CA1189749A - Coated metal container and method of making the same - Google Patents
Coated metal container and method of making the sameInfo
- Publication number
- CA1189749A CA1189749A CA000419495A CA419495A CA1189749A CA 1189749 A CA1189749 A CA 1189749A CA 000419495 A CA000419495 A CA 000419495A CA 419495 A CA419495 A CA 419495A CA 1189749 A CA1189749 A CA 1189749A
- Authority
- CA
- Canada
- Prior art keywords
- container
- resin
- metal
- top coat
- side wall
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
- B65D25/00—Details of other kinds or types of rigid or semi-rigid containers
- B65D25/14—Linings or internal coatings
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Laminated Bodies (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Details Of Rigid Or Semi-Rigid Containers (AREA)
- Paints Or Removers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A metal container comprising a seamless body and an end wall integral therewith and having on at least its interior surface a protective coating which is the reaction product of a citric acid ester utilized as a lubricant in forming the container and an after-applied synthetic resin.
A metal container comprising a seamless body and an end wall integral therewith and having on at least its interior surface a protective coating which is the reaction product of a citric acid ester utilized as a lubricant in forming the container and an after-applied synthetic resin.
Description
~9 ~
BAC~crO~No ~F 5E~ INVENTION
The well kno~, three-piece, sheet metal, food container is fa~
being supplanted by a two-piece container having a seamless body with one end wall integral with the body and the other end wall secured to the ~dy by means of a double seam after filling the container. Such containers for beer and soft drinks are made by the drawin~ and ironing process; whereas containers for fruits and vegetables which require a heavier and sturdier side wall are beginning to be made by a newer proces- known as draw/redraw.
Although the production of sheet metal containers by means of multiple draws i5 not new, the draw/redraw process is an improvement over the older drawing process in that it is done at higher speeds with greater draw ratios in each drawing stepO Achieving this higher productivity-rate requires special machines and, inter alia;
special lubr.icants for th~ metal~working operation; and to maintain this higher productivity-rate, subsequent processing steps to the formed con~iner must also be at high speed or eliminated where possible.
U.S. Patent 4,287,741 describes a class of citric acid esters which are efective as lubricants in the drawing and ironing process. ~e have found that the same citric acid esters are effective lubricants in the draw/redraw process described in relation to the present invention~
The present inventio~ involves the discovery that the citric acia esters d.isclosed in U.S~ Patent 4,287~741 not only act as effective lubricants in the drawing and redrawing of ferrous metal stock to form a container, bu~ that these lubricants, unlike metal-working lubricants used heretofore~ need not be removed from the surface of the formed container, but may be made to react with a s~bsequently applied syn~hetic resin top coat by heating to form a hardened barrier layer over the interior surface of the container.
~ he citric acid ester~ useful in the present invention are dlsclosed in U~S. Patent 4,287,7410~ e~u~r~
h Y~i~ ~ This '741 patent gives the following structural formula for these esters:
CH2-~C--O----R
O~C~ O~R2 wherein Rl, R~ and R3 are selected from the group consisting o hydrogen and alcoholic residues containing 1-10 carbon atoms, R4 is selected from the group consisting of hydrogen and carboxylic acid radical~ containing 1-10 carbon atoms, and at leas one of Rl, R2 and R3 is an alcoholic residue~
We have found that the methcd of the present invention is egually applicable to tinplated ferrous metal and to tin-free, low .. ..
carbon sheet ~teeln Although the comTnon prior art tinplate referred to in column ~, lines 50~56, of U.S. Patent 4,287t741 is usable in the present inYention, non-reflowed9 matte finish tinplate described in U.S. Patent 3,3~0,157 is preferred for the reasons set forth in this ' 157 patent in respect of the drawing and ironing process fsr making containers. The tin weight on the steel basis metal may Yary fr~m 0.10 lbs. to 1.0 lbs~ per base box.
The preferred tin-free steel has a chromium surface treatment.
Wh ile it is s~ill in flat sheet orm prior bo its formation into 2 contailler, a ~ynthetic resin base coat i5 applied and adhered to this treated surface. The most usual compositions for application as a base coat are those containing an epoxy resin or vinyl resin or polye 5 ter r e s in .
DETAILED DESCRIPTION OF T~E INVENTION
IN LUDING P_EFERRED EMBODIMENTS
The tin-free steel preferred for use in the presen~ invention is aluminum-killed, continuous cast steel with a chromium/chromium oxide surace treatment. The chromium in the oxide is present at about 0.5 to 2.0 mg per square feet and the chromium metal at about 3 to 13 mg per sguare foot. The material described is known in the art a~ TTS~CT for tin-free steel, chromium type~ The treatment is described in a paper published in the Journal of the Electrochemical So~iety, ~ol. 116, No. 9, pp 1299-1305.
The preferred tinplate ha the same composition of steel as set forth above and at the steel mill in a well known manner has tin applied to it~ surface electrolytically in various amounts, for example, .25 lb. per base box. As mentioned previously, this ti~plate is left in a matte condition, i.e., is not flow brightened, is oiled for rust inhibition and coiled for shipment to a container-making installatîon~
Thereafter tbe tin-free steel when received in the can-making plant has applied to its surfaces a base coating~ The preferred coating contains an epoxy resin based on bisphenol A with a~ epoxide equivalent weight of 2300 to 4000, a urea formaldehyde crosslinker,
BAC~crO~No ~F 5E~ INVENTION
The well kno~, three-piece, sheet metal, food container is fa~
being supplanted by a two-piece container having a seamless body with one end wall integral with the body and the other end wall secured to the ~dy by means of a double seam after filling the container. Such containers for beer and soft drinks are made by the drawin~ and ironing process; whereas containers for fruits and vegetables which require a heavier and sturdier side wall are beginning to be made by a newer proces- known as draw/redraw.
Although the production of sheet metal containers by means of multiple draws i5 not new, the draw/redraw process is an improvement over the older drawing process in that it is done at higher speeds with greater draw ratios in each drawing stepO Achieving this higher productivity-rate requires special machines and, inter alia;
special lubr.icants for th~ metal~working operation; and to maintain this higher productivity-rate, subsequent processing steps to the formed con~iner must also be at high speed or eliminated where possible.
U.S. Patent 4,287,741 describes a class of citric acid esters which are efective as lubricants in the drawing and ironing process. ~e have found that the same citric acid esters are effective lubricants in the draw/redraw process described in relation to the present invention~
The present inventio~ involves the discovery that the citric acia esters d.isclosed in U.S~ Patent 4,287~741 not only act as effective lubricants in the drawing and redrawing of ferrous metal stock to form a container, bu~ that these lubricants, unlike metal-working lubricants used heretofore~ need not be removed from the surface of the formed container, but may be made to react with a s~bsequently applied syn~hetic resin top coat by heating to form a hardened barrier layer over the interior surface of the container.
~ he citric acid ester~ useful in the present invention are dlsclosed in U~S. Patent 4,287,7410~ e~u~r~
h Y~i~ ~ This '741 patent gives the following structural formula for these esters:
CH2-~C--O----R
O~C~ O~R2 wherein Rl, R~ and R3 are selected from the group consisting o hydrogen and alcoholic residues containing 1-10 carbon atoms, R4 is selected from the group consisting of hydrogen and carboxylic acid radical~ containing 1-10 carbon atoms, and at leas one of Rl, R2 and R3 is an alcoholic residue~
We have found that the methcd of the present invention is egually applicable to tinplated ferrous metal and to tin-free, low .. ..
carbon sheet ~teeln Although the comTnon prior art tinplate referred to in column ~, lines 50~56, of U.S. Patent 4,287t741 is usable in the present inYention, non-reflowed9 matte finish tinplate described in U.S. Patent 3,3~0,157 is preferred for the reasons set forth in this ' 157 patent in respect of the drawing and ironing process fsr making containers. The tin weight on the steel basis metal may Yary fr~m 0.10 lbs. to 1.0 lbs~ per base box.
The preferred tin-free steel has a chromium surface treatment.
Wh ile it is s~ill in flat sheet orm prior bo its formation into 2 contailler, a ~ynthetic resin base coat i5 applied and adhered to this treated surface. The most usual compositions for application as a base coat are those containing an epoxy resin or vinyl resin or polye 5 ter r e s in .
DETAILED DESCRIPTION OF T~E INVENTION
IN LUDING P_EFERRED EMBODIMENTS
The tin-free steel preferred for use in the presen~ invention is aluminum-killed, continuous cast steel with a chromium/chromium oxide surace treatment. The chromium in the oxide is present at about 0.5 to 2.0 mg per square feet and the chromium metal at about 3 to 13 mg per sguare foot. The material described is known in the art a~ TTS~CT for tin-free steel, chromium type~ The treatment is described in a paper published in the Journal of the Electrochemical So~iety, ~ol. 116, No. 9, pp 1299-1305.
The preferred tinplate ha the same composition of steel as set forth above and at the steel mill in a well known manner has tin applied to it~ surface electrolytically in various amounts, for example, .25 lb. per base box. As mentioned previously, this ti~plate is left in a matte condition, i.e., is not flow brightened, is oiled for rust inhibition and coiled for shipment to a container-making installatîon~
Thereafter tbe tin-free steel when received in the can-making plant has applied to its surfaces a base coating~ The preferred coating contains an epoxy resin based on bisphenol A with a~ epoxide equivalent weight of 2300 to 4000, a urea formaldehyde crosslinker,
2 sulfonic acid ca~alyst, and a high-melting polyethylene internal lubricant. The coating has a solids content of 28 percent. Both vinyl and polyester resin compositions have also been used as base coats.
This base coating applied to both sides of the steel may be applied while the s~eel is still in coil form or the steel may be cut into sheets and the coating applied to individual sheets, which coating is subsequently baked to form a tough, adherent base coat on the tin-free steel~
~s~
The citric acid ester of the present invention i.q dip coated onto both ~urace~ of individual sheets of the base coated tin-free steel, the excess ester is removed and the sheets are then fed into a blanking and cupping press which cuts from the sheet one or re circular discs of 7.947 inches in diameter, and draws the disc into a cup of 5.007 inche~ in diameter and 1.850 inches in side wall height. In two subsequent operations, the cup is successively reduced in diameter with concurrent lengthenin~ of its side wall, i,.e., drawn; and simultaneously this side wall is slightly thinned, iOe~ to about 10% less than the starting gauge~ and further elongated, i.e., ironed, in the manner similar to that described in .S. Patent 3,360~157~ The final diameter and side wall height accomplished in the drawing plus ironing are 3.060 in~ and 4.450 in. respectively and are accomplished in a few seconds. The diameter of the starting blank and the height to diameter ratios, draw ratios, in the ensuing metal working process may be varied depending upon the desired size of the finished can. Also, as between different draw/redraw systems, the amount of draw in each step may be varied provided the cumulative effeGt of the plural draws produces the can of desired height and diameter.
It is readily apparent that a draw/redraw system with ironing is a more severe metal working process than a draw/redraw system without ironing. The citrate ester lubricant of the present . . .
invention performs equally well in both systems~
The particular citric acid compound used in the abcve example is acetyl t~ibutyl citrate. It may be applied by any suitable means such as roller coating, immersion coating with excess suitably removed, electrostatic deposition which is accurate in application both as to weight and placement~ or by hot spraying from an oxy-dry unit or cold spraying if the ester i~ reduced with a suitable solvent.
7~
The amount of lubricant applied over the base coat can vary from 10 to 40 and preferrably 10 to 20 milligrams per square foot of total usface, i.e., both sides, of the sheet being fed into the draw~redraw apparatus It has been found that the lubricating efect fall~ off appreciably below 10 mgs/ft2 and for most operations 20 mgs/ft2 is sufficient to achieve the high speed, trouble free, multiple draws from flat blank to formed container.
Due to the severity of the metal-working operation, i.e., the appreciable draw rati~s and draw speed plus ironing~ substantial heat is generated on the surfaces being worked. ~hile not wishing to be bound by any partieular theory, it is possible that this generated heat causes ~t least a partial decomposition of the lubricant on the worked surfaces, the~eby liberating reactive ~ubstances s~ch as those having carboxyl or acetyl functional groups. For example, in the case of the preferred acetyl tributyl citrate, acetic acid would be liberatedO These functional groups are belie~d to attach themselves to the base coat and/or be available for reaction with the postsprayed top coating.
At the completion of the draw/redraw operation, the container is beaded to impart strength to the side and bo~tom wal3.s before being ea into a device for applying a top coat to the container' s inside surface. Most usually this device involve~ a turret which revolves the container past a r~ciprocating spray gun which enters the interior of the container which is spun on it~ longitudinal axis while ~he spray gun, as it is retracted from the container ~ody~
emits a 360 degree spray of a synthetic resin solution to coat the entire inter ior surface of the container.
7~
After completion of the top coating operatlclll, the container is then subjected to a temperature of 400Fo for 4 minutes to harden and cure the top coat. Unlike pr ior art procedures which require the metal-working lubricant to be removed before application of the top coat to avoid cont~mination and improper curing o the top coat, the procedure of the present invention not only eliminates the time-consuming st~p of removing the lubricant and permits the applica~ion of the top coat directly to a still-lubricated internal sur~ace of the container but assists in firmly adhering the top coat to the base coatO Again, not wishing to be bound by any particular theory, it is believed that the reactive groups liberated frQm the applied lubricant previously and/or during the above mentioned bakins operation react with or at least anchor themselves into the top coat as well as the base coat thereby forming a strong adhering medium between the base coat and top coat.
Tbe citric acid ester lubricant and what remains thereof after th~ draw/redraw operation are soluble in organic solvent.s such as butanol~ butyl Ce1losolYe, di-isobutyl ketone, Cellosolve acetate and Solvesso 150~ Therefore, resins for top coats which are also soluble in these same solvents and provide inert, continuous, resin films upon thermal curing are preferred such as epoxy resins and acrylic resins~ Vinyl resins are usable if they are applied over a base other than a thermoset epoxy resin. The citric acid ester may also be used in water base coating compositions provided the liquid system contains a solvent for the citrate ester ~hich is miscible with the water of the system~
Evaluation of top coats applied over an epoxy-UF base coat is done by testing process resistance as well as intercoaS: adhesion bets~een the base coat and the top coat. The follo~iny table summarizes the results of these tests:
~e 37~
Eval~ation of Postsprayed Top Coats.
--~5'L~L ~G#bU~ t- Lse Coat Process Intercoat ToP Coat _ Resistance Adhesion acryllc passed passed vinyl passed failed epoxy-phenolic passed passed epoxy-acrylic passed passed epoxy-phenolic passed passed ep~xy-phenolic passed passed epoxy-phenolic pa~sed passed epoxy passed passed The epoxy-phenolic resin systems in the above table differ from each other in . the propc:rtion of epoxy to phenolic.
Process resistance i~ checked by filling the container with ae~Oni2ed water followed by steam processing at 265F. for 90 minutes. After water cooling and standing overnight, the cans are emptied, cut open, cross hatched, and taped to test intercoat adhesion.
Other suitable base coat/top coat combinations include vinyl and polyester resins as base coats r examples of which are in the table below:
Intercoat Adhesion ~fter Process Base Coa~
V,~
polyester passed passed passed vinyl passed passed passed epoxy passed failed passed epoxy passed failed passed vinyl passed passed passed epoxy passed failed passed The failures noted in the above table result from an attempt to adhere a thermoplastic, vinyl resin top coat to a thermoset, epoxy r e s in ba æ c oat . The se f a il u re~ are independent of the cit ra te ester lubricant of the present invention and would have occurred were the citrate ester not present.
Although the inven~ion described above is in respect o~ a base coated tin-~ree steel, it is also applicable to the utilization of matte-~inish, electrolytic tinplate as the metal starting material.
As set Eorth in U.S. Patent 3,360,157, the matte finished tinplate and a liquid lubricant act synergistically with each other and an analogous situation obtains in the instant invention between the matte tin and citrate ester to augment the lubricant system during the draw~redraw process for forming the container. Further, as theorizea above, it i believed that functional groups, e.g~, carboxyl and/or acetyl, formed either during the metal-working process or during the thermal hardening of the top coat, or i~ both instances, form in effect anchoring chains to hold the top coat firmly adhered to the tinplate surface.
Consistent with this theory are the.results of gas cbromatographic and mass spectrometric analyses which indicate that acetic aeid and butanol are formed and liberated from thermal degradation of acetyl tributyl citrate when it is heated to 195 C., the approximate temperature attained in the thermal cure of th~
top coat.
Furthermore, acetic and citric acids and butanol are produced by hydrolysis of the acetyl tributyl citrate with an amine, such as 2-amino-2-methyl propanol; a solvent generally ~sed as a component o water-base coatings Comparative tests were run forming a base coated tin-free steel inbo containers by means of the draw/redraw with ironing proc~ss using various metal working lubricants. In each instance except for the acetyl tributyl citrate (ATBC) o the instant invention, the lubricant either was inferior to the acetyl tributyl citrate as a metal-working lubricant as exemplified by the required longer time to produce the container or it was incompatible with the top coat preventing the top coat from forming a continuous protective film.
The table set forth immediatedy bel~w shows the results of these comparative tests:
4~
EFFECT OF LUBRICANT TYPE ON DE~AW/REDRAW AND IRONING
TI N--E REE STEEL AND EIECTROLYTIC TINPLATE
LUBRICANT FABRICATIONADHESION OF TQP COAT
Petrolatum (hTP) Good, Very poor Butyl Stearate~ ~ETP) - C;ood Good Dioctyl Stearate~ (ETP~ Good Good Neoderle (o~-olefin) Cracked domes; Good ITF5) Broken radi i Phos pha te E s ter Fa il u re on --(TFS) Second Operation Ac~tyl Tributyl Good Good Citrate ~ETP) ATBC with Carnauba (;ood Good wax ( ~S) Acetyl trihexyl Good Good citrate (TFS) Note~:
1. ~o adhesion before or after process.
20 Application problems due to rapid visc05ity changes as solidi ~ication point (65F. ) is approached.
This base coating applied to both sides of the steel may be applied while the s~eel is still in coil form or the steel may be cut into sheets and the coating applied to individual sheets, which coating is subsequently baked to form a tough, adherent base coat on the tin-free steel~
~s~
The citric acid ester of the present invention i.q dip coated onto both ~urace~ of individual sheets of the base coated tin-free steel, the excess ester is removed and the sheets are then fed into a blanking and cupping press which cuts from the sheet one or re circular discs of 7.947 inches in diameter, and draws the disc into a cup of 5.007 inche~ in diameter and 1.850 inches in side wall height. In two subsequent operations, the cup is successively reduced in diameter with concurrent lengthenin~ of its side wall, i,.e., drawn; and simultaneously this side wall is slightly thinned, iOe~ to about 10% less than the starting gauge~ and further elongated, i.e., ironed, in the manner similar to that described in .S. Patent 3,360~157~ The final diameter and side wall height accomplished in the drawing plus ironing are 3.060 in~ and 4.450 in. respectively and are accomplished in a few seconds. The diameter of the starting blank and the height to diameter ratios, draw ratios, in the ensuing metal working process may be varied depending upon the desired size of the finished can. Also, as between different draw/redraw systems, the amount of draw in each step may be varied provided the cumulative effeGt of the plural draws produces the can of desired height and diameter.
It is readily apparent that a draw/redraw system with ironing is a more severe metal working process than a draw/redraw system without ironing. The citrate ester lubricant of the present . . .
invention performs equally well in both systems~
The particular citric acid compound used in the abcve example is acetyl t~ibutyl citrate. It may be applied by any suitable means such as roller coating, immersion coating with excess suitably removed, electrostatic deposition which is accurate in application both as to weight and placement~ or by hot spraying from an oxy-dry unit or cold spraying if the ester i~ reduced with a suitable solvent.
7~
The amount of lubricant applied over the base coat can vary from 10 to 40 and preferrably 10 to 20 milligrams per square foot of total usface, i.e., both sides, of the sheet being fed into the draw~redraw apparatus It has been found that the lubricating efect fall~ off appreciably below 10 mgs/ft2 and for most operations 20 mgs/ft2 is sufficient to achieve the high speed, trouble free, multiple draws from flat blank to formed container.
Due to the severity of the metal-working operation, i.e., the appreciable draw rati~s and draw speed plus ironing~ substantial heat is generated on the surfaces being worked. ~hile not wishing to be bound by any partieular theory, it is possible that this generated heat causes ~t least a partial decomposition of the lubricant on the worked surfaces, the~eby liberating reactive ~ubstances s~ch as those having carboxyl or acetyl functional groups. For example, in the case of the preferred acetyl tributyl citrate, acetic acid would be liberatedO These functional groups are belie~d to attach themselves to the base coat and/or be available for reaction with the postsprayed top coating.
At the completion of the draw/redraw operation, the container is beaded to impart strength to the side and bo~tom wal3.s before being ea into a device for applying a top coat to the container' s inside surface. Most usually this device involve~ a turret which revolves the container past a r~ciprocating spray gun which enters the interior of the container which is spun on it~ longitudinal axis while ~he spray gun, as it is retracted from the container ~ody~
emits a 360 degree spray of a synthetic resin solution to coat the entire inter ior surface of the container.
7~
After completion of the top coating operatlclll, the container is then subjected to a temperature of 400Fo for 4 minutes to harden and cure the top coat. Unlike pr ior art procedures which require the metal-working lubricant to be removed before application of the top coat to avoid cont~mination and improper curing o the top coat, the procedure of the present invention not only eliminates the time-consuming st~p of removing the lubricant and permits the applica~ion of the top coat directly to a still-lubricated internal sur~ace of the container but assists in firmly adhering the top coat to the base coatO Again, not wishing to be bound by any particular theory, it is believed that the reactive groups liberated frQm the applied lubricant previously and/or during the above mentioned bakins operation react with or at least anchor themselves into the top coat as well as the base coat thereby forming a strong adhering medium between the base coat and top coat.
Tbe citric acid ester lubricant and what remains thereof after th~ draw/redraw operation are soluble in organic solvent.s such as butanol~ butyl Ce1losolYe, di-isobutyl ketone, Cellosolve acetate and Solvesso 150~ Therefore, resins for top coats which are also soluble in these same solvents and provide inert, continuous, resin films upon thermal curing are preferred such as epoxy resins and acrylic resins~ Vinyl resins are usable if they are applied over a base other than a thermoset epoxy resin. The citric acid ester may also be used in water base coating compositions provided the liquid system contains a solvent for the citrate ester ~hich is miscible with the water of the system~
Evaluation of top coats applied over an epoxy-UF base coat is done by testing process resistance as well as intercoaS: adhesion bets~een the base coat and the top coat. The follo~iny table summarizes the results of these tests:
~e 37~
Eval~ation of Postsprayed Top Coats.
--~5'L~L ~G#bU~ t- Lse Coat Process Intercoat ToP Coat _ Resistance Adhesion acryllc passed passed vinyl passed failed epoxy-phenolic passed passed epoxy-acrylic passed passed epoxy-phenolic passed passed ep~xy-phenolic passed passed epoxy-phenolic pa~sed passed epoxy passed passed The epoxy-phenolic resin systems in the above table differ from each other in . the propc:rtion of epoxy to phenolic.
Process resistance i~ checked by filling the container with ae~Oni2ed water followed by steam processing at 265F. for 90 minutes. After water cooling and standing overnight, the cans are emptied, cut open, cross hatched, and taped to test intercoat adhesion.
Other suitable base coat/top coat combinations include vinyl and polyester resins as base coats r examples of which are in the table below:
Intercoat Adhesion ~fter Process Base Coa~
V,~
polyester passed passed passed vinyl passed passed passed epoxy passed failed passed epoxy passed failed passed vinyl passed passed passed epoxy passed failed passed The failures noted in the above table result from an attempt to adhere a thermoplastic, vinyl resin top coat to a thermoset, epoxy r e s in ba æ c oat . The se f a il u re~ are independent of the cit ra te ester lubricant of the present invention and would have occurred were the citrate ester not present.
Although the inven~ion described above is in respect o~ a base coated tin-~ree steel, it is also applicable to the utilization of matte-~inish, electrolytic tinplate as the metal starting material.
As set Eorth in U.S. Patent 3,360,157, the matte finished tinplate and a liquid lubricant act synergistically with each other and an analogous situation obtains in the instant invention between the matte tin and citrate ester to augment the lubricant system during the draw~redraw process for forming the container. Further, as theorizea above, it i believed that functional groups, e.g~, carboxyl and/or acetyl, formed either during the metal-working process or during the thermal hardening of the top coat, or i~ both instances, form in effect anchoring chains to hold the top coat firmly adhered to the tinplate surface.
Consistent with this theory are the.results of gas cbromatographic and mass spectrometric analyses which indicate that acetic aeid and butanol are formed and liberated from thermal degradation of acetyl tributyl citrate when it is heated to 195 C., the approximate temperature attained in the thermal cure of th~
top coat.
Furthermore, acetic and citric acids and butanol are produced by hydrolysis of the acetyl tributyl citrate with an amine, such as 2-amino-2-methyl propanol; a solvent generally ~sed as a component o water-base coatings Comparative tests were run forming a base coated tin-free steel inbo containers by means of the draw/redraw with ironing proc~ss using various metal working lubricants. In each instance except for the acetyl tributyl citrate (ATBC) o the instant invention, the lubricant either was inferior to the acetyl tributyl citrate as a metal-working lubricant as exemplified by the required longer time to produce the container or it was incompatible with the top coat preventing the top coat from forming a continuous protective film.
The table set forth immediatedy bel~w shows the results of these comparative tests:
4~
EFFECT OF LUBRICANT TYPE ON DE~AW/REDRAW AND IRONING
TI N--E REE STEEL AND EIECTROLYTIC TINPLATE
LUBRICANT FABRICATIONADHESION OF TQP COAT
Petrolatum (hTP) Good, Very poor Butyl Stearate~ ~ETP) - C;ood Good Dioctyl Stearate~ (ETP~ Good Good Neoderle (o~-olefin) Cracked domes; Good ITF5) Broken radi i Phos pha te E s ter Fa il u re on --(TFS) Second Operation Ac~tyl Tributyl Good Good Citrate ~ETP) ATBC with Carnauba (;ood Good wax ( ~S) Acetyl trihexyl Good Good citrate (TFS) Note~:
1. ~o adhesion before or after process.
20 Application problems due to rapid visc05ity changes as solidi ~ication point (65F. ) is approached.
3. ~ower stability due to volatilization and oxidation (Ref: U.S.
Patent 3,923,471)~
We believe another factor contributing to the effectiveness of acetyl tributyl citrate is itS ability to increase the wettability of the TFS or ~TP surface by the top coating as shown by the contact angle measurements in the table below. The measurements were taken by applying a coating of the listed lu~ricant to the metal surface, placing a drop of water on the lubricated surface and then measuring the angle between the lubricated surface and an intersecting line tangent to the curved surface of the water droplet. The greater the wettability of the lubricant, the flatter the water droplet and the less the angle.
CONTAC~ ~NGLES
L~ ICANT PLATE CONTACT ANGLE
.
None TFS 83.5 Petrolatum TFS 96 . 7 ATJ3C TFS 7 4 . 5 None ErP . 7 2 . 4 Pe trol atum ESTP 8~ . 5 ATBC E:rP
ATBC with ET}? 7 0 . 6 Carnauba Wax But yl S tea ra teETP 77 . O
Dicctyl Stearate ETP 73.5 Nes~dene EqlP 79 . S
7~
~ igh melting waxes can be added to the citrate es'cer lubricant in concentrat ions of up b~ about 2~ of ~he ester -olids to improve lubricity without adverse effects on intercoat adhesion.
It is understood that the invention is not confined to any particular embodiment described herein as illustrative of the invention but embraces all such modifications thereof as may come w;thin the scope of the following claims.
11~
Patent 3,923,471)~
We believe another factor contributing to the effectiveness of acetyl tributyl citrate is itS ability to increase the wettability of the TFS or ~TP surface by the top coating as shown by the contact angle measurements in the table below. The measurements were taken by applying a coating of the listed lu~ricant to the metal surface, placing a drop of water on the lubricated surface and then measuring the angle between the lubricated surface and an intersecting line tangent to the curved surface of the water droplet. The greater the wettability of the lubricant, the flatter the water droplet and the less the angle.
CONTAC~ ~NGLES
L~ ICANT PLATE CONTACT ANGLE
.
None TFS 83.5 Petrolatum TFS 96 . 7 ATJ3C TFS 7 4 . 5 None ErP . 7 2 . 4 Pe trol atum ESTP 8~ . 5 ATBC E:rP
ATBC with ET}? 7 0 . 6 Carnauba Wax But yl S tea ra teETP 77 . O
Dicctyl Stearate ETP 73.5 Nes~dene EqlP 79 . S
7~
~ igh melting waxes can be added to the citrate es'cer lubricant in concentrat ions of up b~ about 2~ of ~he ester -olids to improve lubricity without adverse effects on intercoat adhesion.
It is understood that the invention is not confined to any particular embodiment described herein as illustrative of the invention but embraces all such modifications thereof as may come w;thin the scope of the following claims.
11~
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a coated metal container comprising a seamless side wall and a bottom wall integral with said side wall, said side wall being substantially the same thickness as or thinner than said bottom wall and the metal of said walls being selected from the group consisting of electrolytic tinplate and tinless, low-carbon steel, said coating being on at least the interior of said container and comprising a hardened top coat covering said walls, the improvement comprising said top coat consisting essentially of the reaction product of a citric acid ester and a synthetic resin selected from the group consisting of an epoxy resin, an acrylic resin, a polyester resin and a vinyl resin, provided however said vinyl resin is not applied over a thermoset epoxide resin.
2. The metal container of claim 1 wherein said citric acid ester is acetyl tributyl citrate.
3. The metal container of claim 1 wherein said top coat contains up to about 2% of high melting point wax based on the total .
weight of said ester and wax solids.
weight of said ester and wax solids.
4. The metal container of claim 1 wherein the metal of the container is non-reflowed, matte finish tinplate.
5. The metal container of claim 1 wherein the metal of the container is tin-free steel.
6. The metal container of claim 5 wherein a hardened synthetic resin base coat is interposed between said tin-free steel surface and said hardened top coat, which base coat covers and adheres to said steel surface, and the resin of which base coat is selected from the group consisting of an epoxide resin, a polyester resin and a vinyl resin.
7. The metal container of claim 6 wherein said base coat is an epoxide resin and the resin of said top coat is selected from the group consisting of an epoxide resin, an acrylic resin and a polyester resin.
8. The method of forming a coated metal container comprising the steps of applying a citric acid ester lubricant to a metal selected from the group consisting of electrolytic tin plate and tinless, low carbon steel, providing a circular flat blank from said metal, drawing said blank into a shallow cup, subjecting said cup to two additional draws in rapid sequence to form said container, applying a synthetic resin coating over the interior of said container and over said lubricant on said container interior and heating said coated container to harden said coating and adhere is to said container interior.
9. The method of claim 8 wherein the side wall of said cup is subjected to ironing during said additional draws whereby the side wall of said container is thinner than the bottom wall of said container.
10. The method of claim 8 wherein a synthetic resin coating is applied to and adhered to said metal prior to the application of said citric acid ester lubricant.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US33963482A | 1982-01-15 | 1982-01-15 | |
| US339,634 | 1982-01-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189749A true CA1189749A (en) | 1985-07-02 |
Family
ID=23329935
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000419495A Expired CA1189749A (en) | 1982-01-15 | 1983-01-14 | Coated metal container and method of making the same |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1189749A (en) |
| DE (1) | DE3301126A1 (en) |
| FR (1) | FR2519939A1 (en) |
| GB (1) | GB2113118B (en) |
| IT (1) | IT1164863B (en) |
| MX (1) | MX157090A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3689142T2 (en) * | 1985-11-08 | 1994-04-28 | Nippon Steel Corp | Containers made from materials with an oxygen-removing effect. |
| DE3840809A1 (en) * | 1988-11-29 | 1990-05-31 | Grace Gmbh | METHOD FOR THE PRODUCTION OF COATED OR PAINTED METAL CONTAINERS AND THEIR USE |
| DE4209502A1 (en) * | 1992-03-24 | 1993-09-30 | Hoechst Ag | Use of esters of citric acid as a lubricant for refrigerant compressors |
| GB2296714B (en) * | 1994-12-15 | 1998-03-25 | Abbey | Coating composition |
| US6460895B1 (en) * | 2001-05-21 | 2002-10-08 | General Motors Corporation | Brake hose sleeve |
| US8267010B2 (en) * | 2010-06-17 | 2012-09-18 | PTR Baler and Compactor Company | Self-contained compactor apparatus with protective coating |
| WO2014025411A1 (en) * | 2012-08-09 | 2014-02-13 | Valspar Sourcing, Inc. | Container coating system |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1448790A (en) * | 1974-04-26 | 1976-09-08 | Nat Steel Corp | Lubricated metallic container |
| US4032678A (en) * | 1974-09-12 | 1977-06-28 | Bethlehem Steel Corporation | Coated sheet metal and method of forming products therefrom |
| CA1058454A (en) * | 1974-10-11 | 1979-07-17 | American Can Company | Drawn and ironed containers and method of manufacture |
| US4062312A (en) * | 1976-05-06 | 1977-12-13 | Astro Containers, Inc. | Method for deforming and coating a metallic surface |
-
1982
- 1982-12-21 GB GB08236243A patent/GB2113118B/en not_active Expired
-
1983
- 1983-01-05 MX MX195826A patent/MX157090A/en unknown
- 1983-01-14 FR FR8300585A patent/FR2519939A1/en not_active Withdrawn
- 1983-01-14 DE DE19833301126 patent/DE3301126A1/en not_active Withdrawn
- 1983-01-14 IT IT47564/83A patent/IT1164863B/en active
- 1983-01-14 CA CA000419495A patent/CA1189749A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1164863B (en) | 1987-04-15 |
| GB2113118B (en) | 1985-08-14 |
| FR2519939A1 (en) | 1983-07-22 |
| GB2113118A (en) | 1983-08-03 |
| MX157090A (en) | 1988-10-27 |
| IT8347564A0 (en) | 1983-01-14 |
| DE3301126A1 (en) | 1983-08-18 |
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