SOFT NON-WOVEN CLOTH FOR USE AS AN OUTER LAYER OF DISPOSABLE ABSORBENT ITEMS

Abstract

The present invention covers a non-woven fabric for laminate on a polyethylene layer, such that a. it is comprised by a mixture of polypropylene hydrophobic and hydrophilic fibers; b. it is manufactured by means of a carding process followed by thermal bonding c. during the thermal bonding is engraved in at least 15% of its area d. has a minimum base weight of 13 gr/m.sup.2.

Claims

1. A disposable absorbent article comprising: an outer laminate including: an impermeable layer to prevent leaking, the impermeable layer including an outer surface and an inner surface; and a non-woven fabric coupled to the outer surface of the impermeable layer, the non-woven fabric including a first film and a second film thermally bonded to the first film, wherein each of the first and second films includes hydrophobic polypropylene fibers and hydrophilic polypropylene fibers that are homogeneously blended together.

2. The disposable absorbent article of claim 1, wherein the impermeable layer includes a plastic layer.

3. The disposable absorbent article of claim 2, wherein the plastic layer includes a polyethylene layer.

4. The disposable absorbent article of claim 1, further including an absorbent core in contact with the impermeable layer opposite the non-woven fabric.

5. The disposable absorbent article of claim 4, further including an inner permeable layer in contact with absorbent core opposite the impermeable layer.

6. The disposable absorbent article of claim 5, wherein the impermeable layer is positioned relative to the absorbent core and the inner permeable layer to prevent fluids absorbed by the absorbent core through the inner permeable layer from coming in contact with clothing in contact with the outer laminate.

7. The disposable absorbent article of claim 6, wherein the non-woven fabric is coupled to the outer surface of the impermeable layer to provide a soft exterior surface of the disposable absorbent article.

8. The disposable absorbent article of claim 1, wherein the first film has a same proportion of the hydrophobic polypropylene fibers and the hydrophilic polypropylene fibers as the second film.

9. The disposable absorbent article of claim 1, further including a soft exterior surface formed by the first film of the non-woven fabric.

10. The disposable absorbent article of claim 9, wherein the soft exterior surface includes engraved images.

11. The disposable absorbent article of claim 10, wherein the soft exterior surface is engraved with between 8 and 12 images/cm2 images per square centimeter, inclusive.

12. The disposable absorbent article of claim 10, wherein the engraved images have a maximum depth of 0.65 millimeters.

13. The disposable absorbent article of claim 1, wherein the first film and the second film are configured to collectively have a longitudinal tension strength of between 1000 and 2500 grams per 2.54 centimeters, inclusive.

14. The disposable absorbent article of claim 13, wherein the first film and the second film are configured further to collectively have a longitudinal elongation of between 50 and 80 percent, inclusive.

15. The disposable absorbent article of claim 14, wherein the first film and the second film are configured further to collectively have a cross-sectional strength of between 90 and 250 grams per 2.54 centimeters, inclusive.

16. The disposable absorbent article of claim 15, wherein the first film and the second film are configured further to collectively have a cross-sectional elongation of between 100 and 300 percent, inclusive.

17. The disposable absorbent article of claim 16, wherein the first film and the second film collectively have a basis weight of between 13 and 15 grams per square meter, inclusive.

18. The disposable absorbent article of claim 17, wherein the first film and the second film collectively have a gauge between 0.1 and 0.2 millimeters, inclusive.

19. The disposable absorbent article of claim 1, wherein: the hydrophilic polypropylene fibers have between 8 and 9 curls per centimeter, inclusive; and the hydrophobic polypropylene fibers have between 5 and 6 curls per centimeter, inclusive.

20. The disposable absorbent article of claim 1, wherein: the hydrophilic polypropylene fibers are between 38 and 42 millimeters long, inclusive; and the hydrophobic polypropylene fibers are between 38 and 42 millimeters long, inclusive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0016] The absorbent articles mentioned herein may be, but are not limited to: disposable diapers and underwear for babies, feminine sanitary napkins, adult diapers, underwear, and protectors, etc. These articles are used for a period of time that may vary depending on use, but generally from 2 to 4 hours during the day or 8 to 12 hours at night, then are disposed off and replaced by another article, such that a person uses 4 to 5 articles per day. Thus, an important aspect to consider in improving these articles is the cost involved in its manufacture, given that the buyers of these type of articles are not amenable to paying a high cost for a product that will be dicharged after some hours of use, and immediately shall be replaced for another one.

[0017] Focusing on the present invention, non-woven fabrics can be developed for use as an outer layer in disposable absorbent articles with optimum softness characteristics and appearance, but with high base weights which increase the cost and preclude its use in such products. In the present invention, a non-woven fabric is described that, due to its mechanical characteristics, softness and appearance, as well as its cost, is ideal for being attached to an impermeable film layer forming a laminate which will be used as an outer layer of disposable absorbent articles.

[0018] A disposable absorbent article is basically comprised by an inner permeable layer, an outer impermeable layer, and an absorbent core placed there between. Generally, a non-woven fabric is used as the inner layer, which allows the passage of fluids, the absorbent core is generally comprised by absorbent material fibers mixed with superabsorbent particulate material, and a film, which impedes the passage of fluids, is used as the outer layer. The disposable absorbent articles can additionally comprise other elements: fastener system, elastic areas, transfer layers, anti-leak barriers, elastic material at the waist and leg portions, etc.

[0019] The main function of the outer layer of the disposable absorbent articles is to stop the fluids absorbed by the absorbent core, protecting the clothing that comes into contact with the article, impermeability therefore is one its main characteristics; further, it should be soft and flexible. Another desirable characteristic in an outer layer of a disposable absorbent article is that it has the appearance of fabric, both visually and to the touch; for obtaining both characteristics, impermeability and fabric-like appearance, a laminate consisting of a plastic film such as a polyethylene and a non-woven fabric can be used, such that the polyethylene layer is placed facing inward, contacting the absorbent core, and the non-woven fabric facing outward. The first one provides the characteristic of impermeability and contributes to the pliability and softness, while the second one contributes to the appearance and fabric-like touch, further contributing to the softness and pliability of the outer layer of the disposable absorbent articles.

[0020] The non-woven fabric used for this type of laminate should have certain mechanical properties for withstanding the longitudinal and cross section strengths used during the lamination and during manufacturing process of the disposable absorbent articles, these mechanical properties are: [0021] Longitudinal strength: 1000 to 2500 gr/2.54 cm [0022] Cross-sectional strength: from 90 to 250 gr/2.54 cm [0023] Longitudinal elongation: 50 to 80% [0024] Transverse elongation: 100 to 300%

[0025] Moreover, it should have a base weight between 13 and 25 gr/m.sup.2 that does not increase the cost of the final product and may be introduced in an industrial process of manufacture of the absorbent articles.

[0026] The non-woven fabric of the invention, in addition to having the cited mechanical characteristics and base weight, is softer than the fabrics with the same mechanical characteristics and base weight that are currently available in the market. This is achieved through a carding process followed by a thermal bonding process that follows the stages listed below: [0027] 1. Pre-opening of the fibers [0028] 2. Opening [0029] 3. Weighing, mixing and homogenization of the fibers in adequate ratios. [0030] 4. Formation of nappa [0031] 5. Weight control of nappa [0032] 6. Carding and combing of the nappa, formation of strands [0033] 7. Thermal bonding [0034] 8. Application of tension [0035] 9. Cutting and spooling

[0036] Each of these steps comprises a series of technical considerations that provide the non-woven fabric of the invention with its final characteristics. Each of these steps is carried out using the necessary means which are, but are not limited to, machinery, independent machinery or assembly systems for non-woven fabric.

[0037] A mixture of hydrophobic and hydrophilic polypropylene fibers is used in a ratio ranging from 90:10 to 10:90, these fibers shall have the following characteristics:

TABLE-US-00001 TABLE 1 Fiber characteristics Parameter Units HYDROPHOBIC HYDROPHILIC Denier gr/9000 m 2.2 0.15 2.17 0.15 Tenacity gr/De 2.5 0.15 1.94 0.15 Elongation % 370 40 338 19.02 Curliness Curls/cm 6.0 1 9.0 1 Length mm 40.0 2.0 40.0 2.0 Cohesion gr 110.0 10.0 110.0 10.0

[0038] The hydrophobic fiber provides the fabric with liquid repellant, while the hydrophilic fiber helps to a better formation of the fibers at the time of the carding and combing of the fiber.

[0039] Once the fibers are weighed and homogenized, the nappa is formed, this nappa will result in the fabric; the nappa is formed with the right amount of fibers for obtaining the required base weight in the final product. Two or more films can be formed in order to obtain a homogenous non-woven fabric in respect to the distribution of the fibers, these films will then be thermally bonded.

[0040] To obtain the required softness, the most important step of the process is the thermal bonding process. This is done by passing the films through two rollers, a top roller with a special protrusion-shaped embossment, and a bottom smooth roller. The rollers operate at a temperature between 120 and 180 C.; and a pressure of between 65 to 95 Kgf/cm.sup.2 is applied there between, such that, when passing the films between the rollers, the fibers are thermally-bonded and the embossment of the top roller is engraved in the non-woven fabric. The preferred temperature for this step in the process is between 130 and 150 C. and the preferred pressure between the rollers is between 70 and 80 Kgf/cm.sup.2.

[0041] To achieve the required characteristics of softness and appearance, the pattern on the top roller should be such that the resulting non-woven fabric has: [0042] An engraving area of between 10% and 25%; [0043] An engraving density of between 8 to 12 images/cm.sup.2 [0044] A maximum engraving depth of 0.65 mm

[0045] Finally, the fabric is tensioned by means of rollers comprising a tension spring or rollers with pneumatic tension controls, in order to provide the required tension for spooling and cutting.

[0046] In any case, the non-woven fabric resulting from the aforementioned process comprises a series of technical characteristics that make it ideal for the exterior of disposable absorbent articles, this is, softness to the touch, easy bonding to the impermeable layer and appropriate mechanical characteristics for a good processability during the laminating process. The following table outlines the mechanical properties of the non-woven fabric of the invention:

TABLE-US-00002 TABLE 2 Non-woven fabric characteristics PROPERTY MEASUREMENT Basis weight 13-15 gr/m.sup.2 Longitudinal strength 1000-2500 gr/2.54 cm Cross-sectional strength 90-250 gr/2.54 cm Gauge 0.10-0.2 mm Longitudinal elongation 50-80% Cross-sectional elongation 100-300%

[0047] The softness of the non-woven fabric of the present invention was evaluated using a sensory test as follows: [0048] Surveyed persons were blindfolded [0049] Two disposable diaper samples were placed in front of them: [0050] Sample A: disposable diaper with an outer layer comprised by a laminate consisting of the non-woven fabric of the invention and a low-density polyethylene; the non-woven fabric with a base weight of 17 g/m.sup.2; [0051] Sample B: disposable diaper with an outer layer comprised by a laminate consisting of the non-woven fabric of the invention now used in our products, with a base weight of 17 g/m.sup.2 combined and the same low-density polyethylene as in Sample A. [0052] The persons were asked to feel the outer layer of both Samples A and B with their hands and to indicate which one felt the softest.

[0053] The results were as follows: [0054] TOTAL NUMBER OF SURVEYED PERSONS: 50 [0055] PERSONS WHO SAID SAMPLE A WAS THE SOFTEST TO THE TOUCH: 32 (64%) [0056] PERSONS WHO SAID THAT SAMPLE B WAS THE SOFTEST TO THE TOUCH: 18 (32%)

[0057] In accordance with the above, it can be concluded that the non-woven fabric of the invention is softer to the touch with a statistical feasibility of 90%.

[0058] While the invention has been described in terms of the preferred embodiments, it should be evident to those skilled in the art that variations and modifications thereof can be implemented without deviating from the scope of the present invention.