AT394669B - METHOD AND DEVICE FOR POWDER COATING - Google Patents

Description

AT 394 669 B

Powder coating process

The invention relates to a method and a device for powder coating with a rotating cylinder having openings on the lateral surface.

Powder coating is used, for example, in the paper, film and textile industry as well as in the print shop for the production of papers, nonwovens, fabrics or films that have been refined or surface-modified and surface-treated with special powders. Thermoplastics such as, for. B. polyamides, polyvinyl chloride, polyethylene or highly water-absorbing substances, so-called superabsorbers, such as. B. polyacrylates or polyacrylamides, especially for the production of hygiene articles, used The powder can be applied directly from a storage container through a nozzle by gravity to the web to be coated. To achieve a somewhat more even powder application, a spreading unit consisting of a corrugated metering roller and a brush roller can also be used. The powder trickles from a storage container into the axially extending grooves of the metering roller, from which it is brushed out with the brush roller and spun onto the web to be coated (Vliesstoffe, G. Thieme Stuttgart, New York 1982, page 198). The disadvantage of the known powder coating process lies above all in the large amount of dust generated, especially when using the brush rollers necessary for brushing the powder out of the corrugated metering roller. In addition, relatively large and bulky coating units are required, which means that the installation in the coating system is complex and takes up a lot of space

US Pat. No. 4,162,752 describes a carpet cleaning device in which the cleaning powder is removed from the powder storage container by means of a rotating perforated roller which has an internal scraper. The powder enters the roller through openings in the side and is pressed against the scraper by the roller rotation, whereby it is pressed through the holes in the perforated roller due to the pressure build-up. The main disadvantage of this powder discharge process is that the powder is compressed due to the build-up of pressure, thereby tending to form lumps, and the loose and uniform powder discharge necessary for a perfect powder coating is not given with good pourability.

The object of the invention is to eliminate the disadvantages of the known powder coating processes, in particular a uniform powder application with good flowability without a great deal of dust being sought. The object can be achieved in that the powder is discharged from a rotating perforated cylinder with an internal powder limiting plate in such a way that it is not pressed against the powder limiting plate but is discharged from the other half of the cylinder lying in the direction of rotation after the powder limiting plate.

The invention accordingly relates to a method for powder coating, in particular for continuous powder coating of sheet-like materials, which is characterized in that a powder is placed in a rotating cylinder, provided on its outer surface with outlet openings, inside, axially along its outer surface, at an angle alpha from 150 ° to 240 ° measured in the direction of rotation from the vertical upper center line of the cylinder cross section according to Fig. 2, approximately downward-pointing powder limiting plate is arranged, is entered on that side of the cylinder which lies in the direction of rotation after the powder limiting plate, and that the powder afterwards, due to the rotation of the cylinder, the surface of the cylinder was partially carried upwards in the direction of rotation, partially mixed, discharged through the outlet openings and applied to the coating »! Object is applied.

The inventive method is particularly suitable for the continuous coating of sheet-like webs, such as. B. paper, textile, fabric or film webs, for example plastic film webs, but it is also suitable for coating, for example, glass, metal, plastic, wood or ceramic plates and composite laminates. In a preferred manner, the coating powder is applied between two continuously rolling paper, textile, fabric or film webs. The powder coating is carried out, for example, on a belt press, a calender or a rewinder and gives a uniform coating even at very high production speeds of up to 600 mAnin.

All powders customary in powder coating can be used. Examples are powders based on thermoplastics, such as. B. polyamides, polyvinyl chloride, polyvinyl alcohol, polyethylene, polypropylene, or superabsorbents based on crosslinked polyacrylates, polyacrylamides, carboxymethyl celluloses, starch derivatives and copolymers of maleic anhydride, and mixtures of these powders. The use of microfibers or fibrous powders is also possible.

The powder limit plate divides the lower part of the cylinder into two parts from the cylinder axis to the cylinder jacket. The position of the powder limit plate is indicated by the angle alpha. Alpha is the angle between the powder limit plate and the vertical top center line of the cylinder in cross section, as indicated in Fig. 2. By changing the angle alpha, it is possible to vary both the ejection point for the powder and the width of the powder jet, as well as the degree of mixing of the powder which is partially entrained on its inner lateral surface during the rotation of the cylinder and falls back again. With an alpha of approximately 150 to 190 °, the ejection point is approximately in the lower part of the cylinder, with a wide powder jet and intensive mixing. With an alpha of approximately 190 to 240 °, the -2-

AT 394 669 B

Ejection point correspondingly higher, the powder jet is narrower, the mixing of the powder is less. Thorough mixing of the powder is particularly advantageous when powder mixtures or non-uniform powders are present, for example with different grain sizes, when the powder tends to form agglomerates or lumps and when special requirements are placed on the homogeneity and flowability of the powder 5.

The position of the powder delimitation plate, the peripheral speed and the degree of filling of the cylinder must be coordinated with one another in order to achieve an optimal procedure for powder coating. A high degree of filling of the cylinder results in a wider powder jet than a low degree of filling. A higher peripheral speed causes an increased powder discharge quantity and a wider powder jet 10 as well as better mixing of the powder. The peripheral speed is usually over 0.15 m / min, preferably 0.3 to 50 m / min. The peripheral speed must not be so high that the powder is carried into the other half of the cylinder divided by the powder limiting plate. The upper limit of the peripheral speed depends primarily on the powder used and is approximately in the range of 100 m / min. 15 Another object of the invention is a device for powder coating, in particular for continuous powder coating of sheet-like materials, which consists of a rotatably mounted cylinder (1) which has an insertion device (2) on one or both end faces and outlet openings (3) on its lateral surface. for a powder In the interior of the cylinder, axially along its circumferential surface, there is a powder limiting plate (4) pointing downward at an angle alpha of 150 to 240 °, measured from the vertical upper center line of the 20 cylinder cross section as shown in Fig. 2. The entry device (2) has outlets (6) which are arranged such that the entry of the powder is distributed as evenly as possible over the length of the cylinder, only in those of the two halves of the cylinder (1) separated by the powder limiting plate (4) , which is in the range of a larger angle than that which corresponds to the position of the powder limiting plate 25 protrudes from the face of the cylinder (1) along the cylinder axis into the cylinder (1). The outlets (6) are only open to that half of the cylinder which is separated by the powder limiting plate (4) and which is in the region of a larger angle than that which corresponds to the position of the powder limiting plate.They consist, for example, of a single slot over the entire length of the Delivery tube or from several openings, which are distributed over the length of the delivery tube, whereby an even powder distribution in the cylinder is achieved. The outlets are covered with a grid if necessary. The position of the outlets can be changed by rotating the tube accordingly. The powder can either enter the delivery tube from one end of the cylinder or from both sides, for example via a filling funnel. The powder can be conveyed in the conveying pipe, for example by means of a screw conveyor, by a vibrating device, by means of air, as a fluidized powder, if necessary with a slight inclination of the conveying pipe.

The cylinder is made of any material, such as metal or plastic, and has openings on its outer surface. The shape and size of the openings depends primarily on the grain size and the flow properties of the powder and is usually from 1 to 5 mm in diameter. In the case of fibrous powders, the openings are preferably designed as slots. Fine and well-flowing powders require smaller openings than coarser powders. Especially at higher peripheral speeds of the cylinder, it proves to be advantageous to form the openings in the shape of a truncated cone, that is to say with an increasing diameter towards the outside. The more and the smaller openings are made on the cylinder jacket, the more uniform the powder discharge. The outer surface of the cylinder is preferably designed as a grid through which the powder emerges. For special protection of the grille, it can be reinforced with a support structure, for example metal or plastic ribs, additional support grids or an additional perforated cylinder.

The powder limiting plate (4) should lie as close as possible to the inner cylinder wall to prevent the powder from flowing into the other half of the cylinder. It consists, for example, of a metal 50 or plastic plate which is fastened, for example, to the insertion device (2) or to special fastening disks (7). For better sealing against the cylinder wall, the powder limiting plate advantageously has a sealing lip made of flexible materials, for example made of rubber or flexible plastic. If a cylinder made of plastic is used, it may prove advantageous to discharge any electrical charges that may occur by covering the sealing lip with a metal layer or metal foil, 55 for example an aluminum foil, or using a sealing lip made of electrically conductive material, for example made of electrically conductive or through additives such as B. metal powder, graphite or soot particles made of conductive plastics or of metals such. B. sheet metal strips or metal foils. The position of the powder limiting plate can be changed, for example, by turning the fastening disks (7) or the entry device (2) and thus the angle alpha can be varied as required.

Fig. 1 shows a possible embodiment of the device according to the invention, Fig. 2 shows the associated cross section (section (A · B)), the arrow indicating the direction of rotation of the cylinder. (1) means the -3-

AT 394 669 B cylinder according to the invention with outlet openings (3) on its outer surface, (2) an entry device, which is shown in the drawing as a feed pipe with a filling opening (5) and an internal screw conveyor. Outlets (6) for the powder are attached to the delivery pipe. The powder limit plate (4) is attached to a mounting disc (7). The angle alpha indicates the position of the powder limiting plate (4), measured in the direction of rotation from the upper vertical center line in FIG. 2, the angle beta the height of the powder level (degree of filling) on the inner wall of the cylinder.

For the continuous powder coating of sheet-like materials, the device according to the invention can be installed, for example, in a belt press, a calender or rewinder. Due to the compact design and the small space requirement, installation in existing presses, rewinder or calenders is very easy.

Example 1:

For the powder coating, a plastic cylinder with a length of 320 mm and a diameter of 110 mm, rotating at 15 revolutions per minute (corresponding to a peripheral speed of 5.18 m / min), was used, the lower half of which was through an angle alpha of 180 ° downward powder limiting plate (4), as shown in Fig. 2, is divided. The holes on the surface of the cylinder are frustoconical, the hole diameter on the inside wall of the cylinder being 2 mm and increasing outwards at an angle of 90 °. The holes are staggered on the lateral surface of the cylinder over a length of 225 mm (corresponding to the discharge length or spreading width) with a hole density of 124 holes per dm.

The inside of the cylinder was charged uniformly with 160 g / min of a carboxymethyl cellulose powder (powder (PI)). The type of powder used is given in Table 1, a class analysis in Table 2. The cylinder is fed with the powder, as shown in FIGS. 1 and 2, via a conveyor tube (2) with a screw conveyor, which is provided with a slot-shaped outlet (6) for the powder that extends over the entire spreading width the powder was conveyed into the half of the rotating cylinder provided for the discharge and divided by the powder limiting plate (4). The height of the powder level on the inner wall of the cylinder, measured as the angle beta in the direction of rotation from the vertical upper center line in FIG. 2, was 270 °. In the area of the feed pipe (2), the height of the powder level is limited by the upper edge of the slot-shaped outlet (6). As a result of the cylinder rotation in the direction of rotation shown in FIG located paper web with a width of 220 mm (coating width) coated with the powder

In the same way, further coatings were carried out at higher speeds of the cylinder, as well as with higher amounts of powder scattering, as indicated in Table 3, whereby a uniform coating without significant dust generation was also achieved.

Examples 2 to 17:

Coatings were carried out analogously to Example 1, but with the type of powder, the position of the powder delimitation plate (angle alpha), the coating width, the inner hole diameter, the number of holes per dm ^, the amount of powder spreading, the powder height on the cylinder wall (angle beta ) and the speed or peripheral speed of the cylinder have been changed in accordance with the information in Table 3.

In Examples 7 to 11 and 13 to 17, a 1400 mm long cylinder, in Example 12 a 500 mm long cylinder, each with a diameter of 110 mm, was used. The powder was in each case discharged uniformly and without any appreciable generation of dust and applied in the coating width given in Table 3 to webs located under the cylinder.

In order to demonstrate the uniformity of the powder discharge or powder application, in Examples 16 and 17 the powder discharged from the cylinder during 1 min was collected in 13 cups, each 104 mm wide, placed under the cylinder and the amount of powder in the individual cups weighed out, the two edge cups were not taken into account. The uniformity of the powder distribution over the discharge width was calculated as the relative standard deviation (RSD) in% of the mean value. The values given in Table 3 are further averaged from 11 tests (11 times 1 min powder discharge) for Example 16 and 5 tests for Example 17.

Comparative example V18:

A powder coating or powder discharge was carried out analogously to Example 17, but the direction of rotation of the cylinder was reversed so that the powder was pressed against the powder limiting plate. The powder discharge was uneven. This can also be seen from the relative standard deviation of 7.2% (average from 5 tests) given in Table 3 compared to 1.8% for the coating according to the invention according to Example 17. -4-

AT 394 669 B

Table 1

Powder used

Powder Powder type Type Manufacturer Pl Carboxymethylcellulose Cekol-HDEP Billerud / Sweden P-2 Carboxymethylcellulose Cekol-HCEP Billerud / Sweden P-3 Carboxymethylcellulose Niklacell HV / 5 Brigl & Bergmeister / Östeneich P-4 Polyvinylalkohol Mowiol 4-88 G Hoechst / BRD P-5 Polypropylene Type-B PCD / Austria P-6 Cationic starch Cationamyl 9852 Agena / Östeireich

Table 2

Class analysis of the powders used (in% by weight 1 (method: Alpine air sieve)

Grain class PI P2 P3 P4 P5 P6 less than 0.032 mm 45.3 30.0 15.9 55.9 less than 0.044 mm 56.6 42.4 25.8 87.9 less than 0.063 mm 65.6 51.8 32.5 98 .7 less than 0.075 mm 71.3 57.1 36.4 99.6 less than 0.090 mm 77.8 64.4 40.6 100.0 less than 0.125 mm 87.7 78.5 49.0 less than 0.16 mm 90 .8 57.1 less than 0.20 mm 96.6 100.0 63.3 0 4.6 less than 0.25 mm 98.9 77.2 16.6 less than 0.354 mm 96.9 66.5 less than 0.50 mm 99.8 12.6 80.2 less than 0.71 mm 100.0 less than 0.85 mm 19.8 99.5 less than 1.40 mm 54.9 -5

AT 394 669 B

Table 3

In- Pul powder coating hole hole rotation Um- litter Pul rel. 5 sp. limited by the number of catches, the standard width of the knife per dm2 (rpm) height (g / min) height of the plate (mm) (mm) black. (beta) chung (alpha) (m / min) (%) 10 1 PI 180 ° 220 2.0 124 15 5.18 160 270 ° 24 8.29 190 33 11.40 218 42 14.51 262 2 PI 180 ° 220 2.5 58 40 13.82 200 270 ° 15 50 17.28 450 60 20.73 580 65 22.46 617 3 P4 180 ° 220 4.0 29 15 5.18 300 270 ° 24 8.29 365 20 33 11.40 415 42 14.51 462 4 P5 180 ° 220 2.0 124 15 5.18 600 24 8.29 910 5 P6 180 ° 220 2.0 124 15 5.18 190 270 ° 25 24 8. 29 320 6 P3 180 ° 225 2.5 117 7 2.41 109 270 ° 14 4.82 213 21 7.26 333 28 9.68 384 30 7 P6 210 ° 1300 2.0 122 13 4.49 565 270 ° 25 8.64 695 40 13.82 825 55 19.01 970 8 P5 210 ° 1300 2.0 122 13 4.49 1425 270 ° 35 25 8.64 1777 40 13.82 2100 55 19.01 2450 9 P2 180 ° 1300 2.0 122 13 4.49 1290 270 ° 25 8.64 1672 40 40 13.82 2280 55 19.01 3374 10 P2 150 ° 1300 2.0 1 22 13 4.49 3240 270 ° 25 8.64 3480 40 13.82 3740 45 11 P2 210 ° 1300 2.0 122 13 4.49 1060 270 ° 25 8.64 1234 40 13.82 1532 55 19.01 1957 12 P3 240 ° 416 2.5 122 41 14.17 206 300 ° 50 13 P3 215 ° 1144 2.5 122 1 0.34 636 270 ° 14 P3 215 ° 1144 2.5 122 130 44.92 5947 270 ° 15 P3 215 ° 1144 2.5 122 250 86.39 10124 270 ° 16 P2 210 * 1144 2.0 122 13 4.49 810 270 ° 3.1 17 P2 200 ° 1144 2.5 122 20 6.91 1098 270 ° 1.8 55 V18 P2 200 ° 1144 2.5 122 20 6.91 1681 270 ° 7.2 -6-

Claims (6)

AT 394 669 B PATENT CLAIMS 1. Process for powder coating, in particular for continuous powder coating of sheet-like materials, characterized in that a powder in a rotating cylinder provided with outlet openings on its outer surface, inside it, axially along its outer surface, at an angle alpha from 150 ° to 240 ° measured in the direction of rotation from the vertical upper center line of the cylinder cross-section according to Fig. 2, approximately downward-pointing powder limiting plate is arranged, is entered on that side of the cylinder which is in the direction of rotation after the powder limiting plate, and that the powder subsequently due to the rotation of the cylinder on its lateral surface in the direction of rotation partially carried upward, partially mixed, discharged through the outlet openings and applied to the object to be coated. 2. The method according to claim 1, characterized in that the cylinder rotates at a peripheral speed of 0.3 to 50 m / min. 3. The method according to claim 1 or 2, characterized in that the powder is applied between two continuously rolling paper, textile, fabric or film webs. 4. Apparatus for powder coating, in particular for continuous powder coating of sheet-like materials, characterized in that it consists of a rotatably mounted cylinder (1) which has an entry device (2) on one or both end faces and outlet openings (3) for a on its lateral surface Has powder, and that in the interior of the cylinder, axially along its circumferential surface at an angle alpha of 150 ° to 240 °, measured from the vertical upper center line of the cylinder cross-section according to Fig. 2, there is an approximately downward-pointing powder pouring plate (4), The feed device (2) has such outlets (6) that the feed of the powder is distributed as evenly as possible over the length of the cylinder, only in that of the two half of the cylinder (1) separated by the powder limiting plate (4), which Range of a larger angle than that of the position of the powder limit gsplatte corresponding. 5. The device according to claim 4, characterized in that the entry device (2) is designed as a delivery pipe with a filling opening (5) and one or more outlets (6) for the powder and from the end face of the cylinder (1) along the cylinder axis in the cylinder (1) protrudes, the outlets (6) being open only to that half of the cylinder which is separated by the powder limiting plate (4) and which is in the region of a larger angle than that corresponding to the position of the powder limiting plate. 6. Apparatus according to claim 4 or 5, characterized in that the outer surface of the cylinder (1) consists of a grid, which is optionally reinforced by a support structure. Add 1 sheet of drawing -7-