Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1999-04-29
2002-12-17
Sellers, Robert E.L. (Department: 1712)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C008S183000, C008S194000, C162S166000, C524S510000, C524S521000, C525S155000, C525S163000, C525S194000, C525S218000
Reexamination Certificate
active
06494990
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions and methods for improving the printability and/or strength of various types of paper and board. More specifically, this invention relates to mixtures of hydrophobic surface sizes and hydrophilic polyacrylamide which, when added to paper or board, improve print quality, sizing, as well as surface strength of the paper or board.
BACKGROUND OF THE INVENTION
Sizing agents have gained wide acceptance in the paper industry for modifying paper to improve its resistance to penetration by liquids, generally water, and to improve various aspects of printability. For example, U.S. Pat. Nos. 5,122,568 and 5,139,614 teach the use of styrene acrylic copolymers for enhancing sizing, inkprint contrast, increasing ink penetration times and reducing feathering. U.S. Pat. No. 3,562,102 discloses amine reaction products of alkyl glycidyl mixed esters which are used in the preparation of sized cellulosic paper substrates, cured films and solid resinous potting compositions.
Efforts have been made to develop improved sizing agents. In U.S. Pat. No. 4,855,343 acrylonitrile acrylate monomers are copolymerized by emulsion polymerization in the presence of degraded starch and a peroxide-containing initiator to provide Improved paper sizing agents. U.S. Pat. No. 5,362,573 describes the use of, titanium, hafnium and zirconium salts such as ammonium zirconium carbonate in conjunction with surface sizing compound containing water-soluble hydroxylated polymer to improve sizing efficiency.
There are many different sizing agents used in papermaking, such as rosin soap, starch, sodium silicate, amine reaction products of alkyl glycidyl mixed esters, such as that described in U.S. Pat. No. 3,562,102, for example, and sizing can be accomplished by either internal sizing processes, which typically involve wet end addition, or surface sizing processes, which typically involve addition at the size press. Surface treatment at the size press typically with sizing agents alters the paper web primarily by imparting an increased degree of hydrophobicity. This sizing effect, in turn, generates higher ink penetration time values, reduced lateral spread of printing inks, as well as improved imaging and contrast with various printing technologies. Thus, hydrophobic surface size agents improve printability primarily by decreasing paper sheet absorbtivity and enhancing surface resistance to liquid (ink) penetration.
Paper printability and other qualities have also been improved through the use of coated paper and various ink jet recording sheets. In U.S. Pat. No. 4,442,172, an ink jet recording sheet made by coating a water-soluble polymer onto the surface of a base sheet containing synthetic silicate, wet strength additive and glass fiber is described as having superior ink absorbency and high recording density without feathering. Combinations of alkyl ketene dimer internal sizing agent, precipitated calcium carbonate and certain cationic synthetic fixing agents have also been incorporated into ink jet recording base layers, see, U.S. Pat. No. 5,126,010. Ink jet recording paper described in JP 06143799 is prepared by applying a surface size treatment of high molecular weight adhesive and styrene-maleic anhydride copolymer to both sides of base paper and disposing an ink-receiving coating containing a white pigment and adhesive on one side of the paper. Ink jet recording transfer sheets containing calcium carbonate as a filler and alkyl ketene dimer or alkenyl succinic anhydride as sizing agents are described in JP 06008617. Auxiliary agents such as starch, polyacrylamide and polyvinylalcohol may be included in the transfer sheet. J56109783-A describes paper for ink jet recording obtained by applying a hydrophilic polymer, e.g., oxidized starch or polyvinyl alcohol, to raw paper of specified water absorption degree to provide paper with balanced ink drying properties and blotting resistance for ink-jet printing. And U.S. Pat. No. 4,900,620 describes ink jet recording sheets having good ink absorption, resolution and color brightness which are made of wood pulp and precipitated calcium carbonate substrate coated with a layer of white pigment. Ink jet recording sheets composed of a support and a cation-modified acicular or fibrous colloidal silica-containing ink-receiving layer are described in U.S. Pat. No. 5,372,884; various polymers may be included in the ink receiving layer for improving ink drying properties, film-forming properties and image sharpness.
In U.S. Pat. No. 4,294,704 paper and board is coated with compositions containing aqueous latex binders of synthetic polymer such as styrene-butadiene copolymers, carboxyl styrene-butadiene copolymers, vinyl polyacetates, carboxyl vinyl polyacetates, alkyl acrylate-vinyl acetate copolymers and carboxyl alkyl acrylate-vinyl acetate copolymers in order to provide improved dry and wet tear resistance. In U.S. Pat. No. 4,439,496 a water-resistant photographic substrate containing an alkylketene dimer, a cationic polyacrylamide and an anionic polyacrylamide is coated with a water resistant polyolefin.
JP05173287 discloses base paper for use in photographic printing paper which is made by adding a cationic polyacrylamide to pulp slurry, then adding a sizing agent which has an effect in the weakly acidic to weakly alkaline pH region, e.g., high organic ketene dimers, and finally adding an anionic polyacrylamide; the base paper is described as being useful in inhibiting the permeation of developing liquids from the cut end surfaces of the photographic printing paper. Another ink jet recording sheet is described in EP 600245.
As new printing technologies continue to emerge and gain acceptance in the market place, the need for developing high performance paper surfaces having improved printability characteristics increases. Despite the benefits obtained from using coated paper or ink jet recording sheets, these materials have certain disadvantages, for example, they require two separate layers and therefore their manufacture Involves numerous paper processing steps and special converting operations. Furthermore, many of the existing coated paper sheets exhibit inadequate color image, color resolution and color bleed. Moreover, as paper products increasingly use multiple colored inks, paper exhibiting controlled ink absorption, optimal color density and reduced color bleed, and with reduced feathering and wicking has been particularly difficult to make. It is desirable, In many instances, to use single sheets of paper having superior color absorption rates, color density and resolution with reduced color bleed and feathering.
Consequently, a need, unsatisfied by existing technology, has developed for a paper additive that provides the above-described benefits in printability and sizing yet also exhibits superior dry strength.
Existing dry strength additives have not met this need. N-(chloroalkoxymethyl) acrylamides and quatemized derivatives thereof are dry strength additives described in U.S. Pat. No. 3,980,800. Canadian patent 1101158 describes improved dry strength properties obtained by admixing a fibre suspension with quaternized acrylamide polymers. The addition of acetone-triethylenetetramine-diethylenetriamine-formaldehyde copolymer and acrylamide-maleic anhydride copolymer to cellulose pulp is described in U.S. Pat. No. 4,036,682 as giving increased strength properties. Polyvinyl alcohol and starch have been applied to paper to improve sheet surface characteristics which may included surface strength, and porosity smoothness. In JP 57139599 and JP 139598 anionic polyacrylamide is added at the wet end and a sizing agent selected from alkyl ketene dimer, cationic sizing agent and substituted cyclic dicarboxylic anhydride is used along with aluminum salt to manufacture neutral paper purportedly having good wet and dry tenacity.
Various printing technologies continue to require paper surfaces with high integrity and resistance to the abrasive effects of the printing processes. Fiber picking, Tinting and filler dusting
Bazaj Rajiv
Dauplaise David
Guerro Gerald
Bayer Corporation
Pennie & Edmonds LLP
Sellers Robert E.L.
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