Hardener component and adhesive composition for use in manufacturing of structural timber products

Abstract

Disclosed is a water-based hardener component and adhesive composition includes a hardener component, and adhesive component and 10-60 wt% of water. The hardener component includes a 4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, the first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof, and 0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8-2.4, the second acid is at least one selected from pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof. The adhesive component includes a resin having a functional amino groups. The water-based hardener component and adhesive composition is used for structural timber product.

Description

[0001] HARDENER COMPONENT AND ADHESIVE COMPOSITION FOR USE IN MANUFACTURING OFSTRUCTURAL TIMBER PRODUCTS

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This patent application claims priority from a Sweden Patent Application Ser. No. 2450332-8 that was filed on March 26, 2024 and entitled: “HARDENER COMPONENT AND ADHESIVE SYSTEM FOR USE IN MANUFACTURING OF STRUCTURAL TIMBER PRODUCTS’, which is hereby incorporated herein by reference in its entirety.

[0004] BACKGROUND OF THE INVENTION

[0005] 1 . Field of the Invention

[0006] The present application generally relates to a hardener component and adhesive composition, and more particularly relates to a water-based hardener component and adhesive composition for use in structural timber productions.

[0007] 2. Description of Related Art

[0008] When producing structural timber products, e.g. laminated beams, for load bearing wood constructions melamine-based amino resins, melamine-form aldehyde (MF) and melamine-urea- formaldehyde (MUF) resins, are commonly used. Various types of adhesive systems / compositions are known to include usage of an amino based resin together with aliphatic alpha- hydroxy- mono or di carboxylic acid.

[0009] The melamine-based amino resins give light-colored joints in contrast to phenolic- based resins such as phenol-formaldehyde- or phenol-resorcinol-form aldehyde resins and may also avoid using a hardener component based on pure formaldehyde as used in phenol-resorcinol- formaldehyde adhesives.

[0010] The melamine urea formaldehyde and urea formaldehyde-based amino resins are often used in furniture manufacturing together with strong acids with low or even very low pKa as a hardener. Furniture manufacturing may withstand usage of stronger acids as it causes damages on the wood but may not cause any danger for the construction. The load bearing wood construction refers to structural element of wood that has been designed to support its own dead load in addition to the weight of other structural and non-structural elements. For example, load bearing wood construction is a structural timber product.

[0011] It would be readily apparent to those skilled in the art that various form of timber may be envisioned such as cross-laminated timber without deviating from the scope of the present invention. The cross-laminated timber refers to several layers of solid wood panels bonded with a structural adhesive at alternating right angles.

[0012] Acid damage on wood is caused due to stronger acids. The stronger acids are negative for structural timber products. These products are meant to withstand heavy weight and be used for many years as well as be exposed to direct contact with water and / or very high humidity.

[0013] Strong acids are not feasible to use in structural timber products today, as it is in e.g. furniture manufacturing. Therefore, there is a need of a hardener based component and adhesive composition having combination of a weak acid, a strong acid and water that increases the bonding performance and inhibits deterioration of wood.

[0014] SUMMARY OF THE INVENTION

[0015] In accordance with teachings of the present invention is to provide a water-based hardener component and adhesive composition for use in structural timber productions.

[0016] An object of the present invention is to provide a water-based hardener component and adhesive composition having a hardener component, an adhesive component, and 10-60 wt% of water. The hardener component includes 4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, and 0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8-2.4.

[0017] The first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof. The second acid is at least one selected from pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof. The adhesive component includes a resin having a functional amino groups. The resin is at least one selected from a Melamine-urea-formaldehyde (MUF) resin, melamine- formaldehyde-resin (MF), glyoxal-formaldehyde-melamine-resin, glyoxal- formaldehyde-urea-melamine-resin, or a combination thereof.

[0018] In one aspect of the present invention, the adhesive component resin comprising 0.001 -1.0% free formaldehyde. The resin further includes 15- 60 wt.% of melamine and 45-80 wt.% of dry content.

[0019] In one aspect of the present invention is to provide 5-50 wt% of one or more additives. Further, the hardener component has a conductivity of 10000-46000 pS / cm. Further, the water-based hardener component and adhesive composition has a conductivity of 4000-25000 pS / cm. Further, mixing ratio between the adhesive component and the hardener component is in the interval of from 100:20 to 100:200 parts per weight.

[0020] In one aspect of the present invention is to provide the first acid is at least one selected from citric acid, a tartaric acid, or a combination thereof, wherein the second acid is at least one selected from nitric acid, hydrochlorid acid, sulfuric acid, oxalic acid or a combination thereof.

[0021] In one aspect of the present invention is to provide a method for manufacturing of a structural timber product. The method provides step to apply the adhesive component and the hardener component on at least one side of each of wooden pieces, contacting the side of a wooden piece with the side of another wooden piece thereby forming a sandwich structure of wooden pieces with the adhesive component and the hardener component forming an adhesive layer between the wooden pieces, and pressing the sandwich structure together to join the at least two wooden pieces and thus creating a glued product of wooden pieces forming a structural timber product.

[0022] In one aspect of the present invention is to provide the hardener component is provided by first mixing the first acid with the second acid in situ. Further, the pressing is performed using radio frequency pressing. In one aspect of the present invention is to provide a structural timber product having at least two wooden pieces, an intermediate adhesive layer to combine the at least two wooden pieces. The adhesive component and the hardener component is provided with 40-70 wt % of water. In one aspect of the present invention, the method is used to glue wooden pieces, such as wooden lamellae, forming structural timber products, such as laminated beam. Laminated beams passing the test EN 301 are produced by the method as disclosed herein. The structural timber product may comprise at least two wooden pieces to form a structural timber product.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 illustrates a schematic diagram of a structural timber product, in accordance with a preferred embodiment of the present invention.

[0025] DETAILED DESCRIPTION OF DRAWINGS

[0026] While this technology is illustrated and described in a preferred embodiment, a waterbased hardener component and adhesive composition may be produced in many different configurations, formulations and materials. There is depicted in the drawings, and will herein be described in detail, as a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and the associated functional specifications for its manufacturing, and is not intended to limit the invention to the embodiment illustrated. Those skilled in the art will envision many other possible variations within the scope of the technology described herein.

[0027] It is intended throughout the present description that the expression “adhesive composition / system” embraces a combination of an adhesive, i.e. a curable resin (a glue), and a hardener for curing the resin. The adhesive composition / system as disclosed herein is suitable for gluing wood.

[0028] Acids are known to be defined in “pKa”. In the present application, pKa values are defined. The pKa value corresponds to the pH value when the acid has dissociated to 50%. Strong acids such as sulfuric acid (pKa -2.8), are almost completely protolyzed in aqueous solution and thus have low pKa values, while weak acids, such as acetic acid (pKa 4.76), are only partially protolyzed and have a higher pKa value.

[0029] In the present application the term “strong acid” means an acid having a pKa value in the range of 0.8-2.4. In the present application the term “weak acid” means an acid having a pKa value in the range of 2.5-10. In the present application the term “very strong acid” has a pKa value below 0.8.

[0030] In the present application the term “structural timber products” refers to timber used or intended for use in a loadbearing capacity in e.g. buildings where the strength of the timber is the primary consideration.

[0031] FIG. 1 illustrates a schematic diagram of a structural timber product 100, in accordance with a preferred embodiment of the present invention. The structural timber product 100 includes at least two wooden pieces 102a, 102b, and an intermediate adhesive layer 104 to combine the at least two wooden pieces 102a, 102b.

[0032] The intermediate adhesive layer 104 includes a hardener component, an adhesive component, and water. The hardener component includes 4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10 and 0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8-2.4.

[0033] The first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof. The second acid is at least one selected from pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof.

[0034] The adhesive component includes resin having a functional amino groups, and 10-60 wt% of water. The term “resin” means a synthetic adhesive that is derived from melamine-urea-formaldehyde (MUF), melamine-formaldehyde (MF), glyoxal- formaldehyde-melamine-resin or glyoxal-formaldehyde-urea-melamine-resin or a combination thereof. In one embodiment of the present invention, mixing ratio between the adhesive component and the hardener component is in the interval of from 100:20 to 100:200 parts per weight. Further in one embodiment, the adhesive component having functional amino groups and the hardener component are mixed in situ.

[0035] The term “resin comprising functional amino groups” relates to a resin exhibiting functional amino groups. For more clarification, the resin exhibits functional amino or amino groups. For example, an epoxide does not exhibit functional amino groups. The term “parts per weight” means parts of mass. Further, the terms “weight%” and “wt%” are same and hereinafter are used interchangeably throughout the specification.

[0036] The water-based hardener component and adhesive composition as disclosed herein is used to join structural timber products. The adhesive component according to the present invention comprises includes a resin comprising functional amino groups and the hardener component includes at least one weak acid and at least one strong acid and are mixed in water.

[0037] In an embodiment of the present invention, the water-based hardener component and adhesive composition includes 5-50 wt% of one or more additives. Examples of the additives include but not limited to polyvinyl alcohol, starch, PVAc dispersion, SBR latex, kaolin, fume silica, cellulose and / or glycol. It would be readily apparent to those skilled in the art that additives are used as a colouring agent, thickening agent, and a rheology modifier.

[0038] It would be readily apparent to those skilled in the art that the first acid may be envisioned as a weak acid, a mineral acid, a volatile acid, without deviating from the scope of the present invention. Further, the first acid may be envisioned as a nonvolatile acid such as glycolic acid, malic acid, and tartaric acid by skilled in the art, without deviating from the scope of the present invention.

[0039] Further the first acid is at least one selected from citric acid, a tartaric acid, or a combination thereof, wherein the second acid is at least one selected from nitric acid, hydrochlorid acid, sulfuric acid, or a combination thereof.

[0040] In one embodiment, the hardener component constitutes 4-35 wt.% of the at least one first acid and 0.05-15 wt.% of the at least one second acid. It would be readily apparent to those skilled in the art that various types of second acid may be envisioned as organic and strong acid without deviating from the scope of the present invention. Further, the strong acid is used as a booster of the adhesive component.

[0041] In one embodiment, the hardener component has a conductivity in range of 10000- 46000 pS / cm, and the water-based hardener component & adhesive composition has a conductivity in range of 4000-25000 pS / cm. The conductivity enables that the waterbased hardener component & adhesive composition hardener component is cured using radio frequency (RF) pressing. The term “conductivity” is a measure of a material's ability to conduct electricity and heat. The hardener component includes a weak acid and a strong acid that enables the adhesive component to be cured using radio frequency pressing (reduce risk of damages to the wooden surface).

[0042] Radio frequency pressing may be performed using a pressure of 8-12 kg / cm2, such as about 10 kg / cm2. Pressing may be performed during 30-300 seconds, such as about 50 seconds. Temperature in the adhesive layer during pressing depends on the conductivity of the hardener component and preferably also the adhesive system. The amount of water-based hardener and adhesive composition is applied in the manufacturing of a structural timber product may be in the range of 200-400 g / m2, such as preferably 250-300 g / m2.

[0043] The hardener component having a conductivity of 10 000-46 000 pS / cm is well suited for curing an adhesive component having a resin comprising functional amino groups, such as for example a formaldehyde based resin or a formaldehyde free resin. A hardener component having a conductivity of about 10000-46 000 pS / cm is well suited for curing an adhesive component having low or even no amount of formaldehyde.

[0044] In one embodiment, the resin is at least one selected from a Melamine-urea- formaldehyde (MUF) resin, melamine-formaldehyde-resin (MF), glyoxal- formaldehyde-melamine-resin, glyoxal-formaldehyde-urea-melamine-resin, or a combination thereof. The resin constitutes low amount of formaldehyde, such as in range of 0.001-1.0% free formaldehyde, preferably the resin 0.001 % of free formaldehyde.

[0045] Melamine-urea-formaldehyde resin (MUF) is poly-condensation products of the reaction of formaldehyde with urea and melamine. Melamine-formaldehyde resin (MF) is poly-condensation products of formaldehyde with melamine. These resins have high water and weather resistance (classified as not dangerous) and therefore are suitable for the production of structural timber products.

[0046] Further, MUF / MF / glyoxal-MF / glyoxal-MUF resins are based on the reaction of chemical compounds containing primary or secondary amino groups i.e. -NH2 or - NH with aldehydes. Due to more stringent formaldehyde emission regulations, MUF / MF / glyoxal-MF / glyoxal-MUF resins with higher percent of melamine and less amount of formaldehyde are becoming the main resin for structural timber products. Very low or Formaldehyde free adhesive component, together with the hardener component presented in this invention facilitates curing with sufficient speed.

[0047] It would be readily apparent to those skilled in the art that the adhesive component may be envisioned in either as powder form and mixed with water to form workable adhesive, without deviating from the scope of the present invention. The resulting water-based hardener component and adhesive composition has a high bond strength, very good water resistance, and a good heat resistance.

[0048] In the present application the term “bond strength” is measured as fibre tear and delamination. The term “delamination” refers to failure of the adhesive system because of the joint opening and the term “fibre tear” refers to tear of wood fibre, rather than tear of adhesive system.

[0049] The function of the water-based hardener component and adhesive composition is to bond two wooden pieces together which is achieved through surface attachment between the water-based hardener component and adhesive component and the wooden pieces. The physicochemical process resulting in this interfacial bonding is explained as an adhesion.

[0050] Adhesion is a phenomenon where two substrates are bonded together through their surfaces by interm olecular forces. Considering the adhesion of MUF / MF / glyoxal- MF / glyoxal-MUF wood adhesives, the adsorption is most dominating. According to this theory, the adhesion between an adhesive system and a wood substrate is caused by secondary forces between the molecules present in the two materials.

[0051] It has been shown that van der Waals forces, electrostatic interactions and hydrogen bonds all contribute to the adhesion. The adhesion occurs through penetration of the adhesive into the pores and cavities of the wood surface. For thermosetting of MUF / MF wood adhesives it is desirable to achieve a certain degree of adhesive penetration into the substrate since the hardening of the adhesive in the cavities is to enhance the strength of the glue joint. The covalent chemical bonding, which states that a reaction between the MUF / MF / glyoxal-MF / glyoxal-MUF adhesive and the wood substrate results in formation of chemical bonds between the two, has shown to be relevant for this type of adhesives. The final properties of the water-based hardener component & adhesive composition such as curing time, water resistance and storage stability are very important for production / manufacturing of structural timber products. In an embodiment, the stability of the hardener component refers to a stable hardener. The stability hardener is a hardener (acids and additives / thickeners) that have a long shelf life (at least 2 months). A “not stable” hardener does not have a long shelf life. It can be due to the fact that the acids and additives / thickeners have reacted with each other, or the acids have a negative impact on the additives / thickeners.

[0052] A way to harden the MUF / MF / glyoxal-MF / glyoxal-MUF resin is by lowering the pH, then the resin reacts and harden on its own. The weak acid especially for MUF / MF / glyoxal-MF / glyoxal-MUF resin with low amount of free formaldehyde results hardening of resin on its own. The strong acid makes the MUF / MF / glyoxal-MF / glyoxal- MUF resin low in pH fast and harden fast.

[0053] However, the strong acid results in causing damages to the wood. Also, as these acids are usually added with additives / thickeners before being mixed in the adhesive. Further, the strong acid makes the blend of acid and additives / thickeners unstable and thus the adhesive has a short shelf life. Thus, the water-based hardener component and adhesive composition constitutes very strong acid is not suitable to be used in structural timber products and might not pass the norm / certification.

[0054] The weak acid is the “main catalyst”. The strong acid acts as a “catalyst for the main catalyst”, giving the weak acid a boost in effectiveness. The strong acid helps lowering the pH quickly and then the weak acid continues to help the resin having functional amino groups, such as MUF / MF / glyoxal-MF / glyoxal-MUF resin, to react and harden. The weak acid used evaporate from the glued wooden product over time, but the strong acid stays, and thus evaporation does not negatively affect the glued wooden product during the life-time of the glued wooden product. It was surprising to find that the combination of a small amount of strong acid and a weak acid provides a fast, strong, non-damaging and norm-passing adhesive system for structural timber products.

[0055] In an embodiment of the present invention, the method for the manufacturing of a structural timber product initiates with the step of providing a hardener component comprising a 4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, the first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof, and a 0.05-10 wt.% of at least one second acid with a pKa in the interval of 0.8-2.4, the second acid is at least one selected from , pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), , hypophosphorous acid (H3PO2), , phosphoric acid (H3PO4), or a combination thereof.

[0056] The above step is then followed by a step of providing an adhesive component comprising a resin having a functional amino groups, 40-70 wt% of water and at least two wooden pieces. The above step is then followed by a step of applying the adhesive component and the hardener component on at least one side of each of the wooden pieces. The resin contains 0.001-1.0% wt.% of free formaldehyde, 15-60 wt.% of melamine and 45-80 wt.% of dry content. The resin is at least one selected from a Melamine-urea-formaldehyde (MUF) resin, melamine-formaldehyde-resin (MF), glyoxal-formaldehyde-melamine-resin, glyoxal-formaldehyde-urea-melamine-resin, or a combination thereof.

[0057] The above step is then followed by a step of contacting the side of a wooden piece with the side of another wooden piece thereby forming a sandwich structure of wooden pieces with the adhesive component and the hardener component forming an adhesive layer between the wooden pieces, and a step of pressing the sandwich structure together to join the at least two wooden pieces and thus creating a glued product of wooden pieces forming a structural timber product.

[0058] In one embodiment, the method further includes a step of mixing the first acid with the second acid in situ. Further, the step of pressing is performed using radio frequency pressing. The term “radio frequency pressing” refers to a curing technique for heating glue lines in wood-to-wood joints. The radio frequency pressing is the same as radio frequency curing.

[0059] In order to bond wood substrates with short pressing time, radio frequency pressing produces a very rapid and uniform rise in temperature. Curing / hardening is a necessary procedure for the formation of bonding strength for the adhesive system. Curing may occur even after press step. Curing of the adhesive component is the choice of acid(s) in the hardener component. When the water-based hardener component and adhesive composition is applied to a wooden surface, the amount of functional amino groups is reduced due to crosslinking during curing. It would be readily apparent to those skilled in the art that various types of pressing techniques may be envisioned such as cold press or heated chamber using hydraulic press, hydraulic press with radio frequency, without deviating from the scope of the present invention.

[0060] In an embodiment, the hardener component is provided by applying the at least one first acid and the at least one second acid separately. Thus, the adhesive component is provided as a three component. The adhesive component together with the hardener component provided as two acids.

[0061] In one embodiment, there are two strings applied onto a wooden piece at the same time (one string adhesive component, one string hardener component), but separate from each other. With pressure applied the strings mix. The hardener component is provided as a mix or blend, thus the weak acid and the strong acid are already mixed. There is no specified time limit. The hardener component does not harden without the adhesive component and vice versa. This is a two-component adhesive system (one adhesive component and one hardener component).

[0062] In one embodiment, the adhesive system is applied as a three-component adhesive system. In this example, the weak acid and the strong acid are provided separately. Thus, the hardener component contains two parts- one part comprising a weak acid and one part comprising a strong acid. The two parts of the hardener component are applied separately, e.g. in separate strings. The three-component adhesive system is preferred to avoid having the hardener component containing only a strong acid, in direct contact with the wood in order to avoid any possible damages to the surface. If the application requires a three-component adhesive system, it is preferred to apply the strong acid as the last component, on top of the other components.

[0063] In one embodiment, the weak acid may be applied onto a wooden piece, such as a wooden substrate and wooden lamellae; before the strong acid. Thus, the wooden piece is protected and less damaged to the wooden piece occurs. The water-based hardener component and adhesive composition may be applied on at least one side of a wooden piece or may also be applied on all sides of the wooden piece (e.g. wooden composites such as particle board materials).

[0064] In one embodiment, the water-based hardener component and adhesive composition allows manufacturing of structural timber products to reach high productivity by providing shorter press times and lower press temperatures ultimately resulting in decreasing the energy.

[0065] In one embodiment, the water-based hardener component and adhesive composition may be applied using a brush, roller, curtain, ribbon, or a mixture of thereof. In one embodiment, the water-based hardener component and adhesive composition is used to glue wooden pieces, such as wooden lamellae, forming structural timber products, such as laminated beam. Laminated beams passing the test EN 301 are produced by the method as disclosed herein. The structural timber product may comprise at least two wooden pieces to form a structural timber product.

[0066] EN 301 is a European standard / norm and a requirement for adhesives intended for the use in structural timber products, for example MUF / MF. The norm uses determination of resistance to delamination of wood construction in its evaluation. This standard specifies delamination methods for continuous quality control of the glue line integrity of structural timber products glued with MUF / MF. Max allowed delamination is 5%.

[0067] 3%, or lower, delamination is considered very good as this gives the safety of being well under the limit. Safety is the most important thing when it comes to structural timber products. Glued products not fulfilling the requirements may lead to collapse when exposed to heavy load. Having a very good result is therefore very advantageous as this gives you a “safety buffer” that it is even lower than the required limit. To test whether a product fulfils EN 301 a test regarding the standard EN 391 B may be performed.

[0068] The structural timber product may have a delamination of < 5 %, such as < 3 %. The structural timber product may have a fibre tear of > 70%, such as > 80 %. The structural timber product may have a delamination of < 5 % and a fibre tear of > 70 %. In an embodiment, the wooden piece in a structural timber product is wooden lamellae, in the form of either a wooden board or a wooden substrate or a laminated beam. The individual wooden piece may have a thickness of from 0.5 cm to 5 cm, such as from 20 mm to 40 mm, or such as from 25 mm to 35 mm.

[0069] The individual wooden piece may have a length of from 2 m to 30 m. The wooden pieces may either be spruce, pine or other wood type. It would be readily apparent to those skilled in the art that various size and form of wooden piece may be envisioned without deviating from the scope of the present invention.

[0070] EXAMPLES

[0071] Example 1 - Hardener components with different acids together with adhesive components comprising formaldehyde or no formaldehyde

[0072] In this example 12 different hardener compositions are used in water-based hardener & adhesive composition with either a melamine-urea-formaldehyde (MUF) resin with free formaldehyde < 0.1 % or with a melamine-urea-glyoxal (formaldehyde-free) resin. Besides acids (as described below) the hardener compositions contain additives. The compositions are water-based.

[0073] Hardener composition No. 1

[0074] 15% weight glycolic acid, 6% weight phosphoric acid, 24.5% weight additives and 54.5% weight water.

[0075] Hardener composition No. 2

[0076] 12% weight formic acid, 6% weight phosphoric acid, 24.5% weight additives and 57.5% weight water.

[0077] Hardener composition No. 3

[0078] 12% weight malic acid, 6% weight phosphoric acid, 24.5% weight additives and 57.5% weight water.

[0079] Hardener composition No. 4 12% weight tartaric acid, 6% weight phosphoric acid, 24.5% weight additives and 57.5% weight water.

[0080] Hardener composition No. 5

[0081] 10% weight citric acid, 5% weight sulfuric acid, 24.5% weight additives and 60.5% weight water.

[0082] Hardener composition No. 6

[0083] 8 weight% para toluene sulfonic acid (PTSA), 6% weight phosphoric acid, 24.5% weight additives and 61.5% weight water.

[0084] Hardener composition No. 7

[0085] 12% weight formic acid, 6% weight sulfuric acid, 24.5% weight additives and 57.5% weight water.

[0086] Hardener composition No. 8

[0087] 12% weight formic acid, 6% weight nitric acid, 24.5% weight additives and 57.5% weight water.

[0088] Hardener composition No. 9

[0089] 12% weight formic acid, 6% weight hydrochlorid acid, 24.5% weight additives and 56.5% weight water.

[0090] Hardener composition No. 10

[0091] 10% weight oxalic acid, 6% weight phosphoric acid, 24.5% weight additives and 59.5% weight water.

[0092] Hardener composition No. 12

[0093] 30% weight formic acid, 24.5% weight additives and 45.5% weight water.

[0094] Each hardener composition (1 -10) was combined with a <0.1 % melamine-urea- formaldehyde (MUF) resin with free formaldehyde and 22% melamine content and having 65% weight dry content. Hardener compositions 2 (noted as No 11 and 12 in Table 1 ) are also combined with a melamine-urea-glyoxal resin (formaldehyde free) with melamine content 24% and having 67% weight dry content.

[0095] The melamine-urea-formaldehyde resin / melamine-urea-glyoxal resin and the hardener compositions were separately applied, in a mixing ratio of 1 : 1 , on 100 cm x 16 cm pieces of spruce and an amount of 280 g / m2 of adhesive component was used. Thereafter, laminated beams are formed from the pieces (5 lamellae and 4 joints each beam), the closed assembly time was 10 minutes, and the lamellae was pressed at a temperature of 20°C, a pressure of 0.8-1 .0 MPa for 50 min. 24 hours after curing time the beams were tested for delamination according to the EN 391 B standard test.

[0096] The results are shown in the following Table 1. The limits are defined as:

[0097] “Very good”: Fiber tear: > 80 % and Delamination: < 3%

[0098] "Good": Fiber tear: > 70 % and Delamination: < 5%

[0099] “Bad”: Fiber tear: > 50 % and Delamination: > 10 %

[0100] “Very bad: Fiber tear: <50 % and Delamination: > 20 %

[0101] Max allowed delamination is 5%. 3% or lower delamination is considered very good as this gives the safety of being well under the limit. Having a very good result is advantageous as this provides a “safety buffer” that it is even lower than the required limit. Hardener compositions being good are well suited to be used in structural timber products. Hardener compositions being very good is very well suited to be used in structural timber products.

[0102] Table 1

[0103]

[0104] Hardener compositions 1 , 2, 3, 4, and 11 fulfils the requirements of EN 391 B. This standard specifies delamination methods for continuous quality control of the glue line integrity of load bearing wood constructions glued with MUF in this case.

[0105] Hardener components constitutes very strong acids, e.g. compositions 5, 6, 7, 8 and 9 do not pass the EN 391 B standard since the very strong acid has a negative impact on the wood, for example the wood decomposes. Hardener composition constitutes two strong acids, e.g. composition 10, does not pass the EN 391 B standard since the strong acids have a negative impact on the wood.

[0106] Hardener compositions 1 , 2, 3, 4 comprises one weak acid and one strong acid and fulfils the standard EN 391 B and are thus suitable for being used in structural timber products. By combining a strong acid and a weak acid the amount of strong acid may be reduced and thus provide a good work environment.

[0107] Hardener composition 11 comprises one weak acid and one strong acid and is tested with a melamine-based resin without any formaldehyde and the adhesive system passes the standard EN 391 B.

[0108] Besides testing whether the compositions meet the requirements of the standard EN 391 B the stability of the hardener compositions were tested. The hardener compositions in tests 1 , 2, 3, 4, 7, 8, 10, 11 and 12 are stable. Thus, these compositions have a shelf life of at least 2 months. There is no correlation between stability and the result (pass or not pass). The norm could still be reached with a “not stable” hardener, it only has to be used quickly enough so that is has not been “destroyed” and no longer effective, due to its instability. Hardener compositions 1 , 2 and 3 are both stable and meets the standard EN 391 B with very good results.

[0109] Example 2

[0110] In this example 2 different hardener compositions are used in an adhesive system together witha melamine-urea-formaldehyde (MUF) resin with free formaldehyde 0.4 %. Hardener composition no 13 and no 14 corresponds with the hardener compositions no. 1 and no. 2 in Example 1.

[0111] Each hardener composition was combined with a melamine-urea-formaldehyde (MUF) resinwith free formaldehyde 0.4 % and melamine content 22% and having 65 weight% dry content. The melamine-urea-formaldehyde resin and the hardener compositions were separately applied, in a mixing ratio of 1 : 1 , on 100 cm x 16 cm pieces of spruce and an amount of 280 g / m2of adhesive system was used.

[0112] Thereafter laminated beams were formed from the pieces (5 lamellae and 4 joints each beam), the closed assembly time was 10 minutes, and the lamellae were pressed at a temperature of 20°C, a pressure of 0.8-1.0 MPa for 50 min. 24 hours after curing time the beams were tested for delamination according to the EN 391 B standard test. The results are shown in Table 2.

[0113] Table 2

[0114] The results in Example 2 corresponds with the results in Example 1. A MUF resin comprising 0.4 % formaldehyde gives the same result as a MUF resin comprising less than 0.1 % formaldehyde.

[0115] Example 3

[0116] In this example 5 different hardener compositions are used in an adhesive system together with a m elam ine-urea-form aldehyde (MUF) resin with free formaldehyde < 0.1 % or 0.4 %. All hardener compositions comprise at least one strong acid and at least one weak acid.

[0117] Hardener composition No. 15

[0118] 15% weight organic acid (glycolic acid), 6% weight mineral acid (phosphoric acid), 24.5% weight additive and 54.5% weight water.

[0119] Hardener composition No. 16

[0120] 12% weight organic acid (formic acid), 6% weight mineral acid (phosphoric acid), 24.5% weight additive and 57.5% weight water. Hardener composition No. 17

[0121] 12% weight organic acid (malic acid), 6% weight mineral acid (phosphoric acid), 24.5% weight additive and 57.5% weight water.

[0122] Hardener composition No. 18

[0123] 12% weight organic acid (tartaric acid), 6% weight mineral acid (phosphoric acid), 24.5% weight additive and 57.5% weight water.

[0124] Hardener composition No. 19

[0125] 10% weight organic acid (citric acid), 5% weight mineral acid (sulfuric acid), 24.5% weight additive and 60.5% weight water.

[0126] Hardener composition (15, 16, 17, 18, 19 respectively) was combined with a melamine- urea-form aldehyde (MUF) resin with < 0.1 % free formaldehyde and 22% melamine content and having 65% weight dry content. In an additional test, hardener composition 16 was combined with a melamine-urea-formaldehyde (MUF) resin with 0.4% free formaldehyde and 22% melamine content and having 65% weight dry content. The melamine-urea-formaldehyde resin and the hardener compositions were separately applied, in a mixing ratio of 1 : 1 , on 100 cm x 16 cm pieces of spruce and an amount of 280 g / m2 of adhesive system was used. Thereafter laminated beams were formed from the pieces (5 lamellae and 4 joints each beam), the closed assembly time was 10 minutes, and the lamellae were pressed at a temperature of 20°C, a pressure of 0.8-1 .0 MPa for 50 min. 24 hours after curing time the beams were tested for delamination according to the EN 301 standard test.

[0127] The results are shown in Table 3. Table 3

[0128] The results in Table 3 show that water-based hardener and adhesive composition constitutes an adhesive component having a resin comprising functional amino groups. In this case MUF with low amount of formaldehyde (< 0.1 % and 0.4% respectively) and a hardener component having at least one strong acid and at least one weak acid provides a suitable adhesive system to be used in structural timber products since it meets the requirements of EN 391 B with good or even very good result.

[0129] Example 4 - Radio frequency pressing

[0130] In this example 4 adhesive components are tested where gluing / curing is performed using radio frequency. The adhesive component is a melamine urea formaldehyde (MUF) resin with < 0.1 % formaldehyde.

[0131] Hardener composition No. 21

[0132] 30% weight formic acid, 24.5% weight additive and 45.5% weight water.

[0133] Hardener composition No. 22

[0134] 30% weight formic acid, 24.5% weight additive and 45.5% weight water.

[0135] Hardener composition No. 23

[0136] 13% weight formic acid, 1 % weight phosphoric acid, 24.5% weight additive and 61.5% weight water.

[0137] Hardener composition No. 24

[0138] 13% weight formic acid, 3% weight phosphoric acid, 24.5% weight additive and 59.5% weight water.

[0139] Information about the gluing process:

[0140] • Press type radio frequency- press

[0141] • Wood moisture content: about 8% Spruce lamellaes 300x30 mm

[0142] • Generator: 8 kW

[0143] • Effect: 3 kV

[0144] Assembly times before pressing: 4 min • Glue+ hardener spreading amount: 280 g / m2

[0145] • Pressure: 10 kg / cm2

[0146] The results are shown in Table 4.

[0147] Table 4

[0148] Higher conductivity needs to be reached in order for the adhesive system to be normpassing when using radio frequency pressing. Adding more formic acid does not result in an increase in conductivity as these weaker acids have a limit. Adding a strong acid in high amounts will increase the conductivity significantly but will result in other negative effects such as a high risk of wood surface damage.

[0149] It is noted that hardener compositions No 23 and 24 are well suited to be used with MUF resins. The hardener compositions No 23 and 24 combined with a MUF resin is cured using radio frequency pressing and provide an adhesive system passing the EN 391 B standard test and thus are suitable for structural timber products.

[0150] Example 5 - Reference example

[0151] As a reference example, epoxy resin was used in an adhesive composition. A hardener component comprising glycolic acid (weak) and phosphoric acid (strong) was used. The test was performed in the same manner as in Example 1. The result is shown in Table 5.

[0152] Table 5

[0153] An adhesive composition using an epoxy resin together with a hardener component comprising a strong acid and a weak acid will not pass the norm EN 391 B. The mix of epoxy resin and hardener component (with a strong acid and a weak acid) is still in a liquid form and will not provide an adhesive system. To summarize, an adhesive system comprising epoxy resin cannot not be used for load bearing wood constructions.

[0154] The aim of different examples was to demonstrate how variations in acids in the hardener particularly the use of first and secondary acid with different pKa values, influence the bonding results. The key observations are summarized as follows:

[0155] Effect of pKa on Bonding Performance:

[0156] Combination of Very strong acids with low pKa values <0.8 and weak acid failed to meet the required performance standards.

[0157] Consistency in Variables: To ensure the results were solely dependent on the choice of acids quality, other variables were held constant, such as Water content and Additive levels

[0158] High-Frequency Testing Observations:

[0159] In high-frequency tests, we evaluated the impact of conductivity across samples while keeping press times constant. The results showed that variations in conductivity, driven by the choice of acids, had a clear and measurable impact on bonding outcomes.

[0160] Conclusion:

[0161] The study highlights that the choice of acids with different pKa their resulting conductivity play significant roles in determining bonding performance and storage time of the water based hardener.

[0162] The present invention offers various advantages such as reducing harmful formaldehyde. Further, the present invention offers better bond quality without losing productivity. Further, the present invention offers melamine-urea-glyoxal resin.

[0163] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. One skilled in the art will appreciate that many variations are possible within the scope of the claims. Thus, while the disclosure is particularly shown and described above, it will be understood by those skilled in the art that these and other changes in form and details may be made therein without departing from the spirit and scope of the claims.

Claims

CLAIMS OF THE INVENTIONCLAIM 1. A water-based hardener component and adhesive composition comprising: a hardener component comprising:4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, the first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof; and0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8- 2.4, the second acid is at least one selected from pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof; and an adhesive component comprising a resin having a functional amino groups; and10-60 wt% of water.CLAIM 2. The water-based hardener component and adhesive composition according to claim 1 further comprising 5-50 wt% of one or more additives.CLAIM 3. The water-based hardener component and adhesive composition according to claim 1 having a conductivity of 4000-25000 pS / cm, and wherein the hardener component has a conductivity of 10000-46000 pS / cm.CLAIM 4. The water-based hardener component and adhesive composition according to claim 1 wherein the resin is at least one selected from a Melamine-urea- formaldehyde (MUF) resin, melamineformaldehyde-resin (MF), glyoxal-formaldehyde- melamine-resin (glyoxal-MF), glyoxal-formaldehyde-melamine-urea-resin (glyoxal- MUF), glyoxal-melamin-resin, glyoxal melamine urea resin, glyoxal melamine urea derivative resin, or a combination thereof.CLAIM 5. The water-based hardener component and adhesive composition according to claim 4, wherein the resin having 0.001-1.0% free formaldehyde.CLAIM 6. The water-based hardener component and adhesive composition accordingto claim 1 , wherein mixing ratio between the adhesive component and the hardener component is in the interval of from 100:20 to 100:200 parts per weight.CLAIM 7. The water-based hardener component and adhesive composition according to claim 4, wherein the resin further having15-60 wt.% of melamine and 45-80 wt.% of dry content.CLAIM 8. The water-based hardener component and adhesive composition according to claim 1 wherein further the first acid is at least one selected from citric acid, a tartaric acid, or a combination thereof, wherein the second acid is at least one selected from nitric acid, oxalic acid, hydrochloric acid, sulfuric acid, or a combination thereof.CLAIM 9. A method for the manufacturing of a structural timber product, the method comprising: providing a hardener component comprising a 4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, the first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof, and a 0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8-2.4, the second acid is at least one selected from, pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof; providing an adhesive component comprising a resin having a functional amino groups, 10-60 wt% of water and at least two wooden pieces; applying the adhesive component and the hardener component on at least one side of each of the wooden pieces; contacting the side of a wooden piece with the side of another wooden piece thereby forming a sandwich structure of wooden pieces with the adhesive component and the hardener component forming an adhesive layer between the wooden pieces; and pressing the sandwich structure together to join the at least two wooden pieces and thus creating a glued product of wooden pieces forming a structural timber product.CLAIM 10. The method according to claim 9, wherein the hardener component is provided by first mixing the first acid with the second acid in situ.CLAIM 11 . The method according to claim 9, wherein the pressing is performed using radio frequency pressing.CLAIM 12. A structural timber product comprising: at least two wooden pieces; and an intermediate adhesive layer to combine the at least two wooden pieces, the intermediate adhesive layer comprising: a hardener component comprising:4-35 wt.% of at least one first acid with pKa in the interval of 2.5-10, the first acid is at least one selected from formic acid (CH2O2), glycolic acid (C2H4O3), malic acid (C4H6O5), or a combination thereof; and0.05-15 wt.% of at least one second acid with a pKa in the interval of 0.8- 2.4, the second acid is at least one selected from pyrophosphoric acid (H4P2O7), sulfamic acid (H2NSO3H), hypophosphorous acid (H3PO2), phosphoric acid (H3PO4), or a combination thereof; and an adhesive component comprising a resin having a functional amino groups; and10-60 wt% of water.CLAIM 13. The structural timber product according to claim 12 further comprising 5- 50 wt% of one or more additives.CLAIM 14. The structural timber product according to claim 12 wherein the hardener component has a conductivity of 10000-46000 pS / cm.CLAIM 15. The structural timber product according to claim 12 wherein the resin is at least one selected from a Melamine-urea-form aldehyde (MUF) resin, melamineformaldehyde-resin (MF), glyoxal-formaldehyde-melamine-resin (glyoxal- MF), glyoxal-formaldehyde-melamine-urea-resin (glyoxal-MUF), glyoxal melaminresin, glyoxal melamine urea resin, glyoxal melamine urea derivative resin, or a combination thereof.CLAIM 16. The structural timber product according to claim 15 wherein resin having 0.001-1.0% free formaldehyde.CLAIM 17. The structural timber product according to claim 12 wherein mixing ratio between the adhesive component and the hardener component is in the interval of from 100:20 to 100:200 parts per weight.CLAIM 18. The structural timber product according to claim 15 wherein the resin further having 15-60 wt.% of melamine and 45-80 wt.% of dry content.CLAIM 19. The structural timber product according to claim 12 wherein further the first acid is at least one selected from citric acid, a tartaric acid, or a combination thereof, wherein the second acid is at least one selected from nitric acid, hydrochloric acid, sulfuric acid, oxalic acid or a combination thereof.CLAIM 20. The structural timber product according to claim 12 having requirements of standard EN 301.

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