Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
2000-10-25
2003-11-18
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S210100, C106S213100, C106S214100, C106S214200, C524S047000
Reexamination Certificate
active
06648955
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an adhesive. In particular, the invention relates to a corrugating adhesive and to corrugated products constructed with the adhesive.
BACKGROUND OF THE INVENTION
Corrugated board conventionally is prepared by a process known as the Stein-Hall process. As is generally described in U.S. Pat. No. 2,102,937, the Stein-Hall process employs a corrugating adhesive to bond a corrugated paper “medium” such as a roll or strip, to a liner board on one or both sides of the corrugated medium.
Adhesives used in conjunction with the Stein-Hall process are traditionally alkaline adhesives comprised of ungelatinized raw starch suspended in an aqueous dispersion of cooked starch (carrier). The adhesive is produced by gelatinizing starch in water with sodium hydroxide (caustic soda) to yield a primary mix of gelatinized or cooked carrier, which is then slowly added to a secondary mix of raw (ungelatinized) starch, borax and water to produce the fully formulated adhesive. In the corrugating process, the adhesive is applied (usually at between 25° C. and 55° C.) to the tips of the fluted paper medium or single-faced board, whereupon the application of heat causes the raw starch to gelatinize, resulting in an instantaneous increase in viscosity and tack and formation of the adhesive bond.
Known corrugating adhesives suffer from a number of drawbacks. For example, the speed of the machinery used to prepare the corrugated board sometimes is limited by the rheological properties of the adhesive. During manufacture of corrugated board, the corrugating adhesive typically is spread across the liner board or the corrugated paper medium with a spreader knife or metering roller. It has been observed that conventional adhesives undergo substantial shear thinning when they are spread too quickly, thus leading to problems in applying the adhesive to a corrugating medium in conventional corrugating equipment. The shear thinning thus may serve to limit the speed of the corrugating equipment, and thus may limit the attainable output of corrugated board.
Another drawback relates to the green bonding strength of conventional corrugating adhesives and, more specifically, to the rate at which the tack of the adhesive increases when the corrugated board is in the green state. Typically, corrugated board is processed and handled before the adhesive has fully dried, the adhesive thus being in the green state. If the adhesive has not become tacky quickly enough, then the corrugated board will delaminate during the processing operations that follow the bonding operation. The rate of increase of tackiness of known adhesives thus may be a further limiting factor in the rate of manufacture of corrugated board.
There continues to be a need in the industry for a corrugating adhesive that will allow the user to control the amount of adhesive applied, minimize the warpage of the final corrugated board and that will allow equipment to run faster and in a more efficient manner.
SUMMARY OF THE INVENTION
The invention provides a composition for producing a stable, consistent aqueous starch-based corrugating adhesive.
One aspect of the invention is directed to an adhesive composition comprising an aqueous solution of a starch, an alkali, and a surfactant. In one embodiment, the adhesive is a foamed adhesive.
Another aspect of the invention is directed to method of producing a corrugating adhesive comprising dispersing a carrier starch in aqueous alkali and borax, uniformly mixing in a raw starch, and adding a surfactant. The surfactant is preferably used at a level of from about 0.05 to about 10 percent actives by weight, based on the total adhesive weight. In the preparation of a foamed adhesive, the process further comprising applying energy to create the foam.
Yet another aspect of the invention is directed to corrugated paperboard constructed with the adhesives of the invention and articles comprising corrugated paperboard.
DETAILED DESCRIPTION OF THE INVENTION
The disclosures of all references cited herein are incorporated in their entireties by reference.
The invention provides corrugating adhesives and, in particular foamed corrugating adhesives.
Foamed adhesives show improved economics and performance over adhesives which are not foamed. Since foamed adhesives do not penetrate porous surfaces to the same extent as non-foamed adhesives, the open time increases and the tendency for pre-cure decreases. In addition, at any given film thickness, a foamed adhesive contains less water than an unfoamed adhesive. Less water in the adhesive leads to little or no warping of the paper substrate. Foamed adhesives also have the ability to hold out on a substrate surface to a greater extent than unfoamed adhesives, resulting in less applied adhesive affording faster machine speeds, faster cure rate and lower adhesive costs.
While methods have been proposed for foaming polymer adhesives, success has been demonstrated only with synthetic polymers. While many surfactants can produce foam, a significant and detrimental impact on the viscosity and flow properties of full formulation corrugating adhesives has been observed. Foamed starched-based adhesives tend to be unstable and dissipate within a few minutes. Starch-based (Stein-Hall) adhesives have the additional requirements of high pH and a heterogeneous system containing both dispersed and granular starch. These latter two requirements have made the task of providing a stable yet effect foamed corrugating adhesive very illusive.
It has now been discovered that surfactants that do not contain, either within the backbone or within a side chain thereof, propylene oxide or ethylene oxide moieties can solubilize ionic groups and are excellent foaming agents for corrugating adhesives. The adhesive of the invention has good foam stability, excellent adhesive properties and good flow characteristics.
The terms “adhesive” and “foamable adhesive,” as used to describe the adhesives of the invention, are used interchangeable herein. While the foamable adhesive is useful in the unfoamed state as a corrugating adhesive, the adhesive may also be foamed, e.g., by the application of energy, to provide a stable and effective foamed corrugating adhesive. Thus, both unfoamed and foamed corrugating adhesives are encompassed by the invention.
The term “corrugated paperboard” as used herein refers to a fluted medium and a facing glued to the tips on one or both sides of the fluted medium. The procedures employed in the production of corrugated paperboard usually involve a continuous process whereby a strip of paperboard is first corrugated by means of heated, fluted rolls. The protruding tips on one side of this fluted paperboard strip are then coated with an adhesive, and a flat sheet of paperboard, commonly known in the trade as a facing, is thereafter applied to these tips. By applying heat and pressure to the two paperboard strips thus brought together, an adhesive bond is formed there between. The above-described procedure produces what is known to those skilled in the art as a single-faced board in that the facing is applied to only one surface thereof. If a double-faced paperboard in which an inner fluted layer sandwiched between two facings is desired, a second operation is performed wherein the adhesive is applied to the exposed tips of the single-faced board and the adhesive-coated tips are then pressed against a second facing in the combining section of the corrugator under the influence of pressure and heat. The typical corrugating process and the operation and use of corrugators in general are described, e.g., in U.S. Pat. Nos. 2,051,025 and 2,102,937.
The foamable adhesive composition of the invention comprises a liquid carrier containing a starch, an alkali, and a surfactant. Each of these ingredients is required to provide the unique blend of adhesive and foam properties. The composition may also, optionally, contain a boron-containing compound.
The liquid carrier is preferably water, but may further also include any other components as may be known
Billmers Robert L.
Mwonya Patrick B.
Seaman Gordon W.
Swiezkowski Frank J.
Brunsman David
Foulke Cynthia L.
National Starch and Chemical Investment Holding Corporation
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