Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N1/00—Pretreatment of moulding material
  • B27N1/003—Pretreatment of moulding material for reducing formaldehyde gas emission

Definitions

• the present invention relates to a method of reducing the emission of formaldehyde from formaldehyde laden layered products having at least two layers, at least one of which being a board or veneer. It also relates to a board, a veneer and a flooring material obtainable by the method, to an aqueous solution comprising ammonium sulphite or bisulphite and urea for use in the method and to a process for preparation of the aqueous solution.
• the method comprises treatment prior to bonding the layers together of at least one of the surfaces of said board or veneer with a solution comprising an inorganic sulphur containing salt.
• Aldehydes especially formaldehyde based resins, are widely used in adhesive compositions, which are used in the manufacture of construction materials such as panelling, decking, etc.; home furnishings such as furniture, flooring material, etc.
• adhesive compositions typically contain a substantial molar excess of formaldehyde. Some of this excess formaldehyde is released upon curing of the resin during the manufacture of the product.
• formaldehyde continues to be released from these products even after the manufacturing process is completed.
• formaldehyde in the indoor air has been a major concern for many years.
• EP 0 027 583 discloses a method of reducing the emission of formaldehyde from particleboard bound with carbamide resin.
• the boards are treated with a thermally decomposable ammonium compound, such as ammonium carbonate, subsequent to pressing.
• the thus treated boards are then stacked and stored at temperatures from 40 to 70 °C, so that ammonia can be released.
• layered flooring material such as three-layer parquet floor can emit formaldehyde due to the different wood layers being normally bonded together by gluing with formaldehyde based adhesives.
• the top layer usually consists of hardwood, the middle layer of softwood or a board, for example, MDF, HDF or particle board and the bottom layer of a veneer.
• the top layer is usually treated with a formaldehyde free UV- lacquer or an oil to protect the surface, which also may function as a barrier to the formaldehyde emission.
• the different parts of a parquet sample such as the front, the back, and the edges, give different emission rates. For example, the formaldehyde emission from the backside can be 20 times higher than that from the front side.
• JAS SIS20 which involves a desiccator measurement where the backside and the edges of the sample cannot be sealed, but they are totally exposed.
• the present invention provides a method of reducing the emission of formaldehyde from wood-based products containing formaldehyde based resins, by which the above mentioned problems are overcome.
• the method according to the invention comprises treatment of at least one of the surfaces of a board or veneer, comprised in a layered product having at least two layers, prior to bonding the layers together, with a solution comprising an inorganic sulphur containing salt.
• formaldehyde laden layered products is herein meant a layered product containing formaldehyde based resins, wherein the layers are bonded to each other by a formaldehyde based adhesive and in case one or more of the layers is a board that the board as such may also be bonded with a formaldehyde based adhesive.
• the concentration of the inorganic sulphur containing salt in the solution is from about 1 to about 30 weight %, preferably from about 5 to about 20 weight %, and most preferably from about 8 to about 13 weight %.
• application of the salt in the form of a solution is preferred, according to the invention, it may also be applied in the form of a powder, if so desired.
• the solution is suitably an aqueous solution, although other solvents than water may be used.
• the salt solution may be applied by using any conventional coating technique, such as roller coating, curtain coating, or, spray coating.
• the amount of salt solution applied when only one of the surfaces is treated, is suitably from about 30 to about 90 g/m 2 , preferably from about 40 to about 80 g/m 2 , and most preferably from about 55 to about 65 g/m 2 . If both of the surfaces are to be treated, then the applied amount per side is suitably half of the amount if only one of the surfaces would be treated. In order to avoid disturbance of the moisture balance of the treated product large amounts of salt solution are undesirable.
• the inorganic sulphur salts according to the invention have a very high water- solubility, whereas carbonate salts have a rather limited water-solubility.
• a larger amount of carbonate salt solution comparing to that of sulphite salt solution is required to be applied onto the surface to be treated, which can affect negatively the moisture balance of the treated product and therefore even of the finished layered product.
• the inorganic sulphur salts according to the invention do not discolour the finished layered product, especially its outer surface, whereas carbonate salts may have a discolouring effect on the outer layer of the finished product and especially on oak surfaces.
• Suitable inorganic sulphur containing salts include sulphite or bisulphite salts such as, for example, alkali metal sulphites or bisulphites or ammonium sulphites or bisulphites. Water-soluble sulphite or bisulphite salts are preferred.
• ammonium sulphite or bisulphite is used, and most preferably ammonium sulphite.
• the method of reducing the amount of formaldehyde liberated by materials and products prepared with formaldehyde based resins is applicable to all formaldehyde based resins, for example, it is applicable to urea-formaldehyde, melamine-formaldehyde, phenol-formaldehyde resins and the like as well as copolymers, blends and mixtures made therefrom.
• urea is added to the inorganic sulphur containing salt solution.
• the inorganic sulphur containing salt does alone effectively reduce the emission of formaldehyde
• the addition of urea to the salt solution improves further the reduction of formaldehyde emission.
• the weight ratio of urea to sulphur-containing salt is from about 1:10 to about 1:1, preferably from about 2:10 to about 8:10, and most preferably from about 3:10 to about 6:10.
• the board to be treated according to the invention may be any kind of board such as particle board, chip board, or, fibre board, and it may be bound with adhesives based on formaldehyde based resins or other non-formaldehyde based resins.
• the veneer to be treated according to the invention may be any kind of wood veneer, preferably untreated veneer.
• the boards or veneers may be conditioned after the application of the salt solution to desired moisture content before the bonding stage. Furthermore, although only one of the surfaces of the veneer or board need be coated with the salt solution to achieve the benefits of the invention, depending on the application method both of the surfaces may be coated if so desired.
• the layers can be bonded by using any of the known conventional techniques, for example, by gluing and pressing.
• the board or veneer treated by the method according to the invention constitutes the backside surface or layer of the layered product. This gives rise to a significant reduction of the emission of formaldehyde from the backside of the layered product.
• the layered product may be any wood-based layered product.
• it is a flooring material, preferably a parquet flooring and most preferably a three-layer parquet flooring.
• the aqueous salt solution comprises an ammonium sulphite or bisulphite and urea. Preferably, it comprises ammonium sulphite and urea.
• the weight ratio between the salt and the urea is suitably from about 1:10 to about 1:1, preferably from about 2:10 to about 8:10, and most preferably from about 3:10 to about 6:10.
• the concentration of the ammonium salt and urea in the solution is from about 1 to about 30 weight %, preferably from about 5 to about 20 weight %, and most preferably from about 8 to about 13 weight %.
• the process for preparation of the salt solution comprises mixing of the salt, the urea and the water in a mixing ratio, which gives the desired concentration of salt and urea in the solution.
• the ammonium salt is in the form of an aqueous solution before mixing with the urea and required additional water for receiving a solution with the desired salt concentration.
• both the ammonium salt and the urea are in the form of aqueous solutions before mixing with each other for preparing an aqueous solution according to the invention with the desired salt concentration.
• the invention is further illustrated by means of the following non-limiting examples. Parts and percentages relate to parts by weight respectively percent by weight, unless otherwise stated.
• the ammonium sulphite solution used in the examples according to the present invention was prepared by mixing 19.7 kg of ammonium sulphite solution (35-36 weight %) and 3.0 kg urea with water to obtain a 10 weight % aqueous salt solution.
• the ammonium carbonate solution used in the comparison examples was prepared by mixing 31.6 kg urea, 40.0 kg ammonium bicarbonate and 28.4 kg ammonium carbonate with water to obtain a 27.8 weight % aqueous salt solution.
• Example 1 (reference): Veneers of spruce (2 mm thick) were glued on both sides of the core material of pine with a thermosetting urea-formaldehyde resin and a hardener.
• Example 2 (comparison): Veneers of spruce (2 mm thick) were pre-treated with an ammonium carbonate solution, on both sides and then left to dry for 4 hours before gluing and pressing in the same way as in example 1.
• Example 3 Veneers of spruce (2 mm thick) were pre-treated with an inorganic sulphite solution, on both sides, left to dry and then glued and pressed in the same way as in example 2.
• Example 4 (comparison): The procedure in example 1 was repeated, except that after gluing and pressing, the sample was left 15 minutes at ambient temperature and then the backside (the side facing away from the glue line) of the veneers was sprayed with an ammonium carbonate solution.
• Example 5 The procedure in example 4 was repeated, except that the backside of the veneers was sprayed with an ammonium sulphite solution.
• the formaldehyde emission from the samples containing treated veneers was generally significantly lowered compared to that of the samples containing untreated veneers.
• treatment of the veneers with a salt solution according to the invention gives rise to an even greater lowering of the formaldehyde emission comparing to that when the veneers are treated with an ammonium carbonate solution.
• concentration of the ammonium sulphite solution used was only about one third of that of the carbonate solution and that the applied amount (g/m 2 ) of the ammonium sulphite solution was less than that of the applied ammonium carbonate solution.
• Example 6 A spruce veneer for use in the manufacture of edge-glued 14 mm 3- layer parquet flooring was pre-treated on both sides with an ammonium sulphite solution. The veneer was conditioned to about 7 % moisture content before gluing to the core material of pine, with a thermosetting urea-formaldehyde resin and a hardener. The face lamella of ash was glued to the top of the core material with the same urea-formaldehyde resin/hardener mixture.
• Example 7 (comparison): Example 6 was repeated except for that the spruce veneer was pre-treated with an ammonium carbonate solution.
• Example 8 (reference): A parquet flooring sample was prepared in the same way as in examples 6 and 7, except for that the spruce veneer used was not treated with any salt solution.
• pre-treatment of the veneers with an inorganic sulphite solution according to the invention unexpectedly reduces the emission of formaldehyde more effectively without need of using large amounts of a rather concentrated salt solution.
• Use of large amounts of the salt solution results in that a larger amount of water is supplied onto the veneers, which can have a negative influence on the moisture balance of the product.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Adhesives Or Adhesive Processes (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Laminated Bodies (AREA)
• Compounds Of Unknown Constitution (AREA)
• Veneer Processing And Manufacture Of Plywood (AREA)

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Publications (1)

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Cited By (8)

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Citations (4)

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• 2002
  • 2002-03-04 SK SK1124-2003A patent/SK11242003A3/sk unknown
  • 2002-03-04 WO PCT/SE2002/000377 patent/WO2002072323A1/en not_active Ceased
  • 2002-03-04 JP JP2002571270A patent/JP2004522628A/ja active Pending
  • 2002-03-04 ES ES02701853T patent/ES2315346T3/es not_active Expired - Lifetime
  • 2002-03-04 CA CA002440349A patent/CA2440349C/en not_active Expired - Fee Related
  • 2002-03-04 EE EEP200300376A patent/EE200300376A/xx unknown
  • 2002-03-04 DK DK02701853T patent/DK1368168T3/da active
  • 2002-03-04 CN CNB028063775A patent/CN1320988C/zh not_active Expired - Fee Related
  • 2002-03-04 EP EP02701853A patent/EP1368168B1/en not_active Expired - Lifetime
  • 2002-03-04 CZ CZ20032392A patent/CZ20032392A3/cs unknown
  • 2002-03-04 AT AT02701853T patent/ATE409558T1/de not_active IP Right Cessation
  • 2002-03-04 PL PL02363912A patent/PL363912A1/xx not_active Application Discontinuation
  • 2002-03-04 SI SI200230782T patent/SI1368168T1/sl unknown
  • 2002-03-04 DE DE60229111T patent/DE60229111D1/de not_active Expired - Fee Related
• 2003
  • 2003-09-10 NO NO20034001A patent/NO20034001L/no not_active Application Discontinuation

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