Articles made from a thermoplastic resin composition comprising a high modulus fiber and a resorcinol polyester or resorcinol polyester carbonate resin showing high strength and stiffness along with surprisingly good retention of gloss and color when exposed to weathering.

This invention relates to article with high stiffness and strength having high retention of color and gloss when exposed to weathering.
Fiber reinforced thermoplastic resins have long been used in a wide variety of applications. The combination of rigid fibers, especially glass fibers, with thermoplastic polymers has joined the easy molding and forming of recyclable plastics with the strength and stiffness of the fiber.
However one drawback to this combination is the poor weathering of the fiber resin combination when used in outdoor applications. After a relatively short period of time the surface of fiber filled thermoplastic articles begin to erode. The erosion process exposes the fiber giving an article that has poor appearance and may no longer serve its intended purpose. For example a surface designed for seating will become uncomfortable as glass fibers begin to protrude from its surface as a result of weathering. Similarly a rigid part designed to carry a load in a structural application may alter its appearance due to loss of gloss or changes of color as the thermoplastic resin weathers to expose the glass fibers in the mixture. Changes in gloss and color may often make the article unacceptable for its intend use.
Fiber reinforced plastics (FRP), when exposed to outdoor weathering, often suffer loss of gloss, discoloration and loss of strength. Poor FRP weathering is thought to occur mainly due to the following reasons. First, fiber and polymer resin do not erode at the same rate, with weathering the surface of the FRP is roughened, leading to loss of gloss and exposing fibers. Second, UV induced degradation of the resin surface leads to crazing and erosion, exposing the fiber. The fibers exposed at the surface and create multiple wicking sites which allow moisture to penetrate beneath the exposed surface of the article formed from the polymer resin fiber mixture. The moisture absorbed may further reduce the interfacial bonding between the resin matrix and the individual reinforcing fibers, resulting loss of strength. Third, photochemical induced degradation of the resin also often leads to discoloration. The loss of gloss due to unequal rate of erosion is a problem of FRP.
The traditional method to address the problem of erosion of the surface of weathering articles formed from fiber filled thermoplastic resins is to apply a coating or protective layer. To address the poor weatherability of FRP, U.S. Pat. No. 4,369,224 teaches application of a gel coat to the surface of FRP product to provide resistance to the deterioration from UV exposure; U.S. Pat. No. 4,117,185 teaches application of a film or a layer of fluoro-plastic materials to provide the resistance to weathering.
This approach is effective, paints or thin films are very commonly used to protect plastic parts used in outdoor applications. However, application of such coatings adds complexity and cost to the article. In addition the issue of coating adhesion to the fiber filled resin substrate must be addressed. Despite many inventions in the area, loss of protective coatings is still common.
We have found that articles made from a combination of fibers with a specific resorcinol based polyester resins have high strength and stiffness, as indicated by flexural strength and modulus with surprisingly good retention of color and gloss when exposed to weathering.
Even though the fiber and the resorcinol based polyester resin: should have different erosion rates, the invented articles defy the expected observation, showing excellent weatherability in terms of gloss retention and resistance to discoloration compared with the similar compositions based on polycarbonate resins.
The composition of the invention may comprise from 1-60% by weight of the composition of fiber. Any rigid fiber may be used for example, glass fibers, carbon fibers, metal fibers, ceramic fibers or whiskers. Preferred fibers will not add color when combined to the polycarbonate ester resin. In one embodiment of the invention glass fibers are employed. In other embodiments of the invention borosilicate glass fibers are used Preferred fibers of the invention will have modulus of grater than or equal to 1,000,000 psi. The fiber may be chopped or continuous. The fiber may have various cross-sections for example, round, crescent, bilobal, trilobal, rectangular and hexagonal.
Preferred fibers will have a diameter of from 5-25 microns with diameter of 6-17 microns being most preferred. In some applications it may be desirable to treat the surface of the fiber with a chemical coupling agent to improve adhesion to the polyester carbonate resin. Examples of useful coupling agents are alkoxy silanes and alkoxy zirconates. Amino, epoxy, amide, or thio functional alkoxy silanes are especially useful.
The composition of the invention will further comprise 99-40% by weight of the entire mixture of a resorcinol based polyarylate resin. The resin should contain at least 30 mole % of units derived from the reaction product of resorcinol, or functionalized resorcinol, with an aryl dicarboxylic acid or dicarboxylic acid derivatives suitable for the formation of aryl ester linkages, for example, carboxylic acid halides, carboxylic acid esters and carboxylic acid salts.
The resorcinol based polyarylate may further contain carbonate linkages derived from reaction of a bisphenol and a carbonate forming species, such as phosgene. In another embodiment of the invention resorcinol polyarylate carbonate copolymers will be comprised of the reaction products of iso and tere phthalic acid, resorcinol and optionally, bisphenol A and phosgene. The resorcinol polyester carbonate copolymer will be made in such a way that the number of bisphenol dicarboxylic ester linkages is minimized, for example by pre-reacting the resorcinol moiety with the dicarboxylic acid moiety to form a polyester block and then reacting a said block with the bisphenol and carbonate moiety to form the polycarbonate part of the copolymer.
Most preferred compositions will have 60-90% resorcinol based polyester with from 10-40% glass fiber.
In one of its aspects the article of the present invention is comprised of polymers containing arylate polyester chain members. Said chain members comprise at least one diphenol residue in combination with at least one aromatic dicarboxylic acid residue. In one embodiment the diphenol residue is derived from a 1,3-dihydroxybenzene moiety, as illustrated in Formula I, commonly referred to throughout this specification as resorcinol or resorcinol moiety. Resorcinol or resorcinol moiety as used within the context of the present invention should be understood to include both unsubstituted 1,3-dihydroxybenzene and substituted 1,3-dihydroxybenzenes unless explicitly stated otherwise.
In Formula I R is at least one of C1-12 alkyl, C6-C24 aryl, alkyl aryl or halogen, and n is 0-3.
Suitable dicarboxylic acid residues include aromatic dicarboxylic acid residues derived from monocyclic moieties. In various embodiments suitable dicarboxylic acid residues include those derived from isophthalic acid, terephthalic acid, or mixtures of isophthalic and terephthalic acids. Suitable dicarboxylic acid residues also include those derived from polycyclic moieties, illustrative examples of which include diphenyl dicarboxylic acid, diphenylether dicarboxylic acid, and naphthalenedicarboxylic acid, especially naphthalene-2,6-dicarboxylic acid. In some embodiments the aromatic dicarboxylic acid residues are derived from mixtures of isophthalic and/or terephthalic acids as typically illustrated in Formula II.
Therefore, in one embodiment the present invention provides thermally stable polymers comprising resorcinol arylate polyester chain members as typically illustrated in Formula III wherein R and n are as previously defined:
In one of its aspects the present invention provides an article made of a resin prepared using an interfacial polymerization method preparing polymers comprising resorcinol arylate polyester chain members substantially free of anhydride linkages, said method comprising a first step of combining at least one resorcinol moiety and at least one catalyst in a mixture of water and at least one organic solvent substantially immiscible with water. Suitable resorcinol moieties comprise units of Formula V:
wherein R is at least one of C1-12 alkyl, C6-C24 aryl, alkyl aryl or halogen, and n is 0-3. Alkyl groups, if present, are typically straight-chain, branched, or cyclic alkyl groups, and are most often located in the ortho position to both oxygen atoms although other ring locations are contemplated. Suitable C1-12 alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, butyl, iso-butyl, t-butyl, hexyl, cyclohexyl, nonyl, decyl, and aryl-substituted alkyl, including benzyl. In a particular embodiment an alkyl group is methyl. Suitable halogen groups are bromo, chloro, and fluoro. The value for n in various embodiments may be 0-3, in some embodiments 0-2, and in still other embodiments 0-1. In one embodiment a resorcinol moiety is 2-methylresorcinol. In another embodiment the resorcinol moiety is an unsubstituted resorcinol moiety in which n is zero. The method further comprises combining at least one catalyst with the reaction mixture. Said catalyst may be present in various embodiments at a total level of 0.1 to 10 mole %, and in some embodiments at a total level of 0.2 to 6 mole % based on total molar amount of acid chloride groups. Suitable catalysts comprise tertiary amines, quatemary ammonium salts, quaternary phosphonium salts, hexaalkylguanidinium salts, and mixtures thereof. Suitable tertiary amines include triethylamine, dimethylbutylamine, diisopropylethylamine, 2,2,6,6-tetramethylpiperidine, and mixtures thereof. Other contemplated tertiary amines include Nxe2x80x94C1-C6-alkyl-pyrrolidines, such as N-ethylpyrrolidine, Nxe2x80x94C1-C6-piperidines, such as N-ethylpiperidine, N-methylpiperidine, and N-isopropylpiperidine, Nxe2x80x94C1-C6-morpholines, such as N-ethylmorpholine, and N-isopropyl-morpholine, Nxe2x80x94C1-C6-dihydroindoles, Nxe2x80x94C1-C6-dihydroisoindoles, Nxe2x80x94C1-C6-tetrahydroquinolines, Nxe2x80x94C1-C6-tetrahydroisoquinolines, Nxe2x80x94C1-C6-benzo-morpholines, 1-azabicyclo-[3.3.0]-octane, quinuclidine, Nxe2x80x94C1-C6-alkyl-2-azabicyclo-[2.2.1]-octanes, Nxe2x80x94C1-C6-alkyl-2-azabicyclo-[3.3.1]-nonanes, and Nxe2x80x94C1-C6-alkyl-3-azabicyclo-[3.3.1]-nonanes, N,N,Nxe2x80x2,Nxe2x80x2-tetraalkylalkylene-diamines, including N,N,Nxe2x80x2,Nxe2x80x2-tetraethyl-1,6-hexanediamine. In various embodiments tertiary amines are triethylamine and N-ethylpiperidine.
Suitable dicarboxylic acid dihalides may comprise aromatic dicarboxylic acid dichlorides derived from monocyclic moieties, illustrative examples of which include isophthaloyl dichloride, terephthaloyl dichloride or mixtures of isophthaloyl and terephthaloyl dichlorides. Suitable dicarboxylic acid dihalides may also comprise aromatic dicarboxylic acid dichlorides derived from polycyclic moieties, illustrative examples of which include diphenyl dicarboxylic acid dichloride, diphenylether dicarboxylic acid dichloride, and naphthalenedicarboxylic acid dichloride, especially naphthalene-2,6-dicarboxylic acid dichloride; or from mixtures of monocyclic and polycyclic aromatic dicarboxylic acid dichlorides. In one embodiment the dicarboxylic acid dichloride comprises mixtures of isophthaloyl and/or terephthaloyl dichlorides as typically illustrated in Formula VI.
Either or both of isophthaloyl and terephthaloyl dichlorides may be present. In some embodiments the dicarboxylic acid dichlorides comprise mixtures of isophthaloyl and terephthaloyl dichloride in a molar ratio of isophthaloyl to terephthaloyl of about 0.25-4.0:1; in other embodiments the molar ratio is about 0.4-2.5:1; and in still other embodiments the molar ratio is about 0.67-1.5:1.
Dicarboxylic acid halides provide only one method of preparing the polymers on the invention. Other routes to make the resorcinol arylate linkages are also contemplated using, for example, the dicarboxylic acid; a dicarboxylic acid ester, especially an activated ester, or dicarboxylate salts or partial salts.
At least one chain-stopper (also referred to sometimes hereinafter as capping agent) may also be present in the method and compositions of the invention. A purpose of adding at least one chain-stopper is to limit the molecular weight of polymer comprising resorcinol arylate polyester chain members, thus providing polymer with controlled molecular weight and favorable processability. Typically, at least one chain-stopper is added when the resorcinol arylate-containing polymer is not required to have reactive end-groups for further application. In the absence of chain-stopper resorcinol arylate-containing polymer may be either used in solution or recovered from solution for subsequent use such as in copolymer formation which may require the presence of reactive end-groups, typically hydroxy, on the resorcinol-arylate polyester segments. A chain-stopper may be at least one of mono-phenolic compounds, mono-carboxylic acid chlorides, and/or mono-chloroformates. Typically, the at least one chain-stopper may be present in quantities of 0.05 to 10 mole %, based on resorcinol moieties in the case of mono-phenolic compounds and based on acid dichlorides in the case mono-carboxylic acid chlorides and/or mono-chloroformates.
Suitable mono-phenolic compounds include monocyclic phenols, such as phenol, C1-C22 alkyl-substituted phenols, p-cumyl-phenol, p-tertiary-butyl phenol, hydroxy diphenyl; monoethers of diphenols, such as p-methoxyphenol. Alkyl-substituted phenols include those with branched chain alkyl substituents having 8 to 9 carbon atoms, preferably in which about 47 to 89% of the hydrogen atoms are part of methyl groups as described in U.S. Pat. No. 4,334,053. In some embodiments mono-phenolic chain-stoppers are phenol, p-cumylphenol, and resorcinol monobenzoate.
Suitable mono-carboxylic acid chlorides include monocyclic, mono-carboxylic acid chlorides, such as benzoyl chloride, C1-C22 alkyl-substituted benzoyl chloride, toluoyl chloride, halogen-substituted benzoyl chloride, bromobenzoyl chloride, cinnamoyl chloride, 4-nadimidobenzoyl chloride, and mixtures thereof; polycyclic, mono-carboxylic acid chlorides, such as trimellitic anhydride chloride, and naphthoyl chloride; and mixtures of monocyclic and polycyclic mono-carboxylic acid chlorides. The chlorides of aliphatic monocarboxylic acids with up to 22 carbon atoms are also suitable. Functionalized chlorides of aliphatic monocarboxylic acids, such as acryloyl chloride and methacryoyl chloride, are also suitable. Suitable mono-chloroformates include monocyclic, mono-chloroformates, such as phenyl chloroformate, alkyl-substituted phenyl chloroformate, p-cumyl phenyl chloroformate, toluene chloroformate, and mixtures thereof. A chain-stopper can be combined together with the resorcinol moieties, can be contained in the solution of dicarboxylic acid dichlorides, or can be added to the reaction mixture after production of a precondensate. If mono-carboxylic acid chlorides and/or mono-chloroformates are used as chain-stoppers, they are often introduced together with dicarboxylic acid dichlorides. These chain-stoppers can also be added to the reaction mixture at a moment when the chlorides of dicarboxylic acid have already reacted substantially or to completion. If phenolic compounds are used as chain-stoppers, they can be added in one embodiment to the reaction mixture during the reaction, or, in another embodiment, before the beginning of the reaction between resorcinol moiety and acid chloride moiety. When hydroxy-terminated resorcinol arylate-containing precondensate or oligomers are prepared, then chain-stopper may be absent or only present in small amounts to aid control of oligomer molecular weight.
In another embodiment the invention may encompass the inclusion of at least one branching agent such as a trifunctional or higher functional carboxylic acid chloride and/or trifunctional or higher functional phenol. Such branching agents, if included, can typically be used in quantities of 0.005 to 1 mole %, based on dicarboxylic acid dichlorides or resorcinol moieties used, respectively. Suitable branching agents include; for example, trifunctional or higher carboxylic acid chlorides, such as trimesic acid trichloride, cyanuric acid trichloride, 3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic acid tetrachloride, 1,4,5,8-naphthalene tetracarboxylic acid tetrachloride or pyromellitic acid tetrachloride, and trifunctional or higher phenols, such as 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-2-heptene, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(4-hydroxyphenyl)-phenyl methane, 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxyphenylisopropyl)-phenol, tetra-(4-hydroxyphenyl)-methane, 2,6-bis-(2-hydroxy-5-methylbenzyl)-4-methyl phenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane, tetra-(4-[4-hydroxyphenylisopropyl]-phenoxy)-methane, 1,4-bis-[(4,4-dihydroxytriphenyl)methyl]-benzene. Phenolic branching agents may be introduced first with the resorcinol moieties whilst acid chloride branching agents may be introduced together with acid dichlorides.
In one of its embodiments the invention comprises thermally stable resorcinol arylate polyesters made by the present method and substantially free of anhydride linkages linking at least two mers of the polyester chain. In a particular embodiment said polyesters comprise dicarboxylic acid residues derived from a mixture of iso- and terephthalic acids as illustrated in Formula VII:
wherein R is at least one of C1-12 alkyl, C6-C24 aryl, alkyl aryl or halogen, n is 0-3, and m is at least about 8. In various embodiments n is zero and m is between about 10 and about 300. The molar ratio of isophthalate to terephthalate is in one embodiment about 0.25-4.0:1, in another embodiment about 0.4-2.5:1, and in still another embodiment about 0.67-1.5:1. Substantially free of anhydride linkages means that said polyesters show decrease in molecular weight in one embodiment of less than 30% and in another embodiment of less than 10% upon heating said polymer at a temperature of about 280-290xc2x0 C. for five minutes.
Also included in the scope of this invention are resorcinol arylate copolyesters containing soft-block segments as disclosed in commonly owned U.S. Pat. No. 5,916,997. The term soft-block as used herein, indicates that some segments of the polymers are made from non-aromatic monomer units. Such non-aromatic monomer units are generally aliphatic and are known to impart flexibility to the soft-block-containing polymers. The copolymers include those comprising structural units of Formulas I, VIII, and IX:
wherein R and n are as previously defined, Z is a divalent aromatic radical, R2 is a C3-20 straight chain alkylene, C3-10 branched alkylene, or C4-10 cyclo- or bicycloalkylene group, and R3 and R4 each independently represent
wherein Formula IX contributes from about 1 to about 45 mole percent to the ester linkages of the polyester. Additional embodiments of the present invention provide a composition wherein Formula IX contributes in various embodiments from about 5 to about 40 mole percent to the ester linkages of the polyester, and in other embodiments from about 5 to about 20 mole percent to the ester linkages of the polyester. Another embodiment provides a composition wherein R2 represents in one embodiment C3-14 straight chain alkylene, or C5-6 cycloalkylene, and in another embodiment R2 represents C3-10 straight-chain alkylene or C6-cycloalkylene. Formula VIII represents an aromatic dicarboxylic acid residue. The divalent aromatic radical Z in Formula VIII may be derived in various embodiments from at least one of the suitable dicarboxylic acid residues as defined hereinabove, and in some embodiments at least one of 1,3-phenylene, 1,4-phenylene, or 2,6-naphthylene. In various embodiments Z comprises at least about 40 mole percent 1,3-phenylene. In various embodiments of copolyesters containing soft-block chain members n in Formula I is zero.
In various embodiments copolyesters containing resorcinol arylate chain members are those comprising from about 1 to about 45 mole % sebacate or cyclohexane-1,4-dicarboxylate units. In a particular embodiment a copolyester containing resorcinol arylate chain members is one comprising resorcinol isophthalate and resorcinol sebacate units in molar ratio between 8.5:1.5 and 9.5:0.5. In one embodiment said copolyester is prepared using sebacoyl chloride in combination with isophthaloyl dichloride.
In another of its embodiments the present invention comprises block copolyestercarbonates comprising resorcinol arylate-containing block segments in combination with organic carbonate block segments. The segments comprising resorcinol arylate chain members in such copolymers are substantially free of anhydride linkages. Substantially free of anhydride linkages means that the copolyestercarbonates show decrease in molecular weight in one embodiment of less than 10% and in another embodiment of less than 5% upon heating said copolyestercarbonate at a temperature of about 280-290xc2x0 C. for five minutes. The block copolyestercarbonates include those comprising alternating arylate and organic carbonate blocks, typically as illustrated in Formula X, wherein R and n are as previously defined, and R5 is at least one divalent organic radical:
The arylate blocks have a degree of polymerization (DP), represented by m, in,one embodiment of at least about 4, in another embodiment of at least about 10, in another embodiment of at least about 20 and in still another embodiment of about 30-150. The DP of the organic carbonate blocks, represented by p, is in one embodiment generally at least about 10, in another embodiment at least about 20 and in still another embodiment about 50-200. The distribution of the blocks may be such as to provide a copolymer having any desired weight proportion of arylate blocks in relation to carbonate blocks. In general, the content of arylate blocks is in one embodiment about 10-95% by weight and in another embodiment about 50-95% by weight.
Although a mixture of iso- and terephthalate is illustrated in Formula X, the dicarboxylic acid residues in the arylate blocks may be derived from any suitable dicarboxylic acid residue, as defined hereinabove, or mixture of suitable dicarboxylic acid residues, including those derived from aliphatic diacid dichlorides (so-called xe2x80x9csoft-blockxe2x80x9d segments). In various embodiments n is zero and the arylate blocks comprise dicarboxylic acid residues derived from a mixture of iso- and terephthalic acid residues, wherein the molar ratio of isophthalate to terephthalate is in one embodiment about 0.25-4.0:1, in another embodiment about 0.4-2.5:1, and in still another embodiment about 0.67-1.5:1.
In the organic carbonate blocks, each R5 is independently a divalent organic radical. In various embodiments said radical comprises at least one dihydroxy-substituted aromatic hydrocarbon, and at least about 60 percent of the total number of R5 groups in the polymer are aromatic organic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Suitable R5 radicals include m-phenylene, p-phenylene, 4,4xe2x80x2-biphenylene, 4,4xe2x80x2-bi(3,5-dimethyl)-phenylene, 2,2-bis(4-phenylene)propane, 6,6xe2x80x2-(3,3,3xe2x80x2,3xe2x80x2-tetramethyl-1,1xe2x80x2-spirobi[1 H-indan]) and similar radicals such as those which correspond to the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438.
In some embodiments each R5 is an aromatic organic radical and in other embodiments a radical of Formula XI:
wherein each A1 and A2 is a monocyclic divalent aryl radical and Y is a bridging radical in which one or two carbon atoms separate A1 and A2. The free valence bonds in Formula XI are usually in the meta or para positions of A1 and A2 in relation to Y. Compounds in which R5 has Formula XI are bisphenols, and for the sake of brevity the term xe2x80x9cbisphenolxe2x80x9d is sometimes used herein to designate the dihydroxy-substituted aromatic hydrocarbons. It should be understood, however, that non-bisphenol compounds of this type may also be employed as appropriate.
In Formula XI, A1 and A2 typically represent unsubstituted phenylene or substituted derivatives thereof, illustrative substituents (one or more) being alkyl, alkenyl, and halogen (particularly bromine). In one embodiment unsubstituted phenylene radicals are preferred. Both A1 and A2 are often p-phenylene, although both may be o- or m-phenylene or one o- or m-phenylene and the other p-phenylene.
The bridging radical, Y, is one in which one or two atoms, separate A1 from A2. In a particular embodiment one atom separates A1 from A2. Illustrative radicals of this type are xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94 or xe2x80x94SO2xe2x80x94, methylene, cyclohexyl methylene, 2-[2.2.1]-bicycloheptyl methylene, ethylene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, adamantylidene, and like radicals.
In some embodiments gem-alkylene (commonly known as xe2x80x9calkylidenexe2x80x9d) radicals are preferred. Also included, however, are unsaturated radicals. In some embodiments the preferred bisphenol is 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A or BPA), in which Y is isopropylidene and A1 and A2 are each p-phenylene. Depending upon the molar excess of resorcinol moiety present in the reaction mixture, R5 in the carbonate blocks may at least partially comprise resorcinol moiety. In other words, in some embodiments of the invention carbonate blocks of Formula X may comprise a resorcinol moiety in combination with at least one other dihydroxy-substituted aromatic hydrocarbon.
Diblock, triblock, and multiblock copolyestercarbonates are encompassed in the present invention. The chemical linkages between blocks comprising resorcinol arylate chain members and blocks comprising organic carbonate chain members may comprise at least one of
(a) an ester linkage between a suitable dicarboxylic acid residue of an arylate moiety and an xe2x80x94Oxe2x80x94R5xe2x80x94Oxe2x80x94 moiety of an organic carbonate moiety, for example as typically illustrated in Formula XII, wherein R5 is as previously defined:
and (b) a carbonate linkage between a diphenol residue of a resorcinol arylate moiety and a xe2x80x94(Cxe2x95x90O)xe2x80x94Oxe2x80x94 moiety of an organic carbonate moiety as shown in Formula XIII, wherein R and n are as previously defined:
The presence of a significant proportion of ester linkages of the type (a) may result in undesirable color formation in the copolyestercarbonates. Although the invention is not limited by theory it is believed that color may arise, for example, when R5 in Formula XII is bisphenol A and the moiety of Formula XII undergoes Fries rearrangement during subsequent processing and/or light-exposure. In one embodiment the copolyestercarbonate is substantially comprised of a diblock copolymer with a carbonate linkage between resorcinol arylate block and an organic carbonate block. In another embodiment the copolyestercarbonate is substantially comprised of a triblock carbonate-ester-carbonate copolymer with carbonate linkages between the resorcinol arylate block and organic carbonate end-blocks.
Copolyestercarbonates with at least one carbonate linkage between a thermally stable resorcinol arylate block and an organic carbonate block are typically prepared from resorcinol arylate-containing oligomers prepared by various embodiments of the invention and containing in one embodiment at least one and in another embodiment at least two hydroxy-terminal sites. Said oligomers typically have weight average molecular weight in one embodiment of about 10,000 to about 40,000, and in another embodiment of about 15,000 to about 30,000. Thermally stable copolyestercarbonates may be prepared by reacting said resorcinol arylate-containing oligomers with phosgene, at least one chain-stopper, and at least one dihydroxy-substituted aromatic hydrocarbon in the presence of a catalyst such as a tertiary amine.
Resorcinol based polyester fiber compositions as described above show improved resistance to weathering under a variety of conditions, for example, natural outdoor weathering with high and low humidity, for example in Florida or Arizona. For ease of testing weathering is often simulated under various accelerated test conditions, for example ASTMG26, ASTM G155 or SAE J1960.
In one embodiment of the invention samples were exposed to weathering in an Atlas Ci4000 xenon arc weatherometer equipped with CIRA glass inner and a sodalime glass outer filters at an irradiance of 0.77 watts per square meter at 340 nanometers. Exposure conditions were black panel 55xc2x0 C., dry bulb 35xc2x0 C., humidity 30% with continuous illumination. Exposure was measured in kilojoules per square meter (KJ/m2) of energy received at 340 nanometers. The samples were exposed to a rain like water spray weekly and wiped with a sponge. Light was left on continuously. Under these aging conditions; 2.7 KJ/m2=xcx9c1 hour of exposure: 1000 hr. equals about 2700 KJ/m2, 3000 hr. equals about 8100 KJ/m2, 5000 hr. equals about 13,500 KJ/m2.
CIRA is an IR reflecting quartz filter manufactured by Atlas Electric Devices Co. It stands for xe2x80x9cCoated InfraRed Absorbingxe2x80x9d quartz. The combination of this filter with a soda lime glass outer filter gives a short wavelength UV cut-off very similar to natural Miami sunlight and reduces slightly the heat load on the samples thus allowing temperature control at higher irradiances than without the IR coating.
Color shift measurements may be measured using the CieLAB system using L, a, b values to calculate a color shift: delta E, compared to an unweathered control. Samples were evaluated for color on a GretagMacbeth(trademark) Color-Eye 7000A colorimeter with results reported as xcex94E ((xcex94E=xcex94L2+xcex94a+xcex94b2)xc2xd). The change in the color of the weathered samples compared to the initial unweathered samples was also measured by the change in yellowness index (YI), according to ASTM D1925.
Surface gloss, often measured as 60 degree gloss values using ASTM D523, can also be monitored as a function of exposure time under normal weathering or in an accelerated weathering apparatus (xe2x80x9cweatherometerxe2x80x9d) to determine resistance of a material to loss of properties due to photo-aging under the conditions described above. Gloss was measured at a 60 degree angle on the samples as they emerged form weathering using a BykGardner microTrigloss meter calibrated against a black glass standard.
Samples which have an initially high gloss, for example greater than about 50 degrees, will show changes in reflectivity more readily than samples which have a low initial gloss.
Articles of the invention will have high gloss as molded, that is with a 60 degree gloss of greater than or equal to 70%, most preferred with a gloss of greater than or equal to 80%, and will show greater than or equal to 50% retention of said initial gloss after 1000 KJ/m2 of accelerated weathering under the accelerated photoaging test conditions described herein. The preferred compositions of the invention will show about 50% retention of initial gloss after 3000 KJ/m2 of accelerated weathering. The most preferred compositions of the invention show 50% or greater retention of the initial gloss after 5000 KJ/m2 of accelerated weathering. The higher the total exposure energy, measured in KJ/m2 the more severe the test becomes and the more difficult it becomes for an article to retain its, gloss, color or properties.
The composition of the invention can also be combined with other ingredients such as mineral fillers; for example, talc, clay, mica, barite, wollastonite, silica, milled glass and glass flake. Colorants such as titanium dioxide, zinc sulfide and carbon black; stabilizers such as hindered phenols, aryl phosphates and aryl phosphinates and thioesters, as well as mold release agents, lubricants, flame retardants, smoke suppressors, ultra violet absorbers and other uv stabilizers anti-drip agents, for instance those based on fluoro polymers, can also be added to the composition in effective amounts.
In some embodiments of the invention combinations of glass fibers with a flat, plate like filler, for example mica or flaked glass, wherein the flat, plate like filler, has a length and width at least ten times greater than its thickness, where the thickness is from 1-1000 microns may give enhanced properties.
Combinations of rigid fibrous fillers with flat, plate like fillers may reduce warp of the molded article. Preferred mold release agents are alkyl carboxylic acid esters, for example, penta erythritol tetrastearate, glycerin tristearate and ethylene glycol distearate. Mold release agents are typically present in the composition at 0.05-0.5% by weight of the formulation. Preferred mold release agents will have high molecular weight, typically greater than about 300, to prevent loss if the release agent from the molten polymer fiber mixture during melt processing.
Preferred flame retardant additives include halogenated compounds especially aromatic chlorine or bromine containing compounds, sulfonate salts, for example potassium sulfone sulfonate and per fluoro butyl sodium sulfonate. Aryl phosphate flame retardants for example, triphenyl phosphate as well as phosphate esters of bisphenol A or resorcinol are also useful flame retardants. Flame retardant compositions may also contain: polymers made from fluorinated olefin monomers, for example poly tetra fluoro ethylene, to retard dripping during buming.
Articles of the invention can be prepared by any number of methods. Preferred methods include, for example, injection molding, compression molding, profile extrusion, sheet or film extrusion, gas assist molding, structural foam molding and thermoforming. Injection molding wherein the article has an inner core of one type of resin and an outer covering of the resorcinol based polyester is also contemplated as a means of making articles. Such multi component molding is often called co-injection molding.
Useful articles of the invention include, for example, benches, seating, doors, window frames, outdoor lighting, transport devices, structural and decorative components of buildings, green houses, siding materials, architectural hardware, mail boxes, post, fencing, enclosures and communication equipment.
Further useful examples of the invention include articles made for use in the following applications: aircraft, automotive vehicle, truck, water-borne vehicle or motorcycle exterior or interior component: an enclosure housing, panel, or part for an outdoor vehicle or outdoor device; an enclosure for an electrical or telecommunication device; outdoor furniture; an article for boat or marine equipment, trim, enclosures, and housings; an outboard motor housing; a depth finder housing; a personal water-craft; a jet-ski; a pool; a spa; a hot-tub; a step; a step covering; a building or construction application glazing, roofs, windows, floors, decorative window furnishings or treatments; display items; a wall panel, or door; an outdoor or indoor sign; a part for automatic teller machines (ATM); an enclosure, housing, panel, or part for tractors or farm equipment, irrigation devices, lawn mowers, or tools, lawn and garden tools; an article of sports equipment or a toy; an enclosure, housing, panel, or part for a snowmobile; a recreational vehicle panel or component; an article of playground equipment; an article made from combinations of plastic and wood; a golf course marker; a utility pit cover; a computer housing; a computer housing; a portable computer housing; a laptop computer housing; a palm-held computer housing; a monitor housing; a keyboard; a telephone housing; a mobile phone housing; a radio sender housing; a radio receiver housing; a light fixture; a lighting appliance; a network interface device housing; a transformer housing; an air conditioner housing; seating for public transportation, trains, subways, or buses; a meter housing; an antenna housing; an article fabrication of satellite dishes; a helmet or other article of personal protective equipment.

High modulus weatherable polyester carbonate articles


A comparatively light and compact permanent magnet arrangement for an MRI apparatus has a pair of opposed permanent magnet arrays with a shimming system to adjust the uniformity and strength of a magnetic field in a central chamber of the apparatus. The MRI apparatus is used to examine the extremities of a patient to determine cardiovascular characteristics from an analysis of the blood flow through selected arteries in the extremity. The information collected can be used to calculate such characteristics as total cardiac output, blood flow, arterial wall thickness and elasticity and the presence of plaque.

This invention relates generally to the measurement of cardiac output and, more particularly, to apparatus and methods for non-invasively measuring cardiac output
Cardiac output is the volume of blood pumped by the heart during a given interval of time. Measuring cardiac output is a diagnostic technique used to evaluate cardiac function and detect the presence of cardiovascular disease or abnormality. Normally, cardiac output varies to meet the body's demand for oxygen and for nutrition. The left side of the heart receives oxygenated blood from the lungs and contracts, pumping the blood through arteries to all parts of the body. Blood flow is affected by such factors as the contractility of the left ventricle, the resistance against which the heart must pump and the volume of blood in the ventricle when pumping occurs.
Changes in cardiac output may indicate disease or may be evidence of an abnormality or change in a patient's cardiovascular system. Accordingly, measurement of cardiac output is a useful diagnostic tool and detection of changes in cardiac output may allow a physician to investigate a patient's condition more thoroughly and take measures to prevent serious or permanent damage.
Ideally, measurement of cardiac output should be quick, convenient, safe for the patient and should use equipment and techniques which are reliable, easy to operate and accurate.
There are a number of known techniques and devices for measuring cardiac output. One is the Fick method based upon work done by Adolph Fick in about 1870. As performed today, the Fick method involves injecting a measured amount of oxygen into an artery and then measuring the concentration of oxygen at a selected site downstream of the injection site. Typically, such a procedure involves the insertion of two catheters into a patient's body, one for the injection of the oxygen and the other for the collection of blood which is then analyzed and the oxygen content determined. While this technique produces satisfactorily accurate results, it does require surgically invasive procedures and the removal of an appreciable amount of blood which must then be analyzed, resulting in a measurement that is not a real time measurement. Whenever an invasive procedure is performed, it carries with it the attendant risk of possible infection.
In another technique for measuring cardiac output a dye is injected into the bloodstream and the dye concentration is measured at a point downstream of the injection site. Alternatively, a bolus of a chilled fluid indicator is injected and the temperature of blood withdrawn from a site downstream of the injection site is measured.
These and other cardiac output measurement techniques are well represented in the prior art.
The following references are representative of known invasive measurement techniques.
U.S. Pat. No. 5,797,395 (Martin) teaches and describes a continuous cardiac output derived from arterial pressure wave form using pattern recognition. Martin uses a fluid catheter installed in the bloodstream to measure the arterial pressure of a patient and to digitize the data collected by the sensors. The collected data is then compared to representative data stored in a database with representative wave forms corresponding to various levels of cardiac output.
U.S. Pat. No. 6,299,583 (Eggers) teaches and describes monitoring total circulating blood volume and cardiac output. Eggers et al uses a variation of the indicator dilution technique in which a test substance or analyte is injected into the body. As seen in FIG. 1 of Eggers et al, analyte is injected into the bloodstream by way of a catheter inserted into the subclavian vein leading to the heart. A catheter with a sensor is inserted into, for example, the radial artery in one of the patient's arms and is used to detect and measure the concentration of analyte.
U.S. Pat. No. 6,186,956 (McNamee) teaches and describes a method and system for continuously monitoring cardiac output without having to inject substances into the patient's body nor withdraw liquids from the body. McNamee does so by using a pressure transducer placed in a patient's mouth or a tracheal cannula in measuring the differential in pressure as the patient breathes in and out. The detection of this signal is then correlated to a table of known values from which cardiac output is deduced. McNamee references the use of MRI as an acceptable non-invasive measurement technique and also states that such techniques typically require large, expensive equipment and highly trained technicians to operate the equipment and interpret the results.
U.S. Pat. No. 6,322,518 (Young et al) teaches and describes a method and apparatus for measuring cardiac output which utilizes an esophageal probe inserted down the patient's throat to measure thoracic impedance variations which are then correlated to a measurement of cardiac output.
Even minimally invasive procedures require skilled technicians, risk infection and allergic responses, and cause apprehension and discomfort in the patient. The advantages of using non-invasive techniques for measuring cardiac output have been recognized in the prior art.
U.S. Pat. No. 6,306,098 (Orr et al) teaches and describes apparatus and method for non-invasively measuring cardiac output. Orr et al use a modification of the Fick approach, measuring the difference in carbon dioxide concentration between the air inhaled and exhaled by a patient through a breathing tube rather than measuring concentration of oxygen at disparate points in the patient's bloodstream. A computer program is used to calculate cardiac output based upon the differential in carbon dioxide concentration.
U.S. Pat. No. 5,458,126 (Cline et al) teaches and describes a cardiac functional analysis system employing gradient image segmentation. Cline et al describe the use of techniques such as computed axial tomography (CAT) and MRI to create a four-dimensional data set to create images of selected portions of the cardiovascular system. Cline et al are representative of the use of complex, expensive and quite large equipment to carry out these measurements.
U.S. Pat. No. 5,417,214 (Roberts et al) teaches and describes quantitative blood flow measurement using steady-state transport induced adiabatic fast passage. Again, Roberts et al is representative of the complexity presently experienced in the use of MRI to carry out cardiovascular measurements and evaluation. In particular, at column 5, lines 26 et seq. Roberts et al describe the necessity for precise techniques for gathering the data used in the analysis.
U.S. Pat. No. 6,348,038 (Band et al) teaches and describes method and apparatus for the measurement of cardiac output using the wave form created by the measurement of arterial blood pressure in a patient. The collected data is used to determine nominal stroke volume and using this determination to obtain a nominal value for the patient's cardiac output.
U.S. Pat. No. 5,360,005 (Wilk) teaches and describes a medical diagnosis device for sensing cardiac activity and blood flow. Wilk uses an acousto-electric transducer as a type of stethoscope to convert heart sounds into electric impulses and then uses a microprocessor to analyze these impulses and correlate them to cardiovascular activity.
U.S. Pat. No. 4,509,526 (Barnes et al) teaches and describes method and system for non-invasive ultrasound Doppler cardiac output measurement. Barnes et al teach the positioning of a transducer at separate locations on a patient's body to determine ultrasonically the cross-sectional area of a patient's ascending aorta and to determine the systolic velocity profile of blood flow through the aorta, enabling the calculation of cardiac output. To practice the technique described in Barnes et al the transducer must be accurately positioned by a technician at two separate sites in order to generate the data required to make the calculations necessary to determine cardiac output.
U.S. Pat. No. 5,178,151 (Sackner) teaches and describes a system for non-invasive detection of changes of cardiac volumes and aortic pulses. Sackner et al use transducers positioned on the patient's body to send and receive signals which include a wave form characteristic of the ventricular volume and then continuously monitors to detect changes in the wave form.
U.S. Pat. No. 5,443,073 (Wang et al) teaches and describes a system and method of impedance cardiography monitoring using body-mounted electrodes to collect EKG signals which are then mathematically processed to predict stroke volume.
U.S. Pat. No. 5,423,326 (Wang et al) teaches and describes apparatus and method for measuring cardiac output in which transducers are attached to a patient's body and the signals generated and collected by these transducers are transformed and analyzed to correlate these signals to cardiac output.
U.S. Pat. No. 5,309,917 (Wang et al) teaches and describes a system and method of impedance cardiography and heartbeat determination using a combination of thoracic impedance and electrocardiogram signals with the data represented by these signals processed to determine such characteristics as stroke volume and cardiac output.
U.S. Pat. No. 5,685,316 (Schookin et al) teaches and describes a non-invasive monitoring of hemodynamic parameters using impedance cardiography. Bioimpedance electrodes are used to collect data across a patient's thoracic region and the data so collected are analyzed and correlated to heart stroke volume from which cardiac output is calculated.
Although diagnostically useful, the foregoing art references demonstrate serious drawbacks ranging from the size, complexity and expense of the equipment used to obtain information to the requirement that the instruments used to collect the data. As an example, thoracic impedance systems use EKG leads which must be accurately positioned on and attached to a patient's body in order to effect the collection of data that is later translated into values for cardiac output.
In a text entitled "Magnetic Resonance of the Heart and Great Vessels", edited by J. Bogaert, A. J. Duerinckx and F.E. Rademakers (Springer-Verlag, Berlin 2000) the principles of MRI as applied to cardiology are set forth in Chapter 1, entitled "Techniques for Cardiac MRI", written by H. Bosmans. MRI examination begins with placing the patient within a strong, static magnetic field which aligns the spins of the protons contained in body tissues and fluids. Thereafter a radio frequency (RF) pulse is used to excite the protons and disturb the alignment of the protons with the magnetic field. A coil or detector is used to capture the signal produced by this change in alignment and return to the original alignment. The signal is influenced by two "relaxation times", T1 and T2, generally described as measuring the times it takes the longitudinal and transverse components of the "excited" protons to return to the aligned state. The resulting signals are characteristic of the type of tissue being examined and are processed to create an image of the tissues being studied.
The use of MRI in cardiac examination is also described in the March 2001 issue of Medica Mundi in an article reprinted from "Heart Care" written by E. Nagel and E. Fleck, beginning at page 23. At page 29 of the article, the use of MRI to determine blood flow velocities is discussed and the need for more accuracy in the equipment used is identified.
MRI technology is used to diagnose coronary disease by examining the flow of blood through blood vessels located in the arms. In one such proposed technique, the flow of blood is occluded with an inflatable cuff and MRI is used to measure the dilation of the blood vessels and the shear stress generated by the force of blood flow against the endothelial cells. Under normal circumstances, the endothelial cells will produce the chemical nitric oxide to cause the coronary arteries to widen thus increasing blood flow to the heart and other muscles during times of stress. In a patient with coronary artery disease this effect my be greatly attenuated.
Accordingly, the need exists for apparatus and methods to determine cardiac output which are wholly non-invasive, require no leads or other data collection devices to be attached to the patient, utilize recognized accurate diagnostic techniques such as MRI and which may be used in obtaining quick and accurate measurement of cardiac output without requiring significantly complex placement or measurement techniques.
A further object of the present invention is to provide an MRI unit which is relatively small and inexpensive yet which provide the precision and resolution necessary to make accurate measurements of cardiac output.
A further object is to make such equipment easy to operate without the use of time-consuming or complex diagnostic techniques.
A further object is to provide methods for the use of such equipment to make the required measurements carrying out such measurements on a patient's extremities rather than the thoracic cavity or the heart itself.
A further object is to avoid the use of drugs, analytes, dyes, tracers and other foreign substances.
The present invention is concerned with apparatus and methods to carry out the analysis of blood flow, preferably in the radial and ulnar arteries. The apparatus consists of an MRI unit significantly smaller in size than the full-body MRI units presently used to conduct cardiovascular examination. A pair of opposed magnet assemblies joined by a magnetically conductive yoke defines an air gap between the assemblies. When a patient's arm is placed within the air gap the unit is used to carry out MRI analysis of the blood vessels in the arm. Internal and peripheral shimming mechanisms allow the uniformity of the magnetic field to be adjusted, and the configuration of the magnets creates a magnetic field of about 1.0 tesla. A preferred configuration of the apparatus will be approximately 60 cm. by 60 cm. in cross-sectional size and will weigh about 250 kg.
While the following describes a preferred embodiment or embodiments of the present invention, it is to be understood that this description is made by way of example only and is not intended to limit the scope of the present invention. It is expected that alterations and further modifications, as well as other and further applications of the principles of the present invention will occur to others skilled in the art to which the invention relates and, while differing from the foregoing, remain within the spirit and scope of the invention as herein described and claimed. Where means-plus-function clauses are used in the claims such language is intended to cover the structures described herein as performing the recited functions and not only structural equivalents but equivalent structures as well. For the purposes of the present disclosure, two structures that perform the same function within an environment described above may be equivalent structures.
Referring now to FIG. 1, the numeral 10 indicates generally a diagnostic apparatus consisting generally of a cabinet 12 within which a permanent magnet assembly is disposed. Access to the cabinet is via a port 14 through which a patient 16 inserts his or her arm to place the arm within a magnetic field created by the magnet assembly. As seen in FIG. 2, the same apparatus can be used for a patient 18 when in the supine position. Apparatus 10 is relatively lightweight, compact in size and capable of providing real-time data.
Referring now to FIG. 3, the numeral 20 indicates generally a sectional view of a first permanent magnet assembly designed for use in diagnostic apparatus 10.
Assembly 20 consists of a steel main magnet 22 formed as a solid right circular cylindrical section having a vertical axis A. A circular toroidal side magnet 24 is positioned coaxially with main magnet 22 about axis A and in this preferred embodiment has a rectangular or square cross-section. A steel pole piece 26, formed as a solid right cylindrical section equal in diameter to main magnet 22 is positioned in face-to-face contact with main magnet 22 at main magnet face 28. This entire assembly is positioned within a hollow steel sleeve 30 which is closed off by a steel end cap 32.
In a preferred embodiment of the present invention, first permanent magnet assembly 20 is placed in face-to-face relationship with an identical permanent magnet assembly 34 having identical components to and spaced apart from first magnet assembly 20 to form an air gap 36 therebetween. Sleeve 30 extends to enclose magnet assemblies 20, 34 and air gap 36. A pair of removable side walls 38, 40 allow access to air gap 36 when removed from sleeve 30.
Permanent magnet assemblies 20, 34 are opposite in polarity to create a magnetic flux field across air gap 36. A centrally located segment of air gap 36 is identified in FIG. 3 as diagnostic zone 42 across which the magnetic flux is at its most powerful and its most uniform.
Magnet assembly 20 includes means for adjusting the flux field across zone 42. In a first embodiment of magnet assembly 20, pole piece 26 has a first centrally located cylindrical cavity 44 formed in interior face 26a. A second, circular cavity 46 is formed coaxial with cavity 44 and a third circular pole piece cavity 48 is similarly formed, coaxial with cavities 44 and 46.
Disposed within cavity 44 is a first cylindrical steel shim 50. Disposed within second circular cavity 46 is a toroidal steel shim 52 and disposed within third circular cavity 48 is a second toroidal steel shim 54.
Each shim 50, 52, 54 is adjustable along an axis parallel to axis A of permanent magnet assembly 20. A preferred embodiment of the adjusting mechanisms for shim 54 is shown in FIG. 3. A shaft 56 is bored through terminating in a countersink 58 larger in diameter than that of shaft 56 and extending to face 60 of pole piece 26. A threaded fastener, such as a bolt 62, is journalled to shim 54 and shim 54 may be adjusted with respect to face 60 by turning bolt 62 to move shim 54 toward or away from face 60.
At least three such bolts are attached to shim 54 and are placed equidistantly about the circumference of shim 54.
FIG. 4 is a view taken along 4-4 of FIG. 3 and illustrates the positioning of the shafts and adjusting bolts for each of the shims. In FIG. 4, bolts 62, 64 and 66 are attached to and serve to adjust shim 54. In like fashion, bolts 68, 70 and 72 are attached to and work to adjust first shim 52. Bolts 74, 76 and 78 are journalled to and serve to adjust cylindrical shim 50.
In a preferred embodiment of magnet assembly 20, a second set of toroidal steel shims are provided for the purpose of strengthening and adjusting the linearity of the magnetic flux field across air gap 36.
As seen in FIG. 3, steel sleeve 30 has a circumferentially extending channel 80, a concentric set of toroidal steel shims 82, 84, 86 are positioned in channel 80 and are supported and adjusted by a series of adjusting bolts such as those described in connection with shims 50, 52 and 54. As seen in FIG. 3, a bore 88 is formed extending through end cap 32 and having a countersink 90 formed at the end thereof. An adjusting bolt 92 is threadedly journaled to sleeve shim 82. A minimum of three such adjusting bolts are provided for each said shim and, as seen in FIG. 4, identical adjusting bolts are provided for sleeve shims 84 and 86. FIG. 4 shows, in section, bolts disposed in bores such as bore 88, with bolts 92, 94 and 96 attached to shim 84, bolts 98, 100 and 102 attached to shim 84 and bolts 104, 106, and 108 attached to shim 86.
Referring now to FIG. 5 the numeral 110 indicates generally a sectional view of a second permanent magnet assembly designed for use in diagnostic apparatus 10.
Magnet assembly 110 consist of a steel main magnet 112, formed as a solid right circular section having an axis B. A circular toroidal side magnet 114 is positioned coaxially with main magnet 112 about axis B. In the embodiment shown herein, side magnet 114 has a square cross section although cross sections of varying shapes may be selected. A steel pole piece 116, formed as a right solid cylindrical section equal in diameter to main magnet 112 is positioned in face-to-face with main magnet 112 and main magnet face 118. The entire assembly is positioned within a right cylindrical steel sleeve 120 which is closed off by a cylindrical steel end cap 122.
As with first magnet assembly 20, and consistent with a preferred embodiment of the present invention, second permanent magnet assembly 110 is placed within sleeve 120 in face-to-face relationship with an identical, mirror image permanent magnet assembly 124 having identical components and construction and spaced apart from second magnet assembly 110 to form an air gap 126 therebetween. Steel sleeve 30 extends to enclose magnet assemblies 110, 124 and air gap 126.
A pair of removable side walls 128, 130 allow access to air gap 126 when removed from sleeve 120. Permanent magnet assemblies 110, 124 are opposite in polarity to create a magnetic flux field across air gap 126. A centrally located segment of air gap 126 is identified in FIG. 5 as a diagnostic zone 132 across which the magnetic flux is at its most powerful and uniform. For purposes of illustration, face 118 of main magnet 112 has a north polarity while the corresponding face of the main magnet in magnet assembly 124 has a south polarity. As with magnet assembly 20, magnet assembly 110 includes means for adjusting the linearity of the flux field across air gap 126. In this second permanent magnet assembly embodiment, 110, exterior face 116a of pole piece 116 has a first centrally located cylindrical cavity 134 formed therein. A second, circular cavity 136 is formed coaxial with cavity 134 and a third circular pole piece cavity 138 is similarly formed, coaxial with cavities 134 and 136.
As seen in FIG. 5, a first steel shim 140 is disposed within cavity 44. Shim 140 is formed as a solid right cylindrical section or disk. Disposed within second circular cavity 136 is second steel shim 142 formed as a toroid and disposed with a third circular cavity 138 is a third steel shim 144 also formed as a toroid. In the preferred embodiment shown in FIG. 5, shims 142 and 144 are formed with square or rectangular cross-sectional shapes although other shapes may be selected as found desirable or necessary.
Each shim 140, 142 and 144 is adjustable along an axis parallel to axis B of permanent magnet assembly 110. A preferred embodiment of the adjusting mechanism for shim 144 is shown in FIG. 6. Shim 144 has a series of tapped or threaded apertures 146 formed parallel to axis B. In a preferred embodiment, apertures 146 are formed midway to the inner and outer diameters of shim 144 and at regularly spaced intervals. For example, three such apertures may be formed displaced one from the other by an angle of 120 degrees. An adjusting screw 148 has a head 150 and a shaft 152, with shaft 152 sized and threaded to engage tapped aperture 146. End 154 of shaft 152 is rotatably journalled to and supported by a support 156, allowing screw 148 to rotate in either a clockwise or counterclockwise direction. As screw 148 is rotated, shim 144 travels along shaft 152 as shaft 152 threads along tapped aperture 146.
Referring again to FIG. 5, a series of sleeve shims 252, 254 and 256 are shown concentrically disposed in a circumferentially extending channel 258 formed in sleeve 120. Shims 252, 254 and 256 are axially adjustable in the same manner as sleeve shims 82, 84 and 86 shown in FIG. 3. A representative threaded adjusting bolt 260 passes through a threaded bore 262 with bolt head 264 seated in countersink 266. Bolt end 268 is journaled to sleeve shim 252 in the same manner as shown in FIG. 6 and shim 252 is adjusted axially by threading bolt 260 along bore 262. Preferably, at least three such adjusting bolts are provided for each sleeve shim, spaced at regular intervals.
Referring to FIG. 7, shim 144 is shown in cavity 138 and supported by adjusting screws 148, 158 and 160. Similarly, shim 142 is shown in cavity 134 and supported by adjusting screws 162, 164 and 166. Central disk shaped shim 140 is shown in cavity 132 and is supported by adjusting screws 168, 170 and 172.
When assembled, the pole piece shims and annular shims described above are adjusted to produce a magnetic field across air gap 36 and air gap 126 with a high degree of uniformity in field strength and field direction.
Apparatus 10 is used to practice non-invasive methods of assessing total cardiac output, relative cardiac output, arterial wall thickness and elasticity and flow mediated dilation. Measurement of these functions is carried out non-invasively on a real-time basis and in a setting which is convenient and comfortable for the patient. These measurements are used for initial examinations and to track changes in the circulatory system before and after a given treatment. Use of apparatus 10 in carrying out MRI examinations is not subject to the variations and results produced using such techniques as ultrasound where personnel must be highly trained to position accurately the probe used during examinations.
In a preferred embodiment of the present invention, apparatus 10 is used to perform an MRI examination of the radial and ulnar arteries in a patient's arm.
Referring now to FIG. 8, the numeral 174 identifies the arm of a patient shown in a schematic-type cross-section. For the purposes of illustrating the present invention, reference will be made to the permanent magnet arrangement shown in FIG. 3. Arm 174 is placed within apparatus 10 as shown in FIG. 1 or 2 with arm 174 extending through air gap 36 and positioned within diagnostic zone 42. An RF coil 176 is positioned above arm 174 and a gradient or pickup coil 178 is positioned beneath arm 174 to receive the signal created when RF coil 176 is pulsed.
As seen schematically in FIG. 8, the radial and ulnar bones 180, 182 are shown, as are the radial and ulnar arteries 184, 186. As the heart beats, the blood pressure within the body's arterial blood vessels varies from a maximum (systolic) and minimum (diastolic) value. The systolic blood pressure represents pressure within the blood vessel during a heartbeat while the diastolic pressure is that measured when the heart is at rest between beats. Arteries 184, 186 are shown during the diastolic portion of the heartbeat cycle. When the heart beats, arteries such as 184, 186 expand as shown at 188, 190.
The apparatus and methods of the present invention measure and record the changes in size of arteries 184, 186 with the heartbeat and between heartbeats. In this fashion, the cross-sectional area of arteries 184, 186 can be determined. It is also known to determine the rate of flow of blood using commonly applicable MRI techniques and the combination of the determination of artery cross-sectional area and rate of flow allows calculation of the portion of the total cardiac output passing through the representative arteries during a heartbeat.
This information can be used to establish a baseline cardiac output for a patient with any deviation in output over time operating as an indicator that the patient's cardiac condition has changed. Cardiac output can also be calculated by using known values of the percentage of cardiac output normally passing through the radial and ulnar arteries and using this ratio to estimate total cardiac output. For the purposes of this description, total cardiac output is defined as the volume of blood pumped from the heart with each beat, approximately 12% of which moves through the brachial arteries of each arm with each beat and the detected blood flow volume can be compared to tables of known blood flow ratios for patients of different ages, weights and other variables.
MRI allows a cross-section to be taken that includes both arteries 184, 186 simultaneously. In order to create a high resolution image, it may be necessary to reposition the arm within the magnetic field prior to pulsing the RF electrodes. An alternative to physical repositioning is the use of an array of electrodes and a computer program to adjust the pulsing of the electrodes to produce improved images.
For purposes of accuracy, pick up coil 178 should be positioned as close as possible to the arteries being measured. Use of the relatively small diagnostic area 42 makes this possible and readings can be taken with the patient's arm extending into apparatus 10 with the palm either facing in the upward or downward position or rotated to produce an optimum image of the arteries.
Referring now to FIG. 9, the numeral 192 identifies generally an array of RF coils positioned around a patient's arm 194. RF coils such as those used as electrodes in MRI diagnostic equipment can be used as pulsing or receiving coils or can function as both pulsing and receiving coils. For a single coil to both pulse and receive, an rf signal is pulsed through the coil. This transmission is gated and after it has ceased the coil goes through a period of quiescent or "dead" time where no signal is being sent nor received. Thereafter, the coil is activated to receive the data produced by its own pulsed signal. The data signal is also gated to create a second period of dead time, after which the coil may then again be pulsed to transmit another signal.
As seen in FIG. 9, an array of RF coils 196, 198, 200 are positioned equidistantly about the circumference of array perimeter 202. It is possible to pulse these coils in sequence to create a "virtual coil" effectively positioned at selected points about the periphery of perimeter 202. It is also possible to mechanically rotate perimeter 202 to bring coils 196, 198, 200 into a different physical location with respect to arm 194. By performing actual or virtual rotation of the positions of coils 196, 198, 200 and selectively using each coil selectively to pulse energy, receive energy or both it is possible to adjust device 10 to produce the clearest possible image of arm 194.
To increase the sensitivity and adjustability of array 192, additional RF coils can be added to the array such as coils 204, 206, and 208 and to control the pulsing and collection capabilities of each coil by computer in order to adjust the received image.
Referring now to FIG. 10, the numeral 210 identifies a cross-sectional view of a tubular sleeve within which RF coils 212, 214 and 216 are disposed. Sleeve 210 can be formed of fabric and is intended to be slipped over the patient's arm or other appendage and to thereafter be placed within device 10. Sleeve 10 allows coils 212, 214, 216 to be placed as close to the area of examination as possible and to provide a uniform dispersion of signal transmission and collection independent of the placement of coils within device 10 itself.
As described in connection with array 192, sleeve 210 can include any selected number of coils and the arrangement shown in FIG. 10 is by way of example only.
Sleeve 210 can be formed as a permanent, flexible and expandable cuff or can be formed as a disposable unit which can be discarded after use. Sleeve 210 can be provided in a range of sizes to accommodate extremities of varying proportions, can be written upon to record patient information, and can contain various numbers and configurations of coils and coil leads that can selectively be connected to provide energy to selected coils.
Referring now to FIG. 11, an alternative construction for pole pieces such as pole piece 60 is shown. FIG. 11 is a cross-sectional view of a pole piece 218 constructed as a series of laminae 220, 224, 226, 228 and 230 glued together in a solid array by non-conductive epoxy glue or other well-known permanent adhesives.
As seen in FIG. 12, a section of laminae 220 is shown in partial perspective. Each laminae is formed of a series of cubes 232 preferably extruded from ferromagnetic material and glued together with the adhesives described above. In a preferred embodiment of the invention, each cube is approximately 10 mm by 10 mm by 10 mm. When cubes 232 have been solidly glued into a planar array, each such array is stacked and glued to corresponding arrays to produce the structure shown in FIG. 11. The completed array may then be machined to the shape desired to use the completed array as a pole piece.
Use of cubic elements are believed to limit the eddy currents created within the ferromagnetic pole piece when the RF coils are pulsed. Referring now to FIG. 13, a top plan view of a segment of pole piece 218 is shown illustrating the appearances of cubes 232 when cemented into the array and shaped to be used as a pole piece. In assembling a laminated pole piece such as 218, cubes 232 are arranged such that the interfaces of adjacent cubes are offset from the interfaces of the cubes in the layers immediately above and below thereby adding strength to the array.
Referring now to FIG. 14, the numeral 234 identifies a segment of an alternative construction of the torroidal shim rings such as 54 of FIG. 3. The embodiment of FIG. 14 shows shim 234 assembled from overlapping segments 236, 238 with segment 236 having an upper edge 240 and intermediate land 242 and a lower edge 244 while segment 238 has an upper edge 246 an intermediate land 248 and a lower edge 250. When assembled, edges 240, 246 abut as do lands 242, 248 and lower edges 244, 250. At each of these abutments, an epoxy or other suitable adhesive is used to permanently attach the segments together.
It is also contemplated that the torroidal and disk-shaped shims described earlier can also be constructed from laminae in the manner shown in FIGS. 11, 12, and 13. In such constructions, it is contemplated that cubes 232, when used in shim constructions, can be extruded from ferromagnetic metals, non-ferromagnetic metals, non-metallic substances or magnetic material.
While not herein specifically shown, it is acknowledged that the use of electromagnetic gradient coils as shims to adjust the linearity and shape of the magnetic field of a permanent magnet array is well known and can be included in the arrangements described herein. Such shim coils can also be used as gradient coils by pulsing the coils to intentionally distort the field of view to aid in distinguishing between tissues of different types. Preferably, separate shim and gradient coils are used to keep voltage to the shim coils constant.
The disclosed methods and apparatus offer advantages over prior known MRI diagnostic methods in that a relatively small permanent magnet arrangement is used to produce a high strength uniform and high resolution magnetic field across a very small part of the body. This is a much different approach than that described in the Nagel and Fleck article referenced above in which a patient is "positioned within the bore of a cylindrical superconducting magnet." The strength of the magnetic field produced by the present invention is estimated in excess of 1.0 tesla and the relatively small size of the body portion being sampled creates an image with a higher signal-to-noise ratio than can be achieved when the entire body is placed within a magnetic field. The resulting high resolution images allow the changes in size of the arteries to be accurately determined.
When performing MRI diagnostic procedures, care must be taken to avoid damage to nerves caused by too high a field gradient across the area of the body being examined. For the purposes of this description, the field gradient is described as the strength of the magnetic field divided by the area of the field of view in question. Using the greatly reduced field of view made possible by the present invention, allows for higher gradients to be safely used when examining patients. This results in higher resolution images and more accurate diagnostic information.
Total cardiac output can be estimated by relating the radial and ulnar arteries and comparing these measurements to known values of percentages of cardiac output measured through such arteries.
Use of the present invention thus allows cardiac functions to be examined in a strong, small magnetic field with a relatively high field gradient. This will also result in the capability of using rapid pulses to produce accurate images showing the changes in size of the arteries in question.
The apparatus described herein uses less energy and is less expensive to build than the presently known full body type MRI diagnostic units.
In evaluating cardiac function, the RF pulses may be timed to commence with the heartbeat and can be used to track changes in the heartbeat. Alternatively, use of the present invention may be used without using the heartbeat as a trigger or marker with the apparatus being operated through a sufficient number of cycles to guarantee that an entire cycle has been captured and accurately characterized.
Use of MRI to create images of arteries 186, 188 is superior to the use of ultrasound because MRI produces a cross-sectional view which allows the system to track the changes in size and configuration of arteries 186, 188. Ultrasound, on the other hand will provide only a lateral view and even though this lateral view can show changes in the apparent diameter of the arteries, it does not provide an accurate view of the actual cross-sectional configuration of the artery. Where an artery is, for example, not perfectly round or in some way impeded, the cross-section will be less than circular. However, MRI will enable the operator to determine the exact shape and, therefore, area of the cross-section and to calculate the blood flow therethrough.

Method for non-invasive measurement of cardiac output