Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F15/00—Screen printers
  • B41F15/14—Details
  • B41F15/40—Inking units
  • B41F15/42—Inking units comprising squeegees or doctors

Definitions

• the invention relates to a screen printing cylinder with a circular screen and a doctor blade placed on the inner surface of the circular screen.
• Screen printing cylinders are equipped with a circular screen and a squeegee attached to the inner surface of the circular screen.
• a doctor blade is usually held stationary while the cylinder rotates in the operation of a screen printing machine.
• ink applied to the inner surface of the circular screen is conveyed in front of the doctor blade and forms a bead of ink there.
• the hydrostatic pressure acting on the ink due to the rotation of the cylinder becomes so great that ink passes through the screen and can be printed.
• the ink bead By rotating the circular screen, the ink bead is also driven to rotate about itself and rises to the squeegee. He tends to avoid areas where the hydrostatic pressure is lower, especially towards the longitudinal ends of the doctor blade. In this way, ink is gradually transported to the edges of the screen printing cylinder, where, if it is not printed, it remains until it has lost its printability. This leads to loss of color and also requires regular cleaning of the screen and the doctor blade.
• the US Pat. No. 6,142,070 describes a squeegee for a screen printing plate on the two longitudinal ends of which a lateral color deflector plate is arranged. These deflectors prevent the paint from escaping sideways. However, during the advancement of this device, the paint accumulates in the corners formed by the longitudinal ends of the doctor blade and the deflectors.
• the patent US 5,503,067 also describes a doctor blade for a screen printing plate.
• the squeegee itself is bent forward at its two longitudinal ends, so that ink escaping to the sides accumulates in the corners thus formed.
• the squeegee also carries a plurality of parallel wings which are oriented transversely to the squeegee surface and reduce the lateral spread of the ink.
• This device has no means to urge the advanced ink flood toward the center of the squeegee.
• the invention has for its object to provide a screen printing cylinder which does not have the shortcomings mentioned above.
• a web parallel to the cylinder axis is arranged on the lateral surface of the doctor facing the ink conveyed to the doctor, the doctor, a section of the circular screen touching it and the web extending from the doctor opposing one form the channel bottom in the direction of rotation of the screen printing cylinder, and that at least in the two longitudinal end regions of the web there are guide means for deflecting paint stripped by the doctor blade from the circular screen in the longitudinal direction of the doctor blade towards the center thereof.
• the paint stripped from the squeegee by the circular screen collects in the channel base to form a bead, which is driven to rotate by the rotation of the circular screen and, by the interaction of the rotation of the bead and the alignment of the guide means according to the invention, becomes the color pushed towards the center of the squeegee.
• the guide means for deflecting ink prevent or at least significantly reduce an accumulation of the ink on an edge of the doctor blade or screen printing cylinder, where it is not printed. Color losses during printing are thus avoided, and the need to interrupt the printing operation in order to clean the squeegee or the screen printing cylinder is at least considerably reduced.
• the guide means for deflecting the ink can preferably be designed such that their effectiveness decreases from the longitudinal ends of the squeegee towards the center thereof ,
• the means for deflecting the ink can also be completely omitted for the sake of simplicity.
• the web can be part of an ink guide plate which bears against the squeegee.
• the ink guide plate can have holding means in order to hold the squeegee stationary in the screen printing cylinder.
• the web of the color guide plate can carry the guide means in or on itself.
• the guide means for deflecting the color comprise ribs oriented obliquely to the circumferential direction of the circular screen. These ribs use the rotation of the ink bead around itself to drive it to move towards the center of the squeegee.
• the ribs engage in a channel which is delimited by the squeegee, a portion of the circular screen which it touches and a web extending from the squeegee and which is open in the direction of rotation of the screen printing cylinder in order to prevent the ink applied to the inside of the circular screen from penetrating into to allow the channel.
• the decrease in the effectiveness of the ribs towards the center of the squeegee can e.g. can be achieved in that the height of the ribs with which they engage in the channel decreases from the longitudinal ends of the squeegee towards the center thereof.
• Another possibility is to reduce the inclination of the ribs with respect to the circumferential direction of the circular screen from the longitudinal ends of the doctor blade to the center thereof. If there are ribs in the middle of the squeegee, these are not oblique, but oriented parallel to the direction of rotation of the squeegee and thus do not cause any shifting of the color.
• the guide means for deflecting the color comprise grooves oriented obliquely to the cylinder axis, the grooves being formed in the web.
• the grooves form a groove system, the effectiveness of which can be modulated by the design and arrangement of the individual grooves.
• the depth of the individual grooves can also decrease from the upper edge of the web in the direction of the doctor surface, so that the hydrostatic pressure of the ink is more homogeneous in the vicinity of the wiping edge.
• Figure 1 is a perspective view of a first embodiment of a doctor blade with web and guide means for a screen printing cylinder.
• 3 shows a second modification of the first embodiment
• 4 shows a schematic partial section through a screen printing cylinder, which shows the doctor blade with web and guide means placed on the inside of its circular screen;
• FIG. 5 shows a perspective view of a color guide plate according to a second embodiment of the invention.
• FIG. 6 shows a front view of a longitudinal end region of the ink guide plate of FIG. 5, from the direction Z of FIG. 7;
• Fig. 7 shows a cross section according to A-A through the ink guide plate of Fig. 6, with doctor blade and holder.
• the squeegee 01 shown in FIG. 1 is a rigid rod which extends over the entire axial length of a screen printing cylinder and from which a longitudinal edge 02 is provided, in order to engage the inside of a circular screen 03 of such a screen printing cylinder in the manner shown in FIG. 4 to be employed in order to partially strip off the ink applied by an inking mechanism (not shown) to the inner surface of the circular screen 03, partly to press it through the circular screen 03 onto the outside of the screen printing cylinder.
• the ink stripped off by the doctor blade 01 collects on its upper side to form a bead 04 which is driven by the rotation of the screen printing cylinder in the direction indicated by arrow 06 in FIG. 4 to rotate about itself, as indicated by an arrow 09 ,
• Ink that flows along the top of the doctor blade 01 during the rotation of the bead 04 finally reaches a web 07 which projects from the top of the doctor blade 01 against the direction of movement of the circular screen 03 and flows up there.
• a plurality of ribs 08 serving as guide means are arranged in the angle spanned by squeegee 01 and web 07, which penetrate into the rotating bead 04 and its rotational movement around itself is an axial component of movement stamp on the middle of the squeegee 01.
• the ribs 08 thus prevent the bead 04 from reaching the ends of the squeegee 01, where the paint would otherwise escape unused and adhere to the edge of the circular screen 03 could and would require cleaning of the screen printing cylinder in a short time.
• the inclined ribs 08 are only arranged in the vicinity of the ends of the doctor blade 01, but are missing in the central region thereof. Under static operating conditions, this is sufficient for a uniform distribution of the ink even in the middle area of the doctor blade 01 free of ribs 08, because the ribs 08 act as barriers which prevent the ink from escaping to the ends, while at the same time in the middle, from the ribs 08 free area of the squeegee 01, ink can migrate in the longitudinal direction of the squeegee 01, so that local differences in thickness of the bead 04 and the associated uneven distributions of the hydrostatic pressure in the bead 04 compensate over time.
• the thickness of the bead 04 tends to decrease rapidly towards the ends of the squeegee 01, which can be troublesome, even if the area of the squeegee 01 on which the ribs 08 are arranged has a printing surface on the circular screen 03 sweeps over.
• FIG 5-7 show a second preferred embodiment of the invention with an ink guide plate, which is also used to hold a conventional doctor blade.
• the ink guide plate 100 shown in FIG. 5 is an elongated plate which extends essentially over the entire axial length of a screen printing cylinder. In the vicinity of the upper edge, the ink guide plate 100 has a plurality of bores 110, 111, which allow the ink guide plate to be screwed in place in the screen printing cylinder. As shown in FIG. 7, the doctor blade 101 clamped between a carrier 112, which is only partially shown, and the ink guide plate 100 is fixed in place in the screen printing cylinder with the aid of screws 113.
• the lower thickened part of the ink guide plate 100 is essentially prismatic and forms a web 107, which protrudes both from the surface of the ink guide plate 100 and from the lateral surface of the doctor blade 101 facing the ink conveyed in front of the doctor blade 101.
• Fig. 7 the circular sieve is indicated by dashed lines. It can be seen from this that the inclined surface 106 of the web 107, the adjoining surface 105 of the doctor blade 101 and the surface of the circular screen 103 sliding on the longitudinal edge 102 of the doctor blade 101 form a channel sole, in which, when the screen printing cylinder rotates, that of the doctor blade 101 stripped paint collects into a self-rotating bead, similar to the first embodiment.
• inclined grooves 108 are designed to lift off the teeth.
• these grooves 108 are inclined by approximately 45 ° with respect to the longitudinal edge 102 of the ink guide plate 100. Thus, they give the rotating bead a component of movement towards the center of the color guide plate 100.
• the outer inclined surface of the web 107 has two different inclinations in the longitudinal end area equipped with grooves.
• the inclination corresponds to that of the surface 106 over the entire length of the doctor blade 101. It is represented by the angle ⁇ of FIG. 7.
• the inclination with respect to surface 105 is less and is represented by the angle ⁇ of FIG. 7.
• the longitudinal axes of the grooves 108 correspond to this latter inclination. Since the angle ⁇ is smaller than the angle ⁇ , as can be seen from FIG. 7, the grooves 108 near the lower edge of the ink guide plate 100 are tapered and flattened, as can best be seen from FIG. 6. As a result, the local distribution of the ink and its hydrostatic pressure in the vicinity of the scraping edge 102 of the doctor blade 101 become more homogeneous.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Screen Printers (AREA)
• Eye Examination Apparatus (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=33394075

Family Applications (1)

Country Status (5)

Families Citing this family (12)

Family Cites Families (9)

• 2003
  • 2003-05-02 DE DE10319773A patent/DE10319773B4/de not_active Expired - Fee Related
• 2004
  • 2004-03-03 AT AT04716532T patent/ATE483582T1/de active
  • 2004-03-03 JP JP2006504153A patent/JP4723478B2/ja not_active Expired - Lifetime
  • 2004-03-03 EP EP04716532A patent/EP1620264B1/fr not_active Expired - Lifetime
  • 2004-03-03 DE DE502004011742T patent/DE502004011742D1/de not_active Expired - Lifetime
  • 2004-03-03 WO PCT/CH2004/000128 patent/WO2004096545A2/fr not_active Ceased

Non-Patent Citations (1)

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