Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-01-10
2003-04-15
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S357000, C428S362000, C428S359000, C428S369000, C428S377000, C428S293100
Reexamination Certificate
active
06548167
ABSTRACT:
BACKGROUND OF THE INVENTION
Technical Field of the Invention
The invention relates to a continuous fiber granulate comprising of granulate corns in which reinforcing staple fibers are helically arranged in a thermoplastic matrix. The invention also relates to a procedure for manufacturing continuous fiber granulate out of a staple fiber mixture of thermoplastic fibers and reinforcing fibers, in which a fiber strip comprised of the staple fiber mixture is guided through a preheating zone, then extruded through a heating nozzle into a strand, and the strand is cut into continuous fiber granulate sections after rotation and consolidation via cooling. Finally, the invention relates to a device for manufacturing continuous fiber granulate out of a staple fiber mixture of thermoplastic fibers and reinforcing fibers with a preheating zone, a heating nozzle, a cooling zone, a rotating element and a granulator.
Chopped fiber-containing granulates are manufactured by compounding reinforcing fibers and the respective matrix material using an extruder. The reinforcing fibers can be metered into the extruder continuously or chopped. The shearing action of the endless screws shortens the reinforcing fibers. At the same time, the reinforcing fibers are finely distributed in the polymer melt and cross-linked with the matrix material. The reinforcing fibers have no aligned orientation in the granulate corn. In these chopped-fiber granulates, the fiber length of the reinforcing fibers is generally smaller than the granulate length, normally lying under one millimeter.
DESCRIPTION OF THE PRIOR ART
Continuous fiber granulates are increasingly being used in the plastics-processing industry for the manufacture of slightly stiff fiber composite components. These continuous fiber granulates can basically be manufactured in different ways. One long-established method is the pultrusion procedure. This procedure is based on the continuous feeding of reinforcing fiber strands (rovings) into a tool while simultaneously supplying melted matrix material. In ideal cases, the polymer melt penetrates through the rovings, and the individual filaments are sheathed with a melt film. At the tool outlet, the strand is passed through a nozzle, giving rise to a defined cross-section. After this, the matrix material is cooled, and the material strand is cut to length. The fiber length in a granulate fabricated in this way corresponds to the granulate length due to the stretched position of the fibers.
The melt pultrusion procedure is known in numerous variations, and is used both for manufacturing continuous fiber granulate and fabricating semi-finished products (Japanese Patent Application 08-047924; Japanese Patent Application No. 06-320536; U.S. Pat. No. 3,993,726; United Kingdom Patent Specification No. 1,439,327; Japanese Patent Application No. 06-315931.) Also known are pultrusion procedures for prepreg processing. In these special pultrusion procedures, melted polymer material need not be supplied, provided that pre-impregnated reinforcing fiber rovings (prepregs) are used.
Also known is the manufacture of continuous fiber granulates using the extrusion procedure (Japanese Patent Application No. 06-254,847.) In this case, a kinking or entanglement of reinforcing fibers can make the length of individual fibers greater than the granulate length. However, most of the reinforcing fibers are shorter than the granulate length owing to the shearing action of the extruder screws.
However, specific reinforcing fiber compositions (rovings or free-flowing continuous fibers) are always necessary for manufacturing continuous fiber granulate in a pultrusion or extrusion process. This cannot be accomplished with all reinforcing fibers.
In addition to the long-known procedures for continuous fiber granulate manufacture, another procedure was also developed for the manufacture of continuous fiber pellets out of fiber strips Federal Republic of Germany Patent No. 197 11 247. This procedure is based on the principle of forming a heated, rotated material strand out of a staple fiber strip, which can then be cooled and cut into pellet sections. In this procedure, the strand is rotated with two rotating elements that rotate at the same speed. The disadvantage to this procedure is that strand rotation is only constant between the two rotating elements. After the strand passes through the second rotating element and is clamped in the granulator, it might rotate in the reverse direction given an inadequate cooling and fixation of the material. This has a negative influence on the strength and free-flowing properties of the granulate.
SUMMARY OF THE INVENTION
The object of this invention is to provide a continuous fiber granulate that has good free-flowing properties, enables a uniform distribution of reinforcing fibers, and incorporates as large a reinforcing fiber length as possible at the given cut length of the granulate corn. In addition, a procedure for manufacturing continuous fiber granulate out of a staple fiber mixture of thermoplastic fibers and reinforcing fibers is to be provided in which the expended energy is lowered. In particular, this procedure is intended to avoid the reverse rotation by the strand after passing the cooling zone. Additional advantages of the invention are mentioned in the description below.
This object is achieved according to the invention for the continuous fiber granulate mentioned at the outset by having the reinforcing staple fibers be located in a sheathed zone of the particles along with the melted matrix material, and in a core zone of the particles along with unmelted thermoplastic staple fibers. The main advantage to this granulate is that reinforcing fibers can be incorporated into the granulate corn with a greater fiber length than the granulate section length. It was surprisingly shown that reinforcing fibers with a fiber length greater than the granulate corn section length due to torsion can be incorporated into the particle even if the strand or granulate corn is not melted through in the core area. In addition, it was shown that, despite the only partial melting of the thermoplastic portion (in the sheath or edge zone), no separation takes place between the reinforcing fibers and matrix material, i.e., the reinforcing fiber load remains essentially the same in the sheath and core. This makes it possible to achieve a very uniform distribution of the reinforcing fibers in the mold units during later processing of the granulate. The energy expended to manufacture the continuous fiber granulates according to the invention is less than during extrusion or pultrusion (the manufacture of conventional granulates), since the thermoplastic polymer material need not be completely melted, but rather only the outside sheath of the strand or granulate corn.
The granulate particles are preferably strand sections, and the length of their reinforcing fibers is greater than the length of the strand sections. The ratio between the lengths of the reinforcing fibers and strand sections depends on the torsion of the strand, and rises as twisting increases. The diameter of the granulate particles generally ranges from 1 to 10 mm. The percentage of reinforcing fibers in the granulate particles can lie in a range of 10 to 80%w/w. The number of reinforcing fiber windings in the granulate particles can vary within broad limits, and generally lies within a range of 0.1 to 5.
The reinforcing staple fibers can be natural fibers, synthetic fibers or mineral fibers. Suitable fibers include flax, hemp and jute fibers, along with glass, aramide and carbon fibers. In particular, the material of the matrix and thermoplastic fibers can include of polypropylene, polyethylene and polyamide.
The object is additionally achieved according to the invention in the procedure mentioned at the outset by first cooling the strand exiting the heating nozzle, then rotating and withdrawing it, and subsequently allowing it to rotate freely as it is cut into sections with no impediment. As opposed to the procedure described in Federal R
Mieck Klaus-Peter
Reussmann Thomas
Dixon Merrick
Ostthuringische Materialprufgesellshaft fur Textil und Kunststof
Schindler Edwin D.
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