Improved methods of joining substrates using a one-component polyurethane adhesive

Abstract

The present invention relates to a method for joining two or more substrates using a one-component polyurethane adhesive wherein a polyol component is applied in order to improve the bonding strength. The present invention further relates to containers comprising a polyol component and no isocyanates, which are fitted with a handheld applicator adapted for spraying the polyol component.

Description

IMPROVED METHODS OF JOINING SUBSTRATES USING A ONE-COMPONENT POLYURETHANE ADHESIVEField of the invention

[0001] The present invention relates to improved methods of bonding or joining substrates with polyurethane adhesives. The invention further relates to a container comprising a polyol component useful in such methods.Background of the invention

[0002] It is well known that polyurethane adhesives exist in two main categories: one-component systems and two-component systems.

[0003] In one-component polyurethane adhesives, all the polyurethane-forming reagents (a diisocyanate or a polyisocyanate, a polyol and a catalyst) are present in the same composition. After dispensing, curing into a polyurethane is triggered by moisture present on the surface being treated and / or by atmospheric moisture.

[0004] An advantage of one-component polyurethane adhesives is that they are cost-efficient and easy to apply due to the somewhat delayed curing (allowing application using a brush). However, since curing heavily relies on moisture, undesirable foaming (due to CO2 formation) may be observed, an in-depth curing is slow.

[0005] In two-component polyurethane adhesives, an “A” component (also called isocyanate component) and a “B” component (also called polyol component) polymerize into a polyurethane when they are mixed. The “A” component comprises a diisocyanate or a polyisocyanate and optionally further additives, and the “B” component generally comprises a polyol, a catalyst, and optionally further additives. The two components are packaged and stored in separate containers or stored in separate compartments within the same container. Typically, the “A” component and the “B” component are delivered through separate lines into a dispensing unit, such as an impingement mixing or static mixing type spray gun or pouring gun, generally at a ratio of around 1 :1 by volume. In a system with two separate containers, the two components are kept separate throughout this entire system until they come together in the mixing section of the dispensing unit, such as a mixing nozzle or mixing chamber. When dispensed, the liquid contents come out as a mixture which reacts and cures to form the polyurethane adhesive. The polyurethane industry traditionally regards the isocyanate component as the “A” component and the polyol component as the “B” component. However, the “A” and “B” designations may be reversed in some areas.

[0006] An advantage of two-component polyurethane adhesives is that they do not show significant foaming, show quicker curing and thus strength development and generally are able to achieve higher performance than one-component systems. However, the cost is generally higher, special equipment is needed for dispensing and applying, and small changes in formulation or application conditions can easily deteriorate performance.

[0007] In order to decrease curing times of one-component systems, some workers have developed a habit of spraying the one-component polyurethane adhesive with water after it has been applied to the surface of a substrate (and before it is joined to the other substrate it is supposed to adhere to). However, the present inventors have found that such water spraying leads to significantly deteriorated strength performance and foaming if too much is applied. It is not a reliable method to improve one-component polyurethane adhesive performance.

[0008] It is an object of the invention to alleviate or overcome one or more of the downsides of one-component polyurethane adhesives, such as a slow curing time, lack of in-depth curing. It is an object of the invention to find a solution which does not cause excessive foaming or strength decrease. It is an object of the invention to provide a solution which can easily be applied by workers on the factory floor, which is robust and does not require special or expensive equipment.Summary of the invention

[0009] The present inventors have found that the performance of a one-component polyurethane adhesive is surprisingly boosted when a polyol component is applied (e.g. via spraying) onto the one-component polyurethane adhesive after said adhesive is applied to a substrate, but before joining with another substrate. As is shown in the appended examples, this results in vastly improved early strength development compared to the one-component polyurethane adhesive used as such, and even compared to the same adhesive sprayed with water. By applying a polyol component, instead of another layer of polyurethane adhesive (or water), the relative amount of polyol (and also catalyst if it is included in the polyol component, as is preferred) will be increased compared to the composition of the one-component polyurethane adhesive. This results in a “boosting” effect on the curing of the polyurethane adhesive, achieving faster curing and allows achieving a higher strength. The diluting effect of spraying water is avoided, foaming is reduced, and the method is much more robust because it is less prone to “overdosing” and thus deteriorating adhesive quality.

[0010] In a first aspect the present invention provides a method for joining two or more substrates with a polyurethane adhesive, comprising the steps of:(i). providing two or more substrates to be joined;(ii). preparing the substrates for joining by(ii)a. applying a one-component polyurethane adhesive to a surface of one or more of the substrates to be joined, and(a1) applying a polyol component to the polyurethane adhesive, and / or(a2) applying a polyol component to a surface of one or more of the substrates to be joined; and / or(ii)b. applying a polyol component to a surface of one or more substrates to be joined and applying a one-component polyurethane adhesive to said polyol component;(iii). contacting the substrates to be joined such that the polyurethane adhesive contacts two or more of the substrates to be joined.

[0011] The polyol component is free of isocyanates and is preferably applied by spraying.

[0012] The one-component polyurethane adhesive comprises an isocyanate-functional urethane prepolymer and a catalyst.

[0013] In another aspect of the invention there is provided a container comprising a polyol component and no isocyanates, wherein the container is fitted with a handheld applicator adapted for spraying the polyol component. The handheld applicator is adapted for spraying the polyol component by an action on the handheld applicator. Preferably, the handheld applicator is adapted for spraying the polyol component through an aperture of less than 2 mm, preferably less than 1 mm.Description of embodiments

[0014] The expression “comprise” and variations thereof, such as, “comprises” and “comprising” as used herein should be construed in an open, inclusive sense, meaning that the embodiment described includes the recited features, but that it does not exclude the presence of other features, as long as they do not render the embodiment unworkable.

[0015] The expressions “one embodiment”, “a particular embodiment”, “an embodiment” etc. as used herein should be construed to mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of such expressions in various places throughout this specification do not necessarily all refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. For example, certainfeatures of the disclosure which are described herein in the context of separate embodiments are also explicitly envisaged in combination in a single embodiment.

[0016] The singular forms “a,” “an,” and “the” as used herein should be construed to include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its broadest sense, that is as meaning “and / or” unless the content clearly dictates otherwise.

[0017] Whenever reference is made throughout this document to a compound which is a salt, this should be construed to include the anhydrous form as well as any solvates (in particular hydrates) of this compound, unless explicitly defined otherwise.

[0018] As used herein, the expression “wt.%” when used in the context of an ionic compound refers to the amount of the compound inclusive of its counterion(s).

[0019] As used herein “polyol” refers to any molecule that has 2 or more hydroxyl groups per molecule. In case of polymers, the exact number of hydroxyl groups per molecule may be different for the various molecules comprised in a polymeric product, such that the number-average hydroxyl functionality is referred to, which is preferably higher than 2.0. Number average hydroxyl functionality refers to the average number of hydroxyl groups that are present on a molecule of the polyol and may be calculated as the ratio of the total moles of OH in the polyol to the total moles of polyol.

[0020] As used herein the expression “isocyanate index” refers to the molar ratio of the total amount of unreacted NCO (isocyanate) groups from the one-component polyurethane adhesive to the total amount of unreacted OH (alcohol) groups from the polyol component, times 100, calculated before the polyurethane adhesive and the polyol component are contacted.The method of the invention

[0021] In a first aspect the invention provides a method for joining two or more substrates with a polyurethane adhesive, comprising the steps of:(i). providing two or more substrates to be joined;(ii). preparing the substrates for joining by(ii)a. applying a one-component polyurethane adhesive to a surface of one or more of the substrates to be joined, and(a1) applying a polyol component to the polyurethane adhesive, and / or(a2) applying a polyol component to a surface of one or more of the substrates to be joined; and / or(ii)b. applying a polyol component to a surface of one or more substrates to be joined and applying a one-component polyurethane adhesive to said polyol component;(iii). contacting the substrates to be joined such that the polyurethane adhesive contacts two or more of the substrates to be joined.

[0022] As used herein, the term “joining” substrates should be interpreted to mean that the substrates are bonded together by the polyurethane adhesive. Typically, the substrates will not actually touch in the area where the adhesive is applied, as a layer of adhesive will be present between the substrates in the area where the adhesive is applied. The polyurethane adhesive functions by moisture curing of the isocyanate-functional polyurethane prepolymer comprised in the polyurethane adhesive, optionally with one or more crosslinkers. Thus, the method of the invention may further comprise a step of curing the polyurethane adhesive, for example by moisture-curing and / or curing with polyol comprised in the polyol component. In some embodiments, the method may further comprise a step of applying pressure during step (iii).

[0023] As the skilled person will understand, in order to join two substrates, there will always be atleast two surfaces being contacted with polyurethane adhesive at the moment in time that the two substrates are actually joined. However, the one-component polyurethane adhesive may be applied in step (ii) to only one of the surfaces being joined (directly or on top of a polyol component), such that the other surface being joined only contacts the polyurethane adhesive at the moment in time that the two substrates are actually joined in step (iii). Alternatively, the one-component polyurethane adhesive may be applied in step (ii) to two surfaces (directly or on top of a polyol component) being joined before the moment in time that the two substrates are actually joined in step (iii). By applying the adhesive on both surfaces independently before they are joined, improved adhesion to the substrate may be obtained. Similarly, the polyol component may be applied to the polyurethane adhesive, but may instead (or additionally) be applied to a surface of one or more of the substrates to be joined such that it can contact the polyurethane adhesive at the time the substrates are being joined in step (iii).

[0024] For the purposes of the present invention, it is considered that upon contacting the substrates to be joined in step (iii), in view of the thin layers conventionally used for joining substrates with adhesive, a significant part of the polyol component which contacts the polyurethane adhesive at the time of joining will mix into the polyurethane adhesive layer. Consequently, in the context of the present invention, it can be considered that during step (iii) the substrates to be joined are simultaneously contacting a mixture of the polyol component and the polyurethane adhesive, which cures into a bonded product. Because of this mixing which occurs at the time substrates are being joined (and often pressurized), the order of applying the polyurethane adhesive and the polyol component is not particularly limited. As is expressed in the definition of step (ii) of the method of the invention, various ways of performing the present invention exist, for example:-the polyurethane adhesive and the polyol component may be applied separately to different surfaces of the substrates to be joined, only contacting for the first time in step (iii);-the polyurethane adhesive may be applied directly to one or more surfaces of the substrates, and the polyol component may be applied to said polyurethane adhesive;-the polyol component may be applied directly to one or more surfaces of the substrates, and the polyurethane adhesive may be applied to said polyol component.It is understood that further applications of products, such as further layers of polyol component or polyurethane adhesive, or water may be employed on top of the requirements of the method of the invention. Preferably no water is applied “as such” in the method of the present invention (although some water may be applied as part of the polyol component), for example in some embodiments the method of the invention does not comprise the application of a composition comprising more than 95 wt.% water, preferably more than 99 wt.% water) to the polyurethane adhesive or the polyol component.

[0025] In preferred embodiments of the invention, preparing the substrates for joining in step (ii) comprises performing option (ii)a of the method described herein. It has been found that by applying the one-component polyurethane adhesive directly to the substrate to be joined, and subsequently providing the polyol (via option (a1) and / or (a2)) improved performance (such as higher strength) is achieved.

[0026] In accordance with the invention, the polyol component and the polyurethane adhesive are applied separately, i.e. not mixed with each other before application, such that no complicated mixing equipment or mixing steps are required.

[0027] Applying the polyurethane adhesive and / or the polyol component may be performed by any means known to the skilled person. It is typically performed by brushing (using a brush), roller coating (using a roller) or by spraying. These may be handheld brushes, rollers or spraying device, but may also be industrial brushes, rollers or spraying devices which are mounted on an automatedproduction line. Typically, a roller is used to apply the adhesive in an industrial setting.

[0028] The present inventors have found that it is highly convenient if the polyol component is applied by spraying. Spraying may be performed using a handheld applicator or by a spraying device which is, for example, mounted on an automated production line. Spraying is preferably performed using a container fitted with a handheld applicator adapted for spraying the polyol component. The handheld applicator is adapted for spraying the polyol component by an action on the handheld applicator. For example spraying is preferably performed using a spraying gun, trigger sprayer or a pressurized spray can. The spraying aperture is preferably less than 2 mm, more preferably less than 1 mm.

[0029] The polyol component preferably contacts substantially the complete surface of the polyurethane adhesive in step (iii) of the method. This is easily achieved when using layers of material, for example-a layer of polyol component which is applied onto substantially the complete surface of a layer of polyurethane adhesive;-a layer of polyurethane adhesive which is applied onto substantially the complete surface of a layer of polyol component; or-a layer of polyol component which is applied onto a surface of a substrate to be joined, and a layer of polyurethane adhesive which is applied onto another surface of a substrate to be joined, wherein the layers are applied such that upon contacting the substrates to be joined in step (iii) substantially the complete surface of the layer of polyol component contacts the layer of polyurethane adhesive (or vice versa). For the purposes of the present invention, an application of polyol component or polyurethane adhesive using a brush, a roller, spraying or similar methods are considered to form a layer. The layer may be discontinuous or irregular (e.g. as is the case when a few disconnected or partially overlapping strokes of a brush are applied on a surface), or may be (as is preferred) a continuous covering layer.

[0030] As will be understood based on the present disclosure, the polyol component of step (ii) is free of isocyanates. It is thus not capable of forming a polyurethane on its own. It is in essence the same as a polyol component employed in two-component polyurethane adhesive forming kits. The preferred composition of the polyol component is discussed herein elsewhere.

[0031] In embodiments, the polyol component in step (ii) comprises less than 5 wt.%, less than 4.5 wt.%, less than 4 wt.%, less than 3.5 wt.%, less than 3 wt.%, less than 2.5 wt.%, less than 2 wt.%, less than 1 .5 wt.%, less than 1 wt.%, less than 0.5 wt.%, less than 0.45 wt.%, less than 0.4 wt.%, less than 0.35 wt.%, less than 0.3 wt.%, less than 0.25 wt.%, less than 0.2 wt.%, less than 0.15 wt.%, less than 0.1 wt.%, less than 0.09 wt.%, less than 0.08 wt.%, less than 0.07 wt.%, less than 0.06 wt.%, less than 0.05 wt.%, less than 0.04 wt.%, less than 0.03 wt.%, less than 0.02 wt.%, or less than 0.01 wt.% water. In embodiments, the polyol component in step (ii) is free of water. In this context, the polyol component in step (ii) may also be called the “non-aqueous” or “water-free” component in this application.

[0032] By using a polyol component in step (ii), instead of another layer of polyurethane adhesive, the relative amount of polyol (and also catalyst if it is included in the polyol component, as is preferred) will be increased compared to the composition of the one-component polyurethane adhesive. This results in a “boosting” effect on the curing of the polyurethane adhesive, achieving faster curing and higher strength. The diluting effect of spraying water, as is done in the art, is avoided and the method is much more robust because it is less prone to “overdosing” and thus deteriorating adhesive quality. The lack of isocyanates also allows the polyol component of step (ii) to be used with less concerns for worker health, need for specialized application equipment or personal protective gear, etc. Consequently, it is also preferred that step (ii) does not comprise the application of an isocyanate-containing composition other than the one-component polyurethane adhesive. In accordance with highly preferred embodiments of the invention, the only isocyanatesapplied throughout the method are those comprised in the one-component polyurethane adhesive of step (ii). thus the only isocyanates applied throughout the method are applied as part of the one- component polyurethane adhesive in step (ii).

[0033] The present invention concerns polyurethane adhesives (which are not foamed), which is markedly different from e.g. polyurethane insulation material (which is foamed) inter alia in that the amount of product applied is rather low. Thus, in preferred embodiments of the invention, the amount of polyurethane adhesive applied in step (ii) is less than 400 g / m2of substrate surface, preferably less than 300 g / m2such as 50-250 g / m2. The amount is calculated based on the surface area of the substrate to which the polyurethane adhesive is applied and which is to be joined with another substrate using the polyurethane adhesive (which may represent only part of the surface area of the substrate, for example in case one side of an object is being joined to another object while the other sides are not). Preferably, step (ii) comprises applying a layer of polyurethane adhesive to a surface of a substrate, wherein the layer has a thickness of less than 400 micron, preferably less than 300 micron, such as 50-250 micron. In preferred embodiments of the invention, step (ii) comprises applying the polyol component in an amount by weight which is 10-150% of the amount by weight of polyurethane adhesive applied in step (ii), preferably 30-150%. In preferred embodiments of the invention, step (ii) comprises applying the polyol component and the polyurethane adhesive in an amount resulting in an index of 30-300, preferably resulting in an index of 70-250.

[0034] If the polyol component is applied to the polyurethane adhesive, the polyol component should be applied before formation of a skin on the polyurethane adhesive. In such embodiments it is preferred that the polyol component contacts the polyurethane adhesive within 30 minutes of applying the polyurethane adhesive, preferably within 10 minutes of applying the polyurethane adhesive, most preferably within 2 minutes of applying the polyurethane adhesive. In preferred embodiments of the invention, step (iii) is performed within 30 minutes of the first application of polyurethane adhesive to a substrate, preferably within 10 minutes of first application of polyurethane adhesive to a substrate, most preferably within 2 minutes of the first application of polyurethane adhesive to a substrate.

[0035] The substrates referred to herein are not particularly limited. The various substrates being joined may be of the same material, or of different materials. In some embodiments the substrates are selected from metal, plastics (including fibre reinforced plastics and foamed polymers), wood, asphalt, glass, fibreglass, mineral wool, bituminous roofing, plaster, and concrete. Preferably, the method of the present invention is for joining a first substrate which is an insulating material (preferably a foamed polymer, such as expanded polystyrene) with a second substrate which is selected from wood, metal or polyvinylchloride. Such applications can be found for example in the production of so-called sandwich insulation panels.

[0036] In some embodiments of the invention, the method is for improving the lap shear strength at 40 min after application of the polyurethane adhesive with at least 50%, preferably with at least 100%. In some embodiments of the invention, the method is for improving the lap shear strength at 20 min after application of the polyurethane adhesive with at least 50%, preferably with at least 100%. The improvement is determined compared to a sample wherein only polyurethane adhesive (and thus no polyol component) is used but test conditions are otherwise identical. The lap shear strength is assessed conforming to ISO 4587 (2019).The one-component polyurethane adhesive used in step (ii) of the method of the invention

[0037] The one-component polyurethane adhesive employed in step (ii) may be any one- component adhesive suitable for joining the substrates. The invention is not particularly limited in this regard. The one-component polyurethane adhesive comprises (before curing) an isocyanate- functional urethane prepolymer and a catalyst. Such isocyanate-functional urethane prepolymersare obtainable by reacting a first isocyanate monomer with a polyol. The reaction typically occurs at stoichiometric excess of isocyanate in order to obtain an isocyanate-functional urethane prepolymer (wherein the prepolymer has at least two isocyanate end groups). The isocyanate monomer used has an isocyanate functionality of 2 or more, and is typically a diisocyanate. The polyurethane adhesive is stored free of moisture and once it has been applied, the prepolymer conventionally cures by reaction with atmospheric moisture. As will be understood by the skilled person based on the present disclosure, in the present invention curing involves reaction with the unreacted polyol supplied by the polyol component.

[0038] As is known to the skilled person, typically the polyurethane adhesive will also comprise significant amounts of monomeric isocyanates (such as 2-5 wt.%). These monomeric isocyanates are typically diisocyanates which are “carried-over” from the production of the prepolymer, which employs an excess of diisocyanates. However, in view of health concerns more attention is being paid to developing low monomeric polyurethane adhesives, which can be prepared by using e.g. distilled prepolymers where the monomeric isocyanates have been removed. Hence, in some embodiments the one-component polyurethane adhesive may comprise less than 0.5 wt.% (by total weight of the adhesive) monomeric isocyanates, preferably less than 0.1 wt.%.

[0039] The isocyanate monomer used to prepare the isocyanate-functional urethane prepolymer comprised in the one-component polyurethane adhesive may be any suitable isocyanate. The isocyanate monomer used to prepare the isocyanate-functional urethane prepolymer comprised in the one-component polyurethane adhesive is preferably selected from the group consisting of the aromatic diisocyanates (such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate, crude toluene diisocyanate, methylene diphenyl diisocyanate, crude methylene diphenyl diisocyanate and the like); the aromatic triisocyanates (such as 4, 4', 4"- triphenylmethane triisocyanate, 2,4,6-toluene triisocyanates); the aromatic tetraisocyanates (such as 4,4'-dimethyldiphenylmethane-2,2',5, 5’-tetraisocyanate); arylalkyl polyisocyanates (such as xylylene diisocyanate); aliphatic polyisocyanates (such as hexamethylene-1 ,6-diisocyanate, lysine diisocyanate methylester); polymethylene polyphenylisocyanates; hydrogenated methylene diphenylisocyanate; m-phenylene diisocyanate; naphthylene-1 ,5, -diisocyanate; I- methoxyphenylene-2,4-diisocyanate; 4,4'-biphenylene diisocyanate; 3,3'-dimethoxy-4,4'-biphenyl diisocyanate; 3,3'-dimethyl-4,4'-biphenyl diisocyanate; 3,3'-dimethyldiphenylmethane-4,4'- diisocyanate; alkylene diisocyanates (such as trimethylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate, isophorene diisocyanate, 4,4'- methylenebis(cyclohexyl isocyanate)); aromatic polyisocyanates (such as m-, and p-phenylene disocyanate, polymethylene polyphenyl isocyanate, 2,4- and 2,6-toluenediisocyanate, dianisidine diisocyanate, bitoylene isocyanate, naphthylene 1 ,4-diisocyanate, bis(4-isocyanatophenyl), methene, bis(2-methyl-4-isocyanatophenyl)methane); and combinations thereof.

[0040] The one-component polyurethane adhesive may comprise the isocyanate-functional urethane prepolymer in any conventionally used amount, such as in an amount of 10-99.9 wt.% (by total weight of the one-component polyurethane adhesive), preferably in an amount of 10-95 wt.%, more preferably in an amount of 10-90 wt.%. In some embodiments of the invention the one- component polyurethane adhesive comprises the isocyanate-functional urethane prepolymer in any an amount of at least 20 wt.% (by total weight of the one-component polyurethane adhesive), more preferably at least 30 wt.%, most preferably at least 40 wt.%.

[0041] The polyol used to prepare the isocyanate-functional urethane prepolymer comprised in the one-component polyurethane adhesive may consist of a single polyol or several polyols, often employed and sold as a polyol pre-mix. The one or more polyols used to prepare the isocyanate- functional urethane prepolymer comprised in the one-component polyurethane adhesive may be any polyol known in the art to prepare a polyurethane adhesive.

[0042] The polyol used to prepare the isocyanate-functional urethane prepolymer comprised in the one-component polyurethane adhesive is preferably selected from the group consisting of asucrose containing polyol; phenols having two or more alcohol groups, a phenol formaldehyde containing polyol; a glucose containing polyol; a sorbitol containing polyol; a methylglucoside containing polyol; an aromatic polyester polyol; an aliphatic polyester polyol; an aromatic polyether polyol; an aliphatic polyether polyol; a polybutadiene polyol; a polycaprolactone polyol; a polycarbonate polyol; a hydroxyl terminated polyolefin polyol; a graft polyol; glycerol; ethylene glycol; diethylene glycol; propylene glycol-containing polyol; graft copolymers of polyether polyols with a vinyl polymer; a copolymer of a polyether polyol with a polyurea; one or more of (a) condensed with one or more of (b): (a) glycerine, ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, soy oil, lecithin, tall oil, palm oil, castor oil; (b) ethylene oxide, propylene oxide, a mixture of ethylene oxide and propylene oxide; and combinations thereof.

[0043] Preferred polyols are selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols and combinations thereof.

[0044] Examples of the polyether polyols include alkyleneoxide adducts of active hydrogen compounds such as water, alcohols, phenols, and the like. Preferred alkyleneoxides are styrene oxide, ethylene oxide, propylene oxide and / or butylene oxide. Examples of the alcohols include bifunctional alcohols such as ethylene glycol and propylene glycol and polycuntional alcohols such as glycerol and sucrose; examples of the phenols include hydroquinone, bisphenol A, and the like.

[0045] Examples of the polyester polyols include condensed polyester polyols prepared by reacting a polyfunctional alcohol (a bifunctional or trifunctional alcohol or the like described above) with a polybasic acid (succinic acid, adipic acid, sebacic acid, maleic acid, dimer acid, trimellitic acid, phtalic acid, terephtalic acid or the like), poly lactone polyols prepared by ring-opening polymerization of a lactone such as 8- caprolactone, the alkyleneoxide adducts thereof, and the like.

[0046] The catalyst present in the one-component polyurethane adhesive may be any catalyst known in the art and suitable to catalyze moisture crosslinking between the isocyanate groups of the isocyanate-functional urethane prepolymer comprised in the one-component polyurethane adhesive. Examples of suitable catalysts include metal catalysts, amine catalysts, and morpholine catalysts. In some embodiments of the invention the one-component polyurethane adhesive comprises a metal catalyst, wherein the metal is selected from Sn, Bi, Zn, Ti, Zr or Al.

[0047] Typically, the one-component polyurethane adhesive will further comprise a filler, such as a filler selected from mineral fillers, metal oxide fillers, fly ash, bottom ash, carbon black, glass, and combinations thereof.

[0048] The one-component polyurethane adhesive may comprise further additives, such as one or more further additives selected from colorants, rheology modifiers, thickeners plasticizers, solvents, acids, bases, crosslinkers, curing agents, adhesion promotors, moisture scavengers, fungicides, biocides, blocking agents, UV-stabilizers, antioxidants, surfactants, monofunctional alcohols, and / or further catalysts. The term monofunctional alcohol as used herein refers to any molecule comprising a single alcohol (-OH) functional group. Preferably, the monofunctional alcohol does not comprise other functional groups, for example the monofunctional alcohol may be phenol.

[0049] The one-component polyurethane adhesive employed in step (ii) of the method of the present invention is essentially free of water. As will be understood by the skilled person, any water present before the product is used, for example applied in step (ii) of the method, will react with the isocyanate groups of the isocyanate-functional urethane prepolymer and thus lead to premature curing.The container of the invention

[0050] The present inventors have found that, so far, polyol components are only available to customers in two forms: (a) as large volume containers which only contains polyol but which hasno spraying means (these are used for coupling via a pump to a spray gun where isocyanate is also mixed before spraying such that a polyurethane is formed) or (b) as small handheld containers which have a polyol compartment and an isocyanate compartment (mixing takes place before exiting the spray nozzle such that a polyurethane is formed).

[0051] Thus, none of these known polyol containers allow the skilled person to easily apply a polyol alone by spraying, which is useful for example to effect step (ii) of the method described herein.

[0052] Accordingly, in another aspect of the invention there is provided a container comprising a polyol component and no isocyanates, wherein the container is fitted with a handheld applicator adapted for spraying the polyol component. The handheld applicator is adapted for spraying the polyol component by an action on the handheld applicator.

[0053] The handheld applicator is adapted for spraying the polyol component without spraying any isocyanates. While the container does not comprise any isocyanates, the handheld applicator thus also does not allow mixing of an external isocyanate component before spraying. It sprays the polyol component alone.

[0054] In preferred embodiments of the invention the handheld applicator is adapted for spraying the polyol component through an aperture of less than 2 mm, preferably less than 1 mm. Such apertures are not used for containers where isocyanate mixing takes place because they clog too easily by the formed polyurethane foam. However, in the context of the present invention, where only polyol component is sprayed, such small apertures can be used, leading to improved atomisation and thus spreading of the product upon spraying. The handheld applicator may for example be a dispensing gun, a trigger sprayer or a pressurized spray can.

[0055] In some embodiments of the invention, the handheld applicator is a dispensing gun, such that the container fitted with a handheld applicator described herein is a container mounted on a dispensing gun. Dispensing guns are known to the skilled person and typically comprise a basket for fluidly connecting the container to the dispensing gun, said basket comprising a flow channel connecting the container to the dispensing gun and typically also comprises a blocking means configured to be moveable between an open position wherein flow from the can to the dispensing gun is enabled and a closed position wherein flow from the can to the dispensing gun through the flow channel is blocked. Such blocking means is typically a spring-loaded check valve. A check valve is also called a backflow-prevention valve, a non-return valve, or a one-way valve. The spring- loaded check valve is preferably a ball-spring check valve. The dispensing gun typically further comprises a handle for holding the gun, a dispensing tube with a spraying nozzle, means for opening and closing the dosing nozzle, and a trigger for actuating said means in order to open the dosing nozzle and to dispense the container contents (here the polyol component) from a dispensing opening at an end of the dispensing tube. The means for opening and closing the dosing nozzle typically comprises a spring-loaded needle which is co-axially moveable in the dispensing tube, and optionally further comprises regulating means for regulating the degree of opening of the outlet of the dosing nozzle, such as a back-screw. It will be understood by the skilled person that in order to dispense the container contents (here the polyol component), upon opening the dozing nozzle a fluid pathway is opened reaching from the can through the basket via the dosing nozzle and into the dispensing tube which opens up to the environment. The spraying nozzle preferably has an aperture of less than 2 mm, preferably less than 1 mm as has been described herein earlier.

[0056] In preferred embodiments of the invention, the container fitted with a handheld applicator described herein is a trigger sprayer or a pressurized spray can. The pressurized spray can is typically pressurized using a propellant, but may also be a can which comprises a mechanical pressurization means, such as a plunger which can be used to increase the internal pressure such that spraying takes place when a trigger is actuated. The spraying aperture is preferably less than 2 mm, more preferably less than 1 mm. In some preferred embodiments the pressurized spray cancomprises a valve for stopping or controlling the flow of the polyol component and the handheld applicator acts on the valve thereby opening the valve.

[0057] In highly preferred embodiments of the invention, the container described herein is ap pressurized spray can further comprising one or more propellants. The one or more propellants comprised in the pressurized can may be any suitable propellant known in the art. The one or more propellants are preferably selected from the group consisting of Ci-Ce saturated or unsaturated hydrocarbons (e.g. n-pentane, n-butane, isobutane, n-hexane, 2-methylbutane, propane, isopentane, 1 -pentene, butene, 2-methyl-2-butene, 10yclobutene, cyclopentane, cyclohexane), vinyl chloride, methyl chloride, chlorofluorocarbons, hydrochlorofluorocarbons, hydrohaloolefins, air, carbon dioxide, argon, nitrogen, nitrous oxide, dimethyl ether, diethyl ether, dimethoxymethane, methyl formate, and combinations thereof.

[0058] Typically the pressurized spray can will have an internal relative pressure at 50 °C of less than 1200 kPa (12 bar). The pressurized spray can preferably has an internal relative pressure at 20 °C of at least 200 kPa (2 bar), more preferably at least 300 kPa (3 bar), most preferably at least 400 kPa (4 bar). The pressurized spray can preferably has an internal relative pressure at 20 °C within the range of 100-1000 kPa (1-10 bar), preferably within the range of 300-700 kPa (3-7 bar), more preferably within the range of 400-600 kPa (4-6 bar), in particular 450-550 kPa (4.5-5.5 bar).The polyol component

[0059] The polyol component used in step (ii) of the method of the invention is the same polyol component as is described herein in the context of the container of the invention. Thus, in preferred embodiments of the invention, the method of the invention is provided wherein the polyol component of step (ii) is provided in the form of the container of the invention.

[0060] In accordance with the invention, the polyol component comprises a polyol. In some preferred embodiments, the polyol component of step (ii) of the method comprises the same polyol as is used to prepare the isocyanate-functional urethane prepolymer comprised in the one- component polyurethane adhesive used in step (ii) of the method. However, the present inventors have found that this is not necessary and good results are achieved with different polyols.

[0061] The polyol present in the polyol component, may comprise a single polyol or several polyols, often employed and sold as a polyol pre-mix. The one or more polyols present in the polyol component may be any polyol known in the art to prepare a polyurethane.

[0062] In preferred embodiments of the invention, the polyol component is selected from the group consisting of a sucrose containing polyol; phenols having two or more alcohol groups, a phenol formaldehyde containing polyol; a glucose containing polyol; a sorbitol containing polyol; a methylglucoside containing polyol; an aromatic polyester polyol; an aliphatic polyester polyol; an aromatic polyether polyol; an aliphatic polyether polyol; a polybutadiene polyol; a polycaprolactone polyol; a polycarbonate polyol; a hydroxyl terminated polyolefin polyol; a graft polyol; glycerol; ethylene glycol; diethylene glycol; propylene glycol-containing polyol; graft copolymers of polyether polyols with a vinyl polymer; a copolymer of a polyether polyol with a polyurea; one or more of (a) condensed with one or more of (b): (a) glycerine, ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, soy oil, lecithin, tall oil, palm oil, castor oil; (b) ethylene oxide, propylene oxide, a mixture of ethylene oxide and propylene oxide; and combinations thereof.

[0063] Preferred polyols are selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols and combinations thereof.

[0064] Examples of the polyether polyols and polyester polyols have been provided herein earlier and are also applicable in the context of the polyol as comprised in the polyol component provided in step (ii).

[0065] The polyol preferably has a number average hydroxyl functionality (Fn) of 2 or more, such as in the range of 2-3. Number average hydroxyl functionality refers to the average number of hydroxyl groups that are present on a molecule of the polyol and may be calculated as the ratio of the total moles of OH in the polyol to the total moles of polyol.

[0066] The polyol preferably has a number average molecular weight between 40 and 3000 Da, preferably between 40 and 2000 Da, more preferably between 40 and 1000 Da.

[0067] The amount of polyol comprised in the polyol component may be up to 100 wt.% (by total weight of the polyol component). However, as is explained herein elsewhere, the polyol component preferably further comprises a catalyst. Hence, the amount of polyol comprised in the polyol component is preferably up to 99.5 wt.% (by total weight of the polyol component), preferably up to 99 wt.%. The amount of polyol comprised in the polyol component is preferably at least 10 wt.% (by total weight of the polyol component), preferably at least 30 wt.%, preferably at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 45 wt.%, at least 50 wt.%, at least 55 wt.%, at least 60 wt.%, at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, at least 80 wt.%, at least 85 wt.%, at least 90 wt.%, at least 91 wt.%, at least 92 wt.%, at least 93 wt.%, at least 94 wt.%, at least 95 wt.%, at least 96 wt.%, at least 97 wt.%, at least 98 wt.%, at least 99 wt.%, at least 99.1 wt.% , at least 99.2 wt.% , at least 99.3 wt.% , at least 99.4 wt.% , at least 99.5 wt.% , at least 99.6 wt.% , at least 99.7 wt.% , at least 99.8 wt.% , at least 99.9 wt.%. In some embodiments of the invention, the polyol component comprises 50-100 wt.% of polyol (by total weight of the polyol component), preferably 50-99.5 wt.%, more preferably 50-99 wt.%. In some embodiments of the invention, the polyol component comprises 60-98 wt.% of polyol (by total weight of the polyol component), preferably 70-95 wt.%, more preferably 78-92 wt.%.

[0068] In preferred embodiments of the invention, the polyol component contains a majority amount of a polyol selected from the group consisting of a sucrose containing polyol; phenols having two or more alcohol groups, a phenol formaldehyde containing polyol; a glucose containing polyol; a sorbitol containing polyol; a methylglucoside containing polyol; an aromatic polyester polyol; an aliphatic polyester polyol; an aromatic polyether polyol; an aliphatic polyether polyol; a polybutadiene polyol; a polycaprolactone polyol; a polycarbonate polyol; a hydroxyl terminated polyolefin polyol; a graft polyol; glycerol; ethylene glycol; diethylene glycol; propylene glycol- containing polyol; graft copolymers of polyether polyols with a vinyl polymer; a copolymer of a polyether polyol with a polyurea; one or more of (a) condensed with one or more of (b): (a) glycerine, ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, soy oil, lecithin, tall oil, palm oil, castor oil; (b) ethylene oxide, propylene oxide, a mixture of ethylene oxide and propylene oxide; and combinations thereof, preferably selected from polyether polyols, polycarbonate polyols, polyester polyols and combinations thereof, such as more than 50 wt.% based on the total weight of polyol present in the polyol component, more than 70 wt.%, more than 85 wt.%, more than 95 wt.%, more than 98 wt.%, preferably more than 99 wt.%. In highly preferred embodiments, the polyol comprised in the component consists essentially of a polyol selected from the group consisting of a sucrose containing polyol; phenols having two or more alcohol groups, a phenol formaldehyde containing polyol; a glucose containing polyol; a sorbitol containing polyol; a methylglucoside containing polyol; an aromatic polyester polyol; an aliphatic polyester polyol; an aromatic polyether polyol; an aliphatic polyether polyol; a polybutadiene polyol; a polycaprolactone polyol; a polycarbonate polyol; a hydroxyl terminated polyolefin polyol; a graft polyol; glycerol; ethylene glycol; diethylene glycol; propylene glycol-containing polyol; graft copolymers of polyether polyols with a vinyl polymer; a copolymer of a polyether polyol with a polyurea; one or more of (a) condensed with one or more of (b): (a) glycerine, ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, soy oil, lecithin, tall oil, palm oil, castor oil; (b) ethylene oxide, propylene oxide, a mixture of ethylene oxide and propylene oxide; and combinations thereof, preferably selected from polyether polyols, polycarbonate polyols, polyester polyols and combinations thereof, preferably having a number average hydroxyl functionality (Fn) of 2 or moreand preferably having a number average molecular weight between 40 and 3000 Da, preferably between 40 and 2000 Da, more preferably between 40 and 1000 Da.

[0069] The polyol component in the context of the present invention preferably comprises a catalyst. The catalyst may be any catalyst known in the art and suitable to catalyze the formation of polyurethane from an isocyanate and a polyol, also referred to herein as a curing catalyst. Examples of suitable catalysts include metal catalysts, amine catalysts, and morpholine catalysts. In some embodiments of the invention the one-component polyurethane adhesive comprises a metal catalyst, wherein the metal is selected from Sn, Bi, Zn, Ti, Zr or Al.

[0070] The one-polyol component may comprise further additives, such as one or more further additives selected from fillers, colorants, rheology modifiers, thickeners plasticizers, solvents, pH adjusters, crosslinkers, curing agents, adhesion promotors, moisture scavengers, fungicides, biocides, blocking agents, UV-stabilizers, antioxidants, surfactants, and / or further catalysts. Examples of suitable fillers are fillers selected from mineral fillers, metal oxide fillers, fly ash, bottom ash, carbon black, glass, and combinations thereof.Examples

[0071] A series of adhesive tests were performed, each test employing two PVC plates, each measuring 100 mm x 25 mm x 2 mm, as substrates to be joined. The substrates are thoroughly cleaned with isopropanol to remove any contaminants or impurities from their surfaces.

[0072] Polyurethane adhesive is applied to one end of the surface of a first substrate, with dimensions of 12,5 mm x 25 mm, ensuring uniform coverage. The mass of applied adhesive is determined by weighing the sample before and after adhesive application.

[0073] In comparative example 1 , polyurethane adhesive is used alone. In comparative example 2, water is uniformly sprayed onto the polyurethane adhesive layer. In example 3, a polyol component is uniformly sprayed onto the polyurethane adhesive layer. The weight of polyol component applied is determined after evaporation of the propellant by weighing of the sample after polyol component application.

[0074] The second substrate is brought into contact with the adhesive area, and a clamp with a standardized pressure of 11 N is used for fixation. The substrates are left to fixate for specific durations (e.g., 20, 40, and 60 minutes).

[0075] The lap shear strength of the glued substrates is assessed conforming to ISO 4587 (2019) - Determination of tensile lap-shear strength of rigid-to-rigid bonded assemblies - using a Zwick shear strength analyser. This test is performed after the defined fixation times. After the lap shear test, the foaming of the glued area has been visually evaluated by looking at the texture of the adhesive layer.

[0076] The polyurethane adhesive used was obtained by reacting the reagents outlined in table 1 to prepare a one-component polyurethane adhesive comprising an isocyanate-functional urethaneprepolymer.Table 1 : preparation of polyurethane adhesive

[0077] The polyol component used in example 3 was as follows. It was sprayed using a can pressurized with dimethylether and having a spraying aperture of < 1 mm.Table 2: polyol component

[0078] The results of the tests are shown in table 3. It can be seen that by spraying a small amount of polyol component, a significant increase in early strength (40 min lap shear strength) is obtained even compared to water-sprayed samples. After prolonged curing (60 min lap shear strength) spraying of a polyol component leads to improved strength, while spraying of water actually results in reduced strength.Table 3: results‘insufficient adhesion to measure a lap shear strength

Claims

Claims1 . A method for joining two or more substrates with a polyurethane adhesive, comprising the steps of:(i). providing two or more substrates to be joined;(ii). preparing the substrates for joining by(ii)a. applying a one-component polyurethane adhesive to a surface of one or more of the substrates to be joined, and(a1) applying a polyol component to the polyurethane adhesive, and / or(a2) applying a polyol component to a surface of one or more of the substrates to be joined; and / or(ii)b. applying a polyol component to a surface of one or more substrates to be joined and applying a one-component polyurethane adhesive to said polyol component;(iii). contacting the substrates to be joined such that the polyurethane adhesive and the polyol component contact each other; wherein the polyol component comprises a polyol, and wherein the amount of the polyol in the polyol component is at least 40 wt.%, preferably at least 70 wt.%, more preferably at least 90 wt.%.

2. The method of claim 1 wherein step (ii) comprises applying a layer of polyurethane adhesive having a thickness of less than 400 micron.

3. The method of claim 1 or 2 wherein the polyol component is free of isocyanates.

4. The method of any one of the previous claims wherein the polyol component is free of water.

5. The method of any one of the previous claims wherein step (ii) does not comprise the application of an isocyanate-containing composition other than the one-component polyurethane adhesive.

6. The method of any one of the previous claims wherein method does not comprise the application of a composition comprising more than 95 wt.% water.

7. The method of any one of the previous claims wherein the polyol component and the polyurethane adhesive are each applied by brushing, roller coating or spraying.

8. The method of any one of the previous claims wherein the polyol component of step (ii) is applied by spraying.

9. The method of claim 7 wherein the polyol component of step (ii) is applied by spraying using a spraying aperture of less than 2 mm, preferably less than 1 mm.

10. A container comprising a polyol component and no isocyanates, wherein the container is fitted with a handheld applicator adapted for spraying the polyol component.11 . The container of claim 9 wherein the handheld applicator is adapted for spraying the polyol component without spraying any isocyanates.

12. The container of claim 10 which is a trigger sprayer or a pressurized spray can, preferably having a spraying aperture of less than 2 mm, preferably less than 1 mm.

13. The container according to claim 11 which is a pressurized spray can, and which further comprises one or more propellants.

14. The method of any one of claims 1 -7 or the container of any one of claims 8-12, wherein the polyol component comprises at least 60 wt.% (by total weight of the polyol component) polyol.

15. The method of claim 13 or the container of claim 13 wherein the polyol component comprises a curing catalyst.

16. The method of any one of claims 13-14, orthe container of any one of claims 13-14, wherein the polyol component comprises one or more further additives selected from fillers, colorants, rheology modifiers, thickeners plasticizers, solvents, pH adjusters, crosslinkers, curing agents, adhesion promotors, moisture scavengers, fungicides, biocides, blocking agents, UV-stabilizers, antioxidants, surfactants, monofunctional alcohols, and / or further catalysts.

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