GB2150051A

GB2150051A - Coating surfaces

Info

Publication number: GB2150051A
Application number: GB08331288A
Authority: GB
Inventors: Harry Russel Hopley
Original assignee: HD ENGINEERING Ltd
Current assignee: HD ENGINEERING Ltd
Priority date: 1983-11-23
Filing date: 1983-11-23
Publication date: 1985-06-26
Also published as: GB2150051B; GB8331288D0

Abstract

A coating material, particularly a hot melt coating material, is applied to a sheet (1), as it advances around a roller (2), with a spreading member such as a knife blade (20). The knife blade (20) is mounted on a pivotal arm (5). The spacing of the blade (20) above the sheet (1) can be accurately pre- adjusted (e.g. with a screw (30)) and the arm (5) can be pivoted to lift the spreading member temporarily away from its pre- adjusted spreading position. The spreading edge (21) of the spreading member is radially aligned with the pivot axis (7) of the arm (5) and the spreading edge moves in an arc towards and away from the roller (2) as the arm (5) pivots. The spreading member may comprise a knife blade (20) which has a reservoir (19) for the coating material. The reservoir (19) is closed except for an inlet (28) which is connected to a supply of the material and an outlet in the form of a narrow gap (between plate 22 and blade 20) which discharges along a rear face of the blade (20). <IMAGE>

Description

SPECIFICATION Coating surfaces This invention relates to the application of thin coatings to surfaces.

A known procedure for applying a thin coating of a plastics material to a substrate in sheet form involves the use of a plastisol which is spread uniformly with a knife blade over the substrate as this is advanced around a roller. In order to obtain a coating of desired uniform thickness whilst avoiding snagging of the blade on raised parts of the sheet (particularly seams) it is known to provide a mechanism which incorporates a screw device for fine pre-adjustment of the spacing of the blade and web, and a lift-off device which can be used to effect rapid movement of the blade away from the substrate and subsequent return thereof to the pre-adjusted spacing.

One such mechanism, as described in U.K.

Patent Application 2104804, comprises a beam which supports the blade and which can be moved about a hinge to lift and lower the blade relative to the roller for adjustment of the spacing and also for lift-off purposes.

With this arrangement, however, due to the mode of movement of the blade relative to the roller, it can be difficult to select and maintain very small spacings with acceptable accuracy and this can be particularly problematical in relation to the substitution of hot melt coatings for plastisols.

In the case of plastisols a relatively thick layer can be applied to the substrate in so far as this forms the required thin coating after evaporation of the plastisol solvent.

Hot melt coatings may be preferable since wasteful and inconvenient solvent evaporation is not required; it is only necessary to allow an applied layer to cool and set. However, in order to obtain a thin coating a correspondingly thin layer of material has to be applied in the first instance.

One object of the present invention is to provide a coating apparatus with which it is possible accurately and convenientiy to select and maintain very small spacings between a spreading member and a substrate advanced around a roller.

According to one aspect of the invention therefore there is provided apparatus for applying a coating to a substrate in sheet form advancing around a roller, said apparatus having a spreading member with a peripheral elongate structure thereto arranged to be located at a spreading position immediately over the surface of said substrate on said roller and extending transversely to the direction of substrate advancement, supply means for supplying a fluent coating material to said substrate surface to be spread thereon by said structure, an arm mounted on a pivot supporting said spreading member, an adjustment mechanism for pivoting said arm for preselectingthe spacing of said substrate surface and saidstructure insaidspreading position and also for moving said structure away from said spreading position thereof, characterised in that said structure faces towards the said pivot whereby said pivoting of the arm effects movement of said structure in an arc towards or away from said surface.

With this arrangement it is possible to achieve accurate control of the spreading position of the said structure even where very small spacings between this and the substrate surface are involved. The apparatus of the invention is therefore particularly suitable for use in the context of hot melt coating materials. It is, however, to be understood that the invention is not intended to be restricted to such materials and the apparatus may also be used, for example, with plastisol or organisol coating materials.

Similarly, although it is visualised that the spreading member will most suitably comprise a knife blade (whereby the said structure will be a knife edge of the blade), any other kind of spreading member may be used, such as a spreading roller (in which case the said structure would be the elongate portion of this roller which contacts the coating material or transfer roller at the nip with the roller supporting the substrate).

Most preferably the said spreading structure is aligned accurately with the said pivot (i.e.

in the case of a blade a radial plane through the knife edge constitutes or is parallel to the mid-plane of the blade), although if desired the said structure may be out of alignment being slightly offset laterally and/or slightly inclined away from the pivot.

In a particularly preferred embodiment, the pivot arm and spreading member are arranged so that the said pivot and the said structure are respectively below and above the axis of the roller supporting the substrate. In this case, the arrangement is preferably such that pivoting of the arm to move the structure away from the spreading position brings this to a rest position at which it is spaced laterally from the support roller. Advantageously drips of coating material from the spreading structure in the rest position can then be collected in a tray or other convenient receptacle, it being understood that with known knife blade arrangements in which lift-off of the blade is effected upwardly there is a tendency for drips to accumulate on the roller.

With regard to the said adjustment mechanism this may comprise any suitable device or combination of devices. Thus, for example, a screw adjustment device may be provided for pre-selection of the spacing, and a piston and cylinder actuator (hydraulically or pneumatically powered) may be used for moving the spreading structure away from the spreading position The piston and cylinder actuator may be connected to the arm between the spreading structure and the pivot, and the screw may operate on the arm at or adjacent to the said structure, the arrangement being such that the actuator moves the arm away from and back to the screw between the spreading and rest positions without disturbing the selected spacing. Other devices and arrangements are, however, also possible.Thus, an accurately controllable dual acting hydraulic or pneumatic piston and cylinder assembly may be provided for pre-selection of the spacing and conveniently this may also be used as the abovementioned actuator. A proportional flow control valve may be used for controlling such assembly.

Having regard to the small operational spacing between the said structure and the substrate surface it is important to minimise backlash particularly in the pivot of the arm and the adjustment mechanism. With this in mind, a spring may be provided between the arm and a fixed stop to take up backlash in the pivot and, if desired, a continuously acting actuator or other device may be used to take up backlash in the adjustment mechanism.

With regard to the said supply means for supplying the coating material to the substrate surface, this may be of any suitable form and thus, for example, where the spreading member comprises a knife blade, the supply means may comprise an open-topped reservoir defined between the knife blade and a wall behind same, of the kind described in the abovementioned Patent Application.However, this kind of reservoir may not be wholly satisfactory in that the coating material may become contaminated with dust and dirt, the reservoir may contain an appreciable quantity of material which may give rise to leakage problems when the spreading member is moved to the rest position and which may involve undue energy consumption where a heated hot melt material is involved, and it may be difficult or inconvenient to ensure spreading of a layer which has a desired profile throughout the entire length of the support roller.

A further object of the present invention is to provide an improved spreading member with which the abovementioned problems can be eliminated or at least appreciably reduced.

According to a second aspect of the present invention therefore there is provided a distribution member, preferably though not necessarily for use as the spreading member of the apparatus of the first aspect of the invention, comprising a blade having a distribution edge thereto, a reservoir which is closed except for an inlet and outlet thereto, said inlet being adapted for connection to a source of material to be distributed and said outlet comprising aa narrow gap extending above and longitudinally of said edge against a rear face of said blade whereby fluent material can flow from said reservoir down said rear face to said blade edge.

Preferably, the said outlet is defined by a gap between the rear face of the blade and an edge of a plate and provision may be made for adjusting the gap along its length to give a desired profile for the outlet. Thus, the plate may be supported on a pivot and may be provided with multiple fixing screws or the like which can be tightened by different amounts thereby to distort the plate slightly as desired. The reservoir may be directly in contact with this plate or may be in communication therewith via a channel or channels and an auxiliary reservoir to facilitate slow, controlled flow of material.

The member may be used for spreading or for providing a coating curtain.

The member may further comprise heating means, for heating the contents of the reservoir, comprising an electrical heater or a passage for circulated hot oil or the like.

The invention will now be described further by way of example only and with reference to the accompanying drawing which is a diagrammatic part-sectional view of one form of coating apparatus according to the invention.

With reference to the drawing, coating apparatus for applying a thin coating of a thermoplastics material to a substrate in sheet form such as a paper web 1 comprises a metal roller 2 which is rotatably mounted about a horizontal axis 3 between fixed opposite end plates 4 (only one of which is shown). The roller 2 is drivably connected to an electric motor and feed and take-up rollers are provided (not shown) all in conventional manner.

At each end of the roller 2 there is a respective upright arm 5 which is pivotally mounted (at 7) on the adjacent end plate 4 below the roller 2 near to the bottom end 6 of the arm. A respective springy steel element 8 is fixed to and extends downwardly from each arm 5 at its bottom end 6 and the two elements 8 have notches 9 which are engageable with a fixed rod 10 extending between the end plates 4 parallel to the roller axis 3.

The two arms 5 are linked by a pivot pin 11 slightly above the pivots 7 and one end of a dual acting piston and cylinder actuator 1 2 is pivotally connected to this. The other end of the actuator 1 2 is connected via a pivotal link 1 3 to the fixed end plates 4.

The two arms 5 are further linked by a knife blade assembly 14 adjacent the top ends of the arms 5 above the roller 2. This assembly 14 comprises first and second elongate blocks 15, 1 6 which are screwed to each other and to the end plates 5. The first block 1 5 is stepped at positions 17, 1 8 along opposite sides, and the second block 1 6 is generally Lshaped in cross-section.An elongate reservoir 1 9 is defined between the angle of the L shaped block 1 6 and one of the stepped positions 1 8. An elongate knife blade 20 is fixed with screws within the recess defined at the other stepped position 1 7. The blade 20 is flat and straight and projects downwardly beyond the block 1 5. The blade 20 is chamfered to give a sharp bottom edge 21.The Lshaped block 1 6 terminates at a position slightly spaced from the blade 20 and a flat, straight plate 22 is fixed to the outer side of the bottom of the block 16, such plate 22 having a sharply chamfered edge 23 which terminates close to a back face 24 of the blade 20 so that an elongate auxiliary reservoir 25 is defined between the blade 20, the plate 22 and adjacent ends of the blocks 15, 1 6. A pivot member 26 is trapped between the plate 22 and the block 1 6. The top surface of the bottom part of the block 1 6 has a plurality of side-by-side parallel grooves 27 therein along the entire length block 1 6 and these provide communication between the reservoirs 19, 25.The blade 20 and the plate 22 extend along the entire length of the roller 2 between the end plates 4 and are fixed to the respective blocks 15, 1 6 by multiple pairs of screws at longitudinally spaced positions.

An inlet 28 extends through the block 1 6 in communication with the reservoir 1 9.

An elongate open-topped tray 29 is fixed between the end plates 4 at one side of the roller 2. At the other side, at each end there is a respective micrometer screw 30 engaged with a threaded block 31 fixed to the adjacent end plate 4. The screws 30 project beyond the blocks 31 for engagement with the block 15.

As shown in the drawing, the back face 24 of the blade 20 which is planar and contains the sharpened edge 27 (i.e. is on the opposite side to the chamfer) lies in a radial plane with regard to the pivot axis 7. This radial plane extends through the axis of the stop 10 and the pivot axis 11 is offset to one side of this (i.e. the opposite side to the screw 30, the springs 8 and the roller axis 3, and on the same side as the tray 29).

The blade 20 is ground so that the sharp edge 21 has a profile which corresponds along its length as closely as possible to the surface of the roller 2. This may be achieved by grinding the blade 20 on the metal surface of the roller.

The plate 22 is tightened against the block 1 6 with the respective fixing screws so that a very small gap is defined between the plate 22 and the blade 20. The gap may be uniform or the screws may be tightened by different amounts so that the gap is of nonuniform shape as desired, this being facilitated by the pivot 26.

In use the web of sheet material 1 to be coated is advanced clockwise around the roller and the inlet 28 is connected to a supply of heated hot melt coating material so that this flows into the reservoir 1 9 and from there via the groove 27 into the reservoir 25. The knife blade 20 and adjacent parts may be heated for example by circulation of hot oil through a passage 32 in the block 1 5.

The actuator 1 2 is operated to cause the arms 5 to pivot clockwise (as seen in the drawing) to bring the springs 8 into resilient abutment with the stop 10 and the block 1 5 into engagement with the screws 30. The screws 30 are adjusted so that the edge 21 of the knife blade is a predetermined small distance above the roller surface as determined by the required coating thickness. The actuator 1 2 holds the block 1 5 against the screws 30 thereby to eliminate backlash therein, and the tensioned springs 8 compensate for backlash in the pivot 7.

Hot melt coating material trickles through the gap between the blade 20 and the plate 22 and runs down the back face 24 of the blade 20 onto the moving web 1 to be spread thereon to a desired thickness. The coated web is cooled as it leaves the roller and the coating material sets.

It will be seen that movement of the screws 30 causes the knife blade edge 21 to move in an arc about the pivot 7 towards and away from the roller surface, the direction of movement of the edge being perpendicular to the blade face 24. With this arrangement very small adjustments in the spacing of the edge 21 and the roller surface can be achieved reliably and accurately.

In the event that it is required to move the blade 20 away from its spreading position for example to provide access to the roller 2 or to allow snag-free passage of a raised part of the web such as a seam, this can be achieved by operating the actuator 1 2 to pivot the arms 5 anticlockwise away from the screws 30 until the blade 20 is in a rest position over the tray 29 clear of the roller. Hot melt material dripping from the blade 20 is collected in the tray 29 in this position. Subsequently the blade 20 can be moved back into its desired spreading position without disruption of the preselected spacing by operating the actuator 1 2 to pivot the arms 5 clockwise until the block 1 5 engages the screws 30.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

For example. the actuator 1 2 and the screws 30 can be connected to the arms 5 at any suitable position not necessarily as shown. Thus. it may be convenient to mount the actuator 1 2 alongside one screw 30 connected to the top part of the adjacent arms 5 on the same side as the screw 30. Also, instead of the adjacent screws 30 it may be possible to use a proportional flow valve which controls the actuator 1 2, such valve having a central valve member which acts to distribute pressure fluid between two outlets connected to opposite sides of the piston of the actuator, the relative flows through the outlets being determined by the positioning of the valve member which can be set with a micrometer. In this case a solenoid valve may be provided to override the valve to permit movement of the blade to the rest position.

Claims

1. Apparatus for applying a coating to a substrate in sheet form advancing around a roller, said apparatus having a spreading member with a peripheral elongate structure thereto arranged to be located at a spreading position immediately over the surface of said substrate on said roller and extending transversely to the direction of substrate advancement, supply means for supplying a fluent coating material to said substrate surface to be spread thereon by said structure, an arm mounted on a pivot supporting said spreading member, an adjustment mechanism for pivoting said arm for pre-selecting the spacing of said substrate surface and said structure in said spreading position and also for moving said structure away from said spreading position thereof, characterised in that said structure faces towards the said pivot whereby said pivoting of the arm effects movement of said structure in an arc towards or away from said surface.

2. Apparatus according to claim 1, wherein said spreading member comprises a knife blade and said structure comprises a knife edge of said blade.

3. Apparatus according to claim 2, wherein a radial plane through the knife edge constitutes or is parallel to the mid-plane of the blade.

4. Apparatus according to any one of claims 1 to 3, wherein the pivot arm and spreading member are arranged so that the said pivot and the said structure are respectively below and above the axis of the roller supporting the substrate.

5. Apparatus according to claim 4, wherein the arrangement is such that pivoting of the arm to move the structure away from the spreading position brings this to a rest position at which it is spaced laterally from the support roller.

6. Apparatus according to claim 5, further including a receptacle for collecting drips of coating material from the spreading structure in the rest position.

7. Apparatus according to any one of claims 1 to 6, wherein said adjustment mechanism comprises a screw adjustment device for preselection of the spacing and a piston and cylinder actuator for moving the spreading structure away from the spreading position.

8. Apparatus according to claim 7, wherein the actuator is connected to the arm between the spreading structure and the pivot and the screw operates on the arm at or adjacent to the said structure.

9. Apparatus according to any one of claims 1 to 6, wherein said adjustment mechanism comprises a piston and cylinder assembly which is used for preselection of the spacing and for moving the spreading structure away from the spreading position.

10. Apparatus according to claim 9, wherein a proportional flow control valve is used for controlling the piston and cylinder assembly.

11. Apparatus according to any one of claims 1 to 10, wherein a spring is provided between the arm and a fixed stop to take up backlash in the pivot.

12. Apparatus according to any one of claims 1 to 11, wherein a continuously acting actuator is provided to take up backlash in the adjustment mechanism.

13. Apparatus according to claim 2 or any claim dependent on claim 2. wherein said supply means comprises an open-topped reservoir defined between the knife blade and a wall behind same.

14. A distribution member, particularly for use as the spreading member of the apparatus of any one of claims 1 to 1 3, comprising a blade having a distribution edge thereto, a reservoir which is closed except for an inlet and outlet thereto, said inlet being adapted for connection to a source of material to be distributed and said outlet comprising a narrow gap extending above and longitudinally of said edge against a rear face of said blade whereby fluent material can flow from said reservoir down said rear face to said blade edge.

1 5. A distribution member according to claim 14, wherein said outlet is defined by a gap between the rear face of the blade and an edge of a plate and provision is made for adjusting the gap along its length to give a desired profile for the outlet.

1 6. A distribution member according to claim 15, wherein the plate is supported on a pivot and is provided with multiple fixing screws which can be tightened by different amounts thereby to distort the plate and attain the said desired profile.

1 7. A distribution member according to any one of claims 14 to 16, wherein the reservoir is in communication with the plate via a channel or channels and an auxiliary reservoir.

1 8. A distribution member according to any one of claims 14 to 17, further including heating means for heating the contents of the reservoir.

1 9. Apparatus according to claim 2, or any one of claims 3 to 12, when dependent on claim 2, wherein said spreading member com prises the distribution member of any one of claims 14 to 18.

20. Apparatus according to claim 1, sub stantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

21. A distribution member according to claim 14, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

22. Apparatus according to any one of claims 1 to 13,or 20 when used in the application of a hot melt coating material.

23. A distribution member according to any one of claims 14 to 18 or 21 when used in the application of a hot melt coating material.