METHOD FOR APPLICATION OF AN EXPANDABLE GLUING SYSTEM

Abstract: A method of gluing pieces of substrate together, by using an expandable gluing system comprising a resin component and a hardener component, wherein the hardener component is acidic, and the resin component comprises one or more gas generating substances capable of forming a gas when contacted with the hardener component, whereby the resin and the hardener components are separately applied onto the substrate. The invention also relates to a device suitable for carrying out the method.

Description: METHOD FOR APPLICATION OF AN EXPANDABLE GLUING SYSTEM The present invention relates to a method for separate application of the components of an expandable gluing system onto a substrate, the hardener of which system is acidic and forms part of the expandable capability of the system The invention also relates to a device for carrying out the method Expandable gluing systems are known in the art Such expandable gluing systems can for example be used where pieces to be glued together exhibit irregularities in the surfaces thereof to which glue is to be applied, such as for example in the gluing of wooden pieces together, such as, for instance, for the manufacture of gluelam or laminated timber The glue will then fill out these irregularities and thereby provide a joint having an improved strength as compared to a gluing system without a gas-forming substance Another object of such systems is to reduce the amount of wood, which has to be removed by means of for instance, planing before gluing in order to make the surfaces to be glued smooth However, in known expandable gluing systems the expandable feature is accomplished by means of, for example, a gas-forming composition or mixture separate from the resin and hardener components, respectively, which is introduced into the gluing system at the time of gluing Such an expandable gluing system, more particularly a carbamide resin based system, has been disclosed in SU-327224, wherein the mixing of a foaming composition with the resin suitably can be effected at the time of introduction of the carbamide resin curing catalyst Hitherto, expandable gluing systems have only been applied to substrates in the form of an admixture of the components included in said system for example as αisclosed in US 3615975 A The expandable systems known in the art, will, for example, be difficult to recirculate due to, interaiia, the risk of clogging, or build up in the application apparatus of hardened or partially hardened, mixture of the components of the gluing system Additionally, the risk of foaming, or undesired gas formation in the application equipment will be present due to the presence of the foaming composition Also start and stop of such application, and operation duπng long periods of time, will be difficult in practise Accordingly, it would be highly desirable to provide a method for application of an expandable gluing system wherein the components of said system can be recirculated, and wherein the formation of expanding agent, i e gas, prior to the pressing of the glued substrates together, is minimised Also, it would be highly desirable to be able to uniformly regulate the process of expansion, i e , gas formation, for example, in order to allow relatively long peπoαs of time from application to pressing, and to secure a uniform formation or gas in tne applied components especially during the pressing Moreover, it would be highly desirable to find simple application systems for separate application of expandable gluing systems, which can be adjusted to the gluing system in question and the desired assembly times Also, it would be highly desirable to find an expandable gluing system that requires small amounts of gas generating substances providing improved adhesive joints By assembly time it is meant the time that lapse from the moment of application of a gluing system onto a substrate to the moment of pressing the substrates to be glued together Thus, according to the present invention, a method for separate application of the components of an expandable gluing system, comprising a resin component and an acidic hardener component and a device suitable for carrying out the method are provided, by which enhanced adhesive and strength properties are obtained and at the same time the above-mentioned problems are overcome The method according to the present invention is defined in the appended claims It comprises gluing of pieces of substrate together, by using an expandable gluing system compπsing a resin component and a hardener component, wherein the hardener component is acidic, and the resin component comprises one or more gas generating substances capable of forming a gas when contacted with the hardener component, whereby the resin and the hardener components are separately applied onto the substrate The acidic hardener component used in the method of the invention comprises an acid, organic or inorganic such as hydrochloric acid, or an acidic salt such as ammonium chloride An especially suitable group of acids are the organic acids Suitable examples of the latter are paratoluene sulfonic acid and carboxyiic acids, the latter of which being preferred Examples of suitable organic carboxyiic acids are, formic acid citric acid, and maleic acid, of which formic acid, and maleic acid are preferred The hardener used also has the additional function of providing a component of the reaction system generating the gas, the other component of the gas-producing reaction system being the gas generating substance Said gas generating substance is provided in admixture with the resin component of the gluing system Depending on the reactivity of the components in the gluing system, the desired assembly times, special considerations about substrate damaging by the acid used in the hardener and emission of vapour of the acid into the surrounding atmosphere, such as in the working environment, the later applied strands may overlap, do not overlap, or do not contact, respectively, the corresponding previously applied strands of the other components As used here, the term "strand" also comprehends the meaning of the term "ribbon", also conventionally used in the art, and any other like term The device according to the invention is defined in the appended claims and can be used for carrying out the method, wherein the components of the expandable gluing system are applied in the form of strands into a substrate The present invention, interalia, offers the advantages of using an expandable gluing system having a reduced number of essential constituents Additionally, according to the invention, the need of a step comprising the addition of a gas-forming system into the gluing system, or into any of its components, prior to application of the gluing system, can conveniently be eliminated Moreover, according to the invention only small amounts of the gas generating substance are needed, which gives rise to improved adhesives and strength properties of the glued products The technique according to the present invention is especially useful with the ammo resin systems, the hardeners of which are generally acidic Examples of such systems are, urea-formaidehyde, melamine-urea-formaldehyde, melamine-formaldehyde, melamine-urea-phenol-formaldehyde resins, and furfuryl alcohol modified varieties thereof The gas producing substance can be any carbonate or hydrogen carbonate that will generate C0 2 upon contact with an acid Suitable examples are, for instance, sodium hydrogen carbonate, calcium carbonate, sodium carbonate, ammonium carbonate, ammonium hydrogen carbonate, magnesium carbonate or a mixture thereof Preferably calcium and/or sodium carbonate is used The gas producing substance can normally be included in the resin component in an amount ranging from 0 1-10 % by weight, suitably from 0 1-5 %, preferably from 0 15-2 % and most preferably from 0 15-1 ,9 %, as calculated on the pure, active form of said substance, i e the form that will generate the gas, with any impurities excluded Other gas generating substances, which generate a gas having a low boiling point on the contact with an acid used in the hardener, couid also be used in the present invention Examples of such gases are, for instance, ammonia, nitric dioxide, etc , although not preferred from an environmental standpoint, for example The gas generating substance can also for example, be used together with a conventional filler such as kaolin, or mixtures thereof However when the filler used comprises, or constitutes one or more gas generating substances as used herein, the total amount of the pure active form of such substances should be kept within the interval stated above In the method of the invention, the two components constituting the gluing system are applied separately Application of the gluing system can be accomplished, for example, by means of curtain, spray or strand type application or any combination thereof Application in the form of separate strands of the respective components is preferred After application of the expandable gluing system to the substrates, such as, for example, wooden lamellae, the substrates are brought together and pressed into an aggregate, such as, for example, a wooden beam It is preferred that the main production of gas in the expandable gluing system essentially occurs at the time of pressing, following the application of said system to the substrates Since the gas-forming reaction commences upon contact of the two components, the contact of the components with each other should desirably not be fully established until such pressing Thus, the method of the invention employs separate application in order to minimise the contact and the degree of mixing of the components prior to pressing, and thereby the extent of the gas-forming process occurring prior to pressing Preferably, a regulated, continuous, minimal contact of the different strands should be secured, in order to secure an adequate miscibility of the strands during pressing Thereby, the gas-forming reaction can be more carefully regulated, while also longer periods of time are allowed to lapse between application and pressing, such as, up to 180 minutes, if desired, preferably 0-90 minutes This object is achieved by using application of the components in the form of strands Depending on the reactivity of the components of the gluing system and the desired assembly time, the strands of the different components, such as the hardener and the resin, can be applied in relation to each other in various suitable ways Thus, for low reactive/slow curing gluing systems, and/or short assembly times, it is suitable that the later applied strands of one component overlap the corresponding strands of the previously applied component(s), or they are applied adjacent to each other so that they are in essentially contact with each other When high reactive/fast curing gluing systems are used, and/or long assembly times are desired, it is suitable that the later applied strands of one component are applied with a certain distance in relation to the corresponding strands of the previously applied component(s) For assembly times of about 60-120 mm a distance of about 4-8 mm between the strands of the different components of the gluing system, such as the hardener and the resin, is suitable, for assembly times of about 15-60 mm a distance of about 2-4 mm is preferred, and for assembly times of about up to 15 mm overlapping of the strands or essentially contact between them is preferred During the pressing, the two components will flow to some extent between the pieces of substrate that are being pressed together, whereby the components also will be mixed with each other to a higher degree than prior to the pressing, and are thereby brought into a more intimate contact with each other In this manner the principal gas- generation will occur during the pressing Also, the gas formation during the pressing will contribute to the mixing to some extent Accordingly, in one embodiment of the method of the present invention, separate application of the components in the form of strands is used A suitable device for such application of the components used in the present method, is a device comprising a unit of at least two hollow members, at least one member for each component, provided with a number of orifices in each member designed to apply the respective component onto a substrate, below said hollow members, to form strands, the hollow members being positioned above the plane of application, wherein each of the orifices of one hollow member are aligned in the machine direction in relation to the corresponding orifices of the other hollow member(s) This device enables application of the components of a gluing system, such as a resin and a hardener, onto a substrate, wherein the later applied strands of one component are overlapping the previously applied strands of the other component(s). Another suitable device for such application of the components used in the present method, is a device comprising a unit of at least two hollow members, at least one member for each component, provided with a number of oπfices in each member designed to apply the respective component onto a substrate below said hollow members to form strands, the hollow members being positioned above the plane of application, wherein each of the orifices of one hollow member are parallel displaced in the machine direction in relation to the corresponding orifices of the other hollow member(s) This device enables application of the components of a gluing system, such as a resin and a hardener, onto a substrate, wherein the later applied strands of one component are app ed at a certain distance, depending on the gluing system used and the wanted assembly time, in relation to the previously app ed strands of the other component(s) A preferred method of separate application in the form of strands is a method wherein the above device is used whereby the corresponding strands of the components used, are in essentially continuous contact with each other throughout the length of said strands In this manner, uniform contact of the resin and hardener strands is secured at the time of application, while the more fully intermixing of the two components generating the gas, is not established until the time of pressing As an example of another suitable embodiment of the method of the invention, a method wherein the resin component preferably is applied first, in the form of strands, which strands optionally can coalesce to form an essentially continuous layer thereof, whereupon the hardener component, in the form of strands, or by means of spraying, is applied, can be used This embodiment is, for example suitable when it is desired to minimise the contact of hardener and substrate In the following two examples, roughly planed pieces of spruce were provided with a conventional non-expandable gluing system, and with an expandable system of the invention, respectively, by means of separate strand application of the two components after each other Thereafter laminates were formed from the pieces with the non-expandable, and the expandable gluing system, respectively, and subsequently tested for delamination EXAMPLE 1 Substrate 90 cm x 15,5 cm pieces of spruce Resin component SL97044 (a melamine-urea formaldehyde resin, containing calcium carbonate as the gas generating substance) Content of gas generating substance in the resin 1 % by weight Hardener component formic acid based Molar ratio of resin/hardener 100 30 Amount applied 400 g/m2 Order of application resin, then hardener After application, the laminates were pressed at a pressure of 7-8 bar during the night After one day of after-curing the laminates were tested for delamination The results are shown in the Table below EXAMPLE 2 (COMPARATIVE) Example 1 was repeated with the only difference that the resin component used was SL97043 (a melamine-urea-formaldehyde resin containing no gas generating substance) The resulting laminates were tested in the same way as described above and the results are given in the Table below TABLE Gluing system=SL Delamination Gluing system Delamination 97043 / formic acid =SL97044 * /formιc based hardener acid based hardener (expandable) Lamιnate=A 18,3% 3,9% B 3,21% 0,7% C 0% 0,7% D 0,5% 0 E 2,9% 0 F 3,4% 1,3% G 6,3% 1 ,3% H 5,6% 0 1 7,5% 0,5% Average 5,9% 0,9% * SL97044 = SL97043 + gas generating substance From the table, it can be clearly seen that the delamination results for the laminates formed using the gluing system according to the present invention are substantially improved, as compared to those for the laminates formed with the non- expandable gluing system The delamination was determined according to EN-391-B Thus, these examples clearly demonstrate the improvements obtained with the method of the present invention, wherein an expandable gluing system is used, as compared to the usage of a non-expandable gluing system

Claims: CLAIMS 1. A method of gluing pieces of substrate together, by using an expandable gluing system comprising a resin component and a hardener component, characteri z e d in that the hardener component is acidic, and the resin component comprises one or more gas generating substances capable of forming a gas when contacted with the hardener component, wherein the resin and the hardener components are separately applied onto the substrate. 2. A method according to claim 1, c h a r a c t e r i z e d in that the gas generating substance(s) is/are included in the resin component in an amount of 0.1-10 % by weight, as calculated on the pure, active form of said substance(s). 3. A method according to claim 2, c h a r a c t e r i z e d in that the gas generating substance(s) is/are included in the resin component in an amount of 0.1-1,9 % by weight, as calculated on the pure, active form of said substance(s) 4. A method according to any of claims 1-3, characterized in that the gas generating substance is a carbonate, or hydrogen carbonate which generates C0 2 upon contact with an acid. 5. A method according to claim 4, c h a r a c t e r i z e d in that the gas generating substance is calcium and/or sodium carbonate. 6. A method according to claim ^ ch a ra ct e rize d in that the acidic hardener comprises a carboxyiic acid. 7. A method according to claim 6, characterized in that the carboxyiic acid is formic acid, or maleic acid. 8 A method according to claim 1, ch a ra cte rized in that that the resin used is an ammo resin. 9. A method according to claim 8, characterized in that the am o resin is selected from the group of melamine-urea-formaldehyde. melamine-formaldehyde, and urea-formaldehyde resins. 10. A method according to any of the previous claims, characterized in that the components of the gluing system, the resin and the hardener, are separately applied, in the form of strands, in optional order, onto the substrate. 11 A method according to claim 10. ch a r a cte r i z e d in that the later applied strands of one component substantially overlap the corresponding previously applied strands of the other component. 12. A method according to claim 11, characterized in that the hardener component is applied in the form of strands on top of the resin strands. 13. A method according to claim 10, c h a ra ct e ri ze d in that the later applied strands of one component do not overlap the corresponding previously applied strands of the other component 14. A method according to claim 10, ch a ra cte rize d in that the later applied strands of one component do not contact the corresponding previously applied strands of the other component 15. A method according to any of the previous claims, characterized in that the substrates are made of wood. 16. A method according to any of the previous claims, characterized in that the mam formation of the expanding agent occurs during pressing of the pieces, to which the gluing system components are applied, for gluing them together, in order to prepare a glued aggregate 17. A device for carrying out the method according to claims 11 or 12, comprising a unit of at least two holiow members, at least one member for each component, provided with a number of orifices in each member designed to apply the respective component onto a substrate below the hollow members to form strands, the hollow members being positioned above the plane of application, wherein each of the orifices of one hollow member are aligned in the machine direction with the corresponding orifices of the other hollow member(s). 18. A device for carrying out the method according to claim 13 or 14, comprising a unit of at least two hollow members, at least one member for each component, provided with a number of oπfices in each member designed to apply the respective component onto a substrate below the holiow members to form strands, the hollow members being positioned above the plane of application, wherein each of the orifices of one holiow member are parallel displaced in the machine direction in relation to the corresponding orifices of the other hollow member(s).

Inventors: LINDBERG STEFAN, NASLI-BAKIR BENYAHIA, LINDBERG, STEFAN, NASLI-BAKIR, BENYAHIA
Applicants: AKZO NOBEL NV, CASCO PRODUCTS AB, LINDBERG STEFAN, NASLI BAKIR BENYAHIA, AKZO NOBEL N.V., LINDBERG, STEFAN, NASLI-BAKIR, BENYAHIA
Application year: 1999
Main classification: C09J5
IPC codes: B05C5, B05C9, B05D1, B05D5, B05D7, B32B7, C08L61, C09J5, C09J161