JP4665975B2 - Tinned steel sheet - Google Patents

Description

  The present invention relates to a surface-treated steel sheet for cans used in DI cans, food cans, beverage cans, and the like, and more particularly to a tin-plated steel sheet excellent in workability, paint adhesion, yellowing resistance and rust resistance. .

  Conventionally, tin-plated steel sheet called tinplate has been widely used as a surface-treated steel sheet for cans. Such tin-plated steel sheet is usually used in a dichromic acid solution after tin plating is applied to the tinplate sheet. In general, the chemical conversion treatment is performed by dipping or electrolysis in this solution. The chromium oxide film formed on the tin plating layer by this chemical conversion treatment prevents the growth of Sn oxide and tin plating. It has the effect of suppressing the so-called yellowing in which the surface of the steel sheet turns yellow due to the Sn oxide film (anti-yellowing resistance), and improving the adhesion to the paint and the rust resistance.

  However, due to recent environmental problems, the movement to regulate chromium is progressing in various fields, and the demand for chromium-free surface treatment steel for cans is increasing day by day.

  As a technology related to chromium-free surface treatment steel sheet for cans, for example, Japanese Patent Publication No. Sho 55-24516 discloses Cr on a tin-plated steel sheet by direct current electrolysis using a tin-plated steel sheet as a cathode in a phosphoric acid solution. A surface treatment method of a tin-plated steel sheet on which a chemical conversion film that does not contain is formed is disclosed, and Japanese Patent Publication No. 1-332308 discloses that the chemical conversion film contains P or P and Al and does not contain Cr. An electroplating tin for a seamless can having a chemical conversion film applied to the surface of a tin plating layer is disclosed.

  However, when comprehensively looking at performance such as paint adhesion, yellowing resistance, rust resistance, etc., all of the chemical conversion films described in the above publications are compared with chemical conversion films formed by conventional dichromic acid solutions. It cannot be said that the above performance is sufficiently obtained.

  Moreover, as a request | requirement with respect to the surface treatment steel plate for cans, the cost reduction as a raw material for cans is mentioned besides the chromium-free-ization mentioned above. Particularly in tin-plated steel sheets, tin is an expensive metal, and therefore the amount of tin-plated coating is being reduced.

  However, tin is a highly lubricious metal, and reducing the amount of tin plating reduces the workability, so there is a limit to reducing the amount of tin plating.

  Furthermore, in the case of a conventional tin-plated steel sheet in which a chromium oxide film is formed on the tin plating layer, the chromium oxide film is advantageous in terms of corrosion resistance but is hard, so that the tin plating as described above. When the amount is reduced, “galling” is likely to occur in the can making process, and the workability is deteriorated. Therefore, the film is not always optimal.

  The object of the present invention is that the chemical conversion film formed on the upper layer of the tin plating layer has the effect of improving its film characteristics, but does not contain Cr, which is undesirable due to environmental problems, The object is to provide a tin-plated steel sheet excellent in paint adhesion, yellowing resistance and rust resistance at low cost.

The present invention is described in further detail below.
When a conversion coating that does not contain Cr is formed on the tin plating layer using the above-mentioned conventional technology, it is difficult to satisfy all of the workability, paint adhesion, yellowing resistance, and rust resistance performance. Met.

  For this reason, as a result of intensive studies to solve the above-mentioned problems in the tin-plated steel sheet, the inventors have formed a chemical conversion film containing two elements of P and Sn on the upper layer of the Sn plating layer. Furthermore, it has been found that when the silane treatment with a silane coupling agent is further performed on the upper layer, all of the above performances can be satisfied.

  More specifically, by forming a chemical conversion film containing an appropriate amount of P and Sn on the upper layer of the tin plating layer, the lubricity is improved, and accordingly, the workability is improved. By further forming a silane coupling layer on the upper layer of the film, the reactive groups present in the silane coupling layer are oriented and greatly contribute to the adhesion to the can inner surface coating, that is, the above-mentioned P and Sn. The chemical conversion film plays a role as an anchor effect for paint adhesion, and the silane coupling layer improves compatibility and reactivity with the paint. all right. In addition, it has also been found that yellowing resistance and rust resistance are improved by the barrier effect of both the chemical conversion film and the silane coupling layer.

The tin-plated steel sheet of the present invention has a chemical conversion film containing P and Sn and not containing Cr in the upper layer of the tin plating layer formed on the steel sheet surface, and the P content in the chemical conversion film is adhered to the tin-plated steel sheet. The amount is in the range of 0.5 to 100 mg / m ² , the Sn content is in the range of 0.01 to 60 in terms of the ratio of the deposited amount to the P deposited amount, and a silane coupling layer is further formed on the chemical conversion film. And having an adhesion amount of the silane coupling layer in the range of 0.1 to 250 mg / m ² in terms of Si adhesion amount, the silane coupling layer has an alcohol content of 77 mass% or more and a silane coupling agent of 0.5 to 20 mass. %, And after applying a solution containing 3% by mass or less of water, the steel sheet is dried so that the surface temperature reaches 50 to 130 ° C.

The present invention includes a chemical conversion film formed on the tin plating layer and a silane coupling layer without containing Cr, which has an effect of improving the film characteristics, but is undesirable due to environmental problems. There is a remarkable effect that a tin-plated steel sheet excellent in workability, paint adhesion, yellowing resistance and rust resistance can be provided.
In addition, the tin-plated steel sheet according to the present invention has a chemical conversion film that can maintain excellent workability in the upper layer of the tin-plated layer even if the amount of the tin-plated layer is reduced as compared with the conventional tin-plated steel sheet. There is also an effect that the cost can be reduced.

The configuration of the present invention will be described in detail below.
The tin-plated steel sheet according to the present invention is obtained by applying a Sn plating layer on a normal tin plate and applying a general treatment (reflow treatment) for heating and melting Sn. Consists of a Fe—Sn alloy layer and a metal Sn layer. In addition, in this invention, it is preferable that the plating adhesion amount of Sn plating layer shall be 0.4-3.5 g / m < ² > per single side | surface. This is because when the adhesion amount is less than 0.4 g / m ² , the rust resistance is poor, and when it exceeds 3.5 g / m ² , the cost reduction effect cannot be obtained sufficiently.

And the main characteristic on the structure of this invention has P and Sn in the upper layer of the tin plating layer formed in the steel plate surface, has a chemical conversion film which does not contain Cr, and contains P in this chemical conversion film amounts, in the range of 0.5 to 100 mg / m ² and its adhesion amount, the Sn content in the range of 0.01 to 60 in the ratio of P adhering amount of the deposition amount, further, an upper layer of the conversion coating, It has a silane coupling layer, and the adhesion amount of the silane coupling layer is in the range of 0.1 to 250 mg / m ² in terms of Si adhesion amount, and the silane coupling layer contains 77 mass% or more of alcohol and silane coupling. After applying a solution containing 0.5 to 20 mass% of the agent and 3 mass% or less of the remaining agent, the steel sheet is dried so that the surface temperature reaches 50 to 130 ° C.

(1) P content of that conversion coating in which the P content range of 0.5 to 100 mg / m ² and its adhesion amount in the chemical conversion coating, a range of 0.5 to 100 mg / m ² and its adhesion amount It is necessary to. If it is less than 0.5 mg / m ² , processability, paint adhesion and yellowing resistance are not sufficiently obtained, and if it exceeds 100 mg / m ² , defects are likely to occur in the conversion coating, and paint adhesion and workability deteriorate. Because it does.
In addition, the P adhesion amount was measured by surface analysis using fluorescent X-rays.

  In addition, as a method for forming a chemical conversion film containing P, for example, it is preferable to carry out by a phosphoric acid-based chemical conversion treatment. It is more preferable to use a metal salt such as sodium, aluminum phosphate or potassium phosphate, or a monohydrogen phosphate.

(2) The Sn content in the chemical conversion film should be in the range of 0.01 to 60 in terms of the ratio of the adhesion amount to the P adhesion amount. The Sn content in the chemical conversion film is to form the most stable tin phosphate film. The ratio of Sn deposition to P deposition needs to be in the range of 0.01 to 60. In particular, within this appropriate range, it is possible to impart lubricity to the chemical conversion coating itself and improve workability.
If the ratio is less than 0.01, unreacted phosphoric acid remains in the chemical conversion film, resulting in deterioration of paint adhesion and yellowing resistance. If the ratio exceeds 60, the chemical conversion film has defects. This is because it tends to occur and rust resistance and paint adhesion deteriorate. In addition, Sn adhesion amount can be measured by a coulometric method or surface analysis by fluorescent X-rays.

  In addition, as a method for forming a chemical conversion film containing Sn, for example, stannous chloride, stannic chloride, stannous sulfate or the like having Sn ions may be added to the phosphoric acid-based chemical conversion treatment solution. Preferably, this makes it possible to form insoluble and most stable tin phosphate in the upper layer of the tin plating layer.

(3) An upper layer of the chemical conversion film has a silane coupling layer, and the adhesion amount of the silane coupling layer is set to a range of 0.1 to 250 mg / m ² as Si adhesion amount. After applying a solution containing 77 mass% or more of alcohol, 0.5 to 20 mass% of silane coupling agent, and 3 mass% or less of the remainder, the steel sheet is dried so that the surface temperature reaches 50 to 130 ° C. In the present invention, it is important to form a silane coupling layer having an appropriate adhesion amount on the chemical conversion film. The silane coupling layer can be formed, for example, by silane treatment using a silane coupling agent. The general chemical formula of the silane coupling agent is X—Si—OR _2or3 (OR: alkoxy group).

  In the silane coupling agent, an alkoxysilyl group (Si—OR) is hydrolyzed with water to form a silanol group, and is adhered to each other by a dehydration condensation reaction with —OH on the surface of the steel sheet. In addition, a reactive group corresponding to X in the general chemical formula is oriented in the upper layer of the steel sheet, and is compatible or bonded with a resin such as a paint.

Examples of the silane coupling agent include γ-methacryloxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-2- ( Aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, γ-mercaptopropyl Methoxysilane, γ-chloropropyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, and the like can be used, and in particular, an epoxy group in X of X-Si-OR _2or3 in the general chemical formula of the silane coupling agent Β- (3,4- Poxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) 3 in the presence of amino group -Aminopropylmethyldimethoxysilane and γ-aminopropyltriethoxysilane are preferred. This is because of excellent compatibility and reactivity with the epoxy paint used on the inner surface of the can.

  If further explanation is added in terms of improving the adhesion, the silane coupling layer is formed on the Sn plating layer after forming a chemical film containing P and Sn rather than directly forming the silane coupling layer on the Sn plating layer. The effect of improving the paint adhesion is greater when formed on top. That is, it is considered that the paint adhesion is improved by a synergistic effect of the anchor effect by the chemical conversion film containing P and Sn and the excellent compatibility and reactivity with the coating film by the silane coupling layer.

In the present invention, the adhesion amount of the silane coupling layer is set to a range of 0.1 to 250 mg / m ² in terms of the Si adhesion amount as a range in which the effect of improving adhesion is remarkably exhibited. If it is less than 0.1 mg / m ² , the coverage of the silane coupling layer is small and the effect of improving adhesion cannot be sufficiently obtained. If it exceeds 250 mg / m ² , the unreacted silane coupling agent is self This is because condensation improves the effect of improving adhesion.

The silane coupling agent treatment can be performed by applying a solution obtained by diluting the silane coupling agent in water. In the present invention, a solution diluted with alcohol is used. Specifically, by using a solution containing 77 mass% or more of an alcohol such as ethanol , 0.5 to 20 mass% of a silane coupling agent, and 3 mass% or less of the remainder, the occurrence of repellency is prevented. It can be uniformly applied to a steel plate.

Temperature of the silane coupling agent treatment, in the range of 50 to 130 ° C.. If the temperature is lower than 50 ° C, a dehydration condensation reaction between —OH on the surface of the steel sheet and the alkoxy group of the silane coupling agent does not occur, and a healthy silane coupling layer may not be formed. This is because although no problem occurs with respect to adhesion, discoloration of Sn plating is likely to occur.

  From the above, in the present invention, by sequentially forming a chemical conversion film containing P and Sn in the appropriate range and an appropriate adhesion amount of the silane coupling layer on the tin plating layer formed on the steel plate surface. It succeeded in satisfying all the performances of workability, paint adhesion, yellowing resistance and rust resistance.

Next, an example of a specific manufacturing method according to the present invention will be described.
After Sn plating is applied to a normal tin plate, a heat melting (reflow) treatment is performed at a temperature equal to or higher than the melting point of tin (231.9 ° C.). Subsequently, after a cathode treatment of 1 C / dm ^{2 in} a 15 g / l sodium carbonate aqueous solution, a chemical conversion treatment is carried out by a known method such as dipping, electrolysis, spraying or roll coating.

  As the chemical conversion treatment liquid, 1-80 g / l of phosphoric acid, sodium phosphate, aluminum phosphate, potassium phosphate and other metal salts in terms of phosphate ions, and / or monohydrogen phosphate, and tin ions A solution obtained by dissolving 0.001 to 10 g / l of stannous chloride, stannic chloride, and / or stannous sulfate in water in terms of conversion is used. At this time, an oxidizing agent such as sodium chlorate may be appropriately added as an accelerator.

  The conditions for the chemical conversion treatment are preferably a temperature of 40 to 60 ° C. and a treatment (immersion) time of 1 to 5 seconds. The tin-plated steel sheet after the chemical conversion treatment is dried with hot air of 35 to 120 ° C.

The silane coupling agent treatment for forming the silane coupling layer is, for example, a solution in which alcohol such as ethanol is 77 mass% or more, silane coupling agent is 0.5 to 20 mass%, and the rest is water of 3 mass% or less. And uniformly applied to the steel plate. Drying is performed so that the steel sheet surface temperature reaches 50 to 130 ° C.

  The above description only shows an example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

Next, embodiments of the present invention will be described in detail below.
Examples 1 to 21
After applying a tin plating layer with an adhesion amount of 0.4 to 2.8 g / m ² per side to a T4 original plate with a thickness of 0.3 mm, reflow treatment was performed, followed by 1 C / dm ^{2 in a} 15 g / l sodium carbonate aqueous solution. After performing the cathode treatment under the conditions, a chemical conversion film was formed under the chemical conversion treatment conditions shown in Table 1, and a silane coupling layer was further formed under the formation conditions shown in Table 1. Table 2 shows the composition of the chemical conversion film and the silane coupling layer formed at this time.

・ Comparative Examples 1-9
For comparison, a tin-plated steel sheet in which at least one of the chemical conversion film condition and the silane coupling layer formation condition is outside the proper range of the present invention was also produced.

(Performance evaluation)
Each tin-plated steel sheet of Examples 1 to 21 and Comparative Examples 1 to 9 was evaluated for workability, paint adhesion, yellowing resistance and rust resistance.

(1) Workability The workability was evaluated based on the appearance of defects such as wrinkles and galling after the drawing and ironing. Table 2 shows the evaluation results. In Table 2, a case where no defects such as wrinkles or gallings are recognized is indicated by “◯”, and a case where the defects are recognized is indicated by “x”. Drawing and ironing was performed under the following conditions.

Blank diameter: 170mmφ
Aperture condition: 1.8 aperture ratio, 1.8 aperture ratio, 1.3 aperture ratio
Diaphragm ironing diameter: 3-stage ironing 60mmφ

(2) Paint adhesion The paint adhesion was evaluated by the following test method.
An epoxy phenol-based paint having an adhesion amount of 50 mg / dm ² was applied to the surface of each tin-plated steel sheet, and then baked at 210 ° C. for 10 minutes. Next, after laminating the two coated and baked tin-plated steel sheets with the coated surfaces facing each other across the nylon adhesive film, the pressure was 2.94 × 105 Pa, the temperature was 190 ° C., and the crimping time was 30 seconds. The samples were bonded together under pressure bonding conditions, and then divided into 5 mm wide test pieces. The test pieces were subjected to strength measurement using a tensile tester, and the primary paint adhesion was evaluated from the measurement results. In addition, another test piece was immersed in a 1.5 mass% NaCl + 1.5 mass% citric acid solution at 55 ° C. for 7 days. Evaluated. The evaluation results are shown in Table 2. In Table 2, when the measured intensity per 5 mm test piece width is 68.6 [N] or more, “◎”, when it is 49.0 [N] or more and less than 68.6 [N], “○”, 29.4 [N] or more. The case of less than 49.0 [N] is indicated by “Δ” and the case of less than 29.4 [N] is indicated by “x”.

(3) Yellowing resistance Each of the above tin-plated steel sheets was left in a constant temperature and humidity chamber at a temperature of 40 ° C. and a relative humidity of 85% for 60 days, and then the surface discoloration was observed to evaluate yellowing resistance. The evaluation results are shown in Table 2. In Table 2, a case where no discoloration is recognized is shown as “◯”, and a case where discoloration is recognized is shown as “x”.

(4) Rust resistance For each of the above tin-plated steel plates, an environment in which a high humidity state at a temperature of 50 ° C. and a relative humidity of 98% and a dry state at a temperature of 25 ° C. and a relative humidity of 60% are alternately repeated every 30 minutes. The number of days until rust was generated on the surface was examined, and thereby the rust resistance was evaluated. The evaluation results are shown in Table 2. In Table 2, “○” indicates that rust is not observed for 30 days or longer, “△” indicates that rust is generated for 15 days or more and less than 30 days, and rust is generated for 15 days. The case where it was recognized in less than is shown as "x".

  As is clear from the results in Table 2, Examples 1 to 21 were all excellent in terms of workability, paint adhesion, yellowing resistance, and rust resistance. On the other hand, Comparative Examples 1 to 9 in which at least one of the chemical film conditions and the formation conditions of the silane coupling layer is outside the proper range of the present invention is any one of workability, paint adhesion, yellowing resistance and rust resistance. It can be seen that the performance is poor and not at a practical level.

The present invention includes a chemical conversion film formed on the tin plating layer and a silane coupling layer without containing Cr, which has an effect of improving the film characteristics, but is undesirable due to environmental problems. There is a remarkable effect that a tin-plated steel sheet excellent in workability, paint adhesion, yellowing resistance and rust resistance can be provided.
In addition, the tin-plated steel sheet according to the present invention has a chemical conversion film that can maintain excellent workability in the upper layer of the tin-plated layer even if the amount of the tin-plated layer is reduced as compared with the conventional tin-plated steel sheet. There is also an effect that the cost can be reduced.

Claims (1)

An upper layer of the tin plating layer formed on the steel sheet surface has a chemical conversion film containing P and Sn and not containing Cr, and the P content in the chemical conversion film is 0.5 to 100 mg / m in terms of the amount of adhesion. ^The Sn content is in the range of 0.01 to 60 in terms of the ratio of the deposited amount to the P deposited amount, and further has a silane coupling layer as an upper layer of the chemical film, and the silane coupling layer The adhesion amount of Si is 0.1 to 250 mg / m ² in terms of Si adhesion amount, and the silane coupling layer has an alcohol content of 77 mass% or more, a silane coupling agent of 0.5 to 20 mass%, and the remainder of 3 mass% or less. A tin-plated steel sheet, which is formed by applying a water solution and then drying so that the steel sheet surface temperature reaches 50 to 130 ° C.