JP6728818B2 - Multi-layer polyurethane coated steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyurethane-coated steel material used in a marine environment.

Steel materials such as steel pipe piles, steel pipe sheet piles, and steel sheet piles that are mainly used in the severe corrosive marine environment are heavy-corrosion coated steel materials coated with organic resins such as polyethylene and polyurethane with a thickness of several mm. Often used. This heavy anticorrosion coated steel has excellent anticorrosion performance and can be manufactured at relatively low cost, but the problem that the resin coating layer is easily damaged by collision with drifting objects or moorings in the ocean There is.

Especially when used in cold regions, the impact resistance is insufficient and there is a problem that cracks occur at the time of construction such as hammering into the soil or the sea bottom and corrosion resistance is lost, so improvement was necessary. .. When the resin coating layer is damaged and a flaw that reaches the surface of the steel material is generated, the steel material is corroded from the collision flaw as a starting point, and the heavy anticorrosion coating layer causes a significant reduction in anticorrosion performance.

Impact resistance is closely related to the physical properties of resin materials. A rigid resin has a high cross-linking density and thus has a small amount of oxygen and moisture permeation and high anticorrosion performance, but cracks easily occur when a load exceeding impact strength is applied, and the steel surface is exposed. On the other hand, a flexible resin does not easily crack even when a load exceeding the impact strength is applied, but has a low crosslink density and a large amount of oxygen and moisture permeation, and thus has a low anticorrosion performance.

On the other hand, for example, Patent Document 1 discloses a steel material coated with a polyurethane resin having a large tensile strength and a large elongation as a protective layer in order to improve the impact resistance of the heavy anticorrosion coating layer. However, in a low temperature environment, the rigidity of the polyurethane resin becomes high, and thus cracks are likely to occur.

Patent Document 2 discloses a urethane elastomer-coated steel material having low-temperature impact resistance by containing a rigid specific bisphenol-based diol and a flexible specific saturated aliphatic diol in a polyol component at a constant ratio. However, in order to secure impact resistance, the crosslink density is lowered and the corrosion resistance is lowered.

JP, 2007-90678, A JP, 2005-264171, A

An object of the present invention is to obtain a polyurethane-coated steel material having high corrosion resistance and preventing the steel surface from being exposed even in a low temperature environment.

The present inventors paid attention to laminating different kinds of polyurethane resins on steel materials. When the polyurethane resin coating has a two-layer structure, high corrosion resistance is maintained by using a rigid rigid polyurethane resin layer (4) as an upper layer. Further, by sandwiching the flexible soft polyurethane resin layer (3) between the steel material and the steel material, the impact can be mitigated, and the steel surface can be prevented from being exposed due to cracking of the upper resin layer. FIG. 1 shows a cross-sectional view of the coating structure of the two-layer polyurethane-coated steel material.

As a result of intensive studies, the present inventors have found that when the polyurethane resin coating has a two-layer structure, a soft polyurethane resin layer having a Shore D hardness of 65 or less is a layer close to steel (lower layer) and a hard polyurethane resin layer having a Shore D hardness of 75 or more. It has been found that by stacking in a layer farther from the steel material (upper layer), it has high impact resistance even in a low temperature environment and prevents flaws reaching the surface of the steel material. When the Shore D hardness of the soft polyurethane resin of the lower layer exceeds 65, the rigidity becomes high and cracking of the resin layer occurs. When the Shore D hardness of the upper layer hard polyurethane resin is less than 75, the impact resistance is low and there is a possibility that a flaw reaching the surface of the steel material may occur.

When the polyurethane resin coating has a three-layer structure, by laminating a hard polyurethane resin layer (4) having a Shore D hardness of 75 or more between the steel material and the soft polyurethane resin layer (3), the uppermost hard polyurethane resin layer (4) It was found that the lower hard polyurethane resin layer (4) closest to the steel material can suppress the permeation of oxygen and water even if () is cracked. FIG. 2 shows a cross-sectional view of the coating structure of a three-layer polyurethane-coated steel material having a soft polyurethane resin layer (3) as an intermediate layer.

In another aspect, when the polyurethane resin coating has a three-layer structure, the impact is mitigated by laminating the soft polyurethane resin layer (3) having a Shore D hardness of 65 or less on the intermediate hard polyurethane resin layer (4). By stacking the soft polyurethane resin layer (3) under the intermediate hard polyurethane resin layer (4) as well, the lower soft polyurethane resin layer (3) prevents the propagation of impact to the steel surface, It was found that the impact resistance was further improved. FIG. 3 shows a cross-sectional view of the coating structure of a three-layer polyurethane-coated steel material having hard polyurethane as an intermediate layer.

When the polyurethane resin coating has a structure of four or more layers, at least one layer except the uppermost layer is a soft polyurethane resin layer. The uppermost layer may be a soft polyurethane resin layer or a hard polyurethane layer, but at least one layer of the plurality of polyurethane resin layers located below the uppermost layer is a soft polyurethane resin layer. This soft polyurethane resin layer may be at any position. Even if the hard polyurethane resin layer located above the soft polyurethane resin layer is impacted and cracked, the soft polymer layer can absorb the impact received by the layers located below it and prevent the steel surface from being exposed. it can.

Further, the film thicknesses of the hard polyurethane resin layer and the soft polyurethane layer are important for achieving both low temperature impact resistance and high corrosion resistance.
As a result of intensive studies, if the ratio of the total film thickness of the hard polyurethane resin layer to the total film thickness of the soft polyurethane resin layer in the multilayer polyurethane coating is in the range of 1 to 10, high impact strength is exhibited without peeling. I found that. When the film thickness ratio is less than 1, the hard polyurethane resin layer is thin, so that the impact strength is low, cracking of the hard polyurethane resin layer occurs, and at the same time the corrosion resistance decreases. When the film thickness ratio exceeds 10, the soft polyurethane resin layer is thinner than the hard polyurethane resin layer, so that the impact relaxation effect of the soft polyurethane resin layer is reduced, and cracks occur in the hard polyurethane resin layer.

That is, the present invention is a multi-layer polyurethane coated steel material having high corrosion resistance and excellent low temperature impact resistance by laminating a hard polyurethane resin layer having high anticorrosion property and a soft polyurethane resin layer having an impact relaxation effect.

As described above, according to the present invention, it is possible to obtain a polyurethane-coated steel material having high corrosion resistance and preventing the steel surface from being exposed even in a low temperature environment. As a result, the corrosion of the coated steel material can be prevented, and stable durability can be maintained for a long period of time even in the marine environment of cold regions.

It is a coating composition sectional view of a polyurethane coating steel material whose polyurethane resin coating is a two-layer structure. It is a coating composition sectional view of the polyurethane coating steel material of 3 layer structure which has a soft polyurethane resin layer in the middle class. FIG. 3 is a cross-sectional view of a coating structure of a polyurethane-coated steel material having a three-layer structure having a hard polyurethane resin layer as an intermediate layer.

Hereinafter, the present invention will be described in detail. The method for producing a polyolefin-coated steel material according to the present invention will be described using a polyurethane-coated steel pipe as a typical example.

FIG. 1 is a cross-sectional view of a coating structure of a multi-layer polyurethane coated steel material showing one embodiment of the present invention. As the steel material used in the present invention, any steel type such as ordinary steel or high alloy steel can be applied. Note that the present invention can also be applied to steel pipes to which heavy anticorrosion coating has been applied, steel pipe piles, steel pipe sheet piles, and steel sheet piles used in offshore structures.

Since it is necessary to remove scales, contaminants, etc. on the surface of the steel material, any pretreatment such as alkali degreasing, pickling, sand blasting, grid blasting, or shot blasting is first performed before use.

Steel is desirable because it is possible to obtain more excellent corrosion resistance by subjecting the steel material to a surface treatment as a base treatment before forming the primer layer. Examples of the surface treatment include chromate treatment and phosphoric acid treatment.

The primer applied to the primer layer preferably has good adhesion to the surface of the steel material and the polyurethane resin layer laminated and coated on the upper layer of the primer layer. As the primer, it is preferable to use a urethane-based or epoxy-based organic resin primer, and a room temperature curing type is desirable. The primer layer has a thickness of about 10 to 100 μm, preferably about 20 to 80 μm. If the film thickness is less than 10 μm, the adhesion will be insufficient, and if it exceeds 100 μm, the solvent may remain in the primer layer.

The primer layer can be applied regardless of the method such as brush coating or roller coating, and it is preferable to use spray coating such as air spray or airless spray to coat the surface of the steel material having various shapes.

Then, a soft polyurethane resin layer is coated on the primer layer. The soft polyurethane resin to be applied has a polyol as a main component and an isocyanate compound as a curing agent as main components.

Examples of the polyol include polyether-based polyols, polyester-based polyols, polybutadiene-based polyols, amine-based polyols, castor oil-modified polyols, epoxy-modified polyols and other polyols alone or in a mixture.

Examples of the isocyanate include tolylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, and a single or mixture of isocyanates such as modified derivatives thereof. Tolylene diisocyanate and diphenylmethane diisocyanate are preferred.

The soft polyurethane resin layer used in the present invention needs to have a Shore D hardness of 65 or less. The soft polyurethane resin layer having a Shore D hardness of 65 or less that can be used in the present invention can be obtained, for example, by using a mixture of a polybutadiene polyol and a castor oil-modified polyol as the polyol.

Various additives can be added to the soft polyurethane resin. For example, pigments such as carbon black and calcium carbonate may be blended in order to impart weather resistance and abrasion resistance. In addition, a desolvent, a plasticizer, an auxiliary agent, a thickener, an antioxidant, a light stabilizer and the like may be contained in order to impart characteristics.

As a coating method, spray coating is preferable because it coats various shapes of steel surfaces. The spray can be used regardless of the method such as air spray or airless spray. The thickness of the soft polyurethane resin layer is preferably 0.5 to 3 mm. When the film thickness is less than 0.5 mm, the impact relaxation effect is deteriorated, and when it exceeds 3 mm, it is economically disadvantageous.

Further, a hard polyurethane resin layer is coated on the soft polyurethane resin layer. The hard polyurethane resin to be applied contains a polyol as a main component and an isocyanate compound as a curing agent as main components.

Examples of the polyol include polyether-based polyols, polyester-based polyols, polybutadiene-based polyols, amine-based polyols, castor oil-modified polyols, epoxy-modified polyols and other polyols alone or in a mixture.

Examples of the isocyanate include tolylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, and single or mixture of isocyanates such as modified derivatives thereof. Tolylene diisocyanate and diphenylmethane diisocyanate are preferable.

The hard polyurethane resin layer used in the present invention needs to have a Shore D hardness of 75 or more. The hard polyurethane resin layer having a Shore D hardness of 75 or more that can be used in the present invention can be obtained, for example, by mixing a castor oil-modified polyol and an amine-based polyol as the polyol.

Various additives can be added to the rigid polyurethane resin. For example, pigments such as carbon black and calcium carbonate may be blended in order to impart weather resistance and abrasion resistance. In addition, a desolvent, a plasticizer, an auxiliary agent, a thickener, an antioxidant, a light stabilizer and the like may be contained in order to impart characteristics.

As a coating method, spray coating is preferable because it coats various shapes of steel surfaces. The spray can be used regardless of the method such as air spray or airless spray. The thickness of the hard polyurethane resin layer is preferably 1 to 5 mm. When the film thickness is less than 1 mm, the anticorrosion property and impact resistance are deteriorated, and when the film thickness exceeds 5 mm, the internal stress of the entire coating film becomes large, so that peeling due to a temperature difference occurs.

In the embodiment of the three-layer polyurethane coating including the soft polyurethane layer in the intermediate layer shown in FIG. A hard polyurethane resin layer is coated on the. The components of the hard polyurethane resin and the soft polyurethane resin to be applied are the same as those of the hard and soft polyurethane resins described above. You may use.

In the embodiment of the three-layer polyurethane coating including a hard polyurethane layer in the intermediate layer shown in FIG. 3, a soft polyurethane resin is coated on a primer layer previously applied, and then a hard polyurethane resin is further coated on the primer layer. A soft polyurethane resin layer is coated on. The components of the hard polyurethane resin and the soft polyurethane resin to be applied are the same as those of the above-mentioned hard and soft polyurethane resins, and if the Shore D hardness is within the desired range of the above regulation, respectively, the different hard and soft polyurethane resins are combined. You may use.

Even when the total number of coating layers is four or more, similar to the above three-layer polyurethane coating, a hard or soft polyurethane resin is coated as a lower layer closest to the steel material on the primer layer previously applied, and then a polyurethane different from the lower layer is used. The resin is coated thereon. For example, when the lower layer is a hard polyurethane resin, a soft polyurethane resin is coated thereon, and when the lower layer is a soft polyurethane resin, a hard polyurethane resin is coated thereon to form a plurality of laminated coating films. The components of the hard polyurethane resin and the soft polyurethane resin to be applied are the same as those of the above-mentioned hard and soft polyurethane resins, and if the Shore D hardness is within the desired range of the above regulation, respectively, the different hard and soft polyurethane resins are combined. You may use.

The total total film thickness of the hard polyurethane resin layer and the soft polyurethane resin layer is preferably 5 mm or less. If it exceeds 5 mm, peeling occurs due to shrinkage of the resin due to temperature difference. Further, the total total film thickness of the multilayer polyurethane resin layer is preferably at least 1 mm or more. When it is 1 mm or less, the permeation of oxygen and water becomes excessive, which is not preferable. The total total film thickness of the multilayer polyurethane resin layer is preferably 2 mm to 4 mm.

Hereinafter, in Example 1, the present invention relates to a polyurethane-coated steel material having a two-layer structure shown in FIG. 1, and in Example 2, a polyurethane-coated steel material having a three-layer structure including a soft polyurethane resin layer as an intermediate layer shown in FIG. In addition, in Example 3, a polyurethane-coated steel material having a three-layer structure including a soft polyurethane resin layer in the intermediate layer shown in FIG. 3 will be specifically described. Table 1 shows the physical properties of the polyurethane resin used. Polyurethane resins A and B are based on Cefcol BL22 (manufactured by Urethane Giken Kogyo Co., Ltd.), and polyurethane resins C, D and E are based on Permaguard 137 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) A polyurethane resin having adjusted Shore D hardness by adjusting the amounts of polybutadiene polyol and castor oil-modified polyol was used.

The multilayer polyurethane-coated steel material samples obtained in the examples and comparative examples were evaluated as follows.

[Evaluation of resin hardness]
The Shore D hardness of the polyurethane resin was measured according to JIS K7215 type D, and the polyurethane resin sample having a thickness of 3 mm was measured at room temperature.

[Evaluation of low temperature impact resistance]
The low temperature impact resistance of the polyurethane-coated steel material was determined by a falling weight impact test at −20° C. using a falling weight having a tip diameter of 15.9 mm and a weight of 2 to 10 kg in accordance with ASTM G14. Whether or not the surface of the steel material was exposed was visually confirmed. The impact strength was calculated by the following equation (1).
m={h ₀ +d(A/N±1/2)}×W/t... (1)
m: Impact strength (kgf·m/mm)
h ₀ : Maximum height without pinhole (m)
d: Drop height increase/decrease pitch (m)
A: Sum of products of the number of pinhole occurrences and increment multiples for each increment of h ₀ or more N: Total number of pinholes not generated W: Mass of weight (kg)
t: Total thickness of the polyurethane resin layer (mm)

[Evaluation of anticorrosion performance]
The evaluation of anticorrosion performance was performed by a cathode peel test. According to ASTM G8, a circular artificial defect having a diameter of 6 mmφ was created in the center of the test material to expose the steel material. An acrylic cylinder having a diameter of 70 mmφ centering on the artificial defect was vertically installed on the coating layer, fixed to the coating layer with a sealant, and the inside was filled with a 3 mass% NaCl aqueous solution to prepare a cell. The potential of the defective steel material was maintained at -1.5 V vs. SCE using a potentiostat in an oven at 40° C. for 30 days using platinum as a counter electrode. The distance of the peeled portion from the end portion of the artificial defect was measured in four directions (12:00, 3:00, 6:00, and 9:00) around the artificial defect, and the average value was defined as the cathode peel distance.

Example 1
As a steel material sample, a 6 mm×100 mm×150 mm hot-rolled steel sheet subjected to grid blast treatment was prepared. A urethane-based primer was applied by airless spraying to a thickness of 50 μm to form a primer layer. Next, the soft polyurethane resin and the hard polyurethane resin shown in Table 1 were laminated on the primer layer by airless spraying so as to have the constitution shown in Table 2, and the two-layer polyurethane-coated steel material of Examples 1-1 to 4 of the present invention. A sample was prepared.

As Comparative Examples 1-1 and 1-2, soft polyurethane resin and hard polyurethane resin single-layer coated steel material samples were produced in the same manner as in the above-described examples.

As Comparative Examples 1-3 and 1-4, polyurethane resin C having a Shore D hardness outside the range of the present invention was used to prepare coated steel material samples in the same manner as in the above-described examples.

In Comparative Examples 1-5 and 1-6, a polyurethane resin coating in which the total film thickness ratio of the hard polyurethane resin to the total film thickness of the soft polyurethane resin is outside the range of the present invention was used, and the same method as in the above-mentioned Examples was used. A coated steel material sample was prepared.

Table 2 shows the results of Examples and Comparative Examples of the present invention.

In Examples 1-1 to 4, the steel surface was not exposed due to low temperature impact, and the cathode peeling was small, and good results were obtained. On the other hand, in Comparative Example 1-1, cracking did not occur, but the corrosion resistance was low and the cathode separation distance was large. In Comparative Example 1-2, the cathode separation distance was small, but cracking due to impact occurred. In Comparative Example 1-3, the hardness of the soft polyurethane resin layer was high, cracks occurred, and the steel surface was exposed. In Comparative Example 1-4, the upper hard polyurethane resin layer could not withstand the impact and cracked to expose the steel surface. In Comparative Example 1-5, the steel surface was not exposed, but the hard polyurethane resin layer responsible for anticorrosion was thin, and the cathode separation distance was increased. In Comparative Example 1-6, since the soft polyurethane resin layer responsible for impact relaxation was thin, the impact was not fully relaxed, cracking occurred, and the steel surface was exposed.

Example 2
As a steel material sample, a 6 mm×100 mm×150 mm hot-rolled steel sheet subjected to grid blast treatment was prepared. A urethane-based primer was applied by airless spraying to a thickness of 50 μm to form a primer layer. Next, the polyurethane resin shown in Table 1 was airless sprayed in the order of the lower hard polyurethane resin layer closest to the steel material, the intermediate soft polyurethane resin layer, and the uppermost hard polyurethane resin layer in the order shown in Table 3. Was laminated on the primer layer to prepare a three-layer polyurethane-coated steel material sample having a soft polyurethane resin layer as the intermediate layer of Examples 2-1 and 2-2 of the present invention.

In Comparative Example 2-1, a coated steel material sample was prepared by using a hard polyurethane resin having a Shore D hardness outside the range of the present invention as the lower layer and in the same manner as in the above-described example.

As Comparative Examples 2 to 2-5, a coated steel material was prepared in the same manner as in the above-described examples using a polyurethane resin coating in which the ratio of the total film thickness of the hard polyurethane resin to the total film thickness of the soft polyurethane resin was outside the scope of the present invention. A sample was prepared.

Table 3 shows the results of Examples and Comparative Examples of the present invention.

In Examples 2-1 and 2-2, the steel surface was not exposed due to low temperature impact, and the cathode peeling was small, and good results were obtained. On the other hand, in Comparative Example 2-1, the hard polyurethane resin layer could not withstand the impact, cracked and the steel surface was exposed. In Comparative Example 2-2, the lower hard polyurethane resin layer was thin, could not withstand impact, and cracked to expose the steel surface. In Comparative Examples 2-3 and 2-4, the steel surface was not exposed, but the cathode separation distance was increased because the hard polyurethane resin layer responsible for corrosion resistance was thin. In Comparative Example 2-5, since the soft polyurethane resin layer was thinner than the upper hard polyurethane resin layer, cracking occurred and the steel surface was exposed.

Example 3
As a steel material sample, a 6 mm×100 mm×150 mm hot-rolled steel sheet subjected to grid blast treatment was prepared. A urethane-based primer was applied by airless spraying to a thickness of 50 μm to form a primer layer. Next, the polyurethane resin shown in Table 1 was applied to the primer layer by airless spraying so that the soft polyurethane resin in the lower layer closest to the steel material, the hard polyurethane resin in the intermediate layer, and the soft polyurethane resin in the uppermost layer were in the order shown in Table 4. And a three-layer polyurethane-coated steel material sample having a hard polyurethane resin layer as the intermediate layer of Examples 3-1 and 3-2 of the present invention was produced.

As Comparative Example 3-1, a coated steel material sample was prepared in the same manner as in the above-mentioned example using a soft polyurethane resin having a Shore D hardness outside the range of the present invention as the upper layer.
In Comparative Examples 3 to 2-5, a coated steel material was prepared in the same manner as in the above-mentioned examples using a polyurethane resin coating in which the total film thickness ratio of the hard polyurethane resin to the total film thickness of the soft polyurethane resin was outside the scope of the invention. A sample was prepared.

Table 4 shows the results of Examples and Comparative Examples of the present invention.

In Examples 3-1 and 3-2, the steel surface was not exposed due to low temperature impact, and the peeling of the cathode was small, and good results were obtained. On the other hand, in Comparative Example 3-1, since the upper soft polyurethane resin layer was hard, it could not withstand the impact and cracked to expose the steel surface. In Comparative Examples 3 to 2-4, the steel surface was not exposed, but the hard polyurethane resin layer responsible for the anticorrosion property was thin, so that the cathode separation distance increased. In Comparative Example 3-5, since the upper and lower soft polyurethane resin layers were thinner than the hard polyurethane resin layer, cracking occurred and the steel surface was exposed.

1 Steel 2 Primer layer 3 Soft polyurethane resin layer 4 Hard polyurethane resin layer

Claims (2)

A primer layer in contact with the steel, thereon, the layer closest to the steel made of soft polyurethane resin layer or a hard polyurethane resin layer, and is further laminated thereon, the kind and the layer closest to the steel A multilayer polyurethane-coated steel material having different n layers (where n is an integer) of alternating layers of a soft polyurethane resin and a hard polyurethane resin , the two layers being different, a soft polyurethane resin layer or a hard polyurethane resin layer . There
When n is 2, the layer close to the steel material is the soft polyurethane resin layer, and the film thickness of the hard polyurethane resin layer thereon is 2 to 5 mm,
When n is 3, the layer closest to the steel material is the soft polyurethane resin layer or the hard polyurethane resin layer,
When n is 4 or more, at least one layer except the uppermost layer is a soft polyurethane resin layer,
The hardness of the soft polyurethane resin layer is 65 or less Shore D hardness, the hardness of the hard polyurethane resin layer is 75 or more Shore D hardness,
A multilayer polyurethane-coated steel material, wherein the ratio of the total film thickness of the hard polyurethane resin to the total film thickness of the soft polyurethane resin is 1 to 10. The multilayer polyurethane-coated steel material according to claim 1, wherein the hardness of the hard polyurethane resin layer is 75 or more and 80 or less in Shore D hardness.

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