Paper making and fiber liberation – Processes and products – Synthetic fiber
Reexamination Certificate
2001-03-05
2002-08-20
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Synthetic fiber
C162S138000, C162S146000
Reexamination Certificate
active
06436236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
This invention relates to an electrically-conductive aramid pulp composition that has high surface area, a high concentration of fibrils and increases strength and high modulus as polymeric reinforcement.
2. Description of Related Art.
U.S. Pat. Nos. 5,788,897 and 5,882,566, issued Aug. 4, 1998 and Mar. 16, 1999, respectively, disclose fibers having a continuous phase of para-aramid and a discontinuous phase of electrically-conductive sulfonated polyaniline.
U.S. Pat. No. 5,094,913, issued Mar. 10, 1992, discloses a pulp refined from fibers having a continuous phase of para-aramid and a discontinuous phase of meta-aramid.
Japanese Patent Publication (Kokai) No. 59/163418, published Sep. 14, 1984, discloses pulp beaten from fibers of a blend of para-aramid and aliphatic polyamide.
BRIEF SUMMARY OF THE INVENTION
This invention includes a composition in the form of a pulp comprising a blend of 65 to 95 weight percent of para-aramid and 5 to 35 weight percent of sulfonated polyaniline (SPA) wherein the para-aramid is present in the composition as a continuous phase and the SPA is dispersed throughout the para-aramid. Pulp particles in the composition generally have a specific surface area of greater than 7.5 m
2
/g and a Canadian Standard Freeness of less than 150 milliliters.
Paper made from the pulp of this invention exhibits a charge decay rate of less than 5 seconds.
DETAILED DESCRIPTION OF THE INVENTION
Electrically conductive pulp is a very desirable product for use in reinforcement of packaging films and polymers, generally, and especially where there is a need to drain or dissipate electrical charges. Electrically conductive pulp finds use in applications where handling dielectric pulp, in dry form, results in charged particles that are difficult to handle or are dangerous due to a threat of sparking on discharge.
This invention utilizes an intimate blend of two polymeric materials to provide a pulp that is not only a good reinforcement for other polymers but is, also, electrically conductive to impart electrical conductivity to normally dielectric materials into which it is added for reinforcement. Fibers of combined polymers are known. Particularly fibers of para-aramid combined with other polymers—and even polyaniline polymers—are known. However, there has been, up to now, no suggestion that such fibers might be refined to make conductive pulp materials.
This invention provides a pulp product that is not only an excellent reinforcement material, is also extremely effective for electric charge dissipation. Moreover, the very material good for such charge dissipation is the material that creates ease in pulp manufacture and excellence in pulp quality.
The materials of this pulp product are para-aramid and SPA and the SPA component provides a dual function with the purposes widely divergent and largely unrelated. First, the polyaniline, as a secondary component in the blend, provides points of fracture for refining and pulping forces to achieve efficient and effective manufacture of high quality pulp with fine, long, fibrils. Second, the polyaniline, as a component effectively on the surface of the pulp particles, provides an electrical conductivity that is effective in dissipating electrical charge by contact of the fibrils on adjacent pulp particles.
By “aramid” is meant a polyamide wherein at least 85% of the amide (—CO—NH—) linkages are attached directly to two aromatic rings. Aramid fibers are described in Man-Made Fibers—Science and Technology, Volume 2, Section titled Fiber-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers are, also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587; 3,673,143; 3,354,127; and 3,094,511.
Para-aramids are the primary polymers of this invention for blending with polyaniline; and poly(p-phenylene terephthalamide) is the preferred para-aramid. By para-aramid is meant the homopolymer resulting from mole-for-mole polymerization of para-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the para-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 30 mole percent of the para-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups that interfere with the polymerization reaction. Para-aramid, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride; provided, only that the other aromatic diamines and aromatic diacid chlorides be present in amounts which permit preparation of anisotropic spin dopes. Preparation of para-aramids and processes for spinning fibers from the para-aramids are described in U.S. Pat. Nos. 3,869,429; 4,308,374; 4,698,414; and 5,459,231.
Sulfonated polyaniline of the present invention can be made by in-situ ring-sulfonation. The term “insitu ring-sulfonation” means that the polyaniline is sulfonated during the polymer solutioning process and not isolated from the sulfuric acid solution before the solution is spun into a fiber. Of course, the sulfonation can, also, be achieved in any other way to make sulfonated polyaniline leading to a conductive pulp.
To be effective in practice of this invention, the sulfonated polyaniline must be sulfonated to a degree that will provide adequate conductivity to drain electrical charges. It has been found that sulfonation is required to a sulfur content of at least 8.5 percent, based on total weight of the sulfonated polyaniline. Sulfonation of less than that amount, results in generally inadequate fiber conductivity. It has, also, been found that increased sulfonation yields improved performance up to a sulfonation level of about 15 weight percent sulfur, based on total weight of the sulfonated polyaniline. Sulfonation to a greater degree has been found to be of little additional benefit. It is noted that sulfonation of polyaniline, to a degree of 8.5 to 15 weight percent, corresponds to a mol percent sulfonation of about 30 to 70 percent of the polyaniline repeat units.
The pulp of this invention can be made by so-called air gap spinning of anisotropic spin dope including the para-aramid and the sulfonated polyaniline. Preparation of such spin dope and spinning of fibers to serve as the basis for the pulp used in this invention, can be found in aforementioned U.S. Pat. Nos. 5,788,897 and 5,882,566.
The molecular weight of the polyaniline employed in the pulp of this invention is not critical. Polyaniline of low molecular weight may result in lower solution viscosity and easier processing, however, it might be more readily removed from the fiber in processing or use.
High molecular weight para-aramid is used—having an inherent viscosity of at least 5. In order to obtain pulp of the desirable high strength and modulus, a spin dope concentration of the para-aramid is employed that results in an anisotropic dope as discussed in U.S. Pat. No. 3,767,756. Spin dopes containing at least 13% by wt. of total polymer content, that is, sulfonated polyaniline plus the p-aramid, meet this requirement. Otherwise the mechanical properties of the spun fiber will not be acceptable for preparation of the pulp to provide antistatic properties.
The concentration of sulfonated polyaniline in para-aramid in the spin solution, and ultimately in the spun fiber and the pulp product, has an important influence on properties. As the content of sulfonated polyaniline increases to and exceeds 40 wt % of the polymer mixture, the tensile strength of the fiber becomes undesirably reduced with no concomitant increase in electrical conductivity. Also, in washing fibers with such a high concentration of polyaniline, some o
Chin Peter
E. I. du Pont de Nemours & Company
Hug Eric
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