Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-03-15
2004-05-11
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S047000, C524S502000, C524S503000, C524S515000, C523S223000
Reexamination Certificate
active
06734232
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a surface size for cellulosic products. In particular, the invention relates to a styrene/acrylate copolymer latex made by emulsion copolymerization conducted without a surfactant.
DESCRIPTION OF RELATED ART
Paper and other cellulosic products often are sized, i.e., are treated by deposition of a composition to ameliorate characteristics related to the porosity and the hydrophobicity of the cellulosic product. Sizing typically is used to control absorption by the substrate of water, water-borne compositions, and inks.
Internal sizing or surface sizing typically sizes cellulosic products. Internal sizing involves mixing sizing agent with pulp and forming a sheet, or web, having uniform distribution of sizing agent and pulp throughout. Surface sizing involves application of the sizing agent to the surface of a previously formed web. Surface sizing typically increases the hydrophobic character, improves product quality and is less expensive than internal sizing because almost the entire sizing agent is retained on the surface of the treated product.
However, surface sizing is not without difficulty. Sizing agent is applied under high pressure to ensure even distribution over the treated product, and there is continual effort to increase production speed. Thus, the ability to distribute sizing agent evenly over the web becomes more important. Sizing agents are subjected not only to mechanical stress during application, but also to potential chemical interactions with chemicals present in and on the cellulosic product to be sized. Many of these chemicals may cause undesirable precipitation of components from the sizing.
Divers natural and synthetic resins have been used as surface sizing agents. Typical of such known sizing agents are modified rosin, modified petroleum resins, and synthetic copolymers, such as copolymers of an ethylenically unsaturated monomer with an acrylate, alkyl ketene dimer, and the like.
The surface-sizing agent should be dissolved or dispersed in water. For dispersions, various compositions, including synthetic polymeric products, are known for use as a stabilizer. For example, use of a copolymer comprising styrene or a similar hydrophobic monomer and (meth)acrylic acid or a low molecular weight (500-50,000) copolymer of an &agr;-olefin and maleic anhydride as an emulsifier is known.
Known synthetic resin dispersions may have broad particle size distributions, and often are made in the presence of surfactant, also known as emulsifiers or soaps. A broad particle size distribution may reduce the effectiveness of the compound as a sizing agent by making it more difficult to ensure even distribution of the sizing agent on the web, and may yield inconsistent surface properties and characteristics. Some synthetic resins are made by emulsion polymerization in the presence of surfactants. The presence of surfactant may interfere with the performance of the material as a sizing agent.
The performance of these known compounds as sizing agents is not entirely satisfactory. Manufacturing techniques typically are complex, often require an emulsifier that may interfere in the performance of the sizing agent, and the resulting product may not have a suitable particle size and particle size distribution. Known sizing agents also may not be stable at low pH values. However, stability at low pH value is important for sizing agents to be used in the manufacture of security papers and other cellulosic products comprising material such as manganese sulphate or polyguanidine, for example. Thus, there exists a need for surface sizing agent that is easily manufactured without surfactants and has a suitable particle size and particle size distribution. There also exists a need for a surface sizing agent that is stable at low pH and is compatible with components found on security paper products.
SUMMARY OF THE INVENTION
The invention is directed to a composition of matter for surface sizing of paper and other cellulosic products. In particular, the composition is styrene/acrylic acid ester copolymer latex made by emulsion copolymerization without surfactants.
DETAILED DESCRIPTION OF THE INVENTION
The invention is directed to composition of matter for surface sizing paper and other cellulosic products. The composition is a styrene/acrylic acid ester copolymer latex made by emulsion copolymerization without surfactants. In one embodiment, the latex is stable at pH values between about 1.5 and about 10. Therefore, the composition is compatible with, inter alia, manganese sulphate (MnSO
4
), a stain commonly used in security paper, and polyguanidine, also used in security paper. In another embodiment, the styrene/acrylic acid ester co-polymer is made in the presence of a solubilized styrene/maleic acid copolymer. Both the styrene/acrylic acid ester copolymer discontinuous phase and the styrene/maleic acid copolymer are suitable sizing agents.
The composition of the invention is manufactured by polymerizing styrene and an acrylic acid ester in the presence of water-soluble compounds, but without surfactant. The water-soluble compounds may have either high or low molecular weights. Low molecular weight water-soluble compounds are able to copolymerize with the styrene and acrylic acid ester or to transfer the free radical species during polymerization. The emulsion polymerization is initiated with a persulfate salt, with a hydroperoxide, whether alone or in a redox system with sodium erithorbate or dimethylaminoproprionitrile, or with an azo-derivative, at a temperature between about 25 and about 90° C.
In one embodiment, two different water-soluble co-monomers are present in the continuous phase of the emulsion. A first water-soluble co-monomer is selected from the group consisting of monomers having an allylic moiety. Preferred monomers having an allylic moiety suitable for use as a first water-soluble co-monomer in accordance with the invention are selected from the group consisting of sodium 1-allyloxy-2-hydroxypropyl sulfonate, allyl acetate, allyl glycidyl ether, allyl lactate, and blends thereof. Sodium 1-allyloxy-2-hydroxypropyl sulfonate is commercially available under the trade name SIPOMER COPS I, available in approximately 40% aqueous solution from Rhodia, Inc. A second water-soluble co-monomer is selected from the group consisting of maleic anhydride, maleic acid, fumaric acid, abietic acid; abietic acid-fumaric acid adduct, itaconic acid; the ammonium, sodium, and potassium salts thereof; and blends thereof. Suitable abietic acid-fumaric acid adducts include NovaFlo® 50 (50% concentration of potassium salt of abietic acid fumaric acid adduct in water) and NovaFlo® 072G43, both available from Georgia-Pacific. None of the water-soluble co-monomers is capable of homopolymerization, and none of the co-monomers is capable of polymerizing with another member of the same co-monomer group, but members of the first co-monomer group can co-polymerize with members of the second co-monomer group and with both styrene and acrylic acid esters. Selective incorporation of the water-soluble co-monomer into the styrene/acrylic acid ester co-polymer can be used to alter the properties and characteristics of the co-polymer. Changing the ratio between water-insoluble co-monomers (styrene, acrylic acid ester) and water-soluble co-monomers changes the hydrophilic/hydrophobic balance of the resultant polymer. A stabilizer is generated in situ and will enhance latex stability. Water-soluble co-monomer is present in a combined amount of between about 0.1 and about 10 weight % of the combined weight of the styrene and acrylic acid ester monomers used in making the styrene/acrylic acid ester polymer. Amounts less than about 0.1 weight % tend to reduce the latex stability. Amounts greater than about 10 weight % may adversely affect the sizing properties.
The latex product of the invention is stable at pH between about 1.5 and 10, in the absence of the solubilized styrene/maleic acid polymer. This stability at low pH affords the opportunity to use the size
Banner & Witcoff , Ltd.
Georgia-Pacific Resins Inc.
Sanders Kriellion A.
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