DD287209A5 - METHOD FOR INCREASING THE ELECTRICAL CHARGING AND LIABILITY OF POWDER AND POWDER MIXTURES IN PASSING THROUGH FRICTION ELECTRIC POWDER LOADING AGENTS - Google Patents

Abstract

The invention relates to a method for increasing the electrical charge and adhesion of powder and powder mixtures to earthed articles, which is based on the object that groszkoernige plastic powder are sufficiently electrically charged when being sprayed with friction electric powder charging members, adhere well to grounded objects, a desired thin or thick single-layer or multi-layered plastic film layer can be achieved, and energy can be saved, and with thinner layers also material can be saved. According to the invention, this object is achieved in that the minimum specific electrical charge required for the adhesion of coarse-grained powders to the grounded objects is increased. Powder mixtures; Charging, electric, electrostatic, friction-electric; Liability; Plast powder; Minimum charge; Pulveraufladeorgane, coarse-grained, feinkoernig; Plast film layer; belongings}

Description

gee _mi

elevated.

2. The method according to claim 1, gekonnzeichnet characterized in that a coarse-grained powder having a mean particle size of> 150 μητι particle diameter, which is in the triboelectric voltage series near the material of the friction body of a triboelectric Aufladesprühorganes, a fine-grained powder having a mean particle size of <60μιη diameter of another material, which lies in the triboelectric voltage range far away from the material of said friction body, in a ratio of <50: 1 is added.

3. The method according to another claim, characterized in that the specific total triboelectric charge of a powder mixture can be calculated from the specific triboelectric charges of the individual sieve fractions according to the following equation:

^Q rub.

-K, (! L + ^G 2 max. -

4. The method according to claim 1 and 3, characterized in that a coarse-grained polyethylene powder having a mean particle size of> 150 \ in diameter, a fine-grained powder of the same material ¹ "iiit with a mean particle size of <60μηη diameter in the ratio <60:40 is added ,

5. The method according to claim 1,3 and 4, characterized in that a coarse-grained epoxy resin powder with a mean particle size of> 90μητι diameter, a fine-grained powder of the same material having an average particle size of <30μηη diameter in the ratio <60:40 is added.

Field of application of the invention

The invention relates to a method for increasing the electrical charge of powder and powder mixtures when passing through triboelectric powder charging members.

Characteristic of the known technical solutions

There are known powder applicators, the pulvur triboelectric (DD-WP 106308, DD-WP 134841) corresponding to the space occupied by the powder material in the triboelectric voltage series (DE-PS 2839578 and M art on, K .: Electricity series according to 2ilka, VII Conference "Electrostatic coating" 1978, HtV Dresden), or electrostatically plus triboelectrically (DD-WP 225921), using for example plastic powders with an average particle diameter of 60pm or less and developing powder mixtures to improve adhesion the melted layer on the support or an increase in the surface hardness result, but the original powder chemically and physically less apparent (Knirsch, G .: formulation of modified polyethylene powder, VIII. Conference "electrostatic coating" 1981, HfV Dresden , DD-WP129623, DD-WP 200 524, DE-OS 3418 406), or it should be the optical and Korro are improved protection (DD-WP 200525, DD-WP 200526, DD-WP 200527, DE-OS 2200747) with the mixing ratio of two polymers to 1: 1 to 96: 4, the mixture of two polymers with metal, an epoxy resin content between 10 and 86% and the grain size of the epoxy resin in the range 75 to 150pm of 95.5% and 49.59%. Furthermore, powders are applied, the solvent vapors have adsorbed to deposition (DD-WP 126873) or a mixture of polyolefins and hydrolyzed ethylene-vinyl acetate (DD-WP 129623) or epoxy resin with polybutyl methacrylate, epoxy resin with polyvinyl acetate, acrylic resin with polybutyl methacrylate and Polyester with polybutylmethacrylate (Funke, W. and Reichert, K.-H .:

Investigations on the production of multilayer paint films from powdered! Polymers on metallic substrates, 12th International Conference on Organic Coatings, Bratislava 1973).

A disadvantage of these Plastoulver and Plastpulvermischungen is their large average particle diameter, which expresses that the fines in the powder mixture is too small and thus the electrical charge of the powder mixture in the powder charging members and the adhesion to the grounded objects is too small. Other disadvantages are that solvent vapors are used, the original powder less appear and optimization of the electrical charge was not provided.

Object of the invention

The object of the invention is to obtain a method in which the plastic powders are sufficiently electrically charged by favorably selecting the mixing ratio of fine to coarse particles of one and the same powder or a fine powder of another material to a coarse powder of low electric charge. which is strongly charged electrically, is mixed.

Explanation of the essence of the invention

The invention is based on the object, coarse-grained plastic powder during spraying with triboelectric. Charge powder charging members sufficiently electrically, so that they adhere well to grounded objects, form a desired thin or thick single- or multi-layer plastic film layer and to save energy and thin films and material.

ErfindungsgemäP. the object is achieved in that the specific triboelectric charge required for the adhesion of the coarse-grained powder on the grounded objects is increased. This is achieved by coarsely mixing coarse-grained powder with low specific triboelectric charge, which are in the triboelectric voltage series close to the material of the friction body of a triboelectric powder charging, a fine powder of another material with high specific minimum friction charge, in the triboelectric voltage series far away from the material of the friction body. In the triboelectric deposition of mixed powder on the grounded object, a specific minimum charge is required, which is composed of the specific minimum charges of the individual powder components. If one component has a higher specific minimum charge than required for adhesion, the minimum specific charge of the other component may be lower, but the mixture still sticks

 The total specific triboelectric charge minimum charge of the powder mixture results after

Here, K _{1 is} Vd _m , the specific triboelectric minimum charge of the coarse powder and Ki · \ / M - ^ - the additional

dim

speciische triboelectric minimum charge by admixing the fine powder.

After Ki = V '~ n - Ki contains the influence constant e ₀ , the dielectric constant ε, the powder layer, the

^T Mc, VAu

_{Gravitational} acceleration g, the coefficient of static friction M _0n , powder metal, the density of the powder _{layer of} the coarse powder γ _Ρ , and a mean reference diameter dm, · M is the mass ratio mp,: m _Pl , where m _p , equal to the mass of the coarse and m _P , is equal to the mass of the fine powder.

If epoxy resin having an average particle diameter of 60 pm charges much more than its minimum specific electric charge, good adherence to the triboelectrical application is still exhibited at a mixing ratio of 40: 1, for example. B. for polyethylene with an average diameter of 220 μητι achieved with this epoxy resin. The limit is 50: 1, d. H. with a mixture of very little epoxy resin powder with fluidized interpolyethylene, it is possible to apply this triboelectrically by means of powder applicators on grounded objects.

Furthermore, the individual sieve classes of a powder are to be chosen so that an optimum mixing ratio arises when the specific maximum Gcsamtladung a plastic powder, which depends very much on the individual shares of the sieve classes, is set by targeted particle size distributions maximum and thus high triboelectric charging at Passage through Pulveraufladeorgane done.

The total mass m _o "of Pulvergerr isches is divided into the individual Siebklassenanteile mi, m ₂ to m" by Prüfsiebung. For the masses, the weight percentages G ,, G ₁ to G _n can also be used. The mean value of the mesh size of two test sieves is denoted by d "," d _m , to d _m . In this case, G _{t represents} the weight percent of the smallest particles with the mean diameter d _m . For the turbulence charging of a plastic powder, the specific maximum total charge results

^lraax ges ³ ^

G, / d _m , mainly determines the specific maximum total charge, since for many small diameter particles the charge increases greatly. Thereafter, the plastic powders for triboelectric powder spraying, z. B. Order on grounded objects with powder applicators, with a high fines content higher than those charged with a large coarse fraction. The constant K _{2 contains} the influential constant ε ₀ , the electric field strength at the surface of the powder particles in air E ₀ , did total mass in percent by weight (G ₀ ,, = 100%) and the material density Ym. It turns out to be

_v 6, .E ₀

'YmG ₈ ..'

exemplary Reference to an embodiment, the invention will be explained in more detail.

Polyethylenpülver with a mean particle diameter of 220μηι reaches a specific minimum electrical charge of 4 · 10 " ⁷ As / g.This is not sufficient for adhesion to grounded objects.If the polyethylene is an epoxy resin powder having a mean particle diameter of 60μπι added in the ratio 20: 1, the minimum specific electrical charge of the mixture rises to 9 · 10 ~ ⁷ As / g, which is sufficient for adhesion to ordered objects.

Claims (1)

A method for increasing the electrical charge and adhesion of powders and powder mixtures on grounded articles, characterized in that the admixture of a fine powder of the same or another material to a coarse powder, the specific triboelectric charge minimum charge of the powder mixture according to the equation ^Q elb - ^K 1 min f \ 2