Patent Application
20220288871
The present invention relates to manufactured articles consisting of the coupling of at least two polyamide-based parts, one of which made of a polyamide, preferably loaded with a dispersed filler, and the other made of a polyamide reinforced with fibres in their turn made of polyamide. The invention also relates to processes for the production of these manufactured articles.
The production of objects consisting of the coupling of two (or more) parts made of different polymer materials is widely known; the objects thus produced may be the most varied, from car parts to items of everyday use (e.g. toothbrushes). Various techniques are used for producing these objects, and they differ depending on the shape of the object to be produced or the geometric relationship between the different polymeric parts of which it is comprised. For example, if the object is comprised of overlapping parallel layers, of essentially uniform thickness, of the different polymers, the production technique may be lamination or co-lamination of pre-formed homogeneous layers, making them adhere by heat treatment, generally with the application of pressure. Vice versa, in the event the object consists of more complex shaped parts, possibly co-penetrating or intersecting with one another, the production generally takes place with the so-called overmolding technique (this technique, or variants thereof, are also known in the sector by the definitions hybrid moulding, back injection or others). Overmolding consists in introducing into a cavity of a mould one part (that may be pre-formed or thermoformed inside the mould, and that may be pre-heated or heated in the mould itself) which does not completely occupy said cavity, so as to leave an empty space around the part; subsequently, a molten polymer is injected into the cavity (process known in the state of the art as back-injection), which completely occupies the empty space of the cavity; after the solidification of the molten material, an object can be removed from the mould consisting of the coupling of two coupled polymer parts.
Objects produced as described above, if made of polymeric materials only, do not have however a high mechanical strength, especially if they are large.
To overcome the problem, it has been proposed to add reinforcement elements to at least one of the two coupled parts.
In general, these reinforcements are comprised of parallel fibres, interwoven fibres or actual fabrics made of materials known to have a high mechanical strength, in particular carbon fibres or glass fibres. At the JEC World 2019 trade fair, held in March 2019 in Villepinte (Paris), various types of prototypes of mechanical parts were shown, in particular car parts, such as rear parts of seats, bumpers, air bag housings and the like; in general, all these prototypes have parts that are flat or at most slightly shaped, made with polymers reinforced with carbon fibres or glass fibres (in some cases also with metal inserts), whereas the ribs are made by overmolding.
However, even parts made with these fibre-reinforced compounds are not free from problems or disadvantages.
In the first place, the chemical and/or physical compatibility between the fibres and the matrix may not be optimal; this can cause difficulties in the production of fibre-reinforced part and require the addition of compounds to make them compatible.
Another disadvantage of traditional fibre-reinforced parts, when they comprise glass fibre, is a relatively high total weight; this characteristic is undesirable particularly in the case of car parts, given the constant search of this industry for methods and materials that can reduce the total weight of vehicles in order to reduce the consumptions thereof.
The aim of the present invention is that of providing manufactured articles consisting of the coupling of at least two polymer-based parts, one of which made of a polyamide matrix, preferably loaded with a dispersed filler, and the other made of a polyamide matrix reinforced with fibres in their turn made of polyamide, as well as to provide a process for producing these manufactured articles.
In a first aspect thereof, the invention relates to a manufactured article consisting of the coupling of at least two polyamide-based parts, one of which made of a polyamide matrix, preferably loaded with a filler dispersed in the matrix, and the other made of a polyamide reinforced with fibres in their turn made of polyamide. Preferably, in the event in which the manufactured article consists of overlapping layers of the different parts, there are at least two parts present therein made of polyamide reinforced with polyamide fibres arranged on the outer faces of the manufactured article, whereas at least a part made of polyamide, preferably loaded with a filler dispersed in the matrix, forms one or more internal layers of the manufacture article itself.
In the second aspect thereof, the invention relates to a process for the production of manufactured articles formed by at least two different possibly mutually co-penetrating polyamide parts, of which at least one made of polyamide preferably loaded with a dispersed filler and at least one made of polyamide reinforced with polyamide fibres, which comprises the steps of:
a) providing at least one part of a fibre-reinforced composite material, consisting of fibres of a polyamide A in a matrix of a polyamide B, wherein the polyamide A has a higher melting point than the polyamide B;
b) arranging said part of fibre-reinforced composite material inside the cavity of a mould, said cavity having a shape and/or size so as not to be completely occupied by said part;
c) pre-heating and possibly thermoforming in the mould said part of fibre-reinforced composite material;
d) injecting a molten polyamide C, either not containing a filler or loaded with a dispersed filler, into the space of said cavity not occupied by said part;
e) allowing the molten polyamide C to solidify, forming a non-fibre-reinforced part and extracting the manufactured article from the mould, wherein steps b) and c) can be performed in any chronological order.
In the present invention, the following terms and abbreviations have the meanings specified here:
In the following description, the polyamides indicated as A, B and C may be co-polyamides, as long as the relative melting point conditions described are respected.
In a first aspect thereof, the invention relates to manufactured articles obtained by coupling at least two (or more) parts formed by composite materials, comprising a polyamide matrix and polyamide fibres in the case of the fibre-reinforced part, and a part made of polyamide, preferably loaded with organic or inorganic fillers dispersed in a polyamide matrix, in the case of the non-fibre-reinforced part.
In the fibre-reinforced part, the polyamide of the matrix, B, has a melting point T lower than that of the fibres, A; this condition can be obtained in different ways. For example, the polyamides A and B may be different; alternatively, the polyamides A and B may be nominally the same (e.g. both polyamides PA6.6), but be used in different crystalline forms having different melting points; still further, the polyamides A and B may be nominally the same but with a different molecular weight, again having different melting points; other ways of realizing the desired condition of having two polyamides with two different melting temperatures will be evident to the experts in the polymer field.
This part may be formed by aligned (parallel) fibres only, or by fibres interwoven to form fabrics. An alternative possibility is to form this part with a non-woven fabric: in this case, the individual fibres generally do not have a length equal to at least one of the lateral dimensions of the fibre-reinforced part, but are interwoven with one another so as to form a single element having the required characteristic. The fibres are embedded in the polyamide matrix. A structure of this type, with fibres immersed in a continuous phase (matrix) can be produced according to various methods.
A first possibility is to prepare a set of fibres in contact with one another and to bring them for a short time to the melting point: in this way, for kinetic reasons only the surface part of the fibres melts, which re-solidifying forms the matrix. This technique can also be adopted with two-component fibres, comprising an inner part (“core”) and an outer one (“shell”) made with different polyamides, in which the outer part is made with a polyamide B having a lower melting point than the polyamide A of the core; fibres of this type can be obtained by co-extrusion. Alternatively, the fibres can have a “core-shell” structure as described above, but obtained starting from a single polyamide in two different crystalline forms or with different molecular weights, so that again the outer crystalline form is characterized by a lower melting point than that of the core. Finally, for this first possible embodiment fibres known as “commingled yarns” can be used, i.e. multi-filament fibres, in which at least one filament is comprised of the polyamide A having a higher melting point (e.g. PA6.6), which in the final manufactured article will constitute the reinforcement fibre, and at least one filament is comprised of a polyamide B having a lower melting point (e.g. PA6), intended to melt and form the matrix. Commingled yarn type fibres are well known in the textile sector, and may be comprised of at least two, but generally more, filaments, interwoven according to many possible different patterns.
The most convenient technique consists in arranging the fibres in a mould, superposing with them (preferably above and below the fibres) sheets or a particulate (e.g. shavings, granules or powder) of the material of the matrix, and bringing the system to the melting point of the polyamide B of the matrix under compression: the polyamide B melts and diffuses among the fibres also due to the pressure applied. By operating according to this last technique flat parts are generally obtained, with thicknesses generally between 0.2 and 3 mm, but it is also possible to obtain higher or lower thicknesses. This process can also be made continuous or semi-continuous, with a procedure similar to calendering, wherein the material intended to constitute the matrix (in the form of powder, film, etc.) and the reinforcing fibres or fabric are passed through rotating and heated cylinders, applying a pressure to impregnate the fibres with the molten matrix material (the instrument is called a belt press); alternatively, in the event of using core-shell or commingled yarn fibres, they are passed alone between rotating and heated cylinders. In case the resulting material is not perfectly consolidated after one passage only in the belt press, a second definitive consolidation passage in a compression moulding press can be performed. Other possible techniques are pultrusion and filament-winding or other similar technologies or that derive from them, well known to experts in the sector of producing thermoplastic composites.
To form the fibre-reinforced part, as mentioned, the polyamide of the matrix must have a lower melting temperature than that of the fibres. The melting temperature (or ranges of temperature) of the different polyamides are known to people skilled in the art; the following table shows some examples of possible matrix-fibre couples that can be used in the present invention:
Particular examples of composite materials for forming the fibre-reinforced part are those with one-directional fibres comprising a matrix of PA6 or co-polyamide PA6/PA6.6 (80-20) and fibres with high tenacity in PA6.6, or those comprising a matrix of PA6 and fabrics of fibre with high tenacity in PA6.6.
The fibre-reinforced part may also be a hybrid fibre-reinforced part, comprising a part reinforced with polyamide fibres according to the invention coupled to a traditional type part, reinforced with glass fibres, carbon fibres or the like, separate or in the form of fabric. In this case the matrix of the two fibre-reinforced parts is preferably realized with the same polyamide B. The coupling of these two fibre-reinforced parts can take place with the same production technologies as a single fibre-reinforced part, therefore in a belt press or static press or similar technologies. The hybrid fibre-reinforced part thus obtained can then be used in the overmolding process of the invention.
The non-fibre-reinforced part comprises a matrix in turn made of polyamide C (e.g. one of those described above) inside which, preferably, a discontinuous phase is dispersed, comprising fillers like glass fibre, carbon fibre, mineral powders or organic fillers.
In the case of fibres, they generally have a diameter in the range between about 5 and about 20 μm, and initial lengths generally less than 5 mm; in the composite formation operations, these fibres generally break (in particular the glass ones) giving rise to a filler with an equal diameter and lengths comprised between about 50 and 300 μm.
In the case of mineral loads, powders with particle size of less than 50 μm, and preferably between 2 and 50 μm, are generally used; the shape of these powders varies substantially according to the mineral, and can essentially be cubic or spheroidal (i.e. with three similar dimensions in space) in the case for example of calcium carbonate, or in the form of thin sheets for some minerals such as clay or mica.
Another possible material to be used as a filler is graphene, generally in the form of “thin sheets” having a thickness between 2 and 4 nm and lateral dimensions of about 10 μm.
The quantity of filler can vary between about 15% and 40% of the weight of the part in the case of carbon or mineral fillers, and between about 15% and 60% in the case of glass fibres. In the case of graphene, the quantity of filler is preferably less than 15%.
The manufactured articles of the invention, consisting of the coupling of at least one fibre-reinforced part and at least one non-fibre-reinforced part as discussed above, can have any shape and the geometric relationship between the two parts may be any.
The most common cases are manufactured articles comprising at least two overlapping layers of different polyamide parts, or manufactured articles comprising at least two different polyamide parts in a complex geometric relationship with each other.
In the case of manufactured articles comprising overlapping layers, the final manufactured article may be planar or, more commonly, shaped, with the parts that form the two layers extending in parallel for the entire extension of the manufactured article. In the automotive industry, parts such as the internal panels of doors or panels for batteries can be produced in this way.
Preferably, manufactured articles comprising overlapping layers are formed by at least three layers, with the two external layers made of fibre-reinforced composite and the central layer made with the composite loaded with filler but not fibre-reinforced. This preferred structure is depicted in a sectional view in
In the case of manufactured articles with parts not simply overlapping, they may have any geometric relationship with one another; for example, one of the two parts may completely or almost completely surround the other, also with different thicknesses in different points of the surface, or let the more internal part emerge in some points of the surface of the final manufactured article; the central part can have through openings, which are occupied by the most external part, so that in those areas of the manufactured article the composite of the most internal part surrounds the composite of the external part; or any other shape and/or geometric relationship. In this second possibility (complex shapes and geometric relationships between the parts), if the fibre-reinforced part is internal it essentially exercises a “skeleton” function of the manufactured article, i.e. it imparts to the article mechanical resistance leaving outside a part with desired characteristics, such as the appearance or pleasantness to touch; if, instead, the fibre-reinforced part is external it has essentially the function of protecting the internal one from mechanical stress and strain, in particular from impact.
An example of this second type of manufactured article of the invention is shown in
In its second aspect the invention relates to the process for producing the manufactured articles described above.
The process is generally of the overmolding type, and comprises the steps of:
a) providing at least one part of a fibre-reinforced composite material, consisting of fibres of a polyamide A in a matrix of a polyamide B, wherein the polyamide A has a higher melting point than that of the polyamide B;
b) arranging said part of fibre-reinforced composite material inside the cavity of a mould, said cavity having shape and/or size so as not to be completely occupied by said part, said part being heated before its insertion into the mould or inside the mould;
c) pre-heating and possibly thermoforming in the mould said part of fibre-reinforced composite material;
d) injecting a molten polyamide C preferably loaded with a dispersed filler into the space of said cavity not occupied by said part of fibre-reinforced composite material;
e) letting the molten polyamide solidify and removing the manufactured article from the mould.
Steps b) and c) can be performed according to any method and sequence; the part in fibre-reinforced composite material can already have the final shape before insertion into the mould, or be thermoformed inside the mould itself, furthermore, it can be inserted pre-heated into the mould or be inserted cold and heated in the mould (even when thermoforming in situ is not envisaged). The possible pre-heating of the part made of fibre-reinforced composite material can be performed in any way, for example with an IR lamp or with hot air.
Step a) consists of the production of the fibre-reinforced part, and has already been described.
Steps b) to e) are the normal steps of an overmolding process, and are known to a person skilled in the art. In the present case, they are applied to the production of manufactured articles comprising parts made with the specific composite materials of the invention.
The invention will be further described by the following experimental part, including the description of the methods of performing the characterization tests, and the examples of production of the various articles manufactured according to the invention and measurement of their properties.
Methods and Instrumentation
Instrumentation Used for Producing Fibre-Reinforced Laminates and Laminas:
Instrumentation Used for the Mechanical Characterization:
This example relates to the preparation of a part made of fibre-reinforced composite.
The following are used as starting materials:
The sheet of PA6 and the PA6.6 fabric are alternated on five layers, according to the order: PA6 sheet-PA6.6 fabric-PA6 sheet-PA6.6 fabric-PA6 sheet.
The assembly comprised of these five layers is fed to a belt press, comprising a heating module and a cooling module; inside the press there are cylindrical rollers that can apply a maximum pressure up to 10 kg/cm2; the passage into these modules takes place in a time comprised between 3-6 minutes, and during the process a maximum T of 245° C. is reached.
A fibre-reinforced laminate of thickness 1.8-2 mm is obtained, wherein 57% of the volume is occupied by the fibre.
This example relates to the preparation of a manufactured article of the invention, having the shape shown in
As a polyamide for realizing the non-fibre-reinforced part (polyamide C according to the present invention) a PA 66 for injection moulding loaded 30% by weight with fillers is used. The percentage is comprised of a part of glass fibre and a part of mineral filler. The formulation of this polyamide is developed by RadiciGroup High Performance Polymers, and consists of PA6.6 having a melting point in the range 260-290° C., loaded with 23% by weight of glass fibres having a diameter between 5 and 20 μm, and 7% by weight of a mineral filler essentially comprising talc with an average particle size of 30 μm.
A lamina of the fibre-reinforced part prepared in Example 1 of dimensions 48 mm×244 mm is cut, it is positioned inside the cavity of the mould (female part of the mould) and fixed to the most internal wall of the mould with high temperature resistant biadhesive tape. Then the hot air heating system is moved manually towards the lamina, so as only to reach a partial melting of the PA 6 matrix on the surface of the lamina. Then the mould is closed (having the male part shaped so as to obtain the ribs of the non-fibre-reinforced part shown in
This manufactured article, which constitutes Sample 1, is comprised of a fibre-reinforced part positioned on the long side of the manufactured article (the wall thickness is 3 mm, therefore the lamina occupies about ⅔ of the wall, whereas the remaining 1 mm of thickness is occupied by the back-injected PA 66), mainly oriented outside, and the remaining part in back-injected polyamide 66, in the ribs, the short and the lateral sides.
Using the same mould used in Example 2, a manufactured article is produced which has the same shape and size as Sample 1, but exclusively made with the polyamide C used in Example 2; this polyamide in this example therefore occupies the entire volume of the mould. The manufactured article obtained constitutes Sample 2.
This example relates to the mechanical characterization of the Samples 1 and 2 with three-point bending tests.
Before being subjected to the tests illustrated below, the Samples were dried for 12 hours at 70-80° C.
The three-point bending test consists of positioning a sample on two supports while applying the load at the centre. In this way tension is generated on the lower face and compression on the upper face and the sample deflects downwards.
The tests are performed with the instrument Instron 5967, with Samples 1 and 2 positioned in the machine with the cavity facing upwards, as shown in
The results of the tests are shown in
The load/displacement curves for the two samples are shown in
From the graph in
The mitigating effect of the polyamide fibres on the otherwise fragile breaking of the non-reinforced layer is to be noted. This prevents dispersion of the scraps of material following the fragile break. The effect is also to keep the polyamide fibres intact, thanks to their ductility, after the fragile break of the non-fibre-reinforced part, unlike what happens in the case of using reinforced parts with classic fragile fibres, in the first place carbon fibres or even glass fibres.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102019000013803 | Aug 2019 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/057312 | 8/3/2020 | WO |
