A METHOD AN APPARATUS FOR SEPARATING TWO SUCCESSIVE STACKS OF INTERFOLDED SHEETS OF A TYPE JOINED BY A PRE-TEAR OR PERFORATION LINE AND FOR OBTAINING A PACK OF INTERFOLDED SHEETS WHEREIN AN END SHEET OF THE PACK IS FOLDED TO DEFINE A GRIPPABLE FLAP FOR A FACILITATED EXTRACTION OF THE SHEETS FROM THE PACK

Abstract

The method for separating two successive stacks (PA. PB) of interfolded sheets comprises: once having released the formed stack (PA) on a conveyor (O), moving the two support tables (11, 12), one following another, in such a way as to fold the strip(S) of sheets hanging below the successive stack (PB) under formation supported by the pair of separator elements (14, 15), in such a way that, when the two support tables (11, 12) are brought to face one another or moved towards one another to support the successive stack (PB) under formation, an end flap (F3) of the lower sheet of the successive stack (PB) under formation is partially folded and hanging between the two support tables to form a grippable flap (L) for a facilitated extraction of the sheets from the pack (P) which is obtained once the formation of the successive stack (PB) is completed.

Claims

1. A method for separating two successive stacks of interfolded sheets of a type joined by a pre-tear or perforation line and for obtaining a pack of interfolded sheets wherein an end sheet of the pack is partially folded on itself to define a grippable flap for a facilitated extraction of the sheets from the pack, comprising: predisposing a pair of support tables movable independently of one another; predisposing a separating board, movable independently of the pair of support tables; predisposing a pair of separator elements arranged facing one another and movable independently of one another and independently of the pair of support tables and of the separating table; and comprising carrying out steps of: positioning the pair of support tables in a raised position facing one another, and in a configuration neared one another, transversally to a vertical direction along which the folding of interfolded sheets joined by a pre-tear or perforation line takes place in order to form stacks of interfolded sheets, for supporting the folded and interfolded sheets during the formation of a stack; translating the pair of support tables vertically downwards to enable complete formation of a stack of interfolded sheets of a predetermined height; positioning the pair of separator elements in a position in which they are splayed and are bilateral to the vertical direction at the sides of the stack of interfolded sheets during the formation and completion of the stack on the pair of support tables; positioning the separating board in a lateral position with respect to the vertical direction along which the formation and completion of the stack of the interfolded sheets on the pair of support tables takes place; having completed the formation of a stack of interfolded sheets of a predetermined height: moving the pair of separator elements transversally to the vertical direction so as to bring them into a position in which they are mutually neared in such a way as to insert the separator elements between consecutive connecting sheets between the folded sheet of the already-formed stack and a first folded sheet of a successive stack under formation in order to support the successive stack under formation, then lowering the pair of support tables so as to move the already-formed stack away from the successive stack under formation supported by the pair of separator elements, unfolding a series of connecting sheets between the last sheet of the already-formed stack and the first sheet of the successive stack under formation; moving the separating board transversally to the vertical direction in order to position the separating board above the already-formed stack supported by the pair of support tables; translating the pair of support tables and the separating board vertically downwards so as to move the already-formed stack away from the successive stack under formation in such a way as to separate the connecting sheets between the two stacks at a pre-tear or perforation line present thereon leaving a strip of sheets hanging below the stack under formation on the pair of separator elements; moving the separating board away from the formed stack; moving the pair of support tables away from one another so as to position the support tables in a reciprocally moved-away position in order to release the stack formed above a conveyor; moving a first support table of the pair of support tables upwards into a lower position than the pair of separator elements and moving the first support table transversally to the vertical direction to abut the strip of hanging sheets and to fold a first portion of the strip of hanging sheets below the successive stack under formation on the pair of separator elements leaving a second portion of the strip of sheets hanging below the first support table; moving a second support table of the pair of support tables upwards into a lower position than the pair of separator elements and moving the second support table transversally to the vertical direction to abut the second portion of the strip of hanging sheets to partially fold the second portion below the first support table leaving an end flap of the second portion partially folded and hanging below the second support table; moving the first support table and the second support table in order to arrange them facing one another and in the configuration neared one another; raising the first support table and the second support table in order to arrange them against the successive stack under formation on the pair of separator elements leaving the end flap partially folded and hanging between the first support table and second support table; moving the pair of separator elements away from one another in order to disengage the successive stack under formation and so as to release the successive stack under formation to rest on the first support table and on the second support table; translating the first support table and the second support table vertically downwards up to complete formation of the successive stack obtaining a pack of interfolded sheets with the end flap partially folded and hanging there-between and remaining projecting below the pack to define a grippable flap for a facilitated extraction of the sheets from the pack.

2. The method as claimed in claim 1, comprising predisposing a sheet stretching element laterally to the vertical direction and maintaining the sheet-stretching element in a lateral position which is external with respect to a stack under formation and, before the step of moving a first support table of the pair of support tables upwards into a lower position than the pair of separator elements and moving the first support table transversally to the vertical direction to abut the strip of hanging sheets and folding a first portion of the strip below the successive stack under formation on the pair of separator elements leaving a second portion of the strip hanging below the first support table, the method comprises carrying out a step of moving the sheet-stretching element transversally to the vertical direction, and below the pair of separator elements in the neared position thereof to support the successive stack under formation, in such a way as to abut the strip of sheets hanging below the stack under formation on the pair of separator elements and stretching an initial part of the strip below the stack under formation leaving the first portion and the second portion of the strip hanging below the stack under formation.

3. The method as claimed in claim 2, comprising moving the sheet-stretching element transversally to the vertical direction, and below the pair of separator elements in the neared position thereof, in such a way as to abut the strip of sheets hanging below the stack under formation on the pair of separator elements and stretching an initial part of the strip below the stack under formation leaving the first portion and the second portion of the strip hanging below the stack under formation, at any time after the step of moving the pair of separator elements transversally to the vertical direction so as to bring them into a position in which they are mutually neared and before the step of moving a first support table of the pair of support tables upwards into a lower position than the pair of separator elements and moving the first support table transversally to the vertical direction to abut the strip of hanging sheets and to fold the first portion of the strip below the successive stack under formation of the pair of separator elements leaving a second portion of the strip hanging below the first support table.

4. The method as claimed in claim 1, comprising, before the step of translating the pair of support tables and the separating board vertically downwards in order to move the already-formed stack away from the successive stack under formation, carrying out a step of raising the pair of support tables towards the separating board, maintaining the separating board stationary, so as to compact the stack already formed.

5. The method as claimed in claim 1, comprising, before the step of mutually moving the pair of support tables away from one another in order to position the support tables in a reciprocally moved-away position so as to release the stack formed above a conveyor, carrying out a step of directing a puff of air against the end flap partially folded and hanging between the pair of support tables and which remains projecting inferiorly from the pack so as to fold the end flap against the lower part of the pack.

6. The apparatus for carrying out the method as claimed in claim 1, comprising: a pair of support tables, wherein a first support table is borne by a first frame which is mounted vertically slidingly along a first vertical sliding guide, with the first frame also being predisposed to be movable transversally to the first vertical sliding guide in such a way that the first support table can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction, wherein a second support table is borne by a second frame which is mounted vertically slidingly along a second vertical sliding guide, parallel to the first vertical sliding guide and arranged on an opposite side to the first vertical sliding guide with respect to the vertical direction of formation of the stack of interfolded sheets, with the second frame also being predisposed to be transversally movable with respect to the second vertical sliding guide in such a way that the second support table can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction; a separating board which is borne by a third frame, wherein the third frame is mounted vertically slidingly along the first vertical sliding guide or the second vertical sliding guide, with the third frame also being predisposed to be transversally movable with respect to the first vertical sliding guide or to the second vertical sliding guide in such a way that the separating board can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction, a pair of separator elements, wherein a first separator element is borne by a fourth frame which is mounted vertically slidingly along the first vertical sliding guide, with the fourth frame also being predisposed to be transversally movable with respect to the first vertical sliding guide in such a way that the first separator element can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction, wherein a second separator element is borne by a fifth frame which is mounted vertically slidingly along the second vertical sliding guide, parallel to the first vertical sliding guide and arranged on an opposite side to the first vertical sliding guide with respect to the vertical direction of formation of the stack of interfolded sheets, with the fifth frame also being predisposed to be transversally movable with respect to the second vertical sliding guide in such a way that the second separator element can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction.

7. The apparatus as claimed in claim 6, comprising a sheet-stretching element borne by a sixth frame, with the sixth frame being mounted vertically slidingly along the first vertical sliding guide or the second vertical sliding guide, with the sixth frame which is also predisposed to be transversally movable with respect to the first vertical sliding guide or to the second vertical sliding guide in such a way that the sheet-stretching element can be movable both vertically and parallel to the vertical direction, along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction.

8. The apparatus as claimed in claim 7, comprising blowing means of an air flow.

9. A pack of interfolded sheets, wherein the interfolded sheets of the pack are joined to one another by a pre-tear or perforation line, with an end sheet of the pack being partially folded on itself so as to form a grippable flap for a facilitated extraction of the sheets from the pack, obtained with the method as claimed in claim 1.

10. The apparatus as claimed in claim 6, comprising blowing means of an air flow.

11. The method as claimed in claim 2, comprising, before the step of translating the pair of support tables and the separating board vertically downwards in order to move the already-formed stack away from the successive stack under formation, carrying out a step of raising the pair of support tables towards the separating board, maintaining the separating board stationary, so as to compact the stack already formed.

12. The method as claimed in claim 3, comprising, before the step of translating the pair of support tables and the separating board vertically downwards in order to move the already-formed stack away from the successive stack under formation, carrying out a step of raising the pair of support tables towards the separating board, maintaining the separating board stationary, so as to compact the stack already formed.

13. The method as claimed in claim 2, comprising, before the step of mutually moving the pair of support tables away from one another in order to position the support tables in a reciprocally moved-away position so as to release the stack formed above a conveyor, carrying out a step of directing a puff of air against the end flap partially folded and hanging between the pair of support tables and which remains projecting inferiorly from the pack so as to fold the end flap against the lower part of the pack.

14. The method as claimed in claim 3, comprising, before the step of mutually moving the pair of support tables away from one another in order to position the support tables in a reciprocally moved-away position so as to release the stack formed above a conveyor, carrying out a step of directing a puff of air against the end flap partially folded and hanging between the pair of support tables and which remains projecting inferiorly from the pack so as to fold the end flap against the lower part of the pack.

15. The method as claimed in claim 4, comprising, before the step of mutually moving the pair of support tables away from one another in order to position the support tables in a reciprocally moved-away position so as to release the stack formed above a conveyor, carrying out a step of directing a puff of air against the end flap partially folded and hanging between the pair of support tables and which remains projecting inferiorly from the pack so as to fold the end flap against the lower part of the pack.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The characteristics of a preferred, but not exclusive, embodiment of the method and apparatus of the present invention will be described in the following description with reference to the appended tables of drawings, in which:

[0037] figures from 1A to 1D, already mentioned in the foregoing, schematically illustrate various modes of folding two continuous strips for the formation of successive stacks of interfolded sheets of a type joined by a pre-tear or perforation line;

[0038] FIG. 1E schematically illustrates a pack of interfolded sheets with an end sheet of the pack being partially folded on itself so as to form a grippable flap for a facilitated extraction of the sheets from the pack obtainable according to the method and apparatus of the invention;

[0039] figures from 2A to 2D, also mentioned in the foregoing, schematically illustrate the apparatus and operating steps described in document EP1640305 for the separation of stacks of interfolded sheets and the obtaining of packs of interfolded sheets without a grippable flap;

[0040] figures from 3A to 3P illustrate, in respective schematic views, a possible succession of operating steps of the method of the invention, and of the apparatus for carrying out the method, for separating two successive stacks of interfolded sheets of a type joined by a pre-tear or perforation line and for obtaining a pack of interfolded sheets in which an end sheet of the pack is partially folded on itself to define a grippable flap for a facilitated extraction of the sheets from the pack, such as the pack (P) illustrated in FIG. 1E.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The method of the present invention, for separating two successive stacks (PA, PB) of interfolded sheets of a type joined by a pre-tear or perforation line and for obtaining a pack (P) of interfolded sheets wherein an end sheet (S1) of the pack (P) is partially folded on itself to define a grippable flap (L) for a facilitated extraction of the sheets from the pack, comprises: [0042] predisposing a pair of support tables (11, 12) movable independently of one another; [0043] predisposing a separating board (13), movable independently of the pair of support tables (11, 12); [0044] predisposing a pair of separator elements (14, 15) arranged facing one another and movable independently of one another and independently of the pair of support tables (11, 12) and of the separating board (13).

[0045] The method comprises carrying out steps of: [0046] positioning the pair of support tables (11, 12) in a raised position facing one another, and in a configuration (R) neared one another, transversally to a vertical direction (Z) along which the folding of interfolded sheets joined by a pre-tear or perforation line takes place in order to form stacks of interfolded sheets, for supporting the folded and interfolded sheets during the formation of a stack (PA) (see for example FIG. 3A); [0047] translating the pair of support tables (11, 12) vertically downwards to enable complete formation of a stack (PA) of interfolded sheets of a predetermined height; [0048] positioning the pair of separator elements (14, 15) in a position in which they are splayed and are bilateral to the vertical direction (Z) at the sides of the stack (PA) of interfolded sheets during the formation and completion of the stack (PA) on the pair of support tables (11, 12); [0049] positioning the separating board (13) in a lateral position with respect to the vertical direction (Z) along which the formation and completion of the stack (PA) of the interfolded sheets on the pair of support tables (11, 12) takes place.

[0050] The method also comprises carrying out steps of: [0051] having completed the formation of a stack (PA) of interfolded sheets of a predetermined height: moving the pair of separator elements (14, 15) transversally to the vertical direction (Z) so as to bring them into a position in which they are mutually neared in such a way as to insert the separator elements (14, 15) between consecutive connecting sheets between the folded sheet of the already-formed stack (PA) and a first folded sheet of a successive stack (PB) under formation in order to support the successive stack (PB) under formation (see FIG. 3B), then lowering the pair of support tables (11, 12) so as to move the already-formed stack (PA) away from the successive stack (PB) under formation supported by the pair of separator elements (14, 15), unfolding a series of connecting sheets (FS) between the last sheet of the already-formed stack (PA) and the first sheet of the successive stack (PB) under formation (see FIGS. 3C and 3D); [0052] moving the separating board (13) transversally to the vertical direction (Z) in order to position the separating board (13) above the already-formed stack (PA) supported by the pair of support tables (11; 12) (FIG. 3E); [0053] translating the pair of support tables (11, 12) and the separating board (13) vertically downwards so as to move the already-formed stack (PA) away from the successive stack (PB) under formation in such a way as to separate the connecting sheets (FS) between the two stacks (PA, PB) at a pre-tear or perforation line present thereon leaving a strip(S) of sheets hanging below the stack (PB) under formation on the pair of separator elements (14, 15) (FIGS. 3F and 3G); [0054] moving the separating board (13) away from the formed stack (PA) (FIG. 3H); [0055] moving the pair of support tables (11, 12) away from one another so as to position the support tables (11,12) in a reciprocally moved-away position in order to release the stack (PA) formed above a conveyor (O) (FIG. 31).

[0056] The method of the invention also comprises carrying out the following special steps: [0057] moving a first support table (11) of the pair of support tables (11, 12) upwards into a lower position than the pair of separator elements (14, 15) and moving the first support table (11) transversally to the vertical direction (Z) to abut the strip(S) of hanging sheets and to fold a first portion (F1) of the strip(S) of hanging sheets below the successive stack (PB) under formation on the pair of separator elements (14, 15) leaving a second portion (F2) of the strip(S) of sheets hanging below the first support table (11) (FIG. 3L); [0058] moving a second support table (12) of the pair of support tables (11, 12) upwards into a lower position than the pair of separator elements (14, 15) and moving the second support table (12) transversally to the vertical direction (Z) to abut the second portion (F2) of the strip(S) of hanging sheets to partially fold the second portion (F2) below the first support table (11) leaving an end flap (F3) of the second portion (F2) partially folded and hanging below the second support table (12) (FIG. 3M); [0059] moving the first support table (11) and the second support table (12) in order to arrange them facing one another and in the configuration (R) neared one another; [0060] raising the first support table (11) and the second support table (12) in order to arrange them against the successive stack (PB) under formation on the pair of separator elements (14, 15) leaving the end flap (F3) partially folded and hanging between the first support table (11) and second support table (12) (FIG. 30); [0061] moving the pair of separator elements (14, 15) away from one another in order to disengage the successive stack (PB) under formation and so as to release the successive stack (PB) under formation to rest on the first support table (11) and on the second support table (12) (FIG. 3P); [0062] translating the first support table (11) and the second support table (12) vertically downwards up to complete formation of the successive stack (PB) obtaining a pack (P) of interfolded sheets with the end flap (F3) partially folded and hanging there-between and remaining projecting below the pack (P) to define a grippable flap (L) for a facilitated extraction of the sheets from the pack.

[0063] Owing also the presence of the pair of support tables, instead of one alone in the above-described prior art, and owing to the special movement mode of the two support tables, with the method of the invention it is possible to use the separating board only for the separation of two consecutive stacks, as the two support tables are utilised to carry out the folding of the strip of sheets which remain hanging below the stack under formation, once separated from the stack already-formed.

[0064] Therefore the two support tables, once the folding has been completed, are already in a position such as to be immediately used for support of the successive stack under formation, enabling the pair of separator elements to be returned into the splayed configuration.

[0065] This enables obtaining a production regime that is higher than in the prior art described in the foregoing.

[0066] Further, the folding of this strip of hanging sheets is carried out by the two support tables in a special mode that enables leaving defined an end flap (F3) partially folded and projecting inferiorly from the pack (P) to define a grippable flap (L) for a facilitated extraction of the sheets from the pack.

[0067] Further special aspects of the method of the invention are described in the following.

[0068] The method comprises predisposing a sheet-stretching element (16) laterally to the vertical direction (Z) and maintaining the sheet-stretching element (16) in a lateral position which is external with respect to a stack under formation. The function of the sheet-stretching element (16) is the following.

[0069] Before the step of moving a first support table (11) of the pair of support tables (11, 12) upwards into a lower position than the pair of separator elements (14, 15) and moving the first support table (11) transversally to the vertical direction (Z) to abut the strip(S) of hanging sheets and to fold a first portion (F1) of the strip(S) of hanging sheets below the successive stack (PB) under formation on the pair of separator elements (14, 15) leaving a second portion (F2) of the strip(S) of sheets hanging below the first support table (11), the method comprises carrying out a step of moving the sheet-stretching element (16) transversally to the vertical direction (Z), and below the pair of separator elements (14, 15), so as to abut the hanging strip(S) below the stack (PB) under formation on the pair of separator elements (14, 15).

[0070] This advantageously enables extending an initial part of the strip(S) below the stack (PB) under formation leaving the first portion (F1) and the second portion (F2) of the strip(S) hanging below the stack under formation(S).

[0071] This moving performed by the sheet-stretching element will facilitate the operations of folding the strip of hanging sheets by the two support tables for the formation of the end flap to be made to remain projecting beneath the pack of sheets.

[0072] In other aspects, the method of the invention can include moving the sheet-stretching element (16) transversally to the vertical direction (Z), and below the pair of separator elements (14, 15) in the neared position thereof, in such a way as to abut the strip(S) of sheets hanging below the stack (PB) under formation on the pair of separator elements (14, 15) and stretching an initial part of the strip(S) below the stack (PB) under formation leaving the first portion (F1) and the second portion (F2) of the strip(S) hanging below the stack under formation(S), at any time after the step of moving the pair of separator elements (14, 15) transversally to the vertical direction (Z) so as to bring them into a position in which they are mutually neared in order to support the successive stack (PB) under formation, but in any case before the step of moving a first support table (11) of the pair of support tables (11, 12) upwards.

[0073] In a further advantageous aspect, the method of the invention can comprise, before the step of translating the pair of support tables (11, 12) and the separating board (13) vertically downwards in order to move the already-formed stack (PA) away from the successive stack (PB) under formation, carrying out a step of raising the pair of support tables (11, 12) towards the separating board (13), maintaining the separating board (13) stationary, so as to compact the stack (PA) already formed.

[0074] A further and other aspect of the method of the invention consists in the fact that the method comprises directing a puff of air against the end flap (F3) partially folded and hanging between the pair of support tables (11, 12) and which remains projecting inferiorly from the pack (P) so as to fold the end flap against the lower part of the pack (P) before the pack (P) is released by the pair of support tables (11, 12) on the conveyor (O).

[0075] In figures from 3A to 3P, reference numeral (100) denotes a preferred embodiment of the apparatus for carrying out the method of the invention. The apparatus (100) comprises a pair of support tables (11, 12), for example the two support tables are constituted by elements having an overturned L shape.

[0076] A first support table (11) is borne by a first frame (110) which is mounted vertically slidingly along a first vertical sliding guide (31), with the first frame (110) also being predisposed to be movable transversally to the first vertical sliding guide (31) in such a way that the first support table (11) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0077] For example, the first frame (110) can be mounted and borne slidably, from a first carriage (not illustrated as of known type) which, in turn, is mounted slidably on the first vertical sliding guide (31).

[0078] A second support table (12) is borne by a second frame (120) which is mounted vertically slidingly along the second vertical sliding guide (32), parallel to the first vertical sliding guide (31) and arranged on an opposite side to the first vertical sliding guide (31) with respect to the vertical direction (Z) of formation of the stack of interfolded sheets, with the second frame (120) also being predisposed to be transversally movable with respect to the second vertical sliding guide (32) in such a way that the second support table (12) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0079] For example, the second frame (120) can be mounted and borne slidably by a second carriage (not illustrated as of known type) which, in turn, is mounted slidably on the second vertical sliding guide (32).

[0080] The apparatus (100) further comprises a separating board (13) which is borne by a third frame (130), wherein the third frame (130) is mounted vertically slidingly along the first vertical sliding guide (31) or the second vertical sliding guide (32), with the third frame (130) also being predisposed to be transversally movable with respect to the first vertical sliding guide (31) or to the second vertical sliding guide (32) in such a way that the separating board (13) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0081] For example, the third frame (130) can be mounted and borne slidably by a third carriage (not illustrated as of known type) which, in turn, is mounted slidably on the first vertical sliding guide (31) or on the second vertical sliding guide (32).

[0082] The apparatus (100) also has a pair of separator elements (14, 15).

[0083] A first separator element (14) is borne by a fourth frame (140) which is mounted vertically slidingly along a first vertical sliding guide (31), with the fourth frame (140) also being predisposed to be transversally movable with respect to the first vertical sliding guide (31) in such a way that the first separator element (14) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0084] For example, the fourth frame (140) can be mounted and borne slidably by a fourth carriage (not illustrated as of known type) which, in turn, is mounted slidably on the first vertical sliding guide (31).

[0085] A second separator element (15) is borne by a fifth frame (150) which is mounted vertically slidingly along a second vertical sliding guide (32), parallel to the first vertical sliding guide (31) and arranged on an opposite side to the first vertical sliding guide (31) with respect to the vertical direction (Z) of formation of the stack of interfolded sheets, with the fifth frame (150) also being predisposed to be transversally movable with respect to the second vertical sliding guide (32) in such a way that the second separator element (15) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0086] For example, the fifth frame (150) can be mounted and borne slidably by a fifth carriage (not illustrated as of known type) which, in turn, is mounted slidably on the second vertical sliding guide (32).

[0087] In a preferred aspect, the apparatus (100) comprises a sheet-stretching element (16) borne by a sixth frame (16).

[0088] The sixth frame (16) is mounted vertically slidingly along the first vertical sliding guide (31) or the second vertical sliding guide (32), with the sixth frame (160) which is also predisposed to be transversally movable with respect to the first vertical sliding guide (31) or to the second vertical sliding guide (32) in such a way that the sheet-stretching element (16) can be movable both vertically and parallel to the vertical direction (Z), along which the formation of the stacks of interfolded sheets takes place, and transversally to the vertical direction (Z).

[0089] For example, the sixth frame (160) can be mounted and borne slidably by a sixth carriage (not illustrated as of known type) which, in turn, is mounted slidably on the second vertical sliding guide (32).

[0090] The apparatus (100) can also comprise blowing means (17) of an air flow. The blowing means (17) of an air flow can for example be constituted by nozzles, advantageously predisposed and mounted on an arm of the L of one of the two support tables (11, 12) and can be connected to a source of compressed air.

[0091] Owing to the above-described structure, the apparatus (100) is thus configured so as to be able to carry out the steps of the method of the invention for obtaining a pack (P) of interfolded sheets, wherein the interfolded sheets of the pack are joined to one another by a pre-tear or perforation line, with an end sheet (S1) of the pack being partially folded on itself so as to form a grippable flap (L) for a facilitated extraction of the sheets from the pack such as the pack (P) illustrated schematically in FIG. 1E.