WO1982004008A1

WO1982004008A1 - A method for staining and impregnating wood

Info

Publication number: WO1982004008A1
Application number: PCT/NO1981/000017
Authority: WO
Inventors: Kjemiske Fabrik As Standard; Svenska Ab Rentokil; Olsen Frank Borch
Original assignee: Rentokil Svenska AB
Current assignee: Rentokil Svenska AB
Priority date: 1981-05-15
Filing date: 1981-05-15
Publication date: 1982-11-25
Anticipated expiration: 1983-11-15

Abstract

Procede de coloration et d'impregnation du bois, dans lequel le bois est d'abord colore et ensuite impregne, sans etape intermediaire de sechage. Facultativement, la coloration et l'impregnation peuvent etre executees par un procede combine a l'interieur d'un cylindre d'impregnation.Method for coloring and impregnating wood, in which the wood is first colored and then impregnated, without an intermediate drying step. Optionally, coloring and impregnation can be performed by a combined process inside an impregnation cylinder.

Description

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It has long been known to impregnate wood in order to improve its resistancy to fungus, decay and attack from in¬ sects. It is also well known to stain wood in order to improv its appearance and to increase its durability, particularly under varying weather conditions.

In order to reduce costs and to save .time and storage space, it is an advantage if the staining and impregnation of wood can be carried out simultaneously, and many attempts have been made in order to provide a suitable method. 10 In the so-called Royal method which is described in Norwe¬ gian Patent Specification No. 117,444, the impregnation and drying of wood are carried out by first impregnating the pro¬ ducts with an aqueous solution of preserving materials, where¬ after the products are dried in a hot, high-boiling liquid. According to a preferred embodiment of the patented invention, said liquid - preferably a high-boiling oil - may be mixed with colouring agents, preferably pigments, so that thejproducts are coloured at the same time. This method, however, is very cost¬ ly and comprises two steps. 20 Thus, it is usual to impregnate the wood prior to the staining thereof. Staining pre-impregnated wood, however, may lead to discolourations on the surface, which, of course, means a rather inattractive appearance._. In addition, several types of stains will have inferior adhesion to pre-impregnated wood, depending on the type of stain and preservative used. Conse¬ quently, it would be of advantage if one could perform the staining operation prior to the impregnation process.

From Swedish Patent No. 77 03 717 is known a method for so-called reverse painting, in which wood is first painted^'with 30 a water-borne dispersion paint, then dried thoroughly and thereafter impregnated with a solvent-borne preservative by the use of vacuum and/or pressure.

The method of the present invention is distinguished from the method according to said Swedish patent by not comprising the drying step.

Thus, the present invention provides a method of staining and impregnating wood, the method being characterized by said wood being first stained with a water dilutable stain, where- after, immediately and without any preceding drying of the

OMPI staining liquid, the impregnating process is carried out with - a solvent-borne preservative being pressed through the stain π d into the wood by means of vacuum and/or pressure. •

Staining and ■impregnating wood may be carried out in two operations, either by the application of .stain outside of the impregnating container and, thereafter-, impregnating with the preservative by means of pressure- and/or vacuum in an impregna¬ tion plant, or by performing said work as a combined process within an impregnation cylinder being specifically equipped for said purpose.

The advantages of the method of the present invention are the following: ^•

1) By staining- the wood prior to the impregnation with a solvent-borne preservative, the adhesion of the stain to the wood substrate is- greatly improved in comparison with the staining being carried out after the impregnation.

2) It is possible to carry out the staining as well as the impregnation in the same operation and in the same- plant "wet-on-wet".- This saves time, handling costs and inter- mediate storage space in the factory.

3) When the impregnation is carried out on stained' wood on which the staining liquid has not yet dried, the penetra¬ tion of the impregnation liquid into the wood will be better than if the staining liquid had previously been dried.

4) A plant as described under item 3 will be far less cost¬ ly to manufacture and to operate than would a correspond¬ ing plant for the Royal method, and the process takes an appreciably shorter time. ^* Experiments which have been carried out by Applicants, unambiguously demonstrate that even if impregnation is carried out after a suitable staining liquid has been applied to the wood, the impregnation liquid will penetrate through the^'stain¬ ed layer to such an extent that Norwegian Standard Require¬ ment for Impregnated wood, NS 3190 B or Bx can be met.

In the following a number of examples are presented which demonstrate how the preservative and the heart wood (the heart wood is not impregnatable) are distributed in the specimen after the process has been carried out. First, however, a

OMPI description of the test methods of the experiments will be presented,, with information regarding the preparation of ' specimen, as well as the impregnation conditions (pressure vacuum, operating times,_. etc.) .

The invention may be utilized in the following manner: In an impregnation cylinder containing wood, the wood is subjected to pre-vacuum of 60 % for 10 minutes in order to reduce the air content of the wood. Thereafter, a water dilut- able stain is applied from a separate storage tank. The impregnation cylinder is filled with stain and thereafter emptied again. Immediately thereupon the impregnation cylin¬ der is filled with the. solvent-borne preservative-, and. the pressure within the cylinder is maintained at 5 bar for 5 . mins. The preservative is then pumped out of the cylinder again and_. returned .to a separate storage tank. . The cylinder is then subjected to a vacuum of 90 %^'for 15 mins. to remove .any excess of impregnation liquid from the wood. TEST METHODS

Preparation of specimen samples of wood for impregnation experiments to class B according to Norwegian Standard NS 3190

(SKF METHOD NO. 27) ^■

Pieces of pine wood having the dimensions 45 mm x 45 mm x 480 mm, are cut out from wooden rafters of identical cross sections, in a number corresponding to twice the number of- tests to be carried out. From each piece of wood, 20 mm are cut off one end, and the cut-off bit of 45 mm x 45 mm x 20 mm is used for determining the content of heart wood in the specimen according to SKF Method No. 18. The remainder of the specimen is marked with the same code mark on the longest side of the piece close to both end surfaces and is then divided in the middle in order to obtain two substantially identical specimens having the dimensions 45 mm x 45 mm x 230 mm and being marked in the same way (identically) . The pieces are isolated at their ends with a polyurethane composition in order to prevent penetration of impregnation liquid in the end of the wood. The specimens are then ready to be used for testing of preservatives and/or according to NS 3190.

OMPI Low pressure impregnation of Class B surface, treated pine wood according to Norwegian Standard NS 3190 (SKF METHOD No. 11) . Ready prepared specimens according to SKF Method No. 27 are surface treated with stain or other surface protecting materials .in such a way that one of two identical. specimens- is treated, the second -one remaining untreated. After a specific drying time (usually 24 hours) 2 x 2 identical wood specimens are placed in a container containing the preservative, and are immersed completely into the liquid. The container is placed 10 in a pressure chamber, and is subjected to pressure and/or vacuum according to a specific- time schedule, wherein pressure, vacuum and operation time may be varied as^' desired. After the impregnation process is completed, the specimens are subjected to a final vacuum without liquid for a specific period of time. Thereafter, the specimens are tested for penetration of preservative and ^"active protecting agents (organotin compounds) in the wood according to SKF Method No. 10.

Testing of the penetration into pine sap wood of preservative containing solvents and organotin compounds (SKF Method No. 10) . 20 Specimens prepared according to SKF Method No. -27 and impregnated -according to SKF Method No. 11 are weighed prior to and after the impregnation process. The difference expresses the liquid -uptake by the wood, i.e. the consumption^' of liquid in the impregnation process. Subsequently, the specimen is divided in the middle, and one half is dusted on the cut sur¬ face with^' a powder composition consisting of:

2.5 per cent by weight of Ceres blue R and

97.5 per cent by weight.of talcum. The powder.dye obtains a strong blue colour at the site, where £0 the preservative has penetrated.

The second half of the specimen is ύried and the follow¬ ing reactant applied thereto:

0.2 gram- of Bromopyrogallol Red dissolved in 100 ml ethanol. The.solution reacts against organic tin and the areas con¬ taining tin are tinted blue. The sensitivity may be improved by exposing the specimen to ultraviolet light or heating. The reactant should only be^" applied to dry wood without solvent Testing of heart wood content of pine (SKF METHOD No . 18 ) .

Reactants

Solution A - 5 grams of ortho-anisidine in a mixture of

17.5 mis of cone, hydrochloric acid and 982.5 is of water.

Solutlόn B -^•■ ^■ 100 grams of sodium -nitrite in 1000 mis of wate

Equal parts of solutions A and B are mixed together before use. The mixture .is applied to the cross-section of the wood of the specimen with a flat, brush.. The hear ^"wood is tinted red on application whereas the sap .wood retains a light orange -colour.-

The mixture keeps for about 3 months, the' parent solu¬ tions for at least one year.

Example 1 It was investigated whether it was possible to impregna te wood with a solvent-containing preservative after the wood had previously been treated with a water dilutable stain.

Using the above mentioned test methods, the following flow schedule was employed:

5 mins. pre-vacuu 0.6 kgs with preservative 10 and 40 mins., respectively, 6 kgs above atmospheric pressure with preservative 10 mins. normal atmospheric pressure and- emptying of the container 20 mins. post-vacuum 0.6 kgs. without preservative. Test result:

Both flow schedules provided approximately equally good results ^'with respect to penetration.

All results satisfy the NS 3190 standard. The result indicates that it should be unnecessary to run the process with a pressure of 6 kgs for more than 10 mins.

Example 2 Experiments were carried out with wood specimens, treat¬ ed with water dilutable stain, and subsequently impregnated with a solvent-containing preservative. The purpose of this was to investigate the possibility of being able to carry out the impregnation process as soon as possible after staining.

The period of time (drying period) between staining and subsequent impregnation was 5, .10, 15, 20, 25, and 30 mins., respectively. The schedule of operation was as follows: 5 mins. pre—vacuum 0.6 kgs with, preservative 10 mins. 6 kgs above atmospheric pressure with preservative 10 mins. normal atmospheric pressure and emptying of •container .20 mins. post-vacuum 0.6 kgs without preservative. The impregnation was satisfactory in all instances. It is remarkable that, even when the stain was- completely wet ^' during the impregnation process, no leaching of stain took place into the preservative. Thus it is possible to carry out both staining and impregnation 'in the same container and in the same operation.

Example 3 A water dilutable stain was applied to wood, which sub¬ sequently was impregnated with a solvent-containing preserva¬ tive, the purpose being to investigate the influence of variations in binders and fillers in water diluted stains on the penetration of the preservative, and what the ratio of solids to solvent means in this connection. The composition of the water dilutable stain (Aqua lasur) was varied with respect to the amount 'of binder, type of binder and the addition of fillers.

The schedule of operation was the same as stated in example 2.

Both the variations in the binder composition, the amount of binder and the addition of filler showed little influence on the penetration of the preservative into the sap wood.

Example 4 Again, water dilutable stain, was applied to wood which was then impregnated with a solvent-containing preservative, the purpose being this time to investigate the significance of variations in the impregnation conditions, preservatives, and surface pre-treatments to the final impregnation result.

- The pressure period was varied, and different preserva¬ tives were employed as well as different surface pre-treatments

Substantially the same test methods as previously described were employed.

The test results demonstrated that with regard to

OMH variation of pressure times it appears to be possible to achieve a tolerably usable result also without any pressure being involved in the process (only vacuum) , whereas a pressure of 2 to 4 kgs appears to be suitable.

With regard to variation^'s in preservatives it appears that solvent-containing preservatives are-excellently suited for the impregnation pμrpose, whereas water soluble salts (e.g. the Celcure O type) appear to have a somewhat smaller permeability through the surface treatment. With regard to variations of .the surface pre-treatments, Aqua lasur water dilutable stains, clear as well as pigmented ones, appear to be excellently suited for surface treatment of wood prior to impregnation.

OMPI

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Claims

P a t e n t C l a i m s

1. A method for staining and impregnating wood, wherein the wood is first stained with a water-dilutable stain and then, without any preceding drying process," is impregnated with a preservative which, by means of vacuum and/or pressure, is pressed through the.wet stain and into the wood.

2. The method of claim 1, wherein the staining and impregnation are carried out as a combined process within an impregnation cylinder.

3. The method of claim 1, wherein the application of stain is carried out outside of the impregnation cylinder and thereafter, without any preceding drying, the impregnation is carried out within the impregnation cylinder.