Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-11-15
2004-03-09
Fortuna, José A. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S168300, C162S179000, C162S109000, C162S169000, C162S158000
Reexamination Certificate
active
06702923
ABSTRACT:
The invention relates to a paper wet strength agent and a method for the production of such an agent. The invention further relates to the production of paper comprising addition of the paper wet strength agent to an aqueous cellulosic suspension and to paper comprising a paper wet strength agent. In addition, the invention relates to the use of a paper wet strength agent as an additive to an aqueous cellulosic suspension.
BACKGROUND OF THE INVENTION
In the papermaking art, wet strength agents like epichlorohydrin-based resins, for examples polyaminoamide epichlorohydrin resins have been used for a long time to enhance the strength of paper. Such resins are disclosed in U.S. Pat. No. 3,700,623 and U.S. Pat. No. 3,772,076. The wet strength of a paper relates to its ability to maintain physical integrity and to resist tearing, bursting, and shredding under use, especially under wet conditions. A further important property of wet strengthened paper is the softness, especially for tissue paper or the like. The softness can be described as the tactile sensation perceived when holding or rubbing a paper across the skin.
U.S. Pat. No. 5,200,036 discloses a wet strength agent which provides paper with enhanced wet strength. A cationic polyaminoamide epichlorohydrin resin is modified by introduction of a polymerisable unsaturated hydrocarbon moiety thus providing it with ethylenically unsaturated side-chain substituents. The resin is then added to latex-forming monomers whereby co-polymerisation occurs forming bonds between unsaturated polymerisable hydrocarbon moieties of the resin and the latex-forming monomers. The reaction may be assisted by addition of an emulsifier to obtain a desirable suspension of the formed latex particles. Resins of the above-mentioned types are also used as emulsifiers. Usually, the resins are not effective enough when used as a sole emulsifier and these are thus used in combination with an additional compound.
U.S. Pat. No. 5,314,721 discloses a process for preparation of vinyl polymer dispersions comprising resin based on a cationic polyaminoamide whose terminal groups have been substituted with long-chain aliphatic hydrocarbon radicals which have at least 7 carbon atoms and are derived from monocarboxylic acids. The product obtained is used as a sizing agent.
U.S. Pat. No. 4,416,729 discloses a method for preparing wet strength additives comprising the steps of contacting a linear polyamidoamide with an &agr;,&bgr;-ethylenically unsaturated carboxylic compound to form a substituted polyamidoamine, contacting the substituted polyamidoamine with a polaymine to form a branched polyamidoamine bearing a pendant amine moiety, and contacting the branched polyamidoamine with an epihalohydrin to form pendant curable ammonium moieties on the branched polyamidoamine U.S. Pat. No. 4,416,729 does not disclose use of the prepared wet strength additives for production of tissue paper.
Although the above epichlorohydrin-based resins in some applications show adequate wet strength and emulsifying properties, it would be desirable to be able to provide further and improved wet strength agents for paper and methods for providing such agents. It would also be desirable to be able to provide wet strength resins and agents exhibiting improved softness properties. Further, it would be desirable to be able to provide further resins having improved emulsifying properties.
SUMMARY OF THE INVENTION
According to the present invention, it has been found that further and improved wet strength agents for paper can be obtained by a composition containing polymeric particles and hydrophobic hydrocarbon groups providing side-chain substituents on wet strength resins. It has also been found a new method for the production of such wet strength resins and agents. It has further been discovered that the wet strength agents and resins produced by the method according to the present invention give paper improved softness properties without negatively affecting the absorbency properties.
DETAILED DESCRIPTION OF THE INVENTION
More specifically, the invention relates to paper wet strength agents comprising polymeric particles and wet strength resins comprising a cationic nitrogen-containing polymer having hydrophobic side-chain substituents. The invention further relates to a method for the production of a paper wet strength agent comprising a first step of reacting a nitrogen-containing polymer with a hydrophobic compound to provide a nitrogen-containing polymer with hydrophobic side-chain substituents, a second step of reacting the product obtained with a crosslinker to form a cationic wet strength resin, and a third step comprising emulsion polymerisation of one or more ethylenically unsaturated monomers in the presence of the wet strength resin formed. Further, the invention relates to a paper wet strength agent obtainable from the method above. The invention further relates to a new wet strength resin and a method for preparing a wet strength resin according to the two first steps as described herein. The invention also relates to the production of paper comprising addition of a paper wet strength resin or agent to a cellulosic suspension and to the use of a paper wet strength resin or agent for the production of paper. The invention also relates to paper comprising paper wet strength resins and agents. The invention is further defined in the appended claims.
The present invention provides resins and agents having the ability to impart improved wet strength properties to paper. The invention further provides a simple, convenient and effective synthetic route for the preparation of wet strength resins and agents. Thereby, the wet strength resins and agents of this invention can be prepared in high yield.
The present invention also provides wet strength resins and agents which make it possible to produce paper having enhanced softness properties. The softness of a paper sheet can be estimated by means of the relative wet strength value, which is defined as the ratio between the wet tensile index and the dry tensile index according to the formula RWS (in %)=(WS/DS)·100, where RWS stands for the relative wet strength, WS is the wet tensile index and DS is the dry tensile index of paper. RWS is hence a measure of the softness of a paper; the higher the RWS, the higher the softness of the paper. The present wet strength resins and agents also provide improved emulsifying properties and can be used as sole emulsifiers without additional compounds which may give rise to undesirable foam formation.
The term “wet strength agent”, as used herein, refers to an agent capable of imparting better wet strength properties to paper compared to paper containing no such agent. The wet strength agent comprises a wet strength resin. The term “wet strength resin”, as used herein, refers to a resin capable of imparting better wet strength properties to paper compared to paper containing no such resin.
The method for the production of a paper wet strength agent comprises a first step of reacting a nitrogen-containing polymer with a hydrophobic compound to provide a nitrogen-containing polymer with hydrophobic side-chain substituents, a second step or reacting the product obtained with a crosslinker to form a wet strength resin, and a third step comprising forming of particles by emulsion polymerisation of one or more ethylenically unsaturated monomers in the presence of the wet strength resin formed. According to a preferred embodiment, no polyamine having at least 2 secondary and/or primary amine moieties, added between the first and the second step, or after the second step, is reacted.
Suitable, the nitrogen-containing polymer is polyaminoamide, a polyamine or other nitrogen-containing polymer. Preferably, a polyaminoamide is used which may constitute the reaction product of a polycarboxylic acid, suitably a dicarboxylic acid, and a polyamine. By the term “carboxylic acid” is meant to include carboxylic derivatives such as anhydrides and esters. Suitable polycarboxylic acids include saturated or unsaturat
Andersson Arne
Biermann Christian
Gorzynski Marek
Macherey Heribert J.
Akzo Nobel NV
Burke Michelle J.
Fortuna Jos'e A.
Parker Lainie E.
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