Abrasive web and method of making same.

0001Nonwoven thermoplastic webs are well known for a wide variety of end-uses, such as for wipes, surgical gowns, dressings, etc. These products are generally made by either meltblowing or spunbonding, both of which are well known in the art (for example U.S. Patent No. 3,978,185 which describes meltblowing and is herein incorporated by reference, and U.S. Patent No. 3,692,618 which describes spunbonding and is herein incorporated by reference).

0002Spunbonding entails extruding a multiplicity of continuous thermoplastic polymer strands through a multiplicity of die orifices in a downward direction onto a moving surface where the extruded strands are collected in randomly distributed fashion. The randomly deposited strands are then bonded together in a heated nip to provide sufficient integrity to the resulting nonwoven web of continuous fibers. Spunbonded webs are characterized by a high strength/weight ratio, isotropic strength, high porosity, and good abrasion resistance and are useful for a wide variety of product applications ranging from diaper liners to street repair fabrics.

0003Meltblowing differs from spunbonding in that the extruded polymer strands are broken up and dispersed into individual fibers by a forced air stream before being deposited onto the collecting surface. In addition, the fibers are substantially cooled by the air so that they do not significantly bond together. Bonding of the web to retain integrity and strength occurs as a separate downstream operation. Meltblown webs are characterized by their softness, bulk, absorbency, low porosity and poor abrasion resistance and are useful for product applications such as surgical drapes and wipes.

0004Notwithstanding the fact that much nonwoven product development is directed toward products which provide enhanced softness and greater flexibility, there is also a need for an inexpensive nonwoven product which is sufficiently abrasive to serve as a cleaning wipe without using added abrasive materials, yet soft enough to reduce or eliminate scratching the surface being cleaned.

0005In accordance with the invention, an abrasive web comprises at least a meltblown abrasive layer.

0006Suitably, the abrasive web comprises at least two layers thermally bonded together.

0007Preferably, the method for making the abrasive web comprises meltblowing a polymer melt onto a supporting web such that the meltblown fibers are at a temperature at or above the polymer softening point and remain sufficiently semi-molten (hot and fusible) to thermally bond to the supporting web. By making a web in this manner, the resulting meltblown fibres, which are thicker than conventional meltblown fibres, intimately bond to the supporting web and harden into an abrasive surface. The resulting layered web thus exhibits the strength of the supporting web, which is preferably a spunbonded web, and the abrasiveness of the meltblown layer.

0008To achieve the desired product characteristics, a number of variables must be considered when practising the above method. These variables include the characteristics of the polymer, the temperature of the melt, the design of the meltblowing die tip, the denier of the extruded melt and resulting fibres, the melt flow rate, the meltblowing air temperature and flow rate, the distance between the die tip and the supporting web, the basis weight of the meltblown layer, and the nature of the supporting web. These variables are manipulated as necessary to achieve semi-molten meltblown fibres capable of bonding to the supporting web.

0009In an alternative, the supporting web and meltblown abrasive layer are thermally bonded by mechanical means such as hot calender rollers.

0010In a further alternative, semi-molten meltblown fibres are thermally bonded to a supporting web, whereafter the composite web is passed through rollers to enhance cohesion between the layers of the web and increase the amount of thermal bonding between the layers of the web.

0011Preferably, the layers of the composite web are hot embossed, whereby the layers are thermally bonded together.

0012Suitably, the layered abrasive web comprises a supporting layer and a meltblown abrasive layer intimately thermally bonded together, the meltblown abrasive layer having a basis weight of from about 5 to about 100 grams per square meter (gsm), preferably from about 5 to about 80 gsm, and most preferably from about 5 to about 25 gsm, and consisting of fibres having an average fibre diameter from about 20 to about 100 micrometers, or of at least about 40 micrometers, preferably from about 40 to about 85 micrometers, and most preferably about 50 micrometers. Such a web provides an abrasive wipe at very low materials costs, which means that such wipes may be disposed of after one or two wipes. The meltblown layer is very thin, having a basis weight lower than typical meltblown webs. The supporting layer, which is preferably a spunbonded web because of its high strength-to-weight ratio, provides the necessary product strength and integrity and, in some instances, absorbency.

0013Various different product forms can utilize the layered abrasive web concept described above. One such embodiment is a single-ply two-layered abrasive meltblown/spunbonded wipe, which can be impregnated with a wide variety of chemical additives, for cleaning household surfaces or for bathing. Another example of a product form is a single-ply three-layered abrasive wipe (meltblown/spunbonded/meltblown) in which both outer surfaces are abrasive meltblown layers. A further example is a three-ply wiping product wherein a first outer ply comprises an abrasive meltblown/spunbonded layered web having the abrasive meltblown layer facing outwardly, an inner ply comprises a water-permeable nonwoven thermoplastic web, and a second outer ply comprises a water-permeable meltblown thermoplastic web. Each of the plies is bonded together along the periphery of the wipe and a detergent is contained between the inner ply and the second outer ply. A still further example of a product form is a shower cloth comprising a two-layered meltblown/spunbonded web, constructed of two separate plies or one ply folded over on itself, such that the abrasive meltblown layer is the exposed layer on both outer surfaces.

0014The invention will now be described, by way of example, with reference to the accompanying drawings, in which:- <ul id="ul0001" list-style="none"><li>Figure 1 is a schematic flow diagram illustrating a method of making a web in accordance with the present invention,</li><li>Figure 2 is a cross-sectional view of the blowing head used for meltblowing in the method illustrated in Figure 1,</li><li>Figure 3 is a cross-sectional view of a web in accordance with the present invention, illustrating a single-ply meltblown/spunbonded layered product,</li><li>Figure 4 is a cross-sectional view of a web in accordance with the present invention, illustrating a single-ply meltblown/spunbonded/meltblown product, and</li><li>Figure 5 is a cross-sectional view of a web in accordance with the present invention, illustrating a three-ply product.</li></ul>

0015Figure 1 illustrates a method wherein a layer of meltblown fibres is deposited upon a supporting web to form a layered abrasive composite web. More specifically, polymer feed pellets are introduced into an extruder 1 in which the polymer is melted and conveyed to the melt blowing head 2. The melt blowing head essentially comprises two forced hot air inlets 3 and 4 and a multiplicity of extrusion orifices through which the polymer melt is extruded. In a preferred embodiment, the blowing head contains about 30 orifices per inch having a diameter of about 0.0145 inch. As the polymer melt is extruded downwardly, the interaction of the extrudate with the forced hot air disrupts the extrudate to form discontinuous, semi-molten fiber fragments 5 which immediately begin to solidify. However, prior to solidification, while still in a bondable condition, the fibers are deposited onto a supporting web 6 and intimately thermally bond thereto as solidification is completed. The resulting layered web 7 is then calendered and wound onto a roll 8 for subsequent conversion into a particular product form. As shown in Figure 1, the supporting web 6 of the product can be provided from a roll 9 which is simply unwound at the desired rate, or it can also be provided by forming it in line on the support fabric 11 prior to deposition of the meltblown fibers.

0016Suitable polymer feed materials for producing the meltblown abrasive layer of the layered web include, without limitation, polypropylene, polyethylene, nylon, polyethers, ethylene vinyl acetate, polyvinyl chloride, polyesters, and copolymers thereof. However, polypropylene having a weight average molecular weight greater than about 200,000 is preferred because of its availability, ease of spinning, and abrasive properties. Suitably commercially available materials include Exxon 3045, Himont PRO-FAX polypropylene pellets, Nesté PD977 and Fina 7060 S.

0017Suitable supporting web materials for the supporting layer of the layered web include spunbonded webs of various polymers as listed above, bonded carded webs, and meltblown webs of various polymers or combinations of polymers and other fibers such as cellulosic fibers. It is important that the substrate material have a softening point sufficiently lower than the temperature of the extruded polymer melt and that the melted substrate material be miscible with the extended polymer melt in order for thermal bonding to occur. Spunbonded polypropylene webs having a basis weight of at least about 5 gsm are preferred because of their uniform formation and relatively high isotropic strength per unit weight. Such a web is available commercially from Lutravil Corporation under the trademark LUTRICIL and has a basis weight of about 10 gsm.

0018Figure 2 illustrates in cross-section the configuration of the blowing head. Shown is a polymer melt supply passageway 16 which is stepped down in size to about 0.0145 inch at the die tip orifice 17. The die tip orifice 17 is recessed about 0.090 inch. The polymer melt temperature can be from about 540°F. to about 600°F. for polypropylene. Converging hot air slots 21 and 22 have a slot opening of about 0.067 inch and extend the width of the blowing head. The length of the channels 21 and 22 is about 1.75 inches. In operation, hot air is supplied to the hot air channels, creating a downward hot air flow which disrupts the polymer extrudate as it leaves the die tip. The hot air flow serves to draw out the extruded fibers and the flow rate can be used to control the resulting fiber diameter and the abrasiveness of the resulting meltblown layer. The lower hot air flow rates provide thicker fibers and higher flow rates create thinner fibers. The resulting extrudate melt fragments (meltblown fibers) are blown downwardly onto the travelling supporting web before they have sufficient time to solidify. Hence the meltblown fibers are deposited while in a semi-molten state sufficient to permit the fibers to intimately thermally bond to the fibers of the supporting web. To achieve deposition of the meltblown fibers while still in a semi-molten state, it is necessary to properly balance the polymer flow rate, the hot air flow rate, the diameter of the die tip orifice, and the distance between the die tip and the supporting web.

0019As an example, it has been found that the abrasive material can be produced from the above-mentioned apparatus and process using a polymer (590°F.) flow rate through the die tip of about 1.1 pounds per inch of die tip width per hour, a hot air (533°F.) flow rate through the die tip of about 75 standard cubic feet per minute (pressure differential of about 3 psi), and a distance between the die tip and the supporting web of about 14 inches. These conditions result in the deposition of semi-molten fibres having an average fibre diameter of about 50.8 micrometers, which is substantially thicker than conventional meltblown fibres, which typically have fibre diameters of about 7 micrometers. The meltblown abrasive layer formed has a basis weight of between 5 and 25 gsm.

0020Figure 3 is a cross-sectional view of a representative abrasive wiping product. Shown is a meltblown layer 31 thermally bonded to a spunbonded supporting layer 32.

0021Figure 4 is a cross-sectional representation of a modified product, which has an abrasive meltblown layer of fibres 31 on both outer sides. Such a product can be manufactured using a web as shown in Figure 3 as the supporting web in the method illustsrated in Figure 1. Such a product can be particularly useful if differing degrees of abrasiveness are desired in a single product.

0022Figure 5 illustrates yet another embodiment having three plies and containing a detergent. Shown is a first outer ply 51 which comprises an abrasive meltblown/spunbonded web as illustrated in Figure 3 and having the meltblown layer facing outwardly, an inner ply of water-permeable nonwoven thermoplastic 52, and a second outer ply 53 comprising a water-permeable meltblown web. In between the inner ply and the second outer ply is entrapped detergent 54. All three plies are suitably bonded about the periphery of the composite web at bonded areas 56 to retain the detergent and the integrity of the composite web.

0023In a product form not shown, a layered abrasive web comprises a meltblown abrasive layer having a basis weight between 30 and 80 gsm and fibres with an average fibre diameter between 20 and 80 micrometers, and a "functional" layer. This functional layer may be water and/or oil absorbent, and is preferably made from meltblown polymer fibres and absorbent particles held therewithin (for example as disclosed in US Patent No. 4100324 and PCT Publication No. WO83/01965, the contents of which are herein incorporated by reference).

0024In particular, the absorbent particles may be wood pulp or cellulosic fibres, wherein the fibres comprise up to 85% by weight of the functional layer.

0025Alternatively, this functional layer is an abrasive layer which is either more or less abrasive than the meltblown abrasive layer.

0026The functional and meltblown abrasive layers are hot embossed, in order to thermally bond such together.

0027The product forms are suitably used as a heavy duty kitchen wipe, or a light duty bathroom wipe.

0028In all of the product forms, it can be advantageous to impregnate the product with various additives, such as detergents, surfactants, cleaners, bleaches, perfumes, disinfectants, germicides, virucides, etc.