FR2688164A1 - Method for the in situ manufacture of thermoplastic articles coated with fabric, the fabric for the implementation of the method and product obtained by this method - Google Patents

Abstract

The invention relates to a method of manufacturing thermoplastic articles coated with fabric; it includes the following steps: - a fabric is selected; - regions of pilosity (8) with a predetermined height are produced on one face of the fabric, on the side intended to be invisible; - the pilose fabric is applied to the walls of a mould, the invisible face being turned towards the space intended for the thermoplastic material to be injected; - the thermoplastic material is injected; and - the article coated with the fabric is extracted from the mould after curing of the thermoplastic material.

Description

PROCESS FOR THE IN SITU MANUFACTURE OF PARTS
THERMOPLASTICS COATED WITH FABRIC, THE FABRIC FOR IMPLEMENTATION
IMPLEMENTATION OF THE PROCESS AND PRODUCT OBTAINED BY THIS PROCESS
The invention relates to a process for the in situ manufacture of thermoplastic parts coated with fabric, the fabric for carrying out said process and the product obtained by the process.

 The invention applies more particularly to the production of molded parts produced in particular by injection, used in the automotive, aeronautical and nautical industry, such as for example dashboards, seats, interior trim parts. or indoor in general.

 It has been known for many years to manufacture parts of thermoplastic material covered with fabric. In the old methods, the fabric was applied to the surface previously constructed and surface heated so that the fabric could be applied to the surface thus softened. The problem was to heat the surface at the right temperature for a specific time to obtain good adhesion without deteriorating the properties of the plastic material.

 This expensive technique has been replaced by that of bonding: the plastic part is simply coated with adhesive product on which the fabric is applied directly.

 In the two preceding cases, the operations are long and costly in terms of labor and volume since they involve first manufacturing the part and then coating it.

 The above difficulties are solved by direct injection on the fabric: the bottom of a mold is coated with a fabric and an injection of a thermoplastic material is carried out which is applied directly to the surface of the fabric.

While this technique makes it possible to significantly reduce production costs, it still has significant drawbacks:
- the adhesion of the material injected on the plastic is poor: the fabric peels off, with more or less pronounced delamination;
- the adhesion can be improved by increasing the injection pressure but the liquid thermoplastic material crosses the thickness of the fabric, or there are folds, in particular near the injection points, and in one like the other case, the parts are discarded.

 To prevent the material from passing through the entire thickness of the fabric, a solution consists in using an external fabric giving the piece exclusively the appearance and the feel, and an internal fabric with a tight weave assembled to the external fabric for example by "f oamage" that is to say by fusion of a polyurethane-based bonding agent presented in the form of foam.

 The two-sided textile material thus produced is suitable for use in molds with a simple geometric shape using a thermoplastic material such as polypropylene, which nevertheless exhibits poor adhesion properties. The generally used process is low pressure injection, that is to say at pressures of 50 bars, of molten thermoplastic material.

 The tight weave of the inner fabric sufficiently retains the molten thermoplastic material, seals the textile, so that the appearance of the outer fabric is very good.

 On the other hand, the undesired appearance, many folds on the surface persists, in particular in the use in molds of complex geometry.

 The use of textile materials in molds is therefore always expensive due to the complexity of the material and particularly delicate in molds of complex geometry.

 The object of the invention is to solve all of the aforementioned drawbacks by a simple and inexpensive method making it possible to produce pieces coated with textile in molds of any shape, possibly of complex geometry without formation of folds, said textile being very strongly adhering to the thermoplastic material.

The subject of the invention is a process for the in situ production of textile-coated thermoplastic parts, characterized in that it comprises the following steps
- we take a fabric,
- One produces on one side of the fabric, on the side intended to be invisible, pilosities in quantity and over a predetermined height;
- Apply the hairy fabric on the walls of a mold, the non-visible side facing the space for the thermoplastic material to be injected;
- the thermoplastic material is injected;
- The textile-coated part is removed from the mold after the thermoplastic material has hardened.

According to other features of the invention
- the pilosities are produced on a woven or knitted fabric by a treatment of cutting or slicing loops;
- hair is produced by a filling treatment.

- pilosities are produced by mechanical scraping, brushing or the like;
The subject of the invention is also a textile material for coating parts made of thermoplastic material produced according to the method defined above, characterized in that the textile is a fabric, woven or knitted, comprising threads composed of very long micro-filaments, so that one can obtain on at least one side, by scraping, brushing, or the like, pilosities composed of very fine filaments; the textile according to the invention can also be a non-woven, woven or knitted fabric comprising fibers, with a finished length of between approximately 5 and 100 millimeters at least.

According to other features of the invention
- The material is a simple knit obtained from son, resistant to a temperature higher than the temperature of the injected molten thermoplastic material.

 - the height of the pilosities produced on the side exposed to the molten thermoplastic material is between 0.3 and 2.5 mm.

 - the titration of the microfilament strands is less than one decitex.

 - the area developed by the pilosities varies between 10 and 100 cm2 for a unitary area of fabric of 1 cm2.

 The invention also relates to the product made of thermoplastic material coated according to the process described above with a textile material or fabric according to the preceding definition.

The invention will be better understood thanks to the description given by way of nonlimiting example which will follow with regard to the appended drawings in which
- Figure 1 is a partial sectional view of a fabric according to the invention;
- Figure 2 is a very enlarged view of the wires on the interior side before mechanical treatment;
- Figure 3 is a very enlarged view of the fabric of Figure 2 after mechanical treatment
- Figure 4 shows a partial sectional view of a molded part obtained by the method according to the invention.

 With reference to FIG. 1, the textile fabric 1 according to the invention has an external textile face 2 of appearance and feel, and an internal textile face 3 having a hairy surface composed of very fine and numerous bristles 8 giving a velvet or felted appearance.

 The fabric 1 is for example a knitted fabric made from yarns, resistant to a temperature above the melting temperature of a thermoplastic material such as polypropylene.

 The knitting is, in the example, made by knitting technique picked on a circular loom. Two qualities of yarns are used: one is the bottom yarns 5 forming the outer face 2 made of yarns of synthetic fibers (for example polyester, polyamide, etc.) standard multifilament titrated at 5.5 g / lOOQOO meters (5.5 dtex), the other are surface threads 6 forming loops 7 on the inner face 3, synthetic material composed of multi microfilaments, the titration of which is preferably less than 1 dtex, this last characteristic does not being not essential. The filaments 4 which make up the threads are very long, and it is commonly said that they are of infinite length because they are continuous.

 The bottom structure constitutes a fixing base for the loops and must be tight enough to produce a relative seal opposing the liquid thermoplastic material.

 The inner face 3 which presents the loops undergoes a mechanical slicing or scraping treatment which cuts each loop in half and individualizes two hair assemblies formed from the free ends of micro-filaments 8 ′ and 8 ". In FIG. 1, only the part right underwent the treatment.

 The loops, cut by tearing, are substantially perpendicular to the base knitting and produce ends of crimped filaments under the effect of the rapid succession of tension / loosening stresses imposed on the wires 6 of loops and on the friction of the wires on the metal of the tools used. , which increase the thickness and volume of the basic knit and form a mat which has the function of distributing, distributing and homogenizing the flow of injected material, each pile 8 or free end of filament having a function of hooking in the material thermoplastic.

 The knitted fabric thus treated is placed at the bottom of a mold 10 having complex shapes with strong stamping.

 In the exemplary embodiment, a molten material 9 such as, for example, molten polypropylene is injected onto the knitted fabric. During the injection, the polypropylene flow is evenly distributed on the side of the fabric facing the polypropylene flow by chicane effect 11 formed by the micro-filaments perpendicular to the flow surface of the resin and we do not observe no penetration of the fabric by the polypropylene after hardening.

 It has also been found, surprisingly, that the risk of folds forming on the coated part obtained was considerably reduced or even eliminated: in particular the folds usually produced at the injection points of the thermoplastic resin no longer appear. This unexpected improvement makes it possible to advantageously use any woven, knitted or even non-woven fabric which nevertheless exhibits maximum deformability characteristics and therefore is favorable to the formation of folds.

 The pilosities 8 are anchored in the cooled thermoplastic material 12 and ensure a very good connection with the whole of the fabric, because of the importance of the attachment zone: the attachment is in fact mainly by the increase in the specific surface of the textile surface in contact with the thermoplastic material, this being represented mainly by the developed surface (section 13 x average height 14 of the loops) of all the filaments per unit of fabric surface, which is much larger than the surface of the fabric itself, and no longer simply by adhesion of a thin interface as in the known technique.

 The effectiveness of knitting can then be measured by its total weight and its structure, in number of stitches per unit area and by the thread and the average height 14 of the loops.

 According to the invention, this developed surface of the strands varies from at least 10 to 100 cm 2 for a unitary fabric surface of 1 cm 2.

 The appearance and feel of the coated part are identical to the appearance and feel of the original textile and the cohesion of the thermoplastic material to the fabric is excellent for a lower cost of producing finished parts.

 The pilosities 4 are substantially perpendicular to the outer surface of the fabric 3 and preferably rise over an average height 14 of between 0.3 millimeter and 3.5 millimeters.

 The predetermined height 14 of the pilosities 4 depends on the fluidity of the molten thermoplastic material which will be used, and on their specific surface.

In the example of two-yarn knitting, a material according to the invention has been produced; it is a knitted fabric weighing approximately 400 g / m2 which has the following characteristics:
- the upper thread is titrated at 2 times 110 dtex (made up in fact of 2 contiguous threads), and is made up of 2 times 128 strands (256 multi microfilaments), or 0.86 dtex per strand,
- the mesh is 8 meshes per centimeter and 12 columns per centimeter, which gives 8 x 12 or 96 loops / cm2, or 96x2x128 = 24576 microfilament strands giving after slicing 49.152 hairs per cm2,
- the height 14 of the loop mat, varies between approximately 1.7 and 3.5 millimeters,
- The density of synthetic material is, in the example, equal to 1.32 tonnes / m3 the diameter of a micro-filamentary strand is of the order of 9.10-6m;
- before mechanical treatment (FIG. 2), each loop 7 has a curved shape comparable to a vertical dihedral making an angle 15 of approximately 45 "with the bottom plane. For an average height h (referenced 14 in the figure) of approximately 1.7 mm the length of the loop is then approximately 4.8 mm (L = 2h / sin 45) and the developed surface of each micro-filament strand (loop) of diameter 13 of approximately 9.10-6m is then l 'order of 137.10-3mm2;
- the specific surface developed for 1 cm2 of knitting, for example, is then 24.576 x 137.10-3mm2, that is to say approximately 34 cm2.

 This developed surface is variable, for a quality of thread determined, in particular by the density of the mesh and the height of the loops. For example, for a tighter mesh, of 9 meshes on 13 columns, the developed surface is of junk of 20 cm2 and at the same density for a height of 3.5 mm it is of the order of 70 cm2.

 The developed surface still varies according to the characteristics of the wire used. Thus in another example, a light knitted fabric was produced having only a weight of 280 g / m2. The thread used for the loops is titrated to 167 dtex and is composed of 46 micro filamentary strands. For an average height of loops varying between 1.7 and 3.5 mm, a developed surface varying from 12.5 to 25.7 cm2 is obtained for a cm2 of fabric.

 The behavior of the textile material on the thermoplastic material is excellent and final: the tearing occurs by tearing of the filaments from the textile surface, that is to say by destruction of the textile, the filaments remaining anchored in the plastic material.

The fabric can only be removed by heating and softening the plastic, if possible.

 Although the invention has been described in relation to a particular embodiment, it is in no way limited thereto, but on the contrary encompasses all variant embodiments within the scope and in the spirit of the invention: a woven fabric of threads composed of multiple microfilaments of infinite length or of finite length fibers (natural or artificial) even a nonwoven fabric in this case with fibers of finite lengths of at least 5 to 100 millimeters at least, the important thing being that the interior surface comprises or consists of micro-filaments in a quantity such that the mechanical treatment gives a pilous surface with a specific anchoring surface, that is to say a satisfactory developed surface of pilosities and that the textile material is temperature compatible with the thermoplastic injection material.

 The production of hairs or pilosities 4 on the aforementioned side is obtained by a known mechanical treatment of filling, scraping, brushing, fluffing, cutting, emerying or shredding.

 It is also possible, without departing from the scope of the invention, to use complex fabrics of the known type with multiple layers assembled by foaming.

Claims (11)

 1 - Process for the manufacture of thermoplastic parts coated with textile, characterized in that it comprises the following stages  - take a fabric (1),  - Producing on one side of the fabric, on the side intended to be invisible, pilosities (8) in quantity and at a predetermined height;  - Apply the hairy fabric on the walls of a mold (10), the non-visible face being turned towards the space intended for the thermoplastic material to be injected;  - inject the thermoplastic material (5);  - extract from the mold the piece coated with the textile (1) after hardening of the thermoplastic material (9).  2 - Process according to claim 1 characterized in that the pilosities (8) are produced by a cutting or slicing treatment of the loop (7).  3 - Process according to claim 1 characterized in that the pilosities (8) are produced by a filling treatment.  4 - Process according to claim 1 characterized in that the pilosities (8) are produced by a mechanical treatment of scraping, brushing or the like.  5 - Textile material for coating parts of thermoplastic material by the method according to any one of Claims 1 to 4, characterized in that the textile is a woven or knitted fabric comprising threads composed of micro-filaments (4 ) very long.  6 - Textile material for coating parts of thermoplastic material by the method according to any one of claims 1 to 4, characterized in that the textile is a nonwoven, woven or knitted fabric comprising fibers of finite length included between about 5 and 100 millimeters at least.  7 - Material according to any one of claims 5 or 6 characterized in that the fabric is a knitted fabric (5) obtained from son (5,6), resistant to a temperature higher than the temperature of the injected molten thermoplastic material .  8 - Material according to any one of claims 5, 6 or 7 characterized in that the height of the pilosities (8) produced on the side exposed to the molten thermoplastic material is between 0.3 and 2.5 mm.  9 - Material according to any one of claims 5, 6 or 7 characterized in that the titration of the micro-filaments is less than a decitex.  10 - Material according to any one of claims 5 to 9 characterized in that the surface developed by the pilosities varies between 10 and 100 cm2 for a unitary fabric area of 1 cm2.  11 - Product made of thermoplastic material coated according to the method of any one of claims 1 to 4 with a textile material according to one of claims 5 to 10.