Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Reexamination Certificate
1998-04-24
2002-04-02
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
C264S319000, C264S115000, C264S122000, C264S128000
Reexamination Certificate
active
06365077
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the preparation of cellulosic composites, in particular panel boards, starting from divided cellulosic fibrous material.
The invention further relates to the panel boards, obtained in the above process.
In industry, in particular in the building and construction industry, cellulosic composites, such as panels for doors, partitions and wall-segments, moulded pieces for furniture and larger parts for prefabricated structures, to be incorporated in houses, bungalows, barns and the like, are in ever increasing demand.
Depending on their properties, the composites will be applied indoors or for exterior use. Of paramount importance in this respect, especially for external applications, is the moisture sensitivity of the composite products, affecting the dimensional stability, the mechanical strength and the (biological) durability.
These properties and the like are affected both by the selection of the cellulosic fibrous starting material and by the selected manufacturing process.
Conventional starting materials for preparing cellulosic composites include wood and other lignocellulosic fibres. Wood and wood based fibres are widely used for the manufacture of panel boards, like particle boards and hardboard, respectively. In most of these manufacturing processes, the starting material is first reduced in size, e.g. shredded to chips, wafers or shavings. This implies that as a rule there is no real shortage in feedstock supply, as residual rest wood and roundwood and small-size residues are available from many other wood or fibre related processes and, instead of being wasted, can be conveniently used as starting materials in the manufacture of panel boards. The further processing of the starting material is known to be performed in the presence or absence of bonding agents.
In the patent and non-patent literature the manufacture of panel boards like particle board and fibreboard has been extensively described.
Thus, “Modern Particleboard & Dry-process Fiberboard Manufacturing” by Thomas M. Moloney, 1977, provides a detailed survey of commercial and semicommercial processes, indicating the many efforts made to simplify and economize the process and the measures taken to improve the properties of the final products.
In GB 959.375 a typical process is disclosed for the production of hardboard, fibreboard or the like comprising shredding rubber wood, treating the shredded wood with boiling water or steam to yield a fibrous pulp and compressing the pulp into the required board.
Another process based on the aggregation of very small pieces of wood, without the addition of a bonding agent is described in EP-A-161766. The process comprises treating the lignocellulosic material in divided form with steam to heat the material to a temperature high enough to release hemicellulose but not exceeding the temperature of carbonisation, for a time sufficient to decompose and hydrolyse hemicellulose into free sugars, sugar polymers, dehydrated carbohydrates, furfural product and other decomposition products: forming the treated lignocellulosic material into a mat and pressing the mat at a temperature not exceeding the temperature at which the mat would char, at a pressure and for a time sufficient to transform and thermoset the free sugars, sugar polymers, dehydrated carbohydrates, furfual products and other decomposition products in the lignocellulose materials into a polymeric substance which adhesively bonds together the lignocellulosic material to yield the reconstituted composite product.
Whereas the operability of the said process in the absence of adhesives in theory would appear cost-beneficial, the document makes clear that the decomposition of the hemicellulose portion of the lignocellulosic material typically proceeds at severe conditions, using high pressure steam and temperatures often in the range of 210 to 280° C. The conditions preferred during the final pressing or moulding step are likewise relatively severe. Moreover, changes in the composition of the starting material will have an impact on the thermosetting during the hot pressing step, so that frequent adjustment of the conditions will be necessary.
Investigation of the products obtained in the process known from EP-A-161766, has shown that their properties, although allegedly fulfilling Canadian requirements for external use, are by no means optimal, so that relatively early replacement of products exposed to severe outdoor conditions has to be taken into account.
It has now been found that by adding a suitable bonding agent after the thermohydrolytic treatment, even when this is performed at less severe conditions than in the process from the aforesaid EP document, products with superior properties are obtained, in particular as regards dimensional stability, mechanical strength and (biological) durability.
SUMMARY OF THE INVENTION
The invention may be defined as relating to a process for the preparation of cellulosic composites from divided cellulosic fibrous material, which process comprises a hydrothermolytic treatment of the divided cellulosic fibrous material, carried out at a temperature in the range of 160 to 200° C., using water as softening agent, a drying step, or a drying and a curing step, and a step in which dried, or dried and cured particles of treated material are contacted with an adhesive, subsequently curing the adhesive-laden particles at increased temperature and pressure under formation of the desired composite.
A preferred source of cellulosic fibrous material is formed by predominantly wood based material which is widely available, for example fresh roundwood and pieces of dried residual wood.
In practice, the cellulosic fibrous materials are sometimes already available in divided form, for example cuttings, shavings and chips, or the mixtures of shavings and sawdust resulting from commercial furniture manufacturing processes. However, the dimensions of these divided materials differ considerably. For example, the materials may consist of mixtures of particles with average dimensions ranging from 1 mm to 15 cm.
These materials, including roundwood and residual wood, must be divided according to the specific manufacturing process.
In the process of the present invention conveniently any of the divided starting materials normally used in the known commercial processes for the manufacture of particle board, fiber board, oriented strand board and the like can be applied.
According to a preferred embodiment of the present process, in particular suitable for the manufacture of oriented strand board, the divided starting material substantially consists of particles having a length of up to 15 cm, e.g. in the range of from 1 mm to 15 cm, a width of up to 5 cm, e.g. in the range of from 1 mm to 5 cm and a thickness of at most 3 mm, preferably of at most 2 mm.
According to another preferred embodiment of the process of the invention, in particular suitable for the manufacture of particle board, the divided starting material substantially consists of particles having a length in the range of from 1 to 12 mm, preferably in the range of from 1 to 10 mm and a diameter in the range of from 0.1 to 5 mm, preferably in the range of from 0.2 to 4 mm.
In order to prepare the starting material for the process of the invention, conventional techniques known in the art may be used such as milling or shredding methods. Thus, raw materials may be segregated by type of material, size and moisture content. They may be stored, or directly transported to the production unit.
The milling or shredding is performed according to any of the conventional techniques known in the art. For example, the milling can be carried out in the presence of steam. Presoftening the material under pressure may be beneficial for converting the raw material into divided materials e.g. particles or fibres.
According to the process of the present invention, the divided material is subjected to a hydrothermolytic treatment under specific conditions. In this treatment the starting material i
Groeneveld Hendrik A. C.
Pott Gerard Tjarko
Wipess by Geeske Martha
Zomers Adriaan Norbertus
Zomers Franciscus Hillebrand Adriaan
Akerman & Senterfitt
CR&DO B.V.
Ortiz Angela
Wipess by Geeske Martha
Zomers Adriaan Norbertus
LandOfFree
Process for preparing cellulosic composites does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing cellulosic composites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing cellulosic composites will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2854898