EP3290172A1 - Use of melt adhesives for reducing the emission of volatile organic compounds (vocs) from wooden materials - Google Patents

Abstract

The present invention relates to the use of hot melt adhesives for reducing the emission of volatile organic compounds (VOC) from wood-based materials. In a further aspect, the present invention is directed to a process for the production of wood-based materials, in particular OSB, wherein these are coated with a hot-melt adhesive. Finally, the invention is directed to wood-based materials produced by the process.

Description

The present invention relates to the use of hot melt adhesives for reducing the emission of volatile organic compounds (VOC) from wood-based materials. In a further aspect, the present invention is directed to a process for the production of wood-based materials, in particular OSB, wherein these are coated with a hot-melt adhesive. Finally, the invention is directed to wood-based materials produced by the process.

State of the art

Wood-based materials, such as wood-based panels, are known to consist of lignocellulose-containing materials, for example wood fibers in fiberboard or strands in OSB. Lignocellulose includes as component cellulose, hemicellulose and lignin. Cellulose is a long-chain macromolecule composed of glucose units, hemicellulose is a short-chain branched macromolecule of pentoses, and lignin is a three-dimensional macromolecule of methoxyphenylpropane units. Cellulose and hemicellulose form the skeletal substance of the cell wall, while lignin as a filling substance in the cell structure causes wood degradation.

Lignocellulosic materials, such as wood pulp products, and derived wood materials, such as wood-based panels, especially OSB, contain, among others, volatile organic compounds (VOCs) and very volatile organic compounds (VVOCs). The emission of VOCs and VVOCs, also referred to as Total Volatile Compounds (TVOCs), from wood-based panels is a serious problem from the point of view of the increasing use of such wood-based panels indoors.

In addition to the saturated and unsaturated aldehydes, volatile organic compounds include all volatile organic compounds whose retention time in the gas chromatograph is between C6 (hexal) and C16 (hexadecane). By definition, formaldehyde does not fall under VOC but is subsumed under VVOC. VOCs are not a homogeneous class of substances but a smorgasbord of compounds. These include, but are not limited to, organic acids, saturated and unsaturated aldehydes, alcohols, terpenes, aliphatic and aromatic hydrocarbons and many more. The very volatile organic compounds (VVOC) include, in addition to formaldehyde, formic acid. An overview of the VVOC and VOC as well as the TVOC can be found in the AgBB assessment scheme of the Committee for the Health Assessment of Construction Products, last amended in 2015.

The emission of VOC is essentially due to a release of compounds derived from the wood-based material, while formaldehyde can be released both from the wood-based material and as part of an adhesive.

The emission of these volatile and highly volatile wood constituents or of the constituents of the adhesive from the wood-based materials, such as wood-based panels, is becoming more and more a problem due to stricter limit values or a greater sensitization of the end users.

The release of the volatile organic compounds and volatile organic compounds depends, inter alia, on the nature and condition of the lignocelluloses, such as the wood species, the storage period, the storage conditions of the wood or of the comminution products of the wood, and can occur in different chemical compositions and quantities. Especially in conifers, which are used as starting material for wood-based panels, there are high levels of VOC. Prominent representatives of these are substances such as α-pinene, β-pinene, δ-3-carene. Other prominent representatives are aldehydes such as pentanal and hexanal as well as acids.

Above all, softwoods from which, for example, chipboard, 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 terpene compounds and aldehydes. Usually, oxidation processes of the wood constituents, such as the fatty acids, take place, which then lead to the secondary or tertiary emission of aldehydes, such as pentanal or of carboxylic acids.

This means that the VOC emission from wood-based materials is based essentially on a release from the wood itself and not by the adhesive used. The release is based, in particular, on the conversion of constituents of the wood-based materials which continues in the wood-based materials; for example, a permanent secondary or tertiary emission of the compounds mentioned takes place by fragmentation of the resins and fats.

A wood material used today for a variety of structural applications is OSB (Oriented Strand Board). Such OSB, which are also referred to as coarse chipboard, are made of thin, flat chips, so-called strands. The strands usually have a maximum length of 200 mm, a width of 20 mm and a thickness of less than 1 mm. Usually, these strands are scattered in at least three layers one above the other, the scattering direction being rotated from one layer to the next by 90 degrees. From these two facts results the high bending strength of OSB, which makes OSB so interesting for many applications. One advantage is that because of the use of mainly fresh softwoods, in particular pine, OSB has a lower bulk density compared to other wood-based materials. OSB has an average bulk density of about 550 kg / m ³ .

Therefore, OSB is preferably used in the structural field. It has also been shown in recent years that OSB is being used in interior and especially in residential areas, where no further extensive coatings of OSB are being made for optical reasons. Rather, it is desirable that the characteristic optics of the strands be maintained in the field of vision.

As stated, the use of softwoods leads to an unpleasant side effect, which can be an exclusion criterion for many uses. In fact, it has been shown that OSB is unsuitable for the very high emission of wood constituents or degradation products of wood constituents. It should be noted that when OSB is used as an interior panel, and be used in buildings over a large area, this has the consequence that it leads to an unfavorable ratio of area OSB to volume of indoor air (loading). For standardized emission tests, the load is around a factor of 1. In reality, however, the load can well reach or even exceed a factor of 2. This leads to a higher volume load by the emitted substances which means that standard indoor OSB can only be used in small quantities.

The problem of emission is all the more serious the lower the density of the wood-based materials produced. The problem of indoor pollution from VOCs and VVOCs is addressed by regulations at national and international level. There is a need for manufacturers of engineered wood materials to reduce emissions.

There have been a number of approaches to reducing the emission of wood-based VOCs, but this is usually associated with higher costs. A simple method is the surface coating, which stops the emission of the ingredients. This also leads to additional costs. Thus, for example, in a paper / impregnated coating, the carrier plate is no longer recognizable, but this is used decoratively just because of their beach surface. Moreover, such processes require the presence of coating equipment.

Another possibility is the coating of the surface with a paint. This requires a Lackierlinie with several commissioned works as well as UV lamps or hot air dryers in the case of the use of water-based paints. Since the order quantities for such paints are more than 100 g / m ² , this method is unattractive because of the high-priced UV coatings, and can also be caused by the UV photoresistant photoinitiators additional odor nuisance.

Another approach to reducing the emission of ingredients and degradation products of the ingredients is the addition of chemicals and / or adsorbents to prevent or reduce emissions to a non-critical range. Such chemicals, referred to as additives, for example reducing agents, have to be added to the lignocellulose-containing comminution products, such as the strands, already in the production of wood-based materials, such as OSB. The amounts are usually in a range of 1 to 5 wt .-%, based on atro wood. This addition of the chemicals significantly increases the cost of the product, since in most cases the proportion of adhesive must be increased. In addition, these chemicals have an unpleasant odor, which is negatively noticeable both during production and in use. The use of certain chemicals continues to lead to changes in the wood material itself, so show when using certain chemicals brownish discoloration, which adversely affect the appearance of wood-based materials, such as OSB. Finally, an addition of adsorbents such as activated carbon has been proposed, but must be discarded in terms of cost. In addition, the addition of zeolites leads to problems due to an increased ash attack during the incineration of wastes of this OSB as well as higher wear during the sawing of such wood-based materials.

There is therefore a continuing need to provide suitable means to help reduce the emission of volatile organic compounds from wood-based materials. These agents are intended to overcome known disadvantages, such as a high investment risk, high material costs, product disadvantages, disadvantages in process technology and / or high costs in general. It is particularly important that even with prolonged use, the desired reduction of VOC and VVOC, ie TVOC, from the wood materials is ensured.

The present invention is therefore based on the technical problem of permanently ensuring the reduction of the emission of VOC from wood material, in particular OSB in a simple, cost-effective manner.

Description of the invention

This object is achieved by the fact that hot-melt adhesives known per se as adhesives, recently used for reducing the emission of volatile organic compounds (VOC) and also of TVOC, in general, from wood-based materials.

The hotmelt adhesive is applied to the surface of the wood material in a layered form in the liquid state.

The object is thus achieved by the use of hot melt adhesives according to the feature of claim 1.

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

In addition to reducing the emission of volatile organic compounds and the total volatile compounds, the use of the hot melt adhesive also makes it possible to make the surface of the wood-based materials or the wood more uniform and to produce as smooth and as smooth a surface as possible. For example, the hotmelt adhesive can fix loose strands and thus reduce the risk of injuries.

In the present context, the expression "reduction of emission" or "reduction of emission", which are used interchangeably, means that the amount of VOC or the total amount of volatile organic compounds, respectively, compared to a wood material or a wood without inventive use of the hotmelt adhesive (TVOC) is lower.

The term "avoidance of emission" includes a percentage reduction or reduction in emission up to such as compared to control which is below the measuring limit. The term "reduction" is understood herein to mean a reduction or reduction until avoided.

Another advantage is that even those substances are reduced in their emission, which contribute to an unpleasant odor.

According to the invention, not only a covering and smoothing of the surface of the wood-based materials is achieved, but surprisingly also a reduction of the emission of VOCs from the wood-based materials, in particular over a longer period of time and with long-term use. This makes it possible to use OSB indoors as well as in the decorative area.

The applied layer of the hotmelt adhesive, which is applied in an embodiment in the molten state and then cured, allows the smoothing of the surface, so that the further handling of corresponding wood materials such as OSB is more pleasant.

The layer formed from the hot melt adhesive is applied at least to the top of the wood-based panel. Optionally, the hot melt adhesive can also be applied to the underside of the wood-based panel and in particular the OSB here. At least on the surface lying in the visible area, the hot melt adhesive is applied. The layer should therefore be designed at least so that emission of the VOC into the interior is largely prevented.

The application of the hot melt adhesive takes place in one embodiment such that the hot melt adhesive is applied after the hot pressing of the wood material, preferably before the complete cooling of the wood material produced. Here, the wood-based panels are smoothed on their surface by the liquefied hot melt adhesive is simply applied and processed flat. The so coated wood-based panels can then be further processed in the desired manner. The plates can then be cooled and optionally water and / or release agents applied to the coating be sprayed to prevent sticking of the plates together in a stack and to ensure the stackability of these plates.

That is, the use of the hot melt adhesive allows easy incorporation of this process in the manufacturing process of wood-based panels, especially OSB.

In one embodiment, the hotmelt adhesive is used in such a way that it is applied by means of roller application, for example a corresponding device which is immediately downstream of the hot press. The hot melt adhesive can be applied in one or more steps by means of roll application in synchronous or countercurrent.

In one embodiment, the wood material is an OSB and the hot melt adhesive is applied after the hot pressing on the uppermost beach layer of a large-scale side of the OSB layer-forming. Optionally, the hot melt adhesive is further applied to the lower surface facing the surface.

According to the invention, a conventional hot melt adhesive can be used. These hot melt adhesives are commonly used for bonding flat elements. These can be edges of furniture parts, profiles or large-scale decorative coatings. Hotmelt adhesives, which are also referred to as hot-melt adhesives, hot-melt adhesives, hotmelt or hotmelt, are usually solvent-free and more or less solid at room temperature, which are applied hot to the corresponding surface and produce a firm bond on cooling. Suitable hotmelt 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 mentioned, the hotmelt adhesives may contain further constituents, such as waxes, resins and stabilizers, and also pigments.

In one embodiment, the layer formed using the hot-melt adhesives is one with a layer thickness of at least 30 μm, for example up to 250 μm. The application rate of the hotmelt adhesive may be in a range from 30 g / m ² to 250 g / m ² , such as 50 g / m ² to 200 g hot melt adhesive / m ² .

By using these hotmelt adhesives, in addition to reducing the emission of VOCs, an improvement in the surface properties can be achieved in order to improve further surface finishes, such as wallpapering, brushing but also the application of further layers, for example decorative layers and other wood-based outer layers. The application of these surface finishes can be carried out more easily and material-saving.

In one embodiment, hot melt adhesives additionally comprise colorants, such as pigments, which permit coloring of these hotmelt adhesives. As a result, both an identification of the wood materials can be achieved as well as a decorative upgrading of the surface done.

The use of the hotmelt adhesive to form the corresponding layer is only necessary in those areas in which the emission is to be reduced, that is, for example, only on the surfaces of the side facing the interior or the viewing areas. In contrast, the emissions reductions achieved using chemicals require that all lignocellulosic crushing products, for example all strands of OSB, be treated.

More preferably, the inventive use of OSB coating with hot melt adhesive may be combined with other known means, methods and uses of VOC and TVOC emission reducing additives.

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;

dadurch gekennzeichnet, dass nach dem Verpressen auf die Oberfläche des hergestellten Holzwerkstoffes eine Beschichtung aus Schmelzklebstoff aufgebracht wird, wobei durch Aufbringen des Schmelzklebstoffes die Emission von flüchtigen organischen Verbindungen aus dem Holzwerkstoff verringert wird.In a further embodiment, the present invention relates to a process for the production of wood-based materials, in particular of OSB, comprising the steps:

1. a) providing lignocellulose-containing comminution products and an adhesive,
2. b) applying the adhesive to the shredded products;
3. c) pressing the lignocellulose-containing comminution products with the adhesive under the action of heat and pressure;

characterized in that after the pressing on the surface of the produced wood material, a coating of hot melt adhesive is applied, wherein the application of the hot melt adhesive, the emission of volatile organic compounds from the wood material is reduced.

Adhesives are conventional adhesives for the production of wood-based materials, such as OSB, including formaldehyde-free adhesives, such as isocyanate-based.

In one embodiment, the application of the optionally melted hotmelt adhesive to the surface of the wood material takes place after hot pressing. In this case, the application of the hotmelt adhesive may also be such that it is not already applied in the molten state, but the heat of the hot pressed wood material is used to make the hot melt adhesive flowing, so that a better processing on the wood material is possible. The application can be done with conventional facilities, namely conventional temperature-controlled hot melt equipment and by means of nozzles, etc.

In particular, according to the invention, terpenes and acids are reduced.

The method according to the invention can be such that the coating with the hotmelt adhesive takes place in one or more steps by means of roll application in synchronous or countercurrent fashion.

By applying, for example by means of roller application device, a closed, smooth surface can be produced so that loose comminution products are fixed and, if appropriate, holes present in the layer are filled up. This surface thus present allows a further improved processing of the wood materials.

In one embodiment, the application of the layer of hotmelt adhesive takes place on the side of the wood material facing an interior space.

According to the invention, in one embodiment, the application rate of the hotmelt adhesive in a range of 30 g / m ² to 250 g / m ² , such as a range of 50 g / m ² to 200g hot melt adhesive / m ² . The amount applied may vary depending on the adhesive and the desired property of the surface.

According to the invention, a hotmelt adhesive 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 is applied as the hotmelt adhesive in one embodiment.

The layer thickness can be in a range of 30 to 250 microns.

In one embodiment, the method for producing the wood-based material may further include applying further layers to the surface of hot-melt adhesive, in particular the application of a decorative layer or other types of cover layers. Furthermore, the hot melt adhesive may be colored, so that a decorative enhancement of the surface takes place. In one embodiment, the hotmelt adhesive is a substantially transparent adhesive, so that the beach structure remains recognizable in the case of OSB wood-based materials. Such plates can be used decorative in particular indoors.

Finally, the present invention is directed to wood-based materials obtainable by the process according to the invention, such as for the production of OSB.

In the following, the invention will be explained in more detail by means of embodiments, without being limited thereto.

Embodiment 1

On an OSB (22 mm), an EVA hotmelt in a quantity of 90 g / m ² was applied on one side with a roller application unit in unison. These were the product Jowatherm 287.10, Jowat Klebstoffe, Detmold, Germany. The temperature in the pre-melter was 200 ° C. After application of the hot melt, the surface was finished with a second roller application unit. The plates were sprayed behind the calender with about 5 g of water / m ² and stacked after cooling. In the surface 90 - 95% of the previously clearly recognizable holes were closed. Overall, the surface made a very smooth impression. Loose strands were no longer observed in the treated surface.

Embodiment 2:

On an OSB (22 mm), a PU hotmelt in a quantity of 80 g / m ² was applied on one side with a roller application unit in unison. These were the product Jowatherm 602.35, Jowat Klebstoffe, Detmold, Germany. The temperature in the pre-melter was 160 ° C. After application of the hot melt, the surface was finished with a second roller application unit. The plates were sprayed behind the calender with about 10 g of water / m ² and stacked after cooling. The post-crosslinking of the PU should be accelerated with the water. In the surface 100% of the previously clearly visible holes were closed. Overall, the surface made a very smooth impression. Loose strands were no longer observed in the treated surface.

The sample of Embodiment 1 was tested for the emission of volatile organic compounds according to the AgBB scheme (2015). A blank without surface coating was tested for comparison. A list of selected connections is shown in the following table. It deals These are the compounds that are the most significant in terms of quantity. Variant parameters OSB with EVA hotmelt (in μg / m ³ ) OSB with EVA hotmelt (in μg / m ³ ) OSB (blank) (μg / m ³ ) OSB (blank 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-pinene 117 75 555 317 3-Caren 75 56 331 239 acetone 222 251 339 381

The measurements were carried out in each case three days and four weeks after the production of OSB.

As can be seen from the table, the surface seal achieves a significant reduction in emissions, which is at least 60% for some parameters. The requirements of the AgBB scheme (2015) are fulfilled by the experimental panel according to the invention. In particular, the strong reduction after 28 days should be emphasized.

Claims (14)

Use of known hot melt adhesives for reducing the emission of volatile organic compounds (VOC) from wood materials, in particular OSB, wherein the hot melt adhesive is applied to the surface of the wood material. Use of hotmelt adhesives for reducing the emission of VOC according to claim 1, characterized in that the hotmelt adhesive is applied to form a layer at least on the surface of a large-area side of the wood material, in particular the OSB. Use of hot melt adhesives for reducing the emission of VOC according to claim 1 or 2, wherein the hot melt adhesive is applied to the top and the bottom of the wood material, in particular the OSB. Use of hot melt adhesives to reduce the emission of VOC, wherein the hot melt adhesive after hot pressing, preferably before the complete cooling, of the wood material, in particular the OSB, is applied. Use of hot melt adhesives for reducing the emission of VOC according to one of the preceding claims, wherein the hot melt adhesive is applied in one or more steps by means of roll application in synchronous or countercurrent. Use of hot melt adhesives for reducing the emission of VOC according to any one of the preceding claims, wherein said hot melt adhesive is selected from the group: ethylene vinyl acetates and copolymers thereof, polyurethanes, polyamides, polyethylenes, polyalphaolefins, polyesters, copolyamides, vinylpyrrolidone / vinyl acetate copolymers or mixtures thereof , Use of hot melt adhesives for reducing the emission of VOC according to any one of the preceding claims, wherein the layer thickness of the hot melt adhesive is at least 30 microns. Process for the production of wood-based materials, in particular OSB, comprising the steps: a) providing lignocellulose-containing comminution products and an adhesive, b) applying the adhesive to the shredded products, c) pressing the lignocellulose-containing comminution products with the adhesive under the action of heat and pressure, characterized in that after the pressing on the surface of the produced wood material, a coating of hot melt adhesive is applied, wherein the application of the hot melt adhesive, the emission of volatile organic compounds from the wood material is reduced. A method according to claim 8, characterized in that the coating with hot melt adhesive in one or more steps by means of roll application is applied in synchronism or in reverse. The method of claim 8 or 9, wherein the layer of hot melt adhesive is applied either only on a large area or on both large-area sides. Method according to one of claims 8 to 10, characterized in that the layer thickness is at least 30 microns and the application rate of the hotmelt adhesive is 30 to 250 g / m ² . The method of any one of claims 8 to 11, wherein the hot melt adhesive is one 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. Method according to one of claims 8 to 12 wherein at least one further layer is applied to the hotmelt adhesive, in particular a decorative layer. Wood material obtainable by a process according to one of claims 8 to 13, preferably OSB.