The present invention relates to sanitary products in the form of diapers, especially for infants but also for incontinence protection, sanitary napkins, incontinence guards, and panty-liners incorporating a biodegradable, essentially liquid-impervious sheet laminate.

The invention also relates to such a biodegradable, essentially liquid-impervious sheet laminate as such, and to a process for the production of such a laminate.

Background of the invention

Biodegradable products help preserve environmental resources and prevent generation of additional waste. Both manufacturers and consumers are aware of the finite amount of space in landfills and other disposal sites and may affirmatively seek biodegradable products over non-biodegradable products. The need for biodegradability is particularly important in disposable, high use products such as baby diapers, feminine hygiene products, hospital drapes, and the like. However, along with biodegradability, it is important that such products have a soft cloth-like feel for comfort and aesthetic purposes.

The production of films that are biodegradable is known in the prior art.

US 5,851 ,937 discloses a totally biodegradable and/or compostable soft cloth-like composite comprising one or more plies of a totally biodegradable and/or compostable plastic film and one or more plies of a totally biodegradable and/or compostable nonwoven web, said composite having incrementally stretched portions substantially across its length and width and throughout its depth to provide a soft cloth-like feel to the composite.

There remains a continued need for production of essentially liquid-impervious sheet laminate that are essentially totally biodegradable yet have retained or even enhanced soft cloth-like feel. A laminate of this type would find use in hygiene fabrics, e.g., baby diapers, adult incontinence products, feminine hygiene products, and wipes; in medical fabrics, e.g., gowns, drapes, protective clothing, head and shoe coverings, and fluid and particle barriers; and in horticulture and agriculture coverings, e.g., protective ground covers for seedlings, where the products' desirable environmental and tactile properties are sought.

Purposes of the invention

One purpose of the present invention is hence to bring about an essentially liquid-impervious sheet laminate that are essentially totally biodegradable yet have retained or even enhanced soft cloth- 1 ike feel.

Another purpose of the present invention is to bring about a sanitary product in the form of a diaper, a sanitary napkin, an incontinence guard, a panty-liner or similar disposable absorbent products incorporating such a biodegradable, essentially liquid-impervious sheet laminate.

Yet another purpose of the present invention is to bring about a process for the production of such biodegradable, essentially liquid-impervious sheet laminate.

Description of embodiments of the invention

Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular configurations, process steps, and materials disclosed herein as such configurations, process steps, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention will be limited only by the appended claims and equivalents thereof. It must be noted that, as used in this specification and the claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The above discussed purposes, as well as other purposes, are brought about by way of the present invention, which in a first main aspect relates to a biodegradable, essentially liquid- impervious sheet laminate comprising a first stratum made of tissue paper and a second stratum made of a biodegradable polymer material which strata have been laminated together by application of glue essentially evenly over at least 80% of one surface of said first stratum followed by lamination of said first stratum to said second stratum with said surface facing said second stratum.

According one embodiment of this first main aspect the tissue paper is wet-laid cellulosic tissue paper. In one aspect of this embodiment the wet-laid cellulosic tissue paper is not a nonwoven fabric.

According to ISO standard 9092: 1988 and CEN Standard EN 29092 a material shall, to distinguish wet-laid nonwoven fabrics from wet-laid papers, be regarded as a nonwoven if

1. more than 50% by mass of its fibrous content is made up of fibers (excluding chemically digested vegetable fibers) with a length to diameter ratio greater than 300; or, if the conditions in 1) do not apply, then 2. if the following conditions are fulfilled: more than 30% by mass of its fibrous content is made up of fibers (excluding chemically digested vegetable fibers) with a length to diameter ratio greater than 300 and its density is less than 0.40g/cm3. Hence, according to one aspect of said embodiment the wet-laid cellulosic tissue paper does not have a fibrous content of more than 50% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, and if the wet-laid cellulosic tissue paper does have a fibrous content of more than 30% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, then the density of the wet-laid cellulosic tissue paper is not less than 0.40g/cm ³ . According a further embodiment of said first main aspect of the present invention said strata have been laminated together by application of glue essentially evenly over at least 90% of one surface of said first stratum followed by lamination of said first stratum to said second stratum with said surface facing said second stratum.

A second main aspect of the present invention relates to a sanitary product in the form of a diaper, a sanitary napkin, an incontinence guard, or a panty-liner, including an outer layer essentially impermeable for liquid, an inner layer at least partially permeable for liquid, and an absorption layer or absorption body between said two layers, wherein said outer layer comprises an outer comfort stratum made of tissue paper and an inner barrier stratum made of a biodegradable polymer material which strata have been laminated together by application of glue essentially evenly over at least 80% of one surface of said comfort stratum followed by lamination of said comfort stratum to said barrier stratum with said surface facing said barrier stratum. According one embodiment of this second main aspect of the present invention the tissue paper is wet-laid cellulosic tissue paper. In one aspect of this embodiment the wet-laid cellulosic tissue paper is not a nonwoven fabric.

According to one specific aspect of said embodiment the wet-laid cellulosic tissue paper does not have a fibrous content of more than 50% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, and if the wet-laid cellulosic tissue paper does have a fibrous content of more than 30% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, then the density of the wet-laid cellulosic tissue paper is not less than 0.40g/cm ³ .

According a further embodiment of said second main aspect of the present invention said strata have been laminated together by application of glue essentially evenly over at least 90% of one surface of said comfort stratum followed by lamination of said comfort stratum to said barrier stratum with said surface facing said barrier stratum.

A third main aspect of the present invention relates to a process for the production of a biodegradable, essentially liquid-impermeable sheet laminate for use in a sanitary product, which sheet laminate comprises a first stratum made of tissue paper

and

a second stratum made of a biodegradable polymer material wherein

- glue is applied essentially evenly over at least 80% of one surface of tissue paper web, providing an essentially evenly glue coated surface, whereafter

- said tissue paper web is laminated to a web of biodegradable polymer material by pressing said essentially evenly glue coated surface towards said web of biodegradable polymer material. According one embodiment of this third main aspect of the present invention the tissue paper web is a wet-laid cellulosic tissue paper web. In one aspect of this embodiment the wet-laid cellulosic tissue paper web is not a nonwoven fabric.

According to one specific aspect of said embodiment the wet-laid cellulosic tissue paper web does not have a fibrous content of more than 50% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, and if the wet-laid cellulosic tissue paper web does have a fibrous content of more than 30% by mass made up of fibers, excluding chemically digested vegetable fibers, with a length to diameter ratio greater than 300, then the density of the wet-laid cellulosic tissue paper web is not less than 0.40 g/cm ³ .

According a further embodiment of said third main aspect of the present invention

- the glue is applied essentially evenly over at least 90% of one surface of tissue paper web, providing an essentially evenly glue coated surface, whereafter

- said tissue paper web is laminated to a web of biodegradable polymer material by pressing said essentially evenly glue coated surface towards said web of biodegradable polymer material.

As used herein, following the definition by the American Society of Testing and Materials (ASTM), the qualifying term "biodegradable" and inflectional forms thereof indicate the ability of undergoing decomposition into carbon dioxide, methane, water, inorganic compounds, or biomass in which the predominant mechanism is the enzymatic action of microorganisms, that can be measured by standardized tests in a specified period of time, reflecting available disposal conditions.

The qualifying term "compostable" and inflectional forms thereof indicate biodegradability relating to solid materials and do not refer to liquids. As used herein, the term "sheet laminate" means a structure composed of thin sheets superimposed and bonded together by binder(s).

As used herein, the term "cellulosic" is meant to include any papermaking fiber having cellulose as a major constituent. "Papermaking fibers" include virgin pulps or recycle cellulosic fibers or fiber mixes comprising cellulosic fibers.

As used herein, the term "tissue paper" means a soft, thin, paper suited to be used in sanitary products such as diapers, sanitary napkins, incontinence guards, panty-liners, and similar absorbent products. It should be realized that it is different from bathroom tissue and toilet tissue in that it has higher dry strength than such tissues.

The basis weight of the tissue paper will depend on its intended use. For instance, the basis weight can range from about 12 g/m ² to about 30 g/m ² , specifically from about 15 g/m ² to about 20 g/m ² .

The basis weight of a tissue paper may be determined according to the test method specified in ISO 12625-6.

The biodegradable polymer material may be any such material suited to be used in a biodegradable, essentially liquid-impervious sheet laminate of the present kind. The biodegradable polymer material may, for instance, be chosen among polyhydroxyalkanoates, aliphatic polyester-based polyurethanes, polylactides, polycaprolactones, polylactides, polyvinyl alcohol) compositions, hydroxypropylcellulose, cellulose esters, starch based polymers based on wheat starch, potato starch, rice starch, or corn starch; interpenetrating networks, hereinafter abbreviated IPN, based on starch chosen among wheat starch, potato starch, rice starch, and corn starch; and copolymers of starch based polymers and any biodegradable hydrolyzable polymer chosen among polycaprolactones, polyvinyl alcohol) compositions, polylactides, polyhydroxybutyrates, and polyhydroxyvalerates; or a mixture of two or more of these polymers.

The biodegradable polymer material may also include a plasticizer and/or additional polymer for enhancing the melt processability of the polymer material.

The biodegradable polymer material may also include one or more fillers, specifically an organic filler material, such as, for instance, nutshell flours, grain flours, starches, cellulose based particulate material, and/or mixtures thereof. The stratum made of a biodegradable polymer material may be essentially liquid impervious, such as, for instance, a plastic film, a nonwoven material coated with a liquid impervious material, or a hydrophobic nonwoven material, which resists liquid penetration. The stratum made of a biodegradable polymer material may be breathable so as to allow vapour to escape from the absorbent core, while still preventing liquids from passing therethrough. Examples of breathable materials are porous polymeric films and nonwoven fabrics from spunbond and meltblown fibers. The basis weight of the biodegradable polymer material will depend on its intended use. For instance, the basis weight can range from about 15 g/m ² to about 25 g/m ² , specifically from about 17 g/m ² to about 23 g/m ² .

The glue used to produce the inventive sheet laminate may be any glue suited to be used in a biodegradable, essentially liquid-impervious sheet laminate of the present kind. The glue may, for instance, be chosen among natural rubber latex, starch, and polyvinyl alcohol (PVOH).

The glue may be applied by any means suitable for the production of a biodegradable, essentially liquid-impervious sheet laminate of the present kind. The glue may, for instance, be applied by way of spraying, by means of a roller, or by way of slot coating. The term "slot coating" refers to a process in which a slot die provides a thin, uniform coating on a substrate to be coated. In slot coating, the coating can be placed using an open gap in which the substrate to be coated is passed under the slot die, or a closed gap in which the slot die is aligned with a coating roll, such that there is a narrow gap or nip between the roller and slot die. The substrate to be coated is passed between the coating roll and the slot die. The amount of glue essentially evenly applied on over at least 80% of one surface of said first stratum will depend on the intended use of the inventive sheet laminate.

For instance, this amount may vary from about 1.5 g/m ² to about 3.0 g/m ² , specifically from about 1.8 g/m ² to about 2.7 g/m ² .

The following non-limiting example serves to further illustrate the present invention.

Example

In this example a set of machinery is used for the production of a sheet laminate according to one embodiment of the present invention, which set of machinery comprises a first roll and a second roll.

The first roll contains a first web of wet-laid cellulosic tissue paper, which tissue paper has a dry strength (in machine direction) of 160 N/m, a wet strength (in machine direction) of 50 N/m, and a basis weight of 17 g/m ² .

The second roll contains a second web of biodegradable polymer material, specifically MATER-BI ^® (trademark of Novamont in Italy: having starch as the major component and biodegradable polyvinyl alcohol resin and aliphatic polyester resin as the minor components). The first web is rolled off from the first roll, and the second web is rolled off from the second roll. Suitable guide rolls are arranged in connection with the rolling off, at the first as well as at the second roll.

The first web passes first through a gluing station, in which glue, specifically NW 1217 ZEROPACK ^® , a hotmelt adhesive available from H.B. Fuller, is applied essentially evenly onto 80% of one surface of the first web, in an amount of 2.5 g/m ² of the first web, by means of spray application devices.

After the gluing station the first web gets in contact with the second web, with the glue coated surface of the first web facing towards the second web, at a pressing station comprising two contra-rotating rollers, forming a nip. In this nip, the two webs are pressed together, whereby the glue joins together the two webs into a sheet laminate web. Thereafter, the sheet laminate web is cut by aid of a cutting device, and the resulting sheet laminates are rolled up on a subsequent take-up roller.

The softness of the resulting sheet laminates is evaluated using Tissue Softness Analyzer (TSA) instrumentation from the company EMTEC having a Haptic Feel (HF) value scale from O to 100.

Test samples of the resulting sheet laminates are conditioned at about 21 °C and about 50% air humidity.

The thus measured Haptic Feel (HF) values of the resulting sheet laminates are in the range of 82 to 88.2 HF.

Although the invention has been described with regard to certain embodiments, including the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention as set forth in the claims appended hereto.