JPH0144579B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a welded tin can for packaging, and more specifically, it is particularly used for filling the pulp of mandarin oranges, peaches, cherries, etc. This invention relates to a welded tin can for canning in which the detining phenomenon and iron elution are eliminated or suppressed. (Prior art) Since the quality of fruit pulp products such as mandarin oranges deteriorates significantly due to oxidation, it is necessary to fill and seal the containers in airtight containers with as little residual oxygen as possible. be. For this reason, the above-mentioned fruit pulp products are mainly degassed by vacuum degassing when they are filled into packages. However, if the oxygen is completely degassed, there is a risk that the flavor, moisture, etc. of the contents will be removed as well.
Furthermore, dissolved oxygen in the contents may be fixed to the contents by adsorption, etc., and is not completely removed. In order to compensate for this, for mandarin orange products, etc., tin cans with unpainted inner surfaces are filled under reduced pressure, and the oxygen remaining in the cans is captured and inactivated by the reducing power developed by tin elution from the inside of the cans, maintaining quality. Measures are being taken to ensure this. However, on the other hand, the phenomenon of abnormal elution of tin sometimes occurs, which poses a problem of causing harmful effects on health. From the above viewpoint, attempts have already been made to utilize the reducing properties of tin to suppress the abnormal elution of tin, as seen in tin cans with unpainted inner surfaces. For example, as an example of such an attempt, (1) a method using a sparrow casing partially coated with enamel (November 20, 1955);
(2) A method of painting the inner surface of the can with a paint in which a tin compound is dispersed (for example, U.S. Patent No. 1811160) (3) method of partially exposing tin solder at the can body joint (for example, , US Pat. No. 3,268,344), and (4) a method of adding stannous chloride to the beverage itself, which is the content, is known. (Problem to be Solved by the Invention) However, the method (4) above has a problem in that stannous chloride is not approved as a food additive and is therefore not applicable in terms of food hygiene. Also, above
Although methods (1) to (3) are somewhat effective in suppressing abnormal tin elution, the elution of tin occurs slowly and the tin remains in the container as soon as possible immediately after filling the contents. It is still unsatisfactory for the purpose of removing oxygen. That is, the deterioration of the contents due to residual oxygen in the container begins immediately after the contents are filled into the container, and particularly rapidly due to exposure to high temperatures during heat sterilization treatment performed subsequent to filling. In recent years, as a can manufacturing method using solder cans, welded cans have been used in which both ends of the can material are joined together by welding, and tinplate is an excellent can material for these welded cans in terms of workability. It is also known that From the viewpoint of suppressing abnormal elution of tin, the present inventors proposed that a welded can made of a can material with a thin chromate layer on the tin layer be used as a can for filling fruit pulp products, etc. I have been considering. However, in the above-mentioned welded tin can, it was found that the detining phenomenon was non-uniform, that is, only the inner surface of the can that came into contact with the pulp was detined, and that in such a canning, a large amount of iron was leached into the contents of the can. The reason for this has not yet been fully elucidated, but in canned fruit pulp, the pulp part contains more oxygen than the syrup part due to adsorption, etc. This is thought to be due to the progress of interfacial corrosion and the higher acidity in the pulp clusters than in the syrup. Therefore, it is recognized that tin is selectively eluted from the inner surface in contact with the fruit pulp, resulting in exposure of the tin-iron alloy layer or the steel matrix. Therefore, the present invention prevents uneven detining in a welded tin can with a tin plated layer and a chromium layer thereon, prevents iron elution into the contents, and prevents iron from leaching into the contents. It is an object of the present invention to provide a welded tin can for filling, which enables rapid removal or inactivation of residual oxygen by supplying tin uniformly and sufficiently, and thereby prevents quality deterioration due to oxidation of the contents. . (Means for Solving the Problems) The welded tin can for packaging of the present invention is formed by forming a tin can material into a cylindrical shape and forming a side seam by welding, and at least the inner surface of the welded can. is 8
A tin plating layer with a coating amount of 15 g/m ² to 15 g/m 2 and a chromium applied to the tin plating layer of 1 to 13 mg/m ²
The chromate layer on the inner surface side is characterized by having grooves uniformly reaching the sparrow layer with a density of 50 to 500 per cm width, which prevents the oxidation of the contents. It becomes possible to effectively suppress the uneven detining phenomenon while preventing the quality deterioration caused by. (Function) In FIG. 1 showing the inner cross-sectional structure of the welded tin can according to the present invention, the surface of the steel substrate 1 has tin-
A tin plating layer 3 is provided with an iron alloy layer 2 interposed therebetween. A chromate layer 4 is provided on the tin plating layer 3. The welded tin can according to the present invention is characterized in that the chromate layer 4 is provided with a groove 5 that reaches the tin plating layer 3. Due to the presence of the chromate layer 4, the tin plating layer 3 is at least partially passivated, and as mentioned above, the uneven elution of tin occurs due to the high acidity and interfacial corrosion at the site of contact with the fruit pulp. However, on the inner surface of the welded tin can of the present invention, the grooves 5 that reach the tin plating layer 3 are uniformly formed in the chromate layer 4, so that acidity and oxygen do not occur between the fruit pulp and the syrup. Even if there is a difference in content concentration, tin is uniformly eluted into the contents through the grooves 5. As a result, according to the present invention, only a portion of tin is eluted, exposing the tin-iron alloy layer 2 and the steel matrix 1, causing iron leaching into the contents, and this non-uniformity. This solves the problem that the black base appears in the pattern of the fruit pulp as tin elutes, spoiling the aesthetic appearance of the inside of the can. Furthermore, sufficient tin is eluted into the contents through the many kerfs 5, making it possible to rapidly remove or inactivate residual oxygen, thereby improving the flavor retention of the contents. In the present invention, the sparrow layer is 8 to 15 g/
It is also important that the amount of coating is less than the ^above range, and the content will be unsatisfactory in terms of its antioxidant effect and prevention of iron elution. Also,
Even if the tin coating amount is increased beyond the above range, there is no particular advantage in terms of the above effects, and it is economically disadvantageous due to an increase in plating cost. Chromate layer is 1 to 13 as chromium (Cr)
It is important to apply the chromate layer at a coating amount of 4 to 10 mg/m ² , especially 4 to 10 mg/m ² .If the chromate layer coating amount is less than the above range, it will prevent abnormal elution of tin into the contents. If the preventive effect is not obtained, and if the amount exceeds the above range, it will be difficult to elute enough tin to prevent oxidative deterioration of the contents, and the grooves leading to the chromate layer may not be leached into the chromate layer. It is also difficult to form the same shape. The kerf 5 provided in the chromate layer 4 has a unit width of 1 cm.
It is also important that they are provided at a density of 50 to 500, especially 100 to 300, per unit. That is, if the density is lower than the above range, no effect of suppressing uneven tin elution can be expected, and on the other hand, if the density is higher than the above range, no effect of preventing abnormal tin elution can be obtained. (Operations and Effects of the Invention) According to the present invention, it is possible to prevent uneven detining in a tin welded can having a tin plating layer and a chromate layer thereon, and to prevent iron elution into the contents. By uniformly and sufficiently supplying tin into the contents, residual oxygen can be rapidly removed or inactivated, thereby making it possible to prevent quality deterioration due to oxidation of the contents. In addition, by using a can material with a specific coating amount of a tin layer and a chromate layer, it is easy to form seams by welding, and the resin coating and outer surface protective coating of the seams have excellent adhesion. It can be easily applied as a. (Description of means of construction) The tin plate used as the material for the can in the present invention may be any known material as long as it satisfies the above-mentioned restrictions. For example, the tin plate may be a no-reflow (matte) tin plate that has been electrically tin plated, or a reflow (bright) tin plate that has been melted after plating. In reflow tin plate, the tin plated layer is melted and densified, and the tin-iron alloy layer formed by mutual diffusion between the steel matrix and the tin layer is formed relatively thick, so it has particularly excellent corrosion resistance. Suitable for problematic packaging applications. On the other hand, with no-reflow tinplate, the tin-iron alloy layer is relatively thin and the amount of tin that can be used to prevent oxidative deterioration of the contents is large, making it particularly suitable for packaging applications where preserving the flavor of the contents is a particular issue. ing. The chromate layer on the sparrow layer may be formed by any method known per se as long as the amount of Cr coated is within the above range. The chromate treatment can be carried out using a known acid bath or alkaline bath, but treatment with an acid bath is generally advantageous. As the acidic bath, a dichromate soda bath is generally used, and if necessary, a degreased and washed tin plate is mixed with the above treatment bath for 40 to 40 minutes.
A chromate layer is formed by treating at a temperature of 80°C for 0.1 to 10 seconds, washing with water, and drying. The thickness of the tin plate used in the present invention is not particularly limited, but is generally 0.15 to 0.35 mm, particularly 0.18 to 0.35 mm.
It is best to keep it within 0.25mm. When manufacturing cans, the outer surface of the can is left unpainted, or a base coating such as epoxy-phenol, epoxy-amino, or epoxy-acrylic is applied, leaving the area that should become the seam, and then printing is applied. ,
If necessary, apply a clear lacquer such as acrylic paint. When printing the above-mentioned can material, welding seams are formed into a cylindrical shape so that the printed surface is the outer surface and the uncoated surface is the inner surface. It is formed by passing it between electrode rollers and performing electric resistance welding. At this time, as described in Japanese Patent Publication No. 60-58098, the welding operation is performed in an inert atmosphere, e.g.
By performing the process in N ₂ , Ar, Ne, and He, and keeping the atmosphere in the above-mentioned inert atmosphere until the surface temperature of the weld zone drops to 550°C, the seam has excellent corrosion resistance and protective coating adhesion. It becomes possible to form The inner surface of the joint can be easily coated by applying a thermoplastic resin such as nylon or a thermosetting resin such as epoxy-phenol resin to the welded joint. In the present invention, the kerfs provided in the chromate layer on the inner surface of the can are provided at a density of 50 to 500 kerfs per 1 cm of unit width, and these kerfs preferably have a certain directionality. In Figures 2-A to 2-D showing several examples of this kerf pattern, the kerf 5 extends straight in the can height direction (Figure 2-A), and horizontally in the can circumferential direction. There are various types such as those that extend (Fig. 2-B), those that are provided in a spiral shape in the can height direction (Fig. 2-C), and those that are provided in a crosshatch shape (Fig. 2-D). It can take a pattern. In order to provide the above-mentioned kerf in the chromate layer on the inner surface of the can, there is a method of rubbing the inner surface of the can body after the welding seam has been formed with a member for forming the kerf, that is, a rubbing material;
A method can be adopted in which a flat material for forming the can body is rubbed against a rubbing material. The chromate layer targeted by the present invention has a significantly small amount of coverage, and the chromate layer is also amorphous, so the above-mentioned grooving treatment is different from ordinary polishing treatment and is a milder treatment. good. For example, cloth, non-woven fabric, leather,
A rubbing material made of a material with a relatively high coefficient of friction such as artificial leather or rubber is used, and if necessary, a polishing agent such as various clays, talc, microcrystalline silicic acid, alumina, etc. is attached to the surface. Then, these materials and the chromate layer may be rubbed together. When performing kerf treatment on the inner surface of the can body, the above-mentioned material is shaped into a disk of a size that just rubs against the inner surface of the can, and this rubbing material and the can body are moved relative to each other in the axial direction. Perform kerfing. In addition, when cutting grooves on a flat can material, the above-mentioned rubbing material can be rolled, for example.
It is preferable to use a form such as a skage blade to rub the two together. The above-mentioned can body is subjected to neck-in processing if necessary, followed by flange processing and double seaming processing with the can lid, and then used as a can for filling fruit pulp, etc. At this time, the can body may be subjected to processing such as multi-bead processing or overhang processing, if desired. Next, examples will be shown. Example 1 A Manufacture of can body Plate thickness 0.23 mm, inner surface tin coating amount 10.5 g/m ² (free tin amount 9.9 g/m ² , tin amount in tin-iron alloy 0.6
g/m ² ) On the surface that should become the outer surface of the can, a tin plate with an outer surface tin coating amount of 2.8 g/m ² , a chromate layer on both the inner and outer surfaces as Cr of 7.1 mg/m ² , and a surface roughness (Ra) of 0.25 μ; Epoxy urea base paint, printing, and clear lacquer were applied except for the areas that should become seams, and this single-sided painted board was cut into a No. 4 can body blank (blank length 233.8 mm, blank height 116.7 mm). This blank was formed into a cylindrical shape using a roll former, and welded using a commercially available seam welding machine for can manufacturing equipped with an inert gas ( _N2 gas) supply nozzle under the following welding conditions. product
Obtain a No. 4 can of 453ml. Electrode: Cu wire wrap width: 0.4mm Welding speed: 45m/min Electrode pressure: 45Kg Primary current value: 39A Epoxy-phenol paint was sprayed only on the joints of the inner and outer surfaces of the resulting can body. A seam coating with a width of about 10 mm and a thickness (after drying) of 10 μm was formed. Additionally, the outer seam was roll coated with epoxy amino paint. For comparison, the can body was subjected to flange processing as it was, and then the easy open end was seamed to produce a can. on the other hand,
For the can body obtained by the above method according to the present invention, a rubbing material (synthetic rubber laminated with cloth, diameter 68 mm, overall length 1.9 mm, rubber A Katasa (JIS A) 81°) attached to one end of the lifting shaft was inserted and slid back and forth in the height direction of the can. As a result of microscopic observation of the inner surface of the can body after rubbing, the density of the grooves was approximately 200 grooves/cm
It was confirmed that there were kerfs leading to the Sparrow layer. When the current value (IEV) was measured for each of the above comparative can bodies and the example can bodies (5 samples) using an IE rater that can determine the degree of iron exposure, the comparative can bodies had an average value of 3.05 mA and a maximum value of 3.34. mA, the minimum value is 2.92mA, and the average value for the can body of the example
3.10mA, maximum value 3.30mA, minimum value 2.95mA, and no difference was observed between the two. On the other hand, in order to know the extent of increase in tin oxide film, (0.1% KCl + 1
%NaH ₂ PO ₄ ) reduce the tin oxide film in the solution,
The amount of electricity required for this was calculated. As a result of measuring the inner surface of the empty can which had been stored at room temperature for 6 months after manufacturing the can, it was 3.4 mc/cm 2 for the example and 3.4 mc/cm ² for the comparative example.
It was 1.4mc/ ^cm2 . In the case of the example, since the chromate film on the metal tin surface was partially removed by a scrubbing machine, the flexible metal tin surface was exposed, and the growth of the tin oxide film was larger than in the comparative example. B. Manufacture of canning 30
The mandarin orange raw material had been treated with dilute hydrochloric acid at 30°C for 45 minutes, then neutralized with alkali at 30°C for 15 minutes, and then exposed to water, and then filled with syrup so that the product temperature after filling was 30°C. The amount of mandarin orange bunches filled was 250 g per can. Using a known double seaming machine, the gauge pressure inside the chamber is 40cmHg.
After reducing the pressure to (absolute) and sealing the lid,
Heat sterilization was performed at a temperature of 82°C for 10 minutes. After aging each canned product at room temperature for 3 days and at 37°C for 17 days, open the can,
The amount of tin eluted and the amount of iron eluted from the contents were measured. In addition, the inner surface of the can was observed after it was opened, and its condition, especially the tin-free condition, was investigated. Furthermore, a sensory test was conducted using three panelists in which they were asked to taste the opened cans of mandarin oranges and rate them as 1 for good and 0 for bad. The results obtained are shown in Table 1 below.

[Table] *1 Interfacial corrosion between the head space and the syrup liquid interface is excluded from the evaluation.
*2 Total evaluation points According to the results in Table 1 above, at the initial stage of filling, the comparison can body has little tin leaching and a considerable amount of iron leaching, whereas the example can body has no tin leaching from the beginning. It is clear that elution is promoted, iron elution is suppressed, uneven tin elution on the inner surface of the can is prevented, and the flavor of mandarin orange is excellent. Example 2 Instead of the tin plate of Example 1, a plate thickness of 0.23 mm and an inner surface tin coating amount of 10.8 g/m ² (free tin amount of 10.2 g/m 2 ) were used.
m ² , tin content in the tin-iron alloy 0.6 g/m ² ), outer surface tin coating amount 2.8 g/m ² , surface chromate layer Cr on the inner and outer surfaces
A welded can body was manufactured in the same manner as in Example 1 except that a tin plate with a surface roughness (Ra) of 4.3 mg/m ² and a surface roughness (Ra) of 0.25 μm was used. For those that have been grooved using rubbing material,
The IEV value is 4.12mA and 4.34 for the untreated one.
It was mA. In addition, as in Example 1, the tin oxide film was measured and found that the kerfing process was not performed.
4.7mc/ ^cm2 , and 2.0mc/cm2 for untreated ones.
It was warm in ^cm2 . When these can bodies were filled with mandarin oranges and subjected to a sealing test, the same results as in Table 1 of Example 1 were obtained.

[Brief explanation of drawings]

FIG. 1 is an enlarged cross-sectional view showing the inner surface side cross-sectional structure of the welded tin can of the present invention, and FIG. 2-A,
FIG. 2-B, FIG. 2-C, and FIG. 2-D are explanatory diagrams showing several examples of groove patterns in the chromate layer. 1 is a steel substrate, 2 is a tin-iron alloy layer, 3 is a tin-metal layer, 4 is a chromate layer, and 5 is a kerf.

Claims (1)

[Scope of Claims] 1. A tin welded can formed by forming a tin can material into a cylindrical shape and forming a side seam by welding, wherein at least the inner surface of the welded can is 8 to 15 g/m ²
, and a chromate layer having a coating amount of 1 to 13 mg/m ² as chromium applied to the tin plating layer, and the chromate layer on the inner surface side has a unit width of 1.
1. A welded tin can for canning, characterized in that it is uniformly provided with grooves extending to the tin plate layer provided at a density of 50 to 500 pieces per cm.