EP0711320A1

EP0711320A1 - Composition comprising a matrix polymer, fibrous reinforcing material and a binder and a method for injection moulding such a composition

Info

Publication number: EP0711320A1
Application number: EP94917830A
Authority: EP
Inventors: Antonius Bernardus Johannes Kroezen; Markus Johannes Henricus Bulters; Alfonsius Antonius Maria Harbers; Hermanus Peter Sunverink Ook Lansink
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 1993-06-10
Filing date: 1994-06-09
Publication date: 1996-05-15
Also published as: WO1994029373A1; BE1007210A3

Abstract

Composition comprising a matrix polymer, fibrous reinforcing material and a binder, the matrix polymer having a processing temperature range with an upper limit and a lower limit, the fibrous reinforcing material being present in bundles that are held together by the binder and the binder having a melting point that lies above the lower limit and also below the upper limit.

Description

COMPOSITION COMPRISING A MATRIX POLYMER, FIBROUS

REINFORCING MATERIAL AND A BINDER AND A METHOD

FOR INJECTION MOULDING SUCH A COMPOSITION

The invention relates to a composition comprising a matrix polymer, fibrous reinforcing material and a binder.

Such a composition is known from EP-A-440970, in which a bundle of fibres is impregnated with a latex binder and then chopped into granules. The granules are mixed with a matrix polymer and the composition thus obtained is used to produce injection-moulded objects in which fibres are dispersed from the granules into the matrix polymer. According to EP-A-440970, this dispersion is possible because the binder melts at a temperature below the processing temperature of the composition.

A drawback of the composition described in EP-A- 440970 is that the objects that can be obtained with it have relatively poor mechanical properties as a result of too much fibre breakage during injection moulding. The injection moulding is done with the aid of an injection- moulding machine in which the composition is subjected to high shearing forces. These shearing forces are necessary to transport and optionally compress the composition, to generate frictional heat, which heats and liquefies the composition, to build up pressure and to disperse the fibres in the composition. In the present application, the phase comprising transportation, compression, generation of heat, heating and liquefying is also referred to as the plastifying step. It is the aim of the present invention to provide a composition that makes it possible to produce objects by injection moulding whereby the reinforcing fibres are uniformly dispersed without too much fibre breakage taking place and to obtain objects with good mechanical properties.

This aim is achieved according to the invention because the matrix polymer has a processing temperature range with an upper limit and a lower limit, the fibrous reinforcing material being present in bundles that are held together by the binder and the binder having a melting point that lies within the processing temperatue range.

The binder preferably has a melting point that lies at least 5°C and more preferably at least 10°C above the lower limit.

Preferably the melting point of the binder is at least 5°C lower than the upper limit and more preferably at least 10°C. The invention also relates to a method for processing a composition as described above, which is characterised in that the composition is introduced into a suitable apparatus and is mixed for some time at a temperature above the lower limit of the processing temperature range of the matrix polymer and below the melting temperature of the binder until the matrix polymer and the bundles of fibrous reinforcing material are at least partly mixed together and the matrix polymer is at least partly heated to above the lower limit of its processing temperature range, after which the temperature is increased to above the melting temperature of the binder and the composition is moulded. This moulding may be for example injection into a mould or extrusion to for example a plate, rod or tube or blowing to a hollow shape, etc. If the composition is injected into a mould, this process will generally be called injection moulding.

The use of the aforementioned binder ensures that the fibrous reinforcing material remains bundled together for a large part of the plastifying step and hence fibre breakage is highly reduced.

Transportation may take place with the aid of an extruder screw or a plunger or in some other manner. The principle of the method is that the temperature in the transport zone is set so that it exceeds the melting point of the binder only at the very end of this zone, i.e. just before the moulding step. The method according to the invention is hence characterised by initially mixing without dispersion of the fibres, followed by mixing with dispersion of the fibres. It is essential that the dispersing of the fibres takes place in the shortest time possible, only at the end of or after the plastifying step and shortly before or during the filling of the mould or even only in the mould.

The mechanical properties of the injection- moulded product are better than the mechanical properties of a product obtained from further comparable compositions with which the fibres were not held together in the way described above during a large part of the processing. EP-A-248384 describes a moulding composition consisting of granules of a thermoplastic resin and granules of a moulding compound. The moulding compound consists of reinforcing filaments surrounded by a specific binder which consists of a poly(C₂-C₆ alkyloxazoline) combined with a poly(vinylpyrrolidone) . However, this binder is not crystalline and has a T_g which is substantially lower than the melting temperature of the binder described of the present invention and also substantially lower than the processing temperature of the present invention.

The moulding compound described in EP-A-248384 has the disadvantage that upon contact with the hot molten thermoplastic during transport to the mould, rapid melting of the binder takes place, resulting in fibre breakage even before moulding. EP-A-278546 describes a moulding composition consisting of strands of fibre bundles embedded in a thermoplastic resin binder, and a matrix polymer. According to that publication a sufficiently uniform dispersion of the fibres without excessive fibre breakage is obtained by embedding the fibres into a thermoplastic resin in the form of bundles of crimped fibres. The fibre bundles are preferably crimped by gear crimping. According to EP-A-278546, the melt viscosity of the thermoplastic resin can either be higher or lower than the melt viscosity of the matrix polymer.

According to JP-A-62288011 uniform dispersion of the fibres can be obtained by using a molding composition consisting of granules of fibres embedded in a thermoplastic resin binder, and granules of a matrix resin. In JP-A-62288011 there is no teaching with respect to reducing fibre breakage, nor the use of a minimum and maximum processing temperature or a processing temperature range. The product also has good fatigue properties, a high surface quality and good cohesion after break. This last property is for example important in applications in which it is important that the product has some cohesion after break, for example in bottom plates of cars. Furthermore the thermal properties are good and the product shows little or no warpage and a good surface quality with no or little short-term or long-term waviness. The resistance to chemical substances and the moisture resistance are better than those of conventional products.

The processing temperature range according to the invention can be described as the temperature range within which a certain matrix polymer, combined with the fibrous reinforcing material and the binder and any other additives, is processable by means of injection moulding or via one of the other suitable moulding routes. This temperature is understood to be the processing temperature of the composition. The processing apparatus may have a temperature that lies slightly above or below that temperature. Below the lower limit such a matrix polymer will not be miscible or will be less miscible with the bundles of fibrous reinforcing material or it will not be possible to inject the composition. Above the upper limit the matrix polymer will degrade entirely or partly or will be no longer processable for some other reason, for example if the polymer cures or crosslinks at that temperature.

The melting temperature of the binder is preferably slightly above the lower limit to enable good processability on an industrial scale without having to define the desired temperature profile too accurately. If the mixing is for example done in an extruder, there may be local differences in temperature within the composition. A difference of 10°C between the lowest processing temperature and the melting temperature of the binder makes it possible to use the method according to the invention without the risk of undesired premature melting of the binder.

'Injection moulding' is in the framework of this application understood to be the compression, under pressure, into a shape of a moulding compound, for example consisting of fibrous reinforcing material and optionally a binder, and a matrix. This can for example be effected with the aid of a plunger or a screw. An example is injection compression moulding. It is also possible to compress a plate or to extrude a profiled part or a tube, which may optionally serve as a parison for blow moulding. 'Compounding' is in the framework of the present application understood to be the combining of fibrous reinforcing material, and optionally a binder, and the matrix material. This usually results in a semi- manufacture, which may consist of particles or of a compound. Compounding can for example be done in a mixer, rollers or an extruder, batchwise or in continuous mode. Other compounding processes are sheathing and pultrusion, which are generally known to a person skilled in the art.

The ratio of the viscosity of the melted binder and the viscosity of the matrix polymer at the processing temperature is preferably lower than four and more preferably lower than one. A low ratio makes it possible to disperse the fibres. The dispersing is preferably done quickly and for that purpose a low viscosity ratio is required. The binder and the matrix polymer preferably have good compatibility or are even soluble in one another when wetted. A compatibiliser may optionally be added. Because, as described above, the length of the fibres in the injection-moulded product according to the invention will always be greater than in a comparable system without the specific binder according to the invention, some deterioration of the mechanical properties as a result of any poorer miscibility of the two components is tolerable. However, if the two components are well chosen it is also possible to let the binder for example function as a low- profile additive (LPA) or to take advantage of the possibilities of two-phase blends in some other way.

The binder is generally used in an amount of 0.5-60 weight , relative to the fibrous reinforcing material and the binder together, preferably between 2 and 35 weight %, more preferably between 5 and 25 weight % and most preferably at least 7 weight %. A somewhat larger amount of binder presents the additional advantage that less air will be incorporated in the end product and that the binder will have a greater lubricating effect during the dispersing.

The binder may be a thermoplastic or a thermosetting resin or a different substance with a suitable melting point. If use is made of a thermosetting resin, this must be chosen so that its melting point meets the requirements imposed according to the invention. This is for example possible by choosing a resin from the group consisting of crystalline unsaturated polyesters, styrenised polyester resins greatly thickened with the aid of MgO, amorphous unsaturated polyester resins, melamine/formaldehyde resins, phenolic resins (resols and novolaks).

The matrix polymer may be a thermosetting resin or a thermoplastic. Examples of thermosetting matrix polymers are unsaturated polyesters or vinyl esters with reactive monomers, melamine resins, phenolic resins (resols and novolaks) or epoxy resins. Examples of reactive monomers are styrenes, acrylates, ethylenically unsaturated carboxylic acids or carboxylic anhydrides, such as maleic anhydride, allyl compounds, such as diallylphthalate (DAP), triallylcyanurate (TAC), etc. If the matrix polymer consists of one of the above thermosetting resins the binder preferably has a melting point of between 60 and 120°C.

It is therefore possible to select a binder and a matrix material from the same group, provided that the binder has a melting point that satisfies the invention. It is for example conceivable to use of a particular polymer a grade with a high melting point as the binder and a grade with a lower melting point as the matrix material. It is possible to use thermoplastic binders in thermosetting matrices and it is possible to use thermosetting binders in thermoplastic matrices.

Because the materials of the above group have an unclearly defined melting point in some cases, the 'melting point ' of such binders is in the framework of the present invention defined as the temperature above which the binder shows a substantial decrease in viscosity. This may hence be the melting point in the case of a crystalline or semi-crystalline resin, but also a glass transition temperature (Tg) or a temperature belonging to some other mechanism, for example to MgO thickening or a degradation temperature. A binder with a glass transition temperature, as describe above, is slightly less advantageous because a Tg will show a relatively slow decrease in viscosity.

The binder therefore needs not always be a polymer but may also consist of other, low-molecular compounds which can give the bundle the desired solidity and which, at the desired temperature, show a substantial decrease in viscosity.

The following table gives a non-limiting survey of examples of thermoplastic binders and thermoplastic matrix polymers that can be used according to the invention.

TABLE 1 Examples of combinations of thermoplastic matrix polymers and thermoplastic binders

MATRIX POLYMER BINDER

PP PMP LDPE PP or PMP

PE PP or PMP nylon 6 nylon 66 or nylon 4,6 nylon 66 nylon 4,6

PET nylon 4,6 PBT nylon 6,6 or nylon 4,6

PC PBT or PET

PPO/PS nylon 66 or nylon 4,6

PPO/PS syndiotactic PS

ABS, SMA, ABS/SMA or SMI nylon 6, 66, 46, PBT or PET nylons or polyesters thermotropic LCPs nylon 6, 66 or 4,6 PEEK or PPS

PP = polypropylene, PE = polyethylene, LDPE = low-density polyethylene, PMP = polymethylpentene, PET = polyethylene terephthalate, PBT = polybutylene terephthalate, PC = polycarbonate, PPO = polyphenylene oxide, PS - polystyrene, ABS = acrylonitrile/butadiene/styrene, SMA = styrene/co-maleic anhydride, SMI= styrene/maleimide, LCP = liquid crystalline polymer.

The bundles of fibres are made by impregnating or sheathing an amount of fibrous reinforcing material with the binder. Fibrous reinforcing material is generally commercially sold in the form of rovings, which consist of a number of strands, which consist of a number of filaments, which consist of a single fibre. When in this application reference is made to a 'bundle of fibres' this is understood to consist at least of several filaments, and usually of one or more rovings. The binder may be added via complete melt impregnation, via incomplete melt impregnation, via slurry impregnation, via dissolution impregnation, via powder impregnation or in a different manner.

In the case of complete melt impregnation the individual filaments are completely surrounded by the binder and the result is a virtually massive bar or lump containing the fibrous reinforcing material.

In the case of incomplete melt impregnation the binder surrounds the individual filaments or the bundle but the space between the individual filaments is not completely filled with binder. An example of an incomplete melt impregnation is a wire coating operation (WCO) , in which a tube of matrix material is extruded around a bundle of fibres, after which the sheathed bundle is generally chopped into pieces.

In the case of a slurry impregnation the binder is added in the form of a slurry of particles in a liquid, usually water, after which the liquid is evaporated and the particles remain on and between the fibres and give the latter a certain degree of cohesion. If the slurry is given film-forming properties, either by adding an extra film-former, or via the choice of the binder and for example the particle size, the cohesion of the binder and the fibres will be increased. Impregnation with the aid of a film former is for example described in EP-A-368,412.

It is possible to perform two successive slurry impregnations, in order to apply first an amount of binder and then an amount of matrix material. This is particularly advantageous in the case of a heat-sensitive binder or matrix material.

In the case of dissolution impregnation the binder is dissolved in a solvent, which is evaporated after the impregnation, the binder remaining on and between the fibres and giving them a certain degree of cohesion.

The composition according to the invention has a physical form that may be chosen from the group consisting of a compound, a collection of particles, a collection of granules, an almost endless sheathed bundle of fibres, optionally in the form of a strip or plate or a combination of one of these forms. The composition may hence consist of a coherent compound, but may also consist of a collection of separate particles, the matrix polymer being contained in different particles than the bundle of fibres and the binder.

The invention also relates to a half product. This half product is characterised in that it consists of a granulate, which can be obtained by mixing a composition as described above for some time, at a temperature above the lower limit of the processing temperature range of the matrix polymer and below the melting temperature of the binder, and then granulating it. Such a half product hence consists of granulate particles, each of which consists of matrix polymer and bundle of fibres, the bundle of fibres still being held together by the binder. The mixing may consist of stirring, kneading, extruding, compressing or combinations of these techniques or of other mixing techniques known to a person skilled in the art.

This granulating may for example take place by extruding the mixed composition into a longitudinal shape and then cutting it into parts with the aid of knives, or in any other manner known to a person skilled in the art.

The invention also relates to an end product, obtained by processing a composition or half product according to the invention or by using a process according to the invention. More specifically the invention relates to an end product whose matrix polymer consists at least of polypropylene and which has an Izod impact strength of between 20 and 80 kJ/m², and preferably of between 30 and 70 kJ/m², in addition to a modulus in flexure of between 2000 MPa and 8000 MPa, preferably 2500-6500 MPa, more preferably 3500-5000 MPa. To our knowledge, this is the first time that such end products are described. In the literature methods are known for processing compositions consisting of, among other substances, a matrix polymer, a randomly selected binder, not according to the invention, and long fibrous reinforcing material via compression. In such methods an amount of material, usually referred to as 'compound', for example Sheet Moulding Compound (SMC), is placed in a compression mould and the press is closed. Then pressure is exerted and heat is supplied, during which an object is moulded and the composition sets. A comparable method is known for the processing of thermoplastic composites with long fibres, for example the so-called GMT material.

Although it is possible to produce objects with the aid of such methods without too much fibre tear occurring in the composition, it is less efficient to produce products in large series. Because of the mixing, cutting, weighing and introducing of the compounds such processes have so far been used mainly for smaller series. With a composition or method according to the invention it is possible to manufacture products in larger series faster and simpler. It is for example no longer necessary to use complex robots, which is a great advantage from the point of view of costs.

In the literature methods are known according to which compositions consisting of a matrix polymer, a binder and reinforcing material with short fibres are processed via injection moulding. With such a method an amount of compound, for example Bulk Moulding Compound (BMC) is forced into a mould by a transport screw. If such a method is carried out with reinforcing material with longer fibres, so much fibre tear takes place that the fibres in the end product are short again.

The fibrous reinforcing material may be used according to the invention in the form of virtually endless fibres or so-called chopped strands, which are then impregnated with the binder. In an alternative method the virtually endless fibres or strands of fibres are first impregnated with the binder and then chopped. The filaments in a bundle of fibrous reinforcing material according to the invention may be parallel or virtually parallel, they may be randomly distributed in the bundle or they may have a certain orientation. In general the fibres will be virtually parallel in a bundle. The fibrous reinforcing material according to the invention is generally used in lengths of up to 25 mm, while the length of the fibrous reinforcing material in a BMC is usually around 5-15 mm before injection moulding and 1-5 mm after injection moulding. In an SMC the fibrous material used generally has a length of around 25 mm, which means that not too much fibre tear takes place during processing via compression. If a compound containing 25-mm long fibrous reinforcing material is processed via injection moulding in the way BMC is processed according to the state of the art, the average length decreases to about 0.7 mm if use is made of a binder that is not very strong. A 'binder that is not very strong' is understood to be a binder whose cohesion- promoting effect decreases already at a slight increase in temperature or at slight shear. The average length decreases to 3-4 mm if a strong binder is used, but in that case the fibres in the end product are not well dispersed. The strength is determined by such factors as the solubility of the binder in styrene or in a different monomer present in the composition.

The bundles of fibre according to the invention may contain any number of fibres and are known from the literature and are commercially available.

The fibres are generally used in amounts of between 0.05 and 70 wt.%, relative to the overall composition, and preferably between 1 and 60 wt.%, more preferably 10-50 wt.%.

The fibres may consist of any material available in the form of fibres, for example glass, carbon, metal, natural materials, such as flax, jute, coconut, wood, cellulose, plastic fibres, such as polyethylene or ara ide, ceramics, etc.

The composition, the half product and/or the method according to the invention are used mainly in industrialised processing methods for fibre-reinforced plastics. They may be for example large series of products, such as car parts, but also tubes, profiled parts, plates or other extrusion products.

The invention will be elucidated with reference to the following examples, without being limited thereto. The degree of dispersion was determined by comparing X-ray photographs of a composition before mixing with X-ray photographs of compositions after injection.

The Charpy impact strength was determined according to ISO 179. The Izod impact strength was determined according to ASTM D256A. The flexural test was carried out according to ASTM 790M.

Example I

Thermoplastic binder and matrix

A bundle of glass fibres (Silenka 084M19® 600 tex) was impregnated with 50 wt.% nylon 66 (Akulon, melting point 260°C) in a pultrusion process. The impregnated bundle was coated with a polypropylene matrix polymer (Stamylan P 13E10® from DSM, Geleen) and was chopped into 10-mm long granules.

The granules had a glass content of 22 wt.%. The granules were compression moulded into test plates at 210°C, i.e. below the melting temperature of the nylon.

The plates were heated in a Couette apparatus to a temperature of 220, 240, 250 or 260°C. The plates were subjected to shear at a shear rate of 100 s^_1 to several different overall degrees of shear. The degree of dispersion was determined with the aid of X- ray photographs.

It may be concluded that the bundles virtually did not disperse at 220°C, not even at an overall shear of 1000, whereas the degree of dispersion at 260°C and an overall shear of 300 was 90%.

Example II

The method of Example I was repeated using a styrene/maleic anhydride copolymer Stapron (SM300® from DSM, Geleen) as the matrix material. The viscosity of this copolymer at 250°C is virtually the same as that of polypropylene at the same temperature. The results show virtually the same picture.

Example III

The effect of the viscosity ratio

A bundle of glass fibres (Silenka 084M19 600 TEX® roving) was impregnated with polystyrene from Dow Chemical (638) by pultruding the bundle through a solution of the polystyrene in toluene. After evaporation of the toluene the glass bundle contained 9 wt.% PS. SEM photography showed that each fibre was well wetted with PS. The impregnated bundle was coated with high density polyethylene (Stamylan HD7058® from DSM, Geleen) in a Wire Coating Operation, through extrusion at 150°C.

Eventually the material was chopped into 10-mm long granules that contained 25 wt.% glass. The viscosity ratio of PS and HDPE is 3.5 at 150°C, 1.0 at 200°C and 0.17 at 250°C.

The samples were tested by compression moulding granules into plates, which were heated in a Couette apparatus. When the sample had reached the desired temperature of

150, 200 or 250°C, it was subjected to shearing forces at different rates and for different lengths of time. The samples were analysed with the aid of X-ray photography. The dispersion proved to be better in the tests in which the viscosity ratio was lower.

Example IV

A crystalline unsaturated polyester as the binder

In this example a crystalline unsaturated polyester was used as the binder: Synolite 1835® from DSM

Resins in Zwolle, having a melting point of 110°C. No catalyst was added to the binder because it was assumed that that would diffuse from the matrix into the binder.

The binder was applied through immersion in a bath having a temperature of 110°C, 20 wt.% resin being thus applied to the fibre. The glass bundle was a Silenka 084® (of 300,

600 or 1200 tex) .

The matrix polymer was an unsaturated polyester paste having the following formula:

parts by weight

Resin Leguval W35®

(DSM Resins) 60 Synolite 40

Millicarb 270

Sacholite L 10

Zn stearate 4

Trigonox C 4 PBQ (ppm) 500

PBQ = parabenzoquinone The composition was injection-moulded using a Battenfeld machine (BDS-C 1200/540) with a butterfly mould (200 g shot weight) of 250 * 120 * 3 mm. The filling pressure was 30 bar and the injection rate was 50 mm/s. The curing time was 210 s and the pressure 1200 KN. The results are shown in Table 2.

Comparative Experiment A

Standard compression moulding of an SMC

A standard SMC consisting of a resin paste as described in Example IV having different glass fibre contents with an average glass length of A-l 25 mm and A-2 15 mm, but without the binder according to the invention, was compression moulded in a standard SMC mould. The results are shown in Table 2.

Comparative Experiment B

Injection moulding of an SMC

The SMC of Comparative Experiment A was injection moulded under the same conditions as in Example

IV. The results are shown in Table 2.

Table 2: Results of mechanical measurements glass flex. Charpy (wt.%) strength impact strength (kJ/m²) (kJ/m²)

Example IV (length = 25 mm) 25

Comp. Exp. A-l 15 (compression moulding of an SMC: 25 length = 25 mm)

Comp. Exp. A-2 15 (compression moulding of an SMC: 25 length = 15 mm)

Comp. Exp. B 15

(injection moulding of an SMC; 25 length = 25 mm) A comparison of Example IV with Comparative Experiments A and B leads to the conclusion that the mechanical properties that can be obtained by compression moulding an SMC cannot yet be obtained with the method according to the invention but that the properties of a product according to the invention are much better than the properties of an injection-moulded product not according to the invention. It must be added that the properties of the product according to the invention can probably be improved via a more appropriate choice of all the conditions. The average fibre length in the product of Example IV was between 5 and 10 times that of the product obtained in Comparative Experiment B, which leads to the conclusion that fibre tear was to a great extent prevented.

Example V

PET as the binder and an SMA as the matrix polymer

The method of Example IV was followed, using polyethylenetherephthalate (PET) (Arnite 02.102® from DSM ΝV; Tm = 255°C) as the binder. The matrix polymer was Stapron SM 300^R from DSM ΝV, which has a processing temperature of 250°C. The PET was applied to a Silenka 084 M19 (600 tex) glass bundle in an amount of 25 wt.%, relative to glass + binder.

This bundle was sheathed with the matrix polymer in a Wire Coating Operation to a total glass content of 30 wt.%, relative to the glass, bundle and matrix polymer together. The sheathed bundle was chopped into 10-mm long granules. The granules were injection moulded with the aid of an Arburg injection-moulding machine with a 22-mm standard screw. The cylinder temperature increased over the length of the screw from 220°C to 250°C, which resulted in a melting temperature of 265°C. The Izod values of specimens perpendicular and parallel to the injection direction were the same, i.e. 22 kg/rn². Example VI

PMP as the binder and PP as the matrix polymer

The method of Example V was repeated, using PMP (polymethylpentene TPX DX 820 from Mitsui; Tm = 235°C) as the binder and PP (19 MN10 from DSM NV, Geleen) as the matrix polymer.

The composition contained 30 wt.% glass. The impact strength (IZOD, ASTM D256A) was measured at different cylinder temperatures. The results are shown in Table 3. The modulus of elasticity is virtually not influenced by the cylinder temperature and is 4000 MPa.

Table 3

Cylinder temperature Izod (average) (°C) (kJ/m²)

215 32

225 40 230 44

235 50

245 51

255 48

Izod (average): the average Izod value obtained for specimens perpendicular and parallel to the injection moulding direction.

Comparative Experiment C 1. An amount of polypropylene (Stamylan P 19 MN10® from DSM NV, Geleen) was mixed with 30 wt.% glass (Vetrotex 5137) with the aid of a twin-screw extruder. After this compounding step the number average fibre length was about 0.5 mm. The compound obtained was then injection moulded. The Izod impact strength and the modulus of elasticity were measured, 2. The same experiment was carried out using 30 wt.% Silenka 084 M19 600 tex glass that had been coated with PP via a WCO and was compared with an amount of that glass that had been impregnated via pultrusion with a PMP binder (30 wt.%, relative to the glass) according to Example VI. The results are shown in Table 4.

Table 4

Experiment IZOD modulus of elasticity

(kJ/m²) (MPa)

Cl C2 VI

This leads to the conclusion that the binder according to the invention leads to a great improvement of the impact strength of the end product.

Comparative Experiment D

Use of a non-melting binder

The method of Example V was followed, using an unsaturated polyester (UP) as the binder. The UP was a

Synolite 1835^R from DSM Resins in Zwolle and this was cured in a drying tunnel after impregnation.

After compression moulding it was found that the fibres were not or virtually not dispersed. A number of bundles had split and/or snapped. The Izod value of 15 kJ/m² is relatively very low.

Claims

C L A I M S

1. Composition comprising a matrix polymer, fibrous reinforcing material and a binder, characterised in that the matrix polymer has a processing temperature range with an upper limit and a lower limit, the fibrous reinforcing material being present in bundles that are held together by the binder and the binder having a melting point that lies within the processing temperature range.

2. Composition according to claim 1, characterised in that the binder has a melting point that lies at least 5°C above the lower limit.

3. Composition according to claim 2, characterised in that the binder has a melting point that lies at least 10°C above the lower limit.

4. Composition according to anyone of claims 1-3, characterised in that the binder has a melting point that lies at least 5°C below the upper limit.

5. Composition according to claim 4, characterised in that the binder has a melting point that lies at least 10°C below the upper limit.

6. Composition according to anyone of the claims 1-5, characterised in that the ratio of the viscosity of the melted binder and the viscosity of the matrix polymer above the melting point of the binder is lower than four.

7. Composition according to claim 6, characterised in that the ratio is lower than one.

8. Composition according to any one of claims 1-7, characterised in that the composition has a physical form chosen from the group comprising a compound, a collection of particles, a collection of granules, a virtually endless sheathed bundle of fibres, a strip or a plate, or a combination of one of these forms.

9. Composition according to any one of claims 1-8, characterised in that the matrix polymer is chosen from the group comprising unsaturated polyesters, vinyl esters, melamine resins, phenolic resins and epoxy resins and that the binder has a melting point of between 60 and 120°C.

10. Method for processing a composition according to any one of claims 1-9, characterised in that the composition is introduced into a suitable apparatus and is mixed for some time at a temperature above the lower limit of the processing temperature range of the matrix polymer and below the melting temperature of the binder, until the matrix polymer and the bundles of fibrous reinforcing material are at least partly mixed and the matrix polymer is at least partly heated to above the lower limit of its processing temperature range, after which the temperature is increased to above the melting temperature of the binder and the fibres are dispersed in the matrix polymer and the composition is moulded.

11. Half product, consisting of a granulate, obtainable by mixing a composition according to any one of claims 1-9 for some time at a temperature above the lower limit of the processing temperature range of the matrix polymer and below the melting temperature of the binder and then granulating it.

12. End product obtained by processing a composition according to any one of claims 1-9 or a half product according to claim 11.

13. End product according to claim 12, characterised in that the matrix polymer consists at least of polypropylene and that the product has an (Izod) impact strength of between 20 and 80 kJ/m² and a modulus in flexure of between 2000 MPa and 8000 MPa.