JP2003127271A - Coated steel plate for metal gasket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated steel plate which can be mass-produced in a short time and has high sealing properties by being coated with a resin in place of rubber. SOLUTION: In the coated steel plate, on one side and/or both sides of a steel plate, an under coat film 1-20 μm in thickness and a top coat film 20-60 μm in thickness containing a urethane resin of a reaction product between a polyesterpolyol and a blocked polyisocyanate as a main component are laminated so that the total thickness of the films is at least 40 μm. The undercoat film is preferably formed by a coating containing an epoxy resin as a resin base. By incorporating 5-70 pts. mass of carbon black into the top coat film and/or the undercoat film, the sealing properties can be improved. An austenitic stainless steel plate at least 310 in Hv is used preferably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel sheet for a metal gasket used for sealing a cylinder head of an automobile engine.

[0002]

2. Description of the Related Art A metal gasket used for sealing a cylinder head of an automobile engine is made of rubber such as silicone rubber or nitrile rubber (NBR rubber) having reversible elasticity on the metal surface in order to improve the sealing property.
It is coated with a thickness of 0 μm or more (Japanese Patent No. 30998).
No. 28). When this rubber-coated metal plate is used for gaskets such as cylinder heads, the force to return when the rubber is tightened, that is, reversible elasticity, does not create a gap at the interface between the cylinder head and the metal gasket and maintains airtightness. You can Rubber generally exhibits reversible elasticity, also called rubber elasticity, because it has an elongation of several hundreds of percent, and has a high sealing property in gaskets and the like.

[0003]

However, when an attempt is made to form a rubber coating layer on the surface of a metal, for example, Japanese Patent Laid-Open No. Hei 6 (1994) -96
As seen in Japanese Unexamined Patent Publication No.-33037, it is necessary to perform cleaning or chemical conversion treatment on the metal surface in advance. Furthermore, after forming the adhesive film, the rubber solution is applied, and it takes several tens of minutes to dry the solvent component in the rubber solution and several tens of minutes to vulcanize. there were. As described above, it is difficult to inexpensively manufacture the rubber-coated metal gasket, and the application is limited to high-class automobiles. In today's demand for improved automobile safety, there is a strong demand for metal gaskets with high sealing properties to be applied to low-priced vehicle models. Therefore, the present invention has been devised to solve the above-mentioned problems, and by coating a resin instead of rubber, it is possible to mass-produce a metal gasket in a short time, and a metal gasket having a high sealing property at low cost. An object is to provide a coated steel sheet that can be obtained.

[0004]

In order to achieve the object, the coated steel sheet for metal gasket of the present invention has an undercoating film having a film thickness of 1 to 20 μm and a polyester polyol on one side and / or both sides of the steel sheet. A top coating film having a film thickness of 20 to 60 μm, which is mainly composed of a urethane resin which is a reaction product with a blocked polyisocyanate, is laminated in a total film thickness of 40 μm or more. The undercoat coating film is preferably formed of a coating material containing an epoxy resin as a resin base. Further, it is preferable that 5 to 70 parts by mass of carbon black is blended in the top coating film and / or the under coating film. Furthermore, as a steel plate, H
It is preferable to use an austenitic stainless steel plate with v = 310 or more.

[0005]

BACKGROUND OF THE INVENTION The present inventors have examined a coating material and a coating method in place of rubber in order to inexpensively manufacture a gasket having a high sealing property. First, a method of laminating a stretchable resin film on the surface of a steel sheet was examined. Cylinder heads for automobile engines are used in environments exposed to 100-200 ° C antifreeze containing various additives such as rust preventive agents, so resin that is simply pasted onto a steel plate with an adhesive, etc. In the case of films, there is concern about peeling at the interface between the steel plate and the resin film. In addition, the base material of metal gaskets for cylinder heads for automobile engines is usually 0.2 m.
A thin steel plate having a thickness of about m is used, and it is extremely difficult to continuously laminate a resin film on the surface of such a thin steel plate.

Therefore, as a second method, a method of forming a resin coating film on the surface of a thin steel sheet was examined. In the resin coating film forming method by painting, the painting itself is a large continuous painting facility,
Moreover, since both sides can be coated and the coating film can be cured in a baking time of about 1 minute, it can be manufactured at a speed 10 times or more as high as that of the rubber coating method which requires vulcanization. However, in order for resin-coated steel sheets to be used as a substitute for rubber-coated steel sheets for metal gaskets, the adhesiveness between the steel sheet and the coated resin layer does not separate even when exposed to high-temperature antifreeze, and a seal equivalent to rubber. It is necessary to have reversible elasticity equal to that of rubber for imparting elasticity.

The adhesiveness between the resin coating layer on the surface of the gasket, which also plays a role of airtightness, and the steel sheet has been solved by forming an undercoat coating film therebetween. That is, by providing an undercoating film with good adhesion and adding an anticorrosive pigment, etc. between the steel plate and a film having a stretch (overcoating film), a topcoating film that is difficult to peel off even if it is contacted with an antifreeze liquid is formed. Could be formed. Next, the elongation of the coating film was examined in order to impart reversible elasticity equivalent to that of rubber. The elongation of the coating film can be improved by polymerizing the organic coating film, and even a general polyester coating film exhibits the same elongation of about 150% as rubber. However, the sealing property was insufficient as a coating film for metal gaskets. It is considered that the cause is that even an organic coating film having the same degree of elongation as rubber cannot obtain reversible elasticity as much as rubber.

Therefore, as a method of improving the sealing property even when the reversible elasticity is small, the inventors of the present invention can reduce the rate of change (ratio of the amount of collapse to the film thickness) of the entire coating film when tightened. We considered that it can be sealed with a small amount of reversible elasticity (return amount), and examined the thickness of the coating film. By stacking experimental examples as studied in the following examples, it was confirmed that a film thickness of 40 μm or more is necessary to obtain sufficient sealing property even with an organic coating film. If the thickness of the coating film is increased, the stability of the sealing property is improved, but if the thickness of the polyester coating film is increased, cracking is likely to occur during the drying / baking process of the coating film. The maximum film thickness that can be obtained in one pass is 40μ considering that the film thickness that can be coated at one time is at most about 20μm, and that a normal continuous coating line is 2 coat 2 bake.
m. However, in the actual production of a continuous coating line, the balance of the film thickness must be considered to be about ± 1 μm, and even if the maximum film thickness is to be produced, the film thickness is 40 μm.
Since a part which does not reach m is generated, it cannot be used as a gasket material.

Therefore, the present inventors have examined various conditions for forming a coating film so that a film having a thickness of 40 μm or more can be formed.
Among them, by using a blocked isocyanate curing agent in which an active end group is blocked by another substance as the top coating film, the film forming rate of the coating surface layer is delayed in the drying / baking process of the coating film, and sufficient solvent is used. Urethane coating film (main resin: polyester polyol) that can balance the volatilization time and the formation time of the entire coating film and suppress the occurrence of armpits to make a thick film
Found. Since this urethane-based coating film can suppress the occurrence of cracking, it can form a coating film with a thickness of up to about 60 μm at a time, and when combined with an undercoating coating film, a coating film of about 80 μm can be formed. Also, its growth is 200%
And better than polyester coatings.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The steel sheet used in the present invention includes ordinary steel,
Special steel, Zn-based, Al-based, Al-Zn-based Al-Zn-
It is possible to use various plated steel sheets such as Mg series and stainless steel sheets. It is preferable to use an austenitic stainless steel sheet having Hv = 310 or more in order that the steel sheet itself having reversible elasticity can improve the sealing property and that the steel sheet itself does not easily rust against antifreeze. Prior to coating the undercoating film, in order to improve the adhesion between the steel plate and the undercoating film and to improve the corrosion resistance, the steel plate may be subjected to pretreatment such as pickling, degreasing, surface conditioning treatment and chromate treatment. preferable.

The undercoat coating may be a coating having excellent adhesion to the steel sheet and the top coating, and examples thereof include an epoxy coating and a polyester coating. When the top coating film is a urethane coating film, the adhesion is excellent if the undercoat coating film is an epoxy coating film. Examples of suitable epoxy resin include bisphenol type epoxy resin, novolac type epoxy resin, and polyester modified epoxy resin and acrylic modified epoxy resin obtained by modifying these. As the curing agent, an amino resin represented by etherified melamine resin and polyisocyanate such as hexamethylene diisocyanate and isophorone diisocyanate are used.

Further, the undercoating film may appropriately contain rust preventive pigments represented by strontium chromate, extender pigments such as silica, talc and barium sulfate, inorganic particles and aggregates such as organic resins. Undercoating film thickness is 1
˜20 μm. Considering the sealing property, thicker one is preferable. However, it is difficult for continuous coating equipment to form a coating film having a film thickness of more than 20 μm without causing cracking. On the other hand, if it is 1 μm or less, sufficient adhesion cannot be obtained with the steel sheet and the top coating film.

Since the coating film is excellent in elongation and strength and can be made thicker, the top coating film is mainly made of urethane resin. As the urethane resin, a resin obtained by reacting polyester polyol and polyisocyanate is used.
Polyester polyol is a polycondensation product of polyhydric alcohol and polybasic acid. As the polyhydric alcohol, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, etc. And one or more selected from these may be mixed and used.

Examples of the polybasic acid include phthalic anhydride, isophthalic acid, terephthalic acid, fumaric acid, succinic anhydride, adipic acid, sebacic acid, cyclohexanedicarboxylic acid, trimellitic anhydride and pyromellitic anhydride. It is possible to use one kind or a mixture of two or more kinds selected from these. As the polyisocyanate used as the curing agent, tolylene diisocyanate, 4,
4-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate and the like can be mentioned. These may be prepolymers, adducts, biurets, isocyanurates and the like.
As the polyisocyanate, those blocked with phenols such as phenol and cresol, lactams such as ε-caprolactam, oximes such as formamide oxime and methyl ethyl ketoxime, and active methylenes such as dimethyl malonate and ethyl acetoacetate are used. By this combination, it is possible to form a top coat film which is excellent in elongation and strength of the coat film and which can be formed into a thick film.

The thickness of the top coating film is 20 to 60 μm. When the film thickness is less than 20 μm, the maximum film thickness obtained by the undercoat coating film is 20 μm, and therefore the total thickness is less than 40 μm and the sealing property is insufficient. On the contrary, it is difficult to form a film thickness exceeding 60 μm without causing cracks. The top coating film may be mixed with a coloring paint, a metallic paint, an extender pigment, etc., which have been conventionally applied to coated steel sheets. Also,
It is preferable to add 5 to 70 parts by weight of carbon black in the topcoat film and / or the undercoat film. Since carbon black itself has a high elasticity, the elasticity of the entire coating film can be improved and the sealing property can be improved by blending it in the coating film. If the compounding amount is less than 5 parts by mass, the effect is small. On the contrary, if the compounding amount exceeds 70 parts by mass, the resin component becomes insufficient even as a binder, the coating film becomes brittle, the elongation decreases, and the sealing property deteriorates.

The coated steel sheet for metal gasket of the present invention is
It can be manufactured by a method similar to that of a conventional coated steel sheet.
That is, the undercoat paint is applied to the pretreated steel sheet by a conventional method such as a roll coater or a curtain coater, and 1
Bake at 90-240 ° C. Subsequently, the top coating composition is applied in the same manner and baked at 200 to 250 ° C.

[0017]

[Example] Test No. After the surface has been alkaline degreasing of SUS301 steel strip 1 thickness 0.2mm (Hv = 440), was painted original plate by coating type chromate treatment. A bisphenol type epoxy resin primer paint containing strontium chromate as a pigment was applied on both sides of the original coating plate by a roll coater type continuous coating line as an undercoating film. When the film thickness was adjusted to a large value under the condition that no cracking occurred, the film thickness obtained was 18 μm. On top of that, as a top coating film, a polyester polyol composed of a polyhydric alcohol mainly composed of neopentyl glycol and 1,6-hexanediol and a polybasic acid mainly composed of cyclohexanedicarboxylic acid was used, and hexablocked as a curing agent was blocked. The paint to which the methylene diisocyanate-based polyisocyanate was added was applied on a roll coater type continuous coating line. The peripheral speed of the roll coater was changed to prepare a film thickness of 30 μm. The urethane-based top coat film obtained was free of cracks and its elongation was 200%.

Test No. 2 Above test No. After forming the undercoating film in the same manner as in No. 1, the peripheral speed of the roll coater was increased at the time of coating the topcoating film, and the film thickness was adjusted to be thick under the conditions of the occurrence of armpits to obtain an overcoating film with a film thickness of 56 μm. . The elongation of this coating film was also 200%.

Test No. 3 An unsaturated polyester primer coating was used as the undercoat coating. Other than that, the test No. The same procedure as 1 was performed.
The thickness of the resulting undercoat coating film was 17 μm.

Test No. 4 except that compounding undercoating film and top coat of carbon black 40 parts by weight in the coating of Test No. The same procedure as 1 was performed. The thickness of the obtained undercoat coating film was 19 μm,
The film thickness of the top coating film was 31 μm. Further, the elongation of the top coating film was 150%.

Test No. 5 Alkaline degreasing of a molten 55% Al-Zn plated steel strip having a plate thickness of 0.3 mm and a coating amount on both sides of 150 g / m ² ,
A coating original plate was prepared by coating type chromate treatment. Test No. The same coating film formation as in No. 1 was performed.

Test No. 6 After degreasing with alkali a molten 55% Al-Zn plated steel strip having a plate thickness of 0.3 mm and a coating amount on both sides of 150 g / m ² ,
A coating original plate was prepared by coating type chromate treatment. Test No. The same coating film formation as in No. 4 was performed.

Test No. 7 lowers the peripheral speed of the roll coater when coating of the top coating film, except that thin prepare thickness Test No. A coating film was formed in the same manner as in 1. The thickness of the obtained top coat film is 17 μm
The elongation was 200%.

Test No. Test No. 8 except that melamine was used as the curing agent for the top coating film.
A coating film was formed in the same manner as in 1. The film thickness was adjusted to be thicker to prevent the occurrence of armpits. The thickness of the obtained polyester-based top coating film was 18 μm and the elongation was 150%.

In any of the above examples, the elongation of the coating film is JIS
  According to the tensile test method of K-6301 1-2 (1)
It was measured. In addition, for the obtained coated steel sheet, the following method
The sealability and adhesion were evaluated by. Sealability evaluation From the obtained coated steel strip, the outer diameter 80 mm, inner diameter 64 mm
Punching on a nut type gasket plate, N from the outside₂Gas
Place it in the opening of the cylinder that can flow in, and make a metal on it
Was closed and tightened at a tightening pressure of 9.8 MPa. This
In N₂Gas may flow in and cause gas leakage from the gasket.
Pressure (N₂Gas seal pressure) is used to evaluate the sealability.
It was Commercially available under the same conditions, 0.2 mm thick SUS301
Metallic girder with steel strip coated with 100 μm thick NBR rubber
N when evaluating a sket₂Gas seal pressure value (3.4
It evaluated based on (MPa). More N₂Gassi
There is no problem if the pressure is low.

Evaluation of Adhesion The obtained coated steel strip was immersed in an antifreeze solution (commercial long life coolant containing ethylene glycol as a main component) at 130 ° C. for 24 hours, and the peeling state was evaluated by the drawing test method of JIS K-6894. did. A score of 4 or more was passed in a 5-point evaluation.

[0027]

The evaluation results are shown in Table 1. Test No. 1-6
From the results, it can be seen that by setting the combined film thickness of the overcoat film and the undercoat film to 40 μm or more, a coated steel sheet for a metal gasket having excellent sealing properties can be obtained. In addition, the test No. 1 and 4 and test No. From the comparison of the results of 5 and 6, it is also understood that the sealing property can be improved by adding carbon black into the coating film. Alternatively, the test No.
1 and 5 and test No. From the comparison of the results of 4 and 6, it is also understood that the use of austenitic stainless steel as the coating base plate improves the sealing property. Further, the test No.
From the comparison between 1 and 3, it can be seen that when the top coating film is a urethane coating film, the adhesion can be improved by using the epoxy coating film as the under coating film. On the other hand, the test No. in which the total film thickness of the upper coating film and the lower coating film was less than 40 μm. 7,
It can be seen that with No. 8, the sealability as a metal gasket is insufficient.

[0029]

As described above, according to the present invention, instead of rubber, a resin is coated as an undercoating film and a topcoating film at a specific thickness, and a specific urethane-based coating film is further coated as a topcoating film. By forming it, it is possible to provide a coated steel sheet for gaskets that can be mass-produced in a shorter time than rubber coating and has a high sealing property. Since a material having excellent performance can be obtained at low cost, it can be applied to a cylinder head for an automobile engine at low cost.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a coated steel sheet for metal gasket of the present invention.

FIG. 2 is a schematic sectional view of a conventional rubber-coated steel plate for metal gasket.

[Explanation of symbols]

1: Urethane-based top coating film 2: Undercoat coating film
3: Steel plate 4: Rubber

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroaki Mori             7-1 Takaya Shinmachi, Ichikawa City, Chiba Prefecture Nisshin Steel             Technical Research Institute Co., Ltd. (72) Inventor Toshie Aramoto             7-1 Takaya Shinmachi, Ichikawa City, Chiba Prefecture Nisshin Steel             Technical Research Institute Co., Ltd. F term (reference) 4D075 DA06 DB04 DC13 DC16 EB38                       EC60                 4F100 AA37B AA37C AA37H AB03A                       AB04A AK51C AK53B BA03                       BA05 BA07 BA10C CC00B                       CC00C GB32 JL02 JL11                       YY00B YY00C

Claims (4)

[Claims] 1. A film mainly composed of an undercoating film having a film thickness of 1 to 20 μm and a urethane resin which is a reaction product of a polyester polyol and a blocked polyisocyanate on one surface and / or both surfaces of a steel sheet. 20-60 μm
A coated steel sheet for metal gasket, wherein the top coating film is laminated in a total film thickness of 40 μm or more. 2. The coated steel sheet for metal gasket according to claim 1, wherein the undercoat coating film is formed of a coating material containing an epoxy resin as a resin base. 3. The coated steel sheet for metal gasket according to claim 1 or 2, wherein the top coating film and / or the under coating film contains 5 to 70 parts by mass of carbon black. 4. The steel sheet is an austenitic stainless steel sheet having Hv = 310 or more.
Painted steel sheet for metal gasket described in.