FI63686C - SAETT ATT MINSKA OCH / ELLER UTJAEMNA HARTSKONCENTRATIONEN HOS FANER AV TRAESLAG MED HOEG HARTSHALT - Google Patents

Description

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Sweden-Sverige (SE) 77U297-7 (71) Norrköpings Träimport AB, Box 69b, S-601 15 Norrköping,

Sweden and Sweden (SE) (72) Sven Ahlström, Norrköping, Carl-Olof Stenerup, Norrköping,

Sweden-Sverige (SE) (7 ^) Berggren Oy Ab (5U) Method for reducing and / or equalizing the resin content of plywood made from wood species with a high resin content - Sätt att minska och / eller utjämna hartskoncentrationen hos faner av träslag med hög hartshalt

Plywood of various types of wood is used for many purposes, including those which, when untreated, contain a considerable amount of resin, e.g. pine and other softwood plywood. The resin content of a log can vary depending on various factors, e.g., soil conditions at the growing site, its latitude, etc. The resin content can also vary considerably in different parts of the same log. Too high a resin content makes plywood processing difficult, e.g. due to clogging of sandpaper and uneven absorption of surface treatment agents. The resin content can also adversely affect the appearance of the product, resulting in a lower price. The object of the invention is therefore to provide a method in which these disadvantages are eliminated or reduced by reducing and / or smoothing the resin content of plywood made from wood species having a high resin content.

The method according to the invention is characterized in that a large number of plywood sheets are placed in a treatment vessel, that a solvent belonging to the group of chlorinated hydrocarbons is added to the treatment vessel and penetrated into the plywood sheets and heated to dissolve a portion of the resin in the plywood sheets. and that the time during which the solvent is in contact with the plywood boards and the pressure and temperature of the treatment vessel are adjusted or 2 6 3686 is selected so that the resin content of the plywood sheets in plywood boards, the remaining solvent is removed by maintaining a pressure in the vessel below atmospheric pressure while supplying heat.

According to the invention, methylene chloride is preferably used as the solvent, but other chlorinated hydrocarbons with a relatively low boiling point, preferably below 100 ° C, which, like methylene chloride, are not flammable, can also be used. Mention may be made here of chloroform, trichloroethane and trichlorethylene, dichloroethane and dichloroethylene, carbon tetrachloride, etc.

The treatment is suitably performed on a plurality of bundles of loosely held plywood sheets between which the solvent can easily penetrate, so that the plywood sheets come into contact with the solvent quickly and on all sides. During the impregnation phase, the solvent must be circulated in the treatment vessel, e.g. by means of one or more propellers. At least two tanks are required for the solvent, one tank being connected for solvent recycling, while the other is available for solvent recovery by removal and recycling. After evaporation, the remaining resin is removed from the tank and can possibly be used for special purposes.

After the liquid solvent has been removed from the treatment vessel, the solvent remaining in the plywood boards is suitably removed by reducing the pressure of the gas and supplying heat. The pressure in the vessel must then be less than about 600 mm Hg, suitably 250-500 and preferably 350-450 mm Hg when the solvent is methylene chloride. The solvent vapor can be condensed or absorbed into an activated carbon absorber and returned to the process. Reuse brings economic and environmental benefits.

To speed up the process, the solvent may be preheated when fed to the treatment vessel, suitably close to the boiling point, e.g. 35-40 ° C in the case of methylene chloride. It must be possible to limit the residence time of the solvent in the treatment vessel to a maximum of n.

30 minutes, although this is not a condition for successful completion of the process. Solvent vapor removal from plywood boards is also provided

II

3 63686 must be completed in a maximum of about 30 minutes, although this is not to be regarded as a necessary condition either. During removal, heat must be supplied to the treatment vessel, suitably by electrical resistance heating elements or externally through a heat jacket surrounding one or more parts of the treatment vessel. The resin content must generally be reduced to a maximum of about 2%, suitably to a maximum of about 1%, preferably to a maximum of about 0.5%. During the treatment, in addition to the extraction of the resin from the plywood sheets, the resin content is redistributed to the sheets, in which case the plywood sheet parts with a initially low resin content may have an increased resin content after treatment, which is acceptable as long as the resin content still does not exceed a predetermined value.

To ensure the desired result, the resin content of the circulating solvent must be checked regularly. If the resin content is too high, pure solvent can be added or a changeover can be performed to a tank with cleaner solvent. The resin content of the solvent should be at most about 2%, suitably at most about 1% and preferably at most about 0.5%.

When methylene chloride and other sparingly water-soluble resin modifiers are used, the moisture content of the plywood boards is not affected or is only slightly affected during the treatment process, which is most often an advantage. On the one hand, the necessary conditioning of the plywood sheets with respect to the moisture content can be carried out in the usual manner without interfering with the resin removal process, and on the other hand, plywood having an arbitrary moisture content can also be pre-conditioned plywood.

In the practical experiments of the treatment method according to the invention, the resin content of the plywood boards in the bundle was examined, whereby a few plywood boards were first removed from the bundle, which were examined separately for resin content, while others were treated according to the invention. The following times were used in the main stages of the process. Solvent: CH 2 Cl 2 · 4 6 3 6 8 6

Time min Pumping of the preheated solvent to 38 ° C into a treatment vessel with a bundle of plywood 10

Extraction of the resin in a circulating solvent 60

Removal from the container and dripping of solvent from the plywood sheets 30

Removal of solvent from plywood boards at a pressure of 300-400 mm Hg by heat supply (max. Temperature 75 ° C) 60

The above times should be shortened for optimal process performance.

The following results were obtained for different plywood boards.

Bundle Number of plywood boards examined Resin content n: ° Untreated Treated Strms * "tTlly 12 12 5.7 0.52 22 14 2.5 1.1 32 14 6.2 0.50 4 2 8 2.3 0, 30

Methylene chloride and the corresponding halogen-substituted hydrocarbons have proved to be clearly superior to other commonly used solvents for the intended purpose according to the invention due to their good resin solubility and difficult flammability.

The method according to the invention achieves even better surface properties in plywoods of high-resin wood species, which results in a corresponding increase in the value of the product. In addition, batches of plywood that would have previously been discarded due to too high a resin content can be used as desired after the treatment according to the invention.

The solvent used may contain additives for special purposes, e.g. various color pigments, such as aniline dyes, fire retardants, decay inhibitors and other wood modifiers.

Il 6 3 6 8 6

The drawing shows a plant used to carry out the method according to the invention. The plant is shown schematically and seen from the side as well as partly in section.

A space for handling plywood boards is placed in the space delimited by the walls 1. The container is elongated, e.g. about 3-4 m long, and can have a circular cross-section, in which case the diameter is e.g. 0.5-1 m. Of course, other cross-sectional shapes are also possible. The container is open at one end 5, whereby an elongate tray 9 can be inserted, which is shown partly in section, showing that the inside of the tray has several trays 11 extending in its longitudinal direction, each of which is intended to receive several e.g. 10-30 plywood boards. The trough can be suitably adapted to run on wheels, the wheels rotating on longitudinal support rails which are not shown in the drawing.

Thermal jackets 13 can be arranged around the vessel 3. The figure also shows a collection tank 15 for the solvent used and two tanks 17 and 19 for a substantially resin-free solution. The drawing also shows a container 21 with connections not shown and to which a vessel liquid for removing solvent can be led from the container 15, which can be led to the containers 17 and 19, whereby the residual resin can be removed from the vessel 21 in a manner known per se. The drawing also shows a number of lines and valves for directing fluid between plant units within the meaning of the invention. Reference numeral 23 denotes a three-way valve located between the vessel 3 and the reservoir 15 and connected to the reservoirs 17 and 19 by a valve 25 and 27, respectively. The new solvent is fed into the tanks via a line via valves 43, 31 and 33.

The device according to the drawing works as follows. When the trays 11 of the trough 9 are provided with loose bundles of plywood, the trough is inserted into the container 3, after which the solvent is added and the treatment is started. During the treatment, the solvent is recycled by means of one or more propellers, indicated by reference number 8. After a certain time, the solvent is removed to the tank 15 and, after the solvent has drained from the plywood sheets, the remaining solvent in the sheets

Claims (14)

1. A method of reducing and / or leveling the resin concentration of wood resins with high resin content, characterized in that a large number of veneer leaves are introduced into a treatment vessel, that a solvent from the group of chlorinated hydrocarbons is added to the treatment vessel and caused to penetrate the veneer sheets at all times. and, in the heated state, dissolve a portion of the resin present in it, that the resin concentration of the solvent in the treatment vessel is kept below 2% by weight, and that the time for the solvent's contact with the fan leaves and the pressure and temperature in the treatment vessel is controlled or selected. in such a way that the resin concentration in the veneer blades substantially everywhere falls below 1% by weight, that the resinous solvent is removed from the treatment vessel, and that the remaining solvents in the veneer blades are removed by maintaining sub-atmospheric pressure in the vessel during heat supply. 2. A method according to claim 1, characterized in that the treatment is operated such that the resin concentration of the leaf blades falls below 0.5% by weight. 3. A method according to claim 2, characterized in that the resin concentration of the solvent in the treatment vessel is poured below 1% by weight. 4. A process according to any preceding claim, characterized in that the resinous solvent removed from the treatment vessel is freed from excess resin, preferably by evaporation, and recycled. 5. A process according to any preceding claim, characterized in that the solvent is methylene chloride C 6. A method according to any of the preceding claims, characterized in that one or more bundles of loosely connected veneer leaves are treated simultaneously in the vessel. 7. A method according to any of the preceding claims, characterized in that the treated veneer sheets are pine veneer. II