Mylläri, Esa (Nikkilänniemi, Pirkkala, SF-33940, FI)
| 1. | Method for manufacturing flexible laminate material windable into a roll, which material has a middle layer (2) of plastics and surface layers (1, 3) laminated on the opposite sides thereof and capable of remaining unchanged at the softening temperature of the material of the middle layer (2) , characterised in that the laminate material is formed by joining together two or several elongate laminate webs (4) comprising the same layers, the joining being effected at the longitudinal edges (4a) of the webs, and that for effecting said junction both adjacent webs (4) have in a margin zone (4a) of a predetermined width a reduced thickness compared with the middle area of the web due to the fact that one (3) of the surface layers (1, 3) does not extend to the outermost edge of the web, the junction being effected in such a fashion that the surfaces of the margin zones (4a) being exposed adjacent to said surface layers (3) are placed together against each other and are heatsealed together by means of the material of the middle layer (2) forming at least one of the surfaces of the margin zones. |
| 2. | Method as claimed in claim 1, characterised in that the material of the middle layer (2) forms the surface in both margin zones (4a) which are to be placed against each other. |
| 3. | Method as claimed in claim 2, characterised in that a lateral space for expansion (5) for the softened material of the middle layer (2) is provided at the joining area in the margin zones (4a). |
| 4. | Method as claimed in claim 2 or 3, characterised in that at least one of the margin zones (4a) which are to be placed against each other has a reduced thickness of the material of the middle layer (2) compared with constant thickness of the middle layer (2) in the middle area of the web. |
| 5. | Method as claimed in claim 1, characterised in that in the margin zones (4a) which are to be placed against each other the sum thickness of the material of the middle layer (2) is substantially equal to the constant thickness of the middle layer (2) in the middle area of the web. |
| 6. | Method as claimed in claim 5, characterised in that in the margin areas (4a) which are to be placed against each other, the material of the middle layer (2) is situated entirely in the margin area of only one of the webs (4) and has substantially the constant thickness of the middle layer (2) of the middle area of the web ( ) . |
| 7. | Method as claimed in claims 2 and 5, characterised in that in both margin areas (4a) which are to be placed against each other the thickness of the material of the middle layer (2) is approximately half the thickness of the middle layer (2) in the middle area of the web (4). |
| 8. | Method as claimed in claim 1, characterised in that in both laminate webs one (3) of the surface layers (1, 3), which does not extend to the outermost edge of the web, is thicker than the surface layer (1) extending to the outermost edge. |
| 9. | Method as claimed in claim 8, characterised in that in each of the webs (4) the thickness of the thicker surface layer (3) is substantially equal to the sum thickness of the thinner layer (1) and the middle layer (2) located in the adjacent web in the margin area (4a) thereof. |
| 10. | Method as claimed in any of the preceding claims, characterised in that the surface layers (1, 3) are constituted of fibrous material, such as paper or paperboard, and the middle layer (2) is of a polyolefiri, such as polyethylene or polypropylene. |
The invention relates to a method for manufacturing of laminate material having the features disclosed in the preamble portion of claim 1.
Such laminate materials are widely used as packaging material wherein between two outermost layers lying on the opposite sides of the plane of the material there is a middle layer of heat-sealable plastics, which acts as a layer joining the outermost layers together and at the same time among other things as a moisture barrier. The outermost layers can be for example fibrous layers, such as paper or paperboard.
The above described laminate materials are used for packaging products wound into rolls, such as large paper rolls produced by big paper manufacturers. It has been prooved difficult to obtain a laminate material of great width, that is of a width exceeding about three metres, by means of modern laminating technique. This type of material would make it possible to package, among other things, wide paper rolls which are produced in an ever increasing scale.
The object of the invention is to provide a method for manufacturing of laminate material which is very suitable for this purpose. The method according to the invention, by which this is realised, is mainly characterised in what is disclosed in the characterising portion of claim 1.
The invention is based on the idea of forming a laminate material by joining together at least two elongate laminate webs having corresponding layers, the joining being effected at their longitudinal edges. The webs are connected by making the margin zones bounded by the longitudinal edges and overlapping each other thinner than the middle portion of the web
by not extending one of the surface layers in each web to the longitudinal edge. The webs are placed side by side in such a fashion that said thinner margin zones overlap and they can be heat-sealed together with the aid of the heat-sealable middle layer material, which forms the surface of at least one of the above mentioned margin zones.
The accompanying subclaims show other advantageous embodiments of the invention. There are, for example, several ways to obtain such configurations of the cross profiles of the margin zones that the connecting area in the finished laminate will be even.
The invention will be described in more detail in the following by reference to the accompanying drawings, wherein
Fig. 1 shows the margin areas of the laminate webs which are to be joined together by the method of the invention at a stage before they are brought against each other r
Fig. 2 shows the finished laminate material manufactured by the method of the invention.
Fig. 3 shows the situation in Fig. 1 in a method according to an alternative embodiment of the invention.
Fig. 4 shows the finished laminate material manufactured by the method of Fig. 3, and
Fig. 5 shows schematically an apparatus which is suitable for manufacturing the laminate material, as seen from above.
Fig. 1 shows two laminate webs which are to be joined together at their sides, seen in cross-section taken perpendicularly to their longitudinal direction and their plane. In the Figure the thicknesses of the material layers are exaggerated for better illustrating the idea.
Each web 4 comprises outermost surface layers 1, 3 lying on the opposide sides of the plane of the web, as well as a middle layer 2 of plastics joining them together. The surface layers 1 and 2 have such properties that they remain unchanged at the softening temperature of the material of the middle layer 2. Each web 4 has a margin zone 4a of constant width, which ends sideways on one side in the outermost edge of the entire web 4 and on the other side towards the middle area of the web the zone ends in the outermost edge of one of the surface layers 3. The margin zones 4a are consequently of decreased thickness compared with the middle area of the web, because the above mentioned surface layer 3 does not extend to the outermost edge of the web.
As illustrated by Fig. 1, the material of the middle layer 2 forms the outermost surface of the margin zone 4a between the outer edge of the surface layer 3 and the outer edge of the whole web 4. The Figure also shows that the layer 1 on the opposite side with regard to the layer 3 forms the outer edge of the whole web 4 in each of the webs and the outer edge of the middle layer 2 does not quite reach said edge, but leaves free an area designated 5 in Fig. 1, on which the surface of the margin area 4a is formed of the material of said layer 1.
As .shown by Fig. 1, two-adjacent webs 4 are guided together in such a fashion, that their margin zones
being of equal width in both webs 4 overlap each other and face each other. At this stage the surfaces exposed adjacent to the surface layer 3 not extending to the outer edge of the web face each other. In this way the middle layers 2 exposed within the margin zone 4a are brought against each other, and by subjecting the connecting area to energy which softens the plastics material of the layer 2 the zones 4a can be sealed together. Any heat-sealable plastics material, preferably a polyolefin, such as polyethylene or polypropylene can be used as the plastics material.
The margin zones 4a can be placed in such a fashion that they overlap almost totally. Hence, the edge of the layer 1 forming the outer edge in one of the webs will always lie adjacent to the edge of the layer 3 in the other web. The placing can be effected at such an accuracy that only very narrow seam will remain on both sides of the finished laminate. Fig. 1 shows that the area between the outermost edge of the web 4 and the layer 2 constitutes at the joining stage a space 5 to which the melted material of the layer 2 can spread laterally in order to compensate the effect of the sum thickness of the layers in the margin zone 4a being greater than the constant thickness of the layer 2 in the middle area of the web. It is also possible to provide such thicknesses of the layers 2 in the margin zone 4a that at least one of the margin zones to be brought against the other is of reduced thickness compared with the above mentioned constant thickness in the middle area of the web. Another possible alternative is the one in which the sum thickness of the materials of the middle layers is substantially equal to the above mentioned constant thickness. This alternative is illustrated by broken lines in Fig. 1, and if the dimensioning is correct the material of
the layer 2 can be extended to the outer edge of the whole web 4 and the lateral spaces 5 for expansion are not needed.
Fig. 1 illustrates by broken lines the case where both margin zones 4a to be brought against each other said thickness of the material of the middle layer 2 is approximately half the above mentioned constant thickness in the middle area of the web. Said thickness can also be steadily decreasing in the margin zone 4a towards the outermost edge. In this context, when thickness of the middle layer 2 in the margin zone is referred to, it shall be understood to mean its average thickness.
One possibility is to form the margin zones 4a in such a fashion, that the material of the middle layer 2 is situated only in one of the margin zones 4a and has substantially the same constant thickness as the middle layer has within the web middle area. In the facing margin zone 4a the surface to be brought against the layer 2 is free from the material of the layer 2, that is, the layer 2 extends not farther than the layer 3 and the joining surface of the margin zone 4a is formed of the material of the layer 1.
The thicknesses of the middle layers 2 in the margin area can be adjusted using common adjusting methods of laminating technique, for example by adjusting the slot die of an extruder feeding the material of the middle layer 2.
Fig. 2 shows a finished laminate material formed of two webs 4. In order to obtain material of equal quality along the whole width, the laminate webs 4 to be joined should be of equal thickness and the layers 1 and 3 coming adjacent to each other should be of equal thickness in adjacent webs. It is most practical
to form the laminate material of such separate webs having a symmetrical structure relative to the middle plane dividing the web 4 in two equal thicknesses. In this case the joining operation can be performed using two identical laminate materials by turning one of the laminate materials upside down and guiding the connecting surfaces of the margin zones 4a against each other.
Figures 3 and 4 shows an alternative embodiment of the method of the invention, based on the thicknesses of the outermost layers 1 and 3. In both laminate webs 4 the surface layer 3, which does not extend sideways to the outermost edge of the web and leaves the material of the middle layer 2 exposed in the adjacent margin area 4a, is thicker than the outermost layer 1 on the opposite side reaching the outermost edge of the web. By this arrangement the above mentioned concern about the thickness of the middle layer 2 due to a possible increased thickness at the connecting area of the two laminate materials can totally be avoided. It is also easier to choose the surface layers 3 and 1 having thicknesses suitable for the properties of the end product than to adjust the thickness of the material of the middle layer 2 in the margin zone 4a.
In the embodiment of Figs. 3 and 4 the thicknesses of the surface layers 1 and 3 can be so chosen that in each of the webs 4 the thickness of the thicker surface layer 3 is substantially equal to the sum thickness of the thinner layer 1 and the middle layer 2 in the margin zone 4a of the adjacent web 4. It is most practical to use two identical laminate webs 4 when manufacturing a joined laminate material, in which case the thicker layer 3 in one of the webs has the same thickness as the corresponding layer 3 in the other, adjacent web, and the remaining layers 2 and 1
have the same thicknesses as the corresponding layers 2 and 1 in the adjacent web.
As illustrated by Fig. 4, in the connecting area 4a the laminate material has the same thickness as the material on both sides thereof formed by the middle areas of single webs 4. The thickness of the middle layer 2 doubled due to the joining of the two middle layers of adjacent webs together is thus compensated due to the thinner surface layers 1 in this area 4a. The product obtained is of uniform thickness at its whole width and it can be wound into a large roll without difficulties.
Fig. 5 shows a constructional solution, by which two or several laminate webs 4 can be guided together at their margin zones 4a. Single webs 4 may be for example on rollers where they are wound into rolls 6. The webs are guided from the rolls such that they travel in different converging planes towards each other to the joining point designated A in Fig. 5. At this point the material of middle layer 2 within the zones 4a is subjected to energy melting the material, such as infrared or microwave radiation. The energy can also be supplied in a form of a heating roller or flame heating (so-called flame seaming method). The methods used are of course dependent on their compatibility with the process, on the velocity of web for example. The zones 4a can be guided against each other to the joining point by means of suitable guiding rollers. Immediately after the joining point A is disposed a pair of pressure rollers 7 extending transversely on the whole width of the final laminate and pressing the zones 4a finally together. At the same time the rollers 7 guide the laminate material of final width to a storage roll 8. Hence, a wider web starting from narrower webs is obtained. The narrower webs are easily manufactured as heretofore using conventional
laminating technique. By the method of Fig. 5 it is possible to manufacture a web whose width exceeds 3 m for packaging large paper rolls.
It shall be understood that even if the use of two webs 4 for manufacturing a wider laminate material has been described in Fig. 5, the material can also be manufactured starting from more than two single webs 4, which can be for example of constant width. In this case the margin areas 4a of the type presented in Fig. 1 or Fig. 3 must be available for sealing at both longitudinal edges of the middle webs 4 lying between the outermost webs.
The width of the margin zones depends on the grammage of the material and it must be such that the finished material has a sufficient tensile strength in the transverse direction.
The outermost edges of the finished wide laminate material may be even, that is, all layers 1, 2 and 3 end at substantially the same point in the outermost edge of the material. The outermost edge of the finished laminate material may be, however, of the type shown by Fig. 1 or 3 even at this area, that is, one of the layers 1 and 3 does not extend to the outermost edge, which makes the material suitable for packaging paper rolls in the way which is described in a previous Finnish patent application No. 873850 by the applicant.