DE3150286A1 - Precoating material for a metallic blank which can be shaped to form a container - Google Patents

Description

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Pre-coating material for a deformable container metallic raw piece

Foods, such as vegetables, fruits, and soups, are many Has been packed in steel or tin-plated containers for years. These containers are according to one Technology have been produced in which 'three different pieces of metal are assumed. That means, The containers are formed by turning a flat metal starting material into a cylindrical Body shaped and the abutting edges soldered or welded together. The cylindrical body is then flanged and a base piece is attached to it using the well-known double crinkling (folding) technique. if the container is filled, the remaining piece is put on or attached by the respective staff.

The containers made of three pieces of metal can have protective enamel coatings to prevent corrosion are applied, which are: in particular containers made of tin-free steel (TFS). Food cans can

They can also be made from tin-coated steel. Such cans can also have protective enamel layers, depending on the type of applied to the food to be packaged.

The protective enamel layers of the metallic tin cans and tin cans are carefully selected in order to obtain the required corrosion resistance and in order to furthermore, not to transfer a characteristic taste to the food. To the typical materials enamels include phenolic resins, epoxy resins, amine-type resins, oleoresins such as Chinese wood oil, Resins of the vinyl type, such as polyvinyl chloride or vinyl chloride-vinyl acetate copolymers. These are in special solvent mixtures, such as ketones, esters, Alcohols and aromatic or aliphatic hydrocarbons, prepared for easy and quick application. These enamel materials are applied by known techniques, such as after roller coating or spray coating. The coatings are usually thermosetting and are made in standard baking ovens implemented or cured.

The coatings that are applied to the three-part containers are used in the manufacture of the Tin can not mechanically deformed excessively. Because of this, the enamel materials can for the three-part container from a large number

selected from resins or resinous materials that form a strongly cross-linked when baking in the oven Harden the structure. This cross-linking leads to maximum corrosion prevention and chemical resistance, thereby the food packaged in the cans

is protected in the desired form.

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In the manufacture of containers from two metallic Pieces by pulling and redrawing the flat metallic blanks are part of the selection of the enamel materials different criteria to be observed. For reasons of economy, it is preferred that the Metal is pre-coated with the enamel and then the pre-coated blank is deformed into the container, by processing it in a suitable mold. The deformation leads to a strong and extensive mechanical stress on the enamel with regard to the adhesion to the metallic substrate and leads to a Examination of extensibility and the ability to flow without breaking. This is why enamels are for Drawn tins difficult to prepare. Furthermore, there is a need to consider the mixtures of the resins and the solvent used in each case required to ensure that firmly adhering films are stoved with the required Degree of crosslinking with the result of good corrosion and chemical resistance. In doing so, however, a high degree of flexibility should remain is comparable to enamels of three-piece cans in order to be subjected to the deformation operation without breaking to be able to 1

about the networking of these enamels from drawn tin cans the crosslinking resins or the baking temperatures can be adjusted accordingly can be slightly lower than that chosen for enamels of three-piece cans

^{be ow} . All of this takes place with the result of forming enamel coatings that are somewhat more soluble in organic solvents after baking than the corresponding counterparts of the three-piece tin cans. That is, the enamels of drawn cans may retain small amounts (ppm) of certain solvents after the baking operation. This solution

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-β-medium residues can then if the tin can is filled, are released and lead to undesirable taste peculiarities of the food. Occasionally the solvent is relatively harmless if it is present inside the filled can. A solvent itself can be relatively harmless. However, it can also react with the food itself, to cause exceptionally undesirable changes in taste.

Metallic containers made by drawing a pre-coated tin-free steel several times can be provided with various types of thermosetting organic coatings consisting of Phenolic resins, epoxy resins, acrylic resins, amine type resins, polyvinyl chloride resins and copolymers of which as well as polyester resins have been prepared. The inside and outside of each sheet the plate or the blank is coated. The "inside" represents the side that the Inside of the container. The "outside" is correspondingly the outside of the container.

When making three-piece containers for food or meat, the sheet metal plate is used, either made of tin-free steel or electrolytically galvanized sheet iron, through a special coating measure coated. As the three-piece food cans have a coating both the inner as well as the outer surfaces require

several passes are generally required to obtain the appropriate corrosion protection for the finished tin can. For example, the outer coating may in one pass ER- ° follow while the internal coating, which can consist of one or two coatings _r a separate

Measure required for each internal coating.

As a result, three passes through one Coaters are required to produce the starting material for a three-piece tin can.

The coated sheet must then be cut into the respective can raw pieces. These raw pieces are then converted into the cylindrical shape in the corresponding device and soldered at its side seam or welded. Finally, a double flare is made on the lower part of the cylindrical body carried out. This multitude of measures requires a considerable amount of time and high costs in production of three-piece containers.

Food containers that are made into shape using the newer method by pulling pre-coated sheets several times made of two pieces result in significant cost savings over the above described method for the production of three-piece tins either the respective measures be reduced or excluded. The metallic base material for the manufacture of two-piece containers A coil coating can be applied by drawing several times. With this type of coating Both the inner and the outer coating can be used for the manufacture of the cans used metal can be applied by a single measure, which is economical for manufacturing Offers advantages.

Multi-drawn food cans can be made from either tin-free steel or electrolytically tinned steel Sheet iron can be produced. For reasons of economy, most containers are made of tin-free Steel made. The tin-free steel can be of any sheet thickness, whereby this is usually preferred

-δι added material a "normal box" (base box) of the marking 75 | [, which is T-4 material, a cast stock, or the 65-f / DR9 material.

A "normal box" is made by the tin manufacturer

ler by a surface (on one side) of 2Ö2 272 cm (31 360 square inches) for a given metal weight. The materials T-4 and DR9 represent type designations of the steelworks for the hardness of the material and allow conclusions to be drawn about the rolling process Manufacture of the sheet metal too.

Careful consideration is given to the manufacture of food cans by drawing the pre-coated starting material several times Selection of organic coating material required. Since the base material is pre-coated, the coating is subjected to the same mechanical stress from drawing and the same deformation measures as does the can material itself. This requires that the coating be on the metallic Substrate adheres well and has the necessary mechanical properties to allow the pulling and deformation measure to withstand without being removed from the metal substrate breaks off or is then noticeably removed. Compared to the technology using three pieces these multiple drawn containers have an integrated bottom without a side fold. This leads to economic Advantages in production, since the soldering or welding of the side seams, the coating of the Side seam strips and double flanging in the bottom area excluded are. In addition, this process of pulling food cans is continuous guided. This means that the pre-coated sheet is fed to a press that is subjected to multiple deformations. Of the The finished sheet metal jacket leaves the press and is continuously fed via a flange device, a crimping device and an air tester continued and closed

lent palletized. The continuous approach to this multi-step process eliminates considerable labor, which means additional economic advantage .

The strong mechanical forces applied to the coating during multiple pulls imposed would suggest that rubbery or rubbery or highly flexible polymeric materials are most useful for the precoated multi-drawn containers. Although you can Allow rubber materials to expand sufficiently while pulling the container several times. Your chemical resistance however, as well as their adhesion, are generally inferior to thermosetting coatings.

This results in the paradoxical contradiction between the required flexibility in multiple pulls and the necessary chemical protection of the metal against the food packed in the container. Another problem when using rubber or rubber is that the taste peculiarities caused by the Vulcanizing agents occur through absorption on the food contained in the metal containers pass over that have been precoated with such rubber materials. Because of this, these materials can are not used for metal container coatings.

If coatings with good flow properties are applied to the metallic surface, then the ^ow leads to an essentially bubble-free and "eyelet-free" or continuous coverage of the metal. This is particularly important when the food is being packaged, since any uncoated area of the food can will provide corrosion sites with the result that perforations will occur at these sites. Coating imperfections generally occur above one inch near the

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-ιοί flange of the can on. So it is well known that the maximum metalworking with regard to the axial stretching or drawing and the circumferential compression occur roughly in the flange area. A frequently used one The method of checking the coverage of the coating on the metal is the enamel measurement or rapid test. This test is carried out with a special test instrument, whereby essentially the electrical conductivity inside the food can is measured while it is filled with an electrolyte.

A special device is required to perform this rapid test. An enamel measuring device becomes very special of the Model 1071 WACO with a 0 to 1 milliampere auxiliary device used. This apparatus has an electrode arranged to be vertical in (along the axis) a tin can, which is arranged below it, is movable in and out. The electrode is positioned about an inch from the bottom of the tin. The tin can is through a Vise-like device held in position that holds it down so that the open end of the can points upwards towards the electrode. The tin can is filled with a 2% solution of sodium sulfate filled. Allow at least 30 seconds for wetting to pass before the electrode is in the tin can is inserted. The solution temperature should be kept between 22.2 and 25.6 ° C (72 to 78 ° F). The tin can should be filled in such a way that that when the electrode is lowered into the test position, the solution is about 0.32 cm (1/8 ") below the upper flange radius of the can rises. Care should be taken that wetting of the flange is avoided, as this leads to a high level of incorrect reading. The milliammeter the tester is with the vice-like device

connected that holds the bottom of the can. The electrode is also connected to another lead of the milliammeter tied together. A zero adjustment of the instrument is required. The operating staff provides insert the milliammeter to the reading "T" on the scale. Shortly after zeroing the milliameter a warning light shows up. The detachment should then be carried out immediately. If this is the case with When properly applied to pre-coated food cans, readings should be in the range of 0 to 8 milliamps

can be obtained. Such values show that the container is satisfactory. Consequently Then a coating material for a metal substrate has been found which has the strong multiple Resists shaping measure without degradation. Such a thing Coating system that on the one hand fulfills a protective function on the metal substrate and prevents corrosion and, on the other hand, excludes undesirable changes in taste, should therefore be aimed for.

The invention therefore aims to provide a precoating material, with which, by pulling several times, a metallic tin can coated with an enamel is available, in which taste-related disorders are essentially excluded. In particular it is The aim of the invention is to provide such drawn cans made of pre-coated metal sheet, such as zirin-free Steel (TFS) or tin-coated steel (ETP). After all, it should be a highly economical one Propose the coating process to be carried out in which a metallic sheet is processed using coatings that are produced by direct roller coating or applied by reverse roller coating

have been.
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Furthermore, the invention is intended to provide an intermediate in Suggest the form of a thermosetting coating preparation that is usually solvent releases to the application on the metal sheet at low temperatures in the course of the glass coating process or, at higher temperatures, by coil coating further focuses on describing a precoatable resin coating composition which results in good corrosion resistance the metallic tin can when filled with the various food products is. In particular, this resin coating mixture is intended to withstand mechanical pulling out and deformation during Withstand multiple pulls without breakage or loss of adhesion. The invention is also intended to provide a solution system for The enamel indicates the properties sought in creating the coating on the metal sheet conveys the undesirable taste properties without, however, containing chemical components pass on the food product or that contains solvents that affect chemical products such as Hydrogen sulphide released by the food react, whereby this chemical reaction results in products leads to the unsavory or harmful 'side-' represent products in food.

Finally, it is the aim of the invention to propose a resinous enamel and a solvent mixture, with which the desired properties are achieved when coating the metal sheet and the release essentially all of the solvents during the stoving process, so that when the precoated Metal is subjected to passive reheating during multiple draws, the rest Traces of the solvent or other small molecules from catalyst residues or plasticizers through the

Enamel cannot be released in gaseous form, which would otherwise have a detrimental effect on the taste of the packaged food.

The invention accordingly relates to a precoating material or a pre-coating system for a deformable by multiple pulling to form a container having the precoating material on the inside metallic blank, which is characterized in that the precoating material is a Phenolic resin, an epoxy resin, a vinyl chloride-vinyl acetate copolymer and contains a polyvinyl chloride dispersion resin in a solvent system and that Polyvinyl chloride dispersion resin has an intrinsic viscosity of about 1.4.

Because of the mechanical stretching and deformation measures involved in the production of multiple Drawn containers are taken, the coatings on the metallic substrate must be excellent Show properties. A system or a material for internal and external coatings is required, which is consistent with multiple pulls in the appropriate procedure. An outer coating is applied by roller or coil coating and cured in an oven. When coating of sheet metal, this coating is applied in a temperature range of 149 to 2O4 ° C (300 to 400 ° F) baked for about 6 to 10 minutes. The coating

^ÖW tung is generally applied to the metallic substrate at a film weight of 0.31 to 0.58 mg / cm (8 to 15 mg / 4 square inches) of sheet surface. This coating can be of various chemical types, such as a vinyl organosol, an epoxy resin, an amine resin, a phenolic resin or suitably prepared mixtures of these resins. The outer coating

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Tung is generally applied at a lower film weight than the inner coating, for which purpose economic reasons as well as less severe corrosion requirements play a role.

The inner coating is generally made with a

2 Film weight from 0.58 to 1.36 mg / cm (15 to 35 mg / 4 Square inches) sheet surface applied. The coating can either be by surface coating (sheet coated) or applied by coil coating (coil coated). A baking temperature of 149 to 204 ° C (300 to 400 ° F) is generally used at the surface coating for a period of 8 to 10 minutes. In addition, the surface coating be done with more than one pass. So

can e.g. for a simply drawn container, one Base coat, such as epoxy type, applied first will. A coating of a different chemical type can be applied on a second pass such as an oleoresin enamel. This kind diverse The process allows the can manufacturer to choose the best enamel system for the inside of the Regarding the adhesion to the metal and the corrosion resistance to choose against the packaged food. 25th

The coating on the inside can also be applied to the metal substrate by coil coating. Be in winding coating both the Innenais also carry the outer coating at the same time be ^ow. This process offers economic advantages in terms of production, since the entire coating operation takes place in a single pass. The bake-in temperatures for coil coating are in the temperature range of 260 to 316 ° C (500 to 600 F) for about 20 seconds. The time mentioned is sufficient to remove any residual traces of solvent, as

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neither the inner coating nor the outer coating contains about 75% solvent in the preparation.

Because of the severe mechanical deformation that the multi-drawn coatings of the can are subjected to special requirements in the In terms of adhesion and mechanical strength. Preferred inner coatings for Multi-drawn cans are of the organosol type.

These coatings contain mixtures of phenolic resin, epoxy resin, vinyl solution resins of the vinyl acetate / vinyl chloride polymer type and high molecular weight polyvinyl chloride dispersion resins. It was found that the Molecular weight range of polyvinyl chloride is a critical consideration in successful manufacture of internal coatings with multiple pulling. If the resin is not above a certain molecular weight then the coating exhibits loss of adhesion or breakage in about the upper third of the food can during the pulling, resulting in an unsatisfactory filled container. It a weight average molecular weight of greater than 110,000 has been found to be required with the preferred molecular weight being greater than 150,000. The molecular weight is determined by measurements determined using a gel permeation chromatograph, with a polystyrene gel of known pore diameter is used as a filler material.

In the mechanical working of the precoated metal in the mold occurs during the formation of the metallic container a rise in temperature. The temperature in the die and consequently also in the The tin can rises to 66 ° C in the first redrawing stage and can rise to 93 ° C in the second redrawing stage. The increased temperature leads to an erosion

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give way to the coating on the can, which leads to a new reflow of the coating. The range of the glass transition temperature Tg of the coatings is important. It is a glass transition temperature Tg is required, which is neither too high so as not to break a coating is still too low for softening and breakdown of the coating to occur. The heating takes place passive in the deforming and particularly in the multiple drawing method. The beneficial effects of heating on the properties of the coating. that described in U.S. Patent 3,206,848. The renewed flow (reflow) of the coating is evident from the increased gloss on the outer coating during drawing. This is due to the higher temperatures and pressures.

The lubricant that is applied to the coating is another critical aspect of the Manufacture of multiple drawn containers. The lubricant provides the necessary slip when precoated Sheets are formed in the press tool. Without a suitable lubricant, the coatings will abraded by the die resulting in unsatisfactory containers and possible damage the tools and the punch in the press leads. Lubricants such as boler wax, lanolin or petrolatum, can be used. With the multiple drawn containers, the petrolatum proves itself with regard to the Tool lubrication and good properties in terms of taste are particularly suitable. The lubricant is done by spraying with standard spray guns or by misting the coated sheet metal with special electrostatically working waxing machines

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applied.

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Maintaining the properties of the coatings is not just in terms of corrosion resistance important, but also with regard to the taste characteristics. That means that residual solvent or small molecules in the film due to incomplete exclusion during curing or baking Coating present, must be reduced to a minimum, otherwise they have the undesirable taste Cause adverse effects on the food.

This is especially true in connection with a drawn tin can, in which this process contains residual solvent expresses from the coating. Materials and solvents that remain in the coatings, must be selected so that the disadvantageous taste or odor defects are excluded. Additionally they must be selected so that there is the correct amount of crosslinking agent and interaction between small molecules is avoided by the food through secondary reactions with solvent residues result in the formation of undesirable taste or odor defects.

A well-known phenomenon with foods such as peas, corn, beans, etc. is the release of small ones Molecules, such as cystine and hydrogen sulfide, after packaging. These chemical compounds lead to one Breakdown of proteins in the food. You can use the remaining solvents and the oligomers in the Coating film react to give reaction products

®0 that lead to undesirable taste properties of the food. In particular, the reaction of mesityl oxide, an impurity in certain coating solvents such as diacetone alcohol, with hydrogen sulfide can result in an offensive odor. The reaction product 4-methyl-4-mercaptopentan-2-one has been identified to the effect that it

and causes odor defects in a particular canned meat and vegetable product. This mercaptoketone is associated with the unpleasant smell. Hence the elimination of, for example Mesityloxid from the coating systems of drawn canned food cans is of great importance, in order to ensure with these containers that there is no effect on the taste or smell of the packaged food adverse influence is exerted.

The invention will be explained in more detail below with reference to figures. Show it:

Fig. 1 is a side partial sectional view of a container made from a pre-coated metallic Raw material was manufactured by drawing,

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

3 shows a partial sectional side view of a container side wall and a double-flanged bottom part, being made by rolling a flat blank of the material into a hollow cylinder with side seam welded together and subsequent flanging of the cylinder and double flanging of a flat one circular end of it took place, and

FIG. 4 shows a cross-sectional view along the line 4-4 in FIG. 3, with in particular the detail of the side fold shown in Fig. 3 is reproduced.

In Figs. 1 to 4, the difference between the multiple drawing of a precoated metallic Two-piece material produced from the starting material

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Container and the three-piece container obtained by rolling and side crimping will. It can be seen that there are fewer coating layers with a two-piece container system than with a three-piece container system are required. In particular, the multi-drawn tin can 10 1 created by precoating inner layers 11 and outer layers 12 which are attached to the base metal 13 made of tin-free steel or electrolytically tinned iron sheet adhere. Still, it's for deforming required by drawing the flat precoated material into a cup-like shape that the Diameter usually less than its height.

In contrast, the three-piece container 14 shown in Figure 3 is provided with two inner coatings 15 and 16 and an outer coating 17 pre-coated. This container is made of the material 18, which to Raw pieces were cut up, shaped, rolled into a hollow cylindrical container and along it Longitudinal edges at 19 by means of welding (as in FIGS. 3 and 4) laterally crimped, connected or crimped and to be soldered. If the side flanging technique is chosen, the coating is still required and repair the interior by means of a strip 20 of the side curled coating material to harden in order to subsequently prevent the packaged food from the side fold or the adjacent Attack metal. It requires an ending

^ow 21 at 22 is double crimped onto the hollow cylindrical container. Consequently, the sealing part must be present in order to hermetically seal this end. The additional side crimping strip 20 and the double crimping on the lower part 21 would be used for the manufacture of the

three-piece container, if compared with the two-piece container drawn several times, an additional one

Mean cost burden. In many areas of application, the outside of the container must be at the side Fold 24 can also be coated and cured for the shooter. It can be seen that the appropriate coating system for the inner coating 11 and the outer coating 12 in the case of a multiple drawn two-piece Container is essential to obtain a safe and inexpensive container that will not corrode and re the taste does not adversely affect the food packaged in it.

The preferred outer coating 12 is primarily an epoxy resin and a small amount of a lubricant in combination therewith, as discussed earlier, the film weight being 0.349 to 0.465 mg / cm ^ g to 12 mg / 4 square inches. The special epoxy resin coating is the commercial material Mobil Chemical MC9372, whereby more than half the weight of the material consists of the epoxy resin. About 75% epoxies have been used with success in this combination. The preferred inner coating 11 consists of a polyvinyl chloride dispersion _{resin /} epoxy resin, phenolic resin, vinyl chloride-acetate copolymers as solvent resins, lanolin as a lubricant aid during the shaping and titanium dioxide as a pigment. The ² ^ above resins, pigment, and lubricants are

dispersed or dissolved in suitable solvents to provide a viscosity of 160 seconds in a number 4 Ford viscosity container. Typically, the solvents are greater than about half the Gesamtge- ^ wichtes. The preparation of the polyvinyl chloride, the epoxy and phenolic resin, the vinyl chloride-acetate copolymer, the lanolin, the solvent and the titanium dioxide can be obtained from Midland-Dexter as MM47 8A. A similar preparation of the dispersion and solution resins, lubricant and pigment can be made as follows

All resins except PVC 30% by weight of the non-volatile components

PVC dispersion resin 43% by weight of the non-volatile components

Pigment 27% by weight of the non-

volatile inventory

share.

It has been found that the molecular weight of the polyvinyl chloride dispersion resin, is particularly important in the manufacture of a satisfactory multi-drawn container with precoating. If that Molecular weight of the polyvinyl chloride dispersion resin below a critical value as specified by the Basic viscosity is defined, then the coating will deteriorate or deteriorate in terms of adhesion tear open near the top of the tin, indicating the mechanical stretching and the axial compression decreases during multiple pulls for high impact.

The coating defects are reflected in the enamel meter readings on the coating be determined. Organosol coatings that with three different molecular weight ranges

of the polyvinyl chloride dispersion resin

2 and in an amount of 1.43 mg / cm by surface coating (sheet coating) and baked at 193 ° C (38O ° F) for 10 minutes

the following readings of the enamel measuring device after drawing and after drawing further or further by one 8,1 cm (3 3 / 16inch) diameter and 11,1 cm (4 3/8 inch) high food can.

Readings on canned food cans drawn several times on an enamel measuring device

(Pre-coating with an internal organosol coating)

,. PVC resin basic viscosity reading (milliamp.)

b ■ * *

A 1.02 50

B 1.00 45

C 1.40 2

It can be seen that the organosol coating with the PVC resin C, which has the highest intrinsic viscosity, the provides the lowest reading, thus providing superior properties in terms of ductility with the metal substrate to be shown.

Another essential step in assessing the properties of internal coatings in multiple drawn ones Food cans is a taste test of the packaged materials in them. A The initial verification test is generally different with three packaged test materials. Water, is used as the one material, since water is in many foods, such as corn, peas or tomatoes represents a very high component. Water causes corrosion very quickly. Coating adhesion is quick lost if the inner coating is discontinuous, has eyelet holes, or is broken. chicken soup Because of its fat content, it is used to test most soups. These fats

have a softening effect on the coating.

When a coating is not baked sufficiently or has not been prepared in an expedient manner to To get adequate crosslinking, the fat in the chicken soup will soften the coating, resulting in a Adhesion reduction or swelling and subsequent breakdown of this coating film leads.

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Apple juice is primarily used as a means of taste verification and also as a material which greatly accelerates the corrosion with discontinuous build-up of the coating film. Apple juice is therefore an important test material for characterizing the taste effects of the inner container coating. The following table explains the coating adhesion canned food cans drawn several times, if a pre-coating on the inside with organosols and the above-mentioned three test materials were packaged therein.

PVC resin

A B C

Basic viscosity

1.02 1.00 1.40

Water 50 min /
121 ⁰ C (25O ° F)

Chicken soup (3 mos)

Apple juice (3 mos)

*) Failure **) Success

It can be seen that the organosol coating with the highest intrinsic viscosity leads to the best test results. The above information was all obtained with food cans that had an organosol interior coating and were baked at a temperature of 193 ° C (380 F) for 10 minutes. Drawn food cans, which were obtained by means of a pre-applied organosol and wherein the baking was carried out at a Spulenbeschichtungseinbrenngrad of 287.5 ° C (550 ⁰ F) for 20 seconds, showed similar readings on Emaillemeßgerät and similar test results.

The Glaijuni change:.; temperature of the inner layer must be set precisely during preparation so that the coating is neither rubbed off nor under the effects of heat and pressure during deformation becomes brittle. Similarly, the composition of the resins is essential to a suitable composition that is also resistant to chemical attack on the packaged products. That is, if the glass transition temperature is too low, it will soften and swell when exposed to the fats exposed and hydrolyzed to acidic products. Certain products are atch a part of the coating leach out and combine with it to cause off-taste and odor defects. The glass transition temperature must be adjusted to prevent degradation of the inner and outer coatings the temperature effects that occur during the deformation are prevented. However, it is supposed to be a passive one be able to flow again. The glass transition temperature must not be so high that the coating is not flexible or pliable and to a certain extent a renewed flow sen during the deformation subject. Consequently, the preparation provides the above in terms of the correct proportions of the Materials, especially the solution resins discussed, have the right amount of crosslinking and therefore the suitable glass transition temperature.

Measurements of the apparent glass transition temperature of the inner and outer coatings are made by the the following results.

Apparent glass transition temperatures of drawn Tin can coatings

Glass transition temperature ° °

Inner coating Outer coating

57.6 (136) 87.4 (189)

When the metallic containers are formed by drawing and redrawing or further drawing, a pre-coated metal is often used in order to avoid expensive post-form coating measures. The deformation leads to a considerable stretching or to a considerable expansion of the coating. The deformation also raises the temperature of the metal substrate and thus also that of the applied coating. If the coating film contains resins below the critical molecular weight, then the draw opens and that
re-drawing the coating film and making it less resistant to chemical penetration
Species of the packaged product in the film and against the leakage of any retained
Solvents, resin oligomers, etc., from the film in which they are present.

A well-known property of food like
Peas, corn, beans etc., the release of small molecules, such as cystine and hydrogen sulfide, is after
Packing. These chemical compounds lead to
a breakdown of the proteins in the food. she
can react with residual solvents and oligomers in the coating film to provide reaction products which adversely affect the taste properties of the packaged food.

-2 δ-It was also found that certain solvents, when added to the organosol coatings, flavor and taste in the packaged product Lead to odor defects, especially when it comes to foods of which it is known that they release sulfides, such as hydrogen sulfide. Examples of these foods are white beans or whole or intact seeds, e.g. of corn. aside from that a coating is prepared in a solvent system of esters and alcohols, which itself does not contain any compounds that interact with sulphides. When the coating materials be diluted in the manufacturing facility to adjust a suitable coating viscosity, then Certain solvents can be used as diluents for this purpose for economic reasons will. An example of such a diluent is a mixture of xylene and diacetone alcohol or Xylene and isophorone. Make diacetone alcohol or isophorone Condensation products of acetone are common

used in metal coatings as a thinner because they are cheap and have excellent solution properties in many industrial coatings or show container coatings. 25th

While these solvents exhibit technically useful properties when used in coatings, so they (isophorone and diacetone alcohol) usually contain trace amounts of mesityl oxide. Mesityloxid represents a highly reactive unsaturated ketone compound that easily adds sulfides, such as hydrogen sulfide harmful smell and taste and odor defects in the food like meat. In the case of hydrogen sulfide, which in the presence of Mesityl oxide is released, the reaction product was identified as 4-methyl-4-mercaptopentan-2-one. the

The following table shows the flavor characteristics Due to a remaining solvent content in multiple deformed cans, their height is greater than their diameter is.

Taste test with whole kernels (maize)

No tin can

Comparative test specimen 3-piece ETP

Pulled several times Organosol 1

Pulled multiple times Organosol 2 (TAI)

Residual Diaceches soldering alcohol
middle
Key figure * Code figure

213

34.0

38.0

2.6

Mesityl taste oxide test

Evaluation measuring scale index 1-9

4.8

1.3

2.6

greater than 9

The test results show that the presence of traces of a sulfide acceptor molecule such as mesityl oxide or their Precursor, diacetone alcohol, cause highly undesirable taste peculiarities in maize. Other food products, like white beans, show a similar trend in terms of taste impact.

Taste test with white beans

No tin can

Comparative test specimen 3-piece ETP

Organosol 1

Organosol 1

Coating Thinner Flavor Rating Solvent Mixture {scale 1-9)

Xylene / butyl cellosolve

Xylene / butylcellosolve xylene / diacetone alcohol

1.0

. 1.0 3.4

The results show that the coating with the xylene / diacetone alcohol mixture was diluted in the diacetone alcohol with a mesityl oxide content of 1-2 ppm is shown to have higher taste ratings than Coatings thinned with xylene / butyl cellosolve shows.

The same results are obtained with such organosol coatings that are obtained with a xylene / isophorone mixture have been diluted.

Stand with the precoating agents according to the invention as a result, internal coating preparations are available which, when used, are deformed many times without degradation can be because the resins are sufficiently pliable, which is due to the molecular weight, among other things. About that in addition, the inner coating layer does not cause any adverse reaction with that packaged in the container Food. Furthermore, no undesirable taste and odor defects are found.

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Claims (8)

Claims 1. Pre-coating material for a by multiple pulling to one the pre-coating material on the inside having a deformable metallic blank, characterized in that the Pre-coating material a phenolic resin, an epoxy resin, a vinyl chloride-vinyl acetate copolymer and a Contains polyvinyl chloride dispersion resin in a solvent system and the polyvinyl chloride dispersion resin has an intrinsic viscosity of about 1.4. 2. precoating material according to claim 1, characterized characterized in that the polyvinyl chloride disposition resin is about 43% by weight of all non-volatile components, the other resins about 30% by weight of all non-volatile components and a pigment component is the remainder. 3. precoating material according to claim 2, characterized in that the pigment is titanium dioxide. -2- 4. precoating material according to claim 2, characterized in that the glass transition temperature, which goes back to the combination of the different resins, a passive reflux due to the during the Deformation operation caused temperature effect permitted. 5. precoating material according to claim 4, characterized in that the metallic blank is a further, has provided pre-coating for the outside of the container and this outer pre-coating primarily contains an epoxy resin and a minor amount of a lubricant. 6. precoating material according to claim 5, characterized in that the epoxy resin is 75 wt .-% of the coating matters. 7. precoating material · according to claim 6, characterized in that characterized in that the outer precoat is in the form of a film having a basis weight of 0.3 49 to 2
0.465 mg / cm is applied. 8. precoating material according to claim 5, characterized in that the inner precoating in the form a film with a basis weight of about 1.279 mg / cm is applied.