FR2631584A1 - METHOD AND EQUIPMENT FOR SCREEN PRINTING FOR METAL COMPONENTS OF HEAT SENSITIVE OBJECTS - Google Patents

Abstract

The invention concerns a process which extends the field of application of silk screen printing to objects containing a metallic part to be printed and a part highly sensitive to heat. It adapts to the highest temperature which the most heat-sensitive material can withstand by allowing only the necessary quantity of ink to pass through a calendered screen having a precise raster. It uses the distance covered by the object and the speed of the object to ensure that the ink dries in the shortest possible time in function of the temperature limit imposed. It uses the transfer and packaging operations to attain an adequate level of hardness of the ink. The new process and equipment are particularly advantageous in the decoration and customization, for advertising or other purposes, of completely assembled and finished objects.

Description

 The present invention relates to a new screen printing process making it possible to increase the field of application of screen printing and in particular to print non-porous materials, for example a metal, under the most restrictive conditions of a definitive connection of this non-porous material with one or more fragile and heat sensitive materials.

 Screen printing is a very well-known process consisting in passing the ink through a silk screen stretched over a frame, the frame of which is sealed with wax on all the parts which should not be printed.

The very high precision, the quality of printing, and the flexibility of screen printing, are sufficient advantages to explain the wide current use of this printing technique, but these advantages should not make us forget certain disadvantages:
- Very slow and uncompetitive rates without additional drying. Since non-porous materials, for example metal, do not absorb ink, you must refrain from handling and stacking printed objects during the entire time that the ink dries, to avoid inevitable smearing.

 - Very strong and very competitive rates with extra drying with Ultra-Violet, but unsuitable for certain supports, including metallic supports, and particularly polished stainless steel.

 - Very strong and very competitive rates with extra drying with hot air, but unsuitable for certain supports, including mixed supports resistant to heat differently. The erasure time of destruction is reached for glues, plastic materials and other materials sensitive to heat, before the ink has reached sufficient drying to adhere to the metal.

 - Separation of the screen printing operation from other transfer, handling and packaging operations. The impossibility of grasping a screen-printed object without risk of smudging before complete drying has hitherto imposed not to simultaneously carry out the drying operations transfer, handling and packaging operations.

 The method, object of the present invention, intends to correct the aforementioned drawbacks and to widen the field of application of screen printing while retaining its undeniable advantages of precision and print quality.

 The process better controls the choice and the quantity of ink to allow not total but partial hardening, insufficient for manual transfer or manual manipulation, but sufficient for mechanical transfer or mechanical manipulation.

 The process adapts the temperature fluxes to the limit conditions required by the materials most sensitive to heat, by varying the running speeds and drying times according to the critical temperature level imposed.

The process integrates the transfer and / or handling phases
mechanical and packaging phases, with drying-cooling phases to reduce travel times by using masked times, to reduce equipment costs and dimensions, to reduce the risk of pollution, burrs and scuffing of objects and to increase the reliability and competitiveness of the new screen printing mode.

The screen printing process for metal components of heat-sensitive objects, object of the present invention is characterized by the succession of the following six phases:
1) Presentation of the composite object sensitive to heat and having a metallic part to be printed under a silk screen characterized by its material and its weft, capable of being let through only by a very small quantity of ink capable of quickly adhere to metal at the limit temperature tolerable by the material most sensitive to heat.

 2) Depositing the ink on the object, characterized by the ability of the ink to pass through the aforementioned screen and quickly dry on the metal part while respecting the integrity of the object and the screen.

 3) First additional drying phase characterized by the confrontation of the deeply inked object, on the one hand with a temperature front equal to the limit temperature tolerable by the material most sensitive to heat and, on the other hand , with forced ventilation or other treatment capable of facilitating the regulatory evaporation of the solvents included in the ink.

 4) Second additional drying phase, characterized by maintaining, on the one hand, the temperature at the limit level tolerable by the material most sensitive to heat for a variable duration of 2 to 5 minutes and on the other hand, ventilation or other means of evaporating the aforementioned solvents.

 5) Third additional drying phase, characterized by the regular and gradual decrease in temperature, with or without the addition of cold, to a temperature of 150 to 250 ° C. allowing handling and packaging, and characterized by variable time of the aforementioned course evolving according to a proportional ratio between the speed of movement and the length of the course of the object subjected to the above-mentioned drying conditions.

 6) Fourth additional drying phase, characterized by continued drying and lowering of the temperature during the transfer and packaging operations.

 Phase 1 of presentation of the object can be done on separate equipment or integrated with other equipment used during the other phases, the presentation of the object to be printed can be manual or automated, individually or in groups, located preferably but not necessarily at the entrance to the inking machine, and which can be done in any position allowing inking.

 Phase 2 of inking the object can be done with all the inks whose quantities deposited through the required screen allow drying respecting the integrity of the object and the screen.

 By way of nonlimiting example, the ink deposited through a calendered screen having 160 to 165 threads per inch, has sufficient fluidity so that the quantity deposited on the metal part can dry with a duration less than or equal to 2 or 3 minutes and with a temperature less than or equal to 800 C.

 phase 3 of the first additional drying can be done by any isolated or combined means allowing the evaporation of the solvents, the rise in temperature of the atmosphere in which the newly inked object is immersed, and the temperature adjustment at the maximum level permitted by the material most sensitive to heat.

The aforementioned means include both the chemicals constituting the ink (volatile solvents, etc.) or the atmospheric sphere (various gases, vacuum, etc.), as well as the equipment (UV, IR generators, hot air, etc.) capable of raising and modulating the temperature of the aforementioned atmosphere to the required level and / or facilitating the polymerization of the ink deposited in phase 2. As a non-restrictive example, the object inked in phase 2, upon entering a ventilated oven, is confronted with air heated to the maximum permissible temperature level of 420 C for the screen printing of cassettes loaded with magnetic tapes.

 Phase 4 of the second additional drying can be done by any isolated or combined means allowing the continued evaporation of the solvents, maintaining the temperature level of phase 3, and continuing the work of polymerization of the ink. deposited in phase 2. In a non-restrictive mound, the means used in phase 3 are reused, and the drying conditions of phase 3 are maintained for 2 to 5 minutes, for the screen printing of cassettes loaded with magnetic tapes.

 Phase 5 of the third additional drying can be done by any isolated or combined means allowing the further evaporation of the solvents, the further polymerization of the ink deposited in phase 2, then the regular and gradual reduction in the temperature limit of phases 3 and 4, with or without cold supply, up to a level of ink hardness allowing the transfer and packaging of screen-printed objects. All isolated or combined means are used to control the speed of movement the length of travel of the inked object in phase 2. All isolated or combined means are used to arrange the travel paths of the object during phases 3, 4, and 5, in terms of width, length and height, on single or multiple planes, horizontal or clinched, straight or curved, with a solid, perforated or perforated surface, with air cushion lift, direct or indirect sliding advance, by rollers, bands, belts, chains, hooks, etc ... At non-restrictive title, the means implemented in phases 3 and 4 are reused, and the temperature lowered to 150-250 C for the screen printing of cassettes loaded with magnetic tapes.

 Phase 6 of the fourth additional drying can be done by any isolated or combined means allowing the polymerization of the ink deposited in phase 2 to continue and temperature reduction in phase 5, during the transfer and packaging of the newly screen printed objects. Phase 6 makes it possible to reduce the journey time from phases 1 to 5 and the possible supply of cold from phase 5, without reducing the required journey times, by reducing the overall journey or increasing the running speed. Phase 6 allows to combine the above advantages with the advantages of a fully mechanized transfer and packaging, less demanding as regards the level of hardness and cooling of the ink than manual transfers and packaging. Phase 6, highly desirable for reasons of cost, bulk of equipment, and competitiveness, can possibly be dissociated from the other phases 3 to 5 by penalizing them.

 The screen printing of metal closing mechanisms of plastic cassettes filled with blank magnetic tapes allows, by way of non-restrictive example, to better understand the conditions of application of the process.

 Since the magnetic tapes cannot withstand heat above 420 ° C., it is decided to define the drying times in relation to a determined length of journey by modulating the speed of movement of a screen-printed cassette.

 In phase 1, several cassettes are stored in a mechanism responsible for presenting them individually or by group (s) under a screen printing screen carrying the selected message.

 In phase 2, bringing the cassette into contact with the screen having a calendered screen of 160 to 165 threads per inch, makes it possible to deposit an ink having an ability to adhere to the metal and a fluidity sufficient for the quantity deposited on the thick metal part to dry as required, during phases 3 to 6.

 In phase 3, the cassette enters a ventilated oven whose hot air is maintained at 420 G, the limit temperature that can be supported by the magnetic strip. The hot moving air accelerates the evaporation of the solvents and initiates the polymerization of the ink.

 In phase 4, the cassette continues to advance in the oven while being kept at the limit temperature of 42 ° C. for 2 to 5 minutes.

 In phase 5, the cassette continues its advance in the oven by approaching the outlet of this oven and moving away from the heat source so that the temperature decreases regularly to the ambient temperature prevailing outside of the oven, for example 180 ° C., the cooling course taking place with a running speed sufficient to be completed in 6 to 15 minutes, without adding cold.

 In phase 6, the cassette continues its advance out of the oven, towards the packing station. Transfer and boxing are mechanized, without any manual operation. The two operations take place directly at the abovementioned ambient temperature of 180 ° C., without bringing in cold, whereas this would become essential for an ambient temperature above 250 ° C. which would interfere with drying by preventing the ink from acquiring a hardness sufficient to support mechanical constraints of transfer and canning. The drying and cooling then continue in the packaging, without any time constraint and immobilization of the screen printing equipment.

 The new screen printing process concerns all objects in which one of the materials is metallic and one of the other materials does not withstand heat well. The decoration and the advertising personalization or not of fully assembled and completed objects must in particular benefit from the advantages of the new process and the related equipment.

Claims (8)

RsvZDICATIONS  1) Screen printing process for metal components of heat-sensitive objects, characterized by the succession of the following six phases:  - Presentation of the composite object sensitive to heat and having a metallic part to be printed under a silk screen characterized by its material and weft, capable of being let through only by a very small quantity of ink capable of adhering quickly to metal at the limit temperature tolerable by the material most sensitive to heat.  - Deposit of ink on the object, characterized by the ability of the ink to pass through the aforementioned screen and quickly dry on the metal part while respecting the integrity of the object and the screen.  - First additional drying phase characterized by the confrontation of the freshly inked object, on the one hand with a temperature front equal to the limit temperature bearable by the material most sensitive to heat and, on the other hand, with forced ventilation or other treatment capable of facilitating the regulatory evaporation of the solvents included in the ink.  - Second additional drying phase, characterized by maintaining, on the one hand, the temperature at the limit level tolerable by the material most sensitive to heat for a variable period of 2 to 5 minutes and, on the other hand , ventilation or other means of evaporation of the above-mentioned solvents.  - Third additional drying phase, characterized by the regular and gradual decrease in temperature, with or without the addition of cold, to a temperature of 150 to 250 C allowing handling and packaging, and characterized by time variable of the aforementioned course evolving according to a proportional ratio between the speed of movement and the length of the course of the object subjected to the above-mentioned drying conditions.  - Fourth additional drying phase, characterized by continuing drying and lowering the temperature during transfer and packaging operations.  2) Method according to Claim 1, characterized in that phase 1 of presentation of the object can be done on a separate equipment or integrated with other equipment used during the other phases, the presentation of the object to be printed can between manual or automated, individually or in groups, preferably but not necessarily located at the entrance to the inking machine, and which can be done in any position allowing inking.  3) Method according to Claims 1 and 2, characterized in that the phase 2 of inking the object can be done with all the inks the quantities of which deposited through the required screen allow drying respecting the integrity of object and screen. As a non-restrictive example, the ink deposited through a calendered screen having 16o to 165 threads per inch, has sufficient fluidity that the quantity deposited on the metal part can dry with a duration less than or equal to 2 or 3 minutes and with a temperature less than or equal to 800 C.  4) Method according to Claims 1 to 3, characterized in that phase 3 of the first additional drying can be done by any isolated or combined means allowing the evaporation of the solvents, the rise in temperature of the atmosphere in which is immersed the newly inked object, and set the temperature to the maximum level permitted by the material most sensitive to heat. The aforementioned means include both the chemicals constituting the ink (volatile solvents, etc.) or the atmosphere (various gases, vacuum, etc.), as well as the equipment (W -IR generators, air hot, etc ...) capable of raising and modulating the temperature of the above-mentioned atmosphere to the required level and / or facilitating the polymerization of the ink deposited in phase 2. At a non-restrictive example, the object inked in phase 2, as soon as it enters a ventilated oven, is confronted with air heated to the maximum admissible temperature level of 42 OC for the screen printing of cassettes loaded with magnetic tapes.  5) Method according to any one of the preceding claims, characterized in that phase 4 of second additional drying can be done by any isolated or combined means allowing the further evaporation of the solvents, maintaining the level of temperature of phase 3, and the continuation of the work of polymerization of the ink deposited in phase 2. As a non-restrictive title, the means used in phase 3 are reused, and the drying conditions of phase 3 are maintained for 2 to 5 minutes, for screen printing of cassettes loaded with magnetic tapes.  6) Method according to any one of the preceding claims, characterized in that the phase 5 of third additional drying can be done by any isolated or conjugated means allowing the further evaporation of the solvents, the further polymerization of the ink deposited in phase 2, then the regular and gradual decrease in the temperature limit of phases 3 and 4, with or without cold supply, to a level of hardness of the ink allowing the transfer and ltembållage of screen-printed objects. All isolated or combined means are used to control the speed of travel to the length of travel of the inked object in phase 2. All isolated or combined means are used to arrange the travel routes of the object during phases 3, 4 , and 5, in width, length and height, on single or multiple planes, horizontal or inclined, straight or curved, with a solid, perforated or perforated surface, with air cushion lift, direct or indirect sliding advance, by rollers, bands, belts, chains, hooks, etc ... Without limitation, the means used in phases 3 and 4 are reused, and the temperature lowered to 150-250 C for the screen printing of cassettes loaded with magnetic tapes.  7) Method according to any one of the preceding claims, characterized in that phase 6 of fourth additional drying can be done by any isolated or combined means allowing the further polymerization of the ink deposited in phase 2 and l lowering of temperature of phase 5, during the transfer and packaging of all newly screen printed objects, characterized in that phase 6 makes it possible to reduce the travel time of phases 1 to 5 and the possible supply of cold from the phase 5, without reducing the journey times required by reducing the overall journey or increasing the running speed, and characterized in that phase 6 allows the abovementioned advantages to be cumulated with the advantages of transfer and completely packaging mechanized, less demanding as regards the level of hardness and cooling of the ink than manual transfers and packaging. Phase 6, which is highly desirable for reasons of cost, material congestion, and competitiveness, can possibly be dissociated from other phases 3 to 5 by penalizing them.  8) Isolated or combined equipment making it possible to implement the process described in Claims 1 to 7, in whole or in part.