Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2002-11-05
2004-06-01
Fortuna, Jose A. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S166000, C162S158000, C162S168300, C162S164600, C162S179000
Reexamination Certificate
active
06743335
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in the making of cellulose-based products e.g. paper. More particularly, it relates to a way of reducing the level of malodorous amines emitted by paper. This is accomplished by making the paper so that it does not contain ammonium groups that are attached to a non-polymeric substance nor that are bonded to any polymer contained in the paper by only one chemical bond. Consequently, improved laminates comprised of this paper, optionally an adhesive, and a third material e.g. metal, wood or plastic, are also provided which emit reduced levels of amines. In a preferred embodiment, the paper is sized with a sizing emulsion comprised of a hydrophobic cellulose-sizing agent e.g. alkenyl succinic anhydride and a cationic water-soluble polymer having ammonium groups that are attached to the polymer by at least two chemical bonds.
BACKGROUND OF THE INVENTION
Paper is typically made with a wide range of additives, including starches, surfactants, synthetic polymers, pigments, fillers, and sizing agents. Many of these additives contain cationic groups, which are believed to render the additive substantive to anionic cellulosic fibers. Frequently these cationic groups are ammonium groups, i.e. quaternary or acid salts of amines. For instance, cationic polymeric emulsifying agents e.g. cationic starches, cationic synthetic polymers, etc. are widely used to help form and stabilize sizing emulsions, see e.g. U.S. Pat. Nos. 5,658,378; 4,657,946; and 4,606,773; which are hereby incorporated herein by reference. These sizing emulsions are widely used in papermaking to introduce sizing agents to the surface and interior of paper. These sizing emulsions typically contain a water-insoluble hydrophobic cellulose-sizing agent such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA) that is dispersed or emulsified in aqueous solution. For example, ASA is a well-known sizing agent that has achieved considerable commercial acceptance in recent years. Since ASA is water-insoluble, it is frequently emulsified in water with a cationic polymeric emulsifying agent to form an ASA sizing emulsion which is then added to the paper stock or applied to the paper web during the papermaking process. Other potential sources of ammonium groups in papermaking are emulsifying agents such as those described in e.g. U.S. Pat. No. 5,759,249 and cationic agents such as those described in e.g. U.S. Pat. No. 3,102,064.
However, there is an odor problem with many paper and paper products made therefrom that contain ammonium groups. For example, when an ammonium group-containing ASA sizing emulsion is used to size paper and a liquid adhesive having an alkaline pH is subsequently used to bond the sized paper to aluminum foil to form a laminate, the laminate may emit an unpleasant amine-type odor. This odor may present an environmental problem for the maker of the laminate. Although in many cases the amine odor dissipates when the laminate is exposed to air, in some cases dissipation of the odor is difficult because all or part of the laminate is not stored in a ventilated condition. For instance, if the sized paper is laminated with aluminum foil and the resultant laminate is subsequently enclosed in packaging which is poorly ventilated e.g., food packaging (e.g., gum wrapper, liner for sticks of butter or margarine), as a liner for cigarette package, urn bag, fast food wrapper, etc, the user may perceive an odor when the package is opened. From a consumer packaging point of view, this is extremely undesirable.
Since an amine-type odor emanating from the paper was a problem and since ammonium groups are often the only source of the cationicity in many of the additives used in papermaking, it has been theorized that these ammonium groups were the source of the amine odor. As a result, some papermakers have been reluctant to use certain ammonium group-containing cationic additives in papermaking, particularly where the paper was being made for consumer packaging or other unventilated applications. In some cases, this reluctance has been to the detriment of the papermaker, especially where the cationic additive would provide a benefit if it were not for the odor problem. For instance, some papermakers do not use ASA sizing emulsions, in spite of their numerous and well-known advantages over other sizing agents, to make paper destined for laminates in consumer packaging applications because these sizing emulsions typically contain cationic polymeric emulsifying agents e.g. starch or synthetic polymers. Methods for reducing odor in paper have been disclosed which involve heating the surface of the paper web, see e.g. U.S. Pat. No. 5,637,195, but these methods may be energy intensive and inconvenient for the papermaker. Replacement of the ammonium groups with other cationic groups e.g. sulfonium or phosponium groups tends to increase the expense of the additive and may present toxicity and/or environmental concerns. Therefore, there remains a problem in that many papermakers would prefer to use ammonium group-containing additives such as these typical ASA sizing emulsions, but have avoided doing so because of the belief that the ammonium groups would lead to amine odors that are unacceptable to the customer.
We have now discovered that the source of the odor problem is the presence in the paper of a particular type of ammonium group, not all ammonium groups as had been previously thought. In particular, we have discovered that the source of the problem is ammonium groups in which the nitrogen atoms are bonded to a non-polymeric substance or to polymer contained in the paper by only one chemical bond. The instant inventors have discovered that when the ammonium groups are bonded to a polymer contained in the paper by two or more chemical bonds, the odor problem is greatly reduced or eliminated.
SUMMARY OF THE INVENTION
The instant invention provides a solution to the amine odor problem discussed above by providing a method for reducing the level of alkyl amines emitted by paper, comprising (a) providing paper that contains ammonium groups and that is substantially free of (i) ammonium groups that are attached to a polymer contained in said paper by only one chemical bond, and (ii) ammonium groups that are attached to a non-polymeric substance, and (b) exposing said paper to a liquid having a pH of at least about 8. The emission of malodorous amine substances from the paper is greatly reduced or eliminated by the practice of the instant invention. The instant invention thus constitutes an effective and efficient solution to the odor problem.
In a preferred embodiment, the instant invention provides a solution to the amine odor problem discussed above by providing a method for sizing paper, comprising intermixing a sizing emulsion comprised of (i) alkenyl succinic anhydride, alkyl ketene dimer, or mixtures thereof, and (ii) a water-soluble polymer comprised of ammonium groups that are attached to said polymer by at least two chemical bonds, with a paper stock, or applying said sizing emulsion to a paper web, and forming paper from said paper web or said paper stock, wherein said sizing emulsion is used in an amount effective to size said paper, and wherein said paper, when contacted with a liquid having a pH of about 8 or greater, emits a lower level of alkyl amines than when said sizing emulsion is comprised of, instead of said (ii), the same amount of a water-soluble polymer comprised of ammonium groups that are attached to said polymer by only one chemical bond.
In another preferred embodiment, the instant invention provides a solution to the amine odor problem discussed above which allows the papermaker to use preferred sizing agents such as ASA, AKD, and mixtures thereof. Thus, the instant invention provides a laminate that does not emit alkyl amines, comprised of (i) paper, (ii) alkenyl succinic anhydride, alkyl ketene dimer, or mixtures thereof, and (iii) a film comprised of metal or plastic.
DETAILED DESCRIPTION
As used herein, “paper” is a general term t
Proverb Robert J.
Scanlon Michael J.
Akorli Godfried R.
Bayer Chemicals Corporation
Eyl Diderico van
Fortuna Jos'e A.
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