CA1039704A

CA1039704A - Resin-containing lubricant coatings

Info

Publication number: CA1039704A
Application number: CA200,310A
Authority: CA
Inventors: Robert E. Parkinson
Original assignee: USS Engineers and Consultants Inc
Current assignee: USS Engineers and Consultants Inc
Priority date: 1973-05-18
Filing date: 1974-05-17
Publication date: 1978-10-03
Also published as: JPS5027802A; FR2229477B1; GB1473235A; FR2229477A1; DE2422013A1; US3873458A; IT1011835B; BE814678A

Abstract

SPECIFICATION
ROBERT E. PARKINSON
RESIN-CONTAINING W BRICANT COATINGS

ABSTRACT OF THE DISCLOSURE
Composition for forming lubricant coating, particularly useful in processes for working of sheet metals, comprising a resin capable of forming a layer adhering to the surface, and an oil for forming an upper layer to enhance the lubricating properties on top of and/or partially distributed within the resin layer; and a method of applying both layers of the coating to the metal surface simultaneously from a single aqueous dispersion or emulsion composition.
The coating has been found to greatly increase the ability of the metal sheet to withstand severe fabrication processes, such as deep-drawing, without tearing or galling, compared with ordinary lubricating oils or greases.

Description

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~ ~ 1039704 ,~. ; . . .. .
; ~ BACKGROUND OF THE I~ENTIOi~
~ ' In deep-drawing, or other severe forming processes for sheet metals, F~ ~ ~I such as carbon steel or stainless steel, there is a need for a lubricant which wnuld make it possible to fabricate parts without tearing or galling that would ~; ~ not be poQsible with ordinary lubricating oils or greases. Such a lubricant ; ohould allow the metal to flow more uniformly during the dra~, so that stresses ~3~ ~ '! are more uniformly distributed and a more seYere draw can be made without metal . tearing or racture. The lubricant should stay in place in areas of severe ¦ pressure and thus prevent galling or welding from metal-to-metal contact with the dies, aQ in ironing methods of metal forming.
;i The use of a resinous coating on metal underneath a layer of oil, soap, ~wax or grease is known to industry as a lubricant syste~ for deep-drawing e.g.,~ ilbond", H. A. Montgo~ery Company). ~,owever, this lubricant system ` '' ~* Trade Mark 103970~
must be applied in two steps: (1) a resinous coating is applied and dried;

(2) the oil or grease is applied in a second operation. Some other lubricant systems use a phosphate or similar conversion coating as the base to hold the lubricant oil or grease. These also are two-step operations in which the metal S must first be treated and then the oil applied separately.
A one-step method of applying both the resin layer and the oil layer simultaneously from a single aqueous dispersion or emulsion would be advantageous -bec~use it would simplify the application process, and may also enhance the ~ lubrication because~the more inti~ate and uniform distribution of the oil phase -- 10 over and throughout the resin layer.
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., SU~S`IA:RY OF THE INVENTION
I haYe developed a composition for the purpose of applying a composite i resin/oil lubricant coating on a substrate such as metal sheets in a single ' coatin& operation. When this composition is applied as a thin coating and dried, -' 15 it separates into two layers or phases: (a) a tough resin layer tightly adhering ,. , to-the substrate~ and (b) an oil layer or phase, separated from the resin by mutual insolubility, covering the resin layer or dispersed therein.
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The tough, adherent resin layer provides a barrier against galling of ~' th~ metal under high pressure forming processes and intimately holds the "oil `' 2Q phase" that provides a lower coefficient of friction. The ability of this ' composition to distribute the two components in layers in proper relationship to , ,j .
J ,I the substrate in a single operation greatly simplifies the application process.
i This resin/oil composite lubricant coating has been found to be particularly useful when preapplied and dried on metal sheets as a once-through -25 lubricant for severe metal-forming processes such as deep-drawing, draw-and-iron ; processesj and roll-forming. (It is not recommended where the lubricant must be ~ continually replaced, as in machine bèarings.) In addition to its lubricating 1- .
' :~ : ! ` ' ' ' 2- Robert E. Parkinson

3.039~04 properties, this coating provides protection for the metal surface against corrosion and abrasion My compositions for applying the lubricant coating are aqueous dispersions consisting essentially of a "resin phase" and an "oil phase" in a single composition. For proper performance, the resin must be a tough polymer, which is dispersable in an aqueous medium, which has ability to form a film ;;
during the drying that adheres strongly to a metal substrate, which is insoluble in the oil phase, and which may easily be dissolved or stripped from the metal ;
surface after use by a process such as alkaline detergent cleaning The preferred resins for my lubricating composition include ethylene-acrylic acid copolymers, containing preferably 15 to 25~ acrylic acid, particu-larly those with high carboxyl content (e.g., 18 to 24 percent) such as Union :::
Carbide Corporation's "EAA 9300 ~trade mark) or EAA 9500 (trade mark). Although either EAA 9300 or EAA 9500 may be used, a more stable emulsion is achieved with the higher molecular weight EAA 9300 copolymer solution. These copolymer resins may be dissolved in hot aqueous alkali to give a soap-like colloidal solution of the salt formed by a reaction similar to saponification They remain in colloidal dispersion on cooling to room temperature. When a volatile ~-- alkali or base, such as ammonium hydroxide or certain volatile amines, is used to disperse the copolymer, the colloidal solution may be applied as a coating that, when dried to drive off the alkali, reconstitutes the original acid copolymer resin on the surface of the substrate. Such coatings have excellent , adhesion to metals and are tough, flexible, and water-resistant; and they may be easily removed by redissolving in hot alkaline solutions such as those used as commercial metal cleaners One advantage to such dispersions of ethylene-acrylic acid copolymers when used in my lubricating composition is that they are themselves excellent emulsifying or dispersing agents for the oil phase and other additives to the composition.
The resin phase of my composition may also contain othe~ resins in addition to or instead of the above-mentioned ehtylene-acrylic acid dispersion.

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~.039704 Aqueous dispersions of other copolymers, terpolymers, or inonomers of e-thylene, preferably present in an amount of 50 to 95% by weight of the copolymer or ionomer, with other ethylenically unsaturated acids, such as methacrylic or crotonic acids, or with ethylenically unsaturated esters, such as vinyl acetate, may be substituted for all or part of the ethylene-acrylic acid copolymer dispersion For example, an aqueous dispersion or latex of a copolymer or a terpolymer of ethylene containing 60 to 85~ ethylene, 0 to ~0% vinyl acetate, and 0 to 25% methacrylic acid, may be used, Preferred esters of the acrylic acid and other ethylenically unsaturated acids are the lower esters of 1 - 4 carbon atoms. Other water-soluble or dispersible resins, such as polyvinyl alcohol, may also be incorporated as a minor portion of the resin phase.
Polyvinyl alcohol was found to improve wetting and give a drier (less greasy) coating by encapsulating most of the oil in the resin, which may be advanta-geous for certain usages. ~owever, polyvinyl alcohol has its disadvantages, sueh as, separation in storage as a gelatinous third-phase in my emulsion, giving coatings with poorer adhesion to the metal substrate, or more difficulty in removal with alkaline cleaners. ~ -~: , . - . .
The second essential component of my lubricating coating composition ~`' is the "oil phase" which is required to reduce the friction of the lubrication 20 eoating. This oil phase may consist of a lubricant oil, by which I mean mineral oil, animal or vegetable oils or fats, fatty-acid soaps, greases, waxes, and other natural or synthetic lubricating materials or combinations thereof. In ~ seleeting material for the oil phase of my eomposition, it is desirable that in ; addition to having a low eoeffieiency of frietion, it be insoluble in the resin ,, .
phase so that the resin eoating layer is not softened, that the oil separates from the resin phase during the drying of the dispersion eoating, and that it does not interfere with the adhesion of the resin layer to the metal substrate.

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In addition to the major resin/oil components, my composition may eontain minor amounts of surfaetants, solvents, thickeners, alkalis, and other material to improve the stability, wetting, defoaming, dispersion, viscosity, ;1 and eoating eharaeteristies of the emulsions and the uniformity, smoothness, ~ thiekness~ and removability of dried coatings. Thickness of the coating may also .
' ~0397~
be controlled by varying the amount of water vs. the total nonvolatile collcen- , -tration of th-c emulsion, or by the means of application. For severe high-pressure metal-forming, it may be desirable to add finely-divided solid lubricants :
such as graphite, carbon mono~luoride or molybdenum sulfide powders. Certain fi].lers selected for low abrasiveness, such as clay, talc, or mica, or oxide pigments may also be dispersed in the emulsion and may be advantageous in certain cases to strengthen the resin barrier layer of the coating. It is also possible to disperse po~dered or emulsified polymers with low coefficient of friction, :i `` such as nylon or teflon* in the composition. I have found that my compositions , are particularly effective in maintaining stable dispersions of such powdered solids ~ith little settling in storage.

~ The composition for the application of my coating is preferably Y prepared by predissolving or dispersing the resins in an aqueous medium and then ., ; . .
emulsifying or dispersing the "oil phase" into this resin dispersion by high- -shear mixing. Minor additions may be blended as desired.
For maximu~ effectiveness of lubrication, the "oil phase" nollvolatiles are preferably 25 to 75 percent by weight of the total nonvolatiles re~aining in the coating after drying? although any amount of oil up to as much as three times the amount of resin may be blended in ~y composition. As little as one percent ~; . . . .
oil, based on the resin, may be desirable where drier coatings are preferred or ;~3 j`where addi.tional oil is being applied over the coating before fabrication.
The dispersion of my composition is prepared as a low-viscosity fluid (preferably 50 to 1000 centipoises) that may be easily applied to metal as a thin coating by conventional methods such as roll-coating, brushing, dipping, spraying, etc. The visc~sity and concentration of the dispersion may be controlled by the ~;~ a~iount o water added or by the addition of fillers, thickeners, or gelling 3 .;agents to adjust desired thickness of the resulting dried coating. Concen-trations of ahout 1~ to 45 percent total resin/oil nonvolatiles in the dispérsion ;. ~ . .
;* Trade Mark .

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~J ~039~0~
have been found to be satisactory for roll-coating. I have found that t~in coatings, with a dried coating weight in the range of approximately 50 to 350 milligrams per square foot (0.54 to 3.77 grams per square meter) or approximately ~,0.5 to 3.0 micron thickness, give satisfactory lubricating properties to sheet ij steel. Heavier coatings up to 25 microns may be desirable for some applications.;
After application, the coating is dried to evaporate the volatiles, such as water and ammonia. Drying at room temperature (for several hours) may be . ~. . ~ I .
used, but it is preferred to dry with heat from about 120 C to about 200 C (for I less than a minute.) Such heat-drying improves the adhesion of the coating to.. ~. ,; I .
. , i !;the metal. Over heating may make some coatings more difficult to remove in '`' 'I j .': ' subsequent alkaline cleaning. j : 'i - ' . I :.
Examples , Example 1 ~See Table I) l An aqueous ammonium solution o~ an ethylene-acrylic acid copolymer ~ ''resin (containing about 20 percent acid) was prepared by heating the resin to 90 .~ llto 130 C in a pressure vessel, in a slightly more than stoichemetric amounts to ~ ~lammonium hydroxide with suf~icient water to give about 22 percent resin solids.
_ j A mixture of surfactants was added to improve the wetting properties, the emulsion stability, and foam reduction of the coating composition but were not . ~ ,, , . :, .
essential. (A combination of an alkyl-phenoxy-polyethoxy-ethanol, a ditertiary acetylenic glycol and a dispersant, such as Tamol 731 (Rohm and Haas) or a lignosulfonate, were found to be satisfactory, but many othsr surfactants may be used.) In the proportions indicated in Table I (Example 1) a mixture of -parafinic mineral oil and lard oil were blended into the ethylene-copolymer resin solution with high-shear mixing. The emulsion formed was quite stable.
Creaming occurred with low molecular weight copolymer tEAS 9500) on storage, but `~ ;~ ' I jJ, !
was easily redispersed. Without further dilution, the total nonvolatiles were ~* Trade Mark 6- 1 ;
~s ,! ~''' ! : : :-:

about 41 percent of the solution. This composition, when dried on steel sheets, gave a smooth coating with a tough layer of resin adjacent and tightly adhering to the steel, with most of the oil in a separate layer over the resin. When applied and dried on stainless steel sheet in coating weights of about 100 mg/ft2 (1.08 g/m2~ to 350 mg~ft2 (3.77 g/m2) the depth of draw was increased 20 to 32 percent (to 0.550 to 0.600 inch) in the Olsen cup ~est tASTM A344) compared to an ayerage of about 0.450 inch depth with the same steel with a standard mineral oil ' lubricant. This lubricant coating was also applied to thin carbon steel sheets ` - (blackplate) and fabricated successfully into cans by a draw-and-iron process without galling or tearing. Tin plating or special phosphate treabments of the '~steel have generally been necessary to obtain satisfactory draw-and-iron processing with ordinary lubricants. The coefficient of friction between this .~. '1 ,A,`, , coating and steel was 0.077. ' ~ -Exam~le 2 3' 15 Molybdenum sulfide of a very fine particle si~e ~0.35 u average) was ~'~ added to the composition of Example 1. An excellent dispersion with practically ~-no settling in storage was obtained. The purpose of the addition was to improve .,; , , , ~resistance to galling under severe high-pressure fabrication conditions. The '~, 'Olsen cup depth of draw and draw-and-iron results in laboratory tests were -essentially the same as Example 1. It is expected that the MoS2 addition may giYe superior performance under more severe fabrication conditions.

'EXaf~ple 3 ' Thi~ composition was prepared by dissolving polyvinyl alcohol in hot ~ ater and then'adding the ethylene-acrylic acid copolymer ammonifum solution and ;¦ 25 emulsifying mixed lard oil and oleic acid into it. This composition gave smooth, f ~ , ~ ~- adherent~ dry coatings in which the oil appeared to be dispersed in a ma~rix of 9 .. : -~s'~ ~ ~ resin. Coating of 52 to 104 milligrams per square foot (0.56 to 1.12 g/m2) ~,-f ~

7- ~ Robert E. Parkinson 10397~)4 increased the Olsen draw depth by about 13 to 25 percent on stainless steel sheet. Carbon steel "blackplate" sheets coated with this composition were successfully draw-and-ironed into cans without galling in laboratory tests.
Initial adhesion of these coatings to the s~eel was good, but after storage for several months this composition gave coatings with poor adhesion. The co-efficient of friction between these coatings and steel was the same as Example 1 (0.077), but there was evidence that resistance to galling was inferior under very severe conditions.

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Example 4 In this composition an inorganic filler was ~dded to the coDposition of ` Example 3. Both talc and a very fine iron oxide pigment were tried. Dispersants , , .
; ',such as lignosulfonates and phosphates were effective in maintaining good suspension of the solids. Concentrations used are given in Table 1. With talc additions, the.e was evidence of slight improvement in resistance to galling in ,. . . .
coatings on blackplate in draw-and-iron can tests on production equipment. -However, iron oxide gave satisfactory results on laboratory equipment but caused.i .
i excessive breakage and galling in more severe processes. ~~

'!'~, , EXample 5 ~ I
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This example illustrates the substitution o another resin dispersion for a portion of the ethylene-acrylic acid copolymer solution. The ethylene- ;

~; I "ionomer" dispersion (Elvax D1249, E. I. du Pont de Nemours Co.) is an ethylene- ~ i , methacrylic acid copolymer partly neutralized with sodium hydroxide and dispersed "b~ an emulsion polymerization process with surfactants. The per~ormance of this ., , ; ::
~ I`composition as a lubricant coating was similar to that of Example 3. , ~
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.'J~ Example 6 This composition contains-a soap ( mmonium oleate) as the oil phase ;

instead of mineral oil or fats. The composition was a uniform, translucent, , ~'. , - - :.
-~ * Trade Nark -.~ .
k~

1¢~397~4 stable, colloidal solution with good wetting properties but with a tendency to foam. Even when diluted to about 14 percent nonvolatile so that an extremely thin coating was applied, it was found that this composition gave a 13 percent improvement in Olsen cup depth on stainless steel compared with the same steel-with a standard lubricating mineral oil.

Example 7 ' Into an ammonium solution of ethylene-acrylic acid copolymer light mineral oil was emulsified with high-shear stirring. Sufficient water was added ;to dilute the mixture to about 24 percent nonvolatiles (of which about 7G percent ' 10 was oil~. This emulsion separated into two layers on standing but was easily redispersed for application. Applied to the same stainless steel as in Example l, - this coating improved the depth of Olsen draw by about 14 percent.

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~ 9- Robert E. Parkinson ,, .
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3974~4 - Table I
Typical Formulae for I.ubricant Coating Materials (parts by weight) Examples Resin Phase:
~:
Et~ylene-acrylic acid copolymer 100100 100 100 100 100 100 (22% solids ammoniu~ soluticn) Polyvinyl Alcohol - - 6.7 6.7 9 Ethylene-ionomer dispersion - s - - - 30 - (Elvax D1249) (42% solids) : ;, . . .
; O~l-Phase:
; . . . :
:~ineral Oil 15 15 - - - - 50 '! ~
Lard Oil 15 1530 30 45 - 15 Oleic Acid - - 3 3 4.5 .'!, ,, Soap - a~monium olea~e - - - - - 25 S~rfactants: 0.75 0.75 0.3 3.3 0.2 0.13 0.13 :., ~i , . j ~ Fillerq or Solid Lubricant:
' 'h~t ~
Talc or iron oxide - - - 15 - - -Nolybdenum Sulfide - 2.5 - - - ~- - ;
to ~j .. 10.0 ~j , Water (To dilute to 14 to 40 percent nonvolatiles according '! to thickness of coating desired).

~ My invention is ~ot restricted to the above specific examples and .,!7: ' . ,' illustrations. It may be otherwise practiced within the scope of the following , claims.

7~ m ~ 0~ Robert E. Parkinson

Claims

"I Claim"

1. Process for cold forming or shaping metal comprising subjecting to de-formation pressure against a solid surface, metal which has been coated with a resin-oil layer by applying to its surface a single aqueous dispersion composition and drying said composition to remove water and other volatiles, said composition prepared by blending or emulsifying a lubricant oil selected from mineral oil, animal or vegetable oils, fats, soaps, fatty esters, or other natural or synthetic oil, grease, or wax lubricant materials or mixture thereof into an aqueous dispersion, latex, or solution of a copolymer, terpolymer, or ionomer of ethylene with ethylenically unsaturated carboxylic acids selected from the group consisting of acrylic acid, methacrylic acid, and crotonic acid, and esters thereof, and vinyl acetate, said lubricant oil comprising from about 1 to about 75% of the total non-volatiles of the coating composition and being substantially insoluble in the resin.

2. Process for cold forming or shaping metal comprising subjecting to de-formation pressure against a solid surface metal which has been coated with a resin-oil layer by applying to its surface a single aqueous dispersion composition and drying said composition to remove water and other volatiles, said composition prepared by blending (a) a lubricant oil selected from mineral oil, animal or vegetable oils, fats, soaps, fatty esters, or other natural or synthetic oil, grease, or wax lubricant materials or mixtures thereof, and (b) a dispersion or solution of a copolymer of ethylene and acrylic acid, containing 15 to 25% acrylic acid, in water containing alkali sufficient to form a water-soluble or dispersable salt or ionomer of the copolymer, said lubricant oil comprising from about 1 to about 75% of the total nonvolatiles of the coating composition and being substantially in-soluble in the resin.

3. Process of claim 2 in which the alkali for dissolving or dispersing the ethylene acrylic acid copolymer is ammonium hydroxide or a volatile amine.

4. Process for cold forming or shaping metal comprising subjecting to de-formation pressure against a solid surface metal which has been coated with a resin-oil layer by applying to its surface a single aqueous dispersion composition and drying said composition to remove water and other volatiles, said composition prepared by blending (a) from about 1% to about 75%
lubricant oil selected from mineral oil, animal or vegetable oils, fats, soaps, fatty esters, and other natural or synthetic oil or grease lubricant materials or mixtures thereof and (b) the balance an aqueous dispersion or latex of a copolymer or terpolymer of ethylene containing 60 to 85% ethylene, 0 to 40% vinyl acetate, and 0 to 25% methacrylic acid.

5. A process for cold-forming or shaping metal of Claim 1, in which a solid powder or solution, from a group consisting of graphite, molybdenum sulfide, carbon monofluoride, tetrafluorethylene, nylon, talc, and kaolin clay is dispersed or suspended in the resin/oil coating composition so that upon application to the metal and drying, the solid powder is distributed in and bound by the coating.

6. Method of forming metal comprising:
(a) emulsifying a lubricating oil in an aqueous suspension of a copolymer terpolymer or ionomer derived from ethylene and an ethylenically un-saturated monomer selected from vinyl acetate, acrylic acid, methacrylic acid, and crotonic acid, their salts and lower esters, the ethylene comprising from about 50% by weight to about 95% by weight of the copolymer or ionomer, the weight ratio of copolymer or ionomer to lubricant oil being from about 100:1 to about 1:3, the lubricant oil being substantially insoluble in the ethylene copolymer or ionomer;

(b) placing on metal to be formed a coating of the emulsion thereby made, (c) drying said coating, and (d) subjecting said metal to deformation pressure against a solid surface.

7. Method of claim 6 wherein the dried coating has an average weight of at least about 50 milligrams per square foot.

8. Method of Claim 6 followed by the step of removing the coating from the formed metal by cleaning it with an alkaline detergent.