ADHESIVE COMPOSITION

Abstract: Adhesive composition comprising a suspension of an aqueous silicate solution and a finally divided inorganic filler, wherein said silicate solution has a silicate content of at least 17 % per weight and comprising as a filler a zeolite having an average particle size of at least 0,4 mu m.

Description: Title: Adhesive composition. The present invention relates to adhesive compositions, comprising a suspension of an aqueous silicate solution and a finely divided inorganic filler. From GB-A-2058818 such an adhesive composition is known. Disclosed is a spray coating adhesive composition comprising (i) a solution of an alkali metal silicate (ii) 1 to 10 % by weight of finely divided inorganic powder containing, mineralogically, more than 15% kaolinite and (iii) finely divided silica. The silica is preferably included in the form of an organic silicic acid. In this patent application, the kaolinite clay is used as filler/stabilizer. The total amount of fine filler material is limited to a maximum of 10 % by weight. Although such known adhesive compositions perform reasonably improvement of the adhesive properties is still required. The present invention now provides an adhesive composition, comprising a suspension of an aqueous silicate solution and a finely divided inorganic filler, said adhesive composition being characterised in that said silicate solution has a silicate content of at least 17% by weight, and comprises as a filler a zeolite having an average particle size of at least 0.4 μm. Surprisingly it was observed that when using zeolite as filler material in an aqueous silicate solution, an adhesive composition can be obtained with a very high initial tack and a strong final bonding which adhesive has a low moisture content allowing fast drying. The silicate in the adhesive remains soluble after drying, as long as the adhesive is not hardened, which allows for excellent recycling properties of the bound substances, e.g. paper etc. Furthermore, the adhesive is more flexible and is superior with respect to initial tack and drying compared to all silicate adhesives known in the art. Zeolites are well known relatively inert environmentally harmless substances. Examples of zeolites, which are available or can be produced in fine particulate form are zeolite 4A, zeolite P, zeolite X and zeolite Y. Zeolite P is preferred, because of its layered structure, being substantially non abrasive and relatively soft, also implicating less wear in machinery. A suspension according to the present invention comprising synthetically produced zeolite P can be produced, having the additioned advantage of not containing carcinogenic crystalline silica (quartz, cristobalite) as can be the case when inorganic mineral fillers are applied. As these crystalline silicas are declared to be carcinogenic, it is to be expected, that their use will have to be restricted or even prohibited globally by law. The average particle size of the zeolite, according to the invention is preferably 0.4-15 μm, more preferably 0.4-5 μm, and most preferred 0.8-2 μm. In a very specific embodiment the average particle size is 0.8-1.5 μm. Preferably the content of the zeolite is comprised between 2 - 50 % by weight, more preferably between 10 - 40 % by weight, and most preferred between 10 - 30 % by weight. The silicate content of the silicate solution is advantageously at least 20% by weight. In the adhesive composition according to the invention the aqueous silicate solution is not specifically limited and can be selected from known silicate solutions depending on the specific application requirements. In particular the silicate solution is an alkali metal silicate solution, i.e. Na-, K- , or Li- silicate solutions or an ammonium silicate solution, or a mixture thereof. In the present specification the Si0 2 /M 2 0 molar ratio of the silicate will be used as a measure to identify the specific silicate solution, wherein M designates the specific alkali metal or ammonium (Na, K, Li, NH 4 ) . The Si0 2 /M 2 0 molar ratio of these soluble silicates can vary from 1.0 to around 4.0 and for lithium silicate even higher up to 4.5. All silicate solutions are alkaline, but the alkalinity decreases with increasing molar ratio. Consequently silicate solutions with higher molar ratios are safer in handling, which is demonstrated by the following safety classification of the standard silicate solutions as offered on the market . Molar Ratio Solutions offered Classification SiONM.,0 : on the market as : in Eurcpe (Safety) : 1.0 Metasilicate Corrosive 2.0 "Alkaline" Silicate Highly Irritant (or: "Alkaline waterglass") 3.3 "Neutral" Silicate Not classified as (or: "Neutral waterglass") unsafe For those applications requiring hardening it is also preferred to maximize the Si0 2 content and consequently also the Si0 2 /M 2 0 ratio to minimize the amount of hardener required. The Si0 2 /M 2 0 molar ratio of the aqueous silicate solution is advantageously comprised between 1 - 4.5, preferably between 2 - 4.2, more preferably between 2.8 - 4.2 and most preferred between 3.3 and 4.2. Advantageously the silicate of the silicate solution in the adhesive composition according to the invention comprises potassium silicate or sodium silicate or mixtures thereof. The adhesive compositions according to the invention can be used for all kinds of adhesion purposes e.g. paper, wood, concrete, bricks, floor tiles, rubber, leather (e.g. shoes) , glass, metal (e.g. aluminium foil) , plywood, plasterboard and woodchip manufacture etc. Especially materials with irregular surfaces which are usually difficult to adhere, like filter paper, wood or concrete can be adhered to each other or other surfaces by use of an adhesive according to the invention. The adhesive is particularly suitable for bonding of perlite, vermiculite, glass fibre, mineral fibre, rockwool, for e.g. thermal or acoustic insulation in blankets, panels, boards, shapes, inserts, spray-on coatings and the like . The suspension according to the invention causes a very fast initial tack and dries relatively quickly, gives a flexible bond and significantly reduces dusting. Advantages of the adhesive compositions according to the invention are a.o.: - There are no organic compounds (incl. volatile solvents) used. - There is no necessity to clean or dry the surfaces before using the silicate suspension as adhesive and the (inorganic) adhesive reduces the flammability of the materials used. Because of the absence of the organic compound, materials, which are safe per se, which are bonded by adhesives according to the invention (e.g. paper, cardboard, wood, sand, soil, etc.) may be safely disposed by e.g. landfill. Adhesive compositions according to the invention comprising pure zeolites of the P-type like Zeocros CG180 as a filler have additional benefits when used for paper and card board, related to the growing demand for recycling of paper and card board, as these adhesives contain exclusively silicate and zeolite, both being beneficial in the recycling process in contrast to the organic compounds used in many alternative adhesives used like PVA, PVOH and dextrine, which can be more detrimental in the recycling process. The Si0 2 /M 2 0 molar ratio of the aqueous silicate solution of the adhesive according to the present invention, M being alkalimetal or ammonium, is preferably comprised between 2.8 and 4.2. A higher molar ratio usually leads to viscous products . These viscous products can however still be used as adhesives and may be, if required, diluted in order to reduce the viscosity. The average particle size is preferably below 3 μm. A preferred example of a suspension which is suitable for use in an adhesive composition according to the invention is a suspension of zeolite Zeocros CG180 of Crosfield (Eijsden, The Netherlands) in a 10% to 30% % by weight suspension thereof in neutral silicate containing around 35% by weight of silicate with a molar ratio of about 3.3, the average particle size of the Zeocros CG180 being about 1 μm. If a small amount of such a suspension is spread over a part of a surface of a paper sheet and then covered with another paper sheet, it was found, that an immediate strong tack was obtained and that drying took place under normal conditions at approximately 20°C within a few minutes . Strong binding between the bound paper parts was realized for filter paper as well as for standard paper and the paper parts could not be separated without tearing. By use of the adhesive according to the invention a reduced flammability of the bound paper parts is obtained, no organic compounds are used and a better binding is obtained. With adhesives, according to the invention laminated paper, like spirally wound laminated paper tubes, cardboard, corrugated cardboard, wall-paper, laminated wood, plywood, leather, e.g. shoe soles and building materials can be manufactured. It was observed that for the adhesion of bricks and shoe soles, the use of suspensions of zeolite Zeocros CG180 with higher zeolite contents (e.g. 27 %) were giving stronger binding and are therefore preferred. The adhesive can also be used to bind powders or other particulate or fibrous materials to form larger agglomerates , e.g. for the production of structural building components, like bricks, roof tiles etc. Also it can be used for the preparation of paper-mache for manufacturing paper articles . Adhesives according to the invention can also be used to bind stones, bricks or concrete building materials for the construction of walls, houses and also for the repairs of shoes and shoe soles, by adhesion of leather components. It was found, that for these applications as adhesive, addition of a surfactant or a hardener was not necessary as long as there is sufficient porosity in the material bound together to allow penetration of the adhesive and to allow the suspension to dry. However in case evaporation of the water present in the suspension is too slow or if better water resistance is required, a hardener and/or a surfactant can be added. As surfactants, cationic surfactants like cetyltetra ammoniumchloride may be preferred. The present invention also relates to the use of an adhesive composition for the manufacture of cellulose containing materials, like paper articles, e.g. papier-mache, laminated paper, such as cardboard, spirally or convolutely (parallel) wound laminated paper tubes and drums and the like. For example, the adhesive can be used in a method for manufacture of tubes comprising two or more layers of cardboard and/or paper, wherein at least an adhesive is applied on at least one of the surfaces of the said layers, the layers being spirally or convolute wound over each other, wherein an adhesive according to the present invention is applied on the said surface (s). By using the adhesive in the method for manufacture of the said tubes and drums, an improved hardness and better crush strength and lower moisture content in the final tubes and drums can be obtained compared to organic adhesives used in practice (e.g. : dextrin or polyvinylacetate (PVA) . Surprisingly, the production speed can be increased compared with adhesives used in the state of the art. Furthermore the same adhesive can be used to adhere the outer layer of the tubes, normally a thin paper layer, to the other layers, normally freshly made of cardboard. In the state of the art, different adhesives have to be used to adhere said thin paper layer to the outer cardboard layer on the one hand and to adhere the cardboard layers with each other on the other hand. Paper material being coated with the adhesive according to the present invention has fire retardant properties. This is a remarkable and important feature, as paper/cardboard products made using the adhesive according to the present invention can be used at high temperatures and are safe in use and during storage. In laminated paper articles the adhesive according to the present invention may be formed as a layer between the paper layers, so that each paper layer therein has the said fire retardant properties. The adhesive suspensions according to the present invention can optionally advantageously be used as fireproof coating on all kinds of substrates which are e.g. discussed above. In particular the adhesive composition according to the present invention can be used as a binder for rockwool of glass fibre . It will be clear that the above cited applications are not meant to be an exhaustive enumeration and that many other applications are feasible. Advantageously the suspensions according to the invention can be hardened by using a hardener system. Preferably said hardener comprises an amorphous silica, or alternatively an amorphous metal silicate, like aluminium silicate, magnesium silicate or calcium silicate. Other hardener systems know in the art may be used as well. The hardener systems, based on amorphous silica and/or amorphous metal silicate is described in the copending PCT application number 98/XXXXXX, having the same filing date as the present application. The use of a hardener improves the waterresistance of the adhesive remarkably. This means that such an adhesive could be used for application where whetherproof properties are required . By the addition of a hardener system, the solubility of the silicate comprised in the dried suspension is reduced substantially. Such adhesive could be used for outside applications, construction of buildings for bonding bricks of outside walls, bonding leather to be used outside like shoe soles etc. or for bonding wood for outside purposes. In a preferred application the adhesive according to the invention comprising a hardener system is used for coating metal or other corrosion sensitive services to provide corrosion protection. In the following a number of examples are provided to illustrate the present invention and these examples are not intended to limit the invention as defined in the enclosed claims. All percentages are percentages by weight unless specifically stipulated otherwise. EXAMPLES Material used: A. Commercial name Crystal 0070 (Crosfield Eijsden (NL) Product Neutral sodium-silicate liquor Dry solid content 35.06 % Si0 2 content 26.81 % Na 2 0 content 8.25 % Density (20 °C) 1355 g/1 Viscosity 51 cP C. P-type zeolite in dry powder form Commercial name Zeocros CG180 (Crosfield Eijsden) Dry solid content * ) 90 % Particle size ** ) 0.7 - 3 micrometer Average particle size ) 0.92 micrometer D50 1.22 micrometer Effective density *** ) 2480 g/1. * ) Measured by heating at 800 °C during 30 minutes **) Measured by the sedimentation technique using Sedigraph type 5100, marketed by Micromeritics *** ) Measured by immersion in water. EXAMPLE 1 AND 2 Preparation of a suspension of 18% and 27% of a P-type zeolite with an averaσe particle size of 0.92 micrometer in a neutral silicate liσuor. 400 g (example 1) or 350 g (example 2) of a neutral silicate liquor (A) was introduced into a beakerglass of 600 ml. Under intensive stirring, 100 (example 1) or 150 g (example 2) of the P-type zeolite powder was added in approximately 5 min. Stirring was continued until the zeolite powder was completely suspended (approximately 5 min) . The suspension obtained had the following characteristics: Example 1 Example 2 Zeolite content (bone-dry zeolite) (%) 18.0 27.0 Si0 2 content (in aqueous phase) (%) 21.45 18.77 Na 2 0 content (in aqueous phase) (%) 6.6 5.77 Silicate content (bone dry) (%) 28.05 24.54 Total Dry Solid content (%) 46.05 51.54 Total H 2 0 content (%) 53.95 48.46 Density (20 °C) (g/1) 1470 1550 Viscosity: cP at D s "1 17.7 3470 27.2 2480 41.7 1790 64 366 1331 99 297 973 150 254 730 232 217 594 358 186 Stah-i lity of the suspensions: The stabilities of the suspensions were assessed as in Example 1 in a 250 ml glass cylinder of the same shape and dimensions . Results : Example 2 Example 3 Storage Phase separation Sediments on Phase separ . Sediments on Time in top layer cylinder bottom top layer cylinder bottom (days) 1 0 0 0 0 2 0 0 0 0 5 0 negligible negligible 0 20 0 negligible negligible 0 Also these suspensions have an excellent stability . From this result it was concluded, that 5 days storage is sufficient for the assessment of the stability of a suspension . EXAMPLE 3 Test on adhesion of filter paper Materials used: - 2 pieces of laboratory filter paper - material from Example 1 (18 % P-type zeolite in neutral silicate liquor) A few drops of the suspension were applied to one surface of one piece of filter paper. The other piece of filter paper was put on the first one and the filter papers were pressed together by hand, whereby the suspension was spread over a surface area of approximately 2 cm 2 . Clear immediate tack could be observed and within 5 minutes the suspension had sufficiently dried and it was then impossible to separate the papers without tearing them. EXAMPLE 4 Adhesion test with writinσ paper The same test as in Example 3 was carried out with standard commercially available paper sheets from a writing pad. The same observation could be made: Good adhesion (tack) and strong binding within 5 min, after which it was also not possible to separate the sheets without tearing them. Excellent and fast adhesion was obtained. EXAMPLE 5 Manufacture of multilayer cardboard tubes With a spiral winder comprising a paper breaking and single sided cascade adhesive application system with variable paper feed speed between 17 - 60 m/min, three types of tubes were produced. Type 1: outer diameter 79 mm, inner diameter 70 mm (4.5 mm wall thickness 8 plies standard Schrenz (Germany) cardboard, COBB value above 200 gsm, 0.5-0.6 mm, with outer ply of thin white paper) . Cut off lengths 1.7 m, cutter time 10-15 s. Type 2: outer diameter 75 mm, inner 70 mm (2.4 mm wall thickness, 4 plies standard Schrenz cardboard, COBB value above 200 gsm, 0.5-0.6 mm, with outer ply of thin brown paper) . Cut off length 2 m. Type 3: outer diameter 76 mm, inner diameter 70 mm (5 plies standard high quality core-board, COBB value approximately 30 gsm, without an outer wrap) . Adhesive formulation: 1000 kg straight sodium silicate (MR 2.95, 39.50 Be (20 °C) . Adjusted with A24 zeolite to a viscosity of 1'20" (DIN cup B funnel 4 mm), which in this case was 300 kg A24 (23.02% wt) . The final density of the mixture was 1520 kg/m 3 . The material was mixed in 100 1 drums until the zeolite was properly dispersed (checked visually) . The production took place 5 days prior to the test. The suspension formed was stored for 4 days under ambient conditions (17 °C) and remixed the day before testing. Application temperature: 21 °C. Test results All tube types could be manufactured without problems . The difficulties to glue type 3 tube encountered with adhesives from the state of the art were not observed. Paper feed speed could be risen till the maximum speed without occurrence of paper slip. The adhesive application related to paper weight was varied from 8 to 20% without occurrence of slip. The tubes were dried at 105 °C. Using 20% adhesive (related to the paper weight) the weight of a 31 cm tube was 297.48 g directly after production. After four days drying at ambient temperature the weight decreased to 241.83 g (6.07 % weight loss) . In a similar experiment, using 8% adhesive (based on paper weight) the weight loss was 3.50 %. Compared to tubes, produced with an adhesive from the state of the art (PVA from Scholten Lijmen) the hardness and therefore the maximum crush strength of the tubes improved with more than 10%. Also, the strength builds up at lower tube deformation and stays constant at higher deformations (measured up to a deformation of 9 mm on an outer diameter of 100 mm) . Cardboard tubes produced with PVA or dextrine as adhesives were easily ignited with a gas burner with a medium flame. The fire was sustained and the cardboard completely burnt . The same cardboard tubes could however not be ignited even by a gas burner at maximum temperature. When the burner was removed there was no sustained fire/flame. EXAMPLE 6 Adhesion test with 2 pieces of wood Materials used: - suspension of Example 1 - 2 pieces of wood with rough surfaces having the same dimensions (18 mm x 10 mm x 64 mm) A very thin layer sufficient to just cover one wood surface (18 mm x 64 mm) was applied on one piece of wood. The wood pieces were then immediately pushed together by hand and left for approximately 1 min. Considerable tack could already be observed then. After approximately 10 min it was already extremely difficult to separate the pieces. High force was needed, although drying was not yet even complete. The pieces could again be fixed together without renewed impregnation. After another 10 min it was even more difficult to separate the pieces. Strong force from only a corner point was needed. The experiment was repeated using the same pieces of wood (using the opposite sides) and the same procedure. The binding strength was assessed after 24 h. Strong men were then not able to separate the pieces any more by hand. Afterwards, the bounded wood pieces were put in a glass of 0.6 1, filled with water in order to assess whether this wetting would negatively influence the binding strength. After 1 hour presence in the water, it was still not possible to separate the wood pieces. After 5 hours it was possible to separate the wood pieces again. This shows, that for normal use, drying under atmospheric conditions without the use of a hardener gives a sufficiently stable binding. However in case the particles bound together by such a suspension are in contact with water it is preferred that a binder is used neutralising the silicate and thus rendering the adhesive insoluble. A preferred binder is amorphous Silica. The adhesive according to the invention therefore provides an extremely good adhesion system for wood. Advantages are: * The wood surfaces need no pre-cleaning * The wood surfaces need no smoothening * The wood surfaces may be wet/humid and need no drying * No organic materials needed and no solvents EXAMPLE 7 and 8 Adhesion test with bricks having very rough surfaces Materials used: - 4 bricks of a type with very rough surfaces, as often used for the inner wall of houses, in case of double outside walls or for industrial buildings. The surface of the brick was having grains sticking out of the surface up to around 2 mm. Brick dimensions: 9.8 cm x 21 cm x 5 cm. - Suspension of EXAMPLE 1 for EXAMPLE 7. - Suspension of EXAMPLE 2 for EXAMPLE 8. A layer of approx. 2 mm of the suspension was brought on the surface (21 cm x 9.8 cm) of one brick and a second brick was immediately placed with the same surface on top of the surface covered with the suspension. After 5 minutes the brick of EXAMPLE 8 lying on top (top brick) could already be lifted, while the lower brick remained fixed to it. This was not yet the case with the bricks bounded by the suspension of EXAMPLE 1 in EXAMPLE 7, in which EXAMPLE the lower brick fell off. As the suspension was not yet dry, the bricks could be bound together again. After approx. 30 minutes also the bricks in EXAMPLE 7 were sufficiently bound, that the lower brick did not fall off any more. After a few hours already strong binding was realized and no separation was realized, when exerting maximum force by hand in EXAMPLE 8. In EXAMPLE 7, using the suspension of EXAMPLE 1, containing 18 % zeolite P, it was observed, that there was clear shrinkage of the suspension between the bricks, while this was minimal in EXAMPLE 8, using the more concentrated suspension of EXAMPLE 2, having a content of 27 % zeolite P. These tests demonstrate, that suspensions of zeolite in silicate solutions according to the invention, provide excellent adhesives for binding bricks and that increasing the zeolite concentration gives better results. EXAMPLE 9 Repair of leather shoe sole by adhesion using a silicate suspension. Material used : Suspension from EXAMPLE 2, i.e.: Suspension of zeolite of a P-type, Zeocros CG 180 in neutral silicate containing 27 % by weight zeolite. The suspension of Example 2 is used to repair a shoe of which the sole had turned loose during prolonged wearing. The used shoe and the used sole, which had turned loose during wearing was not cleaned, having a clearly dirty surface (with soil). The repair was realized as follows: An extremely thin layer of the suspension of EXAMPLE 2 was brought on the leather sole using a spatula. The sole was pressed on the shoe by hand. The excess of suspension was pressed out from the space between shoe and sole and removed, using a cloth. The sole was pressed on the shoe during 10 minutes and then already well stuck to the shoe. After 24 h, the sole was well fixed to the shoe and was carried during more than 3 weeks without any sign of losing binding strength. In the following examples different properties are varied for assessing the influence thereof on the adhesion properties of the adhesive according to the invention. EXAMPLE 10 ADHESION AS A FUNCTION OF INCREASING ZEOLITE CONTENT Substrate used : photocopy paper Raw material for adhesives : * Zeolite P : Crosfield' s ZEOCROS CG 180) * Sodium silicate solution Crosfield' s Crystal 0096: > Molar ratio Si0 2 /Na 2 0 : 2.95 > Silicate concentration : 35.1 % by weight TEST EQUIPMENT USED FOR ADHESION ASSESSMENT The following equipment was applied to assess the bond strength between two pieces of paper or cardboard as a function of time. The equipment comprises a device with two seperately moveable jaws for securing two pieces of material to be tested. Further a disc is present for pressing the two pieces of material together with a predetemined pressure for a predetermined period when adhesive is applied therebetween. The force necessary to seperate the two pieces of material after gluing and pressing can be recorded. The device comprises a CPU which is programmable with respect to pressing force/duration etc. In use two pieces of substrate to be bonded (150 by 45 millimetre and 210 by 45 mm) are fixed in the jaws of the equipment. A drop of adhesive of a predetermined weight/and or volume is brought on the upper side of the smaller piece of the substrate to be bonded (e.g. : paper or cardboard) . One drop of approximately 0.025 ml was used in the present tests. The second piece of substrate (which does not necessarily have to be of the same material) is then put immediately on top of the piece covered with the adhesive and the pieces are pressed together by means of the disc (diameter: 120 mm) , hydraulically pressing on top of the top piece for a predetermined time. After the disc is lifted, the pieces are torn apart laterally with gradually increasing force and the force needed to tear the pieces apart (bond strength) is automatically registered by a number directly correlating with this maximum force exerted. PAPER AND CARDBOARD QUALITIES USED The measurements were carried out using paper as well as a variety of cardboard qualities, i.e.: PAPER QUALITY * Photocopy papers 80 gsm (grammes per square meter) COBB value: 18 - 22 gsm. CARDBOARD QUALITY * Testliner 160 gsm COBB values : 35/60 gsm (different for the two sides of this cardboard) . Adhesives Used: The following suspensions were made with increasing quantities of zeolite P (Crosfield' s ZEOCROS CG 180) suspended in the above sodiumsilicate solution. 1 0 t. % Zeolite P 2 5 Wt. % Zeolite P 3 10 Wt. % Zeolite P 4 15 wt. % Zeolite P 5 20 wt. % Zeolite P Test result;s: The effectiveness of the adhesion of these suspensions (initial bond strength, also called: wet tack) was assessed in the equipment as described, using pieces of the photocopy paper and measuring the maximum strength which could be exerted laterally, 5, 10, 15 and 20 seconds after the pieces were pressed together. The following results were obtained: SUSPENSION TESTED BOND STRENGTH AFTER: 5s 10s 15s 20s 1 0.25 0.3 0.6 0.95 2 0.25 0.3 0.75 1.6 3 0.3 0.6 1.4 2.2 4 0.3 0.75 2.2 2.5 5 0.3 1.5 2.5 2.7 These tests clearly show, that with increasing concentration of zeolite P, the initial tack develops much faster, representing superior binding performance . The results also clearly demonstrate the far superior performance in comparison with the pure silicate solution. EXAMPLES 11-15 VARYING SEVERAL PARAMETERS AND SUBSTRATES A large series of tests was carried out, in which the following parameters were varied: * Substrates: Paper and a series of cardboard qualities with varying "COBB" values , being a standard qualification for cardboard (grammes of water absorbed on 60 seconds per square meter) . * Molar Ratio Si0 2 /NA 2 0 of the sodium silicate * Using potassium silicate Using mixtures of sodium and potassium silicate * Varying the concentration of the silicate in the silicate solution. In view of the excessive number of these tests, only the summary of the results is given, i.e.: EXAMPLE 11 INFLUENCE OF THE SUBSTRATE The substrate to be bonded influences the adhesion results substantially, as a result of which optimum suspension compositions for adhesion can vary for different substrates. The COBB value seems to be an indicative parameter. For substrates with high COBB values (>50) it is generally observed that better adhesion is achieved by increasing the molar ratio and/or by increasing the zeolite content and/or to a lesser extent also by increasing the silicate concentration. For substrates with a low COBB value it was found, that adhesion (initial bond strength) was improved by increasing the molar ratio. However it was also found that for these card boards there is an optimum for the zeolite P content, depending on the molar ratio and the concentration of the silicate. Depending on the concentration and the molar ratio of the silicate, the optimum zeolite P content varies between around 10 - 25 % by weight . There is furthermore a maximum to all these parameters determined by the practical realisation, which is related to a maximum viscosity. For substrates which were of a more hydrophobic nature, it was observed, that addition of small amounts (< 1 % by weight) of a surfactant had a positive effect. EXAMPLE 12 INFLUENCE OF THE MOLAR RATIO SiO.,/Na,0 Molar ratios were varied between 2.6 and 3.9, keeping all other parameters constant, whereby it was observed, that increasing the molar ratio generally improves the tack. EXAMPLE 13 SILICATE CONCENTRATION IN THE SILICATE SOLUTION Generally it was found, that increasing the silicate concentration, keeping other parameters constant, increased the initial bond strength. However, there is a limit to this given by the viscosity. When the viscosity becomes too high, the measured bond strength starts to get worse. EXAMPLE 14 VISCOSITY As mentioned in the previous chapters, it was found, that viscosities should not become too high to maintain favourable adhesion properties and therefore should not exceed a certain level, which mainly depends on the substrate, the temperature and the equipment. The optimum viscosity therefore will have to be determined by a person skilled in the art, but generally lies in the area of 100 - 400 cps, measured at 65 sec _1 . EXAMPLE 15 THE USE OF: * POTASSIUM SILICATE AND * MIXTURES OF SODIUM- AND POTASSIUM- SILICATE It was observed, that when suspensions of ZEOCROS CG 180 were made in which sodium silicate was replaced by potassium silicate with the same molar ratio and the same silicate concentration, higher initial tack was obtained as demonstrated in following test: The Substrate used: Test liner. Suspensions tested : 1: 10% by weight of the P-type zeolite ZEOCROS CG 180 suspended in a sodium silicate solution (Crosfield Crystal 0096) containing 36.3 % by weight sodium silicate with a molar ratio Si0 2 /Na 2 0 of 3.4; 2: 10% by weight of the P-type zeolite ZEOCROS CG 180 suspended in a potassium silicate solution containing 38% by weight potassium silicate with a molar ratio Si0 2 /K 2 0 of 3.2; 3: A mixture of 75% by weight of suspension 1 (Na) and 25% by weight of suspension 2 (K) . 4: A mixture of 50% by weight of suspension 1 (Na) and 75% by weight of suspension 2 (K) . 5: A mixture of 25% by weight of suspension 1 (Na) and 75% by weight of suspension 2 (K) . These suspensions were tested on adhesion in the equipment described above using pieces of the card board with following results: SUSPENSION BOND STRENGTH AFTER 10s : 1 4.2 2 5.9 3 4.4 4 5.5 5 5.5. The results clearly demonstrate, that for the chosen composition of the suspension and the chosen substrate, potassium silicate gives superior initial bond strength. It also shows, that increasing the potassium content in mixtures of sodium- and potassium- silicate increases the initial bond strength. This positive effect of potassium depends on the substrate and the conditions chosen. Furthermore potassium silicate is more expensive. In practice, it will be possible for those skilled in the art to again optimize product composition with respect to the content of sodium and potassium, depending on the particular application for technical and economic reasons. EXAMPLE 16 COMPARISON OF SUSPENSION OF ZEOLITE P IN SILICATE WITH PVA BASED ADHESIVE PVA (Polyvinylacetate) based adhesive is generally used as adhesive for binding cellulose based substrates like paper and card board. A samples of this adhesive obtained from the market was compared with a suspension of zeolite ZEOCROS CG 180 in sodium silicate solution (molar ratio Si0 2 /NA 2 0 : 3.4 : and sodium silicate concentration in the silicate solution 36.3 by weight) . Substrate used: Test liner Suspension used: Zeolite P (ZEOCROS CG 180) was suspended at a concentration of 10% by weight in above sodium silicate solution. Testing: The suspension of zeolite P in sodium silicate was tested in the equipment described before in comparison with a PVA adhesive. Following results were obtained: ADHESIVE TESTED BOND STRENGTH AFTER: 10s 20s ZEOLITE P SUSPENSION: 3.1 5.5 PVA ADHESIVE 2.2 5.5 The results again demonstrate the faster binding of the P-type zeolite based suspension in silicate solution. EXAMPLE 17 INFLUENCE OF PARTICLE SIZE OF THE FILLER MATERIAL Filler Materials tested: 1: Zeolite P ; average particle size 0,65 micrometer 2 Zeolite P average particle size 1.08 micrometer 3 Zeolite P average particle size 2.27 micrometer 4 Zeolite 4A average particle size 3.0 micrometer 5 Zeolite 4A average particle size 1.36 micrometer Silicate solution used for the preparation of the suspensions : A sodium silicate solution with a molar ratio Si0 2 /Na 2 0 of 3.4 and a silicate concentration of 36.3% by weight. Suspensions: The above mentioned filler materials were suspended at a level of 10% by weight in the silicate solution. Results : * It was found, that suspensions prepared with zeolite P gave much better initial bond strength than suspensions produced with zeolite 4A. * Bond strength obtained with zeolite P with an average particle size of 0.65 micrometer and 1.08 micrometer is the same within the accuracy of the measurement, while bond strength obtained with zeolite P with particles with an average size of 2.27 micrometer was less. * Bond strength obtained with suspensions based on zeolite 4A with particles with an average particle size of respectively 3 micrometer and 1.36 micrometer was the same within the accuracy of the measurement .

Claims: C L A I M S 1. Adhesive composition, comprising a suspension of an aqueous silicate solution and a finely divided inorganic filler, characterised in that said silicate solution has a silicate content of at least 17% by weight, and comprises as a filler a zeolite having an average particle size of at least 0.4 μm. 2. Adhesive according to claim 1, characterised in that the zeolite is of a P-type zeolite. 3. Adhesive according to claims 1 or 2 , characterised in that the average particle size of the zeolite is 0.4-15 μm, preferably 0.4-5 μm and more preferably 0.8-2 μm. 4. Adhesive according to one or more of claims 1-3, characterised in that the silicate content of the silicate solution is at least 20% by weight. 5. Adhesive according to one or more of the preceding claims, characterised in that the molar ratio Si0 2 :M 2 0, M being an alkali metal or ammonium, of the aqueous silicate solution is comprised between 1-4.5, preferably between 2-4.2 and most preferably between 2.8 and 4.2. 6. Adhesive according to one of the proceeding claims, characterised in that the silicate of the silicate solution comprises potassium silicate, sodium silicate or mixtures thereof . 7. Adhesive according to claim 6, characterised in that the silicate of the silicate solution comprises potassium silicate. 8. Use of an adhesive composition according to one of the proceeding claims for the manufacture of cellulose contain- ing materials . 9. Use of an adhesive composition according to one of the claims 1-7 for the manufacture of laminated paper tubes. 10. Use of an adhesive composition according to any one of claims 1-7 as a binder for rockwool or glass fibre.

Inventors: BRORENS HACOBUS HENRICUS JOHAN, HOWARTH IAN MAURICE, OSINGA THEO JAN, BRORENS, HACOBUS, HENRICUS, JOHANNES, HOWARTH, IAN, MAURICE, OSINGA, THEO, JAN
Applicants: BRORENS HACOBUS HENRICUS JOHAN, CROSFIELD JOSEPH & SONS, HOWARTH IAN MAURICE, OSINGA THEO JAN, BRORENS, HACOBUS, HENRICUS, JOHANNES, CROSFIELD LIMITED, HOWARTH, IAN, MAURICE, OSINGA, THEO, JAN
Application year: 1998
Main classification: C04B28
IPC codes: C04B14, C04B28, C08L97, C09D1, C09J1, C09K8, D21H17, D21H27