A METHOD OF VIBRATIONALLY DAMPING ARTICLES USING ORGANIC SOLVENT FREE OR REDUCED DAMPERS AND DAMPED ARTICLES

Abstract: The invention relates to a method of vibrationally damping an article using a damper prepared from an organic solvent-free or reduced composition. The invention also relates to articles damped via dampers prepared from organic solvent-free or reduced compositions.

Description: A METHOD OF VIBRATIONALLY DAMPING ARTICLES USING ORGANIC SOLVENT FREE OR REDUCED DAMPERS AND DAMPED ARTICLES FIELD OF THE INVENTION The invention relates to a method of vibrationally damping an article using a damper prepared from an organic solvent-free or organic solvent reduced compositions. The invention also relates to articles damped via dampers prepared from organic solvent-free or organic solvent reduced compositions. BACKGROUND OF THE INVENTION Bolte, U.S. Patent No. 5,371,118 discloses two-component film-forming reactive systems for the surface bonding and/or coating of substrates, more particularly for heat-sealable coatings. The composition contains at least one resin which is curable with an epoxide and an epoxide compound as a curing agent. The resin which is curable with the epoxide is a mixture of a carboxyl or hydroxyl terminated polyurethane with an acrylate or methacrylate polymer or copolymer having hydroxyl or carboxyl groups. According to Bolte the reactive systems are particularly suitable for the production of multilayer composites or laminates. As an example, Bolte discloses composites which are suitable for the production of flexible printed circuits. According to Bolte the reactive systems of the invention may also be used for the production of high temperature-resistant insulating materials. Insulating materials according to Bolte are understood in particular to be cable sheaths, cover films for circuits, and windings for coils. There is no discussion in Bolte of the use of the material for vibration damping purposes. Organic solvent-based damping materials are well known. Examples thereof include solutions, typically containing 20-30% solids of damping polymer(s), such as acrylic polymers, in solvent such as ethylacetate, heptanone, or isopropyl alcohol. Such systems have been used to damp a variety of articles such as cameras, tape recorders, loud speakers, etc. Solvent-based vibration damping materials emit volatile organic compounds thus contributing to environmental pollution. It would be desirable to provide a system which reduces or eliminates such environmental pollution. SUMMARY OF THE INVENTION We have discovered a novel method for damping articles which is capable of making use of an organic solvent-free or an organic solvent reduced vibration damping system. The present invention provides a method of vibrationally damping an article, comprising applying a vibration damper to the article, wherein the vibration damper comprises a vibration damping material, wherein the vibration damping material comprises a viscoelastic material, wherein the viscoelastic material is a polymerization product of a composition that comprises: (a) about 2 to about 18 percent by weight of an epoxy functional compound(s); (b) about 4 to about 40 percent by weight of a carboxyl functional acrylic polymer(s); (c) about 42 to about 94 percent by weight of a polyurethane(s); wherein the weight percentages of (a), (b), and (c) are based upon the total weight of (a) plus (b) plus (c); and (d) 0 to about 80 percent by weight of water based upon the total weight of (a) plus (b) plus (c) plus (d); and wherein the weight ratio of the epoxy functional compound(s) to the carboxyl functional acrylic polymer(s) is about 70:30 to about 5:95; and wherein the weight ratio of the epoxy functional compound(s) to the polyurethane(s) is about 3 : 97 to about 25:75. The above described composition may be, for example, a dispersion or an emulsion. Although minor amounts of organic solvents (such as N- methylpyrrolidone, propylene glycol methylether, ammonia, acetone, and the like) may be present (e.g., 10% or less based on the total weight of the composition, preferably 3% or less); it is most preferred that no organic solvent be present. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a graphical representation of storage modulus (G') versus temperature for the vibration dampers of Examples 1-3. Fig. 2 is a graphical representation of tan delta versus temperature for the vibration dampers of Examples 1-3. Fig. 3 is a graphical representation of storage modulus (G 1 ) versus temperature for the vibration dampers of Examples 4-7. Fig. 4 is a graphical representation of tan delta versus temperature for the vibration dampers of Examples 4-7. Fig. 5 is a graphical representation of storage modulus (G) versus temperature for the vibration dampers of Comparative Examples 1-3. Fig. 6 is a graphical representation of tan delta versus temperature for the vibration dampers of Comparative Examples 1-3. DETAILED DESCRIPTION OF THE INVENTION Vibration Damping Material The vibration damping material useful according to the present invention may or may not have pressure sensitive adhesive properties, yet typically provides good peel and shear adhesion. Such vibration damping materials may potentially adhere well to a variety of surfaces over a broad temperature range and, therefore, have wide utility. Vibration damping performance may be characterized by the following dynamic properties of the viscoelastic material: complex modulus (G*), storage modulus (G), loss modulus (G"), and loss factor (tan delta). Knowing any two of these properties allows the other two to be mathematically determined as follows tan delta=G"/G G*=G'+iG"=G'(l+i tan delta) G'=G*cos delta G"=G*sin delta where i = the square root of -1 The storage modulus represents that portion of the mechanical energy which is stored (i.e., completely recoverable) when the viscoelastic material undergoes cyclic deformation. The stored energy is analogous to that seen in a simple spring going through cyclic deformation. The loss modulus represents that portion of the mechanical energy dissipated (converted to heat) when the viscoelastic material undergoes cyclic deformation. The dissipated energy is analogous to that seen in a simple dashpot going through cyclic deformation. This ability to dissipate energy gives rise to amplitude (and resultant stress) attenuation in resonance vibrations of structures when viscoelastic materials (either constrained layer or free layer) are used in surface layer damping devices. While the performance of a surface layer damping treatment depends largely on the dynamic properties of the viscoelastic material, it is also dependent on other parameters. The geometry, stiffness, mass and mode shape of the combination of the damper and the structure to which it is applied will affect the performance of the damper. Since modern computer technology lends itself to the manipulation of complex numbers, damping treatment designers utilize the dynamic properties in the form of complex numbers (e.g. G'[l + i tan delta]) to predict the performance of a damping treatment on a structure, for both exact solutions to simple structures (beams or plates) or numerical solutions (Finite Element Analysis) to more complex structures. Therefore, the properties of viscoelastic materials typically reported by manufacturers are G' and tan delta. The dynamic properties of a viscoelastic material are temperature and frequency dependent. Optimum damping occurs when the viscoelastic material is going through a modulus transition (from a glassy state to a rubbery state) and tan delta goes through a maximum (typically about 1.0). In general, for most polymer systems, this transition occurs over a fairly narrow temperature range (30° to 40°C range). Previous attempts to broaden the temperature range of the modulus transition of a viscoelastic material resulted in large decreases in the loss factor which resulted in decreased damping capacity. For the system used according to the present invention the modulus transition occurs over a fairly wide temperature range (about -20 to about 80 degrees C). Since vibration problems are subject to both temperature and frequency variations, it is important that variation of the dynamic properties of a viscoelastic material with temperature and frequency be taken into account, both when selecting the appropriate viscoelastic material as well as designing the construction of the damping treatment. In addition, it is often desirable to have a single damping treatment perform over widely varying temperatures such as for aircraft which may operate in both arctic and desert climates. Furthermore, it is often desirable to have a damping treatment perform at a number of frequencies such as when two or more vibration modes are being excited in a single system. Since presently known single component viscoelastic materials perform over fairly narrow temperature ranges, conventional solutions to wide temperature variations incorporate multiple layers of viscoelastic material, with each layer being optimized for a different temperature range. These multilayer systems are expensive and complex. Consequently, it would be highly desirable to have a single viscoelastic material that performs over a broad temperature range. The vibration damping materials of the invention may be utilized as a vibration damping material alone (i.e., free layer damper) or in conjunction with a backing layer (i.e., as part of a constrained layer damper). Preferably, compositions are used in constrained layer constructions with a laminate of one or more backing layers and one or more layers of the composition to damp vibrations. Vibration damping materials are most efficiently used if they are sandwiched between the structure/device to be damped and a backing layer, such as thin sheet metal. This forces the viscoelastic material to be deformed in shear as the structure/device vibrates, dissipating substantially more energy than when the material deforms in extension and compression, as occurs in free layer treatment. Constrained layer constructions can be prepared by two processes. In the first process, a layer of the uncured vibration damping material is coated onto a release liner, the material cured, and the layer of resulting material transferred to a backing layer and adhered thereto, thereby providing a constrained layer construction. In the second process, a layer of uncured material is coated directly onto a backing and the mixture cured "in-situ" to provide the constrained layer construction. In each case, the constrained-layer construction is then affixed to the structure requiring damping. The construction may be attached in any manner provided that the constraining layer is only fixed to the vibrating structure via the vibration damping material interface, i.e., free of mechanical attachment. When the structure subsequently vibrates under the influence of an internally or externally applied force, the vibration is damped. When the vibration damping material has pressure sensitive adhesive properties, the material can usually be adhered to a backing layer without the use of an additional bonding agent. However, it is sometimes necessary to use a thin layer (20-50 micrometers, for example) of a high-modulus adhesive, such as an acrylic adhesive or an epoxy adhesive, to bond the composition to a structure. For most applications, the layer of vibration damping material has a thickness of about 0.01 mm about 100 mm, more preferably about 0.05 mm to about 100 mm. The vibration damping material can be applied by any of the techniques known in the art such as by spraying, dipping, knife coating, curtain coating, molding, laminating, or casting. Backing Any backing material which is typically used in constrained layer dampers can be used as an element of a constrained layer damper used according to the present invention. Examples of useful backing materials include but are not limited to those selected from the group consisting of paper; wood; ceramics; glass; metals; polymeric materials; fiber-reinforced polymeric materials such as glass fiber, ceramic fiber, and metal fiber-reinforced polyester; and combinations thereof. The backing may, for example, be a laminate of multiple layers. Examples of suitable metals include but are not limited to iron, steel, nickel, aluminum, chromium, cobalt, and copper, and alloys thereof. Useful polymeric materials include but are not limited to those selected from the group consisting of polystyrene, polyester, polyvinyl chloride, polyurethane, polycarbonate, polyimide, polyepoxide, polyethylene, and polypropylene. Preferably the backing has a Young's Modulus of at least about 1 x 10 Pascals. The backing should have a Young's Modulus greater than that of the vibration damping material layer. Preferably, the backing has a Young's Modulus of at least about 10 times greater than that of the vibration damping material, more preferably at least about 100 times greater, most preferably at least about 1000 times greater. For optimal damping, the backing should have a stiffness approximately equal to the stiffness of the article being damped. For some uses, the thickness of the backing will need to be limited due to size and/or weight limitations necessitated by the article to be damped or the location where the article is to be used. The desired stiffness of the backing layer can be varied by adjusting the thickness of the layer (for example from about 25 micrometers to 5 centimeters), depending on the modulus of the backing layer. In general, the backing stiffness is related to the thickness of the backing. For a given backing material, the bending stiffness increases as the thickness of the backing increases. Thus, the desired stiffness of the backing can be varied by adjusting the thickness depending on the modulus of the backing. The backing typically has a thickness of greater than about 0.5 mils (0.013 mm), preferably greater than about 1 mil (0.025 mm), and most preferably greater than about 2 mils (0.051 mm). The backing may further comprise an additive such as those selected from the group consisting of fire retardants, colorants, antistatic agents, etc. As mentioned previously the viscoelastic material comprises the polymerization product of a composition comprising epoxy functional compound(s), a carboxyl functional acrylic polymer(s), a polyurethane(s), and optionally water. Epoxy Functional Compounds A variety of epoxy functional compound(s) may be used according to the present invention. The term "epoxy functional compound" is used to refer collectively to oxirane group-containing compounds. Preferably the epoxy functional compound is selected from the group consisting of epoxy functional monomers, epoxy functional oligomers, epoxy functional polymers, and mixtures thereof. The term "polymer" as used herein refers to a macromolecule formed by the chemical union of five or more combining units called monomers. The term "oligomer" as used herein refers to the polymerization product of 2 to 4 monomer units and includes dimers, trimers and tetramers. An extensive series of epoxy functional compounds is well known and includes compounds which may be subdivided into a number of classes such as (a) the diglycidyl ethers of bisphenol A, (b) the epoxy phenol novolak and epoxy cresol novolak type compounds (which are prepared by adding oxirane functional groups to phenol novolak and cresol novolak compounds); and (c) cycloaliphatic epoxy compounds wherein the oxirane functional group is attached to or is part of a cycloaliphatic group. The epoxy functional compound(s) which are used in this invention can be stably emulsified in water. These are emulsified in water using nonionic surfactants, although the emulsifying agent (surfactant) is of secondary significance. These nonionic surfactants are usually ethylene oxide adducts of octyl or nonyl phenols or long chain alcohols, like dodecanol, containing from 5-80 moles of ethylene oxide per mole of the phenol or alcohol. The number of epoxy groups can vary. Suitable epoxy functional compound(s) contain on average at least one epoxy group, preferably from 1.5 to 3 epoxy groups, and most preferably from 1.8 to 2.2 epoxy groups. Preferably the epoxy equivalent weight ranges from about 100 to about 1000, most preferably about 170 to about 700 for reasons of commercial availability and preparation limitations. The composition comprises about 2 to about 18 weight percent epoxy functional compound(s), preferably about 4 to about 16 weight percent, most preferably about 5 to about 14 weight percent based upon the total weight of (a) plus (b) plus (c). Carboxyl Functional Acrylic Polymer A variety of carboxyl functional acrylic polymer(s) may be used according to the present invention. Examples of suitable carboxyl functional acrylic polymers include but are not limited to those selected from the group consisting of acrylate and/or methacrylate homopolymers or copolymers. Suitable comonomers to produce acrylic formulations are those which can be copolymerized with acrylates and/or methacrylates. Typical compounds for this purpose are ethylenically unsaturated monomers such as those selected from the group consisting of vinyl compounds and styrene compounds. Acrylic acid and methacrylic acid and salts and esters thereof are mentioned by way of example as suitable (meth)acrylates for the production of such polymers. The alcohol component of these esters preferably contains 1 to 6 carbon atoms. The vinyl compounds include, for example, vinyl chloride, vinyl esters, such as vinyl acetate, vinyl propionate, and vinyl fatty acid esters, such as vinyl laurate. Suitable styrene compounds include, for example, styrene, halostyrenes, such as chloro styrene, fluorostyrene and iodostryrene, and alkyl styrenes, such as methyl styrenes and 2,4-diethyl styrene. The number average molecular weight of the carboxyl functional acrylic polymer(s) may vary but typically ranges from about 30,000 to about 500,000, preferably greater than about 50,000. The carboxyl functional acrylic polymer(s) may be added by itself in forming the vibration damping material or it may, for example, be added in the form of an emulsion. Preferably the carboxyl functional acrylic polymer(s) has an acid value ranging from about 0.5 to about 50, preferably about 10 to about 25. Some acrylic copolymers, which can generate acid groups on heating are also suitable such as Rhoplex™ 2438 which is an acrylic polymer emulsion, TR-934 H-S which is a self crosslinking acrylic polymer emulsion, and TR 520 which is also an acrylic polymer emulsion, all available from Rohm and Haas Company, Pennsylvania, U.S.A. The composition comprises about 4 to about 40 weight percent carboxyl functional acrylic polymer(s), preferably about 6 to about 35 weight percent, most preferably about 10 to about 30 weight percent based upon the total weight of (a) plus (b) plus (c). Polyurethane A variety of polyurethane(s) may be used according to the present invention. The polyurethane(s) may be anionic, cationic, non-ionic, or combinations thereof. Optionally the polyurethane contains one or more functional groups selected from the group consisting of carboxyl groups, sulfonate groups, phosphate groups, and combinations thereof. Preferably the polyurethane(s) is anionic in order than it may react with epoxy groups to provide crosslinking and thus moisture resistance to the polymerization product. Preferably the anionic polyurethane(s) contains carboxyl group(s) due to their greater reactivity. Examples of suitable polyurethane(s) include but are not limited to those obtained by the polyaddition reactions between polyols such as polyether or polyester or polycarbonate polyols and polyisocyanates such as diisocyanates. Suitable diisocyanates include but are not limited to those selected from the group consisting of aliphatic, aromatic or cycloaliphatics such as 4,4' diphenyl methane diisocyanate (MDI), isophorone diisocyanate (IPDI), tolylene diisocyanate (TDI), tetramethyl xylene diisocyanate (TMXDI), and combinations thereof. The number average molecular weight of the polyurethane(s) may vary but typically ranges from about 20,000 to about 150,000. The polyurethane(s) may be added by itself in forming the vibration damping material or it may, for example, be added in the form of a dispersion. The polyurethane(s) may optionally have one or more isocyanate reactive sites (typically terminal sites). Such polyurethane(s) may be obtained by reacting an excess of isocyanates with polyols as mentioned above. Non-ionic water dispersible polyurethanes are prepared by attaching nonionic hydrophilic polymer segments to polyurethane macromolecules. These are water soluble polyether chains from ethylene oxides. Anionic or cationic polyurethane(s) are obtained by introducing hydrophilic ionic groups within the large hydrophobic chain segments. Examples are described in Frisch Jr. et al, U.S. Patent No. 5,554,686. The composition comprises about 42 to about 94 weight percent polyurethane(s), preferably about 60 to about 90 weight percent, and most preferably about 65 to about 85 weight percent based upon the total weight of (a) plus (b) plus (c). Water Water is optionally included in the composition used according to the present invention prior to drying and curing. The amount of water included can vary. Typically about 0 to about 80 weight percent water is included based upon the total weight of (a) plus (b) plus (c) plus (d). Typically sufficient water is included in the composition so that the composition can be easily coated prior to cure. Typically, the amount of water included is such that the Brookfield viscosity of the composition ranges from about 20 cps to about 40,000 cps, preferably about 300 cps to about 10,000 cps, and most preferably about 500 cps to about 3000 cps. The Brookfield viscosity can be measured according to American Society of Testing Materials (ASTM) D 2196-86 (Reapproved 1991). The amount of water added typically depends on the coating process. The water is not involved in the polymerization reaction. Component Ratios The weight ratio of the epoxy functional compound(s) to carboxyl functional acrylic polymer(s) is about 70:30 to about 5:95, preferably about 60:40 to about 10:90, and most preferably about 55:45 to about 15:85. The weight ratio of the epoxy functional compound(s) to polyurethane(s) is about 3:97 to about 25:75, preferably about 5:95 to about 20:80, and most preferably about 7:93 to about 15:85. Optional Components The composition used in the present invention may optionally further comprise one or more components selected from the group consisting of defoamers, surfactants, corrosion inhibiting agents, impact modifiers, fiber/particulate such as thickeners, fillers (grit), thermally conductive fibers and/or paniculate, electrically conductive particles and/or fibers, glass and/or ceramic microbubbles, expanded or unexpanded polymeric microbubbles, antioxidants, antistatic agents, fungicides, bactericides, solvents, plasticizers, tackifying resins, pigments, dyes, buffering agents, crosslinking agents, catalysts, and the like. Examples of suitable crosslinking agents or coreactants include but are not limited to the following: carbodiimide, polyaziridine compounds, and amines (aliphatic, cycloaliphatic and amidoamines) such as diethylene triamine, aromatic amines, and dicyanodiamide. Tertiary amine catalysts such as DMP-30 available from Rohm and Haas Company can also be added to enhance the reactive value of the epoxy functional compound(s). Examples of suitable defoamers include but are not limited to those selected from the group consisting of Surfynol™ DF110L (a high molecular weight acetylenic glycol nonionic surfactant available from Air Products and Chemical Inc.), Dehydran™ 1620 (modified polyol/polysiloxane adducts available from Henkel Corp.), and DB-31 and DB-65 (silicone additives available from Dow Corning). Examples of useful flow and leveling agents include but are not limited to Igepal™-60 (an ethoxylated nonylphenol nonionic surfactant available from Rhone Poulenc Surfactant and Specialty Company). Examples of suitable surfactants include those selected from the group consisting of nonionic and anionic surfactants. The selection of a surfactant depends upon the polyurethane(s) included in the composition. For example, if one uses an anionic polyurethane(s), one should use a nonionic surfactant to avoid destabilization of the polyurethane(s) dispersion. However, if one uses a nonionic polyurethane(s) one can use a nonionic or cationic surfactant. If one uses a cationic polyurethane(s) one should use a nonionic surfactant Examples of suitable nonionic surfactants include but are not limited to Fluorad™ FC-129 (a fluorinated alkyl alkoxylate nonionic surfactant available from 3M Company) and Fluorad™ FC-430 (a fluorinated alkyl ester nonionic surfactant also available from 3M Company). Another example of a suitable surfactant is Surfactant 465 (an ethoxylate tetramethyl decynediol nonionic surfactant from Air Products). Examples of specific useful anionic surfactants include but are not limited to those selected from the group consisting of alkyl benzene sulphonate, alkyl ester sulfonates, phosphate esters, and lauryl sulphate. A typical example of an anionic surfactant is Triton™ GR5M available from Rohm and Haas Company. Examples of additional specific useful nonionic surfactants include but are not limited to those selected from the group consisting of ethoxylated alcohols, such as ethoxylated octyl phenol and ethoxylated nonylphenol. A typical example is Triton™ X-100 which is an octyl-phenoxy-polyethoxy ethanol available from Rohm and Haas Company. Examples of useful thickeners include but are not limited to thickeners such as Acrysol™ ASE-60, Acrysol™ 615, Acrysol™ RM 825, and Acrysol™ TT 935 available from Rohm and Haas Company. Typically the Brookfield viscosity of the composition prior to coating and curing ranges from about 20 cps to about 40,000 cps. The solids content of the composition and the components which make up the composition can vary. Typically the composition will range from about 20% to 100% by weight solids (i.e., about 0% to 80% by weight water). Each component of the composition can have a different solids content, depending on stability and commercial availability. Typically the solids content will vary between 3% and 100% by weight for the epoxy functional compound(s). For the carboxyl functional acrylic polymer, the solids content will typically vary between 30% and 70% by weight, preferably between 45% and 55% by weight. The typical solids content for the polyurethane will vary between 40% and 70% by weight, preferably between 55% and 65% by weight. The pH of the composition can vary. Typically it ranges from about 2.5 to about 9.5, preferably about 4.5 to about 9, and most preferably about 6.5 to about 8.5, for maximum shelf stability of the composition. Properties of the Vibration Damping Material Used According to the Invention In order to provide useful vibration damping properties the vibration damping material used should typically have a tan delta of at least about 0.3, preferably at least about 0.5, over a temperature range of about -25 degrees C to about 160 degrees C. The vibration damping materials used according to the present invention allow a broadening of the temperature range of the modulus transition to more than 100 degrees C (from about -20 to about 80 degrees C, preferably about -25 to about 160 degrees C) while maintaining a significant loss factor (greater than 0.3). In order to provide useful vibration damping properties the vibration damping material preferably has a shear modulus (G') of at least about 0.1 MPa over a temperature range of about -25 degrees C to about 160 degrees C. In order to provide useful vibration damping properties the vibration damping material preferably has an insensitivity to water. These vibration damping materials are considered to be insensitive to water if the overlap shear strength of substrates bonded with these materials does not decrease more than 50 percent when held at 80 percent relative humidity and 38 degrees C for four weeks. Methods of Preparing. Coating. Drying and Curing the Damping Material The compositions useful herein are typically prepared for use, either as one part or two part systems, depending upon the desired shelf-life. In a particular two part system, one part (Part A) comprises an epoxy functional compound(s) dispersion and the other part (Part B) comprises a mixture of a carboxyl functional acrylic polymer(s) emulsion and a polyurethane(s) dispersion. As another example, Part A may instead comprise 100 percent solids epoxy functional compound (without water) which can be dispersed before mixing with Part B (the same as described above) or may be dispersed in Part B at the time of application. To make a desired vibration damping material from this two part system, the two components are prepared and stored until it is desired to produce film therefrom. To produce a vibration damping material all ingredients are typically mixed thoroughly, cast onto/applied to either a release liner or directly on the desired substrate and left at room temperature for about five minutes to allow for any bubbles to dissipate. The vibration damping materials are then typically heated at about 60 degrees C to about 70 degrees C for about 2 minutes to about 8 minutes, followed by an additional heating for about 15 minutes to about 30 minutes at about 160 degrees C to about 180 degrees C. The vibration damping materials when heated for a shorter time and/or at lower temperature provide a narrower temperature range for the modulus transition, while a broader temperature range for the modulus transition is obtained when the vibration damping materials are heated for longer times and/or at higher temperature, etc. The thickness of the vibration damping materials depends upon the mold thickness in the instance where a mold is used. Otherwise the coating die opening, line speed, pumping rate, etc., control the thickness. Any bubbles in the mixture can also easily be removed by adding a suitable defoamer and surfactant. Optional crosslinking agents or other additives such as antioxidants and fillers may also be incorporated into the vibration damping material. The vibration damping material can be coated onto a suitable substrate and exposed to radiation to obtain a cured vibration damping material. The viscosity of the vibration damping material can be modified, to obtain a viscosity appropriate for the coating method to be used. For good coatability, the vibration damping material utilized in the invention typically has a Brookfield viscosity of about 20 cps to about 40,000 cps. Conventional coating methods such as knife coating and roll coating can be used. The vibration damping material used according to the invention can be coated onto a flexible carrier web and polymerized. Cured vibration damping materials, depending on the specific formulation, can be pressure-sensitive vibration damping materials, heat activated vibration damping materials, or non-adherent materials. To employ non-adherent vibration damping materials typically requires the use of a bonding agent, i.e., a material to affix the damping material to either a constraining layer and/or a resonating structure depending on the particular use geometry desired. Examples of such bonding agents include, for example, adhesives such as acrylics, urethanes, and epoxies. In the case of cured vibration damping materials having pressure-sensitive adhesive properties, these materials are typically cured and applied by first making a laminate construction which comprises a layer of the vibration damping material evenly coated between a constraining layer and a layer coated with a release material. A transfer tape can be made by coating the composition between two layers (e.g., release liners) both of which are coated with a release coating. The release liners typically comprise a polymeric material such as polyester. Preferably, each release liner is first coated or primed with a release material which is incompatible with the vibration damping materials utilized in the invention. The compositions of the invention can also be coated onto a differential release liner; i.e., a release liner having a first release coating on one side of the liner and a second release coating coated on the opposite side. The two release coatings should have different release values. For example, one release coating may have a release value of 5 grams/cm (i.e., 5 grams of force is needed to remove a strip of material 1 cm wide from the coating) while the second release coating may have a release value of 15 grams/cm. The vibration damping material is typically coated over the release liner coating having the higher release value. The resulting laminate product can be wound into a roll. As the laminate product is unwound, the vibration damping material adheres to the release coating with the higher release value. After the laminate product is applied to a substrate, the release liner can be removed to expose the remaining surface for further use. The vibration damping materials useful according to the invention having adhesive qualities adhere well to polymeric substrates such as polyesters and polycarbonates. Damper Uses The damper used according to the invention can be used to damp a variety of articles including but not limited to the following: cameras; tape recorders; loud speakers; covers such as engine covers, oil pan covers, and computer disk drive covers; and panels such as small appliance panels and panels for motor equipment housings. TEST METHODS The following test methods are used herein. OVERLAP SHEAR TEST The overlap shear test was conducted according to American Society for Testing and Materials (ASTM) D-1002 by applying damping materials on a 1 square inch (6.45 cm 2 ) area on both coupons (steel plates), which were then heated at 60 degrees C for 4 minutes. Next, the coupons were bonded via their coated areas and heated at 170 degrees C for 5 minutes. The crosshead speed of the instrument was 2 mm/minute. DAMPING PROPERTIES (LOSS FACTOR AND STORAGE MODULUS) Viscoelastic properties were measured by Dynamic Mechanical Analysis (DMA) using a Rheometrics Mechanical Spectrometer (RMS) Model RDA II. On each sample, a temperature sweep was performed at a fixed frequency of 1 Hertz (Hz), using parallel plates with a radius of 12.5 mm. The sample thickness was about 1 mm and was obtained by laminating several layers of material. In every case, the shear storage and loss modulus, G and G", and their ratio and tan delta, versus temperature were recorded between -20 and 70 degrees C. The performance was assessed using the DMA results. Values of tan delta greater than 0.3 were used as an indication of good damping performance, while a storage modulus ( ) greater than 0.1 MPa was used as an indicator of adequate mechanical properties. The temperature range where both criteria of tan delta and G' were met was taken as the working range for the vibration damping material. EXAMPLES The following examples further illustrate but do not limit the present invention. Example 1 The following components were used: 6.67 grams of Epirez™ 3510-W-60 (60 percent solids), 26.67 grams of Maincote™ AE-58 (42.5 percent solids), and 66.66 grams of Witcobond™ 290H (60 percent solids). The 3510-W-60 (60 percent solids), which was obtained from Shell Chemical Company, is a nonionic bisphenol A type epoxy dispersion. It has an equivalent weight of 187, a pH of 3.5, a solid of 60 weight percent, and a density of 1.08 grams/cm 3 . (It is referred to as "Epoxy" in Table I.) The Maincote™ AE-58 (42.5 percent solids) is a carboxyl functional acrylic polymer emulsion obtained from Rohm and Haas Company. It has a solids content of 42.5 weight percent, a pH value of 7.5 and a viscosity of 700 cps. (It is referred to as "Acrylic" in Table I.) The Witcobond™ 290H (60 percent solids) is an anionic polyurethane dispersion obtained from Witco Chemical Industries. (It is referred to as "PolyU" in Table I.) It has a solids content of 65 weight percent, a pH of 7.5, and a Brookfield viscosity of 400 cps at 25 degrees C. In a polyethylene beaker the above amount of epoxy functional compound dispersion was added followed by carboxyl functional acrylic polymer emulsion and anionic polymer dispersion. The ingredients were mixed for 2 to 3 minutes at about 30 to 40 rpms. The mixed solution was coated at about 0.2 gms per 1 inch square (0.03 g/cm 2 ) area on two steel plates (2.5 cm x 20 cm), the plates were heated at 60 degrees C for 4 minutes, then the plates were joined together via their coated areas to make a lap shear bond and further heated at 170 degrees C for 15 minutes. A sample of the solution was also cast on a release liner and heated under identical conditions. The resulting film was subjected to DMA testing. The weight percent liquids, weight percent solids, and component ratios are listed in the Table I below. Example 2 The following components were used: 11.11 grams of Epirez™ 3510-W-60 (60 percent solids), 22.22 grams of Maincote™ AE-58 (42.5 percent solids), and 66.67 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Example 3 The following components were used: 8.33 grams of Epirez™ 3510-W-60 (60 percent solids), 25.00 grams of Maincote™ AE-58 (42.5 percent solids), and 66.67 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Example 4 The following components were used: 7.69 grams of Epirez™ 3510-W-60 (60 percent solids), 15.39 grams of Maincote™ AE-58 (42.5 percent solids), and 76.92 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Overlap Shear Strength of Example -4 Overlap test samples were prepared as described in the overlap shear test. These samples were exposed to 80% relative humidity at 38°C in a Blue-M relative humidity cabinet (available from Blue M Electric Company, a unit of General Signal) for 8 weeks. The samples were taken out after 2, 6 and 8 weeks (wks) and tested for their overlap shear strength. The results of the average of three samples are given below: Initial 2 wks exposure 6 wks exposure 8 wks exposure (before exposure) 1950 N 1980 N 2200 N 1600 N The above data indicates that samples were able to retain more than 82% of their initial strength. Example 5 The following components were used: 7.69 grams of Epirez™ 3510-W-60 (60 percent solids), 30.77 grams of Maincote™ AE-58 (42.5 percent solids), and 61.54 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Example 6 The following components were used: 12.19 grams of Epirez™ 3510-W-60 (60 percent solids), 14.64 grams of Maincote™ AE-58 (42.5 percent solids), and 73.17 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Example 7 The following components were used: 5.26 grams of Epirez™ 3510-W-60 (60 percent solids), 31.58 grams of Maincote™ AE-58 (42.5 percent solids), and 63.16 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except for the ingredient amounts. Comparative Example 1 (Cl) The following components were used: 100.0 grams of Witcobond™ 290H (60 percent solids). The procedure of Example 1 was followed except that Epirez™ 3510-W-60 and Maincote™ AE-58 were not included and that Witcobond™ 290H was used in a different amount. Comparative Example 2 (C2) The following components were used: 33.33 grams of Epirez™ 3510-W-60 (60 percent solids), and 66.67 grams of Maincote™ AE-58 (42.5 percent solids). The anionic polyurethane dispersion was not included. The procedure of Example 1 was followed except for the components and amounts used. Comparative Example 3 (C3 The following components were used: 20.00 grams of Epirez™ 3510-W-60 (60 percent solids), and 80.00 grams of Maincote™ AE-58 (42.5 percent solids). The anionic polyurethane dispersion was not included. The procedure of Example 1 was followed except for the components and amounts used. Table I *by weight solids Tables II to VII include data, some of which was used in providing Figs. -6, respectively. Table II Table III Table IV Table V Table VI Table VII Fig. 1 is a graphical representation of storage modulus ( G 1 ) versus temperature for the vibration dampers of Examples 1, 2, and 3. The data presented in Fig. 1 demonstrates that for intermediate polyurethane content (72 weight percent solid), increasing the epoxy functional compound content only slightly increases the modulus. The modulus depends almost solely on the polyurethane content. This type of ternary composition provides a modulus that gradually decreases from about 100 MPa to about 0.3 MPa over a broad temperature range (broad transition zone). Fig. 2 is a graphical representation of tan delta versus temperature for the vibration dampers of Examples 1, 2, and 3. The data presented in Fig. 2 demonstrates two damping peaks at low and high temperatures corresponding to the polyurethane and the epoxy functional compound/carboxyl functional acrylic polymer component, respectively. For intermediate polyurethane content (72%wt solid), increasing the epoxy functional compound content slightly increases the tan delta peak at low temperatures while it decreases the peak at high temperature. Fig. 3 is a graphical representation of storage modulus (G) versus temperature for the vibration dampers of Examples 4, 5, 6, and 7. The data presented in Fig. 3 demonstrates that for varying polyurethane content the modulus decreases for increasing polyurethane concentration. Increasing the epoxy functional compound content slightly increases the modulus. The modulus depends almost solely on the polyurethane content. Therefore, the modulus can be adjusted by the polyurethane content, while keeping a broad transition zone. Fig. 4 is a graphical representation of tan delta versus temperature for the vibration dampers of Examples 4, 5, 6 and 7. The data presented in Fig. 4 demonstrates two damping peaks at low and high temperatures corresponding to the polyurethane and the epoxy functional compound/carboxyl functional acrylic polymer component, respectively. For varying polyurethane content, the intensity of the low temperature peak is higher at high polyurethane content (Examples 4 and 6). Similarly, the intensity of the high temperature peak is higher at low polyurethane content (Examples 5 and 7). Fig. 5 is a graphical representation of storage modulus (G 1 ) versus temperature for the vibration dampers of Comparative Examples 1 , 2, and 3. The data presented in Fig. 5 demonstrates that while the polyurethane modulus (Comparative Example 1) is much lower than the modulus of the Examples 1 to 7, it does not offer a broad transition zone. The epoxy functional compound/carboxyl functional acrylic polymer binary blends (Comparative Examples 2 and 3) demonstrate that increasing the epoxy functional compound content increases the modulus. The modulus of Comparative Examples 2 and 3 is higher than the modulus of Examples 1 to 7 and does not offer a broad transition zone either. Fig. 6 is a graphical representation of tan delta versus temperature for the vibration dampers of Comparative Examples 1, 2, and 3. The data presented in Fig. 6 demonstrates two damping peaks at low and high temperatures corresponding to the polyurethane and the epoxy functional compound/carboxy functional acrylic polymer component, respectively. In these comparative examples the damping peaks are narrow. The pure polyurethane (Comparative Example 1) exhibits a peak at low temperature falling below 0.3 at about 10 degrees C. The epoxy functional compound/carboxyl functional acrylic polymer binary blends (Comparative Examples 2 and 3) demonstrate that increasing the epoxy functional compound content increases the peak temperature. However, Comparative Examples 2 and 3 fail to offer a broad damping peak. In this case, tan delta is greater than 0.3 only between 20°C and 65°C approximately for Comparative Example 2. Similarly, it is greater than 0.3 above 40°C for Comparative Example 3. While this invention has been described in connection with specific embodiments, it should be understood that it is capable of further modification. The claims herein are intended to cover those variations which one skilled in the art would recognize as the equivalent of what has been described herein.

Claims: WE CLAIM 1. A method of vibrationally damping an article, comprising applying a vibration damper to the article, wherein the vibration damper comprises a vibration damping material, wherein the vibration damping material comprises a viscoelastic material, wherein the viscoelastic material is a polymerization product of a composition that comprises: (a) about 2 to about 18 percent by weight of an epoxy functional compound(s); (b) about 4 to about 40 percent by weight of a carboxyl functional acrylic polymer(s); (c) about 42 to about 94 percent by weight of a polyurethane(s); wherein the weight percentages of (a), (b), and (c) are based upon the total weight of (a) plus (b) plus (c); and (d) 0 to about 80 percent by weight of water based upon the total weight of (a) plus (b) plus (c) plus (d);. and wherein the weight ratio of the epoxy functional compound(s) to carboxyl functional acrylic polymer(s) is about 70:30 to about 5:95; and wherein the weight ratio of the epoxy functional compound(s) to polyurethane(s) is about 3:97 to about 25:75. The method of claim 1 wherein the composition is free of organic solvent. 3. A method of vibrationally damping an article, comprising applying a vibration damper to the article, wherein the vibration damper comprises a vibration damping material, wherein the vibration damping material comprises a viscoelastic material, wherein the viscoelastic material is a polymerization product of a composition that comprises: (a) about 4 to about 16 percent by weight of an epoxy functional compound(s); (b) about 6 to about 35 percent by weight of a carboxyl functional acrylic polymer(s); (c) about 60 to about 90 percent by weight of a polyurethane(s); wherein the weight percentages of (a), (b), and (c) are based upon the total weight of (a) plus (b) plus (c); and (d) 0 to about 80 percent by weight of water based upon the total weight of (a) plus (b) plus (c) plus (d); wherein the weight ratio of the epoxy functional compound(s) to carboxyl functional acrylic polymer(s) is about 60:40 to about 10:90; and wherein the weight ratio of the epoxy functional compound(s) to polyurethane(s) is about 5:95 to about 20:80. 4. The method of claim 3 wherein the composition is free of organic solvent. 5. The method of claim 1 wherein the composition comprises: (a) about 5 to about 14 percent by weight of an epoxy functional compound(s); (b) about 10 to about 30 percent by weight of a carboxyl functional acrylic polymer(s); (c) about 65 to about 85 percent by weight of a polyurethane(s); wherein the weight percentages of (a), (b), and (c) are based upon the total weight of (a) plus (b) plus (c); and (d) 0 to about 80 percent by weight water based upon the total weight of (a) plus (b) plus (c) plus (d); wherein the weight ratio of the epoxy functional compound(s) to carboxyl functional acrylic polymer(s) is about 55:45 to about 15:85; and wherein the weight ratio of the epoxy functional compound(s) to polyurethane(s) is about 7:93 to about 15:85. 6. The method of claim 5 wherein the composition is free of organic solvent. 7. A damped article comprising: (a) an article to be damped; and (b) a vibration damper applied to the article, wherein the vibration damper comprises a vibration damping material, wherein the vibration damping material comprises a viscoelastic material, wherein the viscoelastic material is a polymerization product of a composition that comprises: (a) about 2 to about 18 percent by weight of an epoxy functional compound(s); (b) about 4 to about 40 percent by weight of a carboxyl fiinctional acrylic polymer(s); (c) about 42 to about 94 percent by weight of a polyurethane(s); wherein the weight percentages of (a), (b), and (c) are based upon the total weight of (a) plus (b) plus (c); and (d) 0 to about 80 percent by weight of water based upon the total weight of (a) plus (b) plus (c) plus (d); and wherein the weight ratio of the epoxy functional compound(s) to carboxyl fiinctional acrylic polymer(s) is about 70:30 to about 5:95; and wherein the weight ratio of the epoxy functional compound(s) to polyurethane(s) is about 3:97 to about 25:75. 8. The article of claim 7 wherein the composition is free of organic solvent. 9. The damped article of claim 7 wherein the article is selected from the group consisting of cameras, tape recorders, loud speakers, covers, and panels. 10. The method of claim 1 wherein the article is selected from the group consisting of cameras, tape recorders, loud speakers, covers, and panels.

Inventors: LAVALLEE CLAUDE, SENGUPTA ASHOK, LAVALLEE, CLAUDE, SENGUPTA, ASHOK
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1997
Main classification: C09D175
IPC codes: C09D175, F16F1