GB2299298A - Lamination of sheet materials - Google Patents

Abstract

A method of laminating a sheet material is described in which a laminate is constructed from a backing sheet, one face of which is coated with silicone to serve as a release agent. A removable sheet material such as paper is bonded to the silicone coated face of the backing material using a hot melt adhesive, which forms a tacky film on the rear of the removable sheet material. This is exposed when the removable sheet material is peeled away from the backing sheet, to allow the removed sheet material to be stuck to another surface. A typical weight of hot melt adhesive employed is in the range 5 to 200 g.s.m., and the removable sheet material is normally printable material. The backing material may be a film of orientated polypropylene (OPP) film of polyethylene terephthalate (PET) or a paper based material.

Description

Title: Improvements in and relatina to lamination of sheet materials Field of invention This invention concerns methods and apparatus for laminating sheet materials, particularly but not exclusively the lamination of paper onto backing material typically to form a laminated label product.

Background to the invention It has become commonplace to lightly adhere sheet material comprising self-adhesive labels onto a backing sheet. By using a release agent on the backing sheet, so that the labels only lightly attach to the backing sheet, the labels can be peeled away from the backing material, when required to be attached to an object to which the label is to be applied. Typically a pressure sensitive adhesive is used so that after the label has been peeled from the backing sheet, it is only necessary to lightly press the label after it has been positioned on the surface to which it is to be secured, to cause the label to become firmly stuck to its new surface.

Although this type of label is used extensively for envelopes and parcels, product labelling and the like, the invention is of particular application in the food industry and in the labelling of food and drink containers.

It is an object of the invention to provide an improved method and apparatus for forming a laminate of label and backing material.

It is a further object of the invention to provide apparatus for performing the aforesaid method which enables thinner backing material to be employed than typically has been the case hitherto, and which can be operated at high throughput speeds.

Apparatus. methods and products made thereby incorporating the invention (a) Final product The final product of a laminating apparatus and method involving the invention is a laminate constructed from a backing sheet (or web) one face of which has been coated with silicone to serve as a release agent, and a removable sheet (or web) of material, wherein the removable material is bonded to the silicone coated face of the backing material using a hot melt adhesive, which forms a tacky film on the rear of the removable material which remains tacky even at room temperatures, and which is exposed when the removable material is peeled away from the backing material to enable the removed material to be applied readily to a surface of an article on which it is to be stuck.

A typical weight of hot melt adhesive employed is in the range 5 to 200 g.s.m. (grams per sq.meter), and preferably it is a pressure sensitive adhesive.

The removable sheet material may be printable material such as paper.

The backing material may be a paper-based material such as Glassine (Registered Trade Mark).

Alternately and more preferably, the backing material comprises a synthetic film of orientated polypropylene (OPP), or polyethylene terephthalate (PET). This has enabled very thin backing sheet material to be used (of the order of 10-30 microns) whilst still operating the coating and surface treatment Steps, and the laminating step, at throughput speeds much higher than is possible using paper based backing material.

The backing material may to advantage be cleaned before silicone is applied thereto.

(b) Methods of making final product The silicone film may be applied using an offset gravure process or a five roll coater process. The offset gravure process may employ a facility to alter the rotational speeds and/or directions of some or all of the various rollers to permit so called differential offset gravure coating.

A typical coating weight using silicone would be in the range 0.5 to 5.00 gram per sq. metre.

After the silicone film has been applied, the backing material may be subjected to ultra-violet (UV) radiation to cure the silicone material.

Alternatively electron beam curing may be utilised in place of W radiation curing.

Preferably the silicone curing step is undertaken in an oxygenfree environment. By oxygen-free is meant not only totally free of oxygen, but also an environment which is substantially oxygen free, eg to less than 200 parts of oxygen to 1,000,000 by volume.

Preferably the silicone curing step is undertaken in a chamber which is continually supplied with an oxygen-free gaseous medium, such as Nitrogen at slightly in excess of atmospheric pressure.

The materials used for silicone coating may be materials such as radiation curable silicone acrylates as supplied by T H Goldschmidt AG of Essen, Germany.

The backing material may be physically cleaned, for example by brushing the surface thereof.

Where brushing is employed, vacuum suction may be provided in conjunction with the brushing so as to collect particles removed from the surface by the brushing action.

Before applying Silicone release agent to the surface of the backing material, the surface of the latter may be treated so as to provide a good key for bonding silicone thereto.

The surface treatment typically roughens the surface to provide the good key therebetween.

The surface treatment may be electrostatic. This may comprise a corona discharge in close proximity to the surface.

Alternatively flame surface treatment stage may be employed.

A preferred apparatus for surface treatment of OPP film is corona discharge surface treatment apparatus as produced by Sherman Treaters Ltd of Dormer Road, Thame, Oxford, England.

Alternatively, or in addition, backing sheet material may be employed which has a suitably prepared or roughened surface formed thereon either during original manufacture or by an intermediate treatment after manufacture but before the sheet material is employed in the method and/or apparatus described herein.

The surface treatment previously referred to is preferably preceded by surface cleaning as follows: 1. ionisation of the surface of the backing material to which a release agent is to be applied (the said "one surface thereof"), 2. brushing the said one surface thereof, together with vacuum suction for particle removal, and 3. further ionisation of both surfaces of the backing material.

Complete backing web treatment thus comprises the above cleaning steps, followed by corona treatment of the said one surface of the backing material to which the silicone release agent is to be applied, so as to roughen the surface of the material, to improve the adhesion of silicone thereto.

The lamps used in W sources tend also to generate heat, so the W curing step referred to tends to generate considerable local heating. Advantageously infra-red filtering may be provided between the source and the backing material. Such heat as reaches the latter is also dissipated by the movement of the backing material through the curing station. As a consequence, continuous movement of the backing material relative to the W source in combination with infra red filtering prevents the backing material from becoming overheated.

This is particularly important where synthetic materials such as OPP and PET are employed. It has been found that by utilising an appropriate throughput speed and IR filtering and a cooled base plate, melting, distortion or stretching of the OPP or PET film, which could be expected, does not occur.

A problem can arise if there is a temporary shut-down of the line for any reason. Such a shut-down will result in the backing material suddenly becoming stationary in the curing stage. Even if the shut-down also removes power to the W source, there is considerable latent heat in the UV curing chamber and source, and heat damage can occur to any backing material trapped in the W curing stage, which is subjected thereto.

The method may include the step of cooling the backing material if the latter becomes stationary or slows down as it passes through the W curing step. This may be effected by at least one thermally conductive plate located relatively close to the backing material path through the UV curing stage and means is provided for bringing the plate and the uncoated side of the backing material into contact in response to any slow down or stoppage of the material through the W curing stage, whether occasioned by line shut-down or otherwise, so as to absorb heat incident on the backing material and prevent the material from overheating.

The contact may be achieved by moving the plate relative to the material or the material relative to the plate.

So as to provide intimate contact between the plate and the backing material the two may be clamped.

The supply of power to the W source in the W curing stage may also be made conditional on appropriate movement of backing material through the W curing stage. Accordingly, backing material movement sensing means may be provided and a signal derived therefrom may be used to control the supply of power to the UV source. Control means may therefore be provided, sensitive to such a signal, to inhibit the supply of power to the source unless appropriate movement of the backing material is detected.

In addition to the foregoing, shutter means may be provided which is normally open to allow UV radiation to impinge on the backing material, but which can be closed to prevent W radiation reaching the backing material in response to a stoppage or slow down of the material through the curing stage.

Depending on the latent heat to be dissipated, the thermally conductive plate may be provided with cooling means such as passageways and may be cooled by causing air or a cooling liquid to flow therethrough. Additionally, the plate may be formed with cooling fins.

In addition or as an alternative to the provision of a cooling plate, the method may include the step of generating a draft of cooling air by fan means which becomes operational in the event that the backing material ceases to move at an appropriate speed through the W curing station, so as to force cooling air through the curing station and thereby dissipate the latent heat.

The W source is typically a W lamp powered by electricity which is separated from silicone coated backing material by a window of material which transmits W radiation but is relatively resistive to the transfer of infra-red radiation.

Typically the window is formed from quartz. In this way infrared energy generated by the W source is largely kept away from the backing material.

In practice it is found that the W transparency of the window can change with time, possibly due to dirt and dust or build up of process material thereon or for other reasons, thereby reducing the W transmission therethrough. Periodically therefore the apparatus has to be stopped for cleaning the window, when it became apparent that the W curing is not occurring reliably.

The UV curing means may comprise two identical sections in series, each section having a source and a window and being capable, when operating, of effecting UV curing of the silicone coating, the path of the silicone coated backing material extending through both of the sections. By supplying power to the source in only one of the two sections at any one time, the window in the section which is not operating can be cleaned and if necessary be removed for cleaning, and this section is also available for servicing and planned replacement of lamps etc.

The switch-over of power can be automatic so that the process does not need to be stopped to effect the change-over.

The power change-over may be effected gradually over a few seconds in a manner such that a gradual increase of power to the new source is coupled with a gradual decrease in power to the previously operating source, so that as one is brought up to full power the other is faded out.

An alternative and possibly simpler method comprises the use of a single Wsource and at least two windows for use therewith, in which while one window is positioned between the source and the backing material, at least one other window is fully exposed and available for cleaning.

Three or more windows may be provided for example around a rotatable disc.

Preferably in such a disc arrangement, the radial separation between adjacent windows is small so that there is minimal blanking of W as one window is moved and replaced by the next.

Although the narrow spacing between the operating window and the last window to be used may prevent proper access to the latter for cleaning, by providing at least one other window around the disc, the latter will be well clear of the window which is currently in use, thereby enabling it (and each of any other windows which occupy that remote position) to be cleaned.

Whether multiple UV sources or a single UV source with two or more windows are employed, the changeover from one source to another, or the movement of one window to the next, may be effected on a periodic basis as part of a planned maintenance schedule associated with the line. Furthermore cleaning of the inoperative window may be effected automatically by powered cleaning means for removing deposits from the surface of the window.

Where automated cleaning is incorporated, the method may further comprise a cleanness check and the apparatus may further incorporate a W source and a W detector, located on opposite sides of the window, and control means may be provided for re-instating the cleaning sequence in the event that insufficient signal is received by the detector and/or generating a warning signal to indicate that insufficient cleaning has occurred.

Lamination may comprise the step of applying hot melt adhesive to the backing sheet or the removable sheet, or both, before nipping and bonding the sheets together. However a preferred method of lamination comprises selectively coating one face of the removable sheet only with a hot melt pressure-sensitive adhesive and securing the adhesive coated material to the backing sheet with the adhesive in contact with the silicone coated surface of the backing material.

This is of importance when the backing material is liable to distort, crumple or deform if subjected to the temperatures normally associated with molten adhesive of the type used, such as in the case if synthetic sheet material is employed such as OPP or PET.

A laminated product may be produced by the aforesaid method.

(c) Apparatus for performing the methods Apparatus for laminating two webs may perform any of the process steps, up to and including the bonding of the two webs.

Apparatus for performing the methods described herein may be adapted to handle either OPP film, PET film, or paper based backing material such as Glassine (Registered Trade Mark).

(l) Lamination step Apparatus for effecting lamination of a web of silicone-coated backing material and a peelable web material having an adhesive applied to the surface thereof, which is in contact with the silicone- coated surface of the backing material, comprises: 1) means for supporting a roll of backing web material, 2) means for supporting a roll of the peelable web material, 3) take-up means for receiving laminated material and forming a roll thereof, 4) backing web and peelable web tensioning means, 5) corona discharge surface treatment means adapted to roughen the surface of the backing material to improve the key between it and a silicone layer to be applied thereto, 6) silicone coating means for applying a film of silicone to one surface of the backing web material, 7) W curing means situated downstream of the silicone coating means, and 8) laminating means adapted to receive the silicone-coated backing web material and the peelable web material and including a reservoir of hot melt impact or pressure-sensitive adhesive, and means for applying the adhesive as a thin film to one face of the peelable material which material has a path therethrough which causes the adhesive coated surface thereof to be brought into contact with the silicone-coated surface of the backing material, to bond the one to the other to form the said laminate.

(ii) Surface cleaning The apparatus advantageously may include brush means which physically brushes at least one surface of the backing material, and an electrostatic treatment stage located before the brushing stage, to reduce static charge and more readily assist in the removal of particles by the brush.

Electrostatic treatment means also may be provided after the brush means.

Vacuum suction and particle collection means advantageously may be included within the apparatus for collecting particles removed by the brushing action.

The rotary brushing mechanism for cleaning the backing material before surface treatment and application of the silicone film conveniently may comprise two endless belts carrying bristles and adapted to be rotated around two elongated paths in opposite directions, each path length being more than half of but less than the overall width of the said backing material, the two belts being located one below the other with parts of each belt overlapping, the two paths extending from opposite sides of the backing material so that brushing is applied over and across the entire width thereof, and separate vacuum suction means is provided in association with each said belt to separately collect and convey away particles removed from the surface of the backing material by each said belt.

In the laminating means the two webs may be brought into contact in a stage therein subsequent to the adhesive application means.

The adhesive applying means may comprise a slot nozzle and may include one or more heated rollers for backing support, or a so-called offset arrangement of rollers may be employed to coat the web with the adhesive from a suitable reservoir.

The bonding is preferably achieved by squeezing the two webs together between two rollers forming a nip.

The squeezing force may to advantage be adjustable and means to adjust it may be provided, to allow for different substrates, different bond strengths and peelability and the like.

The apparatus as aforesaid may include guillotine means downstream of the laminator to enable a full roll of laminate to be separated from the outflowing laminate to enable the full roll of laminate to be removed.

The laminating means may be located intermediate opposite ends of a machine at one end of which is located a roll of backing material and at the other end of which is located a roll of peelable material. In this way the backing material travels towards the laminator from one end of the machine while the peelable web material travels towards the laminator from the other end of the machine.

The laminator may output the laminated material in a direction towards that end of the machine from which the backing material travels, and the take-up means for the laminated material is located between the silicone curing stage and the laminator.

Since it is preferable for a reasonable period of time to elapse between the UV curing and the lamination of the silicone-coated backing material to the peelable web, an extended path is preferably provided between the output of the UV curing stage and the input to the laminator and preferably this extended path is at an elevated position, thereby providing ample space therebelow for the take-up mechanism and support for the roll of laminated material.

(iii) UV curing staae The W curing stage may include chamber means and a source of Nitrogen for filling the chamber with Nitrogen, preferably at slightly above atmospheric pressure, so as to exclude oxygen from the region surrounding the silicone-coated material facing the W source.

The apparatus may include means for locating different ones of a plurality of quartz windows between the W source and the backing material within the chamber so as to enable the windows to be successively cleaned without the need to stop the line.

Cooling means may be provided for absorbing heat from the coated backing material in the chamber, which is rendered effective immediately the movement of the backing material through the chamber is arrested or slows below a predetermined rate of movement.

The cooling means may comprise one or more plate-like structures formed from thermally conductive material with or without additional cooling such as fluid passages and/or means for circulating cooling fluid therethrough.

(iv) Silicone coating step The silicone-coating stage may for example comprise an offset gravure coating apparatus, which may or may not be operated in a so called differential mode, comprising three rollers, around one of which the sheet material passes, a second roller which forms a nip with the first roller, and a third roller which makes contact with the second roller and transfers thereto a film of silicone derived from a reservoir of silicone which permanently feeds another region of the third roller upstream of the point at which the said third roller makes contact with the second roller.

Alternatively a five roller coating device may be used in place of an offset gravure coating device.

(d) Production of laminated peelable labels A method of laminating a web of backing material to form a peelable label web essentially comprises the steps of coating the backing material with a release agent and the peelable label web with a hot melt adhesive and laminating the two with the adhesive surface of the peelable label material in contact with the release agent coated surface of the backing material.

The method may include the step of subjecting the surface of the backing material to a corona discharge prior to the application thereto of the release agent.

The method may also include the step of physically cleaning the surface of the backing material before the release agent is applied thereto.

The method may also include the step of applying a silicone release agent to the surface of the backing material using an offset gravure process, which may be operated in a so called differential mode.

The method may also include the step of exposing the siliconecoated backing material to UV radiation for a sufficient time to cure the silicone.

A thin film of hot melt adhesive is preferably applied to one face of a web of label material shortly before the latter is brought into contact with the release agent coated surface of a backing material, to perform lamination.

A laminated peelable label product may be made by a method involving some or all of the foregoing steps.

A laminated peelable label product comprises a backing film of synthetic plastics material, coated with a silicone release agent and having lightly adhering thereto a hot melt adhesive coated sheet of face material (such as paper) forming a laminate therewith, the face material being semi-cut and printed to define regions thereof which can be peeled away from the surface of the backing material bearing the release agent, and applied to a container or other object to form a label thereon.

Preferably the hot melt adhesive used in the apparatus and method and the laminated product referred to above is a pressure sensitive adhesive which adheres to relatively smooth surfaces of metal, plastics, wood or card and the like with minimal pressure being required.

A preferred hot melt adhesive is hot melt PSA such as Duro-Tak H1540 adhesive from National Starch and Chemical Company.

Products may have secured to a surface thereof labels peeled away from a laminated peelable label product as aforesaid.

Apparatus for applying labels to objects from a laminated peelable label product as aforesaid preferably includes converging paths one for the laminate and the other for articles to be labelled, means being provided within the apparatus for peeling the backing material of the laminate away from the labels to expose the adhesive coated surface of each label in turn to an appropriate region of an article to be labelled, and with subsequent relative movement of the article and the laminate causing the label to be peeled progressively away from the backing sheet and successively applied to the surface of the object until the whole of the label has been removed from the backing web and applied to the article.

Apparatus constructed and operated as herein described surprisingly has operated satisfactorily to laminate sheet materials in which the backing material is OPP film of 20 microns thickness, which is less than half the thickness of backing material conventionally used for such purposes. It is anticipated that the thickness of the backing sheet material can be reduced to 10 microns or less. One reason for this surprising result, despite using such thin web material, is the use of a cold W curing step for curing the silicone coating.

Additionally the strength of the OPP film, even at 10-30 microns thickness is sufficient to permit high speed operation of the laminating apparatus, and subsequent high speed printing and partial cutting to form labels and the high speed application of the labels to articles to be labelled.

For economic reasons the width of the paper and backing sheet forming the laminate, as aforesaid, is typically a multiple of the width of the labels so that, when printed and semi-cut, a plurality of labels are provided across the width of the laminate. Such a roll of laminated printed material may be guillotined to form a plurality of rolls of labels on backing material, each comprising a long and narrow rolled up length of backing material having individual labels located therealong one after the other at regular intervals.

It is to be understood that the printing of the labels and the cutting of the paper material to form the so-called semi-cuts, may be effected before or after the guillotining of the rolls into individual label width rolls.

Apparatus for coating and laminating, constructed as aforesaid, has been operated at a lamination rate of final product of 200 meters per minute.

Description of the drawings The invention will now be described by way of example, with reference to the accompanying drawings, which show different parts of laminating apparatus for laminating a backing web and part cut adhesive backed material, which when laminated can be printed if desired; and apparatus for peeling cut out areas therefrom in the form of labels, for application to objects to be labelled.

In the drawings: Figure 1 is an elevation of the loading and unwinding stage for the web of backing sheet material; Figure 2 is an elevation showing the backing web tensioning mechanism, and the surface cleaning and treatment of the backing web; Figures 2A and 2B are respectively a sectional elevation and a plan view from beneath cf a UV curving unit for the siliconecoated backing web; Figure 2C is an enlarged elevation of the unit for applying a coating of silicone to the backing web; Figure 2D is a plan view of the silicone coating unit; Figure 3 is an elevation of an intermediate section of the apparatus through which the surface treated backing web is passed at high level, and after being laminated with the surface sheet material is then wound up on a rewind mechanism to form a reel of laminated material; ; Figure 4 is an elevation of the apparatus in which the lamination stage occurs, and to which the backing web is supplied from one side and the label material is supplied from the other side, and from which the laminated material is delivered to a tensioning stage before being wound up on the rewind mechanism shown in Figure 3; Figure 4A is a plan view of a unit for applying hot melt adhesive to the label material; Figure 5 is an elevation of the loading and unwinding station for the face material or label material which is delivered thereto in reels and which corresponds to the loading and unwinding station shown in Figure 1; Figure 6 shows a modification to the lamination stage of Figure 4 to provide an alternative backing web path into the laminator for use with different backing material.

Figure 7 is a cross-section through a laminated product; Figure 8 is a plan view of the laminated product of Figure 7; Figure 9 is a perspective view of part of a labelling apparatus, and Figure 10 is a plan view of part of the apparatus of Figure 9.

Detailed description of the drawings As shown in Figure 1, rolls of backing sheet material such as 10 are located below a crane 12 for lifting and conveying the rolls to an unwind mechanism generally designated 14. This mechanism is of well known design and comprises a rotatable carriage on which two rolls of backing material can be mounted as denoted by reference numerals 16 and 18. Roll 16 serves to supply backing material to the laminating line and roll 18 is available to supply the material when roll 16 becomes exhausted. To this end a flying splice of known design is incorporated so that the leading end of the web material on roll 18 can be spliced to the web material leaving the roll 16 without any interruption in the supply of the web material to the laminating line.

A suitable unwind and flying splice apparatus for this purpose is the machine known as the Dixon 1020 Coating and Laminating Machine made by T H Dixon & Co Ltd of Works Road, Letchworth, England.

The carriage is rotated in the direction of the arrow 20 so that the two rolls switch position. Splicing now occurs and roll 18, which now occupies the position of roll 16, delivers web material to the laminating line whilst the empty roll 16 is now in the load/unload position.

The empty roll 16 is removed using the crane 12, and a fresh full roll such as 10 placed in position so that the full roll is ready to be spliced to the end of the material from the roll 18 when the latter is exhausted.

As shown in Figure 2, the backing web is drawn from roll 16 through a web tensioning stage 22 comprising input and output rollers 24 and 26 and a take-up roller 28 which is tensioned by spring means (not shown).

After passing around guide rollers 30 and 32 the web passes below a walkway 34 and below and above further rollers 36 and 38 so as to pass below a differential offset gravure coating facility (to be described later), below further rollers 40 and 42 and a second walkway 44, so as to arrive at the bottom of a generally vertical path during which the web material will be cleaned and prepared ready to be coated with a release agent, such as silicone, by the offset gravure facility.

The vertical treatment path is defined by rollers 46, 48, 50 and 52 around which the web 54 passes as it rises from roller 42.

Ionisers The coating process which is to follow involves bonding to one surface of the web 54 a thin film of a silicone release agent, so that glued label material will only adhere lightly to the silicone coated surface of the backing web and when required can be peeled away therefrom, to permit the adhesive backed label material to be stuck to objects to be labelled. It is important that the surface to be coated with the release agent is appropriately treated before the silicone is applied and to this end the surface which is to be coated with the release agent is first of all subjected to ionisation by an ioniser 56 and is thereafter physically cleaned by rotating brushes 58.

To ensure good brush contact, the brushing stage 58 is located opposite a roller 48 so that the brushing is applied to a surface of the web material which is stretched around and held in place by the roller 48.

Thereafter both surfaces of the web are subjected to ionisation by two further ionisers 60 and 62.

Each of the ionisers is supplied with high frequency single polarity electrical pulses, and each is intended to neutralise the build up of electrostatic charge on the web which can occur due to friction as the web material is unwound. The presence of electrostatic charge of this nature causes dust particles to adhere to the web surface and can also have an effect on the ability of the web material to take up the release agent.

The polarity of the charged ions delivered by each of the ionisers is selected so that it will tend to conduct away electrostatic charge built up on the web material. In general the charge built up on the material will tend to be of one polarity or the other, depending on the material and the environment producing the build up of electrostatic charge.

To this end an initial charge polarity test will allow an appropriate selection of the ionising polarity.

Brushing at 58 can also induce electrostatic charge on the web material, and it is partly for this reason that the additional ionisers 60 and 62 are provided beyond the brushing stage.

Preferred ionisers for neutralising the electrostatic charge operate at a pulsed positive DC frequency of > 30kHz and at a wire potential of approximately 28kV.

An example of an ioniser which may be used comprises a Wandra Surface Cleaning Module Type BRE 41/1/300 including a Lirus No.

STATIC 08 Ionising System as manufactured and supplied by Drive Lines Technologies Ltd of Bedford.

Around and to the rear of the brushes 58 is provided a manifold 64 connected to a vacuum suction device (not shown) so that particulate material removed from the web by the brushing action will tend to be removed by vacuum suction and conveyed away from the web.

Surface preparation Between rollers 50 and 52 the web material is looped around a larger roller 66 located in a housing 68. The latter contains a corona discharge facility which acts on and treats the same surface of the web material which has been brushed by the brushes 58. A corona discharge treatment serves to appropriately prepare the surface of the material to receive a thin film of silicone during a subsequent stage of the processing, and a preferred apparatus for this treatment is the electrostatic surface treater type GX40R manufactured and supplied by Sherman Treaters Ltd of Dormer Road, Thame, Oxford.

This operates to supply up to 30A (RMS) at 600V (RMS) at a frequency in the range 10-26 KHz, and maximum treatment power available is of the order of 4 KW.

Silicone coating After corona treatment 68, the web 54 is now ready to receive a film of silicone release agent, and after passing around guide rollers 70 and 72 the web 54 descends towards a silicone coating facility 73. As best seen in Figure 2C, this facility comprises: a small adjustable pressure roller 74, a driven backing roller 76, a coating or applicator roller 78, a gravure etched transfer roller 80, a small tray or trough 81 for containing silicone material, and a doctor blade 81A engageable with the roller 80 to control the thickness of silicone film picked up by the roller. The web passes around the roller 74 and around the backing roller 76 before it leaves the facility 73 to pass in an upward direction towards and around an upper roller 82.

The backing roller 76 is chrome plated steel, and the roller 74 is adjustably mounted to provide a good nip between it and the backing roller 76. The rollers 74 and 76 are together also adjustably mounted relative to the roller 78 (eg by means of screw wedges, not shown) in order to control the transfer of silicone from roller 78 to the web, as it passes around roller 76. In use rotation of the gravure etched roller 80 causes liquid silicone release agent to be picked up in the cells and this is transferred to roller 78 which becomes evenly and uniformly coated with a thin film of the silicone release agent. In the nip between the roller 78 and the backing roller 76, some of this thin film will be transferred in the manner of an offset printing technique onto the backing web 54.A continuous film of silicone of uniform thickness will be applied to the web material 54 as it travels through the facility 73.

The weight of the coating can be controlled by factors such as (a) the etch on the gravure roller, (b) the speed of rotation of the gravure roller 80 relative to the linear speed of the backing web, (c) the pressure between rollers 78 and 80, (d) the speed and direction of rotation of roller 78, (e) the pressure between rollers 76 and 78; some or all of which factors being adjustable in known manner.

Referring now also to Figure 2D silicone is pumped from a holding tank 81A to partially fill the trough 81. Rotation of the roller 80 causes silicone to fill the gravure cells in the roller. An agitator 83 is driven simultaneously to transverse from one end to the other end and back again of the trough 81, so as to maintain homogeneity of the liquid silicone. Within the tank 81A the silicone is kept in a mixed condition by a stirrer 81B.

W Unit After passing around roller 82, the web 54 is stretched across two rollers 84 and 86 so as to present a flat horizontal surface to the underside of a pair of ultra violet (UV) curing lamps 87 contained in a housing 88.

Referring now also to Figure 2A and 2B, extending between the rollers 84 and 86 is a water-cooled baseplate 85 over which the web 54 passes, the coated surface of the web facing upwardly towards the UV lamps 87. In the event that the web 54 is slowed down or stopped, the web is arranged to contact the baseplate to prevent overheating due to the latent heat in the lamps.

The housing 88 forms a chamber around the web between the rollers 84 and 86, in such a manner that an inert gas, preferably Nitrogen, can be fed into the chamber at slightly in excess of atmospheric pressure, to provide a substantially oxygen-free environment whilst the web is subjected to curing by the W lamps.

Between each W lamp 87 and the web is located a plate 90 made of quartz glass which is relatively transparent to W radiation but relatively resistant to infra-red radiation, enabling the UV radiation from the lamps to pass therethrough onto the coated surface of the web 54. The plates 90 are slidably mounted transversely of the web such that when one half of each plate is in position between the respective lamp and the web, at least the other half is fully exposed and available for cleaning, the permissible sliding movement of each plate 90 being such that each in turn can be rendered available for cleaning.

Although not shown, brushing with or without vacuum suction may be provided for automatically cleaning the plates 90 as they are exposed for cleaning.

Each plate 90 may, alternatively, be arranged to support two quartz glass windows, each having a length (as considered in the direction of sliding movement) greater than the width of the web, and being removable from the plate so as to enable cleaning to be effected remote from the lamination line. In any case, if cleaning is effected at the high level shown, steps must be taken to ensure that dust or dirt particles removed from the windows cannot fall onto the apparatus below, particularly not into or onto the offset coating facility 73.

The purpose of the UV lamps is to cause the silicone material to cure and become firmly bonded to the backing web. To this end the choice of backing material is such that an appropriate bond can be obtained with the chosen silicone, one preferred material being orientated polypropylene (OPP) film and another being polyethylene terephthalate (PET). Polyethylene (PE) sheet may also be used, as also may the proprietary paper-based sheet material sold under the name Glassine (Registered Trade Mark).

After curing, the coated web material passes below a roller 92 and thereafter follows a high level path over and under a number of rollers 96, 98, 100, 102, 104, 106, 108, and 110 and finally under a roller 112 (see Figures 3 and 4) from which it can pass to the input of a laminating facility, shown in Figure 4.

The high level path extending across the apparatus shown in Figure 3 keeps the coated web material well clear of the line, and the section between rollers 94 and 98 bridges a region of the line within which a second or spare differential offset gravure coating apparatus can be located.

This spare or additional coating facility is shown in dotted outline and denoted by reference numeral 114 and may be supplied with the web material from the roller 94 via rollers 116, 118, 120, 122, below the walkways 124 and 126, the transfer between the walkways being controlled by rollers 128, 130 and 132. Then after passing along an upward path defined by rollers 134, 136, 138 and 140 the web material can be fed in a downward sense to the upper roller 142 of the coating facility 114. After passing around the backing roller 144, the coated web passes upwardly and around a further roller 146 and can rejoin the original line under the roller 98.

This additional coating facility may for example be used to apply an adhesive film to the silicone coated surface of the original web material 54, instead of applying adhesive to the rear of the label material before it is to be applied to the backing web.

Alternatively the second facility 114 may operate in place of the original facility 73, for example while the latter is out of commission for servicing or repair. To this end an alternative web path must be organised through the machine to enable uncoated but surface treated web material to be transferred from the corona discharge facility to the input roller 142 of the coating facility 114, and to transfer the coated web issuing therefrom via another path, through either the original UV curing stage 88 or through a second UV curing stage (not shown) located above the coating facility 114.

Laminating Line Figure 4 is an elevation of the heart of the laminating line.

Here silicone coated backing web 54 is laminated with an adhesive backed label material to form the final laminated product which leaves the laminator 148 along the path 150.

Thereafter it passes around a first roller 152, two further rollers 154 and 156 and an intermediate tensioning roller 158, after which the laminate is wound up on a take-up roll 160, the core of which is carried by a rotatable carriage (not shown) similar to the unwind facility shown at 14 in Figure 1.

A second roll 162 carried on the opposite side of the rotatable carriage can be employed as the roll 160 becomes full. By rotating the carriage and using a flying splice mechanism (known per se), the incoming laminate can be spliced and transferred from one roll to the other, enabling the full roll (now occupying the position of roll 162) to be downloaded using the crane facility 164. An empty core can then be mounted thereon ready to be transferred into position when the core on the other side has become full.

During winding onto either of the rolls 160 or 162, the laminate is held down firmly onto the respective roll by a small lay-on roller 163 mounted at the free end of a pivotal arm 165.

It will be seen that by using this type of twin roll and flying splice unwind and rewind mechanism, the take-up process can be operated continuously.

The lamination path is defined by two input rollers 166 and 168, the former receiving the backing web 54 and the latter the label sheet material 170. Both of the input rollers 166, 168 are curved spreader rollers (sometimes referred to as bowed rollers), which serve to present a flat even web to a lamination nip formed between a steel roller 172 and a rubber coated roller 174. Thereafter the laminated material passes around a large diameter roller 176 and exits via an edge cutting station formed by edge cutting knives 178 and anvil roller 180. The exiting laminate is denoted by reference numeral 150, previously referred to.

Referring also to Figure 4A, the sheet label material 170 is coated with a hot melt adhesive before lamination using a slot nozzle applicator denoted by reference numeral 182. The applicator is supplied with liquid hot melt adhesive via transfer hoses 181 from a heated reservoir 183 located to the side of the laminating line. The hoses 181 are also heated and insulated so that the adhesive in the reservoir 183 can be transferred to the nozzle applicator 182 without becoming cooled. The reservoir is, in turn, supplied with hot melt adhesive via a heated hose 183A and a pump 185A from an adhesive melter 185, a suitable unit being the bulk melter Model 5540 supplied by Nordson (UK) Ltd of Wenman Road, Thame, Oxfordshire. A suitable applicator 182 and reservoir 183, supplied by the same Company, are the slot die applicator Model EP51 and the tank unit Model MX40110 respectively.

The applicator 182 is hinged by means of a bracket 184 so as to be capable of being swung, from the position shown in Figure 4 in an anti-clockwise sense, so as to remove the nozzle from contact with the sheet material 170.

Label supply Typically the label sheet material supplied is wound on rolls in a similar manner to the backing sheet material, and as shown in Figure 5 a similar roll handling facility is provided at the label material end of the lamination line, for loading and unloading rolls of label material. To this end a crane 186 is provided for lifting the full rolls such as 188 and locating same on one side of the rotatable carriage as at 190. The other side of the rotatable carriage contains a second roll 192 from which sheet label material is drawn for feeding into the tensioning facility generally designated 194 and illustrated in Figure 4.

The label sheet material unwound from the roll 192 extends from the roll around a first roller 196, a tensioned roller 198 and a further roller 200. Optionally the path may extend through a corona surface treatment facility generally designated 202 and similar to the corona discharge treatment facility 68 of Figure 2. (This will not normally be required if the label material is paper. However if the material from which label are to be formed is sheet plastics material, then the corona discharge treatment stage 202 may be required).

If corona discharge is not required, the sheet label material 204 passes directly from roller 200 around roller 206, and from thence around a further roller 208, below a walkway 210 and into the laminator 148 where it passes around rollers 212, 214, and 216 and thereafter around a rubber backed roller 218 which cooperates with the slot nozzle of the hot melt applicator 182 so as to coat the back of the label material with the hot melt adhesive. Thereafter the material passes around an upper roll roller 220 before passing down over the roller 168 (already mentioned) into the nip between the rollers 172 and 174 (previously described).

If a better adhesive surface finish is required and/or better coat weight control is required, the rubber backed roller 218 may be replaced by a ceramic surfaced or chrome-finished steel roller.

If the corona discharge facility 202 is employed, an additional roller 222 is required to receive the corona treated sheet material and enable it to change direction and pass to the roller 206, as previously described.

Glassine web Figure 6 illustrates a modification to the backing web path through the laminator in the event that a web of Glassine (R.T.M.) backing material is employed instead of OPP film.

This modification involves the addition of two coated rollers to improve the spreading and ensure flatness of the web instead of passing around the input roller 166. The alternative web path is shown at 224 extending around the first coating roller 226 and thence around the second coated roller 228, whereafter the web transfers over the roller 174 and then follows the original path into the nip between rollers 172 and 174. The remainder of the laminator and associated equipment is similar to that described in relation to Figure 4.

Laminated label stock Figure 7 and Figure 8 show one example of a final product produced by the method and apparatus as described.

An OPP backing sheet material or web is identified by reference numeral 230 and the layer of silicone release agent is denoted by 232. Labels 234 and 236 are peelably attached to the backing sheet by a hot melt adhesive 238 which remains tacky even at room temperatures and which lightly bonds to the silicone coating 232 to enable the labels and backing sheet material/web to be handled as a single product.

As shown, the labels are shown spaced from the edges of the backing material edges and from each other, and the backing sheet around each of the labels is covered by more of the label material with the labels being formed as cut-outs therein so that when a label is peeled away (as shown at 240 in Figure 8), an opening 242 in the label sheet is exposed the same size and shape as the label which has been removed. The edge regions 244, 246 with intermediate bridging sections 248 forming a "ladder" are normally removed as shown in Figure 8, before passing to the label application stage shown in Figure 9.

The label can be separated from the backing sheet and applied to products such as bottles which are to be labelled by the apparatus shown in Figures 9 and 10, and which is capable of operating at high speed.

A roll of laminated labels and backing sheets 250 is mounted for rotation on a shaft 252 which can be driven and braked by a motor 254. The laminated material is pulled from the roll 250 towards a labelling station 256 at which it is forced to turn sharply through 90C or thereabouts around a vertical the 258. The sharp change of direction of the laminate causes each label to detach itself from the backing web and to continue to move in the direction in which the web was travelling just before the change of direction around the pin. This is most easily seen in Figure 10.

By arranging that a bottle such as 260 is located at the station 256 ready to receive a label 262 as the latter starts to unpeel from the backing web, so the leading edge of the label will engage and stick to the bottle. By rotating the bottle in the direction of the arrow 264, the label will be drawn off the backing web 230 as the bottle continues to rotate and the web continues to move past the pin 258.

Since the back of the label is tacky the label will stick to the bottle and remain in place thereon.

By locating bottles on a conveyor 266 and advancing the latter in the direction of the arrow 248 in synchronism with the movement of the label and backing web, so each label on the web from the roll 250 can be applied in turn to the next bottle in the line.

Drive means at 270 rotates the bottles which are mounted on rotatable dishes 272 on the conveyor which are engaged and driven by 270 when the dish occupies the labelling position 256.

The web of backing material (less the labels) is collected on a take-up roll 274 which is driven by a drive 276. The empty web passes around a roller 278 to get to the take-up roll 274.

An unlabelled bottle is shown ahead of the labelling station at 280 and a labelled bottle beyond the labelling station is shown at 282.

As shown in Figure 10 a blade 284 serves to guide the leading edge of the label 284 towards a bottle rather than into the gap between the pin 258 and the bottle 260. The blade 284 may be coated with a substance to which the tacky label will not normally adhere.

Claims (25)

1. A method of laminating a sheet material according to which the laminate is constructed from a backing sheet, one face of which is coated with silicone to serve as a release agent, and a removable sheet material such as paper, wherein the removable sheet is bonded to the silicone coated face of the backing material using a hot melt adhesive, which forms a tacky film on the rear of the removable sheet material, which is exposed when the removable sheet material is peeled away from the backing sheet.

2. A method according to claim 1, wherein a typical weight of hot melt adhesive employed is in the range 5 to 200 g.s.m.

(grams per sq. metre).

3. A method according to claim 1 or claim 2, wherein the removable sheet material is printable material.

4. A method according to any of claims 1 to 3, wherein the backing material comprises a synthetic film such as orientated polypropylene (OPP) film or polyethylene terephthalate (PET) film.

5. A method according to any of claims 1 to 3, wherein the backing material comprises a paper-based material such as Glassine (Registered Trade Mark).

6. A method according to any of claims 1 to 5, wherein the backing material is cleaned before the silicone is applied thereto.

7. A method according to any of claims 1 to 6, wherein the silicone film is applied using an offset gravure process.

8. A method according to any of claims 1 to 6, wherein the silicone film is applied using a five roll coater process.

9. A method according to claim 7, wherein the rotational speeds and/or directions of some or all of the various rollers is altered to permit differential offset gravure coating.

10. A method according to any of claims 1 to 9, wherein the coating weight using silicone is in the range 0.5 to 5.00 gram per sq. metre.

11. A method according to any of claims 1 to 10, wherein, after the silicone film has been applied, the backing material is subjected to ultra-violet (UV) radiation to cure the silicone material.

12. A method according to any of claims 1 to 10, wherein, after the silicone film has been applied, the backing material is subjected to electron beam curing.

13. A method according to claim 11 or claim 12, wherein the silicone curing step is undertaken in a substantially oxygenfree environment.

14. A method according to claim 13, wherein the silicone curing step is undertaken in a chamber which is continually supplied with an oxygen-free gaseous medium at slightly in excess of atmospheric pressure.

15. A method according to any of claims 1 to 14, wherein the material used for the silicone coating is a radiation curable silicone acrylate.

16. A method according to any of claims 1 to 15, wherein the backing material is cleaned, before being coated with silicone, by physical brushing of the surface of the backing material.

17. A method according to any of claims 1 to 16, wherein the surface of the backing material which is to be coated with the silicone release agent is surface treated, before the release agent is applied thereto, so as to provide a good key for bonding silicone thereto.

18. A method according to claim 17, in which the surface treatment typically roughens the surface to provide the good key therebetween.

19. A method according to claim 17 or claim 18, wherein the surface treatment may be electrostatic.

20. A method according to claim 19, in which the surface treatment is effected by a corona discharge surface treater.

21. A method according to any of claims 17 to 19, wherein, prior to the backing material surface treatment, the following cleaning process steps are employed: 1. ionisation of the surface of the backing material to which a release agent is to be applied (the "one surface" thereof), 2. brushing the said one surface, together with vacuum suction for particle removal, and 3. subjecting both surfaces of the backing material to ionisation.

22. Apparatus for carrying out the method of claim 16 or any claim appendant thereto, comprising, upstream of a silicone coating stage and a hot melt adhesive bonding stage, a brushing stage at which a vacuum suction device is located in the region of the brush so as to collect particles removed from the surface by the brushing action.

23. Apparatus according to claim 22, wherein the brushing stage comprises a rotary brushing mechanism comprising two endless belts carrying bristles and adapted to be rotated around two elongated paths in opposite directions, each path length being more than half of but less than the overall width of the said backing material, the two belts being located one below the other with parts fr each belt overlapping, the two paths extending from opposite sides of the backing material so that brushing is applied over and across the entire width thereof, and separate vacuum suction means is provided in association with each said belt to separately collect and convey away particles removed from the surface of the backing material by each said belt.

24. Apparatus as claimed in claim 23 or 24, when forming part of a composite processing line in which a roll of backing sheet material is located at one end and a roll of label sheet material is located at the other end and means is provided to draw sheet material from each of the rolls towards a central region of the line at which is located a laminating apparatus in which the backing sheet material is bonded to the label sheet material using a hot melt adhesive which remains tacky at room temperatures to form a laminated label product which is rolled up on a take-up roll located adjacent the central region of the line.

25. Laminate when produced by the method of any of claims 1 to 16.