IT202200023706A1 - MULTILAYER SHEET FOR THE CREATION OF A LIGHTWEIGHT STRUCTURAL PRODUCT WITH SELF-SUPPORTING CHARACTERISTICS. - Google Patents

Description

DESCRIPTION

in support of a patent application for an industrial invention entitled:

?MULTY-LAYERED SHEET FOR THE CREATION OF A LIGHTWEIGHT STRUCTURAL PRODUCT WITH SELF-SUPPORTING CHARACTERISTICS?.

DESCRIPTION TEXT

The present patent application concerns a multilayer plate for the production of a lightweight structural artifact with self-supporting characteristics. Further objects of the present patent application are a process for the production of the multilayer plate and a method for the production of the structural artifact starting from the multilayer plate.

In particular, the reference sector of the present invention is that of composite materials, i.e. those materials that are used for the production of manufactured articles, in which the choice of material is not only subordinated to the aesthetic requirement of the external surface of the article but also to the functional requirement of rigidity and/or resistance and/or lightness linked to the stresses of the environment in which the article operates.

The mechanical performance of a structural product made of composite material generally derives from the mechanical properties of the component materials - fibres and resin - as well as from the quality of the adhesion between the aforementioned materials.

The mechanical loads applied to the structural components are mainly supported by the fibres; while the resin, preferably thermosetting resin, has the task of binding the fibres and transferring the loads between adjacent fibres.

The fibres used in the production processes of structural components in various industrial sectors (automotive, motorcycle, aerospace) are generally long and coupled together to form fabrics (woven) or bands of fibres all parallel to each other (unidirectional). Both types are supplied in the form of rolls of dry material (raw).

The fibres can be pre-impregnated, that is, already impregnated with thermosetting resin, thus obtaining a raw material ready to be worked using appropriate processing methods.

Or the fibres can be of the non-pre-impregnated type in which the resin can be applied during processing or before processing through the intervention of an operator who spreads the resin on the fibres.

To create a structural artifact, it is necessary to implement different methods based on whether pre-impregnated or non-pre-impregnated fibers are used.

For example, a first method commonly defined as "prepreg press moulding" involves placing multiple layers of pre-impregnated fibres (i.e. already impregnated with thermosetting resin) inside a mould which is then closed using a high-pressure counter-mould. The mould and the counter-mould are heated to a high temperature using heating devices.

The high temperature and the crushing of the counter-mold against the mold causes the compaction of the fibers and the simultaneous cross-linking of the thermosetting resin.

A second method commonly called "resin transfer moulding", always involves preparing a mould and a counter mould designed to close the counter mould. In the counter mould there is a channel for the injection of thermosetting resin, while in the mould there are channels for the discharge of excess thermosetting resin. Inside the mould it is planned to arrange several layers of dry fibres, i.e. not pre-impregnated. Then it is planned to close the mould with the counter mould, heat the mould and the counter mould and inject, in the cavity arranged between the mould and the counter mould, the thermosetting resin at high temperature and high pressure until all the resin has impregnated all the fibres and has polymerised.

In both solutions, therefore, it is expected that both heat and pressure will be applied simultaneously so that the resin first becomes fluid and then hardens (polymerizes) and firmly connects the fibers together. Therefore, the resin acts as a binder for the fibers.

Once the resin has hardened, the piece can be removed from the mold.

It is important to highlight that the use of hot molds, which allow the simultaneous application of heat and pressure, involves different problems.

First of all, in order to reuse a hot mold, that is, to be able to place new pre-impregnated or non-pre-engaged fibers inside the mold in order to create a new product, it is necessary for the mold to be cooled. Once the mold has cooled, the new fibers are placed back into the mold and a new operating cycle is started again.

The larger the size of the mold and its heat capacity, the longer it will take to both cool and heat the mold.

Therefore, the time required to cool and heat the mold generates downtime that translates into production volumes that are not adequate for mass production of such composite material products.

Furthermore, heating the molds requires the use of a large amount of energy, making these solutions extremely expensive.

Finally, it is important to highlight that the use of thermosetting resin does not allow for the recycling of the product and therefore the recovery of the materials that compose it, since thermosetting resins, once hardened, cannot be reprocessed.

The purpose of the present invention is to overcome the drawbacks of the prior art by designing a new multilayered composite material sheet that is free of thermosetting resins and that can be used as a base material in a specific process for manufacturing an article, wherein said process does not involve the use of the hot molds used in the prior art, or does not involve simultaneously applying heat and pressure to the sheet.

A further aim of the present invention is to devise a process for the production of such a plate.

Another aim is to devise a new method of manufacturing an artefact that involves working the aforementioned multilayered sheet without using hot moulds.

Another aim is to devise a method of manufacturing an artifact that is economical, simple and quick to implement.

These objects are achieved in accordance with the invention with the features listed in the attached independent claim 1.

The plate according to the invention is defined by claim 1.

For greater clarity of explanation, the description of the present invention continues with reference to the attached drawing tables, which have only an illustrative and non-limiting value, where:

- Fig. 1 is a schematic side view of a first and basic embodiment of the multilayer plate according to the invention;

- Fig. 2 is a schematic side view of a second embodiment of the multilayer plate according to the invention;

- Fig. 2A shows schematically, through an axonometric view, a layer of needled product of the multilayer sheet according to the invention;

- Fig. 2B shows schematically, through a cross-section, a thermoplastic bicomponent fibre;

- Figs. 3A and 3B show schematically the steps of a process for producing the multilayer plate according to the invention;

- Figs. 4A, 4B and 4C show schematically, step by step, a method for the construction of a structural product starting from the multilayered sheet.

- Figs. 5, 6, 7 and 8 schematically show four different multilayer plates according to the invention used to carry out tests.

With reference to Figs. 1 and 2, the new multilayer plate according to the invention is described, indicated overall with the reference letter "L".

The multilayer plate (L) includes:

- a first external covering layer (1a),

- a second external covering layer (1b); and

- a group of layers (G) interposed between said first external covering layer (1a) and said second external covering layer (1b).

The layer group (G) includes:

- at least one layer of needled product (2), shown schematically in Fig. 2A, comprising polyester fibres (21) and thermoplastic bicomponent fibres (20);

- at least one reinforcing layer (3) comprising reinforcing fibres; and

- a plurality of polymeric heat-adhesive films (4), wherein each polymeric heat-adhesive film (4) is interposed between two adjacent layers (1a, 1b, 2 and 3) of said multilayer sheet (L).

In particular, Fig. 1 shows a multilayer plate (L) comprising a group of layers (G) having:

- a layer of needled product (2);

- a reinforcement layer (3);

- three layers of polymeric heat-adhesive film (4) each placed between two layers (1a, 1b, 2 and 3) of the multilayer sheet (L).

In Fig. 2 instead, another example of a multilayer plate (L) is shown in which the group of layers (G) includes:

- two layers of needled product (2);

- two layers of reinforcement (3);

- five layers of polymeric heat-adhesive films (4) each placed between two layers (1a, 1b, 2 and 3) of the multilayer sheet (L).

It should be noted that, although two specific examples of the group of layers (G) are shown in figures 1 and 2, said group of layers (G) may comprise a plurality of layers of needled product (2) and/or a plurality of reinforcement layers (3), and a plurality of layers of polymeric heat-adhesive films (4) interposed between adjacent layers in any sequence according to requirements. Such examples are shown in figures 5, 6, 7 and 8.

Preferably, polymeric heat-sealable films (4) comprise thermopolymers or copolyamides or copolyesters.

Referring to Fig. 2B the thermoplastic bicomponent fibres (20) of the needled product layer (2) comprise an internal core (201) and an external jacket (202) which covers the internal core (201). The external jacket (202) is made of a material having a lower melting point than the material of the internal core (201).

Preferably the internal core (201) comprises polyester fibres or polypropylene fibres and in general thermoplastic fibres;

Instead, the outer jacket (202) preferably comprises co-polyester or polypropylene and in general a thermoplastic material having a lower melting point than the internal core.

The aforementioned reinforcement layer (3) instead comprises glass fibres and/or natural fibres and/or carbon fibres and/or recycled carbon fibres and/or basalt fibres. The aforementioned fibres of the reinforcement layer are interwoven with each other so as to form a sheet of fibres. The fibres of the reinforcement layer (3) have a density between 80 gr/m<2 >and 500 gr/m<2>.

The external covering layers (1a, 1b) are preferably made of non-woven fabric commonly called ?TNT?.

With reference to Figs. 3A and 3B, a process for producing the multilayer sheet according to the invention is described.

First of all, with reference to Fig. 3A, it is planned to prepare the first external covering layer (1a), the second external covering layer (1b), one or more layers of needled product (2), one or more reinforcement layers (3) and a plurality of polymeric heat-adhesive films (4). The number of layers of needled product (2), of the reinforcement layer (3) and of the polymeric heat-adhesive films (4) depends on the needs and the type of product that will have to be made with the multilayer sheet (L).

Subsequently, a stratification step is planned in which the first external covering layer (1a), the second external covering layer (1b), the one or more layers of needled product (2), the one or more reinforcement layers (3) and the plurality of polymeric heat-adhesive films (4) are coupled together to obtain a package (P). It should be noted that in said stratification step, it is planned that the external covering layers (1a, 1b) externally cover the package (P) and that at least one polymeric heat-adhesive film (4) is always placed between two adjacent layers (1a, 1b, 2 and 3) of the package.

With reference to Fig. 3B, once the package (P) has been created, it is planned to laminate it by passing it through a lamination machine (R) so as to obtain the multilayer sheet (L).

The lamination machine (R) comprises a boxed frame defining a lamination chamber (CR) inside which counter-rotating rollers (RL) are arranged between which the package (P) is passed so that the rollers (RL) crush and compact the package (P) obtaining the laminated multilayer sheet (L).

Preferably, the lamination of the package is carried out at a temperature between 130° and 170°.

The lamination machine (R) for this purpose includes heating means suitable for heating the chamber (CR) of the lamination machine (R) while the package is passed through the rollers (RL).

The temperature must be higher than the melting point of the outer jacket (202) of the thermoplastic bicomponent fibres (20) and lower than the melting point of the thermoplastic bicomponent fibres (201) so that the outer jacket (202) can melt, at least partially, binding the various layers (1a, 1b, 2, 3) together while the internal core (201) remains intact preserving its mechanical properties.

Once the lamination is completed, the multilayer sheet (L) is obtained, ready to be worked in order to obtain a structural product (M).

With reference to Figs. 4A, 4B, 4C and 4D, a method for the production of an artefact (M) starting from the multilayer sheet (L) is illustrated.

Referring to Fig. 4A, the multilayer plate (L) is first heated to a temperature between 170° and 250°.

In particular, the multilayer sheet (L) can be heated using a special oven that supplies heat (C) to the multilayer sheet (L) or via heated plates that are placed in contact with the multilayer sheet (L) in order to heat it.

Here too, the heating temperature of the multilayer plate (L) must be higher than the melting point of the external jacket (202) of the thermoplastic bicomponent fibres (20) and lower than the melting point of the internal core (201) so that the material of the external jacket (202) can melt while the internal core (201) remains intact.

With reference to Fig. 4B, once the multilayer plate (L) has been heated, it is planned to set up a cold press (S) comprising:

- a female mold (S1) comprising a seat; and - a male mold (S2) comprising a protrusion conforming to the seat of the female mold (S1).

The seat of the female mould (S1) and the protrusion of the male mould (S2) are shaped in such a way that said seat and said protrusion, when coupled together, define a cavity which has the shape that the product (M) will have.

Still referring to Fig. 4B, the heated multilayer sheet (L) is immediately placed between the two moulds (S1, S2) of the cold press (S), and then the two moulds are brought closer together in such a way that the protrusion of the male mould (S2) penetrates the seat of the female mould (S1), deforming the multilayer sheet (L) and pressing it against the internal wall of the seat of the female mould (S1) so that the multilayer sheet (L) assumes the shape of the desired product (M).

Specifically, during this step the following happens:

- initially, due to the pressure exerted by the press (S), the molten material with which the external jackets (202) of the thermoplastic bicomponent fibres (20) were made impregnates the various layers of the multilayer sheet (L);

- subsequently, the molten material cools and solidifies, binding the layers together (2, 3, 1a, 1b).

After having activated the press, it is however necessary to wait a predetermined time for the product (M) to cool.

In order to speed up the cooling of the product (M), it is possible to equip the cold press (S) with thermal conditioning means configured in such a way as to maintain the male mould (S2) and the female mould (S1) at a temperature between 25 °C and 40 °C, preferably between 30 °C and 35 °C.

By way of example, said thermal conditioning means comprise a cooling circuit comprising ducts that pass through the male mould (S2) and the female mould (S1) in which a cooling liquid flows.

If the cold press (S) includes the aforementioned conditioning means then it is sufficient to wait between 20 seconds and 60 seconds before uncoupling the molds (S1 and S2) and extracting the product (M) from the seat of the female mold as shown in figures 4C and 4D.

The applicant carried out experimental tests to compare the mechanical performance of the multilayer sheet (L) according to the invention with that of sheets known on the market.

In particular, the applicant used for these experimental tests four multilayer plates (L1, L2, L3 and L4) according to the invention and shown schematically in figures 5 to 8 and three plates of the known art not shown in the attached figures.

With reference to Fig. 5, the first multilayer plate (L1) has a thickness of approximately 2 mm and comprises:

- the two external covering layers (1a, 1b);

- two layers of needled product (2);

- three layers of reinforcement (3); and

- six polymeric heat-seal films (4).

With reference to Fig. 6, the second multilayer plate (L2) has a thickness of 3 mm and comprises:

- the two external covering layers (1a, 1b);

- two layers of needled product (2);

- five layers of reinforcement (3); and

- eight polymeric heat-sealing films (4).

With reference to Fig. 7, the third multilayer plate (L2) has a thickness of approximately 2.5 mm and comprises:

- the two external covering layers (1a, 1b);

- two layers of needled product (2);

- five layers of reinforcement (3); and

- eight polymeric heat-sealing films (4).

With reference to Fig. 8, the fourth multilayer plate (L4) has a thickness of 2.5 mm and includes:

- the two external covering layers (1a, 1b);

- a layer of needled product (2);

- eight layers of reinforcement (3); and

- ten polymeric heat-seal films (4).

The three plates of the known technique used to carry out the comparative tests are instead:

A1) a first sheet of the prior art having a thickness of 3 mm and comprising polyester fibres impregnated with polyurethane resin and glass fibres;

A2) a second sheet of the prior art having a thickness of 3 and composed of 50% by weight of natural fibres (flax, hemp and the like) and 50% by weight of polypropylene fibres;

A3) a third plate of the prior art having a thickness of 2 mm and composed of 50% short glass fibres and 50% polypropylene fibres.

The multilayer plates (L1, L2, L3, L4) and the plates of the above-mentioned prior art were compared in a bending test according to the ISO 178 standard (see table 1) and in a tensile test according to the ISO 527 standard (see table 2).

TABLE 1 (ISO 178 Flexural Test)

TABLE 2 (ISO 527 Tensile Test)

From the tables above it is possible to see how the multilayer plates (L1, L2, L3, L4), although presenting a density similar to that of the plates of the known art, still present a higher Young's modulus. This indicates that such multilayer plates (L1, L2, L3, L4) according to the known art present a better rigidity and resistance than the aforementioned plates of the known art.

Furthermore, the applicant also carried out a "Charpy" impact test according to ISO 179-1-2010 on the first multilayer plate (L1) and on the second multilayer plate (L2).

From these tests it emerged that the first multilayer plate (L1) has a resilience of 41.1 KJ/m<2> while the second multilayer plate (L2) has a resilience of 40 KJ/m<2>.

These values further confirm that the multilayer plate (L) according to the invention also has a high capacity to resist forces applied in short times.

It is important to highlight to the reader a particular peculiarity of the present invention that significantly differentiates it from the methods of the art. This difference concerns the way in which the layers of the multilayer sheet (L) or of the product (M) are bonded or joined together. In fact, in the present invention the joining of the various layers does not occur through the use of a thermosetting resin (as instead occurs in the known art), but occurs thanks to the use of the thermoplastic bicomponent fibres (20) of the needled product layer (2). In particular, the external jacket (202) of each bicomponent fibre (20) melts both during the lamination step of the process for the production of the multilayer sheet (L) and during the heating step of the multilayer sheet (L) in the method for the production of the product (M) while the internal core (201) remains intact, guaranteeing a solid structure for the product (M) during its production phase.

Following the above description, the advantages brought about by the present invention now appear.

First of all, the overall time required to produce the multilayer plate (L) and then create the artefact (M) using the aforementioned multilayer plate (L) is much less than the time required in the known technique to produce composite artefacts.

Furthermore, since the modelling of the multilayer sheet (L) occurs without the use of hot moulds but rather through the aforementioned cold press, all the dead times necessary in the known technique to cool the moulds before starting the production of a new product are avoided. Therefore, the use of multilayer sheets (L) to produce products (M) allows for high daily production volumes to be guaranteed.

Furthermore, the absence of hot moulds drastically reduces the costs required for the production of the products (M).

Furthermore, since the multilayer plate (L) and the product (M) are free of thermosetting resins, it is also possible to recycle the product (M) at the end of its life cycle in order to possibly recover the materials that compose it.

Finally, the applicant also found that the artefact (M) obtained using the plate (L) has the following peculiarities:

- it can be made with limited thicknesses while still maintaining high structural and mechanical properties; and

- it is not subject to swelling.

Numerous variations and modifications of detail may be made to the present embodiment of the invention, within the reach of a technician in the field, while still falling within the scope of the invention expressed in the attached claims.

Claims (12)

1) Multilayer sheet (L) intended to be used for the construction of a product (M) with self-supporting characteristics; said multilayer sheet (L) comprising a plurality of layers which include: - a first external covering layer (1a), - a second external covering layer (1b); and - a group of layers (G) interposed between said first external covering layer (1a) and said second external covering layer (1b); wherein said group of layers (G) comprises: - at least one layer of needled product (2) comprising polyester fibres (21) and thermoplastic bicomponent fibres (20); - at least one reinforcing layer (3) comprising reinforcing fibres; and - a plurality of polymeric heat-adhesive films (4), wherein each polymeric heat-adhesive film (4) is interposed between two adjacent layers (1a, 1b, 2 and 3) of said multilayer sheet (L). 2) Multilayer sheet (L) according to claim 1, wherein said polymeric thermoadhesive films (4) comprise thermopolymers or copolyamides or copolyesters. 3) Multilayer sheet (L) according to any of the preceding claims, wherein said thermoplastic bicomponent fibres (20) comprise an internal core (201) and an external jacket (202) covering the internal core (201); wherein the external jacket is of a material having a lower melting point than the material of the internal core. 4) Multilayer plate (L) according to claim 3, wherein: - the internal core (201) comprises polyester fibres or polypropylene fibres and in general thermoplastic fibres; - the outer jacket (202) comprises co-polyester or polypropylene and in general a thermoplastic material having a lower melting point than the internal core. 5) Multilayer plate (L) according to any of the preceding claims, wherein said reinforcing fibres of the at least one reinforcing layer (3) comprise glass fibres and/or natural fibres and/or carbon fibres and/or basalt fibres. 6) Multilayer sheet (L) according to any of the preceding claims, wherein said group of layers (G) comprises a plurality of needle punched product layers (2) and/or a plurality of reinforcing layers (3). 7) Multilayer sheet (L) according to any of the preceding claims, wherein said external covering layers (1a, 1b) are made of non-woven fabric ?TNT?. 8) Process for the production of a multilayer sheet (L) according to any of the preceding claims; said process providing for: - prepare the first external covering layer (1a), the second external covering layer (1b), the at least one layer of needle punched product (2); the at least one reinforcing layer (3) and the plurality of polymeric heat-adhesive films (4); - carry out a stratification in which the first external covering layer (1a), the second external covering layer (1b), the at least one layer of needle-punched product (2), the at least one reinforcing layer (3) and the plurality of polymeric heat-adhesive films (4) are coupled together so as to obtain a package (P); - laminate the package (P) by passing it through a lamination machine (R) to obtain the multilayer sheet (L). 9) Process according to claim 8, wherein said step of laminating the package (P) is carried out at a temperature between 130° and 170°. 10) Method for the production of a manufactured article (M); said method comprising the following operational steps: - preparing a multilayer plate (L) according to any of claims 1 to 7; - heat the plywood plate (L) to a temperature between 180° and 220°; - prepare a cold press (S) comprising a female mould (S1) comprising a seat and a male mould (S2) comprising a protrusion conforming to the seat of the female mould (S1); - place the multilayer plate (L) in the cold press (S); - bring said female mould (S2) and said male mould (S1) closer together so that said protrusion of the male mould (S2) penetrates the seat of the female mould (S1), deforming the multilayer sheet (L) and pressing it against the internal wall of the cavity of the female mould (S1) so that the multilayer sheet (L) assumes the shape of the desired product (M); -wait a predetermined time; - move said female mould (S1) and said male mould (S2) away from each other; - extract the artifact (M) from the seat of the female mold (S1). 11) Method according to claim 10, wherein said cold press (S) comprises thermal conditioning means configured to maintain the male mold (S2) and/or the female mold (S1) at a temperature between 15 °C and 25 °C. 12) Manufactured article (M) produced according to the method of claim 10 or 11.