FR2519939A1 - COATED METALLIC CONTAINER AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

THE INVENTION CONCERNS A METAL CONTAINER INCLUDING A SEAMLESS BODY AND A BOTTOM WALL FORMING AN INTEGRAL PART OF THE SAME AND INCLUDING AT LEAST ON ITS INTERNAL SURFACE A PROTECTIVE COATING WHICH IS THE REACTION PRODUCT OF AN ESTER OF CITRIC ACID USED. AS A LUBRICANT FOR THE FORMING OF THE CONTAINER AND OF A SYNTHETIC RESIN APPLIED SUBSEQUENTLY. APPLICATION TO THE FIELD OF FOOD PRODUCTS.

Description

The present invention relates to a metal container

  coated layer and its manufacturing process.

  The well-known metal sheet and three-piece food container is being rapidly supplanted by a two-piece container having a seamless body with a bottom wall integral with the body and the other wall of the body. bottom being attached to the body with a double crimp after filling the

  These containers for beer and non-alcoholic beverages

  They are made by the drawing and drawing process, while the fruit and vegetable containers that require a thicker and more robust sidewall start to be manufactured by a newer process known as

name stamping / re-stamping.

  Although the production of sheet containers

  of metal using multiple stampings is not new.

  the process of stamping / re-stamping is a perfect

  compared to the older stamping process in that it is performed at higher speeds with

  larger stamping ratios at each stage of stamping

  weaving Achieving this higher rate of productivity requires special machines and, among other things, special lubricants for metal working and, to maintain this rate

  productivity, the subsequent processing phases

  the container formed must also take place at

  speed or if possible be removed.

  U.S. Patent 4,287,741 discloses a class of citric acid esters which are effective as lubricants in the drawing and drawing process.

  found that the same citric acid esters are lubricants

  effective fuels in the stamping / re-pressing process

  described in connection with the present invention.

  The present invention involves the discovery that the citric acid esters disclosed in U.S. Patent 4,287,741 act not only as effective lubricants

  when stamping and re-stamping a metal product

  However, these lubricants, unlike the metalworking lubricants used heretofore, do not need to be removed from the surface of the formed container but can be made suitable for the purpose of forming a container.

  react with a synthetic resin-based topcoat

  subsequently applied by heating to form

  a hardened barrier layer on the inner surface of the container

  tainer. The citric acid esters useful in the present invention are described in U.S. Patent 4,287,741,

  description being mentioned here for reference

  The '741 patent gives the following structural formula for these esters:

R 4 R 2

Re IH 2 _ o a 3

CH 2-_ - -R 3

  wherein R 1 R 2 and R 3 are selected from the group

  taking hydrogen and alcoholic residues containing

  1 to 10 carbon atoms, R 4 is selected from the group

  taking hydrogen and carboxylic acid radicals having 1 to 10 carbon atoms and at least one of the elements

  R 1, R 2 and R 3 is an alcoholic residue.

  The Applicant has found that the method of the present invention

  The present invention also applies to a tin-free ferrous metal and tin-free sheet steel, free of tin. Although the common tin-plated iron of the prior art mentioned in column 2, lines 50 to 56 of the patent US 4,287,741 may be used in the present invention,

  non-blended matt white iron described in the patent application

  vet U S 3 360 157 for the reasons set forth in this patent

  3 360 157 with regard to the stamping and labeling process

  rage for the manufacture of containers The weight of tin on the basis of steel as metal may vary from 45 r 4 to 454 g

by boot.

  The preferred tin-free steel has been treated

  Although it is

  core in the form of a flat sheet prior to forming into a container, a primer layer based on synthetic resin

  is applied and adheres to this treated surface.

  The most common applications for the primer application are those containing an epoxy resin, a vinyl resin or a polyester resin.

  The tin-free steel preferred for use in

  In the present invention, the steel is cast continuously, aluminum quenched with a chromium / chromium oxide surface treatment. The chromium content in the oxide is about 5.38 to 21, 5 mg per m 2 and the metallic chromium occurs at a rate of about 32.3 ga 420 mg per m 2 The material described is known in this field under the name TFS-CT, abbreviation for a chromium-free tin-free steel. treatment is described in an article published in the Journal of Electrochemical Society, vol 116, no 9, pages

1299-1305.

  The preferred tinplate has the same steel composition as above and, in the metallurgical plant, tin is applied in a well-known manner to its surface electrolytically in various amounts, for example 113.5 g. Thus, as mentioned above, this tinplate is left in the dull state, that is to say it is not made glossy by fusion, it is oiled to prevent rust formation and coiled in coil for

  transport to a container manufacturing facility.

  Then, after reception at the box-making plant, the tin-free steel receives by application on its surface a primer. The preferred layer contains an epoxy resin based on bisphenol A with an equivalent weight of epoxy of 2300 a 4000, a urea formaldehyde crosslinking agent, a sulfonic acid catalyst and a high melting polyethylene based internal lubricant The coating has a solids content of 28% Resin compositions This basecoat applied to both sides of the steel can be applied while the steel is still in coil form or the steel can be cut into sheets and the coating-can be applied to the individual sheets, the coating then being cured to form on the tin-free steel a basecoat

hard and adherent.

  The citric acid ester of the present invention

  is applied by dipping on both sides of the indi-

  In the case of tin free steel with a base coat, the excess ester is removed and the sheets are then directed to a cutting press and forming cups, which cut from the sheet one or more circular discs 20.18 am in diameter and: stamps the disc into a cup 12.72 cm in diameter and 4.7 cm

  lateral wall height During two subsequent operations

  The cup then successively undergoes a diameter reduction with simultaneous elongation of its lateral wall, in other words a stamping, and this side wall is in m time slightly thinned, that is to say, approximately 10% less than the initial size. andextended, that is, stretched in the manner described in U.S. Patent 3,360-157. The final diameter and the height of the lateral wall obtained during drawing and drawing are 7.77 cm and 11 respectively. 3 cm and are made in a few seconds The diameter of the initial blank and the ratios bauteur / diameter, that is to say the stamping ratios, during the process of working of the subsequent metal can be nodded according to the dimension desired of the finished box Pn can also vary, as in different systems stamping / re-stamping, the degree

  stamping at each stage provided that the camouflaged effect

  latiff multiple stampings produce the box having the

  height and diameter sought.

  It is obvious that a drawing / re-drawing system with drawing is a more severe metal working process than a drawing / re-drawing system without drawing. The citrate ester lubricant of the present invention

  The invention also behaves well in both systems.

  The particular citric acid compound used in

  the example above is acetyl tributyl citrate II-

  can be applied by any appropriate means such

  roller coating, immersion coating with eli-

  suitable electrostatic discharge, which ensures precise application with regard to weight and placement, or hot spraying with an "oxy-dry" apparatus, or spraying. cold if

  the ester is diluted with a suitable solvent.

  The amount of lubricant applied to the primer may vary from 107.6 to 430.5, and preferably from 107.6 to 215.3 mg per m 2 of the total area, i.e. both

  of the sheet introduced into the stamping machine

  It has been found that the lubricating effect appreciably decreases below 107.6 mg / m 2 and, for most operations, a value of 215.3 mg / m 2 is sufficient to make stampings. multiple high speed

  and without difficulty from a flat blank in order to ob-

  Tightness of the formed container Due to the severe metal working conditions, ie high stamping rates and the high speed of drawing and drawing, considerable heat is generated on the shaped surfaces. not wish to be bound by any particular theory, it is possible

  that this heat produced causes at least one decomposition

  partial removal of the lubricant on shaped surfaces,

  thus promoting reactive substances such as those

  having carboxy or acetyl functional groups.

  For example, acetic acid would be released in the case of acetyl tributyl eitrate These functional groups are expected to attach themselves to the basecoat and / or

  be available for a reaction with the final

applied thereafter.

  After completion of the stamping / stamping operation

  stamping, the container is molded to impart strength to the side and bottom walls before being directed

  to a device for applying a final layer of

  on the inner surface of the container The most common

  This device includes a turret that turns

  the container in front of a spray gun animated with a

  movement back and forth, which enters the interior of the

  which rotates along its longitudinal axis while the spray gun, as it withdraws from the container body, emits a 360 degree jet of a synthetic resin solution to coat the entire surface

inside the container.

  After the end of the deposition operation of the finishing layer, the container is exposed to a temperature of

  204,500 for 4 minutes, for hardening and

  In contrast to the prior art techniques which require removal of the metalworking lubricant prior to the application of the

  topcoat to prevent contamination and poly-

  insufficient completion of the finishing layer, the tech-

  The present invention not only eliminates the step

  tedious removal of the lubricant and allows the application

  cation of the finishing layer directly on the surface '

  already lubricated internal container but promotes adhesion

  No need to be bound by any particular theory again, it is believed that the reactive groups released from the previously applied lubricant and / or during the curing operation referred to above. higher react

  or incorporate themselves into the final layer of

  same as the base layer by forming a half-layer

  Fortenmit place adherent between the bottom layer and the layer

finishing.

  The citric acid ester lubricant and what remains after the stamping / re-stamping operation

  are soluble in organic solvents such as butadiene

  Butyl Cellosolve, Diisobutyl Ketone, Cellosolve Acetate and Solvesso 150 For this reason, resins for topcoats which are also soluble in these same solvents and produce, after thermal curing, continuous resin inert,

  such as epoxy resins and acrylic resins.

  Vinyl resins can be used if they are

  on a basis other than a thermoset epoxy resin

  The citric acid ester may also be used

  in aqueous coating compositions provided

  that the liquid system contains a solvent for the ester

  which is miscible with the water of the system.

  The evaluation of the finishing layers applied on

  an epoxy-UP basecoat is done through a review of the

  resistance to the treatment as well as the adhesion 1 iter-cou-

  between the basecoat and the topcoat The following table summarizes the results of these tests: Evaluation of topcoats, applied

  spray gun on an epoxy base coat.

Resistance to International Adherence

  Accepted epoxy-acrylic epoxy-acrylic n epoxy-phenolic epoxy-phenolic epoxy-phenolic epoxy-phenolic epoxy-phenolic topcoat

  The epoxy-phenolic resin systems in the

  above are different from each other by the proportion of epoxy

to phenolic.

  The resistance to treatment is evaluated by filling the container with deionized water, followed by steaming at 129.50 C for 90 minutes After cooling with water and abandoning overnight, the boxes are emptied, opened by cutting, incised in cross and covered

  an adhesive tape for testing the adhesion between

  layers. Other suitable primer / topcoat combinations include vinyl and polyester resins as primer, examples of which are shown in the table below: Adhesion between coats after treatment Primer Polyester epexy polyester acrylic topcoat accepted accepted accepted vinylic "epoxy" refused "epoxy" "vinyl accepted epoxy # refused The failures noted in the table above result from a test of adhesion of a thermoplastic vinyl resin-based topcoat to a basecoat These failures are independent of the citric ester lubricant of the present invention and would have been produced in the form of thermosetting epoxy resin.

in the absence of citric ester.

  Although the invention described above is relative to tin-free steel coated with a base layer,

  it also applies to the use of tinplate

  trolytic with a matte finish as the starting metallic material.

  As disclosed in U.S. Patent 3,360,157, the white matt finish and a liquid lubricant act as

  synergistic way with each other and an analogous situation

  In the present invention, the use of the matt tin and the citric ester to increase the lubricant system during the drawing / re-pressing process for

  forming of the container Of other party, one thinks according to the hypo-

  thesis issued above the functional groups, by

  carboxyl and / or acetyl, formed either during the

  swimming during the thermal hardening of

  the finishing layer, or in both cases, form

  anchoring chains to ensure strong adhesion

  of the topcoat at the surface of the tinplate.

  the gas chromatographic and mass spectrometric analyzes agree with this theory, which indicates that acetic acid and

  butanol are formed and released by thermal degradation.

  Acetyl tributyl citrate when heated

  at 19500, the approximate temperature reached during

  thermal curing of the topcoat.

  On the other hand, acetic acid, acid,

  and butanol are produced by hydrolysis of citrate

  acetyl tributyl with an amine such as 2-amino-2-methyl-

  thylpropanol, a solvent generally: used as a

killing aqueous coatings.

  Comparative tests were conducted

  tin-free steel coated with a primer

  By use of the stretching / drawing process using various metalworking lubricants In each case, except for acetylbutyl citrate (ATBC) of the present invention, the lubricant was lower than the citrate of the present invention. acetyl tributyl as a metalworking lubricant, as illustrated by the longer time required to produce the container or

  it was incompatible with the topcoat preventing it

  edge to form a continuous protective film The table

  immediately below shows the results of these

comparative tests.

  Effect of lubricant type on stamping / re-forming

  end: bsage and stretching of a tin-free steel and a

electrolytic tinplate.

  Lubricant Manufacturing Adherence of the ________________Layer Finish Petrolatum (ETP) gives very bad Butyl Stearate (FTE) "Good Lubricant Manufacturing Adherence of topcoat Dioctyl Stearate 3 (FTE) Good Good Neodene (" -olefin) d 8 my cracked N (GST) rayena brasa Phosphoric Ester Failure at deu "(TFS) Xth Operation Good Acetyl Citrate" Tributyl (ETP) ATBC with Carnauba Wax (TFS) Good Acetyl Trihexyl Citrate (TFS) Notes:

  1 No adhesion before or after treatment.

  2 Problems applying das to changes in visco-

  quickly as we approach the point of

lidification (18.30 C).

  3 Lower stability due to volatilization and

  oxidation (ref patent U S 3 923 471) -

  The Applicant believes that another contributing factor

  The effectiveness of acetyl tributyl citrate is its ability to increase the wettability of the surface of TFS or FTE by the topcoat, as shown by the contact angle measurements in the table below. performed the measurements by applying a coat of listed lubricant to the surface of the metal, placing a drop of water on the lubricated surface and then measuring

  the angle between the lubricated surface and an intersec-

  tangentially to the curved surface of the water droplet.

  The greater the wettability of lubricant, the greater the

  droplet of water is flat and the angle is less.

CONTACT ANGLES

  Plate Contact Angle Nil TFS 83.5 Petrolatum TFS 96.7

ATBC TFS 74.5

Nil In 72.4 Petrolatum ETP 84, 5

ATBC, FTE 70.5

  ATBC with 'cirede ETP 70,6 carnauba Butyl stearate FTE 77.0 Dioctyl stearate ETP 73.5 N-Èodne FTE 79.5

  Waxes with a high melting point can be added

  based on citric ester lubricant

  up to about 2% of the ester-based solids to improve lubricity without deleterious effects on interlayer adhesion

  It is understood that the invention is not limited

  to any particular embodiment described

  here as an illustration of the invention but that it

  globe all of those changes that can come into

  The scope of the following claims.

Claims

  1 metal container rev 8 including a pa-

  seamless side king and a bottom wall forming an integral part of said side wall, said side wall having substantially the same thickness or being thinner than said bottom wall and the metal of said walls being selected from the group consisting of electrolytic tinplate and in low-carbon tin free steel, said coating being at least on the inner surface of said container

  and comprising a hardened topcoat covering the.

  said walls, characterized in that said layer

  finishing material essentially comprises the reaction product

  cation of a citric acid ester and a synthetic resin selected from the group consisting of an epexy resin, an acrylic resin, a polyester resin and a vinyl resin, provided however that said vinyl resin is not applied to a resin heat-cured epexy resin,

  2 Metal container according to claim 1, characterized

  in that said citric acid ester is citrate

acetyl tributyl.

  Metal container according to claim 1,

  characterized in that said topcoat contains up to about 2% of a high-melting wax compared to

  total weight of said enter and solid wax.

  Metal container according to claim 1, characterized

  characterized in that 1 l metal of the container is matt white iron

not remelted.

  Metal container according to claim 1, characterized in that the metal of the container is steel without

tin.

  6 A metallic container according to claim 5, characterized

  in that a base layer made of synthetic resin dur-

  goose is interposed between said tin-free steel surface.

  and said cured topcoat, which basecoat overlies and adheres to said steel surface and the resin of said bottomcoat is selected from the group consisting of

  a epoxy resin, a polyester resin and a resin

vinyl sine

  Metal container according to claim 6,

  characterized in that said primer is an epoxy resin and the resin of the topcoat is selected from the group comprising an epoxy resin, an acrylic resin and a polyester resin 8 A method of farming a coated metal container, characterized in that it comprises the steps of applying a citric acid ester lubricant to a metal selected from the group consisting of electrolytic tinplate and low carbon tinless steel, to be made a circular flat blank from said metal, to stamp said blank into a shallow cup, to subject said cup to two additional stampings in a rapid sequence to form said container, to be applied

  a layer of synthetic resin within said

  container and on said lubricant inside the container and: heating said coated container to cure said

  coating and adhere it to the inside of said container.

  A method according to claim 8, characterized in that the side wall of said cup is stretched in the course of additional draws, so that the side wall of said container is thinner than the bottom wall of said container. claim 8, characterized in that a layer of synthetic resin is applied and fixed on said metal before application of said citric acid ester lubricant