PARTICLE BOARD AND USE THEREOF

Abstract: The invention relates to a homogeneous particle board having considerably increased strength and moisture resistance and a use of the particle board.

Description: PARTICLE BOARD AND USE THEREOF The present invention relates to a homogeneous particle board having considerably increased strength and resistance against moisture as well as the use thereof. Particle boards have been produced for a very long time. Usually they serve their purpose in a very good way. However there is a problem with these known particle boards. Thus they are sensitive to moisture and swell easily in a moist environment. In addition the strength and the hardness are rather moderate. There is a need for particle boards having a better strength, resistance against moisture and surface hardness. For instance these particle boards are needed as a carrier for so-called laminate floorings. Usually these floorings consist of a particle board having a thin decorative thermosetting laminate glued to its upper side. A balanced laminate is usually glued to the lower side of the carrier to give a dimensionally stable and even flooring material. The carrier has usually a thickness of about 6-9 mm and the two laminate sheets a thickness of about 1 mm together. Accordingly the complete flooring material has a thickness of about 7-10 mm. The laminate coated particle board is sawn up into a number of flooring boards which are provided with groove and tenon in the long sides and the short sides. Bar patterns are very usual for such laminate floorings. The decorative thermosetting laminate is produced in the usual way. Usually you start with a base layer consisting of a number of paper sheeets impregnated with phenol-formaldehyde resin and a decor paper sheet impregnated with melamine- formaldehyde resin. Possible there is also an overlay of^ - cellulose impregnated with melamine-formaldehyde resin. These sheets are bonded together to a laminate by pressing under heat and pressure. Due to the fact that it has not been possible before to produce particle boards with enough strength, resistance against moisture and surface hardness it has not been possible to make laminate floorings which can stand a long time use in a public environment. In such spaces the floors are usually exposed to a higher moisture charge and a greater mechanical strain. ' The surface hardness of the particle board is important for the resistance of the laminated floor against impression marks. A high bending strength and internal bond of the particle board are important for obtaining a strong and resistant laminate floor. Normally particle boards are manufactured by building up a mat of particles in several layers on a forming belt. Than the central layer or layers is usually built up of considerably bigger particles than the two outermost layers on each side of the central layer. Therefore the particle board made of the mat of particles will get the above mentioned drawbacks. According to the present invention it has quite inexpectedly been possible to satisfy the above need and bring about a homogeneous particle board. having considerably increased strength and resistance against moisture. The board is characterized in that, it has a density of 600-1200 kg/m , preferably 850-1100 kg/m a thickness swelling of 3-12%, preferably 4-7 % after 24 hours in water, a water absorption of 14-30 % by weight, preferably 15-28 % by weight after 24 hours in water, a bending strength of 18-35 MPa, preferably at least 24 MPa and an internal bond of 1.2-3.2 MPa, preferably 2.0-3,2 MPa. The particle board is built up of wooden particles having a maximal size of 3 mm. At a temperature of 10-30°, preferably 15-25°C these particles are mixed with 5-18 % by weight of glue calculated as dry glue on dry particles and 0.1-1.0 % by weight of an sizing agent. This particle material mixed with glue is spread on a forming belt or the like in such a way that a mat of particles consisting of one to five preferably at least three layers is built up, which mat of particles is possibly prepressed and then flat pressed at a pressure of 2 1 155--5500 kkpp//ccm 2,, pprreeffeerraabbllyy 2200--4400 kp/cm2 and a temperature of 120-210°C, preferably 130-170°C Often all or mainly all particles in the board have a maximal size of 2 mm. Usually the sizing agent is wax. Suitably the particles in all layers are within the same size interval. According to one preferred embodiment of the invention 60-100 % preferably at least 85 % of the particles in all layers have a size < 1 mm. Normally the particle board according to the invention has a 2 surface hardness of 4-5 kp/cm measured according to Brinell. The remaining internal bond after boiling for 2 hours in water amounts to 0.2-0.9 MPa, preferably 0.4-0.9 MPa. This is a very high value considering the fact that standard particle boards disintegrate at such a treatment. Normally the glue used according to the invention consists mainly or wholly of isocyanate glue, melamine-formaldehyde glue, melamine-urea-formaldehyde glue, melamine-urea-phenol- formaldehyde glue, urea-formaldehyde glue or a mixture of at least two of these. Preferably the glue is used in the form of a liquid. Aqueous solutions are often most suitable even if solvent free liquid state glues are also useful. According to one preferred embodiment of the invention the particles are mixed with 10.0-15.0 % by weight of glue calculated in the above way. Then the glue consists of melamine-formaldehyde glue, urea-formaldehyde glue, melamine- urea-formaldehyde glue, melamine-urea-phenol-formaldehyde glue or a mixture of at least two of these. Normally the completely pressed particle board is ground when it has been taken out of the press. As mentioned above, the invention also comprises the use of the particle board as a carrier for laminate flooring boards. Such boards comprise a thin decorative thermosetting laminate glued to the upper side of the carrier and usually a balanced laminate glued to the under side of the carrier. The laminate flooring boards are provided with groove and tenon in the short sides and the long sides. Of course the particle board can be used for other purposes than as a carrier in laminate floorings. The invention will be further explained in connection with the embodiment examples below of which examples 1, 3, 4, 5, 6 and 7 relate to a particle board according to the inven¬ tion. Example 2 shows the properties of previously known particle boards. Example 8 relates to a production of a laminate flooring with a carrier consisting of a standard particle board disclosed in example 2. Example 9 illustrates the production of a laminate flooring with a carrier produced according to example 1. Example 1 Sawdust was ground in a mill and then dried to a water content of 1.5 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 2 x 2 mm. The particles which passed the sieve were used for the formation of a three layer particle board with a central layer surrounded by one surface layer on each side. The particles for the surface layers were mixed with 14 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue wholly consisted of melamine-urea-phenol-form¬ aldehyde glue in the form of an aqueous solution. The particles for the central layer were mixed with 12.9 % of the same glue and 0.9 % wax calculated in the same way. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with three layers was built up. The particle mat was prepressed between rolls at room temperature and then flat pressed at a temperature of 2 145°C and a pressure of 30 kp/cm . The particle boards produced were allowed to cool down where¬ upon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. 3 Density 918 kg/m Thickness swelling after 24 h in water 9.2 % Water absorption after 24 h in water 28.5 % Bending strength 25.4 MPa Internal bond 2.63 MPa Surface hardness according 2 to Bπnell 4.17 kp/cm Internal bond after boiling 2 for 2 h 0.55 kp/cm Example 2 The properties of two known types of particle boards were measured relating to the same properties as according to example 1. One particle board was a standard board and the other an especially moisture resistant board sold under the designation V 313. The following values were obtained. Standard board V 313 770 kg/m 14 % 35 % 18.5 MPa 1.4 MPa 3.5 kp/crn ^ 0.20 MPa Sawdust was ground in a mill and then dried to a water content of 2.5 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 2 x 2 mm. The particles which passed the sieve were used for the forma¬ tion of a three layer particle board with a central layer surrounded by one surface layer on each side. The particles for the surface layers were mixed with 14 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue wholly consisted of melamine-urea-formaldehyde glue in the form of an aqueous solution. The particles for the central layer were mixed with 13.0 % of the same glue and 0.9 % wax calculated in the same way. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with three layers was built up. The particle mat was not prepressed. Flat pressing took place at a temperature of 145°C and a pressure of 40 kp/cm . The particle boards produced were allowed to cool down where¬ upon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. 3 Density 981 kg/m Thickness swelling after 24 h in water 5.3 % Water absorption after 24 h in water 17.5 % Bending strength 34.7 MPa Internal bond 2.85 MPa Surface hardness according 2 to Bnnell 4.53 kp/cm Internal bond after boiling for 2 h 0.83 kp/cm 2 Example 4 Sawdust was ground in a mill and then dried to a water content of 2-3 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 2 x 2 mm. The particles which passed the sieve were used for the formation of a three layer particle boards with a central layer surrounded by one surface layer on each side. The particles for the surface layers were mixed with 12 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue consisted of a mixture of 50 % melamine-urea-phenol- formaldehyde glue and 50 % urea-formaldehyde glue in the form of an aqueous solution. The particles for the central layer were mixed with 14.0 % glue and 0.9 % wax calculated in the same way. The glue wholly consisted of melamine-urea-phenol- formaldehyde glue. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with three layers was built up. The particle mat was prepressed between rolls at a temperature of 18°C and then flat pressed at a temperature of 2 160°C and a pressure of 38 kp/cm . The particle boards produced were allowed to cool down where¬ upon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. 3 Density 901 kg/m Thickness swelling after 24 h in water 8.1 % Water absorption after 24 h in water 26.3 % Bending strength 24.2 MPa Internal bond 2.20 MPa Surface hardness according 2 to Brinell 4.51 kp/cm Internal bond after boiling for 2 h 0.57 kp/cm 2 Example 5 Sawdust was ground in a mill and then dried to a water content of 2.5 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 1.5 x 1.5 mm. The particles which passed the sieve were used for the formation of a one layer particle board. The particles were mixed with 13 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue consisted of a mixture of 80 % melamine- urea-phenol-formaldehyde glue and 20 % urea-formaldehyde glue in the form of an aqueous solution. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with one layer was built up. The particle mat was prepressed between rolls at at temperature of 21°C and then flat pressed at a temperature of 2 160°C and a pressure of 38 kp/cm . The particle boards produced were allowed to cool down where¬ upon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. 3 Density 902 kg/m Thickness swelling after 24 h in water 5.9 % Water absorption after 24 h in water 21.1 % Bending strength 26.2 MPa Internal bond 2.35 MPa Surface hardness according 2 to Bnnell 4.70 kp/cm Internal bond after boiling for 2 h 0.62 kp/cm Example 6 A mixture of sawdust and cutterdust was ground in a mill and then dried to a water content of 2.5 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 1.5 x 1.5 mm. The particles which passed the sieve were used for the formation of a three layer particle board with a central layer surrounded by one surface layer on each side. The particles for the surface layers were mixed with 14 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue wholly consisted of melamine-urea-phenol-formaldehyde glue in the form of an aqueous solution. The particles for the central layer were mixed with 14.0 % of the same glue and 0.9 % wax calculated in the same way. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with three layers was built up. The particle mat was prepressed between rolls at a temperature of 23°C and then flat pressed at a temperature of 2 160°C and a pressure of 40 kp/cm . The particle boards produced were allowed to cool down where¬ upon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. Density 938 kg/m Thickness swelling after 24 h in water 5.3 % Water absorption after 24 h in water 19,6% Bending strength 28.3 MPa Internal bond 2.60 MPa Surface hardness according 2 to Brinell 4.46 kp/cm ' Internal bond after boiling for 2 h 0.41 kp/cm 2 Example 7 Sawdust was ground in a mill and then dried to a water content of 1.5 % by weight. The ground and dried particles obtained were sieved through a sieve having a mesh size of 2 x 2 mm. The particles which passed the sieve were used for the formation of a three layer particle board with a central layer surrounded by one surface layer on each side. The particles for the surface layers were mixed with 13.9 % glue and 0.75 % wax calculated as dry glue on dry particles. The glue wholly consisted of melamine-urea-phenol-formaldehyde glue in the form of an aqueous solution. The particles for the central layer were mixed with 13.4 % of the same glue and 0.9 % wax calculated in the same way. The particles mixed with glue were spread on a forming belt in such a way that a particle mat with three layers was built up. The particle mat was prepressed between rolls at a temperature of 22°C and then flat pressed at a temperature of 2 145°C and a pressure of 30 kp/cm . The particle boards were allowed to cool down whereupon they were ground to a thickness of 6.0 mm. The properties of the particle boards were measured and the following values were obtained. 3 Density 911 kg/m Thickness swelling after 24 h in water 8.3 % Water absorption after 24 h in water 24,6% Bending strength 24.2 MPa Internal bond 2.20 MPa ^Surface hardness according 2 to Brinell 4.13 kp/cm Internal bond after boiling 2 for 2 h 0.60 kp/cm Example 8 A particle board produced according to example 1 with a thickness of 6 mm was provided with glue on both sides. A 0.7 mm thick decorative thermosetting laminate was placed on the upper side of the particle board and a 0.3 mm thick balanced laminate was placed on the lower side. These three layers were then pressed together in a heated press at a temperature 2 of 100°C and a pressure of 5 kp/cm . After cooling to room temperature the whole board was sawn up to flooring boards with a size of 200 x 1200 mm. By means of cutting the short sides and the long sides were provided with groove and tenon. The properties of the finished flooring boards were measured and the following results were obtained. 3 Density 1057 kg/m Thickness swelling after 24 h in water 0.5 % Water absorption after 24 h in water 7.7 % Impact resistance 45 N Depth of indentation from a falling object from a 0.00 mm height of 800 mm Depth of indentation from a falling object from a 0.10 mm height of 1250 mm Example 9 The process according to example 8 was repeated with the difference that the carrier consisted of a standard particle board disclosed in example 2. The properties of the finished flooring boards were measured and the following results were obtained. 3 Density 805 kg/m Thickness swelling after 24 h in water 16.1 % Water absorption after 24 h in water 52.4 % Impact resistance 27 N Depth of indentation from a falling object from a height 0.53 mm of 800 mm Depth of indentation from a falling object from a height 2.50 mm of 1250 mm

Claims: CLAIMS 1. Homogeneous particle board having considerably increased strength and moisture resistance characterized in that, it 3 3 has a density of 600-1200 kg/m , preferably 850-1100 kg/m , a thickness swelling of 3-12 %, preferably 4-7 % after 24 hours in water, a water absorption of 14-30 % by weight, preferably 15-28 % by weight after 24 hours in water, a bending strength of 18-35 MPa, preferably at least 24 MPa and an internal bond of 1.2-3.2 MPa, preferably 2.0-3.2 MPa, that it is made of wooden particles having a maximal size of 3 mm and an average particle size of 0.2-2.0 mm, whereby the particles are mixed at a temperature of 10-30°C, preferably 15-25°C with 5-18 % by weight of glue calculated as dry glue on dry particles and 0.1-1.0 % by weight of a sizing agent whereupon this particle material mixed with glue is spread on a forming belt or the like in such a way that a mat of particles consisting of one to five, preferably at least three layers is built up, which mat of particles is possibly prepressed and then flat pressed at a pressure of 15-50 kkpp//ccmm 2 2,, pprreeffeerraabbllyy 2200--4400 kkpp//ccmm22 and a temperature of 120-210°C, preferably 130-170°C, 2. Particle board according to claim 1, characterized in that it is made of particles which all or mainly all have a maximal size of 2 mm. 3. Particle board according to claim 1 or 2 characterized in that it is built up of one to five layers, whereby the particles in all layers are within the same size interval. 4. Particle board according to any one of claims 1-3, characterized in that 60-100 % of the wooden particles therein have a size < 1.0 mm. 5. Particle board according to any one of claims 1-4, characterized in that it has a surface hardness of 4-5 kp/cm 2 measured according to Brinell. 6. Particle board according to any one of claims 1-5 characterized in that, it has a remaining internal bond of 0.2-0.9 MPa, preferably 0.4-0.9 MPa after boiling in water for 2 hours. 7. Particle board according to any one of claims 1-6 characterized in that the glue mainly or wholly consists of isocyanate glue, melamine-formaldehyde glue, melamine-urea- formaldehyde glue, melamine-urea-phenol-formaldehyde glue, urea-formaldehyde glue or a mixture of at least two of these. 8. Particle board according to any one of claims 1-7, characterized in that the content of glue in the particle board is about 10.0-15.0 % by weight. 9. Particle board according to any one of claims 1-8, characterized in that it is ground after the pressing. 10. Use of a particle board according to any of claims 1-9 as a carrier for a laminate flooring. 11. Use according to claim 10, characterized in that the laminate flooring consists of boards including a thin decora¬ tive thermosetting laminate glued to the upper side of the carrier and usually a balanced laminate glued to the lower side of the carrier whereby the laminate flooring boards are provided with groove and tenon in the short sides and the long sides.

Inventors: LARSSON ROLAND, RINGOE PETER, LARSSON, ROLAND, RINGOE, PETER
Applicants: LARSSON ROLAND, PERSTORP FLOORING AB, RINGOE PETER
Application year: 1993
Main classification: B27N3
IPC codes: B27N3, E04C2