FR2605928A1 - Matrix for a composite material, its method of manufacture and composite material which includes such a matrix - Google Patents

Abstract

The invention relates to a hybrid matrix intended for making a composite material of either a monolithic or sandwich type. Such a hybrid matrix 11 consists of a thermosetting base resin 1 of known type into which flakes 5 of glass, graphite, etc. and surfactants and have been introduced. Such a hybrid matrix 11 is used as a conventional matrix, that is to say that it is intended to receive reinforcing materials, for example fibrous materials 2 and 3. The distribution of the flakes is either homogeneous or has a density which is locally greater. The "resin-flake" sub-systems (sub-networks) lead to improved physical and mechanical properties (viscosity, flexural modulus of elasticity, shrinkage, etc.). The invention applies to any application using composite materials.

Description

MATRIX FOR COMPOSITE MATERIAL,
ITS MANUFACTURING METHOD,
AND COMPOSITE MATERIAL COMPRISING SUCH A MATRIX.

 The invention relates to a matrix for composite material and its manufacturing method. It also relates to any composite material comprising such a matrix.

 Composite materials fall into two broad categories.

The first groups the so-called "monolithic" composite materials obtained by the use of a matrix obtained from different types of polyester, epoxy, phenolyurethane, among others, this matrix being itself reinforced by a reinforcing material such as in particular fabric, glass fibers, carbon, aramids ... These materials are implemented in successive layers or folds. The second group of composite materials called "sandwiches" in which generally a cellular core is covered on both sides with one or more layers of a material which may itself be a monolithic composite material as described above.

 All of these materials are characterized by a number of physical and mechanical properties related to their structure including hardness, stiffness, tensile strength, impact resistance, and the like. In the known art, to change these properties, either the number of folds is increased, or the stacking techniques are improved, or the nature of the reinforcing materials is changed. For sandwich-type composite materials, the nature and dimension of the soul is generally used. All these modifications may result in particular increases in weight or thickness, which represents serious drawbacks for a large number of applications.

The present invention aims to overcome these disadvantages and relates to a new matrix leading to the production of a new monolithic composite material which offers physical and mechanical characteristics significantly higher than those present materials of this type currently known. This new material is intended to be used as is, or to cooperate with a cellular core as part of a
sandwich type material.

 The invention more specifically relates to a matrix for composite material of the type comprising a thermosetting resin (1) intended to be reinforced by reinforcements such as (2) and (3); matrix characterized in that scales (5) are integrated in the resin (1) to form a new hybrid matrix (11) intended in turn to receive said reinforcements (2) and (3).

The invention will be better understood with the help of the explanations that follow and the attached figures among which:
- Figure 1 schematically illustrates a section made of a monolithic composite material of the prior art;
- Figure 2 schematically illustrates a section of a monolithic composite material made from a hybrid matrix according to the invention;
- Figure 3 schematically illustrates a variant of a composite material according to the invention.

 For the sake of clarity, the same elements bear the same references in all the figures.

 FIG. 1 illustrates, in cross-section, a monolithic composite material of the known art, a matrix (1) produced, as previously mentioned, in thermosetting pure resin with, embedded in the mass, reinforcements (2 ) and (3) which are, in the example chosen in no way limiting, fibrous reinforcements. The latter are represented in number of two, but this is only illustrative. In fact, it is a plurality of reinforcements.

 According to an important characteristic of the invention, and as shown in FIGS. 2 and 3, an additional shell material (5) is added in the thermosetting resin (1) to form a hybrid matrix (11) in which are drowned, as before, the fibrous reinforcements (2) and (3) of Figure 1 to form a new monolithic composite material.

 It should not be confused the addition of these scales (5) to a simple addition of additional reinforcing material, this function remaining as ensured in the art known by the elements (2) and (3). On the other hand, it is a true new matrix qualified as hybrid (11) which, due to the presence of the scales (5), presents unexpected characteristics highlighted by the applicant.

 If the use of scales is already known, especially for the manufacture of special coatings used to fight against corrosion and to seal, the present invention describes a new application of these scales (5) which perform here another function . These scales (5) indeed give the hybrid matrix (11) new isotropic qualities on the one hand, and on the other hand create a lamellar sub-network inside the "matrix-reinforcement" system which leads to to significantly improved physical and mechanical characteristics whose values are given later in a comparative table.

 In addition, according to another important characteristic of the invention, the distribution and location of the scales (5) in the thermosetting resin (1) can be controlled according to the applications for which the hybrid matrices (11) thus obtained are intended. This characteristic is particularly illustrated by means of two figures 2 and 3. In the first, the scales are uniformly distributed; in the second, their density is unequal according to the zones concerned. We can indeed play on the two parameters: distribution and localization.For this, is added in the thermosetting resin (1) base, prior to the addition of scales (5), a variable amount of surfactants selected from those which are capable of sufficiently modifying the surface tensions of the resin (1) vis-à-vis the scales (5), this for a good wetting thereof by the resin (1). This promotes the elimination of any air film present on the surface of the scales (5), an air film detrimental to the bridging resin (1) - scales (5). This bridging may, in addition, be improved by chemical agents appropriate to the type of resin used.

 The process for preparing a hybrid matrix according to the invention is described below. After the bridging agents, such as silane, and the surfactants have been added to the resin, the scales (5) are dispersed by slow stirring in said resin. Thereafter, thixotropic agents can be added as well as pigment pastes, that is products commonly used in the composite materials industry. A suspension (resin, flakes, surfactants and other additives) is obtained so that after polymerization or curing of the hybrid matrix (11), a new solid-scale "resin-scale" network or sub-network is obtained. which improves the transfer of charges between fibers and / or between folds, and which, consequently, improves the characteristics of the composite material obtained from this hybrid matrix (11).

 Surfactants and chemical agents are used at concentrations ranging from 0.25 to 2.5%. The amount of scale (5) is between 2 and 40%, and is more preferably 20% by weight relative to the base resin. The size of the scales can be between 0.3 mm and 3 mm long, with a thickness ranging from 5 to 30 microns. The nature of the scales is varied depending on the application. It may be, for example, glass flakes, mica or graphite, polymethyl methacrylate flakes, but this list is not exhaustive.

 The present invention also relates to any monolithic composite material obtained from a hybrid matrix obtained according to the invention.

Indeed, the latter which is homogeneous can then be used according to the same prescriptions as those recommended by the suppliers of basic resins.

 According to another characteristic of the invention, two variants are feasible for obtaining a composite material from a matrix (11) as defined above. These variants are based on the distribution of scales (5) in the base resin (1). In a first case, it is stable and the structure illustrated by means of FIG. 2 is obtained, and in this case, the volume anisotropic nature of the composite material is reduced, while improving the distribution of the stresses in the material and while reducing contractions in volume, that is to say the withdrawals of the matrix. This removes many problems related to this phenomenon.

 In a second case, by changing the rheological properties of the hybrid matrix (11), the dispersion of the scales (5) in the base resin (1) is made unstable and, as shown in FIG. rapid decantation of the scales (5) in the matrix, even inside a fold during the preparation of the composite material. This has the effect of greatly increasing the isotropic nature in the plane, as shown in Figure 3 where we see areas (a), (b) and (c) with high scale density, while improving the distribution of constraints.

The table below clearly illustrates the improvement of the main technical characteristics of the hybrid matrices according to the invention, compared to the basic matrices of the prior art.

<Tb>

<SEP> Matrices
<tb><SEP><SEP> Characteristics of <SEP> Hybrid <SEP> Base
<tb> Viscosity <SEP> (poises) <SEP> 3.2 <SEP> 5.2
<tb> Modulus <SEP> Average <SEP> Modulus
<tb><SEP> bending <SEP> (daN / mm2) <SEP><SEP> 320 <SEP> 556
<tb><SEP> M1 <SEP> M2 <SEP>M'1<SEP> M-2 <SEP>
<tb> Materials <SEP> composites
<tb> monolithic <SEP> obtained <SEP> with
<tb> modulus <SEP> of average <SEP> elasticity
<tb><SEP> Bending <SEP> (da <SEP> N / mm2) <SEP> 1380 <SEP> 965 <SEP> 1612 <SEP> 1169
<Tb>
The applications of the invention are numerous. They concern all industries that implement ~ monolithic composite materials or sandwich type.

Claims (9)

 1) Matrix for composite material of the type comprising a thermosetting resin (1) intended to be reinforced by reinforcements such as (2) and (3); matrix characterized in that scales (5) are integrated in the resin (1) to form a new hybrid matrix (11) intended in turn to receive said reinforcements (2) and (3).  2) Matrix according to claim 1, characterized in that a surfactant product is added to modify the surface tension of the medium, so that it promotes the wetting of said scales (5), thus facilitating the connection and the distribution of the couple "resin-scales".  3) Composite material characterized in that the matrix used is a hybrid matrix (11) according to one of the preceding claims, matrix with which cooperate reinforcing materials (2) and (3).  4) composite material according to claim 3, characterized in that, by rheological modification of the base resin (1), is formed, after curing or polymerization, a solid sub-network "resin-scales" inside the material composite, which improves the distribution of stresses and - decreases the shrinkage inherent in the transition from the liquid state to the solid state of the resin (1).  5) Composite material according to one of Claims 3 and 4, characterized in that, by modifying the rheological properties of the base resin, the density of the scales increases, in particular by settling, in certain zones (a), ( b) and (c).  - addition of surfactants; these steps leading to obtaining a suspension organized so that after curing or polymerization, one obtains a sub-network "resin-scales" intended to cooperate with reinforcing materials (2) and (3).  - dispersion of scales (5) in the thermosetting resin (1) by slow stirring;  6) Process for the preparation of a composite hybrid matrix (11) according to one of claims 1 and 2, characterized in that it comprises the following steps:  7) Method according to claim 6, characterized in that thyxotropic agents are added in particular to ensure the coloring of said hybrid matrix (11).  8) Method according to one of claims 6 and 7, characterized that flakes have a length of 0.3 to 3 mm and a thickness of 5 to 30 microns.  9) Method according to one of claims 6, 7 and 8, characterized in that the concentration of surfactants and c-chemicals ranges from 0.5 to 2.5% and the amount of scales from 2 to 40% by weight relative to the base resin.