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
  • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
  • B27N3/002—Manufacture of substantially flat articles, e.g. boards, from particles or fibres characterised by the type of binder
• • 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 invention relates to a method for producing medium density fibreboard according to the preamble of the main claim.
• the wood is first crushed into chips with a size of approximately 20 mm x 5 mm and the resulting chips are washed in order to remove the adhering foreign bodies (in particular sand).
• the chips are then treated for a few minutes under steam pressure and a temperature of around 160 ° C and then fed to a defibrator, where they are shredded into single fibers or small tufts of fibers between grinding disks.
• a binder such as urea-formaldehyde resin (UF resin), mixed resin made of urea and melamine (MUF resin), phenol formaldehyde resin (PF resin), tannin formaldehyde resin (TF resin) or diisocyanate adhesive HPMDI is added to the fibrous material.
• the binder is usually added to the still moist fibers before entering the dryer tunnel.
• the glued fibers are briefly exposed to temperatures of 70 ° C to 80 ° C in the dryer. As a result of drying, the effectiveness of the binders used is reduced.
• the binder can also be added to the fibers after drying.
• the fibers run through a special glue application drum.
• the dried and glued pulp is fed to a molding machine where it is sprinkled on a sieve that moves at high speed.
• the mats formed in this way are then pressed into sheets.
• the medium-density wood fiber boards produced with aminoplast resins as binders by the process described above generally have a high formaldehyde release capacity.
• Various methods have been proposed to reduce formaldehyde release. For example, according to DE-OS 28 04 514, attempts have been made to reduce the formaldehyde release from MDF by subsequently treating the fiberboard with ammonia or ammonia-releasing compounds (DE-OS 28 04 514). This aftertreatment must, however, take place in a separate working stage in a special chamber.
• the object of the present invention is to provide a simple process which makes it possible to reduce the formaldehyde release of the MDF produced with aminoplast resins such as UF resin without the plates having to be treated subsequently.
• the fibers are glued in a manner known per se with urea-formaldehyde resins, sprinkled into mats and pressed into plates. It has surprisingly been found that such MDFs have a relatively low release of formaldehyde and that, moreover, the boards produced by this process have better mechanical-technological properties than the boards which are made from fibers which have been subjected to thermomechanical refiner digestion (TMP). Procedure) are open-minded.
• TMP thermomechanical refiner digestion
• CTMP chemo-thermo-mechanical pulps
• the wood chips are impregnated with chemicals such as Na2SO3 under and without the addition of NaOH at high temperatures (140 ° C ... 170 ° C) and then defibrated at high temperatures.
• the fibers obtained are used alone or in combination with other fibers (e.g. waste paper) for the production of newsprint and other types of paper (e.g. tissue paper). So far, this method has not been used for the production of MDF in the form described above.
• the CTMP substance For the production of paper from the CTMP substance, it is washed out after the digestion in order to remove the chemicals that are still present. This leads to a wastewater problem that does not make the production of paper from CTMP material unproblematic and has prevented many companies from introducing this new technology.
• the CTMP substance should not be washed out, especially since the omission of this process step has proven to be particularly advantageous for the MDF.
• the binders used in the process according to the invention are the binders known in the production of MDF (medium-density fiberboard), such as urea-formaldehyde resin (UF resin), urea-melamine resin (MUF), phenol formaldehyde resin (PF resin), Tannin formaldehyde resin (TF resin) or an adhesive based on polymeric diisocyanates (PMDI) is used.
• MDF medium-density fiberboard
• UF resin urea-formaldehyde resin
• UMF urea-melamine resin
• PF resin phenol formaldehyde resin
• TF resin Tannin formaldehyde resin
• PMDI polymeric diisocyanates
• the method according to the invention is also suitable for the use of hardwoods.
• the digestion of the wood or the wood chips takes place according to the invention with chemicals such as Na2SO3 or with NaOH.
• the wood is digested with a mixture of Na2SO3 and NaOH.
• the chemicals mentioned When used in an optimized form, the chemicals mentioned have an advantageous effect on the properties of the finished panels.
• Table 1 below shows the mechanical-technological properties of the MDF produced and its formaldehyde release. This table clearly shows the influence of the washout stage on the mechanical-technological properties of the MDF produced and its formaldehyde release.
• the MDF produced according to the invention from the CTMP substance has comparatively high strength values, but a lower formaldehyde release than the corresponding plates made from the TMP substance (thermo-mechanical method).

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Dry Formation Of Fiberboard And The Like (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=6495480

Family Applications (1)

Country Status (4)

Cited By (5)

Families Citing this family (6)

Citations (3)

Family Cites Families (3)

• 1993
  • 1993-08-18 DE DE19934327774 patent/DE4327774A1/de not_active Withdrawn
• 1994
  • 1994-07-21 ES ES94111375T patent/ES2094601T5/es not_active Expired - Lifetime
  • 1994-07-21 DE DE59400679T patent/DE59400679D1/de not_active Expired - Lifetime
  • 1994-07-21 DK DK94111375T patent/DK0639434T4/da active
  • 1994-07-21 EP EP19940111375 patent/EP0639434B2/fr not_active Expired - Lifetime

Patent Citations (3)

Also Published As

Similar Documents

Legal Events