US 2737465 A
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United States Patent 2,737,465 Y SYNTHETIC RESIN ENAMEL STRIPPING COMPOSITIONS Leopold lessel, Philadelphia, 12:1,, assignon toRadiofCorporationofiAinerica, ,a corporationof Delaware:
No Drawing. Application May- 28; 1948, Serial No. 29,93 1
13 Claims. (Cl. 1344-38) This invention relates, generally, to compositions for: stripping synthetic resin. coatings from various surfaces and; more particularly,-relates to improvements in com positions. whichhaveespecial utility-in removing insula,- tionifrorn copper wire, at thezsame time preparing the wire to receive a coat of solder.
In the electrical industries, it is frequently necessary-to strip coatings comprising synthetic resinous.- materials from the ends of wires preparatory to soldering them to terminals or to other, wires. This necessitates a great deal of hand labor by skilled operators and, in the case ofcertain' insulation materials, such as polyvinyformal,
it is an expensive and'tim'e consuming 'p'rocediir'e'. The. present invention relates to improvements a p series"of-composition'swhichmay be usedtos H H the most-resistantsynthetic resin materials in a" matter offjseconds. These compositions leave the wire base in aclean and bright state to which a layer of solder may immediately be applied without subjecting the Wire to any further'treatment such as the application of a flux.
The methodsdescribed. in. the presentapplicationarl closely relatedto. those disclosed. in co:-pendinge-applica'- tion, Serial No. 744,775, filed April 29.,.1.947.,.Patcnt:':No. 2,563,417, Aug..7, 1951, by. the present inventorz" ms materials disclosed herein are improvements in the compositions disclosed in the said application, in that they are still faster in action. In the previous application, there were. disclosed: compositions containing pentanedione 2,4, with or without a certain amount ofwatenand preferably. containing a'mutualsolvent forthepentane dione 2,4. and the water. It-hasnow been foundthatif:
formic acid or. certain. formic. acid, derivatives-' be sub stitiite'dl'for part of the pentanedione 2,4, thesm'pping action of the composition is fspeeded. up considerably,--enablingit to be used in connectionfwith automaticstrip ping machines. derivative found useful 'in the present invention, the-fume removal problem is not serious and the compositions do; not. introduce any objectionable healthhazardatq the,
One object of the present invention-is to provider'im provementsiincompositions-containing pentanedione 2,4 for stripping any synthetic resin coating froma base.
Another object of the present invention is to provide improved compositions for-facilitating the-stripping of synthetic resin coatings from a wire-base.
Another objectis to provide improved compositions the veryrapidsofteningof synthetic, resinous' materials" comprising oneor more-of the polyvinylacetalseriesr' Another object of the presentinven'tion is the provision of improved compositions for stripping synthetic, resinous With the percentages ofv formic. acid.
2,737,465 Patented M51216; i956 the present inventioin may be used is illustrated in the following example. The end of a coppermagnet wire; n a n a h n ng. of e vinyla s l sy the resin,-isdip ped in av bath of thestrippjng agent; main; tained at l7 5 F., untilthe coating is, softened, The i e s: mov om the q i en l n essui is 3P: p1ib n S of the um and otefi s i ndhe ns' .-,.n t be t z r t a s n le. motion... Automatic machines may also be used ton ap; plyin g the pressure to the coating and pullingit from-the; endof the wire. The end of the wire from which the coating hasbeen removed is then dipped immediatel a tinning orsoldering bath of conventional composition, which provides it with a closely; adherent coating; of,
metal. which. does not deteriorate: on long standing,-
thewire. This tinned or soldered} end mayzthen be: mediately. soldered. to a. terminalfor tofanotl er, wirewithnolfurther treating The solder bath m ay be et) pepper-1t; tin and 40 per centleador 40 per centtintandfifl pe cent lead or. of. any. other conventional solder compositi 5.
The time of treatment necessary to soften. the :coatip'gi, materialisuificiently to be strippedoif with; a single motion yariestwith the temperatureof the-bath. v g
The preferred compositions, accordingto, the present invention, are those which contain pentandione 2,4, formic acid and at least'a small amountofrwater. Use of: a: mutual solvent for the pentanedione 2,4 and the waterproduces equally good results. The pentaned ione 2,4 shouldv be present in the range ofi'about; 30"t6fabout 9,8.v volume per cent. Concentrated formic acid of tor9 O'vpercent strength may be present in the range of about 2-to about 50-volume per cent. Providednhafat least 2 percent of'the composition:is concentrated formic} acid of 85.'to per cent strengthandat'least SOQVQlnrnei' per cent of the composition is pentanedione 2,4, the ref mainder'of the'volume may b'eJmadeup by addingwatei or' mixtures of water with" an organic solvent mutually compatible with Water and pentanedione. 2,4. Composi,-; tions within theabove range are'muchmore rapid irI' their stripping action than either thesamesconcentration; of the pentancdione 2,4, by itself,or concentrated formic acid in the indicated percentage range, dilutedonlywith water, or the water-solvent mixture, by itself.
Since it is desirable to have compositions which will notseparate into two phases at room temperaturegcompositions are preferred which have the desired rapid treatingtirhe at practical elevated temperatures and remain in a single phase even after standing at room tern; peratures of 70 R'for long periods of time. It has be n, found that mutual solvents for pentanedione 2,4 and} watermay be added to the system without changinglthej.
Although. many different types of mutual solvents for pentanedione 2,4 and water were tried, none was found which had any adverse efiect, their inclusion, when used in amounts up to 25 per cent, not slowing down the softening effect of the pentanedione 2,4 and water enough to make their use impractical. Besides diacetone alcohol, other ketones, such as acetone, acetonyl acetone, etc., are almost equally applicable. Esters, such as methyl lactate, ethylene-glycol-rnonoethyl-ether, ethyl lactate, etc., may be used. Alcohols, such as ethyl alcohol, isopropyl alcohol or tetrahydrofurfuryl alcohol, or others, besides diacetonealcohol, have been found almost equally advantageous, while other miscellaneous mutual solvents for pentanedione 2,4 and water, such as gammavalero lactone, propylene oxide and dioxane have all b'n tried and found operative. Although the invention is perhaps most valuable when used with such coatings as the polyvinyl acetal resins or with polymerized oil-resin enamels, since these are extremely diflicult to remove by means formerly in use, these softening agents exert a dissolving or a softening action on synthetic resins in general and have useful application in preparing any wire coated with a synthetic resinous material for the application of solder. Besides those resins already mentioned, there have been used resins of the phenolic type, such as phenol formaldehyde, polymerized allyl esters, copolymers of styrene and allyl esters, furane resins, superpolyamides, alkyds, melamine formaldehyde, etc. Although some of these resins may be softened -with other solvents, it is advantageous to be able to soften them rapidly with a material which leaves no unwanted residue after the coating is stripped from the wire and, in general, the compositions of the present invention are considerably faster in action.
The following table shows the effect on a number of different types of resin coatings of compositions made up according to the present invention, the time given being that required to soften the resin sufficiently to be stripped off in a single motion:
2 or c Pentane- Acid10 gg Type of Coating 2 Seconds Boosting Factor Polyvinyl Acetal 180 30 6.0 Phenolic Resin- 50 20 2. 6 do 150 30 5. 0 do 180 30 5.0 Silicone Resin 30 10 3. 0 Allyl Ester Resin 240 30 8. 0 stiyrene Copolymer Res- 30 6. 0
. Furane Resin 300 60 5.0 Polymerized Oil En- 25 2. 5
ame 30"; Superpolyamide-.-- 4, 000 60 67. 0 Al Sheet; Alkyd Type Enamel... l0 5 2.0 Glass Rod. Melamine Formalde- 60 10 6.0
Wood Pane1 ,do 80 5.3
The above table shows the softening time for various resins with the composition maintained at150 F. and shows the' comparison between using pentanedione 2,4, alone, and compositions in which some of the pentanedione 2,4 has been replaced with formic acid. The boosting factor is obtained by dividing the softening time with pentanedione 2,4, alone, by the softening time required for the corresponding resin composition when using the composition with the formic acid added. This table also indicates that the compositions of the present invention are useful not only in stripping resin coatings from wires but from other surfaces, such as aluminum sheets, glass rods or wood panels. The surfaces listed are merely illustrative and may comprise anything to which synthetic resins are commonly applied as coating materials.
The data given in the above examples were obtained,
using coatings of comparable thickness on commercially available magnet wires. It is quite obvious that the thickness of the coating will influence the speed of softening; the thinner the coating, the more rapid the softening action, providing the same diameter of wire is used. For unexplained reasons, in extremely thin wires, an increase in softening time has been found with decreased wire diameter.
It has been noted that the boosting effect of the water on the softening action of the pentanedione 2,4 increases practically in direct proportion to its content in the compositions up to 50 per cent water or higher but, when using the higher percentages of water, it is necessary to raise the temperature of the compositions to inconvenient points in order to prevent the separation of the mixture into two phases. None of the mutual solvents for water and pentanedione 2,4 which have been used in the compositions, when used alone, has been foundto have any significant softening effect on the resistant types of resinous materials.
In general, the optimum amount of mutual solvent to be added to the compositions varies with the mutual solvent selected. In a composition comprising pentanedione 2,4 and water in a 2:1 ratio, for every 1 parts of diacetone alcohol, for example, there would be needed only 0.8 part of isopropyl alcohol, 0.7 part of tetrahydrofurfuryl alcohol but 1.4 parts of gamma-valero lactone. The addition of more than the optimum amounts of the various mutual solvents exerts a diluting effect and such proportions may be used to lower the cost of the resulting compositions.
Examples of preferred compositions made up according to the present invention will now be given:
' The composition of Example II is somewhat more rapid in its action than that of Example 1.
Although formic acid, itself, has been used as a stripping agent for some time, if formic acid, by itself, is to be used for this purpose, percentages considerably above 50 per cent formic acid must be used to obtain stripping efficiency. When such higher concentrations are used, however, a number of undesirable features are introduced,
such as danger and annoyance due to fumes and contact of'the liquid with the human skin, absorption of the formic acid in'the unstripped portion of the coils with resultant corrosion. Compositions of the present invention, since they enable such low percentages of formic acid to berused, avoid these shortcomings.
It is to be emphasized that the percentage of formic acid used in accordance with the present invention is always less than .50 volume per cent. Percentages of formic acidused in this invention may be so low that an equivalent percentage in an aqueous solution, Without the use of pentanedione 2,4, would be utterly ineifective for the purposes intended. This may be demonstrated by the figures given below which indicate immersion periods in seconds required to render a certain type of Seconds required to soften A stripping agent containing:
Pentaned1one2,4 volume percent 50 Water a (10..-. 25 Diacetone-alcohol ..do 25 27 100 Pentanedionezn do 40 Water 7 do.- 20 Diacetonealcohol... .do 20 15 85%formicacid .do 20 100 Pentanedionetpi do 20 1 Water I v -do- 20 Diace'tonealochol; do'. 20 n 85% formic acid do 40 100 85% formic acid do. 40 Water .do.. 60 30 100 85% formic acid do.... 210 Water do. 80 (1) 100 I Inactive after 60.
From the above examples, it may be seen that the addition of formic acid to a system containg pentanedione 2,4 and water unexpectedly increases the speed of the stripping action to a point considerably above that of either straight pentanedione 2,4 solutions or comparable formic acid solutions.
There is an indication that the effect of the formic acid on the efficiency of the stripping solutions is linked with the molecular structure of this compound. It has also been found that formic acid derivatives show a similar boosting effect on the speed of action. For example, a composition containing pentanedione 2,4, 98 volume per cent, concentrated formaldehyde solution, 2 volume per cent, has a stripping efiiciency 50 per cent higher than straight pentanedione 2,4, while a composition containing pentanedione 2,4, 90 volume per cent, concentrated formaldehyde, volume per cent, has an efficiency thrice that of straight pentanedione 2,4. In comparison With the rapid action of compositions comprising pentanedione 2,4 and formaldehyde, formaldehyde-water compositions containing as much as 20 per cent concentrated formaldehyde are completely inactive in removing most synthetic resin insulation materials. The optimum amount of formaldehyde found useful in the compositions containing pentanedione 2,4 is about 5 to 10 per cent formaldehyde to 90 to 95 per cent pentanedione 2,4. Useful effects, however, have been found by using as much as 50 per cent formaldehyde with 50 per cent pentanedione 2,4. It was found that using an optimum composition of pentanedione 2,4 and formaldehyde on a given polyvinyl acetal coating that the time required for stripping was only one-fourth that required by pentanedione, alone.
Formamide has no stripping effect, whatever, by itself, in aqueous solution, but when combined with pentanedione 2,4-water systems, there is a definite booster effect found when amounts up to 50 per cent formamide are used. The optimum percentage is about 20 to 30 per cent formamide to 70 to 80 per cent pentanedione 2,4. The highest boosting factor obtainable with formamide is about 6 compared with pentanedione 2,4, alone. That is,the time required to strip a given polyvinyl acetal enamel from a given diameter wire is about one-sixth that required using pentanedione 2,4 without the added formamide.
The esters of formic acid also have a boosting effect on the stripping action of pentanedione 2,4 or pentanedione 2,4 and water, although the effect is much weaker than that of formic acid or formamide, for example. Such esters may be methyl, ethyl, n-propyl, or n-butyl formate, etc., or esters such as ethylene diformate or benzyl formate. In fact, any alkyl or aryl group may be present since the action appears to be due to the formyl group and not to the remainder of the molecule. As an example, a compositionv containing, pentanedibne 2,4,. volume per cent, and methyl formate, 20 volumeper cent, strips; a given polyvinyl. acetal enamel in, one-half I the time requiredfor pentanedione, alone. p
In general, it has beenfol d. hat: those-formic acid, derivatives. having. the, formula,
X in which X may be H, O-.H, .-NHz i or where Risany alkyl; or. a-ryl group are. prefer-red. Since;
theimprovement appears t be due to the /H C=O group however, the remainder of the molecule does not appear to make much difference except that some exert more boosting effect than others. In general, also, it has been found that these boosting agents should be present in amounts ranging from 2 to 50 volume per cent for best results although with some, higher amounts exhibit a somewhat increasing effect in proportion to the amount used.
There have, thus, been described improved liquid compositions for stripping a synthetic resinous composition from any surface to which it normally adheres. The stripping compositions comprise pentanedione 2,4 and either formic acid or a formic acid derivative. The stripping action is brought about by a rapid softening of the coating being removed. The use of the improved compositions introduces no health hazard and their use is simply and easily carried out. It will be obvious that the preferred mode of carrying out the invention as described is susceptible of various modifications but it is intended that the invention be limited only as defined in the appended claims.
I claim as my invention:
1. A composition for softening synthetic resinous coat ings consisting essentially of about 30 to about 98 volume per cent pentanedione 2,4, about 2 to about 50 volume per cent of a compound selected from the group consisting of formic acid, formaldehyde, formamide and esters of formic acid, and which contains up to 68 Volume per cent water.
2. A composition according to claim 1 in which said compound is formic acid.
3. A composition for softening synthetic resinous coatings consisting essentially of about 30 to about 98 volume per cent pentanedione 2,4, about 2 to about 50 volume per cent of a compound from the class consisting of formic acid, formaldehyde, formamide and esters of formic acid, and up to 68 per cent water and a mutual solvent for pentanedione 2,4 and water.
4-. A composition according to claim 3 in which said compound is formic acid.
5. A composition according to claim 4 in which said mutual solvent is diacetone alcohol.
6. A composition according to claim 5 containing about 2 to about 20 volume per cent formic acid, about 30 to about 50 volume per cent pentanedione 2,4, and up to about 48 volume per cent of equal parts of water and diacetone alcohol.
7. A composition according to claim 6 containing 20 volume per cent of concentrated formic acid, 40 volume per cent pentanedione 2,4, 20 volume per cent water and 20 volume per cent diacetone alcohol.
8. A composition for softening synthetic resinous coatings consisting essentially of 30 volume per cent pentanedione 2,4, 40 volume per cent of 85 concentrated formic acid, 15 volume per cent water and 15 volume per cent diacetone alcohol.
9. A composition for softening synthetic resinous coatings consisting essentially of pentanedione 2,4 and about 2 to about 50 volume per cent formaldehyde.
10. A composition according to claim 9 in which said formaldehyde is present within the range of to 10 volume per cent.
11. A composition for softening synthetic resinous coatings consisting essentially of pentanedione 2,4 and about 2 to about 50 volume per cent formamide.
12. A composition according to claim 11 in which said formarnide is present within the range of to volume per cent.
13. A method of softening a synthetic resinous coating comprising subjecting said coating to a composition consisting essentially of pentanedione 2,4 and a compound selected from the group consisting of formic acid, formaldehyde, formamide and esters of formic acid, said composition being maintained at a temperature of to References Cited in the file of this patent UNITED STATES PATENTS 871,750 Austen ct al. Nov. 19, 1907 1,095,270 Ellis May 5, 1914 1,884,765 Lougovoy Oct. 25, 1932 2,435,239 Schub Feb. 3, 1948 2,507,985 Kuentzel May 15, 1950 2,563,417 Pessel Aug. 7, 1951 OTHER REFERENCES Gregory: The Condensed Chemical Dictionary, 3rd edition, Rheinhold Publ. Corp., 1942, page 45, column 1.