GB2137246A

GB2137246A - Drying corrugated board

Info

Publication number: GB2137246A
Application number: GB08406686A
Authority: GB
Inventors: Malcolm James Hartle
Original assignee: NEU ENGINEERING Ltd
Current assignee: NEU ENGINEERING Ltd
Priority date: 1983-03-29
Filing date: 1984-03-14
Publication date: 1984-10-03
Also published as: GB8406686D0

Abstract

A method of drying moist corrugated board 6 comprises heating the laterally outer regions 6A of the moist board to a greater extent than the central region 6B during passage of the moist board through drying apparatus to reduce the moisture content of regions 6A to less than that of region 6B, such that, on cooling of the board 6, atmospheric moisture is taken up to produce a board with a substantially uniform moisture profile across its width. This results in a board which is more resistant to warping across its width. Apparatus for carrying out this method may comprise a plenum chamber 5 sub-divided to form laterally outer chambers 9, 10 and a central chamber 11 therebetween. Each chamber is fed with pressurised air. Chambers 9 and 10 may be raised to higher pressure than chamber 11 thereby resulting in increased pressing of regions 6A against steam chests below belt 3 as compared to region 6B, thus producing the differential heating. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing corru gated board The present invention relates to a method and apparatus for producing corrugated paper board, corrugated board and like materials, such materials being referred to herein generi cally as corrugated board for simplicity.

Various constructions of corrugated board of board are known and widely used in the packaging industry. For example one form, known as single wall board, comprises a cor rugated fluting medium bonded between two liner webs. Another product, known as double wall board, comprises a central liner web, two outer liner webs and corrugated fluting me dium bonded between the inner and outer webs.

In a first stage of corrugated board pro duction, a liner web is bonded to one side of a fluting medium. The exposed corrugated tips of the composite material are then coated with an adhesive and at least one run of the thus treated material (depending on whether single wall, double wall, or other type of corrugated board is required) is supplied together with a liner web to apparatus for bonding together the plies of the board in a "double-backing" operation.

The apparatus for performing this double backing operation is known as a ''double backer" and comprises an upstream heating and pressing section for drying or curing the adhesive and bonding the plies firmly together, and a downstream traction section serving to draw the board through the apparatus. During its residence in the traction section the board is cooled and may subse quentiy be cut and/or slotted and/or printed as required.

In the heating section the board locates between a run of an upper endless belt and heating means, usually a heated surface (e.g.

provided by heated plattens, hot plates or steam chests). In this section, pressure is applied to the back of the belt, e.g. by rollers or one or more plenum chambers, so that the belt presses the board against the heated surface as the board is advanced through the section. The adhesive is thus dried and the plies are bonded together.

The board then passes to the traction section where it cools.

There is however the disadvantage that the resultant board tends to warp across its width.

This results from the heating and cooling procedure used producing a differential moisture content across the board width. During heating, the moisture in the adhesive evaporates and the water vapour passes generally transversely through the board to the edges thereof from where it is evolved to the atmosphere. Immediately after heating the moisture content at the edge portion of the board is slightly greater than in the central portion due to the relatively greater difficulty of water vapour escaping from this region during cooling, there is a naturally generated reduced pressure within the board so that air from the atmosphere enters the board at the edges thereof. The water vapour naturally present in this atmospheric air condenses within the cooling board.The bulk of the condensation occurs as the air enters the board edges thereby further raising the moisture content in these regions above that of the central portion thus resulting in the differential moisture content across the board width.

It is an object of the invention to obviate or mitigate the abovementioned disadvantage.

According to a first aspect of the present invention there is provided a method of producing corrugated board in which the board is heated to dry adhesive for bonding the plies of the board together, wherein the board is subjected to greater heating in its laterally outer regions than at its central region to reduce the moisture content at said outer regions to below that of the central region by an amount such that, on cooling of the board, water vapour in atmospheric air is taken up to produce atboard with a substantially uniform moisture profile across the board.

According to a second aspect of the present invention there is provided an apparatus for producing corrugated board by the method of the preceding paragraph, the apparatus comprising a heating section and means for transporting the board through the heating section, the heating section itself comprising heating means, pressure applicator means arranged to press the board against the heating means, and means for ensuring that the laterally outer regions of the board are heated, in use of the apparatus, to a greater extent than the central region.

The invention is thus based on the realisation that heating the laterally outer regions of the board at a higher temperature (or to a greater extent) than the central region will result in a lower moisture content in the latterally outer regions than in the central region. Provided that the temperature difference is selected correctly, this difference in moisture content will be such that it will be substantially made up by virtue of the greater increase in moisture content during cooling at the laterally outer regions than the central region, as discussed above.

The laterally outer regions of the board will generally each extend over approximately 1/4 - 1/3 of the board width.

Generally, the laterally outer regions of the board will be heated by 1-3 C more than the central region.

The initial moisture content of the board will generally be around 10% and after the differential heating, the moisture content of the central region will generally be 4-6% whereas that of the laterally outer region will be about 2% less to achieve the desired result.

It should be appreciated that, during cooling of the board, the central region will also increase in moisture content but this increase will not be as great as that at the edge regions which may therefore increase in moisture content to a value of that equal to the final moisture content of the central region thereby establishing the uniform moisture profile.

In a preferred apparatus in accordance with the invention the heating section comprises a belt arranged such that the board will locate in use of the apparatus between a run of the belt and the heating means and the pressure applicator means is arranged to apply pressure to said run of the belt so that it will press the board against the heating means the pressure applicator means is preferably at least one air pressure plenum chamber for apply gaseous pressures to the reverse side of said belt run whereby the belt presses the board against the heating means. The means for ensuring the greater heating at the laterally outer regions of the board is preferably achieved by applying higher gaseous pressure to those areas of the belt which press against the laterally outer regions of the board than those which press against the central region.

Thus, the pressure applicator means may comprise two laterally outer air pressure chambers and a central air pressure chamber therebetween means also being provided for producing air pressure in the laterally outer chambers than in the central chamber. In this way, the laterally outer regions of the board are pressed more firmly against the heating means than the central region and are thereby heated more.

The invention will be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 schematically illustrates the heating section of one embodiment of the apparatus in accordance with the invention for producing corrugated board; Figure 2 is a transverse sectional view of a plenum chamber for use in the apparatus of Fig. 1 as viewed generally on line A-A of that Figure; and Figure 3 is a plan view of the plenum chamber shown in Fig. 2.

The apparatus 1 illustrated in Fig. 1 includes a heating section 2 comprising an endless belt 3 of suitable absorbent material (for absorbing moisture generated during heating) with a run 3a closely spaced above a heating surface provided by the upper faces of a plurality of steam chests 4. Alternatively belt 3 may be of an openwork construction allowing evaporated moisture to pass therethrough.

A plenum chamber 5 which extends across the width of belt 3 serves to press run 3a towards steam chests 4.

The apparatus will also include a traction section (not shown) which draws or transports the board through the heating section and in which the board cools.

The apparatus may in general be of the form described and illustrated in published European Patent Specification No. 0 077 186, the disclosure of which is incorporated herein by reference.

The apparatus is shown for the production of single wall corrugated board 6 from a liner web 7 and a combined web 8 constituted by a corrugated fluting medium bonded to a further liner web, with the corrugation being transverse to the running length of the board.

As will be appreciated from Figs. 2 and 3, plenum chamber 5 is divided into three sections across the width of belt 3. These sections comprise two laterally outer chambers 9 and 10 and a central chamber 11. Each chamber 9, 10 and 11 is fed with pressurised air along ducts 12, 13, 14 respectively.

Ducts 12 and 13 supply air at a higher pressure to chambers 9 and 10 than duct 14 supplies to chamber 11. Generally the pressure in chambers 9 and 10 will be 20-30% higher than in chamber 11. Purely by way of example, the pressure in chambers 9 and 10 may be 550-650 (e.g. 600) mm water gauge and that in chamber 11 400-500 mm water gauge. It should however be appreciated that the exact pressures and pressure differences required will depend on the type of board being produced.

As a result of this pressure difference, the laterally outer regions 6A of the board (i.e.

those regions under chambers 9 and 10) are pressed more firmly against the steam chests '4 than the inner region 6B. This results in greater heating of regions 6A than 6B to establish a moisture difference between these regions which is such that, after cooling, there is a substantially uniform moisture profile across the board 6, as discussed more fully above. Thus the resultant board is substantially free from warp.

Although the invention has been described and illustrated with reference to the use of laterally arranged plenum chambers 9-11 for effecting the differential heating across the width of the board 6, it should be appreciated that this differential heating may be effected in other ways. Thus, for example, the differential heating may be effected by having the outer regions of the heating surfaces at a higher temperature than the inner region, e.g.

using latter outer steam chests 4. In this way, the pressure applicator means may apply a uniform pressure across the width of the board 6.

Claims

1. A method of producing corrugated board in which the board is heated to dry adhesive for bonding the plies of the board together wherein the board is subjected to greater heating at its laterally outer regions than at its central region to reduce the moisture content at said outer regions to below that of the central region by an amount such that, on cooling of the board, water vapour in atmospheric air is taken up to produce a board with a substantially uniform moisture profile across the board.

2. A method as claimed in claim 1 wherein the laterally outer regions which are subjected to said greater heating each extend over 1/4 to 1/3 of the board width.

3. A method as claimed in claim 1 or 2 wherein the laterally outer regions are heated by 1 to 3"C more than the central region.

4. A method as claimed in any one of claims 1 to 3 wherein, after said heating, the moisture content of the central region is 4-6% and the moisture content of the laterally outer regions is about 2% less.

5. A method as claimed in any one of claims 1 to 4 wherein the pressure applicator means applies greater pressure to said laterally outer region of said board than to said central region thereby to produce said greater heating of the laterally outer regions.

6. Apparatus for producing corrugated board comprising a heating section and means for transporting the board through the heating section, the heating section comprising heating means, pressure applicator means arranged to press the board against the heating means, and means for ensuring that the laterally outer regions of the board are heated, in use of the apparatus, to a greater extent than the central region.

7. Apparatus as claimed in claim 5 wherein the pressure applicator means is adapted to apply greater pressure to said laterally outer regions of the board than to said central region thereby to ensure said greater heating of the laterally outer regions of the board.

8. Apparatus as claimed in claim 7 wherein the pressure applicator means comprise two laterally outer air pressure chambers and a central air pressure chamber therebetween, and means are provided for producing a higher air pressure in said laterally outer chambers than in said central chamber.

9. Apparatus as claimed in claim 8 wherein the pressure applicator means is a pressure hood internally sub-divided into two laterally outer pressure chambers and a central pressure chamber there between.

10. Apparatus as claimed in any one of claims 6 to 9, wherein the heating section comprises a belt arranged such that the board will locate in use of the apparatus between a run of the belt and the heating means, and the pressure applicator means is arranged to apply pressure to said run of the belt so that it will press the board against the heating means.

11. A method of producing corrugated board substantially as hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.

1 2. Apparatus for producing corrugated board substantially as hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.