JPH08108659A - Production of lithographic printing substrate - Google Patents

Abstract

PURPOSE: To stably produce a low-cost lithographic printing substrate having little occurrence of stepped unevenness and a superior face quality after being roughened by a method wherein an aluminum casting material contains Fe, Si, and Al respectively by a specific ratio, and in a continuously casted and rolled plate a ratio of a concentration distribution difference of alloy components in a rolling direction to that in a plate width direction is specified. CONSTITUTION: In the production of a lithographic printing substrate, an aluminum casting material contains 0-0.20wt.% Fe, 0-0.10wt.% Si, 99.7wt.% or more Al, and the casting material is rolled so that in a continuously casted and rolled plate a ratio of a concentration distribution difference of alloy components in a rolling direction 10a to that in a plate width direction 10b is 0.2-5. Additionally, the aluminum casting material also contains 0-0.05wt.% Cu and 0-0.05wt.% Ti. For imparting superior characteristics as a lithographic printing aluminum alloy substrate, the alloy components of the aluminum casting material are specified as mentioned above. For eliminating stepped unevenness 8 occurring on a continuously casted and rolled plate, in the rolled plate a ratio of a concentration distribution difference of alloy components in a rolling direction to that in a plate width direction is specified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lithographic printing plate support, and more particularly to a method for producing an aluminum support having a good electrolytic graining property.

[0002]

2. Description of the Related Art Aluminum plates (including aluminum alloy plates) are used as aluminum supports for printing plates, especially as supports for offset printing plates. Generally, in order to use an aluminum plate as a support for an offset printing plate, it is necessary to have appropriate adhesiveness to a photosensitive material and water retention.

For this purpose, the surface of the aluminum plate must be roughened so as to have a uniform and fine grain. This roughening treatment has a significant influence on the printing performance and printing durability of the plate material when offset printing is actually carried out after plate making, and therefore its quality is an important factor in the plate material production. As a roughening method of the aluminum support for printing plates, AC electrolytic etching method is generally adopted,
As the current, a normal sine wave alternating current or a special alternating waveform current such as a rectangular wave is used. Then, the surface of the aluminum plate is roughened by an alternating current using an appropriate electrode such as graphite as a counter electrode, which is usually performed in a single treatment, but the pit depth obtained there is generally shallow. The printing durability was inferior. Therefore, various methods have been proposed in order to obtain an aluminum plate suitable as a printing plate support having a grain in which pits having a depth deeper than its diameter are present uniformly and densely. As a method thereof, a surface roughening method using a special electrolysis power source waveform (Japanese Patent Laid-Open No. Sho 5)
3-67507), the ratio of the amount of electricity at the time of the anode and the cathode at the time of electrolytic surface roughening using an alternating current (Japanese Patent Laid-Open No. 54-6560).
No. 7), a power supply waveform (JP-A-55-25381), and an energization amount per unit area (JP-A-56).
No. 29699) is known.

Further, a method combined with mechanical surface roughening (Japanese Patent Application Laid-Open No. 55-142695) is also known. On the other hand, as a method of manufacturing an aluminum support, an aluminum ingot is melted and held to form a slab (thickness: 4 mm).
00-600mm, width 1000-2000mm, length 2
000 to 6000 mm) and subjected to a chamfering step of cutting the impurity textured portion of the slab surface with a chamfering machine in 3 to 10 mm increments, and then in a soaking furnace for removing stress inside the slab and homogenizing the texture. A soaking treatment step of holding at 480 to 540 ° C for 6 to 12 hours is performed, and then hot rolling is performed at 480 to 540 ° C. After hot rolling to a thickness of 5 to 40 mm, cold rolling is performed to a predetermined thickness at room temperature. Further, after that, annealing is performed to homogenize the structure to homogenize the rolled structure and the like, and then cold rolling is performed to a prescribed thickness to correct the plate so as to have a good flatness. The aluminum support thus prepared was used as a support for a lithographic printing plate.

However, in the case of electrolytic surface-roughening treatment, it is particularly susceptible to the influence of the aluminum support as a target,
When manufacturing the aluminum support through the process of melting and holding → casting → chamfering → soaking, heating and cooling are repeated,
Even if there is a step of scraping off the surface layer called surface grinding, variations in metal alloy components and the like occur in the surface layer, which causes a reduction in the yield as a lithographic printing plate.

On the other hand, the applicant of the present invention first reduced the variation in the material of the aluminum support and improved the yield of the electrolytic surface roughening treatment to obtain a lithographic printing plate of excellent quality and good yield. As a method that can be made, after casting from an aluminum melt and hot rolling continuously to form a thin plate hot rolling coil, cold rolling, heat treatment, straightening the aluminum support to roughen it A method for producing a support for a lithographic printing plate characterized by the following is proposed (JP-A-3-79).
798 publication).

In addition to this, in JP-A-6-48058, in order to obtain a good suitability for electrolytic surface roughening, Fe: 0.4
~ 0.2 wt%, Si: 0.2-0.05 wt%, C
u: 0.02% by weight or less, aluminum 99.5% by weight
It is proposed that continuous casting is performed from the above molten aluminum and that 2.0 to 90% of the Fe content is present in the crystal grain boundaries.

Further, examples of inventions defining the alloy components of the support are disclosed in JP-A-62-146694 and JP-A-60-2.
30951, JP 60-215725 A, JP 6 A
Nos. 1-26746 and 58-8635 are disclosed. Further, the present applicant defines the alloy component of the support and proposes that the concentration distribution of the Fe alloy component is within an average concentration of ± 0.05% (Japanese Patent Laid-Open No. Hei 5).
-301478 gazette).

[0009]

However, Japanese Patent Application Laid-Open No. 6-48058 and Japanese Patent Application Laid-Open No.
Regarding the manufacturing method described in Japanese Patent No. 301478,
As shown in FIG. 2, when the aluminum melt is continuously cast and rolled using twin rolls, a step-like unevenness 8 extending in the direction perpendicular to the rolling direction, that is, in the width direction of the aluminum plate 7, is formed on the surface of the aluminum plate 7. There was a problem that occurred. In the figure, between the adjacent irregularities 8 is a portion (normal portion 11) having a uniform alloy composition and structure. This unevenness 8
However, there was a problem that it did not disappear even after cold rolling or intermediate annealing, and remained as stepwise unevenness on the surface of the roughened lithographic printing plate.

An object of the present invention is to reduce the occurrence of stepwise unevenness that occurs during twin roll continuous casting and rolling, and obtain a support for a lithographic printing plate that has excellent surface quality after roughening by a twin roll continuous casting and rolling method. An object of the present invention is to provide a method for producing a lithographic printing plate support which can be stably produced at low cost.

[0011]

[Means and Actions for Solving the Problems]
As a result of diligent research on the stepped unevenness that occurs during continuous casting and rolling, the part that looks like stepped unevenness can be classified into two patterns. One is that alloy components such as Fe and Si are densely aggregated in the form of intermetallic compounds. It was found that the alloy has a stepwise distribution, and the other is that the alloy components such as Fe and Si have a dilute concentration. Furthermore, the inventors have found the present invention capable of providing a good lithographic printing plate support by examining the relationship between the nonuniform distribution of these alloy components during continuous casting and rolling and the roughening property of the final plate.

That is, the above object of the present invention is to continuously cast and roll a molten aluminum directly into a plate shape with twin rolls, and then perform either one or both of cold rolling and annealing and further straightening the aluminum support. In the method for producing a lithographic printing plate support, which comprises a series of steps for roughening the surface of aluminum, the component of the molten aluminum is 0 <Fe ≦ 0.
20% by weight, 0 ≦ Si ≦ 0.10% by weight, Al ≧ 99.
7% by weight, and continuous casting and rolling such that the ratio between the difference in concentration distribution of alloy components in the rolling direction of the plate after continuous casting and rolling and the difference in concentration distribution of alloy components in the plate width direction is 0.2 to 5. The method for producing a support for a lithographic printing plate, comprising: 0. <Cu <0.05% by weight and 0 <Ti <0.05% by weight. It is achieved by the method for producing a lithographic printing plate support described in.

In the present invention, as a method for forming a coil continuously cast from molten aluminum by using twin rolls, a thin plate continuous casting technique such as Hunter method or 3C method has been put into practical use. According to these methods, the molten aluminum can be solidified and rolled at the same time, and a continuous cast and rolled plate having a normal thickness of 2 to 10 mm can be manufactured.

In order to obtain excellent properties as an aluminum alloy support for a lithographic printing plate, the present invention defines the alloy composition of the molten aluminum and determines the difference in the concentration distribution of the alloy composition in the rolling direction of the plate after continuous casting and rolling and the plate. By defining the ratio with the difference in concentration distribution of alloy components in the width direction, it is intended to eliminate the stepwise unevenness that occurs in the continuously cast and rolled plate. In the present invention, the Fe component is 0 <Fe ≦ 0.20% by weight, preferably 0.05 ≦ Fe ≦ 0.18% by weight, and particularly preferably 0.08 ≦ Fe ≦ 0.15% by weight. %.

In the present invention, as the Si component, 0 ≦ Si
≦ 0.10% by weight, preferably 0.02 ≦ Si ≦
0.08% by weight, particularly preferably 0.025 ≦ S
i ≦ 0.06% by weight. By setting Al ≧ 99.7% by weight with respect to Al ≧ 99.7% by weight, it is possible to use an Al ≧ 99.7% by weight ingot material that is inexpensively distributed in the general market, and reduce the cost of raw materials. Has an effect on.

In order to prevent the grain shape from becoming distorted, the upper limit is preferably less than 99.99% by weight. As the Cu component, 0 ≦ Cu ≦ 0.05% by weight, preferably 0.001 ≦ Cu <0.008% by weight. As the Ti component, 0 <Ti ≦ 0.05% by weight,
Preferably 0 ≦ Ti <0.03% by weight.

In general, Ti is added as a grain refiner and Cu is added to control the grain pit shape. Other unavoidable impurities (eg, Mg, Mn, Cr, Zr, V, Z
(n, Be, etc.) have a small content, so that they do not particularly affect the stepwise unevenness of the continuously cast and rolled plate, the surface treatment property of the final plate, the stain property, and the burning property.

A commercially available Al-Fe mother alloy having a Fe content of 50% can be used as the raw material of the Fe component, and a commercially available Al-Si alloy having a Si content of 25% can be used as the raw material of the Si component.
A mother alloy can be used, a commercially available Al-Cu mother alloy with a Cu content of 50% can be used as a Cu component raw material, and a commercially available Ti content of 5% Al-with a Ti component raw material. Ti master alloy or linear Al-Ti
-B master alloys can be used.

Each component of Fe, Si, Cu and Ti is Al
≧ 99.7% by weight When the ingot material is melted, each of the above raw materials is added to be used in the intended weight range.
Incidentally, Fe and Si may be contained in a small amount in the 99.7% Al ingot material, and the raw materials of the Fe and Si components are added in consideration of these amounts. Further, Cu and Ti may or may not be contained in a very small amount in the 99.7% Al ingot material, and in Cu and Ti, the respective raw materials are added in consideration of these amounts.

Next, the embodiment of the method for producing the lithographic printing plate support used in the present invention will be described more specifically with reference to the schematic process diagrams of FIGS. 1 (A) to 1 (D). Reference numeral 1 is a melting and holding furnace, in which the ingot is held by melting. From here, it is sent to the twin roll continuous casting machine 2. That is, the coil of the thin plate may be directly formed from the molten aluminum and wound by the coiler 6, or may be subsequently subjected to the heat treatment, the cold rolling mill, and the straightening device.

The manufacturing conditions will be described in more detail. In the melting and holding furnace 1, it is necessary to hold the temperature at the melting point of aluminum or higher, and the temperature changes depending on the aluminum alloy component. Generally, it is 800 ° C or higher. In addition, as a measure for suppressing the generation of oxides in the molten aluminum and for removing alkali metals such as Na, Li, and Ca that are harmful to the quality and are eluted from the furnace wall of the melting and holding furnace 1, an inert gas purge, a flux treatment, etc. are appropriately performed. Be seen.

Subsequently, it is cast by the twin roll continuous casting machine 2. There are various casting methods, but most of them currently in industrial use are the Hunter method, the 3C method, and the like.
The casting temperature varies depending on the cooling conditions of the mold, but the optimum temperature is around 700 ° C. The crystal grain size after continuous casting, the cooling conditions, the casting speed, and the amount of change in plate thickness during casting are controlled, and the plate material thus obtained by continuous casting is rolled to a specified thickness by the cold rolling mill 3. . At that time, in order to make the crystal grains have a predetermined size, the crystal grains may be subjected to a heat treatment machine 4 such as an intermediate annealing, and then a cold rolling machine 3 may be inserted and sandwiched. Next, straightening is performed by the straightening device 5 to give a predetermined flatness, and an aluminum support is prepared and roughened. Further, straightening may be included in the final cold rolling.

The alloying component of the molten aluminum is F
e: 0 <Fe ≦ 0.20% by weight, Si: 0 ≦ Si ≦ 0.
10% by weight, and for Cu and Ti, Cu: 0 ≦ C
u ≦ 0.05 wt%, Ti: 0 <Ti ≦ 0.05 wt%, and Al purity is 99.7 wt% or more. Various methods such as mechanical surface roughening, chemical surface roughening, electrochemical surface roughening, and combinations thereof may be used as the method of surface roughening the lithographic printing plate support of the invention.

Mechanical graining methods include, for example, ball grain, wire grain, brush grain, and liquid honing method. As an electrochemical graining method, an AC electrolytic etching method is generally adopted, and a special alternating current such as a normal sine wave AC current or a rectangular wave is used as a current. In addition, as a pretreatment for the electrochemical graining, an etching treatment with caustic soda may be performed.

In the case of performing electrochemical surface roughening, it is preferable that the surface is roughened by an alternating waveform current with an aqueous solution mainly containing hydrochloric acid or nitric acid. This will be described in detail below. First, the aluminum support is first alkali etched. Preferred alkaline agents are caustic soda, caustic potash, sodium metasilicate, sodium carbonate, sodium aluminate, sodium gluconate and the like. Concentration 0.01-20%, temperature 20-90
It is suitable to select the temperature and the time from the range of 5 sec to 5 min, and the preferable etching amount is 0.1.
~ 5 g / m ² .

In the case of a support containing a large amount of impurities, 0.01
-1 g / m ² is suitable (JP-A-1-237197). Subsequent to the alkali-etched aluminum support surface, a substance insoluble in alkali agents (smut)
Remains, so desmutting treatment may be performed if necessary. The pretreatment is as described above, but is subsequently subjected to AC electrolytic etching in an electrolytic solution containing hydrochloric acid or nitric acid as a main component. The frequency of the alternating electrolysis current is 0.1 to 10
0 Hz, more preferably 0.1 to 1.0 or 10 to 60
Hz.

The liquid concentration is 3 to 150 g / l, more preferably 5 to 50 g / l, and the amount of aluminum dissolved in the bath is preferably 50 g / l or less, more preferably 2 to 20 g / l. is there. If necessary, additives may be added, but in the case of mass production, it becomes difficult to control the liquid concentration. A current density of 5 to 100 A / dm ² is suitable, but 10 to 80 A / dm ² is more preferable.
The power waveform is appropriately selected depending on the desired quality and the components of the aluminum support used, but the special alternating waveform described in JP-B-56-19280 and JP-B-55-19191 is used. More preferable. Such waveforms and liquid conditions are appropriately selected depending on the quality required along with the quantity of electricity, the components of the aluminum support used, and the like.

The electrolytically roughened aluminum support is
Next, as a part of the smut treatment, the smut is dissolved by immersing it in an alkaline solution. There are various kinds of alkali agents such as caustic soda, but it is preferable to perform the treatment in an extremely short time of pH 10 or more, temperature 25 to 60 ° C., and immersion time 1 to 10 sec. Next, it is dipped in a liquid containing mainly sulfuric acid. As a liquid condition of sulfuric acid, it is preferable that the concentration is 50 to 400 g / l and the temperature is 25 to 65 ° C., which is much lower than the conventional one. When the concentration of sulfuric acid is 400 g / l or more or the temperature is 65 ° C. or more, the corrosion of the treatment tank becomes large, and the manganese content is high (for example,
Aluminum alloys (0.3% by weight) break the electrochemically grained grain. Further, when the dissolution amount of the aluminum alloy base material is etched by 0.2 g / m ² or more, the printing durability is deteriorated, so that it is preferably 0.2 g / m ² or less.

The anodic oxide film has a thickness of 0.1 to 10 g / m ² ,
More preferably, 0.3 to 5 g / m ² is formed on the surface. The treatment conditions for anodization are not generally determined because they vary depending on the electrolytic solution used, but generally the concentration of the electrolytic solution is 1 to 80% by weight, the liquid temperature is 5 to 70 ° C,
Current density 0.5 to 60 A / cm ² , voltage 1 to 100 V,
A range of electrolysis time of 1 second to 5 minutes is suitable.

The thus-obtained aluminum support having an anodized film is itself stable and excellent in hydrophilicity, so that a photosensitive coating film can be immediately provided on it. If necessary, further surface treatment can be performed. For example, a silicate layer made of an alkali metal silicate or an undercoat layer made of a hydrophilic polymer compound can be provided. The coating amount of the undercoat layer is 5 to 150 mg / m ^2.
Is preferred.

Next, a photosensitive coating film is provided on the thus treated aluminum support, imagewise exposed and developed to form a plate, which is then set in a printing machine to start printing.

[0032]

【Example】

(Examples 1 to 5 and Comparative Examples 1 to 5) An aluminum plate material having a plate thickness of 7.0 mm was cast at a casting speed of 1.5 m / in a twin roll continuous casting and rolling apparatus as shown in FIG. 1 (A). It was cast in minutes and wound up with a coiler 6. After that, the cold rolling mill 3 shown in FIG. 1 (B) was used to finish to a final plate thickness of 0.24 mm, and the aluminum plate was straightened by the straightening device 5 shown in FIG. 1 (D). At this time, samples of Examples and Comparative Examples of the present invention were prepared by changing the components of the molten aluminum. The plate after continuous casting and rolling of each sample is sampled, and the difference in alloy component concentration distribution in the rolling direction and the difference in alloy component concentration distribution in the plate width direction are measured. The value of (% by weight) / alloy component concentration distribution difference (% by weight) in the plate width direction was calculated. The difference in the concentration distribution in each direction is calculated by the electron probe microanalyzer (abbreviated as EPMA,
Using JXA-8800M manufactured by JEOL Ltd., acceleration voltage of 20 kV, measurement current of 1.0 × 10 ⁻⁶ A, and plate surface F
Surface analysis of e, Si, Cu, Ti by mapping (measurement range 10 mm x 10 mm, 5 measurement points / 1 sample), line analysis in the rolling direction and strip width direction of the obtained data, and the maximum concentration value -Minimum value (% by weight)
The average value of was used as the concentration distribution difference. FIG. 2 is a conceptual diagram for measuring the difference in alloy component concentration distribution.

Table 1 shows the breakdown of each sample and the measurement results of the ratio of the concentration distribution differences.

[0034]

[Table 1]

The aluminum support thus obtained was used as a support for a lithographic printing plate and then etched with a 5% aqueous solution of caustic soda at a temperature of 60 ° C. to an etching amount of 5 g / m ² , and washed with water to give 150 g. It was immersed in a sulfuric acid solution of 1 / l, 50 ° C. for 20 seconds to desmut, and washed with water. Furthermore, the support is placed in a 16 g / l nitric acid aqueous solution,
Electrochemical roughening was performed using the alternating waveform current described in 19191. As electrolysis conditions, the anode voltage V _A = 14 V and the cathode voltage V _C = 12 V were set so that the amount of electricity at the anode was 350 coulomb / dm ² .

Subsequently, desmut treatment was carried out by immersing in a 300 g / l sulfuric acid solution at 60 ° C. for 20 seconds. Furthermore,
Sulfuric acid 150g / l, aluminum ion concentration 2.5g /
Voltage of 22V in 1mm aqueous solution at distance between electrodes of 150mm
Anodizing treatment was carried out for 60 seconds with the direct current.

A photosensitive lithographic printing plate is obtained by applying a photosensitive solution to the support prepared as described above. Here, the surface quality of the support before the application of the photosensitive solution was evaluated.
When the photosensitive lithographic printing plate is exposed through a negative film or a positive film and then developed, the surface of the support itself becomes a non-image part or an image part of the lithographic printing plate. This is because the surface quality of the final plate surface itself greatly affects the printability and the visibility of the printing plate.

With respect to the samples shown in Table 1, Table 2 shows the results of the appearance evaluation of stepwise unevenness in the continuously cast and rolled plate and the appearance evaluation of the final plate.

[0039]

[Table 2]

As shown in the table above, sample N according to the invention
Nos. 1 to 5 (Examples 1 to 5) were less likely to cause stepwise unevenness during continuous casting and rolling, and the final plate also had a good appearance after roughening. On the other hand, of the samples not according to the present invention,
Regarding Nos. 6, 7, and 8 (Comparative Examples-1, 2, and 3), the difference in concentration distribution in the continuous casting and rolling direction was considerably larger than the difference in concentration distribution in the sheet width direction, and the ratio was 5.5 to 8.5. Therefore, step unevenness was generated during continuous casting and rolling, and step unevenness was also generated in the final plate. In addition, among the samples not according to the present invention, in Nos. 9 and 10 (Comparative Examples -4 and 5), the Fe and Si contents satisfy the range of the present invention, and step-like unevenness does not occur in the continuously cast rolled plate. But, Cu,
The content of Ti is out of the range of the present invention, and as a result, the difference in concentration distribution in the strip width direction is considerably larger than the difference in concentration distribution in the rolling direction, and the ratio is 0.1 to 0.15.
Streaky unevenness extending in the rolling direction occurred on the final plate.

In the above examples, after twin roll continuous casting,
Although the sample which is not annealed by the heat treatment machine 4 as shown in FIG. 1 (C) is shown, the present invention is not limited to this, and for example, the heat treatment machine is used to adjust the mechanical strength or control the crystal structure. May be annealed. Further, as the heat treatment machine, a batch type heating furnace (not shown) may be used other than the continuous type as shown in FIG. 1 (C).

[0042]

INDUSTRIAL APPLICABILITY As described above, the lithographic printing plate produced by the method for producing a lithographic printing plate support of the present invention has significantly improved surface quality after roughening as compared with the conventional one. Further, since the twin roll continuous casting method can be adopted, the manufacturing process is greatly streamlined, and the effect of reducing the manufacturing cost becomes large.

Further, by adopting the alloy components within the range of the present invention, the amount of the alloy components added by using an expensive mother alloy is significantly reduced, or the addition of the alloy components becomes unnecessary. The effect of reducing raw material costs is also great.

[Brief description of drawings]

FIG. 1 is a partial step of a method for producing a lithographic printing plate support of the present invention. (A) A side view of one embodiment of a twin roll continuous casting process. (B) The side view of one embodiment of the cold rolling process. (C) A side view of one embodiment of the heat treatment step. (D) The side view of one embodiment of the correction process.

FIG. 2 is a conceptual diagram for measuring a difference in alloy component concentration distribution of a continuously cast and rolled plate.

[Explanation of symbols]

 1 Melt-holding furnace 2 Twin roll continuous casting machine 3 Cold rolling machine 4 Heat treatment machine 5 Straightening device 6 Coirer 7 Continuously cast aluminum plate 8 Stepped uneven part 9 Alloy component distribution measurement range 10a Concentration distribution measurement direction (rolling direction) 10b Concentration distribution measurement direction (plate width direction) 11 Normal part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tsutomu Kakei, 4000 Kawajiri, Yoshida-cho, Hara-gun, Shizuoka Prefecture Fujisha Shin Film Co., Ltd. (72) Akio Uesugi, 4000, Kawajiri, Yoshida-cho, Haibara-gun, Shizuoka Prefecture Fujisha Makoto Within Film Co., Ltd.

Claims (2)

[Claims] 1. A series of continuous casting and rolling from a molten aluminum to a plate shape directly by twin rolls, either or both of cold rolling and annealing, and further straightening and roughening the aluminum support. In the method for producing a lithographic printing plate support, which comprises the steps of
<Fe ≦ 0.20% by weight, 0 ≦ Si ≦ 0.10% by weight,
Al ≧ 99.7 wt%, and the ratio between the difference in the distribution of alloy components in the rolling direction of the plate after continuous casting and rolling and the difference in the distribution of alloy components in the plate width direction should be 0.2 to 5. A method for producing a support for a lithographic printing plate, which comprises continuously performing continuous casting and rolling. 2. The composition of the molten aluminum is 0 ≦ Cu
The method for producing a support for a lithographic printing plate according to claim 1, wherein ≤0.05% by weight and 0 <Ti≤0.05% by weight are contained.