IE57230B1 - Process for the manufacture of shaped products - Google Patents

Abstract

1. A method for producing shaped elements, especially construction panels, made from wood fiber reinforced hydraulically setting material, wherein at most 15 % by weight, in relation to the dry weight of the mixture, of reinforcing wood fibers and/or bundles of wood fibers, as well as water, are admixed to the binding agent and the so obtained slurry is processed into panels on dewatering equipment according to the winding layer process.

Description

The present invention relates to a method for the manufacture of shaped products, in particular sheets, made from wood fiber reinforced hydraulically j, setting material.

Shaped products, in particular sheets of cement compound material have been known for a long time, such material containing wood or cellulosic fibers as reinforcement.

Conventional wood-cement products show an extraordinarily high proportion of wood fibers of approx. 25 to 40% by weight. Generally such wood fibers are relatively very coarse (chips). Part of such wood fibers used are very coarse and are utilized for the central part (core) of the sheet, while finer fibers are employed in the covering outer layers. Additionally, sheets so made have to be subjected to an extended compression process. To date this has prevented economical production, in particular of products of relatively thin walls having good characteristics of strenght particularly in long-term behaviour.

Furthermore, based on DE-OS 30 08 012 a building sheet is known, which is made from a mixture of fibers and hydraulic binders consisting of wood chips and cement with admixture of chemical additives.

Outside of wood chips additional reinforcement fibers (glass fibers, cellulosic fibers, synthetic fibers, rockwool fibers) are being employed so as to attain the desired characteristics of bending strength. Production * was carried out by the continuously travelling long felt method which makes it possible to give the desired orientation to these additional reinforcing fibers.

To obtain satisfactory characteristics of bending strength in a building sheet reinforced with wood fibers only was thus considered not being possible. *4 - 2 10 Although this processing method appears to be relatively simple, it is indispensable to employ for such known building sheets other expensive reinforcement fibers in addition to the low-cost wood fibers.

Purpose of the present invention therefore is the creation of a process for manufacture of shaped products whereby materials widely available are being utilized, such as cement and reinforcement fibers of wood, not requiring complicated pre-treatment, and production of which can be ensured on an economical basis. Products so developed must show optimal strength values.

The method according to the invention, for production of shaped products made from hydraulically setting material such as cement, gypsum, lime, reinforced with wood fibers, is characterized by the admixture to the hydraulic binder of water and of maximum 15% by weight, in relation to the weight of the mixture, of reinforcing wood fibers and/or wood fiber bundles, and such slurry being formed into Sheets by the rolling process on dewatering equipment, for example on Hatschek machines.

In some cases it may be an advantage to employ in addition to the reinforcing wood fibers still other organic fibers, for example with the objective to modify specific characteristics of the products as for instance dilation behaviour, porosity or so as to satisfy particular requirements of strength.

The method according to the invention utilizes in preference wood fibers of different fineness.

Such wood fibers used in preference may for instance have a length of 0,3 to 15 mm, preferably 0,5 to 6 mm and an average diameter of 10 to 500^/Jm depending on the type of wood utilized and defibrillation process applied. - 3 Sheets produced according to the invention can be subjected,· prior to hardening, to a form-giving process as desired (e.g. forming of corrugated sheets).

This method of production is very economical, more especially when manufacturing relatively thinwalled sheets. 1 Due to the employment of a relatively large amount to water which facilitates the formation of the basic conglomerate, an uniform mixture and distribution of the wood fibers is obtained. With this a basic precondition has been attained for obtaining the strength values required. By production of the shaped products on dewatering machines in the layer-winding process, i.e. by superposition of mutliple layers of material, each one of which may be relatively thin, the optimal fiber distribution found in the basic conglomerate can be maintained and thereby the desired strength features (flexural strength) combined with excellent ageing behaviour is ensured as required for the end product.

Surprisingly, the basic conglomerate permits to work with a large proportion of wood fibers (possibly with the addition of filter fibers for retention of cement in the matrix), i.e. without taking recourse to using expensive supplementary fibers.

By using wood fiber bundles in accordance with the invention, in addition to economical advantages, the following substantial improvements may be obtained in comparison to fiber cement products containing cellulose only chemically pre-treated : - considerably lower embrittlement, - good long-term behaviour of wood fibers in the matrix of the entire structure, - a substantially better integration into the matrix in comparison to normally utilized chemically pre-treated cellulose, - 4 - increased toughness.

Shaped products, produced in accordance with the invention, will generally have a proportion of approx. 7% by weight of wood fibers, whereof approx. 60 to 80% are coarse fibers and 20 to 40% are fine fibers, 5 the rest being composed of hydraulic binders and fillers.

For the present purpose fine fibers are fibers which pass through a sieve of mesh 100 (ASTM) and coarse fibers are fibers which are retained by this sieve.

A more detailed description of the invention is given on basis of an example.

Example of trial Compressed sheets have been produced on 15 Hatschek equipment from two mixtures as detailed here below and were allowed to harden during 28 days in a moisture chamber at 100% relative humidity at 25C : Components of mixture Mixture A according to invention Comparative mixture B CTMP wood pulp 6% — Eucalyptus sulfate cellulose - 6% Portland cement 74% 74% 25 Limestone powder 20% 20% The mixture employed according to the invention (Mixture A) has been prepared approximately as follows : kg CTMP (CTMP = chemical-thermo-mechanical pulp) have been pulped in 1 mB of water with the addition of 20 kg aluminium sulfate during 10 minutes in a Solvo pulper.

The following fractions were determined in a - 5 Bauer McNett sieve analysis of the wood pulp : • ASTM Refuse Mesh 34,8% Mesh 35,5% 100 Mesh 12,3% 200 Mesh 3,6% above 200 Mesh 13,8% After pumping the fiber slurry from the system into a horizontal mixer the mixture was further diluted with 2 m3 of water, and 720 kg Portland cement and 180 kg limestone powder werre added. After a mixing phase of 10 minutes the fiber suspension was transferred via agitator vat to the Hatschek machine, whereby also 80 ppm of a polyacrylamide was added. In the processing phase on the machine sheets of 6 mm thickness were manufactured with 7 revolutions of the rotary forming roller. Half of the number of sheets were placed between oiled metal plates and submitted to a compression operation in a stacking press with a specific pressure of 250 bar during 45 minutes to an ultimate thickness of 4,9 mm.

After hardening the specimens were subjected to a process of accelerated ageing. This ageing test is each day composed of the following cycles : hours : drying and heating by IR lamps to 80°C 9 hours : exposure to heat by IR lamps at 80*C 3 hours : cooling off to 25 °C hours : immersion in water at 25°C The composition containing the mixture of comparison B is prepared in a similar way, and, with this composition, sheets are manufactured, hardened and subjected to a process of accelerated ageing in an - 6 identical manner.

Samples were subsequently taken after 1, 3, 6 and 12 months, and in test the fracture-mechanical data were determined on such specimens in water-saturated condition. Results as presented in table II show that sheets manufactured with wood fibers (mixture A) according to the invention, have attained both excellent ageing and long-term stability, whereas sheets manufactured with sulfate cellulose (mixture B) after one year show strong embrittlement and substantial reduction in strength.

Test results are presented in the following table : Period of ageing process Flexural strength N/mm2 Effective fracture energy KJ/n? Density g/ccm water absorp- tion % Mixture A, wood fibers (according to invention) original value 21,2 (measure of toughness) 1,21 1,804 23,0 after 1 month 20,1 1,03 1,827 22,7 3 months 21,0 1,10 1>861 22,2 6 months 21,4 1,00 1,874 22,0 12 months 22,7 0,84 1,886 21,4 Mixture B, cellulose original value 29,1 2,63 1,860 21,8 after 1 month 21,4 2,11 1,883 21,5 3 months 20,0 1,25 1,897 21,0 6 months 18,3 0,98 1,911 20,7 12 months 14,7 0,49 1,971 20,4 - 7 Different types of compositions in accordance with the invention, are indicated below s First type of composition hydraulic binder (cement) : 50 to 90% by weight <, fillers : 5 to 30% by weight filter fibers (natural or not) s 1 to 8% by weight £ wood fibers (reinforcing or not) : 2 to 8% by weight With the compositions of this type, in preference, usual conditions of hydraulic setting are employed, which means after having been given the desired shape, the shaped products are allowed to harden in a moisture chamber at 100% relative humidity at ambient temperature.

Second type of composition hydraulic binder (cement) s 40 to 75% by weight fillers (limestone powder) : 10 to 25% by weight amorphous silica : 10 to 20% by weight calcium hydroxide s 0 to 5% by weight wood fibers : 3 to 15% by weight With the compositions of this type, in preference a hardening process is employed wherein, after having been given the desired shape, the shaped products are simultaneously submitted to a process of compression from 400 to 1000 N/m^ and a thermal treatment of from 50 to 95°C during 4 to 12 hours.

Third type of composition hydraulic binder (cement) : 45 to 65% by weight quartz sand, 2000-9000 Blaine : 30 to 50% by weight wood fibers : 3 to 15% by weight With the compositions of this type, in preference, after having been given the desired shape, the shaped products are allowed to set during 6 to 120 hours and thereafter are subjected to an autoclavage hardening process during 6 to 18 hours under steam pressure of 6 to 12 bars. - 8 10 In this context filter fibers, are generally understood to mean fibrous systems which do not provide any appreciable contribution for reinforcement of cement. The principal purpose of these fibers is that of retention of cement in the compound during the dewatering process of the fiber-cement suspension.

For purposes of the process according to the invention suitable filter fibers are for example cellulosic fibers of any type, e.g. in form of chemical pulp, mechanical pulp, old paper, wood powder, cellulose-containing waste material from waste disposal installations etc. On the other hand it is also possible to utilize fibers from wool, silk or fibrids for example made from polyethylene.

Depending on type and application of the shaped products, the type of wood and the processing method, the wood fibers may be subjected to chemical or physical pre-treatment.

Chemical pre-treatment is understood to mean here e.g. mineralisation of the wood fibers by means of aluminium sulfate with the goal of obtaining an improvement in the setting of the cement, improvement of the bond between matrix and fibers, as well as of fire resistance behaviour. Physical pre-treatment of the fibers by application of heat may be done for the purpose of reducing the swelling capacity of the fibers.

Claims (11)

1. A method for producing shaped elements, especially construction panels, made from wood fibre reinforced hydraulically setting material, <, wherein at most 15% by weight, in relation to the dry weight of the mixture, of reinforcing wood fibres and/or bundles of wood fibres, as £ well as water, are admixed to the binding agent and the so obtained slurry is processed into panels on dewatering equipment according to the winding layer process.

2. The method according to Claim 1, wherein the processing is carried out according to the Hatschek method or the flow-on system.

3. The method according to Claims 1 to 2, wherein the proportion of water, in relation to the dry weight of the mixture, is minimum 300% by weight but preferably minimum 400% by weight.

4. The method according to Claims 1 to 3, wherein the proportion of wood fibres is substantially composed of 60 to 80% coarse fibres and 20 to 40% of fine fibres.

5. The method according to Claims 1 to 4, wherein said wood fibres show substantially a length of between 0.3 to 15 mm, preferably 0 to 6 mm and an average diameter of 10 to 500 urn.

6. The method according to Claims 1 to 5, wherein in addition to the binding agent proper, fillers such as for example limestone powder, ashes, slag or sand are admixed to the mixture.

7. The method according to Claims 1 to 6, wherein fine natural of synthetic fibres are added as process fibres to the reinforcing wood fibres. Jz

8. The method according to Claims 1 to 7, wherein besides said reinforcing wood fibres additional organic fibres are employed. - 10 9. The method according to Claims 1 to 8, wherein a mixture of the following composition is utilized: binder (cement) 50 to 90% by weight filler materials 5 to 30% by weight natural process fibres 1 to 8% by weight reinforcing wood fibres 2 to 8% by weight 10. The method according to Claims 1 to 8, wherein a mixture of the following composition is utilized: binder (cement) 45 to 65% by weight Quartz sand 2000 to 9000 30 to 50% by weight Blaine wood fibres 3 to 15% by weight and the shaped elements, after being brought into the desired form, are subjected to an autoclave hardening process. 15 11. The method according to Claims 1 to 10, wherein the manufactured panels, prior to hardening, are submitted to a shaping process, for instance corrugating.

9. 12. The method according to Claims 1 to 11, wherein the wood fibres utilized, prior to processing, are undergoing a pre-treatment. 2q

10. 13. The method according to Claims 1 to 11, wherein each panel is built-up of at least three wound layers, whereby each layer, prior to compressing, has a thickness of preferably maximum 1.5 mm.

11. 14. A method for producing shaped elements substantially as hereinbefore described by way of Example. - 11 15. Shaped elements whenever produced by a method as claimed in any of the preceding claims.