EP0426793B1 - Process for making a possibly flat synthetic resin moulded block and preform for use in such a process - Google Patents

Abstract

In a process for making a synthetic resin moulded block from fibres containing cellulose like wood fibres and a condensation resin binder like phenolic resin, for the continuous production of a mould blank or plate, a layer (19) of the viscous binder is applied on a web-like conveyor (2), especially a paper impregnated with phenolic resin, and a fibrous mass is then applied to it in the form of a fibre cake (20). A second coated web of conveyor material (7) is then continuously laid upon the fibrous mass with the coating of binder (26) downwards, whereafter the laminated structure (27) thus obtained is heated and compressed in a heated strip press (10), whereby the binder is distributed generally uniformly on the porous volume of the laminated structure. After the compressed laminated structure (27') has cooled it is used as the preform for the production of high-pressure moulded blocks. In another embodiment of the process, the laminated structure may be directly converted into a synthetic resin moulded block by increasing the pressure, pressing temperature and the time in the strip press with the curing of the binder.

Description

Technical field

The invention relates to a method for producing a compression molding, in which a fiber cake is continuously formed from cellulose-containing fibers such as wood fibers and is connected under pressure to a carrier web coated with a binder and is then pressed and cured.

State of the art

A method of the aforementioned type is known from FR-A 1,099184. This describes a process for the production of plates, a carrier material web loaded with a binder being applied to a moist nonwoven fabric with a moisture content of 67% under pressure at elevated temperature. The moist nonwoven fabric is produced by dehydrating a pulp. The pulp contains - as is said on page 2, column 1, lines 24 to 28 - lignin, hemicelluloses and other natural binders which ensure the fibers are connected to one another. The synthetic resin from the binder layer does not penetrate into the fiber pores filled with water due to the high moisture content of the wet nonwoven fabric, so that mainly the paper of the carrier material web is penetrated.

Furthermore, EP-B1-81147 relates to a process for producing a decorative building board, in which an aqueous alkaline solution or dispersion of a phenol-formaldehyde resin is applied to wood fibers and the wood fibers resinated in this way are dried to a residual moisture content of 2 to 15% .

A fiber mat is then formed from the resinated and dried wood fibers, the mat is mechanically pre-compressed and then hot-pressed in one or more layers arranged one above the other to form a core layer, the decorative layer being applied to the core layer simultaneously with or after pressing .

With this known method, a building board is to be produced which has similar properties to the laminated sheets produced in the usual way, which are produced by hot pressing so-called "prepregs", which are papers impregnated with curable synthetic resins in the dry state. However, such laminated sheets now have due to the preferred orientation of the cellulose fibers of the paper in the paper production direction under fluctuating climatic conditions, a different shrinking and stretching behavior in the longitudinal or transverse direction of the papers used, which can have a disadvantageous effect when used. In addition, the paper used is a material that is made from wood as a raw material using a relatively complex and environmentally harmful process.

In the case of the synthetic resin pressure-molded articles produced by the process known from EP 0081147 B1, the anisotropy mentioned in the expansion and shrinkage behavior is avoided and, since wood fibers are used to a large extent directly here, paper fibers are used, viewed globally with less process effort than in the usual production of laminates. However, the drying of the resin-coated wood fibers remains as a complex and possibly environmentally harmful process step.

Presentation of the invention

The invention is now based on the object of specifying a method of the type mentioned at the outset, in which one does not require a special process step for resin coating the wood fibers and in which, according to an advantageous variant of the invention, using readily flowable condensation resin binders, the disadvantages mentioned of the known method described above can be avoided.

The object on which the invention is based is first achieved in the process according to the invention, which is characterized in that for the continuous production of a pre-compact or a raw plate on a longitudinally moving web-shaped carrier material made of fibrous materials such as papers which are impregnated with curable binders, a layer a liquid binder is applied, that a fiber cake is applied to this binder layer, that a second web-shaped carrier material, to which a further layer of the liquid binder has previously been applied, is applied with the binder layer down onto the fiber cake, so that the layer structure thus formed is continuous compressed to an average average density in the range between 600 and 1400 kg / m³, but advantageously between 800 and 1400 kg / m³ and heated to a higher temperature at which the viscosity of the binder ls is reduced, so that the binder penetrates at least almost completely into the pore volume of the compressed fiber cake and, if appropriate, is subsequently cured. In this case, fibrous materials such as paper can advantageously be used as web-shaped carrier materials, which are optionally impregnated with curable binders and which permanently bond to the fiber mass when it is compressed.

According to an advantageous embodiment of the invention, the method according to the invention is characterized in that with a moisture content of the fiber mass used of at most 10% by weight, preferably at most 8% by weight, a condensation resin or resin mixture in liquid form is used as the binder for producing the binder layers which has a solid resin content of more than 80% by weight and a water content of at most 8% by weight, preferably at most 6% by weight, and the additives like contains color pigments.

According to another advantageous embodiment of the method according to the invention, the layer structure is largely heated before it is compressed by means of electromagnetic high-frequency heating.

In a further advantageous embodiment of the invention, the method according to the invention is characterized in that, at or after the end of the heating phase and the compression phase, the layer structure is compressed again briefly and its pore volume is reduced so much that the binder is practically uniformly distributed in the pore volume. This brief compression of the layer structure can advantageously take place in a calender.

In a last advantageous embodiment, the method according to the invention is characterized in that the compressed layer structure passes through a cooling section after the end of the heating phase.

Description of some ways to carry out the invention with reference to the drawing

In the figure, a device for continuously producing a pre-compact is shown in a schematic representation. This device essentially consists - in the production direction (see arrow) of the manufacturing process one after the other - from a rolling device 1 for a first carrier material web 2, a belt conveyor 3 with a first binder application station 4 and a device 5 for producing and feeding a wood fiber cake, a take-off device 6 for a second carrier material web 7 with a second binder application station 8, a heatable belt press 10, as well as a cooled belt press 11 and a cutting device 12.

The invention 5 for producing and feeding a wood fiber cake consists of a wood fiber spreading device 13 with a belt conveyor 14, a compression belt 15, an isotope thickness measuring device 16 and a downstream transfer belt conveyor 17.

• Holzfasern auf einen Feuchtigkeitsgehalt von 4% getrocknet,
• ein Trägermaterial bestehend aus einem Natron-Kraftpapier mit einem Flächengewicht von 200g/m², das mit 40 % Harzauftrag eines Phenol-Formaldehydharzes imprägniert ist,
• ein Bindemittel bestehend aus einem hochkonzentrierten Phenol-Formaldehydharz mit einem Festharzgehalt von 86% und einem Wassergehalt von 5 %.Die Bestimmung des Festharzgehaltes erfolgt durch Rückwägung nach Trocknung im Trockenschrank während 60 min bei 130 °C. Der Wassergehalt des Harzes wird nach der bekannten Methode nach Karl Fischer bestimmt. Die Viskosität des Bindemittels bei Raumtemperatur beträgt etwa 45.000 mPa.s.

In an advantageous process variant, the following are used as order materials:

• Dried wood fibers to a moisture content of 4%,
• a carrier material consisting of a sodium kraft paper with a basis weight of 200g / m², which is impregnated with 40% resin application of a phenol-formaldehyde resin,
• a binder consisting of a highly concentrated phenol-formaldehyde resin with a solid resin content of 86% and a water content of 5%. The solid resin content is determined by reweighing after drying in a drying cabinet for 60 min at 130 ° C. The water content of the resin is determined using the known Karl Fischer method. The viscosity of the binder at room temperature is approximately 45,000 mPa.s.

To carry out the method, the carrier material web 2 is continuously drawn off from the unrolling device 1 and runs over a belt conveyor 3. From the first binder application station 4 arranged above the belt conveyor 3, the viscous phenolic resin binder 18 is used to form a binder layer 19 with a thickness of 0 , 5 mm applied. At the same time, a wood fiber cake 20 is continuously produced, which is placed at 21 on the binder layer 19 applied to the belt conveyor 3. For the continuous production of the wood fiber cake 20, 13 wood fibers in the form of a bed 22 with a bed height of 100 mm and a density of about 30 kg / m³ are scattered with the aid of the scattering device. This bed 22 is then compressed to a thickness of approximately 60 mm by means of the circumferential compression belt 15. The basis weight of the wood fiber cake 20 thus produced is then determined using the isotope thickness measuring device and e.g. kept constant by controlling the spreading device.

At the same time, the second carrier material web 7 is continuously withdrawn from the take-off device 6, which has a supply roll 23, a support plate 24 and a plurality of deflection rollers 25, and when it slides over the support plate 24 from the second binder application station 8 - in an analogous manner to the first carrier material web 2 - provided with a 0.5 mm thick binder layer 26. The carrier material web 7 coated in this way is then continuously pressed onto the wood fiber cake 20 with the binder layer 26 facing downward, so that a layer structure 27 now results, which consists of the wood fiber cake 20 which is provided on both sides by carrier material webs 2 provided with binder layers 19, 26 , 7 is covered.

This layer structure 27 now passes through the high-frequency heating device 9, in which it is heated to a temperature of 80-140 ° C. At these temperatures, the viscosity of the binder drops to viscosity values of 100 to 300 mPa.s. The layer structure 27 heated in this way is fed to the entrance of the heated belt press 10 and compressed to a density of approximately 300 kg / m 3 in its feed area. When passing through the heated belt press, during which the temperature of the compressed layer structure 27 'is maintained, the binder penetrates into the pore volume of the compressed wood fiber cake due to its reduced viscosity due to the heating, with a long residence time in the belt press 10 of 3 min Uniformity of the binder distribution over the pore volume is achieved.

After leaving the belt press 10, volatile constituents of the binder can evaporate from the hot compressed layer structure 27 'before it is cooled to about 30 ° C. during the passage through the cooled belt press 11 and then divided into plate-shaped pre-compacts in the cutting device 12. These pre-compacts, which according to the present process example have a thickness of approximately 5-7 mm, are stacked in the usual way and temporarily stored as a pre-product.

In a modification of the method described above with reference to the figure, the compressed layer structure 27 'passes through an infrared heating device after leaving the belt press 10 and then through a calender in which the layer structure 27' which has already been compressed is briefly further strongly compacted. During this brief compression, the pore volume in the layer structure is reduced to such an extent that it is practically completely filled by the amount of binder and the binder is thereby uniformly wetted the surface of the wood fibers. This can cause any irregularities in the distribution of the binder within the wood fiber mass, which still exist in the layer structure 27 'when leaving the belt press 10, are advantageously further compensated for.

To produce a plate-shaped high-pressure molded body with a thickness of 6 mm, two such pre-pressed materials stacked one on top of the other as the core material are pressed in a high-pressure press at 140 ° C. and 70 bar for 20 minutes between two decorative papers impregnated with melamine resin, the resins contained in the pressed material initially flowing well and subsequently harden.

The plate-shaped high-pressure molded article removed from the press after cooling and cooled has a bending strength of 140 N / mm², a tensile strength of 70 N / mm² and a water absorption of approx. 0.8%.

The method described in the figure for the production of a preform, which is used in the production of a plate-shaped high-pressure molded article, can also be used directly with corresponding modifications for the production of high-pressure molded articles. This is then realized, for example, by increasing the pressing pressure in the belt press 10, for example to 70 bar and the pressing temperature to 150 ° C., and extending the dwell time of the layer structure, for example to 6 minutes, so that the synthetic resin binder contained in the layer structure initially flows well and then hardens. A raw plate is then removed from the belt press 10 and is cooled to 30 ° C. in the downstream cooled belt press 11. The raw plate is then cut to length and decorative lacquered or coated for further use in a known manner.

Commercial usability

The printing moldings produced by the process according to the invention can largely be used in the same field of application as the conventional decorative synthetic resin high-pressure laminates of greater thickness (e.g. between 3 and 15 mm thick), e.g. So for the production of self-supporting components or as weatherproof panels for outdoor use.

Claims (6)

1. A process for manufacturing a moulded block, in which a fibre cake consisting of fibres which contain cellulose, such as wood fibres, is continuously formed and is connected under pressure to a carrier web coated with a liquid binding agent and after that is pressed and cured, characterised in that for the continuous manufacture of a rough-pressed blank or of a crude plate a layer of the liquid binding agent is applied to a web-shaped carrier material (2), moving in the longitudinal direction, consisting of fibrous materials such as papers, which are impregnated with curable binding agents, in that the fibre cake (20) with a moisture content of a maximum of 10% by weight is applied to this layer (19) of binding agent, in that a second web-shaped carrier material (7), to which a further layer (26) of the liquid binding agent has previously been applied, is applied with the layer (26) of binding agent downwards to the fibre cake, in that the layered structure (27) formed in this way is compressed continuously to an average mean volumetric weight in the range between 600 and 1400 kg/m³, but preferably between 800 and 1400 kg/m³, and is heated to a higher temperature, at which the viscosity of the binding agent is reduced, so that the binding agent penetrates at least almost completely into the pore volume of the compressed fibre cake and is subsequently cured, and in that upon the compression the fibre cake unites permanently with the web-shaped carrier material, and in which respect the liquid binding agent is a condensation resin or condensation resin mixture on the basis of phenols and/or amino compounds and aldehyde, such as formaldehyde, which has a solid resin content of more than 80% by weight and a water content of at the most 8%, preferably at the most 6% by weight.
2. A process according to claim 1, characterised in that with a moisture content of the fibre cake used of a maximum of 10% by weight, preferably a maximum of 8% by weight, as binding agent for the production of the layers of binding agent a condensation resin or condensation resin mixture in liquid form is used which has a solid resin content of more than 80% by weight and a water content of at the most 8% by weight, preferably at the most 6% by weight, and which contains additives such as colouring pigments.
3. A process according to claim 1 or 2, characterised in that the heating of the layered structure (27) is effected by means of electro-magnetic high-frequency heating for the most part already prior to its compression.
4. A process according to any one of claims 1 to 3, characterised in that at least after the end of the heating phase the layered structure (27') is briefly compressed once again and its pore volume is in this respect so severely reduced that the binding agent is distributed practically uniformly in the pore volume.
5. A process according to claim 4, characterised in that the brief compression of the layered structure (27') is effected in a calender.
6. A process according to any one of claims 1 to 5, characterised in that after the end of the compression phase the compressed layered structure (27') passes through a cooling section.

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