WO1999029770A1

WO1999029770A1 - Composition based on a polymer with thixotropic and/or pseudoplastic behaviour filled with microbeads

Info

Publication number: WO1999029770A1
Application number: PCT/FR1998/002666
Authority: WO
Inventors: Carl Andreas Paulick; Yves Schmitt; Yves Bour; François Royer
Original assignee: Carl Andreas Paulick; Yves Schmitt; Yves Bour; Royer Francois
Priority date: 1997-12-10
Filing date: 1998-12-09
Publication date: 1999-06-17
Also published as: AU1493199A; FR2772037A1; FR2772037B1; EP0960163A1

Abstract

The invention concerns a composition based on a polymer or a copolymer or a mixture of polymers with thixotropic or pseudoplastic behaviour, characterised in that microbeads are incorporated into said composition before they are solidified, the proportion of microbeads relative to said composition total volume being selected on the basis of the rheological properties of the base polymer or copolymer or mixture of polymers so as to reduce said composition viscosity. The invention also concerns composite fibre-filled materials resulting from said composition.

Description

C ompo s i t i o n à b a s e u n p o l ymè r e à c omp o r t eme n t th ixot rope and / or pseudoplastic loaded with microbi l les

The present invention relates to compositions based on a polymer or on a copolymer or on a mixture of polymers with thixotropic and / or pseudoplastic behavior. The present invention also relates to composite materials and more particularly to composite materials produced from a liquid phase having a non-Newtonian flow and loaded mainly with fibers.

Currently, the methods for reducing the viscosity of such compositions are essentially based on dilution mechanisms with suitable compounds. The latter are most often solvents or liquefiers which have a molecular mass much lower than that of the polymer used to make the compositions. However, dilution based on solvents or liquefiers often leads to harmful repercussions on the environment and does not furthermore give satisfactory results in terms of the final mechanical properties of the parts or of the materials produced from such compositions. The main object of the invention is to provide compositions based on a polymer or a copolymer or a mixture of polymers with a thixotropic and / or pseudoplastic behavior, the fluidity of which is improved, without chemical adjuvants.

In accordance with the invention, a composition based on a polymer or a copolymer or a mixture of polymers with thixotropic and / or pseudoplastic behavior is proposed for this purpose, characterized in that glass microbeads are incorporated in said composition before solidification thereof, the proportion of microbeads relative to the total volume of said composition being chosen as a function of the rheological properties of the polymer or copolymer or mixture of base polymers in order to reduce the viscosity of said composition.

Obtaining a composition according to the invention is carried out according to methods known to those skilled in the art by mixing a polymer or a copolymer or a mixture of polymers with thixotropic and / or pseudoplastic behavior with microbeads before solidification of the base polymer.

It is necessary to uniformly distribute the microbeads in the composition in order to ensure regular properties throughout the composition, therefore thereby in materials or molded parts produced from such a composition.

The viscosity of the polymer composition decreases significantly when adding a relatively small percentage of microbeads chosen as a function of the rheological properties of the polymer or of the copolymer or of the mixture of base polymers. This reduction in viscosity is of a rheological nature and does not depend a priori on other properties and in particular on the chemical properties of the compounds used and is observed only at low levels of glass microbeads.

The present invention thus differs from the techniques using the TOMS effect to reduce the friction forces, said TOMS effect being obtained by adding macromolecules to the flowing liquids with a much higher Reynolds number to move the starting threshold of the turbulent flow (see in particular "Mechanics and rheology of fluids", N. MIDOUX Technologie et Documentation, Lavoisier 1985).

According to a characteristic of the composition, the average size and / or the nature of the microbeads are adapted to the shaping process chosen in the application of said composition.

There are several methods of shaping by injection or molding and their respective variants which are perfectly known to those skilled in the art and which will not be described here. Preferably, said glass microbeads are present in a proportion of between approximately 0.1 and approximately 3% by volume relative to the total volume of the composition, preferably between approximately 0.5 and approximately 2% and more particularly still between approximately 0.7 and 1.3%.

The results with regard to the reduction in viscosity are particularly convincing at around 1%. This decrease in viscosity is explained by the fact that the microbeads introduce volumes in which the flow gradients are greater than the average flow gradients of the composition causing a drop in the average viscosity in the case of a polymer or of a copolymer or of a mixture of polymers with thixotropic and / or pseudoplastic behavior.

The invention also extends to a composite material loaded with fibers, characterized in that it comprises a polymeric material consisting of a composition based on a polymer, a copolymer or a mixture of polymers with behavior thixotropic and / or pseudoplastic in which microbeads are incorporated before solidification of the composition and optionally a hardener and reinforcing fibers embedded in said polymeric matnce.

According to a characteristic of the material according to the invention, the average size and / or the nature of the microbeads are adapted to the process for shaping said composite material. Preferably, said microbeads are present in a proportion compπse between approximately 0J and approximately 3% by volume relative to the total volume of the composition, preferably between approximately 0.5 and approximately 2% and more particularly still between approximately 0.7 and about 1.3%.

Advantageously, the reinforcing fibers represent approximately 20 to approximately 70% by volume of the material, preferably approximately 25 to approximately 65%, and more particularly still approximately 30 to approximately 60%.

Preferably, the reinforcing fibers are short fibers.

For example, the fibers have an average length of 160 micrometers for a size distribution of 50 to 500 micrometers. It is thus possible, thanks to the invention, to obtain composite materials loaded with short fibers having properties very close to or even equivalent to those of metallic materials.

In addition, the reinforcing fibers are chosen without limitation from carbon fibers, aramid fibers, glass fibers.

In the composite materials according to the invention, the proportion of fibers is preferably between about 20 and about 70% by volume relative to the total volume of the material and more particularly between approximately 25 and approximately 65% and more particularly still between approximately 30 and approximately 60%. The invention is therefore particularly advantageous for obtaining composite materials with short fibers by molding / injection or cold casting. Until now, it has in fact been practically impossible to improve or modify the mechanical properties of such composite materials by trying to increase the proportion of fibers incorporated in the polymeric material beyond a ceramic concentration, namely a fiber concentration of about 30 to about 40% of the total volume of the composition used. A higher concentration of fibers no longer makes it possible to inject or cold flow satisfactorily the composition obtained.

The polymers with thixotropic and / or pseudoplastic behavior which can be used in the implementation of the invention are chosen from thermoplastics and thermosets. Said polymers with thixotropic and / or pseudoplastic behavior may, for example, be chosen non-mitatively from the group of epoxy, polysiloxane, polyester, polyurethane, polyethilene, polypropylene polymers.

As polymer or mixture of polymers which can be used for the implementation of the invention, there may be mentioned hmitively the following epoxy resins: bisphenol-A epichlorhydπne, bisphenol-A-épichlorhydπne with 1,6 hexandiolglycidéther-tπméthylolpropanitπglycidéther , bisphenol-A with 1,4-butanedιol diglycidyl ether.

The hardeners which can be used to obtain a composite material according to the invention are for example amine hardeners such as for example diamino-dimethyl-dicyclohexylmethane, tπmethylhexamethylenediamine.

The composite materials according to the invention may also contain all the additives usually used for composite materials.

Other characteristics and advantages of the invention will appear on reading the description made below in particular by relying on a few modes of examples given.

The description includes in the appendix:

- Table 1.1 to 10 representing the results of measurements which will be explained below, - Figures I to IV representing the viscosity of several compositions as a function of a time gradient.

EXAMPLES

1 / the types of compounds and materials used in the examples are listed below: o Araldite LY564HY2954: epoxy resin based on bisphenol-A with approximately at least 25% by mass of 1,4 butanediol diglycidyl ether mixed with the hardener diamino-dimethyl-dicyclonhexylmethane and whose commercial name is Araldite LY564H-Y2954 produced by CIBA GEIGY. R12D15: bisphenol-A-epichlorohydrin resin mixed with a hardener, namely benzyl alcohol-2,4,6-tri- (dimethyl-aminoethyl) phenol-polyethylenamine and whose commercial name is ARC-R12D15 produced by the company BOW R24D32: bisphenol-A-epichlorohydrin resin with 1,6 hexanediol-glycidether mixed with a hardener, namely trimethylhexamethylene diamine and whose commercial name is ARC-R24D32 produced by the company A.R.C. 0 R24R29D32: bisphenol-A-epichlorohydrin resin with 1,6-hexanediol-glycidether trimethylolpropane triglycidether + a bisphenol-A-epichlorohydrin resin mixed with the hardener trimethylhexamethylene diamine and whose commercial name is ARC-R24R29D32 produced by the company A.R.C. Silicone A26: polysiloxane resin whose trade name is Silicone A26 5 produced by KÔMMERLING, Germany.

CTAB / NaNO ^: aqueous solution of methyltrimethylammonium bromide and

NaNOg.

MgO ceramic paste: paraffin oil mixed with MgO ceramic powder with an average grain size of approximately 250 nm (powder marketed by ARC Reinforcement fibers: carbon fiber whose trade name is TORAYCA "T300-MLD". These carbon fibers are short fibers obtained by grinding. The grinding is carried out by the company APPLY CARBON. These fibers have an average length of 160 microns for a size distribution varying from 50 to 500 microns. Before use, these carbon fibers are dried under vacuum at 80 ° C for 24 hours.

Glass microbeads: Kl quality glass microbeads (borosilicate glass) produced by 3M whose average diameter is 50 micrometers for a size distribution varying from 30 to 150 micrometers with a density of 0J25 kg / m2. Before use, the glass microbeads are dried under vacuum at

80 ° C for 24 hours.

11 / Examples of methods of preparing the composite materials according to the invention

1) Preparation of the composite materials without glass microbeads A basic resin constituting the matrix and the carbon fibers is mixed. The mixture is homogenized under vacuum for at least one hour. Then the hardener is added to the mixture obtained at ambient pressure. The mixture (resin / fibers / hardener) is then homogenized for a shorter time compared to the polymerization time of the resin and placed under vacuum for the elimination of any bubbles. Then, the mixture is poured (open mold) or injected (closed mold) to obtain the composite material.

2 °) Preparation of composite materials with glass microbeads

A base resin is mixed beforehand with glass microbeads, then the mixture obtained is homogenized for one hour under vacuum. A composition of carbon fibers is then added by mixing the whole at atmospheric pressure for one hour. A hardener is then added to the polymer matrix formulation obtained at ambient pressure.

The composite material is then obtained by placing the mixture (resin / fibers / glass microbeads / hardener) under vacuum for a period corresponding to the polymerization time of the base resin. We determine the hardness of the composite material as a function of the handling time. 111 / Rheological measures

The rheological measurements are carried out on a cone-plane rheometer with imposed gradients with a cone with a diameter of 36 mm and an angle of 0.3 °. The model used is the Rheotest 2 model from MLW (Germany). The measurements are carried out at 25 ° C. and at increasing gradients. For each imposed gradient value, a stabilization time of two minutes is applied before the measurement. To check the reproducibility of the measurements taking into account the polymerization speed, they are carried out each time on five different mixtures of the same composition. It has been established beforehand that the resins measured have a sufficiently long gelation time during which the viscosity does not vary.

It will be mentioned that the measurements carried out with cone-plane cells (CP) were confirmed by the measurements carried out with quilt cells H / H and SI / S with respectively for H / H a radius ratio equal to 1.24 and for SI / S equal to 1.02.

In the experimental conditions studied, the flow is of the laminar type with very low Reynolds numbers (Re). This number is defined as follows:

P

Re = V _m D η

where p is the density, η the viscosity, V _m the flow speed and D the dimension

maximum flow.

First series of samples

Example 1J.

The variation of the viscosity of the LY564 / HY2954 resin is studied as a function of the rate of microbeads which varies from 0 to 6% and as a function of imposed speed gradients. The results are listed in Table 1.1. Example 1.2. The variation of the viscosity of the resin of example 1.1 charged with fibers at a rate of 20% as a function of the rate of microbeads which ranges from 0 to 3% and as a function of the speed gradient imposed. The results are shown in Table 1.2.

Example 1.3.

The viscosity of the resin of Example 1J loaded with fibers is studied at a rate of 25% as a function of the rate of microbeads which ranges from 0 to 3% and as a function of the speed gradient imposed. The results are shown in Table 1.3.

Example 1.4.

The viscosity of the resin of Example 1.1 loaded with fibers is studied at a rate of 30% as a function of the rate of microbeads which ranges from 0 to 3% and as a function of the speed gradient imposed. The results are shown in Table 1.4.

Second series of samples

Example 2J. The viscosity of the resin R12 / D15 is studied as a function of the rate of microbeads which ranges from 0 to 6% and as a function of the speed gradient imposed. The results are shown in Table 2J.

Example 2.2.

The viscosity of the resin of Example 2.1 loaded with fibers is studied at a rate of 20% as a function of the rate of microbeads which ranges from 0 to 3% and as a function of the speed gradient imposed. The results are shown in Table 2.2.

Example 2.3.

The viscosity of the resin of Example 2.1 loaded with fibers is studied at a rate of 25% as a function of the rate of microbeads which ranges from 0 to 3% and as a function of the speed gradient imposed. The results are shown in Table 2.3.

Example 2.4.

The viscosity of the resin of Example 2.1 loaded with fibers is studied at a rate of 30% as a function of the rate of microbeads which goes from 0 to 3% and depending on the speed gradient imposed. The results are listed in Table 2.4.

Third series of samples

Example 3J. The variation in the viscosity of the R23 / D32 resin is studied as a function of the rate of microbeads which varies from 0 to 6% and as a function of the imposed speed gradient. The results are listed in Table 3J.

The gradients as a function of the viscosity have been reported in FIGS. A and B for rates of microbeads of 0 and 1% respectively, further specifying the type of measurement cells used. Example 3.2.

The variation in the viscosity of the resin of Example 3.1 loaded with fibers is studied at a rate of 20% as a function of the rate of microbeads which varies from 0 to 3% and as a function of the speed gradient imposed. The results are listed in Table 3.2.

Example 3.3.

The variation in the viscosity of the resin of Example 3.1 loaded with fibers is studied at a rate of 25% as a function of the rate of microbeads which varies from 0 to 3% and as a function of the speed gradient imposed. The results are listed in Table 3.3.

Fourth series of samples Example 4J.

The variation in the viscosity of the R24R39D32 resin is studied as a function of the rate of microbeads which varies from 0 to 3% and as a function of the imposed speed gradient. The results are listed in Table 4.1.

Gradients as a function of the viscosity of the levels of microbeads respectively equal to 0 and 1.15% have been reported in FIGS. C and D, further specifying the cell type of the measurements used. Example 4.2. The variation of the viscosity of the resin of example 4.1 charged with fibers at a rate of 20% depending on the rate of microbeads which varies from 0 to 3% and depending on the speed gradient imposed. The results are listed in Table 4.2.

Example 4.3. The variation in the viscosity of the resin of Example 4.1 loaded with fibers is studied at a rate of 25% as a function of the rate of microbeads which varies from 0 to 3% and as a function of the speed gradient imposed. The results are listed in Table 4.3.

Example 4.4. The variation of the viscosity of the resin of example 4.1 loaded with fibers is studied at a rate of 30% as a function of the rate of microbeads which varies from 0 to 3% and as a function of the speed gradient imposed. The results are listed in Table 4.4.

Other samples Example 5J.

The variation of the viscosity of the polyester resin is studied with a rate of microbeads at 0 to 1% and as a function of the imposed speed gradient. The results are listed in Table 5.

Example 6 The variation of the viscosity of the silicone resin A25 is studied with a rate of microbeads which varies from 0 to 1% and as a function of the speed gradient imposed. The results are listed in Table 6.

Conclusion of point III

On reading Tables 1J to 4.4, it can be seen that the resins which belong to families of polymers whose molecular weights vary over a wide range have very similar rheological behavior, namely that the viscosity of the resins with or without fiber fillers decreases significantly when adding microbeads at a relatively low rate.

On the other hand, it can be seen that the resins with the lowest viscosity are obtained with loads of microbeads close to 1% by volume of resin, with or without fiber loading.

We see in Figures I to IV that the resins R24D32 and R24D29D32 have substantially the same behavior. We observe on all the curves a Newtonian regime (zones A) and a pseudoplastic and / or thixotropic regime (zones B).

On the other hand, it can be seen that with a microbead rate of around 1%, the slope of the curve is accentuated in the zones B, which clearly shows the decrease in viscosity. The viscosity of a solution of CTAB / NaNθ3 in water was also studied under the same conditions as in Examples 3J and 4J.

The results are shown in Tables 9 and 10 and the viscosity values as a function of the gradient are reported in Figures V and VI for microbead rates of 0 and 1J25%. The same behavior of the CTAB / NaNO 3 solution and of the ceramic paste based on MgO powder is observed as for the resins, which tends to prove that the phenomenon is not of a chemical nature but of a rheological nature.

TV / Measurement of mechanical properties

The mechanical properties are measured on a traction machine with imposed deformation. The type of traction machine used is the ADAMEL - LHOMARGY DY 25 model with a force sensor of 20kN. The tests are carried out at ambient temperature and at atmospheric pressure.

Mechanical tensile tests are carried out in accordance with ISO standard R527. Mechanical bending tests are carried out in accordance with ISO 4585.

Example 7

The mechanical properties of the LY564 / HY2954 resin are studied at a rate in glass microbeads of 1% as a function of the rate of carbon fibers. The results of this study are shown in Table 7 Example 8

The variation in the viscosity of the resin R24R29R32 is studied at a rate in glass microbeads of 1% as a function of the rate of carbon fibers. The results of this study are listed in Table 8 of the mechanical tests. Conclusion of point IV

The results grouped in Tables 7 and 8 clearly show that at equal viscosity, there is an observable improvement in the mechanical properties verified by the breaking stress and the Young's modulus. For samples with a high fiber content - greater than 35% - but without the addition of microbeads, the appearance of numerous defects during molding means that no noticeable improvement is observed in the tensile strength although the Young's modulus varies considerably. The addition of microbeads for this type of sample with a high fiber content makes possible a very clear reduction in defects while improving the breaking stress.

The present invention allows an increase in the fiber content in composite materials for the same viscosity of the mixture. A 5% increase in the fiber content makes it possible to obtain materials with mechanical properties greater than 10 to 15%. This leads to a considerable weight gain for structures. The values of the specific resistances now reach values comparable to those of commonly used aluminum alloys while allowing the production of complex structures for cold casting, which is not the case for aluminum.

For all the fluids studied, the reduction in viscosity is manifested only in the pseudo-plastic domain of the flow regime. In the Newtonian domain, fluids follow Einstein's law (see "Fundamental Principles of Polymeric Materials" SL ROSEN, Edition BARNES ad NOBLES - 1971 and "The shaping of plastics" JF AGASSANT, P. AVENAS, JP SERGEANT, Technology and Documentation, Lavoisier 1986).

The advantages of the compositions and composite materials according to the invention are numerous and in particular: - the microbeads used being for example made of borosilicate glass are chemically inert. No addition of lubricants is necessary compared to other processes using lubricant coated, this use being often detrimental to the mechanical properties of the materials obtained,

the addition of microbeads to the compositions (fibrous materials) significantly increases the tensile strength of the materials compared to those of the prior art,

the density of the microbeads being lower than that of the resins, this results in a gain in weight, which was not the case with other particles used in the prior art.

Of course, the invention is not limited to the examples which have just been described and many modifications can be made to them without departing from the scope of the invention.

Claims

1. Composition based on a polymer or a copolymer or a mixture of polymers with thixotropic and / or pseudoplastic behavior comprising microbeads incorporated in said composition before solidification thereof, the proportion of microbeads relative to the volume total of said composition being chosen as a function of the rheological properties of the polymer or copolymer or mixture of base polymers in order to reduce the viscosity of said composition, characterized in that said microbeads are present in a proportion of between approximately 0J and approximately 3% by volume relative to the total volume of the composition, preferably between approximately 0.5 and approximately 2% and more particularly still between approximately 0.7 and approximately 1.3%.

2. Composite material loaded with fiber, characterized in that it comprises a polymer matrix consisting of a composition according to claim 1 and optionally a hardener and reinforcing fibers embedded in said polymer matrix.

3. Composite material according to claim 2, characterized in that the average size and / or the nature of the microbeads are adapted to the process for shaping said composite material.

4. Composite material according to one of claims 2 or 3, characterized in that said microbeads are present in a proportion of between approximately 0J and 3% by volume relative to the total volume of the composition, preferably between approximately 0.5 and approximately 2% and more particularly still between approximately 0.7 and approximately 1.3%.

5. Composite material according to claim 2, characterized in that the reinforcing fibers represent approximately 20 to approximately 70% by volume of the material, preferably approximately 25 to approximately 65%, and more particularly still 30 to approximately 60%.

6. Composite material according to any one of claims 2 and 5, characterized in that the reinforcing fibers are short fibers.

7. Composite material according to any one of claims 3, 5 and characterized in that the reinforcing fibers are chosen from carbon fibers, aramid fibers, glass fibers.