Description

AGGLOMERATION PROCESS OF WOOD FIBRES (FIBREBOARD) FOR THE PRODUCTION OF AGGLOMERATE

SLABS OR PANELS

Technical Field of the Invention

[1] This invention refers to an agglomeration process of wood fibres to obtain agglomerated fibreboard slabs of different densities such as medium density fibreboard (MDF) and high density fibreboard (HDF) which consists of an impregnation and/or pulverisation of fibres with a pre-polymer of hydroxyl terminated polybutadiene (HTPB), a di-isocyanate and possibly a catalyst, followed by a com pression.

[2] This process aims to produce wood fibreboard agglomerates with better physical and mechanical properties which result in a better quality product with various applications in the construction and furniture industries for instance. Summary of the Invention

[3] Theprocess that is the subject of this invention consists of an impregnation of wood fibreboard with a pre-polymer of hydroxyl terminated polybutadiene (HTPB), a di- isocyanate and possibly a catalyst followed by a compressionphase of the fibreboard at a temperature between 30 a 90 ⁰ C for a period that may vary between 1 minute and 3 days in order to obtain the agglomerated boards. The agglomeration system used in the process is formaldehyde-free and therefore presents an alternative to the current formaldehyde-based agglomerates and also fulfils the most demanding environmental criteria.

[4] Thisprocess aims to produce agglomerated slabs ofwood fibreboard with better physical and mechanical properties resulting in a better quality product and therefore also enabling exemplary quality slabs to be obtained irrespective of the nature of the wood fibreboard whether it is hardwood or resin-based. Background of the Invention

[5] Thereprocessing or recovery and optimisation of manufactured products is a constant challengeanda crucially important factor for the competitivenessandthe very survival of companies.lt isbecomingmoreandmore common for product reprocessing, recovery and optimisation to consider environmental concerns and industrial practices must have a minimum impact on the environment. The adoption of 'environmentally- friendly' practices were initially imposed by legislation but companies themselves quickly realised that they also could also be a very important factor in productivity, the corporate image and in its relationships with its customers, regulators, supervisory authorities and society as a whole.

[6] Inthis context this invention represents a technological platform of great importance for the fibreboard agglomerate industries, launching them into a strategic framework characterised by an increase in the productivity and the quality of the products and by a cleaner and more environmentally-friendly production thereby contributing to environmental sustainability. But in particular this invention enables the optimisation of already existing products and - in the case of wood fibreboard agglomerates - it can over come difficulties associated with the nature of the raw material itself which at the moment affect the productivityandquality of the finalproduct.

[7] Theagglomerates currently used by the wood agglomerates industry (particle agglomerates and fibreboard agglomerates) are melamine formaldehyde or urea formaldehyde-based products and are often generically described in the sector as 'resins'. As these agglomerates contain formaldehyde they aresubject to European standards (EN 120, EN 312-1, EN 662-1) which aim to regulate and control the maximum concentration of formaldehyde.

[8] Formaldehyde is an organic compound and is part of the aldehyde family and in a more generic mode is part of the volatile organic compound(VOC) family. Formaldehyde is one of the chemical compoundsincluded on the list of the main Internal Air Pollutants' and is directly related to the phenomenon known as 'Sick Building Syndrome' which refers to the degradation of air quality inside residential dwellings. The main source of formaldehyde inside buildings is in wood agglomerates, used frequently as a construction material and for furniture.

[9] According to a study currently underway in the EU, formaldehyde is one of the substances which could be considered as a prime substance in any definition of interior air quality with wood agglomerates being one of the sources indicated of this pollutant.

[10] Italso states that a companyproducing wood agglomerates must refer in its 'Storage

Conditions' for slabs or panels of particle agglomerationsthat 'they must be stored in a dry and ventilated location.'

[11] Thesetypes of pollutants may cause serious public health problems and in particular due to risks that contribute to various illnesses such as allergies, respiratory difficulties, headaches, vertigo, nausea, irritations of the ears, skin and respiratory channels, loss of intellectual capacities and cancer - with children being the most susceptible to these effects.

[12] Another problem that is closely linked to the production processes is the fact that the agglomerating capacity of the current melamine-formaldehyde and urea- formaldehyde resins depend on the nature of the wood fibreboard. In fact current agglomerates manifest a significant reduction in their efficiency when the particles used originate from hardwoods (such as eucalyptus), in comparison with wood fibres from resinous trees (such as the pine tree.) This factor is very important both from a strategic and

sector sustainability viewpoint, given the increasedproliferation of the eucalyptusand itslower commercialvalue in relation to the pine tree.

[13] Document US4803112 describes the use of a formulation com prised of hydroxyl terminated polybutadiene (HTPB), asphalt, a plasticizer and com pounds with one or several isocyanate groups. This type of formulation differs from the disclosure in this invention to the extent that despite using some similar reagents or reagents from the same family to those proposed in this invention, it refers to a formulation designed to obtain an elastic polymer (elastomer) which acts as an impact-cushioner, for example between the fibreboard panels slabs for the production of pavements and not as an agglomerate for the production of fibreboard panels themselves. The use, amongst other reagents, of hydroxyl terminated polybutadiene (HTPB) and isocyanates or polyiso- cyanates in an elastomer formulation is one of the best known applications for these reagents, such as its usage in the production of adhesives and membranes as indicated in the following document.

[14] Document US5872203 describes, amongst many other reagents, the possibility of using hydroxyl terminated polybutadiene (HTPB) and di-isocyanates for producing an adhesive for a polymeric material for insulation or for waterproofing roofs and ceilings which differs from the disclosure in this invention to the extent that despite referring to com pounds that are identical to those described in this invention, it presents a formulation for obtaining a solid adhesive polyurethane to be used as a glue, for use on material surfaces used in roofs.

[15] Document US6451384B1 describes, amongst many other reagents, the possibility of using hydroxyl terminated polybutadiene (HTPB) to produce a thermal adhesion liquid for the treatment/finish of fibreboard panel surfaces. This differs from the disclosure in this invention to the extent that despite using some reagents which are identical or from the same family as those proposed in this invention and which are used for fibreboard panels, it refers to a formulation to obtain a liquid for use on surfaces to increase (reinforcement or temper) resistance of the fibreboard panel surfaces. Moreover document US6451384B1 describes the com position of a liquid temper product for the treatment/finish of fibreboard panel surfaces and not an agglomerate for the production of a fibreboard panel itself.

[16] DocumentUS4752637 describes a ligand for the production of panels made of cellulosic or lignocelulosic materials namely fibreboard panels consisting of poly- isocyanates and polyols. This ligand differs from the disclosure of this invention to the extent that it does not use as its base agglomeratingsystem a pre-polymerof hydroxyl terminated polybutadiene(HTPB). General Description of the Invention

[17] This invention refers to an agglomeration process of wood fibres (fibreboard) to

produce agglomerate slabs of wood fibreboard in different densities such as medium density fibreboard (MDF) slabs and high density fibreboard (HDF) slabs.

[18] Theagglomeration process uses a polymer obtained from the chemical reaction of a pre-polymerof hydroxylterminated polybutadiene also referred to as HTPB with a di- isocyanate, such as toluene di-isocyanate(TDI), isofuran di-isocyanate (IPDI) andmethylenediphenyl di-isocyanate(MDI). The reaction between those two reagents creates a final solid polymer with a large fibre agglomeration capacity. A catalyst can be used in this reaction, such as dibutylbis[(l-oxododecyl)oxy]/stannate or, more gen- erically, (DBTD L-dibutyltin dilaurate), in order to increase the polymerisation speed.

[19] The pre-polymer of hydroxyl terminated polybutadiene (HTPB) was selected because of its ability to distribute itself over an extensive surface area enabling its pulverisation and/or formation of aerosol thereby creating a saturated atmosphere in this pre- polymer. In fact the impregnation of wood fibres with the agglomerate is a fundamental phase in the production process of fibreboard agglomerated panels, due to the fact that the set of fibres represent a vast surface area to agglomerate and to the fact that fibres have a tendency to easily form small entanglements or 'balls' which threaten the efficient impregnation of all the fibres. In fact mixing processes in any horizontal or vertical industrial mixers using shovels, screws or shanks have been shown to be inefficient either due to the great difficulty in operating the mixers due to the formation of entanglements and balls of fibres inside the mixer or due to the (resulting) very heterogeneous distribution of the agglomerate in the fibres.

[20] Through the use of these mixing processes and after the com pression and polymerisation, fibre agglomerates with blemishes may be created, resulting in an inefficient mixing of the agglomerations in the fibres without any mechanical resistance or without any uniform properties in the panel, and presenting zones which have been well agglomerated and non-agglomerated zones. Therefore this invention suggests an alternative process to the mixing process which consists of an impregnation of the fibres in order to obtain a homogenous distribution of the agglomerate as described below.

[21] After a successfully com pleted phase of fibre impregnation with the pre-polymer it is then necessary to trigger a chemical reaction of polymerisation which enables the binding of the various pre-polymer chains in order to obtain a final solid polymer which will foster the efficient agglomeration of the fibres.

[22] Di-isocyanates were selected for this phase because, in addition to bringing about the intended chemical reaction, their different chemical structure enables different reaction speeds and final polymers with different characteristics to be obtained.

[23] Inaddition to fostering the chemical binding of the various chains of hydroxyl terminated polybutadiene, the di-isocyanates enable links to be establishedbetween the

chains of the final polymer (inter-chain links or cross-links), creating a reticular structure which bestows a huge mechanical resistance and some flexibilityto the final polymer.Because of this fact di-isocyanates are often referred to as 'reticulants' or 're- ticulant agents'. Depending on the type of di-isocyanate used different speeds of polymerisation are obtained.

[24] However, the speed of this reaction can also be altered by the use of catalysts.This factor is very important from an industrial point of view becausehere the useof di- isocyanates is more viable and can lead to faster polymerisation speeds whilst using catalysts at the same time.

[25] In the case of catalysed reactions the polymerisation period is often less than the time required for an efficient impregnation of the reagents in the fibres so that in the formulations of agglomerates that include catalysts, the impregnation of the fibres must be carried out in separate phases.

[26] In this context a two-track or two-channel impregnation process is proposed in which the fibres are impregnated separately, in each of the tracks, with a fraction of the agglomerate. Therefore no flow of fibres is impregnated with the com plete com position of the agglomerating system.

[27] After this segregated impregnation process the fibres are channelled towards a single track where a homogenous distribution of the fibres from the two impregnation tracks is carried out for example in an air vortex.

[28] Following this phase the fibres are immediately channelled to the com pression system where there is the first efficient contact of all the reagents in the agglomerating system, with a rapid polymerisation reaction having been unleashed.

[29] This polymerisation process is carried out at a higher temperature than the ambient temperature in order to obtain a faster and more efficient reaction.

[30] The process consists of an impregnation and/or pulverisation of fibres with the pre- polymer of hydroxyl terminated polybutadiene, a di-isocyanate and (possibly) a catalyst followed by a phase where the fibres are compressed at a temperature between 30 - 90 ⁰ C, for a period that can vary from between 1 minute to 3 days (depending on the type of di-isocyanate, the temperature selected and the use or not of a catalyst)to obtain the agglomeration slabs.

[31] Theagglomeration process of this invention is intended to be an alternative to the current agglomerates used in the wood fibreboard sub-sector enabling the production of agglomerateswith properties that complywith the standards established for the product, irrespective of the nature of the fibres (fibre from hardwoods or resinous trees) and formaldehyde-free.

[32] Theresulting product from the agglomeration process of wood fibres, the subject of this invention,can therefore be obtained in the following ways:

• In acontinuous production line in an integrated system of impregnation and/or pulverisationof the agglomerate, compressionand cutting with temperature control;

• In a discontinuous production line which includes the impregnation and pulverisation phases and compression with temperature control;

• In a discontinuous production line in an individual system of impregnation, mould filling, mould compression,greenhouse placement and mould removal.

Detailed Description of the Invention

[33] 1. Preparation of the fractions of HTPB, the catalyst and the di-isocyanate a) Preparation of a fraction for pulverisation com posed of HTPB and the catalyst (such as DBTDL) with a concentration in relation to the former between 0 and 1600 ppm; b) Preparation of a fraction for pulverisation com posed of HTPB and a di-isocyanate so that the concentration of those reagents in the aerosol lies between 60 to 90% (m/m) and 10 to 40% (m/m) respectively.

[34] 2. Impregnation of the fibres

The wood fibres are impregnated, through pulverisation or by passing through an aerosol, with hydroxyl terminated polybutadiene (HTPB) and a di-isocyanate with a proportion of these reagents in the aerosol between 60 to 90% (m/m) and 10 to 40% (m/m) respectively;

To create this result the fibres are transported, in two separate tracks, along tubing to create forced air flow, thereby displacing it along two tubes thrust forward by the air movement;

In a designated section of the tube in the first track, the fibres are impregnated either through vaporisation or passing through an aerosol with hydroxyl terminated polybutadiene (HTPB) or they can also be impregnated with a mixture of hydroxyl terminated polybutadiene (HTPB) and a catalyst;

In a designated section of the other tube, the tube of the second track, the fibres are impregnated with hydroxyl terminated polybutadiene (HTPB) and a di-isocyanate. [35] Each of these flows in the two tubes, already with the impregnated fibres is then channelled to a joint tube creating thereby a single fibre flow.

[36] The impregnation of the fibres in each of the two tracks, is carried out in such a way that in the single flow a proportion of hydroxyl terminated polybutadiene (HTPB), a di-isocyanate and a catalyst between 60 to 90% (m/m), 10 to 40% (m/m) and 0 (zero) to 1600 ppm respectively is obtained: impregnation of a flow of fibres in a 1 ^st track for pulverisation or for passing through an aerosol, with the fraction Ia);

impregnation of a flow of fibres in a 2 ^nd track for pulverisation or through passing through an aerosol with the fraction 2a).

[37] 3. Joining of the flows

The joining of the flow of fibres com ing from the two impregnation tracks is undertaken in order to create a more or less homogenous distribution of the fibres of the two tubes into a single flow. For an equal and efficient distribution of the fibres of the two impregnation tracks in the single tube, it may be necessary to use the air vortex and/or air whirlwind processes thereby increasing the homogenisation of two fibre flows into a single flow.

[38] 4. Compression of the impregnated fibres

The single flow referred to in the previous point is deposited in order to form a layer what is known as a 'mattress' which enables the com pression of the impregnated fibres as follows:

4.1. In a continuous system

In a continuous production line, the fibres are then deposited on a conveyor belt forming what is called a 'mattress' in the sector and com pressed under movement at a temperature between 30 ⁰ C and 90 ⁰ C for the time required for the polymerisation and for a solid slab of fibre agglomerate to be obtained and this normally takes between 3 and 20 minutes.

4.2. In a discontinuous system

In a discontinuous production system, the fibres are deposited in a fixed com pression press, which as a rule consists of various tray-type landing-areas which enable the com pression of various slabs at the same time and the 'mattress' is com pressed at a temperature between 30 ⁰ C and 90 ⁰ C for the time required for the polymerisation and for a solid slab of fibre agglomerate to be obtained and this normally takes between 3 and 20 minutes.

4.3. Compression in a mould

Alternatively the fibres are deposited and com pressed into a mould. The mould is placed in a greenhouse for the time required for the polymerisation, generally for between 5 and 30 minutes at a temperature varying between 40 ⁰ C and 90 ⁰ C, and then it is removed from the mould to obtain a solid slab of particle agglomerate. Example 1 [39] The fibres are impregnated through pulverisation or through passing through an aerosol, with hydroxyl terminated poly butadiene (HTPB), and a di-isocyanate with a concentration of these reagents in the aerosol of 85% (m/m) and 15% (m/m) respectively, and they are then channelled to a fixed com pression press where they are placed until a fibre deposit ('mattress') is formed of a mass and volume appropriate for the agglomerate panel of fibreboard to be produced (such as MDF and HDF) and are

com pressed at 60 ⁰ C for 2.5 hours.

[40] The final product is a solid panel of fibreboard agglomerate with a density between

500 to 1200 kg/m ³ , an internal resistance between 0.78 and 1,3 N/mm and a swelling percentage at 24 hours between 2.5 and 4%. Example 2

[41] The fibres are impregnated through pulverisation or through passing though an aerosol, with 85% (m/m) hydroxyl terminated poly butadiene (HTPB), 500 ppm of a catalyst and 15% (m/m) of a di-isocyanate and they are then channelled to a fixed com pression press where they are placed until a fibre deposit ('mattress') is formed of a mass and volume appropriate for the agglomerate panel of fibreboard to be produced (such as MDF and HDF) and are com pressed in a mould for 15 minutes at 70 ⁰ C.

[42] The final product is a solid panel of fibreboard agglomerate with a density between

500 to 1200 kg/m ³ , an internal resistance between 0.78 and 1,3 N/mm and a swelling percentage at 24 hours between 2.5 and 4%.