The present invention relates to a method for producing wooden products, in particular glued wooden products or composite wooden products in which different wooden parts are fastened to each other using glue or a different adhesive. Examples of such wooden products include parquet flooring products and other engineered wood flooring products; laminated wooden products, such as beams; veneered products; wooden board products, such as core, chip and block boards; plywood and similar. In particular, the invention relates to such a method which is conducted in two adhesive application steps, with a certain waiting time between said steps. The invention also relates to an apparatus for manufacturing such wooden products.

There are many known ways of joining wooden parts together using adhesive. A common way to perform such joining is to first apply a liquid adhesive to the wooden surfaces to be joined, and thereafter to bring said surfaces into contact with each other and to apply a pressure during a certain press time. In such joining, the wetness of the adhesive is in general important for the end result. For instance, WO 2009/014492 Al discloses ways to control the wetness of applied adhesives. Such "wetness" is herein quantified in terms of the relative solid contents of the liquid adhesive in question, in other words its contents of solid matter in relation to a liquid solvent or carrier. The solvent or carrier may preferably be water, but can also be another liquid, such as an alcohol or other suitable liquid. US 8317965 B2 discloses the application of adhesive at room temperature, using relatively short press times.

US 7641759 B2 discloses the controlled application of adhesive and solvent to wooden surfaces before pressing, in order to allow for longer waiting times before adhesive application and pressing. The prior art also comprises EP 1190823 A2, suggesting using heating of the said surfaces, as well as US 3160543 B, US 4812366 B, US 5234519 B and EP 0979712 Al, discussing drying of adhesive-coated surfaces. The precise control of the solid contents, which is required in the prior art, results in problems in terms of production efficiency. In particular, it has proven difficult to scale up production volumes without sacrificing cost-efficiency or final product quality.

It would be desirable to be able to produce composite wooden products in a large-scale, cost-efficient and flexible way, preferably at room temperature and with high quality of the final products.

The present invention solves the above described problems. Hence, the invention relates to a method for producing a composite wooden product comprising a first detail with a first wooden surface and a second detail with a second surface, which method is characterised in that the method comprises the steps a) applying a first adhesive layer to the first surface; b) drying the first adhesive layer, or allowing the first adhesive layer to dry, forming a first dried adhesive surface; c) storing the first detail during a period of at least one hour; d) applying a second adhesive layer to the second surface, forming a second adhesive surface; e) bringing the first dried adhesive surface and the second adhesive surface into contact; and f) applying a pressing force, pressing the first and second surfaces together. Moreover, the invention relates to an apparatus for producing a composite wooden product comprising a first detail with a first wooden surface and a second detail with a second surface, which apparatus is characterised in that the apparatus comprises a detail reception means, arranged to receive at least one a first detail with a dried first adhesive layer applied to the first surface and at least one second detail, in that the apparatus comprises an adhesive application means, arranged to apply a second adhesive layer to the second surface, forming a second adhesive surface, in that the apparatus comprises a first and second detail arrangement means, arranged to bring the first adhesive surface and the second adhesive surface into contact, and in that the apparatus comprises a force application means, arranged to apply a pressing force, pressing the first and second surfaces together.

In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the enclosed drawings, wherein:

Figure 1 is a flowchart illustrating a method according to the present invention;

Figure 2 is a simplified overview of a first 100 and a second part 200 of a method and an apparatus according to the present invention;

Figure 3 is a simplified overview of a third part 300 of a method and an apparatus according to the present invention; and

Figure 4 is a simplified detail view of the first part shown in Figure 2.

Figures 2-4 share the same reference numerals for same or corresponding parts.

Hence, Figure 1 illustrates a method according to the present invention, comprising first 100, second 200 and third 300 parts, for producing a composite wooden product compris- ing a first detail with a first wooden surface, and a second detail with a second surface. By "composite product", as used herein, is meant a product comprising at least two permanently joined parts, namely the first and the second product. The permanent joining together is at least realized using first and second liquid adhesive as described hereinafter. However, such a composite product may also comprise additional parts, such as several first details and/or several second details and/or any additional, third details.

By the term "first detail" is intended any detail which is similar or identical to any other such first detail. By the term "second detail" is intended any detail which is similar or identical to any other such second detail. Hence, there is a "first type" of details and a "second type" of details. The first and second types may be different or be identical. In a first step, the method starts.

In a subsequent first adhesive layer application step 120, a first liquid adhesive is applied to the said first surface so as to form a first liquid adhesive layer on the said first surface.

Thereafter, in a subsequent first adhesive layer drying step 130, the first adhesive layer is dried, employing an active, forced drying mechanism such as exposing the first adhesive layer to heat, radiation, dry gas or a combination thereof. Alternatively, the first adhesive layer is simply allowed to dry passively, without applying any particular type of active or forced drying mechanism. For instance, the first detail, with its first adhesive layer, may be left lying until it has dried sufficiently or completely. Irrespectively of how it is dried, the first adhesive layer thereafter forms a first dried adhesive surface.

An example of this step is illustrated in Figure 2, in which a range of stacked first details 110 are brought onto a conveyor belt 101 and exposed to a first adhesive application step 120, in which the first adhesive is applied to the first surface of the first detail, forming said first adhesive layer. Thereafter, the first details are conveyed to a forced drying step 130, in which the first adhesive layer is dried forming said dried first adhesive layer.

A stack or pile of first details 140, ready for storing and comprising respective dried first adhesive layers, is depicted in Figure 2.

Thereafter, in a subsequent first detail storing step (140, 141, 142), the first detail is stored during a period of at least one hour.

Preferably, a time period between the first adhesive layer drying step 130 ends and a second adhesive layer application step 220 (see below) starts, is at least 4 hours, preferably 24 hours. Even more preferably, the first detail (preferably all first details) is relocated to a different site 141 after the first adhesive layer drying step but before the said second adhesive layer application step. By a "different site" is meant that the first details are transported from one production facility to a different production facility or warehouse, at a different geographic location, such as 1 km away or more. Preferably, at least 100, preferably at least 1000, first details are co-stored 141 together, in same facilities.

It is also realized that the storage 140, 141, 142 time may be substantially more, such as at least one week, or even at least one month. This is in fact one of the advantages of the present invention, allowing extended intermediate storage of the first details after the first adhesive layer drying step 130 and before the second adhesive layer application step 220. This, in turn, allows for more flexible production layout and planning, since it is possible to produce and store dried first adhesive layer first details ahead of time, and start directly with the second adhesive layer application step 220 when a finally assembled end product is to be produced.

In particular, it is preferred that the drying of the first adhesive layer in the first adhesive layer drying step 130 is configured to result in that the first adhesive layer has a solids content that is so low so that it admits that the first detail is stacked together with other details, such as other first details in the stack 140, and stored, in a way so that the first dried adhesive surface is in direct contact with said other details, without the first dried adhesive surface adhering to the said other details in a way jeopardizing the final composite product quality. In other words, the applied respective first adhesive layers of the first details are dried, in step 130, to such an extent so that the first details don't stick to each other, or other details, when stacked with said first adhesive layers in contact with adjacent details, such as in a stack of first details 142 as illustrated in Figure 2.

To achieve this, it is preferred that the dried first adhesive layer, after step 130, is completely dried. In other words, its relative solid contents are 100% or substantially 100%, or at least 95%, with no or substantially no remaining liquid solvent or carrier. However, depending on the type of adhesive used, it may suffice that the dried first adhesive layer comprises a completely dried outer surface layer, with a less dried inner layer. According to one preferred embodiment, however, steps 130, 140 are performed so that the first adhesive layer is fully cured once the first details enter a pressing step 310 (see below). The stack of first details 142, with dried first adhesive layers applied, are thereafter brought to said second part 200 of the process, in which a stack of second details 210 are brought, via a conveyor belt 201, to said second adhesive layer application step 220. In this second layer adhesive application step 220, a second adhesive is applied to the second surface of said second detail, there forming a second liquid layer comprising a second adhesive surface. As is the case for the first adhesive layer application step 120 (in which a respective first adhesive layer is preferably applied to a plurality of first details), this is typically performed for a plurality of second details.

According to one preferred embodiment, the said second surface is a wooden surface. In other words the stack 210 comprises second details each with a fresh wooden second surface onto which the said second adhesive layer is applied in step 220. Then, in step 220 the second adhesive layer is applied directly onto said fresh wooden surface.

Alternatively, the said second surface is the dried surface of an adhesive layer provided on a wooden surface of said second detail. In other words, the stack 210 comprises already preconditioned second details, the respective second surfaces of which have been arranged with adhesive and thereafter been subjected to a drying step (not shown in the Figures), so as to achieve said preconditioned second details each having a dried adhesive layer surface. Then, in step 220 the second adhesive layer is applied onto said dried adhesive layer, which may be of the same or a different type of adhesive than the second adhesive layer applied in step 220.

Regarding the first and second layers of adhesive, they are preferably constituted by mutually compatible adhesives, meaning that the second adhesive is configured to adhere to the dried first adhesive layer with desired adhesion characteristics. Preferably, both the first and second adhesive layers are constituted by adhesives selected from the group comprising EPI (Emulsion Polymer Isocyanate) or PVAc (Poly Vinyle Acetate) adhesives, furthermore each comprising at least one liquid solvent or carrier. Possibly, each of the first and second adhesive layers are constituted by adhesives further comprising one or several additives selected from the group comprising UF (Urea Formaldehyde), MF (Mel- amine Formaldehyde) or MUF (Melamine Urea Formaldehyde). In general, it is preferred that the second adhesive layer is constituted by an adhesive having water as a liquid carrier. Also, it is preferred that none of the used adhesives comprise formaldehyde. In a preferred embodiment, the first and second adhesives are identical or substantially identical with respect to their compositions in liquid, undried state, possibly apart from their respective relative solid matter content.

Preferably, the first and second adhesive layers are both constituted mainly, preferably completely, by a dispersion or emulsion adhesive.

According to a preferred embodiment, the method according to the present invention further comprises an individual drying step 230, performed after the second adhesive layer application step but before a contacting step (see below). In such an individual drying step 230, the second adhesive layer of at least one, preferably of a plurality, even more preferably substantially all, or even each and every one, of said second details, is individually dried. This individual drying is then performed so as to decrease the wetness of the second adhesive layer, in other words increasing its relative contents of solid matter, in an individual manner in terms of the drying action in question. In particular, the individual drying of the second adhesive layer is preferably not a complete drying of the second adhesive layer; the relative solids contents of the second adhesive layer after said individual drying step 230 are preferably less than 100%.

That the drying of the respective second adhesive layer in said individual drying step 230 is "individual" means that it is individually performed, in terms of the drying action and effect in question, for each second detail, based upon individual prerequisites for each such second detail. It is realized that, in particular since there may be very many second details used, even in one and the same production batch, there may be two or more second details that are exposed to substantially identical second adhesive layer drying in the individual drying step 130. However, it is preferred that each second detail receives an individually adapted drying action and effect based upon the particular prerequisites for that particular second detail, and that at least two different second details receive different drying programmes. Differences may, for instance, comprise drying times, intensities, intensity profiles over time and/or even drying methods. According to a preferred embodiment, the individual drying step 230 comprises drying of the second adhesive layer not more than so that the second adhesive layer is able to completely wet the part of the first dried adhesive surface being contacted by the second adhesive surface as a result of the application of the pressing force in a subsequent pressing step 310 (see below). Hence, after the individual drying step 230, for all second details, the respective second adhesive layer surface of the respective second adhesive layer is preferably not completely dried.

Preferably, the individual drying step 230 is performed by subjecting the second adhesive layer to a controlled amount of thermal radiation, convection or transfer energy, or a combination thereof. Examples include individually controlled exposure to flowing hot and/or dried air or other gas, preferably an inert gas; radiation by a lamp, such as an IR lamp; and/or radiation by heat elements. According to a particularly preferred embodiment, illustrated in Figure 4, the individual drying step 230 comprises the exposure of the second details 240 to IR radiation energy from an IR radiation means 231, such as an IR lamp. In Figure 4, the second details 240 are carried on the conveyor belt 201 in a direction D, past the individual drying step 230.

Preferably, the individual drying step may be performed during between 2 s and 20 s. Hence, the individual drying step preferably involves relatively intense heating, at least if compared to merely allowing the second adhesive layer to dry by simply allowing the second details to rest after the second adhesive layer application step 220.

As discussed above, the individual drying step 230 comprises subjecting the said second adhesive layer to a drying action which is individually selected for several of the second details 240. In particular, this is true for several pairs of first and second details (see below), and preferably for all of the processed second details 240. As such, the individual drying of the second adhesive layer in question has the purpose of producing, and preferably is arranged to result in the production of, a respective relative solids content of each of the second adhesive layers in question which is within a certain predetermined interval. Preferably, this interval is selected so as to achieve a desired consistent product quality after the below-described pressing step 310 across different pairs of first and second details, such different pairs being associated with respective different waiting times between the respective second adhesive layer application step 220 and the respective pressing step 310. Since the curing process of the second adhesive may also effect such final product quality, different second details may, in some embodiments, be associated with different such intervals, even within one and the same production batch of one and the same product type. However, in alternative embodiments, for simplicity all second details share one and the same predetermined interval.

Hence, the said final product quality, after pressing 310, is typically determined by several factors external to the first and second details in question, comprising said waiting time and the curing behaviour of the second adhesive, not least during and possibly also after the pressing step 310. Hence, the said final product quality may be measured immediately after the pressing step 310, and/or sometimes after the pressing step 310, such as after complete curing of the second adhesive. In addition thereto, the final product quality is of course also determined by the type and quality of the first and second adhesives; the application method and quality/quantity; and the first and second detail surface material.

As used herein, the term "curing" refers to a process in which the adhesive gains its final adhesive properties.

Preferably, the individual drying step 230 may be controlled, individually for each second detail, to achieve said consistent final product quality, based upon a combination of a priori knowledge of the various details regarding the process and iteratively achieved empiric knowledge about required individual drying effects required, in a particular process according to the invention, as a function of waiting times between the second adhesive layer application step 220 and the pressing step 310. According to one preferred embodiment, the drying performed in the individual drying step 230 is controlled using a feedback mechanism, based upon measurement of the wetness, or relative solid substance, of the individually dried second adhesive layer in question. For instance, in Figure 4, a per se conventional remote dryness measuring sensor 232, such as an online moistures sensor, is used. The sensor 232 measures, preferably continuously or at least several times, the results of the individual drying action, and a control device 233, which is connected to both the sensor 232 and the drying means 231, controls the drying means 231 so as to achieve the desired individualized drying action before each second detail leaves the individual drying step 230. The sensor 232 may also measure other second detail properties, such as temperature and so forth.

The individual drying step 230 may be individually adjusted based upon one, several or all of the factors material temperature (may be measured or estimated); material and/or adhesive moisture content; adhesive amounts used; pressing time; and pressing force (or pressure) used.

It is realized that the individual drying action in step 230 may differ between different second details with respect to, at least, drying times and/or drying intensity.

Again with reference to Figure 1, and moving on to a third part 300 of the inventive process, in a subsequent contacting step 305, the first dried adhesive surface and the second adhesive surface are brought into contact with each other. This contact is preferably a direct contact, whereby the whole or at least substantially the whole first dried adhesive surface and the whole or at least substantially the whole second adhesive surface are brought into direct contact with the other adhesive surface in question. Typically, the first and second details will be arranged on top of each other in the contacting step 305, forming a structure which can then be pressed together. Namely, this contacting step 305 may be performed as a part of, in connection to, or before, a subsequent pressing step 310, in which the first and second surfaces are pressed together in a press. After the pressing step 310, and preferably after a final resting step, in which the pressed-together first and second details are allowed to rest, such as to complete curing of the second adhesive, the composite product is finalized and the method ends.

Preferably, the pressing time, that is the time duration of the application of the pressing force in the pressing step 310, is between 10 s and 240 s. Hence, the pressing step 310 as such does preferably not result in that the second adhesive layer cures.

Rather, the application of the pressing force in the pressing step 310 is preferably interrupted before full curing of the second adhesive layer, but not before mechanical stability has been reached with respect to each pressed together pair of first and second detail. In other words, according to this embodiment the pressed-together first and second details are preferably held together, by the adhesive force provided by the second adhesive layer onto the dried first adhesive layer, sufficiently strongly so that the composite product can maintain its structural integrity and shape even when the pressing force is removed and the composite product is subjected to necessary handling steps subsequent to the pressing.

According to one preferred embodiment, several pairs of first and second details are brought into contact and simultaneously pressed together by the application of said pressing force in said pressing step 310, in a batch processing step, whereby each first detail may be attached to one or several second details and whereby each second detail may be attached to one or several first details. For instance, the first and second details may be arranged with first adhesive layer surfaces facing downwards and second adhesive layer surfaces facing upwards, in contact with corresponding first adhesive layer surfaces, and so that opposite respective surfaces, without adhesive coverings, of first and second details, also face each other. The pressing force may preferably be applied in a staple press or a stacking press (multi- opening press), in which all of said several pairs of first and second details are introduced and thereafter simultaneously pressed together. Depending on the type of press used in said pressing step 310, the respective second details of said several pairs of first and second details may be charged into the press in question simultaneously or at subsequent, different respective time points. Preferably, the charging is not performed simultaneously for all of said second details, affecting the required individual drying action performed in step 230.

Furthermore, it is preferred that the second adhesive layer applied in the second adhesive layer application step 220 is not applied simultaneously to the respective second details of said several pairs of first and second details, also affecting the said required individual drying action.

The present method and apparatus may be used to successfully produce a variety of different types of composite wooden products. One preferred example is the one in which at least one of the respective first details of said several pairs of first and second details constitute a substrate, preferably a wooden substrate, and in which several of the respec- tive second details of said several pairs of first and second details constitute floor, wall or ceiling covering material. For instance, the first details may be plywood or other composite sheet material, and the second details may be veneered or solid pieces of wood (lamellae). Then, the composite wooden product produced may be a building exterior or interior surface covering layer or construction material, such as an engineered wood flooring, a ceiling or wall covering material, a fagade board, a roof covering material or a board material.

Another preferred example is the one according to which at least one of the respective first details of said several pairs of first and second details, and in addition thereto at least one of the respective second details of said several pairs of first and second details, constitute wooden beams. Then, the composite wooden product may be a glulam beam, constituted by first and second details laid on top of each other.

In general, it is preferred that the pressing in step 310 is performed batch-wise, as op- posed to in a continuous process. This means that the pressing is performed intermittently. At the same time, one, several or all of the steps 120, 130, 220 and 230, and in particular step 230 and preferably also step 220, may be performed continuously, using a continuous production line, such as using a conveyor belt 201 production regime. The result of this is that, for different ones of the second details, different times will pass between the second adhesive layer application step 220 and the pressing step 310. in a particularly preferred embodiment, the steps 220, 230 are performed in a serial fashion, preferably in a single serial lane, in which only one, or possible, albeit being less preferred, at least ten, second details are treated in parallel in step 220. Then, these serially treated second details are paired, batch-wise, with a set of prepared first details with dried first adhesive layers, and subsequently charged into the pressing step 310. With such a production layout, it has turned out that very high production outputs are possible to achieve. The pressing step 310 preferably simultaneously handles at least 10, preferably at least 50, pairs of first and second details in each batch, where each first detail may be paired with one or several second details, and vice versa. Hence, at least 10, preferably 50, first details are preferably pressed together with corresponding second details, and/or vice versa.

One main advantage of the present invention is that such high production outputs are possible to achieve quite simply, and in particular without having to use production steps with elevated temperatures. Hence, it is preferred that at least steps 220, 305 and 310, and preferably also step 140, are performed at room temperature, such as at between typically 10°C and 30°C. Preferably, the complete process is performed at such room temperature, possibly with the exception of the said individual drying step 230. All first and second details are preferably substantially room-tempered upon entry into each of the steps 110, 120, 130, 150, 210, 220, 230, 240, 305 and 310. In general, it is preferred that the first dried adhesive layer is configured to contain between 10% and 90%, preferably between 10% and 50%, more preferably between 20% and 40%, of the total amount of adhesive in the first and second adhesive layers.

The waiting time between the individual drying step 230 and the pressing step 310 is preferably at the most 10 minutes, more preferably at the most 5 minutes, and preferably at the most 2 minutes on average as seen across all treated second details. In general, it is preferred that the amounts of first and second adhesive are selected with the aim of fulfilling relevant final product quality requirements, after which selection the individual drying step 230 and the pressing step 310 are configured to reach such quality requirements given the selected amounts of adhesives. In an example, a multi-ply wooden flooring board is manufactured, of engineered wood flooring type. Prefabricated substrate sheets are glued together with sawn or cut veneered lamellae.

The prefabricated substrate is pre-treated with first adhesive, which first adhesive is dried, preferably at the same location. The first adhesive in this example is PVAC having water as carrier.

At a different location, and at a later date, the prefabricated and pre-glued substrate sheets are fed to a layup station. Lamellae are also fed, through a second adhesive appli- cation station, followed by an infrared controlled drying station and on to the same layup station as for the substrate sheets. Each lamella is measured with respect to its current temperature, moisture contents, adhesive amount and expected wait time until the pressure force is to be applied, and an infrared drying program is individually adjusted to each individual lamella. The second adhesive in this example is the same as the first adhesive. Substrate sheets and lamellae are then stacked together in their desired final assembly positions in relation to each other, during about 1 minute, and are thereafter fed to a staple press. The cycle time in this example is 70 seconds, of which both the pressing time and the layup time is 60 seconds. Thus, the first substrate and the lamella that are pressed together during each pressing cycle have a layup (waiting) time of almost 70 seconds, while the last substrate/lamella pair in the stack will have a layup (waiting) time of only 10 seconds. However, the pressing time is the same for the whole stack, 60 seconds.

In case a stacking press, having multiple receiving openings at different floors, is used, charging times are often longer than for a staple press. Then, individual drying times must be adjusted correspondingly. Substrate sheets and lamellae are stacked together and transported to an elevator, arranged to position each first/second detail material combination correctly on the pressing table and floor. Once the stacking press is filled, the pressure force is applied.

In this latter case, the pressing time may be 150 seconds, and the total cycle time may be 170 seconds. This means that the first substrate and lamella being stacked together during each pressing cycle will have a waiting time of almost 170 seconds, while the last substrate and lamella will only have a 20 seconds waiting time. However, the pressing time for these two extremes is the same, 150 seconds.

In another example, a press with a single opening is used. Also in this case, the individual drying times are adjusted using knowledge of the differing expected waiting times involved for different lamellae.

The production method described above solves the initially mentioned problems, being able to produce wooden composite products of high quality in a highly flexible and scalable fashion, and mostly performed in room temperature. In particular, the controlled handling of minimal amounts of moisture during the final assembly step (comprising the pressing step 310), the pressing step 310 can be performed at room temperature, without any supply of additional thermal energy, and during very limited time durations, in turn allowing large single-line throughputs. Further advantages include lower process energy consumptions and minimal waiting times after pressing 310.

The invention further relates to an apparatus, for producing a composite wooden product, as exemplified in Figures 2-4, and specifically arranged to perform a method according to the present invention and as described above.

Such an apparatus hence comprises a detail reception means, such as a conveyor belt, arranged to receive at least one first detail with a dried first adhesive layer, of the above type, applied to the first surface and at least one second detail. Furthermore, the apparatus comprises an adhesive application means 220, arranged to apply the second adhesive layer to the second surface, forming the second adhesive surface. Moreover, the apparatus comprises a first and second detail arrangement means 305, arranged to bring the first adhesive surface and the second adhesive surface into contact with each other. Also, the apparatus comprises a force application means 310, arranged to apply the above-discussed pressing force, pressing the first and second surfaces together.

It is particularly preferred that the apparatus further comprises an individual drying means 230, arranged to apply said individual drying of the second adhesive layer so as to de- crease its wetness, in other words to increase its relative contents of solid matter. As described above, the individual drying of the second adhesive layer is preferably not a complete drying of the second adhesive layer.

Above, preferred embodiments have been described. However, it is apparent to the skilled person that many modifications can be made to the disclosed embodiments without departing from the basic idea of the invention.

For instance, numerous other types of wooden composite products may be produced using a method and an apparatus as described above. For instance, there may also be a third and a fourth detail, of yet different types, as long as the principles described above and defined by the claims are respected. Furthermore, it is possible to use smaller-capacity presses 310 and parallel flows, rather than the above-described high-capacity press with a serial flow.

In addition to the above described method steps, it is also possible to perform other actions. For instance, before the contacting step, the first adhesive layer may be activated, such as remulgating its surface. For example, for some adhesives, this may be performed using the application of a solvent, such as water.

In general, everything which has been said regarding the method is equally applicable to the apparatus, and vice versa.

Hence, the invention is not limited to the described embodiments, but can be varied within the scope of the enclosed claims.