Thermally stabilized initiator composition comprising:

This invention relates to compositions classified in the art of chemistry as dialkyl peroxydicarbonates, more specifically to new and novel thermally-stabilized initiator compositions comprising dialkyl peroxydicarbonates stabilized by the addition thereto of a stabilizing effective amount of at least one stabilizing compound selected from the group consisting of diesters of unsaturated dicarboxylic acids. The invention further relates to the use of such novel compositions as initiators of polymerization or cure of ethylenically unsaturated monomers, oligomers and polymers. The invention still further relates to the stabilization of dialkyl peroxydicarbonates during their manufacture by the inclusion of stabilizing effective amount of at least one stabilizing compound selected from the group consisting of non-hydrolyzable diesters of unsaturated dicarboxylic acids in the mixture of reactants from which a dialkyl peroxydicarbonate is to be prepared prior to, at the commencement of, or during the preparative reaction.
Generally, dialkyl peroxydicarbonates which are in liquid form (molten or in solution) above ca. 10. degree. c. are very hazardous owing to auto-accelerated decomposition attributed to induced decomposition of the dialkyl peroxydicarbonate.
Strain, et al. (J. Am. Chem. Soc., 1950, 72, 1254-1263) found that auto-accelerated decomposition of diisopropyl peroxydicarbonate (IPP) at room temperature could be largely suppressed by incorporating small quantities of additives such as iodine (1%) phenol (1%), hydroquinone (1%), resorcinol (1%), pyrogallol (1%), tetralin (1%), ethyl acetoacetate (1%), acetanilide (1%), trinitrobenzene (1%), 30% hydrogen peroxide (1%) and several other additives. However, when such stabilizing compositions are used to polymerize vinyl chloride monomer (VCM), there is potential for contamination of the resulting PVC resin by the additives. This contamination is undesirable, both for the PVC resin as well as for the environment. Because the thermally stabilized dialkyl peroxydicarbonate compositions of the instant invention contain olefinic unsaturation, the diluent is copolymerized with VCM at very low levels and, thus, does not contaminate the PVC resin or the effluent from the polymerization process.
U.S. Pat. No. 5,155,192 discloses stabilized peroxydicarbonate compositions containing small amounts (0.03 to 3.0 equivalent percent) of compounds containing hydroperoxy groups. Such compositions are claimed to reduce sensitivity to auto-accelerative decompositions, increase safe storage temperatures and increase self-accelerating decomposition temperatures (SADTs). However, polymer producers such as PVC producers do not like to employ initiators containing significant levels of hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide since these impurities are free-radical chain-transfer agents and can become incorporated into the resin molecular chains as peroxy end groups. Such labile end groups can adversely affect the thermal and color stability of the resin. In addition, the lower molecular weight t-alkyl hydroperoxides such as t-butyl and t-amyl hydroperoxides are sufficiently volatile to cause problems during recycle of vinyl chloride and other monomers.
The thermally stabilized dialkyl peroxydicarbonate compositions of the instant invention, which contain compounds having olefinic unsaturation advance the peroxide art and the polymerization art since they do not cause the above resin stability problems or monomer recycle problems.
U.S. Pat. Nos. 5,541,151 and 5,548,046 disclose stabilized peroxydicarbonate solutions containing small amounts (0.05 to 1.4 equivalent percent) of compounds having an ethylenically unsaturated functional group conjugated with an acetylenic or nitrile functional group. Such compositions are stated to enhance safety for manufacture, storage, handling and use of pure liquid dialkyl peroxydicarbonates. Polymer producers, such as polyvinylchloride manufacturers prefer not to use initiators stabilized with compounds having ethylenic unsaturation conjugated with acetylenic or nitrile groups, such as acrylonitrile or methacrylonitrile due to toxicity and waste water concerns. These compounds are toxic and/or carcinogenic and would require special waste water handling and permits.
U.S. Pat. No 5,654,463 discloses the use of xcex1-hydroxyalkyl peroxide compounds to retard the rate of decomposition of organic peroxides such as peroxydicarbonates. However, the addition of such higher half-life peroxides can cause problems during the recycle of vinyl chloride or other monomers and can cause gel formation during stripping of the resin.
U.S. Pat. No. 5,654,464 discloses the use of cyclic xcex1-diketone compounds to retard the rate of decomposition of organic peroxides, such as peroxydicarbonates. U.S. Pat. No. 5,714,626 discloses the use of xcex2-dicarbonyl compounds to retard the rate of decomposition of organic peroxides, such as peroxydicarbonates. U.S. Pat. No. 5,719,304 discloses the use of phosphomolybdic acid to retard the rate of decomposition of organic peroxides, such as peroxydicarbonates. However, polymer producers, including polyvinylchloride manufacturers do not like to employ peroxides stabilized using these materials since their use introduces impurities which can cause toxicity and quality problems in the final resin.
U.S. Pat. Nos. 4,131,728 and 4,178,263 disclose shock desensitized peroxide compositions which comprise a mixture of shock sensitive peroxide and a diluent. The diluent is a monomeric material containing olefinic unsaturation which does not readily homopolymerize. Peroxydicarbonates are not included in the types of peroxides which are illustrated as suitable for use in the invention of these patents. The stabilization by the various monomeric materials is for the express purpose of reducing the shock sensitivity of the peroxides being stabilized and the monomeric materials are also stated to not adversely affect the heat distortion temperatures of the final resin. There is no known correlation between the ability to reduce shock sensitivity and the ability to reduce auto-accelerated decomposition, increase safe storage temperatures or raise SADTs.
The lack of correlation can be seeing using the data in the following tables.
% Assay Loss during Storage
t-Butyl Peroxyneodecanoate (75%) in OMS
t-Butyl Peroxyneodecanoate (75%) in Dibutyl Maleate
The dibutyl maleate will have decreased the shock sensitivity as mentioned in the two aforementioned patents, but did not increase the safety characteristics of the peroxyesters. Quite unexpectedly, the safety characteristics of peroxydicarbonates are increased with the practice of the instant invention (Tables I, II, III, IV).
The above two patents also disclose that any solvent will reduce shock sensitivity but that some will also have a deleterious effect on properties of the polymer produced. Among the monomeric diluents disclosed as suitable for the invention of these patents are many that cannot be used during the manufacturing process of organic peroxides. Solid diluents may interfere with aqueous separations and many of the proposed compounds will hydrolyze under peroxide production conditions leaving pure unstabilized peroxide in the reactor at elevated temperatures; an extremely dangerous and undesirable state. Furthermore, the organic peroxides disclosed in these patents are no longer considered shock sensitive by today""s standard test methods.
It is generally known to organic peroxide producers, see the Strain reference cited above, that lower molecular weight dialkyl peroxydicarbonates (such as diisopropyl peroxydicarbonate), which are in the liquid state during their production by reaction of an alkyl chloroformate with an aqueous solution of hydrogen peroxide and an inorganic base such as sodium hydroxide or potassium hydroxide, can be thermally stabilized and prevented from undergoing auto- or self-accelerating decomposition during manufacture by bubbling oxygen gas or an oxygen containing gas, e.g., air, through the reaction mixture. However, in such processes at least one settling of the reaction mixture into an upper organic phase (dialkyl peroxydicarbonate) and a lower aqueous phase is required. During these separations, agitation necessarily is terminated and bubbling of oxygen gas or an oxygen containing gas is stopped in order to enable complete separation of phases. During this quiescent period the organic dialkyl peroxydicarbonate phase is deprived of oxygen stabilizer and a hazardous self-accelerating decomposition of the liquid dialkyl peroxydicarbonate phase can occur.
This invention provides a novel manufacturing process of enhanced safety for production of liquid dialkyl peroxydicarbonates. The process employs a quantity of a diester of an unsaturated dicarboxylic acid which does not hydrolyze under the reaction conditions during manufacture, thus suppressing self-accelerating decomposition of the liquid peroxydicarbonate during manufacture and enhancing the thermal stability of the liquid dialkyl peroxydicarbonate during subsequent storage and handling.
The novel processes providing enhanced safety for the manufacture, storage, handling and use of pure liquid dialkyl peroxydicarbonates can be of the batch type, continuous type or semi-continuous type.
It should be noted that the addition of the organic hydroperoxide stabilizers for dialkyl peroxydicarbonates known in the art, such as those provided by the aforementioned U.S. Pat. No. 5,155,192, during the process for production of pure liquid dialkyl peroxydicarbonates would not be effective for thermally stabilizing the dialkyl peroxydicarbonates during processing or subsequent to processing since the art organic hydroperoxide stabilizers are reactive with alkyl chloroformates, forming OO-t-alkyl O-alkyl monoperoxycarbonates: which are not known stabilizers for dialkyl peroxydicarbonates. Furthermore, many of the organic hydroperoxides of the art are likely to partition into the aqueous phase that are involved in dialkyl peroxydicarbonate manufacturing processes, and, thus, the thermal stabilizers would not be present in the organic dialkyl peroxydicarbonate phase where thermal stabilization is needed.
Therefore, the stabilizing compounds of this invention are also superior to the stabilizers previously known for thermally stabilizing dialkyl peroxydicarbonates during production.
As used herein and in the appended claims the following terms have the meanings here in set forth:
Substantially pure means at least about 95% pure. Stabilizing effective amount means from about 10% to about 90%, preferably about 20% to about 50% by weight, based on the weight of dialkyl peroxydicarbonate, of a compound of Structure I. In the case of stabilization of a liquid dialkyl peroxydicarbonate during its preparation, stabilizing effective amount means the above stated range of amounts of a compound of Structure I wherein R1 and R2 are 4 carbon atoms or greater added to the reaction calculated on the theoretical yield of dialkyl peroxydicarbonate expected from the reaction. Mixtures of stabilizing diesters of unsaturated dicarboxylic acid, such as those of Structure I may also be employed in the same total quantity proportions.
xe2x80x9cA diester of an unsaturated dicarboxylic acid which does not hydrolyze under the reaction conditionsxe2x80x9d of preparation of alkyl peroxydicarbonate is a compound of Structure I as defined below but wherein the alkyl groups R1 and R2 are limited to 4 or greater carbon atoms.
The invention provides in a first composition aspect, a dialkyl peroxydicarbonate, containing a stabilizing effective amount of at least one compound having the Structure I:
wherein R1 and R2 are the same or different and are selected from the group consisting of alkyl of 1 to 20 carbon atoms, cycloalkyl of 6 to 10 carbon atoms, aralkyl of 7 to 11 carbon atoms, aryl of 6 to 10 carbon atoms and mixtures thereof; and
Special mention is made is made of those compounds of Structure I wherein R1 and R2 are selected from the above defined alkyl, cycloalkyl, aralkyl, aryl groups having 4 or more carbon atoms. Particular mention is also made of compositions of the first composition aspect of the invention wherein the dialkyl peroxydicarbonate is selected from compounds having the Structure II:
wherein R4 and R5 are the same or different and are selected from the group consisting of substituted or unsubstituted alkyl of 2 to 22 carbons, substituted or unsubstituted cyclcoalkyl of 5 to 12 carbons, substituted or unsubstituted bicycloalkyl of 7 to 9 carbons, and substituted or unsubstituted aralkyl of 7 to 12 carbons, with substituents for alkyl being one or more alkyl of 1 to 4 carbons, alkoxy of 1 to 6 carbons or phenoxy, substituents for cycloalkyl being one or more alkyl of 1 to 6 carbons, substituents for bicycloalkyl being one or more alkyl of 1 to 4 carbons and substituents for aralkyl being one or more alkyl of 1 to 4 carbons, chloro, bromo, methoxy and carboxy. Further mention is made of compositions wherein either or both R4 and R5 are selected from the group consisting of substituted or unsubstituted alkyl radicals of 2 to 22 carbons, preferably 2 to 18 carbons, more preferably 3 to 16 carbons, substituents being alkyl radicals of 1 to 4 carbons, alkoxy radicals of 1 to 6 carbons or phenoxy radicals. Further mention is also made of compositions wherein either or both of R4 and R5 are selected from substituted cycloalkyl radicals of 5 to 12 carbons, preferably 5 to 7 carbons, substituents being one or more alkyl radicals of 1 to 6 carbons.
The invention provides in a first process aspect, a process for polymerization of ethylenically unsaturated compounds comprising treating one or more ethylenically unsaturated compounds with an amount of at least one composition of the first composition aspect of the invention sufficient to initiate polymerization under conditions of time temperature and pressure sufficient to initiate polymerization.
Special mention is made of processes of the first process aspect of the invention wherein at least one of the unsaturated compounds to be polymerized is selected from the group consisting of an unsaturated polyester resin blend, vinyl chloride, styrene, diethylene bis(allyl carbonate), and wherein the peroxydicarbonate is selected from at least one compound having Structure II.
The invention provides in a second process aspect, a process for preparing a thermally-stabilized initiator composition of the first composition aspect of the invention which comprises reacting at least one alkyl chloroformate and aqueous hydrogen peroxide under conditions effective to form the dialkyl peroxydicarbonate in the presence of a stabilizing effective amount of at least one compound having Structure I which is a diester of an unsaturated dicarboxylic acid which does not hydrolyze under the reaction conditions.
The stabilized dialkyl peroxydicarbonate compositions of this invention, except for the presence of stabilizing amount of the aforedescribed compound of Structure I, can be in the form of a liquid containing substantially pure liquid dialkyl peroxydicarbonate, can be in the form of a solid as a substantially pure solid dialkyl peroxydicarbonate, can be in the form of a dispersion containing 10 to 50% solid dialkyl peroxydicarbonate, or can be in the form of an emulsion containing 10 to 70% liquid dialkyl peroxydicarbonate. Mixtures of dialkyl peroxydicarbonates prepared by simultaneous reaction of two or more chloroformates with aqueous hydrogen peroxide are specifically contemplated by the invention.
A. List of Illustrative Examples
1. Components
Non-limiting examples of suitable dialkyl peroxydicarbonates that are useful for preparing the thermally stabilized dialkyl peroxydicarbonate compositions of this invention include liquid dialkyl peroxydicarbonates [melting point (mp) below 15xc2x0 C.], such as diethyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate (mp=10xc2x0 C.), di-n-butyl peroxydicarbonate, diisobutyl peroxydicarbonate, di-n-hexyl peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate and di(2-methoxypropyl)peroxydicarbonate, and solid dialkyl peroxydicarbonates (mp above 15xc2x0 C.), such as di(n-tridecyl)peroxydicarbonate (mp=43xc2x0-45xc2x0 C.) di(n-hexadecyl)peroxydicarbonate (mp=52xc2x0 C.), dibenzyl peroxydicarbonate (mp=101-102xc2x0 C.), dicyclohexyl peroxydicarbonate (mp=46xc2x0 C.), di(cis-3,3,5-trimethylcyclohexyl) peroxydicarbonate (mp=81xc2x0-82xc2x0 C.), di(4-t-butylcyclohexyl)peroxydicarbonate (mp=91xc2x0-92xc2x0 C.), dibornyl peroxydicarbonate (mp=94xc2x0-96xc2x0 C.) and di(2-phenoxyethyl)peroxydicarbonate (mp=97xc2x0-100xc2x0 C).
The stabilizing compounds are diesters of unsaturated dicarboxylic acids. While the compounds of Structure I and claimed herein are typical, the invention specifically contemplates as a full equivalent any compound having ethylenic unsaturation conjugated with carboxylic ester functions in the xcex1 position and which is miscible with the dialkyl peroxydicarbonate being stabilized in concentrations capable of providing an equivalent quantity of the conjugated unsaturated conjugated carboxylic ester system to that provided by the compounds of Structure I when those latter compounds are used in their contemplated concentrations. Non-limiting examples of suitable diesters of unsaturated dicarboxylic acids of Structure I that are useful for thermally stabilizing and preparing the thermally stabilized dialkyl peroxydicarbonate compositions of this invention include dibutyl maleate, dibutyl fumarate, diphenyl maleate, diethyl maleate, dimethyl maleate, di(3-methylphenyl)maleate, dioctyl maleate, dibenzyl maleate, dicyclohexyl maleate, di-t-butyl maleate, di-t-amyl maleate. Other compounds falling within the general category are well known in the literature and are readily prepared by methods well known to those skill in the art.
Non-limiting examples of suitable solvents that may optionally be used for preparing the thermally stabilized dialkyl peroxydicarbonate solutions of this invention include odorless mineral spirits (OMS), toluene, dimethyl phthalate, dibutyl phthalate and dioctyl phthalate.
2. Manufacturing Processes
This invention also provides a novel manufacturing process of enhanced safety for production of dialkyl peroxydicarbonates and simultaneously provides an alternate means for producing novel, stabilized dialkyl peroxydicarbonate compositions containing an amount of stabilizing compound sufficient to stabilize the dialkyl peroxydicarbonate that is from about 10 to about 90%, preferably 20 to 50% by weight on dialkyl peroxydicarbonate, of a compound of Structure I which will not hydrolyze under the reaction conditions.
The process employs a quantity (10 to 90%, preferably 20 to 50% by weight based on dialkyl peroxydicarbonate) of a compound of Structure I which will not hydrolyze under the reaction conditions during the processing for enhancing the thermal stability of the dialkyl peroxydicarbonate during manufacture, thus suppressing self-accelerating decomposition of the dialkyl peroxydicarbonate during subsequent storage and handling.
The novel manufacturing process for production of dialkyl peroxydicarbonates involves the following process steps:
a. Reaction Stepxe2x80x94A substantially pure alkyl chloroformate, or a mixture of substantially pure alkyl chloroformates, (1.8 to 2.2 moles, preferably 1.9 to 2.1 moles per mole of hydrogen peroxide) is rapidly reacted with an aqueous solution of hydrogen peroxide (1.0 mole per mole of hydrogen peroxide) and sodium hydroxide or potassium hydroxide (1.9 to 2.6, preferably 2.0 to 2.2 moles per mole of hydrogen peroxide) at about xe2x88x9210xc2x0 C. to 30xc2x0 C., preferably 0xc2x0 C. to 20xc2x0 C., and the reaction mass is agitated for about 15-60 minutes, preferably 20-40 minutes, at 0xc2x0 C. to 30xc2x0 C. preferably 0xc2x0 C. to 20xc2x0 C.
b. Initial organic Phase/Aqueous Phase Separationxe2x80x94Agitation is stopped and the reaction mass is allowed to separate into an upper organic layer and a lower aqueous layer at 0xc2x0 C. to 25xc2x0 C., preferably 5xc2x0 C. to 20xc2x0 C., over a period of 5-40 minutes, preferably 10-30 minutes. The aqueous layer is drawn off and discarded.
c. Aqueous Wash and Separationxe2x80x94To the crude dialkyl peroxydicarbonate from step b is added a saturated aqueous salt solution (i.e., a saturated salt solution derived from ammonium, sodium and potassium chlorides, sulfates and phosphates, preferably sodium chloride) at 0xc2x0 C. to 25xc2x0 C., preferably 5xc2x0 C. to 20xc2x0 C., and the mixture is agitated for about 1-30 minutes at 0xc2x0 C. to 25xc2x0 C., preferably 5xc2x0 C. to 20xc2x0 C. Agitation is stopped and the reaction mass is allowed to separate into an upper organic layer and a lower aqueous layer at 0xc2x0 C. to 25xc2x0 C., preferably 5xc2x0 C. to 20xc2x0 C., over a period of 5-40 minutes, preferably 10-30 minutes. The aqueous layer is drawn off and discarded. This salt wash can be repeated or a different wash treatment can be employed if required, to purify the dialkyl peroxydicarbonate.
d. Drying Stepxe2x80x94The wet dialkyl peroxydicarbonate from step c is dried over about 1-10%, preferably 5%, by weight of anhydrous sodium sulfate or anhydrous magnesium sulfate at 0xc2x0 C. to 25xc2x0 C., preferably 0xc2x0 C. to 15xc2x0 C., and the spent desiccant is separated by filtration or centrifugation at 0xc2x0 C. to 25xc2x0 C., preferably 0xc2x0 C. to 15xc2x0 C., or the wet dialkyl peroxydicarbonate is blown with a relatively dry gas (e.g., dry air) at 0xc2x0 C. to 25xc2x0 C., preferably 0xc2x0 C. to 15xc2x0 C. Then the dry peroxide is packed out and chilled prior to storage at about xe2x88x9225xc2x0 C. to xe2x88x925xc2x0 C.
The addition of a compound of Structure I which will not hydrolyze under the reaction conditions in the process can be made at any of the several steps of the process. Preferably, the addition of the appropriate compound of Structure I is made shortly before the initial organic phase/aqueous phase separation step [i.e., at the end of Step a] and agitation is continued for 1-5 minutes at 0xc2x0 C. to 30xc2x0 C. At this stage of the process, the appropriate stabilizing compound of Structure I (thermal stabilizer) is present in the organic phase that would otherwise contain substantially pure dialkyl peroxydicarbonate. The thermal stabilizer will remain present in the substantially pure dialkyl peroxydicarbonate phase in the subsequent steps of the process, and during storage and handling. Addition of C1 to C3 alkyl diesters, such as those included in Structure I, at the beginning of the reaction stage [i.e., at the beginning of Step a] could result in some loss of thermal stabilizing activity owing to at least partial hydrolysis of the active diester to an inactive unsaturated mono ester or dicarboxylic acid which will be extracted into the aqueous phase.
The novel processes for pure dialkyl peroxydicarbonates can be of the batch type, continuous type or semi-continuous type:
Batch Processesxe2x80x94For economic commercial batch processes, large reactors, agitators and cooling capacities are required, the size of each being determined by the size of the maximum reaction mass encountered during the process and the maximum heat load required during the process. Large quantities of the product are present in crude or pure form during or at the end of the batch process. Large quantities of product are produced discontinuously at various points in time. Typical batch processes for dialkyl peroxydicarbonates are described in the chemical literature (see, for example, the Strain reference cited above).
Continuous Processesxe2x80x94For economic commercial continuous processes, relatively small reactors, agitators and cooling capacities are sufficient as small quantities of reactants, and wash treatments are continuously added at various stages of the process and small quantities of product are produced continuously.
Once a continuous process has been established, addition of reactants and wash treatments at different points in the process and production of product are not only continuous but also simultaneous. Continuous processes are inherently safer than batch processes for production of explosively hazardous products such as organic peroxides. A continuous process for production of pure liquid dialkyl peroxydicarbonates is described in U.S. Pat. No. 3,950,375.
Semi-Continuous Processesxe2x80x94these processes are hybrids of batch and continuous processes, using batch processing at stages of the process where advantageous. Generally, small reactors, agitators and cooling capacities are employed at various continuous stages of the semi-continuous processes. Larger reactors, agitators and cooling capacities are required during the batch stages of the processes. Semi-continuous processes for production of organic peroxides are generally less hazardous than batch processes.
It should be noted that addition of organic hydroperoxide stabilizers (as described in the previously referenced U.S. Pat. No. 5,155,192) for dialkyl peroxydicarbonates during the process for production of pure dialkyl peroxydicarbonates can not be done during processing since such organic hydroperoxide stabilizers are reactive with alkyl chloroformates, forming OO-t-alkyl O-alkyl monoperoxycarbonates, which are not known stabilizers for dialkyl peroxydicarbonates. Furthermore, many of the organic hydroperoxides are likely to partition into the aqueous phases that are involved in dialkyl peroxydicarbonate processes, and, thus would not be present in the organic dialkyl peroxydicarbonate phase where thermal stabilization is needed. Therefore, the diesters of unsaturated dicarboxylic acids of Structure I, of this invention are superior to the art thermal stabilizers for thermally stabilizing dialkyl peroxydicarbonates during manufacture.
3. Compositions
Non-limiting examples of the novel, thermally stabilized dialkyl peroxydicarbonate compositions of this invention, in addition to those of the examples, include those given in Table A.
B. Utility
1. Polymerization of Ethylenically Unsaturated Monomers
In the free-radical polymerizations of ethylenically unsaturated monomers at suitable temperatures and pressures the novel stabilized peroxydicarbonate initiator compositions of this invention were found to be effective initiators with respect to efficiency (initiator requirements, etc.). Ethylenically unsaturated monomers include olefins, such as ethylene, propylene, styrene, alpha-methylstyrene, p-methylstyrene, chlorostyrenes, bromostyrenes, vinylbenzyl chloride, vinylpyridine and divinylbenzene; diolefins, such as 1,3 butadiene, isoprene and chloroprene; vinyl esters, such as vinyl acetate, vinyl propionate, vinyl laurate, vinyl benzoate and divinyl carbonate; unsaturated nitriles, such as acrylonitrile and methacryclonitrile; acrylic acid and methacrylic acid and their anhydrides, esters and amides, such as acrylic acid anhydride, allyl, methyl, ethyl, n-butyl, 2-hydroxyethyl, glycidyl, lauryl and 2-ethylhexyl acrylates and methacrylates, and acrylamide and methacrylamide; maleic anhydride and itaconic anhydride; maleic, itaconic and fumaric acids and their esters; vinyl halo and vinylidene dihalo compounds, such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride and vinylidene fluoride, perhalo olefins, such as tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene; vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether and n-butyl vinyl ether, allyl esters, such as allyl acetate, allyl benzoate, allyl ethyl carbonate, triallyl phosphate, diallyl phthalate, diallyl fumarate, diallyl glutarate, diallyl adipate, diallyl carbonate, diethylene glycol bis(allyl carbonate) (i.e., ADC); acrolein; methyl vinyl ketone; or mixtures thereof.
Temperatures of 25xc2x0 C. to 100xc2x0 C., preferably 30xc2x0 C. to 90xc2x0 C., more preferably 75xc2x0 C. and levels of novel stabilized peroxydicarbonate initiator compositions (on a pure basis) of 0.002 to 3%, preferably 0.005% to 1%, more preferably 0.01% to 0.75% by weight based on monomer (amount effective for initiation), are normally employed in conventional polymerizations and copolymerizations of ethylenically unsaturated monomers. One of skill in art will recognize that some of the above listed monomers will undergo polymerization at still lower temperatures in the presence of the peroxydicarbonates contemplated by this invention and that certain monomers, such as ethylene are conventionally polymerized at pressures greater than atmospheric. The processes contemplated by this invention include such conventional processing conditions. The novel stabilized peroxydicarbonate compositions of this invention can be used in combination with other free-radical initiators such as those disclosed at the bottom of column 4 and the top of column 5 of U.S. Pat. No. 4,525,308. Using the peroxide compositions of this invention in combination with these initiators adds flexibility to the processes of polymer producers and permits them to xe2x80x9cfine tunexe2x80x9d their polymerization processes.
Use of the stabilized percarbonates of this invention in polymerization of vinyl chloride provides polyvinyl chloride suitable for food contact usage.
Polyvinylchloride (PVC) polymer is used as the polymeric component of a wide variety of useful articles such as shoes, tablecloths, wall coverings, floor tiles, phonograph records, upholstery, pipe, house siding and packaging. PVC of itself is virtually unprocessable. It must be compounded with a wide array of additives and modifiers so that it may be thermoformed by molding, extrusion, calendaring and casting. Additives and modifiers include lubricants plasticizers, antistats, pigments, filters, impact modifiers, polymeric process aids and thermal stabilizers.
One class of PVC and PVC-based compounds is that intended for food contact application. These usually take the form of plasticized flexible films for meat wraps, rigid film for candy wrap, rigid clear bottles for oil and aqueous foods, thermoformed packaging for foods and pharmaceuticals and piping systems for potable water. In order to meet the stringent specifications for PVC and PVC compounds intended for food contact applications, it is required that all materials used in the manufacture of the PVC polymer or incorporated as additives or modifiers be of adequate safety for their intended use. Thus, the additives and process aids must be of sufficient low toxicity that they do not present a problem, or they may be essentially non-extractable from the finished article, and therefore, do not become food additives requiring specific regulations. In addition, the polymerization catalyst must at a minimum not leave residues in the resin which are toxic or which exceed regulatory permitted limits.
Within the scope of the present invention, specific organic peroxide polymerization catalyst compositions comprising dialkyl peroxydicarbonate and specific dialkyl ethylenically unsaturated dicarboxylic acid esters are preferred polymerization catalysts for polymerization of food contact PVC and PVC compounds. Most preferred are compositions comprising dialkyl esters of maleic acid in which the alkyl groups consist of C4 or greater. As stated above, dialkyl esters of maleic acid of less than C4 tend to be hydrolytically unstable during the manufacture of the peroxide, but may be added to the peroxide itself as stabilizers.
As stated above, the principal function of the dialkyl ethylenically unsaturated dicarboxylic acid ester in the organic peroxide mixture is to stabilize the organic peroxide against degradation. In this respect, the integrity and catalytic strength of the organic peroxide is preserved and PVC of greater purity is produced when such stabilized catalyst compositions are employed in its manufacture. This is particularly important in the production of PVC intended for food application in order to minimize extractables. It is believed that the extraction of the stabilizing portion of the food-grade polymerization catalyst mixture is reduced, in part, through copolymerization of the ethylenically unsaturated dicarboxylic acid moiety with vinyl chloride monomers during the manufacture of PVC so that they are incorporated in low concentration into the PVC polymer chain and are, thus, not extractable.
It is important in the preparation of PVC compounds intended for food contact application that undesirable extractable residues from reaction of polymerization catalysts and polymerization catalyst stabilizers be avoided.
2. Curing of Unsaturated Polyester Resins
In the curing of unsaturated resin compositions (which are also ethylenically unsaturated compounds) by heating at suitable curing temperatures in the presence of free-radical curing agents, the novel stabilized peroxydicarbonate initiator compositions of this invention exhibit enhanced curing activity in the curable unsaturated polyester resin compositions. Unsaturated polyester resins that can be cured by the novel thermally stabilized dialkyl peroxydicarbonate compositions of this invention usually include an unsaturated polyester and one or more ethylenically unsaturated monomers.
The unsaturated polyesters are, for instance, polyesters as they are obtained by esterfying at least one ethylenically unsaturated di- or polycarboxylic acid, anhydride or acid halide, such as maleic acid, allylmalonic acid, tetrahydrophthalic acid, and others, with saturated and unsaturated di- or polyols, such as ethylene glycol, diethylene glycol, triethylene glycol. 1,2-and 1,3 -propanediols, 1,2-, 1,3- and 1,4-butanediols, 2,2-dimethyl-1,3 propanediol, 2-hydroxymethyl-2-methyl-1,3-propanediol, 2-buten-1,4-diol, 2-butyn-1,4-diol, 2,4, 4-trimethyl-1,3-pentanediol, glycerol, pentaerythritol, mannitol and others. Mixtures of such di- or polycarboxylic acids may be partially replaced by saturated di- or polycarboxylic acids, such as adipic acid, succinic acid, sebacic acid and other, and/or by aromatic di- or polycarboxylic acids, such as phthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid. The acids used may be substituted by groups such as halogen. Examples of such suitable halogenated acids are, for instance, tetrachlorophthalic acid, tetrabromophthalic acid, 5,6-dicarboxy-1,2,3,4,7,7-hexachlorobicyclo(2.2.1)-hept-2-ene and others.
The other component of the unsaturated polyester resin composition, the polymerizable monomer or monomers, can preferably be ethylenically unsaturated monomers, such as styrene, xcex1-methylstyrene, p-methylstyrene, chlorostyrenes, bromostyrenes, vinylbenzyl chloride, divinylbenzene, diallyl maleate, dibutyl fumarate, triallyl phosphate, triallyl cyanurate, diallyl phthalate, diallyl fumarate, methyl acrylate, methyl methacrylate, n-butyl methacrylate, ethyl acrylate, and others, or mixtures thereof, which are copolymerizable with said unsaturated polyesters.
A preferred unsaturated polyester resin composition contains as the unsaturated polyester component the esterification product of 1,2-propanediol (a polyol), maleic anhydride (an anhydride of an unsaturated polycarboxylic acid) and phthalic anhydride (an anhydride of an aromatic dicarboxylic acid) as well as the monomer component, styrene.
Other types of unsaturated polyester resin compositions can be cured using the novel stabilized peroxydicarbonate initiator compositions of this invention as curing catalysts. These resins, called unsaturated vinyl ester resins, consist of a vinyl ester resin portion and one or more polymerizable monomer components.
The vinyl ester resin component can be made by reacting a chloroepoxide, such as epichlorohydrin, with appropriate amounts of a bisphenol such as Bisphenol A [2,2-(4-hydroxyphenyl)propane], in the presence of a base, such as sodium hydroxide, to yield a condensation product having terminal epoxy groups derived from the chloroepoxide. Subsequent reaction of the condensation product with polymerizable unsaturated carboxylic acids, such as acrylic acid and methacrylic acid, in the presence or absence of acidic or basic catalysts, results in formation of the vinyl ester resin component. Normally, styrene is added as the polymerizable monomer component to complete the preparation of the unsaturated vinyl ester resin composition.
Temperatures of about 20xc2x0 C. to 200xc2x0 C. and levels (amounts sufficient to initiate polymerization or cure) of novel stabilized peroxydicarbonate initiator compositions of about 0.05% to 5% or more, preferably 0.10% to 4%, more preferably 0.25% to 3% by weight of curable unsaturated polyester resin composition are normally employed.
The unsaturated polyester resin compositions described above can be filled with various materials, such as sulfur, glass, carbon and boron fibers, carbon blacks, silicas, metal silicates, clays, metal carbonates, antioxidants (AO""s), heat, ultraviolet (UV) and light stabilizers, sensitizers, dyes, pigments, accelerators, metal oxides, such as zinc oxide, blowing agents, nucleating agents and others.
3. Curing of Allyl Diglycol Carbonate (ADC) Resins
In the curing or polymerizing of diethylene glycol bis(allyl carbonate) (ADC), CH2xe2x95x90CHCH2xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94CH2CH2xe2x80x94Oxe2x80x94CH2CH2xe2x80x94Oxe2x80x94(xe2x95x90O)xe2x80x94Oxe2x80x94CH2CHxe2x95x90CH2, by heating ADC monomer at suitable curing temperatures in the presence of free-radical curing agents, the novel stabilized peroxydicarbonate initiator compositions of this invention exhibit enhanced curing or polymerizing activity for ADC monomer compositions. ADC was introduced commercially as CR-39(trademark) monomer (CAS REG. No. 142-22-3) by Pittsburgh Plate Glass Company (PPG) and is produced by reacting diethylene glycol bis(chloroformate) with allyl alcohol in the presence of alkali (R. Dowbenko, in J. I. Kroschwitz and M. Howe-Grant, eds., Kirk-Othmerxe2x80x94Encyclopedia of Chemical Technology, xe2x80x9cAllyl Monomers and Polymers,xe2x80x9d Fourth Edition, Vol. 2, Wiley-Interscience Publication, John Wiley and Sons, Inc., New York, 1992 pp 163-168). ADC monomer can cured or polymerized alone, or with other comonomers such as acrylic acid esters, methacrylic acid esters, allyl esters, diallyl dicarboxylates (e.g., diallyl phthalate), maleic anhydride and other monomers to produce clear castings or lenses that are transparent, tough, break-resistant and solvent-resistant. Curing or polymerizing of ADC monomer compositions are carried out in bulk (no solvent present). In general, curing or polymerizing of ADC monomer compositions to form cast sheets or lenses is carried out in two stages. The first stage involves the major part of the polymerization and occurs in the presence of the curing initiator, usually a lower dialkyl peroxydicarbonate, at temperatures of 35xc2x0 C. to 120xc2x0 C. Curing or polymerization times vary from about 5 hours to 50 hours. Generally a time-temperature profile is employed in the first stage. An example of a time-temperature profile given below:
The second stage of the curing or polymerizing of ADC monomer compositions involves post-curing or annealing of the ADC resin for one to several hours at 100xc2x0 C. to 150xc2x0 C. An example of post-curing of the ADC resin would be 2 hours at 115xc2x0 C.
Levels (amounts sufficient to initiate polymerization or cure) of novel stabilized peroxydicarbonate initiator compositions of about 1% to 6% or more, preferably 2% to 5% more preferably 2.5% to 4% by weight of curable or polymerizable ADC monomer composition are normally employed.
The ADC resin compositions described above can be filled with various materials, such as antioxidants (AO""s), heat, ultraviolet (UV) and light stabilizers, tints, photochromic additives and dyes. In addition, the ADC resin compositions can contain additives such as acrylic polymers and the anti-shrink, low molecular weight acrylic resins disclosed in U.S. Pat. No. 4,217,433. Such anti-shrink additives are employed to counter the 14% shrinkage that occurs when ADC monomer is polymerized.
In all cases the time, temperature and pressure conditions employed in any polymerization are not contemplated as critical by the invention and conditions normally employed by those of skill in the art may be similarly employed in the processes of this invention.
C. Preparative Methods
Preparations of Novel Stabilized Peroxydicarbonate Compositions
The dialkyl peroxydicarbonate portion of the novel, thermally stabilized peroxydicarbonate initiator compositions of this invention can be prepared by methods well known in the art (F. Strain, et al., J. Am, Chem. Soc., 1950, 72, 1254-1263, and U.S. Pat. No. 3,950,375).
The compounds of Structure I are known compounds and are commercially available or may be prepared by synthetic methods well known to a skilled chemist.
The novel, stabilized peroxydicarbonate initiator compositions may also be prepared by thoroughly mixing 10 to 90%, preferably 20 to 50% by weight based on weight of the dialkyl peroxydicarbonate, of a diester of an unsaturated dicarboxylic acid of Structure I with said dialkyl peroxydicarbonate at xe2x88x9220xc2x0 C. to 20xc2x0 C.
The following examples are presented to further illustrate the best mode contemplated for the practice of the invention and to provide detailed preparative illustrations and are not intended to limit the scope of the present invention.

Stabilized organic peroxydicarbonates compositions

Abstract: (a) at least one dialkyl peroxydicarbonate, and

Abstract: (b) a stabilizing effective amount of a compound of Structure I:

Abstract: wherein R1 and R2 are as defined in the summary of the invention section, processes for their preparation and use are disclosed.


A swept-frequency radar system transmits pulses consisting of swept-frequency subpulses of nonuniform duration separated by short nontransmitting periods during which an array antenna is resteered. The pulses reflected from a target are processed by a method including estimating the target ranges, producing a reference signal at the time at which the pulse reflected from the target is expected to return. The reflected pulse is phase detected by means of the reference pulse to produce phase detected signals which include information relating to the error between the actual range and the estimated range. The phase detected signals are Fourier transformed to produce range error information. The nonuniform subpulse durations reduce the magnitude of range sidelobes.

This invention relates to swept-frequency radars in which the subpulse duration is width-modulated to reduce range sidelobes. These sidelobes can obscure targets, or be interpreted as spurious targets.
Radar systems are in widespread use for military, civilian and scientific applications. In radar systems, the direction (such as the azimuth or elevation) of a target is determined by the direction in which the radar antenna is pointed at the time it acquires the target. Thus, the location portion of the information depends in great part upon the accuracy with which the pointing direction of the antenna can be established.
The range of a target from the radar system is determined by the length of time required for a round trip of the signal between the radar transmitter and the target. The maximum distance at which a radar system can sense a target depends upon the power transmitted in each pulse. The maximum or peak power which can be transmitted depends upon many factors, including the type of active device(s) used in the transmitter. It has been found that at a given peak power, the maximum range at which a target can be sensed is increased if the pulse duration is increased, because the transmitted energy thereby also increases. However, in a single-frequency radar system, increasing the pulse width effects a reduction in the minimum distance at which a target can be tracked, and also reduces the accuracy of the range determination.
The swept-frequency radar system overcomes the limitation of reduced range resolution resulting from an extended transmitted pulse. In the swept-frequency system, the frequency of the transmitter is swept (monotonically changed) during the relatively long transmitter pulse. The duration of the dwell of the transmitted pulse at any frequency is very small. The use of pulse compression techniques at the receiver gives the effect of a short transmitter pulse as to range resolution and of a long transmitter pulse as to maximum range.
FIG. 1 illustrates an array antenna arrangement 6. In FIG. 1, elements 10, 12, 14 and 16 of antenna 6 represent substantially omnidirectional antenna elements arranged in a spaced line array 8, where the distance between elements (S) is less than one-half wavelength (.lambda./2) at all frequencies of interest. Antenna 6 includes controllable phase shifter (.DELTA..phi.) 20 connected to antenna 10, and controllable phase shifters 22, 24 and 26 connected to antenna elements 12, 14 and 16 respectively. Phase shifters 20-26 are coupled to an adder/splitter illustrated as a block 28, which has a common terminal 30.
As known, antennas are normally considered to be passive reciprocal devices, in which the transmitting and receiving functions are reciprocals of one another, and in which the antenna pattern when receiving is the same as the radiation pattern in a transmission mode. Very often, the description of the operation of an antenna is couched in terms of only transmission or reception, the reciprocal operation being understood.
In FIG. 1, array 8 of antenna elements 10-16 is illustrated as receiving a plane wave front 18 traveling toward the array at an angle theta (.theta.) relative to the horizontal. At the moment shown, wavefront 18 is just arriving at antenna 10, but is at a perpendicular distance L from antenna element 16. Wave front 18 will arrive in succession at antenna elements 12, 14 and 16. Thus, assuming negligible delay in the phase shifters, a signal is produced at the output of phase shifter 20 at the instant illustrated in FIG. 1, and is not produced at the output of phase shifter 26 until a time L/C later, where C is the speed of light. The signals from phase shifters 20-26 are applied to inputs of an adder/splitter (adder for reception, splitter for transmission) 28 where they are vectorially summed or superposed to produce a net received signal at a common input/output port 30. The distance L may be calculated from the equation L=NS sin.theta., where N is the number of interelement spacings, S is the interelement spacing, and .theta. is the angle illustrated in FIG. 1. In order to superimpose or sum the signal resulting from wavefront 18, phase shifter 20 requires zero phase shift, but phase shifter 26 requires a phase shift of 2.pi.L/.lambda., which is the same as 2.pi.NS sin.theta./.lambda..
Array antennas such as antenna 6 described in conjunction with FIG. 1 are very desirable for modern radar systems because they may resteered by simply adjusting the phase shift of the phase shifters therein, without the need for mechanical motion. Thus, it is desirable to use a phase-shifter controlled steerable array antenna with a swept-frequency radar system. A swept-frequency pulse is illustrated in the frequency-time plot of FIG. 2, in which plots 31 illustrate pulses of transmitted power with monotonically increasing frequency. The transmitted pulses occur between recurrent times T0-T100 (where the hyphen is equivalent to the word "to"), and are reflected from, and returned from the targets to the, radar system for detection in the remaining intervals T100-T0.
The frequency sweep gives rise to a problem when used with an array antenna. Ideally, elements 20, 22, 24 and 26 of FIG. 1 are simple delay elements such as a length of transmission (TX) line, which provides the same delay at all frequencies. At the present state of the art, variable delay elements are expensive and difficult to construct. Consequently, less expensive variable phase shifters are used, which are perfectly adequate when a fixed frequency is transduced by the antenna. However, phase shifters have a delay which changes with frequency. Because of the use of phase shifters rather than delay elements for controlling the direction of steering of the antenna, the antenna can be correctly steered or pointed at only one frequency at a time. The frequency at which the antenna pointing direction is calculated is selected near the center of the range of swept frequencies of the radar system, but the actual direction of transmission or reception of the array antenna will change as the frequency is swept. The error in pointing direction increases as the number of elements in the antenna array grows and also increases as the frequency bandwidth of the swept transmitter pulse increases. Thus, the errors in the pointing directions of the array antenna may be reduced by limiting the bandwidth of the frequency sweep, and by limiting the size of the antenna. If the frequency bandwidth is to be small in order to limit pointing errors, either the maximum duration of the pulse must be limited, thereby reducing the average power and the useful range, or the range resolution must be limited because of a longer dwell at each frequency. Reducing the pointing error by limiting the size of the antenna reduces the antenna gain and the angular resolution.
FIG. 3 illustrates an arrangement wich allows a relatively large array antenna for high gain, but in which the pointing error resulting from a frequency sweep is reduced. Elements of FIG. 3 corresponding to those of FIG. 1 are designated by the same reference numerals. In FIG. 3, antenna 6 of FIG. 1 is illustrated as having its input/output port 30 connected to a controllable delay line 32 such as a switchable tapped delay line. Further antennas 34, 34' and 34" similar to antenna 6 of FIG. 1 are illustrated as being similarly connected to controllable delay elements 36, 36' and 36", respectively. Thus, each antenna array 6 or 34 is a subarray of the array of FIG. 3. Controllable delay elements 32 and 36-36"are connected to an adder/splitter 38 having a common port 40. Delay elements 32 and 36 have a delay which is invariant with frequency, and therefore the sweep of the transmitter pulse does not affect the pointing direction of the overall array, although each individual subarray antenna such as 6, 34, 34', 34". . . may sweep its pointing direction, resulting in some error in the pointing direction of the arrangement of FIG. 3. The arrangement of FIG. 3 is a good compromise between cost and performance, since relatively few of the expensive controllable delay elements are required, and yet the error in pointing direction resulting from a frequency sweep of the transmitter pulse is limited.
Greater pointing accuracy may be maintained or achieved with wideband waveformsif a given swept-frequency transmitter pulse is broken up into a plurality of shorter subpulses, separated from one another by short nontransmitting periods during which the antenna subarrays are resteered to point in the selected direction at a frequency near the center of the next following swept-frequency subpulse. FIG. 4 illustrates a portion of such a pulse. With such a system the expensive time delay elements can be completely avoided.
In FIG. 4, a first straight-line portion 50 represents a subpulse with frequency increasing linearly from a frequency f0 to a frequency f2 in the interval T0-T2. In the interval T2-T4, no transmission occurs and the array is resteered to point in the selected direction at a frequency f3, midway between frequencies f2 and f4. In this context, resteering means selecting the values of phase shift of the phase shifters (such as 20-26 of FIG. 1) so that at the selected frequency (f3 in the example) the phase shifts provide the desired pointing direction. The phase shifts may either be calculated or extracted from a memory (not illustrated). Beginning at time T4, a further line 52 parallel to line 50 in FIG. 4 represents a further subpulse with a frequency sweep from frequency f2 to f4 over the interval T4-T6. Time interval T4-T6 equals interval T0-T2. As the frequency sweeps from frequency f2 through frequency f3 to f4, the antenna pointing direction sweeps through the desired direction, being exactly correct at frequency f3.
Time interval T6-T8 represents a further nontransmitting time during which the antenna is resteered to the selected direction at a frequency midway between f4 and f6, following which transmission of another subpulse occurs, sweeping the frequency from f4 to f6 over the interval T8-T10. The frequency excursions f0-f2, f2-f4, f4-f6 are selected to be small enough so that significant pointing error does not occur over the frequency range. The rate of change of frequency is selected to provide the desired range resolution. The total number of transmitter subpulses such as those represented by 50, 52 and 56 which occur in one transmitter pulse are selected in accordance with the amount of transmitted power which is desired, since additional subpulses increase the pulse duration and therefore the transmitted power per pulse.
It should be noted that the same frequency occurs at the end of each transmitter subpulse interval and at the beginning of the next following subpulse. For example, the frequency is f2 at time T2 in FIG. 4, which in the end of the first subpulse 50, and is also f2 at the following time T4, the beginning of the second subpulse 52. It is desirable that phase coherence be maintained in the interval T2-T4, so that the phase of the transmitter cycle at time T4 is the same as that at time T2. It is not necessary for the nontransmitting period to be an exact multiple of the period of the f2 frequency, because digital signal processing allows the end of one transmission to be "stitched" or connected to the beginning of the next, in effect eliminating the intervening time.
FIG. 5 shows one form of pulse compression receiver which can be used when the time of the received pulse is known. The approximate time at which a pulse will return may be determined by operating the radar system in a conventional mode with reduced bandwidth, without resteering and with a conventional SAW filter pulse compression circuit to establish the approximate range. Once the approximate range is known, the waveform of FIG. 4 is used, with resteering and with the receiver of FIG. 5.
FIG. 5 illustrates, in simplified block diagram form, a receiver for receiving the reflection from a target illuminated by a transmitted pulse such as that of FIGS. 2 or 4. In FIG. 5, antenna 506 receives the reflected pulse, i.e., the waveform of FIGS. 2 or 4, as appropriate. It should be noted that antenna 506 is not necessarily the same antenna as that by which the pulse was originally transmitted. The received signal is coupled from antenna 506 over a conductor 510 to an RF amplifier 520, which amplifies the signal and applies it to a phase detector 530, which also receives a reference waveform over a conductor 570. The reference waveform is a delayed replica of the transmitted pulse, except that the reference subpulses are slightly wider than the transmitted subpulses, as described in detail below. Phase detector 530 responds by producing I (in-phase) and Q (quadrature-phase) signals, which are separately applied to an analog-to-digital converter (ADC).
The I and Q outputs of ADC 540 are applied over conductors 551 and 553, respectively, as inputs to arrays of gates 550 and 552, respectively, of a digital Fourier transform (DFT) 560. As illustrated in FIG. 5, there are 2N+1 gates designated 550, namely gates 550.sup.-N . . . 550.degree.. . . 550N.sup.-1, 550.sup.N for gating the I waveform. Similarly, there are 2N+1 gates designated 552, namely 552.sup.-N . . . 552.degree.: . . . 552N.sup.-1, 552.sup.N. Gate arrays 550 and 552 gate the I and Q componnnts, respectively, of the phase detected received signal to arrays of vector multipliers 554, the outputs of which are coupled to an array of integrators (.intg.) 556. The outputs of all integrators 556 are applied to the inputs of a commutator 558, which sequentially couples the outputs to a conductor set 562.
Each set of gates 550, 552, and the associated vector multiplier 554 and integrator 556 comprises a filter for one return frequency, as described below. For example, the I signal applied over conductor 551 to all gates 550 is gated by gate 550.degree. to an input of vector multiplier 554.degree. if the return occurs at the time at which the gating signal is also applied to gate 550.degree., and otherwise the signal is not applied to vector multiplier 554.degree., but may be applied to one of the other vector multipliers.
The gating pulses or signals for gates 550 and 552 originate at terminal 570 of FIG. 5 and are applied directly to gates 550.sup.-N and 552.sup.-N for enabling these gates first. The gating pulses flow from terminal 570 to a delay element 564-N which delays the gating signal for an incremental time, following which the delayed gating signal is applied to enable the next gates 550, 552 (not illustrated). The delay of the gating signal continues, and eventually the delay is provided by incremental delay element 564.degree., from which the gate pulse is applied to enable gate 550.degree. and 552.degree.. The delay continues in this fashion, enabling those gates between 550.degree., 552.degree. and 550.sup.N-1 and 552.sup.N-1 in succession. Finally, delay element 564.sup.N-1 delays the enable gate pulses for application to gates 550.sup.N-1 and 552.sup.N-1, and delay element 564.sup.N provides a further incremental delay before applying the gate pulse to the last set of gates to be enabled, gates 550.sup.N and 552.sup.N
The delay between the time of transmission of the pulse and the time of application of the reference waveform to phase detector 530 is a coarse indicator of the range of the target. In particular, the round-trip delay is 12.4 microseconds per mile of range. If the reference waveform is applied at exactly the right time (i.e., the beginning of the delayed reference pulse coincides exactly with the beginning of reception of the pulse reflected from the target), the target is not moving, and there are no resteering periods (i.e., the transmitted and reference waveforms correspond to the FIG. 2 waveform), the output of phase detector 530 is a direct voltage. The direct voltage represents zero frequency, which indicates that there is no difference between the time of the reference waveform and the time for the signal to make a round trip to the target. In other words, the difference between the actual range and the coarse range estimate is zero.
The direct voltages produced by phase detector 530, in response to a reference waveform which is identical, arrives at gates 550, 552 at exactly the expected time. The timing of the radar system of FIG. 5 is selected so that the time of arrival of a signal corresponding exactly to the coarse range estimate is the time at which gates 550.degree.: and 552.degree.: are enabled. These gates are enabled in the center of the times enabled in succession by the enable gate applied to terminal 570, so that either positive or negative errors in the coarse range estimate will result in times of arrival which coincide with the opening of one of the gate sets 550, 552. In the particular case when the error in the coarse range estimate is zero and a direct voltage is therefore produced by phase detector 530, DFT 560 produces on conductor 562 a maximum response at a frequency of zero, thereby providing the desired range information.
If the waveform of FIG. 2 is transmitted, and there are therefore no resteering intervals, and the coarse range estimate is in error, the reference waveform will be applied to phase detector 530 either slightly before or slightly after the time of arrival of the signal reflected from the target. The situation is illustrated in FIG. 6, which is a frequency-time plot. In FIG. 6, 610 represents a swept-frequency transmitter pulse occurring in the interval T0-T2. The reflected signal is represented by waveform 612, which is received by antenna 506 (FIG. 5) beginning at time T4 (FIG. 6), and extending to time T8. Ideally, the widened reference waveform 614 applied by way of conductor 570 to phase detector 530 would occur so as to be centered relative to waveform 612, but because of an error in the coarse range estimate, the reference does not begin until a later time such that it crosses frequency f0 at time T6. Consequently, there is a constant frequency difference between the reference and reflected signals. This difference is illustrated as f2-f4 at time T7 in FIG. 6. However, the frequency difference remains constant over much of the waveform. This frequency difference is manifested at the output of phase detector 530 of FIG. 5, and when gated to DFT 560 produces a maximum at a frequency representative of the error between the coarse range estimate and the actual range.
As illustrated in FIG. 6, the coarse range estimate of the target was too distant, so the reference waveform 614 is generated at a time later than the actual return from the target. In this context, "later" means that the reference waveform is generated over a period of time such that the occurrence of any frequency such as f2 occurs later than the return of f2 from the target. The target return is effectively earlier than the reference. The magnitude of the frequency difference between the reference waveform 614 and the return 612 from the target increases with an increase in the coarse range error. Thus, the earlier the return arrives from the target, the larger its frequency error. The earliest-arriving target will therefore have largest frequency error manifested in the signal at the output of phase detector 530. This signal is gated to all of the filters formed by a set of gates 550, 552, vector multiplier 554 and integrator 556 (FIG. 5); the maximum output is produced in the filter matched to the difference frequency.
Each vector multiplier 554.sup.-N . . . 554.degree.. . . 554.sup.N-1, 554.sup.N receives I and Q target return inputs from corresponding gates 550, 552, respectively, gated at times corresponding to the time at which they arrive. Each vector multiplier performs complex multiplication of the target return inputs by filter coefficients and the resulting product is integrated (.intg.) by an integrator illustrated as a block 556. The outputs of integrators 556.sup.-N . . . 556.degree. . . . 556.sup.N-1, 556.sup.N are sequentially commutated to produce signals representative of the error between the coarse angle estimate and the actual range.
If the target is moving, the motion introduces a Doppler frequency shift to the returned signal. The effects of an error in the coarse range estimate can be separated from the effects of motion of the target by reversing the direction of frequency sweep on alternate transmitter pulses (positive frequency slope during one pulse, negative frequency slope during the next). Thus, range error information may be separated from range rate due to target motion for separate processing. This is performed in the tracking computer described below.
In the arrangement as described in conjunction with FIGS. 5 and 6, the range error resolution is inversely proportional to the bandwidth of the frequency sweep. Since the time at which the signal at a particular frequency returns is known, an amplitude weighting may be imposed by reducing the amplitude of the received signal near the beginning and end of the interval during which it is received, to aid in reducing the amplitude of range sidelobes. Since the time of receipt of the signal may vary somewhat within each range cell, the weighting ideally should track the received signal in time to prevent degradation of the signal-to-noise ratio (S/N or SNR) and to avoid possible changes in the sidelobes.
FIG. 7a illustrates the situation in which the coarse range estimate does not coincide with the actual range. In FIG. 7a, waveform portions 750, 752, and 756 represent the returned signal reflected from the target due to earlier transmission of pulse portions 50, 52, and 56, respectively, of FIG. 4. Note that portions 51 and 53 of the pulse of FIG. 4 represent nontransmission periods, so no return is received in the intervals T710-T714 of portion 751, and T718-T722 pulse portion 750 ends at time T710, and no signal is received in the interval T710-T714. Similarly, pulse portion 752 is received in the interval T714-T718, and no signal is received in the interval T718-T722.
In FIG. 7a, the delayed reference waveform applied to conductor 570 (FIG. 5) is illustrated by chain-line portions 760, 765, 767, 761, 762, 769, 763, 766 and 785. If the reference signal were to be completely identical to the transmitted signal, it would include portions 760 and 765 in the interval extending to time T712, it would not include swept-frequency portion 767, but would remain at a constant frequency from time T712 to T716. Further, the reference waveform would include portions 762 and 769 in the interval T716-T720, but would not include swept-frequency portion 785, but would again remain at a constant frequency from time T720 to time T724, and would be followed by portion 766 following time T724. The reference signal as modified therefore includes extended swept-frequency portions 767, 761, 785 and 763. The reference signal is not turned off during swept-frequency portions 760, 765, 762, 769, and 766, nor is it turned off during extended swept-frequency portions 767, 761, 785 and 763, nor between portions 767 and 761; 769 and 763. In order to allow for range errors, swept-frequency portions 760, 765 and an extension 767 of the reference waveform end at time T713, extended swept-frequency portion 761 extends from T714 to T716, a further swept-frequency portion 762, 769 extends from time T716 to T720, an extension 785 extends to time T721, an extended swept-frequency portion 763 extends from time T722 to time T724, and a further swept-frequency portion begins at time T724. Solid-line waveform 764 of FIG. 7b represents the theoretical amplitude of the reflected signal of FIG. 7a, and dashed-line portion 766 of FIG. 7b represents the reference waveform amplitude. Phase detector 530 of FIG. 5 responds to the reflected and reference waveforms to produce I and Q signals which, together, have amplitude-and frequency-time distributions illustrated as 768 and 770, respectively, of FIGS. 7c and d.
DFT processor 560 includes a plurality of frequency filters which correspond to incremental frequency differences between the reference waveform and the return from the target. In the absence of Doppler frequency shifts attributable to motion of the target, these frequency filters receive signals which correspond to different ranges, and which therefore do not return exactly in coincidence with the reference waveform (which in fact is why there is a frequency difference). Thus, the various difference frequencies produced by phase detector 530 actually arrive at slightly different times. For example, a difference frequency of zero means that the coarse range estimate was correct, and the return arrives exactly in coincidence with the reference waveform. The largest difference frequency means that the coarse range estimate was so different from the actual range that a fairly large time difference occurs between the return and reference waveforms. The receiver of FIG. 5 for a particular DFT filter enables particular ones of gates 550 and 552 during the portions.
The gating for each DFT filter is different. FIG. 7e illustrates the gating waveform for the zero frequency filter, since that filter is assumed to be for a signal from the phase detector aligned to the central portion of the reference waveform, i.e., a signal whose range delay exactly equals the assumed value. FIG. 7f illustrates the gating waveform which would be applied to that filter which accepts the difference frequency for the signal represented by the solid line of FIG. 7a. The amplitude of the signal gated through the appropriate gates 550, 552 by the gating waveform in FIG. 7f is as illustrated by waveform 776 of FIG. 7g. As illustrated, there is a gap from times such as T710 until T714 and T718 to T722 during which the reflected signal goes to zero corresponding to resteering periods.
During those intervals in which a particular DFT filter does not receive clock signals, it does not respond to input signals. For example, the zero frequency filter of DFT block 560 is not aware of the existence of time intervals T712-T716 and T720-T724 of FIG. 7, and does not respond in any way to signal applied, or to lack of signal, in that interval.
FIG. 8a illustrates an amplitude-time waveform 810 having a constant amplitude. FIG. 8a represents an output from phase detector 530 of FIG. 5 with no difference in timing between the reflected and reference signals applied to the phase detector as seen by DFT block 560. This corresponds to the condition in which the coarse range estimate happens to be correct. The output from the phase detector is therefore a direct voltage (zero frequency). In FIG. 8a, times T712 and T716 are illustrated as superposed, as are times T720 and T724. They are superposed because, in the intervals T712-T716 and T720-T724, clock signals are not applied to DFT block 560, and therefore it is not aware of the hiatus. Processing therefore is performed on dc signal 810 as though it had no gaps.
FIG. 8b illustrates the signal seen by the portion of DFT 560 including the filter matched to the particular range error of FIG. 5 when the coarse range estimate is in error. The filter input is an uninterrupted sinusoid. Let us return to the case where the signal delay exactly equals the assumed delay. As shown in FIG. 8a, the input to the zero frequency filter of the DFT is a block of direct voltage.
Now consider the input to some other filter in the DFT. The filter gate is set to correspond to a range offset that would result in the frequency of that filter. FIG. 9a shows the signal and reference. FIG. 9b shows the amplitude and FIG. 9c shows the frequency of the output from the phase detector. FIG. 9d shows the gating signal for a filter whose frequency corresponds to a signal with less delay, and FIG. 9e shows the resulting-signal processed by that filter. The signal as seen by the filter is shown in FIG. 10. In FIG. 10, 1000 represents a sinusoidal signal whose frequency is the difference frequency delta (.DELTA.) illustrated in FIG. 7a, the amplitude of which periodically drops to zero in intervals T14-T16 and T22-T24. This effectively pulse-modulates the phase-detected signal with a pulse duration which depends upon the position of the gating signal. The modulation in turn creates sidebands of sinusoid 1000. If appreciable harmonic level exists at the frequency of the filter there will be an output in that filter even though the target is not at the range to which that filter is matched. That is, the signal has a range sidelobe. These low-level responses are spurious responses or sidelobes which may obscure actual range responses of other targets.
FIG. 11 is a plot of a computer simulation of the time sidelobes generated for a receiver such as that of FIG. 5 in response to a periodic frequency-jump waveform such as that illustrated in FIG. 7a with 40 subpulses, each of 2.5 .mu.S duration and bandwidth 25 MHz, with Hamming amplitude weighting of the pulse, with 2 .mu.S resteering periods and no Doppler error. As illustrated in FIG. 10, peaks in the response are only about 24 dB down from the reference peak amplitude of -1.3 dB. When two or more targets are to be tracked which have similar but not identical ranges, such range sidelobes of a large target can obscure the detection and/or prevent accurate measurement of the range of a smaller target. For example, an airplane which reflects a radar signal producing a relatively large-amplitude summed return such as that of FIG. 11 with sidelobes, may obscure or distort a smaller-amplitude return from a missile having a range corresponding to a time error near 0.2 .mu.S or 2.2 .mu.S of FIG. 11. Thus, range sidelobes may give rise to errors in ranging.

Range sidelobe reduction by aperiodic swept-frequency subpulses


Carriers for medical facilities, in particular patient tables, sometimes require a large range of displacement. This situation occurs, for example, in interventional MRI where a patient is to be transferred from an operating table to an MRI table which is situated at some distance therefrom. Components of the table may not form obstacles on the floor of the room and the stiffness and stability of the table construction must be maintained. A carrier for medical facilities includes two adjacent box-shaped spaces provided in the floor of the treatment room, said spaces being separated by a partition. One space accommodates only two rails which carry the pedestal of the table but no other components of the displacement mechanism for the table. The other space contains the further components of the displacement mechanism. A guide member protrudes through the partition, via a sealing device so as to guide the movement of the table.

The invention relates to a carrier for medical facilities which is intended for installation in a medical treatment room and provided with a pedestal for supporting the medical facilities, wherein the pedestal is displaceable relative to the floor of the treatment room on at least one rail, and wherein the rail forms part of a first space which is separated from the medical treatment room by first cover means.
A carrier of this kind is known from the published German patent application No. 36 15 633 A1. The carrier disclosed therein constitutes an X-ray examination apparatus which is displaceable on a rail in the floor of the medical treatment room by way of rollers provided underneath a pedestal of the carrier. The rail is accommodated in a space in the floor, which space is covered by cover means in the form of a flexible belt which rests on the open upper side of the space. When the carrier is displaced, the belt is lifted off the floor by a mechanism which is arranged in the pedestal and in front of the rollers, after which the belt is guided along the upper side of the rollers and is lowered onto the open upper side of the space again behind the rollers. The space for the rail is thus separated from the medical treatment room, so that pollutants in front of and behind the pedestal cannot readily penetrate the space for the rail and the attendant staff in the treatment room nevertheless experiences only little nuisance from the presence of the rail and the spaces in which it is accommodated.
This known carrier, however, still has the drawback that pollutants can still penetrate the space for the rail, notably via the clearance between the rollers which is not covered by the belt since it is lifted at that area. Because of the severe requirements imposed on the cleanliness of a medical treatment room, therefore, this space must be intensively cleaned at regular intervals.
There may also be situations requiring a carrier for medical facilities which has a comparatively large range of displacement. Such a situation occurs, for example in the case of a patient table used for interventional MRI. During such an intervention a patient arranged on the table is treated and an MRI image must be formed during the execution of the treatment. The MRI apparatus is then installed in a neighboring MRI room which can be separated from the relevant medical treatment room by way of special doors. In order to transport the patient from the patient table in the medical treatment room to the table associated with the MRI apparatus, the patient table must have a comparatively large range of displacement. The rigidity and stability of the patient table must be retained during such displacement, thus necessitating a comparatively rigid pedestal having a large width in the displacement direction.
It is an object of the invention to provide a carrier of the kind set forth for which a comparatively large range of displacement is realized, the desired rigidity and stability are maintained, the displacement mechanism does not form an obstacle on the floor of the medical treatment, and easy cleaning of the carrier is achieved.
This object is achieved in that the carrier according to the invention is characterized in that
the first space is connected with a second space which is covered by second cover means,
which first and second space are separated from one another by a partition in which said connection is realized by an opening wherethrough a guide member for guiding the displacement of the pedestal is slidable.
The first space, provided in the floor of the treatment room, can now be used for accommodating one or more rails on which the pedestal of the carrier is displaced. This first space is adjoined by a second space which is also provided in the floor of the treatment chamber in such a manner that the second cover means are flush with the floor of the treatment room. All further components necessary for guiding the displacement of the carrier, for guiding cables, for position sensing and the like are accommodated in said second space. A guide member for guiding the displacement of the pedestal projects through the partition and hence forms a mechanical connection between the displaceable pedestal of the carrier and the second space. As a result, the guide member which is rigidly connected to the pedestal may be of comparatively large length, so that the rigidity and the stability of the pedestal, and hence of the entire carrier, can be realized by way of a comparatively small force applied at the area of the end of the guide member.
The assembly formed by the patient table and the displacement mechanism is constructed in such a manner that the first space which accommodates one or more rails does not contain other components of the displacement mechanism, so that in operating conditions this space accommodates only the guide member, being connected to the pedestal, when the patient table is in a fully or partly displaced position. The cover means of this first space, therefore, must always be provided with an opening for the passage of the link between the pedestal and the guide member, so that via this opening the space situated therebelow could be polluted from the medical treatment room. Because the first space does not accommodate any other components of the displacement mechanism, however, it can be readily cleaned.
The invention offers the additional advantage that the accessibility of the patient table is maintained, despite the facilities providing a large displacement range while maintaining the rigidity and stability. This means that the freedom of movement of attendant staff working at the patient table according to the invention is not restricted by the facilities according to the invention.
It is to be noted that in the context of the present invention the term xe2x80x9cmedical treatmentxe2x80x9d is to be understood to include also a medical examination which is performed without performing a direct therapeutic activity.
The opening in the partition in a preferred embodiment of the invention is provided with sealing means for sealing against pollutants wandering from one of the spaces to the other space. In given operating conditions it may be sufficient to have a partition with an opening which encloses the guide member comparatively tightly. This configuration already offers adequate prevention of the transfer of pollutants from one of the spaces to the other. However, it may be that this partition between the two spaces is not adequate for the described purpose. In that case a collar of an elastic material can be provided in the partition, for example a collar which tightly envelops the guide member and prevents the transfer of contaminations. Moreover, contamination of the first space from the second space (accommodating further components of the displacement mechanism) is thus also prevented.
The guide member in a further embodiment of the invention is constructed as a rod having a circular cross-section. This shape of the guide member makes it easy to purchase it in a commercially available form and to finish it accurately, thus enabling a tight fit with the sealing; the accurately finished and hence smooth surface ensures that any wear will not be extensive.
The first space in a further embodiment is provided with two parallel rails. When these rails are mounted parallel to the longitudinal direction of the guide member, this step considerably enhances the transverse stability (i.e. the rigidity against motions in a direction transversely of the longitudinal direction of the guide member).
The two parallel rails in a further embodiment of the invention form part of respective walls of the first space. As a result, the interior of the first space will contain even fewer obstacles which could impede cleaning, so that this space can be realized in a comparatively simple manner.
The first and the second cover means in another embodiment of the invention are formed by a first and a second detachable lid, respectively. The lids of this embodiment can be manufactured in such a manner that the first lid can be readily removed by hand; this is advantageous with a view to cleaning at regular intervals. Because the second space is not contaminated from the first space, it need be opened only for maintenance and repair activities performed on the components of the displacement mechanism accommodated therein. This lid can then be constructed in the form of a lid which consists of one piece and is screwed onto the second space with a tight fit, for example via a rubber rim, so that it need be removed only by maintenance personnel assigned to this task.
The first detachable lid in another embodiment of the invention is provided with a slot for the passage of a connection piece between the guide member and the pedestal. The connection between the guide member and the pedestal is used not only to create stability, rigidity and accuracy of movement of the patient table, but also for guiding the electrical connection cables between the movable table and the environment. These cables can then be arranged in a bundle in fixed positions relative to one another, so that this bundle has a small width in the direction transversely of the direction of movement of the table. The bundle can then be arranged in the connection piece between the pedestal and the guide member; in that case this connection piece may also have a small width, so that the slot for the passage of the connection piece may be comparatively narrow.

Carrier for medical facilities with a large displacement range


Top and bottom frame supports are spaced apart and secured together by central end posts. Downwardly opening grooves along the arcuate edges of the top frame support align with upwardly opening grooves along the arcuate edges of the bottom frame support to form mating tracks into which credit cards are inserted. The credit cards bend into the shape of the grooves and overlap with two cards on each side to form side enclosure surfaces which enclose a storage space between the cards on each side and the top and bottom frame supports for storing money and other valuables. A holder with a key, pen, knife, or other device may be inserted in a notch in the top frame support. Alternately the framed supports may be hinged together at one end to form a hinged clamshell-type container.

1. Field of the Invention
The present invention relates to wallets and card holders and in particular to a credit card holder and wallet in which the cards themselves form the outer enclosing surfaces for containing money or other items therein.
2. Description of the Prior Art
Most prior art credit card holders and wallets have outer retaining surfaces formed of leather, plastic, or other material for containing the money and credit cards, licenses, and other valuables inside. Most of the material forming the holder or wallet is used for the outer retaining surfaces. In some cases this material takes up considerable space and adds substantially to the bulge in the clothes if carrying the holder or wallet in a pocket or takes up considerable space in a purse or pouch.
Most prior art credit card holders and wallets are box shaped with flat sides which don""t necessarily conform to the shape of a person""s leg if they are carried in a pocket or don""t conform to often curved shaped purses or pouches.
Often the cards contained are not visible from the outside if the outer retaining surfaces are opaque, as in the case of leather.
U.S. Pat. No. 5,358,019, issued Oct. 25, 1994 and U.S. Pat. No. 5,520,230, issued May 28, 1996, both to Sumner, provide a credit card holder and money clip combined. The credit card holding side has two side channels for holding credit cards stacked between the side channels. The Sumner invention has an additional central plate for support of the cards and the money, so that the cards are not self supporting and there is no space between the cards. The second patent adds an additional configuration with the cards oriented transversely to the money.
U.S. Pat. No. 5,417,328, issued May 23, 1995 to Ritter, shows a case for carrying a card having a magnetic strip and chip. Two parallel opposing guide strips receive the card, but a base between the guide strips also supports and protects the card along with a web across a portion of the top of the card. Cleaning elements are provided to clean the magnetic strip on the card.
U.S. Pat. No. 5,038,926, issued Aug. 13, 1991 to van der Toorn, claims a credit card holder having a rectangular frame with a central opening to receive the credit card and with protruding elements into the open portion of the frame to retain the card in the frame. Pivoting top and bottom lids further serve to cover and protect the card. Multiple cards may be stored in the holder. No provision is made for creating a space between cards to hold money, etc.
U.S. Pat. No. 4,450,955, issued May 29, 1984 to Featherston, describes a credit card holder having two opposing parallel side lips to secure the card. A base is provided between the two side lips to protect the card and a protrusion is provided to prevent the magnetic strip on the card from contacting the base.
U.S. Pat. No. 4,518,080, issued May 21, 1985 to Ohlson, discloses an ID card holder a with opposing parallel side slots for retaining the card and a base between the slots with protrusions in the base to bend the card for easier insertion and removal of the card relative to stops at the ends of the card holder.
None of the prior art patents use the credit cards as the sole side supports containing other items therebetween.
Credit cards are made of sturdy slightly flexible plastic. They are waterproof and resistant to wear and tear, thereby forming ideal protective surfaces.
A support frame structure with pairs of diverging tracks or grooves on two opposing sides of the support frame forms the tracks within which credit cards are inserted and held to form a pair of opposing side walls with a storage space in between the opposing walls to contain business cards, money or other valuables, the support frame enclosing the space on the top and bottom.
The primary object of the present invention is to provide a credit card holder and wallet in which the credit cards themselves form the containing surfaces to hold money and other valuables, thereby forming water-resistant sturdy protective surfaces.
Another object of the present invention is to form a credit card holder and wallet which has a concave shape on one side to rest comfortably against and conform to the curved surface of a user""s leg with the invention in the user""s pocket.
An additional object of the present invention is to provide an optional opening in the support frame and a tight friction fit holder inserted in the opening for storing a key, pen, knife, or other utility device normally carried in the pocket or purse.
A further object of the present invention is to provide support frames of varying shapes to suit particular needs.
An added object of the present invention is to provide a hinged support frame that swings open to access the contents.
In brief, a support frame of injection molded plastic, extruded plastic, metal, or other material having a somewhat rigid structural integrity is formed with a top and bottom track portions separated by the length of a credit card and interconnected at one or both ends by a spacer. The support frame is narrow at both ends and widens out in the middle. A groove is formed along each edge of the top and bottom track portions so that the top track portion grooves face and align with the bottom track portion grooves so that the grooves form pairs of opposing tracks along the edges of the support frame. Credit cards slide into the grooves in an overlapping array to enclose the sides of the invention and form a storage space between the cards on opposing sides with the support frame enclosing the top and bottom.
Money, credit cards, business cards, identification, or other items normally contained in wallets or credit card holders may be carried in the storage space.
In one embodiment, straight post-like elements form the spacers at both ends of the invention and the contents of the invention are accessed by sliding one of the credit cards aside to create an access opening.
In another embodiment, a spacer in the form of a hinge connects the top and bottom track portions of the support frame at only one end, so that the side may be pivoted open to access the interior storage space.
In addition, a small opening or notch may be formed in one of the track portions of the support frame and a holder with a key, pen, knife or other utility device normally carried in the pocket or purse, inserted in the small opening or notch for carrying the utility device therein.
An advantage of the present invention is that it creates a credit card holder and wallet which utilizes a minimum of material in its fabrication.
Another advantage of the present invention is that it allows the credit cards to be readily visible and accessible.
An additional advantage of the present invention is that it fits comfortably and conveniently in a pocket or purse.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.

Credit card holder with cards forming enclosing surfaces