JPH01282234A - Powdery polyolefin composition - Google Patents

Abstract

PURPOSE:To obtain the title composition especially having excellent fluidity and dispersibility of pigment, useful powdery coating compound for powder coating such as fluidized bed coating, electrostatic coating or spraying method, comprising powder PE and a small amount of a metallic salt of specific fatty acid. CONSTITUTION:(A) 100 pts.wt. powder PE is blended with (B) 0.005-2 pts.wt., preferably 0.05-1.5 pt.wt. 10-22C fatty acid metallic salt (preferably zinc stearate, calcium stearate or magnesium stearate) to give the aimed composition.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention has particularly excellent fluidity and pigment dispersibility, and is suitable for powder coating such as fluidized dipping, electrostatic coating, and spraying. The present invention relates to powdered polyethylene compositions.

[Conventional technology]

Powdered polyethylene is widely used as a material for powder coating methods such as fluidized dipping, electrostatic coating, and scattering methods. The various powder coating methods described above have a number of advantages, such as not using dangerous solvents, high coating efficiency, and the ability to coat a thick film with just a few coats. Also, among various powder resins, powder polyethylene has particularly good heat resistance,
It has excellent properties such as weather resistance, chemical resistance, and resistance to environmental stress cracking, making it suitable as a powder coating material.

Excellent fluidity is essential for powder coating materials.

For powders with poor fluidity, for example, the fluidized dipping method is used to place the powder in a fluidized tank with a porous sheet at the bottom and try to form a fluidized bed using air sent from the bottom of the porous sheet. However, a good fluidized bed is not formed, and the thickness of the resulting coating film becomes uneven, and pinholes occur in the coating film. Also, in electrostatic coating methods, if the fluidity of the powder is poor, not only will it be difficult to transport the powder from the powder storage tank to the coating gun using air, but the charged powder particles will not be uniform. It does not adhere to the object to be coated, making it impossible to obtain a good coating film.

Therefore, in order to improve the fluidity of powdered polyethylene, research has been carried out from two aspects: improvement of the pulverization method and addition of additives.

Since polyethylene has a relatively low softening temperature and is easily plastically deformed, it is extremely difficult to efficiently produce powder with a uniform shape and particle size by pulverization at around room temperature.

In addition, the obtained powder polyethylene has many fibrous grains (so-called whiskers), and these whiskers are a factor in reducing fluidity.

For this reason, production of polyethylene powder with good fluidity has been attempted and actually carried out by methods such as dissolving it in a solvent and then treating it, or using methods such as so-called cryo-pulverization, in which the polyethylene is crushed while cooling with liquid nitrogen. There is.

Furthermore, as a method for improving fluidity by changing the composition of a powder polyethylene composition, a method of adding a fatty acid amide, which has conventionally been widely used as a lubricant for resins, is disclosed, for example, in JP-A-49-92171 and JP-A-Sho. 58-1762
It has been proposed and implemented in Publication No. 51, etc.

[Problems to be Solved] However, although the polyethylene powder obtained by dissolving it in a solvent and then treating it has a relatively rounded shape and good fluidity, It has various problems such as deterioration of physical properties, discoloration of pigments, deterioration of the working environment due to the use of dangerous solvents such as xylene, and increase in costs. Further, although the cryo-pulverization method is mechanical pulverization, it is possible to obtain powdered polyethylene having good fluidity, but the cost is extremely high and it is not generally employed at present.

On the other hand, powdered polyethylene containing fatty acid amide certainly has relatively good fluidity even if it is a powder that is ground at around room temperature. However, especially in the fluidized immersion method,
Since the objects to be coated heated to a temperature of 100°C are placed one after another into the fluidized tank, the atmospheric temperature inside the tank ranges from 35 to 55°C.
Such a high ambient temperature has the disadvantage that the effect of improving fluidity is significantly reduced.

Furthermore, fatty acid amide has no effect on pigment dispersion and causes color unevenness on the coated object.

[Means to solve the problem]

The present invention provides a powder polyethylene composition that eliminates the drawbacks of the conventional powder polyethylene described above.

That is, the present invention relates to a powder polyethylene composition comprising 100 parts by weight of powder polyethylene and 0.05 to 2 parts by weight of a fatty acid metal salt having 10 to 22 carbon atoms.

The powder polyethylene composition of the present invention has extremely good fluidity and also has good pigment dispersion.

Examples of polyethylene include ethylene homopolymers such as low-density polyethylene and low-density polyethylene, ethylene-propylene copolymers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, and linear low-density polyethylene. Copolymers can be used. Furthermore, polyethylene modified with fatty acids or their anhydrides can also be used.

Fatty acids that form fatty acid metal salts include unsaturated fatty acids such as palmitoleic acid, oleic acid, eicosenoic acid, erucic acid, elaidic acid, linoleic acid, lylinic acid, and ricinoleic acid, and capric acid, lauric acid, myristic acid, and palmitic acid. , stearic acid, alaxic acid, behenic acid, and other saturated fatty acids.

Examples of metals include zinc, calcium, and magnesium.

Examples of fatty acid metal salts include various combinations of the above fatty acids and metals. Particularly suitable are metal stearates such as zinc stearate, calcium stearate, and magnesium stearate.

The amount of fatty acid metal salt added is 0.01 to 2 parts by weight, particularly 0.05 to 1.0 parts by weight, per 100 parts by weight of powdered polyethylene.
Preferably it is 5 parts by weight.

If the amount of the fatty acid metal salt added is less than 0.01 part by weight, not only will the fluidity of the obtained powder polyethylene be hardly improved, but also color unevenness will occur in the coating.

If the amount of the fatty acid metal salt added exceeds 2 parts by weight, although an improvement in fluidity is observed, it is not preferable because the adhesive strength to the coated object decreases.

The pulverization is performed at room temperature using a known pulverizer.

A specific mesh sieve is used, and the larger particles on the sieve are fed again to the crusher.

In the present invention, these fatty acid metal salts may be kneaded in, for example, with an extruder before pulverizing polyethylene, or may be added during pulverization, or they may be mixed into powdered polyethylene using a mill or the like. It may be added depending on the machine. Regardless of the method of addition, an improvement in fluidity is observed compared to when no additive is used.

When a fatty acid metal salt is added before or during pulverization, not only the fluidity of the obtained powdered polyethylene is improved, but also the pulverization efficiency (yield of powdered polyethylene per unit time) is improved. In addition, no matter which grinding method is used, the coated object will have a beautiful finish with no color unevenness.

Hereinafter, the present invention will be explained in detail by way of examples.

In addition, the fluidity of the powdered polyethylene in the examples was evaluated by the following method.

A transparent cylinder made of acrylic resin with a diameter of 80 mm+ and a height of 200 mm is stood upright, and a filter cloth is placed on the bottom of the cylinder.

Next, powdered polyethylene is placed in the cylinder from the bottom to a depth of 10011IIT+, and air is blown through the filter cloth. The height L (unit: mm) of this time-average floating and flowing is measured, and (L/1σ0) is used as a measure of fluidity.

In powdered polyethylene having good fluidity, the entire powder floats and flows uniformly even with a small amount of air without causing bubbling or channeling. In this case, the amount of air supplied is small, so although the height of levitation is small,
The powder density of the fluidized bed is high, and a thick coating film can be obtained by immersion at -degrees.Furthermore, since the amount of air is small, the temperature drop of the coated object is small, and the adhesion is good, so there are no pinholes. It does not cause Powdered polyethylene has poor fluidity,
Uniform flow cannot be achieved unless a large amount of air is supplied. For this reason, the floating height becomes large and the powder density of the fluidized bed becomes small, so it is necessary to repeat dipping many times in order to obtain a thick coating film, and the amount of air is large. The temperature of the object to be coated decreases significantly, and poor adhesion or pinholes are likely to occur. As mentioned above, in this evaluation method, the smaller the value, the better the fluidity. Also, in this evaluation method, 0.
The difference in the numerical values of 5 appears as a clear difference in the fluidity of the actual powder polyethylene and the finish of the coated object.

Example Low density polyethylene (Ml: Log/min, density: 0.
919 g/d, manufactured by Ube Industries) using Turbo Mill T-40
0 (manufactured by Turbo Kogyo ■) using a 50 mesh sieve to obtain a powder with an average particle size of 80 mesh. Next, the following fatty acid metal salts were added to the above powder using a Henschel mixer (manufactured by Mitsui Miike Kakoki M) at 500 ppm and 80 ppm, respectively.
0 ppm and 1200 ppm were added. Table 1 shows the fluidity of the obtained powder polyethylene.

Table 1 1 1 1 1 L Zinc stearate 500 1.35800
1.28 1200 1.22 Calcium stearate 500 i, 38sium 800 1.351200
1.32 Stearic acid mag 500 1.40 Nesium 800 1.371200
1. 34 No additives 1.47 [Effect of the invention] The powder polyethylene composition of the present invention has an extremely low cost and simple composition in which a small amount of fatty acid metal salt is added to powder polyethylene that is ground or ground at room temperature. However, it has excellent fluidity comparable to that of powdered polyethylene obtained by a special pulverization method such as a method of dissolving it in a solvent and then processing it or freezing and pulverization. Furthermore, if a fatty acid metal salt is added to the polyethylene before pulverization or during pulverization, the pulverization efficiency can be improved.

Furthermore, the pigment-containing powder has the effect that the pigment is dispersed very well, and the object to be coated has a beautiful finish.

Claims (1)

[Claims] A powder polyethylene composition comprising 100 parts by weight of powder polyethylene and 0.005 to 2 parts by weight of a fatty acid metal salt having 10 to 22 carbon atoms.