Separating membrane with improved adhesion and process for obtaining it

Abstract

Separating membrane of plastic material, made up of a bossed and waterproof sheet which is coupled with a permeable base layer. The bosses are of the cylindrical type with a double diameter and have such a shape and arrangement as to feature improved adhesion on both faces. The gripping of the adhesive is increased in order to obtain greater tear strength, on the upper face, and at the same time increases the area of contact with the base layer for a greater resistance to delamination on the lower face. In particular, inside each chamber there is an internal crown, which divides it like a necking into two superimposed compartments having the same diameter, wherein the first compartment has a depth amounting to at least ⅓ of the total. A production process for obtaining the membrane is also disclosed.

Claims

1. A process for producing a separating membrane with improved adhesion for use in construction, the process comprising the steps of: extruding a raw plastic material so as to form a waterproofing plastic sheet, the raw material being a thermoplastic material or a mixture of polymers; forming the extruded plastic sheet around a bossed roller having protrusions arranged in a regular matrix so as to form bosses in the plastic sheet; and roughening one face of the plastic sheet by forming superficial microcavities by release of internal gas from the external surface of the plastic sheet, the superficial microcavities opening outwardly and having a depth of greater than 35 micrometers, the superficial microcavities being irregular craters or pores.

2. The process of claim 1, the step of roughening further comprising: forming grooves or cuts in the one face of the plastic sheet by mechanical removal of portions of the plastic sheet.

3. The process of claim 1, further comprising: prior to the step of extruding, adding an additive to the raw plastic material so as to produce the internal gas released during the step of roughening, the additive being a mineral filler or a foaming agent.

4. The process of claim 3, the additive comprising particles of calcium carbonate of nanometric dimensions where 99% of the particles have a diameter smaller than 50 micrometres, wherein the additive quantity is between 1% and 20% of the total raw material, and with a humidity lower than 0.5%.

5. The process of claim 3, the additive comprising a foaming agent between 0.25% and 2% of the total mixture of raw material.

6. The process of claim 5, wherein the foaming agent is azodicarbamide in a polyethylene matrix at 0.5% in weight when extruding the plastic material at 500 g/m.sup.2.

7. The process of claim 3, the additive comprising a foaming agent between 2% and 5% of the total mixture of raw material.

8. A process for producing a separating membrane with improved adhesion for use in construction, the process comprising the steps of: extending a raw plastic material so as to form a waterproofing plastic sheet, the raw material being a thermoplastic material or a mixture of polymers; forming the extended plastic sheet around a bossed roller having protrusions arranged in a regular matrix so as to form bosses in the plastic sheet; and roughening an entirety of one face of the plastic sheet by forming grooves or cuts in the one face of the plastic sheet by superficial mechanical removal of portions of the plastic sheet, the grooves or cuts comprising superficial microcavities opening outwardly and having a depth of greater than 35 micrometers.

9. The process of claim 8, the step of roughening further comprising: prior to the superficial mechanical removal of portions of the plastic sheet, forming additional superficial microcavities by release of internal gas from the external surface of the plastic sheet.

10. The process of claim 8, the step of roughening comprising: passing the bossed plastic sheet through thermal conditioning rollers with integrated rotating means for brushing or grinding so as to form the grooves or cuts.

11. The process of claim 10, wherein the rotating means for brushing or grinding comprise a rotating shaft covered with metal brushes.

12. The process of claim 10, wherein the rotating means for brushing or grinding comprise belt grinders arranged in series.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIGS. 1a-c show a conventional membrane of plastic material with cylindrical bosses arranged with a regular pitch, also being coupled on the lower side with a base layer of nonwoven fabric, according to the prior art; in particular, FIG. 1a is an axonometric view of a portion of said membrane, FIG. 1b is a plan view, FIG. 1c is a detail section on the section plane XI-XI of FIG. 1b.

(2) FIG. 2 shows a plan view of a portion of the separating membrane according to the invention, with undercut protrusions inside the chamber which are shaped as an internal crown.

(3) FIG. 3a is a detail section on the section plane X2-X2 of FIG. 2, in a first variant in which the internal crown has flattened edges; FIG. 3b is an enlargement relating to said internal crown, of FIG. 3a.

(4) FIG. 4a is a detail section on the section plane X2-X2 of FIG. 2, in a second variant in which the internal crown has the lower edge inclined; FIG. 4b is an enlargement relating to said internal crown, of FIG. 3a.

(5) FIGS. 5a-d show plan views of portions of separating membrane, of FIG. 2, in different configuration variants of the bosses in particular referring to a base configuration (FIG. 5a) with individually aligned cylindrical bosses with constant pitch, or even double (FIG. 5b), triple (FIG. 5c) or combined (FIG. 5d) and keeping the same position as said base configuration, the dotted perimeters of the cylindrical bosses being superimposed to facilitate understanding.

(6) FIGS. 6a-d show plan views of the membrane portion of FIGS. 5a-b in which the contact surface between the head of the boss and the base layer is represented in contrast with respect to the non-adherent surface.

(7) FIG. 7a shows a detail section of the membrane formed around the bossed forming roller, it being referred to the variant of FIG. 3a; FIG. 7b is an enlargement relating to the profile of the single boss.

(8) FIG. 8a shows a detail section of the membrane formed around the bossed forming roller, it being referred to the variant of FIG. 4a; FIG. 8b is an enlargement relating to the profile of the single boss.

(9) FIG. 9 is a simplified diagram of the process for roughening a bossed membrane, according to the present invention, depending on the configuration of the roughening.

(10) FIGS. 10a-b, 11a-b and 12a-b schematically show a bossed membrane in the roughened version, according to the present invention. In particular, FIG. 10a is an axonometric view of the roughened membrane in a first variant with porous surface, FIG. 10b being a detail section of FIG. 10a; FIG. 11a is an axonometric view of the roughened membrane in a second variant with cut surface, FIG. 11b being a detail section of FIG. 11a; FIG. 12a is an axonometric view of the roughened membrane in a third variant with combined porous and cut surface, FIG. 12b being a detail section of FIG. 12a.

(11) FIGS. 13a-b indicatively show enlarged orthogonal views, respectively from the top and in section X3-X3, being referred to a portion having a 3×3 mm width of the roughening porous surface as in FIGS. 10a-b, in a first variant with superficial microcavities in the form of single micropores.

(12) FIGS. 14a-b indicatively show enlarged orthogonal views, respectively from the top and in section X4-X4, being referred to a portion having a 3×3 mm width of the roughening porous surface as in FIGS. 10a-b, in a second variant with superficial microcavities in the form of composite pores.

(13) FIGS. 15a-b indicatively show enlarged orthogonal views, respectively from the top and in section X5-X5, being referred to a portion having a 3×3 mm width of the roughening cut surface as in FIGS. 11a-b, in a first variant with superficial brushing microcavities in the form of discontinuous grooves.

(14) FIGS. 16a-b indicatively show enlarged orthogonal views, respectively from the top and in section X6-X6, being referred to a portion having a 3×3 mm width of the roughening cut surface as in FIGS. 11a-b, in a second variant with superficial grinding microcavities in the form of linear, elongate and parallel grooves, in oriented bundles.

DETAILED DESCRIPTION OF THE INVENTION

(15) With reference also to the Figures (FIGS. 2-8), the invention relates to a separating membrane (10) for building and to the industrial process for obtaining it. The structure of the membrane is of the known and conventional type, it being originated from an extruded sheet (100) of plastic material and provided with bosses (102) arranged in a matrix with a regular pitch (P), which protrude from the lower face (111) to lean on the load-bearing structure and allow the bedding layer applied on the upper face (110) to penetrate the related chambers (103), it also being coupled on the lower side, according to the prior art, with a base layer (101) of nonwoven fabric for the purpose of realizing a multi-layer membrane of the separating type. In particular, the membrane (10) provided by the invention has bosses (102-3) having a particular shape and a particular arrangement, in such a way as to have improved adhesion on both faces (110-1), thus increasing the gripping of the cement adhesive for a greater tear strength and, at the same time, increasing the contact area with the base layer for a greater resistance to delamination.

(16) The invention provides a bossed sheet (100, 102-3) of a plastic material such as polyethylene, polypropylene or a mixture thereof; said base layer (101) is preferably of a nonwoven polypropylene fabric, of the type called spunbonded or spunlace. The thickness of the extruded sheet is directly proportional to its weight, which may range from 350 to 1000 g/m.sup.2; in particular, it has been observed that to a weight of 0.9 g/m.sup.2 corresponds more or less a thickness of 1 micrometre, therefore in the case of the preferred but not limitative configuration of extruded product of 500 g/m.sup.2 in weight corresponds a thickness of about 550 micrometres. The total thickness (SI) of the bossed sheet (100), including the protruding bosses and the thickness of the sheet itself, is preferably of 3 mm; however, in case of particular applications it can be greater, being for example of 5 mm and up to 7 mm.

(17) In more detail as to the particular restraint element for the adhesive of the cement type, the invention (FIGS. 2, 3a-b, 4a-b) provides that the chambers (103), obtained on the upper face (110) from the bosses (102) are equipped with an internal crown (104), having a constant width (L) of at least 0.8 mm, and preferably 1 mm, which acts as an undercut restraint element and which divides like a necking (D2) the internal space of the chamber (103, H) into at least two compartments (105-6). The first compartment (105) is cylindrical, has a diameter (D1) of 20 mm, a depth (HI) between ⅓ and ½ of the total depth (H) of the chamber (103) for the purpose of facilitating the entry of the cement adhesive and facilitate the complete filling of the chamber (103, 105-6), acting as a funnel, and increasing the contact surface; the second compartment (106) is formed by the necking (D2) in correspondence of said internal crown (104) and by the underlying and cylindrical (D1) widening (107) which simplifies restraint for the hardened adhesive, with a depth (H2) complementary to (HI) which is between ½ and ⅔ of said total depth (H). Said widening (107) having a depth (H3) at least equal to ⅙ of said total depth (H). All the above-indicated values being considered with a tolerance of +/−10%.

(18) In particular, said internal crown (104) is made during the bossing of the extruded sheet, as described in the following, forcing it into each protrusion (201a-b) of the forming roller (200), which is laterally provided with notches (203) in such a way as to obtain two folded edges joined to each other which protrude towards the inside of the chamber (103). In a first variant (10a), said internal crown has flattened edges (108-9), that is to say pressed in a parallel way one on top of the other in a substantially orthogonal direction with respect to the side walls of the chamber (FIGS. 3a-b, 7a-b); in a second variant (10b), said internal crown has the lower edge (109) inclined by 45° with respect to the upper edge (108), leaving said underlying widening (107, D1) with a depth (H3) at least equal to ⅙ of said total depth (H), as described above (FIGS. 4a-b, 8a-b). All the above-mentioned values being considered with a tolerance of +/−10%.

(19) In more detail as to the overall increase in the contact surface (112) with the base layer (101) stretched below said sheet (100), it is observed that said bosses are of the cylindrical type, with a greater diameter (D1) of 20 mm and arranged in a matrix with a constant pitch (P) of 26 mm; such values being considered with a tolerance of +/−10%. In this way one obtains a contact area (112) between the sheet (100) and the base layer (101), in correspondence of the heads of the bosses, which is larger with respect to the known and conventional configurations, being at least equal to 50% of the total area of the face. For the purposes of the invention, in particular, it is provided that said contact area is between 50% and 75% of the total area of the face, wherein such values are obtained by varying said base configuration (114a) (FIG. 5a), having individually aligned cylindrical bosses, that is to say, being grouped in groups of two (114b) (FIG. 5b), three (114c) (FIG. 5c) or combined (114d) (FIG. 5d) single and grouped, although always maintaining the same setting as said base configuration. Set out below are some application examples.

(20) In a first application example, corresponding to the base configuration of the invention (10) (FIG. 2, 5a), there are provided bosses (102-3) of the cylindrical type with a double diameter (D1, D2) the external cylinder (D1) comprising said internal crown (104, D2) which subdivides the chamber (103) into the two above-described compartments (105-6). Preferably, the bossed sheet (100) is of HDPE with a total thickness (SI) of about 3 mm, with a greater diameter (D1) of the bosses of 20 mm and with a pitch (P) of 26 mm; said sheet also being thermocoupled with a base layer (101) of nonwoven polypropylene fabric and with a contact area amounting to 50% of the whole face. Said internal crown (104) can, preferably but not exclusively, be made in said two variants (10a-b) as described in the following.

(21) As a non-exhaustive example, in a first variant of the bossing (10a) said first compartment (105) has a depth (HI) equal to ⅓ of the total (H), said second compartment (106) has a depth (H2) equal to ⅔ of the total and includes the widening (107) having a depth (H3) equal to about one third of the total; in this way one has experimentally obtained a value of resistance to the delamination between the base layer and the sheet of 0.30 n/mm, and one has also obtained a value of initial adhesion with the cement adhesive of 0.25 N/mm.sup.2. Furthermore, in a second variant (10b) said first compartment has a depth (HI) equal to ½ of the total (H), said second compartment has a depth (H2) equal to ½ of the total with the widening (107) having a depth (H3) equal to about ⅙ of the total; in this way one has equally obtained a value of resistance to said delamination of 0.30 n/mm, and one has also obtained a value of said initial adhesion of 0.25 N/mm.sup.2.

(22) In an embodiment variant (114b) with respect to said base configuration (114a) (FIGS. 5b, 6a), it is provided to group two adjacent cylindrical bosses, that is to say, to replace the single bosses with pairs in the form of elongate bosses of the oval type, two by two and in the same position. Calculating the area corresponding to the head of said grouped bosses, one obtains in percentage a contact surface (112) increased from 50% to 66% with respect to the total area.

(23) In another embodiment variant (114c) (FIGS. 5c, 6b), it is provided to group three adjacent cylindrical bosses, that is to say, to replace the single bosses with triple groups in the form of further elongate bosses of the oval type, three by three and in the same position. Calculating the area corresponding to the head of said grouped bosses, one obtains in percentage a contact surface increased to 72% with respect to the total area.

(24) In a further embodiment variant (114d) (FIGS. 5d, 6c-d), it is provided to combine said configurations of grouped bosses, double or triple, alternating them with single bosses and in the same position. By this solution one advantageously obtains a value of said resistance to delamination of 0.40 n/mm, and one also obtains a value of said initial adhesion of 0.35 N/mm.sup.2.

(25) In another variant of the invention, in order to further increase adhesion, it is provided to roughen at least one face of said bossed sheet by means of superficial microcavities, which are open towards the outside of the surface in such a way as to allow for a gripping of the widespread type and realizing at least one of the following roughening configurations of the membrane: with porous or cut surface.

(26) The process for industrially obtaining the above-described separating membrane includes the following operating phases: extruding the raw material in such a way as to form a thin sheet (100), said raw material consisting of at least one thermoplastic polymer or a mixture of polymers; then forming said sheet around a forming roller (200) of the bossed type, that is to say, being provided with protrusions (201) arranged in a matrix with a constant pitch (P) and a height between 2.5 mm and 7 mm, and preferably in such a way as to obtain a total thickness of the sheet (SI) of 3 mm; at the end of the forming, coupling on the lower side (111) of said sheet (100) the base layer (101) of nonwoven fabric, of the type called spunbonded. The invention, for the purpose of obtaining said bosses (102) of the cylindrical type with a double diameter (D1, D2) which also include the particular above-described internal crown (104, L), provides that each protrusion (201) of the roller (200) laterally comprises a main notch (202), shaped as a continuous cavity and orthogonal to the side walls of the boss, which is intended to fold the sheet (100) forcing its forming in such a way as to realize two folded edges (108, 109), undercut-joined, which protrude towards the inside of the chamber (103) in said first variant (10a) or in said second variant (10b) of configuration of said internal crown (104). Said main notch preferably having a width (L) of 1 mm and a height at least equal to twice the thickness of the sheet.

(27) In a first embodiment variant of the protrusion (201a) said main notch (202a) is configured with a rectangular section, in such a way as to form said internal crown (104) with the edges (108-9) flattened one on top of the other, that is to say, pressed in a horizontal direction and namely substantially parallel to the external surface of the roller (FIGS. 3a-b, 7a-b).

(28) In a second embodiment variant (200b) said main notch (202b) is configured with a triangular section with the lower face inclined by 45°, in such a way as to form an internal crown (104) with the lower edge (109) inclined by 45° with respect to the upper edge (108), which is substantially parallel to said roller (FIGS. 4a-b, 8a-b).

(29) Preferably, each protrusion (201) of the roller also has a secondary notch (203), shaped as a thin and continuous cavity, placed laterally at the base of the protrusion, which substantially reduces the portion of connection of the protrusion to the roller. Said secondary notch is intended to facilitate the forming operations at the base of the boss (102) allowing the sheet (100) to adapt itself to forming, by deforming and expanding.

(30) Said notches (202-3) subdivide the protrusion (201) into four main portions (204-7) (FIGS. 3a-b, 4a-b, 7a-b, 8a-b): a first portion (204) is cylindrical and is in correspondence of the secondary notch (203); a second portion (205) is cylindrical and corresponds to the greater diameter (D1) of the boss (102); said first and second portion (204-5) forming said upper compartment of the boss (102, HI); a third portion (206) is alternatively cylindrical (206a, D2) or shaped as a truncated cone (206b) and is in correspondence of said primary notch (202) to form respectively said internal crown in the two above-described embodiment variants (104a-b); a fourth portion (207) is cylindrical (D1) and corresponds to the greater diameter (D1) of the boss on the widening (107, H3) underlying said internal crown (104); said third and fourth portion (206-7) forming said lower compartment of the boss (106, H2).

(31) In more detail as to said four main portions: said first portion is cylindrical, has a diameter between 13 mm and 18 mm and a height of 0.5 mm; said second portion is cylindrical, has a diameter of 20 mm and a height between 0.5 mm and a maximum height equal to ½ of the total height; said third portion is alternatively cylindrical, with a diameter 18 mm and a height equal to twice the thickness of the sheet (100), or is shaped as a truncated cone with an inclination of 45° starting from 18 mm up to 20 mm towards said fourth portion; said fourth portion is cylindrical, has a diameter of 20 mm and a maximum height equal to ⅙ of the total height of the protrusion.

(32) Furthermore, the industrial process (30a-c) for obtaining a roughened membrane is described, said process being suitable for any bossed membrane (40a, 40b, 40c) (FIGS. 10-16) consisting of an extruded sheet of plastic material and formed around a bossed roller equipment, and being particularly suitable for the separating membrane (10a, 10b) described above (FIGS. 2-8), that is to say, according to the invention; it must be noted that said process (30a-c) can also be used to roughen any configuration of bossed membrane in correspondence of at least one face of the plastic sheet. With reference also to the schematic figures (FIGS. 9-16), enclosed for illustrative purposes only, said process (30a-c) allows to advantageously obtain a roughened membrane (10a-b, 40a-c) comprising particular roughening superficial microcavities (411a-d) which are open outwards in such a way as to realize a micro-gripping of the widespread type, for example to facilitate the adhesion of a cement adhesive; said superficial microcavities, having a depth greater than 35 micrometres, form one of the following roughening configurations: with porous surface (40a, 401) (FIGS. 10a-b), with cut surface (40b, 402) (FIGS. 11a-b) or with combined surface (40c, 401-2) (FIGS. 12a-b).

(33) In said first configuration (FIGS. 10a-b), the roughening of the membrane (40a) occurs with a porous surface (401) wherein the microcavities are of the type with pores (411a-b) formed by the bubbles of the gas which is advantageously contained in the material constituting the sheet and which comes out in a controlled way during the production phases in such a way as to leave in the material some gaps shaped as craters (412-3) and distributed in a random way, with a homogenous distribution density, over the entire surface of the face and also in the chambers (406). In said second configuration (FIGS. 11a-b) the roughening of the membrane (40b) occurs with a cut surface (402) wherein the microcavities are of the type with cuts (411c-d) mechanically obtained in correspondence of the portions of non-protruding surface of the roughened face, that is to say, on the most external surface and not inside the chambers and namely on the non-bossed parts of the sheet. In said third configuration (FIGS. 12a-b) the roughening of the membrane (40c) occurs with a combined surface (401-2) where there are simultaneously both said porous surface (401) and said cut surface (402); in that case, said microcavities with cuts (411c-d) are mechanically made on a surface which already comprises said microcavities with pores (411a-b).

(34) Said process (30a-c) in short provides the following operating phases: extruding the raw material in such a way as to form a sheet (400), said raw material consisting of at least one thermoplastic material or a mixture of polymers; then forming said sheet (400) around a bossed roller equipment provided with protrusions arranged in a regular matrix in such a way as to form a membrane with bosses (405); optionally realizing the coupling of a nonwoven fabric, on the face where the roughening is not provided; and wherein in particular the process provides, depending on each of said roughening configurations (40a-c) (FIG. 9): to obtain said first roughening configuration (40a), the process (30a) provides to join to the plastic material, before extrusion, an additive producing some gas which comes out during the forming phase, said additive being alternatively a mineral filler or a foaming agent; to obtain said second roughening configuration (40b), the process (30b) provides that, after the forming around the bossed roller, the bossed sheet crosses some thermal conditioning rollers where there are also some driving means which force it to pass on a working surface under rotating means which are intended to cut it mechanically, said rotating means being alternatively of the type for brushing or grinding; to obtain said third roughening configuration (40c), the process (30c) provides to combine said processes (30a-b) realizing mechanically said microcavities of the type with cuts (402a-b, 411c-d, 40b) on a surface which already comprises said microcavities with pores (401a-b, 411a-b, 40a).

(35) In more detail as to the carrying out of the process (30a) for obtaining said first configuration (40a), with porous roughening surface (401), it is provided: in a first variant (401a) (FIGS. 13a-b), to add to the plastic material some particles of mineral filler of nanometric dimensions where 99% of the particles have a diameter smaller than 50 micrometres, in a quantity between 1% and 20% of the total raw material, and with a humidity lower than 0.5%; wherein said mineral filler is calcium carbonate; in a second variant (401b) (FIGS. 14a-b), to add to the plastic material a quantity of foaming agent between 0.25% and 2% of the total mixture of raw material, said foaming agent being compatibilized with said plastic matrix in such a way that at the moment of extrusion it reacts with the atmosphere; and wherein said quantity of foaming agent forms a roughened membrane of the waterproof type; wherein said foaming agent alternatively is: of the type azodicarbamide in polyethylene matrix at 0.5% in weight on extrusion of HDPE at 500 g/m.sup.2, or of the type Hostatron AEL 601 in polyethylene matrix at 1.5% in weight on extrusion of HDPE at 600 g/m.sup.2; in a further variant with respect to the previous one, to add to the plastic material a quantity of foaming agent between 2% and 5% of the total mixture of raw material in such a way as to form a roughened membrane of the permeable and microperforated type; wherein said foaming agent is alternatively of the type Hostatron AEL 601 in polyethylene matrix at 2.5% in weight on extrusion of HDPE at 600 g/m.sup.2.

(36) In more detail as to the carrying out of the process (30b) for obtaining said second configuration (40b), with cut roughening surface (402), it is provided: in a first variant (402a) (FIGS. 15a-b) said rotating means are intended for brushing being of the type with a rotating shaft covered with metal brushes which act in such a way as to cut it forming said microcavities in the form of discontinuous grooves (411c); wherein the mouth (415) of said discontinuous grooves (411c) has a mainly circular and/or ovalized and/or irregularly polygonal shape, a depth (V2) between 35 micrometres and 200 micrometres and a width (VI) which is between 1 mm and 2 mm if measured on the diagonal in the brushing direction, and is between 0.5 mm and 1 mm if measured on the diagonal in a direction perpendicular to it; wherein said shaft is provided with said brushes over its entire width and wherein the metal bristles which make them up are spaced 2.5 mm to 5 mm from one another, with a rotational speed of the shaft higher than 1000 revolutions/minute, while the product advances at linear speeds of 3 metres/minute; wherein the removed chip (416) of each of said microcavities (411c) obtained by brushing can alternatively be left, that is to say, it is joined to the mouth (415) in a protruding way to increase the wrinkledness of the surface, or can be removed; in a second variant (402b) (FIGS. 16a-b) said rotating means are intended for grinding being of the belt grinder type arranged in series in such a way as to cut said sheet for a depth (V2) smaller than 100 micrometres, forming multiple microcavities (411d) mainly in the form of elongate grooves, oriented in at least two different directions to form a net-like geometry, wherein the pitch (V4) between two successive and parallel grooves is between 0.1 mm and 0.2 mm and the angle (β) between a primary direction (417a) and a secondary direction (417b) is between 15° and 90°.

(37) In more detail as to said porous surface (401) made by the above-described process, the first version (401a) features superficial microcavities (411a) shaped as single micropores having the crater (412) with the mouth (415) of a mainly circular shape, a width (VI) smaller than 200 micrometres and a depth (P) smaller than 95 micrometres; said superficial microcavities (411a) realizing a roughened membrane with a porous appearance of the waterproof type (FIGS. 13a-b).

(38) Moreover, in the second version (401b), said porous surface comprises superficial microcavities (411b) shaped as composite pores, with craters of the single type (412) and of the multiple type (413) as well; and wherein said craters of the multiple type (413) comprise at least two sub-craters (414a-b) joined to each other, being intersected and/or incorporated; and wherein said craters of the multiple type (413) have a width (VI) smaller than 300 micrometres and a depth (V2) which is variable depending on the type and on the quantity of the gas which has come out of the material and which is also variable depending on the production modes; and wherein said superficial microcavities (411b) realize a roughened membrane with a porous appearance which is of the waterproof type, if said depth (V2) is smaller than the thickness (V3) of the sheet, or is of the permeable and microperforated type if they are pass-through, that is to say, open on the lower face (410) as well (FIGS. 14a-b).

(39) In more detail as to said cut surface (402) made by the above-described process, in a first version (402a) it comprises superficial microcavities (411c) which are made mechanically by brushing, wherein said superficial microcavities (411c) are shaped as discontinuous grooves, with the mouth (415) having a mainly circular and/or ovalized and/or irregularly polygonal shape, a depth (V2) between 50 micrometres and 200 micrometres and a width (VI) between 0.5 mm and 2 mm; said superficial microcavities (411c) realizing a roughened membrane (40c) of the waterproof type with a wrinkled appearance. Furthermore, it is provided that said superficial microcavities (411c) can have on the outside the related removed chip (416), which remains joined to the surface in correspondence of the mouth (415) without being removed completely; in this case, therefore, one obtains a roughened membrane of the waterproof type with a wrinkled appearance with an improved gripping (FIGS. 15a-b) as well.

(40) Moreover, in a second version (402b), said cut surface comprises superficial microcavities (411d) shaped as linear, elongate and oriented grooves, assimilable to continuous grooves, which are made mechanically by grinding; the superficial microcavities (411d) are distributed in a regular way being parallel and grouped in bundles (418a-b), said bundles (418a) being oriented at least according to a primary grinding direction (417a) and also intersected by other bundles (418b) according to a secondary direction (417b) which cuts through said primary direction (417a) with a relative angle (a) which is between 15° and 90°. The depth (V2) of said superficial microcavities (411d) is between 100 micrometres and 500 micrometres; the pitch (V4) between two parallel and successive microcavities (411d) of the bundle (418a-b) is between 0.1 mm and 0.2 mm. Said superficial microcavities (411d) realize a roughened membrane of the waterproof type with a wrinkled appearance (FIGS. 16a-b).

(41) In particular, it is observed that said superficial microcavities of the type with cuts (402, 411c-d) are made mechanically in correspondence of the external surfaces and come into contact with the cutting equipment, that is to say, in correspondence of the non-extruded portions of surface of the face outside the chambers (406) (FIGS. 11a-b).

(42) In an alternative configuration, it is provided that said superficial microcavities (411a-d) are made both on the upper face (409) and on the lower face (410) of the sheet (400). In case of combined porous and cut surfaces, in particular, it is observed that on the lower face said superficial microcavities of the type with cuts (411c-d) are made only in correspondence of the heads (408) of said bosses (405), that is to say, on the surfaces which come into contact with the cutting equipment.

(43) Furthermore, as to said porous surface (401) made by the above-described process, it is observed that said microcavities (411) of the type with pores (411a-b) are formed by the bubbles of a gas which is contained in the material of the sheet and has come out in a controlled way during the production process, leaving in the material some gaps shaped as small craters (412-3) and distributed in a random way with homogenous density over the entire surface of the face (409) and also inside the chambers (406) (FIGS. 10a-b). To this purpose, in the first variant (401a) of roughening with pores where said superficial microcavities (411a) are shaped as micropores (FIGS. 13a-b), it is provided to use in the raw material some mineral additives, which are also called mineral fillers, preferably calcium carbonate; in fact, experiments have shown that the use of a mineral filler leads, in the operating conditions provided by the invention, to a roughened surface with small-sized pores having a generally circular area. In the second variant (401b) of roughening with pores, on the other hand, where said superficial microcavities (411b) are shaped as composite pores with craters of the single type (412) and also of the multiple type (413), it is provided to use in the raw material some foaming agents; in fact, experiments have shown that the use of a foaming agent leads, in the operating conditions provided by the invention, to a roughened surface with larger-sized composite pores with respect to the micropores of the previous variant, both with reference to the area and to the depth (V2) of each crater, also being joined to form sub-craters (414a-b). Furthermore, it has been observed that, if said sub-craters are numerous and joined to each other inside the same microcavity, the related crater (413) has on the inside a foam-like structure of the material.

(44) In more detail as to said first variant (401a) of roughening with pores (FIGS. 13a-b), it is provided to add to the plastic material some particles of mineral filler, preferably calcium carbonate, of nanometric dimensions, that is to say, with 99% of the particles having a diameter smaller than 50 micrometres, and being in a quantity between 1% and 20% of the total raw material, and also being with low humidity, that is to say, lower than 0.5%. In particular, it has been observed that, upon growing of the quantity of said mineral filler up to a maximum of 20% on the total raw material, one obtains superficial pores with a growing diameter, that is to say, up to 200 micrometres, and a depth (V2) up to 50 microns; substantially said superficial pores are formed because of the relative humidity present in the calcium carbonate. This phenomenon can be advantageously used for the purposes of the invention by not degassing the melted material during extrusion but allowing, and at the moment of the casting from the extrusion head, the gas microbubbles to spread out in a homogenous way in correspondence of the surface of the roller, to then come out naturally leaving on the entire hardened surface of the membrane the respective microcavities, in the form of micropores.

(45) In more detail as to said second variant (401b) of roughening with pores (FIGS. 14a-b), it is provided to insert in the mixture of plastic materials in extrusion, a foaming agent, compatibilized with the plastic matrix, which at the moment of extrusion reacts with the atmosphere. In general, one can consider as known various foaming substances, organic or inorganic, which are used to produce low-density polymer products; such substances, once the reaction temperature has been reached, expand in an exothermic and irreversible way, releasing a gas which generates in the products of plastic material a foam-like structure.

(46) For the purposes of the invention, in particular, experiments have shown that by applying such a foaming system directly in the extrusion with flat head for membranes, that is to say, by adding to the mixture of the raw materials a quantity of foaming agent between 0.25% and 2% of the total raw material, one obtains an extruded waterproof sheet of the rough type, characterised by the presence of microcavities whose volume and concentration are directly proportional to the percentage of foaming agent used. It has also been observed that, if dosed in greater quantities, the foaming agent may lead to the production of an extruded permeable sheet in which the cavities created by the expansion are pass-through; in fact, an addition between 2% and 5% allows to obtain a microperforated extruded sheet which is effective as a separating membrane for internal use, or even for external use if the stratigraphy provides the insertion of a drainage and waterproofing element under the screed.

(47) In a first production example of said second variant (401b) of roughening with pores, particularly suitable for the invention is a foaming agent of the type azodicarbamide in polyethylene matrix, at 0.5% in weight, on extrusion of HDPE at 500 g/m.sup.2; the so extruded membrane is no longer smooth but has a roughness extending over the entire surface of the face, and wherein each microcavity mainly has a diameter smaller than 100 micrometres and a depth (V2) smaller than 50 micrometres. In a second production example of said second variant (401b) of roughening with pores, particularly suitable for the invention is a foaming agent of the type called Hostatron AEL 601 in polyethylene matrix, at 1.5% in weight, on extrusion of HDPE at 600 g/m2; the so extruded membrane is no longer smooth but has a roughness extending over the entire surface of the face, and wherein each microcavity mainly has a diameter ranging between 200 and 400 microns and a depth (V2) smaller than 50 micrometres. In a third production example, particularly suitable for the invention is a foaming agent of the type called Hostatron AEL 601 in polyethylene matrix, at 2.5% in weight, on extrusion of HDPE at 600 g/m.sup.2; the extruded membrane is no longer continuous but is perforated thanks to the formation of pass-through cavities having a diameter greater than 500 microns.

(48) Furthermore, as to said cut surface (402), it is observed that said superficial microcavities are obtained by means of a mechanical action and not an action of the chemical-physical type, as occurs for said porous surface (401), and it is also observed that the action concerns only the most external portion of the sheet, that is to say, the non-bossed part, cutting only the surface in direct contact with the cutting equipment and not that inside the chambers (406). To this purpose, in a first variant (402a), by means of brushing one creates by removal some superficial microcavities in the form of discontinuous grooves; in a second variant (402b), by means of grinding one creates by removal some superficial microcavities in the form of linear, elongate and parallel grooves, in oriented bundles, assimilable to continuous grooves.

(49) In more detail as to said first variant (402a) of roughening by brushing (FIGS. 15a-b), once extruded and if necessary coupled with a nonwoven fabric, said sheet passes through some thermal conditioning rollers; between said rollers there is a driving system which guides the product to pass under a shaft covered with metal brushes: in fact, it has been observed that the rotation of said brushes creates on the surface of the sheet said microcavities in the form of discontinuous grooves (411c). In an advantageous production configuration, using a shaft provided with said brushes over its entire width and wherein the metal bristles which make them up are spaced 2.5 mm to 5 mm from each other, with a rotational speed of the shaft greater than 1000 revolutions/minute, while the product advances at a linear speed of 3 metres/minute, irregularly shaped grooves are formed, affecting areas having a length between 1 mm and 2 mm and a width between 0.1 mm and 0.5 mm, the dimensions being greater in the brushing direction. Such a configuration allows to obtain discontinuous grooves with the mouth (415) having a mainly circular and/or ovalized and/or irregularly polygonal shape, a depth (V2) between 50 micrometres and 200 micrometres and a width (VI) which is between 1 mm and 2 mm if measured on the diagonal in the brushing direction, and which is between 0.5 mm and 1 mm if measured on the diagonal in a direction perpendicular to it; such grooves can still be connected to the removed chip or not.

(50) In more detail as to said second variant (402b) of roughening by grinding (FIGS. 16a-b), which is also called lapping, instead of said shaft covered with metal brushes there is a series of belt grinders which act on a working surface through which the product is sent, being pulled by a drive; in particular, such grinders operate in such a way as to obtain multiple continuous grooves, having a depth (V2) smaller than 100 micrometres, which are oriented in at least two different directions to form a net-like geometry, wherein the pitch (V4) between two successive and parallel grooves is between 0.1 mm and 0.2 mm.

(51) In more detail as to the third variant (30c, 40c) of combined roughening (FIGS. 12a-b), it is easily carried out by producing a sheet provided with a porous surface (401a-b, 411a-b) according to at least one of the above-described processes, wherein then said cut surface (402a-b, 411c-d) is also made by means of a mechanical action according to at least one of the above-described processes.

(52) Finally, it is observed that each reference to said membranes of the roughened type (40, 40b, 40c), according to the above-described and represented embodiment configurations (FIGS. 9-16), is meant to be included in the advantageous embodiment configuration according to invention (10a, 10b), in particular as in said detail sections (FIGS. 3a, 3b, 4a, 4b).

REFERENCE

(53) (10) separating membrane of the bossed type, according to the invention, in a first variant (10a) with chambers provided with an internal crown with flattened edges, or in a second variant (10b) with chambers provided with an internal crown with inclined lower edge; (100) waterproof extruded sheet; (101) permeable base layer, of a nonwoven fabric; (102) boss, protruding from the lower face, in the cylindrical base configuration (102a) or double grouped (102b) or triple grouped (102c); (103) internal chamber of the boss, open on the upper face; (104) internal crown, continuous and protruding to form a necking which divides the chamber into two compartments, an upper compartment above it and an undercut lower compartment, said crown in the first variant having superimposed edges (104a) or in the second variant having the lower edge inclined (104b); (105) upper compartment, above the crown; (106) lower compartment, which is formed by the necking, corresponding to said internal crown, and by the underlying widening; (107) widening below the internal crown; (108) upper edge of the internal crown; (109) lower edge of the internal crown, undercut; (110) upper face of the membrane, facing upwards; (111) lower face of the membrane, facing downwards; (112) contact surface between the head of the boss and the base layer; (113) non-bossed surface of the sheet, at the extrados; (114a) membrane portion in the base configuration with cylindrical bosses; (114b) membrane portion in the variant with two by two grouped bosses; (114c) membrane portion in the variant with three by three grouped bosses; (114d) membrane portion in the combined variant, single-grouped; (200) forming roller; (201a-b) protrusion which forms the boss, in the two variants for forming the internal crown, respectively in the first variant with superimposed edges (201a) or in the second variant with inclined lower edge (201b) (202a-b) main notch, intended to form the internal crown, in the rectangular variant (202a) or in the triangular variant at 45° (202b); (203) secondary notch at the base of the protrusion, intended to facilitate the forming of the boss; (204) first portion of the protrusion of the roller, cylindrical, in correspondence of the secondary notch; (205) second portion of the protrusion of the roller, cylindrical, in correspondence of the greater diameter; (206a-b) third portion of the protrusion of the roller in correspondence of the internal crown, in the two embodiment variants: cylindrical (206a) with the smaller diameter, or shaped as a truncated cone (206b); (207) fourth portion of the protrusion of the roller, cylindrical, in correspondence of the widening underlying the internal crown; (30a-c) production process for roughening a bossed membrane, according to the invention, realizing a roughening configuration of the type: with porous surface (30a), with cut surface (30b) or with both porous and cut combined surface (30c); (40a-c) roughened membrane, according to the invention, in a first roughening configuration (40a) with porous surface, or in a second configuration (40b) with cut surface, or in a third configuration (40c) with both porous and cut combined surface; (400) plastic sheet; (401) porous roughening surface, in a first variant (401a) with superficial microcavities in the form of single micropores, or in a second variant (401b) with superficial microcavities in the form of composite pores; (402) cut roughening surface, in a first variant (402a) with superficial microcavities obtained by brushing in the form of discontinuous grooves or in a second variant (402b) with superficial microcavities obtained by grinding in the form of linear and parallel grooves, in oriented bundles; (404) smooth surface; (405) boss protruding from the lower face; (406) internal chamber of the boss; (407) side walls of the boss; (408) head of the boss; (409) upper face of the membrane, that is to say, facing upwards; (410) lower face of the membrane, that is to say, facing downwards; (411a-d) roughening superficial microcavities, in the variants of the type micropores (411a), composite pores (411b), discontinuous grooves obtained by brushing (411c), linear and oriented grooves obtained by grinding (411d); (412) single crater; (413) multiple crater; (414a-b) sub-craters joined to form a multiple crater; (415) mouth of the crater; (416) brushing removed chip; (417a-b) primary and secondary grinding directions; (418) oriented bundle formed by a group of grinding superficial microcavities, in the form of linear and parallel grooves, being oriented according to a primary direction (418a) and a secondary direction (418b); (a) relative angle between the direction of protrusion of the upper edge of the internal crown and the inclined lower edge; (ß) relative angle between the primary and secondary grinding directions; (D1) greater diameter of the chamber inside the boss; (D2) smaller diameter, corresponding to the internal crown; (L) width of the internal crown; (H) total depth of the chamber; (HI) depth of the first compartment; (H2) depth of the second compartment; (H3) depth of the widening below the internal crown, in correspondence of the fourth portion of the protrusion of the roller; (P) pitch of the bosses arranged in a matrix; (SI) total thickness of the bossed sheet. (VI) width of the superficial microcavity; (V2) depth of the superficial microcavity; (V3) thickness of the sheet of plastic material; (V4) pitch between the superficial microcavities in the form of parallel grooves obtained by grinding.