JP3346058B2 - Resin composition for steel coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for coating steel materials. More specifically, the present invention relates to a resin composition for coating a steel material having excellent wear resistance, chemical resistance, surface appearance, moldability and heat resistance, especially excellent scratch resistance at high temperatures, and significantly improved impact strength at low temperatures. It is about things.

[0002]

2. Description of the Related Art Steel pipes used for transporting natural gas, crude oil and the like are used after being coated with a polyolefin resin for the purpose of corrosion prevention and protection from the external environment. As the polyolefin resin used for the anticorrosion protective layer, high-pressure low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and ethylene-vinyl acetate copolymer are used.
There is a disadvantage that the impact resistance is lowered at a low temperature of not more than ℃. In recent years, natural gas and crude oil mining sites have been deployed in high temperature regions such as the Middle East, as well as in polar regions north of Alaska, Siberia, and so on. Storage, transportation, and burial operations are increasingly being performed. Under such low temperature, an impact force is applied to the protective coating layer, and if a crack occurs, corrosion of the steel pipe may proceed from that part, which is important for safe transport of natural gas and crude oil. Concerns arise.

[0003] On the other hand, there is still a great demand in high-temperature regions such as the Middle East, and when steel pipes are transported just below the equator, they are still deposited in high-temperature holds and exposed to vibration.

Conventionally, a method of using a specific ethylene-vinyl acetate copolymer (Japanese Patent Publication No. 62-9138) and a method of using a specific ethylene-α-olefin copolymer for improving the low-temperature impact strength (Japanese Patent Publication No. Hei. No. 8605), but none of them mentions the impact strength on a notched test piece, which is a measure of the resistance to a shocking destructive force at extremely low temperatures. Use in an environment of 45 ° C. or less was not considered.

[0005]

SUMMARY OF THE INVENTION In view of such circumstances, the problems to be solved by the present invention are abrasion resistance, chemical resistance,
An object of the present invention is to provide a resin composition for coating a steel material having excellent surface appearance, moldability and heat resistance, particularly excellent scratch resistance at high temperatures, and significantly improved impact strength at low temperatures.

[0006]

That is, the present invention relates to a composition comprising the following component (A): 25 to 60% by weight;
70% by weight and the following component (C): 0 to 65% by weight (provided that (A) + (B) + (C) = 100% by weight)
Wherein the resin composition has a melt flow rate of 0.3 to 1.0 g / 10 minutes and a vinyl acetate content of 0.5 to 2.5 g in the resin composition. The present invention relates to a resin composition for coating steel material, which is a percentage by weight. Component (A): density of 0.918 to 0.927 g / cm ³
And the melt flow rate is 0.5 to 1.2 g /
Ethylene-α-olefin copolymer for 10 minutes (B) component: vinyl acetate content is 1.5 to 5.5% by weight
Ethylene-vinyl acetate copolymer (C): High pressure polyethylene

The details will be described below.

The component (A) of the present invention has a density of 0.918.
A ~0.927g / cm ^3, and melt flow rate of ethylene -α- olefin copolymer is 0.5 to 1.2 g / 10 min.

The density of the component (A) is 0.918 to 0.92.
7 g / cm ³ , preferably 0.919 to 0.924 g /
cm ³ . Here, the density is measured at 23 ° C. according to JIS K6760. If the density is too low, the abrasion resistance, chemical resistance and heat resistance are inferior, while if the density is too high, the impact strength at low temperatures is greatly reduced.

The melt flow rate of the component (A) is 0.5
~ 1.2g / 10min, preferably 0.6 ~ 1.0g / 1
0 minutes. In addition, the melt flow rate (MFR) in the present invention is a temperature of 1 according to JIS K6760.
It is measured at 90 ° C. and a load of 2.16 kg. If the melt flow rate is too low, the torque at the time of extrusion increases, and sharkskin is generated on the coating surface, making molding difficult. On the other hand, if the melt flow rate is excessively high, the impact strength at low temperatures is reduced, and the melt tension is further reduced, so that uneven wall thickness tends to occur during coating.

As the α-olefin in the component (A), 1-butene, 1-hexene, 1-octene, 4-methylpentene-1 and the like can be mentioned, but from the viewpoint of industrial availability, etc. -Butene is preferred.

The content of the α-olefin in the component (A) is usually 3 to 14% by weight, preferably 4 to 10% by weight.
It is. If the content is too low, the impact strength at low temperatures may be poor, while if the content is too high, the wear resistance, chemical resistance and heat resistance may be poor.

The component (A) of the present invention is a so-called LLDP
It belongs to a type called E (linear low-density polyethylene).

As a method for obtaining the component (A), for example, a so-called Ziegler-type catalyst comprising a combination of a compound of a transition metal belonging to Groups IVa to VIa of the periodic table and an organometallic compound of a metal belonging to Groups I to III of the periodic table. Or using a Phillips catalyst, polymerization temperature of about 30 to 300 ° C., polymerization pressure of normal pressure or
Under the condition of about 3000 kg / cm ^{2 in} the presence of a solvent,
A method in which ethylene and an α-olefin are ion-polymerized in a gas-solid phase, a liquid-solid phase, or a homogeneous liquid phase can be used. In addition, other than ethylene and α-olefin,
Other comonomers may be copolymerized. The density is controlled by the type and copolymerization amount of the α-olefin, and the melt flow rate is controlled by the type and amount of the chain transfer agent. The polymerization process is not particularly limited, and any of so-called slurry polymerization, gas phase polymerization, liquid phase polymerization and the like can be used.

The content of the component (A) in the resin composition of the present invention is 25 to 60% by weight, preferably 30 to 40% by weight. If the content is too low, heat resistance, particularly, scratch resistance at high temperatures is inferior. On the other hand, if the content is excessive, sharkskin is generated on the coating surface during coating processing, resulting in poor appearance, high extrusion torque, and poor workability.

The component (B) of the present invention is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 1.5 to 5.5% by weight.

The vinyl acetate content of the component (B) is 1.5
To 5.5% by weight, preferably 2.0 to 5.0% by weight. If the content is too low, the effect of improving the impact strength at low temperatures is poor, while if the content is too high, the heat resistance is poor.

As a method for obtaining the component (B), for example,
If free radical generators such as organic peroxides and oxygen are used,
130-300 ° C polymerization temperature, 500-3000kg
/ Cm ^TwoCopolymerizes ethylene and vinyl acetate under polymerization pressure
There are ways to do that.

The content of the component (B) in the resin composition of the present invention is 10 to 70% by weight, preferably 25 to 50% by weight. If the content is too low, it is assumed that low-temperature impact resistance, especially cracks generated at the time of collision between sharp rocks and steel pipes at low temperature added during the actual work of transporting, storing and burying steel pipes and their propagation. No improvement in the impact resistance of the notched specimens can be obtained. On the other hand, when the content is excessive, heat resistance, particularly, scratch resistance at high temperatures is inferior.

The component (C) of the present invention is a high-pressure polyethylene, which is a homopolymer of ethylene.

The component (C) belongs to a type called HPLD (high-pressure low-density polyethylene).

As a method for obtaining the component (C), for example,
If free radical generators such as organic peroxides and oxygen are used,
130-300 ° C polymerization temperature, 500-3000kg
/ Cm ^TwoThe method of polymerizing ethylene under the polymerization pressure of
Can be

The content of the component (C) in the resin composition of the present invention is 0 to 65% by weight, preferably 10 to 45% by weight. That is, in the present invention, the component (C) is not an essential component, but by using the component (C) within the above range, it is possible to improve heat resistance while maintaining good moldability. it can. If the content of the component (C) is excessive, the low-temperature impact resistance is poor.

The resin composition of the present invention has a melt flow rate of 0.3 to 1.0 g / 10 min, preferably 0.4 to 1.0 g / 10 min.
0.8 g / 10 min. If the melt flow rate is too low, the torque increases, resulting in poor workability. On the other hand, if the melt flow rate is excessively high, the impact resistance and heat resistance at low temperatures, particularly the scratch resistance at high temperatures, are poor.

The resin composition of the present invention has a vinyl acetate content of 0.5 to 2.5% by weight, preferably 1.0 to 2.
0% by weight. If the content is too low, it is assumed that low-temperature impact resistance, especially cracks generated at the time of collision between sharp rocks and steel pipes at low temperature added during the actual work of transporting, storing and burying steel pipes and their propagation. No improvement in the impact resistance of the notched specimens can be obtained. On the other hand, when the content is excessive, heat resistance, particularly, scratch resistance at high temperatures is inferior.

The vinyl acetate content in the present invention refers to the content of vinyl acetate units contained as a structural unit in a copolymer or a resin composition.

The resin composition of the present invention is obtained by uniformly melting and kneading the above-mentioned components. Incidentally, other known compounding agents usually used, such as antioxidants, neutralizers, ultraviolet absorbers, internal lubricants, pigments, flame retardants, processing aids, inorganic or organic fillers and the like of the present invention You may mix | blend in the range which does not impair the objective.

The resin composition of the present invention is optimally used for coating steel. Here, the steel material refers to a steel pipe, a steel plate, and the like.

[0029]

The present invention will be described below with reference to examples. The measurement and evaluation methods are as follows.

(1) Low Temperature Impact Strength (Using Notched Specimen) A 45 ° V-shaped notch (the V-shaped notch) was formed at the upper side of the horizontal center of a 9.53 mm × 63.5 mm rectangle. The lower point is located 5.0 mm from the lower side of the rectangle.) Using a notched test piece having a pendulum-type tensile impact tester manufactured by Toyo Seiki Co., Ltd. in accordance with ASTM D-1822,
The measurement was performed at 60 ° C. The test piece was prepared by punching out a 1 mm thick press sheet.

(2) Torque (Indicator of workability) The torque was measured at 160 ° C., 60 rotations and 30 minutes after using a Brabender plastic coder manufactured by Brabender. The filling amount of the sample was 40 g, and 0.2% of Sumilizer WXR (manufactured by Sumitomo Chemical Co., Ltd.) was used as an antioxidant.
% By weight.

(3) Vicat Softening Point (Indicator of Heat Resistance) A test piece was applied to a needle having a tip area of 1 mm ² with a load of 1 kg using a thermal deformation tester manufactured by Toyo Seiki according to ASTM D-1523. And the temperature was raised at a heating rate of 50 ° C./hr, and the temperature when the needle tip penetrated 1.0 mm into the sample was defined as the Vicat softening point. The test piece was prepared by pressing.

(4) Shark Skin (Surface Roughness) The granulated resin composition obtained by the following method was prepared by using a 65 mmφ T die sheet extruder at 250 ° C. and a die width of 200.
A sheet having a thickness of 0.5 mm and a width of 180 mm was extruded with a coat hanger type T-die having a lip gap of 0.5 mm and a lip gap of 0.5 mm. The appearance of the sheet surface was observed, and the occurrence of sharkskin was determined. The extrusion rate at this time is 7
5 kg / h and the shear rate at the die exit is about 52
0 sec ^-1 . Although the actual shear rate in the actual extrusion coating process which is industrially performed is slightly higher than this, it is a sufficient condition as a criterion for determining the surface appearance. The results of the shark skin were evaluated as ○ (good without rough surface) and × (bad with rough surface).

(5) Scratch Resistance at High Temperature (Dynamic Penetration Test) A pressed sheet having a thickness of 2.5 mm was replaced with a pickled steel sheet having a thickness of 2 mm and an adhesive resin film (trade name “Bond First 7B” manufactured by Sumitomo Chemical Co., Ltd.). ) At 250 ° C., and immersed in hot water at 60 ° C. for 1 hour. Immediately after being taken out of hot water, 1k through a punch with a tip diameter of 15.9mm
g of weight was dropped from a height of 1 m, and at that time, the depth at which the punch penetrated the press sheet was measured.

Examples 1 to 8 and Comparative Examples 1 to 12 The blends of Tables 1, 3, 5, 7 and 9 were kneaded and granulated by a 30 mmφ single screw extruder to obtain a granulated resin composition. Various physical properties of the granulated resin composition were measured and evaluated by the methods described above. The conditions and results are shown in Tables 2, 4, 6, 8 and 10.

The following can be understood from the results. All examples satisfying the conditions of the present invention show satisfactory results in all evaluation results. On the other hand, each comparative example that does not satisfy the conditions of the present invention is unsatisfactory in the following points. Comparative Example 1, in which the vinyl acetate content of the component (B) is excessive, is inferior in the items of Vicat softening point and high-temperature scratch resistance.
Comparative Example 2 in which the vinyl acetate content of the resin composition is excessive is inferior in the items of Vicat softening point and high-temperature scratch resistance. Comparative Example 3, in which the content of the component (A) is excessive, is inferior in the items of torque and sharkskin. Comparative Example 4 in which the vinyl acetate content of the resin composition is excessive is inferior in the items of Vicat softening point and high-temperature scratch resistance. Comparative Example 5, in which the density of the component (A) is too low, is inferior in the items of Vicat softening point and high-temperature scratch resistance. Comparative Example 6, in which the density of the component (A) is excessive, is inferior in the item of low-temperature impact strength. Comparative Example 7, in which the vinyl acetate content of the component (B) and the resin composition is too low, is inferior in low temperature impact strength. (A)
Comparative Example 8 in which the content of the component is too small and the content of the component (B) is too large is inferior in the items of Vicat softening point and high-temperature scratch resistance. Comparative Example 9 in which the vinyl acetate content of the resin composition was too low
Is inferior to the item of low-temperature impact strength. Comparative Example 10 in which the melt flow rate of the resin composition is too large is inferior in the items of low-temperature impact strength and high-temperature scratch resistance. Comparative Example 11 in which the melt flow rate of the resin composition was too low was inferior in the items of torque and sharkskin. Comparative Example 12 in which the melt flow rate of the component (A) is too large is inferior in the item of low-temperature impact strength.

[0037]

[Table 1] ----------------------------------------------------------------------------------------------------------- Example 1 Component 2 3 4 5 Component (A) Component Type * 1 A1 A2 A1 A3 A3 Density g / cm ³ 0.919 0.919 0.919 0.921 0.921 MFR g / 10 min * 4 0.8 0.8 0.8 0.7 0.7 Content wt% 35 30 50 40 60 (B) Component type * 2 B1 B1 B1 B1 B2 Acetate content wt% 5.0 5.0 5.0 5.0 3.0 MFR g / 10 min * 4 0.4 0.4 0.4 0.4 0.4 Content wt% 35 35 50 15 40 (C) Component type * 3 C1 C1-C1-Density g / cm ³ 0.921 0.921-0.921-MFR g / 10 min * 4 0.3 0.3-0.3-Content wt% 30 35 0 45 0 Composition MFR g / 10 min * 4 0.5 0.5 0.6 0.5 0.6 Vinyl acetate content wt% 1.75 1.75 2.50 0.75 1.20 ---------------------------------------------------------------------------------

[0038]

Table 2 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Example 1 2 3 4 5 Evaluation Low temperature impact strength kg・ Cm / cm ² 80 100 100 60 60 Torque g ・ m 2400 2400 2500 2440 2500 Vicat softening point 96 96 95 98 97 High temperature scratch resistance 1.8 1.7 1.9 1.5 1.9 Shark skin ○ ○ ○ ○ ○ −−−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

Table 5 --------------------------------------------------------------------------- Comparative Example 1 2 3 4 5 Component (A) Component Type * 1 A1 A1 A1 A1 A3 Density g / cm ³ 0.919 0.919 0.919 0.919 0.900 MFR g / 10 min * 4 0.8 0.8 0.8 0.8 0.8 Content wt% 35 35 75 20 40 (B) Component type * 2 B4 B1 B1 B1 B1 B2 Acetate content wt% 6.0 5.0 5.0 5.0 3.0 MFR g / 10 min * 4 0.4 0.4 0.4 0.4 0.4 Content wt% 35 65 25 55 60 (C) Ingredient type * 3 C1--C1-Density g / cm ³ 0.921--0.921-MFR g / 10 min * 4 0.3--0.3-Content wt% 30 0 0 25 0 Composition MFR g / 10 min * 4 0.5 0.5 0.7 0.4 0.5 Vinyl acetate content wt% 2.10 3.50 1.25 2.75 1.80 ------------------------------------------------------------------

[0042]

Table 6-------------------------------------Comparative Example 1 2 3 4 5 Evaluation Low-temperature impact strength kg・ Cm / cm ² 100 120 60 100 80 Torque g ・ m 2400 2350 2600 2300 2450 Vicat softening point ℃ 93 90 98 92 91 High temperature scratch resistance 2.3 2.5 1.6 2.5 2.5 Shark skin ○ ○ × ○ ○ −−−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

[0043]

Table 7: Comparative Example 6 7 8 9 10 Component (A) Component------------------------------- Type * 1 A4 A3 A3 A3 A3 Density g / cm ³ 0.930 0.921 0.921 0.921 0.921 MFR g / 10 min * 4 0.8 0.7 0.7 0.7 0.7 Content wt% 40 40 20 40 40 (B) Component type * 2 B2 B1 B2 B5 B6 Acetic acid content wt% 3.0 5.0 3.0 2.0 3.0 MFR g / 10 min * 4 0.4 0.4 0.4 0.4 5.0 Content wt% 60 5 80 20 30 (C) Ingredient type * 3-C1-C1 C2 Density g / cm ³ -0.921-0.921 0.921 MFR g / 10 min * 4-0.3-0.3 4.0 Content wt% 0 55 0 40 30 Composition MFR g / 10 min * 4 0.5 0.5 0.4 0.5 2.0 Vinyl acetate content wt% 1.80 0.25 2.40 0.40 0.90 -----------------------------------------------------------

[0044]

Table 8-------------------------------------Comparative Example 6 7 8 9 10 Evaluation Low-temperature impact strength kg・ Cm / cm ² 5 20 150 30 5 Torque g ・ m 2450 2460 2300 2450 1300 Vicat softening point ℃ 102 105 92 100 92 High temperature scratch resistance 1.2 1.0 2.3 1.5 2.8 Shark skin ○ ○ ○ ○ ○ −−−−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

[0045]

Table 9 ------------------------ −−−−−−−−−−−−−−−−−−−−−−−−−−−−
−−−−−−−−−

[0046]

[Table 10]

* 1 Types of (A) A1, A3 to A7: ethylene-1-butene copolymer (L
LDPE) (Sumitomo Chemical Co., Ltd. product name "Sumikacene L") A2: Ethylene-1-hexene copolymer (LLDPE)
(Sumitomo Chemical Co., Ltd. product name "Sumikasen α") * 2 Type of (B) B1 to B7: ethylene-vinyl acetate copolymer (Sumitomo Chemical Co., Ltd. product name "Evatate") * 3 (C) Type C1 to C3: High pressure polyethylene (Homopolymer of ethylene, trade name “Sumikasen” manufactured by Sumitomo Chemical Co., Ltd.) * 4 MFR: Temperature 1 according to JIS K6760
Melt flow rate measured at 90 ° C under a load of 2.16 kg

[0048]

As described above, according to the present invention, abrasion resistance, chemical resistance, surface appearance, moldability and heat resistance,
In particular, it was possible to provide a resin composition for coating a steel material having excellent scratch resistance at high temperatures and significantly improved impact strength at low temperatures.

Claims (3)

(57) [Claims] 1. The following component (A) 25 to 60% by weight, the following component (B) 10 to 70% by weight and the following component (C) 0 to 6:
5% by weight (provided that (A) + (B) + (C) = 100% by weight), wherein the resin composition has a melt flow rate of 0.3 to 1.0 g. / 10 minutes, and the vinyl acetate content in the resin composition is 0.1.
5 to 2.5% by weight of a resin composition for coating a steel material. Component (A): density of 0.918 to 0.927 g / cm ³
And the melt flow rate is 0.5 to 1.2 g /
Ethylene-α-olefin copolymer for 10 minutes (B) component: vinyl acetate content is 1.5 to 5.5% by weight
Ethylene-vinyl acetate copolymer (C): High pressure polyethylene 2. The resin composition according to claim 1, wherein the α-olefin of the component (A) is 1-butene. 3. The content of the component (C) in the resin composition is 1
The resin composition for coating steel material according to claim 1, wherein the content is 0 to 45% by weight.