NL1013642C2 - Production of a heat-curable composition comprises impregnating reinforcing fibers spread in a strip with a heat-curable component - Google Patents

Abstract

Production of a heat-curable composition comprises impregnating reinforcing fibers spread in a strip with a heat-curable component.

Description

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PROCESS FOR PREPARING THERMO-HARDBARE

SAHENS.TSLLIN.aEH

The invention relates to a method for preparing thermosetting compositions comprising a thermosetting component and reinforcing fibers, wherein a bundle of the reinforcing fibers is impregnated with the thermosetting component.

Such a method is known from WO-A-9802485. Described herein is a method for preparing a thermosetting composition containing a thermosetting component and reinforcing fibers and which is deformable using temperature and pressure, wherein the reinforcing fibers are impregnated with a suspension and / or solution containing mainly a thermosetting component and optionally comprises a filler, the impregnated fibers are dried and chopped or cut into granulates, whereby a thermosetting compound is obtained which contains fibers of a length greater than 1 mm.

A drawback of this method is that by using a suspension and / or solution of the thermosetting component in the impregnation of the bundle of reinforcing fibers, a shell of the thermosetting component is formed, as it were, around the bundle of the reinforcing fibers without the individual fibers in the bundle are hereby impregnated 1 01 36 4 2 - 2 -. After drying, this results in a bundle of reinforcing fibers which is provided with an envelope layer of thermosetting component. When a number of thermosetting components are used, such as thermosetting resins, in particular for example amino / aldehyde resins, this coating layer can be very brittle. As a result of this brittle character, chopping, cutting and / or cutting this enveloped fiber bundle creates (partial) segregation between the thermosetting component and the reinforcing fibers, as a result of which a lot of dust is formed during the comminution process. For example, this mixture of granulate and dust results in a laborious injection molding process during the processing of the granulate. In addition, granulates are obtained in which the reinforcing fibers are not homogeneously impregnated. Therefore, articles made from these granulates exhibit inferior mechanical properties.

The object of the present invention is to prepare a thermosetting composition in which there is no segregation between the reinforcing fibers and the thermosetting component during the comminution process and wherein the reinforcing fibers in the thermosetting composition are homogeneously impregnated with the thermosetting component. This ultimately results after the molding process in a cured end product with good mechanical properties in that the reinforcing fibers are homogeneously distributed in the thermosetting composition.

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This object is achieved by spreading the bundle of the reinforcing fibers into a fiber web before impregnating these fibers with the thermosetting component. In a preferred embodiment of the invention, the fiber web is impregnated with a powder-form thermosetting component.

All thermosettable polymers are suitable for use as a thermosetting component in the present invention. Mixtures of thermosetting polymers and thermoplastic polymers are particularly suitable.

Suitable thermosetting polymers are, for example, amino / aldehyde resins, epoxy resins, phenolic resins, thermosetting polyacrylates, unsaturated polyesters, vinyl esters and resins which, for example, cure by 2 or more different mechanisms. Particularly suitable for the present invention are amino / aldehyde resins.

As the aldehyde compound in these amino / aldehyde resins, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, furfural etc. and mixtures thereof can be used. Formaldehyde is preferably used.

As the amino compound in these amino / aldehyde resins, both acyclic and heterocyclic amino compounds can be used. Examples of acyclic amino compounds are urea, thiourea or ethyl urea. As heterocyclic amino compounds, there are used, for example, compounds 1013642-4 which have a triazine structure such as melamine, melam, higher condensation products of melamine, ammeline, ammelide, cyanuric acid and uridomamine. Melamine or a mixture of melamine with urea is preferably used.

Melamine-formaldehyde, urea / formaldehyde and melamine / urea / formaldehyde resins are used as amino / aldehyde resins. Preferably, a melamine / formaldehyde resin is used, and in particular a melamine / formaldehyde resin with a ratio of formaldehyde: melamine between 1.4 and 2.5. Even more particularly, a melamine / formaldehyde resin having a formaldehyde: melamine ratio of between 1.5 and 2.0 is used.

Particularly good results are obtained by using a mixture of a thermosetting polymer and a thermoplastic polymer. It is important here that both polymers melt and / or soften at approximately the same temperature. Examples of these mixtures are melamine / formaldehyde resin or meiamine / urea / formaldehyde resin mixed with thermoplastic polymers such as, for example, copolyesters, copolyamides, polyolefins or polyalkylene oxides such as polyethylene oxide or polypropylene oxide.

Particular preference is given to a mixture of a melamine / formaldehyde resin and a thermoplastic copolyester or thermoplastic copolyamide. The amounts in which the thermosetting 1 01 3642-5 polymer and the thermoplastic polymer can be used are resp. 90-99 wt% and 1-10 wt%.

Suitable reinforcing fiber is fibers such as, for example, glass fiber, carbon fiber or aramid fiber. Glass fibers, glass fiber bundles, carbon fibers or carbon fiber bundles are preferably used.

The thermosettable composition obtained according to the method of the present invention mainly comprises the following components: 10-60 wt.% Thermosetting component and 40-90 wt.% Reinforcing fibers.

Preferably, the thermosetting composition mainly comprises the following components: 10-50 wt% thermosetting polymer 1-10 wt% thermoplastic polymer 40 - 89 wt% reinforcing fibers The thermosetting composition may further contain fillers in an amount which, however, 20 must never exceed the amount of thermosetting component. As filler, any material can be used, for example organic material such as cellulose, wood flour, cotton and / or starch, etc. Also inorganic materials can be used as filler, such as talc, plaster, chalk, aluminum trihydrate and / or clay. etc .... Furthermore, the thermosetting composition may contain other additives such as plasticizers, flow improvers, flame retardants, antioxidants, etc ...

The preparation of the thermosetting composition with the above-mentioned composition can be effected, for example, according to the method shown below.

First, a bundle of reinforcing fibers is spread into a fiber web in a manner known to those skilled in the art. Through this treatment, a fiber bundle, which has a substantially circular cross section of, for example, a diameter of 2-10 mm, is transformed into a fiber web, the height of the cross section of which is less than the width of the cross section. The cross-sectional height / width ratio obtained is preferably between 0.40 and 0.05.

In a next step, the fiber web is impregnated with a thermosetting component mainly comprising a thermosetting polymer or preferably a mixture of a thermosetting polymer and a thermoplastic polymer as already described above. Preferably, the fiber web is impregnated with a powder-form thermosetting component. This impregnation step can be carried out by, for example, sprinkling, spraying or spraying a thermosetting polymer powder on the fiber web.

Because the polymer composition is applied to the fiber web, not only is a layer of polymer formed around the fiber bundle, but layers of the polymer are also built up around the individual fibers from the fiber bundle, and polymer is also sandwiched between the individual fibers.

Then the impregnated fiber web is heated to a temperature in the vicinity of 1013642-7 - the melting point of the thermosetting polymer, for example, by means of radiation or in an oven. To obtain a good distribution of the thermosetting polymer, the whole can still be compressed during. 5 or after heating.

The impregnated fiber web is then granulated using a comminution method such as, for example, a chopping machine or cutting device. The length of the incorporated fibers almost corresponds to the length of the granulate and is usually larger than 0.5 mm. Preferably, the length is between 0.5 and 150 mm and in particular the length is between 1.5 and 50 mm. The cross-section of the granulate is determined by the cross-section of the fiber web and therefore preferably has a height / width ratio between 0.4 and 0.05.

The thermosetting compositions obtained in this way are cured under the influence of temperature and pressure during the processing into final product. The methods that can be used herein are already known per se to the person skilled in the art, such as for instance processing in a hot mold during injection molding or pressing.

It has now been found that using the method of the present invention there are obtained thermosetting compositions with a uniform distribution of long reinforcing fibers, which after processing at elevated pressure and temperature result in end products with excellent mechanical properties over the entire product.

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The invention is further illustrated by the following examples.

Example 1 5 A mixture consisting of 95% by weight melamine / formaldehyde resin with a ratio of formaldehyde: melamine = 1.6 and 5% by weight Vestamelt 4480 (copolyester from Hüls) was spread on a glass fiber web with a width of 2 cm and a height of 2 mm. The fiber web with the mixture applied thereon was passed through an oven at a temperature of 150 ° C. The impregnated fiber web obtained was then passed through a constriction and thereby compressed into a fiber having a width of 15 cm and a thickness of 4 mm. The impregnated fiber web was then reduced to a granulate of 10 x 10 x 4 mm with a chopping machine. No dust was formed during comminution in the chopper, nor was any segregation between the thermosetting component and the glass fibers observed. The granulate obtained had a glass fiber length of 10 mm and a glass fiber content of 58% by weight. The resulting compound was mixed with melamine / formaldehyde resin until a glass fiber content of 30% by weight was obtained.

Test rods were injection molded from this material and the following mechanical properties were measured: - flexural modulus (according to ISO 178): 20 GPa - flexural strength (according to ISO 178): 180 MPa - Charpy impact strength (according to ISO 179): 19 kJ / m2 30 Example 2 1013642 - 9 -

Process as described in Example 1, in which a mixture of 95% by weight melamine / formaldehyde resin and 5% by weight Vestamelt 730 (copolyamide from Hüls) was used. The oven temperature used was 120 ° C. No dust was formed during comminution in the chopper and no segregation between the thermosetting component and the glass fibers was observed. The resulting compound was mixed with melamine / formaldehyde resin until a glass fiber content of 30% by weight was obtained.

Test rods were injection molded from the obtained material and the following mechanical properties were measured: - flexural modulus (according to ISO 178): 19 GPa 15 - flexural strength (according to ISO 178): 160 MPa - Charpy impact strength (according to ISO 179): 21 kJ / m2

Example 3

Method as described in example 1 in which a carbon fiber web with a width of 2 cm and a height of 2 mm was used.

No dust was formed during comminution in the chopper and no segregation between the thermosetting component and the carbon fibers was observed.

Test rods were injection molded from the obtained granulate after mixing with melamine / formaldehyde resin to a fiber content of 40% by weight and the following mechanical properties were measured: 30 - flexural modulus (according to ISO 178): 29 GPa 1 01 36 4 2 - 10 - - flexural strength (according to ISO 178): 380 MPa - Charpy impact strength (according to ISO 179): 18 kj / m2

Example 4 Method as described in example 2, in which a carbon fiber web with a width of 2 cm and a height of 2 mm was used.

During comminution in the chopper, no dust was formed and no segregation between the thermosetting component and the carbon fibers was observed.

Test bars were injection-molded from the obtained granulate after mixing with melamine / formaldehyde resin to a fiber content of 30% by weight and the following 15 mechanical properties were measured: - flexural modulus (according to ISO 178): 21 GPa - flexural strength (according to ISO 178): 310 MPa - Charpy impact strength (according to ISO 179): 17 kJ / m2 20 Comparative example

In a reactor, 30 parts of water and 135 parts of formaldehyde solution (30 wt% formaldehyde in water with a pH of 9.4) were added to 100 parts of melamine. The condensation reaction was carried out at 95 ° C until the resin dilutability at 20 ° C was 1.2 kk resin per kg water (formaldehyde / melamine ratio was 1.7). The resin was transferred to a thermostatic bath at also 95 ° C and mixed with 7 grams of cellulose. A glass fiber bundle with a diameter of 2 mm 2 was passed through the bath at a speed of 0.05 m / sec. The impregnated glass fiber bundle was dried 1 01 3642-11 in two ovens placed in series. The first oven had a temperature of 240 ° C and the second 160 ° C.

The length of both ovens was 0.60 m. The dried impregnated glass fiber bundle was cut into pieces to obtain granulate with a length of 8 mm and a cross section of 2 mm2. At this comminution phase, a lot of dust was formed and segregation was observed between the melamine / formaldehyde resin and the glass. Finished products were then produced from the obtained granulate using an injection molding machine (Arburg 270-90-350) via an injection molding process. The cylinder temperature during injection molding was 80-100 ° C and the mold temperature 170 ° C.

The final products obtained by this process exhibited inferior mechanical properties over all or part of the final product obtained.

In addition, it was found to be very difficult to produce finished products with the resulting granulate since the segregation between the melamine / formaldehyde resin and the glass resulted in insufficient fiber transport in the injection molding machine.

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Claims (15)

1. A method of preparing thermosetting compositions comprising a thermosetting component and reinforcing fibers, wherein a bundle of the reinforcing fibers is impregnated with a thermosetting component, characterized in that the bundle of the reinforcing fibers 10 is spread into a fiber web before impregnate these fibers with a thermosetting component. 2. A method according to claim 1, characterized in that the bundle of reinforcing fibers is spread into a fiber web whose height / width cross-section ratio is between 0.40 and 0.05. 3. A method according to any one of claims 1-2, characterized in that the fiber web is impregnated with a powder-form thermosetting component. 4. A method according to any one of claims 1-3, characterized in that a thermosetting polymer or a mixture of a thermosetting polymer with a thermoplastic polymer is used as the thermosetting component. A method according to any one of claims 1-4, characterized in that the thermosetting component consists of a mixture of 90-99% by weight thermosetting polymer and 1-10% by weight thermoplastic polymer. Process according to any one of claims 1 to 5, characterized in that an amino / aldehyde resin is used as the thermosetting polymer. 1 01 36 4 2 - 13 - 7. Process according to any one of claims 1-6, characterized in that a thermamine-curable polymer uses a meiamine / formaldehyde, urea / formaldehyde and / or a melamine / urea / formaldehyde resin. Process according to one of Claims 1 to 7, characterized in that a melamine / formaldehyde resin is used as the thermosetting polymer. 9. A method according to any one of claims 1-8 wherein the thermosetting composition essentially comprises: 10-60 wt% thermosetting component 40-90 wt% reinforcing fibers 10. A method according to any one of claims 1-9, wherein the thermosetting composition essentially comprises: 10-50 wt% thermosetting polymer 1-10 wt% thermoplastic polymer 40-89 wt% reinforcing fibers. 11. A method of preparing thermosetting compositions comprising a thermosetting component and reinforcing fibers, wherein a bundle of the reinforcing fibers is first spread into a fiber web, then this fiber web is impregnated with a thermosetting component, the impregnated fibers are then heated and then reduced to granulate. 12. A method according to claim 11, characterized in that the bundle of reinforcing fibers is spread into a fiber web whose height / width cross-section ratio is between 0.40 and 0.05. 1013642 - 14 - A method according to any one of claims 11-12, characterized in that the fiber web is impregnated with a powder-form thermosetting component. 14. A method according to any one of claims 11-13, characterized in that the impregnated fibers are compressed during or after heating. 15. Method as substantially described in the description and examples. 1 01 36 4 2 REPORT CONCERNING THE NEW YEAR RESEARCH OF INTERNATIONAL TYPE OF IDENTIFICATION OF THE NATIONAL APPLICATION Characteristic of the applicant or of the authorized representative 9920NL Dutch application no. type Granted by the International Research Authority (ISA) to the request for an international type investigation. SN34016EN I. CLASSIFICATION OF SUBJECT MATTER when using different classifications. Please specify classification symbols) According to International Classification (IPCI ———— lnt.CI.7: C08J5 / 24 B29B15 / 10 B29B9 / 14 II. _ ^ Examined minimum documentation '~ - _Classification system_) Classification symbols' ~~ ”- lnt.CI.7: C08J B29B ____ Other documentation and minimum documentation insofar as such documents are contained in the undesired items. ---- Onion. I_j SEEN OFiDEPTOEK MAY '' JK FOR CERTAIN (~ CV.C 'UVvi-S ^ rmim oo aam / üllincKolgd)! "" "* .............. * ''" "---- -----. ---- _ - I _ ιν · II LACK OF UNIT OF INVENTION ( comments on supplementary sheet) iff ---—------- / Port * f * CT / ISA / ZOt <* J 07.J979