EP3290172B1 - Use of hotmelt adhesives for reducing the emission of volatile organic compounds (voc) from wood-based materials - Google Patents

Description

The present invention relates to the use of hot melt adhesives to reduce the emission of volatile organic compounds (VOCs), whose retention time in gas chromatography lies between C6 (hexane) and C16 (hexadecane), from OSB wood-based panels. In a further aspect, the present invention relates to a method for producing OSB wood-based panels, wherein these are coated with a hot melt adhesive.

State of the art

Wood-based materials, such as engineered wood panels, are known to consist of lignocellulose-containing materials, for example, wood fibers in fiberboard or strands in OSB. Lignocellulose comprises cellulose, hemicellulose, and lignin. Cellulose is a long-chain macromolecule consisting of glucose units, hemicellulose is a short-chain, branched macromolecule made up of pentoses, and lignin is a three-dimensional macromolecule made up of methoxyphenylpropane units. Cellulose and hemicellulose form the structural components of the cell wall, while lignin, as a filler substance within the cell structure, causes lignification.

Lignocellulosic materials, such as wood chips, and wood-based materials manufactured from them, such as engineered wood panels, especially OSB, contain, among other things, volatile organic compounds (VOCs) and highly volatile organic compounds (WOCs). The emission of VOCs and VVOCs, also referred to as the total amount of volatile organic compounds (TVOCs), from these wood-based materials poses a serious problem, especially given the increasing use of such materials indoors.

Volatile organic compounds (VOCs) include saturated and unsaturated aldehydes, as well as all volatile organic compounds whose retention time in gas chromatography lies between C6 (hexane) and C16 (hexadecane). By definition, formaldehyde is not classified as a VOC but as a VVOC. VOCs are not a homogeneous class of substances, but rather a collection of compounds. These include, among others, organic acids, saturated and unsaturated aldehydes, alcohols, terpenes, aliphatics, aromatic hydrocarbons, and many more. Formaldehyde and formic acid are also classified as VVOCs. An overview of VVOCs, VOCs, and TVOCs can be found in the AgBB assessment scheme of the Committee for Health-Related Evaluation of Building Products, last amended in 2015.

VOC emissions are primarily based on the release of compounds originating from the wood-based material, while formaldehyde can be released both from the wood-based material and as a component of adhesives.

The emission of these volatile and highly volatile wood components or the components of the adhesive from wood-based materials, such as wood-based panels, is becoming an increasing problem due to stricter limit values and greater awareness among end consumers.

The release of volatile organic compounds (VOCs) and highly volatile organic compounds depends, among other things, on the type and condition of the lignocellulose, such as the wood species, the storage duration, the storage conditions of the wood or the wood pulp products, and can occur in varying chemical compositions and quantities. Particularly high levels of VOCs are found in coniferous trees used as raw material for engineered wood products. Prominent examples include substances such as α-pinene, β-pinene, and δ-3-carene. Other prominent examples are aldehydes such as pentanal and hexanal, as well as acids.

Coniferous woods, in particular, from which particleboard, medium-density fiberboard (MDF), or OSB are produced, contain large amounts of resins and fats as wood constituents, which contribute to the formation of volatile organic compounds (VOCs) and aldehydes. Oxidation processes of the wood constituents, such as fatty acids, typically occur, leading to the secondary and tertiary emission of aldehydes, such as pentanal, or of carboxylic acids.

This means that VOC emissions from wood-based materials are primarily due to release from the wood itself and not from the adhesive used. This release is mainly due to the ongoing transformation of components within the wood-based materials; for example, there is a continuous secondary and tertiary emission of the aforementioned compounds through the fragmentation of resins and fats.

Oriented strand board (OSB) is a wood-based material used today for a wide variety of structural applications. OSB, also known as chipboard, is manufactured from thin, flat wood strands. These strands are typically no more than 200 mm long, 20 mm wide, and less than 1 mm thick. They are usually laid in at least three layers, with the strand direction rotated 90 degrees from one layer to the next. This combination of factors results in OSB's high bending strength, which makes it so attractive for many applications. Another advantage is that, due to the use of primarily fresh softwood, especially pine, OSB has a lower density compared to other wood-based materials. OSB has an average density of approximately 550 kg/ ^m³ .

Therefore, OSB is primarily used in structural applications. However, in recent years it has also become apparent that OSB is used indoors, particularly in residential areas, where extensive coatings are not typically applied, especially for aesthetic reasons. Rather, it is desirable to preserve the characteristic appearance of the strands in visible areas.

As explained, the use of softwood leads to an undesirable side effect that can be a disqualifying factor for many applications. Specifically, OSB has been found to be unsuitable due to its very high emission of wood extractives and their degradation products. It is important to consider that when OSB is used as an interior finishing panel, and especially when used extensively in buildings, this results in an unfavorable ratio of OSB surface area to room air volume (air loading). In standardized emission tests, the loading factor is around 1. In reality, however, the loading factor can easily reach or even exceed 2. This leads to a higher indoor air pollution level from the emitted substances, meaning that standard OSB can only be used in small quantities in interior spaces.

The lower the density of the manufactured wood-based materials, the more serious the emission problem becomes. The issue of indoor air pollution from VOCs and VVOCs is addressed through regulations at both national and international levels. This creates a need for wood-based material manufacturers to reduce emissions.

Numerous approaches have already been taken to reduce VOC emissions from wood-based materials, but these are usually associated with higher costs. One simple method is surface coating, which stops the emission of these substances. However, this also leads to additional costs. For example, with a paper/impregnated coating, the substrate is no longer visible, yet this is precisely why it is used decoratively, due to its textured surface. Furthermore, such processes require the availability of coating facilities.

Another option is to coat the surface with a lacquer. This requires a coating line with multiple application units, as well as UV lamps or hot air dryers in the case of water-based lacquers. Since the application rates for such lacquers exceed 100 g/ ^m² , this method is not recommended due to the... High-priced UV lacquers are unattractive, and the photoinitiators necessary in UV lacquers can also cause additional odor nuisances.

Another approach to reducing emissions of the components and their degradation products is the addition of chemicals and/or adsorbents to prevent emissions or reduce them to a non-critical level. These chemicals, known as additives, such as reducing agents, must be added to the lignocellulosic shredded products, such as strands, during the production of wood-based materials like OSB. The amounts typically range from 1 to 5% by weight, based on the dry wood content. This addition of chemicals significantly increases the product's cost, as the proportion of adhesive usually also needs to be increased. Furthermore, these chemicals have an unpleasant odor that is noticeable both during production and use. The use of certain chemicals also leads to changes in the wood-based material itself; for example, brownish discoloration can occur, negatively impacting the appearance of wood-based materials like OSB. Finally, the addition of adsorbents such as activated carbon has been proposed, but this has been rejected due to cost considerations. Furthermore, the addition of zeolites leads to problems due to increased ash production during the combustion of waste from this OSB, as well as increased wear when sawing such wood materials.

The document " VOC Emission Barrier Effects of Laminates, Overlays and Coatings for Particleboard, Medium Density Fiberboard (MDF) and Hardboard", August 27, 2003, pages 1-8, URL: http://www.arauco-na.com/_file/voc-emission-barrier-effect.pdf , discloses the use of hot melt adhesives to reduce the emission of volatile organic compounds from fiberboard or particleboard.

There is therefore still a great need to provide suitable means that contribute to reducing the emission of volatile organic compounds (VOCs) from wood-based materials. These means should overcome known disadvantages such as high investment risk, high material costs, product drawbacks, disadvantages in process technology, and/or high costs in general. It is particularly important that the desired reduction of VOCs and WOCs, i.e., TVOCs, from the wood-based materials is ensured even over extended periods of use.

The present invention is therefore based on the technical problem of ensuring the reduction of VOC emissions from OSB in a simple and cost-effective manner on a permanent basis.

Description of the invention

This problem is solved by using hot melt adhesives, which are generally known as adhesives, to reduce the emission of volatile organic compounds (VOCs) and also TVOCs from wood-based materials in general. The hot melt adhesive is applied in liquid form to the surface of the wood-based material, forming a film.

The stated problem is thus solved by the use of hot melt adhesives according to the feature of claim 1. The hot melt adhesive is applied to the surface of the OSB wood-based material, wherein this hot melt adhesive is selected from the group consisting of: ethylene vinyl acetates and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinylpyrrolidone/vinyl acetate copolymers or mixtures thereof, wherein the application rate of the hot melt adhesive is between 30 g/ ^m² and 250 g/ ^m² , and wherein the hot melt adhesive is applied after hot pressing and before the OSB wood-based panels have completely cooled down.

When using the hot melt adhesives according to the invention, which are applied, for example, in the molten state to the surface of the wood-based material or to the surface of the wood, it has surprisingly been shown that the use of the hot melt adhesives leads to a significant reduction in the emission of VOCs including aldehydes, but also acids and terpenes.

In addition to its ability to reduce the emission of volatile organic compounds and total volatile compounds, the use of the Hot melt adhesives can also be used to make the surface of wood-based materials or wood more uniform, creating a smooth and closed surface. For example, hot melt adhesives can fix loose strands and thus reduce the risk of injury.

In the present context, the terms "reduction of emissions" or "reduction of emissions", which are used synonymously, are understood to mean that, compared to a wood-based material or wood without the use of the hot melt adhesive according to the invention, the amount of VOCs or the total amount of volatile organic compounds (TVOCs) is lower.

The term "emission avoidance" implies a percentage reduction or decrease in emissions compared to the control level, down to a level below the measurement limit. The term "reduction" in this context refers to a decrease or decrease up to the point of avoidance.

Another advantage is that the emission of substances that contribute to an unpleasant odor is also reduced.

According to the invention, not only is the surface of the wood-based materials covered and smoothed, but surprisingly, the emission of VOCs from the wood-based materials is also reduced, particularly over a longer period and with prolonged use. This now makes it possible again to use OSB indoors and in decorative applications.

The applied layer of hot melt adhesive, which in one embodiment is applied in a molten state and then cured, allows the surface to be smoothed, making further handling of corresponding wood-based materials such as OSB more pleasant.

The layer formed from the hot melt adhesive is applied at least to the top surface of the wood-based panel. If necessary, the hot melt adhesive can also be used... The hot melt adhesive is applied to the underside of the wood-based panel, and in particular to OSB. At least on the visible surface, the adhesive is applied. The layer should therefore be thick enough to largely prevent VOC emissions into the interior.

In one embodiment, the hot melt adhesive is applied after the wood-based panel has been hot-pressed and before it has completely cooled. The surface of the wood-based panels is smoothed by simply applying and working the liquefied hot melt adhesive over the entire surface. The coated wood-based panels can then be further processed as desired. After cooling, water and/or a release agent can be sprayed onto the coating to prevent the panels from sticking together in a stack and to ensure their stackability.

This means that the use of hot melt adhesive allows for the easy integration of this process into the manufacturing process of wood-based panels, especially OSB.

In one embodiment, the hot melt adhesive is applied by means of roller application, for example by a suitable device immediately downstream of the hot press. The hot melt adhesive can be applied in one or more steps by roller application in the same direction or in opposite directions.

In one embodiment, the wood-based material is OSB, and the hot melt adhesive is applied in a layer-forming manner to the top strand layer of a large surface area of the OSB after hot pressing. Optionally, the hot melt adhesive is also applied to the lower layer opposite the surface.

According to the invention, a conventional hot melt adhesive can be used. These hot melt adhesives are typically used for bonding flat elements. These can be edges of furniture parts, profiles, or large-area decorative coatings. Hot melt adhesives, also known as hot glues, are usually solvent-free products that are more or less solid at room temperature. They are applied to the surface while hot and form a strong bond upon cooling. Suitable hot melt adhesives are selected from the group consisting of ethylene vinyl acetates (EVA) and copolymers thereof, polyurethanes (PU), polyamides, polyethylenes, polyalphaolefins (PO), polyesters, copolyamides, vinylpyrrolidone/vinyl acetate copolymers, or mixtures thereof. In addition to these base polymers, the hot melt adhesives can contain other components such as waxes, resins, stabilizers, and pigments.

In one embodiment, the layer formed using the hot melt adhesives has a layer thickness of at least 30 µm, for example up to 250 µm. According to the invention, the application rate of the hot melt adhesive is in the range of 30 g/ ^m² to 250 g/ ^m² , as is the case with 50 g/ ^m² to 200 g of hot melt adhesive/ ^m² .

By using these hot melt adhesives, in addition to reducing VOC emissions, surface properties can be improved, thus facilitating further surface finishing processes such as wallpapering, painting, and the application of additional layers, for example, decorative layers and other external coatings applied to wood-based materials. The application of these surface finishes can then be carried out more easily and with greater material efficiency.

In one embodiment, hot melt adhesives additionally contain colorants, such as pigments, which allow these hot melt adhesives to be colored. This enables both the marking of the wood-based materials and a decorative enhancement of the surface.

The use of hot melt adhesive to form the corresponding layer is only necessary in those areas where emissions need to be reduced, for example, only on the surfaces facing the interior or in visible areas. In contrast, emission reductions achieved using chemicals require that all lignocellulosic shredded products, such as all strands of OSB, be treated.

Particularly preferably, the use of coating the OSB with hot melt adhesive according to the invention can be combined with other known means, methods and uses of additives to reduce the emission of VOC and TVOC.

1. a) Bereitstellen von lignocellulosehaltigen Zerkleinerungsprodukten und einem Klebstoff,
2. b) Aufbringen des Klebstoffs auf die Zerkleinerungsprodukte;
3. c) Verpressen der lignocellulosehaltigen Zerkleinerungsprodukte mit dem Klebstoff unter Wirkung von Wärme und Druck;

wobei nach dem Verpressen auf die Oberfläche des hergestellten OSB-Holzwerkstoffplatten eine Beschichtung aus Schmelzklebstoff aufgebracht wird, wobei durch Aufbringen des Schmelzklebstoffes die Emission von flüchtigen organischen Verbindungen aus dem Holzwerkstoff verringert wird, wobei dieser Schmelzklebstoff ausgewählt ist aus der Gruppe: Ethylenvinylacetate und Copolymere hiervon, Polyurethane, Polyamide, Polyethylene, Polyalphaolefine, Polyester, Copolyamide, Vinylpyrrolidon/Vinylacetat-Copolymere oder Mischungen hiervon, wobei eine Auftragsmenge des Schmelzklebstoffes zwischen 30 g/m² und 250 g/m² liegt und wobei der Schmelzklebstoff nach dem Heißverpressen vor dem vollständigen Auskühlen der OSB-Holzwerkstoffplatten aufgebracht wird.In a further embodiment, the present invention relates to a method for the production of OSB, comprising the steps:

1. a) Providing lignocellulosic grinding products and an adhesive,
2. b) Applying the adhesive to the crushed products;
3. c) Pressing the lignocellulosic grinding products with the adhesive under the influence of heat and pressure;

wherein, after pressing, a coating of hot melt adhesive is applied to the surface of the manufactured OSB wood-based panel, wherein the application of the hot melt adhesive reduces the emission of volatile organic compounds from the wood-based panel, wherein this hot melt adhesive is selected from the group consisting of: ethylene vinyl acetates and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinylpyrrolidone/vinyl acetate copolymers or mixtures thereof, wherein the application rate of the hot melt adhesive is between 30 g/ ^m² and 250 g/ ^m² , and wherein the hot melt adhesive is applied after hot pressing and before the OSB wood-based panel has completely cooled down.

Adhesives include common adhesives used in the production of wood-based materials, such as OSB, including formaldehyde-free adhesives, such as those based on isocyanates.

In one embodiment, the hot melt adhesive, which may be molten, is applied to the surface of the wood-based material after hot pressing. Alternatively, the hot melt adhesive can be applied not in its molten state, but by utilizing the heat from the hot-pressed wood-based material to make it more fluid, thus facilitating better processing on the wood-based material. This application can be carried out using conventional equipment, namely standard temperature-controlled hot melt adhesive applicators and by means of nozzles, etc.

According to the invention, terpenes and acids are particularly reduced.

The method according to the invention can be such that the coating with the hot melt adhesive is carried out in one or more steps by means of roller application in the same direction or in opposite directions.

Applying the coating, for example using a roller applicator, creates a smooth, closed surface, thus fixing loose shredded material and filling any holes present in the layer. This surface allows for further improved processing of the wood-based materials.

In one embodiment, the layer of hot melt adhesive is applied to the side of the wood material facing an interior space.

According to the invention, the application rate of the hot melt adhesive is in a range of 30 g/ ^m² to 250 g/ ^m² , for example, a range of 50 g/ ^m² to 200 g hot melt adhesive/ ^m² . The application rate can vary depending on the adhesive and the desired surface properties.

According to the invention, in one embodiment, a hot melt adhesive is selected from the group consisting of ethylene vinyl acetates and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinylpyrrolidone/vinyl acetate copolymers or mixtures thereof.

The layer thickness can range from 30 to 250 µm.

In one embodiment, the method for producing the wood-based material can further include applying additional layers to the surface using hot melt adhesive, in particular applying a decorative layer or other types of topcoats. Furthermore, the hot melt adhesive can be colored, thus providing a decorative enhancement to the surface. In one embodiment, the hot melt adhesive is essentially transparent, so that the strand structure remains visible in the case of OSB wood-based materials. Such panels can be used decoratively, especially in interior applications.

Finally, the present disclosure relates to wood-based materials obtainable by the inventive method, such as for the production of OSB.

The invention will be explained in more detail below using exemplary embodiments, without being limited thereto.

Example 1:

An EVA hot melt adhesive ^, Jowatherm 287.10, manufactured by Jowat Klebstoffe, Detmold, Germany, was applied to one side of a 22 mm OSB board using a roller applicator. The temperature in the premelter was 200°C. After the hot melt application, the surface was smoothed with a second roller applicator. Behind the smoothing unit, the boards were sprayed with approximately 5 g of water/ ^m² and stacked after cooling. 90-95% of the previously visible holes in the surface were closed. The surface appeared very smooth overall. No loose strands were visible on the treated surface.

Example 2:

A PU hot melt adhesive of 80 g/ ^m² was applied to one side of a 22 mm OSB board using a roller applicator. The product used was Jowatherm 602.35, manufactured by Jowat Klebstoffe, Detmold, Germany. The premelter temperature was 160°C. After the hot melt application, the surface was smoothed with a second roller applicator. Behind the smoothing unit, the boards were sprayed with approximately 10 g of water/ ^m² and stacked after cooling. The water was intended to accelerate the post-curing of the PU. 100% of the previously clearly visible holes in the surface were closed. The surface appeared very smooth overall. No loose strands were visible on the treated surface.

The sample from embodiment 1 was tested for the emission of volatile organic compounds according to the AgBB scheme (2015). A blank sample without a surface coating was also tested for comparison. A list of selected compounds is shown in the following table. These are the compounds that account for the largest amounts. Variant Parameter OSB with EVA hot melt (in µg/m ³ ) OSB with EVA hot melt (in µg/m ³ ) OSB (baseline sample) (µg/ ^m³ ) OSB (zero sample) (in µg/m ³ ) 3 days 28 days 3 days 28 days acetic acid 28 21 79 56 Pentanal 71 41 91 56 Hexanal 232 138 440 338 α-Pinen 117 75 555 317 3-Caren 75 56 331 239 acetone 222 251 339 381

The measurements were taken three days and four weeks after the OSB production.

As can be seen from the table, the surface sealing achieves a significant reduction in emissions, reaching at least 60% for some parameters. The requirements of the AgBB scheme (2015) are met by the test plate according to the invention. The substantial reduction after 28 days is particularly noteworthy.

Claims (9)

1. Use of hot-melt adhesive to reduce the emission of volatile organic compounds (VOC) with a retention time in the gas chromatograph between C6 (hexal) and C16 (hexadecane) from OSB wood-based panels,
   wherein the hot-melt adhesive is applied to the surface of the OSB wood-based material, said hot-melt adhesive being selected from the group: ethylene vinyl acetate and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinyl pyrrolidone/vinyl acetate copolymers or mixtures thereof, wherein an application quantity of the hot-melt adhesive lies between 30 g/m² and 250 g/m² and wherein the hot-melt adhesive is applied after the OSB wood-material panels have been hot-pressed but before they have completely cooled.
2. The use of hot-melt adhesives for reducing the emission of VOCs according to claim 1, characterised in that the hot-melt adhesive is applied to a side of the OSB wood-material panels with a large surface area such that it forms a layer.
3. The use of hot-melt adhesives for reducing the emission of VOCs according to claim 1 or 2, wherein the hot-melt adhesive is applied to the upper side and lower side of the OSB wood-material panels.
4. The use of hot-melt adhesives for reducing the emission of VOCs according to one of the preceding claims, wherein the hot-melt adhesive is applied synchronously or in reverse-rotation in one or multiple steps by means of roller application.
5. The use of hot-melt adhesives for reducing the emission of VOCs according to one of the preceding claims, wherein the layer thickness of the hot-melt adhesive is at least 30 µm.
6. A method for producing OSB wood-based material panels comprising the steps:

   a) Providing comminution products containing lignocellulose and an adhesive,

   b) Applying the adhesive to the comminution products,

   c) Pressing the comminution products containing lignocellulose with the adhesive under the effect of heat and pressure

   wherein a covering of hot-melt adhesive is applied to the surface of the OSB wood-based material panels after pressing, wherein the application of the hot-melt adhesive reduces the emission of volatile organic compounds from the wood-based material panels, said hot-melt adhesive being selected from the group: ethylene vinyl acetate and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinyl pyrrolidone/vinyl acetate copolymers or mixtures thereof, wherein an application quantity of the hot-melt adhesive lies between 30 g/m² and 250 g/m² and wherein the hot-melt adhesive is applied after the OSB wood-material panels have been hot-pressed but before they have completely cooled.
7. The method according to claim 6, characterised in that the coating with hot-melt adhesive is applied synchronously or in reverse-rotation in one or multiple steps by means of roller application.
8. The method according to claim 6 or 7, wherein the layer of hot-melt adhesive is applied either to one large-surface side only or to both large-surface sides.
9. The method according to claims 6 to 8, wherein at least one further layer is applied to the hot-melt adhesive, especially a decorative layer.