MXPA99010208A - Adhesive compositions for corrugated boxes - Google Patents

Abstract

Novel starch-silicate adhesive compositions are disclosed which are of particular advantage in the manufacture of corrugated board. By the controlled combination of starch, alkali silicate and, optionally, caustic soda and borax it has been found possible to produce useable adhesives having much higher levels of solids content than conventional starch-based adhesives, thereby allowing for lowered energy costs in use of the adhesive formulation to manufacture boxboard, as well as improved product quality. The formulation of starch-silicate adhesives according to the invention allows viscosity, rheological characteristics - in particular gelation temperature - and the speed of"green-bond"formation to be controlled and adapted to the requirements of modern high-speed corrugating equipment.

Description

COMPOSITIONS g? VDHESIVES FOR CORRUGATED BOXES BACKGROUND OF THE INVENTION This invention relates to the invention of novel adhesive silicate-starch compositions. In particular, this invention relates to the formulation of adhesives for the manufacture of corrugated cardboard by the use of improved mixtures of starches and alkali silicates. The technique of using soluble alkali silicates as adhesives for paper and cardboard boxes has been known for a long time. Alkaline silicates are cheap, fire resistant, bugs resistant, recyclable and provide excellent resistance to the products in which they are used. Among other applications these compounds are in use as adhesives for paper and wood chipboard products, as well as paper cores and tubes. The alkali silicates, however, have several disadvantages which have resulted in discontinuing their use in certain industrial applications. A major disadvantage of silicate-based adhesives is that the adhesive bond forms relatively slowly. This is a serious problem in the high speed corrugation machines used today that require the formation of a strong "green union" in a few seconds between the lining board and the corrugated intermediate that is being put in contact. Another disadvantage of alkaline silicates is that they are prone to deposit an untreatable, hard varnish on any surface on which it is allowed to dry. Because starch exhibits performance properties that are superior in rapid bond formation and does not form hard deposit, starch has almost completely replaced alkali silicates in corrugated board manufacturing for some years. However, the same starch is not a perfect adhesive for this application. For one reason, the maximum solids content of these additive compositions usually achievable is in the range of 25-30%. Thus about 75% of the adhesive formulation applied to the board consists of water, whose removal reduces the operating speed of the rebar equipment, and increases the energy costs associated with water evaporation. The higher water content of the adhesive also contributes to loss of paper strength as well as quality problems during the manufacture of boxes such as deformation, blistering or a "washboard" effect. It has long been known that the agglomeration force of the edges of the glued boxes with adhesive additives based on starch is not as high as would be achieved by the use of silicate. These strength properties are now of considerable importance, due to the fact that the specification of the boxes is now based on their edge agglomeration force (Alternative Freight Regulation Rule 41, as described in Tappi Test Methods T811) instead of based on weight (as was the case in the past). The use of silicates in the adhesives thus opens up the possibility of manufacturing boxes with equivalent edge agglomeration force either using paper of a lower basis weight or using poor quality recycled paper. Various attempts have been made to combine the alkali silicates and the starch in adhesives for the manufacture of corrugated boxes and similar applications, in order to realize the benefits described. Thus, U.S. Patent No. 2,669,282 (Kreyling) discloses a mixture of starch, clay and sodium silicate adhesive. U.S. Patent No. 2,772,996 (Sams) teaches a method for producing an adhesive by mixing silicate, starch and borax. More recently, Canadian Patent Number 1,056,107 (Falcone, 1979) describes a class of starch-silicate adhesives in which some of the starch in the starch-based adhesive compositions is replaced by alkali silicate., but the total solids content of the adhesive compositions does not change significantly. However, to date, none of the compositions or methods for combining the starch and the silicate for the manufacture of corrugated cardboard boxes has found commercial application because none has been shown to be capable of satisfying the requirements of the demand of the equipment of the Modern high-speed corrugated, none of the previous combinations of starch and silicate has demonstrated the ability to impart greater edge agglomeration. The main requirements for these performance characteristics are, first, formulation of adhesives so that their viscosity, rheological properties, gelatination temperature, and rate of "green bonding" are all within a very narrow range. Thus, it is essential that the finished adhesive have low thixotropy and a viscosity of between 20-60 seconds Stein-Hall in order to achieve a smooth and rapid transfer of the adhesive from the storage tanks to the corrugator adhesive applicator stations. A second essential aspect of the starch-based adhesive formulations is the temperature at which the gelatinization of the starch occurs. This usually occurs at a temperature between 60 and 70 ° C, the operation of modern corrugation equipment is not generally possible if the gelatination temperature is outside this range. Although the Falcone patent mentioned above reveals that the addition of sodium silicate to the starch leads to a significant increase in gel temperature, teaching has not yet been provided on how to satisfactorily formulate the starch-silicate compositions having sufficient gel temperatures. low to be within a permissible operating range or viscosity stability in the course of time at elevated temperature, ie above 50 ° C. There is another aspect of starch gelatinization important for this invention. During the normal operating procedure the starch-based adhesive is kept in the storage tank at a temperature between 38 and 40 ° C. The stability of conventional starch-based adhesives is such that this material is prone to premature gelatinization due to fluctuations in the temperature of the operating environment, and these starch-based adhesives can not be stored for more than three days. We have discovered that by modifying the starch-based adhesives by the addition of alkali silicate, in addition to other ingredients such as caustic soda and borax commonly used in starch adhesives, in a precisely controlled and ordered manner, it is possible to realize all the known advantages of the alkali silicates without incurring the problems of viscosity or high gelatination temperatures that prevent the commercialization of the above descriptions. These formulations are also found to exhibit unusually good stability at high temperatures. The discovery of stability at high temperature has allowed storage at a higher temperature which helps to displace the higher temperature of the gel. Furthermore, we have also discovered, to our surprise, that the methods described herein allow the preparation of starch-based adhesives with a much higher solids content than previously achievable. As will be demonstrated in the examples below, this discovery increases the solid content of these compositions in the range of 25 to 30% achievable using conventional technology, at approximately 45% solids. As mentioned above, reducing the water content in this way leads to significant benefits in the operation of the corrugating equipment by reducing the loss of strength in the liner and the intermediate caused by the addition of water from the adhesive, the amount of steam energy required to evaporate the water and the production of boxes with improved dimensional stability. As the examples given below will demonstrate, the invention described herein also leads to improvements both in the strength of the adhesive bond, and in the same box. The examples also demonstrate that these formulations are fully compatible with a wide range of operational variables that are commonly encountered and well known to those skilled in the art. The formulations according to the present invention are: (i) applicable to raw starches and modified from a variety of sources; (ii) compatible with insolubilizing resins such as cross-linked melamine-formaldehyde, urea-formaldehyde and ketone-aldehyde polymers commonly used to impart water resistance to starch-based adhesives; and (iii) compliant for preparation using conventional techniques for preparing starch-based adhesives, such as the "two-step" manufacturing processes (Example 8, below), "without carrier" (Example 9, below), and " carrier-non-carrier ". Although most of the examples presented reveals the preparation of adhesives using liquid ingredients, Example 10 is also presented to demonstrate that similar results can be obtained if only dry ingredients are employed, this being of potential advantage in the commercialization of these materials. Example 11 below is presented to demonstrate that when these formulations are prepared using recycled water from the corrugating printing station (referred to as "flexo" water), the concentration of soluble copper in the adhesive is reduced to an unexpectedly low level. The importance of this observation arises from the fact that although the use of flexo water in the preparation of starch-based adhesives is an increasingly popular method for recycling waste streams, the conventional starch-based compositions employed have not yet been found to be capable of reducing the solubility of toxic copper ions or other metal ions present in waste water. The specific reduction of copper observed in the compositions described herein will be attributed to the well-known sequestering properties of the alkali metal silicates. Although the focus of this description is directed towards the manufacture of corrugated boxes, it should also be noted that this is only one of the many areas of potential applications of the silicate-starch compositions described herein. The adhesives according to the invention can be used with other cellulosic materials, such as wood and other paper products.

SUMMARY OF THE INVENTION With a view to providing improved adhesives for the manufacture of boxes and other industrial wood and paper products, based on the combinations of silicate and starch but having the requirements of viscosity control of adhesive and gel temperature to allow the use of adhesives in corrugating equipment, the invention is directed in one aspect to adhesive compositions having solids content of 30 to 45% by weight and consisting essentially of: (i) 12 to 35% by weight of a starch , - (ii) 1.5 to 12% soluble alkali metal silicate; (iii) 0.25 to 2.5% by weight of alkali hydroxide; (iv) optionally, up to 2% borax (anhydrous or in hydrated form) or boric acid; and (v) 55 to 70% by weight of water, and in another aspect, to processes for preparing improved starch-silicate adhesives of this class. In the present invention, "starch" refers to the carbohydrate reserve of a plant. It is usually deposited in the form of tiny granules from 1 to 100 microns and swelling in water of 55 to 80 ° C. Although starches are found throughout the plant world, those with particular commercial advantage for use in the present invention are corn starch, wheat starch and potato starch, although others may be used, including modified starches. An example of a preferred starch is corn starch sold as 3005 by Corn Products International, Illinois. Soluble alkali silicates useful in carrying out the present invention include materials in solution as well as hydrated solids and anhydrous silicates, which exhibit molar proportions of SiO2 against M20 in the range of 1.5 to 4.0 wherein M is preferably sodium or potassium. The description of Canadian Patent Number 1,056,107 is incorporated herein by reference to its general teaching of alkali metal silicates used in starch-silicate adhesive compositions. A particular silicate found useful in the present invention is the N®-brand sodium silicate manufactured by the PQ Corporation (Valley Forge, Pennsylvania), which has a weight ratio of SÍO 2 to Na 20 of 3.2.

DETAILED DESCRIPTION OF THE INVENTION The compositions according to the present invention are illustrated in Examples 2 and 3 in which starches with modified and unmodified carrier are respectively used to prepare the adhesive compositions according to the invention, which exhibit superior bonding and strength of paper when used in the manufacture of corrugated boxes. A demonstration of the superior heat stability of this composition (Example 4) is provided, and a method for varying the gelatinization characteristics including the temperature of the gel of the starch-silicate adhesives of the invention by changing the relative amounts of caustic soda and borax used in its preparation (Example 5), this being of particular importance to ensure that the gelatination characteristics are compatible with the operation of the modern corrugation equipment.

The prior art related to combinations of starch-silicate adhesives is limited to the total solids content in the range of 15 to 30%, a limit dictated by the high viscosity, instability and gel temperature that were observed in the formulations contained within these previous descriptions. According to another advantage presented by the present invention, however, a silicate-starch adhesive with a solids content as high as 45% can be manufactured. (Example 6). This provides numerous significant advantages that include: (i) realization of energy savings as a result of a reduction in the amount of water that requires evaporation; (ii) less deformation of the bonded cardboard product, again due to a lower initial water content; (iii) faster machine speeds; and (iv) less loss of strength of the liner and the intermediate due to the adhesive water. A currently preferred embodiment of the process of the invention, comprises the following steps for preparing new and useful starch-silicate adhesives: (a) preparing a portion of gelatinized carrier by the addition of 1.5 to 10% starch by weight of the final adhesive composition of 20 to 45% by weight of water, mix until the starch is dispersed in the water, and then add 0.25 to 2.5% by weight of sodium or potassium hydroxide, after which the composition is mixed or preferably sheared, until a gel is obtained complete and constant viscosity of this carrier portion; (b) adding from 10 to 30% by weight of liquid sodium or potassium silicate to the carrier portion and shearing the mixture until it is homogeneous; (c) optionally adding to the mixture produced in step (b) up to 2.5% by weight of sodium or potassium hydroxide, after which the material is mixed or sheared until homogeneous; (d) optionally, adding up to 2% by weight of borax followed by mixing or shearing at constant viscosity; (e) add from 3 to 20% water and mix or shear until homogeneous; and (f) adding from 2 to 35% starch by weight and shearing by mixing at constant viscosity to produce the final adhesive composition. As will also be shown in the examples that follow, these compositions are also compatible with other chemical products and industrial processes well known to those skilled in the art of manufacturing adhesives, such as insolubilizing resins (Example 7); the process of adding "two steps" (Example 8) and the "non-carrier" methods well known to those skilled in the art (Example 9). According to another aspect of this invention, the silicate-starch adhesives of this type can be prepared as a premixed dry mix by the use of a dry form of alkali silicate (Example 10). Finally, yet another aspect of this invention illustrated in Example 11, reveals that the use of recycled "flexo" water results in a composition containing significantly lower levels of soluble copper. Those skilled in the art will also be aware that the formulation processes described herein also apply to other types of starches (such as acid-stable starches) as are commonly used as adhesive compositions. Nor do these examples mean that the use of other common additives such as surfactants, or polymers such as polyvinyl alcohol that are used from time to time to improve the performance of these adhesives, is avoided.

EXPERIMENTAL EXAMPLES In the following examples, certain embodiments of the invention are illustrated and compared with the prior art. All proportions used in the examples are parts by weight (ppp) unless otherwise noted. The proportions of the silicates are proportions by weight of SiO2 / Na20, with sodium generally being the alkali metal of choice. The first example shown illustrates the preparation of a typical starch-based adhesive commonly used in industrial applications, the method of preparation of this standard composition will be used as a control and is as follows: Example 1.- Preparation of adhesive based on conventional starch for use in the manufacture of corrugated boxes. The carrier portion of the pure starch adhesive is prepared by combining 39.2 ppp of water with 5.2 ppp of modified corn starch (manufactured by Corn Products International under the name Surebond®) followed by 1.1 ppp of sodium hydroxide (50% solution). The resulting slurry is maintained at 45 ° C and allowed to gelatin while mixing under high shear. After reaching a stable viscosity, 0.39 ppp of borax (pentahydrate) is added to the gel mixture and mixed to a stable viscosity. 31.41 ppi of water is added to the mixture and mixed until it is homogeneous. 22.7 ppp of initiator (unmodified) of corn starch (Corn Products International, 3005) is added to the mixture and mixed until homogeneous. Initial viscosity Stein-Hall - 25-35 seconds at 38 ° C gel temperature - 61 ° C.

Example 2: An adhesive composition prepared under commercial conditions using a modified carrier starch. The adhesive composition demonstrates superior bond strength and edge agglomeration strength of corrugated cardboard made with starch-silicate. The carrier portion of the starch-silicate adhesive was prepared by combining 36.1 ppp of water with 4.9 ppp of modified corn starch (Corn Products International, Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry was maintained at 55 ° C and allowed to gelate in low shear mixing. After reaching a stable viscosity, 18.9 ppi of sodium silicate (Silicate N®, PQ Corporation) was added and mixed until homogeneous. 1.4 ppp of caustic soda (50%) was added to the mixture and mixed until homogeneous. 0.37 ppp of borax (pentahydrate) was added to the mixture and mixed to a stable viscosity. 15.7 ppi of water was added and mixed until homogeneous. 21.6 ppp of starter corn starch (unmodified) (Corn Products International, 3005) was added to the mixture and mixed until stable viscosity. After finishing, the temperature of the starch / silicate adhesive is 45 ° C. Results Stein-Hall initial viscosity - 35 seconds @ 51 ° C gel temperature - 71 ° C solids - 35% Example 3: The formula in Example 2 is used to prepare a laboratory sample to test the green binding strength (duplication of the bond strength immediately after the single coating layer). The sample prepared in the laboratory demonstrated a significantly higher green binding strength. Control (Example # 1) - 332 grams of starch / silicate strength (Example # 3) - 449 grams of strength Example 4: Preparation of silicate-starch adhesive showing stability at high temperature. The carrier portion of the starch / silicate adhesive was prepared by combining 36.0 ppi of water with 3.0 ppp of modified corn starch (Corn Products International, Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry was maintained at 60 ° C and allowed to gelatin under high shear mixing. After reaching a stable viscosity, 20.0 ppi of sodium silicate (Silicate N®, PQ Corporation) was added and mixed until homogeneous. 1.5 ppi of caustic soda (50%) was added to the mixture and mixed until homogeneous. 0.37 ppp of borax (pentahydrate) was added to the mixture. After reaching a stable viscosity, 11.13 ppi of water was added and mixed until homogeneous. 27.0 ppp of corn starch (unmodified) primer (Corn Products International, 3005) was added to the mixture and mixed until stable viscosity. Initial viscosity Stein-Hall - 23 seconds @ 45 ° C gel temperature - 72.5 ° C solids content - 39.1% Example 5: A method for varying the gelatin characteristics of silicate-starch adhesives by changing the amounts of caustic soda and borax used in their preparation. The adhesive was prepared using unmodified starch as the carrier. The carrier portion of the starch / silicate adhesive was prepared by combining 39.2 ppi of water with 3.7 ppi of corn starch (unmodified) starch (Corn Products International, 3005) followed by 0.78 ppi of caustic soda (50%). The resulting slurry was maintained at 45 ° C and allowed to gelate under high shear mixing. After reaching a stable viscosity, 20.0 ppi of sodium silicate (Silicate N®, PQ Corporation) was added and mixed until homogeneous. Caustic soda (50%) was added to the amount shown in the Table, and mixed until homogeneous, after which borax (pentahydrate) was added to the mixture as shown in the Table. After reaching a stable viscosity, 12.2 ppi of water were added and mixed until homogeneous. 23.7 ppi of corn starch (unmodified) starter (Corn Products International, 3005) was added to the mixture and mixed at a stable viscosity. The gelatination characteristics were determined using a Brabender instrument.

Example 6: A process for preparing a stable adhesive composition having a very high solids content. The carrier portion of the starch / silicate adhesive was prepared by combining 36.0 ppi of water with 3.0 ppp of modified corn starch (Corn Products International, Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry was maintained at 60 ° C and allowed to gelatin under high shear mixing. After reaching a stable viscosity, 22.0 ppi of sodium silicate (Silicate N®, PQ Corporation) was added and mixed until homogeneous. 1.5 ppp of caustic soda (50%) was added to the mixture and mixed until homogeneous. 0.40 ppp of borax (pentahydrate) was added to the mixture. After reaching a stable viscosity 4.1 ppi of water were added and mixed until homogeneous. 32.0 ppp of corn starch (unmodified) primer (Corn Products International, 3005) was added to the mixture and mixed at a stable viscosity. Initial viscosity Stein-Hall - 39 seconds @ 45 ° C gel temperature - 73 ° C solids - 44.9% Example 7: Compatibility and effectiveness of silicate-starch compositions with water-proof resins. The carrier portion of the starch / silicate adhesive was prepared by combining 36.1 ppp of water with 4.3 ppp of modified starch (Corn Products International, Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry was maintained at 55 ° C and allowed to gelate under high shear mixing. After reaching a stable viscosity, 18.9 ppi of sodium silicate (Silicate N®, PQ Corporation) was added and mixed until homogeneous. 1.4 ppp of caustic soda (50%) was added to the mixture and mixed until homogeneous. 0.37 ppp of borax (pentahydrate) was added to the mixture. After reaching a stable viscosity, 15.83 ppi of water was added and mixed until homogeneous. 22.1 ppp of initiator (unmodified) of corn starch (Corn Products International, 3005) was added to the mixture and mixed at a stable viscosity. Two of the most common waterproof resins, a melamine-formaldehyde resin (Corn Products International, Coragum®) and a ketone-formaldehyde resin (Cellbond Inc., Watertite®) were post-added to the prepared starch / silicate adhesive . As is common practice in the rebar industry, the subsequent addition of the resin was measured as a percentage of the starch solids. The starch / silicate showed no compatibility problems with either Coragum® or Watertite®. In the specific case of Coragum®, the viscosity was monitored for 24 hours.

* The sample was mixed with shear for one minute.

The water resistance of the starch / silicate with resin was measured in two ways: The starch / silicate with 6% Coragum® added subsequently was tested by gelatinizing the adhesive samples, immersing the samples in water and then observing the rate of disintegration of the gelatinous samples. The results showed a much slower rate of disintegration of the starch / silicate gel with Coragum®. The starch / silicate with 5% Watertite® subsequently added was tested using TAPPI T812 and passed with equal strength for 24 hours as the starch adhesive with 5% Watertite® subsequently added.

Example 8: Starch / silicate adhesive prepared using the Stein-Hall two-step method. This method is conventionally used to prepare starch-only adhesives for making corrugated boxes. We have found that it can easily be adapted to the manufacture of starch-silicate adhesives according to the present invention by the steps of the following process: The first stage is prepared by combining 13.31 ppi of water with 3.63 ppp of modified corn starch (Corn Products International, Surebond®) followed by 1.03 ppp of caustic soda (50%). The resulting slurry was maintained at 57 ° C and allowed to gelatin under high shear mixing, after which 9.70 ppp of water was mixed into the gel. The second stage was prepared by combining 34.87 ppi of water with 15.98 ppi of sodium silicate (Silicate N®, PQ Corporation) followed by 0.73 ppp of caustic soda (50%) and then 0.41 ppp of borax (decahydrate) and finally 20.34 ppp of initiator (unmodified) of corn starch (Corn Products International, 3005). The mixture of the first stage was allowed to drip into the mixer of the second stage for a period of 20 minutes. The combined mixtures were stirred until stable viscosity. Initial viscosity Stein-Hall - 62 seconds @ 34 ° C gel temperature - 68 ° C solids content - 31.2% green bond strength - 475 grams strength Example 9: The "bearerless" technique used in the manufacture of starch adhesives is characterized in that the controlled swelling of the entire starch determines the viscosity of the finished adhesive. As it adapts to the preparation of the starch-silicate adhesives according to the present invention, the viscosity increase is terminated by the addition of a second silicate portion. The starch / silicate adhesive is prepared by combining 40.0 ppi of water with 9.5 ppi of sodium silicate (Silicate N®, PQ Corporation) followed by 2.5 ppp of caustic soda (50%) and then 0.37 ppp of borax (pentahydrate). To the resulting solution is added 25.0 ppi of corn starch (unmodified) starch (Corn Products International, 3005) under stirring. After reaching a viscosity of "7000 centipoise @ 35 ° C the viscosity advancement is stopped by the addition of 10.5 ppi of sodium silicate (Silicate N®, PQ Corporation) 12.13 ppi of water is added to further reduce the viscosity. initial - 21 seconds @ 36 ° C viscosity at 18 hours (stored at 50 ° C) - 21 seconds @ 45 ° C gel temperature - 74 ° C Example 10: Silicate-starch adhesives prepared as a dry mixture by the use of a solid form of alkali silicate. Before making the adhesive mixture, a dry mix is prepared by combining 72.29 ppi of corn starch (unmodified) starch (Corn Products International, 3005) with 26. 50 ppi of sodium silicate powder (Silicate G®, PQ Corporation) and 1.21 borax (pentahydrate). The carrier portion of the starch / silicate adhesive is prepared by combining 36.1 ppp of water with 4.3 ppp of modified corn starch (Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry is maintained at 55 ° C and allowed to gelatin under shear mixing. After reaching a stable viscosity the gel is diluted with 26.22 ppp of water. To the diluted gel is added 30.57 ppp of the previously prepared dry mixture of starch / sodium silicate / borax. After thoroughly mixing until homogeneous, 1.81 ppi of highly alkaline sodium silicate (Metso Pentabead®, PQ Corporation) is added to the mixture and mixed to stable viscosity. Initial viscosity Stein-Hall - 35 seconds at 45 ° C gel temperature - 73 ° C pH - 11.2 solids - 37.2% Example 11: Preparation of silicate-starch adhesives using recycled water from the corrugator printing station, ie water "flexo". The carrier portion of the starch / silicate adhesive is prepared by combining 36.1 ppi of "flexo" water with 4.3 ppp of modified corn starch (Surebond®) followed by 1.0 ppp of caustic soda (50%). The resulting slurry is maintained at 55 ° C and allowed to gelatin under high shear mixing. After reaching a stable viscosity, 18.9 ppi of sodium silicate (Silicate N®, PQ Corporation) is added and mixed until homogeneous. 1.4 ppp of caustic soda (50%) is added to the mixture and mixed until it is homogeneous. 0.37 ppp of borax (pentahydrate) is added to the mixture. After reaching a stable viscosity 15.83 ppi of flexo water is added and mixed until homogeneous. 22.1 ppp of initiator (not modified) of corn starch (CPC 3005) is added to the mixture and mixed at a stable viscosity. Initial viscosity Stein-Hall - 24 seconds @ 45 ° C viscosity at 24 hours at 48.4 ° C - 29 seconds @ 45 ° C gel temperature - 72 ° C pH - 11.2 solids - 35.1% These results in a composition containing levels Lower soluble copper measured by atomic absorption spectrometry. Starch / silicate - 31 ppm measurable copper "flexo" water * - 56 ppm measurable copper

Claims (14)

1. CLAIMS 1. A process for preparing an adhesive composition for wood and paper products, having a solids content greater than 30% by weight and up to 45% by weight, comprising the steps of: (a) preparing a gelatinized carrier portion , adding from 1.5 to 10% by weight of a starch, based on the weight of the adhesive composition, to 20 to 40% by weight of water, mixing to disperse the starch in the water, then adding from 0.25 to 2.5% by weight of NaOH or KOH and mixing the constant viscosity to produce the gelatinized carrier portion; (b) adding to the gelatinized carrier portion from 10 to 30% by weight of water-soluble alkali silicate characterized by a molar ratio Si02: M20 in the range of 1.5 to 4.0 where M is Na or K, then mix everything until be homogeneous; (c) adding others from 3 to 20% by weight of water and mixing until homogeneous; and (d) adding others from 2 to 25% by weight of starch and mixing until the viscosity is stable to produce the final adhesive composition. 2. A process according to claim 1, comprising the additional step, after step (b) and before step (c), of further adding NaOH or KOH up to
2. 2.5% by weight and mixing until homogeneous.
3. 3. A process according to claim 1, comprising the additional step, after step (b) and before step (c) of adding up to 2% by weight of borax and mixing it until it is homogeneous. A process according to claim 1, comprising the additional steps, after step (b) and before step (c), of adding more NaOH or KOH up to 2.5% by weight, mixing until homogeneous, then add up to 2% by weight of borax and then mix until homogeneous. 5. A process according to claim 4, wherein the starch is selected from the group consisting of corn starch, wheat starch, potato starch and modified starches. 6. A process according to claim 5, wherein the starch is corn starch. 7. A process according to claim 5, wherein the starch is SUREBOND (registered trademark) modified corn starch (Corn Products International). 8. A process according to claim 4, wherein the alkali silicate is sodium silicate having a weight ratio of SiO2: Na20 of about 3.2. 9. A process for preparing an adhesive composition for wood and paper products, having a solids content greater than 30% by weight and up to 45% by weight, comprising the steps of: (a) preparing a gelatinized carrier portion by adding from 1.5 to 10% by weight of a starch, based on the weight of the adhesive composition, to 20 to 40% by weight of water, mixing to disperse the starch in the water, then adding 0.25 to 2.5% by weight of NaOH or KOH and mix at a constant viscosity; (b) adding to the gelatinized carrier portion about 30% by weight of a dry mixed mixture comprising about 72 parts by weight of corn starch, about 26 parts by weight of sodium silicate powder soluble in water and the remainder of Borax pentahydrate powder, then mix with dry shear mix in the gelatin carrier portion until a stable viscosity is reached, to produce the final adhesive composition. A process for preparing an adhesive composition for wood and paper products, having a solids content greater than 30% by weight and up to 45% by weight, comprising the steps of: (a) preparing a solution containing the 35 al 55% by weight of water, based on the weight of the adhesive composition, with 7.5 to 12.5% by weight of sodium silicate and then add 1 to 2% by weight of sodium hydroxide or potassium hydroxide, then add up 2% by weight of borax; (b) adding to the solution produced in step (a) from 20 to 30% by weight of starch under stirring and monitoring the viscosity which increases; (c) when the desired peak viscosity of a mixture has been reached, add between 8 and 15% by weight of sodium silicate to complete the viscosity increase; (d) adding up to 15% by weight of water to adjust the final viscosity and the solids content of the adhesive composition to the desired level. 11. An adhesive composition for wood and paper products, having a solids content greater than 30% by weight and up to 45% by weight, the composition consisting essentially of: (i) 12 to 35% by weight of a starch; (ii) 1.5 to 12% by weight of a soluble alkali metal silicate; (iii) 0.25 to 2.5% by weight of an alkaline hydroxide; (iv) from 55 to 70% by weight of water. 12. An adhesive composition according to claim 10, further comprising up to 2% borax or boric acid. 13. An adhesive composition according to claim 11, wherein the starch is corn starch. 1
4. 4. An adhesive composition according to claim 11, wherein the silicate is sodium silicate.