WO1994001282A1

WO1994001282A1 - A method of applying ink to a printing block, a pad printing machine for performing the method, and an ink vessel for use in the pad printing machine

Info

Publication number: WO1994001282A1
Application number: PCT/DK1993/000224
Authority: WO
Inventors: Alain François JÉRON
Original assignee: Jeron Alain Francois
Priority date: 1992-07-06
Filing date: 1993-07-05
Publication date: 1994-01-20
Also published as: AU4417693A; DK88392D0; DK88392A

Abstract

A pad printing machine transfers a print pattern from a printing block (11) to an object (60) and comprises an ink reservoir (5) from which ink is applied to the printing block (1), as well as a wiper means (11) for wiping excess ink from the printing block (1) before the print pattern is transferred to the object (60) with a flexible pad (15). A flexible ink pad (7) through which the ink is transferred from the ink reservoir (5) has a plane side which is caused to contact the printing block (1) in the application of ink. The ink pad (7) is compressible and is made of a material permeable to the ink. An ink vessel for use in the pad printing machine comprises a container with ink which is transferred through one or more openings (54) to apply part of the ink to a printing block (1). A plate-shaped ink pad of a spongy material is provided in connection with said openings (54), which absorbs and transfers the ink to the printing block (1) by contact with it.

Description

A method of applying ink to a printing block, a pad print¬ ing machine for performing the method, and an ink vessel for use in the pad printing machine

The invention concerns a method of applying ink to a printing block for a pad printing machine and comprising the steps stated in the introductory portion of claim 1. The invention moreover concerns a pad printing machine as defined in the introductory portion of claim 4, and an ink vessel of the type defined in the introductory portion of claim 10 for use in such a pad printing machine.

Pad printing is a printing technique which is used e.g. in connection with printing tasks where the object to be printed is uneven. The actual print is transferred from the printing block to the object by a soft pad of e.g. silicone rubber, the pad surface being capable of conform¬ ing to the surface of the object. However, pad printing has other advantages, and e.g. a very distinct sharpness of the print has made the method very attractive for high quality prints on minor objects, such as paper or plastics cards, e.g. credit cards, smart cards, telephone pay cards and visiting cards.

However, the prior art is vitiated by some drawbacks with respect to the application of ink to the printing block. Thus, open ink vessels are used, in which the ink is lo¬ cated in a reservoir in extension of the printing block and periodically overflows it. Excess ink is wiped off by a doctor back to the reservoir. These ink vessels permit free evaporation of the solvents of the ink, which consti¬ tute an environmental risk to the user.

To avoid this risk of evaporation, closed ink vessels have been developed, shaped as an inverted cup (with the open- ing downwards) , whose open side faces the printing bloc . Thus, the ink is directly above the printing block. Tight¬ ness is ensured in that the edges of the vessel taper to¬ ward the opening and serve as doctors which are pressed against the printing block. The pressure must be of such a size as to overcome the hydrostatic pressure generated by the ink and to avoid unintentional leakage of ink. The doctor will thus affect the printing block to such a de¬ gree as to make huge demands on the mechanical strength of the printing block. Closed ink vessels are therefore only used in connection with steel printing blocks, because plastics printing blocks will be worn down after a rela¬ tively short time. Closed ink vessels are therefore used only in large productions of the order of up to one mil- lion prints. In case of small productions cheaper plastics printing blocks having open ink vessels are used.

The object of the invention is to provide a method making it possible to use closed ink vessels in connection with plastics as well as steel printing blocks.

This object is achieved by the features defined in the characterizing portion of claim 1, since it is then not necessary to have a strong engagement pressure between printing block and ink vessel. The ink pad blocks outflow from the vessel, and the ink is discharged through the ink pad when this moves.

After the ink pad has applied ink to the printing block by engagement with it, the depressions of the printing block will be filled with ink, and excess ink is removed from the printing block by a doctor arranged in extension of the ink pad. When the printing block is wiped clean, part of the ink pad is lifted so that only the part positioned closest to the doctor contacts the printing block. The sponge will hereby absorb the ink amount moved in front of the doctor during wiping.

The invention also concerns a pad printing machine as stated in claim 4. The features defined in the character- izing portion of claim 4 ensure slow, controlled discharge of ink to the printing block as the ink pad moves with re¬ spect to it.

The ink pad is preferably constructed as stated in claim 5, since the application of ink can take place as a sub¬ stantially translatory movement of the ink pad against the printing block. The ink pad may advantageously be rein¬ forced by textile fibres, as stated in claim 6, thereby imparting good dimensional stability to the ink pad in its longitudinal directions. This ensures that the ink pad is only slightly deformed by the friction which occurs when the ink pad is used for wiping off excess ink from the printing block. In some cases it may be expedient to coat the ink pad with a textile layer as stated in claim 7, since this enhances the durability of the ink pad. The ink pad may preferably be mounted as stated in claim 8, since this imparts a rigidity to the pad which is expedient for the present purpose. Mounting can take place by glueing, sewing or the like.

Claim 9 defines how the supply container may be con¬ structed in the form of replaceable ink vessels, so that the entire ink vessel with the sponge is replaced when the ink on the printing machine is changed. The ink vessels may e.g. be retained by a snap or frictional coupling with the ink vessel frame.

Claim 10 states how such a replaceable ink vessel is con¬ structed. The invention will be explained more fully by the follow¬ ing description of preferred embodiments and with refe¬ rence to the drawing, in which

fig. 1 is a partially sectional side view of a preferred embodiment of a pad printing machine according to the in¬ vention,

fig. 2 is a partially sectional front view of the pad printing machine of fig. 1,

fig. 3 is an exploded view of a preferred embodiment of the doctor holder shown in fig. 1,

fig. 4 is a perspective view of an embodiment of the ink vessel frame shown in fig. 1,

fig. 5 is a perspective view of an embodiment of an ink vessel according to the invention to be mounted in the ink vessel frame shown in fig. 4,

fig. 6 is a sectional view of the ink vessel of fig. 5, but provided with a cover, and

fig. 7 is a view of the perforated wall of the ink vessel of fig. 5 on which the ink pad is mounted.

The invention will be explained more fully below with reference to figs. 1 and 2, which are a side view and a front view, respectively, of a pad printing machine ac¬ cording to the invention. A printing block 1 contains the information necessary for the print, the printing block 1 being provided with depressions, such as screen sections, which may be provided by photographic processes known per se followed by an etching treatment of the printing block surface. The printing blocks may be of steel as well as of plastics, the latter being preferred in connection with minor number of prints (e.g. 100,000 prints) owing to the manufacturing costs. The printing block 1 is secured to a slide table 2 by means of pins (not shown) protruding from the table and/or a magnet coupling between the printing block and the plate and the slide table 2. The slide table 2 has a V-shaped slide rail 20 in its entire length which communicates with a corresponding complementary slide rail 21 on the frame of the pad printing machine. The slide rails 20, 21 hereby form a slide bearing so that the re¬ ciprocating movements of the table will be extremely stable. The underside of the slide table 2 is formed with two downwardly extending bosses 22 at each side, respec¬ tive piston rods 23 on respective pressure cylinders 3 being secured to said bosses. The other part of the pres¬ sure cylinders 3 is secured with respect to the frame of the pad printing machine. The movements of the slide table 2 and thus also of the printing block 1 can hereby be con¬ trolled so that the print of the printing block 1 is al- ternately mrved inwardly below the ink applying device and the ink transfer mechanism. The print transfer mechanism consists of a pad 15 known per se which is made of sili- cone rubber or a similar material, so that when engaging an object 60 the pad 15 conforms to the surface of the object. The pad 15 is mounted on a piston rod 24 on a compressed air cylinder 16. The stationary part of the compressed air cylinder 16 is secured to a pad frame part 17 which moreover have longitudinal bores in the longitu¬ dinal direction of the compressed air cylinder in which control rods 25 are received. These control rods 25 are moreover secured to the pad head 26, thereby providing a very precise control of the translatory movement of the pad 15.

The print is transferred to the object 60 by causing the pad 15 to engage the inked part of the printing block 1 when the printing block 1 assumes the position shown in fig. 1, following which the pad 15 is again moved upwards (backwards). The printing block 1 on the table 2 is then moved inwardly so that there is a free downward passage for the pad, following which it is moved downwardly by activating the compressed air cylinder 16. A conveyor on which the objects to be printed are conveyed may then expediently be mounted below the slide table 2. This is not shown, because this is trivial to a skilled person and will not contribute to the understanding of the invention. When ink has been applied to the object, the pad 15 is moved upwards again, so that the slide table 2 can again be moved out with new ink for printing a new object.

It will be seen that the pads 15 (fig. 2) are replaceable, since they have a channel which during mounting is pushed inwardly over a locking boss 27 on the pad head 26. This mounting is terminated by tightening a screw 29, causing the pads 15 to be firmly mounted on the head 26 until the screw 29 is loosened again.

The actual application of ink to the printing block 1 is performed by an ink application mechanism provided behind the pad 15 and comprising an ink vessel frame 28 in which a plurality of ink vessels 5 are mounted. The number of ink vessels corresponds to the number of pads 15, so that in the embodiment shown in figs. 1 and 5 there will be five ink vessels juxtaposed. These ink vessels 5 are re¬ tained detachably in the ink vessel frame 28, e.g. by means of a snap function. When this is the case, the ink vessels are moved into the ink vessel frame from below. The ink vessels 5 preferably have a ridig plate-shaped part 6 which serves to attach an ink pad 7. The ink vessels 5 have an amount 30 of ink which is gradually released through the plate-shaped part 6 to the ink pad 7, from which the ink is finally applied to the printing block 1 .

The actual ink application device is mounted on a trans¬ verse beam 33 which forms part of the frame of the pad printing machine, which is not shown in its entirety. The transverse beam 33 extends transversely in the pad print¬ ing machine and has a vertical carrier wall 34, which is connected with another vertical carrier wall 36 by a hori¬ zontal connecting member 35. Two control bolts 37, 38 are mounted in each of the vertical carrier walls 34, 36, one in each of the ends of the carrier walls 34, 36. These control bolts constitute guides for the raising and lower¬ ing mechanism 39 of the ink application device which can be moved along the bolts 37, 38. A pressure cylinder is interposed between the mechanism 39 and the horizontal connecting member 35 on the transverse beam 33. The cy¬ linder part 40 of said pressure cylinder is secured to the mechanism 39, while the piston part 41 is secured to the connecting member 35. The mechanism 39 can hereby be moved up and down by actication of the pressure cylinder 40. This takes place when the ink vessel is periodically raised or lowered with respect to the printing block 1. The mechanism 39 is moved right up to its outer position when the ink vessel frame 28 is to be replaced.

The ink vessel frame 28 is pivotally hinged to the raising and lowering mechanism 39 through a bolt 10 which serves as a shaft. The bolt 10 is coated with a flexible rubber coating, which absorbs vibrations between the mechanism 39 and the ink vessel frame 28.

A pressure cylinder 9 is additionally secured to the rais¬ ing and lowering mechanism 39, and the piston rod 42 of the pressure cylinder is secured to the ink vessel frame 28. The ink vessel frame 28 hereby rotates about the shaft formed by the bolt 10 upon activation of the pressure cy- Under 9 .

A doctor 11 is arranged in front of the ink vessel 5, said doctor being mounted on the ink vessel frame 28 by means of two wedge-shaped elements 31, 32. These wedge-shaped elements 31, 32 determine the angle which the doctor forms with the engagement face of the ink pad 7. It will be seen that the doctor is arranged quite close to the termination of the plate-shaped part 6 and the ink pad 7 mounted on it. The ink pad will hereby absorb ink when the doctor wipes off excess ink. The excess ink will accummulate in the space between the ink pad and the doctor, so that the ink pad absorbs the greater part of this ink.

Ink application thus takes place in that the pressure cy¬ linder 40 is activated so that the ink pad 7 of the ink vessel 5 is pressed against the part of the printing block 1 which is provided with depressions to receive ink. The ink pad 7 is pressed against the outer part of the print- ing block 1, which is the part shown below the pad 15 in fig. 1. The ink pad is thus in contact with the printing block 1 with the part located at the doctor 11, but the ink pad part facing away from the doctor 11 is lifted slightly from the printing block 1, e.g. h - 1 mm (the ink pad typically has a thickness of 4.5 mm). Then the slide table 2 is driven outwardly toward the position shown in fig. 1, whereby the doctor 11 removes excess ink from the printing block 1 provided with depressions, so that ink will only be present in the depressions of the printing block. When the pad 15 has collected the ink from the depressions in the printing block 1, the slide table 2 is again moved into the pad printing machine. The pressure cyinder 9 contracts until the slide table 2 has been re¬ turned to the ink application position, following which the doctor 11 and the ink pad 7 again engage the printing block. The printing block part provided with depressions will again be provided with ink, following which the pro¬ cedure is repeated.

Control of the pressure cylinders incorporated in the pad printing machine takes place by means of compressed air, and the pad machine has a control unit (not shown) whose structure will be trivial to a skilled person in view of the above description.

The ink vessel does not have to be arranged in the vici¬ nity of the ink pad, because the ink transfer can take place by means of supply pipes to the ink pad.

Fig. 3 shows the structure of the doctor 11 and the wedge- shaped elements 31, 32. It will be seen that the wedge- element 32 closest to the ink vessel 28 (fig. 1) has a transverse depression 46 which receives a preferably cy¬ lindrical, resilient rod 43, preferably of rubber. Below the rod 43 the wedge-shaped part 32 is formed with a plu- rality of depressions 44 which are recessed with respect to the rest of the surface 45 by a depth which is just slightly smaller than the thickness of the individual doctor elements 11. It will be seen that the other wedge- shaped element 31 has a depression 48 complementary with the flexible rod 43, so that the flexible rod 43 is re¬ tained safely when the two wedge-shaped elements 31, 32 are caused to engage each other. It will moreover be seen that the other wedge-shaped element 31 has a depression 49 to receive another flexible rod 47, e.g. of rubber, which has smaller dimensions than the first rod 43. Upon as¬ sembly of the wedge-shaped elements 31, 32 the individual doctor elements 11 will be received in the depressions 44, the rear edge of the doctor elements 11 being caused to engage the flexible rod 43. There will be a quite small play in the transverse direction toward the bridges 45 such that the individual doctor elements have a certain freedom of movement, i.e. partly a movement in the for- wardly and rearwardly extending direction of the doctor elements, partly a tilting of the individual doctor ele¬ ments 11. The flexible rod 47 on the other wedge element engages the surface of the knife elements 11, so that these are retained in their position. Variations in the load against the doctor elements 11 originating from en¬ gagement with the printing block 1 will thus be essen¬ tially absorbed in the flexible rod 43 so that the doctor elements 11 will be self-centering.

As will be understood by a skilled person, the sectionally divided doctor elements 11 may be constructed as one con¬ tiguous doctor that will be able to operate according to the same principle. The advantage of sectionally dividing the doctor into a plurality of doctor elements 11 is that this permits the use of control pins on the slide table 2 to retain the printing block 1. These control pins will protrude quite slightly above the surface of the printing block and can expediently be positioned in the spaces between the doctor elements 11. For clarity, the wedge- shaped elements 31, 32 are not shown to be provided with holes to attach the elements to the ink vessel frame, but this can expediently take place by means of screws or the like. However, this will be well-known to a skilled person.

Fig. 4 is a perspective view of the ink vessel frame 28. The doctor 11 of fig. 3 with wedge elements 31, 32 is secured to the front 50 of the ink vessel frame 28 in the preferred embodiment. As mentioned previously, this can take place by means of screws. In this embodiment the underside of the ink vessel frame 28 is formed with five substantially rectangular recesses to receive the ink vessel 5. These ink vessels are preferably replaceable and are shown in figs. 5-7. Thus, depressions 52 will be formed along at least part of the rim of the recesses 51, said depressions 52 in combination with corresponding complementary projections 53 on the ink vessels serving as a snap lock. The ink vessels 5 are hereby retained in the ink frame 28 in a safe and releaseable manner.

Fig. 5 is a perspective view of an ink vessel and shows that this ink vessel has a substantially box-shaped struc¬ ture that can be received in the ink vessel frame 28. As mentioned, the ink vessel 5 has projections 53 which are complementary with the depressions 52 on the ink vessel frame, as well as a carrier plate 6 on which the ink pad 7 is mounted. A layer 56 of silicone or a similar material may expediently be applied around the edge of the ink pad so as to block the pores in the transverse direction of the ink pad originating from the orientation of the fibres. This ensures that pumping of ink does not just bring the ink to the edge of the ink pad. Fig. 6 is a sec¬ tional view of the ink vessel and shows that the carrier plate 6 has perforations 54 at one end. This appears more clearly from fig. 7, which shows five perforations 54 close to the edge of the ink vessel. When the ink pad 7 of the ink vessel 5 slides across the printing block, the ink spreads from these perforations 54 so as to soak the en- tire sponge. However, nothing prevents the performations from being provided in another pattern. As regards the pressure exerted by the pad printing machine on the printing block, it will be expedient to provide the ink vessel 5 with a central brace 57 to obtain the stiffest possible carrier plate 6. This is the case in particular when the ink vessel is substantially made of plastics. It is moreover visible from fig. 6 that the ink vessel, when it is not mounted in the ink vessel frame, may be provided with a cover 55 that forms a tight seal. This also avoids evaporation from the ink vessel when this is not in use. A natural fibre sponge cloth having a textile reinforce¬ ment is presently preferred as the ink pad. Such a sponge cloth may be made of cellulose (wood fibres) and is e.g. of the type manufactured by the French company Spontex.

The ink pad may suitably have a thickness of the order of e.g. 3 - 6 mm and a water absorption capacity of 2 - 10 1/m² depending upon the purpose. As mentioned, the ink pad may be made of cellulose fibres, and this cellulose fibre structure may be reinforced by cotton fibres or the like and optionally with a polyester net. The ink pad will then be extremely stable and be capable of withstanding the stresses to which it is subjected in use. If it is deemed expedient owing to wear or the like, the cellulose fibre sponge may be coated with a textile layer, e.g. of silk. However, other types of ink pads can also be used if they have expedient absorption capacities and resistance to the chemicals forming part of the inks and the necessary me¬ chanical stability.

In an embodiment (not shown) of the invention the ink vessels 5 are adapted to be secured to the ink vessel frame 28 in that these are pushed into position from the end. The front wall 50 of the ink vessel frame 28 will then be open in extension of the recesses 51, so that the ink vessels 5 may be introduced from there. The ink vessels are then retained when the wedge-shaped elements 31, 32 are mounted on the ink vessel frame 28.

Claims

P a t e n t C l a i m s :

1. A method of applying ink to a printing block (1) by a pad printing process, wherein the ink (30) is transferred from an ink reservoir (5) to a print pattern on the print¬ ing block (1), and wherein a flexible pad (15) then trans¬ fers the ink to an object (60) to be printed, c h a ¬ r a c t e r i z e d in that ink (30) is applied to the printing block (1) from the ink reservoir (5) through an ink pad (7) which is porous and can contain ink, and which is caused to contact the printing block (1) during the application.

2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the the ink pad (7) is in the form of a thin plate which is caused to engage the printing block (1) during the application of ink.

3. A method according to claim 1 or 2, wherein excess ink is wiped off the printing block by a doctor (11), c h a ¬ r a c t e r i z e d in that when wiping off the excess ink the ink pad (7) is lifted at its side facing away from the doctor (11) while the doctor (11) wipes off excess ink from the printing block (1) .

4. A pad printing machine for transferring a print pattern from a printing block (11) to an object (60), comprising an ink reservoir (5) from which ink is applied to the printing block (1), as well as a wiper means (11) for wiping off excess ink from the printing block (1) before the print pattern is transferred to the object (60) by a flexible pad (15), c h a r a c t e r i z e d by a flexible ink pad (7) through which the ink is transferred from the ink reservoir (5), and which has a plane side which is caused to contact the printing block (1) during the application of ink, said ink pad (7) being compres¬ sible and being made of a material permeable to the ink.

5. A pad printing machine according to claim 4, c h a - r a c t e r i z e d in that the ink pad (7) is made of natural sponge with the fibres extending substantially in parallel with the engagement side of the sponge.

6. A pad printing machine according to claim 4 or 5, c h a r a c t e r i z e d in that the ink pad (7) is re¬ inforced with woven textile fibres.

7. A pad printing machine according to claims 4-6, c h a r a c t e r i z e d in that the ink pad (7) is coated with a textile layer of e.g. silk on the side fac¬ ing the printing block ( 1 ) .

8. A pad printing machine according to claims 4-7, c h a r a c t e r i z e d in that the ink pad (7) is mounted on a plane face having perforations (54) through which the ink is transferred from the reservoir (5) to the ink pad (7) .

9. A pad printing machine according to claims 4-8, where- in the ink reservoir ( 5 ) comprises one or more replaceable ink vessels, c h a r a c t e r i z e d in that the pad printing machine has an ink vessel frame (28) with holders for releaseable attachment of the exchangeable ink vessel or vessels, said ink vessels being substantially box- shaped and having a plane wall ( 6) on which the ink pad (7) is mounted, said plane wall (6) being provided with perforations (54) through which the ink of the ink vessel is discharged, as well as a printing block holder (2) for detachable mounting of associated printing blocks (1 ) .

10. An ink vessel for use in a pad printing machine and comprising a container with ink, said ink being trans¬ ferred in use through one or more openings (54) to apply part of the ink to a printing block (1), c h a r a c - t e r i z e d in that a plate-shaped ink pad of a spongy material is provided in connection with said openings (54), said ink pad (7) absorbing and transferring the ink to the printing block (1) upon contact with i .