Composition comprising a phenolic resin, composite material comprising such a composition and process for preparing a composite material

Abstract

The composition includes: at least one binder chosen from phenolic resins, and particles formed from at least one pulverulent solid chosen from glass, polymers and silica, and mixtures thereof, the particles having an average size of less than 1 mm, wherein the composition includes between 34% and 50% by weight of the pulverulent material relative to the total weight of the composition. A sandwich composite material including such a composition and a process for preparing such a sandwich composite material are also described.

Claims

1. A composite sandwich material comprising at least one cellular material having voids, said cellular material being arranged between at least two outer skins, each outer skin being formed of at least one composite material comprising at least one reinforcement in the form of fibres and at least one polymer material, named the polymer matrix, within which the fibres extend, wherein the sandwich material comprises a composition comprising: at least one binder chosen from phenolic resins, particles formed of at least one pulverulent solid selected from the group consisting of glass, polymers, silica and mixtures thereof, said particles having an average size of less than 1mm, from 34 wt. % to 50 wt. % of said pulverulent material, based on the total weight of said composition, said at least one binder and particles providing a fire resistance and: said composition is free of a catalyst or a curing agent of said binder, at least some of the voids of said cellular material are filled with said composition, and said composition contains no additive and no filler that would reduce the fire resistance, wherein said cellular material is chosen from materials having a honeycomb structure.

2. A process for preparing a material, named a composite sandwich material, comprising at least one cellular material having voids, said cellular material being arranged between at least two outer skins, each outer skin being formed of at least one composite material comprising at least one reinforcement in the form of fibres and at least one polymer material, named the polymer matrix, within which the fibres extend, said process comprising: preparing a composition comprising: at least one binder chosen from phenolic resins, from 34 wt. % to 50 wt. % particles formed of at least one pulverulent solid chosen from glass, polymers, silica and mixtures thereof, based on the total weight of the composition, said particles having an average size of less than 1 mm, said composition being free of a catalyst or a curing agent of said binder, said at least one binder and particles providing a fire resistance, filling at least some of the voids of said cellular material with said composition, polymerizing said binder at a temperature of from 110 C. to 250 C., wherein said composition contains no additive and no filler that would reduce the fire resistance, and wherein said cellular material is chosen from materials having a honeycomb structure.

3. The process according to claim 2, further comprising subjecting said composite sandwich material to a temperature of from 120 C. to 180 C. and to a pressure of from 100,000 Pa to 700,000 Pa.

4. The process according to claim 3, wherein the polymerizing of said binder is carried out simultaneously with polymerization of the polymer matrix of said composite material at a temperature of from 110 C. to 250 C.

5. The process according to claim 2, wherein the polymerizing of said binder is carried out simultaneously with polymerization of the polymer matrix of said composite material at a temperature of from 110 C. to 250 C.

Description

(1) Other objects, features and advantages of the invention will become apparent from reading the following description of a preferred embodiment thereof, which is given by way of a non-limiting example and which refers to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of a composite sandwich material according to a first embodiment of the invention,

(3) FIG. 2 is a schematic view of a composite sandwich material according to a second embodiment of the invention.

(4) A composition according to the invention is prepared by mixing at least one binder chosen from the phenolic resins with particles, preferably spherical particles, formed of at least one pulverulent solid chosen from glass, polymers, silica and mixtures thereof, said particles having an average size of less than 1 mm. A composition according to the invention is in particular characterised in that it comprises from 34 wt. % to 50 wt. % of said pulverulent material, based on the total weight of the composition.

(5) The binder is chosen from the phenolic resins, which are obtained by polycondensation of formaldehyde (formol) and phenol and/or a phenol derivative such as cresol, resorcinol or xylenol.

(6) The binder may be composed, for example, of at least one phenolic resin such as the resins CELLOBOND J2042L, J2027L or J2018L marketed by HEXION (Sully, WALES) or a resin FXFNO26 marketed by SI GROUP (Schenectady, USA).

(7) The particles formed of at least one pulverulent solid are hollow or solid. In a particularly advantageous embodiment according to the invention, the particles formed of at least one pulverulent solid are hollow. In a particularly advantageous embodiment of a composition according to the invention, said particles formed of at least one pulverulent solid have an average diameter of less than 1 mm, especially from 20 m to 200 m and in particular from 40 m to 150 m.

(8) In a particularly advantageous variant of a composition according to the invention, the particles formed of at least one pulverulent solid are hollow or solid glass beads, preferably hollow glass beads.

(9) In a particularly advantageous variant of a composition according to the invention, the polymeric particles are chosen from particles based on phenolic resin. Such particles in fact have good compatibility with the binder, a lower density than glass beads and improved fire resistance.

(10) Particles of silica include, for example, particles of pyrogenic silica, particles of precipitated silica or particles named fumed silica particles.

(11) The phenolic resin and the pulverulent solid(s) can be brought into contact by means of any device adapted to bring the binder and the particles formed of at least one pulverulent solid into contact and, preferably, adapted for preparing a homogeneous mixture of said binder and said particles. In order to permit the preparation of a homogeneous composition, it is preferable to use a mixer or kneader, such as a RUBIMIX L-120-R liquid kneader marketed by RUBI (Rubi, Spain).

(12) The binder and the particles formed of at least one pulverulent solid may, if required, further be heated gently (for example at from 20 C. to 50 C., especially from 25 C. to 30 C.) before and/or during mixing so as to accelerate and facilitate the preparation of a homogeneous mixture.

(13) In a particularly advantageous embodiment, a composition according to the invention is arranged within at least some of the voids of a cellular material, said cellular material being arranged between at least two outer skins of a composite sandwich material, each outer skin being formed of at least one composite material comprising at least one reinforcement in the form of fibres and at least one polymer material, named the polymer matrix, within which the fibres extend.

(14) The cellular material is preferably chosen from materials having a honeycomb structure (also called NIDA). It is, for example, NIDA NOMEX, which is formed of a matrix of phenolic resin and aramid fibres and is marketed by HEXCEL (Sully, WALES).

(15) The composition according to the invention is arranged, at the desired location, within the voids of the cellular material, and the composite sandwich material is subjected to a step of polymerisation, which allows the phenolic resin and optionally simultaneously the polymer matrix of the outer skins of the composite sandwich material to cure.

(16) Polymerisation of the phenolic resin can be carried out at ambient temperature or at a temperature above ambient temperature and at atmospheric pressure or at a pressure above atmospheric pressure. In particular, the temperature is from 15 C. to 250 C. and the pressure is from 100,000 Pa to 700,000 Pa.

(17) According to a particularly advantageous embodiment of the invention, the phenolic resin is polymerised at a temperature of from 150 C. to 220 C. and preferably from 155 C. to 170 C. It is thus possible to carry out simultaneously the polymerisation of the phenolic resin and the polymerisation of the polymer matrix of the outer skins of the composite sandwich material, for example an epoxy resin.

(18) The step of polymerisation of the phenolic resin is carried out for a duration which is adapted to permit curing of the phenolic resin, especially a duration of from 10 minutes to 5 hours, preferably from 30 minutes to 3 hours.

(19) The step of polymerisation of a composition according to the invention is, for example, carried out in an oven at 160 C. for 1 hour.

(20) The step of polymerisation of the phenolic resin is carried out in an autoclave, an oven or in a furnace, according to the chosen temperature and pressure.

(21) In the presence of a catalyst of polymerisation of the phenolic resin, the phenolic resin can be polymerised at ambient temperature (from 20 C. to 25 C.).

(22) It should further be noted that, before the polymerisation of the phenolic resin, the composition according to the invention is advantageously in the form of a paste, the viscosity of which may vary according to the nature and proportions of the binder and solid particles used. The composition according to the invention preferably has a viscosity of from 300 mPa.Math.s to 700 mPa.Math.s.

(23) In a first embodiment shown in FIG. 1, the composition 10 according to the invention is arranged at the edge of a composite sandwich panel 1 comprising a cellular material 6, which forms the honeycomb core of the panel 1, and two outer skins 4 formed of a composite material comprising, for example, carbon fibres within a polymer matrix such as an epoxy resin. The composite sandwich panel 1has, for example, a total thickness of from 3 mm to 45 mm. The composition 10 according to the invention is arranged along the entire edge of the panel 1, over the entire thickness of the panel and, for example, over a width of 1.5 cm (that is to say 1.5 cm from an outside edge of the panel). The width over which the composition is arranged depends on the type of composite sandwich panel prepared and is, for example, adapted to fill at least one and a half cells of the honeycomb core of the panel 1 from the outside edge of the panel. A composition according to the invention thus both allows the edges of a composite sandwich panel to be reinforced mechanically and allows the fire resistance of the composite sandwich panel to be improved, without significantly increasing the mass of said panel.

(24) In a second embodiment shown in FIG. 2, the composition 10 according to the invention is arranged around an insert 14 made of polymer or metal material. The insert 14 (of the spool insert type) has, for example, a diameter of 10 mm, the ends of which in the form of discs have a diameter of 20 mm. A hole has first been formed by cutting in the thickness of the composite sandwich panel, and then an insert has been introduced and fixed by means of the pasty composition according to the invention. The composition has been applied so as to surround the insert and fill at least partially the voids adjacent to the insert in a radius of from 20 mm to 30 mm around the insert, that is to say so as to produce an edging for the insert having a diameter at least equal to twice the diameter of the insert. The composition according to the invention is thus applied, for example, in a radius of at least 15 mm around the insert.

(25) A composition according to the invention thus allows an insert placed inside a composite sandwich panel to be held and the zone of the panel in which the insert is arranged to be reinforced mechanically. Furthermore, the composition according to the invention allows the fire resistance of the composite sandwich panel to be improved, without significantly increasing the mass of said panel.

EXAMPLE 1

(26) A composition comprising 1 kg of phenolic resin CELLOBOND J2042L marketed by HEXION and 550 g of hollow glass particles having an average diameter of 70 m (measured by screening) is prepared. Such a composition therefore comprises 35 wt. % glass particles. No catalyst or curing agent for the phenolic resin is added to the composition. The phenolic resin and the glass particles are brought into contact and mixed in a RUBIMIX L-120-R kneader marketed by RUBI.

(27) A cellular honeycomb material having a thickness of 15 mm made of NIDA HOMEX, formed of a matrix of phenolic resin and of aramid fibres, marketed by HEXCEL, is prepared. Moreover, plies of prepregs comprising an epoxy polymer matrix and glass and carbon fibres are chosen. Three plies of honeycomb prepregs are placed on a working surface, and the cellular material is arranged on the first three plies of prepregs. The previously prepared composition is arranged within all the voids of the cellular material, and three further plies of prepregs are placed on top of the cellular material whose voids are filled with said composition. Each ply of prepregs has a thickness of 0.1 mm. The composite sandwich material so prepared therefore has a thickness of 15.6 mm.

(28) The composite sandwich material so prepared is then subjected to a step of polymerisation at 150 C. in an oven and under a vacuum obtained by means of a MINIVAC 1 PS PS5 pump marketed by MILS (Genas, France). The total duration of the polymerisation cycle is 4 hours and 50 minutes (rise in temperature of 2 C/minute for 50 minutes, from 22 C. to 150 C.; maintenance at the temperature of 150 C. for 2 hours; then cooling for one hour with ventilation to a temperature of 22 C.).

EXAMPLE 2

(29) A composition comprising 1 kg of phenolic resin CELLOBOND J2042L marketed by HEXION and 550 g of hollow phenolic resin particles (BJO-0930 marketed by Asia Pacific Microspheres) having an average diameter of 90 m (measured by screening) and a density of 0.228 is prepared. Such a composition therefore comprises 35 wt. % phenolic resin particles. No catalyst or curing agent for the phenolic resin is added to the composition. The phenolic resin and the particles of phenolic resin are brought into contact and mixed in a RUBIMIX L-120-R kneader marketed by RUBI.

(30) A cellular honeycomb material having a thickness of 15 mm made of NIDA HOMEX, formed of a matrix of phenolic resin and of aramid fibres, marketed by HEXCEL, is prepared. Moreover, plies of prepregs comprising a polymer matrix based on phenolic resin and glass and carbon fibres are chosen. Three plies of honeycomb prepregs are placed on a working surface, and the cellular material is arranged on the first three plies of prepregs. The previously prepared composition is arranged within all the voids of the cellular material, and three further plies of prepregs are placed on top of the cellular material whose voids are filled with said composition. Each ply of prepregs has a thickness of 0.1 mm. The composite sandwich material so prepared therefore has a thickness of 15.6 mm.

(31) The composite sandwich material so prepared is then subjected to a step of polymerisation at 110 C. in an oven and under a vacuum obtained by means of a MINIVAC 1 PS PS5 pump marketed by MILS (Genas, France). The total duration of the polymerisation cycle is 5 hours and 50 minutes (rise in temperature of 2 C/minute for 50 minutes, from 22 C. to 110 C.; maintenance at the temperature of 150 C. for 3 hours; then cooling for one hour with ventilation to a temperature of 22 C.).

EXAMPLE 3

(32) A composition and a composite sandwich material are prepared in accordance with Example 1. Polymerisation of the composite sandwich material is carried out in the same manner as in Example 1 but in an autoclave at a pressure of 1.5 MPa.

EXAMPLE 4

(33) A composition and a composite sandwich material are prepared in accordance with Example 2. Polymerisation of the composite sandwich material is carried out in the same manner as in Example 2 but in an autoclave at a pressure of 1.5 MPa.

(34) Each of the composite sandwich materials prepared in Examples 1 to 4 permits simultaneous polymerisation of the polymer matrix of the outer skins of the composite sandwich material and of the phenolic resin of the composition filling the cells of the composite sandwich material, without any leak of the composition or any phenomenon of foaming. In particular, no air bubble was noted within the composition filling the cells of the composite sandwich material.

(35) Each of the composite sandwich materials prepared in Examples 1 to 4 further exhibits excellent fire resistance in tests in which a portion of said panel is exposed to a flame, such as a flame formed by a Bunsen burner for 60 seconds.

COMPARATIVE EXAMPLE

(36) A composition comprising 50 wt. % phenolic resin CELLOBOND J2042L marketed by HEXION, 35 wt. % hollow glass particles and 5 wt. % catalyst of the polymerisation of the phenolic resin is prepared. The phenolic resin and the glass particles are brought into contact and mixed in a RUBIMIX L-120-R kneader marketed by RUBI.

(37) A cellular honeycomb material having a thickness of 15 mm made of NIDA HOMEX, formed of a matrix of phenolic resin and of aramid fibres, marketed by HEXCEL, is prepared. Moreover, plies of prepregs comprising an epoxy polymer matrix and glass and carbon fibres is chosen. Three plies of honeycomb prepregs are placed on a working surface, and the cellular material is arranged on the first three plies of prepregs. The previously prepared composition is arranged within all the voids of the cellular material, and three further plies of prepregs are placed on top of the cellular material whose voids are filled with said composition. Each ply of prepregs has a thickness of 0.1 mm. The composite sandwich material so prepared therefore has a thickness of 15.6 mm.

(38) The composite sandwich material so prepared is then subjected to a step of polymerisation at 150 C. in an oven at atmospheric pressure. The total duration of the polymerisation cycle is 4 hours and 50 minutes (rise in temperature of 2 C/minute for 50 minutes, from 22 C. to 150 C; maintenance at the temperature of 150 C. for 2 hours; then cooling for one hour with ventilation to a temperature of 22 C.).

(39) Foaming of the phenolic resin is observed during the polymerisation, which causes deformation of the outer skins of the composite sandwich material and does not allow a satisfactory composite sandwich material to be obtained. Furthermore, the mechanical properties of the composite sandwich material so obtained are very poor owing to the many air bubbles present within the material.

(40) The invention can be the subject of a very large number of variant embodiments. In particular, it is possible to use a composition according to the invention for other applications, for example as an adhesive for composite materials.