WO1994016027A1

WO1994016027A1 - Liquid adhesive thermoset composition

Info

Publication number: WO1994016027A1
Application number: PCT/US1993/004679
Authority: WO
Inventors: James A. E. Hagquist
Original assignee: H.B. Fuller Licensing & Financing Inc.
Priority date: 1992-12-30
Filing date: 1993-05-18
Publication date: 1994-07-21
Also published as: NZ253458A; AU676170B2; AU4379393A; CA2152776C; CA2152776A1; GB2289683B; GB9512788D0; GB2289683A

Abstract

A liquid adhesive dispersion comprised of a powdered thermosetting adhesive composition comprising thermoset and curing agent and having a particle size of about 25 microns or less. The composition may also comprise a film-forming polymer composition, and a liquid vehicle, wherein the dispersion remains storage stable at ambient temperatures and after application the adhesive forms a physically stable intermediate film.

Description

LIQUID ADHESIVE THERMOSET COMPOSITION

Field of the Invention

The invention generally relates to liquid, * 5 film-forming, thermosetting adhesive compositions. More

^ specifically, the invention relates to adhesive

- compositions that can form an adhesive film which cures to a rigid bond.

Background of the Invention 10 Thermoset compositions are well-known within the coating, adhesive, composite, and plastics industry. Recently, powdered thermosets have become desirable due to their long-term storage stability and ease of handling. However, difficult problems arise when 15 applying powdered compositions in various applications. For instance, in applications where the powder is applied directly to a substrate, the substrate must be held stationary until the powdered thermoset is cured. Exposure of the powder-laden substrate to movement, 20 vibration, air flow or other environmental stresses may result in the removal of the powdered thermoset from the substrate. Moreover, simply applying the powdered thermoset from a solvent such as water or ethanol often does not provide the means necessary to maintain the 25 powder on the intended surface as these solvents may evaporate leaving the powdered thermoset free to fall from the intended surface.

Certain solvents may not allow for the long term storage of the adhesive composition in the liquid state. 30 Also, once the thermoset composition is applied onto or into a carrier to form a preimpregnated composite or deposited film, the system may require refrigeration to ensure that the composite will remain reactive and capable of curing once applied to the desired

> 35 application. In fact, even when refrigerated the shelf life of certain composite materials may often be measured in terms of days or weeks instead of months.

Furthermore, certain methods of applying powders such as electrostatic applications are limited by factors such as the particle size of the powdered thermoset composition or the geometry of the area of application. These methods may not allow for the most uniform application of particles into narrow or tight areas due to electrical forces created by the surfaces of application. Overall, present methods of applying powdered thermoset compositions do not accurately control particle concentration over the surface of application, or the size of the particle domain for each individual particle. As a result, present compositions and processes of application may result in a bond having variable uniformity and strength.

Accordingly, there is a need for a powdered thermoset composition which has extended stability at room temperature and preferably avoids stability and toxicity problems as well as providing for a method of application which results in a bond having a higher degree of uniform strength than those found in the prior art. Summary of the Invention

The present invention comprises a thermosetting adhesive dispersion in a liquid vehicle that can form a stable intermediate film which can cure, when intended, to a thermoset bond, comprising an effective amount of a finely divided powdered thermosetting composition having a particle size of about 25 microns or less, an effective amount of film-forming polymer composition, and a liquid vehicle, wherein said liquid dispersion remains storage stable at ambient temperatures and after application said dispersion forms a physically stable film which will remain reactive and curable when stored at ambient temperature.

A further aspect of the present invention is a method of using this thermosetting dispersion comprising the steps of applying the thermoset dispersion to a substrate, forming a stable thermosetting film on the substrate, and optionally, forming a workpiece by contacting a second substrate with the thermoset containing film, and curing the thermoset so as to bind the first substrate with the second substrate.

An additional aspect of the invention is an article of manufacture or a workpiece comprising a substrate bearing a film of the composition of the present invention which may optionally include a second substrate or a series of substrates to form a composite matrix. Prior to deposition, the liquid dispersion composition of the present invention preferably remains storage stable and fully dispersed within the liquid vehicle. Storage stability in accordance with the present invention means that the level of particle separation or the degree of particle dispersion present after storage of the dispersion for the desired period of time remains substantially constant and will not prevent the formation of an effective bond. Moreover, the dispersion composition of the present invention remains substantially unreacted and the dispersion remains partially, if not wholly, undissolved in the solvent over the intended storage period.

After deposition on a substrate but prior to curing, the composition of the present invention forms an intermediate film. The intermediate film results from the evaporation of the liquid vehicle from the composition which, in turn, tends to congeal the film-forming polymer composition. The particulate thermoset adhesive becomes cast within the resulting film.

Prior to curing, the film formed by the present composition provides a high degree of physical stability holding the powdered thermoset material on the surface where it was deposited. This stabilizing character is effective against mechanical stresses which arise in the environment of use such as vibration, water or air flow, horizontal or inclined movement, and prolonged exposure of the adhesive to ambient atmospheric conditions among other factors.

Upon curing, the resulting film may become an integral element of the crosslinked bond or the film-forming polymer may be fugitive (i.e. may leave or be removed from the bond site) .

Brief Description of the Figure Figure 1 is a graphical depiction of lap shear strengths plotted against compositional particle size. Detailed Description of the Preferred Embodiment

The composition of the present invention comprises a dispersion having at least two phases containing a thermosetting composition, a film-forming polymer, and a liquid vehicle. The first phase comprises a solid powdered thermosetting composition and may additionally comprise any of a variety of curing agents, fillers, or added functional elements as needed. The second phase of the present composition is a liquid polymeric film- forming composition which may generally comprise a liquid vehicle and any number of film-forming agents. While the film-forming polymer has been expressly included in the liquid phase it should be understood that the film-forming agents may be dissolved in the liquid vehicle or, alternatively, dispersed in the liquid vehicle as either a liquid or a solid. The liquid vehicle may be aqueous, organic in nature, or a combination thereof. Optionally, as desired, the liquid phase of the present composition may also comprise dispersing agents, thixotropes, wetting agents, or any other variety of constituents depending on the intended application.

Solid Phase The first phase of the present invention comprises a powdered solid composition. The solid powdered phase, in turn, comprises at least the powdered thermosetting resin and any needed curing agent in each discrete particle. Optionally, the solid phase may also comprise fillers or other functional material, such as, conductive particles depending on the intended application.

Thermosetting Composition The thermosetting composition functions to promote adhesion to the substrate and to form a cohesively stable bonding mass after curing. The thermoset composition also functions together with the film-forming phase of the present invention as a carrier for any particulate substance included in the composition such as, for example fillers, electrically conductive particle or constituents which may add flexibility, high temperature resistance or any number of other pre-cured physical characteristics to the liquid adhesive once the film is formed.

Thermosetting coating powders, with some exceptions, are based on resins that are cured by addition reactions rather than condensation reactions. Thermosets are synthetic resins which solidify or set upon heating and cannot be remelted.

Generally, thermosetting compositions useful in the present composition are those thermosets which can be powdered and which remain stable once combined with the chosen film-forming polymer and solvent in the liquid pre-application state. The present invention offers a further advantage over prior art compositions, in that, powdered thermosets having a particle size in excess of 150 microns may be used effectively in the present composition. In sharp contrast, prior art compositions using thermoset powders having this particle size may fail to effectively deposit onto or into the intended surface especially when applied by methods such as electrostatic deposition. The thermoset composition useful in the present invention are partially or wholly insoluble in the liquid vehicle comprising a solid phase within the dispersion composition. Thermosetting compositions useful in the present invention are also those which provide chemical and physical storage stability upon film deposition given evaporation of the liquid vehicle under elevated heat and prolonged stability over time in the intermediate film state.

Generally, any well known thermosetting composition can be used in the present invention. Thermosetting compositions useful in the present invention include epoxies, polyurethanes, polyesters, hybrid thermosets, and acrylics among a large number of other compositions. Also useful in the present invention are bis-maleimides such as the partial reaction product of the bis maleimide of methylene dianaline with methylene dianaline.

Exemplary thermosetting compositions useful in the present invention include the reaction product of orthotolylbiguanide known as Casamine and commercially available from SBS Chemicals Inc. and bisphenol A-epichlorohydrin available from Ciba-Geigy Corporation under the commercial name Araldite GT 7013; triglycidyl isocyanurate thermosetting compositions; bisphenol A-epichlorohydrin cured with phenolic crosslinking agents, the epoxy composition being available from Ciba-Geigy Corporation Araldite GT 7013 and the phenolic curing agent being available from Dow Chemical Company under the brand name DEH 84; aliphatic urethane thermosetting compositions such as an unblocked isophorone diisocyanate-E-caprolactam available from Ruco Polymer Corporation under the commercial name NI2 which may be used with Rucote HBF which is a hydroxyl terminated polyester resin also available from Ruco Chemicals; BTDA thermosetting compositions which are generally the reaction product of 3,3,4,4-benzophenone tetracarboxylic dianhydride and a bisphenol

A-epichlorohydrin; hybrid thermosetting compositions which are the reaction product of a carboxylated saturated polyester curing agent such as Arakote 3001 available from Ciba-Geigy Corporation and a bisphenol A-epichlorohydrin; standard bisphenol A-epichlorohydrin thermosets such as those which are cured with 2-methyl imidazole; and standard bisphenol A-epichlorohydrin thermosets which are cured with 2-methyl imidazole and dicyandiamide.

Preferably, the thermosetting composition used in the present invention are those selected from the group consisting of polymerized triglycidyl isocyanurate, aliphatic urethane thermosets, BTDA cured bisphenol A-epichlorohydrin thermosets, polyester-bisphenol A-epichlorohydrin thermoset complexes, 2- methylimidazole cured bisphenol A-epichlorohydrin thermosets, and orthotolylbiguanide cured bisphenol A-epichlorohydrin thermosets. These compositions, as can be seen in Table I, provide maximum storage stability in the liquid state when used in the preferred mode with an aqueous carrier. Generally, the concentration of the powdered thermoset may be varied from 5 wt-% to 95 wt-% of the adhesive dispersion, preferably 20 wt-% to 80 wt-% of the adhesive dispersion and most preferably 40 wt-% to 60 wt-% of the adhesive dispersion. The concentration of powdered thermoset in the resulting film will range from about 30 wt-% to 95 wt-%, preferably 60 wt-% to 95 wt-% and most preferably 80 wt-% to 95 wt-% depending on the specific application. The concentration of . thermoset may range as a percentage of either the liquid composition or the resulting film outside the range as provided above depending on the application.

Increasing the concentration of the powdered thermoset will tend to increase the viscosity of the aqueous liquid composition depending on the relative particle size of the powdered thermoset used. A higher viscosity may be desirable to develop a compositional consistency of a caulk or putty which may be used as an adhesive sealing agent for any variety of applications. Moreover, the use of an increased concentration of powdered thermoset may be desirable to promote an increased spreading or wetting of the surface of application once the thermoset adhesive is heated.

In contrast, reducing the relative concentration of the powdered thermoset within the composition of the present invention may reduce the degree of relative bonding strength in the resulting composition. Moreover, reducing the relative concentration of the powdered thermoset may potentially allow for a thinner more uniform film as deposited across the surface of application.

The present invention allows for varying the concentration of the thermoset composition within the dispersion and as a result varying the domain size of each powdered thermoset particle. The present invention also allows for the deposition of very fine particle thermoset powders of about 25 microns or less, preferably about 1 to 15 microns, and most preferably about 1 to 5 microns. The ability to vary particle concentration and, in turn, particle domain size combined with the use of very fine particle size thermosets allows the resulting adhesive composition to have a higher relative adhesion than higher particle size thermosets which are applied in a less uniform manner.

The powdered thermoset may be combined with a curing agent commonly used to promote cross-linking within the powdered thermoset. Curing agents commonly known to the art include melamines such as dialkylmelamine; amides such as dicyandiamide, adipamide, and isophthalyl diamide; ureas such as ethylene thiourea or guanylurea; azides such as thiosemicarbazide, or adipyl dihydrazide, and isophthalyl dihydrazide; azoles such as guanazole, or 3 amino-1, 2, 4 triazole; and anilines such as diethylaniline. The curing agents generally useful in the composition of the present invention are subject to the same stability limitations as the powdered thermoset resin. Specifically, the curing agent may be partially or wholly insoluble in the liquid vehicle. However, the curing agent must have an effective degree of chemical stability so that the required amount of cross-linking takes place at the intended point of curing. Accordingly, the curing agent may be solubilized in the liquid vehicle or remain in powder form with the powdered thermoset. Crosslinking mechanisms may be additionally retarded by intentionally including a crosslinking agent which will be solubilized within the liquid vehicle while retaining the powdered thermoset in the powdered form as a separate solid phase.

When present, the curing mechanism may be a single curing agent or any combination of curing agents having a concentration between about 0.1 wt-% and 50 wt-% of the initial solid phase, preferably between about 1 wt-% and 30 wt-% of the initial solid phase, and most preferably about 5 wt-% and 25 wt-% of the initial solid phase.

The solid phase may also contain other constituents including dispersing agents, fillers or any other element which is insoluble in the liquid phase, remains effectively dispersed in the composition and provides the intended functional characteristic to the composition.

Preferably, the solid phase of the invention will comprise a powdered composition of minimal particle size which comprises both thermoset and curing agent within each individual powdered particle. Individual particles may be formed by melt mixing' and extruding thermoset and curing agents below curing temperatures. The resulting extrudate, in the form of, for example, a rope, a sheet, etc., may then be particlized. Particle sizes which are generally acceptable range from about 25 microns to 1 micron or less, preferably about 15 microns to 1 micron or less, and most preferably about 5 microns to 1 micron or less.

As will be reflected in the working examples, and as can be seen in Figure 1, smaller particle size compositions are believed to provide more uniform domains and as such result in higher lap shear strengths.

Liguid Phase The liquid phase of the present invention generally comprises the film-forming polymer, a solvent and optionally solubilized dispersing agents, thixotropes, or hardeners among other potential constituents, which may be wholly or partially dissolved in the liquid phase of the present invention.

Film-Forming Agent The function of the film-forming agent is to carry the thermoset and deposit it on the surface. After liquid vehicle removal the film holds the powdered thermosetting composition on the surface of application. Specifically, the film-forming polymer may form a liquid solution or an insoluble dispersion in the liquid vehicle (i.e. the film former may be a part of the dispersed solid phase or in solution as part of the liquid phase) .

Preferably, the film-forming polymer should not impair the reactivity of the powdered thermosetting composition. Once the film-forming polymer is either dispersed or dissolved, the liquid is applied through any variety of means. The liquid vehicle may be evaporated from the surface of application and the powdered thermosetting composition is retained or encapsulated on the surface by the film-forming polymer. The film-forming polymer may also be used to provide added functional character to the pre-cured or post-cured composition such as, for instance, pre- cured tack, solubility, adhesion, or wettability as well as post-cured hardness, or water-resistance.

Generally, compounds useful in the present invention are organic or inorganic film-forming agent which impart the intended character to the resulting film. Generally, thermoplastic resins are preferred film-forming agents as they soften or melt at a given temperature, and when cooled, recover the physical and chemical properties of the original resin.

Generally, the physical and chemical properties of the original resin as well as any resulting films formed from the thermoplastic include a variable degree of plasticized flexibility, easy solubilization and emulsification in various liquid aqueous and organic vehicles, variable surface stability and stability against mechanical forces such as vibration, and horizontal or inclined movement, various degrees of stability when subjected to environmental forces such as heat, wind, or any other number of environmental forces which might impinge upon the composition within the area of use or application, various degrees of pre-application thickness or viscosity depending upon the choice of liquid vehicle.

At a minimum, any thermoplastic film-forming agent may be used which encapsulates the powdered thermosetting composition and does not adversely detract from the functioning of the thermoset once it is applied to the intended surface. Compounds and polymers which may function as film formers include plasticizers, wetting agents, tackifiers, elastomers, thixotropes, as well as coalescing agents used alone or with inert fillers.

Exemplary polymeric film-forming dispersions or solutions can be made from polymerizing one or more of the following monomers in a solvent medium, such as, vinyl acetate, ethylene, acrylic acid, methacrylic acid, crotonic acid, or itaconic acid; esters of acrylic and methacrylic acid including methyl esters, ethyl esters,' butyl and 2-ethylhe.xyl esters; as well as styrene, butadiene, vinyl chloride, vinylidene chloride, isoprene, and chloroprene.

Synthetic polymers resulting from polymerization of many of the preceding monomers which are useful as film-forming elements of the present composition include generally, polyvinyl alcohol (with varying degrees of hydrolysis), ethylene/acrylic acid copolymers, ethylene/maleic anhydride copolymers, and styrene/maleic anhydride copolymers among others.

Naturally derivativized and naturally occurring polymers such as casein compositions, natural gum compositions including karaya gum and guar gum, cellulosic and ether cellulosic compositions, starch, protein compositions, and starch-grafted copolymers are also useful as a film-forming polymer of the present invention. Inorganic compounds such as sodium silicate may also be useful as the film-forming agent in the present invention. Those skilled in the art will realize that the preceding compounds and polymers are only exemplary of compounds and polymers which may be used as film-forming agents in the composition of the present invention and this list should not be viewed as limiting. The concentration of the film-forming polymer used in the composition of the present invention will generally range from about 1 to 99 wt-%, preferably range from about 2 to 50 wt-%, and most preferably range from about 4 to 7 wt-% depending on the characteristics to be imparted to the resulting film and the physical and chemical characteristic of the powdered thermoset adhesive. As a percentage of the resulting film, the film- forming polymer may again generally range from about 1 to 99 wt-%, preferably range from about 4 to 75 wt-%, and most preferably range from about 8 to 14 wt-% again depending upon the character and quantity of powdered thermoset adhesive to be encapsulated within the film and the desired character which the film is intended to have in either the pre-cured or post-cured state.

Generally, the film-forming ability of the polymer depends on the film's ability to support the powdered thermoset. However, diminishing or increasing the concentration of film-forming agent within the composition of the present invention may limit or increase, respectively, the thermoplastic character of the film former and the ability of the film-former to retain the powdered thermoset on the surface of application. Moreover, pre-cure and post-cure film characteristics may be increased or diminished by the use of, for instance, thixotropes which can be used to affect changes in the viscosity and flowability of the composition of the present invention.

Liguid Vehicle The liquid phase of the present composition also principally contains a liquid vehicle. The liquid vehicle facilitates transport and deposition of the adhesive used in the composition of the present invention. Use of the liquid vehicle may also allow reduction of the concentration of the film-forming component. Generally, the liquid vehicle may be aqueous, organic or a mixture thereof. While the liquid vehicle preferably does not interact with the thermoset, the liquid vehicle may generally be used to modify the effect of the thermoset by enhancing or reducing adhesion.

Organic liquid vehicles useful in the present invention are limited to those which maintain the dispersed character of the thermoset within the liquid phase of the present invention without reacting and destabilizing either the thermoset or any curing agent which may be present in the system. Organic liquid vehicles which function accordingly may partially or wholly displace any aqueous solvent used in the composition.

Organic liquid vehicles useful in the present invention include but are not limited to low molecular weight (600-650 m.w.) fatty acid polymers including dimer and trimer acid compositions resulting from the polymerization of long chain (C20-C40) aliphatic dibasic acids with long chain (C50-C60) aliphatic tribasic acids polymers having such as those fatty acid polymers available from Emery under the Empol brand name; liquid curing agents including dicyanamide; liquid epoxy compositions including liquid bisphenol A-epichlorohydrin low molecular weight epoxies such as the Epon brand epoxies available from Shell Chemical Company; mineral solvents; naptha; and liquid polyamides such as N-ethyl 0, P-tolue'ne sulfonamide available from Monsanto Corporation as Saniticizer 8.

Alternatively, the liquid vehicle may be aqueous or an aqueous-organic solvent mixture. Such a liquid vehicle is useful in minimizing environmental and safety hazards often prevalent with the use of volatile organic. Also, a mixture of aqueous and organic liquid vehicles may be useful in maintaining, for example, a curing agent and resin in separate phases and thus increasing the chemical stability and storage life of the present composition prior to application. Such a system will comprise a liquid vehicle or combination of liquid vehicles which may completely solubilize the curing agent yet retain the thermoset resin in solid undissolved form.

Preferably, if minimal toxicity and flammability is desired the liquid vehicle is water. Generally, an aqueous or aqueous- organic may avoid or reduce toxicity and volatility problems which may be prevalent with certain organics, and is generally compatible with many known powdered thermoset adhesive compositions resulting in a unreacted composition having an extended shelf life. Water provides a nonreactive environment together with the film-forming polymer which can be used to store the powdered adhesive for extended periods of time. Moreover, water may be readily vaporized to form the thermoset encapsulating stable intermediate film. Generally, regardless of the aqueous or organic character of the liquid vehicle, concentrations of the liquid vehicle will range from about 1 to 99 wt-% of the liquid dispersion composition of the present invention, preferably from about 25 to 75 wt-% and most preferably from about 45 to 55 wt-%.

Varying the concentration of the liquid vehicle promotes differing characteristics within the composition. For instance, reducing the concentration of liquid vehicle within the composition of the present invention may increase the viscosity of the composition and may provide for a material which has a physical character somewhat like a paste or a putty. Such a character is more applicable to environments which do not require a uniform coating.

In contrast, increasing the concentration of liquid vehicle within the composition of the present invention may result in a much less viscous composition. Such a formulation allows for the application of a thinner adhesive coat. However, higher liquid vehicle concentrations may result in a settling of the thermoset powder making the composition inoperable as an adhesive dispersion. As a result, some thixotropic character is preferred within the composition in order to provide the proper level of dispersion necessary to provide an effective adhesive composition.

Dispersing Agents Optionally, the composition of the present invention may also contain a dispersing agent dispersed as a element of the solid phase or dissolved dispersed as an element of the liquid phase. The dispersing agent functions to efficiently disperse the powdered thermoset composition of the present invention when the film-forming agent alone is not adequate to keep the powdered thermoset dispersed within the solvent. The dispersing agent may also assist in forming the stable intermediate film used to hold the powdered thermoset on the surface of application prior to curing. Dispersing agents may also be used to lower surface tension and modify rheology within the system providing a thermoset composition which has a higher degree of wettability once applied to the intended surface.

Dispersing agents which can be used in the composition of the present invention generally include any physical or electrical dispersant which is not deleterious to the stability or curing ability of the thermoset. The dispersing agents preferably does not affect the chemical stability of the powdered thermoset adhesive by reducing shelf life either in the liquid state or in the solid film state prior to cure but after the composition is applied. To this end, the dispersants used in the composition of the present invention may either be retained in the film once formed or vaporized upon evaporation of the liquid vehicle from the composition or upon curing of the powdered thermoset. Solid and liquid dispersing agents which are exemplary of those useful in the present invention include those film-forming agents having a dispersing character disclosed as useful in the liquid phase of the present composition. Also useful as dispersants in the present invention are compounds such as complex phosphates such as sodium hexametaphosphate, sodium tetraphosphate, sodium tripolyphosphate, and tetrasodium pyrophosphate; colloidal compositions such as casein, soybean protein; cellulosic compositions such as carboxymethyl cellulose, carboxymethyl starch, and hydroxyethyl starch; silicates, such as sodium orthosilicate, sodium sesquasilicate, sodium methylsilicate, and sodium disilicate; various surface active agents including nonionic surfactants such as the condensation products of alkanols or ethylene oxide and the condensation products of fatty acids and ethylene oxide, anionic surfactants such as the alkali metal salts of alkyl or alkyl aryl sulfonic acid, and cationic surfactants such as alkyl and alkyl aryl quaternary ammonium salts; as well as miscellaneous other compositions such as polyacrylate polymers composed of monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate or ethyl hexyl acrylate.

In the liquid state, prior to application of the composition of the present invention, the concentration of dispersant within the present invention may generally vary from 0 wt-% to 5 wt-%, preferably from 0.5 to 4 wt-% and most preferably from 1 to 3 wt-%.

Generally, increasing the concentration of dispersant within the composition of the present invention tends to decrease the adhesive effect of the powdered thermoset. Accordingly, a dispersant may be used to regulate or reduce the bonding ability of the powdered thermoset adhesive. In sharp contrast, reducing the concentration of the dispersant may also result in a settling out of the thermoset powder in instances where the film-forming composition does not provide an adequate dispersing effect.

Concentration Ranges in Liguid Composition

CONSTITUENT USEFUL WORKING PREFERRED

Thermoset 5-95 wt-% 20-80 wt-% 40-60 wt-%

Curing Agent 0.1-50 wt-% 1-30 wt-% 5-25 wt-%

(when present)

Film-Forming 1-99 wt-% 2-50 wt-% 4-7 wt-%

Polymer

Liquid 1-99 wt-% 25-75 wt-% 45-55 wt-%

Vehicle

Dispersing 0-5 wt-% 0.5-4 wt-% 1-3 wt-%

Agent

Particle 1-25 μm 1-15 μm 1-5 μm

Size

Applications

The liquid thermoset dispersion of the present invention may be incorporated into any number of products useful in a variety of applications.

The liquid thermoset dispersion of the present invention can easily be applied onto almost any surface. The liquid dispersion of the present invention may be cast into or onto a unidirectional, woven, or nonwoven carrier for a later application to a substrate or in the formation of a composite laminate. At the point of application the solvent may be flashed off or dried from the composition. If the surface is a unidirectional, woven, or nonwoven carrier a film adhesion impregnate is formed. Generally, tack, drape or the ability to conform a material to a specific surface, and adhesion can be varied as desired by varying the concentration of film-forming agent, and liquid vehicle.

Multiple layers of different or similar materials can be applied to achieve desired characteristics. The unique advantage of this type of film adhesive or impregnated composition is the room temperature stability of the composition which does not require refrigeration of the material. Specifically, once deposited on or in the carrier the powdered thermoset remains reactive and storage stable for extended periods of time.

Additionally, the liquid thermoset dispersion may be used as a film adhesive. In this case, the liquid dispersion may be cast onto a release liner where the intermediate film is formed. At a later time the film adhesive is applied to the intended substrate and the release liner removed. Furthermore, the liquid dispersion may be cast into or onto a unidirectional, woven, or nonwoven carrier and then combined with a release liner. In application the composite complete with the release liner is applied onto a substrate and the release liner is then removed from the composite system.

The adhesive composition of the present invention can be loaded into or onto a woven or nonwoven carrier which could be used by itself or in a multiple layer composite system for the fabrication of a rigid composite laminate. Carrier systems commonly used in the formation of a composite include but are not limited to nonwoven carriers such as glass or polyester mats. Unidirectional or woven carriers include but are not limited to carbon, ceramic, thermoplastic, aramide, natural clothing fibers such as wool or cotton, synthetic clothing fibers, glass fibers and hybrids thereof.

The systems may be used in any number of applications by providing an adhesive with or without a carrier as well as including any number of additives in the adhesive composition. For instance, these systems could be used to replace sewing by heat sealing fabrics, the unused thermoset being washed out after the fusing processes are completed. This composition may be used to precoat metal against corrosion by forming the intermediate thermoset film on a substrate and then structurally bonding additional substrates to the surface of application by heat activating and curing the thermoset.

The easy application of the composition of the present invention allows the adhesive to be used as a primer for application to surfaces having a lower affinity for accepting a continuous adhesive layer. Intumescents or flame retardants may be used in the adhesive composition of the present invention which once applied may additionally function to protect the substrates carrying the adhesive layer. Additionally, hydrophobic particulate elements may be included within the composition of the present invention to define a resulting bond which is highly water resistent. These applications are only representative of the number of uses for the composition of the present invention.

Working Examples The Working Examples of the present invention were formulated first as solid phase premixes comprising dry thermoset compositions additionally containing curing agents, preservatives, defoamers, and fillers among other agents. The premixes were then used in the formulation of the two phase dispersed liquid systems of the present invention.

Premixes An initial step in preparing the thermoset adhesive compositions of the present invention was the preparation of dry powdered thermoset adhesive premix compositions. Premix compositions 1-9 were prepared by dry mixing the various elements listed under each formulation. Once the dry mixing was completed the compositions were melted and then screw extruded and cast into a uniform sheet. Once solidified, the premix compositions were pulverized into a fine powder. The premix compositions were either taken from production runs of 650 to 1,000 pounds each or taken from lab batches which were made 1,000 grams at a time. PRE-MIX 1

Ingredient Parts By

Weight

RUCOTE HBF (Aliphatic-urethane 80.3213 epoxy reaction product of unblocked isopherone diisocyanate- E-caprolactone monomer commercially available from Ruco Polymer Corporation)

2 Methyl Imidazole 17.6707

RESIFLOW P-67 (acrylate/silicon 1.2048 dioxide compound commercially available from Estron Chemical, Inc.)

Benzoin 0.8032

PRE-MIX 2

Ingredient Parts By Weight ARAKOTE 3010 (carboxylated 90.9091 saturated polyester resin commercially available from Ciba-Geigy Corporation) triglycidyl isocyanurate 6.8426

RESIFLOW P-67 (acrylate/silicon 1.4663 dioxide compound commercially available from Estron Chemical, Inc. )

Benzoin 0.7820

PRE-MIX 3

Ingredient Parts By Weight Araldite GT 7013 (bisphenol 58.6262

A-epichlorohydrin commercially available from Ciba-Geigy Corporation ARAKOTE 3001 (carboxylated saturate 37.9839 polyester resin commercially available from Ciba-Geigy Corporation) RESIFLOW P-67 (acrylate/silicon 1.6910 dioxide compound commercially available from Estron Chemicals, Inc. ) Benzoin 0.9813

XB-3126 (curing accelerator 0.7136 commercially available from Ciba-Geigy)

PRE-MIX 4

Ingredient Parts By Weight

Araldite GT 7013 (Bisphenol A- 93.3707 Epichlorohydin commercially available from Ciba-Geigy Corporation)

Orthotolylbiguanide 1.8553 Benzoin 0.8735

RESIFLOW P-67 (acrylate/silicon 1.4006 dioxide compound commercially available from Estron Chemicals, Inc.) PRE-MIX 5

Ingredient Parts By Weight

Araldite GT 7013 (Bisphenol A- 97.9132

Epichlorohydrin commercially available from Ciba-Geigy

Corporation) 2 methylimidazole 0.5877

RESIFLOW P-67 (acrylate/silicon 1.4691 dioxide compound commercially available from Estron Chemicals, Inc. )

PRE-MIX 6 Ingredient Parts By Weight

Araldite GT 7013 (bisphenol A- 94.1620 epichlorohydrin commercially available from Ciba-Geigy Corporation)

2-methylimidazole 0.1883 dicyandiamide 4.2373

RESIFLOW P-67 (acrylate/silicon 1.4124 dioxide compound commercially available from Estron Chemicals, Inc. )

PRE-MIX 7

Ingredient Parts By Weight

Araldite GT 7013 (bisphenol 85.7633

A-epichlorohydrin commercially available from Ciba-Geigy Corporation) 3,3,4,4-Benzophenone 11.14192 Tetracarboxylic Dianhydride

RESIFLOW P-67 (acrylate/silicon 1.2865 dioxide compound commercially available from Estron Chemical, Inc. )

Benzoin 0.6861

OCTAFLOW ST70 (stannous 1.1149 octoate/amorphous silica catalyst commercially available from Estron Chemical, Inc. ) PRE-MIX 8

Ingredient Parts By Weight

Araldite GT 7013 (bisphenol 72.8332 A-epichlorohydrin commercially available from Ciba-Geigy Corporation)

DEH 84 (phenolic curing 25.4916 agent commercially available from Dow Chemical Company)

RESIFLOW P-67 (acrylate/silicon 1.0925 dioxide compound commercially available from Estron Chemicals, Inc. )

Benzoin 0.5827

PRE-MIX 9

Ingredient Parts By Weight

Shell 2002 (bisphenol A- 60.1400 epichlorohydrin commercially available from Shell Chemical Company)

Dicyandiamide 1.4700

Epon P101 Curing Agent (amine 0.6300 condensate of an epoxy resin commercially available from Shell Oil Company)

RESIFLOW P-67 (acrylate/silicon 0.8700 dioxide compound commercially available from Estron Chemicals Inc. )

Pigments (titanium dioxide and 30.0030 carbozole violet)

Barium Sulfate 5.8870 1 Tetramethyl decynediol 1.0000

Storage Stability

The solid phase premix formulations were then formulated into aqueous dispersion compositions generally comprising 43 parts powdered premix, 50.5 parts water as a liquid vehicle, 5 parts of a vinyl acrylic latex binder composition (available from Union Oil Company as 76 Res 661), and 1.5 parts of a magnesium aluminum silicate thixotrope and defoamer comprising a blend of emulsifiable mineral oils, silica derivatives and esters (available from Drew Chemical Company as surfactant Y-250). The resulting compositions were then subjected to stability testing at room temperature (approximately 25~ C.) over a period of 100 days.

TABLE I

WORKING EXAMPLE MATERIAL STABILITY AT ROOM

TEMPERATURE Aqueous Consistency

24 Hours 10 Days 100 Days

1 Ok - low Ok - low Ok (Premix 4) vise. vise.

2 Ok - low Ok - low Ok (Premix 2) vise. vise.

3 Ok - low Ok - low Ok

(Premix 1) vise. vise.

4 Ok - low Ok - low Ok (Premix 3) vise. vise.

5 Very Ok - low Ok (Premix 5) thix. vise.

As can be seen, the compositions reported in Table I had a stability of at least to 100 days. While other premix formulations did not provide this degree of storage stability, these dispersions did provide compositions useful for applications which allowed for, or required, more immediate deposition on the intended surface.

Another set of Working Examples, Numbers 6-22 were then prepared using the premix formulations previously prepared. Generally, the Working Examples were prepared in three steps. First, a liquid vehicle, was introduced into a mixing vessel with an appropriate amount of surfactant. Once the surfactant was dispersed in the liquid vehicle a dispersant and the intended premix formulation was added to the mixture. Once the premix was fully dispersed, an additional amount of thixotrope and liquid vehicle was added to the mix and stirred until homogeneous.

WORKING EXAMPLE 6 Ingredient Parts By Weight

H₂0 49.50

Defoamer (Blend of .50 emulsifiable mineral oils, silica derivatives and esters available from Drew Chemical Company as blend Y-250)

Pre-Mix 4 43.00

76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp.) Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 7

Ingredient Parts By Weight

H₂0 49.50

Pre-Mix 2 43.00

76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 1.00 Silicate (5% w/v) WORKING EXAMPLE 8

Ingredient Parts By Weight

H₂0 49.50

Pre-Mix 8 43.00

76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 9 Ingredient Parts By Weight

H₂0 49.50

Defoamer (Blend of .50 emulsifiable mineral oils, silica derivatives and esters available from Drew Chemical Company as blend Y-250) Pre-Mix 1 43.00

76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 10

Ingredient Parts By Weight H₂0 49.50

Pre-Mix 3 43.00 76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 11 Ingredient Parts By Weight

H₂0 49.50

Defoamer (Blend of .50 emulsifiable mineral oils, silica derivatives and esters available from Drew Chemical Company as blend Y-250) Pre-Mix 5 43.00

76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 12

Ingredient Parts By Weight H₂0 49.50

Pre-Mix 6 43.00 76 RES 661 (vinyl 6.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 1.00 Silicate (5% w/v)

WORKING EXAMPLE 13 Ingredient Parts By Weight

H₂0 50.50

Defoamer (Blend of .50 emulsifiable mineral oils, silica derivatives and esters available from Drew Chemical Company as blend Y-250) Pre-Mix 6 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 1.00 Silicate (5% w/v) WORKING EXAMPLE 14

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 4 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 0.50 Silicate (5% w/v)

WORKING EXAMPLE 15

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 2 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 0.50 Silicate (5% w/v) WORKING EXAMPLE 16

Ingredient Parts By Weight H₂0 51.00

Pre-Mix 8 43.00 76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 0.50 Silicate (5% w/v)

WORKING EXAMPLE 17

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 1 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 0.50 Silicate (5% w/v) WORKING EXAMPLE 18

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 7 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 0.50 Silicate (5% w/v)

WORKING EXAMPLE 19

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 3 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

Magnesium Aluminum 0.50 Silicate (5% w/v) WORKING EXAMPLE 20

Ingredient Parts By Weight

H₂0 51.00

Pre-Mix 5 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 0.50 Silicate (5% w/v)

WORKING EXAMPLE 21 Ingredient Parts By Weight

H₂0 51.00

Defoamer (Blend of .50 emulsifiable mineral oils, silica derivatives and esters available from Drew Chemical Company as blend Y-250) Pre-Mix 9 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp. )

Magnesium Aluminum 0.50 Silicate (5% w/v)

WORKING EXAMPLE 22

Ingredient Parts By Weight H₂0 51 . 00

Pre-Mix 2 43.00 Gion Brand 5.00 acrylonitrile latex butadiene styrene terpolymer (commercially available from B. F. Goodrich)

Magnesium Aluminum 0.50

Silicate (5% w/v)

Cured Strength In Working Examples 23-27 a slightly different mixing process was used. First a surfactant was dispersed in a liquid vehicle after which the powdered adhesive premix and a dispensing agent were mixed slowly into the composition. The strength of these compositions was then tested and is shown in Table II.

WORKING EXAMPLE 23 Ingredient Parts By Weight

H₂0 45.00

Pre-Mix 4 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.) WORKING EXAMPLE 24

Ingredient Parts By Weight H₂0 45.00

Pre-Mix 2 43.00 76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

WORKING EXAMPLE 25

Ingredient Parts By Weight

H₂0 45.00

Pre-Mix 8 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer available from Union Oil Corp.)

WORKING EXAMPLE 26

Ingredient Parts By Weight

H₂0 45.00

Pre-Mix 2 43.00

76 RES 661 (vinyl 5.00 acrylic latex copolymer .available from Union Oil Corp.) Cured Bond Strength

The lap sheer strength and T-Peel strength Working Examples 23 through 26 was then compared with the following results provided in Table II. TABLE II

Lap Sheer

Working Example Strength T-Peel Strength

(lb/ in') (lb/inch width) init./open 2 days

24 (cohesive) 3878.4 ± 352.8 10.8/7.3

25 (adhesive) 3810.7 ± 96.5 9.0/7.0

26 (cohesive) 4322.2 ± 419.4 11.0/4.7

As can be seen from Table II Working Examples 23-26 showed substantial lap sheer strength and T-Peel strength both initially and after two days. Working Examples 24 and 26 provided a cohesive bond where upon failure, the bond was split evenly down the middle leaving adhesive material on both substrates. Working Example 25 provided an adhesive bond leaving areas on both substrates where the adhesive material was completely stripped from the surface of application.

Lapshear Strength as a Function of Particle Size

A tenth premix was formulated as shown below:

Material Premix 10 WT-%

Araldite GT 7013 (bisphenol A- 75.4717 epichlorohydrin available from Ciba-Geigy Corporation)

P-101 Curing Agent (Amine 2.6415

Condensate of an epoxy resin available from Shell Oil Company)

RESIFLOW P-67 1.1321

(acrylate/silicon dioxide compound available from Estron Chemicals, Inc.)

Uraflow B (benzoin flow agent, 0.7547 GCA Chemical Co.) BARTEX 65 (barium sulfate, 18.8679 Chromalloy Industrial Minerals)

Pigments (Black beads) 1.1321

An eleventh premix was formulated as shown below:

Pre-Mix 11 Material Wt-%

Araldite GT 7013 (bisphanol A- 94.1620 epichlorohydrin available from Ciba-Geigy Corporation)

2-methylimidazole 0.1883 dicyandiamide 4.2373

RESIFLOW P-67

(acrylate/silicon dioxide compound available from Estron

Chemicals, Inc.) 1.4124

The premixes were then used in the thermosetting compositions shown in Table 3. In each instance, the particle size of the powder coating used in the composition is shown in Table III. Table III Formulations regarding micron sizes

3 Micron 4.9 Micron 62 Micron 103 Micron

8% 8% 8% 8%

Carboxylated Carboxylated Carboxylated Carboxylated

Acrylic Acrylic Acrylic Acrylic

Copolymer Copolymer Copolymer Copolymer

44% Premix 10 44% Premix 11 44% Premix 11 44% Premix 11

.4% TAMOL 850 .4% TAMOL 850 .4% TAMOL 850 .4% TAMOL 850 (Sodium Salt (Sodium Salt (Sodium Salt (Sodium Salt of Polymeric of Polymeric of Polymeric of Polymeric

Carboxylic Carboxylic Carboxylic Carboxylic

Acid Acid Acid Acid

Dispersing Dispersing Dispersing Dispersing Agent; Rohm & Agent; Rohm & Agent; Rohm & Agent; Rohm &

Haas) Haas) Haas) Haas)

47.48% H₂0 47.6% H,0 47 . 48% H₂0 47 . 48% H₂0

.03% XANTHAN . 03% XANTHAN . 03% XANTHAN GUM GUM GUM

.09% Guar Gum .09% Guar Gum .09% Guar Gum

Aluminum lapshears were wiped with methyl ethyl ketone, acid etched for ten minutes and washed in deionized water before being air dried. Lapshears were assembled with 7781 volan fiberglass cloth which was impregnated with products above. Coat weights were 28% by weight of epoxy powder. The impregnated cloth was sandwiched between the lapshears and cured for one hour at 350°F at 1,000 psi. Lapshears were evaluated using ASTM D1002-72.

As can be seen in Figure One, 3 micron and 4.9 micron particle size compositions were compared to 62 and 103 micron formulations to determine lapshear strength. The difference in strength with smaller particle size compositions was notable.

The above discussion. Examples and data illustrate our current understanding of the invention. However, since many variations of the invention can be made without departing from the spirit and scope of the invention, the invention resides wholly in the claims hereinafter appended.

Claims

I CLAIM :

1. A liquid adhesive dispersion which can cure to a thermoset bond, comprising in a solid phase and a liquid phase: (a) an effective amount of a powdered thermosetting composition said composition having a particle size of about 25 microns or less;

(b) an effective amount of film-forming agent composition; and (c) an aqueous liquid vehicle; wherein said dispersion remains storage stable at ambient temperatures and, after application, said dispersion can form a physically stable intermediate film.

2. The composition of claim 1 wherein said thermoset is selected from the group consisting of an epoxy, a polyurethane, a polyester, a bisrnaleimide, an acrylic, mixtures thereof and hybrids thereof.

3. The composition of claim 1 wherein said film forming agent comprises a thermoplastic polymer composed of one or more monomers selected from the group consisting of vinyl acetate, ethylene, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, esters of acrylic acid, esters of methacrylic acid, styrene, butadiene, vinyl chloride, vinylidene chloride, isoprene, chlorprene, polyvinyl alcohol, and aleic anhydride.

4. The composition of claim 1 wherein said film-forming agent comprises a polymer selected from the group consisting of cellulose polymers, ether cellulose polymers, derivatized cellulosic and ether cellulosic polymers, starch, starch grafted copolymers, guar gum, karaya gum, and dextrine.

5. The composition of claim 1 additionally comprising a dispersant selected from the group consisting of silicates, polyphosphate salts, colloidal proteins, surfactants, cellulosic polymers, starch compositions, and fatty acid soaps.

6. An article of manufacture comprising a substrate coated with a physically stable thermoset film dispersion which can cure to a thermoset bond, said adhesive dispersion comprising:

(a) an effective amount of thermosetting composition said composition having a particle size of about 25 microns or less; and

(b) an effective amount of film-forming agent; wherein said film dispersion remains storage stable at ambient temperatures.

7. A method of using a liquid adhesive dispersion composition which can cure to a thermoset bond, said adhesive composition comprising an effective amount of powdered thermoset composition said powdered thermosetting composition having a particle size of about 25 microns or less, an effective amount of film-forming agent, and an aqueous liquid vehicle wherein said dispersion remains storage stable at ambient temperatures and after application said dispersion forms a physically stable intermediate film, said method comprising the step of applying said liquid adhesive dispersion composition to a substrate and forming a physically stable intermediate film capable of curing to a thermoset bond.

8. The method of claim 7 additionally comprising the steps of: (a) placing a second substrate onto said intermediate film; and

(b) curing said thermoset contained within said intermediate film to create an adhesive bond.

9. The method of claim 7 additionally comprising the steps of:

(a) placing a plurality of said thermoset film laden carriers together in series; and

(b) heat curing said thermoset film laden carrier to produce a composite laminate structure.

10. The product resulting from the method of claim 7.