FIELD OF THE INVENTION

[002] The invention relates generally to low emission one part adhesives and methods of making the same, and more particularly to adhesives, such as flooring adhesives, that have low emissions of undesirable materials, such as volatile organic compounds (VOCs).

BACKGROUND OF INVENTION

[003] Many products are assembled using adhesives. For example, various flooring products made from wood, vinyl, tile, carpet and so forth are permanently adhered to a surface or substrate through the use of an adhesive. Commonly used adhesives include those sold under the trademarks Taylor Enviotec 2090 Vinyl Adhesive and Taylor Envirotec 2055 Premium Carpet Adhesive sold, by W.F. Taylor Co. of Fontana, California. [004] There are at least two general types of adhesives: two component adhesives and one component adhesives. Two components reactive adhesives are generally formed with a resin component and a hardener component and the resin and hardener are mixed immediately prior to application. This causes a chemical reaction to occur which typically initiates some type of cross-linking process. Two component adhesives are often considered undesirable because considerable mixing of the components must occur just prior to use. This can be inconvenient. Also, just the right amount of adhesive must be mixed prior to application. If too much is mixed, or the working "pot" time is exceeded, the adhesive will harden and the excess must be discarded. Reactive urethane type adhesives contain materials such as isocyanates, which are often considered undesirable. [005] Single component adhesives can be more convenient to use than two component adhesives. Many single component adhesives are solvent-based adhesives in which an adhesive composition is mixed with a solvent and packaged in a drum, can or tube.

After the adhesive is applied to a substrate, the solvent evaporates, which causes the adhesive to cure.

[006] The solvents used in certain conventional solvent-based adhesives are believed by some to be undesirable. Solvents commonly used in construction and flooring adhesives include, but are not limited to, acetone, cyclohexane, methyl ethyl ketone, perchloroethylene, toluene, trichloroethylene and xylene. These solvent-based adhesives are undesirable because they emit VOCs. Depending on the working environment, available ventilation, and the amount of adhesive to be used, some consider the VOCs and other emitted chemicals to be disadvantageous. Other single component adhesives contain excessive amounts of water, which can damage wood surfaces. There are other single component reactive adhesives such as moisture cure urethanes, but they typically exhibit emission problems because they give off solvents and other potentially dangerous materials including isocyanates such as toluene diisocyanate and methylene bisphenyl diisocyanate, which are considered to pose a substantial risk of serious or fatal respiratory disease.

[007] Accordingly, it is desirable to provide an improved adhesive which overcomes drawbacks and inadequacies of conventional adhesives.

SUMMARY OF THE INVENTION

[008] Generally speaking, in accordance with the invention, a one component high strength adhesive composition which can be formulated to have low or substantially no VOC emissions is provided. Adhesives in accordance with the invention can be formulated as high solids, one-part, reactive, cross-linked adhesives. This can be achieved by utilizing amide- ester-acrylate reactions or reactions with any other carboxylated polymers. Adhesive compositions in accordance with the invention can include a viscous mixture of drying oil, such as renewable soybean oil, linseed oil and sunflower oil, inorganic fillers, renewable

tackifiers such as rosins, polymers with carboxyl and/or hydroxyl functionality, metal catalysts and a non-toxic cross-linking agent.

[009] Adhesives in accordance with the invention can also include various hydrocarbon resins, particularly crosslinkable hydrocarbons having a melting point in the range 70 ⁰ C to 140 ⁰ C. These can be dissolved or otherwise mixed in the drying oil component. For example, C-5 hydrocarbon resins formed from hydrocarbons having an average of about five carbon atoms and C-9 hydrocarbon resins formed of hydrocarbons having an average of about 9 carbon atoms and preferably both, mixed in effective proportions to provide desired cured strength, green strength, open working times and so forth can be satisfactory.

[0010] Adhesives in accordance with the invention can also include fugitive alkali agents, such as ammonia, monomethanol amine (MEA) and triethanol amine (TEA). Cross linking agents, such as Oxazoline with pendant groups; n-Methylol acrylamide; Glycidyl methacrylate; 3-Methacryloxypropyl-Trimethoxysilane; 3-Mercaptopropyl Trimethoxysilane; Polyvalent metal carboxylate salts; Diacetone acrylamide; Acid diahydrazide; Adipic dihyrazide; DAAM/Glyoxal; Urea/Glyoxal; Carbodiimide functionalized material such as polycarbodiimides and carbodiimide; Epoxy functional water miscible/emulsifiable additives such as aziridine; Metal ionic cross-linkers, such as zirconium, zinc, calcium; Polyisocyanates; Organosilanes, Urea formaldehyde/melamine formaldehyde resins; Aziridine functionalized materials and Polyethylenimine are also advantageously included. Various other mixing, flow and other handling ingredients can also be included. [0011] High solids construction adhesives in accordance with the invention can be particularly useful in assembling various flooring products made from wood, vinyl, ceramic, rubber to various substrates common to flooring installations including: concrete, plywood, underlayment grade particle board, vinyl, ceramic tile, cement patches and underlayments,

radiant heat flooring and terrazzo. Adhesives in accordance with the invention can benefit from polymer emulsions with carboxyl functionality, polymer emulsion cross-linkers containing pendant oxazoline group are also advantageously employed. Other useful ingredients include tackifying hydrocarbon resins dissolved in drying oils; napthanates of metals such as cobalt, calcium, zirconium, and manganese; fugitive bases for pH adjustment; and other stabilizing agents, such as fugitive anti-oxidants.

[0012] The initial chemical reactions involved in the curing process of the adhesive in accordance with the invention are believed to be mainly a result of autoxidation of the drying oil. The process is believed to involve formation of hydroperoxide-substituted fatty acids and breakdown of the hydroperoxides, giving rise to highly reactive radicals and subsequent cross-linking. The cross-linking reaction can be catalyzed by the presence of transition metals. The resulting cross-linked bonds can be covalent ethers, peroxide and carbon-carbon bonds. As the cross-linking proceeds and the adhesive solidifies, a three-dimensional network can be formed when there is more than one reactive site on the unsaturated fatty acids in the drying oil, hence more than one point to create a cross-link bond. [0013] Accordingly, it is an object of the invention to provide an improved adhesive.

[0014] Another object of the invention is to provide an improved method of making an adhesive.

[0015] Still other objects of the invention will in part be obvious and will, in part, be apparent from the specification. The invention accordingly comprises the composition of matter, the method of making a composition of matter and the method of using the composition of matter which will be exemplified in the compositions and methods hereinafter described, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the drawing figures, which are merely illustrative:

[0017] FIG. 1 is a graph depicting shear strength development over three months aging, comparing the performance of a preferred embodiment of the invention with a leading moisture cure urethane adhesive on the market. As demonstrated in FIG. 1, an adhesive in accordance with the preferred embodiments of the invention is immediately stronger than a leading moisture cure urethane adhesive, cures to have higher shear strength and does not give off unacceptable VOCs while curing.

[0018] FIG. 2 is a graph showing increase in cross link density of an adhesive formulated in accordance with a preferred embodiment of the invention, with progressing time.

[0019] FIG. 3 depicts a fresh un-reacted adhesive film.

[0020] FIG. 4 depicts a partially cross-linked film.

[0021] FIG. 5 depicts a fully cross-linked adhesive.

[0022] FIGS. 3-5 are schematic models depicting different stages in the developing of the three dimensional network of cross-linked bonds in an adhesive based on drying oils.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The invention is directed to adhesive compositions and methods of making adhesive compositions which can include ingredients set forth below. The invention also relates to methods of applying flooring involving the use of those adhesives. As will be evident to those of ordinary skill in the art, substitutions, omissions and additions will be possible in order to provide adhesives with customized selected properties. [0024] Preferred ingredients, preferred percentages of components and mixing processes in accordance with preferred embodiments of the invention will be set forth below in Table 1.

TABLEl

[0025] Adhesive compositions in accordance with the invention advantageously include liquids that can be used to dissolve and blend other ingredients, but which can be easily and readily oxidized and/or polymerized to transform into a hard, dry material after exposure to air. Examples of such material include relatively highly unsaturated oils and polymers, such as those identified above as drying oils. The drying oil component can be included as about 1 to 20%, preferably 4 to 10%, more preferably about 2% to 5%. By

dissolving (mixing) the resins in the drying oil component and the addition of fugitive anti¬ oxidants, the resins can be prevented from cross-linking until the drying oil is exposed to air and hardens. The cross-linking starts as the composition starts to dry and the fugitive anti¬ oxidant starts to evaporate. Thus, there should be sufficient anti-oxidant to prevent the composition from curing too quickly, and to provide sufficient open time and ease of handling. Preferred open time should be up to about 30 and sometimes up to about 60 minutes and depend on the desired application.

[0026] Adhesives in accordance with the invention can also include hydrocarbon resins. The resins are selected to give the cured adhesive the desired amount of cured strength. Appropriate selection of resins also affects the uncured strength (initial shear strength) of the adhesive, often referred to as green strength. For example, if the adhesive is used as a flooring adhesive, it is desirable that the uncured adhesive maintain the applied flooring in place with reasonable security so that tiles, for example, can be aligned properly and so that minor bumps and nudges do not require reseating and realignment of the flooring materials. Below in Table 2 is a comparison of typical green strength in psi, of adhesives in accordance with a preferred embodiment of the invention compared to a leading VOC emitting Moisture Cure Urethane Adhesive currently on the market:

TABLE 2

[0027] Conventional moisture Cure Urethane adhesives can contains up to 1% 4,4'-

Diphenylmethane Diisocyanate (MDI), up to 1% Toluene Diisocyante, up to 10% Aliphatic Petroleum Distillates, up to 1% Ethyl Benzene, Up to 5% Xylene, Up to 7% Mineral Spirits

and up to 1.5% 1,2,4-Trimethyl Benzene. All these VOCs are listed in the hazardous materials section of the MSDS for most commercial grade moisture cure urethane adhesives. [0028] It has been determined that the cured strength and green strength of the adhesive can be related to the softening points of the resin material. As used herein, softening point will refer to the temperature at which viscous flow of a material that does not have a definite melting point changes to plastic flow.

[0029] Resins in accordance with preferred embodiments of the invention generally have softening points between 75°C and 140 ⁰ C. It has also been determined that by mixing resins with different softening points, advantageous characteristics of each resin can be realized. For example, resins with a relatively low softening point, e.g., about 95-105 ⁰ C will have up to 30-40% less green strength and cured strength than resins with a relatively high softening point in the range of e.g., 115-130 ⁰ C. Softening point also affects processing and handling properties. If a softening point is too high, desired materials might be difficult to emulsify at temperatures needed for proper mixing.

[0030] In one embodiment of the invention, a resin formed with hydrocarbons having, on average, 6 or fewer carbon atoms and a softening point preferably between 75 ⁰ C and 115 ⁰ C is combined with a relatively harder resin formed from hydrocarbons having an average of 7 or more carbon atoms and a softening point preferably about between 100 ⁰ C and 14O ⁰ C.

[0031] In preferred embodiments of the invention, the relatively soft resin is an aliphatic hydrocarbon resin formed of hydrocarbons having an average of about 5 carbon atoms. Advantageous resins can be formed from acyclic aliphatic monomers, such as cis 1, 3 pentadiene, trans 1, 3 pentadiene, and 2-methyl 2 butene and cyclopentadienes. [0032] Adhesive compositions in accordance with the invention also advantageously include a relatively harder hydrocarbon resin, particularly one having a higher temperature

softening point in the range of 100 ⁰ C to 140 ⁰ C. In particular, alkylated aromatic resins, particularly those formed from hydrocarbons having an average of 8 to 10 carbon atoms, such as those produced from C-8, C-9 and C-10 monomers, such as sryrene, vinyl toluene, indene, methyl indene, alpha methyl styrene. Particularly suitable C-9 resins include petroleum aromatic hydrocarbon resins having softening points in the range 100 ⁰ C to 135°C. These relatively harder resins are advantageously included as 10 to 20%, preferably 12% to 18%. Other non-limiting examples of suitable C-9 and C-5 Resins are described below in Table 3. Adhesives in accordance with the invention can also be formulated with Versadil 100, Versadil 101 and Versadil 200.

TABLE 3

[0033] When preparing adhesive compositions in accordance with the invention, the low softening point resins (with 6 or fewer carbon atoms) are advantageously provided in the drying oil component in about a 2: 1 to 1 :2, preferably 1 : 1 weight ratio. The mixture of ingredients 1 and 2 of Table 1 can then be advantageously heated to a temperature above the softening point of the high temperature resin, preferably in the range of 115°C to 140 ⁰ C with mixing, to form a generally homogeneous combination. Care should be taken to insure that the composition is not heated to a temperature too far over the softening points of the materials or it can be difficult to blend with the rest of the ingredients. Thus, after a homogeneous combination is achieved, the temperature can be reduced to a point when ease of mixing is maintained, generally approximately 115°C to 130 ⁰ C.

[0034] Surfactants, such as 6 to 10 mole ethoxylates of nonylphenols can be included, advantageously in the range of less than 5% by weight, advantageously 0.5 to 1.5%. [0035] It is also advantageous to include anti-foaming agents, in particular, non- silicon anti-foaming agents. These are advantageously included as less than about 0.5 weight percent, preferably 0.05 to 0.10 weight percent.

[0036] Adhesives in accordance with the invention also advantageously include polymer emulsion materials, particularly those having carboxyl functionality to provide enhanced adhesive properties, such as those having acrylic, styrene butadiene, ethylene vinyl acetate copolymer (EVA) and vinyl acetate ethylene copolymer can be included as about 20 to 80%, preferably about 30 to 60%, more preferably about 35 to 55% of the composition. The emulsion should be maintained at a temperature of about 15 to 30 ⁰ C. Ingredients 4 and 5 can then be added and mixed until uniform. Ingredients 1 , 2 and 3 are then added with high shear agitation until the ingredients form a substantially homogeneous blend. [0037] Compositions in accordance with the invention also advantageously include fugitive anti-oxidants, such as oximes, such as methyl ethyl ketoxime, bactericides, fungicides and freeze/thaws stabilizers.

[0038] Compositions in accordance with the invention also advantageously include fugitive alkali agents, such as ammonia, monomethanol amine (MEA) and triethanolamine (TEA). This alkali agent can be useful to adjust the pH of the emulsion to at least 7, preferably between about 8 and 10 before the oxazoline containing component is added. [0039] Adhesive compositions in accordance with the invention can also include up to 2%, preferably 2.1 to 1% dispersing agents, such as salts of polyacrylic acids and dryers, in particular naphthanates of metals, such as cobalt, calcium, zirconium and manganese. The dryers should be included in an effective amount to catalyze the drying speed of the drying oil to a desired rate. The precise amount will depend on both the desired speed of cure and the particular composition of the adhesive. These should be added with agitation. [0040] Adhesive compositions in accordance with the invention also advantageously include cross-linking agents. Prefered cross-link agents include: oxazole containing materials, in particular, polymer emulsion materials that include pendant oxazoline groups; 3- methacryloxypropyl-trimethoxysilane (MEMO); 3-mercaptopropyl trimethoxysilane

(MTMO); glyoxal such as DAAM/glyoxal or urea/glyoxal; epoxy functional, water miscible/emulsifiable additives such as aziridine; polyvalent metal carboxylate salts or metal ionic cross-linkers, such as zirconium, zinc, calcium; carbodiimide functionalized material such as polycarbodiimides and carbodiimide; polymerizable organosilanes; aziridines functionalized materials. Other likely crosslinkers include n-methylol acrylamide, glycidyl methacrylate, acid dihydrazide such as diacetone acrylamide or adipic dihyrazide, and water dispersible polyisocyanates

[0041 ] When oxazoline with pendant groups act as the cross-linking agents, there should preferably be about a 1 : 1 mole ratio between carboxly groups in the composition and oxazoline groups. If too much of these materials are added, it will lower the possible solids content. If too little is added there will be lower cross link density and a weaker adhesive. [0042] Oxazolines are 5-membered heterocyclic compounds, having the general formula C ₃ H ₃ NO and are frequently used in organic synthesis. Emulsions containing particles of an oxazoline-modified polymer containing pendant oxazoline groups are discussed in U.S. Patent Nos. 4,474,923, 4,508,869 and 4,325,856, the contents of which are incorporated herein by reference. Preferred oxazolines have the following formula:

[0043] wherein R ¹ is an acyclic or organic radical having addition polymerizable unsaturation; each R is independently hydrogen, halogen or an inertly substituted, organic

radical and n is 1 or 2. The oxazoline containing emulsion preferably also includes at least one other addition polymerizable monomer which is copolymerizable with the oxazoline and discrete particles of a coreactive polymer which coreactive polymer had been prepared in an emulsion polymerization process from (1) an addition, polymerizable coreactive monomer containing pendant groups which are capable of reacting with an oxazoline group to form covalent bonds thereto and (2) at least one other monomer which is copolymerizable with said coreactive monomer.

[0044] Adhesive compositions in accordance with the invention can also include effective amounts of fillers, such as calcium carbonate, kaolin clay, mica powder, talc and so forth. Fillers should generally represent less than 50% of the composition, preferable in the range of 20-40% of the composition. If too much filler is included the cohesive strength of the product can be reduced. If too little filler is included, the solids content will be too low for many applications.

[0045] These components should be added slowly, with high shear agitation, to ensure a substantially homogeneous mixture.

[0046] After adhesive compositions in accordance with the invention are deposited, the polymer emulsion containing the oxazoline groups is believed to become available to act as a cross-linking agent to cure the carboxylated polymers. Accordingly, a one component self-curing adhesive which can be made substantially or entirely free of VOCs can be achieved.

[0047] In another non-limiting embodiment of the invention, the process by which the adhesive in accordance with the invention is made can be split into two stages. The first stage can comprise the blending of the first seven ingredients and storing, with constant slow agitation, the resulting mixture as a premix to be used the final blend. The second stage comprises blending the last five ingredients with the premix.

[0048] Prior to blending the premix with the remaining ingredients, the premix may be cooled to a temperature preferable in the range of 75°F to 110 ⁰ F. The cooling may occur using such devices as: a cooling jacket with cold water, a cooling jacket with a cooling tower, heat exchanger, a flash vacuum cooling system, or any other cooling device that can lower the temperature to within the desired range. Heat exchangers such as shell and tube heat exchangers, spiral heat exchangers, plate and frame heat exchangers, or compabloc welded plate heat exchangers may be used.

[0049] After blending the premix with the remaining ingredients and prior to packaging the composition, the final temperature of the batch should be cooled to a temperature of preferably not more than 90 ⁰ F.

[0050] Areas designed to house electrical equipment or various manufacturing or testing procedures often need to avoid the build-up of static electricity. In another non- limiting embodiment of the invention, adhesives in accordance with the invention can be rendered electrically conductive. Conductive adhesive are advantageously used in constructing Electrostatic Dissipative Floors (ESD) by the inclusion of electro-conductive agents in the adhesive composition. Particularly suitable electro-conductive agents include carbon black, synthetic conductive fibers, electrically conductive metal chips or fragments, or any other conductive materials such as conductive nano materials. [0051 ] Table 4, below provides formulation information for preparing electrically conductive adhesives in accordance with the invention. Table 4 also shows an alternative manufacturing process, which can also be used with the non-conductive adhesive. Other processing steps can be substituted such as those in Table 1.

TABLE 4 Conductive Adhesive

[0052] The following examples are provided for purposes of illustration only and should not be construed as limiting the scope of the invention.

TABLE 5 Shear Strength Data (psi) at various Cure Times

P ure

P rethaπe

[0053] As shown in Table 5, the adhesive of Examples 1 -3, set forth below, exhibited excellent green strength and cure strength compared to conventional adhesives such as moisture cure urethane and exhibited acceptably low VOC emissions while curing. [0054] Table 6, below, provides non-limiting examples of application examples. As shown, adhesive in accordance with the invention can be used to apply a wide variety of flooring. Acceptable coverage depends on the underlying floor substrate and the backing of the flooring to be applied. However, coverage in the range of about 20 to 300 ftVgallon can be acceptable, preferably about 20-150 tf/gallon for wood; 100-300 tf/gallon for vinyl or ceramic and 50-150 ftVgallon for carpet. The adhesive can be applied using any suitable dispensing method such as trowelling, spray pumping, extrusion and so forth.

TABLE 6 Application Devices and Application Rates

Example 1 - Construction Adhesive

Example 2 for Construction Adhesives

Example 3 - Construction Adhesive

[0055] Table 7 below provides Moisture Transmission Data (per ASTM 96-00) of adhesive in accordance with a preferred embodiment of the invention versus leading Moisture Cure Urethane Wood Adhesive which emit undesirable VOCs.

Table 7

[0056] Low moisture transmission permits an adhesive to act as a moisture barrier.

Table 6 shows that adhesives in accordance with the invention can be formulated to have at least as good moisture barrier properties as conventional urethane adhesives, but without the same level of VOC emissions.

[0057] FIG. 1 shows that in certain respects, adhesives in accordance with the invention can have enhanced adhesive properties compared with conventional urethane adhesives. Adhesives in accordance with the invention can be formulated to have a shear strength of over 5 psi, even over 10 psi at 15 minutes, and over 10 psi, even over 20 psi at 30 min. Final cure strengths (at 3 months) can exceed 200 psi, and can even exceed 300 psi or 400 psi. The adhesive used for FIG. 1 exhibited a shear strength of 450 psi. In addition to exhibiting advantageous green strengths, adhesives in accordance with the invention also exhibit desirable open times. Even at open times of up to 60 minutes the adhesive will still exhibit advantageous strength characteristics.

[0058] FIG. 2 shows the progression of cross-link density with time for one embodiment of the invention. Adhesives in accordance with the invention can be formulated

to exhibit an immediate initiation of cross-linking and a steady progression for the first hour. Different embodiments of the invention can be formulated to exhibit faster or slower progressions, varying by e.g. - about 10 or 20%, or otherwise depending on the desired applications.

[0059] It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and, since certain changes may be made in carrying out the above method and in the compositions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

[0060] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. [0061] Particularly it is to be understood that in said claims, ingredients or compounds recited in the singular are intended to include compatible mixtures of such ingredients wherever the sense permits.