JPH07207215A - Polyethylene resin composition for powder coating - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance, hygienic properties, resistance to environmental stress crack, etc., of a polyethylene resin compsn. for powder coating when applied to a metal by mechanically grinding a resin compsn. comprising a linear low-density PE, an ethylene-alpha-olefin copolymer, and a PE resin modified with an unsatd. carboxylic acid. CONSTITUTION:This compsn. is obtd. by melt mixing 100 pts.wt. linear low- density PE having a density of 0.91-0.93g/cm<3>, 5-20 pts.wt. ethylene-alpha-olefin copolymer having an alpha-olefin content of 10-25wt.%, and a PE resin modified with 0.01-5.0wt.% unsatd. carboxylic acid and mechanically grinding the resulting mixture to a particle size of 100-500mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating polyethylene resin composition which imparts excellent coating properties to a metal surface.

[0002]

2. Description of the Related Art Conventionally, powder coating has been carried out for the purpose of imparting anticorrosion properties, hygiene properties, cosmetic properties, insulating properties and the like to metals. An example of coating a metal with a composition comprising an ethylene-vinyl acetate copolymer and an unsaturated carboxylic acid-modified polyolefin on polyethylene is disclosed in JP-A-58-2358, wherein an ethylene-α-olefin copolymer and an unsaturated carboxylic acid are used. An example of an acid-modified polyethylene resin composition is JP-A-60-1.
It is described in Japanese Patent No. 30636.

However, in recent years, there has been an increasing demand for a water supply pipe material in which a lead pipe for water supply is lined with a resin on both the inner surface and the outer surface and lead is not eluted. That is, it is strongly desired to prevent corrosion from the inner and outer surfaces while leaving the flexibility which is a characteristic of the lead pipe.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to have corrosion resistance, hygiene, workability, insulation, etc. when coated on a metal, especially a lead pipe, and also environmental stress crack resistance, flexibility, It is an object of the present invention to provide a polyethylene resin composition for powder coating, which has excellent cosmetic properties and adhesion.

[0005]

[Means for Solving the Problems] The inventors of the present invention have conducted diligent research for the purpose of improving the drawbacks of conventional resin compositions for powder coating.
When a resin composition consisting of an ethylene-α-olefin copolymer and an unsaturated carboxylic acid-modified polyethylene resin is mixed and mechanically pulverized, it has anticorrosion properties, hygiene properties, processability, insulation properties, etc. when coated on a metal. The present invention has been accomplished by knowing that a polyethylene resin composition for powder coating having excellent resistance to environmental stress cracking, flexibility, beauty, adhesiveness, etc. can be obtained.

This invention comprises (a) 100 parts by weight of a linear low-density polyethylene resin, (b) 5 to 20 parts by weight of an ethylene-α-olefin copolymer, and (c) 5 to 5 unsaturated carboxylic acid-modified polyethylene resin. The present invention relates to a polyethylene resin composition for powder coating, which comprises mixing 20 parts by weight of a resin composition and mechanically pulverizing the resin composition.

In the present invention, examples of the linear low-density polyethylene resin include a linear low-density polyethylene resin prepared by a high-pressure polymerization method, a medium / low-pressure polymerization method, a solution polymerization method or a gas-phase polymerization method. It is also possible to use an α-olefin copolymer or a copolymer obtained by copolymerization with a non-olefin comonomer such as vinyl acetate or acrylic ester.

Low density polyethylene resin has a density of 0.9
According to the above method in the range of 1 to 0.93,
It is preferable because the polyethylene resin composition for powder coating of the present invention has excellent properties. However, if these densities are too high, the environmental stress crack resistance and flexibility deteriorate, which is not suitable. If these densities are too low,
It is not suitable because the workability is lowered, the coating film becomes soft, and the coating film is easily scratched during installation.

In the present invention, the ethylene-α-olefin copolymer may be any copolymer of α-olefin with propylene, butene-1, pentene-1,4-methylpentene-1, and the like. -Butene-1 copolymer is preferable from the viewpoint of appearance, adhesion, environmental stress crack resistance and the like.

Α in the ethylene-α-olefin copolymer
The olefin content is 10 to 25% by weight, preferably 15 to 20% by weight. If the content of these is too large, the above-mentioned processability and mechanical pulverizability are deteriorated, which is not suitable. When the content of these elements is small, the environmental stress crack resistance and flexibility are deteriorated, which is not suitable.

In the present invention, the ethylene-α-olefin copolymer is a linear low-density polyethylene resin 1
It is 5 to 20 parts by weight, preferably 10 to 20 parts by weight, based on 00 parts by weight. If the amount of the low-density polyethylene resin used is too large, the above-mentioned processability and mechanical pulverizability are deteriorated, which is not suitable. If the amount of these used is small, the environmental stress crack resistance and flexibility are deteriorated, which is not suitable.

In the present invention, as the unsaturated carboxylic acid-modified polyolefin resin, high density polyethylene is grafted with an unsaturated carboxylic acid such as acrylic acid, maleic acid, fumaric acid, itaconic acid or glycidyl acid and its anhydride or derivative. The derivatives also include unsaturated carboxylic acid esters and metal salts.

In the present invention, the unsaturated carboxylic acid-modified polyethylene resin includes (1) high density polyethylene resin, (2) unsaturated carboxylic acid, and (3) dicumyl, or organic peroxide such as dicumyl peroxide. using,
Kneading using various mixers such as Banbury mixer, roll mixer, kneader, high speed rotary mixer, extruder
It is obtained by modification.

As the high-density polyethylene resin, if the density is 0.94 or more by the medium pressure method / Philips method, the low pressure method / Ziegler method, the polyethylene resin composition for powder coating of the present invention has excellent characteristics. It is suitable. However, if these densities are too low, the adhesion to the metal is reduced, which is not suitable.

In the present invention, the unsaturated carboxylic acid content as the unsaturated carboxylic acid-modified polyethylene resin is
It is appropriately determined depending on the type of unsaturated carboxylic acid and the ratio of the polyethylene composition to other compositions, but it is usually 0.01 to 5.0% by weight, and preferably 0.10 to 2. It is 0% by weight. If the content of these components is too large, a crosslinking reaction will occur during compounding into the composition, resulting in poor dispersion, which is not suitable. When these contents are low,
It is not suitable because the adhesion to the metal is reduced.

In the present invention, the unsaturated carboxylic acid-modified polyolefin resin is 5 to 20 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the linear low density polyethylene. If the amount of the linear low-density polyethylene resin used is too large, the environmental stress crack resistance and flexibility are deteriorated, which is not suitable. If the amount of these used is small, the adhesion to the metal is lowered, which is not suitable.

The polyethylene resin composition for powder coating of the present invention comprises the above-mentioned (a) linear low-density polyethylene resin 10
0 parts by weight, (b) ethylene-α-olefin copolymer 5
˜20 parts by weight and (c) 5 to 20 parts by weight of unsaturated carboxylic acid-modified polyethylene resin, using various mixers such as a Banbury mixer, a roll mixer, a kneader, a high-speed rotary mixer, and an extruder. It is obtained by mechanically crushing after mixing and kneading to form a pellet.

In the present invention, the polyethylene resin composition for powder coating has a melt viscosity index (hereinafter referred to as MI).
Is 3 to 20 g / 10 minutes, preferably 5 to 10 g
/ 10 minutes. If the MI is too small or too large, the coating film strength is lowered, sagging occurs, the workability is deteriorated, and a good appearance cannot be obtained, so that the above range is suitable.

In the present invention, the particle diameter of the polyethylene resin composition for powder coating is 100 to 500 μm, preferably 100 to 300 μm. If the particle size of the polyethylene resin composition is too large or too small, the fluidity of the powder will be reduced, and voids and pinholes will be generated in the resulting coating film, so that the above range is suitable.

In the present invention, in addition to the above, the polyethylene resin composition for powder coating contains various additives such as usual antioxidants and pigments, fillers such as talc and mica, ultraviolet absorbers and plastics such as lubricants. You may add suitably in the range which does not spoil the purpose.

The (a) linear low-density polyethylene resin, (b) ethylene-α-olefin copolymer, and (c) unsaturated carboxylic acid-modified polyethylene resin used in the present invention are produced by a conventional method. Alternatively, a commercially available product may be used as appropriate.

As the powder coating method using the polyethylene resin composition of the present invention, various methods such as fluidized dipping method, electrostatic coating method, thermal spraying method and rotational molding method can be applied to metals, ceramics and other materials. Can be painted. The article to be coated may be subjected to a primer such as an epoxy type or a urethane type, or may be subjected to a chemical conversion treatment, a sand plast, a shot plast or the like. The coating thickness varies depending on the application, but it is 300 μm
It is about several mm, and a range of 500 μm to 1 mm is usually suitable.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 3 High-density polyethylene resin (density: 0.965, MI: 1
(3 g / 10 min) 100 parts by weight, 0.25 parts by weight of dicumyl as a reaction initiator, and 1 part by weight of maleic anhydride were dry-blended with a Henschel mixer for 3 minutes to give a mixture having a resin temperature of 250 ° C. in a single screw extruder of 65 mm. Was extruded to produce a modified polyethylene. The modified polyethylene has a maleic anhydride content of 1% and an MI of 10 g.
/ 10 minutes. 100 parts by weight of linear low-density polyethylene (LLDPE manufactured by Ube Industries, density: 0.920, MI: 12), ethylene-butene-1 copolymer (Mitsui Petrochemical Co., Tuffmer A4085, density: 0.89, MI: 3)
And maleic anhydride-modified polyethylene were mixed as shown in Table 1 and dry-blended with a Henschel mixer for 3 minutes. The mixture was melt-kneaded at a resin temperature of 250 ° C. with a 65 mm uniaxial extruder and extruded into pellets. This composition was mechanically pulverized at room temperature to produce powder of 50 mesh pass, and powder coating was performed by a fluidized dipping method. The properties of the obtained coating film were evaluated and are shown in Table 1.

Comparative Examples 1 to 3 In the same manner as in Examples, the resins of the types shown in Table 1 were blended and mechanically pulverized in the same manner as in Examples to prepare powder of 50 mesh pass, which was flowed. The properties of the coating film obtained by performing powder coating by the dipping method were evaluated and are shown in Table 1. Comparative Examples 1, 2 and 3 are anhydride maleic acid modified polyethylene (manufactured by Mitsui Petrochemical Co., Admer NE050, density: 0.93, MI: 3.5), ethylene-glycidyl methacrylate copolymer (Sumitomo Chemical Co., Ltd. Industrial use, Bondfast E, density: 0.94, MI: 3.0) and maleic anhydride-modified linear low-density polyethylene (maleic anhydride addition rate 1%) were used.

Coating method Using each powder obtained as described above, using an untreated lead tube (nominal diameter 13 mm) Coating conditions: coating temperature 2
It was heated at 90 ° C. for 8 minutes, coated by a fluidized immersion method at an immersion time of 10 seconds, and then heated at 180 ° C. for 10 minutes. The thickness of the membrane was 0.4 to 0.6 mm.

The physical properties of the obtained coating film are shown in Table 1, and the respective physical property values were measured by the following methods.

Melt viscosity index (MI: g / 10 minutes); JI
According to SK7210, temperature 190 ℃, load 2160g
It was measured at.

Environmental stress crack resistance [ESCR: F ₅₀ (h
r)]; A coating lead tube was bent at 90 °, and the time at which 50% of the coating film immersed in a 10% aqueous surfactant solution at 50 ° C cracked was measured.

Adhesion (kg / cm); JIS G346
180 ° peel strength was measured according to 9.

Appearance: Observing the surface of the coating film, ○: no unevenness, Δ: slightly uneven, ×: considerably uneven,
Evaluated as.

Tensile strength, elongation: Measured according to JIS K7113.

Hardness: Shore D; JIS K721
It was measured according to 5.

Softening point (° C.): Measured according to JIS K7206.

Surface treatment method: In order to improve the adhesion, the surface of the lead tube is treated with 0.01 mol / L potassium permanganate aqueous solution (7
Adhesion was measured by treating with 0%) or 10% zinc phosphate aqueous solution (room temperature). The results are shown in Table 1.

[0036]

[Table 1]

As is clear from the examples and comparative examples, the coating film obtained by using the polyethylene resin composition for powder coating of the present invention has adhesion strength, tensile properties, environmental stress cracking resistance and flexibility. It turns out that it is excellent in a balanced manner.

[0038]

The polyethylene resin composition for powder coating of the present invention is used to coat the inner surface and the outer surface of a water supply lead pipe,
Since it prevents the corrosion from the inside and outside while keeping the flexibility which is the characteristic of the lead pipe, it is effective in completely suppressing the elution of lead into water and preventing the deterioration of the surrounding soil and the mechanical damage of the lead pipe.

Claims (1)

[Claims] 1. (a) Linear low density polyethylene resin 1
00 parts by weight, (b) 5 to 20 parts by weight of ethylene-α-olefin copolymer, (c) 5 to 20 unsaturated carboxylic acid-modified polyethylene resin
A polyethylene resin composition for powder coating, which comprises blending a resin composition consisting of parts by weight and mechanically pulverizing the resin composition.