NONWOVEN COVERSTOCK FOR ABSORBENT ARTICLES

Abstract: Hydrophobic nonwoven coverstock for absorption hygienic items made of microfibres of a titre of less than 1.5 dtex and containing less than 0.15 % titaniumdioxide as dulling agent.

Description: NONWOVEN COVERSTOCK FOR ABSORBENT ARTICLES The invention provides a soft hydrophobic nonwoven coverstock for absorption hygienic items made of microfibres with a fibre titre less than 1.5 dtex and containing 0.00 to 0.15 % titaniumdioxide as dulling agent. Most advantageous concentration of titaniumdioxide is between 0.01 to 0.12 %. The invention provides further such nonwoven coverstock consisting of more than 65 % polypropylene. Finally this invention provides a nonwoven coverstock made of continuous filaments i. e. a spunlaid nonwoven fabric. Background of the invention Hydrophilic and permeable coverstock materials of similar kind is well known and they will be used for manufacturing of hygienic absorption items such as baby diapers, diapers for incontinent adults and similar. Such items consist of a absorption core made of wood pulp and containing granulated SAP (superabsorption polymer). The backside of such absorption items which is opposite to the users body is made of a nonpermeable sheet, mostly of a polymer film which eventually can be laminated with a nonwoven fabric. The inner face of such items, which is in contact with the users body, will be made of a permeable material, mostly a permeable nonwoven fabric. In order to limit the reverse penetration of the absorbed fluid, it is useful to use a permeable coverstock not at the entire area of the item but only for a central strip. The rest of the surface, or the side panels, can be made of a soft textile material which is hydrophobic. Same hydrophobic material can be used to form barrier leg cuffs providing an additional sealing and hindering leakage of the fluid (urine) outside of the item. As state-of-the-art composite multiply nonwoven fabrics will be used as barrier leg cuff. Typical composite fabrics of this kind consist of two nonwoven plies made of continuous filaments of a filament denier 1.5 dtex to 3.0 dtex with a smooth ply made of hyperfme fibrils called "meltblown". Such laminates would typically provide a standard weight of 17 to 20 g/m 2 , where the central meltblown ply provides 15 to 25 % of the total weight. The most important criterion for such composite barrier leg cuff material called SMS is their level of hydrophobia expressed as waterhead which has to exceed 100 mm. The hydrophobia of this composite material is governed by the meltblown ply. The contribution of the regular fibres is rather limited, but they are important as constituents responsible for the strength properties. A SMS composite as described is opaque due to the optical properties of the meltblown microfibrils. In addition, the basic nonwoven is regularly dulled by adding 0.4 % titaniumdioxide or more. It is known to apply cosmetic lotion at the coverstock of hygienic items for improved skin protection of the user. Such treatment is described in DE-PS 35 36 318 as well as in DE-PS 35 36 319. When a simple nonwoven fabric will be used in combination with the treatment, as described in the patents mentioned above, no particular optical problems occur. This is due to the fact, that simple nonwoven coverstock, even if made of dull filaments containing regularly about 0.4 % titaniumdioxide, are not particularly opaque. Just in difference, when cosmetic lotions, which are normally water dispersions containing oil and/or fat, will be applied to highly opaque nonwoven sheet, non regular oil or fat spots can occur even, when the application will be provided very carefully uniformly. Such spots are very detrimental for general optical impression. Thereby such spots are not necessarily due to quantitative irregularities of the application. They are rather optical phenomena based on differences in the surface wetting of fibres. It has been surprisingly demonstrated, that nonwovens made of microfibres with titre per fibre of less than 1.5 dtex and particularly such of more than 0.01 and less than 1.2 dtex, are capable to reach high level of hydrophobia with waterhead figures of more than 100 mm, due to their geometry and non favourable wetting angles. This enables a use of such microfibres nonwovens as breathable barrier fabric for hygienic items without need for employment of any meltblown ply. It has been further surprisingly demonstrated, that nonwoven fabrics made of microfibres keep their favourable surface properties even when their will be made with very low portion of titaniumdioxide below 0.15 % or without any titaniumdioxide at all. However he preferred portion of titaniumdioxide will be in a range between 0.01 and 0.12 %, a range which improves the spinning and bonding processes. It as further demonstrated, that nonwoven fabrics according to this invention can not only be made of simple fibres but in similar way of bi- component fibres or of a fibre mix of two different kinds of fibres. As second constituent it is possible to use another polyolephine, e. g. polyethylene, a random co-polymer of polypropylene or another spinnable polymer, as polyester. The nonwoven fabric according to this invention can be manufactured of staple fibres by using carding technology. However it is an advantage to manufacture such nonwovens of continuous filaments by means of spunlaid technology. Example 1 Spinning machine for nonwoven fabrics of type Reicofil ^ -3 (made by the Reifenhauser Company) consisting of two spinning beams was adjusted as necessary for manufacturing of microfilaments. As raw material has been used polypropylene Metocene with a MFR 30 manufactured by the Targor AG Company. Both spinning beams used same spinning conditions as follows: At a spinning beam of a width of 3.2 m was installed a spinneret with 17 700 orifices. The melt temperature was 245-250 °C, the temperature of the spinneret 250-255 °C. The total throughput of polymer was 5.8 kg/min, i.e. 0.33 g/min pro orifice. The dosage of titaniumdioxide masterbatch was installed so, that the polymer melt as spun contained 0.1 % of the pigment. Continuous filaments extruded into the quenching and drawing cabinet have been quenched by air of a temperature of 25 °C, which has been accelerated in the drawing part of the cabinet and used for drawing. The width of the narrow part of the cabinet has been 17 mm. The bottom part of the cabinet broadened and formed a diffuser where the drawed continuous filaments were laid up at a collector screen in form of fibrous sheet whereby this web forming section of the collector screen has been equipped from the bottom side with suction cabinet. The collector screen transported the fibrous sheet to a hot calender for bonding. The screen speed was adjusted at 200 /min so, that the weight of the nonwoven fabric was 17 g/m 2 . The calender bonding temperature was 155 °C at the patterned cylinder and 143 °C at the smooth one. The manufactured spunlaid nonwoven provided following laboratory test results (MD is for "machine direction", CD for "cross machine direction"): The spunlaid nonwoven fabric manufactured in this trial was almost transparent and it allowed to apply a fat or oil dispersion so that no spoils have been watched. Such nonwoven fabric was very suitable as barrier coverstock for manufacturing of baby diapers. Example 2 In this case same two spinning beam manufacturing line as described in Example 1 was used. In same way, the spinning conditions corresponded exactly to what has been described in Example 1. Only the throughput was increased up to 7.0 kg/min or 0.40 g/min per orifice respectively. No titaniumdioxide as pigment has been added. To keep the basic weight of the manufactured web unchanged, the speed of the collector screen has been increased to 234 m/min. The manufactured spunlaid nonwoven fabric provided following laboratory test results: The nonwoven spunlaid web manufactured according to this example has been fully transparent. It allowed a treatment with a fat or oil dispersion without any visible spoils. Such nonwoven was very good suitable as hydrophobic barrier fabric for manufacturing of baby diapers. Comparative example 1 A spunlaid nonwoven web has been manufactured exactly according the Example 2. The only difference was in an addition of 0.5 % titaniumdioxide in form of masterbatch. The test results of this material were exactly according to the table in Example 2. The manufactured web was quite opaque, which was the main difference to the Example 2. After application of an oil dispersion non defined spots have been experienced which resulted in non-favourable visual impression. The possibility of use of such material as barrier fabric for baby diapers was quite limited even if all laboratory tests provided excellent results. Comparative example 2 A the same machine as described in Example 1 a meltblown spinning beam has been installed between both spinning beams for continuous filaments. In this way a composite material has been manufactured consisting of a meltblown ply sandwiched between two spunlaid plies. Such material will be called "SMS". Out of the total basic weight of 17 g/m 2 , the constituting plies provided twice 7 g/m 2 of spunlaid with 3 g/m 2 meltblown in-between. The spunlaid materials provided filament titre of 1.2 dtex, meltblown fibrils was as usual quite irregular with average of 0.4 dtex. Following are the results of laboratory tests: The composite SMS material manufactured according to this example provides an excellent fluid barrier. It is highly opaque and even when a treatment with oil dispersion is provided very carefully, there is a strong tendency to form spots detrimental for visual impression.

Claims: Claims 1. Hydrophobic nonwoven coverstock for absorption hygienic items made of microfibres of a titre of less than 1.5 dtex and containing less than 0.15 % titaniumdioxide as dulling agent. 2. Hydrophobic nonwoven coverstock of claim 1 made of microfibres of a titre less than 1.2 dtex. 3. Hydrophobic nonwoven coverstock of claims 1 and 2 in which microfibres contain 0.01 to 0.12 % titaniumdioxide as dulling agent. 4. Hydrophobic nonwoven coverstock of claims 1 to 3 where the portion of polypropylene in the microfibres is higher than 65 %. 5. Hydrophobic nonwoven coverstock of claims 1 to 4 where the microfibres used are continuous filaments.

Inventors: KLASKA FRANTISEK, R URING, KLA&SCARON, R&URING
Applicants: PEGAS A S, PEGAS A.S.
Application year: 2000
Main classification: A61F13
IPC codes: A61F13