METHOD FOR PRODUCING A LAMINAR PRODUCT

Abstract

The invention relates to a method for producing a laminar product suitable for manufacturing external covers of sanitary towels and nappies, formed by a polymeric coating deposited over the surface of a non-woven fabric substrate, as well as to the laminar product obtained using said method. The method comprises the following steps: obtaining adhesive polymeric mixtures, feeding the mixtures, in a melted state, to a curtain-type applicator, coating the substrate with the adhesive polymeric mixtures, and winding the laminar product obtained. The product obtained comprises a polymeric coating bonded to the non-woven fabric substrate, wherein the polymeric coating consists of an adhesive polymeric layer that has a reduced thickness, ranging between 1 and 10 micra, said product being suitable for medical and personal hygiene applications.

Claims

1-25. (canceled)

26. A laminar product suitable for manufacturing external covers of sanitary towels and nappies, of the type formed by a polymeric coating deposited over a non-woven fabric substrate, the laminar product comprising: a polymeric coating bonded on one of the faces thereof, by curtain coating technology, to a non-woven fabric substrate, wherein the polymeric coating consists of an adhesive polymeric layer that has a thickness value ranging between 1 and 10 microns; wherein the laminar product has a total weight ranging between 10 and 30 g/m.sup.2 and permeability values greater than 2000 g/(m.sup.2 day); and wherein the adhesive polymeric layer comprises a base polymer plus a tackifying agent at a mass proportion of the base polymer ranging between 60% and 95%.

27. The laminar product according to claim 26, wherein the base polymer is a polyolefin, which is selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene, ethylene-vinyl acetate (EVA) and co-polymers thereof, and ethylene-based or propylene-based plastomers.

28. The laminar product according to claim 26, wherein the base polymer is selected from the group consisting of thermoplastic polyurethanes, acrylic resins, styrene-butadiene resins, or mixtures thereof, biodegradable polymers, polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and mixtures thereof with synthetic polymers, polyamides, polystyrene, ethylene-vinyl acetate (EVA) co-polymers, acrylonitrile/butadiene/styrene (ABS) co-polymers, polyethylene terephthalate (PET), polyurethane (PU), and polylactic acid (PLA).

29. The laminar product according to claim 26, wherein the tackifying agent is selected from the group consisting of Hydrogenated aliphatic polyolefins, amorphous polyolefins, aromatic polyolefins, and tackifying agents of the rosin and terpene types.

30. The laminar product according to claim 26, wherein the tackifying agent is selected with a softening temperature ranging between 80° C. and 100° C.

31. The laminar product according to claim 26, wherein, when the base polymer has natural water vapour permeability values lower than 3 g/(m.sup.2 day), in addition to the tackifying agent, a hydrophilising agent is added to the base polymer which is selected from the group consisting of highly hydrophilic polymers, such as: polyvinyl alcohol, polyvinyl acetate, polyethylene oxides, polypropylene glycols and thermoplastic polyurethanes, which have highly hydrophilic polar groups in their molecules, preferably polyethylene glycol with a weight ranging between 500 and 1000, where the hydrophilising agent is dosed at a proportion ranging between 3% and 20% of the base polymer; and wherein an adhesive/dispersant agent is added, which is selected from co-polymers of the base polymer, grafted with polar groups selected from the group consisting of: maleic anhydride, acrylic acid, acrylates or acetates, glycidyl acetate derivatives, as well as mixtures thereof, where the adhesive/dispersant agent is dosed at a proportion ranging between 1% and 5% of the base polymer.

32. The laminar product according to claim 26, wherein, when the base polymer has natural water vapour permeability values lower than 3 g/(m.sup.2 day), in order to increase the permeability, only an adhesive/dispersing agent is added, dosed at a proportion ranging between 2% and 20% of the base polymer, without the presence of a hydrophilising agent.

33. The laminar product according to claim 26, wherein the side of the polymeric coating that is not adhered to the substrate has a printing or decoration performed via a printing method, such that the residual adhesion of the side disappears.

34. The laminar product according to claim 26, comprising a second coating layer without adhesive capacity, adhered to the side of the polymeric coating that is not bonded to the substrate.

35. A method for producing a laminar product according to claim 26, particularly suitable for manufacturing external covers of sanitary towels and nappies, of the type formed by a polymeric coating deposited over a non-woven fabric substrate, the method comprising: obtaining adhesive polymeric mixtures, wherein a base polymer is combined with a tackifying agent in a mass proportion ranging between 60% and 95% of the base polymer; feeding the mixtures, in a melted state, to a curtain-type coating applicator; coating the substrate with the polymeric mixture, wherein the melted polymeric mixture is applied over the substrate via the curtain-type coating applicator, such that a laminar product is formed that is composed by a polymeric coating consisting of an adhesive polymeric layer, which is deposited over the non-woven fabric substrate, wherein the adhesive polymeric layer that forms the polymeric coating has a thickness ranging between 1 and 10 microns; and winding the laminar product obtained, the laminar product having a total weight ranging between 10 and 30 g/m.sup.2, and permeability values greater than 2000 g/(m.sup.2 day).

36. The method according to claim 35, wherein, in the obtaining step, when the base polymer has natural water vapour permeability values lower than 3 g/(m.sup.2 day), in order to increase the permeability, to the base polymer it is added or either a hydrophilising agent selected from the group consisting of highly hydrophilic polymers, such as: polyvinyl alcohol, polyvinyl acetate, polyethylene oxides, polypropylene glycols and thermoplastic polyurethanes, which have highly hydrophilic polar groups in their molecules, preferably polyethylene glycol with a weight ranging between 500 and 1000, and where the hydrophilising agent is dosed at a proportion ranging between 3% and 20% of the base polymer; and wherein an adhesive/dispersant agent is added, selected from the co-polymers of the base polymer, grafted with polar groups selected from the group consisting of: maleic anhydride, acrylic acid, acrylates or acetates, glycidyl acetate derivatives, as well as mixtures thereof, where the adhesive/dispersant agent is dosed at a proportion ranging between 1% and 5% of the base polymer; or either, only an adhesive/dispersing agent, dosed at a proportion ranging between 2% and 20% of the base polymer, without the presence of a hydrophilising agent.

37. The method according to claim 35, comprising: printing on the side of the polymeric coating that is not adhered to the substrate; wherein the printing is performed on the production line prior to the winding, via a method selected from the group consisting of photogravure, flexography, and transfer printing.

38. The method according to claim 35, comprising applying a second coating without adhesive capacity over the side of the polymeric coating that is not bonded to the substrate.

39. The method according to claim 35, wherein, prior to the winding, the laminar product is subjected to a cross-linking treatment selected from the group consisting of: corona treatment ranging between 30 dynes/cm and 45 dynes/cm; radiation treatment; and plasma treatment.

40. The laminar product of claim 27, wherein the ethylene-based or propylene-based plastomers comprise at least one of ethylene/octene, ethylene/alpha-olefin, ethylene/octane, ethylene/butane, and propylene/butylene co-polymers.

41. The laminar product of claim 28, wherein the biodegradable polymers comprise polylactic acid (PLA).

Description

DESCRIPTION OF THE FIGURES

[0070] Below we include a list of the different parts of the invention, which, with the aid of the corresponding numbers, are found in the figures: (1) unwinder, (2) continuous mixer, (3) curtain-type applicator, (4) printing equipment, (5) winder, (10) laminar product, (11) polymeric coating, (11a) side of the polymeric coating, (12) substrate, (13) second coating layer, (21) heated pipe.

[0071] FIG. 1 is a schematic representation of the application line of the method of the invention, which comprises a non-woven fabric unwinder (1), a curtain applicator (2) and a finished product winder (5).

[0072] FIG. 2 is a schematic representation of the step for coating the substrate with the polymeric mixture.

[0073] FIG. 3 corresponds to a schematic representation of the application of another polymeric layer without adhesive capacity.

[0074] FIG. 4a is a schematic representation of the thickness profile of the polymeric coating placed over the substrate with the curtain-type coating applicator used in the invention.

[0075] FIG. 4b is a schematic representation of the thickness profile of the polymeric coating placed over the substrate using a conventional method.

PREFERRED EMBODIMENT OF THE INVENTION

[0076] The method of the proposed invention involves producing a laminar product (10) formed by a polymeric coating (11) placed over a non-woven fabric substrate (12), said laminar product (10) being particularly suitable for manufacturing external covers of sanitary towels and nappies.

[0077] As shown in FIG. 1, the method of the invention is performed on an application line (production line) that comprises a non-woven fabric unwinder (1), a curtain-type applicator (3) for the adhesive polymeric mixture, and a winder (5) for the finished product, i.e. the final laminar product.

[0078] In essence, the method of the invention comprises the following steps: [0079] a)—Obtaining adhesive polymeric mixtures, wherein a base polymer is combined with a tackifying agent, in a mass proportion ranging between 60% and 95% of the base polymer. In this step, the polymeric mixture is manufactured in continuous mixing equipment (co-rotating twin-screw extruders; single-screw extruders-mixers; Buss-type continuous mixers); or batch equipment (Brabender-type batch mixers). The polymeric mixture may be manufactured in line with the production, as shown in FIG. 1, wherein a continuous mixer (2) is illustrated, or separated in time, in a previous step, by storing the mixture in the form of pellets that will be pumped into the main line once they are melted. [0080] b)—Feeding the melted mixtures to a curtain-type applicator (3). In this step, the curtain applicator is fed by pumping the melted mixture obtained in step “a” through a heated pipe (21). [0081] c)—Coating the substrate (12) with the polymeric mixture, wherein the melted polymeric mixture is applied over the non-woven fabric substrate (12) by means of a curtain-type coating applicator (3), such that a laminar product (10) is created which is formed by a polymeric coating (11), consisting of an adhesive polymeric layer placed over the non-woven fabric substrate (12), wherein the adhesive polymeric layer has a thickness ranging between 1 and 10 microns, and is homogeneously distributed, with a constant thickness, over the surface of the substrate. This step is performed by means of the applicator (3), using equipment such as, for example, equipment from the German manufacturer Dynatec. [0082] d)—Winding of the laminar product (10). In this step, the laminar product (10) obtained is wound using the winder (5).

[0083] As illustrated in FIG. 2, in step c), the melted polymeric mixture is applied, in the form of a sheet, over the non-woven fabric substrate (12) on the application line shown in FIG. 1.

[0084] Application of the melted polymeric mixture in the form of a sheet guarantees that the adhesive polymeric layer that forms the polymeric coating has a uniform thickness throughout the entire substrate (12), as illustrated in FIG. 4a, which shows the thickness profile of the adhesive polymeric layer when it is applied over the substrate using the curtain technique according to the present invention, unlike what is shown in FIG. 4b, wherein the adhesive polymeric layer that forms the polymeric coating is applied using conventional techniques in the prior art.

[0085] When comparing the two figures, FIGS. 4a and 4b, it may be observed that, using the method of the present invention, a smaller quantity of adhesive polymeric material is used to form the adhesive polymeric layer that forms the coating (11), unlike what happens when traditional application methods are used, all of which entails considerable savings in polymeric material and the production of a laminar product (10) with a smaller thickness and a lower weight.

[0086] In essence, the technology used in the present invention makes it possible to obtain a polymeric coating (11) with a thickness ranging between 1 and 10 microns and, therefore, makes it possible to obtain a laminar product (10) with a weight ranging between 10 and 30 g/cm.sup.2, which is substantially lower than the weight of similar products found in the prior art.

[0087] Moreover, the adhesive polymeric layer that forms the polymeric coating (11), uniformly distributed over the substrate, is impermeable to liquid water, but permeable to water vapour, with permeability values greater than 2000 g/(m.sup.2 day).

[0088] In addition, in order to substantially reduce the residual adhesive capacity of the side (11a) of the polymeric coating (11), i.e. the side of the adhesive polymeric layer that is not adhered to the substrate (12), one or a combination of the following steps are performed: [0089] Printing on the side of the polymeric coating (11a) that is not adhered to the substrate, wherein said printing (4) may be performed on the application line prior to the winding step, as illustrated in FIG. 1, or in a subsequent treatment of the coated product bobbins, using a method selected from photogravure, flexography or transfer printing. [0090] Applying a second coating (13) without adhesive capacity over the side (11a) of the polymeric coating (11) that is not bonded to the substrate. This step may be performed at the same time as the coating of the substrate with the polymeric mixture, using a dual-layer curtain applicator for this purpose, as illustrated in FIG. 3, or subsequently, by means of a second applicator. [0091] Performing a cross-linking treatment of the tackifying agent, selected from: corona treatment, ranging between 30 dynes/cm and 50 dynes/cm, radiation treatment, or plasma treatment.

[0092] On the other hand, in order to increase the breathability of the polymeric coating (11), thereby increasing its water vapour permeability to values greater than 2000 g/(m.sup.2 day), during the step for obtaining the polymeric mixtures, hydrophilic agents are added in a proportion ranging between 3% and 20% of the base polymer, consisting of polymers or oligomers with highly hydrophilic polar groups in their molecules, polyethylene glycol, with a weight ranging between 500 and 5000, being particularly suitable for this purpose, and combined with adhesive/dispersing agents consisting of co-polymers of the base polymer, grafted with polar groups selected from the group formed by: maleic anhydride, acrylic acid, acrylates or acetates, glycidyl acetate derivatives, as well as mixtures thereof, dosed at a proportion ranging between 1% and 5% of the base polymer.

[0093] Other hydrophilic agents may also be used, such as, for example, polyvinyl alcohol, polyvinyl acetate, polyethylene oxides, polypropylene glycols and thermoplastic polyurethanes.

[0094] In the event that only moderate increases in permeability are required, it is sufficient to add the adhesive/dispersing agent in a proportion ranging between 2% and 20%, without the need to add the hydrophilising agent.

[0095] Following the method described in the present invention, laminar products with the following characteristics were obtained:

Example 1

[0096] Cross-coat contactless coating equipment manufactured by Dynatec. [0097] Substrate: Spun-bond non-woven fabric of 13 g/m.sup.2 Polypropylene (PP), manufactured by PGI. [0098] Polymeric coating: Ethylene-vinyl-acetate (EVA)-based adhesive, ref. Pergimelt 21340, manufactured by Wetzel, 3 g/m.sup.2. [0099] Flexographic printing: 1 g/m.sup.2. [0100] Total weight of the product: 17 g/m.sup.2. [0101] Corona treatment: 46 dynes/cm.

Example 2

[0102] Substrate: Spun-bond non-woven fabric of 13 g/m.sup.2 “PP”, manufactured by PGI. [0103] Polymeric coating: “EVA”-based adhesive, ref. Pergimelt 21340, manufactured by Wetzel: 2 g/m.sup.2. [0104] Flexographic printing: 1 g/m.sup.2. [0105] Total weight of the product: 16 g/m.sup.2. [0106] Corona treatment: 46 dynes/cm.

Example 3

[0107] Substrate: Spun-bond non-woven fabric of 12 g/m.sup.2 “PP”, manufactured by Texbond. [0108] Polymeric coating: “PP”-based adhesive, ref. Technomelt 2146, manufactured by Henkel: 2 g/m.sup.2. [0109] Flexographic printing: 1 g/m.sup.2. [0110] Total weight of the product: 15 g/m.sup.2. [0111] Corona treatment: 46 dynes/cm.

Example 4

[0112] Substrate: Spun-bond non-woven fabric of 10 g/m.sup.2 “PP”, manufactured by Texbond. [0113] Polymeric coating, 2 g/m.sup.2: Thermoplastic elastomer Engage 8402, manufactured by Dow: 80%; tackifying agent Eastotac H130W, manufactured by Eastman: 20%. [0114] Flexographic printing: 1 g/m.sup.2. [0115] Total weight of the product: 13 g/m.sup.2. [0116] Corona treatment: 46 dynes/cm.

Example 5

[0117] Substrate: Spun-bond non-woven fabric of 10 g/m.sup.2 “PP”, manufactured by Texbond. [0118] Polymeric coating, 3 g/m.sup.2: Thermoplastic elastomer Engage 8402, manufactured by Dow: 77%; tackifying agent Regalite R1125, manufactured by Eastman: 20%; low-density-polyethylene (LDPE)-acrylic co-polymer Primacor 3460, manufactured by Dow: 3%. [0119] Flexographic printing: 1 g/m.sup.2. [0120] Total weight of the product: 14 g/m.sup.2. [0121] Corona treatment: 46 dynes/cm.

Example 6

[0122] Substrate: Spun-bond non-woven fabric of 10 g/m.sup.2 “PP”, manufactured by Texbond. [0123] Polymeric coating, 3 g/m.sup.2: Thermoplastic elastomer Engage 8402, manufactured by Dow: 72%; tackifying agent Regalite R1125, manufactured by Eastman: 20%; “LDPE”-acrylic co-polymer Primacor 3460, manufactured by Dow: 3%; polyethylene glycol (PEG) 3350 Carbowax, manufactured by Dow: 5%. [0124] Flexographic printing: 1 g/m.sup.2. [0125] Total weight of the product: 14 g/m.sup.2. [0126] Corona treatment: 46 dynes/cm.

Example 7

[0127] Substrate: Spun-bond non-woven fabric of 10 g/m.sup.2 “PP”, manufactured by Texbond. [0128] Polymeric coating: Thermoplastic elastomer Engage 8402, manufactured by Dow: 77%; tackifying agent Eastotac H130W, manufactured by Eastman: 20%; acrylic co-polymer Primacor 3460, manufactured by Dow: 3%: 1 g/m.sup.2. [0129] Flexographic printing: 1 g/m.sup.2. [0130] Total weight of the product: 12 g/m.sup.2. [0131] Corona treatment: 46 dynes/cm.

[0132] Table no. 1 shows a summary of the values for the total weight of the laminar product obtained, the weight of the polymeric coating, as well as the total barrier and the breathability (water vapour permeability), obtained for each of the products in the examples.

TABLE-US-00001 TABLE NO. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Total weight of the 17 16 15 13 14 14 12 product g/m.sup.2 Weight of the 3 2 2 2 3 3 1 polymeric coating g/m.sup.2 Total barrier of the 584 382 1151 1504 2356 2242 504 product mm of H.sub.2O Breathability of the 2324 3502 10 21 1937 4841 5802 product g/(m.sup.2day)

[0133] As illustrated in said Table no. 1, all the products obtained had a total weight ranging between 10 and 30 g/m.sup.2, with permeability values greater than 2000 g/(m.sup.2 day), except in the case of Examples 3 and 4, the low permeability values whereof may be explained because their base polymers, polypropylene and polyethylene, respectively, have very low natural permeability values, 0.2 and 0.45 g/(m.sup.2 day), respectively. In example 5, we may observe the effect of adding the adhesive/dispersing agent, in this case Primacor 3460, manufactured by Dow, an ethylene-acrylic acid co-polymer, which increases the permeability from 21 g/(m.sup.2 day) to about 2000 g/(m.sup.2 day), and, in Example 6, we may observe that the permeability increases to about 5000 g/(m.sup.2 day) by also adding the hydrophilising agent polyethylene glycol Carbowax 3350, manufactured by Dow.

[0134] Moreover, as may be observed in Table no. 1, the weights of the polymeric coatings obtained range between 1 and 3 g/m.sup.2; this is achieved thanks to the method of application of the polymeric coating over the substrate, by means of the curtain coating technology, which achieves uniform distribution of an adhesive polymeric layer over the substrate, with a thickness ranging between 1 and 10 microns. This entails a considerable reduction in the quantities of polymeric material used to produce the coatings of nappies and sanitary towels, and, consequently, considerable savings in the production costs of these products.

[0135] Having sufficiently described the present invention, in line with the embodiments explained, it is evident that those modifications deemed convenient may be made to details thereof, provided that they do not alter the essence of the invention, which is summarised in the following claims.