US2746884A - Method of tin plating and activated fatty oil composition therefor - Google Patents

Description

METHOD OF TIN PLATING AND ACTIVATED FATTY OIL COMPOSITION THEREFOR Ludwig Rosenstein and Manuel H. Gorin, San Francisco, Calif.

No Drawing. Application August 13, 1952-, Serial No. 304,215

18 Claims. (Cl. 117-114) This invention relates to an improvement in the process of making hot-dipped tinplate.

Tinplate is made by two prevailing processes; one of these, known as the electrolytic tinning process, consists in depositing tin electrolytically on sheets of steel and then subjecting said plated sheet to a temperature above the melting point of tin. The second process, known as hot-dip tinning, consists of passing a sheet of steel successively through (a) a flux, (b) a body of molten tin, and (c) a body of oil overlying the body of molten tin. Our invention bears mainly on the second of these processes and more specifically to improvement on the step (c).

The steel industry has for many years used one oil almost exclusively as suitable oil for the above mentioned step (c) of the hot-dip tinning process; this is palm oil. Palm oil is a product derived from the nut of certain types of tropical palms and has unique properties with respect to molten tin, said unique properties being that:

1. It keeps the surface of molten tin bright and shiny, probably by keeping it free of tin oxide.

2. It does not adhere to the tin surface and therefore tinplate emerging out of a layer of palm oil is clean in the sense that it has no more than a trace of adherent oil.

3. Palm oil is not excessively voltatile.

4. It oxidizes and polymerizes slowly compared with other fatty oils at about the temperature of molten tin.

When an oil has and exhibits the properties described in i and 2 above, it is called an active oil in the tinplate industry; if the oil does not have and exhibit these properties, it is called inactive, and is useless as a bath over the molten tin in the hot-dip process. The relative activity of oils is the first measure of their usefulness in this art.

Palm oil is an imported material coming mainly from the East Indies and Africa. The tin-plate industry has long sought an acceptable substitute among domestic oils in order to avoid the necessity of importation especially in times of national emergency and also as a means of mitigating the historic and wide price fluctuations which have been encountered. As an indication of the seriousness with which the steel industry regards this problem, we mention that the American Iron and Steel Institute established a fellowship at the Armour Research Institute, Chicago, Illinois, for a study of possible substitutes for palm oil. A progress report was made by the American Iron and Steel Institute entitled Contribution to the Metallurgy of Steel, No. 32, May 1949 and this research has been continued under the sponsorship of a Department of the United States Government.

We have found ways and means of modifying, by certain additions, a number of domestic vegetable and animal fats and oils and imparting to them properties equal, and in some cases superior, to those of palm oil for use in hot-dip tinning.

Briefly, we have found that the addition of certain resinous substances in varying proportionsaccomplishes 2,746,884 Patented May 22, 1956 the desired objective. Compositions of resinous substances dissolved in oils are old and well known in the art of varnish making, but in these known compositions the resinous substances are compounded with drying oils, i. e., with oils containing sufficient glycerides of unsaturated fatty acids so that oxygen is rapidly absorbed with the formation of films. Linseed oil and tung oil are the outstanding examples of the type of oils used in varnish making. Such oils are unsuited for hot-dip tinning purpose. We have found that by mixing certain resinous substances with non-drying oils, such as ricebran oil, cottonseed oil, tallow, etc., and heating until homogeneous, we obtain compositions which behave towards hot tin surfaces comparably to the way palmoil behaves.

Resinous substances which have been found to impart the desirable properties include:

1. Gum rosin 2. Wood rosin 3. Ester Gum g 4. High boiling (rosin) fraction of tall oil, also known as liquid rosin 5. Hydrogenated rosin 6. Tall oil esters in which the resin acids content are not esterified 7. The reaction product of rosin with an aldehyde.

The materials in the above list are natural products (or their derivatives), all of which have complex structures built upon a phenanthrene skeleton with attachments of one or more carboxyl groups. Physically they are highly viscous, sticky liquids or resinous to glassy solids.

We have mentioned hydrogenated rosin as suited for compounding with non-drying fatty oils. Rosin has two conjugated double bonds, and the first effect of hydrogenation is to add hydrogen at one of the double bonds, leaving a structure with only one double bond. We have not experimented with completely hydrogenated rosin; that is, a rosin no longer containing a double bond, because such material is not commercially available. We believe, however, that such completely hydrogenated rosin will function at least as well as the commercial partially hydrogenated rosin.

The method we used for testing any given composition with regard to its usefulness for hot dip tinplating is described on page 10 et seq. of the previously mentioned Contributions to the Metallurgy of Steel. Briefly, it consists in establishing a molten tin surface in a Petri dish at a temperature somewhat above the melting point of tin and applying to said surface a limited quantity of the material to be tested. Inactive substances, such as mineral oil and unmodified cotton-seed oil, spread uniformly over the surface of the molten tin and manifest no reactivity towards the surface layer. Active substances, such as palm oil, on the other hand, leave considerable areas of the tin surface unwetted and move vigorously across the surface with a peculiar scouring action, which removes surface layers and leaves a clean, mirror-like surface on the tin. The distinction between active and inactive substances is unmistakable and the level or degree of activity can be judged by the length of time that a clear tin surface persists. The activity decreases with time and the more rapidly the higher the temperature. Eventually the movement ceases and the surface becomes covered uniformly with a layer of oil.

We will now give a number of examples of specific embodiments of our invention.

Example I Rice bran oil which was produced by extraction of rice bran with hexane, followed by evaporation of the hexane, was blended with 20% by weight of ordinary wood rosin. This composition was tested simultaneously with one control of palm-oil and another control of unmodified rice-bran oil. The temperature was 290-300 C. The palm oil remained active for ten minutes; the rice-bran oil remained active. for six minutes. Rice-bran oil plus 20% rosin remained active sixteen. minutes.

Examplel illustrates the enhancement of the. activity of rice-bran oil, which by itself has a certain amount of natural. activity; that. is, it is active to some degree without additive.

Example II A hydrogenated cottonseed. oil, commercially known as Crisco, was blended with 5% of a hydrogenated rosin commercially produced by Hercules Powder Co. and. known as Staybelitef This was compared with palm-oil and with uncompounded Crisco at 290 C. Palm oil remained active fourteen minutes, Crisco plus 5% Staybelitc was still active. after 132 minutes, but had, through oxidation and polymerization, become very viscous. Crisco alone showed no activity whatever.

This experiment demonstrates the activation of an oil that has no activity in itself.

Example 111 Ricebran oil was compounded with 10% by weight of the resinous high-boiling fraction of a refined tall oil. It was compared with palm-oil at 290 C., and with ricebran oil to which nothing has been added. The palm oil remained active 16 minutes; the untreated rice-bran oil remained active 9 minutes; the rice-bran oil+10% tall-oil rosin was still active after 36 minutes, but had become quite viscous.

Example IV A tallow of about 35 C. titer to which 5% hydrogenated rosin had been added was compared at about 290 C. with palm-oil and untreated tallow. The palmoil remained active l6 minutes; the plain tallow remained active 2-4 minutes; the tallow+5% Staybelite remained active 32 minutes.

This illustrates the effect of the same activating agent as in Example H on another fat.

Example V Palm-oil. was compounded with 5% Staybelite and this blend was compared with the original uncornpounded palm-oil at 290 C. The palm-oil; compounded with Staybelite was one of the most active of all the preparationsmade to date, as judged by the vigor of the surface movement and the brilliancy of the molten tin surface. it remained active for an indefinite time, but after about Hi minutes at the high temperature the movement had become sluggish because of the increased viscosity of the oil.

This example illustrates the enhancement of activity of palm-oil and lengthening its life by compounding with hydrogenated rosin.

Example VI Refined cotton-seed oil compounded with 10% Staybelite at 290 C. was extremely active and remained so for more than 100 minutes, whereas a palm-oil control remained active 16 minutes.

This experiment was designed to shown that refined cotton-seed oil can be activated similarly to the hydrogenated oil.

Example VI! Hydrogenated cotton-seed oil blended with of a woodrosin which had been. reacted with paraformaldehyde to raise its softening point from 64 C. to 84 C., was compared with palm-oil at. 290 C. After an initial heating period'of l0 minutes'at 290 C, the compounded oil remained active indefinitely, whereas the palm-oil control remained active only 16 minutes.

This experiment was designed to show that an aldehyde modified rosin is a suitable activating compound.

Palm-oil as well as other oils from difierent sources, and even different lots from the same source, behave somewhat difierently toward molten tin. This accounts for the fact that the palm-oil controls mentioned in the various examples did not all have the same degree of activity when measured as herein described.

We have further found that the way in which the blends of oils and resinous substances are made has a marked effect on the activity'toward molten tin. We prefer to heat the oils to a temperature of about 150 C. and then add the resinous substance. either as a line powder or small lumps. The material is kept Well stirred until all resinous substance has dissolved and is then held quiescent at a temperature between 100 and 200 C. for about 1 to 3 hours. The mentioned limits of time and temperature will cover the majority of practical cases.

Early experiments with crude cotton-seed oil. indicated that it. was not active and could not. be easily activated by the addition of. resinous. substances, while refined cotton-seed oil responded very well to such activation. It was concluded. that the particular sample of crude cottonseed oil, which was very dark in color, contained interfering impurities. A simple clay-filtration, such as is commonly practiced in. the fatty oil industry to lighten the color, was sufiicient to remove. the interfering impurities, and thereafter the crude oil responded as well as did the highly refined oil.

While all the resinous materials mentioned impart some degree of activity to inactive fatty oils, or enhance the activity of those which have varying degrees of natural activity, one preferred embodiment is to use hydrogenated rosin for the activator. We have found that as little as 1% hydrogenated rosin, blended as described, into hydrogenated cotton-seed oil (which of itself is substantially inactive) will impart to it a degree of activity which makes it as active as palm-oil.

Early experiments showed that hydrogenated cottonseed oil responded in the most marked degree to the addition of resinous. substances. The difference between hydrogenated and ordinary cotton-seed oil is mainly in the ratio of unsaturated to saturated fats; that is, more specfically the ratio of oleins to stearins. The addition of a high stearin fat to cotton-seed oil will change this ratio in somewhat the same sense as hydrogenation. A blend of about 30%-40% tallow with cotton-seed oil will respond to blending with resinous substances about as well as hydrogenated cotton-seed oil.

One composition well suited for a tinning oil is:

Another composition which We have found especially desirable is:

Per cent Clarified rice-bran oil 95-995 Hydrogenated resin /2- 5 Rice-bran oil is somewhat more heat-stable than cottonseed oil, and for this reason may be preferred, although the eventual choice of the particular non-drying fatty oil to compound may depend on costas much as on its heat-stability.

A third. useful composition is:

Percent Hydrogenated cotton-seed oil -98 Rosinous fraction of tall-oil 2-15 Our invention is not confined to these compositions, which are given byway of a: practical example, but includes various blends of non-drying fatty oils compounded with resinous substances.

While we have designated certain compositions of fatty, non-drying oils with resinous substances especially suitable for use in production of tin-plate, we do not confine our invention to these examples or to this sole purpose. Other compositions of these classes of compounds can be used, and usefulness can be extended to production of terneplate, and to the finishing operation characteristic of the electrolytic tin-plate process.

The term fatty oils or fatty oil as used in this specification and in the claims designates those commercial products which are essentially glycerides of high-molecular weight fatty acids, and are of plant or animal origin. This term, which is commonly used in the trade, distinguishes these substances from any of the oily or waxy products derived from petroleum. (See for example Chemicals of Commerce, Snell and Snell, D. Van Nostrand and Company, New York, 2nd edition, the heading on p. 348.)

We claim:

1. A new composition of matter for use, cojointly with molten tin, in tin-plate production containing only a solution in a non-drying fatty oil of a resinous organic substance selected from the group comprising gum rosin, wood rosin, hydrogenated rosin, rosin esters, the rosin fraction of tall-oil, and rosin modified by treatment with an aldehyde; said resinous substance constituting 1% to 20% of the composition.

2. A composition of matter as in claim 1 wherein the fatty oil is cotton-seed oil.

3. A composition of matter as in claim 1 wherein the fatty oil is hydrogenated cotton-seed oil.

4. A composition of matter as in claim 1 wherein the fatty oil is tallow.

5. A composition of matter as in claim 1 wherein the fatty oil is rice-bran oil.

6. A composition of matter as in claim 1 wherein the fatty oil is palm-oil.

7. A composition of matter as in claim 1 wherein the resinous organic substance is gum rosin.

8. A composition of matter as in claim 1 wherein the resinous organic substance is wood rosin.

9. A composition of matter as in claim 1 wherein the resinous organic substance is hydrogenated rosin.

10. A composition of matter as in claim 1 wherein the resinous organic substance is aldehyde treated rosin.

11. A composition of matter as in claim 1 wherein the resinous organic substance is substantially the resinous fraction of tall-oil.

12. A composition of matter useful in tin-plate production containing only a solution of hydrogenated rosin in a fatty non-drying oil, said solution containing from 1% to 20% of said hydrogenated rosin.

13. A composition of matter as in claim 12 wherein the oil is hydrogenated cotton-seed oil.

14. A composition of matter as in claim 12 wherein the oil is rice-bran oil.

15. A composition of matter as in claim 12 wherein the oil is tallow.

16. A composition of matter as in claim 12 wherein the oil is palm-oil.

17. In a process of tinning metal plates by passing said plates through a body of molten tin, the step comprising passing the plates as they emerge from the body of molten tin through a body floating on said molten tin consisting essentially of a fatty non-drying oil which has dissolved therein, in an amount from 1% to 20%, a resinous substance selected from the group rosin, wood rosin, hydrogenated rosin, rosin esters, the rosin fraction of tall oil, and rosin treated with paraformaldehyde.

18. In a process as in claim 17 wherein the non-drying oil is tallow and the resinous substance is hydrogenated IOSlIl.

References Cited in the file of this patent UNITED STATES PATENTS 1,242,532 Dreymann Oct. 9, 1917 2,136,681 Fulton et a1. Nov. 15, 1938 2,275,583 Catlow Mar. 10, 1942 2,293,580 Walker Aug. 18, 1942 2,350,977 Agthe June 13, 1944 2,357,016 Miller Aug. 29, 1944 2,395,925 Walton et al. Mar. 5, 1946

Claims (1)

17. IN A PROCESS OF TINNING METAL PLATES BY PASSING SAID PLATES THROUGH A BODY OF MOLTEN TIN, THE STEP COMPRISING PASSING THE PLATES AS THEY EMERGE FROM THE BODY OF MOLTEN TIN THROUGH A BODY FLOATING ON SAID MOLTEN TIN CONSISTING ESSENTIALLY OF A FATTY NON-DRYING OIL WHICH HAS DISSOLVED THEREIN, IN AN AMOUNT FROM 1% TO 20%, A RESINOUS SUBSTANCE SELECTED FROM THE GROUP ROSIN, WOOD ROSIN, HYDROGENATED ROSIN, ROSIN ESTERS, THE ROSIN FRACTION OF TALL-OIL, AND ROSIN TREATED WITH PARAFORMALDEHYDE.