Patent Application
20070034432
The present application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/696,183, filed Jul. 1, 2005, hereby incorporated by reference.
Thermally expansible materials have long been used in the automotive industry and in several other industries. Thermally expansible materials are used for sound-deadening (baffling) purposes and for structural reinforcement purposes. For example, certain expansible materials can be molded onto a carrier and placed into an automotive cavity such as a pillar. Then, the expansible materials can be heated to an activation temperature. When the material is activated, it expands. Upon expansion, the material adheres to at least part of the automotive cavity, effectively sealing the cavity. Following expansion, the material is cured. The cured material has a sound-deadening or baffling effect.
Additionally, by way of example, certain expandable materials can provide structural reinforcement to surfaces, including surfaces in automobiles. For example, an expansible material (by itself or together with a carrier) can be disposed on, adjacent or near a substrate such as a plastic surface or a metal surface in an automotive structure such as a frame rail. The material is then heated to an activation temperature. When the material is activated, it expands. Upon expansion, the material adheres to at least a portion of the substrate. Following expansion, the material is cured. The cured material provides structural reinforcement for the substrate. That is, the substrate is less easily bent, twisted, crinkled and the like due to the presence of the cured material.
The Sika Corporation of Madison Heights, Mich., sells thermally expansible materials under the SIKABAFFLE trade name, which are described in U.S. Pat. Nos. 5,266,133 and 5,373,027, both of which are incorporated herein by reference in their entireties. The Sika Corporation also sells thermally expansible reinforcer materials under the trade name SIKAREINFORCER. A series of these thermally expansible reinforcer materials, owned by the Sika Corporation, are described in the U.S. Pat. No. 6,387,470, incorporated herein by reference in its entirety.
There are certain desirable traits for thermally expansible materials used for reinforcement purposes. It is favorable for a thermally expansible material, in its uncured state, to be of a consistency that is easy to process using existing manufacturing equipment and to have a surface that is substantially tack free for ease of handling. It is favorable for an uncured expansible material to avoid premature curing and/or other degradation that could result from exposure to a high humidity, high temperature environment.
A thermally expansible material, in its cured state, should substantially maintain its mechanical properties across a temperature range of from about −40° C. to about 80° C. A mechanical property is substantially maintained if it is of the magnitude x at its highest point in that temperature range and is about 0.8 x at its lowest point in that temperature range. A cured material should have a glass transition temperature of at least about 90° C. or higher. Other desired glass transition temperatures for cured materials are at least about 95° C., at least about 100° C., and at least about 105° C.
A solid thermally expansible material is provided to satisfy one or more of the desired traits for thermally expansible reinforcement materials. Several embodiments of a solid thermally expansible material are described herein. The described embodiments are not intended to limit the scope of the appended claims. A solid thermally expansible material comprises a solid epoxy resin (and is substantially free of liquid epoxy resin and semi-solid epoxy resin), an impact modifier and a curing agent. The uncured expansible material has an outer surface that is substantially tack free in at least temperatures ranging from about 0° C. to about 40° C., and can remain substantially tack free at temperatures nearing 50° C. because there is substantially no presence of a liquid epoxy resin or a semi-solid epoxy resin sufficient to migrate to the outer surface of the material to cause such tack. Surprisingly, the uncured solid thermally expansible material is not brittle. Thus, the uncured material is surprisingly easy to process using common manufacturing equipment, even in the absence or substantial absence of liquid epoxy resin and semi-solid epoxy resin.
An embodiment of the solid thermally expansible material comprises an impact modifier that is substantially free of natural or synthetic rubber. In this embodiment, the impact modifier comprises one or more thermoplastic chemicals that include functional groups to react with the epoxy groups of the epoxy resin to increase the over-all stability of the expansible material. The solid thermally expansible material in this embodiment is unexpectedly stable, exhibiting little to no phase separation between the epoxy resin and the one or more thermoplastic impact modifiers. This impact modifier brings a surprising degree of processibility to the solid thermally expansible material, given the absence or substantial absence of rubber, liquid epoxy resin, or semi-solid epoxy resin. The absence or substantial absence of rubber in the impact modifier provides an added advantage: the glass transition temperature of the cured material in this embodiment is at least about 100° C., and can be at least about 105° C. or at least about 110° C.
An embodiment of the solid thermally expansible material comprises an impact modifier that comprises natural or synthetic rubber. This embodiment can additionally include one or more thermoplastic compounds, which include functional groups to increase the over-all stability of the expansible material. The rubber in this embodiment provides additional processibility to the solid material, while permitting the glass transition temperature of the cured material to be at least about 90° C., and can be at least about 95° C.
An embodiment of the solid thermally expansible material includes a moisture release control system comprising aramid fibers. It is difficult to fully resist or avoid all absorption of water into uncured thermally expansible materials during transport and storage in high temperature/high humidity environments. This embodiment complements efforts to avoid water absorption by regulating how water is released from the uncured material during heating/expansion. The presence of too much water in uncured expansible material is undesirable because it can cause damage to the expansible materials during expansion. This is because the heat during expansion causes violent bursts of steam through the foaming material, which results in irregular, non-uniform cell structure in the cured material. Surprisingly, it has been found that aramid fibers form a mesh-like physical screen that regulates the release of steam during expansion. This regulation reduces or minimizes the violent bursts of steam. Although aramid fibers have been disclosed in thermally expansible materials as thixotropic agents, they have not been disclosed for this new use.
In
Solid Epoxy Resins
“Epoxy resins” refer to a large range of chemicals containing multiple epoxy groups. Epoxy resins are well-known in the art and are described in the chapter entitled “Epoxy Resins” in the Second Edition of the Encyclopedia of Polymer Science and Engineering, Volume 6, pp. 322-382 (1986).
The term “solid” is used according to its ordinary meaning. A “solid” epoxy resin is solid and tack free at about room temperature (from about 20° C. to about 27° C.), and at about standard pressure. A solid epoxy resin as used herein is substantially free of liquid epoxy resin and semi-solid epoxy resin as those terms are used according to their ordinary meanings. A liquid epoxy resin is liquid at about room temperature and at about standard pressure, and a semi-solid epoxy resin has both solid and liquid physical characteristics, especially tackiness and tendency to block at about room temperature and at about standard pressure. “Substantially free” in this context means from 0% by weight of the epoxy resin content to less than about 1.5% by weight of the epoxy resin content of the solid thermally expansible material. In functional terms, the presence of liquid and semi-solid epoxy resin should be so minimal that any migration of liquid and semi-solid epoxy resin to an outer surface of the solid expansible material in its uncured form would be insufficient to cause the surface to have discernable tackiness to a human touch.
Solid epoxy resins that can be used with the solid thermally expansible material include solid bisphenol A resins made by advancement of bisphenol-A-diglycidyl ether with bisphenol A or by a taffy process, including without limitation type 1 to type 9 resins, such as: EPON 1001, 1004 and 1007 (available from Resolution Performance Products); ARALDITE GT7004, GT7071, GT7014, GT7255, GT7097 and GT9654 (available from Huntsman Advanced Materials), and DER 661, DER 663, and DER 664 (available from The Dow Chemical Co.). Additional solid epoxy resins include novolac-based epoxy resins, including without limitation: EPON Resin 1031 and 164 1007 (available from Resolution Performance Products), ARALDITE EPN 1180, ECN 1280, ECN 1285 and ECN 9699 (available from Huntsman Advanced Materials); and DEN 438 and 439 (available from The Dow Chemical Co.). Additional solid epoxy resins include multifunctional epoxy resins such as tris(hydroxyphenyl)methane triglycidyl ether (available as TACTIX 742 from The Dow Chemical Co.), glyoxal phenol novolac tetraglycidyl ether (available as ARALDITE XB 4399-3), crystalline epoxy resins such as triglycidyl isocyanurate (available as PT810 from Huntsman), and terephthalic acid diglycidyl ester with trimellitic acid triglycidyl ester (available as PT910 from Huntsman).
Suitable solid epoxy resins can have Mettler softening points in the range of from about 65° C. to about 160° C. (more preferably, about 70° C. to about 120° C.). Suitable solid epoxy resins can have an average of about two epoxy groups per molecule. Suitable solid epoxy resins may show epoxide equivalent weights in the range of from about 350 to about 2000 (more preferably, about 375 to about 1000). Numerous epoxy resins meeting these requirements are available from commercial sources known to those of skill in the art and/or can be created by blending more than one commercially available epoxy resins.
A solid epoxy resin or combination of solid epoxy resins can be present in the solid thermally expansible material, by weight percent, from about 40% to about 80% (more preferably, about from 50% to 80% or from 60% to about 75%), wherein 100% is the weight of the solid thermally expansible material.
Impact Modifiers or Tougheners
An “impact modifier,” also known as a “toughener,” refers to any material that is added to a formulation to improve the impact resistance of the formulation. Many commercially available impact modifiers are known in the art and are suitable for use in a solid thermally expansible material.
In one embodiment, an impact modifier comprises one or more thermoplastic chemical and the impact modifier is substantially free of natural or synthetic rubber. It is surprising that an impact modifier that is substantially free of rubber could impart sufficient processibility on a solid thermally expansible material. “Substantially free” in this context means from 0% to about 1.5% by weight of rubber. Thermoplastic chemicals that have functional groups capable of reacting with the epoxy groups on the solid epoxy resins are suitable for use with the solid thermally expansible material. In particular, as non-limiting examples, ethylene butyl acrylate with glycidyl methacrylate (EBA with GMA) to provide epoxy functionality (to react with the epoxy groups of the solid epoxy resin) may be used. Ethylene vinyl acetate with maleic anhydride (EVA with MAH) to react with the epoxy groups of the solid epoxy resin may be used. The solid thermally expansible material in this embodiment is unexpectedly stable, exhibiting little to no phase separation between the epoxy resin and the one or more thermoplastic impact modifiers. This impact modifier brings a surprising degree of processibility to the solid thermally expansible material, given the absence or substantial absence of rubber, liquid epoxy resin, or semi-solid epoxy resin. In Examples 10-14, these thermoplastic impact modifiers, substantially free of rubber, led to solid thermally expansible materials having a glass transition temperature of 102° C., 112° C., 108° C., 108° C. and 109° C., respectively.
In another embodiment, an impact modifier comprises rubber. The rubber can be natural or synthetic. In this embodiment, the impact modifier may also include one or more thermoplastic chemicals that are functionalized to react with the epoxy groups of the solid epoxy resin. Exemplary impact modifiers for this embodiment include, without limitation, the rubbers disclosed in WO 2004/055092 (incorporated herein by reference in its entirety), solid grafted rubber, epoxy-polyurethane hybrids, isocyanate prepolymers (such as isocyanate-terminated polyether polyols) having molecular weights in the range between 1,000 to 10,000 daltons, maleic anhydride-modified ethylene propylene diene monomer (EPDM), styrene-butadiene block copolymers with hydrogenated polybutadiene (SEBS); acid-functional ethylene-vinyl acetate terpolymers (EVA), carboxylated styrene-butadiene rubber (CSBR), carboxylated nitrile rubber (such as HYCAR CTBN from Noveon); epoxidized polybutadiene, epoxidized natural rubber, epoxidized soybean oil; thermoplastic elastomers such as HYTREL, available from DuPont or poly-p-phenylene ether; solid hydroxyl-containing materials such as bisphenol A; and polyesters with terminal carboxylic functional groups. Other impact modifiers suitable for use with this embodiment include core-shell impact modifiers including, without limitation, triblock copolymers like methacrylate-butadiene-styrene (MBS) impact modifiers and acrylate-styrene-acrylic acid (ASA) impact modifiers. Commercially available MBS core shell impact modifiers include PARALOID BTA-753 (available from Rohm & Haas) and KANA ACE B-564 (available from Kaneka) and SBM (like SBM AF-X22 available from Arkema). Commercially available ASA core shell impact modifiers include GELOY 1020 from General Electric. Suitable examples include core shell impact modifiers of polysiloxane modified acrylates commercially available as GENIOPERL M23A from Wacker.
In Examples 1-5, the use of rubber-containing impact modifiers led to solid thermally expansible materials having a glass transition temperature of 95° C., 99° C., 100° C., 101° C. and 101° C., respectively.
An impact modifier or combination of impact modifiers can be present in the solid thermally expansible material, by weight percent, from about less than about 20% (more preferably, from about 5% to about 15%), wherein 100% is the weight of the solid thermally expansible material.
Heat-Activated Foaming Agents
A “heat-activated foaming agent,” sometimes referred to by those of skill in the art as a “blowing agent,” is a physical agent or chemical agent that causes its host to expand by a pre-determined amount upon the application of a pre-determined amount of heat.
Any known heat-activated physical foaming agent may be used in a solid thermally expansible material. Suitable physical heat-activated foaming agents include, without limitation, those in the EXPANCEL microsphere product line manufactured by Akzo Nobel. EXPANCEL microspheres are small, spherical plastic particles that encapsulate a low molecular weight hydrocarbon like isobutane or isopentane. When heated to the boiling points of the particular hydrocarbon, the microspheres can expand more than 40 times in volume. EXPANCEL is commercially available in many different grades and forms.
Any known heat-activated chemical foaming agent may be used in a solid thermally expansible material. Suitable chemical heat-activated foaming agents include azodicarbonamide and its modified compounds, p,p′-oxybis(benzenesulfonyl hydrazide), benzenesulfonyl hydrazide, dinitrosopentamethylene tetramine, p-toluenesulfonyl semicarbazide, and 5-phenyltetrazole.
Heat activation may result from either the external application of heat, or internal activation resulting from the release of heat in an exothermic reaction. In one embodiment, the temperature at which the expansion is activated is at least about 180° C., more preferably at least about 150° C.
A heat activated foaming agent or combination of foaming agents can be present in the solid thermally expansible material, by weight percent, from about 0.1% to about 5% (more preferably, about 0.5% to about 3%) wherein 100% is the weight of the solid thermally expansible material. A heat-activated foaming agent or combination of heat-activated foaming agents cause expansion from its original pre-activation uncured state (which is 100% for reference purposes) by about 20% to about 300% (more preferably, by about 50% to about 200%).
Other Ingredients
Embodiments of a thermally expansible material may comprise at least one “filler.” Suitable fillers include fibrous fillers, spherical fillers, plate-like fillers, and nanoparticle fillers. Fibrous fillers can be inorganic, such as glass fiber or wollastonite fiber, or in the alternative, can be natural or organic. Natural or organic fillers include, without limitation, carbon fiber, aramid KEVLAR fiber, cellulosic fibers, jute, hemp, and the like. Spherical fillers can be organic or inorganic. Without limitation, organic spherical fillers can be polymeric spheres, and inorganic spherical fillers can be glass microballons, ceramic microspheres, fumed silica (organically modified or unmodified), pyrogenic silica (organically modified or unmodified), and the like. Plate-like fillers may be inorganic, such as graphite, talc, mica, and other materials known to those of skill in the art. Nanoparticle fillers can include, without limitation, phyllosilicate like illites or organically modified montmorillonite nanoclays (such as CLOISITE 30B or CLOISITE 93A available from Southern Clay), nanosilica (preferably with reactive groups), and carbon nanotube, hybrid organic-inorganic copolymers-polyhedral-oligomeric silsesquioxanes (POSS).
Other suitable fillers known in the thermosettable resin art may be used including, for example, calcium carbonate (including coated and/or precipitated calcium carbonate), ceramic fibers, calcium oxide, alumina, clays, sand, metals (for example, aluminum powder), glass or ceramic macrospheres, thermoplastic resins, thermoset resins, and carbon (all of which may be solid or hollow, expanded or expansible) and the like.
Fillers can be conical in shape or plate-like. Platelet sizes may range from 1 to 10 mm in length, and 5 to 10 microns in width. In one embodiment, a filler comprises a mixture of fibers having different shapes and sizes. Such a mixture has improved packing density, which results in improved impact resistance at low temperatures, such as temperatures ranging from about −40° C. to about −5° C. Mineral fillers may be surface treated with example silanes to improve adhesion to the organic matrix. Epoxy silanes or amino silanes are suitable surface treatment.
A filler or combination of fillers can be present in the solid thermally expansible material, by weight percent, from about 5% to about 45% (more preferably, about 10% to about 30%, still more preferably from about 15% to about 25%), wherein 100% is the weight of the solid thermally expansible material.
Embodiments of a thermally expansible material may comprise at least one “curing agent” or “hardener,” sometimes described as a “curative.” A curing agent is used herein to describe a chemical composition that aids in the hardening of a thermally expansible material. Those of skill in the art sometimes refer to such chemicals as activators, catalysts or accelerators. While certain curatives promote curing by catalytic action, others participate directly in the reaction of the solid epoxy resin and are incorporated into the thermoset polymeric network formed by a ring-opening reaction, ionic polymerization, and/or crosslinking of the resin. Many commercially available hardeners known to those of skill in the art are described in the chapter in the Encyclopedia of Polymer and Engineering referenced above.
A suitable curing agent or hardener is solid at about room temperature, and remains latent (does not promote any cross-linking reactions) up to about 140° C. Such a hardener can be referred to as being “latent.” More than one hardener may be used.
Suitable curing agents or hardeners include dicyandiamide; aromatic diamines including without limitation 3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, and blends thereof; imidazoles; multifunctional solid anhydrides/acids; and phenols, including mononuclear phenols, such as resorcinol, hydroquinone and N,N-bis(2-hydroxyethyl)aniline, or polynuclear phenols, such as p,p′-bis(2-hydroxyethylamino)diphenylmethane.
Other suitable curing agents or hardeners include amino compounds, amine salts, and quaternary ammonium compounds, amine-epoxy adducts, boron trihalide amine adducts, ureas, and guanidines. Suitable boron trihalide adducts include boron trichloride adducts of amines such as monoethanolamine, diethylamine, dioctylmethylamine, triethylamine, pyridine, benzylamine, benzyldimethyl amine, and the like. Boron trichloride amine adduct curatives are commercially available from CVC Specialty Chemicals, Inc.
A curing agent or combination of curing agents can be present in the solid thermally expansible material, by weight percent, from about 0.1% to about 5% (more preferably, about 0.2% to about 2%), wherein 100% is the weight of the solid thermally expansible material.
Embodiments of a thermally expansible material may comprise at least one “accelerator,” which can either quicken the cure speed or lower the cure temperature of a thermally expansible material. Those of skill in the art sometimes use this term interchangeably with “hardeners” and “curatives,” as described above. Suitable accelerators include, without limitation, substituted ureas, phenols, and imidazoles and imidazole salts. Exemplary ureas include phenyl dimethyl urea, 4-chlorophenyl dimethyl urea, 2,4-toluene bis(dimethyl urea), 4,4′-methylene bis(phenyl dimethyl urea), cycloaliphatic bisurea, and the like. Exemplary imidazoles include 2-methyl imidazole, 2-isopropyl imidazole, 2-phenyl imidazole, 2-phenyl 4-methyl imidazole, 2-heptadecyl imidazole, and the like.
Some accelerators are commercially available through CVC Specialty Chemicals, such as the OMICURE U Series and the OMICURE B Series. Others are available through Air Products, including the IMICURE series, the CUREZOL series and the AMICURE UR series, from Degussa as the Dyhard UR series and Dyhard MI series. Also available from Adeka is Adeka 4338S. A suitable imidazole salt is Vestagon B55 available from Degussa.
An accelerator or combination of accelerators can be present in the solid thermally expansible material, by weight percent, from about 0.01% to about 5% (more preferably, about 0.1% to about 2%), wherein 100% is the weight of the solid thermally expansible material.
Embodiments of a thermally expansible material may comprise at least one “thixotropic agent,” which is an additive that brings thixotropy to a product. “Thixotropy” refers to a property of certain materials to soften upon agitation, and to return to its original state when allowed to rest. Thixotropic agents help prevent and reduce sag at the temperature of the final composition following thermal expansion.
Suitable thixotropic agents include unmodified or hydrophobically modified fumed silica and precipitated silica. Other suitable thixotropic agents include organically modified phyllosilicate clays such as bentonite, laponite, montmorillonite, and the like. Other thixotropic agents are known to those of skill in the art, such as coated precipitated calcium carbonate and polyamide waxes are suitable for use in a solid thermally expansible material, whether organic or inorganic. Also suitable are urea derivatives, which can by made, without limitation, by reacting butylamine with MDI, and used as a dispersion in a non-migrating reactive liquid rubber. Some materials identified as fillers above also have thixotropic effects, such as platelet fillers and fiber fillers.
A thixotropic agent or combination of thixotropic agents can be present in the solid thermally expansible material, by weight percent, from about 0.5% to about 10% (more preferably, about 1% to about 6%, still more preferably from about 2% to about 5%), wherein 100% is the weight of the solid thermally expansible material.
Embodiments of the solid thermally expansible material may also be include other additives including but not limited to adhesion promoters, colorants, stabilizers, plasticizers, wetting agents, antioxidants, each of which is commercially available and well known in the art.
Other additives can be present, by weight percent, from about 0.01% to about 10% (more preferably, about 0.1% to about 5%, still more preferably about 0.2% to about 3%), wherein 100% is the weight of the solid thermally expansible material.
Processing the Solid Thermally Expansible Material
A solid thermally expansible material may be compounded or formed into pellets using standard manufacturing equipment, then injection molded onto a carrier as described in U.S. Pat. No. 6,649,243, hereby incorporated by reference in its entirety. Alternatives to injection molding are well known in the art and contemplated for use with the solid thermally expansible material. The injection molding (or any other method selected to process the uncured material) occurs at temperatures below the cure activation temperature for the expansible material. The expansible material may be processed, shaped or molded using any method known to those of skill in the art, including extrusion, performs, thermoforms with a carrier, including without limitation, a joint, a frame, or a pillar, and thermoforms without a carrier.
As exemplified in
The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the present invention and/or the scope of the appended claims.
The following examples were prepared by mixing the ingredients in a blender, then compounding same in a twin screw extruder with a pelletizer. Specimens for mechanical testing were prepared by injection molding. Glass transition temperatures were measured by DSC unless otherwise specified. All percentages of ingredients are weight percents.
The mechanical properties for examples 1 and 2 are listed below in Table 2.
*Approximation based upon measurement of identical formulation absent blowing agent.
The mechanical properties for examples 3 -5 are listed below in Table 4.
*Approximation based upon measurement of identical formulation absent blowing agent.
The mechanical properties for example 6 are listed below in Table 6.
*Approximation based upon measurement of identical formulation absent blowing agent.
The mechanical properties for examples 8 and 9 are listed below in Table 8.
*Approximation based upon measurement of identical formulation absent blowing agent.
The mechanical properties for examples 10 - 14 are listed below in Table 10.
*Measured by DMA.
Those skilled in the art will recognize that the present invention is capable of many modifications and variations without departing from the scope thereof. Accordingly, the detailed description and examples set forth above are meant to be illustrative only and are not intended to limit, in any manner, the scope of the invention as set forth in the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| 60696183 | Jul 2005 | US |
