CA2032170A1

CA2032170A1 - Process for making a possibly flat synthetic resin moulded block and preform for use in such a process

Info

Publication number: CA2032170A1
Application number: CA002032170A
Authority: CA
Inventors: Fritz Haunold; Gerhard Melcher
Original assignee: Individual
Current assignee: Isovolta AG
Priority date: 1989-05-03
Filing date: 1990-04-27
Publication date: 1990-11-04
Also published as: JPH03506001A; BR9006755A; AU5550590A; AU632811B2; WO1990013403A1; AT392758B; EP0426793A1; ATA106189A; ATE92393T1; EP0426793B1

Abstract

(57) Abstract In a process for making a synthetic resin moulded block from fibres containing cellulose like wood fibres and a condensa-tion 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 in-creasing the pressure, pressing temperature and the time in the strip press with the curing of the binder.

Description

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Process Eor Making a Possibly Flat Molded ~esin Article, ~nd Preform For Use In Such A Process Technical Field The invention reEers to a process for making a molded resin article, in which cellulose-containing fibers such as wood fibers and a binder containing a condensation resin or condensation resin mixture on the basis of phenols and/or amino compounds and aldehyde like formaldehyde are blended and hot pressed possibly together with other materials like covering layers and/or intermediate layers, with the binder being cured. The invention refers further to a preform which is suitable for use in such a process.

State of the ~rt A process of the above-mentioned type is known from the EP 0081147 Bl. This patent refers to a process for making a decorative structural board by applying an aqueous alkaline solution or dispersion of phenolformaldehyde resin upon wood fibers and by drying the thus resined wood fibers to a residual moisture of 2 to 15%. From the resined and dried wood ~:~ fibers a fiber mat is formed, the mat is mechanically pre-compressed and subsequently in one or more superimposed layers hot pressed to a core layer, with the decorative layer ~: . ' ;' ''''' ' .

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being applied upon the core layer simultaneously with or after pressing.

This known process desires to make a structural board with similar prouerties as conventionally made laminated sheets which are made by hot pressing so-called "prepregs" which are papers impregnated with curable resins in dried condition. Due to the preferred orientation of cellulose fibers of the paper in the paper making direction, such laminated sheets show at fluctuating weather conditions in longitudinal direction and transverse direction of the utilized papers a different shrinkage and exp~nsion behavior which m~y disadvllnt;(~Jeou~ly affect their application. Moreover, the utilized papers constitute a material which is made from the raw material wood through a relatively complicated and environmentally polluting process.

With regard to the molded resin article produced by the conventional process according to the EP 0081147 Bl, the stated anisotropy in the expansion and shrinkage behavior is avoided, and since' papers are substituted directly with wood fibers the overall process is less cumbersome than conventional processes for making laminated sheets. ~owever, the required drying of the resined wood fibers still constitutes a cumbersome an~l possibly environmentally polluting process step.

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Presentatlon of the Inventlon The invention is primarily based on the objective to set forth a method of the above~stated type which allows the wood fibers to be coated with resin without a special process step and in which in accordance with an advantageous variation of the invention the stated drawbacks of the previously described ~l~erc lv conventional method is avoided ~ 'using easily flowing condensation resin binders.

~rhe object upon which the invention is based is now attained by the process in accordance with the invention which is characterized in that for continuously making a preform or a raw plate a~ff~er of a liquid binder is applied upon a weblike base material which is advanced in longitudinal direction, that upon this fiber mass of cellullose-containing fibers such as wood fibers or bleached cellulose a bed, fiber cake or a mat is applied at even thickness, that a second weblike base .
::~ material, which has previously been laminated with a further : ~ coat of liquid binder, may be applied upon the fiber mass, ~ with the binder c~at facing downwards, that the thus formed , .
laminated :structure is continuously compressed to an average mean~ bulk ~density ranging between 600 and 1400 kg/m3, preferably between 800 and 1400 kg/m3 and heated to a higher temperature ~at which the viscosity of the binder is decreased so~;that the binder at least almost completely penetrates the pore volume of the compressed fiber mass and possibly is , : . .
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subsequently cured. Advantageously, the weblike base materials may be provided by fibrous materials such as paper which may be impregnated with curable binders and which upon compression of the fiber mass retain their bonding with the latter.

According to an advantageous embodiment of the invention, the process according to the invention is characterized in that at a moisture content of the utilized- fiber mass of maximal weight-%, preferably maximal 8 weight-%, the binder for providing the binder coats is obtained by a condensation resin or condensation resin mixture in liquid form which has a solid resin content of more than 80 weight-% and a water content o~
at most 8 weight-%, preferably at most 6 weight-%, and which j may contain additives such as coloring pigments.
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In another advantageous embodiment of the process according to the invention, the heating o the laminated structure is attained by means of an electromagnetic high-frequency heating essentially before its compression.

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process according to the invention is characterized in that at :or after: termination of the heating phase and the compression phase, the~laminated structure is compressed again for a short time to ~thereby reduce its pore volume to such a degree that : the~:~ binder is practically evenly distributed in the pore I ,:

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volume. Preferably, the short-time compression of the laminated structure is obtained in a calender.

In a last advantageous embodiment, the process according to the invention is characterized in that the compressed laminated structure passes a cooling stretch after termination of the heating phase.

The invention further refers to the use of the compressed laminated structure, which is produced during the process according to the invention, as preliminary product which is advantageously employed as preform for making molded resin articles during the further process steps.

Descrl~ion of Various Ways for Carryinq out the_Invention with Reference to the Drawinq `: :
The Figure shows a schematic iliustration of an apparatus for contlnuously making a preform. This apparatus essentially includes - successively in direction of production (see arrow) of the manufacturing',process - a reel-off device 1 for a first web 2 of base material, a belt conveyor 3 with a first binder application station 4 and a device 5 for making and supplying a ~wood fiber cake, a reel-of~ device 6 for a ~econd web 7 of base material 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.
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~he device 5 for making and supplying~ a wood flber cake includes a wood fiber spreading device 13 with a belt conveyor 14, a compression belt 15, an isotopic thickness gage 16 as well as a subsequent transfer belt conveyor 17.

The following material are applied in accordance with an advantageous variation of the process:

:- Wood fibers dried to a moisture content of 4~, . .
- a base material, consisting of soda kraft paper with a substance of 200g/m2, impregnated with 40% resin coat of a phenolformaldehyde resin, ' .~ - a binder, consisting of a highly cancel-trated phenolformaldehyde resin with a solid resin content of 86% and a water content of 5%. Determination of the ~, .
solid resin content is attained by re-weighing after ' oven-drying over 60 min at 130C. The water content of the ~resin is: determined according to the conventional mçehod~ of Karl, Fi~scher. The viscosity of the binder is about 45,000 mPa~s at room temperature.

When carrying out the process, the base material web Z is Ç~cont~lnuously reeled ~off from the reel-off device 1 and is :advanced by ~a~ belt conveyor 3. The first binder application statlon 4 :which~is arranged above the belt conveyor 3 applies , , ' '' . . ' . ~................. ~
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viscous phenol resin binder 16 of a thickness of 0.5 mm for formation oE a binder coat 19. At the same time, a wood fiber cake 20 is continuously produced and placed at 21 upon the binder coat 19 which has been applied upon the belt conveyor 3. For the continuous production of the wood fiber cake 20, the spreading device 23 sprinkles wood fibers in form of a bed 22 at a dumping height of 100 mm and a bulk density of about 30 kg/m3. Subsequently, this bed 22 is compressed by the circulating compression belt 15 to a thickness of ~r~ ns~
about 60 mm. The~6ub6~a~e o~ the so-formed wood fiber cake 20 is then maintained constant by means of the isotopic thickness gage and e.g. through control of the spreading device.

;: :At the same time, the second base material web 7 is continuously drawn off from the reel-off device 6 which includes a storage reel 23, a support plate 24 and several deflection pulleys 22. During gliding over the support ;~; plate 2i, the second base material web 7 is provided with a :binder coat~ 26 ~of 0.5 mm thickness from the second binder application station 8 in a same manner as the first base material web~ 2.~With the binder coat 26 facing downwards, the .thus~ ~coated base:~ material web 7 is then continuously pressed upon~;the wood :~flber cake 20 so that a laminated structure 27 is~ obtalned whlch ~comprises the wood ~iber cake 20 lined at both~sides~ with ~base material webs 2, 7 which are provided with binder:~coats l9;:, 26.

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Vuring advance through the high-frequency heater 9, this laminated structure 27 is heated to a temperature of 80 -140C. At these temperatures, the viscosity of the binder decreases to viscosity values of 100 to 300 mPa- s. The laminated structure 27 heated in this manner is fed to the entrance of the heated belt press 10 and is compressed in its sphere of inEluence to a density of about 300 kg/m3. During passage through the heated belt press 10, with the temperature of the compressed laminated structure 27 being kept constant, the binder, which has decreased viscosity because of heating, penetrates the pore volume of the compressed wood fiber cake 20. ~t a re~en~ion time oE 3 min in the belt press 10, a high evenness o~ the binder distri~ution across the pore volume is accomplished.

After exiting the belt press 10, volatile fractions of the binder can evaporate out of the hot, compressed laminated structure 27 before being cooled down to about 30C d~ring its passage through.the cooled belt press 11 and cut to length into flat preforms by the cutting device 12. These preforms which in the present exemplified process have a thickness o~
about 5 - 7 mm are stacked in a conventional manner and temporarily stored as preliminary product.

According to a modification of the process set forth above with reference to the Figure, the compressed laminated structure 27 passes after exiting the belt press 10 an . .

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infrared heater and subsequently a calender in which the already compressed laminated structure 27 is further substantially compressed for a short period. During this short-time compression the pore volume in the laminated structure is Eurther reduced to such a degree so as to be cssentially Eully filled by the amount oE binder, with the surface of the wood fibers being wetted by the binder at the same tirne. Thus, possible irregularl-ties in the distribution of the binder within the wood fiber mass which are encountered in the laminated structure 27 upon exiting the belt press 10 can be further compensated in an advantageous manner.

In order to make a flat high-pressure molded article with a thickness of 6 mm - between two decoration papers impregnated with melamine resin two stacked preforms which constitute the core material are pressed in a high-pressure press at 140 C
and 70 bar for 20 min, whereby~the resins contained within the preform initially easily flow and cure subsequently.

~fter being cooled, and removed from the press, the flat high pressure molded article has a bending strength of 140 N/mm2, a tensile strength of 70 N/mm and a water absorption of about 0.8%.

The process as described in the Figure for making a preform for use in the making of a flat high-pressure molded article may be used directly for making high-pressure molded articles : ~ _ 9 _ . . .
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with respective modifications. This can be realized e.g. by increasing the pressure in the belt press 10 e.g. to 70 bar and the pressin~ temperature to 150 as well as by extending the retention time of the laminated structure to e.g. 6 min so that the resin binder contained in the laminated structure suitably flows initially and is subsequently cured. Then, a raw plate is discharged from the belt press 10 and cooled down in the subsequent cooled belt press 11 to 30. The raw plate is then cut to length and decoratively lacquered or coated in conventional manner for further application.

Commercial UtilitY

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The molded article made by the process according to the invention can be essentially used in the same field of application as conventional decorative high-pressure resin laminates of greater ~fe*gt~ (e.g. between 3 and 13 mm thickness) for example for the making of self-~ ~ fa~n~d~
structural elements or as weather resistant boards for . 1 .
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Claims

Patent Claims:

1. Process for making a molded resin article in which cellulose-containing fibers such as wood fibers and a binder containing a condensation resin or condensation resin mixture on the basis of phenols and/or amino compounds and aldehyde such as formaldehyde are blended and hot pressed possibly together with other materials like coatings and/or intermediate layers hot-pressed, with the binder being cured, characterized in that for continuously making a preform or a raw plate a coat of the liquid binder is applied upon a weblike base material (2) which is advanced in longitudinal direction, that a fiber mass of cellulose-containing fibers like wood fibers or bleached cellulose is applied upon this binder coat (19) in form of a bed, a fiber cake (20) or a mat, that a second weblike base material (7), with a further coat (26) of the liquid binder being previously laminated thereupon, may be applied upon the fiber mass, with the binder coat (26) facing downwards, that the thus formed laminated structure (27) is continuously compressed to an average mean bulk density ranging between 600 and 1400 kg/m3, preferably between 800 and 1400 kg/m3 and heated to a higher temperature at which the viscosity of the binder is decreased so that the binder at least almost completely penetrates the pore volume of the compressed fiber mass and may subsequently cure.

2. Process according to claim 1, characterized in that the weblike base materials are provided by fibrous materials such as paper which may be impregnated with curable binders and which upon compression of the fiber mass retain their bonding with the latter.

3. Process according to claim 1 or 2, characterized in that at a moisture content of the utilized fiber mass of maximal 10 weight-%, preferably maximal 8 weight-%, the binder for providing the binder coats is obtained by a condensation resin or condensation resin mixture in liquid form which has a solid resin content of more than weight-% and a water content of at most 8 weight-%, preferably at most 6 weight-%, and which may contain additives such as coloring pigments.

4. Process according to one of the claims 1 to 3, characterized in that the heating of the laminated structure (27) is attained by means of an electromagnetic high-frequency heating essentially before its compression.

5. Process according to one of the claims 1 to 4, characterized in that at least after termination of the heating phase, the laminated structure (27') is again compressed for a short time to thereby reduce its pore volume to such a degree that the binder is practically evenly distributed in the pore volume.

6. Process according to claim 5, characterized in that the short-time compression of the laminated structure (27') is obtained in a calender.

7. Process according to one of the claims l to 6, characterized in that the compressed laminated structure (27') passes a cooling stretch after termination of the heating phase.

8. Preform, made by the process according to the claims 1 to 7, characterized in that the preform is the compressed laminated structure (27') made during the course of the process.