Patent Application
20130287980
The present disclosure relates generally to curable sealant compositions having low temperature sealing ability improved over convention curable sealing compositions.
Sealants are used in a broad range of applications from automobiles to aircraft engines to contain or prevent solids, liquids, and/or gases from moving across a mating surface, boundary or interfacial region into or on a surrounding or adjacent area, region or surface. Sealants are available in many forms from low viscosity liquids to highly thixotropic pastes and depending on the application can vary in properties from a rigid glassy material to a rubbery elastic network. Elastomers are an important class of polymeric materials useful as sealing compositions and the focus of the current invention.
Sealants formulated with monomers, oligomers, polymers and/or other ingredients that react to form new covalent bonds that increase the molecular weight of the chemical backbone leading to entanglements and/or chemical cross-links that exhibits elastic properties are generally referred to as “curing” compositions. Sealants containing ingredients that do not react but exhibit elastic properties based on the thermodynamic properties of the polymer, entanglement of network chains or other molecular interactions are generally referred to as “non-curing” formulations.
Definitions used in the literature to describe rubbery and elastomer materials are very similar and sometimes used interchangeably. Elastomer is more general and typically refers to the elastic-bearing properties of a material. Rubber was originally referred to as an elastomer derived from naturally occurring polyisoprene and has expanded over the years to include both natural and synthetic based materials. IUPAC Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”); compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997) defines an elastomer as a polymer that displays rubber-like elasticity. Elastomers are defined in the Physical Polymer Science Handbook by L. H. Sperling John Wiley & Sons, Inc., Publications, New York (2001) as an amorphous, cross-linked polymer above its glass transition temperature (Tg).
The equation of state for rubber elasticity describes the relationship between macroscopic sample deformation of a polymer (chain extension) and the retractive stress of the elastomer. The theory of rubber elasticity, derived from the second law of thermodynamics, states that the retractive stress of an elastomer arises as a result of the reduction in entropy upon extension and not changes in enthalpy. As a polymer chain is extended the number of conformations decrease (entropy decreases) and the retractive stress increases. Sperling writes that a long-chain molecule, capable of reasonably free rotation about its backbone, joined together in a continuous network is required for rubber elasticity.
Where σ is the stress, n is the number of active network chains per unit volume, R is the ideal gas constant, T is temperature, a is the chain extension, and ri2/ro2 is the front factor that is approximately equal to one. The equation of state predicts that as the extension of an elastomer increases the observed stress increases. The stress is the retractive force created when for example an elastomer is placed under tension, biaxial tension or compression.
The theory of rubber elasticity can be observed in practice when a cured seal operating at a temperature above its glass transition temperature is compressed and exhibits sealing forces that can be measured using instruments know in the art. The glass transition temperature of the elastomer in the cured seal defines an important boundary condition where free rotation of the main chain is restricted as the elastomer transitions from the rubbery to the glassy region resulting in a loss of molecular free rotation, molecular chain extension and the resulting retractive stress. As the temperature of the elastomer approaches the glass transition temperature, the resulting elastic retractive force approaches zero.
The utility of an elastomeric sealant is measured by the ability of the cured sealant composition to provide a positive sealing force when exposed to operating conditions over the lifetime of the product. Temperature is an important factor that affects the performance of a sealant and can have a significant impact on the operating lifetime. The temperature range in harsh ambient conditions can vary from +150° C. to −65° C. In less severe applications temperatures can vary from +100° C. to −40° C.
It was observed that some cured elastomeric sealants at temperatures well above the glass transition temperature of the overall polymer network have a sealing force that decreases to nearly zero. In one case a cured, elastomeric sealant with a −61° C. Tg, measured by DSC, had a very low sealing force at −40° C. that would be unacceptable for most sealing applications.
It is known from statistical thermodynamics of rubber elasticity that the force generated during the deformation of an elastomer is directly proportional to the end-to-end distance of the cross-linked network and the temperature of the matrix. When an elastomer is deformed the retractive force should remain positive, in the rubbery region, as long as the temperature is above the Tg. There is nothing in the above equation of state of rubbery elasticity that would predict that changing the glassy or hard segment in an elastomer having a single Tg, and which exhibits no other first or second order thermodynamic transitions, could increase the low temperature sealing force within the rubbery region.
One aspect of the disclosure provides a curable elastomeric sealant composition. The composition is flowable and can be cured to a cross linked form to provide cured reaction products that exhibit elastomeric properties. The curable elastomeric sealant composition can include a cross linkable elastomeric oligomer; an initiator or cross-linking agent; a glassy monomer and/or a rubbery monomer; and optionally one or more of a catalyst; a filler; an antioxidant; and an optional reaction modifier. The cross linkable elastomeric sealant composition can be prepared by reacting a cross linkable elastomeric oligomer having a Tg with at least one of a glassy monomer and a rubbery monomer. Cured reaction products of the composition have a single Tg and retain a higher sealing force at low temperatures (but above the cured product Tg) as compared to a curable composition made from the same cross linkable elastomeric oligomer but without the glassy and/or rubbery monomer.
In one embodiment the cross linkable elastomeric oligomer is a telechelic polyisobutylene (PIB) based material terminated at each end with acrylate moieties.
Another aspect provides a component having a first predetermined sealing surface aligned with a second predetermined sealing surface. A cured reaction product of a polyisobutylene (PIB) based composition is disposed between the sealing surfaces to prevent movement of materials such as liquids, gasses or fuels between the aligned sealing surfaces. The composition may be cured in contact with one, both or none of the sealing surfaces. Advantageously, the seal formed by the cured reaction product provides low temperature sealing (about −40° C.) within the rubbery region along with excellent resistance to moisture, water, glycols, acids, bases and polar compounds.
The disclosed compounds include any and all isomers and stereoisomers. In general, unless otherwise explicitly stated the disclosed materials and processes may be alternately formulated to comprise, consist of, or consist essentially of, any appropriate components, moieties or steps herein disclosed. The disclosed materials and processes may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants, moieties, species and steps used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objective of the present disclosure.
When the word “about” is used herein it is meant that the amount or condition it modifies can vary some beyond the stated amount so long as the function and/or objective of the disclosure are realized. The skilled artisan understands that there is seldom time to fully explore the extent of any area and expects that the disclosed result might extend, at least somewhat, beyond one or more of the disclosed limits. Later, having the benefit of this disclosure and understanding the concept and embodiments disclosed herein, a person of ordinary skill can, without inventive effort, explore beyond the disclosed limits and, when embodiments are found to be without any unexpected characteristics, those embodiments are within the meaning of the term about as used herein.
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
A curable elastomeric sealant composition is a composition that is flowable and can be cured to a cross linked form to provide cured reaction products of the composition that exhibit elastomeric properties. The curable elastomeric sealant composition can include a cross linkable elastomeric oligomer; an initiator or cross-linking agent; a glassy monomer and/or a rubbery monomer; and optionally one or more of a catalyst; a filler; an antioxidant; and an optional reaction modifier. The cross linkable elastomeric sealant composition can be prepared by reacting a cross linkable elastomeric oligomer having a Tg with at least one of a glassy monomer and a rubbery monomer. The cross linkable elastomeric sealant composition can be cured by exposure to conditions and for a time sufficient to at least partially cross-link and cure that composition. Suitable cure conditions, depending on formulation of the cross linkable elastomeric sealant composition include exposure to heat and radiation such as actinic radiation.
Cured reaction products of the composition have a single Tg as measured by Differential Scanning calorimetry (DSC) and retain a higher sealing force at low temperatures (but above the cured product Tg) as compared to a curable composition made from the same cross linkable elastomeric oligomer but without the glassy and/or rubbery monomer.
A number of sealant chemistries are believed to be suitable for use in the sealant composition. These chemistries include fluoroelastomer; EPDM and other hydrocarbons; styrenic block elastomer; C4 and C5 monomers such as isoprene and isobutylene; acrylates and methacrylates; acrylic emulsion; ethylene acrylate elastomer; functionalized polyacrylate; silylated acrylate; silicone; silylated polyether; silylated polyester; silylated polyamide; polyurethane; silylated polyurethane; plastisol and polyvinyl chloride; polysulfide and polythioether; flexible epoxy; vinyl acetate-ethylene latex; unsaturated polyester; polyolefins, amides and acetates for example EVA. Non-curable chemistries such as oleoresinous based (for example linseed oil) sealants and bituminous sealants may also be useful.
The curable elastomeric sealant composition advantageously includes a cross linkable elastomeric oligomer. In one desirable embodiment the cross linkable elastomeric oligomer is a telechelic, polyisobutylene polymer with acrylate moieties at each end (polyisobutylene diacrylate or PIB diacrylate).
The curable elastomeric sealant composition can include a glassy monomer that is reacted with the cross linkable elastomeric oligomer. A glassy monomer has a glass transition temperature above the glass transition temperature of the cross linkable elastomeric oligomer. Typically the glassy monomer has a glass transition temperature above 20° C.
Some examples of glassy monomers include stearyl acrylate (Tg 35° C.); trimethylcyclohexyl methacrylate (Tg 145° C.); isobornyl methacrylate (Tg 110° C.); isobornyl acrylate (Tg 88° C.); and the FANCRYL methacryl esters marketed by Hitachi Chemical Corporation such as dicyclopentanylmethacrylate (FA-513M Tg 175° C.) and dicyclopentanyl Acrylate (FA-513AS, Tg 140° C.). Other examples of glassy and rubbery monomers are listed in the Tables at the end of the specification.
The curable elastomeric sealant composition can include a rubbery monomer that is reacted with the cross linkable elastomeric oligomer. A rubbery monomer has a glass transition temperature below the glass transition temperature of the glassy monomer. Typically the rubbery monomer has a glass transition temperature below 20° C. Some examples of rubbery monomers include isooctyl acrylate (Tg −54° C.); isodecyl acrylate (Tg −60° C.); isodecyl methacrylate (Tg −41° C.); n-lauryl methacrylate (Tg −65); and 1,12-dodecanediol dimethacrylate (Tg −37° C.). Other examples of glassy and rubbery monomers are listed in the Tables at the end of the specification.
The curable elastomeric sealant composition can include an initiator or cross-linking agent to at least partially cross-link and cure that composition.
The initiator or cross-linking agent can be a heat-cure initiator or initiator system comprising an ingredient or a combination of ingredients which at the desired elevated temperature conditions produce free radicals. Suitable initiators may include peroxy materials, e.g., peroxides, hydroperoxides, and peresters, which under appropriate elevated temperature conditions decompose to form peroxy free radicals which are initiatingly effective for the polymerization of the curable elastomeric sealant compositions. The peroxy materials may be employed in concentrations effective to initiate curing of the curable elastomeric sealant composition at a desired temperature and typically in concentrations of about 0.1% to about 10% by weight of composition.
Another useful class of heat-curing initiators comprises azonitrile compounds which yield free radicals when decomposed by heat. Heat is applied to the curable composition and the resulting free radicals initiate polymerization of the curable composition. Compounds of the above formula are more fully described in U.S. Pat. No. 4,416,921, the disclosure of which is incorporated herein by reference.
Azonitrile initiators of the above-described formula are readily commercially available, e.g., the initiators which are commercially available under the trademark VAZO from E.I. DuPont de Nemours and Company, Inc., Wilmington, Del.
The initiator or cross-linking agent can be a photoinitiator. Photoinitiators enhance the rapidity of the curing process when the photocurable elastomeric sealant composition is exposed to electromagnetic radiation, such as actinic radiation, for example ultraviolet (UV) radiation. Examples of some useful photoinitiators include, but are not limited to, photoinitiators available commercially from Ciba Specialty Chemicals, under the “IRGACURE” and “DAROCUR” trade names, specifically “IRGACURE” 184 (1-hydroxycyclohexyl phenyl ketone), 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369 (2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500 (the combination of 1-hydroxy cyclohexyl phenyl ketone and benzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (the combination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethyl pentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), and 819 [bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide] and “DAROCUR” 1173 (2-hydroxy-2-methyl-1-phenyl-1-propan-1-one) and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one); and the visible light [blue] photoinitiators, dl-camphorquinone and “IRGACURE” 784DC. Of course, combinations of these materials may also be employed herein.
Other photoinitiators useful herein include alkyl pyruvates, such as methyl, ethyl, propyl, and butyl pyruvates, and aryl pyruvates, such as phenyl, benzyl, and appropriately substituted derivatives thereof. Photoinitiators particularly well-suited for use herein include ultraviolet photoinitiators, such as 2,2-dimethoxy-2-phenyl acetophenone (e.g., “IRGACURE” 651), and 2-hydroxy-2-methyl-1-phenyl-1-propane (e.g., “DAROCUR” 1173), bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide (e.g., “IRGACURE” 819), and the ultraviolet/visible photoinitiator combination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethylpentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (e.g., “IRGACURE” 1700), as well as the visible photoinitiator bis(η5-2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium (e.g., “IRGACURE” 784DC). Useful actinic radiation includes ultraviolet light, visible light, and combinations thereof.
Desirably, the actinic radiation used to cure the photocurable elastomeric sealant composition has a wavelength from about 200 nm to about 1,000 nm. Useful UV includes, but is not limited to, UVA (about 320 nm to about 410 nm), UVB (about 290 nm to about 320 nm), UVC (about 220 nm to about 290 nm) and combinations thereof. Useful visible light includes, but is not limited to, blue light, green light, and combinations thereof. Such useful visible lights have a wavelength from about 450 nm to about 550 nm. Photoinitiators can be employed in concentrations effective to initiate curing of the curable elastomeric sealant composition at a desired exposure to actinic radiation and typically in concentrations of about 0.01% to about 10% by weight of composition.
The curable elastomeric sealant composition can include a catalyst to modify speed of the initiated reaction.
The curable elastomeric sealant composition can optionally include a filler. Some useful fillers include, for example, lithopone, zirconium silicate, hydroxides, such as hydroxides of calcium, aluminum, magnesium, iron and the like, diatomaceous earth, carbonates, such as sodium, potassium, calcium, and magnesium carbonates, oxides, such as zinc, magnesium, chromic, cerium, zirconium and aluminum oxides, calcium clay, fumed silicas, silicas that have been surface treated with a silane or silazane such as the AEROSIL products available from Evonik Industries, silicas that have been surface treated with an acrylate or methacrylate such as AEROSIL R7200 or R711 available from Evonik Industries, precipitated silicas, untreated silicas, graphite, synthetic fibers and mixtures thereof. When used filler can be employed in concentrations effective to provide desired physical properties in the uncured composition and cured reaction products and typically in concentrations of about 0.1% to about 70% by weight of composition.
The curable elastomeric sealant composition can optionally include an anti-oxidant. Some useful antioxidants include those available commercially from Ciba Specialty Chemicals under the tradename IRGANOX. When used, the antioxidant should be used in the range of about 0.1 to about 15 weight percent of curable composition, such as about 0.3 to about 1 weight percent of curable composition.
The curable elastomeric sealant composition can include a reaction modifier. A reaction modifier is a material that will increase or decrease reaction rate of the curable elastomeric sealant composition. For example, quinones, such as hydroquinone, monomethyl ether hydroquinone (MEHQ), napthoquinone and anthraquinone, may also be included to scavenge free radicals in the curable elastomeric sealant composition and thereby slow reaction of that composition and extend shelf life. When used, the reaction modifier can be used in the range of about 0.1 to about 15 weight percent of curable composition.
The curable elastomeric sealant composition can include one or more adhesion promoters that are compatible and known in the art. Examples of useful commercially available adhesion promoters include octyl trimethoxysilane (commercially available from Chemtura under the trade designation A-137), glycidyl trimethoxysilane (commercially available from Chemtura under the trade designation A-187), methacryloxypropyl trimethoxysilane (commercially available from Chemtura under the trade designation of A-174), vinyl trimethoxysilane, tetraethoxysilane and its partial condensation products, and combinations thereof. When used, the adhesion promoter can be used in the range of about 0.1 to about 15 weight percent of curable composition.
The curable elastomeric sealant composition can optionally include a thixotropic agent to modify rheological properties of the uncured composition. Some useful thixotropic agents include, for example, silicas, such as fused or fumed silicas, that may be untreated or treated so as to alter the chemical nature of their surface. Virtually any reinforcing fused, precipitated silica, fumed silica or surface treated silica may be used.
Examples of treated fumed silicas include polydimethylsiloxane-treated silicas, hexamethyldisilazane-treated silicas and other silazane or silane treated silicas. Such treated silicas are commercially available, such as from Cabot Corporation under the tradename CAB-O-SIL ND-TS and Evonik Industries under the tradename AEROSIL, such as AEROSIL R805. Also useful are the silicas that have been surface treated with an acrylate or methacrylate such as AEROSIL R7200 or R711 available from Evonik Industries.
Examples of untreated silicas include commercially available amorphous silicas such as AEROSIL 300, AEROSIL 200 and AEROSIL 130. Commercially available hydrous silicas include NIPSIL E150 and NIPSIL E200A manufactured by Japan Silica Kogya Inc.
When used rheology modifier can be employed in concentrations effective to provide desired physical properties in the uncured composition and cured reaction products and typically in concentrations of about 0.1% to about 70% by weight of composition.
The curable elastomeric composition can be clear to translucent. For some applications a colored composition can be beneficial to allow for inspection of the applied composition. A coloring agent, for example a pigment or dye, can be used to provide a desired color beneficial to the intended application. Exemplary coloring agents include titanium dioxide, C.I. Pigment Blue 28, C.I. Pigment Yellow 53 and phthalocyanine blue BN. In some applications a fluorescent dye can be added to allow inspection of the applied composition under UV radiation. The coloring agent will be present in amounts sufficient to allow for detection. If present, the coloring agent is desirably incorporated in amounts of about 0.002% or more by weight. The maximum amount is governed by considerations of cost and absorption of radiation that interferes with cure of the composition. More desirably, the dye is present in amounts of about 0.002% to about 1.0% weight by weight of the total composition.
The curable elastomeric sealant composition can optionally include other additives at concentrations effective to provide desired properties so long as they do not inhibit the desirable properties such as curing mechanism, elongation, low temperature sealing force, tensile strength, chemical resistance. Example of such optional additives include, for example, reinforcing materials such as fibers, diluents, reactive diluents, coloring agents and pigments, moisture scavengers such as methyltrimethoxysilane and vinyltrimethyloxysilane, inhibitors and the like may be included.
A curable elastomeric sealant composition can typically comprise:
about 50 to 99 wt % of a cross linkable elastomeric oligomer;
about 1 to 30 wt % of a glassy monomer;
about 0 to 30 wt % of a rubbery monomer;
about 0.01 to 10 wt % of an initiator or cross-linking agent;
about 0 to 5 wt % of a catalyst;
about 0 to 70 wt % of a filler;
about 0 to 15 wt % of a antioxidant;
about 0 to 15 wt % of a reaction modifier;
about 0 to 15 wt % of adhesion promoter;
about 0 to 70 wt % of rheology modifier;
about 0 to 1.0 wt % of coloring agent.
The glassy monomer(s) and the rubbery monomer(s) can be chosen so that a desired average glass transition temperature for that combination of monomers is obtained. The average glass transition temperature for a combination of monomers is defined by the Fox equation (1/Tgcomb=M1/Tg1+M2/Tg2 see T. G. Fox, Bull. Am. Phys. Soc., 1, 123 (1956), the contents of which are incorporated by reference herein.
The ratio of cross linkable elastomeric oligomer to glassy monomer must be chosen to provide sufficient glassy monomer to increase low temperature sealing force of the cured sealant reaction products. However, the ratio must not add so much glassy monomer that the elastomeric properties of the cured sealant reaction products are undesirably affected. Thus, there is a need to balance the ratio of cross linkable elastomeric oligomer to glassy monomer depending on desired properties: too little glassy material and the cured sealant composition will not have a desirable low temperature sealing force but too much glassy material and sealing ability of the cured sealant at higher temperatures is lost.
The ratio of cross linkable elastomeric oligomer to glassy monomer will depend on the oligomer and monomer used; the final application for the sealant; and the cured sealant properties desired for that application. A ratio of cross linkable elastomeric oligomer to glassy monomer in the range of 75:25 to 95:5 respectively provides a general starting point. At present there is no way to predict cured sealant properties for a cross linkable sealant composition formulation. Testing of formulations for low temperature sealing force and higher temperature sealing properties is required to arrive at a formulation and ratio providing desired properties.
Specific physical properties required for the uncured, sealant composition will depend on application. For example, sealant composition viscosity can be formulated for application method and desired cycle time. Viscosity of the uncured sealant composition can be 10,000 Cps to 1,000,000 Cps at 25° C.
Specific physical properties required for cured reaction products of the sealant composition will depend on sealing application, minimum and maximum operating temperatures within the application, desired tensile strength at high temperatures and desired sealing force at low temperatures. Some useful physical properties for the cured reaction products include: Hardness, Shore A about 20 to about 90 and desirably about 40 to about 60. Tensile strength, about 100 psi to about 2,000 psi and desirably about 500 psi to about 1,000 psi. Elongation, about 10% to about 1,000% and desirably about 100% to about 500%. Low temperature (−40° C.) sealing force, about 0 Newtons to about 50 Newtons and desirably about 6 Newtons to about 30 Newtons. Desirably the cured reaction product has a compression set value that allows a seal made therefrom to maintain a predetermined minimum sealing force throughout the design life of the seal.
Components to be sealed by the disclosed curable compositions have a first predetermined sealing surface that is aligned with a second predetermined sealing surface. Typically, the aligned sealing surfaces are in a fixed relationship and move very little relative to each other. The aligned sealing surfaces are generally in fluid communication with a chamber. The seal formed between the aligned sealing surfaces prevents movement of materials between the surfaces and into, or out of, the chamber.
One or both of the sealing surfaces can be machined or formed. The predetermined sealing surfaces are designed to allow a curable composition to be disposed on one or both surfaces during initial assembly of the component to form a seal therebetween. Design of the predetermined sealing surfaces enhances parameters such as alignment of the surfaces, contact area of the surfaces, surface finish of the surfaces, “fit” of the surfaces and separation of the surfaces to achieve a predetermined sealing effect. A predetermined sealing surface does not encompass surfaces that were not identified or designed prior to initial assembly to accommodate a seal or gasket, for example the outside surface of a component over which a repair material is molded or applied to lessen leaking. Sealing surfaces on an engine block and oil pan or engine intake manifold are examples of sealing surfaces in fixed relationship.
The disclosed curable compositions can be in a flowable state for disposition onto at least a portion of one sealing surface to form a seal between the surfaces when they are aligned. The curable composition can be applied as a film over the sealing surface. The curable composition can also be applied as a bead in precise patterns by tracing, screen printing, robotic application and the like. In bead applications the disclosed compositions are typically dispensed as a liquid or semi-solid under pressure through a nozzle and onto the component sealing surface. The nozzle size is chosen to provide a line or bead of composition having a desired width, height, shape and volume. The curable composition can be contained in a small tube and dispensed by squeezing the tube; contained in a cartridge and dispensed by longitudinal movement of a cartridge sealing member; or contained in a larger container such as a 5 gallon pail or 55 gallon drum and dispensed at the point of use by conventional automated dispensing equipment. Container size can be chosen to suit the end use application.
The curable composition can be used to form a formed in place gasket (FIPG). In this application the composition is dispensed onto a first predetermined sealing surface. The first predetermined sealing surface and dispensed composition is aligned and sealingly engaged with a second predetermined sealing surface before the composition has fully cured. The composition will adhere to both sealing surfaces as it cures.
The curable composition can be used to form a cured in place gasket (CIPG). In this application the composition is dispensed onto a first predetermined sealing surface and allowed to substantially cure before contact with a second predetermined sealing surface. The first sealing surface and cured composition is sealingly engaged with the second sealing surface thereby compressing the cured composition to provide a seal between the sealing surfaces. The composition will adhere to only the first sealing surface.
The curable composition can be used to form a mold in place gasket (MIPG). In this application the part comprising the first predetermined sealing surface is placed in a mold. The composition is dispensed into the mold where it contacts the first sealing surface. The composition is typically allowed to cure before removal from the mold. After molding, the first sealing surface and molded composition is sealingly engaged with a second predetermined sealing surface thereby compressing the cured composition to provide a seal between the sealing surfaces. The composition will adhere to only the first sealing surface.
The curable composition can be used in liquid injection molding (LIM). In this application uncured composition is dispensed into a mold without any predetermined sealing surface under controlled pressure and temperature. The composition is typically allowed to cure before removal from the mold. After removal the molded part will retain its shape. In sealing applications the molded gasket is disposed between two predetermined sealing surfaces and compressed to provide a seal between the sealing surfaces.
The following examples are included for purposes of illustration so that the disclosure may be more readily understood and are in no way intended to limit the scope of the disclosure unless otherwise specifically indicated.
Unless otherwise specified the following test procedures were used on cured specimens in the Examples.
set “A” ASTM D395. Samples were allowed to cool to room temperature in the uncompressed stated before testing.
set “B” ASTM D395 modified. Samples were allowed to cool to room temperature in a compressed state before testing.
glass transition Tg Differential Scanning calorimetry (DSC).
Curable, elastomeric gasketing compositions were made. Polyisobutylene diacrylate (PIB diacrylate) is a telechelic, polyisobutylene polymer with acrylate moieties at each end, with a molecular weight of about 1,000 to about 1,000,000 and a very low glass transition temperature (Tg) of −67° C. PIB diacrylate was chosen as the rubber matrix of the elastomeric gasketing compositions. PIB diacrylate can be prepared using a number of known reactions schemes, some of which are listed below and the contents of which are incorporated by reference herein in their entirety. The method of scheme 2 can be used to prepare the PIB diacrylate used in the following compositions.
Various acrylates and methacrylates having a Tg greater than 20° C. were selected as the glassy monomer. Various acrylates and methacrylates having a Tg less than 0° C. were selected as the rubbery monomer and as a reactive diluent. The ratio of rubber phase over glass phase was adjusted by trial and error to provide the desired elasticity and sealing force at lower temperature.
1) Premix preparation: Charge all liquids including initiator, antioxidant, reaction modifier. Mix until no solids remain.
2) Charge elastomeric oligomer into premix. Mix until uniform.
3) Add fillers and mix until uniform.
4) Apply vacuum to degas sample. Discharge bubble free material into storage container.
1Dicyclopentanylmethacrylate glassy monomer marketed by Hitachi Chemical Corporation.
2available from Ciba.
3available from Ciba.
4Available from Evonik.
5Available from Wacker.
62 CsT polyalphaolefin diluent.
Compression set B values of greater than 0 but less than 40 indicate a cured material may have an advantageous low temperature sealing force. The high compression set B value (62) of Example 1 indicates a cured material that will not maintain desirable sealing force at low temperatures.
1Glassy monomer marketed by Hitachi Chemical Corporation.
Example 43 is a UV curable composition. Example 43 was formed into samples. The samples were exposed to an UV A radiation source having an intensity of about 1434 mw/cm2 for an energy of about 9872 mJ/cm2. Cured samples of composition 43 had a sealing force at −40° C. of 8N at 25% compression. Example 44 is a thermally curable composition.
The sealing force for example 24 is shown in the table below as a function of temperature and percent compression. The composition in example 24 exhibits typical elastomeric properties. The sealing force at a constant temperature increases as the percent compression is increased, which is expected based on the theory of rubber elasticity as the extension increases. The force, at a constant compression, increases as the temperature is increased. This is also expected based on the temperature dependency defined in the equation of state of rubber elasticity.
The sealing force at −40° C. for several cured films that were compressed twenty-five percent are shown in the table below, titled UV cured Isoprene & PIB Cured-In-Place Gasketing Compositions. It was observed as shown in examples 1, 2 and 3 that the sealing force at −40° C. and 25 percent compression varied significantly as a function of the monomer content as shown in the table and graph below. The step function in change from examples 1, 2, and 3 was surprising and not expected based on observing a single glass transition temperature in the DSC scan. If there was a distinct or separate glassy phase that occurred as a result of the higher glass transition monomer, it should appear as a first or second order thermodynamic transition as measured by DSC. No such first or second order thermodynamic transition is observed in the DSC scans for examples 1, 2 and 3 shown in the figures. High monomer content is desirable to lower the viscosity of the uncured sealant. This allows the sealant to be dispensed quickly while obtaining a cured elastomer with high tensile strength and high elongation. As the monomer content decreases the viscosity increases, tensile strength decreases and the elongation decreases. A high viscosity is undesirable as it is difficult to rapidly dispense the composition. A low elongation is undesirable which can lead to cracks in the seal. A high sealing force at low temperature is desirable as this defines the practical lower limit of ability of the elastomeric seal to perform its intended function over the operating temperature range. The low temperature sealing force, i.e. at −40° C., can be modulated dramatically with changes in the glassy and/or rubbery monomer ratio.
Each of these cured networks exhibited a single glass transition temperature when measured with a differential scanning calorimetry (DSC) as shown in
While preferred embodiments have been set forth for purposes of illustration, the description should not be deemed a limitation of the disclosure herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | |
|---|---|---|---|
| 61479710 | Apr 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2012/035094 | Apr 2012 | US |
| Child | 13796588 | US |
