WO1998002485A1

WO1998002485A1 - Method for the preparation of thermosetting compositions that can be shaped by application of heat and pressure

Info

Publication number: WO1998002485A1
Application number: PCT/NL1997/000412
Authority: WO
Inventors: Roland Alexander Korbee
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 1996-07-12
Filing date: 1997-07-14
Publication date: 1998-01-22
Anticipated expiration: 1999-01-12
Also published as: AU3362797A; NL1003581C2

Abstract

Method for the preparation of thermosetting compositions which comprise thermosetting compounds and reinforcing fibres and which are mouldable by application of heat and pressure wherein the reinforcing fibres are impregnated with a suspension and/or solution which substantially consist of a thermosetting compound and optionally a filling substance, drying the impregnated fibre and chopping or cutting the impregnated fiber into granules whereby a thermosetting compound is obtained comprising fibres with a length greater than 1 mm.

Description

METHOD FOR THE PREPARATION OF THERMOSETTING COMPOSITIONS THAT CAN BE SHAPED BY APPLICATION OF HEAT AND PRESSURE

The invention relates to a method for the preparation of thermosetting compositions which comprises thermosetting compounds and reinforcing fibres and which are mouldable by application of heat and pressure. Preferably the invention relates to a method for the preparation of thermosetting compositions which comprises aminoaldehyde condensation products and reinforcing fibres and which can be shaped by application of heat and pressure.

A method for the preparation of a fibre- reinforced aminoaldehyde resin composition which can be shaped into an object is described for instance in US- A-3.007.885. In that process a fibrous filling substance, such as for instance chopped alphacellulose pulp, is impregnated with a resinous syrup. This resinous syrup may consist of a thermosetting condensation product of an aldehyde, such as for instance formaldehyde, and a compound which reacts with this aldehyde because the compound contains reactive amino groups, such as for instance melamine. The impregnated composition is dried until it has a volatile matter content of less than about 10 wt.% The dried product, consisting of fibrous filling substance impregnated with resin, is comminuted in a ball mill and mixed to a homogeneous composition. This results in a composition in the form of a powder having a very low bulk density. Next, the composition is deaerated to a bulk density of at least 600 kg/m³, after which the densified composition is densified further with the help of a set of pressure rolls until a composition is obtained which has a bulk density of at least 1000 kg/m³. Subsequently the composition is processed to granulate.

The process according to US-A-3.007.885 results in a fine powder being obtained in the ball mill, which powder is processed to granulate in a following step by application of pressure. The drawback involved is that the material mouldable by application of heat and pressure which is obtained by that process has very short reinforcing fibres. As a result, a cured product based on this composition has insufficient mechanical properties.

The applicant has found that the abovementioned drawback can be eliminated by a method for the preparation of thermosetting compositions which comprise thermosetting compounds and reinforcing fibres and which are mouldable by application of heat and pressure wherein the reinforcing fibres are impregnated with a suspension and/or solution which substantially consists of a thermosetting compound and optionally a filling substance, drying the impregnated fibre and chopping or cutting the impregnated fiber into granules whereby a thermosetting compound is obtained comprising fibres with a length greater than 1 mm. Preferably the fibres have a length between 1.5 and 15 mm, in particular between 2 and 10 mm.

In a preferred embodiment of the invention the applicant has found a method for the preparation of thermosetting compositions which comprise aminoaldehyde condensation products and reinforcing fibres and are mouldable by application of heat and pressure wherein the reinforcing fibres are impregnated with a suspension and/or solution which substantially consists of an aminoaldehyde condensation product and optionally a filling substance, drying the impregnated fibre and chopping or cutting the impregnated fiber into granules whereby a thermosetting compound is obtained comprising fibres with a length greater than 1 mm. Preferably the fibres have a length between 1.5 and 15 mm, in particular between 2 and 10 mm.

The thermosetting granules can be processed to a cured product in a manner known per se. This processing takes place at a temperature between 70 and 250°C, preferably between 90 and 200 °C. 'Mouldable by application of heat and pressure' means that it is possible to subject the granules to any process of shaping in a hot mould under the influence of heat and pressure. This can be done for instance by compression or injection moulding.

The advantage of the method according to the invention is that it is possible to obtain granules from reinforced resin whereby granules can be obtained with fibres of any desired length. This offers the advantage that granulate comprising long fibres as mentioned above is obtained, which is not achieved if the thermosetting composition is ground in an intermediate step.

Suitable aldehydes in the aminoaldehyde condensation product for the present invention are formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, furfural, etc. and mixtures of these. By preference formaldehyde is used. Suitable thermosetting compounds and their solvents (in brackets) for the present invention are phenolic resins (in hydrocarbons, acetone, or esters), epoxy resins (in acetone or methylethylketone) and amino resins (in water ) .Suitable amino resins are resins comprising acyclic as well as heterocyclic amino compounds. Examples of acyclic amino compounds are urea, thiourea or ethyl urea. Suitable heterocyclic amino compounds are for instance compounds having a triazine structure, such as melamine, melam, melem, melone, ammeline, ammelide and ur idomelamine. Preferably melamine is used or a mixture of melamine - A -

and urea .

The aminoaldehyde condensation products used are preferably melamine formaldehyde (MF) , urea formaldehyde (UF) and/or melamine urea formaldehyde (MUF) resins. More preferably melamine formaldehyde resin is used with a formaldehyde : melamine ratio of between 1.3 and 2.5, preferably between 1.5 and 2.0.

If, however the granulate of MF, UF or MUF is processed to an object at a mould temperature of 150- 250°C, the viscosity of the thermosetting composition may become too low, which may result in leakage from the mould. As a result of such leakage, the pressure in the mould will decrease and consequently the water present in the resin will cause foaming, so that a product with insufficient quality is obtained by the inclusion of gas bubbles. Fo example a brittle product of insufficient impact resistance and strength will be obtained. This problem can be avoided by raising the viscosity, for example adding a viscosity-raising agent to the thermosetting composition. The viscosity-raising agent used is for example a water-soluble polymer, such as for instance polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidinone or hydroxyethyl cellulose. However as talc, cellulose, glass etc may also be used as viscosity-raising agent. If a viscosity-raising agent is used, the viscosity of the thermosetting composition is between 25 Pa.s and 15.10³ Pa.s at 120°C. Partly precuring of the thermosetting composition is also a possibility to increase the viscosity.

Suitable reinforcing fibres are fibres to which the aminoaldehyde resin adheres, such as for instance glass fibre, carbon fibre, aramid fibre, flax fibre, cotton fibre, cellulose fibre or cellulosediacetate fibre. Glass fibre is used by preference.

Any material can be used as filling substance, by preference organic material such as for instance cellulose, wood flour, cotton and/or amylum, etc. Inorganic materials are also suitable for use as filling substance, such as for instance talc, gypsum and/or clay, etc.

The thermosetting composition mouldable by application of heat and pressure according to the present invention substantially consists of the following components:

15 - 95 wt% aminoaldehyde condensation product 5 - 80 wt% reinforcing fibre 0 - 25 wt% filling substance 0 - 10 wt% plasticizer

Suitable plasticizers are compounds which are soluble in the aminoaldehyde resin such as ethylene glycol , glycerol, caprolactam etcetera. The adventage of the use of a plasticizer is the use of a lower processing temperature and as a result thereof avoiding premature curing of the resin.

In a special embodiment the composition additionally comprises: 0.1 - 25 wt% viscosity-raising agent.

The following method can be applied to obtain granules from the above-mentioned composition. An amino compound is dissolved in an aldehyde-containing aqueous solution in a ratio of for instance 1 part of amino compound to 6 parts of aldehyde at a temperature of 60- 100°C, for instance 1 part of melamine to 6 parts of formaldehyde at a temperature of 95 °C. Next, the aminoaldehyde resin thus obtained is introduced into a bath, through which is passed a bundle of fibres of the reinforcing material, such as for instance a bundle of glass fibres, in which process the fibre bundle is impregnated with the resin composition. The impregnated fibre bundle is passed through one long oven or two or more shorter ovens in series with a temperature of 100- 300°C so that the impregnated fibre bundle is dried. The temperature applied in the drying process depends on the length of the oven(s), the speed with which the fibre bundle is pulled through the oven(s), the resin composition or the thickness of the reinforcing fibre bundle. Subsequently, by application of a comminution method, for instance with the help of a chopping or cutting device, the thermosetting composition is converted to granulate having a length of more than 1 mm, preferably between 1.5 and 15 mm, in particular between 2 and 10 ram. The cross-sectional area of the impregnated fibre bundle and thus the cross-sectional area of the granulate as well is between 0.2 and 10 mm², preferably between 1 and 5 mm². The thermosetting composition mouldable by the effect of temperature and pressure is cured while it is processed to end product, so for instance in the hot mould during the injection or compression moulding.

Experiments which have been conducted by the applicant have shown that impregnated fibre bundles which will splinter during a chopping or cutting operation when the impregnated bundle is at ambient temperature and so do not yield the aimed-at granulate with longer fibres (of a few millimetres). When the impregnated bundle was cut at ambient temperature it was found that the resin and the reinforcing fibres were separated from each other again, with formation of much dust. This problem was effectively solved by heating the impregnated bundle before cutting. When the bundle was heated, preferably above the glasstransition temperature of MF resin, the resin became soft and could be cut without the formation of dust.

The thermosetting resin may further contain colorants and/or additives such as release agents, flameproof ing agents, etc.

The invention will be further elucidated by means of the following examples.

Example I

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 dilutability of the resin at 20°C amounted to 1.2 kk of resin per kg of water (formaldehyde/melamine ratio was 1.7). The resin was transferred to a bath and mixed with 7 g of cellulose. A glass fibre bundle with a diameter of 2 mm² was passed through the bath at a speed of 0.05 m/sec. The impregnated glass fibre bundle was dried in two ovens in series. The first oven had a temperature of 240°C, the second one a temperature of 160°C. The length of both ovens was 0.60 metre. The dried impregnated glass fibre bundle was cut into pieces, yielding granulate with a length of 8 mm and a cross-sectional area of 2 mm². The granulate was processed to end products by an injection moulding process with the help of an injection moulding machine (Arburg 270-90-350). The cylinder temperature during the injection moulding process was 80-100°C and the mould temperature was 170°C.

Example II

In a reactor 40 parts of water and 215 parts of formaldehyde solutiΩn (30 wt% formaldehyde in water with a pH of 9.4) were added to 160 parts of melamine. The condensation reaction was carried out at 95°C until the dilutability of the resin at 20°C amounted to 1.2 kk of resin per kg of water (formaldehyde/melamine ratio was 1.7). The resin was mixed with 10 g of cellulose and 20 g of polyethylene oxide. A glass fibre bundle with a diameter of 2 mm² was passed through the bath at a speed of 0.05 m/sec. The impregnated glass fibre bundle was dried in two ovens in series, first at 240°C, then at 160°, after which the impregnated strand was chopped into pieces of granulate having a length of 6 mm and a cross-sectional area of 2 mm². The granulate was processed to objects by an injection moulding process in a mould having a temperature of 170°C. The cylinder temperature of the injection moulding machine (Arburg 270-90-30) was 80-100°C.

Claims

C L A I S

1. Method for the preparation of thermosetting compositions which comprise thermosetting compounds and reinforcing fibres and which are mouldable by application of heat and pressure wherein the reinforcing fibres are impregnated with a suspension and/or solution which substantially consist of a thermosetting compound and optionally a filling substance, drying the impregnated fibre and chopping or cutting the impregnated fiber into granules whereby a thermosetting compound is obtained comprising fibres with a length greater than 1 mm.

2. Method according to claim 1 wherein the fibres have a length between 1.5 and 15 mm.

3. Method according to claim 1 wherein the fibres have a length between 2 and 10 mm.

4. Method according to claims 1-3, characterized in that during the impregnation a water soluble polymer is also present.

5. Method for the preparation of thermosetting compositions which comprise aminoaldehyde condensation products and reinforcing fibres and are mouldable by application of heat and pressure wherein the reinforcing fibres are impregnated with a suspension and/or solution which substantially consists of an aminoaldehyde condensation product and optionally a filling substance, drying the impregnated fibre and chopping or cutting the impregnated fiber into granules whereby a thermosetting compound is obtained comprising fibres with a length greater than 1 mm.

6. Method according to claim 5, characterized in that during the impregnation a water soluble polymer is also present.

7. Method according to claims 5-6 wherein the aminoaldehyde condensation product used is melamine formaldehyde, urea formaldehyde and/or melamine urea formaldehyde resins.

8. Method as substantially described in the specification and the examples.