Composite article and process for manufacturing it

Composite article comprising an injected hollow body or a solid body based on at least one plastic A, reinforced by at least one bundle of continuous reinforcing fibers, the bundle being wound externally at its surface, substantially perpendicular to its axis, as well as by reinforcing fibers dispersed within it, substantially parallel to its axis, and continuous process for manufacturing it.

The present invention relates to a composite article based on plastic 
reinforced by means of reinforcing fibres. 
TECHNOLOGY REVIEW 
Plastics are currently widely used for the manufacture of all types of 
articles, especially for the manufacture of injected or blown hollow 
bodies, or else for the manufacture of solid bodies such as profiles or 
bars. 
In order to reduce the wall thickness of certain other articles, it has 
already been proposed to reinforce them by means of reinforcing fibres 
arranged at their surface. Such a solution is especially disclosed in 
Document GB-A-2,077,880 which describes a pipe made of plastic reinforced 
both by bundles of continuous reinforcing fibres parallel to its axis and 
arranged at its surface and by bundles of helically wound continuous 
reinforcing fibres (wound at an angle which can vary from 30.degree. to 
90.degree.). 
The manufacture of such articles using a continuous process is quite 
complex; this is because, in addition to one or more rotating reels for 
paying out bundles of continuous reinforcing fibres serving to produce the 
helical reinforcement around a central body, it is necessary to provide a 
large number of fixed pay-out reels in order to produce the axial 
reinforcement (a number which is all the greater the closer together the 
bundles of continuous fibres used for the axial reinforcement and the 
greater the external dimensions of the article). 
Furthermore, the fact that the bundles of continuous axial reinforcing 
fibres are arranged in a thin thickness so as to be concentrated on the 
external surface of the body can prejudice them taking up the axial 
forces. In addition, this uptake depends on the adhesion of the bundles to 
the central body, which adhesion itself depends greatly on operating 
conditions, for example on the temperature of these bundles and of the 
body, on the accuracy of the "deposition" of the bundles or else on the 
pressure exerted on them during their application. 
In a novel manner, the subject of the present invention is therefore a type 
of composite article which exhibits excellent long-term strength and can 
be manufactured simply. 
SUMMARY OF THE INVENTION 
More precisely, the invention relates to a composite article comprising an 
injected hollow body or a solid body based on at least one plastic A, 
reinforced by at least one bundle of continuous reinforcing fibres, the 
bundle being wound externally at its surface, substantially perpendicular 
to its axis, which is characterized in that the said body is furthermore 
reinforced by reinforcing fibres dispersed within it, substantially 
parallel to its axis.

DETAILED DESCRIPTION OF THE INVENTION 
Injected hollow body is understood to mean any type of hollow part, such as 
a bottle for example, obtained by one of the known injection processes, 
with or without blowing, for example by injection over a meltable core, 
over a soluble core or over an inflatable core, or by gas-assisted 
injection. By extension, we also term here as injected hollow bodies 
parts, such as tanks, manufactured by extrusion-blowing, which have 
finished dimensions. 
Solid body is understood to mean any type of solid part, whether it has 
been manufactured by injection, by extrusion or by any other process. By 
way of examples of solid bodies, mention may especially be made of bars, 
profiles, etc. 
Advantageously, the bundle of continuous reinforcing fibres is impregnated 
by a plastic B. Such a bundle, generally termed COFIT (continuous fibre 
impregnated by a thermoplastic), may in particular be obtained by 
impregnating the continuous reinforcing fibres with a polymer in the 
molten state. It may also be obtained by employing a co-mingled bundle of 
continuous reinforcing fibres and of continuous plastic fibres. It may 
also be obtained by employing a bundle of continuous reinforcing fibres 
between which a powdered plastic has been dispersed. In the last two ways 
of obtaining the bundle, it is, of course, absolutely essential to heat 
it, before winding it around a body, so that the plastic melts and 
impregnates the reinforcing fibres uniformly. 
According to a preferred variant, the body is reinforced by two bundles of 
continuous reinforcing fibres wound helically in opposite directions. 
Preferably, the bundle or bundles of continuous reinforcing fibres arranged 
helically around the body are wound so as to be approximately 
perpendicular to the axis of the latter. Preferably, they are wound at 
more than 80.degree. with respect to the said axis. 
Advantageously, the article is coated on the outside with a finishing layer 
comprising a plastic C. This finishing layer, which may be made by any 
known technique, especially by over-extrusion or extrusion-coating, has 
several advantageous effects--first of all, it protects the bundle(s) of 
continuous reinforcing fibres from any mechanical degradation, especially 
during handling, transportation and use of the article. It may also 
chemically protect the bundles of reinforcing fibres, the body and its 
possible contents. It may especially prevent contaminants, present on the 
outside of a hollow article in accordance with the invention, from 
contaminating the fluid that it contains. Finally, application of the 
finishing layer by means of a sizing device enables the external surface 
of the composite article to be made dimensionally very precise, something 
which makes it easier to insert it into orifices or into connection 
elements, etc. 
The article may also possibly comprise other layers, for example an 
impermeability layer consisting of a thin metal foil wound around the body 
reinforced by the bundle(s) of reinforcing fibres. In such an article, the 
finishing layer, which is arranged over the said metal foil, also 
mechanically protects the latter. 
The plastics A, B, or C mentioned hereinabove may essentially consist of 
one or more polymers of any type, whether thermosetting or thermoplastic. 
Often A, B or C essentially consist of one or more thermoplastic polymers. 
Preferably, the plastics employed are thermoplastics, that is to say that 
the polymer or polymers of which they are essentially comprised are 
thermoplastic polymers. If several different polymers as a blend are used 
for the body (plastic A), they must be mutually compatible, or rendered 
compatible by the use of one or more suitable compatibilizers so that the 
body exhibits satisfactory mechanical properties. This remark applies 
similarly to the plastics B and C. By way of example of thermoplastic 
polymers, particular mention may be made of polyolefins, for example 
polyethylene (PE) or polypropylene (PP), vinyl chloride polymers, 
including poly(vinyl chloride) (PVC) for example, as well as polymers 
derived from vinylidene fluoride, including poly(vinylidene fluoride) 
(PVDF) for example. Good results have been obtained from polyolefins, in 
particular from PE. High-density polyethylene (HDPE) is most particularly 
preferred. 
In order especially to ensure good adhesion between the body and the COFIT, 
and therefore good uptake of forces by the latter, the plastic B is 
preferably compatible with the plastic A or, better still, of a similar 
chemical nature. By way of pairs of plastics of similar chemical nature, 
it is possible, for example, to use two ethylene polymers or two vinyl 
chloride polymers. Their compatibility is thus ensured. These two plastics 
may also be made compatible by the use of one or more suitable 
compatibilizers mixed with at least one of them. A layer of adhesive may 
also be interposed between them. 
When a finishing layer is present, good adhesion is desirable between it 
and the "layer" formed by the COFIT or COFITs at the surface of the body 
so as to avoid any risk of the finishing layer delaminating. Furthermore, 
the finishing layer may thus contribute, even if slightly, to taking up 
the forces. In order to improve this adhesion, the plastic C is 
advantageously compatible with the plastic B or, better still, of a 
similar chemical nature. These two plastics may also be rendered 
compatible by the use of one or more compatibilizers mixed with at least 
one of them. A layer of adhesive may also be interposed between them. 
With the purpose of obtaining good and uniform mechanical properties in the 
article, the plastics employed are preferably compatible or, better still, 
of a similar chemical nature. 
It is therefore more particularly preferred that the plastics employed 
should essentially consist of high-density polyethylene. 
It is also possible to add any known conventional additive to the plastics 
employed, for example one or more pigments, processing aids, antioxidants, 
UV stabilizers, other stabilizers, mineral fillers, etc., as long as their 
presence does not appreciably affect their mechanical properties. 
The body may consist of one or more layers. In particular, bodies may be 
produced consisting of several separate layers of different plastics. 
Thus, in the case of a hollow article intended to contain a corrosive 
fluid, it may be useful to provide, in addition to an external layer 
comprising a plastic A reinforced with predominantly axial fibres, a thin 
internal layer consisting of a plastic exhibiting good chemical resistance 
to the fluid in question. It is possible, for example, to use a vinylidene 
fluoride polymer for this purpose. In order to ensure adhesion of this 
internal layer to the adjacent layer, it may be useful to interpose a 
suitable adhesive between them. 
In accordance with the invention, the body is reinforced by reinforcing 
fibres dispersed within it, substantially parallel to its axis. These 
fibres may be of any type, for example glass, carbon or aramid fibres. It 
is preferred to use glass fibres. The diameter of the fibres is generally 
of the order of 7 to 100 .mu.m. The reinforcing fibres dispersed within 
the body are preferably short reinforcing fibres; in particular, their L/D 
(length/diameter) ratio is of the order of 10 to 10,000. In order to 
obtain reinforcing fibres having a relatively high and constant length, it 
is advantageous to employ a plastic A in the form of cylindrical granules 
of a defined length, for example by means of a first step of extrusion of 
the plastic with reinforcing fibres of long length followed by a second 
step of uniform cutting of the rods thus obtained. It is preferred that 
the quantity of fibres dispersed within the plastic A be from 2 to 30% by 
volume. It is important that the reinforcing fibres used be dispersed 
substantially parallel to the axis of the body. If the body does not 
strictly speaking possess an axis, the axis of the body is generally 
understood to mean here the direction of its largest dimension. 
It is necessary that the chosen fibres be chemically compatible with the 
plastic A; in order to increase this compatibility, and therefore their 
adhesion to their matrix, they are possibly coated with a suitable 
coupling (or sizing) agent. In the case of glass fibres, it is possible, 
for example, to use for this purpose one of the compounds of the family of 
silanes well known in this context. 
As already mentioned, in the composite article, it is the body which 
contributes essentially to the uptake of the axial forces. For this 
purpose, it is advantageous that the material forming the body, that is 
the plastic A reinforced by the fibres dispersed within it, exhibits a low 
elongation at break in a tensile test. In particular, the material forming 
the body advantageously exhibits an elongation at break in a tensile test 
according to the ISO 527 standard, at a rate of 10 mm/min and at a 
temperature of 23.degree. C., not exceeding 100%. Preferably, this 
elongation does not exceed 25%. More preferably still, it does not exceed 
15%. 
The reinforcing fibres used in the bundle wound around the body may also be 
of any type, for example one of the types mentioned hereinabove. Here too, 
it is preferred to use glass fibres. Whatever their nature, these fibres 
are continuous, that is to say at least of very great length, for example 
of the order of several hundreds of metres. When the bundle of reinforcing 
fibres is impregnated by a plastic B, it is preferred to use respective 
quantities of plastic B and of reinforcing fibres such that the COFIT thus 
formed contains at least of the order of several hundreds of fibres per 
mm.sup.2 of cross-section. The remark made hereinabove, concerning the 
compatibility of the glass fibres and the plastic, also applies here. 
The characteristics of the composite article according to the invention are 
preferably determined in such a way that its strength limit with respect 
to the stresses imposed in service is firstly reached in the axial 
direction. 
The present invention also relates to a continuous process for 
manufacturing a composite article as described hereinabove, in which the 
operations of manufacturing the body, of winding the bundle or bundles of 
reinforcing fibres and, if necessary, of producing the finishing layer 
take place in line. 
The manufacture of the body is carried out by any known process (injection, 
etc.), so as to orient the reinforcing fibres dispersed within it 
essentially parallel to its axis. 
The winding of the bundle or bundles of continuous reinforcing fibres may 
be performed by using a planetary device, that is to say a large-sized 
annular plate, the axis of rotation of which coincides with that of the 
body to be reinforced, carrying one or more reels for paying out bundles 
of reinforcing fibres. The speed of rotation of this annular plate is 
adapted, especially as a function of the speed of translation of the body, 
of the width of the bundles of reinforcing fibres, of their winding angle, 
etc., so as to obtain touching turns at the surface of the body. If it is 
desired to wind several bundles of reinforcing fibres in different 
directions, it is necessary, of course, to use two such annular plates, 
axially offset and rotating in opposite directions. It is furthermore 
preferable, just before the bundles of reinforcing fibres come into 
contact with the body, to preheat at least the surface layer of one of 
these two elements to a temperature greater, preferably by more than 
5.degree. to 100.degree. C., than the melting or softening temperature of 
its constituent plastic so as to improve their adhesion. It is also 
recommended to wind the bundles of reinforcing fibres around the body by 
applying a certain tension to them. 
In the cases where a single bundle of reinforcing fibres is used that is 
wound virtually perpendicular to the axis of the body, it suffices to use 
a single annular plate carrying a single reel for paying out bundles of 
reinforcing fibres, this making it possible to use an extremely simplified 
manufacturing installation. 
After winding the bundle or bundles of continuous reinforcing fibres, it is 
possible to produce the finishing layer, for example in the case of a body 
of constant cross-section, bypassing the reinforced body into an extrusion 
crosshead that is fed with the molten plastic C. 
This process is very simple and particularly economical to employ. In 
particular, if the "deposition" of the finishing layer on the reinforced 
body takes place immediately after the latter has been reinforced by 
winding of bundle(s) of continuous reinforcing fibres, the superficial 
heating of the reinforced body will not require a large amount of energy 
because of the high temperature to which the body and/or the bundles of 
reinforcing fibres have generally been superficially preheated before the 
mandrel is reinforced by the latter. 
By way of non-limiting examples, the invention makes it possible especially 
to produce: 
containers manufactured by injection and intended to contain a pressurized 
fluid, such as vehicle brake-fluid reservoirs or gas bottles (for example 
bottles intended for subsea diving, the weight of which is advantageously 
small compared to their metallic counterparts); 
cylindrical or prismatic solid bars manufactured by extrusion, these being 
intended to increase the flexural and/or torsional rigidity of various 
assemblies, such as doors or other parts of vehicles, or alternatively 
drive shafts.