JPS5920362A - Powder coating resin composition - Google Patents

Abstract

PURPOSE:To provide a polyethylene powder coating resin compsn. excellent in powder characteristics and film performance, by mixing a particular ethylene/alpha- olefin copolymer powder, dibenzylidenesorbitol or its derivatives, and an antioxidant. CONSTITUTION:100pts.wt. ethylene/alpha-olefin copolymer powder whose density is 0.910-0.935g/cc, bulk density is 0.25-0.55g/cc, angle of repose is 25-45 deg., particle size is 500mu or below and average particle size is 70-250mu, and shape is sphere, oval, or similar forms free from well-defined sides, edges, strings, or whiskers, and which is prepd. by suspension polymn. or gas phase polymn., 0.1-1.0pts.wt. dibenzylidenesorbitol and/or its derivatives, and 0.1-1.0pts.wt. antioxidant are mixed together.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyethylene powder coating resin composition having excellent powder characteristics and coating performance.

Due to its excellent properties, polyethylene has found applications in powder coating, particularly powder coating by fluidized dipping. As such polyethylene, high-pressure low-density polyethylene is generally used, and has excellent decorative performance and protection/corrosion prevention performance as a coating film. However, with the diversification and sophistication of applications and requirements, improvements in heat resistance, chemical resistance, environmental stress cracking resistance (ESCR), hardness, oil resistance, weather resistance, etc. are required, and furthermore, cost reduction is required. There are also strong demands.

On the other hand, in order to obtain polyethylene powder for powder coating, polyethylene pellets are usually mechanically pulverized. This is unavoidable, and there is a problem in that the powder fluidity required for powder coating is insufficient and the powder fluidity tends to fluctuate. If the powder fluidity deteriorates, the thickness of the coating film becomes uneven, the surface texture becomes rough, and pinholes occur, which is undesirable.

On the other hand, it can be said that directly using the powder obtained from polymerization for powder coating is suitable from the viewpoint of energy saving, as long as the powder fluidity and coating performance are good. However, this attempt has not yet been successful. The reason for this is that the powder properties are not fully satisfactory, and when the above powder is directly powder coated, it is not melted and kneaded to make it uniform, so the gloss and smoothness of the coating film is significantly impaired, and the coating has a citron skin-like appearance. Only an appearance with poor decorativeness was obtained, and the physical properties of the coating film, such as coating film ESCR, were also extremely poor.

On the other hand, as a method for improving the gloss of polyethylene, a method of adding various nucleating agents is known, and many proposals have been made. There are also examples of using substitutions. However, it is believed that these compounds exhibit their effects only when they are uniformly melted and dispersed in polyethylene, and conventionally, they have been used by melt-kneading them with polyethylene. However, as a result of extensive research into the use of powder obtained by polymerization in powder coating, the present inventors found that the above-mentioned dibenzylidene sorbitol and/or The gloss, smoothness, and ESCR of the paint film after powder coating can be improved simply by mixing the nuclear-substituted product thereof, and furthermore, the ESCR property of the paint film can be improved by using it in combination with an antioxidant. The present invention has been achieved based on the discovery that this can be dramatically improved.

That is, the present invention provides: (A) a density of 0.910 to 0.935 y/cr;
, (B) The bulk density of the powder is 0.25-0.55 f
/CL, (C) The angle of repose of the powder is 25 to 45°, (D
) The particle size of the powder is 500μ or less and the average particle size is 70~2
50μ, (E) The shape of the powder is spherical or elliptical, or
(F) The powder must be produced by suspension polymerization or gas phase polymerization; ethylene-α olefin copolymer powder 100
parts by weight, 0.1 to 1.0 parts by weight of dibenzylidene sorbitol and/or its nuclear substitute, and 0.1 to 1 part by weight of antioxidant
．． This is a new powder coating resin composition containing 0 parts by weight.

In the present invention, the ethylene-α-olefin copolymer powder obtained by polymerization is a copolymer with α-olefin containing 50 moles or more of ethylene, and is produced by a suspension polymerization method or a gas phase polymerization method. It is a powder that is Examples of α-olefins include propylene, butene, pentene,
Examples include 4-methylpentene-1, hexene, and octene.

These ethylene-α-olefin copolymer powders may be copolymers containing two or more α-olefins, or may be a mixture of two or more ethylene-α-olefin copolymer powders. Further, as the α-olefin, it is preferable to use crow-like α-olefins such as 4-methylpentene-1, hexene, and octene because they have better coating film ESCR properties.

The density of the above copolymer powder is 0.910~(1-935r
/cc, more preferably 0.910-0.
It is in the range of 930 r/mark. If the density is higher than the above range, the gloss and smoothness of the coating film will be poor, and the coating ESC
The R properties are also lowered, which is not preferable. If the density is lower than the above range, use suspension polymerization to obtain powder with good powder properties.
It becomes substantially difficult to produce by gas phase polymerization.

2. Melt index (MI) is 5 to 100
f/lO−, more preferably 10 to 50
A range of about t/10 is preferred.

Furthermore, the bulk density is in the range of 0.25 to 0, s5r/medium, more preferably in the range of 0.35 to 0.55. If the bulk density is higher than the above range, it becomes substantially difficult to manufacture the powder while satisfying other non-inventive powder properties. - If the bulk density is still lower than the above range, it is undesirable because workability decreases, pinholes occur in the coating film, and poor smoothness occurs.

Further, the angle of repose is in the range of 25 to 45°, more preferably in the range of 25 to 40°. If it exceeds 450, the fluidity of the powder will be poor and the powder coating properties will be insufficient. Further, if the angle is less than 25°, it becomes difficult to manufacture the powder while satisfying the other powder characteristics of the present invention.

In the present invention, the particle size distribution of the powder is JIS-Z880.
Sieve residue test method using No. 1 sieve (JIS K
Cumulative distribution curves are obtained by the test method defined by OO69). From this cumulative distribution curve, 5 of the cumulative distribution
The diameter at 0 percent value, that is, the 50% particle diameter is determined as the average particle diameter. The particle size of the copolymer powder is 500μ or less, and the average particle size is in the range of 70 to 250μ. More preferably, it is 300μ or less, and the average particle size is preferably in the range of ioo to 250μ.

If the particle size is larger than the above range, the smoothness of the coating film will be impaired, which is undesirable. If the particle size is smaller than the above range, the coating film may become uneven in thickness or the coating workability may be deteriorated, which is undesirable.

In the present invention, the shape of the powder is spherical or elliptical as shown in the IT diagram photograph, or a similar shape,
It should be essentially free of distinct edges, ridges and threads or whiskers. The powder obtained by milling pellets at room temperature contains quite a few thread-like or whisker-like substances, as shown in the photograph in Figure 2, and the shape of the powder particles is also complex, as if they had been torn apart. shows. Further, the powder obtained by freezing and pulverizing pellets at liquid nitrogen temperature has a small amount of thread-like or string-like substances, but the powder particles have clear edges and edges. When the shape of powder particles is complex like this,
Powder fluidity is not good, pinholes occur in the coating film, and smoothness is poor, which is not preferable. In addition, such powders are manufactured by suspension polymerization method or gas phase polymerization method,
It may be a powder obtained by crushing a powder produced by the polymerization method, or a powder obtained by classifying such a powder.

Dibenzylidene sorbitol used in the present invention is represented by the chemical formula (C6HIO06) (CHO)2, and the nuclear substituents of dibenzylidene sorbitol include methyl group, ethyl group, propyl group, isopropyl group, and butyl group. Nuclear substitution products such as , methoxy group, ethoxy group, propoxy group, butquine group, and phenol group are possible. These may be used alone or in combination of two or more.

The present invention (in which dibenzylidene sorbitol and/or
Or, the amount of the nuclear substituted product used is in the range of 0.1 to 1.0 parts by weight, more preferably in the range of 0.2 to 0.6 parts by weight, based on 100 parts by weight of the above copolymer. . If the amount used is less than the above range, the effect of improving the gloss, smoothness and ESCR properties of the coating film will be poor, and if it is greater than the above range, the effect of improving the gloss, smoothness and ESCR properties of the coating film will be saturated. Antioxidants used in the present invention include, for example, octadecyl 3- (3', 5' ditertiarybutyl 4' hydroxyl enyl) propionate, tetrakis [methylene-(3,5-ditertiarybutyl 4-hydroxyno-
Hydrocinnamate)] Methane, 2,2'-methylenebis(4-methyl-6-tert-butylphenol)
, 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-p-cresol, etc. Phenolic antioxidants, sulfur antioxidants such as dilaurylthiodiglopionate and distearylthiodipropionate, tetrakis (2,4-ditertiarybutylphenyl) 4.4'
- Biphenylene diphosphonite, tris(2,4-
Possible antioxidants include phosphorous antioxidants such as ditarjarifthylphenyl) phosphite. Particularly preferred are phenolic antioxidants. These antioxidants may be used alone or in combination of two or more.

In the present invention, the amount of the antioxidant used is in the range of 0.1 to 1.0 parts by weight, more preferably 0.2 to 0.8 parts by weight, and even more preferably is in the range of 0.3 to 0.6 parts by weight.

Antioxidants are usually used in polyethylene resins in an amount of 0.1% by weight or less, but the present inventors have found that by using other antioxidants in the above range in combination with dibenzylidene sorbitol and/or a nuclear substituted product of shisotake, Paint film gloss, smoothness, film strength,
It has also been found that the ESCR properties are dramatically improved. If the amount of antioxidant used is less than the above range, the effect of improving coating film strength and ESCR properties will be poor; if it is more than the above range, the improving effect of coating film strength and ESCR properties will become saturated, and the effect of improving coating film strength and ESCR properties will decrease. This is not preferred because it bleeds and impairs the appearance of the paint film.

The resin composition for powder coating of the present invention can be prepared by mixing the copolymer powder, dibenzylidene sorbitol and/or its nuclear substituted product, and antioxidants, colorants, and other additives using a tamper, ribbon blender, or Henschel blender. It is adjusted by a commonly used mixing means such as a mixer. They may be mixed when crushing coarse polymer powder. In particular, it is best to mix thoroughly using a high-speed fluid mixer such as a Henschel mixer. Furthermore, in order to improve the dispersion of dibenzylidene sorbitol and/or its nuclear substituted product, antioxidant, and other additives, they can be dissolved in a solvent and then mixed with the copolymer powder. Alternatively, dibenzylidene sorbitol and/or its nuclear substitutes, antioxidants and other additives may be added to 300μ or less, more preferably 150μ or less.
It may be pulverized or pulverized to less than μ and then mixed.

Powder d of the present invention: In addition to the above composition, the wearing composition contains pigments, colorants, ultraviolet absorbers, antistatic agents, lubricants, thickeners, coating aids, flame retardants, fillers and other additives. can also be added.

The powder coating composition of the present invention can be used to coat metals, ceramics, and other materials by various powder coating methods such as fluidized dipping, electrostatic coating, electrostatic current dipping, thermal spraying, and rotational molding. be able to. The object to be painted may be coated with an epoxy, urethane, or other primer, or may be coated with a chemical conversion treatment or
Sandblasting or other surface treatment may be performed.

The coating conditions when performing powder coating using the composition of the present invention are the conditions generally used in each yuzu powder coating method, but preferably the temperature of the composition of the present invention is 20°C.
The temperature is preferably 0°C or higher, more preferably 2
Preferably, the temperature is 30°C or higher.

The thickness of a coating film coated using the powder coating composition of the present invention varies depending on the application, but is approximately 30 μm to 3 N, and a range of 100 μm to 1 N is usually applied.

The present invention will be explained below with reference to Examples.

In addition, parts in Examples and Reference Examples indicate parts by weight and weight %, respectively.

Further, the various properties that define the powder of the present invention were measured by the following methods: Density: ASTM D1505 Melt Index: ASTM D1238 Bulk Density: ASTM D1895 Angle of Repose: Measured by injection method.

Particle size distribution: JIS KOO69 Examples 1-1 to 4 and Comparative Example 1 MI 159710 m, density 0.930 seconds t1 bulk density of powder 0.37 y/ct-1 angle of repose 37°, particle size 50
Dibenzylidene is added to 100 parts by weight of ethylene-butene-1# polymer powder, which has an average particle size of 0 μ or less and a nearly spherical shape and is substantially free of whiskers and is produced by a suspension polymerization method. Sorbitol and tetrakis[methylene-(3,5-ditertiary-phthyl-4-hydroxyhydrocinnamate)]methane as an antioxidant
The powder was pulverized to a size of 50 μm or less and mixed using a Hen-7er mixer at the blending ratio described in Section 1a to produce a resin powder for powder coating.

Using this powder, by the fluidized dipping method,
Steel plate test panel (JI) with length 150IIJs width 70m
A coating film with a thickness of 0.3.0 was formed on SG3141).

Conditions for fluidized immersion C: Preheat the steel plate at 350°C for 4 minutes, fluidized immersion time for 2 seconds, post-heat at 200°C for 3 minutes, bottom surface $ 20
The test was carried out in a 0 tri cylindrical fluidized tank with a powder amount of I kg.

The amount of air required to fluidize the powder is 23N27m
The fluidization state was also good.

The coating film performance was evaluated as follows.

The result is shown in the first robe.

■Coating film ES CR property = 4 coated test panel R = 10
The sample was bent by 180° at 50° C. and immersed in a 0.5 titantalox C0630 aqueous solution at 50° C., and the time until cracks appeared was measured.

I tried it on n-6 and cracks appeared on 3 of them. time until birth.

■Gloss: ASTM D523 60°-60° ■Smoothness Evaluated by second sight.

○: Smooth X: Uneven Example 2 MI 20f710m, density 0.925 y/cr
Ethylene-butene-1 produced by the gas phase polymerization method of
Copolymer powder is coarsely ground to a bulk density of 0.38 f/cc
, angle of repose 3601 grain size finer than 500μ, average grain size 1
A powder having a diameter of 80 μm, nearly spherical in shape, and substantially free of whiskers was obtained. These powders were mixed using a Henschel mixer at the blending ratio described in Section 1i to produce a resin powder for powder coating. This powder was subjected to fluidization immersion in the same manner as in Example 1, and the coating film performance was evaluated.The fluidization air amount was 22 Nt/m, indicating a good fluidization state. The results are shown in Part 2.

Comparative example 2 MI 20 r/10 mtn, density 0.950 r/
cc, bulk density of powder 0.40 t/mark, angle of repose 36°
, using an ethylene-butene-1 copolymer powder directly produced by a suspension polymerization method that has a particle size of 500 μm or less, an average particle size of 150 μm, and a particle shape close to spherical, and does not substantially contain whiskers. Resin powder for powder coating was produced in the same manner as in Example 1 at the blending ratio described in the first coating, and the coating film performance was evaluated by the fluidized dipping method. The amount of fluidizing air was 2 tHz/=, and the fluidization state was good, but the gloss and ESCR properties of the coating film were low. The results are shown in Figure 1.

Comparative example 3 Δ'II 2017m, density 0.933 t/cr:
,, bulk density of powder 0.24 y/ω, angle of repose 49°,
100 parts of ethylene butene-1 copolymer powder produced by a suspension polymerization method with a particle size of 500μ or less and an average particle size of 60μ, 7 parts of dibenzylide 7 sorbitol, 4 parts of NJt and tetrakis[methylene-(3,5-ditertiary)] Butyl-4-hydroxyhydrocinnamate) Memetsu 00.
Parts by weight were mixed using a Henschel mixer to produce resin powder for powder coating.

When fluidized immersion was performed using this powder, the amount of air required for fluidization was as large as 53 Ht/IIth, and the fluidized state was poor, with large bubbling and a lot of powder blowing up and scattering.

Comparative Example 4 100 parts of high-pressure polyethylene with an MI of 209710 m and a density of 0.92017 and 0.2 parts of dibenzylidene sorbitol were uniformly kneaded at 120°C for 10 minutes using a Banbury mixer, and then pelletized using a granulator. It became.

The above pellets were mechanically crushed at room temperature, and the bulk density was 0.33.
A powder was obtained with a f/phrase, an angle of repose of 41°, a particle size smaller than 500μ, and an average particle size of 180μ.

Using this powder, the coating film was evaluated by the fluidized dipping method in the same manner as in Example 1. The results are shown in Table 1.

Margin below

[Brief explanation of drawings]

Figure 1 is a scanning electron micrograph (50x magnification) of the polyethylene powder used in the present invention, and Figure 2 is a scanning electron micrograph (30x magnification) of the powder obtained by mechanically crushing pellets. ) is shown. Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] (A) Density is 0.910 = 0.935 r/c
c, (B) The bulk density of the powder is 0.25-0.55
r/cc, (C) The angle of repose of the powder is 25 to 45°, (
D) The particle size of the powder is 500μ or less and the average particle size is 70~
250 μ, (E) The shape of the powder is spherical or elliptical, or
(F) The powder must be produced by suspension polymerization or gas phase polymerization; ethylene-α olefin copolymer powder 100
Heavy background, 0.1 to 1.0 parts by weight of dibenzylidene sorbitol and/or its nuclear substitute, and 0.1 to 1.0 parts by weight of an antioxidant.
Resin composition for powder coating prepared by mixing 1.0 parts by weight