Coating material, oriented silicon steel sheet having a coating formed from the coating material, and method for producing the same

Abstract

The present invention relates to a coating material for surface coating of grain-oriented silicon steel. The coating material has: a phosphate; colloidal silica; and at least one vanadate selected from vanadates of Ce, Mn, Co, Cu or Fe. The coating material does not have Cr. The present invention further relates to grain-oriented silicon steel having a surface coating formed from the coating material. The present invention further relates to a method for manufacturing grain-oriented silicon steel having a surface coating formed from the coating material. The coating material of the present invention does not have chromium. The coating formed from the coating material can provide sufficient moisture absorption resistance while protecting the environment, and can apply sufficient tension to the grain-oriented silicon steel sheet, so that the iron loss and magnetostriction of the grain-oriented silicon steel are further reduced, and a high-quality iron core material for transformers can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of steel plate coating, and particularly to a coating material for surface coating of grain-oriented silicon steel, a grain-oriented silicon steel plate having the surface coating, and a method for manufacturing the same.

Background Art

[0002] A grain-oriented silicon steel plate refers to a steel plate obtained by cold rolling and heat treatment processes, having a silicon content in the range of 2.8 wt% to 3.5 wt% and a {110}<001> texture. The magnetic properties along its rolling direction are significantly better than those in the transverse direction. Grain-oriented silicon steel plates are mainly applied as core materials for transformers. In order to reduce the energy loss and noise level of transformers, it is preferable for grain-oriented silicon steel plates to have low iron loss and low noise. Currently, it is known that by applying an appropriate tensile stress to a grain-oriented silicon steel plate, the iron loss value and magnetostriction value of the grain-oriented silicon steel plate can be reduced.

[0003] In the prior art, usually, the above problems are solved by applying a chromium-containing coating on the surface of a grain-oriented silicon steel plate. The chromium-containing coating has good insulating properties. Furthermore, the coating generates a tensile stress on the steel plate, thereby reducing the iron loss and magnetostriction value of the steel plate due to the different thermal expansion coefficients of the coating and the steel plate during heat treatment. However, since the coating solution used for the coating contains hexavalent chromium, the waste liquid generated during its production will have a large amount of hexavalent chromium harmful to the environment and will seriously pollute the environment.

[0004] In recent years, there has been an increasing concern for environmental protection, and the demand for products without harmful substances such as chromium and lead has been on the rise. For grain-oriented silicon steel, the development of chromium-free coatings (coatings without chromium) is also expected. However, grain-oriented silicon steel using chromium-free coatings usually suffers from a significant decrease in moisture absorption resistance and insufficient tension development, which has been a problem. Therefore, chromium-free coatings are hardly used or cannot be adopted.

[0005] The Chinese patent document (publication number: CN101790599A, publication date: July 28, 2010) titled "Insulating Coating Film Treatment Solution for Grain-Oriented Electromagnetic Steel Sheet and Method for Manufacturing Grain-Oriented Electromagnetic Steel Sheet with Insulating Coating Film" discloses an insulating coating film treatment solution for chromium-free grain-oriented electromagnetic steel sheets, which has at least one phosphate of Mg, Ca, Ba, Sr, Zn, Al, and Mn, and a chelate of colloidal silica and titanium. It can improve the adhesion and the tension of the coating. However, the chelate tends to decompose during heat treatment to generate carbon, which has an adverse effect on the tension of the coating.

[0006] The Chinese patent document (publication number: CN101223300A, publication date: July 16, 2008) titled "Grain-Oriented Electromagnetic Steel Sheet with Chromium-Free Insulating Coating and Insulating Coating Agent Therefor" discloses a chromium-free insulating coating agent for grain-oriented electromagnetic steel sheets. Its main components are phosphates, colloidal silica, and inorganic compounds of Fe, Ni, Co, Cu, Sr, or Mo with a particle size of 15 nm or less, such as hydroxides, oxides, carbonates, silicates, and molybdates. However, hydroxide colloids are not stable in a phosphate solution system, and their ability to fix free phosphate radicals is not sufficient, so they can easily reduce the moisture absorption resistance and anti-adhesion properties of grain-oriented silicon steel sheets.

[0007] The Chinese patent document (publication number: CN102119239A, publication date: July 6, 2011) titled "Chromium-free coating agent for grain-oriented electrical steel sheet, its preparation method, electrical steel sheet using the same, and its manufacturing method" discloses a chromium-free coating agent for grain-oriented electrical steel sheet having phosphate, colloidal silica, and hematite silicon sol. However, since hematite silicon sol is difficult to stably exist in a phosphate system and its preparation is also difficult, it is difficult to achieve industrial production.

[0008] In view of the above problems, it is expected to obtain a coating material for grain-oriented silicon steel that meets the requirements of industrial production, is chromium-free, remains stable during heat treatment, and has good coating performance. In addition, the surface coating of the grain-oriented steel sheet obtained by this coating material has good moisture absorption resistance, corrosion resistance, heat resistance, and anti-adhesion properties, and can provide a sufficient tension effect to further reduce the iron loss and magnetostriction of the grain-oriented silicon steel.

Summary of the Invention

[0009] The object of the present invention is to provide a coating material for surface coating of grain-oriented silicon steel. This coating material does not contain chromium. Thereby, good moisture absorption resistance, tension, corrosion resistance, heat resistance, and anti-adhesion properties can be provided to the grain-oriented silicon steel, and while protecting the environment, the iron loss and magnetostriction of the grain-oriented silicon steel can be further reduced.

[0010] In order to achieve the above object, the inventors of the present invention have unexpectedly found that by using a combination of at least one vanadate selected from Ce, Mn, Co, Cu, and Fe and a phosphate in a coating material, vanadate and phosphate radicals in the phosphate form an insoluble substance during the heat treatment of the coating material. As a result, the phosphate radicals are fixed, and an effect of applying tension to the grain-oriented silicon steel is obtained. Therefore, a coating with good moisture absorption resistance, tension, corrosion resistance, heat resistance, and anti-adhesion is formed on the surface of the grain-oriented silicon steel, and thereby, a grain-oriented silicon steel with good iron loss and magnetostriction can be obtained.

[0011] The present invention relates to a coating material for surface coating of grain-oriented silicon steel, and the coating material: has a phosphate; has colloidal silica; and has at least one vanadate selected from vanadates of Ce, Mn, Co, Cu or Fe; the coating material does not have Cr.

[0012] After applying the above-described coating material on a grain-oriented silicon steel sheet, the coating material is heat-treated to surely form a coating, and the phosphate can form a phosphate coating having a network or chain structure on the steel sheet surface after heat treatment. In the present invention, colloidal silica is used as a filler, and by forming a ceramic layer with a small coefficient of thermal expansion after heat treatment, tension is provided to the coating, which is beneficial for improving the coating performance of the coating material. In the present invention, "colloidal silica" generally refers to an aqueous dispersion of nanoscale silica having silanol groups. During the heat treatment, Ce, Mn, Co, Cu, Fe, and V in the vanadate can form an insoluble phosphate compound with the phosphate radicals in the phosphate, whereby the phosphate radicals are fixed on the grain-oriented silicon steel, and free phosphate radicals are prevented from remaining in the coating. Therefore, the moisture absorption resistance, tension, corrosion resistance, and anti-adhesion of the coating can be improved.

[0013] In the present invention, the vanadate is not particularly limited as long as it can form insoluble vanadium phosphate together with the phosphate radical. Examples of the vanadate include orthovanadate, pyrophosphate, or metavanadate. Preferably, the vanadate is an orthovanadate of Ce, Mn, Co, Cu, or Fe (VO4 3- ), pyrophosphate (V2O7 4- ), and / or metavanadate (VO3 - ).

[0014] Preferably, the coating material has, by mass%, 25 to 50% of phosphate, 25 to 50% of colloidal silica, and 10 to 50% of vanadate.

[0015] Preferably, the phosphate is at least one selected from phosphates of Mg, Al, Ca, Zn, and Mn.

[0016] Preferably, the phosphate is magnesium dihydrogen phosphate, aluminum dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, and manganese dihydrogen phosphate.

[0017] Preferably, the mass ratio of colloidal silica to phosphate is 0.5 to 1.5, preferably 1.0 to 1.5. Within this range, good coating performance can be obtained, which is beneficial for improving the coating performance of the coating material of the present invention.

[0018] Preferably, the mass ratio of vanadate to phosphate is 0.2 to 2.0, preferably 0.2 to 1.5, more preferably 0.2 to 1.0, and even more preferably 0.2 to 0.5.

[0019] In the technical solution of the present invention, when the mass ratio of at least one vanadate (such as orthovanadate, pyrophosphate vanadate, metavanadate, etc.) to phosphate is 0.2 or more, the moisture absorption resistance of the coating can be significantly improved. However, when the mass ratio of vanadate to phosphate exceeds 2.0, the tension and corrosion resistance of the coating will decrease. Therefore, in the coating material for the grain-oriented silicon steel sheet of the present invention, the mass ratio of vanadate to phosphate is limited to 0.2 to 2.0.

[0020] Preferably, the coating material for the surface coating of the grain-oriented silicon steel also has boric acid. By adding boric acid to the coating material, the sintering density, tension, and heat resistance of the coating can be further improved.

[0021] Preferably, the content of boric acid is 0.02 to 0.2 parts by mass with respect to 100 parts by mass of colloidal silica.

[0022] By adding an appropriate amount of boric acid, the sintering density, tension, and heat resistance of the coating can be further improved. However, when the mass ratio of boric acid to colloidal silica exceeds 0.2, the tension effect, heat resistance, and corrosion resistance will decrease. Therefore, in the coating material of the present invention, the mass ratio of boric acid to colloidal silica is limited to the range of 0.02 to 0.2.

[0023] Preferably, the particle size of the colloidal silica is 5 to 50 nm. Adjusting the particle size of the colloidal silica is beneficial for forming a dense ceramic layer after heat treatment and obtaining a better tension effect and coating surface morphology.

[0024] The present invention also provides a grain-oriented silicon steel sheet. The grain-oriented silicon steel sheet includes a substrate and a coating formed on the surface of the substrate. The coating is formed from the coating material described above. By the coating of the coating material formed on the surface of the grain-oriented silicon steel sheet of the present invention, the iron loss value and the magnetostriction value of the grain-oriented silicon steel sheet are reduced, and the tensile stress exerted by the coating of the grain-oriented silicon steel sheet is utilized to make it suitable as a material for transformers, and effectively reduce the energy loss and noise level of the transformers.

[0025] Preferably, the phosphate in the coating forms a network or chain structure.

[0026] Preferably, the coating has vanadium phosphate.

[0027] Preferably, in the grain-oriented silicon steel sheet of the present invention, the dry film thickness of the coating is 2 to 10 g / m on one side 2 is. If the dry film thickness on one side of the coating is less than 2 g / m 2 the coating cannot provide sufficient tension, and if the dry film thickness on one side of the coating exceeds 10 g / m 2 the amount of the coating material becomes too large, so that the thickness of the coating after heat treatment becomes non-uniform, and it is likely to cause a decrease in the lamination coefficient of the steel sheet.

[0028] The substrate of the grain-oriented silicon steel of the present invention is not particularly limited. A grain-oriented silicon steel substrate generally used in the art can be used. For example, a grain-oriented silicon steel substrate having a Si element content of 2 to 4 wt% can be used.

[0029] Preferably, the thickness of the substrate is 0.18 to 0.35 mm.

[0030] Preferably, the grain-oriented silicon steel sheet also has a magnesium silicate bottom layer, which is formed by the reaction of a separating agent (usually MgO) on the steel sheet surface with silicon oxide (SiO2) under high-temperature annealing conditions (e.g., 1200 °C). The silicon oxide bottom layer is located between the substrate and the coating of the grain-oriented silicon steel sheet, thereby enhancing the adhesion between the coating and the steel sheet.

[0031] Preferably, the coating of the grain-oriented silicon steel sheet has a tension of 7.1 to 10.5 MPa and a phosphorus elution content lower than 75 μg / 150 cm 2

[0032] The present invention further provides a method for manufacturing a grain-oriented silicon steel sheet, the surface of the grain-oriented silicon steel sheet having a coating formed from the above-described coating material, the manufacturing method comprising the following steps: 1) A step of applying the above-described coating material onto the substrate of the grain-oriented silicon steel sheet to form a coating on the surface of the substrate of the grain-oriented silicon steel sheet; and 2) A sintering step.

[0033] Preferably, in step 2), sintering is carried out under the conditions that the substrate surface temperature is 800 to 900 °C and the sintering time is 20 seconds or more. If the temperature is less than 800 °C, the flatness of the steel sheet will be insufficient, and the tension effect imparted by the coating to the steel sheet will not be significant. If the temperature exceeds 900 °C, the silica in the coating will be prone to crystallization, and the denseness and tension effect of the coating will decrease.

[0034] Preferably, the coating material is applied onto the substrate of the grain-oriented silicon steel sheet in the form of an aqueous solution.

[0035] Preferably, the manufacturing method satisfies at least one of the following: The coating material is applied with a dry film amount of 2 to 10 g / m on one side of the substrate 2 ; The manufacturing method also includes forming a magnesium silicate layer between the substrate and the coating.​

[0036] Compared with the prior art, the directional silicon steel sheet having the coating material of the present invention and the coating formed from the coating material has the following beneficial effects: (1) The coating material of the present invention does not contain the harmful metal element chromium, and has little pollution to the surrounding environment, and has good environmental advantages; (2) The coating material of the present invention has good stability and coating performance, and can achieve industrial production and use; and (3) The surface coating of the directional silicon steel sheet according to the present invention has good moisture absorption resistance, tensile strength, corrosion resistance, heat resistance, and anti-adhesion properties, whereby the iron loss and magnetic strain of the directional silicon steel can be further reduced.

Embodiments for Carrying Out the Invention

[0037] Detailed Description of Embodiments A more detailed description of the present invention is provided by way of examples, which will increase clarity and facilitate a better understanding of its content. However, it should be noted that the examples disclosed below are merely illustrative examples of the detailed description of the embodiments of the present invention. The present invention is not limited to these examples.

[0038] 1. Preparation of a Coating Material for Surface Coating of Grain-Oriented Silicon Steel The coating materials for the surface coatings of the directional silicon steels of Examples 1 to 28 and Comparative Examples 1 to 6 of the present invention were prepared by the following method: According to the formulations listed in Table 1, a phosphate solution and colloidal silica were directly mixed, and then boric acid was optionally added in the form of a solid reagent (boric acid was not added in Example 28). After sufficient stirring to completely dissolve the boric acid, vanadate powder was added to the solution in the form of high-speed dispersion or ultrasonic dispersion to form the coating material.

[0039] Table 1 lists the mass % (wt%) of each component in the coating materials of Examples 1 to 28 and Comparative Examples 1 to 6, and the particle size of the colloidal silica. Among these, the amounts of vanadates in Comparative Examples 1 to 6 do not meet the requirement of the present invention that the mass ratio of vanadate to phosphate is 0.2 to 2.0.

[0040]

Table 1-1

[0041]

Table 1-2

[0042]

Table 1-3

[0043]

Table 1-4

[0044] 2. Manufacture of a Grain-Oriented Silicon Steel Sheet Having a Surface Coating The coating materials of Examples 1 to 28 and Comparative Examples 1 to 6 were applied onto the substrates of grain-oriented silicon steel sheets. Each grain-oriented silicon steel sheet having a coating formed from the coating material was obtained by the following steps (the main technical parameters are shown in Table 2), where the substrate of the grain-oriented silicon steel sheet has the following chemical elements, and the mass % of the chemical elements are: C: 0.046%, Si: 3.32%, S: 0.006%, soluble Al: 0.027%, N: 0.006%, Mn: 0.012%, and the balance is Fe and other inevitable impurities: (1) A step of smelting and casting based on the mass % of each of the above chemical elements to obtain a steel slab. (2) A step of heating the steel slab at 1150 °C and then hot-rolling it into a hot-rolled sheet with a thickness of 2.8 mm. (3) A step of pickling the hot-rolled sheet and then cold-rolling it into a cold-rolled sheet with a thickness of 0.18 to 0.35 mm. (4) After decarburization annealing, the cold-rolled sheet is subjected to continuous nitriding treatment in a wet ammonia-filled nitrogen and hydrogen protective atmosphere. (5) A step of coating the magnesium oxide-based release agent on the steel sheet after nitriding treatment. (6) After winding the steel sheet into a coil shape, secondary recrystallization annealing is performed in a dry protective atmosphere (such as a mixture of nitrogen and hydrogen). The annealing temperature is maintained at 1200 °C for 20 hours to obtain a substrate with a Gaussian texture covered with a bottom layer of magnesium silicate on the surface. (7) A step of coating the surface of the substrate with the coating material of the present invention. (8) A step of sintering at 800 to 900 °C for 20 seconds or more to obtain a grain-oriented silicon steel sheet having a surface coating. The dry film coating amount of the surface coating is 2 to 10 g / m on one side 2 is.

[0045] Table 2 shows the main process parameters of the manufacturing methods of the grain-oriented silicon steel sheets of Examples 1 to 28 and Comparative Examples 1 to 6.

[0046]

Table 2-1

[0047]

Table 2-2

[0048] 3. Performance Evaluation of a Grain-Oriented Silicon Steel Sheet Having a Surface Coating The grain-oriented silicon steel sheets of Examples 1 to 28 and Comparative Examples 1 to 6 of the present invention were subjected to performance tests including tests on the coating tension, moisture absorption resistance, heat resistance, corrosion resistance, and anti-adhesion properties. The test methods are as follows: (1) Coating tension σ: With the rolling direction as the length direction, the grain-oriented silicon steel sheet was cut into a sample plate with a length of 300 mm and a width of 30 mm. Then, the coating was removed, the sample plate was bent to measure the amount of warp, and the coating tension σ was calculated by the following formula.

[0049]

Equation

[0050] In the above formula, σ represents the coating tension, and its unit can be MPa; E represents the Young's modulus of the steel plate, and its unit can be GPa; t represents the thickness of the steel plate, and its unit can be mm; H represents the amount of warp, and its unit can be mm; L represents the length of the steel plate, and its unit can be mm. (2) Moisture absorption resistance: After boiling the grain-oriented silicon steel sheet in pure water at 100 °C, the phosphorus content eluted in the coating per unit area was quantitatively analyzed in μg / 150 cm 2 . (3) Heat resistance: The deterioration of the coating tension and insulation of the surface coating of the grain-oriented silicon steel sheet after stress relief annealing treatment was tested. The process conditions of the stress relief annealing treatment were 850 °C and 4 hours under 100% N2 gas. The heat resistance was evaluated in four grades: excellent (decrease in tension and insulation < 20%), good (20% ≤ decrease in tension and insulation < 30%), medium (30% ≤ decrease in tension and insulation < 40%), and poor (decrease in tension and insulation ≥ 40%). (4) Corrosion resistance: The corrosion resistance of the coating was evaluated by a salt spray test. The salt spray test solution was a 5% NaCl solution, the test temperature was 35 °C, and the test time was 10 hours. The evaluation of the corrosion resistance was in four grades: excellent (rust area < 5%), good (5% ≤ rust area < 10%), medium (10% ≤ rust area < 30%), and poor (rust area ≥ 30%). (5) Adhesion resistance: Grain-oriented silicon steel sheets of the same size were laminated, and a pressure of 80 kg / cm 2 was applied vertically to the surface of the laminated grain-oriented silicon steel sheets. Then, heat treatment was performed at 850 °C for 4 hours in N2 gas with a dew point of 10 °C. The average value of the peeling force F between each grain-oriented silicon steel sheet was measured to evaluate the adhesion resistance of the coating. The smaller the peeling force, the better the adhesion resistance. The evaluation of the adhesion resistance was in four grades: excellent (F < 100 g / m 2 ), good (100 ≤ F < 250 g / m 2 ), medium (250 ≤ F < 500 g / m 2 ), and poor (F ≥ 500 g / m 2) into four steps.

[0051] Table 3 shows the test results of the grain-oriented silicon steel sheets of Examples 1 to 28 and Comparative Examples 1 to 6 obtained according to the above method.

[0052]

Table 3

[0053] From Table 3, it can be seen that the coatings of the grain-oriented silicon steel sheets of Examples 1 to 28 of the present invention have excellent tension effects (the tension is in the range of 7.1 to 10.5 MPa), moisture absorption resistance (the phosphorus elution content is 75 μg / 150 cm 2 or less), and excellent or good heat resistance, corrosion resistance, and anti-adhesion properties.

[0054] The coatings of the grain-oriented silicon steel sheets of Comparative Examples 1 to 6 cannot satisfy all the characteristics of Examples 1 to 28 at the same time. Specifically, when the content of vanadate is too small, although the coating has the required tension, its phosphorus elution amount becomes relatively large, indicating poor moisture absorption resistance. Also, when the content of vanadate is too large, although phosphate radicals are fixed in the coating material by the excessive vanadate, the tension of the coating cannot meet the requirements of the present invention. Moreover, the excellent or good heat resistance, corrosion resistance, and anti-adhesion properties required by the present invention cannot be ensured either.

[0055] As described above, the preferred specific examples of the present invention have been described in detail. Those skilled in the art should understand that various modifications and changes can be made based on the concept of the present invention without creative efforts. Therefore, the technical solutions that can be obtained by those skilled in the art through logical analysis, inference, or limited experiments based on the concept of the present invention according to the prior art should be within the protection scope defined by the claims.

[0056] Furthermore, the mode of combination of the technical features presented in this application is not limited to the combinations described in the claims or the specific examples provided in this specification. All the technical features described in this application may be freely combined or incorporated in any mode as long as they do not conflict with each other.

Claims

1. A coating material for the surface coating of oriented silicon steel, wherein the coating material comprises: having a phosphate, preferably, the phosphate is at least one selected from phosphates of Mg, Al, Ca, Zn, and Mn, more preferably, the phosphate is magnesium dihydrogen phosphate, aluminum dihydrogen phosphate, calcium dihydrogen phosphate, zinc dihydrogen phosphate, and / or manganese dihydrogen phosphate; having colloidal silica; having at least one vanadate selected from vanadates of Ce, Mn, Co, Cu, or Fe, preferably, the vanadate is an orthovanadate, pyrophosphate, and / or metaphosphate of Ce, Mn, Co, Cu, or Fe; wherein the coating material does not contain Cr; the coating material.

2. The coating material according to claim 1, having 25 to 50% phosphate, 25 to 50% colloidal silica, and 10 to 50% vanadate by mass%.

3. The coating material according to claim 1, wherein the mass ratio of the colloidal silica to the phosphate is 0.5 to 1.5, preferably 1.0 to 1.

5.

4. The coating material according to claim 1, wherein the mass ratio of the vanadate to the phosphate is 0.2 to 2.0, preferably 0.2 to 1.

0.

5. The coating material further comprises: having boric acid, wherein the content of the boric acid is 0.02 to 0.2 parts by mass based on 100 parts by mass of the colloidal silica; the coating material according to claim 1.

6. The coating material according to claim 1, wherein the particle size of the colloidal silica is 5 to 50 nm.

7. An oriented silicon steel sheet having a substrate and a coating formed on the surface of the substrate, and the coating is formed using the coating material according to any one of claims 1 to 6.

8. The oriented silicon steel sheet according to claim 7, wherein the phosphate in the coating forms a network or chain structure.

9. The oriented silicon steel sheet according to claim 7, wherein the coating has vanadium phosphate.

10. The dry film thickness on one side of the coating is 2 to 10 g / m ２ The oriented silicon steel sheet according to claim 7, wherein the dry film thickness is as described above.

11. The grain-oriented silicon steel sheet further has a magnesium silicate layer, and the magnesium silicate layer is located between the substrate and the coating of the grain-oriented silicon steel sheet. The grain-oriented silicon steel sheet according to claim 7.

12. The coating of the grain-oriented silicon steel sheet has a tension of 7.1 to 10.5 MPa and a phosphorus elution content lower than 75 μg / 150 cm ２ The grain-oriented silicon steel sheet according to claim 7, having a phosphorus elution content lower than 75 μg / 150 cm

13. A method for manufacturing a grain-oriented silicon steel sheet, the manufacturing method having the following steps, the steps being: 1) A step of applying a coating material according to any one of claims 1 to 6 onto a substrate of the grain-oriented silicon steel sheet; and 2) A step of performing sintering to form a coating on the surface of the substrate of the grain-oriented silicon steel sheet, wherein the surface temperature of the substrate during the sintering is 800 to 900 ° C, and the sintering time is 20 seconds or more. The manufacturing method.

14. The manufacturing method satisfies one or more of the following items, the items being: The coating material is applied onto the substrate at a dry film thickness of 2 to 10 g / m² on one side; ２ ; The manufacturing method further includes forming a magnesium silicate layer between the substrate and the coating. The manufacturing method according to claim 13.

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