AU642468B2 - Surface-treatment method for tin-plated drawn and ironed cans - Google Patents

Description

WO 91/10756 PCT/US91/00202 -1- SURFACE-TREATMENT METHOD FOR TIN-PLATED DRAWN AND IRONED CANS TECHNICAL FIELD The present invention relates to a novel surface treatment method for tin plated DI cans, cans formed by the drawing and ironing of tin plated steel sheet. The method imparts excellent corrosion resistance and paint adhesivity to the surface of the can prior to its being painted or printed, and also imparts the excellent slideability (low frictional resistance) that is required for smooth transport of the can by automatic conveying equipment, particularly modern high speed conveying equipment.

BACKGROUND ART The invention of Japanese Patent Application Laid Open [Kokai or Unexamined] Number 1-100281 [100,281/89] is an example of a surface treatment liquid for tin plated DI cans. This teaching of the prior art employs a film forming liquid for the treatment of metal surfaces. This solution has a pH of 2 to 6 and contains 1 to 50 gram per liter of phosphate, 0.2 to 20.0 g/L of oxyacid ions, 0.01 to 5.0 g/L of tin ions, and 0.01 to 5.0 g/L of condensed phosphate. Treatment with this conversion treatment solution afforded a highly corrosion resistant phosphate film on the surface of tin-plated DI cans.

However, in recent years tin-plated DI cans have been produced using low levels of tin plating in response to economic considerations, and this has required that its surface treatment provide far more corrosion resistance than before. Moreover, when treatment is conducted by prior methods, in some cases the gloss of the base metal is degraded due to etching of the base metal. Accordingly, there is a demand for a surface treatment which does not damage the external appearance by reducing the gloss.

Treatment methods intended to provide corrosion resistance and adhesivity through the use of water soluble resin are exemplified by the invention in Japanese Patent Application Laid Open Number 1-172406 [172,406/89]. This invention provided aF an example of the prior art comprises WO 91/10756 PCT/US91/00202 2 a method in which the metal surface is treated with a solution which contains an effective derivative of a polyhydric phenol compound. However, the disclosed method does not generate a satisfactorily stable corrosion resistance.

In addition, the metal can manufacturing process often suffers from a problem with transfer or transpo the slideability of the outer surface of the can during conveyor transport of the can may be poor due to a high friction coefficient of the outer surface, so that the can may be tipped over sideways. Can transport to the printer in the most modern high speed can lines is a particular problem in this regard. Accordingly, there is demand in the can manufacturing industry for a reduction in the static friction coefficient of the outer surface of cans, which at the same time does not cause any adverse effects on the adhesion of any paint or lacquer subsequently coated on the can. The invention of Japanese Patent Application Laid Open Number 64-85292 [85,292/89) comprises a method for improving this slideability. The reference teaches a surface treatment composition for metal cans which contains water-soluble organic material selected from phosphate esters, alcohols, monobasic, and polybasic fatty acids, fatty acid derivatives, and mixtures of the foregoing. While the disclosed method does in fact generate an increase in the slideability, it does not improve the corrosion resistance or paint adhesion.

United States Patent 4,517,028 teaches in general terms treatment of metals with aminated derivatives of poly{vinyl phenols). This reference, however, makes no specific reference to treating tin plate or DI cans.

DESCRIPTION OF THE INVENTION Problem to Be Solved by the Invention The principal goal of the invention is to provide a single treatment for DI cans that will result in increased corrosion resistance, good adhesion to subsequently applied paint or similar organic coatings, and a low coefficient of friction on the outside can surface, for efficient processing in automated can processing lines using high speed conveyors and printers.

Summary of the Invention It was discovered that a film with excellent corrosion resistance, paint adhesion, and slideability could be formed on at least one surface of a DI can,by controlling the conditions of treating the surface as follows: A liquid treating composition is prepared by dissolving in water an oligomer having a chemical composition specified by the general formula:

OH

X Y 0 H-CH,) 2 wherein n is a number with a value between 10 and and each of X and Y independently represents hydrogen or a group Z, wherein Z has a chemical composition conforming to the general formula: H R i I Z -C-N I H R 2 wherein each of R and R 2 is an alkyl or hydroxyalkyl group having from 1 to 5 carbon atoms, except that 6t least 25 of the total of all the X and Y groups in the oligomer are Z rather than hydrogen.

The pH of the surface treatment solution containing the oligomer described in item is adjusted to a value between 4 and 6 by the addition of orthophosphoric acid and/or condensed phosphoric acid.

The surface treatment liquid as prepared in step (2) is heated to a temperature of at least 40 but prefer- ALn^ ably to not more than 60 degrees Centigrade and the ASU1STITUTE S1r.

I

WO 91/10756 PCr/US91/00202 4 ably to not more than 60 degrees Centigrade and the heated surface treatment liquid is then sprayed on the cleaned surface of tin plated DI can for a time of at least 5 and preferably not more than 60 seconds.

The aforesaid spray treatment is followed by thermal drying or by a water rinse and then thermal drying.

Preferably, there is no water rinse before drying after contact of the surface of the DI can with the heated surface treatment liquid as specified above. If there is water rinsing before drying, it is preferred that at least the last such water rinse be with deionized or other purified water substantially free from dissolved solids. If there is no rinsing with water before drying, it is normally preferred to let the sprayed cans drain under the influence of gravity, and/or to remove some of the liquid from the can surface by mechanical means such as an air flow, rollers under slight pressure, or the like, to avoid the presence of excessive amounts of the surface treatment liquid on the surface during drying.

Details of Preferred Embodiments of the Invention The value of n in the general formula given above for the oligomer dissolved in the surface treatment liquid is to 30. At values of n below 10, little or no improvement in corrosion resistance will be observed on DI tin plated cans. A value of 31 or more for n results in a poorly stable aqueous solution which cannot readily be used in practical applications.

In the general formula for group Z, R 1 and R 2 represent alkyl or hydroxyalkyl groups having 1 to 5 carbon atoms. When they contain six or more carbons, the stability of the aqueous solution is reduced. The introduction ratio for the group Z should be 25 to 100 mole referred to the total number of X and Y groups in the oligomer. The water solubility of the oligomer may not be adequate when over 75 of the total of X and Y groups present are hydrogen.

The oligomer solids content in the treatment liquid preferably is from 0.1 to 0.5 by weight of the total liquid. Below 0.1 by weight it is very difficult to form a stable film on a DI tin can surface. On the other hand, the treatment solution is costly above 0.5 by weight with little or no additional technical benefit.

The pH of the treatment solution should be adjusted to 4 to 6 through the use of orthophosphoric acid and/or a condensed phosphoric acid such as pyrophosphori. acid.

Substantial etching of the can surface occurs at a pH below 4 and .mpairs film formation. At a pH above 6, the solution has a short life because the oligomer tends to precipitate and sediment. The pH can normally be adjusted into the range of 4 to 6 by the addition of 0.05 to 0.3 Dv weight orthophosphoric acid or 0.03 to 0.2 by weight pyrophosphoric acid referred to-the total surface treatment liquid. Other condensed phosphoric acids and mixtures of condensed acids or of condensed and orthophosphoric acids can also be used 7 In addition, the ,reatment liquid should be heated to at least 40 degrees Centigrade during use. The treatment liquid is poorly reactive below 40 degrees Centigrade, and this wcrks against the formation of a highly corrosion resistant film. On the other hand, little or no benefit due to heating is observed when the liquid is heated to above degrees Centigrade, and unnecessary heating As expensive.

The spraying time should be at least 5 seconds. Only an inadequate reaction is obtained at less than 5 seconds, and a strongly corrosion resistant film is not developed.

On the other hand, treatment times in excess of 60 seconds do not afford any increase in performance and increase the expense.

The surface treatment method of the present invention is described below through several illustrative examples of particularly preferred embodiments of the invention, and its usefulness will be demonstrated by comparison with comparison examples. The examples are not to be regarded as limiting the invention, except in so far as noted in the z 03aSTITUTE

Claims (1)

1. 99.7 weight pH WO 91/10756 PCT/US91/00202 8 Example 2 Tin plated DI cans werr cleaned as in Example 1, then spray treated for 40 seconds with surface treatment liquid 2, heated to 50 degrees Centigrade. This was followed by a water wash and drying as in Example 1. The composition of surface treatment liquid 2 was: oligomer solids 0.2 weight pyrophosphoric acid 0.1 weight water 99.7 weight pH The oligomer used was the same as in Example 1. Example 3 Tin plated DI cans were cleaned as in Example 1, then spray treated for 10 seconds with the above described surface treatment liquid 1 (cf. Example which had been heated to 50 degrees Centigrade. This was followed by a water wash and drying as in Example 1. Example 4 Tin plated DI can was cleaned as in Example 1, then spray treated for 40 seconds with the above described sur- face treatment liquid 1 (cf. Example which had been heated to 50 degrees Centigrade. This was followed by draining, without water rinsing, and then drying in a hot air dryer at 180 degrees Centigrade for 3 minutes. Comparison Example 1 Tin plated DI cans were cleaned as in Example 1, spray treated for 40 seconds with comparison surface treat- ment liquid 1, heated to 50 degrees Centigrade, then washed with water and dried as in Example 1. Comparison surface treatment liquid 1 had the following composition: oligomer solids 0.2 weight orthophosphoric acid 1.5 weight water 98.3 weight pH The oligomer used was the same as in Example 1. WO 91/10756 PCT/US91/00202 9 Comparison Example 2 Tin plated DI cans were cleaned as in Example 1, spray treated for 2 seconds with the above described sur- face treatment liquid 1 (cf. Example which had been heated to 50 degrees Centigrade, then washed with water and dried as in Example 1. Comparison Example 3 Tin plated DI cans were cleaned as in Example 1, then spray treated for 40 seconds with the Comparison surface treatment liquid 2, heated to 50 degrees Centigrade, then washed with water and dried as in Example 1. The composi- tion 'f Comparison surface treatment liquid 2 was: oligomer solids 0.2 weight orthophospho- acid 0.1 weight water 99.7 weight pH The oligomer used for Comparison surface treatment liquid 2 was not the same as that used for the Examples and the preceding Comparison examples, but instead had the ap- proximate formula: OH X CH 2 SO 3 H (CH-CH 2 wherein n has an average value of 20 and X represents hydrogan. This oligomer was synthesized as follows: 100 g of poly(4-vinylphenol) (average molecular weight 2,500) was charged to a 1 liter reaction flask equipped with a condenser, nitrogen inlet tube, overhead stirrer, and thermometer, ai it was then dissolved by the addition of 500 g of 1,4-dioxane. This solution was maintained at approximately 10 degrees Centigrade, and 80 g of liquid sulfur trioxide (SO 3 was added over 1 hour. This was WO 91/10756 PMr/US91/00202 followed by heating to 80 degrees Centigrade axnd reaction for 4 hours with stirring. Neutralization with 10% sodium hydroxide solution and removal of the solvent by distilla- tion afforded the oligomer used above. Table 1 reports the results of the Examples and Com- parison Examples, which confirm an excellent corrosion re- sistance, adhesiveness, and slideability for the conditions according to the present invention and superiority over all the Comparison Examples. Thus, treatment of DI tin cans according to the present invention provides an excellent corrosion resistance and paint adhesion to the surface of tin plated cans and also imparts the excellent slideability that is required for a smooth conveyor transport of the cans. Table 1 TEST RESULTS OF THE EXAMPLES AND COMPARISON EXAMPLES IEV Peel Strength, Coefficient Ka Force/5 mm Width of Friction Example 1 100 2.0 0.3 Example 2 100 2.0 0.8 Example 3 100 2.0 0.8 Example 4 40 2.0 0.7 Comparison 350 1.5 Example 1 Comparison 550 1.7 Example 2 Comparison 700 1.5 Example 3 PCT/US 91/00202 AvK/HPJ/eo Henkel Corporation January 3, 1992 CLAIMS 1. A method for treating at least the outer surface of a tin plated DI can formed by drawing and ironing of tin plated ste-al, characterjzed in that the precleaned" surface to be treated is sprayed for at least 5 seconds at a te=mperatura of at least 40° C with aY aqueous surface treatmnent liquid having a pH between 4 and 6 and comprising acids selec'ced from the group consisting of orthophosphor.c acid and condensed phosphoric acids and (ii) a concentration of at least 0.1 by weight of a water soluble oligomer according to the general fornula: OH Y (C H-CH wherein n is a number with i value between 10 and 30 and each of X and Y independently represents hydrogen or: a group Z, vherein Z has a chemical composition conforming to the general formula: H RI z -C -N I H R 2 wherein each of 'i and R 2 is an alkyl or hydroxyalkyl group having from 1 to 5 carbon atoms, except that at least 25 of the total or all the X and Y groups in the oligomer are Z rather than hydrogen; and drying the sur- face thus sprayed, optionally after having first rinsed the sprayed surface with water. 2. A method according to claim 1, wherein the concen- tration of oligomer in the aqueous surface treatment li- quid is not more than 0.5 by weight. /A I SUSTIT WO 91/10756 PC/US91/00202 12 3. A method according to claim 2, wherein the time of spraying is not more than 60 seconds. 4. A method according to claim 1, wherein the time of spraying is not more than 60 seconds. 5. A method according to any of claims 1, 2, 3, or 4, wherein the water soluble oligomer has a chemical struc- ture according to the formula: OH CH 2 CH0OH X C H 2 "N\H3 SCH,N 100 wherein n has an average value of 20 and X represents hydrogen. 6. A method according to any of claims 1, 2, 3, or 4, wherein the sprayed can surface is not rinsed with water before drying. 7. A method according to claim 6, wherein the water soluble oligomer has a chemical structure according to the formula: OH CH 2 CH 2 0H CH CH 3 -(CH -CH n wherein n has an average value of 20 and X represents hydrogen. 8. A method according to any of claims 1, 2, 3, or 4 wherein the sprayed can surface is rinsed with deionized water as the last step before drying. WO091/10756 PCr/US91/00202 13 9. A method according to claim 8, wherein the water soluble oligomer has a chemical structure according to the formula: 0H C2C20 CH 2 \H3 H C H 2 wherein n has an average value of 20 and X represents hydrogen. -NTERNATJONAL SEARCH REPORT International Application No PCT/US 91/00202 CLASSIFICATION OF SUBJECT MATTER (if several classification symbols apply, Indicate a11)6 According to Intesisatloral Patent Classification (IPC) or to both National Classification and irC Int.Cl. 5 C23C22/08 C23C22/23 11. FIELDS SEARCHED Minimum Documentation Searched 7 Classification System Classification Symbols Int..Cl. 5 C23C Documentation Searched other than Minimum Documentation to the Extent that such Documents are Included in the Fields Searched$ Ill. DOCUMENTS CONSIDERED TO BIE RELEVANT 9 Calegory" Citation of Document, 11 with Indication, where appropriate, of the relevant passages 12 Relevant to Claim NoPt A I EP,A,0091166 (SOCIETE CONTINENTALE PARKER) 12 October 1983 see page 6, last paragraph page 8, paragraph 1; claims 1-3, 8, 9 see page 9, paragraph 3 (cited in the application) A LS,A,4457790 (ANDREAS LINDERT ET AL.) 1-6 03 July 1984 see page 6, lines 1 22; claims 1, 2-8; page 6, example 2 A FR,A,2552112 (ELSO VEGYI INDUSTRIA SZOVETKEZET) 22 March 1985, A G8,A,2112409 (PYRENE CHEMICAL SERVICES LTD) July-1983 Special categories of cited documents T later document published after the international filing date or priority date and tot In conflict with the application but document defining the generai state of the art which Is not died tolanderstand the principle or theory underlying the considered to be of particular relevance inventioon earlier document but published on or after the International Or document of particular relevance; the claimed Invention filing date cannot Le considered novel or cannot be considered to LV document which may throw doubts an priority cilm(s) or Involve all Inventive step which Is cited to establish the publication date of another document of prIcular relevance; the cdalme. inventit. citation or other special reason (a sp5etfiA) cantb cosdved to Invoive an Inventive step when M~e I(Y document referring to an oral dclosure use, exthibition or document is combi-ed with one or more oher such do(.u- other means meats, such combinv~ion being obvious to a person skh!.Al "r dP ocument ptblshed prior to the Intematlonal filing date but itt the art. later than, the priority date claimed 0& dlocument member of the sume patent family IV. CERTMFCATION Date of the Actual Completion of the Intesnational Search, Date of Mailing of this International Search Report 13 MAY 1991 -507.9 International Searching Authority Signature of Awthorized fe EUROPEAN PATNT OFFCE ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION NO. PCT/US 91/00202 SA 44163 This annex lists the patent family members r4clating to the patent documents cited in the above-mentioned international search report. The members are as contained in the Europe.n Patent Office EDP ile on The European Patent Office is in no way liable for these particui'ars which are merely given for the purpose of informantion. 21/06/9 1 EP-A-0091166 12-10-83 US-A- 4433015 21-02-84 AU-B- 564972 03-09-87 CA-A- 1197082 26-11-85 DE-A- 3311129 20-10-83 GB-A, B 2119805 23-11-83 JP-A- 58185661 29-10-83 US-A- 4517028 14-05-85 US-A-4457790 03-07-84 AU-B- 575563 04-08-88 AU-A- 2779684 15-11-84 CA-A- 1214036 18-11-86 JP-A- 59207972 26-11-84 FR-A-2552112 22-03-85 DE-A- 3331099 14-03^-85 MU-A- 29370 GB-A-2112409 20-07-83 None A For m detal about "hi aumex :sec Official Journal of the Evre~an Patent Offic, No. 12182