Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-08-28
2004-12-21
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S035000, C536S035000, C536S056000, C019S145500
Reexamination Certificate
active
06833399
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a flowable flax bast fiber and flax shive blend which may be used as a reinforcing agent for thermoplastic resins.
BACKGROUND OF THE INVENTION
A number of different materials, such as organic and inorganic fibers, have been used to make thermoplastic composite reinforcements. Inorganic fibers include glass, carbon, metals or metal alloys, such as steel or aluminum, and stone. Organic fibers include aramid, nylon, polyester, polypropylene, polyethylene and natural fibers, such as cotton and wood.
Traditionally, milled fiberglass has been the most popular material for reinforcement of thermoplastic compounds. Fiberglass has a unique combination of versatility and strength that makes this reinforcement a material of choice for more than 50% of all composite articles manufactured in the year 2000, and the most popular choice for thermoplastic reinforcement as well. Synthetic organic fibers (nylon, polypropylene, aramid, etc.) are used occasionally and for specialty applications only. Despite their good availability, man-made fibers have significant disadvantages, including high prices tied to crude oil prices. All of these materials pressure the environment because they are not necessarily renewable, are not biodegradeable and generate significant Green House Gas emissions upon manufacture and/or destruction. Key disadvantages of fiberglass also include the worker-unfriendly nature of the material (fiberglass is an irritant), its fragility which makes it difficult to process; and finally, its density (natural fibers have specific density that is 40% less than density of fiberglass).
Because flax bast fibers are difficult to feed into resin molding equipment, they have not been used for thermoplastic reinforcing agents. Although the potential of using flax fibers in plastic applications as a substitute for synthetic fibers such as glass, carbon, nylon, polyester, etc. has been recognized, for example, GB 2090849 describes the incorporation of flax bast fibers into a thermoplastic resin blend. The use of flax bast fibers for reinforcing resins results in processing problems, as the flax bast fibers tend to “ball up” during processing. Thermoplastic resins blended with specific amounts of flax shives and bast fibers are not described. Further, purposeful attempts have been made to exclude flax shive from flax fiber preparations used for reinforcing composites. For example, Mieck et al. (
Polymer Composites
, December 1996, Vol. 17, No. 6), suggest that for better composite characteristics, the fibers should be free from shives. Flax bast fibers have very low-bulk density which tends to cause the aforedescribed clumping or balling. At the same time, almost all inorganic fibers have a very good feeding properties due to high-bulk density. However, this feeding advantage of inorganic fibers creates a problem for the composite. It makes composites heavy.
U.S. Pat. Nos. 6,133,348 and 6,114,416 to Kolla et al. describe a shive/bast fiber blend used as a resin reinforcing agent where the blend has 30 weight percent bast fibers as a maximum. If the blend described in these patents has more than 10 weight percent bast fibers, without using shives and bast fibers as described herein, feeding problems will be incurred because the bast fibers will ball and clump. Neither the '348 patent or the '416 patent suggest a flax bast fiber/shive blend with the aspect distribution and/or particle size distribution described herein.
It also has been known that fibers could be chopped or reduced in their length to improve the reinforcement feeding properties. This approach is widely used with inorganic fibers. Milled glass fibers are glass fibers processed by a hammer mill into lengths of {fraction (1/32)}″ to {fraction (1/81)}″. There are many brands of milled inorganic fibers (e.g., West System {fraction (1/32)}″ Milled Glass Fiber), which found broad application as reinforcement for thermoplastic compounds.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a blend of flax bast fibers and flax shives which are flowable and which will not clog or clump in thermoplastic resin forming equipment.
This and other objects of the invention will become apparent with reference to the specification.
SUMMARY OF THE INVENTION
This invention relates to free flowing fiber reinforcing material which includes a blend of flax bast fibers and flax shives with a specific distribution of particle sizes and aspect ratios, thermoplastic pellets which include such reinforcing fiber blend, thermoplastic composites which include such reinforcing fiber blend and method for making such pellets and composites. The flax bast fibers and flax shives each have particle size ranges in amounts which are sufficiently similar and short which makes the blend free flowing and feedable into equipment which receives and shapes thermoplastic resins without the addition of other surface treating agents for the flax bast fibers. The particle sizes of the bast fiber are sufficiently long to make the bast fiber/shive blend an effective reinforcing agent for thermoplastic resins. Moreover, for a given particle size, the shives have a smaller average aspect ratio value than the plant bast fibers. The similarity of the amounts of flax shives and bast fibers in a given particle size range, and the smaller aspect ratio of the shives compared to the aspect ratio of the bast fiber all are effective for making the reinforcing blend freely flowable and feedable into resin processing equipment. Once introduced into such resin processing equipment, the blend can be easily compounded with a thermoplastic resin, which is softened by heating, and the resulting flowable mixture can be thermoformed into desired bast fiber/shive reinforced composite shape.
The resulting fiber reinforced composites are relatively light-weight yet strong and flexible structures well-suited for diverse applications. In one aspect, solid flowable pellets are made as an intermediate product which is a mixture of the flax bast fiber/flax shive blend and thermoplastic resin to provide an intermediate composite product. The fiber reinforced resin pellets can be used subsequently as a convenient ready-to-use feed for an injection mold or extruder.
As noted above, heretofore flax bast fibers have been known to clump or “ball up” and obstruct their feeding into and or within passageways in resin processing equipment. Surprisingly, the blend of the invention which has at least about 15 weight percent flax bast fibers can significantly minimize or eliminate such clumping, and, in general, the blend should have at least about 30 weight percent bast fiber to further enhance the reinforcing properties of the blend. The blending of the flax bast fibers and flax shives can be accomplished before or during compounding with the thermoplastic matrix resin in resin processing equipment. When preblended, a free flowing form of flax fibers and shives is provided suitable for clog-free feeding into resin processing equipment. Once introduced into the resin processing equipment, the flax bast fibers and shives in the blend continue to interact in a manner that effectively inhibits and curbs clumping problems arising from the bast fibers. These problems would occur if a natural ratio of flax bast fiber and flax shive were used during compounding and movement of the fiber/flax shive/resin blend within the equipment.
While not desiring to be bound to any theory, it is believed that the flax shives surround exterior portions of the low bulk density flax bast fibers when blended according to the particle size and aspect ratio distribution criteria of this invention. This sufficiently inhibits the bast fibers from physically bridging or hooking together to otherwise form undesired clumps or agglomerates of bast fibers. It is believed that the flax shives serve to “lubricate” the flax bast fibers to effectively suspend them as a shive/bast fiber dispersion and keep the bast fibers from mechanically entangling with on
Isman Barbara
Khavkine Mikhail
Cargill Limited
Fitch Even Tabin & Flannery
Szekely Peter
LandOfFree
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