JP4806995B2 - Laser cutting steel and coating composition therefor - Google Patents

Description

  The present invention provides a steel composition pretreatment coating composition that enables high-speed laser cutting of a steel material in a state of being coated with a primary anticorrosive paint containing zinc powder, and a steel material coated with this coating composition, and The present invention relates to a method for manufacturing a cut steel material using the steel material. The coating composition of the present invention contains zinc dust and can give not only corrosion resistance to steel materials but also excellent laser cutting properties to steel materials.

  For steel materials used in the construction of large steel structures such as ships, bridges, plants, etc., corrosion protection and top coatability are generally used as primary anti-corrosion paints to temporarily prevent the generation of steel materials during processing and assembly. An inorganic zinc-based anticorrosive paint (zinc primer) containing zinc powder is applied.

  In recent years, even when manufacturing such a large structure, laser cutting has been increasingly employed for cutting steel materials for the purpose of quickly processing and assembling to shorten delivery time. Compared to gas cutting, plasma cutting, and other methods that have been used for this purpose, laser cutting has better cutting accuracy and cut surface quality, and the heat affected area of the cutting portion is smaller. This is because there is an advantage that night-time automatic driving is possible.

  Laser cutting has been mainly used for cutting steel sheets not coated with a primer such as automobile parts and industrial machines. However, in recent years, since high-speed cutting with high-power lasers such as 5 KW and 6 KW has become possible, the use of laser cutting has rapidly expanded to cut large steel materials such as shipbuilding and bridges.

  However, since laser cutting is strongly influenced by the surface of steel, it is known that there are various problems in laser cutting of steel coated with a zinc primer containing zinc dust. The biggest problem is that if the cutting speed is increased, scratches and dross adhere to the cut surface easily, and the cutting speed cannot be increased. In particular, if the cutting operation is interrupted during the unattended operation at night, the post-process is greatly affected, and the productivity is significantly reduced.

Regarding the improvement of the cutting speed, the following Patent Document 1 discloses a steel material in which the amount of Zn and SiO ₂ (silica) in the zinc primer to be coated on the steel material is limited, and in particular, the amount of SiO ₂ is reduced as much as possible to improve the laser cutting performance. Is disclosed. SiO ₂ is a component contained in the primer from the viewpoint of improving the fire resistance and strength of the primer layer, but because SiO ₂ is stable up to high temperature, it prevents the conduction of laser energy to the steel sheet and adversely affects the cutting speed. Is described as being very large.

  Patent Document 2 listed below contains a silicate condensate, a zinc powder, and a pigment having a melting point lower than that of iron (eg, talc, mica, ferroalloy, fluorite, etc.) for primary rust prevention with excellent laser cutting properties. A coating composition (primer) is disclosed.

However, none of the above-mentioned primers or coating compositions is still effective for laser cutting using a recent high-power laser cutting machine, and sufficiently corresponds to a high cutting speed of 1300 mm / min. I can't. In addition, since measures against the occurrence of defective cutting are not taken into account, cutting interruption is likely to occur particularly during nighttime unattended operation. Furthermore, Patent Document 1 has a problem that the amount of SiO ₂ in the paint is remarkably reduced, and Patent Document 2 has a problem that the fire resistance and strength of the coating film become insufficient because the paint does not contain SiO ₂ at all.
Japanese Patent Laid-Open No. 10-226846 JP 2002-114944 A

  An object of the present invention is to increase the laser cutting speed of a steel material coated with a zinc primer to, for example, a high speed of 1300 mm / min, and to prevent interruption of cutting in an unattended operation at night. It is to provide a coating composition (containing zinc powder), a laser cutting steel material coated with the coating composition, and a method for producing the cutting steel material.

  In order to solve the above-mentioned problems, the present inventors have intensively studied a zinc primer paint using a high-power laser cutting machine, and as a result, a steel material coated with a conventional zinc primer in a cutting operation with a high-power laser cutting machine. We determined that the cause of cutting failure, especially during nighttime unattended automatic operation, was the fluctuation of the laser focal length caused by swells and scratches in the steel.

  Therefore, if the primer layer is insensitive to fluctuations in the laser focal length, cutting failures and interruptions during unattended operation at night can be prevented, and at the same time the cutting speed can be significantly increased. Therefore, further investigation was made on the coating composition capable of forming such a primer layer, and the following knowledge was obtained.

As a paint component of the zinc primer, Zn and SiO ₂ are essential as a paint component in order to ensure the corrosion resistance and mechanical properties of the primer layer. However, together with SiO ₂ , metal Al and / or Al When the compound coexists, the laser cutting property of the formed primer layer is remarkably improved, and the laser cutting speed can be increased without deteriorating the advantages (good anticorrosive property and top coatability) of the conventional zinc primer, In addition, since the laser focal length that can be cut is wide, it is insensitive to fluctuations in the laser focal length, and cutting failures due to the fluctuations and interruptions during cutting at night are prevented. This is because the eutectic point or viscosity of Fe ₂ SiO ₄ produced by oxidation of the steel during laser cutting is reduced by the inclusion of Al, and iron (or iron oxide) melted during cutting is easily discharged from the cut part. It is considered a thing.

  It has also been found that an alkoxysilane capable of forming a dense film having a siloxane bond (Si—O) as a skeleton and / or a hydrolyzate or condensate thereof is suitable as the binder component of the primer.

In one aspect, the present invention is formulated so that the amount of alkoxysilane having two or more alkoxy groups as a binder component and / or a hydrolyzate or condensate thereof in a dry coating film is 40 to 80% by mass. Zinc powder, SiO ₂ , and total Si in a solid content containing Al source powder blended so that the amount in the dry coating film is 10 to 60% by mass, and excluding the binder component A coating composition for application to a steel material for laser cutting, wherein the mass ratio of / Al is 20/1 to 1/1.

From another aspect, the present invention provides an alkoxysilane having two or more alkoxy groups as a binder component and / or a hydrolyzate or condensate thereof, in an amount of 40 to 80% by mass in a dry coating film. In a solid content containing zinc powder, SiO ₂ , and Al source powder blended so that the amount in the dry coating film is 10 to 60% by mass, and excluding the binder component A steel material for laser cutting, wherein a coating composition having a total mass ratio of Si / Al of 20/1 to 1/1 is applied.

From still another aspect, the present invention provides an alkoxysilane having two or more alkoxy groups as a binder component and / or a hydrolyzate or condensate thereof, in an amount of 40 to 80% by mass in the dry coating film. Containing the powdered zinc powder, SiO ₂ , and Al source powder formulated so that the amount in the dry coating film is 10 to 60% by mass, and excluding the binder component A coating composition having a total Si / Al mass ratio of 20/1 to 1/1 is applied to a steel material, and the steel material is cut by irradiating a laser to the coating portion of the coating composition. It is a manufacturing method of cutting steel materials.

  When the coating composition of the present invention is applied to a steel material, a primer layer having excellent laser cutting properties is formed. This primer layer has a wide laser focal length, and is insensitive to fluctuations in the laser focal length due to undulations and scratches on the steel material. Therefore, in the steel material coated with the coating composition of the present invention, cutting failure in laser cutting is unlikely to occur, cutting interruption in unattended operation at night is prevented, and laser cutting operation of steel material is performed stably at a high speed of 1300 mm / min. It becomes possible to do.

The coating composition for applying to the steel for laser cutting according to the present invention comprises (1) an alkoxysilane having two or more alkoxy groups and / or a hydrolyzate or condensate thereof, (2) zinc dust, (3) It contains four types of components: SiO ₂ and powder of (4) Al source (metal Al and / or Al compound). Each component can be used alone or in combination of two or more. Among them, the alkoxysilane (1) and / or the hydrolyzate or condensate thereof is a binder component, and forms a film having a siloxane bond (Si—O) as a skeleton upon hydrolysis and condensation. The remaining (2) to (4) are all contained as dispersed particles in the primer layer.

  The alkoxysilane having two or more alkoxy groups used as the binder includes tetraalkoxysilane, alkyltrialkoxysilane, and dialkyldialkoxysilane. Specific examples of tetraalkoxysilane include, for example, tetramethoxysilane (methyl silicate), tetraethoxysilane (ethyl silicate), tetrapropoxysilane (propyl silicate), tetraisopropoxysilane (isopropyl silicate), and tetrabutoxysilane (butyl silicate). , Tetraisobutoxysilane (isobutyl silicate), ethyl silicate 40 (manufactured by Nippon Colcoat Co., Ltd.) and the like. Specific examples of the alkyltrialkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane. Specific examples of the dialkyl dialkoxysilane include dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane and the like. Compounds other than those exemplified can also be used. In the case of an alkoxysilane containing an alkyl group, an alkoxysilane called a silane coupling agent in which the alkyl group is substituted with a functional group such as a vinyl group, an amino group, an epoxy group, or a mercapto group can also be used. It is preferable to use only a part. It is also preferable that at least a part of the alkoxysilane is tetraalkoxysilane.

  The alkoxysilane can be used as a hydrolyzate or a condensate thereof because it promotes film formation. For example, it may be used in the form of a partial hydrolyzate obtained by hydrolyzing alkoxysilane in the presence of water or water and an acid catalyst, or an initial condensate that has been completely hydrolyzed and further advanced to a condensation reaction. it can.

  A commercial item can be used for zinc dust. The average particle size of the zinc powder affects the elution rate of zinc, that is, the anticorrosive property. The preferable average particle diameter of zinc powder is 3 to 15 μm, and more preferably 5 to 13 μm. Zinc powder is blended in an amount of 30 to 80% by mass, preferably 40 to 60% by mass, in a dry coating film (primer layer) formed by coating the coating composition of the present invention. If the blending amount is less than 30% by mass, good anticorrosive properties cannot be obtained, and if it exceeds 80% by mass, the laser cutting property is lowered. Moreover, although it can be used even if a part of zinc dust is oxidized and becomes zinc oxide, in that case, it is preferable that the ratio of Zn of zinc oxide in all Zn is 10% or less.

SiO ₂ means, in the context of the present invention, silica fine particles of colloidal particle size used in anticorrosion paints. The silica fine particles may be either sol-like wet silica (aqueous silica) or dry silica (fumed silica) produced by a gas phase method, and commercially available products can be used. SiO ₂ is effective in improving the mechanical properties and fire resistance of the coating film, thereby improving the corrosion resistance. For this purpose, SiO ₂ is contained in the dry coating film in an amount of 5 to 40% by mass, preferably 10 to 35% by mass.

The Al supply source may be either Al metal (which may be alloyed with other metals) or an Al compound, and in either case, it is used in powder form. The metal Al may be flaky powder. As the Al compound, salts such as aluminum sulfate and aluminum phosphate can be used, but an oxide type compound is preferable. In particular, alumina and its composite oxide with silica, and aluminosilicate. Specific examples include KAlSi ₃ O ₈ , CaAl ₂ Si ₂ O ₈ , NaAlSi ₃ O ₈ , Al ₂ O ₃ .2SiO ₂ .2H ₂ O, K ₂ O.3Al ₂ O ₃ .6SiO ₂ .H ₂ O, Examples include Al ₂ O ₄ · 4SiO ₂ · H ₂ O, Al ₂ O _{3 and the} like. The particle size of the powder may be at the pigment level. For example, the average particle size may be in the range of 0.2 to 50 μm.

The Al supply source is blended so that the content in the dry coating film is 10 to 60% by mass, preferably 15 to 50% by mass. Moreover, when an Al supply source is added so that the mass ratio of total Si / Al in the solid content (total amount of powder components) excluding the binder component in the dried coating film is 20/1 to 1/1, laser cutting is performed. The characteristics are further improved. Here, the amount of Si of the Si / Al mass ratio is the case where the Al supply source is an Al compound containing Si, such as an aluminosilicate or a silica-alumina composite oxide, in addition to the Si amount of the SiO ₂ component. The amount includes the amount of Si derived from the Al compound.

As described above, the effect of the present invention is that the eutectic point or viscosity of Fe ₂ SiO ₄ generated by oxidation of steel at the time of laser cutting decreases due to the inclusion of Al, so that molten iron or iron oxide generated by laser cutting It is presumed that this is related to the promotion of discharge from the cut portion. If the Si / Al mass ratio is too large, the amount of Al is too small to sufficiently obtain the effects of the present invention. On the other hand, if the Si / Al mass ratio is too small, the proportion of SiO _{2 in} the coating film becomes too small and the laser cutting property is also lowered.

Analysis of the powder component in the dried coating film can be carried out by dissolving the coating film in chloroform and analyzing the precipitate after ultrasonic dispersion and centrifugation by an appropriate means.
As other components used in the coating composition of the present invention, in addition to the above essential components, various pigments (colored pigments, extender pigments, rust preventive pigments) that have been used in ordinary coatings, particularly conventional zinc primers, Other additives (an anti-settling agent such as organic bentonite, a dispersing agent, etc.) can be optionally mixed depending on the purpose. However, since a large amount of these has an adverse effect on the laser cutting property, it is desirable that the amount in the dry coating film is 5% by mass or less in total.

  In the coating composition of the present invention, since the binder component is alkoxysilane, it is preferable that the solvent contains a water-miscible organic solvent such as alcohol as a main component. The solvent may contain water, but if it contains a large amount of water, the hydrolysis and condensation of the alkoxysilane tends to proceed during storage of the paint, and the storage life may be shortened. A water-immiscible organic solvent can also be contained as appropriate.

  Application | coating of the said coating composition can be performed by conventionally well-known application means, such as an air spray, an airless spray, a brush, for example. The coating film after application can be dried at room temperature, but may be dried by heating. When the alkoxysilane of the binder is not completely hydrolyzed, water for hydrolysis is required for film formation, but this water is supplied from the atmosphere. However, in order to accelerate the film formation, the humidity of the dry atmosphere may be increased by spraying water vapor or the like.

  The film thickness of the dried coating film formed on the steel material is preferably in the range of 9 to 25 μm. Even if the coating film is thinner than 9 μm or conversely thicker than 25 μm, the laser cutting property is lowered. When the coating film is thinner than 9 μm, the corrosion resistance is also deteriorated. In addition, this film thickness means an average film thickness, For example, the film thickness of the coating film on the surface of steel materials is measured using an electromagnetic film thickness meter, for example, CRT-2000II electromagnetic digital film thickness meter manufactured by Sanko Electronics Laboratory. It can obtain | require as an average value measured 10 points or more.

  It is desirable from the viewpoint of maintaining corrosion resistance that the steel material to which the coating composition is applied is previously removed from the surface by a known rust removal method such as shot blasting or sand blasting. Further, since the surface roughness of the steel material affects the laser cutting property, it is preferable that Rz = 15 to 85 μm, more preferably 15 to 70 μm. When Rz is less than 15 μm, sufficient adhesion durability of the coating film cannot be obtained, and when it exceeds 85 μm, the laser cutting characteristics are deteriorated. Rz is a 10-point average roughness defined in JIS B 0601-1994.

  The steel material to which the present coating composition is applied is not particularly limited in steel type, and may be ordinary steel or low alloy steel. However, since the steel material component also affects the laser cutting property, the following steel material is preferable (the balance of the component is Fe and inevitable impurities, and% means mass%).

C: 0.01% or more and 0.20% or less C is an element effective for the laser cutting property of the primer-coated steel material. If the amount of C is less than 0.01%, the laser cutting property is deteriorated. The lower limit of the C content is preferably 0.06% or more, more preferably 0.10% or more. The upper limit is desirably 0.15% or less.

Si: 0.03% or more and 0.6% or less Si is also an element effective for the laser cutting property of the primer-coated steel material. If the amount of Si is less than 0.03%, a notch is generated on the laser cut surface, and the cutting performance deteriorates. On the other hand, if the Si content exceeds 0.6%, the weldability deteriorates. The lower limit of the Si content is desirably 0.10% or more, and more desirably 0.3% or more.

Mn: 0.3% or more, 2.0% or less Mn is an element effective for securing the strength of steel materials, and also affects laser cutting properties. If the Mn content is less than 0.3%, the strength of the steel material is insufficient. On the other hand, when the amount of Mn exceeds 2.0%, in addition to the deterioration of toughness, the laser cutting property deteriorates.

solAl: more than 0.005% and not more than 0.10% Al is an element necessary for deoxidation. When the amount of solAl is not more than 0.005%, deoxidation of the steel material is insufficient and toughness deteriorates. On the other hand, when the amount of solAl exceeds 0.10%, hard island martensite is generated in the welded portion and the toughness deteriorates.

N: 0.0005% or more and 0.008% or less When the N amount is less than 0.0005%, the crystal grain size of the steel material becomes coarse and the toughness deteriorates. On the other hand, when the N content exceeds 0.008%, the toughness is also deteriorated.

In addition to the above elements, in order to ensure strength, one or more elements selected from the following may optionally be further added.
Nb: 0.005% or more, 0.08% or less Nb is an element effective for securing strength. When added, the effect is not exerted unless the content is 0.005% or more. On the other hand, if the content exceeds 0.08%, the toughness deteriorates.

Ti: 0.005% or more, 0.03% or less Ti is also an element effective for securing strength, and is effective for preventing cracks in continuous casting. When added, the effect is not exerted unless the content is 0.005% or more. On the other hand, if the content exceeds 0.03%, the toughness deteriorates.

V: 0.005% or more, 0.08% or less V is also an element effective for securing the strength. When added, the effect is not exhibited unless the content is 0.005% or more. On the other hand, if the content exceeds 0.08%, the toughness deteriorates.

Cu: 1.5% or less,
Cu is also an element effective for securing the strength. When added, the content is preferably 0.3% or more. On the other hand, even if it contains exceeding 1.5%, the effect corresponding to content is not seen.

Ni: 3.0% or less,
Ni is an element effective for securing strength and toughness. When added, the content is preferably 0.2% or more. On the other hand, even if the content exceeds 3.0%, an effect corresponding to the content is not seen.

Cr: 1.0% or less Cr is also an effective element for securing strength. When added, the content is preferably 0.2% or more. On the other hand, even if it contains exceeding 1.0%, the effect corresponding to content is not seen.

Mo: 0.8% or less Mo is an element effective for securing the strength. When added, the content is preferably 0.1% or more. On the other hand, even if the content exceeds 0.8%, an effect corresponding to the content is not seen.

  The shape of the steel material is not particularly limited as long as laser cutting is possible, and is selected according to the application. For example, a thick plate, a tube material, a deformed material, etc. are exemplified, but it is of course possible to have other shapes.

  Two types of test steel materials having chemical compositions shown in Table 1 (both 500 × 500 × 16 mm thick plate materials) were rusted by shot blasting, and then a coating composition having the composition shown in Table 2 was applied by air spray. The surface roughness after shot blasting was 50.2 μm.

  Among the components used in the coating composition, as alkoxysilane, 50 parts by mass of commercially available ethyl silicate 40 (manufactured by Tama Chemical Industry Co., Ltd.) is used, and this is 1 part by mass of 0.1N hydrochloric acid and 6 parts by mass of water. , And 43 parts by mass of isopropyl alcohol (IPA) with stirring and mixing. The zinc powder was a commercial product having an average particle size of 7 μm. SiO2 was a commercial product having an average particle size of 20 nm.

As the Al supply source, KAlSi ₃ O ₈ , CaAl ₂ Si ₂ O ₈ , NaAlSi ₃ O ₈ , Al ₂ O ₃ and metal Al (with an average particle diameter in the range of 2 to 5 μm) were used. In some paints, TiO ₂ or hematite was added as a color pigment. “Other additives” listed in Table 2 are organic bentonites as anti-settling agents.

In addition, the numerical value of each component of the coating composition of Table 2 is the mass% based on the total solid content (total amount of components other than the solvent) including the binder component.
Coating is carried out using a small coating robot (PX-800 manufactured by Yaskawa Electric Co., Ltd., moving linear speed 380 mm / sec) and a coating gun (Devil screw T-AGHV, nozzle diameter 1.2 mm, cap No. 807). The air pressure was 1.3 kgf / cm ² , the pattern air pressure was 1.0 kgf / cm ² , the paint discharge rate was 132 g / min, and the gun distance was 150 mm. The paint film was naturally dried after painting. The film thickness of the formed dried coating film was measured at 81 points on the surface of the steel sheet using a CRT-2000II electromagnetic digital film thickness meter manufactured by Sanko Electronic Laboratory Co., Ltd., and the average value was obtained. Further, the Si / Al mass ratio of the coating film was determined by fluorescent X-ray. These measurement results are shown in Table 2 together with the types of steel materials.

  A laser cutting test was performed on the plate of 500 × 500 × 19 mm thickness coated as described above. The laser cutting machine used for the cutting was 5 kW made by Koike Oxygen, and the cutting conditions were a duty of 100%, a frequency of 1000 Hz, and an oxygen gas pressure (inside: 0.05 MPa, outside: 0.03 MPa). After piercing from the coated plate material, 50 × 50 squares (corner: R3 mm) were cut out, and the notch phenomenon or the adhesion state of noro at that time was observed. The cutting speed was 1300 mm / min.

In the evaluation, the laser focus was determined on the steel surface, and the focal length was varied at a pitch of 0.5 mm from the steel surface, and whether or not notch phenomenon or adhesion or cutting failure occurred was determined as follows:
: No, no notch phenomenon,
▽: Noro adhesion,
Δ: Notch generated,
×: Cannot be cut.

  The results are shown in Table 3. In this test, the larger the width (range) of the cutting focus of 焦点, the more stably the steel material can be cut at high speed.

  As shown in Test Nos. 1 to 12, which are examples of the invention, when a steel material is applied with the coating composition of the present invention, the laser focal length that can be cut is wide regardless of the type of the steel material. It can be seen that stable cutting is possible without being affected by undulations, scratches, etc. of the steel material even during high-speed cutting using a machine. As a result, it is possible to prevent cutting interruption due to cutting failure during unattended automatic driving at night, which greatly contributes to the improvement of laser cutting productivity.

  On the other hand, in the comparative example, which is a coating composition not containing an Al supply source, the width of the laser focal length that can be cut is very narrow, and if the focal length changes by only 0.5 mm or 1 mm, cutting becomes impossible and the cutting is interrupted. Be driven into. Accordingly, unattended driving at night becomes difficult.

Claims (3)

Alkoxysilane and / or its hydrolyzate or condensate, the amount in a dry coating film is formulated such that from 40 to 80 wt% zinc powder having two or more alkoxy groups as a binder component, SiO _2, And Al, Al alloy, alumina, alumina / silica composite oxide, and aluminosilicate added so that the mass ratio of total Si / Al in the solid content excluding the binder component is 20/1 to 1/1 A coating composition for applying to a steel material for laser cutting, comprising an Al source powder selected from acid salts. Alkoxysilane and / or its hydrolyzate or condensate, the amount in a dry coating film is formulated such that from 40 to 80 wt% zinc powder having two or more alkoxy groups as a binder component, SiO _2, And Al, Al alloy, alumina, alumina / silica composite oxide, and aluminosilicate added so that the mass ratio of total Si / Al in the solid content excluding the binder component is 20/1 to 1/1 A steel material for laser cutting, which is coated with a coating composition containing powder of an Al supply source selected from acid salts. Alkoxysilane and / or its hydrolyzate or condensate, the amount in a dry coating film is formulated such that from 40 to 80 wt% zinc powder having two or more alkoxy groups as a binder component, SiO _2, And Al, Al alloy, alumina, alumina / silica composite oxide, and aluminosilicate added so that the mass ratio of total Si / Al in the solid content excluding the binder component is 20/1 to 1/1 A coating composition containing an Al supply source powder selected from acid salts is applied to a steel material, and the coated portion of the coating composition is irradiated with a laser to cut the steel material. Method.