DE2452170A1 - HARD OR SEMI-HARD WOOD FIBERBOARD, METHOD OF MANUFACTURING THEREOF AND ARRANGEMENT FOR CARRYING OUT THE METHOD - Google Patents

Description

Livcnska Traforskningsinstitutet, 53-67 Drottning p; ri.stir.cis vä <j S-114 28 Stockholm, Schv / ccicn

Hard or semi-hard wood fiber board, demonstrations of manufacture ¹ thereof and arrangement for carrying out the process

The present invention relates to a hard or preferably semi-hard wood fiber board, a process for the production of this wood fiber board and an arrangement for carrying out the process,

It is known from the Swedish patent 318 H66 that the addition of curable plastic and thermoplastic during the production of a wood fiber board improves the mechanical properties of the board, especially its transverse tensile strength and dimensional stability, and that it is made possible by such an addition of resin to take the plate out of the hot press at a moisture content of 10-25 % , which gives a shortened pressing cycle and thus better capacity utilization.

It has now been found that similar improvements in the properties of the wood fiber boards are achieved in a wood fiber board, which is characterized in that its central layer (insert) has a significantly higher content of hardened resin than its outer layer, the content of hardened resin in the central layer is 1-15 JS (wt %) .

The present wood fiber board can be produced according to a method which is characterized in that a solution (including emulsion, dispersion, etc.) of curable resin or a fiber suspension with a high content of curable resin in the pulp suspension before or after the outflow of the pulp suspension is introduced from the headbox onto the fourdrinier wire of a fiberboard machine. The ^ rl ^ tte-is dayin in conventional V / eise,

eg by post-curing, conditioning, etc., treated. By the present method it is achieved that the Heissprenszoit is shortened in wet production of fibreboards (typically 10 -. ¹ IO%), so that 'the plates at an average moisture content of 10 - can be taken out of 25% over the cross section of the disk without that the plate has a tendency to peel open when the press is opened and the plate is removed. The final drying of the plate takes place in the subsequent post-curing.

According to the present invention, the reinforcing Resin concentrated to the central layer, as it has been found to be of the greatest importance there and as beneficial as is possible. It has been shown that division (peeling, delamination) takes place normally in the central layer of the plate, where the moisture content is greatest. The transverse tensile strength the plate and the screw retention at the edge are also largely dependent on the strength of the central layer addicted. The present invention thus provides an overall reinforcement achieved by wood fiber boards with significantly lower amounts of resin than bsi the methods used so far have been, in which resin supplied to the whole substance and thereby more or less over the cross-section of the whole plate has been distributed equally. .

The term "central layer" means the layer which can be as much as 70 % of the plate thickness and in which the mathematical center plane of the plate is present. The central layer can be moved to one of the surfaces (main surfaces of the plate)

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and does not have to be symmetrical in relation to the mathematical center plane. Any surface layer that is at least 10 % of the plate thickness must nevertheless always be present on both sides of the central layer. The thickness of the central layer can vary, eg depending on the panel thickness »material and panel type (hard or semi-hard). In the case of semi-hard panels, i.e. with a density (volume weight) of 500 - 800 kg / m ', and with a' thickness of 9-19 mm, the thickness of the central layer is between 10 and 70 % of the panel thickness, preferably between 10 and 50 % s e.g. between 20 and 35 %. If 70 % of the panel thickness is the central layer, ie with a higher content of hoarded resin, the central layer is approximately 50 % of the panel weight;

The resin content of the central layer can also, as mentioned above, vary between 1 and 15% , and is preferably between 2 and 6 %. The resin content of the central layer is advantageously at least ten times greater than that of the surface layer. In this case, the resin content is analyzed on the center plane of the central layer and on the surface of the plate. If a water solution (including dispersion or emulsion) of the curable resin is used as an additive in plate production, the resin content of this solution is, for example, 20-50% by weight. The resin content of the pulp to be used when the resin is added to the central layer is also usually the same as that mentioned for the water solution.

As the curable resin, phenol-formaldehyde resin is preferably used, but various other curable resins can be used e.g. melamine resins, acrylic resins, resorcinol resins, urea

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Formaldehyde resins and protein such as blood albumin.

According to the invention, a wood fiber board is produced which is reinforced with hardened resin which is concentrated in the central layer of the plate, e.g. by having a Solution of curable resin fed to the central layer in the pulp suspension on the sieve at the wet end of the fiberboard machine will. The addition is preferably carried out by a distribution device which is sunk into the pulp suspension. With "Solution of curable resin" also means suspensions, emulsions and the like of curable resin.

The present arrangement for making hard or semi-hard fibreboard is accomplished by an at the wet end of a fibreboard machine such attached distribution device characterized that the distribution of the solution of curable resin or Stock suspension containing a high content of curable resin, in the company in a central layer of the pulp suspension takes place, which flows in the headbox or on the wire, wherein the outlet (s) of the distribution device is (are) directed essentially in the direction of flow of the pulp suspension.

The accompanying drawings show preferred embodiments of the invention. Show it

1 shows an arrangement which is suitable for being attached above the wire section at such a height that in operation the pulp suspension is distributed in a central layer on the fourdrinier wire, Fig. 2 is a vertical section along the line II-II of Fig. 1,

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3 shows a cross section along the line ITI-III of Fir ,. 2 and part of the arrangement that is in Pip ,. 1 and fin ;. 2 illustrates will, and

Fig. K shows an additional embodiment of the arrangement used in a manner similar to the arrangement of Figs. 1-3

The embodiments according to the Fip ;. 1 - h are preferably used when a solution of curable resin is added to the fiber suspension or wet plate.

5 and 7 are other embodiments of the arrangement according to of the invention, which is used to add pulp suspensions with a high concentration of curable resin to the fiber suspension or preferably the wet plate are particularly suitable.

The. Fig; 6 and 8 are cross-sections along the line VI-VI of FIGS. -5 and VIII-VIII of FIG. 7, respectively. " · ■ - ·,

In Fig. 1 an arrangement is shown, which consists of a horizontal There is pipe 1 that is to be sunk in the pulp suspension on the sieve. It is also possible to have it in the pulp suspension to have sunk in a headbox. Solution of curable resin is supplied to the tubes 1 through tubes 2, the Number which depends on the length of the pipe 1. In Fig. The tubes 1 and 2 are shown in cross section. The pipe 1 is provided with a plate 3 arranged transversely to the flow direction of the resin solution, which is provided with holes along its length, which are preferably semicircular. The sheet distributes the

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Resin solution evenly over the entire length of the pipes 1, through . A column 4 in the tube 1, the resin solution flows to an or multiple nozzles 5 · The nozzle 5 can be a single one, you? extends as a column along the entire length of the tube 3 or it can be divided into several small columns or circular nozzles which carry the resin solution along the entire length of the tube Distribute evenly in the pulp suspension on the dome sieve. the Direction of flow; the resin solution in the nozzle 5 is essential same as the pulp suspension on the sieve.

The embodiment of an arrangement according to the invention shown in FIG. 1 comprises a pipe 1, one, two or more feed pipes 2 and a sheet metal 3, which have three parts analogous to the corresponding parts according to FIG. 1 and 2 are arranged. In tubes 1, a column ^2, J is further arranged, from which the solution of a curable resin the same direction as the suspension flows substantially in., Which flows around the tube 1. The tube is also surrounded by a tube 6 with a gap 7. By rotating the tube 6, the gaps 4 and 7 can be adjusted in such a way that a suitable width of the exit gap is obtained for regulating the amount of the solution of curable resin flowing out.

It is also possible to use an arrangement consisting of a Series consists of nozzles that are mounted on a pipe.

In these three described embodiments, the solution of the hardenable resin is preferably used in pipes with a high pressure pump supplied by a high pressure vessel «These arrangements

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can in a simple way on existing fiberboard .machines can be used without the machine remaining

to
changed / needs to be changed. It is also possible to use these arrangements for the supply of other chemicals, for example fire protection chemicals, at the desired level in the material flow.

If the higher resin content in the central layer of the plate is to be achieved by a suspension of Fabric fibers (lignocellulosic fibers) with increased resin content is supplied as a central layer, with the curable resin already deposited on the fibers, the supply takes place but-preferably through a separate headbox, which is in the normal material flow at the wet end., the Paser plate machine sunk is. In Figures 5 and 6 is an embodiment of a such a separate headbox shown, which is preferably in the Material flows are sunk in the normal headbox. The pulp suspension, the fabric is going to this headbox through a Cross distributor 10 supplied. This cross distributor can be attached directly after the additional headbox, so that this headbox as well as the cross manifold in the Stof f. Streams are sunk. In the one shown in Figs Headbox 11, the cross distributor 10 is outside the normal headbox and the stock is transported through pipes 12 from the cross distributor fed to the additional headbox. In this In this case, the rear part 13 of the headbox 11 is triangular, so that the material flow in the normal headbox is not is significantly disturbed. This additional headbox 11 is also with baffles I ^ to balance the material flow in this Headbox provided.

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The one in the puddle. 7 and 8 shown embodiment of the present Arrangement comprises a stuffing box 11 with a transverse distributor 10 built into it. The stuffing box is also provided with cones l'1 Mistake. This headbox can be in the material flow on the Sieve inserted v / earth, the material being fed to the transverse distributor 10 through pipes 15 which pass through the cover of the fiberboard machine are drawn. This headbox 11 also has a triangular shape Rear part 13. It is also possible to place this headbox in a normal headbox of a fiberboard machine to be built in.

The additional headbox according to Figures 5-8 can in a simple manner on ordinary fiberboard machines of the Fourdrinier type with very few changes to the machine design be used.

The present method can also be carried out in such a way that stock for the central layer with an increased content of curable resin is fed centrally to a headbox with a plurality of vertically different gaps. The substance concentrations are usually between 1 and 5 % and the machine speeds between 5 and 50 m / min.

The invention is described in more detail in the following examples.

Example 1 . A suspension in water at a temperature of 50 C was prepared from a mill-made pulp without any additions, which pulp was intended for the manufacture of semi-rigid wood fiber boards. 0.5 % of alum

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(Alurainium Sulphate) calculated on the weight of dry Pasern and sulfuric acid were added to the suspension Amount added that brought the pH of the suspension to 4.0

became. The pulp suspension was formed on a fiberboard machine to give boards with a weight per unit area of about 7.5 kg / m 2. The wet board formed was partially drained through suction boxes and was wet-pressed to a dry matter content of about 40%. The wet plate was then sawn to a format of 60 χ cm and was pressed in a hot press, which was provided with spacer strips, to a thickness of 10 mm with a closing pressure of 0.59 MPa. The press temperature was 230 ⁰ C, and the wet board was pressed until the temperature reached in the central layer of the disk 200 ⁰ C. The required pressing time was 23 minutes. This corresponds to the normally used pressing cycle for such a plate. Immediately after the pressing, the flexural strength and flexural modulus of elasticity of a part of the hot plate that had been sawn in advance were measured. The rest of the plate was then post-cured at 160 ° C. for 2 hours. After conditioning, the board received the following properties: Density (volume weight) 750 kg / nr

Transverse tensile strength 0.22 MPa

Flexural strength '· "26 MPa

Flexural modulus of elasticity '3300 MPa

Flexural strength directly after hot

pressing and before post-curing 13 MPa

(IPa (PaSCaI) = IN ₇ 2 '"N = Newton; kPa = lo ³ Pa; MPa = Io ⁶ Pa; iMPa = lobar = ^ cm ² IkPa = O, 145 psi'T

The same fiber suspension as in the previous experiment was 2% by weight before the pH was adjusted. Phenol-formaldehyde resin calculated on the Weight of dry fibers added, according to which the pH of the

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Suspension 'was reduced to ¹ KO with 0.5% alum and sulfuric acid. This suspension was also formed into a wet plate, which was cold-pressed and hot-pressed in the manner described; some plates were pressed with a press time of 23 minutes and some with a press time of 11 minutes. These later plates achieved a dry content of 80 % after hot pressing. After post-curing for 2 hours at 160 ° C and conditioning, the plate had the following properties:

Press time 11 min. Press time 23 min,

thickness 10.6 mm 10 mm density • 710 kg / m ³ . 750 kg / m ³ Transverse tensile strength 0.33 MPa 0.60 MPa Flexural strength 23 MPa 27 MPa Flexural modulus of elasticity 2600 MPa 3300 MPa Flexural strength directly after Hot pressing and before post-curing 5.9 MPa 13 MPa

It can be seen from the table that the plates that were used during 11 Min had a much lower flexural strength immediately after pressing, indicating that they were during subsequent presses Treatments are more easily damaged. It can also be seen from the table that this plate has a lower Density but have the same weight per unit area, which indicates that the plate had expanded back after hot pressing.

Through the in the Fir *. 3 described, additional stock on run with the cross manifold 10 behind the ordinary headbox, a wet board was formed in a fiberboard machine of Fourdrinier type, with 2/3 of the stock through the ordinary headbox

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and 1/3 of the fabric was called up by the additional fabric. This was sunk in the main stream of material in such a way that the fiber suspension coming from it formed a central layer in the finished panel. 6% Pneno] formaldehyde resin was added to the fiber suspension which was fed through this additional ^{headbox and its pH was adjusted to 1} I / O with 0.5 % alum and sulfuric acid. The main stream, which was free of resin, was also adjusted to pH 0.1. The wet plates obtained from this production thus contained 2 % resin, calculated on the whole plates, just like the plates produced in the previous experiment. In this case, however, the resin was concentrated in the middle third of the plate. The wet plate was cold-pressed and hot-pressed in the manner described above with a hot-pressing time of 11 minutes. After the same curing and conditioning as in the previous experiment, the panels obtained had the following properties: Thickness 10 mm

Density ⁷⁵ ° ^{ks / m3} Transverse tensile strength ° * ^{62 MPa} flexural strength. . '26 MPa flexural elasticity module ^{1 550} ° ^MPa flexural strength directly after
Hot pressing but before post-curing 13 MPa dry content after hot pressing 81 %

Despite the short pressing time, this plate showed the same strength after hot pressing as that obtained in the first two tests.

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ten panels with O or 2 % phenolic resin content, but in this panel with 2 % phenolic resin, the resin was distributed throughout the panel. The plates, in which the resin was concentrated in the central layer, were just as easy to handle after hot-pressing as a conventionally finished-pressed plate. The transverse tensile strength of the plate after post-curing and conditioning is also very good.

Example 2 . Wet panels were produced in the manner described above with a central layer of separate fibrous material, to which 15 % of phenolic resin, ie 5 % of resin calculated on the entire panel, had been added. After hot pressing for 11 minutes, post-curing and conditioning, this plate had the same properties as the one with 6 % resin in the central layer. An increase from 6 % to 15 % resin does not affect the panel properties with the phenolic resin used here.

)
Wet panels were made from the same fiber suspension on a laboratory sheet-making machine with 6 % phenolic resin added to the central layer of the panel. The thickness of the central layer was this time 1 / 1J of the total plate thickness. The plates were cold-pressed to a dry content of about ho%, and then hot-pressed for 11 min at 230 ⁰ C., As described above. These plates had the same high flexural strength immediately after hot pressing and showed no re-expansion after pressing. After Naehfaärtung and conditioning the plate had the following properties ι -

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- 13 - thickness 2452170 10 mm density 750 kg / m ³ Transverse tensile strength 0. ^ 5 MPa Flexural strength 26 MPa ' Bending load izitfitmodule 3300 MPa Flexural strength after hot pressing but before post-curing ¹ 12 MPa

Panels were produced in the manner indicated, but the phenolic resin content in the central layer was Ί % and the thickness of the central layer was 1/3 of the total thickness. The plates were hot-pressed during 16 minutes at 230 ⁰ C, giving a dry matter content after pressing of 90%. The plates obtained had the following properties
Thickness 10 mm

Density. 750 kg / m ⁵

Transverse tensile strength 0.43 MPa

Flexural strength - 25 MPa

Flexural modulus of elasticity '3200 MPa

Flexural strength after hot pressing
but before post-curing 11 MPa

EXAMPLE 3 Wet plates were produced in the manner described in the form of toroidal plates. The thickness of the central layer was 1/3 the thickness of the wet panel and contained 3 % phenolic resin, ie the total resin content of the panel was approximately 1 %. The board had a density of 700 kg / m ^3. "

The following table shows the properties of a plate,

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which was produced with 1 % phonol resin evenly distributed throughout the board, compared with the board produced according to the present example and the present invention with 3 % phenolic resin in a central layer. Full press time was used in both cases.

1 % phenolic resin 3 % phenolic resin evenly distributed in a central layer

■ zen plate from 1/3 Transverse Tensile Strength, MPa 0.38 0.53 Relative screw holding capital in the margin kN / m 26th 12th in flat side kN / m H ₇ 61 Cleavage sensitivity 0.35 0.20 Water absorption % 13.5 13.8 Thickness swelling % 7.5 7.6

The sensitivity to cleavage in a sawn cut is called the

^z ? __ defined,

where M "_ is the transverse tensile strength with a wood screw on the edge screwed in and (Γ means the transverse tensile strength without a screw The screw, which is a 22mm 6mm wood screw, is 15mm at the edge in a 10 mm pre-drilled hole with the diameter 2 mm screwed in. The sensitivity to splitting becomes normal to specified to 0.05 mm.

The relative screw holding capacity is in kN / m 'screw-in length specified. During the test, when screwing in the edge, the same Diameter, drilling depth and screw-in depth are used as when measuring the sensitivity to cleavage. "When screwing in shallow

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side was the drilling depth 2/3 of the plate thickness and the screw v / was screwed through the whole plate, but not so far that it pushed out on the underside. The pull-out speed was 1 mm / min.

Example k . In another experiment, a board with a density of 700 kg / Nm and a total resin content of 2 % was produced in the manner indicated. If the resin content was evenly distributed, the transverse tensile strength was 0.2 MPa. When all the resin was fed to a central layer which was 1/3 the thickness of the wet plate and thus contained 6% resin, the transverse tensile strength was increased to 0.52 MPa, despite the fact that the plate was removed from the hot press at a safe dry content of 85 % was compared to the 100 % dry content of the board with evenly distributed resin.

Transverse tensile strength, screw retention and sensitivity to splitting are of great importance for the assemblability of the panels, as they have different types of thickness and Include composition options. Plates can be in different Way to be jointed and assembled. It can be simple nailing through the whole panel or in an overlapped joint be of the groove and spunt type or with a rebate. These panel edges and joints can be easily damaged during assembly. A good joint strength is therefore for an easy and fast Mounting work essential. During the last decade the demands on the transverse tensile strength of the chipboard and medium hard fiberboard has become bigger. One consequence of this has been that the density of records for sale has increased.

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The invention therefore has to Ροίζβ that a sufficiently high Querzußfestißkeit can be achieved at lower density.

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Claims (12)

Expectations /l.JHard or semi-hard wood fiber board made by the wet process and reinforced with a hardened or hardenable resin, characterized in that the central layer of the board has a significantly higher content of hardened resin than its outer layer and that the content of resin of this central layer is 1-15% (wt. Si). 2. Wood fiber board according to claim 1, characterized in that the central layer is between 10 and 50 % of the board thickness, preferably between 20 and 35 % 3. Wood fiber board according to claim 1 or 2, characterized in that that the cured resin is a phenol-formaldehyde resin. k. Wood fiber board according to one of Claims 1-3, characterized in that the resin content in the central layer is between 2 and 6 % . 5. A method in the production of a hard or semi-hard wood fiber board according to claim 1 by the wet process, wherein the plate is reinforced with a hardenable resin, characterized in that a solution of hardenable resin or a Fiber suspension with a high content of curable resin in the pulp suspension directly before or after the outflow of the pulp suspension from the headbox to the fourdrinier of a fiberboard machine of Fourdrinier type is introduced. 509820/0342 6. Arrangement for carrying out the method according to claim 5, characterized by a distribution device. (1, H), dnc am Wet end of a Fourdrinier fiberboard machine mounted in this way is that the distribution of the solution of curable resin or pulp suspension that has a high content of hardenable hara contains »in the company in a central layer of the pulp suspension takes place, which flows in the headbox or on the Fourdrinier wire, the outlet (s) of the distribution device (1, 11) is preferably directed essentially in the direction of flow of the pulp suspension (are). . 7. Arrangement according to claim 6 _S, characterized in that the distribution device (1) consists of a tube (11) with a left-facing slot ( ¹ O » 8. The arrangement according to claim 6 _9, characterized in that the distribution device (1) consists of a series of nozzles which are mounted, for example, on a pipe, the supply from a high-pressure container taking place in an air-free manner. 9. Arrangement according to claim β or 7 _S, characterized in that the distribution device (1) consists of a tube with a longitudinal slot ( ¹ J) that consists of an outer rotatable tube (6) is surrounded by a longitudinal slot (7), which slot (7) ^{is adapted to the slot (1} J) in the inner tube (1) for regulating the outlet opening of the arrangement. 10. Arrangement according to claim 6, characterized by a separate Headbox (ll) 'for the central layer, which in normal, 509 * 20/0342 / J Conventionally shaped material flow at the wet end of a parallel platform machine is sunk by Fourdrinier type, so that this stream of material surrounds the material flow that comes out of the separate headbox and consists of a suspension of lignocellulosic fibers with hardenable resin deposited thereon. 11. The arrangement according to claim 10, characterized in that the stock inlet to the separate headbox (11) is a transverse distributor (10) is directly connected to the separate headbox (11) so that · the headbox (11) as well as the cross distributors (10) are sunk into the material flow. 12. Arrangement according to claim 10, characterized in that the stock inlet to the separate headbox (11) consists of a transverse distributor (10), the one behind the ordinary headbox attached and through pipes (12) to the separate headbox (11) is connected · which pipes through the posterior wall of the ordinary Headbox are pulled. . 509820/0342 to Blank page