JPH10329269A - Resin-coated metal material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To incorporate easiness of long term durability and external appearance regulation, by specifying a melt flow rate of a polyethylene inner layer coating to polyethylene outer layer coating formed in a laminated state on a surface of a base metal material. SOLUTION: Polyethylene powder for an inner layer coating is brought into contact with a surface of a clean base metal material heated to a temperature higher, for example, by 100 to 200 deg.C than a melting point of polyethylene to form an inner layer coating 2. Then, an outer layer coating 3 is formed continued to the formation of the coating 2 within one time heating chance. Here, as the polyethylene for the outer coating, polyethylene having a lower melting point than that of the polyethylene for the inner coating is used. And, the coating 2 of rough polyethylene having a melt flow rate of 1 to 7 g/10 min is functioned as a coating layer of considering anticorrosion, and the coating 3 of the polyethylene having a plenty of fluidity of 8 to 10 g/10 min of a melt flow rate is functioned as a coating layer of considering an external appearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal material having a polyethylene coating which is excellent in long-term corrosion resistance and whose appearance is easily adjusted.

[0002]

2. Description of the Related Art Polyethylene coatings are highly evaluated as long-term anticorrosion means because they have excellent scratch resistance and environmental barrier properties and can inexpensively protect metal materials such as steel pipes for a long period of several decades. On the other hand, since polyethylene has no polarity, paint does not adhere and it is difficult to adjust the appearance by painting.However, in recent years, polyethylene materials have been used for bridges and harbor facilities, and coloring has been used. Appearance adjustments such as are beginning to be required.

[0003] As a typical means for applying polyethylene coating, there are an extrusion coating method and a powder fusion method. In the extrusion coating method, a polyethylene melt film supplied from an extruder is applied to the surface of a base material heated to a temperature several tens of degrees higher than the melting point of polyretylene through an adhesive layer, and then cooled and solidified to form a coating. The coating can be efficiently performed on the outer surface of a straight pipe or the like, but it is difficult to perform coating on a surface having a concave portion such as an inner surface of a pipe, an outer surface of a bent pipe or a shaped steel.

On the other hand, in the powder fusion method, a polyethylene powder is brought into contact with the surface of a base material heated to a temperature higher than the melting point of polyethylene by 100 ° C. or more, and is melted by the heat of the base material to form a film. The coating is formed by cooling and solidifying, and the object to be applied is not limited to the outer surface of a straight pipe or the like, and can be applied to a surface having a concave portion. Therefore, for example, when the outer surface of the pipeline is protected by polyethylene coating, it is possible to coat all the parts by the powder fusion method, and even when the straight pipe part is formed by the extrusion coating method, a bent pipe or the like is used. In other parts, construction by the powder fusion method is required.

[0005]

That is, in light of the above-mentioned requirement for appearance adjustment such as coloring with respect to the polyethylene coating, means for appearance adjustment in the powder fusion method is first required. However, since polyethylene having a high molecular weight is used for long-term anticorrosion polyethylene to ensure toughness, the viscosity at the time of melting is high and the fluidity is insufficient.
There is a problem that it is difficult to obtain an appearance comparable to that of a paint even if a pigment is blended and colored, and a solution has been required.

[0006]

The gist of the present invention to solve the above-mentioned problem is that a melt flow rate conforming to JIS K6760, which is formed on a surface of a metal base material by a powder fusion method, is one layer. It is a resin-coated metal material having an inner layer coating with polyethylene of up to 7 g / 10 min and an outer layer coating with polyethylene of 8 to 18 g / 10 min. Here, the melt flow rate (MFR) is an index that indicates the ease with which a thermoplastic resin flows when it is melted. It is specified in JIS K6760 that the amount extruded during 10 minutes when extruded is expressed. That is, the lower the melt flow rate, the higher the melt viscosity,
In other words, it is a tough resin having a large molecular weight.

According to the constitution of the present invention, the inner layer coating with a tough polyretylene having a melt flow rate of 1 to 7 g / 10 min is used as a coating layer of anticorrosion, while a melt flow rate of 8 to 18 g / 10 min at the time of melting is used. The outer layer coating made of polyethylene having a high fluidity functions as an appearance-oriented coating layer, and it becomes easy to obtain an appearance comparable to painting by blending a pigment in the outer layer coating and performing coloring. Is resolved.

With respect to the inner layer coating, if the melt flow rate is less than 1 g / 10 min, it is difficult to apply the coating due to insufficient fluidity at the time of melting, and it is too tough to increase the cost for preparing the powder. On the other hand, if the melt flow rate exceeds 7 g / 10 min, the toughness required for long-term corrosion protection is insufficient.

[0009] With respect to the appearance coating, the flowability upon melting with a melt flow rate of 8 g / 10 min or more enables formation of an appearance comparable to that of coating, while reducing the molecular weight to a level where the melt flow rate exceeds 18 g / min. In addition, the toughness is insufficient even for a coating based on appearance.

In the present invention, the inner layer coating and the outer layer coating are formed with polyethylene having a melt flow rate in the above-mentioned range, respectively. The smaller the difference in the melt flow rate, the better the cohesion of the two layers. In view of this, it is desirable to use a combination in which the difference in melt flow rate between the outer layer-coated polyethylene and the inner layer-coated polyethylene does not exceed 12 g / 10 min. It has been confirmed that such a combination provides a fused state in which delamination is difficult.
In the present invention, polyethylene refers to not only homopolymers of ethylene but also copolymers with vinyl acetate (EV).
Ethylene copolymers such as A), and acid-modified products of the above homopolymers or copolymers and modified ethylene-based polymers such as saponified products are also included.

[0011]

FIG. 1 is a sectional view conceptually showing an embodiment of a coated metal material of the present invention in the form of a steel pipe, where 1 is a steel pipe as a base material, and 2 is an inner layer made of polyethylene having a small melt flow rate. Coating No. 3 is an outer coating made of polyethylene having a high melt flow rate.

As described above, the powder fusion method is carried out by bringing the polyethylene powder into contact with the base material heated to a temperature higher than the melting point of polyethylene by 100 ° C. or more. A chemical bond occurs between the material and the resin layer. That is, since the adhesive is firmly fused in a form in which a chemical bond is added, the intervention of an adhesive layer as in the extrusion coating method is unnecessary.

The thickness of the inner layer coating 2 and the outer layer coating 3 may be arbitrarily set according to the intended use. However, in order to ensure that both layers have the required functions, the inner layer coating 2 must have a thickness of 0.5 to 5 m.
m, it is desirable to form the outer layer coating 3 to a thickness of about 0.1 to 0.5 mm. This is because the inner layer coating 2 has a thickness of 0.5 mm or more, which secures the environmental barrier properties required for anticorrosion for several decades. On the other hand, as the thickness increases, the toughness increases. Because you do. The outer coating 3 having a thickness of 0.1 mm or more facilitates the formation of an external appearance that is not affected by the appearance of the inner coating 2, while such a blocking effect is saturated at about 0.5 mm.

The color tone of the outer layer coating 3 is to be set according to demand, and can be achieved by applying polyethylene having been subjected to a desired color tone with a coloring pigment. It is also possible to perform only smoothing of the coated surface by using transparent polyethylene containing no pigment. The color tone of the inner layer coating 2 is arbitrary. Therefore, based on known knowledge, 0.5 to 3
% Of the carbon black to provide durability against ultraviolet deterioration, the long-term corrosion resistance of the inner layer coating is further enhanced separately from the outer layer coating. In addition, since the durability against ultraviolet rays and the like is improved by blending auxiliary agents such as an ultraviolet absorber, an antioxidant, and a stabilizer, it can be blended with the outer layer coating 3 to improve the durability without affecting the coloring. it can.

The coated metal material of the present invention can be prepared by forming the above-mentioned inner layer coating 2 and outer layer coating 3 sequentially by a usual powder fusion method. That is, from the melting point of polyethyne
First, the inner layer coating 2 is formed by bringing the polyethylene powder for the inner layer coating into contact with the surface of the clean base material heated to a high temperature of about 100 to 200 ° C. Next, the outer layer coating 3 may be formed by applying the same operation starting with heating to the cooled coated metal material on which the inner layer coating 2 has been applied, as in the inner layer coating 2, but twice. Heating is not only uneconomical, but also causes thermal degradation. Therefore, it is desirable to form the outer layer coating 3 subsequent to the formation of the inner layer coating 2 within one heating chance. Here, as the polyethylene for the outer layer coating, allotting a lower melting point than the polyethylene for the inner layer coating,
By coping with the temperature drop of the metal material within the single heating chance, the outer layer coating following the inner layer coating can be performed at a suitable temperature condition without auxiliary intermediate heating. Here, for example, the above-described EVA is useful as a material having a high melt flow rate and a low melting point. In the case of a normal cooling rate, the above-mentioned orientation is satisfied by keeping the melting point of polyethylene for the outer layer coating lower than that of the inner layer coating by 15 ° C. or more. On the other hand, setting a melting point difference exceeding 25 ° C. is not recommended because it imposes undesirable restrictions on the physical properties of either layer.

The base material or the metal material coated with the inner layer in the above-mentioned powder fusion method may be heated by applying means such as induction heating, gas flame heating, hot air heating, infrared heating, and furnace heating. The contact of the polyethylene powder with the base material or the like may be performed by a method such as a fluid immersion method, a sprinkling method, a pressing method, or a centrifugal method on the inner surface of the tube. The electrostatic flow immersion method, the electrostatic spraying method, and the like in which an electrostatic field is introduced into the above methods are useful for increasing the utilization yield of the powder and reducing the scattering of dust. Furthermore, by preheating or pre-melting the powder using a thermal spray gun or the like and applying the powder, the formation of the molten film can be promoted and the construction efficiency can be improved.

(Embodiment) A 200 A steel pipe was coated with polyethylene of various specifications colored in pale green, and the appearance and performance were evaluated to verify the effects of the present invention. As a comparative material, a coated steel pipe provided with an undercoat layer of 250 μm of zinc rich paint and an overcoat layer of 150 μm of light green acrylic paint was used as a comparative material. <Evaluation method> Appearance: A visual rating was performed. In addition,
This rating is the ratio of the luminous reflectance corresponding to the clear glossiness (reflected light aperture area of 4: 100 with respect to the flat sample,
(4% for a perfect irregular reflection surface and 100% for a perfectly smooth surface)). ◎: 60 to 80%, ○ 40 to 60%, Δ: 20 to 40%, ×: 4 to 20
% Fusibility between the inner layer and the outer layer: A 180 ° peel test was performed at a pulling speed of 50 mm / min to measure the strength and to examine the peeling state. <Test specifications and test results> Table 1 shows the results.

[0018]

[Table 1]

As can be seen from the results shown in Table 1, according to the constitution of the present invention, a polyethylene coated metal material having an appearance comparable to that of a coating and having the conventional durability is obtained.

[0020]

According to the present invention, as described above, a polyethylene-coated metal material coating is formed in a laminated form, and the inner layer coating is filled with polyethylene having a low melt flow, and the outer layer coating is made of polyethylene having a high melt flow rate. By using the inner layer coating as an anticorrosion-based coating layer and the outer layer coating as an appearance-oriented coating layer, a polyethylene-coated metal material having both long-term durability and easy appearance adjustment was obtained. Things.

Polyethylene coating is considered to be the best means for long-term corrosion protection of metal materials, and has a long history of application to pipe corrosion protection.
In addition, maintenance-free orientation has become stronger in bridges and port facilities, and polyethylene coating has been adopted as described above. In recent years, since bridges and the like are required to be beautiful as part of the scenery, the coating of the present invention enables beautiful appearance adjustment at the same level as painting, while ensuring long-term durability and at the same time as painting. The role played by the provision of metal materials is extremely significant.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view conceptually showing an embodiment of the coated metal material of the present invention using a steel pipe as an example.

[Explanation of symbols]

 1 Steel pipe of mother plate 2 Inner layer coating 3 Outer layer coating

[Procedure amendment]

[Submission date] June 4, 1997

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Resin-coated metal material

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal material having a polyethylene coating which is excellent in long-term corrosion resistance and whose appearance is easily adjusted.

[0002]

2. Description of the Related Art Polyethylene coatings are highly evaluated as long-term anticorrosion means because they have excellent scratch resistance and environmental barrier properties and can inexpensively protect metal materials such as steel pipes for a long period of several decades. On the other hand, since polyethylene has no polarity, paint does not adhere and it is difficult to adjust the appearance by painting.However, in recent years, polyethylene materials have been used for bridges and harbor facilities, and coloring has been used. Appearance adjustments such as are beginning to be required.

[0003] As a typical means for applying polyethylene coating, there are an extrusion coating method and a powder fusion method. In the extrusion coating method, a molten film of polyethylene supplied from an extruder is applied to the surface of a base material heated to a temperature several tens of degrees higher than the melting point of polyethylene through an adhesive layer, and then cooled and solidified to form a coating. The coating can be efficiently performed on the outer surface of a straight pipe or the like, but it is difficult to perform coating on a surface having a concave portion such as an inner surface of a pipe, an outer surface of a bent pipe or a shaped steel.

On the other hand, in the powder fusion method, a polyethylene powder is brought into contact with the surface of a base material heated to a temperature higher than the melting point of polyethylene by 100 ° C. or more and melted by the heat of the base material to form a film. , To form a coating by cooling and solidifying,
The construction object is not limited to the outer surface of the straight pipe or the like, and can be constructed on a surface having a concave portion. Therefore, for example, when the outer surface of the pipeline is protected by polyethylene coating, it is possible to coat all the parts by the powder fusion method, and even when the straight pipe part is formed by the extrusion coating method, a bent pipe or the like is used. In other parts, construction by the powder fusion method is required.

[0005]

That is, in light of the above-mentioned requirement for appearance adjustment such as coloring with respect to the polyethylene coating, means for appearance adjustment in the powder fusion method is first required. However, since polyethylene having a high molecular weight is used for long-term anticorrosion polyethylene to ensure toughness, the viscosity at the time of melting is high and the fluidity is insufficient.
There is a problem that it is difficult to obtain an appearance comparable to that of a paint even if a pigment is blended and colored, and a solution has been required.

[0006]

The gist of the present invention to solve the above-mentioned problem is that a melt flow rate conforming to JIS K6760, which is formed on a surface of a metal base material by a powder fusion method, is one layer. It is a resin-coated metal material having an inner layer coating with polyethylene of ７7 g / 10 min and an outer layer coating with polyethylene of 8 to 18 g / 10 min.
Here, the melt flow rate (MFR) is an index indicating the ease with which a thermoplastic resin flows when it is melted. In the case of polyethylene, a 190 ° C. molten resin is pressed from a predetermined die at a pressure of 2160 g. It is prescribed in JIS K6760 that the extruded amount is expressed in 10 minutes when extruded. That is, the lower the melt flow rate is, the higher the melt viscosity is, and the more it is a tough resin having a large molecular weight.

According to the structure of the present invention, the inner layer coating made of a tough polyethylene having a melt flow rate of 1 to 7 g / 10 min is used as the anticorrosion coating layer, while the melt flow rate of 8 to 18 g / 10 min during melting is used. The outer layer coating made of polyethylene having a high fluidity functions as an appearance-oriented coating layer, and it becomes easy to obtain an appearance comparable to painting by blending a pigment in the outer layer coating and performing coloring. Is resolved.

With respect to the inner layer coating, if the melt flow rate is less than 1 g / 10 min, it is difficult to apply the coating due to lack of fluidity at the time of melting, and it is too strong to increase the powder preparation cost. On the other hand, when the melt flow rate is 7 g / 1
If the molecular weight exceeds 0 min, the toughness required for long-term corrosion protection is insufficient.

[0009] With respect to the appearance coating, the flowability at the time of melting at a melt flow rate of 8 g / 10 min or more enables formation of an appearance comparable to that of coating, while reducing the molecular weight to a level at which the melt flow rate exceeds 18 g / min. In addition, the toughness is insufficient even for a coating based on appearance.

In the present invention, the inner layer coating and the outer layer coating are formed with polyethylene having a melt flow rate in the above-mentioned range, respectively. The smaller the difference in the melt flow rate, the better the cohesion of the two layers. From this point, it is desirable to use a combination in which the difference between the melt flow rates of the outer layer-coated polyethylene and the inner layer-coated polyethylene does not exceed 12 g / 10 min. It has been confirmed that such a combination provides a fused state in which delamination is difficult. The polyethylene referred to in the present invention includes not only a homopolymer of ethylene, but also an ethylene copolymer such as a copolymer with vinyl acetate (EVA), and an acid-modified or saponified product of the homopolymer or copolymer. And modified ethylene-based polymers.

[0011]

FIG. 1 is a sectional view conceptually showing an embodiment of the coated metal material of the present invention in the form of a steel pipe, wherein 1 is a steel pipe as a base material, and 2 is an inner layer made of polyethylene having a small melt flow rate. Coating No. 3 is an outer coating made of polyethylene having a high melt flow rate.

As described above, the powder fusion method is performed by bringing the polyethylene powder into contact with the base material heated to a temperature 100 ° C. or higher than the melting point of polyethylene. A chemical bond occurs between the material and the resin layer. That is, since the adhesive is firmly fused in a form in which a chemical bond is added, the intervention of an adhesive layer as in the extrusion coating method is unnecessary.

The thickness of the inner layer coating 2 and the outer layer coating 3 may be arbitrarily set according to the intended use. However, in order to ensure that both layers have the functions required, the inner layer coating 2 must have a thickness of 0.5 to 0.5 mm.
It is preferable to form the outer layer coating 5 to a thickness of about 0.1 to 0.5 mm by 5 mm. This is because the inner layer coating 2 has a thickness of 0.5 mm or more, which secures the environmental barrier properties required for anticorrosion for several decades. On the other hand, as the thickness increases, the toughness increases. This is because it saturates. Further, the outer layer coating 3 having a thickness of 0.1 mm or more facilitates formation of an external appearance that is not affected by the outer layer coating 2, while such a blocking effect is saturated at about 0.5 mm. is there.

The color tone of the outer layer coating 3 is to be set as required, and can be achieved by applying a polyethylene which has been subjected to a desired color tone with a coloring pigment. It is also possible to perform only smoothing of the coated surface by using transparent polyethylene containing no pigment. The color tone of the inner layer coating 2 is arbitrary. Therefore, based on known knowledge,
If 3% carbon black is blended and has durability against UV degradation, the long-term corrosion protection of the inner layer coating will be improved.
Apart from the outer coating, it will be further reinforced. In addition, since the durability against ultraviolet rays and the like is improved by blending auxiliary agents such as an ultraviolet absorber, an antioxidant, and a stabilizer, it can be blended with the outer layer coating 3 to improve the durability without affecting the coloring. it can.

The coated metal material of the present invention can be prepared by forming the above-mentioned inner layer coating 2 and outer layer coating 3 sequentially by a usual powder fusion method. That is, first, the inner layer coating 2 is formed by bringing the polyethylene powder for the inner layer coating into contact with the surface of the clean base material heated to about 100 to 200 ° C. higher than the melting point of the polyethylene. Next, the outer layer coating 3 may be formed by applying the same operation starting with heating to the cooled coated metal material on which the inner layer coating 2 has been applied, as in the inner layer coating 2, but twice. Heating is not only uneconomical, but also causes thermal degradation. Therefore, it is desirable to form the outer layer coating 3 subsequent to the formation of the inner layer coating 2 within one heating chance. Here, as the polyethylene for the outer layer coating, a polyethylene having a melting point lower than that of the polyethylene for the inner layer coating is applied so as to correspond to the temperature decrease of the metal material within the single heating chance. Application of the outer layer coating can be carried out at suitable temperature conditions without auxiliary intermediate heating. Here, for example, the above-described EVA is useful as a material having a high melt flow rate and a low melting point.
In the case of a normal cooling rate, by making the melting point of the polyethylene for the outer layer coating lower than the inner layer coating by 15 ° C. or more,
Complies with the above orientation. On the other hand, setting a melting point difference exceeding 25 ° C. is not recommended because it imposes undesirable restrictions on the physical properties of either layer.

The base material or the metal material coated with the inner layer in the above-mentioned powder fusion method may be heated by applying means such as induction heating, gas flame heating, hot air heating, infrared heating, and furnace heating. The contact of the polyethylene powder with the base material or the like may be performed by a method such as a fluid immersion method, a sprinkling method, a pressing method, or a centrifugal method on the inner surface of the tube. The electrostatic flow immersion method, the electrostatic spraying method, and the like in which an electrostatic field is introduced into the above methods are useful for increasing the utilization yield of the powder and reducing the scattering of dust. Furthermore, by preheating or pre-melting the powder using a thermal spray gun or the like and applying the powder, the formation of the molten film can be promoted and the construction efficiency can be improved.

(Example) A 200A steel pipe was coated with polyethylene of various specifications colored in pale green, and the appearance and performance were evaluated to verify the effects of the present invention. As a comparative material, a coated steel pipe provided with an undercoat layer of 250 μm of zinc rich paint and an overcoat layer of 150 μm of light green acrylic paint was used as a comparative material. <Evaluation method> Appearance: A visual rating was performed. In addition,
This rating is defined as the image glossiness (the ratio of the luminous reflectance corresponding to the aperture area of reflected light of 4: 100, which is 4% for a perfectly irregularly-reflected surface and 100% for a perfectly smooth surface) for a flat sample. The following correspondences are roughly provided. ◎: 60 to 80%, ４０ 40 to 60%, Δ: 20 to 40
%, ×: 4 to 20% Fusibility between inner layer and outer layer: A 180 ° peel test was performed at a pulling speed of 50 mm / min to measure the strength and to examine the peeling state. <Test specifications and test results> Table 1 shows the results.

[0018]

[Table 1]

As can be seen from the results in Table 1, the configuration of the present invention provides a polyethylene-coated metal material having an appearance comparable to that of a coating and having the conventional durability.

[0020]

According to the present invention, as described above, a polyethylene-coated metal material coating is formed in a laminated form, and the inner layer coating is filled with polyethylene having a low melt flow, and the outer layer coating is made of polyethylene having a high melt flow rate. By using the inner layer coating as an anticorrosion-based coating layer and the outer layer coating as an appearance-oriented coating layer, a polyethylene-coated metal material having both long-term durability and easy appearance adjustment was obtained. Things.

Polyethylene coating is considered to be the best means for long-term corrosion protection of metal materials, and has a long history of application to pipe corrosion protection.
In addition, maintenance-free orientation has become stronger in bridges and port facilities, and polyethylene coating has been adopted as described above. In recent years, since bridges and the like are required to be beautiful as part of the scenery, the coating of the present invention enables beautiful appearance adjustment at the same level as painting, while ensuring long-term durability and at the same time as painting. The role played by the provision of metal materials is extremely significant.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view conceptually showing an embodiment of the coated metal material of the present invention using a steel pipe as an example.

[Description of Signs] 1 Steel pipe of mother plate 2 Inner layer coating 3 Outer layer coating

Claims (5)

[Claims] 1. An inner layer coating of polyethylene having a melt flow rate of 1 to 7 g / 10 min according to JIS K6760 and a polyethylene of 8 to 18 g / 10 min, which are formed in a laminated state on the surface of a metal base material by a powder fusion method. And a resin-coated metal material having an outer layer coating. 2. The resin-coated metal material according to claim 1, wherein the difference in melt flow rate between the outer layer-coated polyethylene and the inner layer-coated polyethylene is within 12 g / 10 min. 3. The resin-coated metal material according to claim 1, wherein the inner layer coating has a thickness of 0.5 to 5 mm, and the outer layer coating has a thickness of 0.1 to 0.5 mm. 4. The resin-coated metal material according to claim 1, wherein the inner layer coating is formed of polyethylene containing 0.5 to 3% by weight of carbon black. 5. The resin-coated metal material according to claim 1, wherein the outer layer coating is formed of polyethylene having a melting point lower by 15 to 25 ° C. than that of the inner layer coating polyethylene.