Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
1999-04-05
2002-04-30
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S205200, C106S205720, C106S206100, C106S210100, C106S215500
Reexamination Certificate
active
06379447
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to selected polysaccharide laminating or bonding adhesives having high bond strength and low bleed properties and which are useful in multi-ply, light weight paper products.
The use of paper, particularly light weight paper in articles such as tissue or towels is well known. In order to add and improve properties such as absorbency, bulk, smoothness, drape and hand (feel), these products are often fabricated in multi layers, i.e., multi-ply articles. In the end use of these multi-ply articles and in converting steps such as slitting, rewinding, folding and printing, it is desirable that the plies remain in register and not slip in relation to each other. This is accomplished by bonding the plies and is conventionally done by mechanical means such as embossing or through the use of an adhesive.
Mechanical means of bonding multi-ply articles by embossing through all plies in bands near the article's edge or in partial coverage patterns distributed across the surface is often used. However, such means generally provide low bond strength.
Adhesives have also been used to provide bonds for multi-ply articles. They are generally applied at low solids (typically less than 10% by weight) and depending on the articles being made, either by non-contact methods such as spraying or by contact methods using transfer rolls. While various adhesive materials such as cellulose, polyvinyl alcohol and starch have been used in these applications, depending on the particular composition they often have one or more problems such as bleed, low strength or application difficulties (e.g., slow fabrication speeds and slow bond development) due to low solids content.
Illustrative preparation of multi-ply paper products is disclosed in WO 96/24485 published on Aug. 15, 1996 to T. Rydell et al. This patent publication discloses the use of various adhesives such as silicates, glue, starch adhesives, cellulose and polyvinyl alcohol and utilizes the high bleed, strike through characteristics of these materials in preparing mutli-ply paper laminates.
Another disclosure of preparing multi-ply paper products is found in U.S. Pat. No. 3,673,060 issued Jun. 27, 1972 to J. Murphy et al. This patent discloses the combination of embossing means plus the use of an adhesive such as polyvinyl alcohol to prepare laminated napkins.
Despite the well known use of different adhesives in preparing multi-ply paper products as illustrated above, there is still the need for new adhesive materials which can provide high strength, low bleed characteristics and are readily applicable in different application techniques.
SUMMARY OF THE INVENTION
It has now been found that selected high solids, polysaccharide based aqueous adhesives that provide high bond strength and low bleed properties and also are repulpable, have other properties that makes them particularly useful in the preparation of multi-ply light weight paper products.
More particularly, this invention involves an aqueous, high-solids, polysaccharide based adhesive composition comprising a continuous aqueous phase of from about 15 to 50% by weight of starch/dextrin material or blend thereof dispersed in water, the continuous phase starch/dextrin or blend having:
a) a zero-shear viscosity of greater than 0.07 Pa·s when measured at 26% (+/−1%) solids, 120° F. (49° C.) and a shear rate of 0.1s
−1
,
b) a shear thinning index of 0.9 to 1.1 and
c) a bleed time of greater than 15 seconds.
This invention further involves an adhesive composition comprising the continuous phase starch/dextrin dispersed aqueous component described above, as well as a second component comprising a water swellable, insoluble polysaccharide particulate phase, the adhesive composition having a bleed time of greater than 70 seconds when measured at 19% (+/−1%) solids at 120° F. (49° C.).
This invention further involves a continuous phase polysaccharide adhesive composition, particularly for contact applications, comprising a starch/dextrin material wherein the continuous phase has a zero-shear viscosity of greater than 0.05 Pa·s measured at 26% (+/−1%) solids, 120° F. (49° C.) and a shear rate of 0.1s
−1
and a bleed time of greater than 7 seconds.
DETAILED DESCRIPTION OF THE INVENTION
This invention is directed to adhesives used in the fabrication of multi-ply light weight paper products. Such products include tissue and towels such as facial tissue, toilet or sanitary tissue, napkins, paper towels as well as embossed towels. The term “paper” as used herein refers to products made from cellulosic fibers in a wet end or wet laid process. This includes pulp or paper derived from wood pulp, sulfate or sulfite pulp. The light weight paper products as described herein are typically made using paper of less than about 30 lb/3300 ft
2
.
The methods of applying adhesive for use in the manufacture of multi-ply paper products are well known. Typically, they involve a non-contact method where the adhesive is applied by spraying or atomization or a contact method where the adhesive is transferred from a roll in contact with the inner surface of a web. The spray, non-contact method is particularly useful in the preparation of tissue products while the contact transfer method is predominantly used in the preparation of paper towels where embossing is often employed. The adhesive that is used in preparing multi-ply paper products will depend on the particular application and the conditions used. The polysaccharide based adhesive composition of this invention can be used or varied and adapted so that it can be used in either non-contact or contact applications as further described herein.
The base polysaccharide material used in the continuous phase of the adhesive of this invention is characterized by specific rheological properties. The polysaccharide may comprise a starch or dextrin or a blend of starch and dextrin. The polysaccharide may comprise a starch derived from any plant source including corn, potato, wheat, rice, tapioca, waxy maize, waxy rice, sago, sorgum, high amylose starch such as high amylose corn, etc. Also include are the conversion product derived from any of the former bases including, for example, dextrins prepared by the hydrolytic action of acid and/or heat such as maltodextrin and pyrodextrin; oxidized starches prepared by treatment with oxidants such as sodium hypochlorite; fluidity or thin-boiling starches prepared by enzyme conversion or mild acid hydrolyses; derivatized starches such as starch ethers and esters and physically modified starches. The polysaccharide component may also include water soluble gums to help the composition satisfy desired properties such as solids content, Theological and bleed properties.
The aqueous dispersed continuous phase must satisfy certain rheological properties including a zero-shear viscosity and shear-thinning index as well as providing selected bleed requirements. Typical polymeric solutions, such as the aqueous dispersed-continuous phase types described herein, can show a viscosity that is dependent on rate, i.e., the resistance to deformation (viscosity) is a function of the deformation rate (shear rate). It is well known in the rheology literature that the viscosity of these materials approach a constant value at low shear rates called “zero-shear viscosity”. The test procedure for determining the zero-shear viscosity is described below. The starch-dextrin dispersed phase as used in this invention will have a zero-shear viscosity of greater than 0.07Pa·s when measured at 26% (+/−1%) solids, 120° F. (49° C.) and a shear rate of 0.1s
−1
. Preferably the zero-shear viscosity will be greater than 0.1 Pa·s.
The other rheological property for the aqueous dispersed, continuous phase component is known as the “shear-thinning index” (n′). The shear-thinning index is a measure of the reduction in viscosity across a defined deformation rate change. The test procedure for determining the shear-thinning index is also described below. The
Eden James L.
Solarek Daniel B.
Weisser Eric M.
Brunsman David
Duncan, Esq. Laurelee
National Starch and Chemical Investment Holding Corporation
Zagarella, Esq. Eugene
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