WATER-BASED EDGE-PADDING ADHESIVE COMPOSITION THAT IS LOW IN VOLATILE ORGANIC COMPOUNDS

Abstract: An edge-padding adhesive is provided having a VOC content of less than 250 grams per liter less water and less exempt solvents. This edge-padding adhesive comprises by weight a) from 7.5 to 27 % dry weight of a water-based latex adhesive polymer; b) from 0.5 to 15 % of a water-dispersible transport agent comprising at least one poly(alkyleneoxide)mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms; and c) water. The composition contains a much lower proportion of volatile organic compounds as compared to prior edge-padding adhesive compositions for carbonless copy paper. A method of adhesively edge padding a stack of sets of collated carbonless copy paper sheets to permit the stack to be fanned apart into individual sets is also provided.

Description: WATER-BASED EDGE-PADDING ADHESIVE COMPOSITION THAT IS LOW IN VOLATILE ORGANIC COMPOUNDS BACKGROUND OF THE INVENTION This application is a continuation-in-part of U.S. Serial No. 07/548,676 filed on July 5, 1990. FIELD OF THE INVENTION The invention concerns water-based adhesive compositions used for adhesively edge-padding stacks of collated paper, especially carbonless or no-carbon required (ncr) copy paper, so that upon being fanned-out a stack spontaneously separates into individual form-sets, each set being adhesively bonded together at one edge. The invention is particularly concerned with providing edge- padding adhesives that do not release volatile organic compounds (VOCs) into the atmosphere. DESCRIPTION OF THE RELATED ART U. S. Patent No. 4,217,162 (Glanz, et al.) says: "For many years, carbonless copy paper has been made into form sets from a lift of collated sheets by applying an adhesive to one edge of the lift, drying the padded edge and fanning the lift into individual form sets" (col. 1, lines 19-22) . The Glanz patent goes on to discuss a number of patent publications, all of which employ water-based adhesives for edge padding. Several adhesive compositions are currently marketed specifically for the purpose of edge-padding collated stacks of carbonless copy paper to be fanned into sets. Of these, the following are predominant in the U. S. market: "Fanapart High-Strength Padding Adhesive" from Appleton Papers, Inc. " , Appleton, WI; "Mead Fan-Apart Adhesive" from the Fine Paper Division of Mead Paper Corp. , Chillicothe, OH; and "Fan-out Padding Adhesive" from 3M Co., St. Paul, MN. Each of these is a water based adhesive composition. The aforementioned dominant edge-padding adhesive compositions have been analyzed and are believed to have the following approximate compositions: "Mead Fan-Apart Adhesive": % by wt. poly(ethylacrylate/methylacrylate) (92/8) 13 (dry wt.) 1,2-propanediol 19 ethyl alcohol 7 water 61 "Fanapart ..." from Appleton % by wt. poly(ethylacrylate/N-methylolacrylamide 17 (dry wt.) 1,2-propanediol 28 ethyl alcohol 8 water 47 "Fan-out Padding Adhesive" from 3M: % by wt. poly(ethylacrylate/N-methylolacrylamide) 15 (dry wt.) ethyl alcohol 18 isopropyl alcohol 3 non-crystallizing sorbitol 1.5 water 62.5 In each of these adhesive compositions, the first-named ingredient is a water-based latex adhesive polymer. The monohydric alcohol increases the rate of penetration and enhances drying. Each of the polyhydric alcohols, including sorbitol, has a Hansen Dispersion Solubility Parameter close to that of the polymer and thus may serve to plasticize the edge-padding adhesive. When each of these adhesive compositions is used for edge-padding collated carbonless copy paper, the ethyl alcohol and 1,2-propanediol volatilize, the latter quite slowly. These volatile organic compounds have an air- polluting effect, and attempts have been made to regulate, via legislation, the amount of volatile matter that may be contained in articles of commerce. The term "volatile organic compounds" includes any compound having a vapor pressure above 0.02 torr at 25 °C. In addition, many of these volatile organic compounds are flammable. It would be desirous to provide adhesives that are both environmentally responsible and less flammable or combustible. It is believed that in every adhesive composition now being marketed for edge-padding collated carbonless copy paper, at least 550 g/L of the nonaqueous components are volatile organic compounds. Furthermore, some such compositions have an undesirably low flash point. The flash points (determined according to ASTM - D57 standard) of the above-described fan-apart adhesives from Mead, Appleton, and 3M are 112 °F (45 °C) , 106 °F (41 °C) , and 82 °F (28 °C) , respectively. Materials with flash points between 0-99 °F (-18 to 38 °C) are classified as flammable. Materials with flash points between 100 °F and 199 °F (38 °C to 93 °C) are classified as combustible. Materials with flash points greater or equal to 200 °F (>93 °C) are non-regulated. Edge padding adhesives have previously been used to join multiple sets of carbonless paper. Commercially available edge padding adhesives are typically tailored for the particular chemistry of one brand of carbonless paper, and have relied on the incorporation of Volatile Organic Compounds (VOCs) to achieve penetration and rapid drying of the adhesive. With the advent of strict environmental controls on VOC content in all commercial compositions, there is a great need for an acceptable edge padding adhesive that will provide adequate adhesion levels in a short time so that the paper can be handled without delay by the pad manufacturer Additionally, the adhesive composition ideally will be essentially universal, so that it may be used effectively on multiple brands of carbonless paper. SUMMARY OF THE INVENTION An edge-padding adhesive is provided having a VOC content of less than 250 grams per liter less water and less exempt solvents. This edge-padding adhesive comprises by weight a) from 7.5 to 27% dry weight of a water-based latex adhesive polymer, b) from 0.5 to 15% of a water-dispersible transport agent comprising at least one poly(alkyleneoxide) mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms, and c) water. For purposes of the present invention, a volatile organic compound (VOC) is any volatile organic material having a vapor pressure at 20°C greater than 0.1 Torr (mm Hg) . This definition, however, does not include what are known as "exempt solvents." Exempt solvents for purposes of the present invention are methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates , ammonium carbonate, 1,1,1-trichloroethane, methylene chloride, trifluoromethane (FC-23) , trichloro- trifluoroethane (CFC-113) , dichlorodifluoromethane (CFC12) , trichlorofluoromethane (CFC-11) , chlorodifluoromethane (CFC-22) , dichlorotetrafluoroethane (CFC-114) , and chloro- pentafluoroethane (CFC-115) . The measurement of VOC content is in the units of grams of volatile organic material per liter less water and less exempt solvents. This measurement is calculated according to the following formula: VOC(g/L) = wt of VCfα,-wt water(c)-wt exempt solvents (a) vol total(l)-vol water(l)-vol exempt solvents(1) wherein, wt of VC(g) is the total weight of volatile compounds in grams, wt water(g) is the weight of water in the material in grams, wt exempt solvents(g) is the weight of exempt solvents in grams, vol total(1) is the total volume of the material in liters, vol water(1) is the volume of water in liters and, vol exempt solvents(1) is the volume of exempt solvents in liters. The composition contains a much lower proportion of volatile organic compounds as compared to prior edge- padding adhesive compositions for carbonless copy paper. Considering that prior water-based adhesive compositions for fan-apart edge padding of carbonless copy paper relied on volatile alcohols to carry the adhesives between the sheets of paper, it is surprising that in the absence of major amounts of a volatile alcohol, any water-based adhesive composition could provide a satisfactory edge padding for carbonless copy paper. A method of adhesively edge padding a stack of sets of collated carbonless copy paper sheets to permit the stack to be fanned apart into individual sets is also provided. This method comprises the steps of 1) applying to an edge of the stack a water- based adhesive composition having a VOC content of less than 250 grams per liter less water and less exempt solvents, which comprises by weight: a) from 7.5 to 27% dry weight of a water-based latex adhesive polymer. b) from 0.5 to 15% of a water-dispersible transport agent comprising at least one poly(alkyleneoxide) mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms, and c) water, and 2) allowing the applied adhesive composition to dry. Unless otherwise stated, all percentages and ratios described herein are by weight. BRIEF DESCRIPTION OF THE DRAWING Figure 1 schematically indicates in cross section the edge padding of a stack of sets of collated sheets of carbonless copy paper, which stack upon fanning separates into individual sheets. DETAILED DESCRIPTION OF THE INVENTION A difficulty in formulating a useful fan-apart adhesive is attributable to the nature of carbonless copy paper. Carbonless impact marking papers for the transfer of images, i.e., carbonless papers, generally involve coating one reactant, the color-former on one substrate, and the developer (the other reactant) on another, mating, substrate. Means for separating and preventing reaction of the two until intended, i.e., until activating pressure is applied, are also provided. This is typically accomplished by encapsulation of one of the reactants. Herein, the terms "encapsulation" and "encapsulated compounds" refer to microcapsules enclosing a fill material therewithin. Preferably, it is the color-forming compounds that are contained or encapsulated in microcapsules on one sheet of paper. The reactant for the color-forming compound, i.e., the developer, is carried on a mating sheet of paper. The microcapsules serve the purpose of isolating the reactants from one another (i.e., preventing reaction) until such ti e as pressure is applied to the paper for the purpose of creating an image. Generally, a carbonless paper construction comprises at least two substrates, for example two sheets of paper, each with one surface, or face, coated with one of the two primary reactants. The two substrates are generally referred to as a donor sheet and a receptor sheet. Once rupturing pressure is applied to the construction, as from a stylus or business-machine key, the two substrates come into contact under sufficient pressure so that the capsules are broken, the solution of encapsulated reactant is released and transferred from the donor sheet to the receptor sheet. The color-former and developer mix, a reaction between the previously separated reactants occurs, and an image forms on the receptor sheet. In general, the resulting reaction will, of course, form a colored image corresponding to the path traveled by the stylus, or the pattern of pressure provided by the stylus or key. A preferred construction comprises the encapsulated color-formers dissolved in an appropriate solvent(s) within microcapsules and coated onto a back side of a donor sheet in a suitable binder. The back side of the donor sheet is sometimes referred to herein as a "coated back" (CB) sheet. The developer, also optionally in a suitable binder, is coated onto a front side of a mating, or receptor sheet herein sometimes referred to as a "coated front" (CF) sheet. As stated previously, in imaging, the two sheets are positioned such that the back side of the donor sheet faces the developer coating on the front side of the receptor sheet. When activating pressure is applied to the face of the donor sheet, the capsules rupture and release the ligand for transfer to the receptor sheet, forming a colored pattern due to the reaction between the color-former and developer. Herein, "activating pressure" includes, but is not limited to, pressure applied by hand with a stylus or pressure applied by a business machine key, for example a typewriter key. Constructions comprising a first substrate surface, on which is coated the encapsulated color-former; and, a second substrate surface, on which is coated a developer; are often prepared. The coated first substrate surface is positioned within the construction in contact with the coated second substrate surfaces. Such a construction is known as a "set" or a "form-set" construction. Substrates, with one surface on which is coated the encapsulated color-former, and a second, opposite, surface on which is coated a developer can be placed between the CF and CB sheets, in a construction involving a plurality of substrates. Such sheets are generally referred to herein as "CFB" sheets (i.e., coated front and back sheets) . Of course, each side including color-former thereon should be placed in juxtaposition with a sheet having developer thereon. CFB sheets are also typically used in form-sets. In some applications, multiple CFB sheets have been used in form-sets. These contain several intermediate sheets, each having a developer coating on one side and a coating with capsules of color-former on the opposite side. Form-sets prepared by collating from 2 to 8 sheets are common in the carbonless paper industry. Pads are often prepared by edge-padding or gluing the edges of a stack of form-sets. Each of the coated sheets in a form- set is somewhat porous, and permits the adhesive to penetrate into the pores of the paper, such penetration being necessary to attain satisfactory adhesion. However, the degree of porosity varies from supplier to supplier and even among categories of carbonless copy paper from a single supplier. In one commercial product, the capsules on a first sheet (donor sheet) contain dithiooxamide (DTO) derivatives, and the mating sheet, sometimes referred to as the receptor sheet, contains a coating of selected salts of nickel. The encapsulated dithiooxamide ligands, in a suitable binder, are coated onto one face of the donor sheet; and the metal salt, optionally in a suitable binder, is coated onto one face of the receptor sheet. Herein, the term "suitable binder" refers to a material, such as starch or latex, that allows for dispersion of the reactants in a coating on a substrate. When the two coated faces are contacted such that the ligands and the metal salt can combine and react, a coordination complex forms and an image results. Typically, this occurs by transfer of the ligand to the site of the metal salt, i.e., transfer of the ligand from the donor sheet to the receptor sheet. The image, of course, forms on the receptor sheet. In another type of carbonless paper, the image results from the reaction between an encapsulated leuco dye color-former and an acid developer. The capsules on the back side of donor sheet comprise leuco dye color-formers such as crystal violet lactone, 3,3-bis(l-ethyl-2-methyl- indolyl)-3-phthalide, 3-N,N-diethylamino-7-N,N- (dibenzylamino)floran, or benzoyl leuco methylene blue. The developer, usually contained on a receptor sheet, comprises an acidic material such as .sheets coated with an acidic clay, a phenolic, or a similar reagent, optionally in a suitable binder, to convert the colorless precursor to its colored form. In this system, imaging as with a pen, pencil, hand-held stylus, or typical business machine key pressure results in contact between the two coated faces such that the leuco-dye color-former and acid developer combine and react to form the colored image. Typically, this occurs by transfer of the leuco-dye color-former to the site of the acid developer, i.e., transfer of from the donor sheet to the receptor sheet. Here again, the image forms on the receptor sheet. Carbonless copy paper form-sets often have a coating (as for example a fluorocarbon coating) on at least one of the outer faces of each form-set. Fluorocarbon coatings provide low adhesion properties to the said outer faces and promote the !•fan-out properties" in the edge padding. In collated carbonless copy papers currently on the market, at least one of the outer faces of each form- set typically has been treated with a silicone, fluorocarbon, or some other coating which counteracts curling that otherwise would result from the functional coating on the other surface of that sheet. That treatment also acts as a release agent for the edge-padding adhesive and can allow the adhesively edge-padded stack to "fan-out" or "fan-apart" and separate into individual form-sets upon fanning, assuming that the edge-padding adhesive is not so thick as to create bridges that would inhibit such separation. Because of the differences in porosities of the coated front and coated back of various papers as well as differences in the release coatings, an adhesive that affords fan-apart edge-padding of a certain carbonless copy paper may not be operative with other carbonless copy papers manufactured by different companies. "Fan-out" is a method of separating a stack or pad of multiple form-sets into individual sets. One method of "fanning-out" or "fanning-apart" a stack of collated sheets involves gripping the edge-padded end of the stack with one hand and the unpadded and with the other, and bending the stack into a "U" shape. While holding the stack horizontally, the padded end is released and allowed to droop downward. This provides enough stress on the adhesive to separate the pad or stack into individual sets. The novel adhesives of this invention are useful for the padding of carbonless papers using either ligand/metal or leuco dye/acid imaging chemistry. These adhesives also are useful for different grades of paper and papers having a wide variety of coatings and of light or heavy coating weights. The transport agent according to this invention comprise at least one poly(alkyleneoxide) mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms. The alkylene and alkyl groups may optionally be straight or branched carbon chains. The number of alkylene oxide moieties are preferably between 2 and 10, and more preferably between 2 and 4. Poly(alkyleneoxide) mono-alkyl ethers useful as transport agents include: Diethylene glycol mono-alkyl ethers. Such compounds are commercially available under the trade name Carbitol™ from Union Carbide Corporation. Examples of Carbitols™ are Butyl Carbitol™, or diethylene glycol monobutyl ether and Hexyl Carbitol™, or diethylene glycol monohexyl ether. Dipropylene glycol mono-alkyl ethers. Such compounds are commercially available under the trade name Diproposol™ from Union Carbide Corporation. An example of a Diproposol™ is Butyl Diproposol™, or di(l,2-propylene glycol) monobutyl ether. Mixtures of Poly(alkyleneoxide) mono-alkyl ethers and long-chain Poly(alkyleneoxide) mono-alkyl ethers generally known as surfactants in the art. Examples of such surfactants include the Alfonic™ Surfactants from Vista Chemical Co., the Tergitol™ Surfactants from Union Carbide Corp., and the Witconol™ surfactants from Witco Chemical Co. Preferred surfactants are: Alfonic™ 610-5OR - This material is reported to be a mixture of mono-hexyl, octyl, and decyl ethers of poly(ethyleneoxide) having about 3 ethylene oxide units and to have the formula C n H 2n+lo (CH 2 CH 2 0) H where n is 6, 8, and 10 and p is about 3. It is a mixture of CAS registry numbers 31726-34-8, 27252-75-1, and 26183-52-8. Alfonic™ 810-60 - This material is reported to be a mono-octyl and decyl ethers of poly(ethyleneoxide) having about 4.8 ethylene oxide units and to have the formula C n H 2n+10 (CH 2 CH 2 0) p H where n is 8,and 10 and p is about 5. It is a mixture of CAS registry numbers 27252-75-1 and 26183- 52-8. Alfonic™ 810-40 - This material is reported to be a mixture of mono-hexyl, octyl, decyl, and dodecyl ethers of poly(ethyleneoxide) having about 2.5 ethyleneoxide units and to have the formula C n H 2n+10 (CH 2 CH 2 0) p H where n is 6, 8, 10, and 12 and p is between 2 and 3. It has a CAS registry number 68439-45-2. Tergitol™ TMN 6 - This material, also known as isolaureth-6, is believed to have the formula C 12 H 25 0(CH 2 CH 2 0) 6 H and to be a 2,6,8-trimethyl-nonyloxypoly- ethyloxyethanol with 6 ethylene oxide units. It has a CAS registry number of 61702-78-1. Tergitol™ TMN 10 - This material, also known as isolaureth-10, is believed to have the formula C 12 H 25 O(CH 2 CH 2 O) 10 H and to be a 2,6,8-trimethyl-nonyl- oxypolyethyeleoxyethanol with 10 ethylene oxide units and to have the CAS registry number CAS 60824-78-6. "Witconol™" 171 and 172 - These materials are believed to be poly-alkylene-glycol ethers "Witconol™" 1206 - This material is believed to be an alkyl polyoxyethyleneglycol ether and is understood to have long alkyl (hydrophobic) chains pendant from a polyalkyleneglycol (hydrophilic) backbone. Thus, this surfactant has hydrophobic alkyl groups at one end and hydrophilic hydroxyl and ether groups at the opposite end. Additional ingredients may be incorporated together with the poly(alkyleneoxide) mono-alkyl ethers as the transport agent component of the adhesive. Such additional ingredients may be any compound that will enhance the solvation of impurities on the paper, ox enhance drying of the adhesive. Examples of additional ingredients suitable for inclusion in the transport agent include alkyl alcohols having at least 3 carbon atoms in their alkyl groups, and preferably from 4 to 6 carbon atoms. The alkyl alcohols preferably are monohydric, but can be polyhydric when all of the hydroxyls are at one end, e.g., 1,2-hexanediol. Preferred monohydric alcohols include l-propanol, 1-butanol, 1-pentanol, and l-hexanol. The minimum amount of transport agent necessary to achieve the objectives of the invention differs for different transport agents. The amount of transport agent required to afford good bond strength of the adhesive is surprisingly larger than the amount of surfactant that would be required to afford good surface wetting of the adhesive. The amount of transport agent required could not be predicted by contact angle of the adhesive. In general, a transport agent level of 2-8% is preferred, but at levels above 10-15% by weight, the latex may destabilize. While not being bound by theory, it is believed that the transport agents incorporated in the present adhesives provide penetration enhancement between the carbonless sheets, and an enhanced binding effect of the adhesive to the coated papers. The inventive adhesives have specific utility for heavily coated sheets where microcapsules in binder have excess solvent available to disrupt the adhesion process. Such adhesion interference is typically noted where the pad edge is guillotined immediately before application of adhesive to provide a clean edge. This freshly cut pad necessarily includes cut and broken microcapsules, which have thereby released their solvents and color-forming agents. The transport agents apparently solvate these interfering materials and sweep them from the edge area of the pad to be adhered. The described adhesive is particularly used advantageously in a new and developing area of carbonless paper form preparation. Preferably, businesses will be able in the future to custom-prepare their own carbonless form-sets to prepare forms of their own design in limited quantities. Also, businesses may significantly reduce inventories of preprinted carbonless forms because they will have the ability to prepare their own on a short-term need basis. Such form-sets may be made by running plain carbonless stock paper through an electrophotographic process, such as a standard office photocopier, and binding the sets together using their own edge-padding adhesive. The process of photocopying on paper, however, has been found to introduce contaminants on the paper in the form of copier oils, paper detritus, toner particles or combina¬ tions of these materials. The presence of the contaminants significantly interferes with edge padding adhesion. Incorporation of an effective amount of transport agent in the edge padding adhesive provides good to excellent adhesion properties with low or no VOC content. As noted above, Volatile Organic Compounds are materials having a vapor pressure at 20°C greater than 0.1 Torr. More preferably, VOCs may be defined as having a vapor pressure greater than 0.02 Torr. The transport agent as delineated herein apparently does not adversely affect the integrity of the microcapsules to the extent of causing leakage of their contents. Transport agents that are mixtures of poly(alkylene oxide)mono-alkyl ethers with alkyl alcohols comprise at least 1-1.5% of the poly(alkylene oxide)mono-alkyl ether component based on total adhesive weight to provide the desired level of adhesion of the ultimate adhesive. The alkyl alcohol component of such a transport agent mixture preferably comprises at least 0.4% alkyl alcohol as a percentage of the total adhesive. Alkyl alcohols appropriate for use preferably have between 3 and 8, and more preferably between 3 and 6, carbon atoms. Particularly preferred transport agents are blends of poly(alkylene oxide)mono-alkyl ethers. More preferably, the transport agent is a blend of diethylene glycol monoalkyl ethers. Most preferably, the transport agent is a blend of diethylene glycol monobutyl ether and diethylene glycol monohexyl ether. Preferred water-based latex adhesives are poly(styrene/butadiene) and poly(ethylacrylate/N- methylolacrylamide) . Their use affords novel adhesive compositions that are highly resistant to destabilization and provide excellent adhesive values. Other useful water- based latex adhesive polymers include poly(vinyl acetate), poly(vinylidene chloride/butadiene/styrene) , poly(ethyl- acrylate/methylacrylate) , and poly(ethylacrylate) . When used for edge padding carbonless copy papers, it is preferred to employ less than about 18% by weight (dry basis) of the water-based latex adhesive polymer to ensure that the edge-padded stack separates into sets upon fanning. It also is preferred to employ more than 10% by weight of the water-based latex adhesive polymer to ensure adequate adhesion between individual sheets of the sets. In addition to components a) , b) , and c) , the novel adhesive composition may contain small amounts of other ingredients, such as antioxidants, bactericides, and plasticizers. For example, up to 10% by weight of the composition preferably is a noncrystallizing modified sorbitol which is substantially nonvolatile and should have a substantially permanent plasticizing effect by staying with the dried adhesive. (By "modified" is meant sorbitol treated to render it noncrystalline) . The presence of such a modified sorbitol has improved the versatility of the novel adhesive composition for use with different carbonless copy papers. At amounts of modified sorbitol substantially above 6%, the novel adhesive composition might not adhere well to some carbonless copy papers. More preferably, noncrystallizing modified sorbitol comprises from 0.5 to 1.25% by weight (dry basis) of the novel adhesive composition. Noncrystallizing forms of sorbitol are available as "Sorbo," "Sorbo Special," and "Arlex" from ICI Americas, Inc. The invention may be more easily understood in reference to the drawing, the single figure of which schematically indicates in cross section the edge padding of a stack of sets of collated sheets of carbonless copy paper, which stack upon fanning separates into individual sets. Shown in the drawing is a stack 10 of 4-part carbonless copy paper sheets including top sheets 11 (coated back CB) , intermediate sheets 12 and 13 (coated front and back CFB) , and bottom sheets 14 (coated face CF) resting on a table 15. Each CB coating contains rupturable capsules which when ruptured release reagents to produce a color-changing reaction at the adjacent CF coating. The outer, uncoated faces of the top sheet 11 and bottom sheet 14 of each 4-part set have been treated with release agent 16 and 17, respectively. A flat plate (not shown) can been used to afford a smooth edge 18 to the stack 10. While compressing the edge 18 with a steel bar 19, a water-based adhesive composition 20 has been applied to the edge and has flowed into the stack to produce an adhesively edge-padded stack of the invention. To provide complete assurance of adequate adhesion between individual sheets of each set in a collated stack, sufficient amounts of the novel water-based adhesive composition should be applied to the edge of the stack until excess adhesive composition runs down the edge of the stack. Greater amounts cause no problem except to be wasteful. Carbonless copy paper is often collated into sets as follows: For 2-part sets — First sheet: CB = coated back Second sheet: CF = coated front For 3-part sets— First sheet: CB = coated back Second sheet: CFB = coated front and back Third sheet: CF = coated front For 4 -part sets — First sheet: CB = coated back Second sheet: CFB = coated front and back Third sheet: CFB - coated front and back Fourth sheet: CF = coated front Each CB coating contains rupturable capsules which, when ruptured, release reagents to produce a color- changing reaction at the adjacent CF coating. In order to ensure that the edge of the stack remains uniform, the edge preferably is compressed by a weight during the edge-padding step. The amount of compression is not material as long as it is not so great as to rupture the reagent-containing capsules (preferably not more than about 50 psi (340 kPa)) . When there are no capsules to rupture, there is no practical limit to the amount of compression. It is more difficult to form a strong CB/CF bond in 2-part sets than it is to form CB/CFB and CFB/CF bonds between the individual sheets of 3-part sets. In 4-part or greater sets, it is more difficult to form strong CFB/CFB bonds than it is to form strong CB/CFB and CFB/CF bonds. Consequently, in 4-part or greater sets, CFB/CFB bonds are the bonds most likely to break upon fan-out or crash printing. The most stringent testing of the ability to form strong bonds between sheets is in 2-part sets (CB/CF) and in 4-part sets (CFB/CFB), rather than in 3-part sets. It has further surprisingly been found that, for some carbonless papers, there is no need to physically fan the stack of collated papers to separate them into form-sets when using the present edge-padding adhesives. In these papers, no significant adhesion between form-sets is created, and the sets may be removed one from another without a separate fanning operation. This represents a significant advantage to the form-set producer, who does not need to worry about performing a fanning function at an appropriate level of dryness of the adhesive. The present invention will be further described by reference to the following detailed examples. These examples are presented to illustrate the operation of the invention and are not to be construed as limiting its scope. TEST METHODS The quality of an edge-padding adhesive composition can be determined by two tests, one showing how readily a stack of collated sheets separates into sets ("Fan-Out Rating Test") and the other showing the strength of the adhesive bond between individual sheets of a set ("Bond Strength Test") . The stack is first trimmed and the trimmed edge is compressed. Within 5 minutes, the edge is adhesively edge-padded unless otherwise specified and, while maintaining the compression, the edge-padding is allowed to dry overnight before testing. Fan-Out Rating Test A stack of sets of collated sheets that has been edge-padded is tested for fan-out into sets as follows: 1) While gripping the edge-padded end of the stack with one hand and the unpadded end with the other, bend the stack into a "U" shape. Then while holding the stack horizontally, release the padded end, allowing that end to droop downward. If complete fan-out has been accomplished, rate as a 3.5; if not, continue. 2) Place the stack on a flat surface with fingers one inch (2.5 cm) back from the edge padded end on top and thumbs under the corners, and simultaneously fan upwards on both corners of the edge padded end. If complete fan-out has been accomplished, rate as 3.0; if not, continue. 3) Place on a flat surface with fingers on top and the thumbs under the edge-padded end approximately 3 inches (7.6 cm) from the corners of the edge-padded end, and simultaneously fan upwards once. If complete fan-out has been accomplished, rate as 2.5; if not, continue. 4) Place stack on a flat surface with fingers on top and thumbs under the edge-padded end wherever needed, and simultaneously fan upwards twice. If complete fan-out has been accomplished, rate as 2.0; if not, continue. 5) While holding the stack as in step 4) , fan with both thumbs three times wherever needed. If complete fan-out has been accomplished, rate as 1.5; if not, continue. 6) While holding the stack as in step 4) , fan with the thumbs six more times wherever needed. If complete fan-out is accomplished, rate as 1.0; if not continue. 7) While holding the stack as in step 4) continue to fan with the thumbs wherever needed. If complete or partial fan-out can be accomplished, rate as 0.5; if not, rate as 0. Generally, the carbonless copy paper industry will accept a Fan-Out Rating of 2.0, but a higher value would be preferred. Bond Strength Test The strength of the adhesive bond between two individual sheets of a set of carbonless copy paper is tested using a tension measurement device, i.e., "Digital Force Gauge Model DFG RS-50" available from John Chatillon & Sons, Inc., Greensboro NC. With the unpadded end of one sheet in the clamp, the unpadded end of the other sheet is gripped by the thumb, fingers and palm of one hand and pulled slowly until the bond fails. In 4-part sets, measurements are made between the coated front sheet and a coated front and back sheet (CF/CFB) , between two coated front and back sheets (CFB/CFB) , and between a coated front and back sheet and the coated back sheet (CFB/CB) . Typically, the lowest ChatilIon "Bond Strength" in a 4-part set is CFB/CFB. When the "Bond Strength" exceeds 10 N (10 Newtons) across a width of 8.5 inches (21.6 cm), a set of the edge-bonded sheets should withstand premature separation in any ordinary printing operation, including crash printing or perforating. Higher bond strengths than this minimum level are preferred. EXPERIMENTAL EXAMPLES In the following examples, all parts are by weight. The weight reported for each latex used is the dry weight. Each "Bond Strength" reported below is an average of at least five measurements. Examples 1 - 4 The effectiveness of the present adhesives on papers having different edges was carried out. An edge- padding adhesive composition was prepared having the formulation as described below as Adhesive Composition A. The results are shown in Table I. Testing was carried out using 2-part sets of "blue/purple" (b/p) , and 4-part sets of "blue/purple" carbonless copy paper from 3M Co. Examples 1 and 2 were carried out on freshly cut sheets and are said to have a "cut edge." Examples 3 and 4 were carried out on sheets that were trimmed at the paper mill and are said to have a "milled edge." Adhesive Composition A C nent wt% Rhoplex HA-24 is a water-based poly(ethyl-acrylate/poly N- methylolacrylamide) latex adhesive polymer available from Rohm and Haas, Philadelphia. PA. Table I - Fan-Out Rating and Bond strength for Various Edged Papers J≥ZP_ M . A series of edge-padding adhesive compositions were prepared having identical formulations except using different transport agents and amounts of transport agent. Table II reports the level of transport agent (wt%) , and the "Bond Strength" using 2-part "blue/purple" (b/p) , "4- part blue purple", 2-part Scotchmark™, or 4-part Scotchmark™, carbonless copy-papers, all available from 3M Co. In multi-part sets, the CFB/CFB bond is the weakest bond. In all cases, the Fan-Out rating was 3.5. The results, shown in Table II, indicate that the absence of both sorbitol and a transport agent, or the absence of only a transport agent, results in poor bond strength for 4-part Scotchmark™ CFB/CFB bonds. Also, the presence of between 2% and 3% of a carbitol transport agent promotes good adhesion between CFB/CFB sheets in a form- set. Table II - Bond Strength for Various Transport Agents 2-part sets 4-part sets L Scotchmark™ ws_ Scotchmark™ Bond Bond Bond Bond Transport Agent Strength Strength Strength Strength Ex. Percentages Newtons Newtons Bond Newtons Newtons Butyl Carbi ol Hexyl Carbitol O CFB/CF 58 41 35 22 CFB/CFB 45 41 η 30 21 CFB/CFB 21 38 42 21 CFB/CFB 68 36 30 14 CFB/CFB 54 36 22 22 CFB/CFB 25 27 CFB/CFB 42 30 12 CFB/CFB 39 33 25 CFB/CFB 45 35 20 22 CFB/CFB 35 30 24 21 - z- Table II - Bond Strength for Various Transport Agents - (cont.) Transport Agent EX. Percentages CO 39 1.5/0.75 40 1.5/1.0 CD CO 41 H 1.5/1.25 42 1.5/1.5 C H 43 1.25/0.75 m co 44 1.0/0.5 m 45 1.0/0.6 46 1.0/1.0 ~ Butyl Diproposol 47 4.0 34 27 Butyl Diproposol/Hexyl Carbitol 48 2.5/0.5 29 Aerosol AY 100 49 2.0 28 51 2.0 29 CFB/CFB 36 Table II - Bond Strength for Various Transport Agents - (cont.) 2-part sets 4-part sets b/p Scotchmark™ w__ Scotchmark™ Bond Bond Bond Bond Transport Agent Strength Strength Strength Strength Ex. Percentages Newtons Newtons Bond Newtons Newtons 32 CFB/CFB 29 61 2.0 30 62 3.5 28 Examples 63 - 76 A study of levels of adhesive polymer necessary for adhesion was carried out. Edge-padding adhesive compositions were prepared having the formulation as described below, but varying the percentage of Rhoplex HA- 24 polymer. The results indicating fan-out rating and bond strength are shown in Table III. Testing was carried out using 2-part sets of "blue/purple" (b/p) , 4-part sets of "blue/purple 11 , 2-part Scotchmark™, or 4-part Scotchmark™, carbonless copy papers, all available from 3M Co. In multi-part sets, the CFB/CFB bond is the weakest bond and only CFB/CFB bond strengths were measured in 4-part sets. Component wt% Rhoplex HA-24 latex indicated Butyl Carbitol 2.0 Hexyl Carbitol 0.6 water balance Total 100.0% O D π o π These results indicate that good bond strength was observed in edge-padding adhesives combining up to 27% polymer, but that above about 22% polymer, little further increase in adhesive strength is achieved. Above about 17% polymer, fan-out begins to decrease but remains acceptable (i.e., >2.0) . Exampl s 77 - 79 A study of the necessity of modified sorbitol in the presence of carbitols was carried out. Edge-padding adhesive compositions were prepared having the formulation as described below, but varying the percentage of modified sorbitol. The fan-out rating and bond strength results, shown in Table IV, indicate that using carbitols as transport agents may eliminate the need for modified sorbitol. Testing was carried out using 2-part sets of "blue/purpie" (b/p) , 4- part sets of "blue/purple", 2-part ScotchmarkTM, or 4-part ScotchmarkTM, carbonless copy papers, all available from 3M Co. In multi-part sets, the CFB/CFB bond is the weakest bond and only CFB/CFB bond strengths were measured in 4- part sets. In all cases, the Fan-Out rating was 3.5. Table IV - Relationship Between Sorbitol Level and Bond Stren th 1 1 2 Table V - Bond Stren ths Usin Butyl Carbitol and Various Levels of Hexanol COMPARATIVE EXAMPLES The adhesion of the inventive adhesive was compared with that of the prior art VOC-containing adhesives on various carbonless paper substrates. Adhesion values were comparable, within a standard deviation, even though the inventive adhesives do not contain substantial amounts of VOCs. Minimum acceptable adhesion values are greater than 10 Newtons. Adhesives compared were: Adhesive Composition B 2.0 Butyl Carbitol 0.6 Hexyl Carbitol 15.0 Rhoplex HA-24 latex (dry weight) 82.4 water Comparative Adhesive C poly(ethylacrylate/N- methylolacrylamide) ethyl alcohol isopropyl alcohol non-crystallizing sorbitol water Comparative Adhesive D % bv wt. poly(ethylacrylate/ methylolacrylamide) 17 (dry wt.) 1,2-propanediol 28 ethyl alcohol 8 water 47 Comparative Adhesive E % bv wt. poly(ethylacrylate/ methylacrylate) (92/8) 13 (dry wt.) 1,2-propanediol 19 ethyl alcohol 7 water 61 SCOTCHMARK™ Basis wt. Adhesion (newtons) of paper Adhesive B Comp. Ad. C 2PT 23.0 24.4 3PT 69.9 6.9 67.9 67.2 PT 69.1 66.6 52.7 58.2 69.5 71.2 PT 67.0 62.6 60.1 77.9 55.2 43.8 93.9 67.7 71.6 63.6 SCOTCHMARKTM con't. Basis wt. Adhesion (newtons) of paper Adhesive B Comp. Ad. C 2PT 54.4 70.0 3PT 69.3 76.2 48.4 73.1 4PT 67.0 66.3 63.5 75.0 31.9 32.9 2PT 61.0 50.3 3PT 70.2 55.8 33.4 28.6 PT 67.7 61.2 63.4 68.2 38.1 31.8 BLUE-PURPLE IMAGE BLUE-PURPLE IMAGE (WITH BUFF CF LEDGER) -38- XEROXTM BLACK IMAGE Basis wt. Adhesion (newtons) of paper Adhesive B Comp. Ad. C 39.3 34.2 71.7 57.5 73.9 67.7 87.2 75.8 72.8 51.7 87.5 89.4 77.8 84.8 56.2 47.0 97.5 47.0 81.6 79.2 Tartan™ and Black Image papers are commercially available coated papers for use as carbonless form-sets from 3M Company. Xerox Brand Carbonless paper is commercially available from Xerox Corporation. Four part forms of manila tag, ledger, and Xerox™ continue to be low in adhesional strength for both of the adhesives. However, the bond between the canary (CFB) to pink (CFB) increases significantly in adhesional strength on the 4pt, 5pt, and 6 pt papers when using Adhesive B. The larger form sets should then have a stronger "spine" creating a better form set. Results of padding Black Image show that Adhesive B should not cause padding problems with this paper. In fact, Adhesive B is stronger in adhesional strength than Comparative Adhesive C on Black Image. The effectiveness of the inventive adhesives on carbonless papers of multiple sources was also shown: ,TH MEAD TRANS/RITE Adhesion (newtons) Comp. Adhesive E Blue- Black- Image Image 34.0 38.0 66.4 61.9 61.5 57.4 46.1 41.7 74.7 64.6 66.0 66.4 MEAD TRANS/RITE,TH - (cont.) Adhesion (newtons) Comp. Adhesive E Blue- Black- Image Image 6PT 56.0 . MEAD EXCELT 1 H Adhesion (newtons) Adhesive B Comp. Adhesive E Black-Image Black-Image 2PT CO X 4PT rπ 52.8 52.2 -\ 28.7 39.3 74.4 68.5 NCR BLACK Adhesion (newtons) Adhesive B Comp. Adhesive D Black-Image Black-Image 2PT 23.7 23.8 3PT 57.4 43.1 ? 59.3 46.7 4PT 68.0 60.0 57.9 38.4 72.7 51.1 5PT 65.3 44.5 53.9 51.0 71.0 63.3 69.5 54.8 NCR BLACK - (cont.) Adhesion (newtons) Adhesive B Comp. Adhesive D Black-Image Black-Image 6PT 15 lb. 67.9 48.9 17 lb. 74.5 60.4 17 lb. O 92.5 64.7 D 17 lb. 105.9 78.0 17 lb. 79.6 55.5 15 lb. π 1 NCR PERFORM,TH Adhesion (newtons) Adhesive B Comp. Adhesive E Blue- Black- Blue- Black- Image Image Image Image 17 lb. 21.0 21.8 50.3 54.4 41.0 44.4 44.9 58.3 41.7 45.2 NCR PREMIUM™ AND SUPERIOR™ Adhesion (newtons) Adhesive B Comp. Adhesive D PREMIUM SUPERIOR PREMIUM SUPERIOR 2PT o 4PT 54.5 49.9 52.8 40.7 64.6 62.6 Fan-Apart on all tests rated a 3.5 for Adhesive B, Comparative Adhesive D and Comparative Adhesive E. Adhesive B provided good adhesion on all the papers tested. Adhesive B either outperformed or equaled the adhesive strength (within standard deviation) of the prior art VOC-containing adhesives. Adhesive B worked extremely well on the Mead Transrite™, NCR Black and NCR Perform™ carbonless papers. Greater adhesion and less rippling of form sets was observed. Adhesion over time of Adhesive B and Comparative Adhesive C was evaluated. The adhesives were tested under two environmental conditions of controlled temperature and humidity. In the first set of conditions, the temperature was held at 23°C and 50% humidity, hereafter referred to as the "23-50" Room." The second set of conditions was controlled to 27°C and 80% humidity, hereafter referred to as the "27-80 Room." The adhesives were tested on 2 pt„ and 4 pt. Blue-Purple Image paper. Testing three reams of paper, the adhesives were allowed to dry at intervals of 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, and approximately 16 hours (overnight) . The stacks were tested for fan-out and adhesion. The three test values for each specific time were then averaged together and plotted on a graph of adhesion (newtons) versus time, thus allowing the adhesives to be compared to each other at the two conditions. ADHESION VS. TIME 2PT BLUE-PURPLE IMAGE TCB-CF) st. dev. 3.5 2.8 2.6 2.0 4PT BLUE-PURPLE IMAGE (CB-CFBΪ st. dev. 4.3 2.2 3.0 2.1 4PT BLUE-PURPLE IMAGE fCFB-CFB st. dev. 5.7 4.8 3.5 3.1 4PT BLUE-PURPLE IMAGE fCB-CFΪ st. dev. 5.4 3.1 2.0 3.2 23-50 Room Conditions All tests rated a 3.5 for fan-out. During the first 30 to 45 minutes of drying. Adhesive B is weaker in adhesional strength when compared to Comparative Adhesive C. At a one hour waiting time. Adhesive B is equal to, if not stronger than. Comparative Adhesive C. After one hour. Adhesive B is stronger for all bonds when compared to Comparative Adhesive C. This trend occurs for both 2-part and 4-part data. 27-80 Room Conditions All tests rated a 3.5 for fan-out. During the first hour. Adhesive B exhibits the same trend of lower adhesional strength when comparing to Comparative Adhesive C. After 1 to 2 hours. Adhesive B is essentially equal in adhesional strength when comparing to Comparative Adhesive C. There are slight variations between the two adhesives; however, all data are within standard deviation. 23-50 Room vs. 27-80 Room Conditions Results indicate that conditions (temperature/- humidity) definitely have a significant impact on the adhesional strength of Adhesive B and Comparative Adhesive C adhesives. In the 27-80 Room, both adhesives decreased in adhesional strength at all data points when comparing to the 23-50 Room. Since both adhesives are mainly comprised of water, the decrease in adhesional strength is probably due to the increase of humidity in room conditions. In the 27-80 Room, one might assume Comparative Adhesive C would have an overall increase in adhesional strength because of the 21% alcohol in solution. However, this is not the case. In both environmental conditions, the alcohol only seemed to improve the adhesion during the first hour of drying. After the one hour, both adhesives are approximately equal in adhesional strength. Because current edge padding adhesives have a recommended one hour drying time, the waiting time required before fanning the stack of carbonless papers is not increased, even though the inventive adhesive contains no VOCs to shorten dry time. In high humidity conditions, a slight increase in time to two hours would be recommended for the present adhesives. TRANSPORT AGENT MIXTURES Mixtures of more than one component in the transport agent were tested on Black Image carbonless paper from 3M, which is a coated paper having comparatively heavy coating weight of color-former agents. A series of edge-padding adhesive compositions were prepared having the formulation as described below, but varying the percentage of Butyl Carbitol and Hexyl Carbitol. Component wt% Rhoplex HA-24 latex 15.0 B indicated water balance Total 100.0% Bond Strength is reported in TABLE VI. Butyl Carbitol in combination with Hexyl Carbitol provides superior adhesion levels than either component alone for two-part form-sets and for the CFB/CF bond. A solvation effect also appears to be taking place, wherein a minimum amount of Hexyl Carbitol is preferably present with a preponderance of Butyl Carbitol for most beneficial effect. A series of edge-padding adhesive compositions were prepared having the formulation as described below, but varying the percentage of Butyl Carbitol and Hexanol. Component wt% Rhoplex HA-2 latex 15.0 Butyl Carbitol indicated Hexanol indicated water balance Total 100.0% Bond Strength is reported in TABLE VII. Butyl Carbitol in combination with Hexanol provides superior adhesion levels than either component alone for two-part form-sets and for the CFB/CF bond. A solvation effect also appears to be taking place, wherein a minimum amount of Hexanol is preferably present with a preponderance of Butyl Carbitol for most beneficial effect.

Claims: CLAIMS What is claimed is: 1. A water-based adhesive composition that is suitable for fan-apart edge-padding of collated carbonless copy papers, said composition comprising by weight a) from 7.5 to 27% dry weight of a water-based latex adhesive polymer, b) from 0.5 to 15% of a water-dispersible transport agent comprising at least one poly(alkyleneoxide) mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms, and c) water, wherein said adhesive composition has a VOC content of less than 250 g/1 less water and less exempt solvents. 2. A water-based adhesive composition as defined in claim 1 wherein the amount of said transport agent is from 2 to 8%. 3. A water-based adhesive composition as defined in claim 1 wherein the transport agent has between 2 and 10 alkylene oxide moieties. 4. A water-based adhesive composition as defined in claim 1 wherein the transport agent has between 2 and 4 alkylene oxide moieties. 5. The adhesive composition of claim 1, wherein said transport agent is a diethylene glycol monoalkyl ether. 6. The adhesive composition of claim l, wherein said transport agent is diethylene glycol monobutyl ether. 7. The adhesive composition of claim 1, wherein said transport agent is diethylene glycol onohexyl ether. 8. The adhesive composition of claim 1, wherein said transport agent is a dipropylene glycol monoalkyl ether. 9. The adhesive composite of claim 1, wherein said transport agent is a mixture of a poly(alkylene oxide) mono-alkyl ether or alkyl alcohol. 10. The adhesive composite of claim 7, wherein said alkyl alcohol has 3 to 5 carbon atoms. 11. The adhesive composite of claim 1, wherein said transport agent is a mixture of more than ne poly(alkyleneoxide) mono-alkyl ethers. 12. The adhesive composite of claim 9, wherein said poly(alkyleneoxide) mono-alkyl ethers are diethylene glycol monoalkyl ethers. 13. The adhesive composite of claim 10, wherein said transport agent is a mixture of diethylene glycol monobutyl ether and diethylene glycol monohexyl ether. 14. A water-based adhesive composition as defined in claim 1, which composition is substantially free from volatile organic compounds. 15. A water-based adhesive composition as defined in claim 1 and further comprising up to 10% by weight of a noncrystallizing modified sorbitol. 16. A water-based adhesive composition as defined in claim 7 wherein the amount of the modified sorbitol is from 2 to 6%. 17. A water-based adhesive composition as defined in claim 1 wherein the amount of the water-based latex adhesive polymer is from 10 to 18% (dry weight) . 18. A water-based adhesive composition as defined in claim 1 wherein the water-based latex adhesive polymer comprises poly(styrene/butadiene) . 19. A water-based adhesive composition as defined in claim 1 wherein the water-based latex adhesive polymer comprises a poly(ethylacrylate/N-methylolacrylamide) . 20. A water-based adhesive composition as defined in claim 1 wherein said poly(alkyleneoxide) mono-alkylether comprises an alkyl group of at least 4 carbon atoms. 21. A water-based adhesive composition as defined in claim 1, which has a flash point above 94°C. 22. A water-based adhesive composition as defined in claim 1 where the VOC content is calculated using the definition of volatile organic compound as having a vapor pressure at 20°C greater than 0.02 Torr. 23. A method of adhesively edge padding a stack of sets of collated carbonless copy paper sheets to permit the stack to be fanned apart into individual sets, said method comprising the steps of 1) applying to an edge of the stack a water-based adhesive composition which comprises by weight: a) from 7.5 to 27% (dry weight) of a water- based latex adhesive polymer. b) from 0.5 to 15% of a water-dispersible transport agent comprising at least one poly(alkyleneoxide) mono-alkyl ether having alkyl groups of from 4 to 12 carbon atoms and alkylene groups of from 2 to 4 carbon atoms, and c) balance water, which composition has a VOC content of less than 250 g/1 less water and less exempt solvents, and 2) allowing the applied adhesive composition to dry. 24. The method as defined in claim 13, further comprising a step 3) that is fanning the stack into individual sets of the sheets. 25. A method of preparing sets of collated carbonless copy paper comprising a) forming an image onto donor and receptor papers suitable for carbonless impact marking through an electrophotographic process, b) collating said donor and receptor papers into a stack of form-sets, c) applying to an edge of the stack a water- based adhesive composition of claim 1, and d) allowing the applied adhesive composition to dry. 26. A stack of sets of collated carbonless copy paper that have been adhesively edge-padded using the adhesive composition defined in claim 1.

Inventors: CHRISTEN DANIEL P, EMERY CLAIR J, KLEITER MICHAEL A, PERRINGTON KENNETH J, CHRISTEN, DANIEL, P., EMERY, CLAIR, J., KLEITER, MICHAEL, A., PERRINGTON, KENNETH, J.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1991
Main classification: B42C9
IPC codes: C08K5, C09J133