An adhesive and a layered wood product

Abstract

Disclosed is an adhesive comprising a binder composition combined with a hardener, wherein: the hardener comprises kaolin, and wherein the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive. Further is disclosed a layered wood product and the use of kaolin for decreasing dry- out of an adhesive during the production of a layered wood product.

Description

[0001] AN ADHESIVE AND A LAYERED WOOD PRODUCT

[0002] FIELD OF THE INVENTION

[0003] The present disclosure relates to an adhesive comprising a binder composition combined with a hardener . The present disclosure further relates to a layered wood product and to the use of kaolin for decreasing dry-out of an adhesive during the production of a layered wood product .

[0004] BACKGROUND OF THE INVENTION

[0005] Layered wood products are generally formed by gluing together at least two veneers with an adhes ive . The adhesive used plays a big role on the production process and on the properties of the layered wood products e . g . on how easily the veneers are detached and on the shear strength values of the layered wood products . The inventors have recogni sed the need for an adhes ive with improved properties to be used for producing a layered wood product .

[0006] SUMMARY OF THE INVENTION

[0007] Disclosed is an adhesive, wherein the adhesive comprises a binder composition combined with a hardener, wherein :

[0008] - the hardener comprises kaolin ; and

[0009] - the adhesive comprises kaol in in a total amount of 0 . 1 - 5 weight-% based on the total weight of the adhesive .

[0010] Further is disclosed a layered wood product , wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line , wherein :

[0011] - the adhesive comprises a binder composition combined with a hardener ;

[0012] - the hardener comprises kaolin ; - the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive; and the glue line comprises aluminium in an amount of up to 2.5 weight-% and silicon in an amount of up to 2.5 weight-%.

[0013] Further is disclosed the use of kaolin for decreasing dry-out of an adhesive during the production of a layered wood product, by combining kaolin as hardener with a binder composition to prepare the adhesive comprising kaolin in a total amount of 0.1 - 5 weight- % based on the total weight of the adhesive.

[0014] DETAILED DESCRIPTION

[0015] The present disclosure relates to an adhesive, wherein the adhesive comprises a binder composition combined with a hardener, wherein:

[0016] - the hardener comprises kaolin; and

[0017] - the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive.

[0018] The present disclosure further relates to a layered wood product, wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line, wherein:

[0019] - the adhesive comprises a binder composition combined with a hardener;

[0020] - the hardener comprises kaolin;

[0021] - the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive; and the glue line comprises aluminium in an amount of up to 2.5 weight-% and silicon in an amount of up to 2.5 weight-%.

[0022] The present disclosure further relates to the use of kaolin for decreasing dry-out of an adhesive during the production of a layered wood product, by combining kaolin as hardener with a binder composition to prepare the adhesive comprising kaolin in a total amount of 0 . 1 - 5 weight-% based on the total weight of the adhesive . The term "dry-out" of the adhesive may be taken to refer to the phenomena, which cause or promote the starvation of the glue line , that is formed between veneers , i . e . to the los s of liquid components of the adhesive , during the production of the layered wood product . Having applied the adhesive on a veneer, the adhesive tends to start drying, i . e . liquid components may e . g . evaporate or be adsorbed by wood substrate to an excessive extent , whereby the adhesive is dried .

[0023] The layered wood product may be a plywood or a laminated veneer lumber product .

[0024] A layered wood product , such as plywood, is formed by gluing together at least two wood veneers with an adhesive whereby a glue line is formed between the wood veneers . The production of a layered wood product may be carried out by applying, such as spreading, an adhesive on the surface of one veneer, putting another veneer thereon such that the adhesive is between the veneers and then the same is subj ected to cold pressing followed by hot pressing to produce the layered wood product . The time it takes from applying the adhesive on the surface of a veneer up to the start of the cold pressing step may be referred to as the "open time" .

[0025] In one embodiment , the adhesive is applied on a veneer with a glue factor of 100 - 200 g / m2, 128 - 170 g / m2, or 140 - 150 g / m2. The term "glue factor" may be defined as the ratio of the mass of adhesive (glue , expressed in grams ) applied to the surface of the veneer ( surface area expressed in square meters ) .

[0026] For production of layered wood products , a long open time is usually a desired . However, when producing a layered wood product , one may be faced with the challenge that the used adhesive provided on one veneer may dry to an adverse extent before wood veneers are pres sed together, which may result in the lack of sufficient adhesion between the veneers and thus lack of sufficient attachment thereof. Also the shear strength values of the layered wood product may be affected in an adverse manner if the adhesive is drying too fast on the veneer. The lack of adhesion may be the result of the adhesive penetrating too fast into the veneer, whereby the adhesive is dried out too fast. The inventors surprisingly found out that it is possible to reduce this dry-out phenomenon during the production of the layered wood products, e.g. plywood, when using the adhesive as disclosed in the current specification. Especially the inventors surprisingly found out that the use of kaolin has the added utility of providing an adhesive having properties resulting in plywood with better adhesion and attachment of the veneers being formed.

[0027] Kaolin, or kaolinite as it may also be called, is a clay mineral with the chemical composition of A12Si20s (OH) 4. Kaolin is considered a soft, earthy, and usually white, mineral. The inventors surprisingly found out that the use of kaolin has the added utility of being able to reduce the increase of the adhesive viscosity over time and slow down the water loss of the adhesive when applied on the veneer. Also, the use of kaolin has the added utility of improving the fire retardation and lowering formaldehyde emissions.

[0028] In one embodiment, the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-%, 0.2 - 4 weight-%, or 0.25 - 3 weight-%, or 0.5 - 1.5 weight-%, or 0.7 - 1.0 weight-%, based on the total weight of the adhesive. The inventors surprisingly found out that the use of such an amount of kaolin efficiently affected the properties of the layered wood product produced with the adhesive especially what comes to the pre-tack.

[0029] By the term "total weight" is to be understood in this specification unless otherwise stated the total weight of components forming the adhesive including water .

[0030] As is clear to the skilled person, the total amount of the different components / elements in the adhesive may not exceed 100 weight-%. The amount in weight-% of the different components / elements in the adhesive may vary within the given ranges.

[0031] The term "pre-tack" as used in the current specification is to be taken as to refer to as a measurement method that may be used to determine or estimate the dry-out phenomenon of the adhesive. The pre-tack may be evaluated after the cold pressing of the layered wood product. The pre-tack may be evaluated on a scale of 1

[0032] - 5 as follows:

[0033] In one embodiment, the adhesive comprises hardener in a total amount of 0.1 - 50 weight-%, or 0.5 - 30 weight-%, or 1 - 18 weight-%, based on the total weight of the adhesive. The kaolin is used as a hardener. In addition to kaolin the hardener used in the adhesive may comprise also other components or materials, that then together with kaolin makes up the total amount of hardener. In one embodiment, the hardener, in addition to kaolin, comprises soda, starch, flour, or any combination or mixture of two or more of these. In one embodiment, the hardener consists of kaolin.

[0034] In one embodiment, the adhesive comprises the binder composition in a total amount of 50 - 99.9 weight- %, or 60 - 99.7 weight-%, or 70 - 99.5 weight-%, or 82

[0035] - 99 weight-%, based on the total weight of the adhesive.

[0036] In one embodiment, the binder composition is a lignin-based binder composition. In one embodiment, the binder composition is a lignin-based binder composition, which is prepared by polymerizing at least polymerizable substance and crosslinking agent, wherein 50 - 100 weight-%, 60 - 99 weight-%, or 70 - 97 weight-%, or 80

[0037] - 95 weight-%, or 85 - 93 weight-%, or 87 - 91 weight- % , of the polymerizable substance originates from lignin .

[0038] In the context of this specification, the term "lignin" may refer to lignin originating from any suitable lignin source. In one embodiment, the lignin is essentially pure lignin. By the expression "essentially pure lignin" should be understood as at least 70 % pure lignin, or at least 90 % pure lignin, or at least 95 % pure lignin, or at least 98 % pure lignin. The essentially pure lignin may comprise at most 30 % , or at most 10 % , or at most 5 % , or at most 2 % , of other components and / or impurities. Extractives and carbohydrates such as hemicelluloses can be mentioned as examples of such other components.

[0039] The lignin used for preparing the binder composition may be selected from a group consisting of kraft lignin, steam explosion lignin, biorefinery lignin, supercritical separation lignin, hydrolysis lignin, flash precipitated lignin, biomass originating lignin, lignin from alkaline pulping process, lignin from soda process , lignin from organosolv pulping, lignin from alkali process , lignin from enzymatic hydrolysis process , and any combination thereof . In one embodiment , the l ignin is wood based l ignin . The l ignin can origi nate from softwood, hardwood, annual plants or from any combination thereof .

[0040] By "kraft lignin" is to be understood in this specification, unless otherwise stated, lignin that originates from kraft black l iquor . Black liquor is an alkaline aqueous solution of lignin residues , hemi cellulose , and inorganic chemicals used in a kraft pulping process . The black liquor from the pulping process comprises components originating from different softwood and hardwood species in various proportions . Lignin can be separated from the black l iquor by different , techniques including e . g. precipitation and filtration .

[0041] Lignin usually begins precipitating at pH values below 11 - 12 . Different pH values can be used in order to precipitate lignin fractions with different properties . These lignin fractions differ from each other by molecular weight distribution, e . g. Mw and Mn, polydispersity, hemicellulose and extractive contents . The molar mass of lignin precipitated at a higher pH value is higher than the molar mass of lignin precipi tated at a lower pH value . Further, the molecular weight distribution of lignin fraction precipitated at a lower pH value is wider than of l ignin fraction precipitated at a higher pH value . The precipitated lignin can be purified from inorganic impurities , hemicellulose and wood extractives using acidic washing steps . Further purification can be achieved by filtration .

[0042] The term "flash precipitated lignin" should be understood in this specification as lignin that has been precipitated from black liquor in a continuous process by decreasing the pH of a black liquor flow, under the influence of an over pressure of 200 - 1000 kPa, down to the precipitation level of lignin using a carbon dioxide based acidifying agent, preferably carbon dioxide, and by suddenly releasing the pressure for precipitating lignin . The method for producing flash precipitated lignin is disclosed in patent application FI 20106073 . The residence time in the above method is under 300 s . The flash precipitated lignin particles , having a particle diameter of less than 2 pm, form agglomerates , which can be separated from black liquor using e . g. filtration . The advantage of the flash precipitated lignin is its higher reactivity compared to normal kraft lignin . The flash precipitated lignin can be purif ied and / or activated if needed for the further processing .

[0043] The l ignin may be derived from an al kali process . The alkali process can begin with liquidi zing biomass with strong alkali followed by a neutrali zation process . After the alkali treatment , the l ignin can be precipitated in a similar manner as presented above .

[0044] The lignin may be derived from steam explosion . Steam explosion is a pulping and extraction technique that can be applied to wood and other fibrous organic material .

[0045] By "biorefinery lignin" is to be understood in this specification, unless otherwise stated, lignin that can be recovered from a refining facility or process where biomass is converted into fuel , chemicals and other materials .

[0046] By "supercritical separation lignin" is to be understood in this specification, unless otherwise stated, lignin that can be recovered from biomass using supercritical fluid separation or extraction technique . Supercritical conditions correspond to the temperature and pres sure above the critical point for a given substance . In supercritical conditions , distinct liquid and gas phases do not exist . Supercritical water or liquid extraction is a method of decomposing and converting biomass into cellulosic sugar by employing water or liquid under supercritical conditions . The water or liquid, acting as a solvent , extracts sugars from cellulose plant matter and lignin remains as a solid particle .

[0047] The lignin may be derived from a hydrolysis process . The lignin derived from the hydrolysis process can be recovered from paper-pulp or wood-chemical processes .

[0048] The lignin may originate from an organosolv process . Organosolv is a pulping technique that uses an organic solvent to solubili ze lignin and hemicellulose .

[0049] In one embodiment, the binder composition is a phenolic resin -based binder composition . Such a binder composition may be a phenol-f ormaldehyde binder composition .

[0050] The polymeri zing agent may in addition to lignin comprise a compound selected from the class of phenols . In this specification, unless otherwise stated, the term "compound selected from the clas s of phenols" should be understood as meaning a fossil-based compound of phenols . I . e . phenol s are compounds consisting of a single aromatic ring where to one or more hydroxyls (— OH) are bonded . The compound selected from the class of phenols may be selected from a group consisting of phenol , cresol , resorcinol , and any combinations thereof . In one embodiment , the compound selected from the clas s of phenols is phenol . Such phenols are toxic compounds .

[0051] In one embodiment , no compound selected from the class of phenols is used in the binder composition . Thus , a binder composition, such as a lignin-based binder composition, may be provided that is free of materials of fossil origin . The binder composition produced may thus be free of fos sil-based phenol compound ( s ) . The binder composition as disclosed in the current specification may thus be prepared as a nontoxic binder composition . I . e . a binder composition with reduced share of toxic or hazardous compounds may be prepared. The binder composition as disclosed in the current specification may be prepared as a binder composition having 100 % biological origin. Thus, all the components used for preparing the binder composition may be of biological origin and thus no fossil-based components may need to be used.

[0052] The crosslinking agent may be an aldehyde, such as formaldehyde or paraformaldehyde. In one embodiment, the aldehyde is prepared from bio-methanol. The aldehyde may thus be of biobased origin. The aldehyde may alternatively be of fossil origin. In one embodiment, the aldehyde is prepared from methanol.

[0053] The binder composition may be prepared by polymerizing the crosslinking agent and the polymerizable substance in an aqueous composition under heating at a temperature of 60 - 95 °C, or 75 - 90 °C, or 70 - 80 °C, or 70 - 90 °C. The heating may be continued until a binder composition with a desired viscosity value is formed .

[0054] In one embodiment, the adhesive comprises a binder composition combined with a hardener and at least one surfactant, wherein the adhesive comprises the at least one surfactant in a total amount of up to 0.5 weight-%, or 0.005 - 0.45 weight-%, or 0.01 - 0.4 weight- % , based on the total weight of the adhesive.

[0055] In one embodiment, the adhesive comprises water .

[0056] The at least one surfactant agent may be selected from a group consisting of anionic surfactant, nonionic surfactant, cationic surfactant, amphoteric surfactant, silicon surfactant, polymeric surfactant, and any combination or mixture thereof. The at least one surfactant agent may be selected from a group consisting of ethoxylates, carboxylates, alcohol alkoxylates, diols, fatty acid esters of polyols / polyhydroxy compounds, siloxanes, and any combination or mixture thereof .

[0057] The surfactant may have the added utility of affecting the kaolin by helping the swelling thereof. The surfactant may further have the added utility of being able to retain water e.g. lessen the dry-out. The surfactant may affect the viscosity of the adhesive.

[0058] In one embodiment, the glue line comprises aluminium in an amount of 0.1 - 2.5 weight-%, or 0.15 - 2 weight-%, or 0.2 - 1.5 weight-%, or 0.25 - 1 weight-%, or 0.3 - 0.55 weight-%, or 0.35 - 0.50 weight-%, or 0.4 - 0.45 weight-%. In one embodiment, the glue line comprises silicon in an amount of 0.1 - 2.5 weight-%, or 0.15 - 2 weight-%, or 0.2 - 1.5 weight-%, or 0.25 - 1 weight-%, or 0.3 - 0.55 weight-%, or 0.35 - 0.50 weight- % , or 0.4 - 0.45 weight-%. The amount of aluminium and of silicon in the glue line may be determined with an Energy-dispersive X-ray spectroscopy (EDS, which may also be abbreviated EDX or XEDS) detector. EDS is an analytical technique that enables the chemical charac- terization / elemental analysis of materials. A sample excited by an energy source (such as the electron beam of an electron microscope) dissipates some of the absorbed energy by ejecting a core-shell electron. A higher energy outer-shell electron then proceeds to fill its place, releasing the difference in energy as an X- ray that has a characteristic spectrum based on its atom of origin. This allows for the compositional analysis of a given sample volume that has been excited by the energy source. The position of the peaks in the spectrum identifies the element, whereas the intensity of the signal corresponds to the concentration of the element. Being able to determine that a glue line of a layered wood product includes aluminium and silicon may be used as an indication of kaolin having been used in the adhesive . In one embodiment, the layered wood product has a shear strength (soaking) of 0.5 - 2.8 N / mm2, or 0.6 - 2.5 N / mm2, or 0.8 - 2.2 N / mm2, as measured in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) . In one embodiment, the layered wood product has a shear strength (boiling) of 0.5 - 2.8 N / mm2, or 0.6 - 2.5 N / mm2, or 0.8 - 2.2 N / mm2, as measured in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) . In one embodiment, the layered wood product exhibits a wood failure (soaking) value of 60 - 100 %, or 70 - 100 %, or 75 - 100 %, or 80 - 100 %, as measured in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) . In one embodiment, the layered wood product exhibits a wood failure (boiling) value of 60 - 100 %, or 70 - 100 %, or 75 - 100 %, or 80 - 100 %, as measured in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) . The adhesive as disclosed in the current specification has the added utility that the use of which for producing a layered wood product may result in the layered wood product exhibiting both shear strength values and wood failure values needed for the layered wood product to be used for further applications.

[0059] The adhesive as disclosed in the current specification has the added utility of exhibiting decreased dry-out phenomenon. The adhesive as disclosed in the current specification has the added utility enabling a long open time to be used during the production of a layered wood product without drying to an adverse extent .

[0060] Using the adhesive as disclosed in the current specification for producing layered wood products has the added utility of resulting in layered wood products exhibiting high shear strength values and high wood failure values.

[0061] EXAMPLES Reference will now be made in detail to the described embodiments , examples of which are illustrated in the accompanying drawings .

[0062] The description below discloses some embodiments in such a detail that a person skilled in the art is able to uti li ze the method based on the di sclosure . Not all steps of the embodiments are discussed in detail , as many of the steps will be obvious for the person skilled in the art based on this specification .

[0063] EXAMPLE 1 - Producing and testing plywood

[0064] In this example different adhesives were prepared and used for producing plywood by gluing together veneers . Phenol-formaldehyde-based binder composition ( PF) or lignin-based binder compositions (LPF500 and LPF650 ) were used in the adhesives prepared .

[0065] In LPF500 , 50 weight-% of the polymeri zable substance used for preparing the lignin-binder composition was lignin ( kraft lignin) while the rest being phenol . In LPF650 , 65 weight-% of the polymeri zable substance used for preparing the lignin-binder composition was lignin ( kraft lignin) while the rest being phenol .

[0066] Formaldehyde was used as the crosslinking agent when producing the binder compositions .

[0067] All the binder compositions were prepared by polymeri zing the crosslinking agent with the polymeri zable substance ( s ) in an aqueous composition under heating .

[0068] The prepared adhesives were then combined with kaolin and some also with a surfactant . The reference samples did not contain any kaolin or surfactant .

[0069] The prepared adhesives were then used to prepare plywood samples by applying the prepared adhesive by a roller and allowing the adhes ive to remain there for a predetermined open time before subj ecting to cold pressing ( 1 N / mm2, 10 min) . The cold pressing was followed by hot pressing. The hot pressing conditions were the following:

[0070] For 7 ply structure: 140 °C, total time of 8 min: 1.0 N / mm2• 3 min + 0.4 N / mm2• 3.5 min + 0.2 N / mm2• 1.5 min) ,

[0071] For 9 ply structure: 130 °C, total time of 10 min: 1.7 N / mm2• 4.5 min + 0.9 N / mm2• 3.5 min + 0.2 N / mm2• 1 min.

[0072] The formed plywood samples were subjected to the following testing:

[0073] - The amount of aluminium and silicon in the glue line was analyzed with an energy-dispersive X-ray spectroscopy (EDS) detector after hot pressing.

[0074] - The pre-tack was evaluated as described above the description .

[0075] - The wood failure (soaking) , the shear strength (soaking) , the wood failure (boiling) , and the shear strength (boiling) were determined in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) .

[0076] Five replicates of each sample were prepared and the average of their results were calculated. The formed samples and their test results are presented in tables 1, 2, and 3.

[0077] Table 1. Prepared samples and their test results

[0078] Table 2 . Prepared samples and their test results

[0079] Table 3 . Prepared samples and their test results

[0080] From the above results one can see that the use of kaolin in the adhesive increased the pre-tack values of all the samples . The addition of the surfactant fur- ther increased the pre-tack values when tested . From the above results one may also see that a very long opentime may be used with the adhesives as disclosed in the current specification without adverse effects on the properties of the produced plywood . The presence of kaol in in the adhes ive can be evidenced by measuring the presence of aluminium and silicon in the glue line .

[0081] It is obvious to a person skil led in the art that with the advancement of technology, the basic idea may be implemented in various ways . The embodiments are thus not limited to the examples described above ; instead they may vary within the scope of the claims .

[0082] The embodiments described hereinbefore may be used in any combination with each other . Several of the embodiments may be combined together to form a further embodiment . An adhesive , a layered wood product , or a use , as disclosed herein, may comprise at least one of the embodiments described hereinbefore . It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item refers to one or more of those items . The term "comprising" is used in this specification to mean including the feature ( s ) or act ( s ) followed thereafter, without excluding the presence of one or more additional features or acts .

Claims

CLAIMS1. An adhesive, wherein the adhesive comprises a binder composition combined with a hardener, wherein:- the hardener comprises kaolin; and- the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive.

2. The adhesive of claim 1, wherein the adhesive comprises kaolin in a total amount of 0.2 - 4 weight-%, or 0.25 - 3 weight-%, or 0.5 - 1.5 weight-%, or 0.7 - 1.0 weight-%, based on the total weight of the adhesive .

3. The adhesive of any one of the preceding claims, wherein the adhesive comprises hardener in a total amount of 0.1 - 50 weight-%, or 0.5 - 30 weight- % , or 1 - 18 weight-%, based on the total weight of the adhesive .

4. The adhesive of any one of the preceding claims, wherein the adhesive comprises the binder composition in a total amount of 50 - 99.9 weight-%, or 60 - 99.7 weight-%, or 70 - 99.5 weight-%, or 82 - 99 weight-%, based on the total weight of the adhesive.

5. The adhesive of any one of the preceding claims, wherein the binder composition is a lignin-based binder composition, which is prepared by polymerizing at least polymerizable substance and crosslinking agent, wherein 50 - 100 weight-%, 60 - 99 weight-%, or 70 - 97 weight-%, or 80 - 95 weight-%, or 85 - 93 weight-%, or 87 - 91 weight-%, of the polymerizable substance originates from lignin.

6. The adhesive of any one of the preceding claims, wherein the hardener, in addition to kaolin, comprises soda, starch, flour, or any combination or mixture of two or more of these.

7. The adhesive of any one of the preceding claims, wherein the adhesive comprises a binder composition combined with a hardener and at least onesurfactant, wherein the adhesive comprises the at least one surfactant in a total amount of up to 0.5 weight-%, or 0.005 - 0.45 weight-%, or 0.01 - 0.4 weight-%, based on the total weight of the adhesive.

8. The adhesive of any one of the preceding claims, wherein the adhesive is an adhesive for a layered wood product.

9. A layered wood product, wherein the layered wood product comprises at least two veneers that are glued together with an adhesive forming a glue line, wherein :- the adhesive comprises a binder composition combined with a hardener;- the hardener comprises kaolin;- the adhesive comprises kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive; and the glue line comprises aluminium in an amount of up to 2.5 weight-% and silicon in an amount of up to 2.5 weight-%.

10. The layered wood product of claim 9, wherein the adhesive comprises kaolin in a total amount of 0.2 - 4 weight-%, or 0.25 - 3 weight-%, or 0.5 - 1.5 weight-%, or 0.7 - 1.0 weight-%, based on the total weight of the adhesive.

11. The layered wood product of any one of claims 9 - 10, wherein the adhesive comprises hardener in a total amount of 0.1 - 50 weight-%, or 0.5 - 30 weight-%, or 1 - 18 weight-%, based on the total weight of the adhesive.

12. The layered wood product of any one of claims 9 - 11, wherein the adhesive comprises the binder composition in a total amount of 50 - 99.9 weight-%, or 60 - 99.7 weight-%, or 70 - 99.5 weight-%, or 82 - 99, based on the total weight of the adhesive.

13. The layered wood product of any one of claims 9 - 12, wherein the binder composition is alignin-based binder composition, which is prepared by polymerizing at least polymerizable substance and crosslinking agent, wherein 50 - 100 weight-%, 60 - 99 weight- %, or 70 - 97 weight-%, or 80 - 95 weight-%, or 85 - 93 weight-%, or 87 - 91 weight-%, of the polymerizable substance originates from lignin.

14. The layered wood product of any one of claims 9 - 13, wherein the hardener, in addition to kaolin, comprises soda, starch, flour, or any combination or mixture of two or more of these.

15. The layered wood product of any one of claims 9 - 14, wherein the adhesive comprises a binder composition combined with a hardener and at least one surfactant, wherein the adhesive comprises the at least one surfactant in a total amount of up to 0.5 weight-%, or 0.005 - 0.45 weight-%, or 0.01 - 0.4 weight-%, based on the total weight of the adhesive.

16. The layered wood product of any one of claims 9 - 15, wherein the glue line comprises aluminium in an amount of 0.1 - 2.5 weight-%, or 0.15 - 2 weight- % , or 0.2 - 1.5 weight-%, or 0.25 - 1 weight-%, or 0.3- 0.55 weight-%, or 0.35 - 0.50 weight-%, or 0.4 - 0.45 weight-% .

17. The layered wood product of any one of claims 9 - 16, wherein the glue line comprises silicon in an amount of 0.1 - 2.5 weight-%, or 0.15 - 2 weight- % , or 0.2 - 1.5 weight-%, or 0.25 - 1 weight-%, or 0.3- 0.55 weight-%, or 0.35 - 0.50 weight-%, or 0.4 - 0.45 weight-% .

18. The layered wood product of any one of claims 9 - 17, wherein the layered wood product is a plywood or a laminated veneer lumber product.

19. The layered wood product of any one of claims 9 - 18, wherein the layered wood product has a shear strength (soaking) of 0.5 - 2.8 N / mm2, or 0.6 - 2.5 N / mm2, or 0.8 - 2.2 N / mm2, as measured in accordancewith standards in accordance with standards SFS-EN 314- 1 (2005) and SFS-EN 314-2 (1993) .

20. The layered wood product of any one of claims 9 - 19, wherein the layered wood product has a shear strength (boiling) of 0.5 - 2.8 N / mm2, or 0.6 - 2.5 N / mm2, or 0.8 - 2.2 N / mm2, as measured in accordance with standards in accordance with standards SFS-EN 314- 1 (2005) and SFS-EN 314-2 (1993) .

21. The layered wood product of any one of claims 9 - 20, wherein the layered wood product exhibits a wood failure (soaking) value of 70 - 100 % , or 75 - 100 % , or 80 - 100 % , as measured in accordance with standards in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) .

22. The layered wood product of any one of claims 9 - 21, wherein the layered wood product exhibits a wood failure (boiling) value of 70 - 100 % , or 75 - 100 % , or 80 - 100 % , as measured in accordance with standards in accordance with standards SFS-EN 314-1 (2005) and SFS-EN 314-2 (1993) .

23. Use of kaolin for decreasing dry-out of an adhesive during the production of a layered wood product, by combining kaolin as hardener with a binder composition to prepare the adhesive comprising kaolin in a total amount of 0.1 - 5 weight-% based on the total weight of the adhesive.

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