Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-09-03
2002-11-19
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S734000, C427S326000
Reexamination Certificate
active
06482886
ABSTRACT:
The present invention relates to the external sizing of fibrous materials, particularly cellulosics such as paper. The external sizing agent is an interpolymer of an ethylenically unsaturated monomer and an ethylenically unsaturated carboxylic acid comonomer.
Sizing is the process of providing fibrous materials such as cellulosics (e.g., paper) and textiles (e.g., fabrics) with resistance to penetration by liquids. Sizing may be accomplished via an internal sizing process, an external sizing process, or as is usually the case, a combination of both.
The processes of internal sizing and external sizing are very different from each other in many respects. Many materials that are known to be effective as internal sizing are generally not effective as external sizing agent and vice versa. Internal sizing is a method by which the sizing is initiated before the fibrous material is formed. This is usually accomplished by adding an internal sizing agent, in conjunction with a retention aid, directly to a fiber slurry to precipitate the sizing agent upon the fibers. Internal sizing agents are generally hydrophobic in nature, i.e., the sizing agents will have their nonpolar portions oriented about the surface of the fibers forming a protective layer wherein the penetration of liquids is retarded once the fibers are fabricated into a finished fibrous product such as paper and a fabric. See Biermann, C. J., Essentials of Pulping and Papermaking, Academic Press, Inc., 1993, p. 197.
External sizing, which is also referred to as surface, tub, or calender sizing, is substantially different from internal sizing in that external sizing agents are applied to one or both surfaces of already-formed fibrous products in the absence of retention aids. Because external sizing is accomplished by a different mechanism than internal sizing, certain hydrophobic materials as well as non-hydrophobic materials, such as starch, can be effectively used as external sizing agents. Whereas internal sizing takes place on a substantial portion of the fibers throughout the three dimensional matrix of the paper or fabric and generally involves modification of the surface energy of the fibers, external sizing occurs when an external sizing agent is applied to a surface of a fabricated fibrous product and either fills the capillaries and voids between individual fibers, or acts to modify the surface energy of the fibers nearest the surface rather than all the fibers throughout the matrix, rendering liquid penetration more difficult. See Biermann, p. 197. Because of the requirement of filling surface capillaries, the surface tension or energy of the external sizing agent is an important factor in successful external sizing of fibrous products.
Interpolymers of an ethylenically unsaturated monomer and an ethylenically unsaturated carboxylic acid comonomers have been used for internal sizing of paper previously. See, for example, U.S. Pat. Nos. 3,872,039; 3,899,389; and 4,181,566. However, heretofore, such interpolymers have not been employed as external sizing agents. That is, these disclosures by Vaughn et al. teach the use of such interpolymers as internal sizing agents.
For internal sizing of paper, Vaughn et al. in U.S. Pat. Nos. 3,872,039; 3,899,389; and 4,181,566, described the combination of an ammoniated copolymer of ethylene and an ethylenically unsaturated carboxylic acid comonomer and a cationic retention aid. The advantage of the internal sizing systems disclosed by Vaughn et al. is said to be their utility over the complete range of pH conditions found in paper-making operations. For these systems, Vaughn et al. taught the order of addition of the sizing agent and the retention aid to a conventional paper making process was non-critical, however, Vaughn et al. preferred to introduce their sizing agent prior to the addition of a retention aid.
Rowland et al. in U.S. Pat. Nos. 5,206,279 and 5,387,635 disclosed aqueous dispersions of interpolymers of ethylene and an ethylenically unsaturated carboxylic acid comonomer. Rowland et al. described the combination of two bases, one as a weak cation and the other as a strong cation. Rowland et al. teach that this combination permits the preparation of stable dispersions of interpolymers having relatively low carboxylic acid concentrations (e.g. less than 15 weight percent acrylic acid content). However, Rowland et al. did not disclose that their dispersions were useful as external sizing agents for fibrous materials.
While there are a variety of known sizing systems and alleged solutions, there is still a need for an external sizing system that provides improved sizing performance, i.e., higher Hercules Size Test (HST) values as measured by accordance with TAPPI method T 530 pm-89. Higher HST values translate into improved hydrophobicity and liquid penetration resistance.
To fulfill these objects, we have discovered a novel process for external sizing fibrous materials and products. The process comprises applying a basic aqueous dispersion of an interpolymer of an ethylenically unsaturated monomer and an ethylenically unsaturated carboxylic acid to a fibrous material after the fibrous material has been finished or fabricated into its final form. In one preferred embodiment, the basic aqueous dispersion is prepared at a controlled reduced viscosity to provide dilute solution with a starch having higher viscosities.
The present process is particularly suitable for external sizing of paper and paper products. Further, in addition to providing improved external sizing, the present process provides fibrous products with improved cohesive strength and improved printability. An advantage of the inventive process is now processors and mills can employ the same or similar basic aqueous dispersions for purposes of external sizing and internal sizing, thereby eliminating the need to buy, receive, store and use different substances for internal sizing and external sizing. Another advantage provided by the present process is the use of basic aqueous dispersions which are stable and do not require the use of surface active ingredients.
The term “external sizing,” is used herein, to refer to a method of sizing in which a sizing material is contacted with fabricated finished fibrous material under conditions effective to size the fibrous material, i.e., deposit the sizing agent on the fibrous material and increase the hydrophobicity of the fibrous material as measured in seconds by the Hercules Size Test, TAPPI method T 530 pm-89. Accordingly, the term “external sizing” is used herein generically and as such is inclusive of such terms as “surface sizing,” “tub sizing,” “calender sizing” and the like.
The term “water-dispersible,” as used herein, refers to a material which can exist in the form of a stable aqueous colloidal dispersion in the absence of a surface active agent or surfactant.
The term “ethylenically unsaturated monomer,” as used herein, refers to any water-immiscible monomer containing a terminal double bond capable of polymerization under normal conditions of free-radical addition polymerization to form a water-insoluble homopolymer having a polyethylenic backbone.
The term “ethylenically unsaturated carboxylic acid comonomer” is used herein to refer to a comonomer containing alpha-beta unsaturation and a carboxylic acid group and which is capable of free-radical addition interpolymerization through the ethylenically unsaturated group with ethylenically unsaturated monomers.
The term “interpolymer”, as used herein, refers to polymers prepared by the polymerization or interpolymerization of at least two different types of monomers. The generic term “interpolymer” is inclusive of the term “copolymer” and the term “terpolymer.” The term “copolymer” is usually employed to refer to a polymer prepared from two different monomers such as an ethylene-acrylic acid (EAA) copolymer. Conversely, the term “terpolymer” is usually employed to refer to a polymer prepared from three different types of monomers such as an ethylene-acrylic acid-vinyl acetate (EAA/VA) terpolymer.
The term
Cooper James L.
Finlayson Malcolm F.
Gathers John J.
Oliver Stephen M.
Schumann Brian H.
Jagannathan Vasu
Shosho Callie E.
The Dow Chemical Company
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