FELTS AND NON-WOVEN FABRICS BASED ON POLYESTER FIBERS AND GLASS FIBERS AND PROCESS FOR OBTAINING SAME

Abstract: Felts and non-woven fabrics comprising glass fibers and unstretched polyester fibers having a titer higher than 3 dtex, a break elongation higher than 100%, a modulus lower than 200 g/tex, a crystallinity lower than 20%, and a toughness lower than 20 g/tex.

Description: This invention relates to a process for obtaining felts and non-woven fabrics based on blends of polyester and glass fibres, which can be transformed into manufactured articles of different kinds, according to technologies known in the paper industry. The preparation of felts and of non-woven fabrics consisting of blends of thermoplastic and glass fibers is well known in the art. It is also known that these felts and non-woven fabrics can be obtained by known methods, either by a "dry" process involving the use of carding machines (or of garnet machines or of air-forming machines) or by a "wet" process involving the use of the usual equipment employed in paper manufacture. This last method shows undoubted advantages as to cheapness as well as to the physical properties of the thus-obtained products and therefore is the preferred method. The activities in this field have been and are still focused on the analysis of fibrous materials, which may allow one to obtain fibrous structures endowed with sufficient cohesion as to make them utilizable in subsequent transformation or processing operations, using techinques common to paper preparation. US-A-4,431,696 describes the preparation, by the usual methods of self-supporting sheets or felts starting from blends of glass fibers with fibrils or fibrides of olefinic polymers having a surface area higher than 1 m²/g. In that case, the self-supporting properties of the sheets come from the particular polyolefinic fibers used by the patentee. Their morphology, which is very irregular, allows one to create a physical bond with the glass fibers, sufficient to obtain a remarkable structural completeness. IT-B-1,161,880, following the common methods used for paper, coherent veils of glass fibers are prepared using blends of said fibers with conventional thermoplastic polymers. These last, after the drying of the veil, are allowed to melt, thus obtaining satisfactory adhesion among the glass fibers and the formation of a stable and coherent structure. From the reference 32721v of Chemical Abstracts, vol.82, 1975, page 94 the use of polyethyleneterephthalate fibers in sheets from mixtures of glass fibers and polyester fibers obtained by a standard paper-making method is known. In accordance with the present invention, it has now been discovered that it is possible to prepare felts, veils or non-woven fabrics of glass fibres and thermoplastic fibres showing a stable and coherent structure which can be used for the preparation of manufactured articles of different shape, if specific polyester fibres are used and the heat treatment is carried out under the conditions defined below. Accordingly the invention is directed to a process for the preparation of felts, veils or non-woven fabrics endowed with stable and coherent structure, consisting essentially of the following successive operations or steps: (a) preparation of an aqueous dispersion of a homogenous blend of fibers consisting essentially of a blend of from 10 to 90% by weight of glass fibers and from 90 to 10% by weight of unstretched or not wholly stretched polyester fibers containing at least 90% by moles of polyethyleneterephthalate and having a length between 2 and 25 mm; a titer greater than 3 d/tex; a toughness lower than 20 g/tex; a break elongation greater than 100%, and a modulus lower than 200 g/tex; (b) formation of a veil or felt of said blend of fibers by introducing the fibrous aqueous dispersion onto a filtering baffle, and promoting the elimination of the excess liquid from the veil or felt by sucking or by using vacuum; and (c) heat-treatment of the thus-obtained veil or felt characterized in that the polyester fibers have a crystallinity lower than 20% and the heat-treatment is carried out under a stream of inert gas heated at 50 to 150°C. Polyester fibers used for the preparation of the felts or non-woven fabrics according to the present invention are prepared by the melt-spinning of a polyester containing at least 90% by moles of polyethyleneterephthalate. A polyethyleneterephthalate having an intrinsic viscosity between 0.5 and 0.7, as measured in o-chlorophenol at 35°C by means of a Ubbelohde viscometer, and a density between 1.3 and 1.5 g/cm³ is particularly preferred. Polyester fibers may contain small amounts of well-known dulling or delustering agents, antistatic agents, antioxidants, optical brighteners, etc., generally used in the preparation of conventional polyester fibers. The polyethyleneterephthalate fibers having a length between 4 and 10 mm, a titer between 5 and 15 dtex, a break elongation between 300 and 700%, a modulus between 100 and 150 g/tex, and a crystallinity between 1 and 10% are preferably used for the preparation of felts or non-woven fabrics according to the present invention. Particularly preferred is the use of polyester fibers with such parameters and a toughness between 5 and 15 g/dtex. The glass fibers, in particular those of E glass, used in the present invention, are well known in the literature and are marketed for instance by VITROFIL S.p.A., by Owens-Corning Fiberglass, and by the PPG Company. They have a diameter between 5 and 15, and in particular between 10 and 13 micrometers, and a length between 2 and 25 mm. These glass fibers may be coated with a finish, such as for instance an epoxy resin, or in general by finishes suitable for polyester resins. For the preparation of felts and non-woven fabrics according to the present invention blends containing from 50 to 80% by weight of polyester fibers and correspondingly from 50 to 20% by weight of glass fibers are preferred. The manufacture of the above-mentioned felts, veils and non-woven fabrics is performed by preparation methods commonly used for paper, which generally consist or consist essentially in placing the fibers in an aqueous medium, and thereafter in forming the veil, the felt or the non-woven fabric by deposition of the fibrous dispersion on a filtering baffle, and finally in drying it. The preparation of the aqueous dispersion described under (a) may be performed in vats or hollanders under agitation until the fiber concentration is about 0.5-2% by weight, preferably in the presence of dispersing agents or surfactants, in order to secure a good dispersion of the fibers. The presence of these agents in the bath is not necessary when the fibers have been previously treated for this purpose. The formation of the veil or felt described under (b) may be easily done by means of well-known types of machines used in the paper industry; in particular, by means of a Rotiformer or by means of raked boards, which as known are suitable for the manufacture of sheets starting from a wet mixture containing synthetic fibers. However, other types of machines may be used for this operation, such as for instance Fourdrinier machines either cylindrical or sloping. Fibers of thermoplastic polymers different from polyesters may be present in the dispersion in amounts up to 10 parts by weight based on 100 parts of the fibrous mixture. Felts, veils and non-woven fabrics obtained according to this invention are particularly suitable for the manufacture of molded articles by means of the known "flow-molding" technic for the preparation of molded manufactured articles from reinforced thermoplastic sheets. According to this technic, the felt is heated in an infrared oven at 300°C, by hot nitrogen circulation, so that the polyester resin melts and impregnates the glass fibers. The "molten felt" is then transferred into the mold of a vertical press and is molded by total filling of the hole. The following example is given in order still better to illustrate the present invention but without limiting its scope in any way. Example In the mixing box connected to a Rotiformer unit equipped with 2540 mm of board, a 1% aqueous dispersion of a blend of fibers was prepared consisting of: -- 30% by weight of glass fibers having a length of 6mm; -- 70% by weight of uncrimped polyethyleneterephthalate fibers having the following properties: Titer: 12.3 d/tex Toughness 12.5 g/tex Length 6.5 mm Elongation: 618.6% Modulus: 145 Crystallinity: 3.8% These polyester fibers were obtained by the melt-spinning of polyethyleneterephthalate having a density of 1.34 g/cm³ and an intrinsic viscosity of 0.625, measured in o-chlorophenol at 35°C by means of a viscometer of the Ubbelohde type. The polyethyleneterephthalate fibers were collected in a tow of 100 ktex, which was then cut in chops of 6.5 mm by means of a slash cutter working at 150 strokes/min. The fibrous dispersion was then fed to the Rotiformer unit with a flow of about 27,000 liters/min. The Rotiformer unit was working in the presence of suction boxes inside the drum, completely soaked (or immersed) the sloping zone where said formation occurred. Thus a felt was obtained of 2 kg/m², and having a thickness of 5 mm, which was dried by passage through an oven through which was circulated nitrogen at 90°C. The thus-obtained felt had the following properties: -- Longitudinal tensile strength: 20 deca N/5 cm -- Transversal tensile strength: 16 deca N/5 cm Determinations were carried out on 10 series of 4 specimens each, having a size of 5 x 30 cm, drawn from the production lines every 20 minutes, transversely and longitudinally with respect to the direction of production, using a dynamometer whose clamps moved away at a speed or 10 cm/minute.

Claims: A process for the preparation of felts, veils or non-woven fabrics endowed with stable and coherent structure, consisting essentially of the following successive operations or steps: (a) preparation of an aqueous dispersion of a homogenous blend of fibers consisting essentially of a blend of from 10 to 90% by weight of glass fibers and from 90 to 10% by weight of unstretched or not wholly stretched polyester fibers containing at least 90% by moles of polyethyleneterephthalate and having a length between 2 and 25 mm; a titer greater than 3 d/tex; a toughness lower than 20 g/tex; a break elongation greater than 100%, and a modulus lower than 200 g/tex; (b) formation of a veil or felt of said blend of fibers by introducing the fibrous aqueous dispersion onto a filtering baffle, and promoting the elimination of the excess liquid from the veil or felt by sucking or by using vacuum; and (c) heat-treatment of the thus-obtained veil or felt characterized in that the polyester fibers have a crystallinity lower than 20% and the heat-treatment is carried out under a stream of inert gas heated at 50 to 150°C. Process according to claim 1, wherein said polyester fibers have a crystallinity between 1 and 10%. Process according to claim 1 or 2, wherein the blend contains from 50 to 80% by weight of polyester fibers and correspondingly from 50 to 20% by weight of glass fibers. Process according to claim 1 or 2, wherein the polyester is polyethyleneterephthalate having an intrinsic viscosity between 0.5 and 0.7, measured in o-chlorophenol at 35°C by means of an Ubbelohde viscometer, and a density between 1.3 and 1.5 g/cm³. Process according to claim 4, wherein the aqueous dispersion contains from 0.5 to 2 % by weight of the fibrous blend.

Inventors: MELACINI, PAOLO, PIERI, GIOVANNI, DR.
Applicants: MONTEFIBRE S.P.A.
Application year: 1988
Main classification: D21H11
IPC codes: D21H13, D04H1