JP3903743B2 - Galvanized steel sheet with excellent adhesiveness, workability, and weldability and its manufacturing method - Google Patents

Description

(評価基準)
◎： ＞70 kN 、
○：50〜70 kN 、
×： ＜50 kN 。
【００９５】
亜鉛系めっき鋼板の加工では、加工性確保のために、高潤滑性の防錆油を使用することが一般的である。参考のために、ＥＧ、ＳＺおよびＧＡの各亜鉛系めっき鋼板に高潤滑性防錆油である出光製オイルコートSP２を２g/m²塗油して、同じ試験を行ったところ、成形限界荷重が50〜70 kN であった。この結果から、加工性の目標レベルを50 kN 以上、好ましくは70 kN 超に設定した。なお、本試験では、上記のように、一般防錆油である出光製オイルコートSKを２g/m²塗油してから、加工性試験に供した。
【００９６】
接着性評価
接着性は、車体構造用接着剤 (アドヒーシブシーラー用のエポキシ系接着剤：ヘンケル白水製) と、車体構造用接着剤よりも接着強度が小さく、接着性に関してはより厳しいマスチック型接着剤という２種類を用いて試験した。その際の接着試験方法として、マスチック型接着剤では剪断引張強度を測定し、車体構造用接着剤は、より剥離を起こしやすいＴ字剥離での接着強度を測定した。また、車体構造用接着剤は、仮止め状態の接着強度も要求されるために、焼付け条件の影響を考慮し、170 ℃×30分焼き付けのフルキュア条件と、160 ℃×10分焼き付けのプレキュア条件の２種類の焼付け条件でＴ字剥離強度を測定した。
【００９７】
油面接着性を評価するため、接着剤を塗布する前に、一般防錆油である出光製オイルコートSKを２g/m²を試験片２枚の両方の接着面に塗油し、湿潤雰囲気 (50℃×95％RH) 下で７日間スタックして保管した後、１枚の試験片の所定領域に接着剤を塗布し、スペーサーを用いて厚さ0.15 mm の接着剤厚みとなるように２枚の試験片を重ね合わせ、所定の焼付け条件で焼付けを行って接着剤を硬化させ、接着強度を調査した。
【００９８】
各接着試験の試験条件と評価基準 (○までが合格) は次の通りである。

【００９９】
(評価基準)
潤滑皮膜を形成しなかった同じ母材の冷延鋼板に一般防錆油（出光製オイルコートＳＫ）を2.0 g/m²塗油したときの同じ試験条件での接着強度が0.20 MPaであり、それから30％強度が落ちた際の接着強度＝0.14 MPa以上あれば、実用上問題は生じないことから、次の基準で接着性を評価した。
【０１００】
◎：剪断強度≧0.20 MPa
○：剪断強度＝0.14〜0.20 MPa
×：剪断強度＜0.14 PMa。
【０１０１】

【０１０２】
(評価基準)
潤滑皮膜を形成しなかった同じ母材の冷延鋼板に一般防錆油（出光製オイルコートＳＫ）を2.0 g/m²塗油したときの同じ試験条件での接着強度が、プレキュア条件で30 KPaであり、それから30％強度が落ちた際の接着強度＝21 KPa以上あれば、実用上問題は生じないことから、次の基準で接着性を評価した。
【０１０３】
◎：剥離強度≧30 KPa、
○：剥離強度＝21〜30 KPa、
×：剥離強度＜21 KPa。
【０１０４】
溶接性評価
溶接性は、下記に示す条件で連続打点スポット溶接試験を実施し、100 打点毎にナゲット径をチェックし、ナゲットが形成できなくなる (ナゲット径が得られなくなる) までの連続打点限界数を求めることにより評価した。比較対照となる、ＥＧ、ＳＺおよびＧＡの各亜鉛系めっき鋼板に高潤滑性防錆油である出光製オイルコートSP２を２g/m²塗油して同じ条件でスポット溶接性を試験した時の連続打点限界数が2500〜5000打点であることから、2500打点以上、好ましくは、4000打点以上を目標レベルとした。本試験でも、一般防錆油である出光製オイルコートSKを２g/m²塗油してから試験に供した。
【０１０５】
(溶接条件)
電極材質：Cu−１％Cr
電極形状：CF型 (先端径＝５mm)
加圧力：200 kgf
スクイズ時間：15サイクル
(鋼板を押さえてから通電するまでの時間)
通電時間：10サイクル
保持時間：20サイクル
(通電完了してから、電極開放までの時間)
設定電流：10.5 kA
打点速度：２秒／点。
【０１０６】
(評価基準)(○までが合格)
◎：＞4000打点、
○：2500〜4000打点、
×：＜2500打点 。
【０１０７】
以上の試験結果を、亜鉛系めっき鋼板の種別、処理液の組成や処理条件と共に、表１、２にまとめて示す。
【０１０８】
【表１】

【０１０９】
【表２】

【０１１０】
表１、２からわかるように、亜鉛系めっき鋼板のままで、リン酸亜鉛系潤滑皮膜を形成しなかったNo.1の比較例では、溶接性および接着性は良好であるが、プレス成形性が非常に劣る。
【０１１１】
これに対し、本発明に従ってリン酸亜鉛系無機潤滑皮膜を形成した本発明例では、接着性や溶接性を保持したまま、プレス成形性が著しく向上している。めっき種、リン酸種、添加剤、塗布方法を変化させても、いずれの場合も十分な性能が得られる。
【０１１２】
しかし、皮膜最表層の組成もしくは皮膜付着量または製造条件が本発明の範囲から外れると、プレス成形性、溶接性、接着性のいずれかの性能が劣る。
例えば、縮合促進剤の酸化剤を添加しないと、最表層のZn／Ｐ比が高く、期待される接着強度の向上が得られない (No.2〜4)。酸化剤を添加した場合の接着強度の改善は、液中のＰに対する酸化剤のモル比が本発明の範囲内である時に得られる。処理液のｐＨも影響を及ぼし、ｐＨが0.7 以上、５以下、特に 1.5〜3.5 の範囲の時に、皮膜組成が適正となり、接着性が改善される。皮膜の付着量は、Ｐ換算付着量が５mg/m² 以上であると、十分な加工性が確保できる。好適な加工性を確保するには、下地のめっきの種類によって変わるが、亜鉛合金めっき鋼板で20 mg/m²以上、軟質な純亜鉛めっき鋼板で50 mg/m²以上の付着量が好ましい。付着量が500 mg/m² を超えると、スポット溶接性が確保できず、最表層の皮膜組成が適正でも接着性が若干低下する。スポット溶接性の点では300 mg/m² 以下の付着量が好ましい。
【０１１３】
焼付け温度が低い場合は、皮膜が形成されるものの十分ではなく、接着強度が確保できない。焼付け温度が高い場合は、表面が過酸化状態になり、皮膜表面に亜鉛酸化物の脆弱層ができ、Ｏ／Ｐ原子比が高すぎ、接着性が不芳となる。Ｐ付着量が多すぎる場合、脆弱層が形成されやすく、接着性、溶接性ともに劣化する。Ｐ付着量が少なく、水洗工程で塗布したリン酸が洗い流された場合などは、十分な加工性が確保できなくなることが分かる。
【０１１４】
結晶質の存在の有無は、最表層Zn／Ｐ原子比、Ｏ／Ｐ原子比の確保による接着性への影響は少ないが、結晶質が存在すると加工性が低下する傾向が認められる。前処理として、酸および／またはアルカリへの浸漬を行うと、Ｐ付着量が多くなり、容易に加工性を改善できる。。
【０１１５】
(実施例２)
本実施例では、亜鉛系めっき鋼板の表面に、本発明の方法に従って、メタリン酸水溶液 (酸化剤を含有せず) を使用して無機潤滑皮膜を形成する例について示す。
【０１１６】
処理方法および試験条件は、処理液がリン酸としてメタリン酸を含有し、酸化剤を含有していない点を除いて、実施例１と同一である。試験結果を、亜鉛系めっき鋼板の種別、処理液の組成や処理条件と共に、表３にまとめて示す。
【０１１７】
【表３】

【０１１８】
表３に示すように、ｐＨを適宜調整したメタリン酸水溶液を使用して無機潤滑皮膜を形成すると、酸化剤を添加しなくても、本発明に従った最表層のZn／Ｐ原子比とＯ／Ｐ原子比を容易に確保することができ、適正なＰ付着量を確保できれば、良好な性能が得られることが判る。
【０１１９】
本発明の条件を外れた比較例では、プレス成形性、溶接性、接着性のいずれかの性能が劣る。処理液のｐＨが高い場合は、リン酸塩皮膜の形成が不十分であり、皮膜組成が範囲外となり、皮膜が脆く、特に接着性を全く確保することができない。ｐＨが低すぎると、エッチングが強すぎて、亜鉛酸化物が表面に残存し、最表層おんＯ／Ｐ原子比が高すぎるため、加工性と接着性に劣る。焼付け温度が低い場合は、皮膜が形成されるものの、十分ではなく、接着強度が確保できない。焼付け温度が高い場合は、表面が過酸化状態になり、皮膜表面に酸化亜鉛の脆弱層ができ、接着性が不芳となる。
【０１２０】
実施例１および実施例２で得られた接着性の総合的な試験結果を、皮膜最表層のZn／Ｐ原子比とＯ／Ｐ原子比との関係として図３に示す。図３に表示した試験結果 (記号) の判定基準を表４に記載する。これからわかるように、図３では、すべての接着性試験において最良の結果（◎）であったものを●、すべての試験において合格（○）以上であったものを○、すべての試験において一つでも不合格（×）であったものを×と表した。
【０１２１】
【表４】

【０１２２】
図３より、本発明に従った皮膜最表層の組成比を有するリン酸亜鉛系皮膜は、車体構造用接着剤だけでなく、接着強度の弱い接着剤であるマスチック型接着剤でも良好な接着性を確保できることが明らかである。特にZn／Ｐ＝ 0.7〜1.8 の範囲で接着性が優れており、最表層の亜鉛酸化物の残存を抑制し、最表層をメタリン酸亜鉛主体の皮膜にすると、接着性が著しく改善されることがわかる。
【０１２３】
【発明の効果】
本発明に従って亜鉛系めっき鋼板に無機潤滑皮膜を形成すると、亜鉛系めっき鋼板の溶接性と接着性を損なわずに、過酷なプレス成形に耐えるように加工性を大幅に向上させることができる。それにより、従来の無機潤滑皮膜では困難であった接着性と加工性の両立が可能となり、自動車車体用に使用されている多様な接着剤 (車体用接着剤だけでなく、強度の弱いマスチック型接着剤も含む) による接着を可能にする広範囲の接着剤適合性が付与され、焼付け条件の甘い仮止め状態 (プレキュア条件) での接着強度や各種条件での接着強度等、潤滑皮膜がない状態と同じように接着剤を使用することができる、無機潤滑処理亜鉛系めっき鋼板が提供される。
【０１２４】
従って、本発明の無機潤滑処理亜鉛系めっき鋼板は、プレス成形により所定形状に加工した後、スポット溶接と接着剤のいずれを利用しても組立てが可能であるので、自動車車体用鋼板として最適の性能を備えている。
【図面の簡単な説明】
【図１】マスチック型接着剤での接着性評価に用いた剪断引張試験方法を示す説明図である。
【図２】車体構造用接着剤での接着性評価に用いたＴ字剥離引張試験方法を示す説明図である。
【図３】各種潤滑処理皮膜のＸＰＳにて測定した表層元素存在比と車体構造用接着剤およびマスチック型接着剤での接着強度の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention can ensure excellent workability to withstand severe press forming, and can adhere to galvanized steel sheets and zinc alloy plated steel sheets (both are collectively referred to as galvanized steel sheets in the present invention) The present invention relates to a surface-treated steel sheet provided with an inorganic lubricating film that does not deteriorate spot weldability and a method for producing the same.
[0002]
The galvanized steel sheet according to the present invention uses an adhesive having a weak adhesive strength (for example, a sheet adhesive for reinforcing a steel sheet, an adhesive for a high rust prevention spot sealer, a mastic type adhesive such as a highly foaming filling sealant). It is characterized in that stable adhesion can be ensured even if it is adhered, and extremely excellent adhesion is exhibited.
[0003]
[Prior art]
Zinc-based galvanized steel sheets represented by electrogalvanized steel sheets, hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, Zn-Ni alloy electroplated steel sheets, Zn-Al alloy hot-dip steel sheets, etc. It is widely used in home appliances, building materials, etc., and its demand will continue to increase in the future.
[0004]
Along with this increase in demand, various performances other than corrosion resistance have been required for zinc-based plated steel sheets. For example, a zinc-based plated steel sheet used for an automobile body is required to have spot weldability and adhesiveness required for assembly in addition to press formability.
[0005]
However, galvanized steel sheets tend to cause phenomena such as plating peeling and die seizure due to the presence of soft zinc. There was a problem that the sex was not enough. Therefore, a method is generally employed in which oil is applied to one or both of the steel plate and the mold, and an oil film is interposed at the contact interface between the two to improve workability. However, in oil coating, oil film breakage occurs when the mold and the steel plate come into contact with each other under conditions where workability is severe, so that sufficient formability cannot be ensured.
[0006]
From such a background, for example, in Japanese Patent Laid-Open Nos. 3-183797 and 3-249180, an Mn oxide film or phosphoric acid and an oxide of Mo, W or V coexist in the Mn oxide. It has been proposed to increase the press formability by forming an inorganic lubricating film composed of a coated film on the surface of a zinc-based plated steel sheet to prevent metal contact between the plated film and the mold.
[0007]
In Patent No. 2,819,427, an amorphous phosphorus oxide film is applied to the surface of a zinc-based plated steel sheet in an amount of 1 to 500 mg / m.²It is disclosed to improve the press formability by forming and secure chemical conversion treatment. Patent No. 2,691,797 and Patent No. 2,826,902 describe the press formability and chemical conversion treatment in which a coating containing a metal oxide film having an anti-adhesion function and a P or B oxide film having a roller lubrication function is formed. A galvanized steel sheet excellent in resistance is proposed.
[0008]
All of the conventional inorganic lubricating films described in the above patent publications are aimed at improving the workability of galvanized steel sheets and further ensuring chemical conversion properties. Nothing has been considered.
[0009]
[Problems to be solved by the invention]
Improvement of workability of galvanized steel sheet is very important for automobile body applications, but in addition to welding, a wide variety of adhesives have been used for the assembly of automobile bodies. Similar to steel plates used for automobile bodies, wide adhesive compatibility applicable to all types of adhesives is required.
[0010]
There are roughly two types of adhesives used for automobile bodies. That is, structural adhesives, adhesives for vehicle bodies with relatively high adhesive strength, such as rust-proof sealants, and mastic adhesives with relatively low adhesive strength for the purpose of reinforcing panels and improving rust-proofing of welds With drugs.
[0011]
In general, the conventional inorganic lubricating film as described above has a very poor compatibility with the adhesive, and when applying a zinc-based plated steel sheet subjected to such an inorganic lubricating treatment as a steel sheet for an automobile body, it has an adhesive property. Ensuring of this was a big problem.
[0012]
For the purpose of improving the adhesiveness, for example, JP-A-8-296058 discloses that before the inorganic lubrication treatment, the plating surface is activated by alkali degreasing or the like as the pretreatment, and the adhesion between the inorganic lubrication film and the plating layer is achieved. It has been proposed to improve adhesiveness and ensure adhesive compatibility.
[0013]
However, even with this activation treatment, it can be expected to improve the adhesiveness for car body adhesives with high adhesive strength, but in adhesives with low adhesive strength, especially mastic adhesives mainly composed of synthetic rubber. However, it cannot be said that sufficient adhesive strength could not be secured and adhesive compatibility could be improved sufficiently.
[0014]
As a method of applying an adhesive in an automobile body, there is a case where a two-step baking is performed in which the adhesive is sufficiently hardened by baking after painting after securing temporarily at a relatively low baking temperature to ensure adhesive strength. However, in the pre-cured state of this temporary fixing stage (adhesive is not sufficiently hardened and the adhesive strength is weak), the conventional inorganic-lubricated galvanized steel sheet has sufficient adhesive strength to withstand subsequent handling. It cannot be secured.
[0015]
In addition, the adhesive strength can be peeled by T-type adhesion even if the adhesive strength is sufficiently high in a test method such as shear tension, which is generally practiced, where local stress concentration is unlikely to occur in the adhesive. In a test method in which a local stress concentration is easily applied to the adhesive, the adhesive strength is extremely lowered, and the adhesive strength cannot be sufficiently ensured depending on the application part of the automobile body.
[0016]
The present invention solves the problems of the conventional inorganic lubrication treatment technology of the above-described zinc-based plated steel sheet, can secure high adhesive strength when bonded with various adhesives including mastic type, and is sufficient even in a precure state It is intended to provide a zinc-based plated steel sheet that has been subjected to an inorganic lubrication treatment, exhibiting high adhesive strength and exhibiting high adhesive strength even in a T-type peel test, and having sufficient workability and weldability.
[0017]
[Means for Solving the Problems]
In examining the inorganic lubrication treatment of galvanized steel sheet, the present inventors have examined the improvement of adhesiveness, which was the problem without impairing the extremely excellent workability of the conventional inorganic lubricating film. .
[0018]
Specifically, adhesive compatibility so that adhesive strength equivalent to that of conventional steel plates for vehicle bodies can be secured under severe adhesive conditions such as mastic adhesive, precure condition, and T-type adhesion. With the aim of improving the above, various effects of the inorganic lubricating film formed by treating a zinc-based plated steel sheet with a phosphoric acid aqueous solution on the adhesion were studied.
[0019]
As a result, in the adhesion / peeling test of galvanized steel sheet having this kind of inorganic lubricating film, peeling occurs at the interface of the inorganic lubricating film / adhesive, and the film composition is controlled so that this peeling hardly occurs. As a result, in addition to workability and weldability, the inventors have found a new finding that extremely excellent adhesiveness can be secured.
[0020]
Phosphoric acid is oritriic acid (H_ThreePO_Four) From polyphosphoric acid such as pyrophosphoric acid (diphosphoric acid), tripolyphosphoric acid (triphosphoric acid), etc._{n + 4}P_{n + 2}O_{3n + 7}When the dehydration condensation proceeds further, metaphosphoric acid (H_nP_nO_3n) To the ultraphosphoric acid having the structural unit as a structural unit.
[0021]
The present inventors investigated various adhesive properties by treating various zinc-based plated steel sheets with various phosphoric acid aqueous solutions having different degrees of dehydration condensation. As a result, the adhesiveness of the inorganic lubricating film formed varies greatly depending on the degree of dehydration condensation of phosphoric acid used in the treatment, and the adhesiveness is insufficient with the orthophosphoric acid treatment, but pyrophosphoric acid, tripolyphosphoric acid, metaphosphoric acid In this order, the adhesion improved, and the film formed by the treatment with metaphosphoric acid was particularly excellent in adhesion.
[0022]
The reason why the inorganic lubricating film formed by the metaphosphoric acid treatment has extremely excellent adhesiveness is not completely elucidated, but is presumed to be due to the following mechanism.
[0023]
When zinc-plated steel sheet is treated with an aqueous solution of orthophosphoric acid, zinc in the plating is dissolved by the etching action of phosphoric acid [Zn → Zn²⁺+ 2e^-] Zinc ions and phosphate ions react [3Zn²⁺+ 2PO_Four ^3-→ Zn_Three(PO_Four)₂As a result, a zinc orthophosphate film is formed on the plating surface. This zinc orthophosphate is a tetrahydrate hopite [Zn at temperatures below 100 ° C._Three(PO_Four)₂・ 4H₂O] precipitates as crystals. Since this hoplite crystal is a needle-like crystal, when an inorganic lubricating film made of hopite is formed, the surface of the film is rough, the slidability during processing is lowered, and the workability is deteriorated. Moreover, when there is much amount of hopping adhesion, since this is an insulator, resistance weldability, such as spot welding, will also deteriorate.
[0024]
Further, when the hopping film containing water of crystallization comes into contact with an alkaline adhesive, dissolution of the hopping crystals that easily dissolve in the alkaline region occurs, and the hopping crystals at the interface with the adhesive become brittle. Will cause peeling.
[0025]
  In addition, when the zinc-based plated steel sheet is treated with phosphoric acid, particularly orthophosphoric acid having a very low pH, zinc (Zn) dissolved by the etching of the plating layer described above is obtained.²⁺ )As zinc is dissolved more than is consumed in the production of hopite, the remaining dissolved zinc ions that cannot be consumed are precipitated as zinc oxide and / or zinc hydroxide when the film is dried. The formation of a brittle layer of zinc oxide and / or zinc hydroxide on the coating) is also a cause for deterioration in adhesion.
[0026]
On the other hand, an inorganic lubricating film made of zinc polyphosphate or zinc metaphosphate, which is produced by reacting zinc ion produced by the plating etching action of polyphosphoric acid or metaphosphoric acid polymerized through a dehydration condensation reaction, In addition to being excellent in alkalinity, excess dissolved zinc once dissolved by etching is also effectively incorporated into the film during dehydration condensation, and as a result, zinc oxide or hydroxide is weak at the interface between the inorganic lubricating film and the adhesive. No layer is formed. Therefore, it is estimated that very excellent adhesiveness is expressed.
[0027]
In addition, when a film in which polymerized zinc metaphosphate is at least partially formed is used, the workability is improved even with a smaller amount of P adhesion compared to a conventional zinc phosphate film mainly composed of a white hopite. The reason for this is that, as described above, as the polymerization of the phosphate proceeds, it is modified to a denser and stronger hard film as compared with the conventional zinc phosphate film mainly composed of opium. This is probably because of this. When polymerization progresses and finally the zinc metaphosphate film is formed, an extremely dense and strong hard film is formed, and seizure due to metal contact between the mold and the plating layer during press molding is more effective. Will be prevented.
[0028]
As described above, in the inorganic lubricating film made of zinc phosphate, the film performance greatly changes depending on the progress of partial polymerization of the phosphate, and in order to improve adhesion and workability, polyphosphoric acid is used. The conclusion is that it is necessary to create a polymerized zinc phosphate film from zinc to zinc metaphosphate, and it is advantageous to produce as much of the polymerized zinc metaphosphate as possible in the film. Reached. However, it is not necessary to make the entire film in this manner, and it is sufficient that zinc metaphosphate is generated at least partially on the outermost layer of the inorganic lubricating film, as will be described later.
[0029]
Orthophosphoric acid and polyphosphoric acid or metaphosphoric acid have different atomic ratios of Zn and O to P. Therefore, orthophosphoric acid, polyphosphoric acid, and metaphosphoric acid in the film depend on the Zn / P atomic ratio and O / P atomic ratio in the film. Can be determined. In the present invention, since the outermost layer of the film only needs to be at least partially metaphosphorylated, the Zn / P atomic ratio and the O / P atomic ratio are obtained from the elemental analysis results of the outermost layer of the film by conventional surface analysis means. These values only need to be within a certain range that means the production of metaphosphoric acid.
[0030]
The zinc metaphosphate coating can be formed by treating a zinc-based plated steel sheet with an aqueous solution of metaphosphoric acid, and this method forms an inorganic lubricating coating consisting entirely of zinc metaphosphate. However, metaphosphoric acid is very viscous and has poor liquid stability, and may be difficult to use because it decomposes into oritriic acid and polyphosphoric acid after long-term storage.
[0031]
As another method, a phosphoric acid aqueous solution having a lower degree of dehydration condensation such as orthophosphoric acid or polyphosphoric acid is used for the treatment, and a condensation accelerator such as an oxidizing agent is included in the treatment liquid, and a dehydration condensation reaction is performed during film formation. By promoting and polymerizing the phosphoric acid portion in the film from the surface side, it is possible to form an inorganic lubricating film in which at least the outermost layer of the film is at least partially zinc metaphosphate. This method is superior in the stability of the coating solution, and the film formation is easier.
[0032]
This invention is completed based on the above knowledge, and is the following galvanized steel sheet and its manufacturing method.
(1) Zn / P atomic ratio [Zn / P] and O / P atomic ratio on the surface of the galvanized steel sheet or zinc alloy plated steel sheet satisfying the following formulas (1) and (2): O / P], P conversion adhesion amount 5 to 500 mg / m²A zinc-plated steel sheet excellent in workability, adhesion, and weldability, characterized by having a zinc phosphate-based film of:
(1) [Zn / P] + 1.0 ≤ [O / P] ≤ 3 x [Zn / P] + 1.5
(2) 0.5 ≦ [Zn / P] ≦ 2.8.
[0033]
Here, as described in detail later, the outermost layer means from the surface of the coating to a depth of 60 mm, which can be analyzed by XPS (X-ray photoelectron spectroscopy) in the present invention. That is, the values of [O / P] and “Zn / P” in the above formula are calculated from the elemental composition of the outermost layer obtained by XPS.
[0034]
(2) Concentration on the surface of a galvanized steel sheet or zinc-based alloy-plated steel sheet, the main component of which is one or more selected from orthophosphoric acid and polyphosphoric acid, and the molar ratio of the condensation accelerator to phosphorus in the liquid is 0.03 to 3.0 The aqueous solution having a pH of 1 to 5 contained in the solution is applied and baked and dried at a temperature of 50 to 200 ° C. without being washed with water.²A method for producing the zinc-based plated steel sheet, comprising forming a zinc phosphate-based film.
[0035]
(3) Apply an aqueous solution of pH 1-7 containing metaphosphoric acid as the main component to the surface of a galvanized steel sheet or zinc-based alloy-plated steel sheet, and bake and dry at a temperature of 50-200 ° C without washing with water. Amount of deposit 5 to 500 mg / m²A method for producing a zinc-based plated steel sheet excellent in workability, adhesion, and weldability, characterized by forming a zinc phosphate-based film.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
The zinc-based plated steel sheet targeted in the present invention means a steel sheet in which a zinc-containing plated layer is formed by various methods including a hot dipping method, an electroplating method, a vapor deposition plating method, a thermal spraying method and the like. The plating may be either single-sided plating or double-sided plating. The amount of plating is not particularly limited, but usually 10 to 90 g / m per side²Range.
[0037]
The plating composition is not particularly limited as long as it contains zinc, and is pure Zn plating, Zn alloy plating with one or more elements including Zn and Fe, Al, Ni, Co, etc. SiO for plating₂Including precipitation plating in which fine particles such as carbon are deposited. It may be a plating in which Zn is a small amount of element, such as a 55% Al—Zn hot-dip plated steel sheet. Further, the plating layer is not limited to one layer. It is possible to have a plating film having two or more layers, or a plating film whose composition changes continuously in the thickness direction, but in this case, the plating surface must be plated with zinc. is there.
[0038]
Typical galvanized steel sheets include electrogalvanized steel sheets, hot dip galvanized steel sheets, electric Zn-Ni alloy plated steel sheets, alloyed hot dip galvanized steel sheets, and hot-dip Zn-Al alloy face steel sheets. Of these, electrogalvanized steel sheets, electric Zn-Ni alloy plated steel sheets, and galvannealed steel sheets are frequently used for automobile bodies.
[0039]
In the present invention, at least a part of the outermost layer forms an inorganic lubricating film made of zinc phosphate that has been polymerized to metaphosphoric acid, so that weldability is not deteriorated, and in addition to workability, various adhesives are used. Significantly improves adhesion and adhesive compatibility.
[0040]
The adhesion amount of this inorganic lubricating film is 5 to 500 mg / m as the P amount.²The range. This adhesion amount is 5mg / m²If it is less than 1, the film is too thin to exhibit the lubricating effect, and the workability deteriorates. This adhesion amount is 500 mg / m²If it exceeds 1, the lubricating film is too thick, and in the adhesion test, cohesive failure is likely to occur in the lubricating film, resulting in a decrease in adhesion. In addition, when the zinc phosphate coating that is an insulating coating becomes too thick, weldability also decreases. In order to ensure good workability, adhesion, and weldability, the amount of adhesion of the inorganic lubricating film of the present invention is 20 to 300 mg / m as the P amount.²Is preferred, more preferably 50-200 mg / m²It is.
[0041]
The inorganic lubricating film is a film made of zinc phosphate in which at least a part of the outermost layer is zinc metaphosphate. In zinc phosphate coatings that are at least partially metaphosphorylated by depolymerization and condensation, zinc orthophosphate has almost completely disappeared, and the coating is composed of zinc metaphosphate and zinc polyphosphate (such as zinc pyrophosphate and zinc tripolyphosphate). ) Coexist.
[0042]
In the present invention, the Zn / P atomic ratio [Zn / P] and O / O determined from the surface analysis indicate that the outermost layer of the formed inorganic lubricating film has a composition that is at least partially zincated. Determined based on P atomic ratio [O / P]. That is, if these atomic ratios satisfy the following formulas (1) and (2), the outermost layer of the coating has the above composition:
(1) [Zn / P] + 1.0 ≤ [O / P] ≤ 3 x [Zn / P] + 1.5
(2) 0.5 ≦ [Zn / P] ≦ 2.8.
[0043]
The formula (1) defines that the film does not contain excessive oxygen with respect to zinc phosphate including orthophosphoric acid to metaphosphoric acid, and zinc oxide, zinc hydroxide, etc. , Which is generically referred to as zinc oxide). That is, in the outermost layer of the film, all Zn and phosphoric acid are fixed in the film as a zinc phosphate compound, and Zn and P are not present in other forms, so zinc oxide is present in the outermost layer of the film. There is nothing.
[0044]
Formula (2) is a formula that defines the degree of polymerization of phosphoric acid, and means that the zinc phosphate coating of the present invention does not contain orthophosphate as a main component.
As a result of measuring the values of [Zn / P] and [O / P] for various electrogalvanized steel sheets treated with bonderite whose outermost layer is completely zinc phosphate (hopete crystal). [Zn / P] was in the range of 3.0 to 3.5, and [O / P] was in the range of 8 to 12. From this result, it can be seen that as [Zn / P] becomes smaller than 3.0 and approaches 0.5, the condensation of phosphoric acid proceeds and the production rate of zinc metaphosphate increases. The reason why the [Zn / P] value of the bondelite-treated galvanized steel sheet does not agree with the stoichiometric value of 1.5 in the Hopeite is unclear, but in the outermost layer, it is relatively affected by the effect of the remaining zinc oxide. It is thought that the amount of Zn increases. In addition, the normal zinc phosphate crystal has a zinc phosphate film formed on a galvanized steel sheet in view of the fact that Zn in excess of the stoichiometric ratio is incorporated into the bonderite crystal and the film is dense. It is conceivable that Zn from the base plating is detected even in the outermost layer.
[0045]
Regarding (1), if [O / P] <[Zn / P] + 1.0, the amount of phosphoric acid is relatively large, and phosphoric acid other than the zinc phosphate crystals precipitated by the reaction remains and cannot be dried. Alternatively, brittle zinc phosphate powder with excess phosphoric acid remains on the surface of the steel sheet, and the workability and adhesiveness are significantly lowered. [O / P]> 3 × [Zn / P] + 1.5, there is relatively much Zn and O, and undesirable zinc orthophosphate and zinc oxide produced by excessive plating etching are present on the surface. Adhesiveness deteriorates significantly. In addition, such a film may reduce the strength of the film itself, and may form a remarkable needle-like white crystal, resulting in a decrease in workability, an increase in the resistance of the film, and a deterioration in weldability. There is also a problem.
[0046]
Thus, in order to secure good adhesion after forming a film satisfying the formula (1) in which Zn and phosphoric acid are all zinc phosphates, as defined in the formula (2), Zn / The P atomic ratio is in the range of 0.5 to 2.8. Films with [Zn / P] of less than 0.5 have a form in which the precipitation reaction of phosphoric acid and zinc is normally carried out and the phosphoric acid crystals are deposited as they are. In addition, since the fragile zinc phosphate powder remains on the surface of the steel sheet, adhesion and workability cannot be ensured. This film appears even when the phosphoric acid concentration is very low and the amount of the film attached is small, but sufficient workability cannot be ensured. In such cases, it cannot be said that a strong film that can function as an inorganic lubricating film is formed.
[0047]
On the other hand, when [Zn / P] is more than 2.8, a film in which at least a part of zinc metaphosphate having very excellent compatibility with adhesiveness is not formed, and zinc orthophosphate having poor adhesion is not formed. The film becomes a large amount. As the production of zinc orthophosphate increases, the strength of the coating decreases and the workability tends to deteriorate.
[0048]
In the present invention, as described above, the adhesive property and workability are improved by forming the zinc phosphate-based inorganic lubricating coating into a coating that satisfies the above formulas (1) and (2) and is at least partially metaphosphated. To do. In the adhesion test of this film, peeling occurred at the interface between the lubricant film and the adhesive, so that the outermost layer of the lubricant film near the interface with the adhesive was at least partially dense and strongly metaphosphorylated. If it is a composition, workability is also improved. That is, it is not necessary to metaphosphorylate the entire film, and the outermost layer is made of a composition in which at least a part of zinc metaphosphate is formed, and the composition (Zn / P atomic ratio or O / P atomic ratio) is in the thickness direction of the film. Even if it fluctuates, the improvement of the adhesiveness and workability intended by the present invention can be sufficiently ensured.
[0049]
  In this way, the outermost layer of the inorganic lubricating film is zinc metaphosphate ([Zn (PO_Three)₂]_n), And the outermost layer of the film is stoichiometrically close to [Zn / P] = 0.5, [O / P] = 3, which is the composition ratio of metaphosphoric acid Is preferred. However,,Regarding [Zn / P], as described above, the value obtained by the XPS measurement is larger than the stoichiometric value, and therefore, the range of 0.7 to 1.8 is actually preferable.
[0050]
The determination of the film structure is performed by conducting an elemental analysis of the outermost layer of the film by XPS capable of elemental analysis of the solid surface and obtaining the above composition ratio. In XPS, the XPS intensity at the binding energy of each element is measured, and the amount of each element present on the surface is calculated from the intensity as the element abundance ratio. The Zn / P atomic ratio and the O / P atomic ratio are obtained from the elemental analysis values, and the above formulas (1) and (2) may be satisfied. The film may be either crystalline or amorphous, and both may be mixed.
[0051]
In the present invention, the outermost layer of the film means from the surface that can be analyzed by XPS to a depth of 60 mm. Sputtering is performed to a depth of 60 mm by XPS analysis, and the atomic ratio of Zn / P and the atomic ratio of O / P at that time are taken as the Zn / P atomic ratio and O / P atomic ratio of the outermost layer of the film.
[0052]
The zinc phosphate coating used as an inorganic lubricating coating in the present invention may incorporate other metal salts (eg, metal soap) and colloidal particles (eg, colloidal silica) into the coating to improve workability. it can. However, the total amount should not be more than zinc phosphate. Other metal salts are preferably insoluble. If it is soluble in water or an aqueous phosphoric acid solution, it reacts with phosphate ions during film formation, and the Zn / P atomic ratio of formula (2) does not accurately reflect the degree of metaphosphorylation.
[0053]
The formation method of the inorganic lubricating film in which at least a part of the outermost layer of the present invention is zinc metaphosphate is not particularly limited, and an arbitrary film capable of forming a film whose composition of the outermost layer satisfies the formulas (1) and (2). The zinc-plated steel sheet can be surface-treated by the method. As a treatment method, a coating type treatment is preferable from the viewpoint of waste liquid treatment, equipment, cost, and the like.
[0054]
The inorganic lubricating film can be formed by treating a zinc-based plated steel sheet with an aqueous solution containing metaphosphoric acid. Metaphosphoric acid is a colorless glassy solid, but is readily soluble in water and retains the structure of metaphosphoric acid for a while even in an aqueous solution. Inorganic lubrication consisting essentially of zinc metaphosphate on the surface of the zinc-based plated steel sheet when the zinc-based plated steel sheet is treated (eg, coated) with a treatment solution comprising a metaphosphoric acid aqueous solution and then baked and dried to remove moisture. A film can be formed. However, if the metaphosphoric acid aqueous solution is left in an aqueous solution state, it undergoes hydrolysis and gradually changes to orthophosphoric acid, so that there is a problem that the life of the treatment liquid is short.
[0055]
Therefore, an inorganic lubricating film in which at least a part of zinc metaphosphate is generated can be formed using at least one of orthophosphoric acid and polyphosphoric acid (such as pyrophosphoric acid and tripolyphosphoric acid) instead of metaphosphoric acid. This method has a long processing solution life.
[0056]
In the case of using orthophosphoric acid and / or polyphosphoric acid, it is preferable that a condensation accelerator coexists in the treatment liquid in order to promote metaphosphorylation (polymerization) by dehydration condensation. The condensation accelerator may be any substance that can promote polymerization by the dehydration condensation reaction of orthophosphoric acid or polyphosphoric acid, but is typically an oxidizing agent. Oxidizing agents that can be used include inorganic peroxides, nitric acid, permanganate, dichromate, and salts thereof.
[0057]
As the inorganic peroxide, peroxo acid or a salt thereof, hydrogen peroxide and the like can be used. Examples of peroxo acids are peroxosulfuric acid, peroxoboric acid, peroxocarbonic acid, peroxophosphoric acid and the like. Since it is not preferable in terms of performance that other elements enter the lubricating film as impurities, it is preferable that the reaction product does not become an impurity. For example, peroxophosphoric acid that is directly incorporated into the film as a constituent element even when decomposed, or hydrogen peroxide that is decomposed into water and oxygen by an oxidation-reduction reaction is preferable.
[0058]
From the same viewpoint, use of nitric acid or zinc nitrate is also preferable. Nitric acid is decomposed into nitrogen dioxide and oxygen by an oxidation-reduction reaction during dehydration condensation, and is not gasified and remains in the film. In the case of zinc nitrate, nitrate ions are gasified in the same manner as nitric acid, and zinc ions are taken into the lubricating film as a constituent element.
[0059]
In the case of permanganate or dichromate, the reaction product remains as a metal salt in the lubricating film. However, permanganates such as potassium permanganate can improve workability by strengthening the phosphoric acid film, and dichromates such as potassium dichromate can improve rust prevention. That is, these oxidizers can be used as long as the Zn / P atomic ratio and the O / P atomic ratio of the outermost layer can be ensured within the range defined in the present invention, since performance improvement other than adhesiveness can be expected. .
[0060]
The amount of the oxidizing agent (or other condensation accelerator) added depends on whether the phosphoric acid used is orthophosphoric acid or polyphosphoric acid, but generally the molar ratio of the oxidizing agent to phosphorus (P) in the liquid is 0.03 to 3.0, The amount is preferably 0.08 to 2.0. If the addition amount of the oxidizing agent is too small, the polymerization by the dehydration condensation reaction of the phosphoric acid compound is insufficient, and the metaphosphoric acid compound is not formed on the outermost layer, so that the Zn / P atomic ratio increases. If the amount of the oxidant added is too large, polymerization by the dehydration condensation reaction is promoted and metaphosphorylation proceeds, but excess oxidant remains in the film. The remaining oxidizer accelerates the etching reaction of the plating, so excess Zn²⁺Is generated and remains as surface zinc oxide, which increases the O / P atomic ratio and also increases the Zn / P atomic ratio, thereby deteriorating the adhesion.
[0061]
It is of course possible to use a mixed aqueous solution of metaphosphoric acid and orthophosphoric acid and / or polyphosphoric acid as the phosphoric acid aqueous solution. In that case, a condensation accelerator such as an oxidizing agent may not be added.
[0062]
When an aqueous solution of orthophosphoric acid and / or polyphosphoric acid is used, the pH of the treatment solution is in the range of 1 to 5, preferably 1.5 to 3.5. If the treatment solution pH is too high, an etching reaction in the plating film is difficult to occur, Zn is not taken into the film effectively, and film formation is difficult to occur. Moreover, the dehydration condensation promotion reaction of orthophosphoric acid or polyphosphoric acid to metaphosphoric acid by the condensation accelerator does not proceed. As a result, if the treatment solution pH is too low, the etching reaction proceeds excessively and the elution of the plating layer becomes intense. As a result, excess Zn is formed in the film more than the formation of zinc phosphate, and zinc oxide remains in the surface layer, so that a film satisfying the formula (2) cannot be formed.
[0063]
When metaphosphoric acid is used as an aqueous phosphoric acid solution and a condensation accelerator is not required, it is not necessary to maintain a low pH for the condensation promoting reaction, and the pH of the treatment solution is such that etching of Zn in the plating film occurs. All that is necessary is to incorporate Zn. In this case, the treatment solution pH is in the range of 1 to 7, preferably 1 to 5.
[0064]
If necessary, an etchant such as hydrofluoric acid may be added to remove dirt before forming the lubricating film or to promote etching to effectively incorporate Zn into the film during the formation of the lubricating film. It is also possible to heat. When heating the treatment liquid, the treatment liquid temperature is preferably maintained at 70 ° C. or lower. If the treatment liquid temperature is too high, the etching becomes excessive, so that zinc oxide tends to remain on the surface, the O / P atomic ratio increases, and it becomes difficult to ensure stable adhesion. Further, the evaporation amount of the treatment liquid increases, and it becomes difficult to stably maintain the treatment liquid composition due to the concentration of the phosphoric acid solution, the decomposition of the oxidizing agent, and the like.
[0065]
Furthermore, Zn can be added to the treatment liquid in order to promote the formation of the zinc phosphate film. In that case, it is conceivable to add Zn as a soluble primary zinc orthophosphate or as a zinc nitrate as a condensation accelerator.
[0066]
The treatment solution pH is adjusted by adding an alkali as a pH adjuster to the phosphoric acid aqueous solution as necessary. As an alkali, any of inorganic alkalis, such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide, and organic bases, such as an amine, may be sufficient.
[0067]
The concentration of phosphoric acid in the treatment liquid affects the amount of film deposited. A preferable phosphoric acid concentration is in a range of 0.05 to 3.0 mol / l as a molar concentration as P in the treatment liquid. The adhesion amount can be easily controlled by the phosphoric acid concentration and the coating amount.
[0068]
The above-mentioned treatment solution is applied to a galvanized steel sheet and heated to 50 to 200 ° C. without being washed with water, and the film is baked and dried. During this baking and drying, a part of the zinc of the plating film is dissolved by the reaction between the applied treatment solution and the plating, and is combined with phosphate ions to become zinc phosphate, and phosphoric acid is orthophosphoric acid and / or Alternatively, in the case of polyphosphoric acid, polymerization (metaphosphorylation) by dehydration condensation also proceeds, resulting in a film in which dense zinc metaphosphate is generated at least partially.
[0069]
Baking and drying is performed so that water of crystallization remaining in the polymerized zinc phosphate film and zinc oxide on the film surface disappear. Thereby, the adhesiveness of the film is significantly improved. When the heating temperature is lower than 50 ° C., the dehydration condensation reaction is difficult to proceed, and it becomes very difficult to form a polymerized zinc phosphate film, which requires a very long time which is not practical. On the other hand, when the heating temperature exceeds 200 ° C., the efficiency of the polymerization is not further improved, and on the contrary, the surface oxidation proceeds too much, and zinc oxide is formed in the outermost layer, and O / Zn of the outermost layer The ratio increases, resulting in a decrease in adhesion. A preferred heating temperature is 70 to 150 ° C.
[0070]
In this way, since a coating-type treatment method that does not wash with water is used, a reaction in which a plating film is dissolved by a treatment solution as in the prior art, a film is formed by the reaction, and then unreacted substances are removed by washing with water. Compared with mold processing, in addition to the advantage that the water washing step can be omitted, it is also advantageous in that it is not necessary to consider contamination of the processing liquid.
[0071]
The treatment liquid may be applied by any method such as dipping, spraying, and roll coater as long as the treatment liquid can be uniformly applied to the plated steel sheet. The treatment liquid temperature is not particularly limited, but as described above, it is preferable to increase the treatment liquid temperature from the viewpoint of promoting the etching of Zn from the plating film for the purpose of promoting film formation. In order to ensure the uniformity of the film forming reaction, it is preferable to maintain the liquid temperature at a constant temperature. Also, it is not preferable to make the temperature of the treatment liquid too high in order to avoid concentration by evaporation or destabilization of the treatment liquid composition due to suppression of decomposition of the condensation accelerator in the liquid.
[0072]
Considering the above, the treatment liquid temperature is preferably 30 ° C. or higher and 70 ° C. or lower. Even in a treatment liquid containing metaphosphoric acid, it is preferable to heat the treatment liquid and maintain it at a constant temperature in the range of 30 to 70 ° C. in order to accelerate etching from the plating film.
[0073]
When the galvanized steel sheet is double-sided plating, it is preferable to apply the treatment liquid on both sides, but it is also possible to treat only one side.
Before applying the treatment liquid, the galvanized steel sheet may be pretreated with an alkaline aqueous solution, an acid aqueous solution, or both. This pretreatment removes dirt and impurity components from the plating surface, and the surface is etched and activated, facilitating the formation of a zinc metaphosphate-based film by dissolution of Zn and the reaction between dissolved Zn and phosphoric acid. Is done. When the metaphosphate formation of the film is promoted in this way, the adhesion and workability may be improved as compared with the case without pretreatment.
[0074]
The aqueous alkaline solution may be an aqueous solution of any compound that is dissolved in water and exhibits alkalinity (basic). For example, any of inorganic alkalis such as sodium hydroxide, potassium hydroxide and ammonium hydroxide (ammonia) and organic amines can be used. The liquid temperature is not particularly limited, but is preferably in the range of 40 to 70 ° C. in order to shorten the processing time. The pH of the aqueous solution only needs to be alkaline enough to etch the plating surface, and is preferably 9 or more.
[0075]
The aqueous acid solution may be an aqueous solution of any compound that dissolves in water and exhibits acidity. For example, any of inorganic acids such as sulfuric acid and hydrochloric acid and organic acids such as citric acid and acetic acid can be used. An acidic electroplating solution containing Zn, Fe, or the like can also be used. The liquid temperature is not particularly limited, but is preferably in the range of 40 to 70 ° C. in order to shorten the processing time. The pH of the aqueous solution only needs to be acidic enough to etch the plating surface, and is preferably 5 or less.
[0076]
Pretreatment with an aqueous alkali solution and / or an aqueous acid solution is economical and simple to perform by immersion, but can also be carried out by other methods such as spraying and roll coating. The treatment time varies depending on the liquid temperature of the aqueous solution, but it is preferably about 1 to 10 seconds at a liquid temperature of 40 to 70 ° C., regardless of whether the aqueous solution is an acid aqueous solution or an alkaline aqueous solution. If it is shorter than 1 second, etching is insufficient and the effect of the pretreatment does not appear sufficiently. If it exceeds 10 seconds, etching of the galvanized plating film becomes excessive, and in the case of immersion, the aqueous solution deteriorates immediately and the etching effect is lost.
[0077]
Before performing this pretreatment, it is preferable to wash the galvanized steel sheet with water. Without washing with water, when pre-treated by dipping, the deposit on the plating surface that was dissolved during dipping will re-attach to the surface, hindering the formation of the zinc phosphate coating, and the deposit will form unevenness and patterns. The appearance of the product may be damaged. It is preferable to wash with water after pretreatment with an aqueous alkali solution and / or an aqueous acid solution. Moreover, also when processing directly with phosphoric acid aqueous solution, without performing such a pretreatment, you may wash a zinc-plated steel plate before a process.
[0078]
The zinc-based plated steel sheet having a zinc phosphate-based inorganic lubricating film produced by the method of the present invention is a remarkably improved press while maintaining the good weldability, adhesiveness, and chemical conversion property of the zinc-based plated steel sheet. It has moldability and can perform severe press molding without causing galling or powdering. Therefore, it is particularly suitable for automobiles where press molding is frequently used, but it can also be used for home appliances and building materials.
[0079]
In addition, with regard to adhesiveness, for example, for automobiles, comparative adhesives with relatively high adhesive strength such as structural adhesives and rust-proof sealants, and comparisons aimed at reinforcing panels and improving rust-proofing of welds Both mastic type adhesives with low mechanical bond strength are used, but the inorganic lubricant film of the present invention is excellent in adhesive compatibility, so that any type of adhesive can obtain good adhesion results. it can. Moreover, since the improved adhesiveness is exhibited, sufficient adhesive force can be secured even in a temporary fixing (precure) stage or T-type bonding.
[0080]
【Example】
In the following examples,% is% by mass unless otherwise specified. The concentration of phosphoric acid is the molar concentration (mol / l) as P.
[0081]
(Example 1)
In this example, an example in which an inorganic lubricating film is formed on the surface of a zinc-based plated steel sheet by a treatment using a phosphoric acid treatment solution containing orthophosphoric acid or polyphosphoric acid and an oxidizing agent according to the method of the present invention will be described.
[0082]
The following double-sided zinc-based plated steel sheet (weight per side) was used for the treatment, using an ultra-low carbon IF steel with a thickness of 0.80 mm as the material to be plated.
Galvanized steel sheet
Symbol Plating type Weight per unit area
EG Electrogalvanized steel sheet 40 g / m²
SZ Electric Zn-13% Ni alloy plated steel sheet 30 g / m²
GA alloyed hot-dip galvanized steel sheet (Fe: 10%) 55 g / m².
[0083]
Various phosphoric acid treatment liquids of the following types, concentrations (mol / l), pH, and liquid temperature were applied to both surfaces of these galvanized steel sheets by spraying or dipping. In the dip coating, after the immersion for 3 seconds, it was adjusted so as to have a predetermined adhesion amount by roll drawing. The coated steel sheet is immediately put into an infrared oven without being washed with water, and baked and dried under the conditions of a maximum plate temperature of 30 to 250 ° C. and a baking time of 7 seconds to form a zinc phosphate coating on the plating surface. Formed. Thus, the workability, adhesion and weldability of the zinc-based plated steel sheet on which the inorganic lubricating film was formed were tested by the methods described later.
[0084]
Formation of zinc phosphate inorganic lubricant film
Types of phosphoric acid: orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid
Phosphoric acid concentration: 0.10 to 1.0 mol / l
Molar ratio of oxidizing agent / phosphoric acid in liquid: 0 to 0.3
Solution pH: 0.5 to 5.5
Liquid temperature: 45 ℃
Maximum plate temperature: 40-250 ° C.
[0085]
In some phosphating solutions, aqueous ammonia is used as a pH adjuster and / or hydrogen peroxide (H₂O₂), Potassium permanganate (KMnO_Four), Nitric acid (HNO_Three) Or zinc nitrate [Zn (NO_Three)₂] Was added to study the modification of the formed zinc phosphate coating. The adhesion amount (P amount) of the zinc phosphate coating was adjusted by changing the concentration of the treatment liquid and the coating method.
[0086]
Prior to the treatment with the above phosphoric acid treatment liquid, some zinc-based plated steel sheets were subjected to the following immersion treatment with an alkaline aqueous solution and / or an acid aqueous solution as a pretreatment. When both aqueous solutions were used for the pretreatment, first, alkali immersion and then acid immersion were performed.
[0087]
Alkaline soaking: After soaking in a 10 mass% sodium hydroxide aqueous solution at 60 ° C, washing with warm water at 80 ° C;
Acid dipping: After dipping in a 10% by mass sulfuric acid aqueous solution (pH = 1.5) at 50 ° C., it was washed with warm water at 80 ° C.
[0088]
Amount of coating and surface composition
The adhesion amount (P equivalent amount) of the formed zinc phosphate coating was determined from the characteristic X-ray intensity of P by FX (fluorescence X-ray) analysis. Moreover, the outermost layer composition of the film was measured with an X-ray photoelectron analyzer (XPS). In XPS, the XPS intensity at the binding energy of the solid surface is measured, and the surface abundance ratio of each element can be obtained from the intensity. The XPS measurement was carried out under the following conditions.
[0089]
(XPS measurement conditions)
X-ray source: Mg-Kα (8 kA-30 mA)
Sputtering: Ar fast ion etching (50 kV-0.6A)
Sputtering speed: 12-13mm / s
After sputtering under the above conditions for 5 seconds (about 60 mm in the depth direction), the abundance of each element in the surface layer is determined from the peak area of the XPS intensity peak at the binding energy of each element based on theoretical calculations, and Zn / P atomic ratio and Zn / O atomic ratio were calculated. The reason why the electrode surface layer having a thickness of about 60 mm is removed from the surface by sputtering for 5 seconds before the XPS measurement is that the electrode layer is difficult to accurately determine due to contamination.
[0090]
When the values of the Zn / P atomic ratio and Zn / O atomic ratio thus obtained satisfy the conditions of the formulas (1) and (2) defined in the present invention, at least the outermost layer of the coating contains zinc metaphosphate. It can be determined that a film is formed.
[0091]
Separately, X-ray diffraction (XD) was used to determine whether the coating was at least partially crystalline or completely amorphous. The X-ray diffraction conditions at that time are as follows.
(XD measurement conditions)
Tube: Co-Kα
Tube voltage: 40 kV
Tube current: 400 mA
Diffraction angle: 10-100 °.
[0092]
For the determination, the zinc orthophosphate [Zn_Three(PO_Four)₂・ 4H₂O] Crystal or zinc metaphosphate [Zn₂P_FourO₁₂・ 8H₂O] When a diffraction peak of the crystal was detected, it was judged that crystalline was present in the film. The diffraction peak planes in this case include (020) plane, (220) plane, (040) plane, (151) plane, etc. for the Hopeite crystal, and (100) plane, (-110) plane for the zinc metaphosphate crystal. Surface, (-201) surface, (200) surface and the like.
[0093]
Processability evaluation
The workability was evaluated by measuring the limit load that can be formed when the blank holder load was increased by 5 kN pitch in cylindrical drawing press forming. The processing conditions and evaluation criteria (up to ○ are acceptable) are as follows.
[0094]

(Evaluation criteria)
◎:> 70 kN
○: 50 to 70 kN
×: <50 kN.
[0095]
In the processing of galvanized steel sheets, it is common to use a highly lubricious rust preventive oil to ensure processability. For reference, 2 g / m of Idemitsu oil coat SP2, which is a highly lubricious rust preventive oil, is applied to each EG, SZ and GA galvanized steel sheet.²When the same test was carried out with oiling, the forming limit load was 50 to 70 kN. From this result, the target level of workability was set to 50 kN or more, preferably more than 70 kN. In this test, 2 g / m of Idemitsu oil coat SK, which is a general anti-rust oil, as described above.²After oiling, it was subjected to a workability test.
[0096]
Adhesive evaluation
Adhesion is an adhesive for car body structure (adhesive sealer epoxy adhesive: made by Henkel Hakusui) and has a lower adhesive strength than car body structure adhesive, and is said to be a more stringent mastic adhesive. Two types were tested. As an adhesion test method at that time, the shear tensile strength was measured for the mastic type adhesive, and the adhesive strength at the T-shaped peeling that was more likely to cause peeling was measured for the body structure adhesive. In addition, since the adhesive for body structure is also required to have an adhesive strength in the temporarily fixed state, considering the influence of baking conditions, full curing conditions for baking at 170 ° C for 30 minutes and precuring conditions for baking at 160 ° C for 10 minutes The T-peel strength was measured under the two types of baking conditions.
[0097]
In order to evaluate the oil level adhesion, before applying the adhesive, Idemitsu oil coat SK, a general anti-rust oil, is 2 g / m.²Apply oil to both adhesive surfaces of the two test pieces, store them in a humid atmosphere (50 ° C x 95% RH) for 7 days, and then apply the adhesive to a predetermined area of one test piece. Two test pieces were stacked using a spacer so that the thickness of the adhesive was 0.15 mm, and the adhesive was cured by baking under predetermined baking conditions, and the adhesive strength was investigated.
[0098]
The test conditions and evaluation criteria for each adhesion test (passed up to ○) are as follows.

[0099]
(Evaluation criteria)
2.0 g / m of general rust-preventive oil (Idemitsu oil coat SK) is applied to cold-rolled steel sheets of the same base material without a lubricating film.²If the adhesion strength under the same test conditions when oiled is 0.20 MPa and then the adhesive strength when the strength drops by 30% is 0.14 MPa or more, there is no practical problem. Sex was evaluated.
[0100]
A: Shear strength ≥ 0.20 MPa
○: Shear strength = 0.14 to 0.20 MPa
X: Shear strength <0.14 PMa.
[0101]

[0102]
(Evaluation criteria)
2.0 g / m of general rust-preventive oil (Idemitsu oil coat SK) is applied to cold-rolled steel sheets of the same base material without a lubricating film.²If the adhesive strength under the same test conditions when oiled is 30 KPa under the pre-curing condition, and the adhesive strength when the strength drops by 30% = 21 KPa or more, there will be no practical problem. The adhesiveness was evaluated based on the following criteria.
[0103]
A: Peel strength ≧ 30 KPa,
○: Peel strength = 21-30 KPa
X: Peel strength <21 KPa.
[0104]
Weldability evaluation
For weldability, a continuous spot spot welding test is performed under the conditions shown below, the nugget diameter is checked every 100 spots, and the limit number of continuous spots until the nugget cannot be formed (the nugget diameter cannot be obtained) is obtained. It was evaluated by. For comparison, each EG, SZ and GA galvanized steel sheet is coated with 2 g / m of Idemitsu oil coat SP2, which is a highly lubricating anti-rust oil.²When the spot weldability was tested under the same conditions after oiling, the limit number of continuous hit points was 2500 to 5000 hit points. Therefore, 2500 hit points or more, preferably 4000 hit points or more were set as target levels. In this test as well, Idemitsu oil coat SK, a general anti-rust oil, was 2 g / m.²After oiling, it was used for the test.
[0105]
(Welding conditions)
Electrode material: Cu-1% Cr
Electrode shape: CF type (tip diameter = 5mm)
Applied pressure: 200 kgf
Squeeze time: 15 cycles
(Time from pressing the steel plate to energizing)
Energizing time: 10 cycles
Retention time: 20 cycles
(Time from energization to electrode opening)
Setting current: 10.5 kA
Riding speed: 2 seconds / point.
[0106]
(Evaluation criteria) (Up to ○ pass)
A:> 4000 RBIs
○: 2500 to 4000 RBIs
×: <2500 RBIs.
[0107]
The above test results are shown in Tables 1 and 2 together with the type of galvanized steel sheet, the composition of the treatment liquid and the treatment conditions.
[0108]
[Table 1]

[0109]
[Table 2]

[0110]
As can be seen from Tables 1 and 2, in the No. 1 comparative example in which the zinc phosphate coated steel sheet was not formed and the zinc phosphate lubricant film was not formed, the weldability and adhesion were good, but the press formability Is very inferior.
[0111]
On the other hand, in the present invention example in which the zinc phosphate inorganic lubricating film is formed according to the present invention, the press formability is remarkably improved while maintaining the adhesiveness and weldability. Even if the plating type, phosphoric acid type, additives, and coating method are changed, sufficient performance can be obtained in any case.
[0112]
However, when the composition of the outermost layer of the film, the film adhesion amount, or the manufacturing conditions are out of the scope of the present invention, the performance of any of press formability, weldability, and adhesiveness is inferior.
For example, unless an oxidant as a condensation accelerator is added, the Zn / P ratio of the outermost layer is high, and the expected improvement in adhesive strength cannot be obtained (No. 2 to 4). An improvement in adhesion strength when an oxidizing agent is added is obtained when the molar ratio of oxidizing agent to P in the liquid is within the scope of the present invention. The pH of the treatment solution also has an effect, and when the pH is 0.7 or more and 5 or less, particularly in the range of 1.5 to 3.5, the coating composition becomes appropriate and the adhesiveness is improved. The amount of film deposited is 5 mg / m in P equivalent.²If it is above, sufficient workability can be secured. To ensure suitable workability, it depends on the type of plating on the base, but it is 20 mg / m for zinc alloy-plated steel sheets.²50 mg / m for soft pure galvanized steel sheet²The above adhesion amount is preferable. Adhering amount is 500 mg / m²If it exceeds 1, spot weldability cannot be ensured, and even if the film composition of the outermost layer is appropriate, the adhesiveness is slightly lowered. 300 mg / m in terms of spot weldability²The following adhesion amounts are preferred.
[0113]
When the baking temperature is low, a film is formed but it is not sufficient, and the adhesive strength cannot be secured. When the baking temperature is high, the surface is in a peroxidized state, a fragile layer of zinc oxide is formed on the surface of the film, the O / P atomic ratio is too high, and the adhesiveness is poor. When the P adhesion amount is too large, a fragile layer is easily formed, and both adhesiveness and weldability deteriorate. It can be seen that when the amount of P deposited is small and the phosphoric acid applied in the water washing step is washed away, sufficient processability cannot be secured.
[0114]
The presence or absence of the crystalline material has little influence on the adhesiveness by securing the outermost layer Zn / P atomic ratio and the O / P atomic ratio, but when the crystalline material is present, there is a tendency for the workability to decrease. As pretreatment, when immersion in acid and / or alkali is performed, the amount of P adhesion increases and the processability can be easily improved. .
[0115]
(Example 2)
In this example, an example in which an inorganic lubricating film is formed on the surface of a zinc-based plated steel sheet using a metaphosphoric acid aqueous solution (containing no oxidizing agent) according to the method of the present invention will be described.
[0116]
The treatment method and the test conditions are the same as in Example 1 except that the treatment liquid contains metaphosphoric acid as phosphoric acid and no oxidizing agent. The test results are shown in Table 3 together with the type of galvanized steel sheet, the composition of the treatment liquid and the treatment conditions.
[0117]
[Table 3]

[0118]
As shown in Table 3, when an inorganic lubricating film is formed using a metaphosphoric acid aqueous solution whose pH is appropriately adjusted, the Zn / P atomic ratio and O of the outermost layer according to the present invention can be added without adding an oxidizing agent. It can be seen that a good performance can be obtained if the / P atomic ratio can be easily secured, and an appropriate amount of deposited P can be secured.
[0119]
In the comparative example which deviates from the conditions of the present invention, any one of the press formability, weldability and adhesiveness is inferior. When the pH of the treatment liquid is high, the formation of the phosphate film is insufficient, the film composition is out of range, the film is brittle, and in particular, adhesion cannot be ensured at all. If the pH is too low, etching is too strong, zinc oxide remains on the surface, and the O / P atomic ratio on the outermost layer is too high, resulting in poor workability and adhesion. When the baking temperature is low, a film is formed, but it is not sufficient, and the adhesive strength cannot be ensured. When the baking temperature is high, the surface is in a peroxidized state, and a fragile layer of zinc oxide is formed on the surface of the film, resulting in poor adhesion.
[0120]
FIG. 3 shows the comprehensive test results of adhesion obtained in Example 1 and Example 2 as the relationship between the Zn / P atomic ratio and the O / P atomic ratio of the outermost layer of the coating. Table 4 shows the criteria for the test results (symbols) displayed in FIG. As can be seen, in FIG. 3, the best results (◎) in all adhesion tests are marked with ●, all tests with a pass (◯) or better are marked with ○, and all tests have one. However, what was rejected (x) was represented as x.
[0121]
[Table 4]

[0122]
As shown in FIG. 3, the zinc phosphate-based coating having the composition ratio of the outermost coating layer according to the present invention is good not only for the vehicle structural adhesive but also for the mastic adhesive which is an adhesive having low adhesive strength. It is clear that can be secured. Adhesiveness is excellent particularly in the range of Zn / P = 0.7 to 1.8. When the outermost layer of zinc oxide is suppressed and the outermost layer is made of a zinc metaphosphate-based film, the adhesiveness is remarkably improved. I understand.
[0123]
【The invention's effect】
When an inorganic lubricating film is formed on a galvanized steel sheet according to the present invention, the workability can be greatly improved so as to withstand severe press forming without impairing the weldability and adhesiveness of the galvanized steel sheet. This makes it possible to achieve both adhesiveness and workability, which was difficult with conventional inorganic lubricating coatings. Various adhesives used for automobile bodies (not only body adhesives, but also low-strength mastic types) A wide range of adhesive compatibility that enables bonding with adhesives (including adhesives) is provided, and there is no lubricating film such as adhesive strength under pre-cure conditions (pre-cure conditions) and adhesive strength under various conditions. An inorganic lubricant-treated galvanized steel sheet that can use an adhesive in the same manner as described above is provided.
[0124]
Therefore, since the inorganic lubricated zinc-based plated steel sheet of the present invention can be assembled using either spot welding or adhesive after being processed into a predetermined shape by press molding, it is optimal as a steel sheet for automobile bodies. Has performance.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a shear tensile test method used for evaluating adhesiveness with a mastic type adhesive.
FIG. 2 is an explanatory view showing a T-peeling tensile test method used for adhesive evaluation with an adhesive for vehicle body structure.
FIG. 3 is a diagram showing the relationship between the surface layer element abundance ratio measured by XPS of various lubricating treatment films and the adhesive strength of an adhesive for body structure and a mastic type adhesive.

Claims (5)

On the surface of a galvanized steel sheet or a zinc alloy plated steel sheet, the zinc equivalent eluted from the plating is used as the zinc supply source, and the P conversion deposit is 5 to 500 mg / m ² Zn / P atomic ratio [Zn / P] and O / P atoms in which the elemental composition of the outermost layer of the zinc phosphate coating satisfies the following formulas (1) and (2) : and wherein the benzalkonium give the ratio [O / P], processability, adhesion, good galvanized steel sheet weldability.
(1) [Zn / P] + 1.0 ≦ [O / P] ≦ 3 × [Zn / P] +1.5
(2) 0.5 ≤ [Zn / P] ≤ 2.8   The surface of the galvanized steel sheet or zinc-based alloy plated steel sheet contains at least one selected from orthophosphoric acid and polyphosphoric acid as a main component, and contains a condensation accelerator at a concentration such that the molar ratio to phosphorus in the liquid is 0.03 to 3.0. The method for producing a galvanized steel sheet according to claim 1, wherein an aqueous solution of pH 1 to 5 is applied and baked and dried at a temperature of 50 to 200 ° C. without washing with water.   The method of claim 2, wherein the condensation accelerator is an oxidizing agent.   A surface of a galvanized steel sheet or a zinc-based alloy-plated steel sheet is coated with an aqueous solution having a pH of 1 to 7 containing metaphosphoric acid as a main component, and baked and dried at a temperature of 50 to 200 ° C. without washing with water. Item 2. A method for producing a galvanized steel sheet according to Item 1.   The method according to any one of claims 2 to 4, wherein the galvanized steel sheet or the zinc-based alloy-plated steel sheet is pretreated with an alkaline aqueous solution and / or an acid aqueous solution before application of the aqueous solution.

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