GB2336428A

GB2336428A - Method and apparatus for thermography

Info

Publication number: GB2336428A
Application number: GB9807945A
Authority: GB
Inventors: Peter Colin Galilee
Original assignee: FAUST THERMOGRAPHIC SUPPLY Ltd
Current assignee: FAUST THERMOGRAPHIC SUPPLY Ltd
Priority date: 1998-04-14
Filing date: 1998-04-14
Publication date: 1999-10-20
Also published as: GB9807945D0

Abstract

An apparatus and method are disclosed for selective removal of thermographic material from a substrate (2) comprising magnetic material, in which suction is applied to the substrate to effect the removal while the substrate is maintained in position, despite the force due to the suction, by a magnetic field applied by magnet 116. The substrate may be concurrently advanced along a feed direction, eg. by a conveyor (104). Also disclosed is a method and apparatus for selective removal of material from a thermographic substrate in which the substrate is mechanically agitated, eg. by a reciprocally driven hammer (126) to assist in detaching material therefrom so that it can be removed eg. by suction.

Description

2336428

1 DESCRIPTION METHOD AND APPARATUS FOR THERMOGRAPHY

Thermography is a process by which raised markings are produced on a substrate. The technique has typically been used for marking sheets of substrate - ie. individual pieces, such as sheets of paper. The substrates used have traditionally been lightweight - particularly paper and flexible.

In known thermographic processes, finely chopped or ground solids or other materials, typically resins, are applied to a pre-printed substrate by sprinkling, dipping or other means. Such materials may be applied singly or in combination. The substrate then passes into a suction section, which removes the thermographic material from the non-printed areas. This is accomplished by applying suction near to the surface of the substrate. Following this the subgrate may be further processed, for example by heating, which in the case of resin would cause the resin material to melt, flow and create a raised surface.

Apparatus for a conventional thermographic process is illustrated schematically in Fig. 1. Sheets 2 of-zubstrate (in this case paper) are borne by a conveyor (or a series of conveyors) 4 and moved thereby in the direction indicated by arrow (1 tom right to left. Before reaching the illustrated apparatus, selected a of the sheets, corresponding to the areas to be thermographically marked, have been printed with ink or glue 2 by a printing machine of well known type. Thermographic material 8 is deposited from a variable rate hopper 10 onto the upper surface of the sheets, which then pass forward to a thermographic material removal system 12 which operates by suction. The system 12 comprises a semi sealed suction box 14 into which air is drawn through an inlet 16 disposed immediately above the conveyor, so that the sheets pass under the inlet 16 and are subjected to suction. The inlet 16 is illustrated at an enlarged scale in Fig. 2, and is provided with wheels or rollers 18 which bear on the sheets 2 as they pass to prevent the sheets from being sucked upward to the inlet itself.

The effect of the suction is to remove the thermographic material from the non-printed areas of the sheets 2, while in the areas to be marked some of the thermographic material adheres to the ink or glue and so remains in place. The material removal system 12 comprises a cyclone suction system effective to extract ultra fine particles and recycle useable thermographic material by returning it through valve 20 to the hopper1O.

The sheets of substrate then pass through a heating system 22 which causes the thermographic material to melt and flow or partially flow. The sheets of substrate then pass through a cooling system 24 and then on to a delivery tray or stacking system (not shown).

Resins typically used in the process have been thermoplastic, 3 typically shellac-based or polyamide-based.

Attempts to produce thermography on heavy, inflexible or, in particular, metal substrates have encountered a number of problems: (a) marking of the substrate by the wheels or rollers of the suction system used to remove excess powder from the areas not requiring thermography; (b) the adhesion of small amounts of thermographic material to the non-printed side of the substrate, which could potentially cause problems bearing in mind potential food packaging use, or the necessity to form and seam the thermographed substrate, for example, into containers; (c) surface coatings sometimes used on such materials which are naturally retentive of thermographic materials by virtue of static electricity, which can result in incomplete removal of surplus thermographic material from the substrate and consequent blemishes on the substrate.

The present invention is intended to overcome or alleviate one or more of the above problems.

Referring to point (a) above, attempts to produce thermography on heavy or inflexible substrates, or onto a web (continuous reel) have encountered a number of problems, one of which is the tendency for such substrates to scuff or mark where the wheels or rollers of the known suction apparatus are in contact with the printed area. This can cause smearing or wiping of the printed image and can disturb the 4 thermographic material such that blemishes are left in the finish. These problems are less obvious on lightweight sheet substrates since such substrates rise up against the wheels or rollers and conform to their movements. Problems arise when using heavy, inflexible, or web substrates, due to differential movement between the wheels or rollers of the suction apparatus and the substrate.

The problems described above for processing heavy and inflexible substrates, pertain for metal substrates such as sheet steel or tinplate.

G132315544, standing in the name of the present applicant, describes a thermographic apparatus in which the substrate is held away from the material-removing suction inlet above by means of a restraining suction inlet below. The constructional complexity of this arrangement is disadvantageous.

In accordance with a first aspect of the present invention, there is provided a suction apparatus for use in thermography for selective removal of thermographic material from a substrate comprising a magnetic material, the suction apparatus comprising a suction inlet and a magnet arranged such that the substrate can be moved past the inlet while separation of the substrate from the inlet is maintained by the effect of the magnet on the substrate.

Suitable substrates include sheet metal eg. tin plate or sheet steel.

The magnet in question may be a permanent magnet, or may be an electromagnet or other magnetic field generating means.

The apparatus does not require rollers or other means bearing on the substrates' printed surface, and hence avoids damage to substratelmarkings.

In one preferred embodiment of the present invention, a surface of the magnet over which the substrate is moved is curved to correspondingly curve the substrata. curvature of the substrate can improve removal of excess material.

The magnetic material of the substrate must be capable of interaction with a magnetic field, but need not be permanently magnetised.

In accordance with a second aspect of the present invention, there is an apparatus for use in thermography for selective removal of thermographic material from a substrate, comprising means for agitating the substrate such as to detach or assist in detaching thermographic material from the surface of the strate and means for applying suction to the substrate for removal of this thermographic material.

In this way, removal of unwanted material is improved.

Also according to the pre invention, there is a method of selective removal of thermographit material from a thermographic substrate comprising magnetic material, the method comprising applying suction to the printed surface of the substrate for effecting the selective 6 removal of material while maintaining the substrate in position against the force due to the suction by means of a magnetic field.

A further method of selective removal of thermographic material from a thermographic substrate comprises the step of mechanically agitating the substrate to detach or assist in detaching thermographic material therefrom.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which:Fig. 1 is a schematic illustration of a known thermographic apparatus; Fig. 2 is a vertical section through an inlet of the apparatus illustrated in Fig. 1; Fig. 3 is a schematic illustration of a thermographic apparatus embodying the present invention; Fig. 4 is a vertical section through a secondary material removal apparatus forming part of the apparatus illustrated in Fig. 3; Fig. 5 is a perspective illustration of a suction apparatus according to a further embodiment of the present invention for use with a substrate in the form of a continuous sheet or web; Fig. 6 is a vertical section through a suction apparatus according to another embodiment of the present invention, using a continuous belt for 7 delivery of individual sheets of substrate; Fig. 7 is a vertical section through a suction apparatus according to still another embodiment of the present invention, having magnetic rollers, Fig. 8 is a vertical section through an apparatus according to an embodiment of the present invention for removal of thermographic material from the non-printed (rear) surface of the substrate; and Fig. 9 is a vertical section through a further apparatus according to an embodiment of the present invention for removal of thermographic material from the non-printed surface of the substrate.

The apparatus embodying the present invention illustrated in Fig. 3 has, like the conventional apparatus illustrated in Fig. 1, a conveyor 102 which transports sheets 104 of a substrate to be thermographically marked in a direction from right to left in the drawing, past/through a hopper 106 by which thermographic material is deposited on the sheets, a suction apparatus 108, a heater 110 and a cooler 112. The illustrated embodiment further comprises a sndary material removal system 114 past which the sheets are moved.,, The sheets 104 comprise a magnetic material - that is, they comprise a material which can ict with a magnetic field resulting in a force. They may for example be ts of tin plate for use in packaging. The thermographic material used,inthe Fig. 3 embodiment of the present invention is in powder form.

8 The suction apparatus 108 of the illustrated embodiment of the invention differs from the conventional apparatus described above in that no wheels or other means contacting the upper surface of the sheets 104 is provided to prevent the sheets from being drawn toward the suction inlet 118. The illustrated embodiment comprises a magnet 116 disposed beneath the path of the sheets 104 (in the illustrated embodiment, it is beneath the conveyor 102) and in the vicinity of the inlet 118 of the suction apparatus. As the sheets 104 move past the suction inlet 118, they are drawn against the conveyor 102 by the magnet and so prevented from upward motion toward the inlet. The problem of marking the upper surface of the substrate by the wheels or rollers of the existing suction apparatus is thereby overcome.

After passing the suction apparatus 108, the substrate proceeds to the secondary material removal system 114, details of which are illustrated in Fig. 4.

In the secondary material removal system the substrate is vibrated so that the thermographic material momentarily becomes airborne and may be removed from the substrate by suction. In this case high volume low pressure air is utilised, and substrates are selected for the process such that their weight is sufficient to prevent the substrate from being drawn into the suction apparatus, if in sheet form. If the substrate is in the form of a continuous web or reel, then the substrate should be held in 9 tension or otherwise prevented from being drawn toward the suction tube.

The system comprises cyclone suction means 120 connected via a duct 122 (see Fig. 3) to an inlet opening 124 adjacent the upper surface of the conveyor, to apply suction to the sheets 104 of substrate as they pass. Compared with the suction apparatus 108, the secondary material removal system applies suction air at a lower velocity.

A hammer 126 disposed below the conveyor is reciprocally driven by a crank 128 to repeatedly impact against the underside of the conveyor, thereby vibrating the substrate and causing any particles of the thermographic material remaining on the non-printed portions of the sheets 104 to become detached therefrorn and to be drawn into the inlet opening 124.

The sheets 104 pass from the secondary material removal system to the heater and then the cooler.

Alternative embodiments of certain parts of the above described apparatus will now be described. --.

Fig. 5 concerns an appa for thermographic marking of a substrate formed as a continuous sheet or web 150. In this apparatus no conveyor surface carries the substrate, which may instead be drawn through the apparatus onto eg. a drum. The figure shows the inlet, again labelled 118, of the suction appa and below it the magnet 116 over whose upper surface 152 the substrate rides, being held down onto this surface by magnetic attraction.

It must be understood that the term "magnet" as used herein is not limited to permanent magnets - it encompasses electromagnets and indeed any other source of magnetic field by which the substrate can be subjected to a force..

While in the illustrated embodiment the surface 152 of the magnet over which the substrate rides is planar, it may instead by shaped to form a curve in the substrate.

Fig. 6 shows in section an alternative arrangement of the system for sheet-fed work. An endless belt 160 conveys sheets of substrate 162 above the magnet with suction applied from above to remove excess thermographic material. Surfaces of the magnet may be flat or curved. In order to reduce friction between the endless belt and the magnet, small wheels or rollers (not shown) may be interposed between the belt and the magnet, preferably in a staggered arrangement, and preferably partially recessed into the surface of the magnet.

Fig. 7 illustrates a further exemplary embodiment of the present invention comprising magnetic rollers 170 beneath a continuous web or reel 17 with suction applied from above. Arrangement of the rollers may be as shown, or they may be arranged so as to form a curve in the web or reel. Rollers of this type may replace the magnet used in any of the above described embodiments.

11 A conveyor or endless belt is not essential even where the substrate is sheet-fed; the substrate may be pushed, pulled or otherwise forwarded past the magnet and suction inlet.

It has been noted above that adhesion of small amounts of thermographic material to the non-printed side of the substrate could potentially cause problems in food packaging uses, or when further processing the thermographed substrate, for example by forming or seaming. Apparatus for removing thermographic material from the nonprinted face of the substrate is illustrated in Fig. 8. This may be incorporated in an apparatus of the type illustrated in Fig. 3 (or indeed, where necessary, in a conventional thermographic apparatus such as that shown in Fig. 1) and is disposed at a point in the substrates' path prior to the heater.

This apparatus comprises a semi-sealed suction box 200 so arranged as to be in contact with or adjacent the non-printed side of the thermographed substrate 202 which is travelling in direction 204 while suction is applied to remove thermographic material 206 from the substrate. Wheels 208 support the substrate preferably hold it clear of the apparatus.

An alternative apparatus for removing thermographic material from the nonprinted face of the substrate is illustrated in Fig. 9, and comprises a suction tube 250 placed between rollers or conveyors 252 to remove 12 thermographic material from the non-printed surface of the substrate 256. This system is suitable for relatively rigid materials which would resist curvature sufficiently to prevent them being sucked into the suction system, and preferably utilises a relatively small diameter roller or conveyor turn point-for example 20 mm or less-in order to minimise the gap between the two rollers or conveyors.

Claims

13 CLAIMS

1. A suction apparatus for use in thermography for selective removal of thermographic material from a substrate comprising a magnetic material, the suction apparatus comprising a suction inlet and a magnet arranged such that the substrate can be moved past the inlet while separation of the substrate from the inlet is maintained by the effect of the magnet on the substrate.

2. A suction apparatus as claimed in claim 1, wherein the magnet has a substantially flat surface over which the substrate is moved.

3. A suction apparatus as claimed in claim 1, wherein a surface of the magnet over which the substrate is moved is curved to correspondingly curve the substrate.

4. A suction apparatus as claimed in claim 1, wherein the magnet is formed as a wheel or roller.

5. A suction apparatus as claimed in any preceding claim wherein the substrate is moved by means of a conveyor.

6. A suction apparatus as ced in claim 5, wherein the conveyor runs between the magnet and the suction inlet.

7. A suction apparatus as clakned in any of claims 1 to 4, for use with a substrate formed as an elongate, continuous web, the apparatus providing a path running between ",magnet and the suction inlet along which the substrate can be drawn.

14

8. A thermographic apparatus comprising a suction apparatus as claimed in any preceding claim.

9. An apparatus for use in thermography for selective removal of thermographic material from a substrate, comprising means for agitating the substrate such as to detach or assist in detaching thermographic material from the surface of the substrate and means for applying suction to the substrate for removal of this thermographic material.

10. An apparatus as claimed in claim 9, comprising means for percussively agitating the substrate.

11. An apparatus as claimed in claim 10, comprising a reciprocally driven body arranged to repeatedly impact either the substrate or a body through which the impact is transmitted to the substrate.

12. An apparatus as claimed in claim 11, comprising a hammer driven by a crank, cam or other reciprocal drive means to repeatedly impact either the substrate or a conveyor for bearing the substrate.

13. A thermographic apparatus for use with a substrate comprising a magnetic material, comprising a suction apparatus as claimed in any of claims 1 to 8.

14. A thermographic apparatus as claimed in claim 13, further comprising an apparatus as claimed in any of claims 9 to 12.

15. A thermographic apparatus as claimed in claim 13 or claim 14, further comprising means for applying suction to the non-printed surface of the substrate to remove thermographic material therefrom.

16. A method of selective removal of thermographic material from a thermographic substrate comprising magnetic material, the method comprising applying suction to the printed surface of the substrate for effecting the selective removal of material while maintaining the substrate in position against the force due to the suction by means of a magnetic

17. A method as claimed in eJaim 16, wherein the substrate is, concurrently with the removal of the material, advanced along a feed direction.

18. A method as claimed in claim 16 or claim 17, comprising the further step of application of suction to the non-printed surface of the substrate for removal of thermographic material therefrom.

19. A method of selective removal of thermographic material from a thermographic substrate, the me comprising the steps of agitating the substrate to detach or assist in detaching thermographic material therefrom and applying suction to the substrate for removal of this thermographic material.

20. A method as claimed in claim 19, wherein the agitation of the substrate is percussive.

21. A method of thermography comprising a stage involving selective removal of thermographic material from the substrate as claimed 16 in any of claims 16 to 18 and a further stage involving selective removal of thermographic material from the substrate as claimed in either of claims 19 and 20.

22. A suction apparatus for use in thermography substantially as herein described with reference to, and as illustrated in, any of accompanying figures 3 to 9.

23. An apparatus for use in thermography for selective removal of thermographic material from a substrate substantially as herein described with reference to, and as illustrated in, accompanying Fig. 3.

24. A method of thermography substantially as herein described with reference to accompanying figures 3 and 9.