A METHOD OF JOINING MATERIALS

Abstract: In the bonding of materials using water based adhesives or adhesives which liberate water at curing water from the glue joint is bound by means of a compound which combines with water of crystallization. The method can be utilized in several types of joining processes using drying or curable adhesives and the method speeds up the gluing process.

Description: A method of joining materials The present invention relates to a method of binding water at joining of materials using water based adhesives or adhesives which liberate water at curing. More particul- 5. arly the invention relates to such a method wherein water is bound to a compound in the form o"r water of crystalliz¬ ation. The method of the invention can be uti lized in many fields such as for example in the production of composite wood and wood based materials, in the production of cellu- 10. lose based board materials, in the bonding of carpets to different kinds of substrates and in other types of bonding operations at eg mounting and renovation. The method of the invention is particularly suitable for gluing of dense materials and at thick glue joints and another field in 15. which the present method is very advantageous is in the production of paper cores for the paper industry. Different kinds of binders, adhesi es, which solidify and give the desired glue joint through release of water are per se well known and used in a number of fields. "Dry- 20. ing" adhesives in which the binder is dispersed or dissolved in water give a joint by release of water and formation of a continuous phase without any actual chemical reaction, or curable adhesives the transformation to a solid phase, or the development of the binding capabi lity, includes 25. a chemical reaction. Several types of water based curable adhesives and adhesives w ich liberate water at the curing exist and they are usually used in the form of two-component systems, ie in the form of a resin which at the joining is mixed with or applied in combination with a hardener. 30. Whi le drying adhesi es are mainly used for gluing of paper, wallpaper, floors and simi lar products, curable adhesives such as formaldehyde based amino- and phenolic resins, are mainly used for bonding wood, wood based and cellulose based materi a I s . 35. A common problem when using adhesives which are water based and/or liberate water at curing is that the water as a rule must be made to be released as uniformly as poss ble to give a final strong joint and a joint over the entire intended area in such a manner that the dimen- sional stability and the strength propert es are not nega ¬ tively influenced. In certain applications, such as for example the production of particle board and plywood, high temperatures and pressures are used in the presses to re- 5. lease the main part of water, while the release of water in other applications must occur at ambient temperature or only somewhat elevated temperatures. The simplest way of reducing the drying time is of course to use aqueous adhesive compositions of as high dry contents as possible, 10. but here factors such as d stribution at spreading, wetting and penetration give certain limits and even when adhesives in more or less entirely dry form are used these can libe¬ rate water at curing which it is desirable to remove. Thus there remains a desire to remove water in processes for 15. joining wherein water based adhesives or adhesives which gi e off water at curing are used and to do this in such a manner that strength properties and dimensional stability at least are retained. The present invention offers a method of binding 20. water so that it is not present in free form and needs to be removed by heating, prolonged storage, other waiting- times etc, at joining materials using adhesives of the above mentioned types and the method of the invention can considerably speed up the gluing process. The method of 25. the invention can be utilized in most types of joining of different kinds of materials and give great advantages. The method is particularly advantageous at thick glue joints, eg when bonding wood having poorly treated surfaces or when low pressures are used, for example at bonding 30. processes within house building, and at bonding of dense materials, such as bonding of metal to wood where the prob- ' lems with water release are particularly pronounced. The method of the invention is par icularly advantageous at the joining of materials which cannot be subjected to higher 35. drying temperatures without risking an uneven release of water and wherein very high demands are made on dimensional stability and strength. Acccording to the invention con¬ siderably reduced times for development of the final oint strength and at the same time a substantial improvement of this can be otained at such types of joining processes. The present invention thus relates to method of bind ¬ ing water from the glue joint at joining of materials using water based adhesives or adhesives which liberate water 5. at curing according to which method water is bound as water of crystallization to a compound wh'ich is present in at least one of the materials to be joined, or to a compound which is formed in connection with the joining. The method of the invention can be used at joining 10. of materials using water based adhesives and/or adhesives which liberate water at curing. These adhesives can funda¬ mentally be classified as drying adhesives i .e. adhesives which set by drying, and curable adhesives. According to the invention a compound which can bind water of crystal- 15- Lization is present at the joining process and hereby a substantial acceleration of the drying or the curing can *r be obtained for these types of adhesives. The drying adhesives are aqueous dispersions of par¬ ticles of natural or synthetic materials or water solutions 20. for which the bonding capabi lity is obtained through release of water and transition to a solid continuous phase. Examp¬ les of this type of adhesives are sodium si licate and natu¬ ral polymers such as animal glue, starch, natural rubber etc, and synthetic polymers ' sueh as synthetic rubber, poly- 25. vinyl alcohol, polyvinyl acetate etc. The drying adhesives are usually used in the form of aqueous dispersions or solutions with dry contents of from about 20 to about 80 per cent by weight and the principal applications for these are in bonding of paper products and other types of lamina- 30. tion processes, in bonding at renovation and assemblying etc and in other applications where the demands on strength under load and under outdoor conditions are not particularly emphasi zed . The curable adhesives give rise to the bonding capabi- 35. Lity through a chemical reaction which in most cases in¬ volves release of water. The curable adhesives are usually used as two-component systems, i .e. in the form of a resin and a hardener for the acceleration of the chemi cal reac¬ tion. When the term adhesive herein is used for curable adhesives this then also includes such two-component systems and hereby also, with regard to the compound which according to the invention shall be formed at the joining, that com¬ pound or compounds from which this is formed, can be present 5. in either of the two components or in both. Examples of this type of adhesives are amino-formaldehyde resins, such as urea-formaldehyde resins and melamine-formaldehyde resins, mixtures and co-condensates of these, phenolic resins and resorcinol resins. Ami no-for a Idehyde resins 10. are cured under acid conditions while phenolic resins and resorcinol resins in most cases are cured under alkaline or neutral conditions. The curable adhesives are generally used in the form of aqueous solutions of resin and hardener respectively and the dry contents for the resin solutions 15. are generally from about 40 to about 70 per cent by weight and the dry contents for the hardener solutions are gene¬ rally from about 5 to about 75 per cent by weight. It does, however, happen that both resin and hardener are used in dry form. The principal applications for these curable 20. adhesives are in the production of composite cellulose based board materials such as particle board and fibre board, in the production of plywood and wood or wood based .constructions where the demands on strength usually are very high. 25. According to the present invention water is chemically bound at joining as water of crystallization to one or several compounds, e.g. salts, and this is the fundamental idea behind the present invention. The method of the inven¬ tion is thus generally applicable in connection with bonding 30. processes using water based adhesives, drying and curable adhesives, and the method can be used when bonding different kinds of materials, as stated above. However, the method of invention is particularly suitable when curable adhesives are used for the bonding and it is hereby especially advant- 35. ageous to use as the compound which combines with water of crystallization, or which takes part in a reaction for formation of one or several such compounds, a compound which also can act as hardener for the resin. According to the present invention water from the glue joint is bound by the presence of a compound which can bind water as water of crystallization or by the forma ¬ tion of such a compound, or of course several such com¬ pounds, at the bonding. The compound should be able to 5. combine with at least one mole of water per mole, and suit ¬ ably with at least 4 moles of water, and hereby it is under ¬ stood that at a reaction for formation of two or several compounds which combine with water of crystallization these together should combine with at least one mole of water 10. and preferably with at least 4 moles of water per mole of formed compounds. The compounds which are used for thei r capabi lity of combining with water of crystallization or for reaction to compounds with this capabi lity are of course selected with regard to the adhesive used in he bonding 15. and with regard to other conditions at the bonding so that negative effects are avoided. Thus when a curable adhesive is used and the curing is obtained by acidic compounds, as is the case for ami no-forma Idehyde resins, the compound should be an "acid salt" and hereby is then understood 20. a salt which gives an acid reaction in aqueous solution and thus lowers the pH of the original resin solution. For adhesives which are cured in alkaline or neutral environment such as phenol and resorcinol resins "basic or neutral salts" should of course be used, ie salts which in aqueous 25. solutions give a neutral or alkaline reaction and thus increases the pH of the original resin solution. When drying adhesives are used the demands on a pH range at the actual bonding are often not that specific and here salts for the b nding of water of crystallization can thus be chosen 30. more freely. As examples of suitable compounds having water of crystallization which can be used according to the inven¬ tion as acid salts the follwing can be mentioned: sulphates, particularly different aluminum sulphates, sulphates of alkali metals and alkaline earth metals such as sodium, 35. calcium and magnesium sulphate, other aluminum compounds, such as for example aluminum chloride and aluminum nitrate. As particularly suitable aluminum sulphates can be mentioned AL_(S0 ) 3 -18H-0, NaAl(S0, ) 2 -12H-0, K-S0 4 • AI_ ( S_ 4 ) - - 24H-0, (NH, )-S0. Al_ (SO. )_ -24H-0. As examples of basic or neutral ά 5 _ salts can be mentioned carbonates, halides and phosphates of ammonium, alkali metals and earth alkaline metals. Further nitrates, nitrites and borates of alkali and earth alkaline metals can for example be used and also, for 5. example, barium hydroxide. As examples of particularly suitable neutral and basic salts can be mentioned: Ba(0H)_ -8H 2 0, CaBr_-6H_0, CaCl-'όH-O, Ca (NO- ) - • 4H-0, MgBr -6H-0, Na-B.O -10H-0, Na CO -10H-0 and Na PO^IOH.O. The compounds can be added in wholly or partly dehydrated 10. form or be formed in their hydrated form by reaction between added compounds for this formation. As example of formation of compounds with the capabi¬ lity of binding water the following reaction can be given Al-CSO. ),*18H-0 + 6NaCl > 2AIC I, -6H-0 + 3Na_SO . • 10H-.0 _ 4 _ -> _ _ _ 15. As evident, two compounds are formed at this reaction and the net binding of water in the reaction is 24 moles of ^_ H-0. A certain part of the water of crystallization in the aluminum sulphate that is used could be evaporated for example from material impregnated with this and thus 20. increase the net amount of bound water of crystallization. The above reaction is particularly advantageous since two compounds which combine with water of crystallization are formed and also since the original aluminum sulphate and also the formed aluminum chloride can act as hardener when 25. amino-formaldehyde based res ns are used. With regard to the different fields wherein the present method can be utilized and with regard to the vary¬ ing molecular weights for compounds which combine with water of crystallization it is difficult to state general 30. amounts for addition to the materials or the adhesives. Naturally as high amounts as possible in each application are used to bind as much water as possible. However, con¬ sideration must be taken in order not to get a negative influence on the function of the adhesive. The compound 35. or the compounds which are added are suitably used in such amounts that at least 10% of added and/or formed water is bound and preferably so that at least 50% of the water i s bound. The actual addition of the compounds can be carried out in several different ways. A compound can for example be mixed into a solution of resin or of hardener, or in both. When two compounds capable of forming a compound which binds water of crystallization are mixed in a resin 5. and a hardner the compound which binds water of crystalliza ¬ tion is formed when the resin and the hardener are con¬ tacted. It is also possible to mix one of these compounds in the adhesive or a component of the adhesive and add 10. the other compound to one of the materials to be joined, whereby the compound which binds water of crystallization is formed at the joining. The compound which binds water of crystallization, or the compound or compounds which give a compound which binds water at the bonding, can be 15. added separately. The compound which binds water of crystal¬ lization can be formed at contact between one of the mate¬ rials to be joined and a separatley applied compound or at contact between the adhesive and a separatley applied compound. It is further also within the scope of the inven- 20. tion that when it is stated that a compound is present in one of the materials to be oined this compound can be present either by having been separately appl ed and impregnated in the material, which can be suitable for example at the production of tubes for the paper industry, 25. or have been applied on the surface "of one of the materials to be oined, for example at covering of floors or bonding of wood to metal etc. It is thus possible to apply a dehyd¬ rated salt in dry form on one of the surfaces to be bonded or to apply, in wet or dry form, a compound which is to 30. take part in a reaction for formation of a compound capable of combining with water of crystallization. Impregnation of a material with a dehydrated compound can be carried out using a solvent based or water based solution of hyd¬ rated compound followed by heating of the material for 35. release of water of crystallization from the compound. One field in which the present method is of great importance is the production of tubes for the paper in¬ dustry, ie in the production of spi ral wound tube formed products of board or paper board. Conventionally sodium silicate or polyvinyl alcohol are used as binders for the production of paper cores for the paper industry. These adhesives do give good adhesion but since they can only be used with low dry contents very long drying times are 5. necessary. Attempts have been made to use ami no-forma Idehyde resins ith higher dry contents in order to shorten the drying time. These attempts have, however, not given satis¬ factory results but it seems as if the denser glue joints which are obtained with these adhesives prevent the diffu- 10. sion of water vapour from the core. The cores which are produced for use in the paper industry should be capable of withstanding very high loads, thick cores should for example be capable of being loaded with up to 4 tons of paper. The demands on dimensional 15. stability are thus very high and consequently drying after bonding can generally not be carried out at temperatures above 30°C as water would otherwise be released unevenly, resulting in shrinkage and negative effects on the dimen¬ sional stability. At conventional production of cores it 20. takes from 3 to 6 days and nights and up to 12, varying with the thickness of the material, the type of adhesive and the relative humidity of the drying air, to liberate the water and obtain a core ready for use. Through binding water chemically as water of crystal- 25. lization according to the method of the invention consider¬ ably decreased drying times at the production of cores can be obtained and at the same time a substantial increase of the strength of the product is obtained. The method of the invention is of course applicable when the at this 30. production, conventional binders such as sodium silicate and polyvinyl alcohol are used and hereby gives a decreased .drying time. It is, however, particularly preferred to make use of the chemical binding of water in combination with the use of am no-formaIdehyde resins as adhesives, 35. and then preferably urea-formaldehyde resins but also mela- mi ne-forma Idehyde resins, mixtures and co-condensates of these . Compounds which combine with water of crystallization and which can be used in this embodiment are such compounds which have been enumerated above and when amino-forma Idehyde resins are used as binder particularly compounds with acid reaction. Most preferably different kinds of aluminium sulphates are used, in dehydrated form or in hydrate form 5. for reaction to other compounds which can combine with water of crystallization, and preferably also such aluminum sulphates which can act as accelerators for the curing or give rise to compounds functioning as such accelerators. The model reaction given above is particularly suitable 10. in this embodiment of bonding. At the production of the cores the paperboard for the core can for example be impregnated with a compound which combines with water of crystallization before the gluing or with a salt having water of crystallization w ich 15. can be evaporated by means of moderate heat, eg on the rolls in the drying section at the production of the paper- ^. board or in the size press. Alternatively, the impregnation can be carried out in an impregnating machine. Other methods which have been described above can of course also be used 20. in this production process, eg dissolution or dispersion of two compounds which do not have any water of crystalli¬ zation in resin and hardener respectively. At the production of cores in conventional equipment and bonding with ami no-forma ' ldehyde resin this is suitably 2 25. applied in an amount of from 25 to 150 g/m , as a 40 to 70% resin solution. As an example it can be mentioned that when an alu inum sulphate is used, dehydrated or for forma¬ tion of compounds which combine ith water of crystalliza¬ tion, an amount of aluminum sulphate in the range of from 2 30. about 5 to 90 g/m is required to bind principally the entire amount of water added with the resin. The invention is further illustrated in the following examples which, however, are not intended to limit the same. Parts and per cent relate to parts by weight and 35. tie r cent by weight respect ely, unless otherwise stated. Example 1 A paperboard material intended for the production of cores was impregnated with a 50% aluminum sulphate solu¬ tion and dried in a continuous heating oven for removal of the water of the solution and the water of cr sa11i zat on in the aluminum sulphate. The paperboard was then glued with an urea-formaldehyde resin containing 10 per cent by weight of NaCl. The dry content of the adhesive was 5. 70 per cent, after the addition of NaCl. After the gluing a core was obtained which did not show any change in weight 1 hour after the gluing and up to two weeks after this. The strength of the produced core was thus fully developed already after an hour or two n room temperature, which 10. should be compared with the traditional gluing with poly¬ vinyl alcohol or sodium silicate where drying in a drying equipment for several days and nights and is required to obtain fully developed strength. Example 2 15. 38 per cent by weight of NaNO, were added to a resor- cinol-phenol resin having a dry content of 56 per cent by weight. A hardener solution having a dry content of 64 per cent by weight was prepared from paraforma Idehyde, formaldehyde, filler and water. 30 g of K-CO, were added 20. to the hardener solution. Uneven material was glued and the glue joint was thick. The hardener solution and the resin solution were applied separately on two wood boards in an amount of 250 2 g/m for both. The boards were pressed .together using slight 2 25. pressure, 0.1 kg/cm , at room temperature. After 5 minutes the joint strength had been developed to such an extent that fibre breakage occured when testing by breaking the joint. At a corresponding gluing without addition of the compounds, sodium nitrate and potassium carbonate which 30. form a compound which combines with water of crystalliza¬ tion - sodium carbonate, about 40 minutes curing time is required for development of this joint strength. The hardener and resin solutions described above were also mixed as such and the mixture cured very rapidly. 35. The dry content befor the mixing was 69.8 per cent by weight and after the mixing it was 75 per cent by weight. An in¬ crease of the dry content of 7.5% was thus obtained through binding of water of crystallization and thus 17.2% of the water from the resin and hardener solutions had been bound.

Claims: Claims 1. A method of binding water from the glue joint at the joining of materials using water based adhesives or adhesives which liberate water at curing, characterized 5. in that water is bound as water of crystallization to a compound which is present in at least one of the materials to be joined, or to a compound which is formed in connection with the joining. 2. A method according to claim 1, character zed in 10. that the adhesive is a resin and a hardener for this and in that water is bound as water of crystallization to a compound which is formed at contact betwee.n these. 3. A method according to claim 1, characterized in that water is bound as water of crystallization to a com- 15. pound which is formed at contact between at least one of the materials to be joined and the adhesive, or a component of the adhesive. 4. A method according to claim 1, characterized in that water is bound as water of crystallization to a com- 20. pound which is formed at contact between at least one of the materials to be joined and a separately applied compound or at contact between the adhesive and a separately applied compound . 5. A method according to any of the preceding claims, 25. characterized in that the adhesives is a curable adhesive and that the compound which combines with water of crystall¬ ization or which takes part in a reaction for formation of a compound which combines with water of crystallization is a hardener component for the adhesive. 30. 6. A method according to claim 1, characterized in that water is bound as water of crystallization to a com¬ pound which is present in board or paperboard, at the production of tube formed products, or in that water is bound as water of crystalliza ion to a compound which is 35. formed in connection with the joining of board or paperboard to tube formed products. 7. A method according to claim 6, characterized in that water is bound as water of cr stallization at the joining of board or paperboard to tube formed products by means of an aqueous solution of an amino-forma Idehyde based resin. 8. A method according to claim 6 or 7, characterized in that the board or paperboard is impregnated with a salt 5. which at the joining takes part in a reaction for formation of a compound which binds water in the form of water of crystallization. 9. A method according to any of the preceding claims, characterized in that the compound which binds water of 10. crystall zation combines with at least 1 mole of water per mole. 10. A method according to any of the preceding claims, characterized in that at least 10 per cent by weight of added or formed water is bound. 15.

Inventors: KARLSSON INGVAR, KARLSSON, INGVAR
Applicants: CASCO NOBEL AB
Application year: 1987
Main classification: C09J5
IPC codes: C09J5, C09J201