Multilayer sheet and blister pack comprising said multilayer sheet, method for manufacturing a multilayer sheet and method for manufacturing a blister pack

Abstract

A mono-oriented multilayer sheet (4) comprises two external monolithic layers (42, 44) and at least one intermediate microporous layer (40), interposed between said monolithic layers (42, 44). The microporous layer (40) comprises a polymeric matrix (400) in which mineral fillers are dispersed. A press-through blister pack (1) for the pharmaceutical and nutraceutical sector comprises an upper wall (12) and a breakable wall (14) mutually constrained so as to form and tightly seal one or more containment chambers (3) for drugs or supplements. The upper wall (12) and the breakable wall (14) are both made of polymeric material, and the breakable wall (14) comprises a multilayer sheet (4) according to the present invention. A method for manufacturing a multilayer sheet (4) and a method for manufacturing a blister pack (1) according to the present invention.

Description

"MULTILAYER SHEET AND BLISTER PACK COMPRISING SAIDMULTILAYER SHEET , METHOD FOR MANUFACTURING A MULTILAYER SHEET AND METHOD FOR MANUFACTURING A BLISTER PACK" DESCRIPTIONField of application

[0001] The present invention relates to a multilayer sheet and a press-through blister pack for the pharmaceutical , nutraceutical , cosmetic, or food sector for containing pharmaceutical or nutraceutical or cosmetic products such as drugs , supplements or the like , for example in the form of tablets , powders , liquids , hard or soft capsules , comprising a multilayer sheet according to the present invention .

[0002] The present invention also relates to a method for manufacturing a multilayer sheet and a method for manufacturing a blister pack according to the present invention .

[0003] In the field of blister packs for pharmaceuticals and nutraceuticals , in particular for press-through blister packs , the use of polymeric materials is known for the manufacture of the rigid portion of the blister pack, also known as the top, i . e . , the part in which the seats for the drugs or supplements are obtained, generally by thermoforming .

[0004] The closing sealing sheet , also known as the lid,i . e . the portion of blister pack material that is broken under pressure in order to access the contents of said blister pack, is currently made mainly of aluminum, due to good features of strength and the intrinsic fragility of the material , which makes the product extremely easy to open . These portions are generally welded together by heat-seal resins , generally belonging to classes of materials that are di f ferent from both those used for the top and those used for the lid .

[0005] Disadvantageously, this classic solution is no longer up to date with current sustainability requirements . In fact , blister packs made of such materials are currently not manageable as di f ferentiable wastes at the end of their li fe , since the separation of the rigid part from the sealing sheet is extremely complicated, especially at sealing points .

[0006] Therefore , these solutions have to date a high environmental impact and do not meet the increasingly stringent demand for ecological solutions .

[0007] Alternative blister pack solutions that satis fy the recyclability requirement are also being studied and developed; for example , polymeric mono-material blister packs have been proposed on the market .

[0008] Some recently promoted solutions provide for blister packs made entirely of polypropylene ( PP ) or polyethyleneterephthalate ( PET ) .

[0009] Disadvantageously, these solutions have drawbacks linked to the inadequate mechanical properties of the material for this type of application . For example , such blister packs were found to be di f ficult to open, due to the poor breakability of the sealing sheet . According to a further disadvantage , such solutions of fer insuf ficient impermeability to the passage of oxygen, which compromises the contents of said blister pack .

[0010] In order to overcome these drawbacks , some known solutions provide for incisions or pre-cuts made in the sealing sheet to facilitate the opening thereof .

[0011] Disadvantageously, it is immediately understood that these solutions are of poor quality since they expose the pharmaceutical and nutraceutical products contained in the blister pack to any external contamination, as well as the passage of oxygen and humidity, negatively af fecting the premature degradation of the product and / or its beneficial ef fects .Solution of the invention

[0012] There appears to be a signi ficant need therefore to provide a multilayer sheet , a blister pack, and the manufacturing methods thereof that are capable of overcoming the drawbacks typical of the prior art .

[0013] There also appears to be a need to limit the use ofmulti-material blister packs , which are di f ficult to separate at end-of-li fe collection and therefore have a signi ficant environmental impact .

[0014] In particular, the obj ect of the present invention is to provide a multilayer sheet that may be applied for the breakable wall in pharmaceutical blister packs to make them more sustainable from an environmental impact point of view, while maintaining discrete properties of oxygen resistance , mechanical resistance , and ease of opening .

[0015] This requirement is satis fied by a multilayer sheet , by a blister pack, and by manufacturing methods according to the accompanying independent claims . The dependent claims describe preferred or advantageous embodiments of the invention, comprising further advantageous features . Description of the drawings

[0016] The features and advantages of the multilayer sheet and of the blister pack will become apparent from the description provided hereinafter of some preferred embodiments , given by way of indicative and non-limiting example , with reference to the accompanying figures , wherein :Fig . 1 is a schematic view of a press-through blister pack according to the present invention ;Fig . 2 is a schematic view of a multilayer sheet inone embodiment of the invention;Fig . 3 is a schematic view of a polymeric layer assembly according to one embodiment of the invention;Fig . 4 is a schematic view of a press-through blister pack in one embodiment of the present invention . Detailed description

[0017] With reference to the aforesaid figures , a blister pack 1 for the pharmaceutical , nutraceutical , cosmetic, or food sectors has been indicated as a whole with the reference numeral 1 .

[0018] The blister pack 1 is preferably a press- through blister pack .

[0019] The blister pack 1 comprises an upper wall 12 and a breakable wall 14 mutually constrained to form and seal one or more containment chambers 3 suitable for housing pharmaceutical or nutraceutical or cosmetic or food products , e . g . , in the form of tablets , powders , liquids , or hard or soft capsules .

[0020] Preferably, the upper wall 12 and the breakable wall 14 are at least partially welded together, even more preferably heat-sealed .

[0021] Preferably, the upper wall 12 and the breakable wall 14 are welded together along the entire surface surrounding such one or more chambers 3 , i . e . , along the wall surface not facing said one or more chambers 3 .

[0022] In one embodiment , the breakable wall 14 comprises a multilayer sheet 4 .

[0023] Preferably, the breakable wall 14 is composed of such multilayer sheet 4 .

[0024] Preferably, the breakable wall 14 is composed exclusively of such multilayer sheet 4 .

[0025] In a preferred embodiment , the upper wall 12 and the breakable wall 14 are both made of polymeric material , preferably of the same polymeric material or of di f ferent polymeric materials but belonging to the same family of polymers .

[0026] It is clear that it is intended that the walls are predominantly made of polymeric material unless there are additives and inorganic fillers and impurities in the material . Preferably each wall is made of polymeric material by at least 95% .

[0027] Preferably, the multilayer sheet 4 is formed of layers made of materials that all belong to the same family of polymers .

[0028] Preferably, both the upper wall 12 and the breakable wall 14 are made of materials belonging to the polyolefin family, even more preferably belonging to the polyethylene ( PE ) family .

[0029] According to the present invention, with reference to Fig . 2 , the multilayer sheet 4 comprises at least oneintermediate microporous layer 40 , interposed between two monolithic layers 42 , 44 , preferably external .

[0030] The term "microporous" , in the present discussion, refers to a structure having microcavities that interrupt its continuity, said microcavities preferably allowing the passage of humidity and oxygen .

[0031] On the contrary, the term "monolithic" refers to a structure that does not have discontinuities , clearly, once again, unless there are impurities and additives .

[0032] The multilayer sheet 4 identi fies in space an imaginary plane of predominant extension and in particular a longitudinal direction and a transverse direction of predominant extension in which the multilayer sheet predominantly extends . These longitudinal and transverse directions are orthogonal to each other and lie on such imaginary plane .

[0033] Furthermore , the multilayer sheet is small in thickness , i . e . , it extends much less , in a direction orthogonal to said plane .

[0034] In the present discussion, the strati fication of the multilayer sheet is carried out along such orthogonal direction, i . e . , all the layers extend predominantly in the longitudinal and transverse directions and are superimposed on each other .

[0035] The term " interposed" indicates precisely that themicroporous layer is located between the monolithic layers in the orthogonal direction .

[0036] Preferably, the microporous layer 40 and the monolithic layers 42 , 44 are coextruded .

[0037] According to the invention, the multilayer sheet 4 is mono-oriented .

[0038] In the present discuss ion, the term "mono-oriented" refers to a layer that has undergone a stretching process in one direction only (mono-orientation) . In other words , the mono-oriented multilayer sheet has polymer chains oriented predominantly along a preferred direction . Preferably, the mono-orientation is applied to the sheet in the longitudinal direction ( i . e . , in one of the directions of greatest extension of the multilayer sheet , preferably a direction tangent to the imaginary plane identi fied by the multilayer sheet 4 ) .

[0039] The stretching process will be better described later in the present discussion .

[0040] According to the invention, the microporous layer 40 comprises a polymeric matrix 400 in which a mineral filler is dispersed .

[0041] The term "mineral filler" refers to one or more additives preferably inorganic .

[0042] Preferably, the mineral filler is dispersed in the polymeric matrix in a concentration between 10% and 50%(w / w) with respect to the total mass of the microporous layer 40, even more preferably between 30% and 50% (w / w) .

[0043] In one embodiment, the mineral filler is selected from the group comprising calcium carbonate, talc, zeolites, kaolin, silica, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, aluminum hydroxide, magnesium hydroxide, zinc oxide, alumina, mica.

[0044] In a preferred embodiment, the mineral filler is only calcium carbonate.

[0045] Advantageously, calcium carbonate utilized for this application, due to a low hygroscopicity, allows particle sizes to be obtained that are smaller than those obtainable with other fillers. Preferably, the low hygroscopicity is further ensured through the use of a calcium stearate coating that coats the calcium carbonate particles .

[0046] Furthermore, advantageously, the synergistic combination of mono-orientation and mineral filler, i.e., mono-orientation and microporosity, generates microcavities 410 in the polymeric matrix that give the multilayer sheet a low resistance to breakage (more specifically, to tearing or to bursting) , thus making it suitable for being applied for the breakable wall of the blister pack, giving said wall good breakability andtherefore ease of opening .

[0047] Furthermore , advantageously, the presence of microcavities 410 distributed in the polymeric matrix 400 makes the multilayer sheet 4 particularly fragile when cut and therefore suitable for being easily broken by pressing in the through direction with respect to the imaginary plane identi fied by the breakable wal l .

[0048] In one embodiment , the mineral filler also comprises talc .

[0049] By definition, preferably, the microporous layer 40 comprises microcavities 410 homogeneously dispersed in the polymeric matrix .

[0050] In one embodiment , the breakable wall 14 has a thickness of less than or equal to 50 microns , more preferably less than or equal to 25 microns , even more preferably equal to 25 microns .

[0051] In one embodiment , the breakable wall 14 is formed exclusively of such second multilayer sheet 4 .

[0052] In one embodiment , the polymeric matrix is composed of polyolefins , preferably a polymer belonging to the polyethylene family .

[0053] Even more preferably, the polymeric matrix 400 comprises a material selected from LLDPE ( linear low- density polyethylene ) with a density between 910 and 940g / cc, ethylene and hexene copolymers , ethylene andoctene copolymers with a density greater than 940g / cc, compounds thereof . In one embodiment , the monolithic layers 42 are made of polyolefins , preferably from a polymer belonging to the polyethylene fami ly .

[0054] Even more preferably, the monolithic layers 42 , 44 comprise a material selected from LLDPE ( linear low- density polyethylene ) with a density between 910 and 940g / cc, ethylene and hexene copolymers , ethylene and octene copolymers with a density greater than 940g / cc, or compounds thereof .

[0055] In one embodiment , the polymeric matrix 400 and the monolithic layers 42 , 44 comprise ionomers .

[0056] Preferably, on the whole , the multilayer sheet 4 is characteri zed by an elongation at break in the transverse direction of less than or equal to 100% , even more preferably less than or equal to 25% , even more preferably less than or equal to 15% , where the elongation at break in the transverse direction is calculated by the method according to the ASTM D882 standard .

[0057] In one embodiment , on the whole , the multilayer sheet 4 is characteri zed by an elongation at break in the longitudinal direction of less than or equal to 100% , preferably less than or equal to 25% , even more preferably less than or equal to 15% , where theelongation at break in the transverse direction is calculated by the method according to the ASTM D882 standard .

[0058] In one embodiment, on the whole, the multilayer sheet 4 is characterized by a breaking load in the transverse direction less than or equal to 30 N / inch and preferably less than or equal to 20 N / inch.

[0059] In a preferred embodiment, the mineral filler has a particle size between 1 and 5 microns, more preferably between 1.5 and 2.5 microns, even more preferably equal to 1.7 microns .

[0060] In fact, the Applicant has verified that smaller particle sizes do not allow for the effective formation of microfractures, while particle sizes larger than this maximum value lead to breakage of the polymeric matrix.

[0061] In one embodiment, the upper wall 12 comprises a polymeric layer assembly 2, preferably coextruded.

[0062] In one embodiment, the polymeric layer assembly 2 comprises HDPE (high-density polyethylene) and VLDPE (very low-density polyethylene) .

[0063] In one embodiment, the upper wall 12 has a thickness between 300 microns and 400 microns, endpoints included.

[0064] Preferably, the polymeric layer assembly 2 comprises HDPE (high-density polyethylene) and VLDPE (very low- density polyethylene) with a thickness ratio between HDPEand VLDPE between 1.5 and 19, endpoints included.

[0065] That is, the ratio of the thickness of the HDPE layer to the VLDPE layer coextruded to form the polymeric layer assembly 2 is between 1.5 and 1.9, endpoints included .

[0066] In other words, the proportion HDPE: VLDPE is between 60:40 and 95:5.

[0067] Preferably, for example, with reference to Fig. 3, the polymeric layer assembly 2 is a film comprising two layers 20, 21 of HDPE (high-density polyethylene) and a sealing layer 22 of ethylene-hexene copolymer.

[0068] In a preferred embodiment, the polymeric layer assembly constitutes an asymmetrical film comprising the layers in the order:- HDPE layer 20- HDPE layer 21- sealing layer 22.

[0069] The outermost layer of HDPE 20 is suitable for acting as a barrier layer.

[0070] Preferably, the HDPE layers 20, 21 are characterized by a density between 0.952 and 0.962 g / cm3 (ASTM D1505) , endpoints included.

[0071] Preferably, the ethylene-hexene copolymer is a resin that acts as a sealing layer 22, i.e., it is suitable for being heated in order to heat-seal the upper wall 12 andthe breakable wall 14 therebetween .

[0072] That is , the ethylene-hexene copolymer layer 22 is suitable for facing the breakable wall 14 to allow heatsealing to the upper wall 12 in the blister pack assembly condition .

[0073] Preferably, also the multilayer sheet 4 comprises a sealing layer . Preferably, the sealing layer of the multilayer sheet has a thickness of 10% with respect to the total thickness of the breakable wall 14 .

[0074] Preferably, such a sealing layer coincides with one of the monolithic layers 42 , 44 .

[0075] Even more preferably, also the multilayer sheet 4 comprises a sealing layer made of ethylene-hexene copolymer suitable for acting as a sealing agent with the upper wall 12 . That is , the breakable wall 14 has the sealing layer on the side facing the upper wall 12 to allow heat-sealing to the upper wall 12 .

[0076] Preferably, the sealing layer 22 , 42 ( in the multilayer sheet 4 or in the layer assembly 2 ) is made of a plastomeric res in, preferably of an ethylene-hexene copolymer having a density less than 0 . 910 g / cm3 (ASTM D792 ) , a melt index ( 190 ° C / 2 . 16kg) between 1 and 4 g / 10 min, preferably between 2 and 4 g / 10 min (ASTM D1238 ) and a peak melting temperature less or equal to 114 ° C, preferably measured by di f ferential scanningcalorimetry ( DSC ) , preferably measured according to the ISO11357 standard .

[0077] Preferably, this ethylene-hexene copolymer has a Vicat softening temperature of 90 ° C, calculated according to the ASTM D1525 standard .

[0078] In one embodiment , the multilayer sheet 4 comprises additives suitable for decreasing the permeability to oxygen . Such additives are also known as gas-stop particles .

[0079] The microporous layer 40 of the multilayer sheet 4 according to the present invention is obtained by means of a stretching process in the longitudinal direction of the polymeric matrix in which the mineral fillers are dispersed . This stretching, applied only along one direction ( the longitudinal direction) , determines an elongation of the polymeric matrix, while the mineral fillers contained therein, being substantially inert and rigid, do not undergo any elongation . This di f ferent behavior of the polymeric matrix and the mineral fillers contained therein causes microfractures in the polymeric matrix that generates microcavities that make the layer microporous .

[0080] Said elongation is preferably implemented by means of the passage of the polymeric matrix loaded with mineral fillers through a stretching machine comprising aseries of cylinders that rotate at progressively increasing tangential speeds . Said cylinders are thermally controlled so as to allow the material that makes up the polymeric matrix to reach the softening temperature thereof , so as to be easily elongated but without excessive plasticity in order to allow the formation of microfractures in the vicinity of the mineral filler particles .

[0081] The stretching ratio typically applied, where " stretching ratio" means the ratio between the final speed of the cylinders and the initial speed before the stretching machine , is between 2 and 4 .

[0082] In the coextrusion process the monolithic layers 42 and the microporous layer 40 are combined to form the multilayer sheet 4 .

[0083] The multilayer sheet is preferably made by means of filming, either cast or blown .

[0084] It is clear that the present invention relates per se to a multilayer sheet 4 for a breakable wall 14 of a press-through blister pack 1 , according to any of the embodiments described in the present discussion .

[0085] The present invention also relates to a method for manufacturing a multilayer sheet 4 according to the present invention .

[0086] The method for manufacturing a multilayer sheet 4comprises the following steps :

[0087] a ) co-extruding two monolithic layers 42 , 44 with a microporous layer 40 interposed therebetween, wherein the microporous layer 40 comprises a polymeric matrix 400 and a mineral filler dispersed therein;

[0088] b ) applying an in- line filming process to the coextrusion to obtain a multilayer sheet ;

[0089] c ) applying a stretching process along a single direction to the multilayer sheet to make it monooriented .

[0090] Furthermore , the present invention also relates to a method for manufacturing a blister pack 1 according to the present invention, comprising the following steps :- providing an upper wall 12 for a blister pack, said upper wall 12 having one or more containment chambers 3 at least partially accessible , and providing a multilayer sheet 4 according to the present invention ; filling the one or more chambers 3 with a pharmaceutical or nutraceutical or cosmetic product ;- heat-sealing the multilayer sheet 4 to the upper wall 12 so as to surround and seal such one or more chambers 3 .

[0091] In one embodiment , the method also provides for a primary thermoforming step of the upper wall 12 for making said one or more chambers . In one embodiment , alsothe multilayer sheet 4 may also be thermoformed to make part of the volume of said one or more chambers 3 .

[0092] Innovatively, the present invention solves the drawbacks of press-through blister packs that are typical of the prior art .

[0093] Advantageously, the present invention has a considerably reduced environmental impact compared to the solutions available today . In fact , the blister pack according to the present invention comprises portions made from materials belonging to the same class or even the same material and is therefore suitable for being di f ferentiated in a single piece and allows a disposal that is suitable for the increasingly stringent need for sustainability and ecology .

[0094] Advantageously, the blister pack according to the present invention is recyclable according to the current regulation (EN 13430 ) .

[0095] Advantageously, the blister pack according to the present invention is characteri zed by excellent ease of opening, which is comparable to that provided by current solutions which use aluminum . Therefore , this blister pack may be easily opened even by patients with limited mobility .

[0096] The ease of opening was evaluated by the Applicant on the basis of pressuri zed dynamometric tests in whichthe pressure at the time of fracture with a known surface tip is evaluated, performed both on samples of the material and on the finished product , according to the most common test methodologies for the push-out tests developed by maj or manufacturing companies , such as the "Pill Push-out test" developed by SHIMADZU CORP or the "push-out test" developed by IMADA Inc .

[0097] The Applicant has carried out several experimental tests on press-through blister packs according to the present invention, to evaluate the breakability thereof and veri fy that such blister packs indeed exhibit easy- tear properties .

[0098] The tests were carried out with pressing probes with a diameter of approximately 12 mm .

[0099] All of the tests performed returned fracture force values well below the upper speci fication limit (UPS ) . This maximum acceptable threshold value , set at S ON, has been empirically identi fied through various experimental tests and essentially corresponds to the maximum force required to break the same surface of blister pack lids made in the materials of prior art .

[0100] All the tests performed gave values lower than this acceptable maximum value , and in particular fracture forces between 20 N and 26 N . These values are advantageous with respect to known blister packs ,especially mono-material .

[0101] Advantageously, therefore , the Applicant has veri fied that the synergistic combination of the choice of materials and the post- filming stretching process gives the multilayer sheet used to make the breakable wall the features that make it easily breakable and at the same time resistant and compatible with the contents .

[0102] According to an even further advantage , the multilayer sheet may be easily opened even when intact and does not require the presence of pre-cuts or incisions that facilitate the breaking thereof .

[0103] Thus , advantageously, the blister pack according to the present invention ensures long-term integrity and is safe against any contamination .

[0104] According to a further advantage , the blister pack according to the present invention is suf ficiently impermeable to oxygen and protects the contents from premature degradation .

[0105] According to a still further advantage , the blister pack according to the present invention is suitable for being assembled in plants already in use for current commercial solutions and by the thermoforming, filling, and heat-sealing processes currently used for solutions involving the use of other materials .

[0106] Advantageously, the multilayer sheet may beprocessed in such plants to allow the heat-sealing of the breakable wall to the upper wall of the blister pack at temperatures generally between 100 ° C and 160 ° C, i . e . at temperatures that are about 20% lower than the temperatures necessary to perform the assembly of the blister packs currently on the market , such as those made of aluminum . This clearly has a considerable energy savings and consequently makes the proposed solution even more sustainable .

[0107] It is clear that , to the embodiments of the aforesaid blister pack and the aforesaid multilayer sheet , a person skilled in the art , in order to meet speci fic needs , could make variations or substitutions of elements with functionally equivalent ones .

[0108] These variants are also contained within the scope of protection as defined by the following claims . Moreover, each variant described as belonging to a possible embodiment may be implemented independently of the other variants described .

Claims

CLAIMS1. A press-through blister pack (1) for the pharmaceutical or nutraceutical or cosmetic or food field, comprising an upper wall (12) and a breakable wall (14) mutually constrained so as to form and tightly seal one or more containment chambers (3) suitable for housing pharmaceutical or nutraceutical or cosmetic products, for example in the form of tablets, powders, liquids, or hard or soft capsules, wherein the upper wall (12) and the breakable wall (14) are both made of a polymeric material, and wherein the breakable wall (14) comprises a monooriented multilayer sheet (4) comprising two monolithic layers (42, 44) and at least an intermediate microporous layer (40) , interposed between said monolithic layers (42, 44) , wherein the microporous layer (40) comprises a polymeric matrix (400) in which a mineral filler is dispersed.

2. Blister pack (1) according to claim 1, wherein the monolithic layers (42, 44) and the microporous layer (40) are co-extruded.

3. Blister pack (1) according to claim 1 or 2, wherein the mineral filler is dispersed in the polymeric matrix (400) in a percentage between 10% and 50% (w / w) , preferably between 30% and 50% (w / w) with respect to themass of the microporous layer (40) .

4. Blister pack (1) according to claim 1 or 2 or 3, wherein the mineral filler is selected from the group comprising calcium carbonate, talc, zeolites, kaolin, silica, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, aluminum hydroxide, magnesium hydroxide, zinc oxide, alumina, mica .

5. Blister pack (1) according to any one of the preceding claims, wherein the mineral filler is only calcium carbonate .

6. Blister pack (1) according to any one of the preceding claims, wherein the mineral filler has a particle size between 1 and 5 microns, more preferably between 1.5 and 2.5 microns, even more preferably 1.7 microns, preferably measured according to the ISO13317 standard.

7. Blister pack (1) according to any one of the preceding claims, wherein the breakable wall (14) has a thickness less than or equal to 50 microns, more preferably less than or equal to 25 microns, even more preferably equal to 25 microns.

8. Blister pack (1) according to any one of the preceding claims, wherein the upper wall (12) has a thickness between 300 microns and 400 microns, endpoints included.

9. Blister pack (1) according to any one of the precedingclaims, wherein the polymeric matrix (400) and the monolithic layers (42) comprise a material selected from LLDPE (linear low-density polyethylene) with a density between 910 and 940g / cc, ethylene and hexene copolymers, ethylene and octene copolymers with a density greater than 940g / cc, or mixtures thereof.

10. Blister pack (1) according to any one of the preceding claims, wherein the multilayer sheet (4) is characterized by an elongation at break in the transverse direction less than or equal to 100%, even more preferably less than or equal to 25%, even more less than or equal to 15%, where the elongation at break in the transverse direction is calculated by the method according to the ASTM D882 standard.

11. Blister pack (1) according to any one of the preceding claims, wherein the upper wall (12) comprises a coextruded polymeric layer assembly (2) , comprising HDPE (high-density polyethylene) and VLDPE (very low-density polyethylene) , with a thickness ratio of HDPE to VLDPE between 1.5 and 19, endpoints included.

12. Blister pack (1) according to claim 11, wherein the polymeric layer assembly (2) is a film comprising two layers (20, 21) of HDPE (high-density polyethylene) and a sealing layer (22) of ethylene-hexene copolymer.

13. Blister pack (1) according to claim 12, wherein thesealing layer (22) is made of an ethylene -hexene copolymer having a density less than 0.910 g / cm3(ASTM D792) , a melt index ( 190 °C / 2.16kg) between 1 and 4 g / lOmin (ASTM D1238) , and a peak melting temperature less than or equal to 114°C, preferably measured by differential scanning calorimetry (DSC) , preferably measured according to the ISO11357 standard.

14. A multilayer sheet (4) for manufacturing a breakable wall (14) for a press-through blister pack (1) , wherein said multilayer sheet (4) is mono-oriented and comprises two monolithic layers (42, 44) and at least an intermediate microporous layer (40) , interposed between said monolithic layers (42, 44) , wherein the microporous layer (40) comprises a polymeric matrix (400) in which mineral fillers are dispersed.

15. A method for making a multilayer sheet (4) intended to manufacture a blister pack comprising the following steps : a) co-extruding two monolithic layers (42, 44) with a microporous layer (40) interposed therebetween, wherein the microporous layer (40) comprises a polymeric matrix (400) and a mineral filler dispersed therein; b) applying an in-line filming process to the coextrusion, to obtain an unoriented multilayer sheet (4) ; c) applying a stretching process to the multilayer sheet(4) along a single direction to make it mono-oriented.

16. A method for manufacturing a blister pack (1) according to any one of claims 1 to 13, comprising the following steps: - providing an upper wall (12) for a blister pack, said upper wall (12) having one or more at least partially accessible containment chambers (3) , and providing a multilayer sheet (4) according to claim 14; filling the one or more chambers (3) with a pharmaceutical or nutraceutical or cosmetic product;- heat-sealing the multilayer sheet (4) to the upper wall (12) so as to surround and seal such one or more chambers (3) .

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