JP2009183810A - Coating method using electrostatic action - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method which can prevent the adhesion of coating particles to a masking material and the circumference, and further, can paint in safety in the coating method of allowing the charged coating particles to adhere after the masking material is arranged at the part of a coating object not requiring coating. <P>SOLUTION: After a resin masking base material is arranged at the part of the coating object not requiring coating, the coating object is connected to ground, and the masking base material is positively charged by a corona charging machine to turn to electret. Next, the coating object provided with the masking material of electret is connected to ground, and the coating particles positively charged is sprayed from a Tribo-charging type powder coating gun. According to the method, since the coating particles do not adhere to the masking material and the circumference by the electrostatic repulsion of the coating particles and the masking material of electret, no burr occurs in detaching the masking material, and since a high voltage is not applied to the masking material in coating, even if a discharge phenomenon occurs, it does not occur continuously, and the safe coating is possible. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a masking step in which a masking material is disposed in advance on a part where coating is not required, and a coating object in which positively or negatively charged paint particles are grounded or charged in the opposite polarity to the paint particles. The present invention relates to a coating method using an electrostatic action including a coating process for coating an object to be coated by adhering to an object.

  As a coating method using an electrostatic action, an electrostatic powder coating method using a powder paint, an electrostatic fluid immersion method, and an electrostatic coating method using a liquid paint are generally used.

  In the electrostatic powder coating method, the resin powder coating is charged by applying a high voltage of several tens to hundred kV to the electrode provided at the tip of the powder coating gun to ionize the surrounding air, Corona electrification in which the powder coating is passed by compressed air or the like, or a tribo (friction) that causes the powder coating to collide with and contact the inner wall of the powder coating gun composed of materials with different charging order inside the powder coating gun. ) Perform by electrification. In corona charging, paint particles are positively or negatively charged depending on the polarity of the voltage applied to the electrode of the powder coating gun. In tribocharging, the polarity of paint particles is determined by the charging sequence, and the paint particles are positively charged when the inner wall of a powder coating gun made of polytetrafluoroethylene is used. When the object to be coated is grounded or charged to a polarity opposite to that of the paint particles and sprayed with the paint particles charged from the powder coating gun, the paint particles adhere to the surface of the object by electrostatic action.

  In the electrostatic fluidized immersion method, paint particles are charged by feeding ionized air into a fluidized tank filled with a resin powder coating or by corona discharge using an electrode installed at the bottom of the fluidized tank. The object to be coated, which is grounded or charged with the opposite polarity to the paint particles, is immersed in the fluid tank and pulled up from the fluid tank after a predetermined time, so that the paint particles adhere to the surface of the object by electrostatic action. Let

  Liquid paint is used in the electrostatic coating method. A high voltage of several tens to hundreds of kV is applied to the electrode provided at the tip of the coating gun to ionize the surrounding air, and the paint particles atomized by compressed air or the like are allowed to pass therethrough. Charge positively or negatively. When the paint particles charged from the paint gun are sprayed onto the object to be grounded or charged to the opposite polarity to the paint particles, the paint particles adhere to the surface of the object to be coated by electrostatic action.

  When the coating is dried or baked by heating the article to be coated to an appropriate temperature following painting, a coated product is obtained.

  By the way, when only a part of the object to be coated is to be painted, the surface of the object to be painted is applied after preventing the paint particles from adhering to the unpainted part (referred to as “painting unnecessary part”). There is a need. FIG. 9 is a diagram showing a process of coating a part of the object to be coated by the electrostatic powder coating method. First, as shown in (a), a masking material 32 formed of polyurethane or the like is temporarily fixed to a coating-unnecessary portion 31b of the object 31 to be coated. Next, as shown in (b), when the powder coating particles charged from the powder coating gun 41 are sprayed onto the object to be coated 31, a portion to be painted on the surface of the object to be coated 31 ("painting required part"). The paint particles adhere to both 31a and the masking material 32, and the coating film 33 is formed. Paint particles accumulate at the boundary portion between the masking material 32 and the required coating portion 31a, and when the coating film 33 is baked, a so-called bridge 33a is formed at the boundary portion between the masking material 32 and the required coating portion 31a. Next, as shown in (c), when the masking material 32 is removed, there is a problem that the bridge 33a of the coating film 33 is turned up and burrs are formed. Although it is possible to remove the masking material 32 before baking the coating film 33, in this case, the problem is that the shape of the coating film 33 in the boundary region between the masking material 32 and the object 31 is disturbed during the removal. was there.

  In addition, when the coating film 33 on the surface of the masking material 32 is peeled for reuse of the masking material 32, there is also a problem that the peeling work of the coating film 33 is very troublesome.

  In order to solve this problem, Patent Document 1 (Japanese Patent Application Laid-Open No. 2001-212479) discloses that a masking material that is charged to the same charge as the paint particles is disposed in a coating unnecessary portion of an object to be coated, and the masking material is charged Discloses a method of performing electrostatic coating while applying the coating. FIG. 10 is a diagram showing masking in the coating method disclosed in this document. In the method disclosed in this document, a masking material 54 made of polytetrafluoroethylene is disposed on the painting-unnecessary portion 51 b of the workpiece 51. A hole 55 is provided on the masking material 54 on the side facing the coating-unnecessary portion 51 b, and a copper plate 56 is provided on the inner top surface of the hole 55. A lead wire 57 for applying a high voltage is attached to the copper plate 56. When a negative voltage is applied to the copper plate 56 via a lead wire 57 from a high voltage generator (not shown), the outer surface of the masking material 54 is negatively charged and the inner surface is positively charged. When negatively charged paint particles 52 are sprayed from the coating gun 61 to the grounded workpiece 51 with a negative high voltage applied to the copper plate 56, the negatively charged paint particles 52 and the negative charge are discharged. Due to the electrostatic repulsion generated between the masking material 54 and the outer surface of the masking material 54, the paint particles 52 are not directed to the masking material 54, but adhere to the painting required portion 51 a of the article 51 to be coated. As a result, the paint particles 52 hardly adhere to the outer surface of the masking material 54, and the area of the surface of the object 51 to be coated does not adhere to the area near the masking material 54 so that the paint particles 52 hardly adhere. Part is formed.

JP 2001-212479 A

  According to the coating method disclosed in Patent Document 1, the amount of coating particles adhering to the masking material can be greatly reduced, and the coating particles are also present in the vicinity of the masking material on the surface of the object to be coated. Since it hardly adheres, when removing the masking material after baking the coating film, the coating film will not turn up and burrs will not be generated, and even if the masking material is removed before baking the coating film, The shape of the coating film is not disturbed.

  However, since the process of applying a high voltage to the copper plate for charging the masking material is performed at the same time as painting, if a discharge phenomenon occurs in the vicinity of the masking material during painting, the discharge phenomenon will continue to occur. The paint particles adhering to the surface of the object to be coated and the paint particles approaching the surface are disturbed due to the discharge, causing troubles such as the shape of the coating film around the masking material is disturbed and the surface is rough. Also, the painting operation becomes extremely dangerous due to the discharge. In addition, if you want to paint multiple objects at the same time, or if there are multiple parts that do not need to be painted on a single object, the manufacture of complicated and cumbersome masking materials and charging of each masking material Wiring processing to the copper plate for making it necessary is necessary.

  Accordingly, an object of the present invention is to charge a masking material in a coating method in which a masking material is disposed on an unnecessary part of an object to be coated, and then charged paint particles are attached to the object by electrostatic action. This is a safe coating method that can avoid the adhesion of paint particles to the masking material and its surroundings without performing coating at the same time as painting. An object of the present invention is to provide a painting method that eliminates the need for complicated and troublesome masking material manufacturing and wiring processing even when an object has a plurality of portions that do not require painting.

  The above-mentioned problems include a masking process in which a masking material is disposed in advance on a part that does not require painting, and a paint particle that is positively or negatively charged or is grounded or charged with a polarity opposite to that of the paint particle. A coating method using an electrostatic action including a coating process for coating an object to be coated by adhering to an object, wherein the masking process has a charged surface charged with the same polarity as the paint particles as a masking material Using electrets and avoiding adhesion of paint particles to the masking material in the vicinity of the masking material on the surface of the object to be coated, using electrostatic repulsion between the masking material and the paint particles in the painting process. It is achieved by a coating method using an electrostatic action characterized by

  In the present invention, the term “avoids the adhesion of paint particles” means that there is no adhesion of the coating particles to the masking material and its surroundings. It means that a continuous coating film (bridge) is not formed between the masking material surface and the surface of the object to be coated because it hardly occurs. In addition, the electret constituting the masking material has a charging surface charged to the same polarity as the paint particles, and has a single-polar charging type having only a charging surface charged to either positive or negative charge. The electret may be a bipolar electret having both a positively charged surface (for example, a front surface) and a negatively charged surface (for example, a back surface). However, in the case of the latter, it arrange | positions so that the charged surface charged by the same polarity as the coating particle may face the side which the coating particle approaches.

  In the present invention, in the masking step, the masking material obtained by previously electretizing the masking base material (the starting member before the electretization process is referred to as “masking base material”) is disposed in the painting-free portion of the object to be coated. Alternatively, the electret process may be performed after the masking base material is disposed in the portion where the coating is not required. In addition, the masking material composed of electrets may be disposed on the entire portion of the object to be painted that does not require painting, and if the masking material is disposed on a portion of the portion that does not require painting, the coating particles are coated on the entire portion that does not require painting. If it can be prevented from adhering, it may be arranged only in that portion.

  The decay rate of charges accumulated in the masking material composed of electrets is remarkably slow, and a sufficient amount of charges are accumulated in the masking materials even after the day after the electretization process. Therefore, in the present invention, electrostatic repulsion occurs between the positively or negatively charged paint particles and the charged surface charged with the same polarity as the particles without applying a high voltage to the masking material simultaneously with the coating. It is possible to avoid adhesion of paint particles to the masking material and its surroundings.

  In a preferred embodiment of the present invention, the object to be coated is a set of objects to be coated composed of two or more components, and the masking material is arranged at an overlapping portion of each component and the object to be painted is assembled. The above coating process is performed. In this preferable form, the penetration of the paint particles into a slight gap in the overlapping portion of each constituent member is preferably avoided.

  In a preferred embodiment of the present invention, an insulating masking base material composed of a hydrophobic polymer, particularly a fluororesin, and containing a small amount of conductive agent and plasticizer is electretized. This form is preferable because the decay rate of the charge accumulated in the masking material is particularly slow.

  In a preferred embodiment of the present invention, the coating step is performed by an electrostatic powder coating method. According to the electrostatic powder coating method, the adhesion of the paint particles to the masking material of the electret and its surroundings is particularly preferably avoided. Moreover, it is preferable because a high-quality coating film can be obtained and the thickness of the coating film can be adjusted over a wide range. In addition, since no solvent is used, VOC (Volatile Organic Compounds) is not released into the atmosphere. In addition, the powder paint that has not adhered to the object to be coated can be recovered and reused.

  According to the coating method of the present invention, since the decay rate of the charge accumulated in the masking material composed of electrets is remarkably slow, it is charged positively or negatively without applying a high voltage to the masking material simultaneously with painting. Electrostatic repulsion occurs between the coating particles and the charged surface charged with the same polarity as the coating particles in the masking material, and adhesion of the coating particles to the masking material and its surroundings can be avoided. Therefore, when removing the masking material after baking the coating film, the coating film will not turn up and burrs will not occur, and even if the masking material is removed before baking the coating film, the coating film around the masking material Is not disturbed.

  Also, in the painting process, no high voltage is applied to the masking material at the same time as painting, so no discharge phenomenon occurs in the vicinity of the masking material during painting. Troubles such as turbulence do not occur, and the painting work can be performed very safely.

  Furthermore, since the decay rate of the charge accumulated in the mask material of the electret is remarkably slow, it is possible to carry out the coating process after a certain time after performing the masking process. Therefore, the coating process of a plurality of objects to be coated can be performed collectively from the next day, and at this time, a complicated wiring process for applying a voltage to the masking material is unnecessary. Even when there are multiple places where painting is not required on a single object, it is only necessary to place a masking material with the desired shape in the places where painting is not needed, making complex and cumbersome masking materials There is no need to perform wiring processing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1st Embodiment FIG. 1: has shown the to-be-coated object used in one Embodiment of this invention, and the masking base material before an electret process. Reference numeral 1 denotes an object to be coated, and 2A denotes a masking base material. The object to be coated 1 is a steel plate-like body, and the masking base material 2A is a sheet made of polytetrafluoroethylene, and has a shape that can substantially cover the entire portion of the object 1 to be painted that is not required for painting. ing. Prior to the electret processing of the masking base material 2A, the masking base material 2A is temporarily fixed to the painting unnecessary portion 1b of the article 1 with a fixing tool (not shown). Of the surface of the object 1 to be coated, the area excluding the unnecessary part 1b is the necessary part 1a.

  Subsequently, the masking base material 2A is electretized. FIG. 2 is a diagram schematically showing the electretization process. The workpiece 1 is grounded, and a positive high voltage is applied to the corona charger 11 connected to the high voltage generator 10. Corona discharge occurs in the vicinity of the pin electrode 11a of the corona charger 11, and ions having a positive charge are generated in the air, and these ions are directed toward the object 1 to be coated. The positive charge attached to the grounded workpiece 1 will immediately escape, but the positive charge attached to the masking base material 2A is accumulated and the masking base material 2A is electretized. As a result, an electret masking material 2 having a positively charged surface is obtained. The charged masking material 2 is attracted to the grounded object 1 by electrostatic force.

  The surface potential of the masking material 2 after the electret process changes depending on the voltage value applied to the corona charger 10, the distance between the corona charger 10 and the masking base material 2 </ b> A, the thickness of the masking base material 2 </ b> A, and the like. . The surface potential of the masking material 2 after the electret treatment is sufficient if it is a value that causes electrostatic repulsion with the charged paint particles, and can be easily set by a preliminary experiment. If the surface potential of the masking material 2 is about 500 V or more, preferably about 1000 V or more, electrostatic repulsion between the charged paint particles and the masking material 2 occurs even in the coating on the next day or later.

  Next, in the present embodiment, the coating process is performed by an electrostatic powder coating method. FIG. 3 is a diagram schematically showing the painting process. In the present embodiment, a tribochargeable powder coating gun 22 is used. When the epoxy powder coating material filled in the powder coating tank 20 is conveyed to the powder coating gun 22 via the tube 21, the coating particles are positively charged and discharged from the powder coating gun 22. When the object 1 with the electret masking material 2 is grounded and positively charged paint particles are sprayed from the powder coating gun 22, the paint particles are applied to the object 1 by electrostatic action from the object 1. Attracted in the direction.

  FIG. 4 is a cross-sectional view showing a state in the vicinity of the end portion of the masking material 2 during the painting process. The paint particles 3 discharged from the powder coating gun 22 have a positive charge, and are attracted by the electrostatic action in the direction of the object 1 to be grounded. When the coating particle 3 approaches the object 1 to be coated, the coating particle 3 is subjected to electrostatic repulsion between the positively charged surface of the masking material 2 disposed on the coating unnecessary portion 1 b of the object 1 and the coating particle 3. 3 is attracted and adhered onto the painting required portion 1a of the article 1 to be coated, and the coating film 4 is formed. On the other hand, the coating particle 3 hardly adheres to the outer surface of the masking material 2, and the uncoated portion having a width d where the coating particle 3 hardly adheres to the area near the masking material 2 on the surface of the object 1 to be coated. Is formed.

  When the coating film 4 having a desired thickness is obtained, the coating is stopped, the coating object 1 is heated with a heating device to cure the epoxy paint, and the coating film 4 is baked onto the coating object 1. Since the coating material particles 3 are hardly adhered to the masking material 2 and its surroundings, the coating film 4 is not turned up when the masking material 2 is removed, and burrs are not generated.

Second Embodiment The present invention is suitable for coating after assembling and integrating a set of objects to be coated composed of two or more components. In the present embodiment, the outer surface of a set of objects to be coated including a housing and a lid is painted. FIG. 5 shows a steel object 1 made up of a housing 1A having an opening and a lid 1B that can be opened and closed, and cyclic polytetrafluoroethylene used in the present embodiment. A masking base material 2A is shown.

  When the outer surface is painted after the housing 1A and the lid 1B are integrated using screws without using the masking base material 2A, the overlapping peripheral edge of the housing 1A and the peripheral edge of the lid 1B Paint particles intrude through a slight gap. For this reason, paint particles adhere to the inner surfaces of the casing 1A and the lid 1B and the overlapping peripheral edge, and it is difficult to separate the casing 1A and the lid 1B after baking the coating film. Burr occurs.

  In the present embodiment, an electret masking material is used to avoid the above-described problems. The masking base material 2A is arranged so that the opening of the housing 1A and the opening of the masking base material 2A overlap each other, and the housing 1A is grounded in the same manner as shown in FIG. A positive charge is accumulated in 2A. The masking material 2 in which positive charges are accumulated is attracted to the grounded casing 1A by electrostatic force. Next, the lid 1B is disposed on the electret masking material 2, and the housing 1A, the masking material 2 and the lid 1B are assembled together with screws. Thereafter, electrostatic powder coating using a polyester powder coating is performed by the same method as shown in FIG.

  FIG. 6 is a cross-sectional view showing a state in the vicinity of the end of the masking material 2 after painting. Due to electrostatic repulsion between the positively charged surface of the masking material 2 and the positively charged coating particles, the coating particles adhere to the outer surfaces of the housing 1A and the lid 1B, and the coating film 4 is formed. . The masking material 2 prevents the paint particles from adhering to the inner surfaces of the housing 1A and the lid 1B, and the paint particles hardly adhere to the outer surface of the masking material 2 and the vicinity thereof.

  Next, the object to be coated 1 is heated in a heating furnace to cure the polyester-based paint, and the coating film 4 is baked on the housing 1A and the lid 1B. It is easy to separate the housing 1A and the lid 1B, and no burrs are generated.

  As mentioned above, although two embodiment of the coating method of this invention was described, this invention is not limited to these embodiment, The change in the range which does not deviate from the meaning of this invention is possible.

  In the present invention, a masking base material of a molded body, a woven fabric, or a nonwoven fabric made of any plastic or rubber can be used. When an insulating masking matrix composed of a hydrophobic polymer and containing a small amount of conductive agent such as carbon and plasticizer such as phthalate is electretized, the decay rate of charges accumulated in the masking material is significantly reduced. It is preferable because it is slow. Examples include olefinic resins such as polyethylene, polypropylene and ethylene-propylene copolymers, tetrafluoroethylene-perfluoroalkoxyethylene copolymers, polytetrafluoroethylene and tetrafluoroethylene-hexafluoropropylene copolymers. Fluorinated resins such as, chlorinated resins such as polyvinyl chloride, polyvinylidene chloride and chlorinated polyolefin, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamide, polyimide, polycarbonate, polyacetal, polyacrylate, polystyrene, polyphenylene sulfide , Chloroprene rubber, isoprene rubber, butyl rubber, styrene-isoprene rubber, styrene-butadiene rubber, and silicone rubber Hydrophobic polymer, particularly preferably can be preferably used a fluorine-based resin, in the content of the configured conductive agent and plasticizer is less insulating masking matrix.

  The electret used as a masking material in the present invention is not limited to a single-pole electret electret having a positively charged surface, and if it has a charged surface charged to the same polarity as the paint particles, It may be a single-pole electret electret or a bipolar electret electret. In the case of the latter, it arrange | positions so that the charged surface charged with the same polarity as the coating-material particle | grains may face the side which a coating-material particle approaches.

  The electretization treatment of the masking base material in the present invention is not limited to the method by corona charging, and various known electretization methods can be used. For example, by applying a high voltage with a sheet-like masking base material sandwiched between two flat plate electrodes, a bipolar electret electret can be obtained, and friction charging is applied to one side of the sheet-like masking base material. Thus, a monopolar electret electret can be obtained. Other electretization methods such as liquid contact charging and radio charging can also be used.

  The electretization of the masking base material in the present invention can be performed either before or after the masking base material is placed on the object to be coated. For example, when electretization is performed by corona charging before placing the masking base material on the object to be coated, after placing the masking base material on the grounded flat plate electrode, the masking base material is corrected by a corona charger. Alternatively, it may be negatively charged. The masking material that has been electretized in advance is attracted to and adhered to an object to be coated that is grounded or charged with a polarity opposite to that of the paint particles.

  The shape of the masking material is selected according to the shape of the painting unnecessary portion of the object to be coated. FIG. 7 shows a modification of the shape of the masking material. Masking material 2 shaped to cover the convex part of lid 1B, masking material 2 shaped to close the concave part of lid 1B, and affixed to the inner surface of lid 1B to prevent paint from entering from the opening of lid 1B A masking material 2, a washer-like masking material 2 for preventing the screw 1C and the casing 1A and the lid 1B from sticking to each other can be preferably used, and a plurality of masking materials 2 can be used simultaneously. .

  Further, it is possible to use a masking base material 2A in which a serrated projection 2a is provided on the peripheral edge as shown in FIG. In the electretization process, the electric charge tends to accumulate more in the angular part and the pointed part than the flat part of the masking base material 2A. However, if the serrated projection 2a is provided on the peripheral part of the masking base material, Since many angular portions and sharp portions can be present in the peripheral portion of the masking base material 2A, adhesion of coating particles around the masking material is effectively avoided.

  As for the thickness of the masking base material, the thicker the surface potential of the masking material after electretization is, the thickness is not particularly limited, and the thickness is such that electrostatic repulsion occurs between the charged paint particles and the masking material. If it is enough. From the viewpoint of masking workability, a thickness of 0.5 mm to 3 mm is preferable.

  In the painting process, any method can be used as long as it is a method of adhering charged paint particles to an object to be coated using electrostatic action, and is not limited to the electrostatic powder coating method. Immersion methods and electrostatic coating methods can also be used. At this time, it is possible to use an arbitrary powder paint or liquid paint selected according to the application with the same polarity as that of the masking material. The removal of the masking material after the coating process may be performed before or after the coating film is dried or baked, and may be selected in consideration of the heat resistance and workability of the used masking material. Furthermore, in the painting process, a conductive object to be coated is often used while being grounded, but it is also possible to apply to an insulating object to be charged with a charge opposite to that of the paint.

It is a perspective view which shows the to-be-coated object and masking base material which are used in one Embodiment of this invention. It is the schematic explaining the electretization process process of a masking base material. It is the schematic explaining a coating process. It is sectional drawing which showed the state of the edge part vicinity of the masking material in the middle of a painting process. It is a perspective view which shows the to-be-painted object and masking base material which are used in other embodiment of this invention. It is sectional drawing which showed the state of the edge part vicinity of the masking material after coating. It is sectional drawing which shows the modification of a masking material. It is a perspective view which shows the modification of a masking base material. It is explanatory drawing which showed the coating method of the to-be-coated object by the electrostatic powder coating method, (a) is the figure which showed the state which has arrange | positioned the masking material in the coating unnecessary part of the to-be-coated object, (b) It is the figure which showed the process of spraying the charged powder coating material particle | grains to a to-be-coated object, (c) is the figure which showed the state which removed the masking material after baking of the coating film. It is explanatory drawing which showed the conventional masking method in an electrostatic coating method.

Explanation of symbols

1 Object to be painted 1A Housing (component of the object to be painted)
1B Lid (component of the object to be painted)
DESCRIPTION OF SYMBOLS 1a Painting required part 1b Painting unnecessary part 2 Masking material 2A Masking base material 3 Charged paint particle 4 Coating film 22 Powder coating gun

Claims (4)

A masking process in which a masking material is placed in advance on the part of the object to be painted that is not needed,
By applying the positively or negatively charged paint particles to the object to be grounded or charged with a polarity opposite to that of the paint particles, an electrostatic action including a painting process for coating the object to be painted is performed. The painting method used,
In the masking step, as a masking material, using an electret having a charged surface charged to the same polarity as the paint particles,
In the coating step, by utilizing electrostatic repulsion between the masking material and the paint particles, avoiding adhesion of the paint particles to the masking material in the vicinity of the masking material on the surface of the object to be coated. A painting method using the characteristic electrostatic action. The object to be coated is a set of objects to be coated composed of two or more components.
The coating method using electrostatic action according to claim 1, wherein the coating step is performed after the masking material is arranged at an overlapping portion of each component member and the object to be coated is assembled.   The coating method using electrostatic action according to claim 1 or 2, wherein the masking material is an electret formed from an insulating masking base material composed of a hydrophobic polymer.   The coating method using electrostatic action according to claim 1, wherein the coating step is performed by an electrostatic powder coating method.

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