Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
1999-04-06
2001-01-30
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S211100, C106S215400, C106S215500, C428S154000, C156S210000, C156S291000, C435S099000, C435S101000
Reexamination Certificate
active
06179905
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is drawn to an adhesive composition that is useful for preparing corrugated board, a method for preparing corrugated adhesive, and a corrugated board constructed therewith.
BACKGROUND OF THE INVENTION
Corrugated board is typically prepared by a process known as the Stein-Hall process. As is generally described in U.S. Pat. No. 2,102,937 (issued to J. V. Bauer), 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 that are used in conjunction with the Stein-Hall process long have been known, and such adhesives generally comprise an aqueous emulsion of raw starch; caustic; pasted modified or unmodified starch; and a cross-linking agent. The raw starch serves as a binder in the finished corrugated board, while the pasted starch and cross-linking agent form a tacky composition that holds the plural layers of green corrugated board together before the primary starch adhesive has set. The cross-linking of the pasted starch is further thought to impart suspending power and to affect the viscosity of the corrugating adhesive during storage and application.
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.
It is believed that the Theological instability of conventional corrugating adhesives can be attributed to the exclusive reliance of the adhesive composition on pasted starch to provide tack in the green state. Recent prior art has taught to replace a portion or all of the pasted starch in the corrugating adhesive with hemicellulose, a plant derivative obtained from a hemicellulose-containing plant source such as corn hulls. For example, U.S. Pat. Nos. 5,358,559 and 5,503,668 each purport to provide a corrugating adhesive composed of starch and hemicellulose, the hemicellulose being derived from corn hulls. Similarly, U.S. Pat. No. 5,777,005 purportedly provides a corrugated starch based on a combination of corn hulls and tapioca fiber. Each of these patents teaches to blend corn hulls with starch and to extract hemicellulose in-situ from the corn hulls to provide a hemicellulose-based adhesive composition.
While such recent art purports to provide hemicellulose-containing corrugating adhesives, these adhesives are unsatisfactory in some respects. For example, the rate of increase of tack of these adhesives when in green state is unsatisfactory, thus potentially leading to delamination problems if the corrugating operation is run at too high a speed. Thus, while the rheological stability of such corrugating adhesives may be improved as compared with those of corrugating adhesives based on pasted starches, these adhesives still are of limited value in increasing the rate of production of corrugated board.
An improved hemicellulose-based adhesive, and relative advantages thereof as compared with known adhesives, are described in copending U.S. patent application Ser. No. 09/182,918, filed Oct. 30, 1998, and assigned to Grain Processing Corporation of Muscatine, Iowa. As disclosed therein, hemicellulose is obtained from the soluble phase of an extract obtained from hydrolysis of a hemicellulose-containing plant source. The hemicellulose-containing soluble phase is separated from insoluble portions of the extract and is blended with starch to form an adhesive composition. The improved hemicellulose-based adhesive described in U.S. Pat. No. 6,063,178 has significant advantages over known hemicellulose-based adhesives, such as improved green tack properties. Despite these advantages, however, even these soluble phase hemicellulose-based adhesives exhibit somewhat higher water-retention properties than is sometimes desired (albeit to a lesser degree than known hemicellulose-based adhesives). High water retention slows the rate of increase of tackiness when the corrugated board is in the green state, and thereby limits the rate of manufacture of the corrugated board.
In view of the foregoing, there exists a need in the art for a hemicellulose-based corrugating adhesive that has improved green tack property and reduced water-retention relative to conventional corrugating adhesives. The present invention provides such an adhesive. These and other advantages will be apparent from description of the inventions provided herein.
THE INVENTION
It has now been found that partially depolymerized hemicellulose may be blended with a starch to form an adhesive composition that has excellent green tack and dewatering properties. For example, the soluble phase of an extract from a hemicellulose-containing plant source in which at least a portion of the hemicellulose is partially depolymerized may be mixed with starch and optionally one or more other components to form an adhesive composition with surprisingly superior properties. The partially depolymerized hemicellulose used in the composition and method of the present invention preferably is derived from a hemicellulose-containing plant source via hydrolysis. The soluble phase is separated from other insoluble portions, is partially depolymerized, and is blended with starch to form an adhesive composition.
The adhesive composition of the present invention has superior green tack properties as compared with known adhesive compositions that rely exclusively on pasted starch for tack in the green state. Moreover, when the adhesive is in the green state in a corrugated board, the tack of the adhesive will be surprisingly improved as compared with other hemicellulose-based adhesives. The adhesive composition of the present invention exhibits superior dewatering (reduced water retention) properties over known hemicellulose-based adhesives, and even over the relatively improved hemicellulose-based adhesive described in U.S. Pat. No. 6,063,178. A higher corrugating speed is thereby made possible using the adhesive composition of the present invention. The rheological properties of the adhesive composition are surprisingly stable, and the adhesive will provide a strong adhesive bond in a corrugated board product.
In accordance with a preferred embodiment of the invention, a hemicellulose-containing plant source is substantially separated into a soluble phase and an insoluble phase. At least a portion of the hemicellulose from the soluble phase is then partially depolymerized (e.g. via chemical or enzymatic methods). The partially depolymerized hemicellulose includes or is mixed with a liquid carrier, and is mixed with starch to form a corrugating adhesive composition. The invention also encompasses a method for preparing a corrugating adhesive, a corrugated board made with the adhesive of the invention, and a method for prepar
Antrim Richard L.
McPherson Roger
Schmidt Arthur G.
Brunsman David
Grain Processing Corporation
Leydig , Voit & Mayer, Ltd.
LandOfFree
Corrugation adhesive, corrugated board, and preparation... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Corrugation adhesive, corrugated board, and preparation..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Corrugation adhesive, corrugated board, and preparation... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2555426