US2918445A - Polyester plasticized vinyl polymer organosol composition - Google Patents

Description

United States Patent POLYESTER PLASTICIZED VINYL POLYMER ORGAN OSOL COMPOSITION Wesley A. Tarwid, Barrington, Ill., assignor to American Can Company, New York, N.Y., a corporation of New Jersey No Drawing. Application December 31, 1956 Serial No. 631,431

11 Claims. (Cl. 260-323) The present invention pertains to a novel organosol coating composition and in particular it pertains to an organosol coating composition having a relatively high nonvolatile content with a relatively low viscosity.

By nonvolatile content as used herein is meant those ingredients having a very low vapor pressure whereby when once incorporated in the organosol, they are not vaporized to anyappreciable extent even at the elevated temperatures at which the organosol is fused into a solid film.

Qrganosols, as the term is generally understood in the art, are essentially a dispersion of a high molecular weight, insoluble polyvinyl chloride resin in a liquid vehicle comprising a careful balance of dispersant and diluent. Because of the inertness and chemical resistance of the films formed therefrom, organosols have found great utility as protective coatings for various substrates, including sheet metal. However, when formulated to give the maximum protection as a sheet metal coating, organosols have the disadvantage of exhibiting a relatively high viscosity preventing rapid and efiicient application to the sheet metal, particularly when individual sheets are coated rather than a continuous web of metal.

In the past, the results of thickness, cohesion and flexibility desired of an organosol have been obtained by various means. Thickness is often obtained by building up the organosol film in layers. The most usual means of obtaining cohesive strength and flexibility is by incorporating lower molecular weight solution resins and chemical plasticizers which practice produces high viscosity organosols. Each of these prior art devices for producing a satisfactory organosol coating for sheet metal, because of the high viscosity of the composition, necessitates multiple passes through the coating apparatus and/or single pass coating methods which are not practicable for coating individual sheets, such as knife coating or reverse roller coating.

In the metal can manufacturing industry, and in many other industries, by far the most usual method of protectively coating individual metal sheets is by single pass, direct roller coating, i.e. the applicator roller and the sheet being coated are traveling in the same direction at their line of contact. The high viscosity prior art organosols are unsuitable for application by the direct roller coating technique causing the operation to be slow and inefficient and tending to produce a finished coating having unsightly and deleterious ridges. Knife-coating, reverse roller coating, i.e. the applicator roller and the sheet are traveling in opposite directions at their line of contact, and similar methods, compared to direct roller coating, as stated previously, are practicable only for coating continuous webs but not for rapidly coating individual, spaced sheets passed through the coating apparatus in sequence.

To produce the final, coherent protective film, the wet organosol coating must be fused by heating to a tem- =-perature in the range of about 350 F. to 400 F. This necessity gives rise to another disadvantage of prior art organosols in that the plasticizers used tend to evolve an undesirable amount of obnoxious smoke during the fusing or baking operation.

It is, therefore, an object of the present invention to provide a fluid organosol coating composition which contains sufficient film forming nonvolatiles to produce a highly inert, corrosion resistant, ridge free coating for sheet metal while at the same time having a sufliciently low viscosity at application temperatures so that the organosol can be efiiciently applied by direct roller coating.

A further object is to provide a fluid organosol coat- .ing which can be applied with equal facility to both a moving, continuous web of sheet metal and to individual sheets of sheet metal passing through the coating apparatus in rapid succession.

Another object is to provide a composition of the character described that contains only a minimal amount of liquid ingredients that adversely affect the polyvinyl chloride dispersion resin.

Still another object is to provide a fluid organosol coating composition for sheet metal which, upon the fusing or baking thereof, knits well to form a continuous, chemically resistant, flexible film which is ridge free and has cohesive strength.

Yet another object is the provision of a composition of the class described which evolves little or no obmolecular weight, insoluble vinyl chloride polymer as the dispersion resin, a specific vinyl chloride-vinylidene chloride interpolymer as the solution resin, a polymeric, resinous plasticizer and a careful balance of organic liquids constituting the dispersants and diluents.

The dispersion resin is a vinyl chloride polymer which is relatively insoluble in the dispersants usually used in organosols such as ketones, e.g. acetone, and even to a lesser degree in aromatic and aliphatic hydrocarbon solvents. At most, the polyvinyl chloride dispersion resin must be no more than swelled by the action of ketone solvents. Although aromatic hydrocarbons also have a swelling action on the dispersion resin, their swelling action is not as great as the swelling action of the usual organosol dispersants. Aliphatic hydrocarbons have little or no swelling action on the dispersion resin. The average molecular Weight of the dispersion resin must be at least 20,000 and preferably above 20,000. Dispersion resin composed wholly of polyvinyl chloride or copolymers of vinyl chloride with other polymerizable olefins, in which copolyrner the combined vinyl chloride .methyl and ethyl acrylate or methacrylate, and maleate esters such as dibutyl maleate. The amount of dispersion resin operable is about from 50% to and preferably about 60% to 70% of the nonvolatiles in the organosol.

The primary utility of the organosol coatings of the present invention are as coatings on the inside of metal cans where the organosol is in constant contact with the packed product during the useful life of the can. For this reason, chemical plasticizers, most generally used as dispersants in prior art organosols, cannot be used where good chemical resistance is desired. Aside from the fact that these chemical plasticizer dispersants tend to evolve obnoxious smoke during the fusing of the film, they reduce if not destroy the resistance and inertness of the final coating film to many of the various products packed .into the can, especially corrosive products such as strong acids or alkalies, e.g.' high pH liquid detergents, by being leached out of the film over a period of time. The dispersant used in the present invention is a low boiling ketone, or an ether-alcohol or mixture of the two. This dispersant performs the function necessary for an organosol dispersant of forming strong attachments to the dispersion resin, aiding in the Wetting of the resin and swelling and softening of the dispersion resin to permit reduction of agglomerates to their basic particles and to give the organosol sufficient viscosity to prevent settling of the particles. In addition, during fusion or baking of the film, the volatile dispersant aids in knitting the dispersion resin particles into a continuous film. After having performed its necessary functions, the dispersant is completely and readily removed from the film by the heat of the baking operation without evolution of smoke, leaving behind no undesirable component or residue.

The amount of dispersant in the organosol must be sufficiently high to produce the results stated above but at the same time must not be so high as to cause excessive swelling of the dispersion resin, too great an increase in viscosity and possibly gelation of the organosol. In the instant invention, the range of dispersant content in the organosol must be about from to 50% and preferably about 36% by weight of the volatile liquid constituents of the organosol.

Any aliphatic ketone having a boiling point in the range of 235 F. to 425 F. may be used as the dispersant ketone. Examples of such ketones are diisobutyl ketone, methyl isobutyl ketone, 2,6,8-trimethyl nonan- "one 4, with diisobutyl ketone being preferred. As an ether-alcohol dispersant there may be used any etheralcohol having a boiling point in the range of 255 F. to 450 F. To be operable, it is necessary for the dispersant to be of sufficiently high volatility to be removed completely from the organosol during the fusing thereof; but at the same time, to be of sufficiently low volatility to remain in the fluid organosol for as long as possible in order to perform its functions as a dispersant. Specific ether-alcohols useful in the present invention are the l to 4 carbon atom alkoxy mono-ethers of ethylene glycol, such as Z-methyoxy ethanol, etc. and diethylene glycol monobutyl ether, with the diethylene glycol monobutyl ether being preferred. If a mixture of ketone and etheralcohol is used, the weight ratio of ketone to ether-alcohol must be about from 0.05/1 to 1/ 0.5 and preferably about 0.75/1.

Xylene, toluene, benzene or similar aromatic hydrocarbons or mixtures thereof are used as the volatile diluent in the organosols of the present invention. Although these aromatic hydrocarbons have a swelling effect on the polyvinyl chloride dispersion resin, they have little or no dispersing action thereon and, therefore, cannot be considered as a substitute for or equivalent to the dispersant. In other words, to produce the desired results, the instant organosol can contain only sufficient dispersant to provide a certain amount of dispersion resin swelling and a good dispersion of the resin. The diluent provides the remainder of the volatile liquid necessary to produce additional resin swelling, if needed, proper nonvolatile content and viscosity of the organosol. The aromatic hydrocarbon diluents serve another important function more fully described hereinafter. In the instant invention, the amount of aromatic diluent used is in the range of about from 50% to 90%, and preferably about 64% by weight of the volatile liquid constituents of the organosol, ie, the combined dispersant and diluent content. The diluent is also smokelessly removed from the composition during fusing.

The solution resin which gives the organosol o th 4 nstan nve ion ts. uni ue, nd. nov l, P o e ties. an: forms to the schematic formula (CH CH ,,Cl,,) in which n is either 1 or 2 and x is a positive number greater than 1. Since, in a given group of chloroethylene units, it is impossible to determine which chloroethylene units have a single chlorine atom and which have two chlorine atoms, n is said to have an average valuev of greater than 1 but less than 2 forsuch a group. Such resins are characterized by being at least 97% completely soluble in liquid benzenoid aromatic hydrocarbons in concentrations up to at least 32% by weight; and their total content of chlorine lies between 61 and 64% by weight.

Specifically, the useful solution resin is composed of thermoplastic chemically saturated polymeric material made up exclusively of carbon, hydrogen and chlorine atoms and comprising recurring units of chloroethylene having from 1 to 2 chlorine atoms on only one of the ethylene carbons and is further characterized by possessing a chlorine content of about. 61% to 64% by weight, by having a specific viscosity within the range of about 0.15 to 0.30 as determined at 20 C. using a 0.4% solution of the resin in nitrobenzene and by possessing substantially complete solubility in aromatic hydrocarbons, by which is meant that at least 97% of the resin is completely soluble in the familiar benzenoid aromatic hydrocarbons such as benzene, toluene and xylene. At weight concentrations of the resin up to and including 32 percent, solution viscosities are within a range which enables the compositions to be applied to surfaces by the usual means of application, such as direct roller coating. Polymeric materials containing only carbon, hydrogen and chlorine having such chloroethylene units in which the chlorine content may be from 61% to 64% and which are within the above definition, provided of course, that they possess the required viscosity and-solubility charactericstics, include certain interpolymers made from monomeric mixtures containing vinyl and vinyli dene chloride only, or vinyl and vinylidene chloride together with polymerizablehydrocarbons or chlorinated hydrocarbons, such as styrene, dichlorostyrene, isobutylene and ethylene and mixtures of such interpolymers with each other or with other chlorine containing polymers such as polyvinyl chloride and polyvinylidene chloride which may result from the primary interpolymerization process. Polyvinyl chloride itself, and polyvinylidene chloride itself are, of course, not included since the chlorine content of the first named polymer is below 61 %"and the chlorine content of pure polyvinylidene chloride is above 64%.

As mentioned previously, the aromatic hydrocarbon diluent not only serves the diluent function with respect to the dispersion resin but also acts as a solvent for the solution resin. This aromatic hydrocarbon solvent solubility of the vinyl chloride-vinylidene chloride solution resin permits the inclusion of a much larger percentage of solution resin in the organosol, and thereby a greater quantity-of nonvolatiles in the organosol, while still maintaining a relatively low viscosity, than has heretofore been possible. This property of the organosols of the present invention enables them to be quickly and efiiciently applied to flat metal sheets by the direct roller coating technique and to produce an easily fused, inert and protective film, ridge free with excellent smoothness, hardness and gloss, a result unobtainable with prior at t organosols.

The specific solution resin, in combination with "the specific proportions and types of dispersants and diluents set forth above, 'also obviates the need for monomeric 'chemicalplasticizers usually used in organosol composimo m ic c emicalp ss isize fmmthe Cummin s-the.

difficulties and disadvantages occasioned thereby, i.e. smoke evolution during fusing, lowered inertness and resistance of the film, are obviated. The solution resin imparts substantial cohesive strength to the final film and being polymeric, it is not leached out of the coating or appreciably attacked by strongly acid or alkaline fluids as are monomeric plasticizers. Further, due to the low volatility of the solution resin in comparison to monomeric plasticizers, the instant organosols containing the specific solution resin and no monomeric chemical plasticizer evolve no obnoxious smoke during fusing of the dispersion resin.

The amount of the vinyl chloride interpolyrner solution resin in the organosol must be in the range of from about 5% to 25%, and preferably about by weight of the nonvolatile content. Quantities less than the specified minimum result in a final, dry coating having insufficient cohesive strength which tends to mud-crack. Amounts of solution resin greater than the indicated maximum cause too great an increase in the viscosity of the fluid organosol composition; and over-shadow the inert and resistant properties of the dispersion resin giving the dry film more of the properties of the solution resin.

A polymeric plasticizer is included in the instant organosol to provide the final film with flexibility. The polymeric plasticizer is not to be confused with the monomeric chemical plasticizers generally used as dispersants in organosols. The polymeric plasticizer has little or no swelling or dispersing action on the dispersion resin. Although it is liquid at room temperature, it has very low volatility and, therefore, does not distill or smoke during the fusing operation. Because it is polymeric, the plasticizer is much more resistant than the monomeric plasticizers to chemical attack by such materials as strong acids or bases.

I have found that a saturated polyester formed from a dibasic alkanoic acid of 6 to 10 carbon atoms and an alkandiol of less than 8 carbon atoms and having an average molecular weight between 600 and 1000 and preferably between 800 and 900 is operable in the present invention as a polymeric plasticizer. An example of such a polymeric plastizer is the polymeric reaction product of ethylene glycol and azelaic acid having an average molecular weight of about 850. The polyester plasticizer is what is referred to in the art as a primary plasticizer. By this is meant that the saturated polyester may be used as the sole plasticizer in the organosol and still produce a final, dry film having the particular, desired properties; or it may be used in combination with one or more polymeric, secondary plasticizers, the latter supplying some other desired property. Secondary plasticizers are not operable as the sole plasticizer in subject organosol.

The plasticizer used in the present invention, whether it is composed solely of the polyester primary plasticizer or of a combination of the primary plasticizer and a secondary plasticizer, must be compatible with both the dispersion resin and the solution resin and must have a low volatility even at the fusing or baking temperature of the organosol. The final, dry film must have sufiicient flexibility to withstand the bending and forming operations performed on the metal substrate during its fabrication into a commercial item, such as an end for a metal can; but at the same time, the film must be sulficiently hard to resist abrasion during the forming operations and inert to provide chemical resistance. To accomplish these results, the total amount of plasticizer that may be present in the organosol, whether it be all primary or a combination of primary and secondary plasticizers, is in the range of from about 10% to 25%, and preferably about by weight of the novolatiles. The ratio of primary to secondary plasticizer can be adjusted as desired according to the specific property sought. However, the amount of secondary plasticizer must be less than the amount of primary plasticizer, i.e. the weight ratio of primary to Y secondary plasticizer must be greater than 1 to 1, so that the properties of the primary plasticizer predominate.

The secondary plasticizers are also polymeric materials so as to be substantially non-fugitive by the action of heat and to be chemically inert. Examples of such secondary plasticizers are highly chlorinated paraffin waxes, and epoxidized esters of a polyhydric alkanol and oleic or linoleic acid. These last mentioned epoxidized esters are described in United States Patent 2,485,160. They produce the best final coatings and are therefore preferred, especially an epoxidized soybean oil polymer.

In addition to the essential ingredients set forth hereinbefore, other ingredients commonly added to organosols may be incorporated as desired. For example, there may be added pigments such as titanium dioxide and/or carbon black, and/or heat stabilizers for the vinyl chloride resins such as blue lead. The amounts of these optional ingredients added to the organosol will depend upon the particular result desired, but the total weight thereof should be less than 20% and preferably less than 10% of the nonvolatiles.

The following example is for the purpose of illustration only and is not to be considered as limiting the invention.

On a conventional 3 roller ink mill, the following ingredients are ground together to produce a paste having a 5 to 6 grind as determined by a Hegman grind gauge; 45.4 lbs. dibasic lead phosphite, 45.4 lbs. titanium dioxide, 10.7 lbs. blue lead, 1.5 lbs. carbon black, and 231 lbs. polyester polymeric plasticizer. After the paste is ground to the proper fineness, i.e. 5-6 grind, 331 lbs. thereof are charged into a commercial ball mill along with lbs. diethylene glycol monobutyl ether and 500 lbs. of a toluene-xylene solvent mixture. This ball mill mill charge is ground for 10 minutes after which is added 1,000 lbs. of the dispersion resin, i.e. polyvinyl chloride having an intrinsic viscosity in cyclohexanone at 20 C. of 1.52, according to the following schedule: 400 lbs. and grind for 15 minutes, an additional 300 lbs. with another 15 minutes grinding, then add the last 300 lbs. and continue grinding.

The temperature of the batch is maintained at below 90 F. and grinding is continued until a 5 to 6 grind (Hegman grind gauge) is obtained. The time needed to obtain this fineness of grind varies between 8 and 24} hours. About 30 minutes after the full amount of the polyvinyl chloride dispersion resin has been added, the viscosity of the mixture should reach 60-90 KU (Krebs- Storrner units), and this viscosity should be maintained throughout the grinding operation.

As the grinding continues and the dispersion resin becomes more dispersed, the viscosity of the mixture tends to increase. This tendency is offset by periodically adding portions of the solution resin composition. The solution resin composition contains 143 lbs. of the particular vinyl chloride-vinylidene chloride interpolymer described hereinbefore, 34.6 lbs. of a resinous epoxy polyether of the Epon type as a heat stabilizer, 163 lbs. diethylene glycol monobutyl ether, 191 lbs. diisobutyl ketone, and 298 lbs. of the toluene-xylene solvent mixture.

After the above dispersion resin composition attains the desired 5-6 grind, the remainder of the solution resin composition is added in two equal parts. The organosol is ball milled for 15 minutes after the addition of the first portion and for 30 minutes after adding the second portion. The organosol is then ready for applica tion to the desired surfaces or may be stored for future use.

The fluid organosol coating compositions of the pres ent invention have a nonvolatile content of from about 45% to 65% and preferably about 55% by weight of the organosol, and a viscosity at room temperature, i.e. 70 to 80 F., of about from 210 to 560, and preferably about from 315 to 420 centistokes seconds. The amount of film forming resins contained in the nonvolatiles is from 7 aboiit 70% to'80%, andprefer'abl'y "about-% 'by weight of the n onvolatile. The relatively high 'ler'ce'ntage of iiohvolatilesQincluding film forming resins,and low vis- "cosity of thesubject organosols permits the quick and e fiicient application of these organosols by the direct ''r'oller coating technique and the ready formation of smooth, ridge free, glossy inert and resistant protective "coatings for sheet metal. Coatings deposited from the subjectorganosol have special utilityasthe interior protec tive lining for metal cans containing caustic liquids such as high pH detergents. Theinstant"organosols are stable over long periodsof time whereby little or no settling of the solid articles therein occur. 'Any false 'b'ody resulting from long standing is easily overcome bya'brief period of stirring.

It :is thought that the invention and many of its *attendant advantages Will be understood from the fore goinjg description, and it will be apparent that various changes 'm'ay be made in the matter of'the ingredients, their identity and their proportions'without departing from the spirit and scope of the invention or s'acrificing'allof its 'r'nateri'al advantages, the forin 'hereinbe'for'e "described "being merely 'aprefer'red embodiment thereof.

I claim; A 1. A fluid organosol coating composition containing about from 45% to 65% nonvolatile ingredients by 'weightof the total composition, the remainder of said composition comprising a volatile liquid dispersant and 5a" volatile liquid'diluent, said dispersant being s'e lecte d froi'n-the group consisting of an aliphatic 'ketone andan fa'liphatic ether-alcohol and mixtures thereof "and constitutingfabout frorn'10'% to 50% byw'eight o'f'the vola- "tile liquid constituents of said composition, said diluent comprising an aromatic hydrocarbon solvent and conf stitutingabout from 50% t'o 90% bywei'ght of saidliquid icon stitutents, saidinonvolatiles comprising'byweightabout "from 50% to 80% of a vinyl'chloi'ide polyrn'erin'partic'ulateform uniformlydispersed in saiddispersant and "diluent and having a combined 'vinyl chloride 'content *of at least 90% by 'weight'ofsai'd polymer, 'about from 5% to 25% by weight of a'vinyl chloride vinylidene :chloride interpolyrner' consisting of recurring chlorethyl- "ene units having from 1 to 2 chlorine atoms on only one of the ethylene carbonsand a chlorine content of about61% to 64% by weight'dissolved'insaid dispers- 'an't and diluent, and ab0ut'from"10% 'to 25 by 'weight of al'polye'ster"plasticiier compatible'withea'ch of said dispersed polymer and said dissolved interpoly'm'er in their solid state, said polyester plasticizer formed from a -dicaiboxylic alkanoic acid and an alkandiol, s'aidc'o'rnposition having a viscosity of about from -210 to 560 'centistokes-ata temperature of from F. to F.

2. The organosol composition set forth in 'claim 1 having 'anonvolatile content of about 55% by weight of said composition.

3. The organosol composition 'set forth in "claim 1 wherein the volatile liquid dispersant constitutes about 36% by weight of the combined dispersant-diluent mix- 'ture.

4. :The organosol composition set forth in claim 3 wherein the dispersant is composed of diisobutyl ketone and diethylene glycol monobutyl ether in a weight ratio of about 0.75/1.

'5. The organosol composition set forth in claim "1 wherein the volatile liquid diluent is selected from the group consisting of benzene, toluene, Xylene and-mixtures 'thereof.

' volatiles.

9. The organosol composition 'set forth in 'claim 1 wherein said vinyl chloride-vinylidene'chloride interpolymm is soluble in said diluent.

10. The organosol composition set forth in clair'n 1 wherein "said polyester plasticizer comprises about 15% by weight of the nonvolatiles. t

11. The organosol composition set forth in claim 1 having a viscosity of about 315 to 420 centistokeswhen measured at 80 F.

References-Cited in the file of this patent UNITED STATES PATENTS Powell Mar;l4, 1944 Powell Jan. 15, 1952 ttr-4

Claims (1)

1. A FLUID ORGANOSOL COATING COMPOSITION CONTAINING ABOUT FROM 45% TO 65% NONVOLATILE INGREDIENTS BY WEIGHT OF THE TOTAL COMPOSITION, THE REMAINDER OF SAID COMPOSITION COMPRISING A VOLATILE LIQUID DISPERSANT AND A VOLATILE LIQUID DILUENT, SAID DISPERSANT BEING SELECTED FROM THE GROUP CONSISTING OF AN LAIPHATIC KETONE AND AN ALIPHATIC ETHER-ALCOHOL AND MIXTURES THEREOF AND CONSTITUTING ABOUT FROM 10% TO 50% BY WEIGHT OF THE VOLATILE LIQUID CONSTITUENTS OF SAID COMPOSITION, SAID DILUENT COMPRISING AN AROMATIC HYDROCARBON SOLVENT AND CONSTITUTING ABOUT FROM 50% TO 90% BY WEIGHT OF SAID LIQUID CONSITUENTS, SAID NONVOLATILES COMPRISING BY WEIGHT ABOUT FROM 50% TO 80% OF A VINYL CHLORIDE POLYMER IN PARTICULATED FORM UNIFORMLY DISPERSED IN SAID DISPERSANT AND DILUENT AND HAVING A COMBINED VINYL CHLORIDE CONTENT OF AT LEAST 90% BY WEIGHT OF SAID POLYMER, ABOUT FROM 5% TO 25% BY WEIGHT OF A VINLY CHLORIDE-VINYLIDENE CHLORIDE INTERPOLYMER CONSISTING OF RECURRING CHLORETHYLENE UNITS HAVING FROM 1 TO 2 CHLORINE ATOMS ON ONLY ONE OF THE ETHYLENE CARBOBS AND A CHLORINE CONTENT OF ABOUT 61% TO 64% BY WEIGHT DISSOLVED IN SAID DIPERSANT AND DILUENT, AND BAOUT FROM 10% TO 25% BY WEIGHT OF A POLYESTER PLASTICZER COMPATIBLE WITH EACH OF SAID DISPERSED POLYMER AND SAID DISSOLVED INTERPOLYMER IN THEIR SOLID STATE, SAID POLYESTER PLASTICIZER FORMED FROM A DICARBOXYLIC ALKANOIC ACID AND AN ALKANDIOL, SAID COMPOSITION HAVING A VISCOSITY OF BAOUT FROM 210 TO 560 CENTISTOKES AT A TEMPERATURE OF FORM 70*F. TO 80*F.