NO316860B1 - Wood for protection of wood and its use - Google Patents

Description

The present invention relates to an agent or stain and its use for the protection of wood against degradation caused by the surrounding atmosphere, moisture, insects, etc. In particular, the invention relates to a stain composition containing water and organic solvents, or water alone.

Environmental requirements from authorities, increasing environmental awareness and quality demands from consumers have caused a growing interest in solvent-based staining and painting systems. Various systems have been launched for the external protection of wood with water as a solvent, but due to unfavorable technical and application conditions, these products have had a very low spread. The disadvantages of today's alternatives are that they do not have properties that give the wood the necessary internal protection.

Existing stain and paint systems with water as solvent generally contain a combination of emulsion alkyds and thermoplastic plastic raw materials such as acrylates and the like. These alkyds and acrylates have a very high molecular weight, often 100 - 200 times higher than that of solvent-based oil alkyd products and therefore give poor or no penetration, which entails a significant risk of moisture absorption which can result in rot formations. However, these cover stains/paints have good protective properties against degradation of the outer film when exposed to sunlight (UV resistance, cosmetic effect). Furthermore, the paint film is unstable in that the thermoplastics can expand in water. When moisture penetrates the wood, the plastic will normally expand and will then contract under drying conditions, and this results in a film with a much slower release of moisture.

Moisture migration mechanisms should ideally be such that the paint film should prevent moisture from the outside from coming into contact with the wood, at the same time the paint film should be so open to diffusion that it allows excess water vapor and condensation to escape. For paint films based on water-based systems with a high molecular weight, this mechanism has not been satisfactory in relation to solvent-based oil-alkyl systems, which has resulted in a limited use of such products alone without treatment with an oil primer.

According to the present invention, there is provided a stain for the protection of wood, which is characterized in that it contains: (i) vegetable oil alkyd emulsion which includes a combination of non-ionic emulsifier selected from alkylated C10-C26 fatty oils, and ionic emulsifier selected from

fatty alcohol alkoxylates,

(ii) pigment,

(iii) refined wood tar;

(iv) vegetable oil,

(v) water and organic solvent, or water alone, and

(vi) conventional additives.

The invention also provides for the use of such a stain, as a combined primer and cover paint on wood.

It is preferred that the alkoxylated C10-C26 fatty oil consists of ethoxylated castor oil. Furthermore, it is preferred that the fatty alcohol alkoxylate is made up of fatty alcohol ethoxylate.

Actual quantity ratios for the stain's various components are such that it includes 10-60 vol-% and more preferably 30-40 vol-% vegetable oil alkyd emulsion; 0.5-25% by volume and more preferably 1-10% by volume of wood tar; 0.5-25 vol-% and more preferably 1-25 vol-% vegetable oil, and the rest i.e. pigment, water and organic solvent, or water alone, as well as conventional additives, to 100 vol-%.

The oil alkyd used is an alkyd to which an emulsifier has been added so that it becomes emulsifiable/soluble in water and organic solvent, or water alone. The emulsifier can be selected from a number of different types of surfactants commonly known to the person skilled in the art.

The organic solvent can suitably be white spirit, and the vegetable oil can suitably be boiled linseed oil.

In ready-to-use state, the stain is prepared with water as a solvent, but an organic solvent and/or water can be added for thinning purposes. Aqueous stain can thus be thinned either (i) with water alone, (ii) with only organic solvent, or (iii) with both water and organic solvent. Preferably, only water is used as a thinner.

Treatment of wood with the present stain replaces previous treatment systems where a priming stain as well as covering stain or paint must be used. Thus, the stain according to the invention has properties which mean that it represents a combined primer and cover paint product. This gives great advantages, especially for new wood, whereby a cleaning layer is saved.

Present stains can be produced by emulsifying refined wood tar and vegetable oil, typically boiled linseed oil together with oil alkyd, pigment and conventional additives with water as solvent. A major advantage of the present stain is thus that the environmentally harmful conventional use of toxic solvents such as white spirit is avoided at the same time as a purely economic gain is achieved by using water as a solvent instead of organic ones, such as white spirit for example.

In order to meet both environmental requirements and requirements for satisfactory protection of wood, binding agents have been developed on a pure oil basis that can form emulsions with both water and organic solvents. These binders, which are preferably made up of special water-emulsifiable oil alkyds (both mineral and vegetable), can be added to wood tar together with vegetable oil additives such as boiled linseed oil. In the present stain, an oil alkyd of vegetable type is preferably used.

Typical properties for a combination on this basis can be directly compared to those of solvent-based oil stains/coating stains/paints with regard to penetration, conservation, diffusion, UV resistance, external film formation and ease of use. Such properties for water-based stain/top stain/paint products have previously not been achievable as you have had to use an oil stain primer, i.e. you are dependent on a two- to three-coat system (including primer).

The present product represents an agent which is a primer, stain and paint in one and the same product, and is hereinafter referred to as stain. This stain has been given some thixotropic properties. It moistens the applied material in depth and provides a homogeneous surface film that ensures a long-term protective effect. This effect is due to the natural products used, tree tar and vegetable oil, the latter preferably consisting of boiled linseed oil which also dries up slowly. Furthermore, the present stain is very temperature and weather resistant, and has great coverage, namely approx. 6 -10 mVliter depending on the substrate. As examples of areas of use for the present stain, exterior woodwork, houses, cabins, outbuildings and the like can be mentioned. It can be used on both untreated and previously stained and painted surfaces.

After application of the present stain and evaporation of the solvent, a homogeneous film is formed which is not water soluble at normal temperatures and weather conditions. This film behaves similarly to traditional solvent-based oil stains/coating stains and paints with low moisture absorption and good exhalation of water vapour/condensation (diffusion) and a stable outer film with regard to humidity. At the same time, it turns out that the outer film is just as stable as other solvent-based oil stains/cover stains and paints with regard to external degradation by sunlight (UV resistance).

Two of the most important properties in addition to the moisture migration mechanism and UV resistance of the present stain are the properties of the wood tar and the vegetable oils, such as linseed oil, in the paint film: 1) The wood tar delays the drying/hardening process and results in very good penetration, adhesion and protection. The wood tar also has good impregnating properties. This is due to the chain structure and very low average molecular weight. 2) Vegetable oils, for example boiled linseed oil, contribute to a homogenization of the density of the paint film which contributes to low moisture penetration, as well as to a strengthening of the surface film and, together with the oil alkyd used, provides good UV resistance. The chain structure and molecular weight of wood tar and most vegetable oils such as boiled linseed oil are very low and allow good penetration into the wood.

The present stain exhibits a moisture migration comparable to that of a traditional organic solvent-based stain. Wood tar and boiled linseed oil in the present stain, however, contribute to significantly better penetration properties in surfaces of previously treated or untreated wood. The fact that the present stain dries oxidatively means that the penetration mechanism continues after the water or solvent has evaporated (in contrast to traditional water-based systems that dry only physically, see table below). The wood tar significantly delays the oxidative drying and means that the vegetable oils, preferably boiled linseed oil, as well as oil emulsion alkyds and the wood tar itself have better time to soak into the wood and moisten in depth.

All these factors give a moisture migration/perrneability in the stain/paint film in line with a traditional solvent-based oil alkyd system. Table 1 below shows the above-mentioned properties for known and existing stains:

Comparison tests and results

Testing of the present stain (colour red) has been carried out and comparison of this with (i) Tjæralin Landrød (colour red) which is a known commercially available product including an oil alkyd which is soluble in organic solvent as well as wood tar and fillers, and (ii) ) Drygolin (reference product in color red) which is a well-known commercially available oil alkyd stain. The samples were tested according to ER guidance "Paint and stain for exterior wood. Declaration of properties of paint and stain for exterior wood, August 1983 in addition to some other relevant test methods.

Tested properties

1. Adhesion to dry substrate

The test was carried out according to ISO 4624 "Paint and varnishes - Pull-off test for adhesion". Planed spruce panels were stained with a brush in an amount (nWliter) and number of coats as recommended by the manufacturer. Primer was used for the Drygolin sample.

The panels were allowed to dry for 14 days in an air-conditioned room, after which an extraction device, i.e. a dollier (area 3.14 cm<2>) was glued to the samples with standard Araldit two-component epoxy glue. The glue hardened for 1 day, after which the dollies were free-cut down to the substrate and pulled off with an electric extractor, PAT Automatic AT 101 E (speed 5). 5 parallels were taken per product.

ISO requirements: Minimum withdrawal value, 1.25 MPa.

The obtained test results are shown in table 2 below.

Table 2 Attachment, ISO 4624

Test: Adhesion to dry substrate

Deke possible to separate the coats with the same paint.

Adhesion to wet and dried surfaces

The experiment was carried out according to the above-mentioned IS 4624.

Spruce panels were applied with paint/stain in the same way as for testing adhesion on a dry surface. After 14 days of drying, the panels were placed horizontally in a tub of water with the painted surface facing up. The water stood about S mm up along the side surfaces of the panels. After 7 days of immersion, the panels were taken up and dollies were glued on immediately. The glue was allowed to dry for 1 day, after which the dollies were free-cut down to the substrate and pulled off correspondingly as adhesion. S parallels were taken per stain. The panels were also examined for visible defects.

The panels were then allowed to dry in a climate room until the humidity in the panels was below 14%. Dollier was glued on and subtraction was made.

ISO requirements: No visible defects (dissolution, swelling, blistering, peeling)

Extraction value wet substrate: Minimum 0.45 MPa.

Withdrawal value after drying: Minimum 1.1 MPa.

The obtained test results are shown in table 3 (wet substrate) and table 4 (dried substrate) below:

It is not possible to separate the layers with the same paint.

Deke possible to separate the coats with the same paint.

2. Luster

The tests were carried out according to ISO 2813 "Paints and vamishes - Measurement and specular gloss of non-metallic paint films at 20°, 60° and 85°".

The products were applied with the applicator on glass (gloss and dry through). It was

used application amounts based on stated or calculated volume percentage of dry matter and recommended dry film thickness from the manufacturer. One coat of stain was used. Gloss was measured at 60° of the painted panels for exposure in VOM. In addition, the products were applied with an applicator on black glass plates. The gloss was measured in S points.

The obtained test results are indicated in table 5 below:

2. Degree of heat protection

The tests were carried out according to prEN 927-4 'Taints and varnishes - Coating materials and coating systems for exterior wood. Measuring the water and water vapor permeability of exterior wood coatings"

Planed spruce panels were stained with a brush in an amount (mVliter) and the number of coats recommended by the manufacturer. Primer was used for reference sample (ii).

The system is applied to half the area of the spruce panel. After the last application, the panels were left to dry in a climate room to a stable weight before they were sealed on the back and edges. The panels were divided so that part was painted and part was unpainted. A small ground piece was cut off for measurement of dry film thickness. The dry film thickness was measured by microscopy. The back and edges were sealed with a solvent-free epoxy paint. After drying to a stable weight, the panels were placed in a tub of distilled water for 14 days. The panels were dried and weighed after 1, 2, 3, 7, 10 and 14 days. The panels were then left to dry in an air-conditioned room for 14 days with weighing similar to that for water absorption.

Percentage resistance to water absorption (WPE % - Water Protection Efficiency) was calculated according to the following formula after 10 and 14 days of water absorption:

Wu = The weight increase for unpainted panels after respectively 10 and 14 days of immersion Wc = The weight increase for painted panels after respectively 10 and 14 days of immersion.

The obtained test results are indicated in table 6 below:

5. Elasticity

The tests were carried out according to ISO 1519 "Paints and vamishes - Bend test (cylindrical mandrel)"

The products were applied to aluminum sheets with an applicator (adjustable) in one coat using application quantities based on the stated and calculated volume percentage of dry matter and recommended dry matter thickness from the manufacturer. The products were allowed to dry for 7 days in a climate room. The plates were then bent 180° around cylindrical mandrels with plate temperature 0°C and 23°C. The plates were examined for cracking visually and with 10 times magnification.

ISO requirements: 0°C - no cracking when bending around a mandrel with a diameter of 4 mm 23°C - no cracking when bending around a mandrel with a diameter of 2 mm.

6. Water resistant

The tests were carried out according to IS 2812-1 "Paints and vamishes - Determination of resistance to liquids - Part 1: General methods".

Spruce panels were applied with one coat of stain on the upper side with a brush in the quantity (mVliter) and number of coats recommended by the manufacturer. Primer was used for reference sample (ii). The products were also applied to the back and edges.

After 7 days of drying in a climate room, 3A of the panels were immersed in distilled water (23°C). After exposure for 7 days, the panels were taken up and dried for 2 days and then examined for defects (swelling, blistering, adhesion failure, flaking).

ISO requirements: No defects or changes apart from weak shields after matting.

For results see table 7.

7. Craftsmanship assessment

An assessment was made of the condition in the bucket, application properties, drying properties and appearance of the dry top coat. For results see table 7 below.

8. Weight percent dry matter

The experiment was carried out according to IS 3251. About 1 gram of sample was weighed and placed in an oven at 105°C for 1 hour. 2 parallels were used in the measurement. For results see table 7 below.

9. Dry thoroughly

Tests were carried out according to ISO 9117 "Paints and vamishes - Determination of through-dry state and through-dry time - Method of test". One coat of the stains was applied to a flat glass plate with an applicator (adjustable) in a climate room (23°C, 50% RH). Application quantities were used based on stated or calculated volume percentage of dry matter and recommended dry film thickness from the manufacturer. The painted panels were left to dry for a given time interval (5 different times) before the measurement of through drying was carried out. The time was noted when the wet film had been applied and during the testing.

The painted glass plate was placed in the apparatus and a stamp was lowered manually until it was on the paint film. The piston was pressed automatically for 10 seconds before automatically rotating 90° for 2 seconds. The piston was lifted manually. 2 parallels of each paint were run.

Evaluation: When the paint is completely dry, there will be no visible marks in the paint film or the test. For results see table 7 below. 10. Duration - accelerated degradation in Xenon weatherometer Tests were carried out according to IS 11341 "Paints and vamishes - Artificial weathering and exposure to artificial radiation - Exposure to filtered xenon-arc radiation" ISO 11341 was introduced instead of ISO 4892, as it was found appropriate to adopt a standard that has been prepared for use in connection with paint (published in 1994). ISO 4892 is primarily prepared for use in the plastics context. Planed spruce panels were stained with a brush in the quantity (nWliter) and number of coats recommended by the manufacturer. After 2 weeks of drying in a climate room, the panels were inserted into the Xenon weatherometer. The panels were exposed for 701 hours. Color and gloss were measured before and after exposure. After exposure, the panels were assessed with regard to degree of contamination (chalking), cracking and flaking. Gloss before and after exposure was measured according to ISO 2813 and the percentage gloss change was calculated. Color was measured on a spectrophotometer marked SK 482 (Instrumental Color System Limited) before and after exposure and color change calculated according to the principle described according to ISO 7724. Degree of infection was assessed using the tape method, ISO 4628-6, cracking according to ISO 4628-4 and flaking according to ISO 4828-5. For results see table 7 below. 11. Bleeding of existing stain to white cover stain Spruce panels were applied 3 coats of existing stain with a brush in the quantity (nWliter) and number of coats as recommended by the manufacturer.

After 2 weeks of drying in a climate room, the panels were inserted into the Xenon weatherometer. The panels were exposed for 386 hours, after which half the surface on each parallel was overpainted with white Trebitt cover stain and white Drygolin paint from Jotun.

After 1 week of drying, the panels were exposed for 315 hours in the Xenon weatherometer.

After the end of exposure, the panels were evaluated with regard to the bleeding of the present stain (red) into the white cover stain.

Table 7 below gives an overall overview of the test results obtained above in experiments 1-11.

Based on the obtained test results, the following can be concluded:

Adhesion to both dry and wet surfaces is approximately the same for Tjæralin Landrød and Drygolin (red). For the present stain, the adhesion is slightly lower than for Drygolin, but the difference is borderline to be considered significant. In addition, for the present stain there was a large element of breakage in the wood.

The main trend for fracture types was either in the wood or between the coats in addition to something between the wood and the 1st coat. The fracture types for all the extracts are not commented on in detail as there were only small differences between Tjæralin Landrød and Drygolin (red).

Both elasticity and water resistance are satisfactory based on the requirements of the ER orientation.

Numerically, the resistance to water ingress is slightly better for Tjæralin Landrød than for Drygolin, while the present stain has a significantly worse degree of water protection than both Drygolin and Tjæralin Landrød.

There were sometimes large differences in gloss measured on black glass and on wooden panels. Tjæralin Landrød had a higher gloss than Drygolin (red) on both glass and wood, while the present stain had a lower gloss than the other two stains.

In terms of craftsmanship, there was little difference between Drygolin (red) and Tjæralin Landrød. Both were easy to stir up, had good spreading, good coverage and a good surface. In the present stain there were a lot of particles that could not be dissolved by agitation. There was poor flow when applied with a brush, the brush strokes remained and the surface had a "bumpy" appearance.

Tjæralin Landrød had a slightly higher weight-% of dry matter than Drygolin (red), while the present stain had somewhat lower than the reference.

Both Tjæralin Landrød and the present stain needed considerably longer than Drygolin (red) to dry thoroughly.

During the weatherometer exposure, no blistering, cracking or flaking occurred on any of the samples. However, the gloss reduction was very large and cannot be said to be in accordance with the ER guideline of "moderate gloss reduction rate". Drygolin (red) had less loss of gloss than Tjæralin Landrød and the present stain. The present stain lost 90% of its gloss before 250 hours of exposure, but had no significant further loss of gloss. Drygolin (red) and Tjæralin Landrød had a more gradual loss of gloss.

Color change was measured after 250 and 701 hours of exposure. The color change after 250 was similar for Tjæralin Landrød and Drygolin (red), while after 701 hours a slightly smaller color change was measured for Drygolin (red) than for Tjæralin Landrød. Drygolin (red) was somewhat bleached (due to chalking) and shielded, while Tjæralin Landrød was very bleached (due to chalking) but not shielded.

The present stain (which will be marketed as "Tjæralin Environmental Stain") had significantly less color change than the other two products and had virtually no chalking. Measurement of the degree of contamination showed that Tjæralin Landrød had the highest degree, while the present stain had the lowest.

Claims (9)

1. Stain for the protection of wood, characterized in that it contains: (i) vegetable oil alkyd emulsion which includes a combination of non-ionic emulsifier selected from alkylated C10-C26 fatty oils, and ionic emulsifier selected from fatty alcohol alkoxylates, (ii) pigment, (iii) refined wood tar, (iv) vegetable oil, (v) water and an organic solvent, or water alone, and (vi) conventional additives. 2. Stain according to claim 1, characterized in that it contains 10-60 vol-% vegetable oil alkyd emulsion, 0.5-25 vol-% wood tar, 0.5-25% vegetable oil, and the rest, i.e. pigment, water and organic solvent, or water alone, as well as conventional additives, to 100% vol. 3. Stain according to claim 2, characterized in that it contains 30-40 vol-% vegetable oil alkyd emulsion, 1-10 vol-% refined wood tar, 1-25 vol-% vegetable oil, and the rest i.e. pigment, water and organic solvent, or water alone , as well as conventional additives, to 100 vol-%. 4. Stain according to claims 1-3, characterized in that the alkylated C10-C26 fatty oil consists of ethoxylated castor oil. 5. Stain according to claims 1-3, characterized in that the fatty alcohol alkoxylate consists of fatty alcohol ethoxylate. 6. Stain according to claims 1-3, characterized in that the oil alkyd is an alkyd to which an emulsifier has been added so that it becomes emulsifiable/soluble in water and organic solvent, or water alone. 7. Stain according to claims 1-3, characterized in that the organic solvent is white spirit. 8. Stain according to claims 1-3, characterized in that the vegetable oil is boiled linseed oil. 9. Use of stain according to claim 1, as a combined primer and cover paint on wood.