compared to unmodified corn starch. In other words, a saponifiable starch ester which will exhibit a 30% Instron improvement (greater area) under both heating and cooling curves will produce machine speeds at least about 20%
faster than machine speeds obtainable using unmodified corn starch, on the same machine.
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The useful starch ester materials may also be defined as having -- a total saponifiable degree of substitution (D.S.) of at least about 0.015. The upper limit on saponifiable D.S. is economic and functional.
It lS necessary that the material have a-gel temperature high enough so that it will not gelatini~e prior to use; such as during manufacture of the derivative or during formulation of the adhesive composition.

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While the exact upper limit on saponifiable D.S. will depend on the parti~
cular substituent being used, in general, for esters of monocarboxylic acids it will be about 0.1 and for mono-esters of dicarboxylic acids about 0.06.

It is kno~n that in the environment of the adhesive formulation, the ester will saponify in a relatively short time. This means that the ester will have substantially completely saponified prior to its appli- -cation to the flute tips. The exact form of the saponified starch material is not known. It is possibly a complex with either the caustic or borax which are generally present in the system.

It is believed that a portion of the imp~Qvement in machine speed may be ascribed to a reduced alkali level in the formulation. ~s ~;
the ester material saponifies,- some of the alkali is used up.
.' - ~ `., Certain of the beneficial properties of the starch esters are retained in the saponified product. Prior to acLually being applied to the flute tips, the ester has substantially completely saponified. It has been found that a modified starch material may be produced by saponifying the starch ester. The saponification is carried out in the presence of alkali and may further include borax in the sapon~fication med~um. The modified material may then be dried. This process, i.e., esterification followed by saponification yields a material which is ` different from the original unmodified starch material. This modified ` material may be used in a corrugating adhesive formulation in a manner :
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similar to the use of the starch esters. Improved green bond strength compared with unmodifie~ corn starch is found. The exact mechanism of the modification is not known, but may be a physical disruption of the granules, or may be a small amount of a complex formed between the alkali and the starch.

~' i The use of a reduced quantity of alkali in the corrugating adhesive formulation does not account for all of the machine speed improvement. When unmodified corn starch and a starch ester in accord-ance with this invention are run at identical actual alkali levels, machine speeds are still greatly faster using the starch ester materials.

The starch esters may be formed in situ at the corrugating machine when preparing the adhesive formulation. It is merely necessary to add an ester forming reagent to the formulation. The conditions are those which will permit very rapid esterification, followed by irreversible saponification to take ... . :
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place. The esterifying reagents are the aforementioned conventional materials.
The quantity of reagent to be added is that amount which would, in the absence of saponification, produce a product having a saponifiable D.S. suitable for use in accordance with this invention. Generally, a reagent such as acetic anhydride will have a reaction efficiency of about 50% to about 70% under the conditions found in a corrugating adhesive formulation.

The order of addition of the materials to the adhesive ~ormulation is not critical to the success of the in situ method. It is, of course, necessary that the esterification reagent not be allowed to remain in an environment for any lengthy period of time where it might, at least in part, decompose.

In order to more fully understand the invention the following demon-strations of specific embodiments of the invention are described. They are illustrative and informative in nature and in no way are intended to limit the -~
scope of the invention.
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Com arative Corru ated Board Production Runs P g -In order to demonstrate that the corrugating adhesives of the present invention provide improvements over conventional unmodified starch Stein-Hall adhesive formulations, it was necessary to establish a limit, above which speed, conventional starch adhesives no longer bind the corrugating board sufficiently to prevent delamination during the subsequent operations, and then determine at ;
what machine speed corrugated board using adhesives prepared in accordance with the present invention could be prodùced before they reached the failure point.

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The corrugated board manufactured in all tests of this example was a double backer board consisting of a 26 pound corrugated sheet positioned between two 42 pound Kraft liners. A commercial double-backer corrugated paper machine was used. All hot plate temperatures were set at 300 F. for this trial.
Initially tlle glue clearance of the adhesive applicator was set at 0.014 in. A
Stein-Hall type conventional corrugating adhesive, for use as a control, and corrugating adhesive formulations prepared in accordance with the present invention, were made as tabulated below.

Conventional Double Backer Formuia Primary Mixer ' ' ,, Add 10.0 gal. water Add 20.0 lb. unmodified corn starch ~`
Heat to 150 F. ~-~
Add 3.3 lb. NaOH dissolved in 2.0 gal. water Agitate for 15 min~ .
Then add 10.0 gal. cooling water Mix for 10 min. and hold at 110 F.
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Secondary Mixer Add 30 gal. water and heat to 90 F.

Add 3.4 lb. 10 mol borax ~--Add 100 lb. unmodified corn starch Add primary to secondary over a period of 30 min. `
and hold at 110 F.
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Adjust viscosity to 60 sec. with 4.5 gal. water ~ ;

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Double Backer Formula According ~ ;o~
Primary Mixer Add 10.0 gal. water Add 19.0 lb. unmodified corn starch Heat to 150 F.
Add 3.9 lb. NaOH disso~ved in 2.0 gal. water Agitate for 15 min.
Add 10.0 gal. cooling wat~r and hold at 110 F.

Secondary Mixer Add 30.0 gal. water and heat to 90 F. `~
Add 1.5 lb. 10 mol borax Add 100 lb. starch acetate succinate (0.027 D.S.
acetate, 0.01 D.S. succinate).
Add primary to secondary over a period of 30 min.
and hold at 110 F.
Mix 5 min. and add 1.5 lb. 10 mol borax Add 4.5 gal. water to adjust viscosity in 60 sec.
The adhesive properties of these formulations were determined to be as indicated below.
' Double Backer Adhesive Properties ;~
Stein-Hall Temp.
% SolidsViscosity Sec. ~F.
Conventional l9ol 65 110 Acetate/Succinate 20.0 45 110 i Both of ~hese adhesive formulations were evaluated, successively, on the same corrugating machine.

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Using the control adhesive above, the maxim~ speed obtainable on the corrugating machine, before the corrugated board began to dela~inate at the cutting knife, was 450 fpm.

Using the starch acetate succinate as the raw starch portion of the Stein-Hall double backer adhesive formulation, speeds of 600 feet per minute were achieved. At this point, the glue clearance on the double backer ;~
applicator was increased from 0.014 inches to 0.01~ inches and the corrugating machine was run at 700 feet per minute, or 55% better than the control, with excellent double backer green strength. Above this speed the single facer corrugating machine, which was supplying the single face corrugated paper to the double backer, would not keep up due to the fact that the adhesive formulation being used in the single facer stage was a typical conventional unmodified starch adhesive and not enough heat could be applied by the machine to cause sufficiently rapid gelatinization of that adhesive.

However, with the single facer bridge full of board made at lower machine speeds,the double backer section could be run in brief spurts at speeds well over 800 feet per minute. The limitation on these spurts occurred when unbonded single facer sheets would reach the double backer glue machine. It is apparent, therefore, that the starch acetate succinate adhesive will produce good double backer corrugated board at corrugator speeds considerably in excess of 700 feet per minute.

EXAMPLE II
Corrugated Board Production Runs A further test of corrugating was conducted using the same corrugating = chine, and substantially the same operating conditions, as for the runs in . :
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Example I. The machine was used for making board using 42 pound liners and a 26 pound corrugated medium, with glue clearances of 0.013 inches and 0.014 inches.

The starch derivative used as the primary adhesive component was characterized as follows. It was a starch acetate succinate having a D.S.
acetate = 0.011; D.S. succinate = 0.015. It was found that an adhesive formu-lation made up as described below could be run successfully at quite high machine speeds. The formulation was as follows~

Primary Water 50 gal.
10 - I Unmodified corn starch 90 lbs.
Caustic Soda (dissolved in 5 gals. water)20 lbs.
Heat to 160 F. and hold 15 minutes , Water 33 gals. ;~
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Secondary : Water 200 gals.
Borax (lO mol) 9 lbs.
Starch Acetate ; 20 Succinate 500 lbs.
Add the primary over a - period of 30 min.
Add additional Borax (10 mol) 5 lbs.

With the glue settings set a 0.013 inches, the corn~gator could be run'efficiently at 700 feet per minute. Decreasing the glue clearances to 0.009 inches allowed the attainment of sustained corrugator speeds of over ~;~
800 fpm. At this point the corrugating machine had reached its practical limit and 62 pound liners were then substituted for the 42 pound liners.

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~3 ' With the heavier liner, the corrugating machine effic:iently produced cor~ Lcd board at specds of 650 fpm. at a setting of 350 F. on the corrugator hot plates. Conventional starch adhesives have a limit of 300~500 fpm. at ~00 F. and 350-400 fpm at 350 F. hot plate temperatures when using these liners on this machine. Corrugating efficiency was dramatica~ly superior, using the formulations of the invention.
EXAMPLE III ~;
Additional Production Runs; Stein-Hall Formulations Additional runs were made on the same machine in accordance with the last-mentioned procedure of Example II using 62 pound liners with primary ad-hesive components characterized as follows:

~ Starch Derivative Starch acetate succinate (D.S. acetate = 0.013;
D.S. succinate = 0.016).

Starch acetate succinate (D.S. acetate = 0.018;
D.S. succinate = 0.014) The starch derivative identified as (a) was prepared in an adhesive formulation as described in Example II, and used on a corrugating machine with glue clearances of 0.007 inches with the hot plate set at 300 F. Initially machine speeds of 600 fpm were attained. As the glue clearance was opened up to 0.010 inches, machine speeds of up to 750 fpm were achieved. When the hot plate temperatures were raised to 350 F., machine speeds of 775 fpm were attained, with satisfactory board production. ~-.

When an adhesive formulation as described in Example II, incorporating the starch derivative identified above as (b), was run on the corrugating machine with the glue clearances at 0.007 inches, and the hot plates set at 350 F., corrugated board was made successfully at 800 fpm.

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~XAMPL~ IV
No-Carrier Type Formulation ~ small-scale demonstration was conducted with an adhesive formulation (IV-l) containing 18-20~ of starch acetate succinate (D.S. aceta~e 0.0266;
D.S. succinate 0.018) as the primary adhesive component, in an aqueous slurry.
This is equivalent, in composition, to a conventional ll-bag mix in a mill (i.e., equivalent to a formulation containing 11 bags of the adhesive component in approximately 650 gallons of total adhesive).

A second demonstration was conducted with an adhesive formulation (IV-2) made of a mixture of unmodified corn starch and the primary adhesive component, in such proportions that on a mill scale, 2 of the 11 bags (i.e., about 18%) would be unmodified corn starch, the remainder being the primary adhesive component.

Stein-Hall VlSCoSity measurements were made on each of these formu-lations after they were made up ready for use. The make-up procedure was that described in U. S. 3,355,307, and was as follows. 250 g of starch material was slurried in 890 ml of water at 105 F. 275 ml of 4.0~ sodium hydroxide (caustic) was added to the starch slurry at room temperature over a period of 4.5 min. The reaction was then stopped at 600 cps. with 4.7g boric acid. The resulting paste consisted in each case of a substantially homogeneous suspension of partially swollen granules `~
The Stein-Hall viscosity observations were made at once9 and then after each formulation had been stored for 24 hours, at 100 F. with mild ag~tation. Viscosities were similar to those for typical conventional formu-lations.

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g ~ .

Viscosities o[ l~lo-Carrier ~dllesive FormulLItions IV-l IV-2Typical conventional f o rmu la tio n Steil~-Hall Viscosity seconds after makeup 21 20 21 after overnight storage 20 20 20 EXAMPL~ V

An adhesive composition having the following formulation was prepared.

Primary Mixer Water 100 gal.
Unmodified corn gtarch 220 lb.
NaOII (dissolved in lO gal.) 40 lb.
Heat to 160 F and hold 15 min.
Water 66 gal. ~-~
Secondary Mixer ~. :
Water 380 gal. -Borax (lO mol) 18 lb.
Starch acetate succinate lOOO lb. ~- -Drop primary over 30 minutes -Water 20 gal.
Borax (lO mol) lO lb.

This composition was run on a eommereial machine using a 90 lb. liner ;~
on the single faee side and two 90 lb. liners laminated on the machine on the ~ ;

double backer side. Good bonding was observed at speeds of 320 fpm. Conventional adhesives ean normally be run at about 200-250 fpm under the same test eonditions.
' The same eomposition was used as a laminating adhesive with satisfaetory results. However, no numerical data was obtained as this particular machine was abl~ to operate at its top speed when using either a conventional formulation or a formulation in aceordanee with this invention.

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EXAMPL.E VI

Another batch of adhesive was prepared using the same starch acetate succinate as in ~xample V. The amount of carrier starch was 210 lbs; Lhe remainder of the formulation identical to that of Example V. Using the identical 90, 90/90 laminate, liners as in Example V, speeds of 420 fpm were achieved. A
further run was made where the double backer liner consisted of a 90 ib. liner laminated on the machine using this adhesive formulation to a 69 lb. liner.
Speeds of 410 fpm. were obtained. The average speeds for both of these grades of board was 200 fpm. using conventional adhesives. The machine speed was not limited in these two cases by glue line failure, but by the possibility of drive overload at higher speeds.

~ EXAMPLE VII

To a slurry of 24O6g of unmodified corn starch in 330 ml water, 25 ml of a 2.75% (wt/vo]) borax xolution, 45 ml of 3.09% (wt/vol) NaOH and a mixture of ~.018 mole of succinic anhydride and 0.048 mole of acetic anhydride were added. -A laboratory evaluation of the resulting slurry indicated it to have superior adhesive properties.

EXAMPLE VIII ~;

Example VII was repeated except that the succinic anhydride was re-placed by adipic anhydride. The product was again evaluated as being a superior corrugating adhesive.

. EXAMPLE IX

Commercial runs were made on a series of products using the following formulations.

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~6~

Primary Mixer ;

Water 50 gal.
Unmodified corn starch100 lb~s.
NaOII 17 lbs.
Heat to 160 F. and hold 15 min.
Water 33 gal.
Secondary Mixer Water 200 gal.
Borax (10 mol) 17 lbs.
Test starch 500 lbs.
Drop primary over 30 min.
When using the ester materials, the NaOH was increased to 20 lbs. and ~ ' the borax to 18 lbs.
,~:

The~ formulations were run using 60 lb. liners with glue settings of 0.020" on the single facer and 0.018" on the double backer.

Run Machine speed~ fpm ~;
1. Unmodified corn starch ~ 425 2. Starch acetate succinate (D5 0.016~ 525 3. Starch acetate succinate (DS 0.024) 575 4. Starch acetate (DS 0.020) 625 ~ ; -EXAMPLE X

Instron force-time curves were produced foll3w~ng the standard method for the following starch materials.

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tS;C~

Heat Cycle Cool Cycle Material % Imp. % Imp. D.S.
acetate/succinate 40 78 .OIfi (a) acetate/succinate 53 98 .024 S acetate/succinate 62 95 .024 (b) acetate/succinate 74 134 .021 ::
acetate 55 113 .020 (c) acetate/succinate 71 163 .039 (d) acetate/succinate 88 170 .026 (e) acetate/succinate 22 75 .024 (f) acetate/succinate 44 88 .028 (g) acetate/succinate 68 118 .026 (h) acetate/succinate 79 122 .023 (i) `~

; ' (a) This is material from Example IX, Run 2. :~ ;
(b) This is material from Example IX, Run 3.
(c) This is material from Example IX, Run 4.
(d~ This is material from Example I. -(e) This is material from Example V.
(f) This product showed only 13% machine speed improvement. ~ :
-~g) This is material from Example III, Run a.
(h) This is material from Example III, Run b.
(i) This product showed 38% machine speed improvement. ;

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t~
~X~MPLE X-L

Standard Instron force-time areas were determined for the follow-ing starch materials.

Heat Cycle Cool Cycle ~:
Material % Imp. % Imp. D.S.
Maleate 143 196 .037 Phthalate 138 64 .031 Proprionate 72 147 . .035 Butyrate 74 133 .041 10 Iso-butyrate 75 - 110 .036 Acetate 110 337 .102 :
Acetate 67 101 .033 Succinate 57 46 .014 Succinate 76 174 .044 15 Acetate 80 336 .080 Succinate 76 108 .024 acetate/succinate 86 228 .058 acetate/succinate 63 113 .029 acetate/~uccinate 27 25 .014 20 acetate/succinate 31 20 .009 Proprionate 40 42 .018 :~
ProFrionate 35 ;

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s~

EXAMPLE XXI

The material from Example I was saponified in the presence of NaOH and borax. It was then washed with water to remove the caustic, borax and salts~ A standard Instron force-time determination was made.
The material showed 58% heating cycle improvement and 82% cooling cycle improvement EXAMPLE XIII

Example XII was repeated using the material of Example ~. This showed 58% heating cycle improvement and 102% cooling cycle improvement. ;

When an acid neutralization step was introduced, no significant improvement compared with unmodified corn starch was shown.
". ,'`' ', While the starch acetate succinate, and the other specific primary adhesive components identified herein, produce superior results ` as compared to formulations based on unmodified corn starch and other 15 conventional materials, generally they may be used in making up -~
corrugating adheslve formulations in the same general malmer and in substantially the same proportions as conventional materials, such as unmodified corn starch, would be used. Generally, the primary adhesive components of this invention may be used to replace a portion, or preferably aIl, of the conventional prlmary adhesive components in both Stein-Hall type and no-carrier type adhesive formulations. Specific ~ variations in amounts of components and the addition of other components ; may be made in the formulations using these primary adhesive components :
, . - 32 -.~3ti,3t7~

in the same manner as are made for conventional adhesive formu-lations. Thesevariations are wel:L known to those 8killed in the art.
The details of the Stein-Hall type adhesive system may be found in the aforementioned U.S. Patent Nos. 2,051,02S
and 2,102,937. The details of no-carrier type adhesive ~ystems may be found in the disclosure of U.S. Patent No. 3,355,307.
When utilizing the novel compositions in a no-carrier environment, reaction stoppers such as acid anhydrides and acid chlorides may be used. These may be broadly defined as acid or acid producing materials. Careful selection of the reaction stopper may thus allow the same material to serve as reaction stopper and ester-~li ifying reagent.
It is, of course, necessary that the final bond ; strength, ascontrasted with the green bond strength be suffi-ciently high to permit all conventional use of the product.
Pin adhesion tests have shown that the final bond strength~
using the adhesive formulations of this invention are sub-stantially equal to bond strengths of conventional adhesives.
~ The adhesive formulations of this invention are also useful in applications other than producing corrugated paper~
board. For example, these formulations can find application in tube winding and manufacturing laminated board and multiwall `
. . ~
paper sacks.
In addition, the conventional additives which will ;~
impart water-resistance to the cured bonds may also be incorpor-ated into the formulation.

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l~hile the invention has been described in connection with specific embodiments thereof, it will be unclerstood that it is capable of further modification, and this application is intended to covcr other variations, uses, or adaptions of the invention following, in general, the principles of the invention and including such departures from the present disclosure as are within known or customary practice in the art -to ~hich the invention pertains and as may be applied to the essential features hereinbefore set forth, and as are within the scope of the invention.
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Claims (12)

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

1. A method for the in situ preparation of a composition suitable for use in a corrugating machine, that permits operation of the corrugating machine at speeds of operation at least about 20% higher than those obtainable using unmodified corn starch as the primary active component in the composition, comprising the steps of:
a) forming an aqueous slurry of an unmodified granular starch material;
b) introducing under alkaline conditions, into said slurry, i) a reagent capable of forming a saponifiable ester with said starch material, and ii) a quantity of alkali sufficient to substantially completely saponify said saponifiable ester, to destroy any unreacted reagent and to neutralize any acid formed, to form a reaction mixture, and, c) admixing the reaction mixture with an aqueous slurry of a carrier material.

2. A method in accordance with claim 1, wherein said unmodified, granular starch material is an unmodified, granular corn starch material.

3. A method in accordance with claim 1, wherein said aqueous slurry of granular starch material includes from about 10% to about 25% starch material, commercial basis, based on the total weight of the composition.

4. A method in accordance with claim 1, wherein said aqueous slurry of granular starch material is heated to a temperature of up to about 125°F.

5. A method in accordance with claim 1, wherein said reagent is utilized in a quantity sufficient to form a saponifiable D.S. of at least about 0.015 on said unmodified starch material.

6. A method in accordance with claim 1, wherein said reagent is selected from the group consisting of carboxylic acid anhydrides, carboxylic acid halides, vinyl esters and mixtures thereof.

7. A method in accordance with claim 6, wherein said reagent is selected from the group consisting of acetic anhydride, succinic anhydride and mixtures thereof.

8. A method in accordance with claim 1, wherein said alkali is sodium hydroxide.

9. A method in accordance with claim 1, wherein said carrier material comprises a gelatinized starch material.

10. A method in accordance with claim 9, wherein the quantity of gelatinized starch material utilized is in the range of from about 12% to about 25%, based on the total weight of starch, commercial basis.

11. A method in accordance with claim 1, and further includ-ing the step of introducing up to about 5% additional alkali and up to about 5% borax, based on total weight of starch, commercial basis, into at least one of: the reaction mixture, the aqueous slurry of carrier material, or the admixture thereof.

12. A method for the in situ preparation of a composition suitable for use in a corrugating machine, that permits operation of the corrugating machine at speeds of operation at least about 20% higher than those obtainable using unmodified corn starch as the primary active component in the composition, comprising:
forming under alkaline conditions an aqueous slurry of unmodified, granular starch material, a carrier material, a reagent capable of forming a saponifiable ester with said starch material, and a quantity of alkali sufficient to substantially completely saponify said saponifiable ester, to destroy any unreacted reagent and to neutralize any acid formed.