Method for producing multi-layered lignocellulose materials having a core with special properties and at least one upper and one lower cover layer

Abstract

The invention relates to a method for producing multi-layered lignocellulose materials having a core and an upper and a lower cover layer, said method comprising the following steps a) mixing the components, b) spreading the mixtures in layers, c) pre-compressing, d) applying a high-frequency electric field e) hot pressing. According to the invention, a mixture of C) 1-15 wt.-% of a binding agent selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups [components C)], F) 0.1-3% alkali-/akaline earth salts, for the cover layers of the lignocellulose particles G) with H) 1-15% of a binding agent selected from the group consisting of aminoplastic resin and an organic isocyanate is mixed. After step a) the mixture for the core contains, with respect to the total dry weight of the mixture of the components A)-F) 3-15% water, the mixture for the cover layers of the components G)-K) contains 5-20% water, and the following conditions are met: F)1,1components K) and [components F)+components D)]1,1[components K)+components I)].

Claims

1. A multilayer lignocellulose material with a core and with at least one upper and one lower outer layer, where the core comprises the following components A) lignocellulose particles A) {component A)}, B) from 0 to 25% by weight of expanded plastics particles with bulk density in the range from 10 to 150 kg/m.sup.3 {component B)}, C) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups {component C)}, D) from 0 to 3% by weight of ammonium salts {component D)}, E) from 0 to 5% by weight of additives {component E)} and F) from 0.1 to 3% by weight of alkali metal salts or alkaline earth metal salts selected from the group consisting of the nitrates, halides and mixtures of these {component F)}, wherein the amounts of components B through F are based on 100 wt. % of the lignocellulose particles A) and where the outer layers comprise the following components: G) lignocellulose particles G) {component G)}, H) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups {component H)}, I) from 0 to 2% by weight of ammonium salts {component I)}, J) from 0 to 5% by weight of additives {component J)} and K) from 0 to 2% by weight of alkali metal salts or alkaline earth metal salts selected from the group consisting of the sulfates, nitrates, halides and mixtures of these {component K)}, wherein the amounts of components H through K are based on 100 wt. % of the lignocellulose particles G) and the following conditions are met: component F)1.1*component K) and {component F)+component D)}{component K)+component I)}.

2. The multilayer lignocellulose material according to claim 1, wherein the multilayer lignocellulose material comprises, in the core, from 0.2 to 2.5% by weight of component F).

3. The multilayer lignocellulose material according to claim 1, wherein the multilayer lignocellulose material comprises, in the core, from 0.25 to 2% by weight of component F).

4. The multilayer lignocellulose material with a core and with at least one upper and one lower outer layer according to claim 1, wherein the total thickness of said material is from 0.5 to 100 mm.

5. The multilayer lignocellulose material with a core and with at least one upper and one lower outer layer according to claim 1, wherein the average density of said material is from 300 to 700 kg/m.sup.3.

6. The multilayer lignocellulose material according to claim 5, wherein the multilayer lignocellulose material comprises, in the core, from 0.2 to 2.5% by weight of component F).

7. The multilayer lignocellulose material according to claim 5, wherein the multilayer lignocellulose material comprises, in the core, from 0.25 to 2% by weight of component F).

8. The multilayer lignocellulose material according to claim 1, wherein the difference between density maximum in the outer layers and density minimum in the core is at least 50 kg/m.sup.3.

9. The multilayer lignocellulose material according to claim 1, wherein the outer layers do not contain any components K).

10. A material for furniture or as packaging material which comprises the multilayer lignocellulose material according to claim 1.

11. A roof paneling or wall paneling, infill, shuttering, floors, door inlays, partitions or shelving or as support material for unit furniture, as door material, as worktop, as kitchen front, as outer layers in sandwich structures, or as elements in tables, chairs, and upholstered furniture which comprises the multilayer lignocellulose material according to claim 1.

Description

EXAMPLES

(1) Mixture 1

(2) 402 g of Kaurit 347 glue (BASF SE, solids content 67%) were mixed with 50.1 g of HydroWax 140 (Sasol, solids content 60%) and 72.0 g of water, with stirring. This mixture was added to 3123 g of sprucewood particles in a paddle mixer, and mixed.

(3) Mixture 2

(4) 402 g of Kaurit 347 glue (BASF SE, solids content 67%) were mixed with 20.1 g of sodium nitrate, 20.4 g of 40% ammonium nitrate solution, 50.1 g of HydroWax 140 (Sasol, solids content 60%) and 65.4 g of water, with stirring. This mixture was added to 3123 g of sprucewood particles in a paddle mixer, and mixed.

(5) Determination of Dielectric Loss

(6) Dielectric loss was determined on both mixtures. For this, the respective mixture was charged to a test chamber composed of an exterior and interior metal cylinder. The structure corresponds to that of a cylindrical capacitor where the basal surfaces of the exterior and the interior cylinder lie in the same plane and the two cylindrical surfaces (internal side of the exterior cylinder and external side of the interior cylinder) are coaxial. The mixture to be tested is charged to the annular intervening space between the exterior (inside diameter 9.5 cm) and interior (diameter 5 cm) metal cylinder. The material is charged to a height of 11.9 cm. An alternating electrical field is applied to the cylindrical capacitor and the dielectric response at various frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz, 10 MHz) is determined by measuring the current flowing through the mixture of materials. An HP 4192A LF impedance analyzer from Hewlett-Packard was used for this purpose. Dielectric loss was determined by extrapolation as 27.12 MHz for both mixtures.

(7) (mixture 1)=0.0134

(8) (mixture 2)=0.0230

(9) Particle Board of the Invention

(10) A mat made of three layers was scattered into a scattering frame (4644 cm), the ratio of the undermost layer (outer layer) made of mixture 1, the middle layer (core) made of mixture 2 and the upper layer (outer layer) made of mixture 1 being 33:34:33 (total weight of mat: 2893 g). The scattered mat was precompacted at room temperature for 60 seconds in the scattering frame at a specific pressure of 10 bar in a down-stroke press. Using a 125 mm mat here (depth after scattering), outgoing compacted depth was 60 mm. The scattering frame was then removed. For monitoring of the temperature profile in the middle of the sheet and in the middle of the outer layers, optical sensors were introduced into the edge of the mat, respectively into a horizontal hole in the center of the outer layers and of the core. Nonwoven separators were then provided to the upper and lower side of the mat, and this was compacted to 20 mm in a HLOP 170 press from Hoefer Presstechnik GmbH within a period of 2 s, and then heated by applying a high-frequency alternating field (27.12 MHz). The press was opened once a temperature of 130 C. had been reached in the core. Said opening took place 105 seconds after application of the high-frequency alternating field. The temperature in the outer layers at this juncture was 118 C. An automatic transfer system was used to move the mat into a heated press from Hfer, where it was pressed to a thickness of 19 mm at a temperature of 220 C. (press time 152 s).

(11) The transverse tensile strength of the resultant three-layer particle board in accordance with EN 319 was 0.98 N/mm.sup.2, with a density measured (EN 1058) as 675 kg/m.sup.3.

(12) Reference Particle Board

(13) A mat made of three layers was scattered into a scattering frame (4644 cm), the ratio of the undermost layer (outer layer) made of mixture 1, the middle layer (core) made of mixture 1 and the upper layer (outer layer) made of mixture 1 being 33:34:33 (total weight of mat: 2884 g). The scattered mat was precompacted at room temperature for 60 seconds in the scattering frame at a specific pressure of 10 bar in a down-stroke press. Using a 125 mm mat here (depth after scattering), outgoing compacted depth was 60 mm. The scattering frame was then removed. For monitoring of the temperature profile in the middle of the sheet and in the middle of the outer layers, optical sensors were introduced into the edge of the mat, respectively into a horizontal hole in the center of the outer layers and of the core. Nonwoven separators were then provided to the upper and lower side of the mat, and this was compacted to 20 mm in a HLOP 170 press from Hoefer Presstechnik GmbH within a period of 2 s, and then heated by applying a high-frequency alternating field (27.12 MHz). The press was opened after 105 seconds. At this juncture the temperature in the core and in the outer layers was 130 C. An automatic transfer system was used to move the mat into a heated press from Hfer, where it was pressed to a thickness of 19 mm at a temperature of 220 C. (press time 152 s).

(14) The transverse tensile strength of the resultant three-layer particle board in accordance with EN 319 was 0.81 N/mm.sup.2, with a density measured (EN 1058) as 668 kg/m.sup.3.