NZ204652A - Making vulcanised rubber sheet from several narrow sheets of vulcanisable rubber - Google Patents

Description

204652 Priority Date(s): /. .7. .?.?.

Complete Specification Filed: Class: Publication Date: [1 J. .^k j?86; P.O. Journal, No: N .Z .No, NEW ZEALAND Patents Act ]953 COMPLETE SPECIFICATION "SHEET MATERIAL" We, DUNLOP LIMITED, a British company of Dunlop House, Ryder Street, St. James's, London S W 1, ENGLAND, do hereby declare the invention, for which we Pr^y that a Patent may be granted to us, and the method by -which it is to be performed, to be particularly described in and by the following statement : - - i . (followed by 1A) |*24APR 1986mj 204652 it SHEET MATERIAL This invention relates to a method of making one sheet from a plurality of smaller profiled sheets and to the resulting product.

Known methods of producing large sheets of e.g. vulcanized rubber from a plurality of smaller, vulcanizable rubber sheets involve winding the smaller sheets onto a mandrel so that adjacent edges overlap and then vulcanizing the assembly, thereby bonding the overlapped edges. The 10 disadvantages are that (i) in the region of the joints the sheet is of variable thickness which is unsightly and can cause handling difficulties in operation before, during and after vulcanization and (ii) joints are longitudinal of the mandrel which can limit the finished sheet size. 15 The aim of the present invention is to produce a sheet by joining a plurality of smaller sheets whilst avoiding the formation of thickened seams.

According to one aspect of the present invention, a method of making a discontinuous sheet comprises: 20 (i) providing a plurality of vulcanizable rubber sheets the bonding edges of which comprise complementary formations, (ii) overlapping said bonding edges by engaging said complementary formations, the thickness of the resulting overlap being substantially equal to that of the surroun ding sheet, thereby forming an assembly and (iii) subjecting the assembly to conditions which will vulcanize the assembly and bond the overlapped edges.

Also described in this specification is an apparatus 30 for assembling a plurality of sheets to form a single sheet construction which comprises carrier means for receiving a plurality of sheets and supply means for feeding the sheets to said carrier means so that adjacent sheets overlap. Optionally means for 35 squeezing the overlapping portions together can be provided.

*' 'X 2 4 APR W86™ 2. 204652 According to a further aspect of the present invention, a discontinuous vulcanized rubber sheet comprises a plurality of smaller sheets, the 5 adjacent edges of which are provided with complementary formations in overlapping bonded engagement, and the thickness of the overlap being substantially equal to that of the surrounding sheet.

The embodiments of the present invention are 10 particularly applicable to the formation of profiled vulcanized rubber sheets which can subsequently be bonded together and vulcanized simultaneously without the need for an adhesive into an elongate sheet. By discontinuous is meant that the sheet is not endless 15 e.g. is not annular. A proprietary processing aid may be incorporated when preparing the vulcanizable rubber composition. The vulcanizable rubber composition usually contains at least 2556 "by weight of rubber. Examples of rubber include EPDM, natural 20 rubber, SBR and any others usually used in the manufacture of sheet materials. Preferably the surfaces of the vulcanizable rubber sheets are not treated with an antistick agent such as talc as this may impair the bond obtained between the sheets when 25 overlapped.

An example of a pair of complementary formations consists of a rib on each sheet member, the resultant overlap interface of the engaged formations being between the outer surfaces of the two sheets so 30 joined but preferably not extending continuously between them. Preferably the overlap interface is at a small angle e.g. up to 1° to the plane of the sheet.

Preferably the bonded overlapped edges are longitudinal of a finished elongate sheet, rather than 35 lateral, and are substantially parallel to the edges of the finished sheet, and of course to any other bonded overlap.

One or more of the sheets to be joined tog^air " ' ^ z 24 APR 1986 ml \ /* F I Nj ' 3. 204652- may be a laminate of thinner layers. "When such a laminate is formed it may be designed so that the laminae are of different widths, thereby forming a stepped edge. Such a laminate can then be used in the method of the present invention without the need for any further shaping. "When calendering single ply rubber membranes occasional flaws or pin holes may occur, giving rise to problems with the quality and acceptance of the product. If a laminate of two or more sheets is used, the probability of superimposing flaws or pin holes is extremely small.

A sheet may be shaped by urging it in contact with a profile roller the roller having a collar adjacent at least one end thereof, the collar being tapered towards the adjacent end of the roller and having a maximum depth less than that of the sheet. If a single profile roller is to be used to shape the edges of each sheet in one process, then alternate sheets will need to be reversed in order to engage the complementary formations. Alternatively a profile roller with a single collar could be used to shape one sheet, the sheet could then be reversed and the same roller used to shape the reverse surface.

Where a single profile roller is used, the complementary formations will be symmetrical about the plane of overlap and one surface of each formation will be that of its respective sheet (e.g. see Figure VI).

Uses of the final sheet product of the present invention include roofing membranes and reservoir liners.

Preferred embodiments according to the present invention will now be described by way of example only with reference to the accompanying drawings in which Figure I is an axial view of a 3-roll calender in combination with a profile roller for producing profiled sheet rubber; Figure II is a side view of the profile ro^'ea* ~ '• ; ^ f = 2 4 APR 1986 i 204652 4. shown in Figure I; Figure III is of a schematic apparatus "by which a plurality of rubber sheets are vulcanization bonded to form a single 5 sheet; Figure IV is a perspective view of part of the apparatus shown in Figure III; Figure V is a plan view of the single vulcanized rubber sheet resulting from the 10 process described with respect to Figures III and IV; Figure VI is a sectional view along line AA1 of Figure V; Figure VII is an axial view of a 4-roll calender 15 for producing a stepped sheet.

Referring to Figures I and II, the 3-roll calender consists of a tdp roller 1, a calender roller 2, and a bottom roller 3. The nips 4a,4b between rollers 1/2 and 2/3 are the same and equal to the thickness desired for 20 the final sheet product. A driven profile roller 5 having a diameter half that of the calender roller 2 is provided adjacent the calender roller 2 at a distance governed by the height of nips 4a, 4b and degree of profiling required.

Each end 6,7 of the profile roller 5 is provided with a 25 circumferential collar 8,9 an enlargement of one of which is shown. Each collar 8,9 tapers radially inwards in the direction towards the respective end 6,7. of the roller and the maximum collar depth 10 at the axially inner edge of the collar is about one half of the desired calendered 30 sheet thickness. The angle of taper is less than 1° and the drawings are exaggerated to show this.

"When the calender is in operation, vulcanizable rubber stock 11 is fed through the nip 4a of the rotating rollers 1,2 to produce a sheet 12. The sheet 12 is then fed between calender roller 2 and driven profile roller-5. The collars 8,9 of the profile roller 5 profile the outer edges of the rubber sheet, the % fa* O' //iv ? i ' %n4'' J . 204652 : *«\ /.

J tapering causing the rubber stock to move outwardly rather than towards the centre of the sheet. Excess rubber is trimmed away by a nip roller (not shown). The surface speed of the profile roller 5 is usually from 1 to 5% faster than that of the calender roller 2. The profiled sheet is then fed through nip 4b, around the bottom rcLler 3 and over a roller 13 to take-up means (not shown). A modification of this apparatus would be a 4-roll calender in which two sheets of different widths could be brought together to give a profiled 2-ply sheet in a single "pass,. e.g. as in Figure VII.

Referring to Figures III and TV, the apparatus consists of three main units i.e. a liner feed/tension adjuster 14, a mandrel on rails 15 and a calender stock feed station 16. Liner 17 "which is of woven synthetic/cotton fabric is fed between two rotating rollers 18, 19, around another two rollers 20,21, over a hydraulic arm 22, and onto a rotating mandrel 23. At the same time strips 24 of calendered profiled vulcanizable rubber stock such as those produced by the apparatus shown in Figure I are fed onto the mandrel 23 from rollers 25 in the calender stock feed station 16. Alternate rollers 25 are inverted. As the stock is wound from the rollers 2s the liners of woven synthetic/cotton fabric separating each turn on each roller 25 are taken up on rollers 26. The strips of calendered profiled stock 24 are aligned so that complementary rib formations are engaged at the surface of the mandrel 23 and tension is adjusted so that there is no stretching of the vulcanizable rubber during the winding. The speeds of the liner feed, mandrel rotation and calender feed stock are synchronised to ensure smooth running of the continuous .process. The hydraulic arm 22 is used as a pressure bar to consolidate the overlap of the complementary edges of the strips 24.

The liner is kept under tension and,after the rubber stock has been completely wound onto the 6. 204652- at least three complete turns of liner are added. The wound liner is then secured in tension before the mandrel is removed to an autoclave for vulcanization.

The resulting sheet which may "be about 20 feet 5 wide and 500 feet long is shown in Figures V and VI. Although the overlaps 27 are shown in the drawings the aim of the invention is to make the seams as unobtrusive as possible and to avoid any appreciable variation in thickness across the finished sheet as 10 a result of the joints. The width 28 is that of each calendered strip and the seams run parallel to the winding direction of the mandrel upon which the sheet was consolidated and vulcanized. The overlap interfaces of the engaged ribs are substantially in 15 the plane of the sheet and do not extend between the outer surfaces of the dieet as would be the case e.g. if two sheets with 45° complementary sloped edges were joined.

Referring to Figure VII, the 4-roll calender 20 consists of a pair of top rollers 29,30, a pair of bottom rollers 31,32 and a pair of compaction rollers 33,34o The nips 35 and 36 are not necessarily the same'but are substantially equal to the required thickness of the upper lamina 37 and lower lamina 38 25 respectively. When the calender is in operation vulcanizable rubber stock 39,40, not necessarily of the same composition, is fed through nips 35,36 respectively by movement (shown by arrows) of rollers 29 and 30 or 31 and 32 respectively. The resulting laminae 37,38 30 are then fed between the compaction rollers 33,34 which squeeze them into a tack-held assembly. By forming two laminse of different dimensions a sheet having readymade "stepped" edges can be made without the need for a profile roller or the like. Lengths 35 of the resulting sheet can be joined using the apparatus shown in Figures III and IV0 204652 7.

Claims (15)

WHAT WE CLAIM IS ■ , r If- i pas htK-mb«=W« defii\ea

1. A method of making a discontinuous sheet! which comprises: (i) providing a plurality of vulcanizable rubber sheets the bonding edges of which comprise complementary formations, (ii) overlapping said bonding edges by- engaging said complementary formations, the thickness of the resiting overlap being substantially equal to that of the surrounding sheet, thereby forming an assembly, and (iii) subjecting the assembly to conditions which will vulcanize the assembly and bond the overlapped edges.

2. A method according to claim 1 wherein there is no adhesive layer between the overlapped edges.

3. A method according to claim 1 or 2 wherein the vulcanizable rubber sheets are not treated with an antistick agent before overlapping the bonding edges thereof.

4. A method according to any preceding claim wherein the discontinuous sheet is elongate.

5. A method according to claim 4 wherein the bonded overlapped edges are longitudinal of the sheet.

6. A method according to any preceding claim wherein the overlap interface of the engaged formations is between the outer surfaces of the two sheets to be joined but does not extend continuously between them.

7. A method according to claim 6 wherein the overlap interface is up to 1° to the plane of the sheet product.

8. A method according to any preceding claim wherein one or more of the sheets to be joined together is a laminate of two or more thinner layers.

9. A method according to any preceding claim wherein the complementary formations consist of a rib on each sheet member.

10. A method according to any preceding claim wherein the sheets are fed onto a carrier means in such a way that the bonding edges of the sheets overlap by engagem^rt? of the complementary formations. f!z - 6MAY1986 .9 x-P f i >J V 204652 8.

11. A method according to Claim 10 wherein the carrier means is a mandrel.

12. A method according to claim 11 wherein the sheets are fed on to the mandrel circumferentially.

13. A method according to any preceding claim wherein the overlapping edges are squeezed together.

14. A method substantially as hereindescribed with reference to the accompanying drawings.

15. A discontinuous vulcanized rubber sheet comprises a plurality of smaller sheets, the adjacent edges of which are provided with complementary formations in overlapping bonded engagement, and the thickness of the overlap being substantially equal to that of the surrounding sheet. DUNLOP LIMITED By Their Attorneys HENRY HUGHES LIMITED