Polyolefin reinforcing fibre, use thereof and products comprising same

Abstract: The subject of the invention is a polyolefin fiber for the reinforcement of products based on fibers and a hydraulic-setting substance, characterized in that it includes a size carrying a function which assists the fiberizing operation, a function in which the fiber can be wetted by the composition of the hydraulic-setting substance, and a function of promoting adhesion to the hydraulic-setting substance. The fiber is used as reinforcing fiber in a product based on fibers and a hydraulic-setting substance. (end of abstract)

Agent: C. Irvin Mcclelland Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US
Inventors: Eric Dallies, Richard Morlat, Christelle Pousse, Gael Cadoret
USPTO Applicaton #: #20060234048 - Class: 428364000 (USPTO)
Related Patent Categories: Stock Material Or Miscellaneous Articles, Coated Or Structually Defined Flake, Particle, Cell, Strand, Strand Portion, Rod, Filament, Macroscopic Fiber Or Mass Thereof, Rod, Strand, Filament Or Fiber

Polyolefin reinforcing fibre, use thereof and products comprising same description/claims

The Patent Description & Claims data below is from USPTO Patent Application 20060234048, Polyolefin reinforcing fibre, use thereof and products comprising same.

Brief Patent Description - Full Patent Description - Patent Application Claims

[0001] The present invention relates to the field of hydraulic-setting materials and more particularly to products based on a hydraulic binder and fibers.

[0002] These products may especially be in the form of shaped articles in the form of boards (or plates), such as plane or corrugated boards for covering or building elements, such as roof or wall boards, but also in other forms, especially hollow or tubular forms.

[0003] Such articles may be manufactured by a technique involving the filtration of an aqueous suspension, comprising a hydraulic-setting binder, reinforcing fibers and, optionally, fillers. A process commonly used that relies on this technique is known as the Hatschek process: a very dilute aqueous suspension is contained in a tank fitted with means for uniformly distributing the constituents within the volume of the tank; a filter drum is partially immersed in the tank and its rotation causes the deposition, on its surface, of a thin film of material (fibers and hydrated binder); this film is carried by a felt towards a size (or format) roll onto which it is continuously wound up; when the film has reached the desired thickness, it is cut so as to unwind from the roll an individual sheet of hydraulic-setting material. The sheet may then be made in the form of a shaped product and it acquires its final characteristics by the curing of the binder. A product of larger thickness may be obtained by superposing a suitable number of sheets and by pressing them together in order to ensure cohesion of the whole assembly.

[0004] For a long time asbestos has been used as fibers for forming the framework of the filtered film, asbestos fibers having the property of being dispersed in the aqueous suspension without forming agglomerates deleterious to the regularity of the process, the said fibers being even capable of "opening up" in the aqueous medium so as in this way to constitute, at the surface of the drum, a highly entangled filtering network capable of retaining the hydraulic binder particles, including the fines, with a very high filtration efficiency. Asbestos fibers also have good tensile strength properties, which contribute to the mechanical properties of the final product when mainly stressed in bending. Asbestos fibers therefore have two functions, namely a framework function (in the sense of forming a filtering network) and a reinforcement function (which contribute to the final mechanical properties). Asbestos is furthermore a highly competitive material from the cost standpoint.

[0005] However, this material is tending to be discarded from the manufacture of a large variety of common consumer products and from the building field for public health reasons.

[0006] For this reason, there is a demand for a replacement material that does not have the drawbacks of asbestos.

[0007] However, at the present time, it has not been possible to find a natural or synthetic fibrous material capable of fulfilling the same role as asbestos, that is to say one that combines filtration capability, mechanical properties and resistance to the alkaline medium of hydraulic-setting substances.

[0008] Cellulose fibers prove to be suitable for forming a framework of filtration of the mineral binder particles, but are inadequate from the mechanical reinforcement standpoint.

[0009] Glass fibers have an intrinsic mechanical strength, but are generally sensitive to attack by the alkaline medium of the hydrated mineral matrix, which means modifying the matrix by additives intended to protect the glass and/or using an alkaline-resistant glass suitable for such aggressive environments. However, these solutions involve a not insignificant cost burden.

[0010] PVA (polyvinyl alcohol) or PAN (polyacrylonitrile) fibers are also envisaged as reinforcing fibers, to complement possible filtration fibers, but they also have an economic disadvantage associated with the cost of the raw material.

[0011] Polypropylene fibers would be good candidates as reinforcing fibers, as they are less expensive and do have a high mechanical strength. However, they exhibit a rather mediocre reinforcement effect in a matrix of a hydraulic-setting mineral binder, because of a low affinity of the lipophilic olefin material for hydrophilic hydrated matrices.

[0012] Many attempts have been made to improve this interaction.

[0013] Thus, it has been attempted to modify polypropylene by means of organic or mineral additives introduced into the mass of the polymer.

[0014] This modification inevitably results in an increased cost of the fibrous raw material and a not insignificant effect on the intrinsic properties of the fibers especially a lowering of the mechanical properties.

[0015] Another modification approach consists of surface treatments, such as texturizing, sandblasting, corona effect, etc. These solutions considerably complicate the fiber manufacturing process and are generally of no interest from the economic standpoint.

[0016] The present invention aims to provide a reinforcing fiber for hydraulic-setting products, which has good reinforcing properties while still remaining inexpensive.

[0017] The invention relies on the fact that a simple modification of the exposed surface of the fibers by a suitable size effectively and lastingly improves the interaction between the fibers and the matrix. Since the amount of material provided by the size is minimal compared with the weight of fibers, this modification does not substantially increase the cost of the fibrous material.

[0018] In this regard, the subject of the invention is a fiber as claimed in claim 1.

[0019] According to the invention, the surface properties of the filaments constituting the polyolefin fiber are modified by one or more sizing agents bringing three functions, that of assisting the fiberizing operation, that of being able to be wetted by the hydraulic-binder-based composition, and that of promoting adhesion to the hydraulic-setting matrix.

[0020] In the present application, the term "fiberizing" means in general the manufacture of the polyolefin fiber, starting at the die or spinning of the molten material, passing through a drawing stage and going until at least the chopping of chopped yarns.

[0021] The function of assisting in the fiberizing operation consists in making it easier to form the polyolefin fiber from polyolefin filaments, at least at one stage of the fiberizing operation: this especially involves the lubrication of the filaments in order to improve their handling by the yarn transporting and assembling members at various stages in the manufacture of the fibers, the minimizing of the electrostatic charges carried by the filaments, so as to allow them to be assembled into a yarn, or the providing of the cohesion or integrity of the yarn formed by the assembly of filaments.

[0022] The function of being able to be wetted by the hydraulic-binder-based composition consists in facilitating the dispersion of the polyolefin fibers in the matrix, ensuing from the good dispersion of the fibrous material within the initial binder/water mixture from which the product is manufactured. This function principally relies on the surface polarity of the fibrous material in order to make it hydrophilic.

[0023] The function of promoting adhesion to the hydraulic-setting matrix consists in increasing the interaction between the fibrous reinforcement and the matrix of the hardened product. The latter function also relies on the presence of polar functional groups on the surface of the fibers.

[0024] These functions may be provided by one or more agents chosen from lubricants, antistatic agents, surfactants, fatty-chain compounds and polymers having polar functional groups, in which a lubricant may be a fatty-chain compound, likewise a surfactant may be a fatty-chain compound, or an antistatic agent may be a polymer having polar functional groups.

Brief Patent Description - Full Patent Description - Patent Application Claims
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