Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F15/00—Screen printers
  • B41F15/14—Details
  • B41F15/44—Squeegees or doctors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41P—INDEXING SCHEME RELATING TO PRINTING, LINING MACHINES, TYPEWRITERS, AND TO STAMPS
  • B41P2215/00—Screen printing machines
  • B41P2215/10—Screen printing machines characterised by their constructional features
  • B41P2215/13—Devices for increasing ink penetration
  • B41P2215/132—Devices for increasing ink penetration by increasing pressure above the screen

Definitions

• the object of the present invention is a capillary doctor blade with surface injection for screen printing in optimal conditions of liquid products to viscous liquids through the openings of a screen printing screen.
• This member is in particular adaptable to the device which is the subject of patent application FR 96.12671 or any other existing device with incorporated reservoir in which a pressure can be adjusted. DESCRIPTION OF THE PRIOR ART
• the deposition of liquid products on a surface is done by spraying, by dipping, or by brush when there are no complex areas to be protected. Otherwise, ie if there are complex areas to be protected, the screen printing process is used.
• the screen printing process consists of a screen or screen mask generally made from a canvas of synthetic material or stainless metal. This screen printing screen is made in such a way that it has closed areas and open areas corresponding to the drawings whose reproduction is desired.
• the screen printing screen is applied to the surface to be screen printed and an inclined doctor blade simultaneously pressed and moved in a direction parallel to the screen forces the liquid product to pass through the open areas of the mask.
• the doctor blades are generally formed either by a more or less hard rubber profile, or by stainless steel blades.
• the transfer force imparted to the product depends on the angle formed between the plane of the mask and the active face of the doctor blade. The smaller the scraping angle, the greater the transfer force.
• the masks can be made from a woven mesh of stainless steel, polyester or silk or it can be a stencil. These masks can be either planar or cylindrical in the case of continuous screen printing. Screen printing, as described above is a very old process but which has a certain number of drawbacks such as for example the change in rheology of the product to be transferred during work, either by evaporation of solvents contained in the product, or by interaction with the surrounding environment. This change in rheology results in an obligation to readjust the working parameters or to replace the altered product with good quality product.
• Patent application FR 96.12671 proposes another device with improved sealing, but here again, significant product leaks have been observed as soon as it is sought to transfer liquid products and in this case also, the product contained between the elements. seal leaks from the device when separated from the mask.
• the invention described and claimed by said French patent application is moreover limited to the application of pasty products such as soldering creams.
• German patent n ° DE 43 30 681 in the name of ROLAND MAN DRUCKMASH proposes to ensure the coating of a product on a printing roller, an applicator device comprising a capillary element impregnated with the product to be coated in direct and constant contact with the roller to be coated.
• This capillary element has the function of ensuring a homogeneous coating of the roller with which it is in contact.
• This device although of interest in the exploitation of a capillary element intermediate, can not be used in the context of screen printing since the latter incorporates the use of a screen printing mask whose function is to ensure a good transfer of the product on the substrate to be screen printed.
• the main drawback of conventional methods and devices lies in the difficulty of preventing the flow of the product when the latter is particularly fluid, when the applicator device is no longer in contact with the mask.
• the present invention overcomes the various problems associated with transfer devices of the prior art. According to the device, object of the present invention, there is between the closed reservoir which contains the product to be transferred and the screen printing mask an organ called capillary scraper with surface injection for the production of deposits by screen printing of a liquid to viscous liquid product.
• the liquid product being placed in a pressurizable reservoir open on the side of the mask by a distribution surface of dimension adapted to the width of the substrate on which the deposit is to be made;
• the said reservoir integral with the surface injection capillary doctor blade is mounted on a screen printing machine and, in conjunction with the pressurization of the liquid, the reservoir plus surface injection capillary doctor blade assembly is subjected to a relative movement of translation relative to the mask and is pressed on it.
• the capillary scraper with surface injection is interposed between said reservoir and said mask with surface injection, integrates a capillary element and has a more or less flow resistance so as to prevent the flow of liquid from the reservoir, when it is not under pressure and to allow it, when it is under pressure.
• the said capillary scraper with surface injection is closed on the front part and on the rear part by sealing lips inclined in opposition which come into constant contact with said mask.
• said doctor accepts elastic deformations through its sealing lips and contains an available volume of product which increases when the pressure is released on said capillary doctor blade with surface injection and which decreases when the 'we press the said injection doctor blade.
• the invention consists of a means of using the capillary effect to avoid the natural flow of the product, associated with a very wide distribution slot provided by the doctor blade, object of the invention, the contact surface of which with the very important screen printing screen, represents the injection site in order to reduce the pressure to be exerted on the product while increasing the flow rate.
• this surface-injected capillary doctor blade has a sufficiently high resistance to flow (capillarity) so that the product to be transferred does not flow from the device when the latter is separated from the screen printing mask and the product n is not under pressure.
• the resistance to flow (capillarity) of the capillary element may be adjusted according to the viscosity of the product to be transferred.
• the surface injection capillary doctor blade has a permeability in accordance with the requirements of the application, that is to say that the flow rate of the product under pressure through the surface injection capillary doctor blade is adaptable as a function of the range of desired screen printing speed, the nature of the substrate and the viscosity of the product to be transferred. It being understood that the flow rate through the surface injection capillary doctor blade is also adjustable by adjusting the pressure applied to the product in the reservoir.
• the surface injection capillary doctor blade has an available volume occupied by the product which decreases if the contact force exerted to push the device in contact with the mask increases and which increases if the contact force is reduced. In this way, the residual liquid which is located at the level of the distribution surface will be re-aspirated by vacuum at the end of scraping or at the time of separation of the device and the screen.
• the capillary doctor blade with surface injection has on the front and on the rear, two sealing lips inclined in opposition which have the function of scraping the excess product and thus of confining it inside. of the device. Additional sealing blocks arranged on either side of the device make it possible to avoid product leakage on the ends of the surface injection capillary doctor blade.
• the surface injection capillary squeegee is flexible enough to conform to the variations in height linked to irregularities in the substrate or the mask and thus allow the sealing lips which delimit the distribution surface. to fulfill their role of scraping the surplus.
• an intermediate capillary element between the product to be screen printed under pressure and the screen printing mask is not a simple adaptation of a known device in a new field of application but indeed the fruit of studies and of research aiming to meet a need different from that of a homogeneous coating of a printing roller but well to avoid the loss of product to be screen printed or at least the loss of its initial rheological characteristics by integration a capillary element retaining it when the pressure on the product is interrupted.
• said sealing lips coming into contact with said mask and the opening of which determines the injection surface of the product accept elastic deformations and are in connection with said capillary element so as to change its volume depending on whether or not pressing said capillary doctor blade.
• the surface injection capillary doctor blade constitutes an independent module which can be mounted on a transfer device comprising a pressurizable reservoir.
• all of the constituent parts of the surface injection capillary doctor blade chemically resist the products used as well as the cleaning solvents which can be used for cleaning the transfer device.
• FIG. 1 shows in section the traditional screen printing using a doctor blade according to the prior art
• Figure 2 shows in section a screen printing device of pasty product according to patent application 96.12671 by the same inventor
• - Figure 3 shows in section, the capillary scraper surface injection according to the present invention.
• FIG. 4 represents a perspective view of the capillary scraper with surface injection.
• Figure 5 shows in section a variant of the present invention.
• Figure 6 shows the variant in a perspective view.
• Figure 1 is shown the implementation of a screen printing using a doctor blade 3 of a product 4 through a mask 2 on the substrate 1.
• the doctor blade which is inclined at an angle "a" relative to the surface of the substrate, moves in the direction E, it imparts a force perpendicular to the edge of the doctor blade on the product of which only the vertical component T, called transfer thrust, makes it possible to transfer the product through the mask.
• FIG 2 there is shown a technique for direct transfer of pasty product through a mask invented by the same depositor.
• the product 4 contained in the reservoir constituted by the flexible membrane 5 and the assembly 9 is transferred to the substrate 1 through the mask 2.
• the force FI pushes the device against the mask and therefore generates a sealed contact between the sealing members or lips 6a and 6b and the mask.
• the lips are fixed to the assembly 9 by means of the parts 7.
• the transfer thrust generated by the force F2 on the piston 8 expels the product 4 by the distribution surface 10 delimited on either side, by the lips 6a and 6b.
• This type of device is particularly suitable for the transfer of pasty products such as soldering creams or epoxy adhesives having a viscosity greater than or equal to 1000 poises. Indeed, for such high viscosities the product does not flow naturally from the device even when the latter is separated from the mask provided that the force F2 on the piston is zero. On the other hand, this type of device cannot be used for the transfer of liquid products. Not only is the seal not sufficiently effective at the ends and in the areas where the mask is not supported by the substrate, but also the product flows freely from the device either during the fitting of the latter. , either during separation with the mask or at rest if the lips do not perfectly fit the surface of the mask.
• Figure 3 shows an embodiment of the present invention. It consists of interposing an autonomous element called a capillary scraper with surface injection between the reservoir constituted by the flexible membrane 5 and the assembly 9 containing the product to be transferred and the mask.
• the surface injection capillary doctor blade is fixed to the assembly 9 using the screws 17.
• the surface injection capillary doctor blade integrates a capillary element consisting of an elastically deformable profile 13, for example RTV 71557 silicone from Rhône Poulenc and d 'a mesh 12 fixed to the profile 13 and which has orifices 14 for feeding the product, uniformly distributed in the distribution zone 10, which open on the mask side in a counterbore 11.
• the mesh 12 has the function of bringing all the orifices 14 and to homogenize the pressure of the liquid to be transferred over the entire surface 10 of the mask facing the counterbore.
• the weft of the mesh 12 can be adjusted as a function of the viscosity of the product to be transferred. We will choose a mesh with lower opening rates that the product will have a low viscosity. In all cases, all of the openings 14 and of the mesh 12 have sufficient flow resistance (capillarity) so that the product cannot flow freely from the device when the latter is separated from the mask and the force F2 is released.
• the set of orifices 14 and the opening rate of the mesh 12 must allow a flow of product subjected to the pressure in the reservoir in accordance with the target screen printing speed and the nature of the substrate to be printed.
• the elastic profile is crushed so that the sealing members 6a and 6b arranged around the distribution surface 10 can conform to the variations in height and closely fit the mask so as to to avoid leaks.
• This overwriting also performs another function.
• the volume available inside the capillary scraper with surface injection and occupied by the product 4, determined by the orifices 14 and the countersinking decreases and conversely increases when the prestressing is released as can be the case during a downtime or between two screen prints. Consequently, in the latter case, the product which is situated at the level of the dispensing surface is re-aspirated into the reservoir and thus cannot escape from the device.
• the materials of the various constituent parts of the surface injection capillary squeegee can be adapted according to the application and their chemical resistance to the product to be transferred.
• the choice of mesh 12 will preferably be carried out on a mesh of the same type. nature.
• the profile 13 is glued to a rigid support plate 18 which closes the reservoir and which supports the profile 13 so that it does not flex in the middle.
• the plate 18 also has product passage holes 15 opposite the holes 14 in the profile 13. The diameter of these product passage holes 15 is advantageously calculated and adapted to the viscosity of the product as well as in adequacy with the size. cells constituting the capillary element.
• FIG. 4 is a perspective view of the surface injection capillary doctor mentioned in FIG. 3.
• the counterbore 11 which contains the mesh 12 does not extend over the entire length of the surface injection capillary doctor so that the product cannot not escape from both ends.
• the surface injection capillary doctor blade is presented as an independent module which can be mounted on the reservoir of a direct transfer device.
• the capillary element consists of an elastically deformable profile 16 made of open cell foam such as, for example, polyurethane foam which has both permeability sufficient for the product flow rate to be adequate for the need of the application when pressing with force F2 on the piston 8, but also sufficient flow resistance (capillarity) so that the product cannot flow freely from the device when it is separated from the mask and the force F2 is released.
• open cell foam such as, for example, polyurethane foam which has both permeability sufficient for the product flow rate to be adequate for the need of the application when pressing with force F2 on the piston 8, but also sufficient flow resistance (capillarity) so that the product cannot flow freely from the device when it is separated from the mask and the force F2 is released.
• the capillary scraper with surface injection has a volume occupied by the product which varies according to the preload FI applied to the device so that when the pressure is released the product which is at the around the distribution surface 10 is re-aspirated inside the device.
• the foam profile occupies the entire volume between the lips 6a and 6b and the support plate 18.
• FIG. 6 a perspective view of the capillary scraper with surface injection as described in FIG. 5.
• the open cell foam does not extend over the entire length of the distribution surface in order to avoid lateral leaks from product.
• a profile 19 of closed cell foam such as for example silicone foam or EPDM.
• the lips 6a and 6b as well as the support plate 18 are bonded to the sections 19 so the capillary scraper with surface injection constitutes an independent and interchangeable module.
• Interchangeability is particularly advantageous when it is desired to change the viscosity of the product or the range of screen printing speed, in this case it suffices to change the capillary scraper with surface injection by choosing a foam with an open cell dimension adapted to the need. of the new application.
• Advantage can also be taken of interchangeability during cleaning since it can be done in masked time if two capillary injection scrapers are available identical surface.
• Another way of ensuring the sealing at each end of the surface injection capillary doctor blade can be carried out by sealing the open cells for example with silicone, which can be poured into the foam in order to fill the cells, thus a single foam. is necessary to make an injection doctor blade.
• silicone which can be poured into the foam in order to fill the cells, thus a single foam. is necessary to make an injection doctor blade.
• the surface-injected capillary squeegee is in contact with the mask over the entire surface of the dispensing slot so that the product cannot accumulate in a pocket which would risk being emptied on the mask during a period of time. '' or when the device is removed from the mask.
• the device according to the invention is therefore particularly suitable for rotary or flat screen printing of liquid products to viscous liquids on all kinds of substrates.
• Operating in a sealed manner any interaction between the product and the external environment is avoided, which has the consequence of increasing the life of the products to be transferred and of limiting losses.
• being able to act independently on the transfer thrust it therefore follows that the product flow rate through the capillary scraper with surface injection becomes adjustable, that is to say that it now becomes possible to increase considerably the speed of screen printing.
• the device according to the invention can be adapted to existing devices.
• it can be adapted to the PROFLOW device which is the trade name of the product which is the subject of patent application FR 96.12671 which has the consequence of considerably increasing the field of application. possible of this product.
• This invention will in particular apply to industrial sectors already using screen printing for the deposition of liquid products: printing, manufacturing of posters, decoration (tiles, enamels, textiles %), glass industry, automobile ...
• the liquid product is placed in a pressurizable reservoir open on the side of the mask by a distribution surface of dimension adapted to the width of the substrate on which the deposit is achieve; the said reservoir integral with the surface injection doctor blade is mounted on a screen printing machine and jointly with the pressurization of the liquid, the assembly consisting of the pressurizable reservoir and the capillary surface injection doctor blade are subjected to a relative movement of translation relative to the mask and is pressed on the latter.

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 1998
  • 1998-09-03 FR FR9811005A patent/FR2782945B1/fr not_active Expired - Fee Related
• 1999
  • 1999-09-02 CA CA002342816A patent/CA2342816A1/en not_active Abandoned
  • 1999-09-02 EP EP99940274A patent/EP1109672B1/de not_active Expired - Lifetime
  • 1999-09-02 DE DE69943046T patent/DE69943046D1/de not_active Expired - Lifetime
  • 1999-09-02 WO PCT/FR1999/002088 patent/WO2000013904A1/fr active Application Filing
  • 1999-09-02 AU AU54278/99A patent/AU5427899A/en not_active Abandoned
  • 1999-09-02 AT AT99940274T patent/ATE491573T1/de not_active IP Right Cessation
  • 1999-09-02 JP JP2000568687A patent/JP2002524310A/ja not_active Withdrawn
  • 1999-09-02 US US09/786,115 patent/US6588335B1/en not_active Expired - Lifetime

Non-Patent Citations (1)

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