the principal object of the present invention therefore is to provide a denture adhesive comprising a salt of an alkyl vinyl ether / unsaturated anhydride or polycarboxylic acid copolymer with acceptable organoleptic properties and good processing properties . the denture adhesive compositions of the present invention can be formulated in liquid , cream , liner , and possibly powder forms that , when in contact with saliva , develop a high degree of tack and uniform viscous mucilages of high cohesive strength and that , when spread over the denture - mucosa interface , provide superior denture stabilizing properties . the compositions contain a denture adhesive salt together with excipients . the denture adhesive employed in the composition is a partial salt of a copolymer of maleic acid and an alkyl vinyl ether ( collectively referred to as &# 34 ; pvm / ma &# 34 ;). preferably , the alkyl group has from about 1 to about 5 carbon atoms , but a more preferable copolymer includes methyl vinyl ether . as is known by those skilled in the art , the molecular weight of such copolymers can affect the properties of the copolymer and , by extension , the denture adhesive comprising the copolymer . polymers generally do not have one precise molecular weight . rather , polymers are made up of many polymer molecules , each having a different molecular weight . one way to measure the &# 34 ; average &# 34 ; molecular weight of a polymer is to measure its specific viscosity under specified conditions . the preferred copolymer of the invention generally has a specific viscosity ( measured as a 1 % weight / volume solution of methyl ethyl ketone at 25 ° c .) of at least about 1 . 5 . more preferably , the specific viscosity is at least about 2 . 5 . the preferred copolymer of the invention is generally used as its partial salt . the maleic anhydride group can be hydrolyzed to form the corresponding dicarboxylic acid which can , in turn , react with metal compounds that partially neutralize the carboxylic acid groups on the copolymer . preferably less than 100 % of the carboxylic acid groups on the copolymer chain are neutralized . more preferably , about 26 % to about 15 % of the carboxylic acid groups are left unneutralized of the copolymer and most preferably from about 24 % to about 15 % of the carboxylic acid groups . one of the cations in accordance with the invention is calcium . another cation in accordance with the invention is an alkali metal cation , preferably sodium and / or potassium . as indicated before , it has been suggested in the prior art that the addition of the cation calcium beyond 70 % degree of substitution causes precipitation of the pvm / ma copolymer , thus making it impossible to manufacture the ca / na salt composition . it has also been suggested that the calcium be replaced by caustic . instead of replacing calcium with sodium and / or potassium as suggested in the prior art , it has been surprisingly found that the problematic ca / na pvm / ma salt precipitate formation can be eliminated even with high levels of calcium substitution ( 69 % or greater ) by holding the substitution level of the other cation , i . e ., sodium and / or potassium within certain limits . the substitution level of the other cation is preferably kept at a decreasing level with increasing level of substitution of calcium . more preferably , the substitution level of the other cation is kept within the range of about 1 to 10 %. most preferably , the substitution level of the other cation is kept approximately within the following range with respect to the degree of substution in calcium : table 1______________________________________most preferred embodiment - degree of substitution of ca : na degree of substitution - ca degree of substitution - na______________________________________69 % 1 - 10 % 71 % 2 - 8 % 73 % 2 . 5 - 8 % 75 % 3 - 6 % 77 % 4 - 5 . 5 % 80 % 4 . 5 - 5 . 5 % ______________________________________ the dental adhesive compositions of the present invention may further comprise a water - soluble cellulosic polymer as is known in the art such as methyl cellulose , sodium carboxymethyl cellulose , hydroxyl propyl methyl cellulose and the like . the cellulosic polymer , preferably sodium carboxymethyl cellulose , is a powder which when moistened , becomes hydrated and tacky or gummy thereby providing additional adhesive functionality to the dental adhesive composition . the sodium carboxymethyl cellulose gums are water - soluble , anionic long chain polymers whose properties vary to some extent depending on the number of carboxymethyl groups that are substituted per anhydroglucose unit in each cellulose molecule . these cellulose polymers comprise from about 15 % to about 35 %, and preferably from about 17 % to about 28 % of the dental adhesive composition . the denture adhesive may also comprise an activator such as a polyacrylic acid , polycarbophil , citric acid , sodium or calcium citrate and / or a polymeric acid such as a gantrez ® acid . preferably , the activator comprises a polymer , such as relatively short chain resins and longer polymers , copolymers , graft or block copolymers , and linears or network polymers . such materials can be naturally - occurring or derived or entirely artificial . preferred materials include chelating polymeric acids and salts . preferred chelating acids and salts comprise copolymers of dicarboxylic materials such as methyl - vinyl ether / maleic acid copolymers and acrylic acid / maleic acid copolymers . preferably , the lower alkyl vinyl ether - maleic acid is present in an amount of about 0 . 1 % to about 1 . 5 % by weight based on the total weight of the denture adhesive composition . more preferably , the lower alkyl vinyl ether - maleic acid is present in an amount of about 1 % by weight based on the total weight of the denture adhesive composition . typical excipients include waxes and oils . other excipients often included in denture adhesives include flavoring agents , sweetening agents , viscosity modifiers , coloring agents , preservatives and thickeners . other water soluble polymers such as xanthan gum , polyvinyl pyrrolidone ( pvp ), carboxymethyl cellulose , methyl cellulose and hydroxyl propyl guar may also form part of the final denture adhesive formulation . vehicles such as petrolatum , mineral oil , vegetable oil and the like may form part of cream - type formulations , and non - toxic anti - caking agents such as silica , talc , dicalcium phosphate anhydrous and the like can be present . the compositions can also contain , if desired , other known denture adhesives . the oils useful in the invention include without limitation is mineral oil . however , vegetable oils such as corn , soybean , cottonseed , castor , palm and coconut oils and animal oil such as fish oil may also be used in addition to mineral oil . in general , amounts of oil from about 1 % to about 30 % by weight of the total denture adhesive composition are usable , with amounts of about 10 % to about 25 % being preferred . the colorants useful in the present invention include pigments such as titanium dioxide , and may also include the lakes of dyes suitable for food , drug and cosmetic applications . these colorants are known as d & amp ; c dyes . two preferred colorants are the lakes of d & amp ; c red no . 7 and d & amp ; c red no . 30 . fumed silica can also be used as a thickener for the adhesive . a fine white powder , fumed silica is the colloidal form of silica ( silicon dioxide , sio 2 ) made by the combustion of silicon tetra - chloride in a hydrogen - oxygen furnace . the amount of fumed silica used in the composition may range from about 0 . 7 % to about 2 %. the denture adhesive composition of the invention can be prepared by mixing the components until a homogeneous mixture and is obtained and recovering the resulting product . for example , if polyethylene and mineral oil are to be employed , such material may be heated to temperatures from about 90 to 95 ° c ., and are preferably cooled prior to blending with other components such as the polymeric acid and coloring agents . whether formulated as a powder , liner , liquid or cream , the denture adhesive composition of the present invention hydrates to form an adhesive composition when applied to moist dentures or exposed to water or saliva . in order to further illustrate the present invention , various illustrative examples are set forth below . in these examples , as well as throughout the specification and claims , all parts and percentages are by weight and all temperatures in degrees celsius unless otherwise specified . polymer salts were prepared in the following manner . 900 g of room temperature water were charged into a main reactor kettle equipped with a high speed stirrer . the anhydrous mve / ma copolymer was slowly added to the main mix kettle with continuous mixing . 250 g of room temperature water were charged into a secondary kettle and either sodium hydroxide or potassium hydroxide and calcium hydroxide were added slowly . this slurry was well mixed to form a homogenous slurry . the slurry was slowly added into the main reactor kettle while mixing at high speed to prevent localized precipitation . the batch was heated to 85 ° c . (± 5 ° c .) and maintained at about 85 ° c . for two hours with vigorous mixing , forming the salt . these salts remained in solution and did not precipitate or settle thus ruining the batch . the resulting mixture was put in trays and dried at 85 ° c . in an oven or dried on a drum drier . the dried ca / na , or ca / k 75 / 5 , 80 % degree of substitution salt was then milled through a suitable mill and screened through a 60 mesh screen . a one percent solution of the resulting powder had a ph of about 5 . 5 - 6 . 5 and a bulk density of 0 . 7 - 0 . 8 . the materials used and the amounts used are set forth in table 2 . these salts did not precipitate or settle . table 2______________________________________formulation of examples 1 and 2 ingredient example 1 example 2______________________________________water 1150 g 1150 g gantrez ® an169 72 . 38 g 72 . 79 g calcium hydroxide 25 . 77 g 25 . 90 gsodium hydroxide 1 . 82 g -- potassium hydroxide -- 2 . 6 g______________________________________ a polymer was made according to example 1 , except that an amount of sodium hydroxide was employed that was sufficient to form a ca / na 75 / 8 , 83 % degree of substitution salt . after the mixer was turned off , a heavy deposit of precipitate was observed on the bottom of the glass reactor and the batch had to be discarded . the purpose of the above description is to illustrate some embodiments of the present invention without implying a limitation . it will be apparent to those skilled in the art that various modifications and variations may be made in the apparatus or procedure of the invention without departing from the scope or spirit of the invention .
a denture adhesive comprising a partial , mixed salt of a copolymer of an alkyl vinyl ether and maleic acid copolymer produced by a wet process , wherein the cations of said salt comprise i ) calcium with a degree of substitution of the copolymer in calcium of at least about 69 %; and ii ) at least one other cation selected from the group consisting of sodium and potassium .