JP2734892B2 - Colored polyethylene resin coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion coating material coated with a colored polyethylene resin obtained by adding a color pigment and an antioxidant to a polyethylene resin.

[0002]

2. Description of the Related Art Steel materials used for a long time outdoors may be exposed to severe corrosive environments. For example, steel sheet piles and steel pipe sheet piles are continuously driven into the ground to form protective fences, mainly for the protection of rivers, coasts, ports, etc., and steel pipe piles are used for foundations of offshore structures. Has been used for Steel pipes are often used as gas pipes and water pipes. These steel materials are exposed to water such as river water, drainage, rainwater, seawater, the atmosphere, sunlight, etc. in the outdoor natural environment, and come into direct contact with soil, mud, rubble, etc. Easy to happen. Therefore, for a long time
Effective anticorrosion measures (about 20 years) have been desired.

In recent years, as a countermeasure for this, a resin is used as a thick film (1 to 3).
mm) Heavy corrosion-resistant coated steel materials that have been provided with excellent corrosion protection by being coated are being used. As the coating resin, a polyethylene resin is frequently used in consideration of economy and various characteristics.

[0004] However, polyethylene resin is liable to be deteriorated by the influence of ultraviolet light contained in sunlight. Therefore, when it is used outdoors as in this application, carbon black is required to be 1%.
It is common to add about 3% to improve the weather resistance, and the color tone is limited to black. However, in places where the living environment and the natural environment are to be maintained comfortably and neatly, it is required to color the steel sheet pile and the steel pipe sheet pile so as to conform to the environment. For this reason, attempts have been made to color the polyethylene resin used as a coating material into an arbitrary color with a coloring pigment after taking measures against ultraviolet degradation.

[0005] Conventional measures against degradation of polyethylene resin by ultraviolet rays include, in addition to coloring pigments, substances such as benzotriazole compounds that absorb ultraviolet rays and convert them to low energy (ultraviolet absorbers), hindered amines, and binder phenols. system compounds, are known to be added to the resin in combination with an antioxidant such as sulfur compounds (see Japanese Patent Laid public <br/> Akira 63-60712).

[0006]

These antioxidants and ultraviolet absorbers (collectively referred to as anti-deterioration agents in the present invention) are expensive, and cost several tens of times as much as the base polyethylene resin. , Its addition causes a rise in product cost. In particular, the outer coating of outdoor piping such as water and gas,
For heavy corrosion protection of steel pipe piles, steel sheet piles, steel pipe sheet piles, etc.
While a large amount of antioxidant needs to be added, excessive antioxidant addition design impairs the economics of the product.

An object of the present invention is to provide a steel sheet such as a steel sheet pile, a steel pipe sheet pile, a steel pipe and the like by designing the addition of a minimum deterioration inhibitor without impairing the economy and without adding carbon black. An object of the present invention is to provide a colored polyethylene resin-coated steel material capable of imparting weather resistance (more than 20 years).

[0008]

The present inventors have conducted various studies on the weather resistance of a colored polyethylene resin to which various amounts of an antioxidant have been added, and have found that by limiting the thickness of the degraded layer to the surface, the polyethylene is reduced. It has been found that long-term weatherability of the coating can be realized. Based on this finding, the relationship between the thickness of the polyethylene coating, the ultraviolet ray transmission depth, and the concentration of the antioxidant added has been elucidated, and the present invention has been achieved.

The present invention is characterized in that it is coated with a colored polyethylene resin to which a colored pigment and an antioxidant are added, and that the total amount of the antioxidant in the colored polyethylene resin coating satisfies the following formula: The gist is a colored polyethylene resin coating material having excellent properties.

2.0 ≧ C ≧ 1.56 / (A × T ² ) ‥‥ (1) where C = total amount (parts by weight) of antioxidant per 100 parts by weight of polyethylene resin, T = Thickness (mm) of the colored polyethylene coating, A = absorbance of a 50 μm-thick colored polyethylene coating to ultraviolet light at a wavelength of 300 nm.

[0011]

The base material coated with the polyethylene resin in the present invention is generally a steel material, but the material is not limited to steel, but may be other metal materials such as aluminum,
Furthermore, stone, wood, ceramics, etc. are also possible. Hereinafter, a steel material which is a typical material will be described. The shape of the steel material is not particularly limited, and may be a tubular material such as a steel pipe or a steel pipe pile, a plate material such as a steel sheet pile, a bar steel, or a deformed material. In addition, steel materials are plated or chemically treated.
An appropriate underlayer treatment such as (chromate treatment, zinc phosphate treatment) may be performed.

If necessary, the surface of the steel material may be pretreated with an appropriate primer (eg, epoxy primer) before coating with the polyethylene resin in order to enhance the adhesion to the polyethylene resin layer as the coating material. it can. This pretreatment can be carried out by applying a primer and baking and drying or curing by irradiation with ultraviolet rays, as in the prior art. Also, since the adhesion of polyethylene resin to steel is relatively low,
As is well known, it is preferable to provide a resin layer (for example, a maleic anhydride-modified polyethylene layer) for providing adhesion at the interface between the steel material and the resin in order to enhance the adhesion to the steel material. The thickness of the polyethylene resin coating layer is selected according to the desired degree of corrosion protection. 0.5 to 5 for heavy corrosion protection
mm, especially for long-term weatherability (over 20 years)
About 3 mm is preferable.

The deterioration inhibitor added to the polyethylene resin coating is roughly classified into an ultraviolet absorber and an antioxidant.

An ultraviolet absorber absorbs ultraviolet light that causes deterioration, converts the absorbed light energy into a harmless form such as heat, and allows incident light to reach a chromophore, which is a deterioration starting point. Acts to prevent Examples of useful UV absorbers include benzotriazole-based compounds, benzophenone-based compounds, benzoate-based compounds, cyanoacrylate-based compounds, and the like.

Antioxidants include those that act as radical chain inhibitors that trap active radical species generated in the degradation process by ultraviolet light, and those that decompose unstable hydroperoxides generated in the degradation process to form stable compounds. To
There are two types that act as hydroperoxide decomposers that block the progress of autoxidation.

Examples of the antioxidant acting as the former (radical chain inhibitor) include hindered phenol compounds and hindered amine compounds generally abbreviated as HALS, and the hindered amine compounds include aromatic amine derivatives. And piperidine derivatives are useful. On the other hand, examples of the latter antioxidant acting as a hydroperoxide decomposer include a sulfur-based compound, a phosphorus-based compound, and an organometallic compound.

Although one type of antioxidant may be used,
Usually, it is preferable to use one or more of the above-described radical chain inhibitors and one or more of the hydroperoxide decomposers in combination. Further, as a radical chain inhibitor, hindered phenol compounds and hindered amine compounds
(In particular, a hindered piperidine compound) is particularly preferable. Many of these various antioxidants are known, and commercially available products can be used.

The antioxidant used in the present invention has a molecular weight of 100
~ 2000, especially 200-1200 are preferred. Molecular weight 100
With less than the antioxidant, diffusion in the resin occurs promptly, and the antioxidant itself is expired due to ultraviolet rays on the surface of the resin and consumption due to elution is promoted, and deterioration cannot be prevented for a long time. Antioxidants with a molecular weight exceeding 2,000 diffuse slowly in the resin, the internal antioxidant does not sufficiently diffuse into the resin surface, does not catch up with the generation rate of active species of the degradation reaction by ultraviolet rays, and Cannot sufficiently cope with deterioration prevention. On the other hand, the antioxidant having a molecular weight in the range of 100 to 2,000, particularly 200 to 1200, diffuses from the inside of the coating to the surface at an appropriate speed, and the antioxidant continues to be supplied to the surface, so that the The effect of preventing the deterioration can be effectively exerted.

According to the study of the present inventors, the weather resistance of the colored polyethylene resin coating is closely related to the thickness of the polyethylene resin coating and the penetration depth of ultraviolet rays. It was also found that high weather resistance can be realized by adding a minimum amount of an antioxidant by varying the depth according to the UV transmission depth. That is, the concentration of the antioxidant for achieving high weather resistance is inversely proportional to the absorbance A and inversely proportional to the square of the polyethylene coating thickness T, as shown in the above equation (1). If the amount of the coloring pigment or the ultraviolet absorber increases and the absorbance A increases, or if the coating thickness increases, the amount of the antioxidant added can be reduced accordingly.

In other words, when the total amount C of the antioxidant in the colored polyethylene resin coating satisfies the above equation (1), the deterioration of the resin due to ultraviolet rays is limited to only the surface layer, and the internal action is caused by the action of the antioxidant. Is prevented from deteriorating.
Long-term weather resistance of more than one year can be achieved. On the other hand, if the total amount of the antioxidant is smaller than the amount specified in the above formula (1), the deterioration cannot be stopped at the surface layer, and the inside will be deeply deteriorated and the weather resistance will be reduced.

Furthermore, a longer term weather resistance of 30 years or 40 years can be ensured by adding an antioxidant in an amount corresponding to the expected life L so as to satisfy the following equation (2). it can. C ≧ 7.8 × 10 ⁻² × L / (A × T ² ) ‥‥ (2) where C, A, and T have the same meanings as above, and L is the expected life of the polyethylene coating (years). Means

Although the upper limit of the total amount of the antioxidant is not particularly limited, as described above, the addition of an excessive amount of the antioxidant causes an increase in cost. Therefore, it is usually preferable that the amount is not more than three times the amount defined by the above formula (1) or (2). Furthermore, the total amount of antioxidant added is
At most, 2 parts by weight or less for 100 parts by weight of polyethylene .

The pigment to be added for coloring the polyethylene resin may be any of known organic pigments and inorganic pigments. Usually, two or more pigments are used in combination to impart a desired color. The total amount of the coloring pigment added is 0.100 parts by weight of the polyethylene resin in order to give sufficient coloring.
05 parts by weight or more is desirable.
It is desirable that the content be not more than parts by weight.

Since the ultraviolet ray shielding ability differs depending on the type of the added pigment, a known ultraviolet absorber such as a benzotriazole compound can be added as needed to adjust the absorbance to ultraviolet rays. Excessive addition of an ultraviolet absorber impairs the economics of the product, so it is desirable to add the ultraviolet absorber to 0.5 part by weight or less based on 100 parts by weight of polyethylene.

In addition to the above-mentioned antioxidants, coloring pigments and, if necessary, ultraviolet absorbers, polyethylene resins further include extender pigments, rust preventive pigments, dispersants, softeners,
One or more known additives such as a flame retardant may be optionally added.

When producing a colored polyethylene resin composition, one or more master batches containing about 0.5 to 50% by weight of a coloring pigment and about 1 to 20% by weight of an antioxidant in a resin are prepared. By mixing the masterbatch and a polyethylene resin containing no pigment or a deterioration inhibitor in a predetermined ratio to prepare a colored polyethylene resin composition,
It is easy to obtain a homogeneous composition, which is economically advantageous.

As described above, according to the present invention, the total amount of the antioxidant to be added can be determined by the above equation (1) or (2) according to the required years of weather resistance. For example, if it is desired to secure the weather resistance for 20 years, the total amount of the antioxidant added may be set to an amount close to the lower limit specified by the above formula (1), and in the case of 30 or 40 years, May be an amount close to the lower limit amount defined by the above equation (2). As a result, a colored polyethylene-coated steel material having the required weather resistance can be manufactured by adding a minimum amount of an antioxidant, and deterioration in physical properties and economic efficiency due to excessive addition of the antioxidant can be prevented.

The method of coating the steel material with the colored polyethylene resin may be carried out in the same manner as in the prior art, and is not limited to a specific method. For example, there is a method in which a colored polyethylene sheet formed in advance is bonded to a steel material via a pressure-sensitive adhesive or an adhesive layer, or the steel sheet is coated while being continuously extruded by a molding machine. It is also possible to coat the colored polyethylene resin by using coating means such as electrostatic powder coating, fluid immersion, and thermal spraying.

[0029]

[Example] Surface adjustment of steel sheet pile (Sumitomo Metal Industries: SKSP-II type) surface by shot blasting (Sa.2.5 or more)
After that, the coating type chromate solution (Kansai Paint Co., Ltd .: Cosmer 100) so that the chromium adhesion amount becomes 200 mg / m ²
For chromate treatment. An epoxy resin primer (Nippon Paint: No.66 primer) was applied to this steel sheet pile so that the dry film thickness became 30 μm, and the steel material was heated to 190 ° C using an induction heating device. And preheating of steel.

On the other hand, the colored polyethylene resin composition to be coated is a medium-low pressure polyethylene (manufactured by Showa Denko: Shorex S4002 EX, MFR 0.20 g / 10 min, density 0.938 g / cc),
It was prepared by blending the following four kinds of antioxidants (a) to (d), a pigment and an ultraviolet absorber in the proportions shown in Table 1. This preparation was performed using a masterbatch.

Antioxidant used (a) bis (2,2,6,6-tetramethyl-4-piperidinyl)
Sebacate (a hindered piperidine antioxidant having a molecular weight of 480), (b) 3,9-bis [2- [3- (3-t-butyl-
4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane (hindered phenolic antioxidant having a molecular weight of 741) , (C) Tris (2,4-di-t-
(Butylphenyl) phosphite (phosphorus antioxidant having a molecular weight of 647), (d) 4,4′-thiobis (3-methyl-6-t-
Butylphenol) (a hindered phenolic antioxidant with a molecular weight of 358).

The antioxidants (a) to (d) are (a) :( b):
(c) :( d) was added at a ratio of 3: 1: 2: 2. When an ultraviolet absorber is added, 2- (3'-t
-Butyl-5'-methyl-2'-hydroxyphenyl) -5
-Chlorobenzotriazole was used. A film having a thickness of 50 μm was prepared from the colored polyethylene resin composition used by hot pressing, and the result of measurement of the absorbance A at a wavelength of 300 nm is also shown in Table 1.

By extruding two layers of the colored polyethylene resin composition and maleic anhydride-modified polyethylene (Admer manufactured by Mitsui Petrochemical) as an adhesive layer, a multilayer polyethylene sheet was obtained. The thickness of this sheet was 0.3 mm for the adhesive layer and 2.2 mm for the colored polyethylene resin layer. After heating the multilayer sheet to about 80 ° C. with an infrared heater, the modified polyethylene layer of the adhesive layer is fused and coated on the steel sheet pile while being pressed with a press roll on the convex part of the preheated steel sheet pile, A colored polyethylene resin-coated steel sheet pile was obtained.

Using a 150 mm × 70 mm steel sheet cut from the polyethylene resin-coated steel sheet pile as a test piece, an accelerated weathering test (black panel temperature: 63 ° C.) using a sunshine weatherometer (WOM) was performed for 4000 hours (WOM 4000). The time was equivalent to the amount of ultraviolet irradiation for about 20 years in a real environment), and the impact strength retention after 4000 hours was measured. The test results are also shown in Table 1.

[0035]

[Table 1]

Examples 1 to 20 of the present invention all have the formula (1)
Satisfies [C ≧ 1.56 / (A × T ² )]. In these examples, it can be seen that the impact strength retention rate hardly decreased even after 4000 hours of the WOM accelerated test. Example 1
As can be seen from Fig. 3, even if the amount of the antioxidant is reduced by increasing the pigment addition concentration and enhancing the ultraviolet ray shielding effect (increase the absorbance), as long as the above-mentioned formula (1) is satisfied, the WOM after 4000 hours No decrease in the impact strength retention was observed. Examples 4 to 6 show examples in which the absorbance was maintained at the same level as in Examples 1 to 3 only by adding a pigment without adding an ultraviolet absorber. Also in this case, as the amount of the pigment added increases, the impact strength retention can be maintained with a smaller amount of the antioxidant.

Examples 7 to 10 show examples in which the concentration of the antioxidant added was reduced and the film thickness was increased. Also in this case, if the antioxidant is added so as to satisfy the expression (1), the impact strength retention rate does not decrease. Similarly, for polyethylene resin coatings colored in other colors, those satisfying the expression (1) show no decrease in impact strength retention.

Further, as shown in Example 21, the following equation (2)
≧ 7.8 × 10 ^-2 × L / (A × T ² )] [L in this case
= 40 (years)] and antioxidants were added,
No reduction in the impact strength retention rate was observed after 8000 hours of WOM (8000 hours of WOM is equivalent to 40 years of irradiation in a real environment).

However, when the concentration of the antioxidant added is above (1)
In Comparative Examples 1 to 4, which do not satisfy the formulas, the antioxidant is insufficient and the impact strength retention is reduced even if the same amount of antioxidant is added and the film thickness is the same. From this, it can be seen that by adding the antioxidant to the colored polyethylene resin in an amount that satisfies the above expression (1), the life of the resin can be prolonged with a minimum amount of the antioxidant added.
As shown in Comparative Example 5, when the added amount of the antioxidant did not satisfy the expression (2), the assumed WOM 8000
Long-term (40 years) long-term weather resistance has not been obtained.

[0040]

As is apparent from the above description, in the colored polyethylene resin coating material of the present invention, the amount of the antioxidant necessary for preventing the deterioration of the polyethylene resin coating is determined by taking the degree of coloring and the coating thickness into consideration. By minimizing it, long-term weatherability (about 20 years) can be imparted to the colored polyethylene resin coating without impairing the necessary corrosion protection, impact resistance, and economy.

Claims (1)

(57) [Claims] Claims: 1. A long-term weathering resistance, characterized by being coated with a colored polyethylene resin to which a coloring pigment and an antioxidant are added, and wherein the total amount of the antioxidant in the colored polyethylene resin coating satisfies the following formula: Excellent colored polyethylene resin coating material. 2.0 ≧ C ≧ 1.56 / (A × T ² ) Here, C = total amount of the antioxidant added per 100 parts by weight of the polyethylene resin (parts by weight), T = thickness of the colored polyethylene coating (mm) A: Absorbance of a colored polyethylene coating having a film thickness of 50 μm to ultraviolet light having a wavelength of 300 nm.