Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-06-12
2001-10-09
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S052000, C524S503000
Reexamination Certificate
active
06300393
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to insolubilizing agents for binders in paper coatings and paper surface sizes.
BACKGROUND OF THE INVENTION
Paper coating compositions are generally fluid aqueous suspensions of one or more pigments, such as kaolin, titanium dioxide, calcium carbonate, or alumina; and one or more pigment binder materials derived from starch, protein, or synthetic polymers. Insolubilizing agents for the pigment binders are used to reduce the water sensitivity of the binders and improve the surface strength of the coated sheet, qualities necessary to allow the use of aqueous inks and allow the paper to withstand the mechanical stresses of printing.
Paper sizing compositions are used to improve the water and oil resistance and printability of the paper to which they are applied. They are applied by either of two methods; (1) They can be added to the pulp or furnish immediately prior to the formation of the sheet. This is commonly called “wet end” or “internal” sizing. Internal sizes can be rosin based, often used in combination with alum, alkyl ketene dimer compositions, or alkenyl succinic anhydride compositions. (2) They can be applied in a separate size press or surface coating operation after the sheet has been formed and dried. The insolubilizing agents of this invention are applicable to sizing compositions which are applied by the second method, in a size press or surface coating operation. The sizing compositions applied in this manner are commonly starches or synthetic polymers. The use of insolubilizing agents for these sizing compositions decreases their water sensitivity and improves the printability of the paper produced. For the purposes of this patent, paper sizing compositions applied in a size press or surface coating operation (method 2) will be referred to as “paper coatings” to distinguish them from internal sizing compositions.
A number of insolubilizing agents are commercially available and have been used to insolubilize binding materials in paper coatings and paper surface coatings. Formaldehyde has been used in the past but is no longer widely used due to highly restrictive environmental laws that limit vapor concentrations of formaldehyde to extremely low levels. It is quite effective as an insolubilizer with protein binders but is not as effective with starch and synthetic polymers at the alkane pH values in paper coatings.
Glyoxal does not have the severe environmental restrictions of formaldehyde and is effective with synthetic polymers and starch as well as with protein. However, the addition of glyoxal tends to undesirably increase the viscosity of the coating compositions, which renders the coatings difficult to apply on modern high speed paper making machinery. The use of glyoxal can also cause discoloration of the coating compositions and the papers to which they are applied.
At one time urea formaldehyde and melamine formaldehyde resins were the predominant insolubilizers in the paper industry, and melaminue formaldehyde resins and particularly the alkylated resins are still widely used. However, the resins contain up to about 1% free formaldehyde and can evolve formaldehyde vapors in the drying and curing operations and thus their use requires strict environmental controls. Also, an acid catalyst may be required to effect the cure. In addition they do not cure rapidly and may require an aging period before a complete cure is effected.
Modified glyoxal resins have come into wide use most recently. They do not release formaldehyde vapors, they do not require a catalyst, and the paper is cured immediately on drying. These resins are highly reactive and tend to crosslink and precipitate in concentrated solutions containing more than about 10 percent by weight resin material. Thus they are difficult to manufacture in a stable concentrated form, and a compromise is necessary between the degree of dilution of the agents and the expected shelf life.
Metal salts can also be used as insolubilizers. The most commonly used is ammonium zirconium carbonate, primarily for protein coatings. These products are quite unstable to heaing, dilution, and pH changes. They also give off an undesirable ammonia odor on curing.
Maleic anhydride copolymer derivatives are used extensively in the manufacture of paper, usually as surface coating agents. To prepare them for use in this application, the maleic anhydride copolymers are either neutralized by the addition of basic materials to form salt solutions, or they are modified by esterification or amide formation prior to their addition to or use as coating compositions. The anhydride moieties are destroyed by these treatments and are no longer available to react with and insolubilize the binders and coatings used in these formulations.
A further requirement for reagents to be used in paper manufacture is that they be nontoxic so that the paper products manufactured can be used for packaging foods without introducing harmful substances.
It would be desirable to have effective insolubilizing agents for paper coatings which do not have adverse toxicity or environmental effects, do not cause undesirable color formation in the paper, do not increase the viscosity of the paper coatings to which they are added, and can be marketed as shelf stable compositions with high levels of reactive functionality.
Objects of the Invention:
The primary object of this invention is the provision of effective insolubilizing agents for paper coatings.
Another object is the provision of insolubilizing agents for paper coatings that do not contain aldehydes.
Another object is the provision of insolubilizng agents for paper coatings that do not increase the viscosity of the paper coating suspension.
Another object is the provision of insolubilizing agents for paper coatings that can be marketed in shelf stable formulations with a high content of reactive functionality.
A further object is the provision of insolubilizing agents for paper coatings that do not present environmental hazards in use and are not toxic and so that they can be used in paper products that come in contact with food.
SUMMARY OF THE INVENTION
These and other objectives are achieved by the provision of insolubilizing agents for starch, protein, synthetic polymers, and modifications thereon which are used as pigment binders and surface coatings in paper manufacture. The insolubilizing agents are polymers or other compounds containing a plurality of carboxylic acid anhydride moieties per molecular entity. The pigment binders and surface coatings useful in this invention contain functional groups capable of reacting with carboxylic acid anhydride moieties to form chemical bonds. The anhydride moieties do not substantially hydrolyze or otherwise react until the paper coating is applied to the paper and dried and cured, at which time the anhydride moieties react with the functional groups, which usually contain “active” or labile hydrogen functionality, on the starch, protein, or synthetic polymer binder or coating agent, and render the binder or coating agent water insoluble.
Another aspect of the invention is the provision of a method to improve the water resistance and printability of coated paper. The method consists of adding polymers or other compounds containing a plurality of carboxylic acid anhydride moieties to paper coating compositions containing natural or synthetic polymers with functional groups reactive with the anhydride moieties. The coating compositions are applied to paper products and cured. In the curing step of the method, usually accomplished by heating the coated paper, the anhydride moieties of the insolubilizing agent react with the reactive functional groups of the polymers in the coating compositions and render them water insoluble.
A further aspect of the invention is the provision of paper compositions wherein paper bases are coated with paper coating compositions containing pigment binders and coatings which are insolubilized with the carboxylic acid anhydride containing agents of this invention.
DESCRIPTION OF THE PREFERR
Hudson Alice P.
Nevin James E.
LandOfFree
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