JP2541524B2 - Multilayer nonwoven - Google Patents

Description

Description: The present invention relates to a non-woven fabric having at least two layers of non-woven web. Furthermore, the present invention relates to a non-woven fabric comprising one web comprising a web having monofilaments or fibers made of polypropylene and the other layer comprising a non-woven web having monofilaments or fibers made of polyethylene.

Of course, non-woven materials are well known in the art. Such materials were first developed in the 1950s and 1960s, but at least one reference can be traced back to 1943 [see, for example, Manning, US Pat. No. 2,336,743].

One of the important industrial applications of nonwovens is in the production of single-use disposable products. Typical of such products are disposable diapers, feminine hygiene products, surgical gowns,
Such as industrial wipers. In these applications, non-woven fabrics are considered as a substitute for cloth, and there have been extensive efforts to improve the properties of non-woven fabrics to make them more like cloth. The most important thing is the softness of the non-woven fabric. That is, it is to improve the feel and feel of the nonwoven fabric and reduce the folding resistance or bending resistance of the web. Another important aspect was the improvement in the tensile strength or tear resistance of the non-woven fabric. Yet another aspect was the development of nonwovens with special wettability. With the few exceptions noted below, most efforts to improve the properties of these nonwovens have focused on the use of fibers having a circular cross section.

U.S. Pat. No. 2,336,743 to Manning discloses a method and apparatus for solution or melt spinning of non-woven fabrics. According to this specification, the spinning material can be extruded through an orifice in the spinneret, which orifice can have a slit-like, circular or other cross section.

U.S. Pat. No. 3,314,840 to Lloyd et al. Relates to a method of making nonwoven fabrics and apparatus therefor.
Although the disclosure of this patent appears to be primarily related to solution spinning, it is not believed to exclude melt spinning.
The spinneret preferably has a circular or slit-shaped opening, but the opening may be circular, triangular, crescent-shaped, or any other shape.

U.S. Pat. No. 3,508,390 to Bagnall et al. Relates to improved filaments and fabrics made therefrom. The disclosure of this patent emphasizes the production of known knitted fabrics, but also mentions non-woven fabrics. The filament has a cross-sectional shape composed of three integrally joined, substantially symmetrical legs, so that it has a substantially uniform, Y-shaped cross-section with defined dimensions. .

US Patent No. 3,509,009 by Hartmann
The invention relates to non-woven fabrics made by melt spinning a fiber-forming high molecular weight polymer in a directional, high-velocity gas stream to form a high strength, uniform non-woven fabric. Filaments made in accordance with the invention disclosed in this patent typically have a circular cross-section, but other cross-sections such as star-shaped, Y-shaped, or combinations thereof are also mentioned.

A non-woven fleece manufacturing apparatus is described in Hartman, US Pat. No. 3,528,129. This patent appears to be an improvement on existing equipment by identifying holes in the spinneret having a branched cross section. In particular, Y-shaped and T-shaped holes are mentioned.

Finally, Parker US Patent No. 3,630,816
No. relates to a non-woven sheet made from filaments having a rectangular cross section. The rectangular cross section of these filaments is specified to have an aspect ratio of at least 3: 1.

A general object of the present invention is to provide a nonwoven fabric having improved softness and tensile strength. It is also a general object of the invention to provide a method of making such a nonwoven. A more specific object of the present invention is to provide a non-woven disposable liner for diapers having improved softness, tensile strength and moisture permeability. It is another specific object of the present invention to provide a sanitary non-woven wrap with similarly improved softness, tensile strength and moisture permeability.

These and other objects are achieved according to the present invention by providing a non-woven fabric comprising at least two layers of non-woven web. Each nonwoven web contains a plurality of thermoplastic monofilaments. In at least one web, the monofilament has a cross section with two bulges. By this term "two bulge shapes", we have an elongated substantially rectangular section, with an enlarged section of typically circular cross section at each of its most distant ends. It means such a shape. The enlarged portion has a diameter larger than the thickness of the rectangular portion. We have found that non-woven webs made from monofilaments in the shape of such two bulges provide significantly higher softness as well as other desirable properties, especially those having "two bulges". Shape "
Have been found to have many desirable properties when used as a multilayer structure.

According to a preferred embodiment, the non-woven fabric consists of two layers of non-woven web. The non-woven web of the first layer comprises a plurality of substantially similarly made continuous but substantially randomly deposited thermoplastic polymer monofilaments, the monofilaments having two bulging shapes. It has a cross section. The second layer non-woven web also comprises a plurality of substantially similarly made continuous and substantially randomly deposited thermoplastic polymer monofilaments, the second layer monofilaments being most preferred. Has a shape with three bulges or a branched cross section.

Furthermore, the non-woven fabric of this preferred embodiment is stabilized by a discontinuous densified region with heat-induced filament bonding over most of both webs. The densified regions are distributed as a discontinuous regular pattern and occupy about 10 to about 30% of the area of the cloth. Also,
According to this preferred embodiment, the thermoplastic is a polyolefin. Most preferably the polyolefin is polypropylene, polyethylene or an ethylene-propylene copolymer, where polypropylene is preferred as the first layer polyolefin and polyethylene is preferred as the second layer.

According to another preferred embodiment of the present invention, a disposable diaper non-woven liner is constructed similarly to the preferred embodiment just described, but with a first layer having two inflated shaped filaments. Is intended to be directly adapted to the user. The second layer is also used as a permeable layer and facilitates the migration of water into the absorbent material present through the nonwoven. This is accomplished by adding a wetting agent to the polyolefin monofilament to make the second layer, which was originally hydrophobic, somewhat hydrophilic or wettable. The addition of the wetting agent can be carried out by mixing the polymer with the wetting agent and then extruding the polymer or, more preferably, forming a nonwoven web and then applying the wetting agent solution.

According to yet another preferred embodiment, the sanitary non-woven wrap is also provided with polypropylene as the first layer in close proximity to the user. Also, the second or transfer layer of polyethylene is made wettable, similar to the preferred embodiment of nonwoven liners for disposable diapers.

According to still another preferred embodiment of the present invention, the method for producing the nonwoven web of each layer includes the following steps. A polymer in the molten state, either polypropylene or polyethylene, is extruded from a spinneret, preferably with a multiplicity of holes having a predetermined cross section, to produce a plurality of monofilaments having approximately the same cross section. These monofilaments are then drawn, preferably by pneumatic action. After stretching,
The monofilaments are mounted on a moving belt in an essentially chaotic orientation relative to each other.

In a preferred embodiment, at this point, the webs of each layer can be bonded together according to one of three methods: The first and most preferred method involves the use of web formers arranged in parallel, i.e. spinnerets with stretching devices. Thus, the first former deposits the non-woven web on the deposition belt and the second former immediately behind it deposits the second web. As a result, the second web is deposited on the first web, and the two are passed together in a later pressing step. The two webs are then slightly compressed by passing them through a pair of compression rolls.
The two webs are then bonded and stabilized together through a pair of counter-rotating heated rolls.
The first of the pair of rolls has a smooth surface and the second roll has a relief pattern. As a result, the two webs are thermally bonded in the discontinuous regions arranged in a pattern corresponding to the raised pattern of the one heated roll. The pattern of the thermally bonded areas is preferably formed so as to occupy about 10 to about 30% of the surface of the nonwoven fabric.

The second bonding method involves the use of two side-by-side forming machines, as in the first method, but here the first deposition web is passed through a thermobonding roll as previously described before the second web. Is deposited on it. These two webs, the bonded and the unbonded, are then slightly compressed,
And it passes through a 2nd pair of heat-bonding rolls. Preferably, in view of obtaining the optimum softness, the second thermal bond pair is 2
Form a bond pattern on two webs. Here, the multilayer fabric is provided with a lower proportion of the bond pattern than the bond pattern of the first deposited web.

A third bonding method involves forming a first deposited web in a previous step and then winding it. The fabric is then formed by laying this first web on a belt on which a second deposited web is placed.

In its most general sense, the present invention is understood to relate to multilayer nonwovens having at least two layers of nonwoven web, at least one of which comprises a plurality of thermoplastic monofilaments or fibers. , The monofilament or fiber has a cross-section in the shape of two bulges. In particular, the cross-sectional shape of these two bulge-shaped monofilaments includes an elongated substantially rectangular section, each of which has its most distant end having a substantially circular section. The diameter can be described as being greater than the thickness of the rectangular section. This shape can also be described as a "dogbone" or "dumbbell" shape. To further enhance the characteristics of this web, it is preferred that the monofilaments be made of polyethylene, polypropylene or ethylene-propylene copolymers.

Generally, each web is made from discontinuous fibers, continuous monofilaments or combinations thereof. The preferred method of making each web is by the spin bond method. However, it should be understood that meltblown processes for forming discontinuous fibers are also within the scope of the present invention. At present, continuous monofilaments made by the spin bond method are preferred.

The thermoplastic of each web may be the same or a different material than that of the other webs. Each thermoplastic can be spun into monofilaments. Practically spinable materials such as glass can be used, but it is preferred to use polymeric materials in both webs. For purposes of illustration only, examples of such polymers include polyolefins, polyamides, polyesters,
Examples thereof include polyurethanes, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, polyethyl acrylate, cellulose acetate, viscose and the like. Further, the thermoplastic can be a homopolymer, a copolymer or a blend of at least two polymers thereof. Presently, polyolefins, homopolymers, copolymers and polymer blends are preferred, with homopolymers and copolymers being most preferred. The most preferred homopolymers are polypropylene and polyethylene and the most preferred copolymers are ethylene / propylene copolymers. The term "polypropylene" as used herein and in the claims includes copolymers of propylene and ethylene, in which case it includes the propylene unit proactively. The preferred copolymer is
Contains 97% propylene and 3% ethylene. Similarly, by the term "polyethylene" we shall also mean copolymers of ethylene and propylene predominantly containing ethylene units.

For various reasons it is not necessary to have optimal properties in the nonwoven web, but in the present invention several materials may be used in combination with webs made from different materials to have better properties. Being able to obtain the material is one of the great advantages of the present invention. For example, polyethylene is generally too soft and too plastic to be used for certain non-woven web applications. However, in accordance with the teachings of the present invention, a nonwoven web made of polyethylene can be bonded to a stronger nonwoven web, such as a web made of polypropylene, thereby producing a more desirable web. it can. At present, such pairing is most preferred. Thus, the most preferred embodiment comprises a polyethylene nonwoven web combined with a nonwoven web made of polypropylene.
Such special non-woven fabrics exhibit high softness and tensile strength.

FIG. 1 is a schematic diagram showing a preferable apparatus for producing a nonwoven fabric from such a polymer. However, both of these devices are Appel & Morman (Appel & Mor
Man) and manufactured and operated in accordance with the teachings of U.S. Pat. No. 4,405,297. The entire disclosures of these patents are incorporated herein by reference. It should be noted that in the present invention, instead of using just one web forming machine, ie, spinneret and cooling / drawing equipment, two such forming machines 11, 122 are installed in the production line. The first former 11 deposits a first web 13 on a moving belt 15, while the second former 12 deposits a second web 14 onto the first web 13.
13 is to be deposited on top.

While this is the preferred array of web formers, other types of web formers can be used. For example, in another aspect, US Pat. No. 3,6,6 to Dorschner et al.
Nonwoven webs are formed by the apparatus and method described in No. 92,618, which is also incorporated herein by reference.

Briefly, the nonwoven web former 11 shown in FIG.
Each of 12 and 12 includes a spinneret box 21 containing the polymer in the melt. As mentioned above, the polymers constituting each web may be the same or different,
In a preferred embodiment, the polymer comprising one web is polypropylene, while the polymer comprising the other web is polyethylene. The temperature of each polymer melt is selected as a value sufficient to impart sufficient fluidity to spin the melt. For example, when spinning polypropylene, the preferred temperature is about 237.8 ° C.
(About 460 ° F). Also, when spinning polyethylene, the preferred temperature is about 375 ° F (190.6 ° C). Spinneret plate 2 by applying pressure to each polymer melt
Extrusion through holes or orifices in 2, 23 forms a curtain of monofilaments 24, 25, respectively. Each curtain 24
And 25 fall through the cooling chambers 26 and 27 where they come into contact with the cooling air. The cooling air in each forming machine is supplied at a relatively low pressure, but the monofilament is drawn by the drawing nozzle
Sufficient pressure is applied to produce some degree of stretching as it passes through 29.

Upon leaving the lower unend of the draw nozzle 28, a first curtain of monofilaments 24 is deposited on a moving porous surface 15, such as an endless screen or belt, to form a first nonwoven web 13. To do. Upon leaving the lower end of the drawing nozzle 29, a second curtain of monofilaments 25 is deposited on top of the first nonwoven web 13 to form a second nonwoven web 14.

It should be noted that there is no critical meaning to depositing the polypropylene web first or the polyethylene web first. That is, the polypropylene can be a nonwoven web from either the first forming machine 11 or the second forming machine 12. For reasons discussed below, it is preferred to first deposit the polypropylene, i.e. form it in the first former 11.

After depositing the second web 14 on the first web 13, the webs are then passed through a pair of compression rollers 19 and 20. At this time, the filaments in the web are slightly compressed to enhance the integrity of the web and aid in subsequent processing.

The two webs 13 and 14 are then passed through two heated binding rolls 21 and 22. These rolls are preferably described in the Hansen & Pennings U.S. Pat.
Create and operate according to the teachings of No. 3,855,046. The entire disclosure of this patent is incorporated herein by reference. Simply put,
The device and method described in this patent have two rolls.
And 22, and at least one, and preferably both, are heated. The lower roll has a smooth surface, while the upper roll 21 has a periodic relief pattern on its surface. In another embodiment, the bond roll can be reversed so that the roll with the pattern is below the web and contacts the first deposited web.

Since the two webs 13 and 14 are passed between these two heated rolls, each web forms a discontinuous densified region with thermally induced filament bonds over most of its thickness. Stabilize by. These densified regions are distributed as a periodic pattern corresponding to the relief pattern of roll 21, providing unbonded filament span between the patterns. In addition, the two webs 13 and 14 are bonded together into a two-ply nonwoven fabric 18.

11a to 11c illustrate three types of patterns that can be used on the roll 21 and give the nonwoven 18 the same pattern. FIG. 11a includes circular areas arranged in a hexagonal and triangular shape. FIG. 11b contains circular regions arranged in a constricted repeating array. Figure 11c, the presently preferred pattern, includes equilateral diamond shaped regions arranged in alternating rows.

Two parameters related to the particular pattern used are the size of the densified regions formed as well as the distance between these regions. Both of these two parameters influence the percentage of area on the web that is bonded. It is important that the proportion of this bond area is large enough to ensure sufficient bondability for the intended use of the web. It is also important that the proportion of this binding area is not too large. This is because the larger the proportion of bonded regions, the lower the web in general. It is currently preferred to have the bond area be within the range of about 10 to about 30% of the surface area of the nonwoven fabric. More preferably in this case about 12 to about 20%
And most preferred is about 17%.

Another important factor related to web bonding is the temperature at which rolls 21 and 22 are heated and held. Of course, for each polymer some temperature has no effect on the bond, while temperatures above other points are too high to melt most of the web. It was also observed that the temperature of this roll could affect both the tensile strength and the softness of the produced web. In particular, in a certain temperature range, a higher temperature gives a higher strength web.
However, at this same high temperature, less soft webs may form. This is considered to be due to the degree of bonding that occurs within such a temperature range. That is, at higher temperatures more and stronger interfilamentary bonds, which favor tensile strength, are formed, which on the other hand is rather detrimental to softness. Currently, the preferred bonding temperature for polypropylene monofilaments is from about 104.4 to about 160 ° C (about 220 to
It is in the range of about 320 ° F). Most preferred is about 275 ° F (135 ° C).

For polyethylene, the bonding temperature is about 110 to about 115 ° C.
It is preferably in the range of (about 230 to about 240 ° F). Most preferred is about 112.8 ° C (about 235 ° F). Since polyethylene has a lower melting point than polypropylene, it is important that the bond roll be operated near the polyethylene bond temperature range. It has also been observed that when bonding these two webs, they can be bonded at temperatures below the melting point of polypropylene, as long as the temperature is near the melting point of polyethylene. This is believed to be possible due to the polyethylene melting into the polypropylene layer. In other words, molten ethylene can bond these webs well.

After the non-woven fabric 18 is bound by the rolls 21 and 22, it is wound on the winding roll 23. It is also desirable to devise this device so that it is connected to the production line of the final product.

The basis weight of the resulting non-woven fabric can be easily varied depending on the application of the web. For example, a non-woven fabric can be made having a basis weight of about 0.3 to about 3 ounces / (yard) ² . In another embodiment, the basis weight of the first web can be made larger than that of the second web and vice versa, but in a preferred embodiment the first and second nonwoven webs of equal basis weight. including. The basis weight of the disposable diaper liner for each layer is about 0.8 ounces / (yard) ² and the preferred basis weight of the sanitary non-woven wrap is about 0.4 ounces / (yard) ² .

FIG. 2 is a schematic view showing another manufacturing apparatus for a two-layer nonwoven fabric according to a preferred embodiment of the invention. This device is equivalent to that illustrated in FIG. 1 with one exception.
The exception to this is the inclusion of an additional pair of compression rolls 219 and 220 and another pair of binding rolls 221 and 222 between the first and second forming machines 111 and 112, which rolls are as described above. In addition, it stabilizes the first web 113.
In addition to the one collecting belt 115, the first non-woven web 113
It has an additional belt 215 for mounting. These compression and bonding rolls 219-222 are arranged and operated in the same manner as above, but they are installed to compress and bond a single nonwoven web.

After densification and bonding, the first non-woven web 113 is placed on the collection belt 115 and then the second non-woven web 114 is placed thereon. These two webs or combined webs 113
And unbonded web 114 through compression rolls 119 and 120. Then, they are passed through binding rolls 121, 122, where the second web 114 is stabilized and the two webs 113 are
And 114 are combined to form a two-layer nonwoven fabric 118. This non-woven fabric 118
The film is then wound on the take-up roll 123.

FIG. 3 is a view showing still another apparatus for producing a multilayer nonwoven fabric. In this machine, the first nonwoven web 313 is rolled 3
Supplied from 01. At this point, the nonwoven web 313 is in a bonded or unbonded state. It is preferably in a bound state. The web 313 travels along the collection belt 315, after which the second web 314 is deposited. Then, these two webs are passed through compression rolls 319 and 320, and further passed through coupling rolls 321 and 322 to stabilize either or both or the second web, and the two webs 313 and 3 as described above are stabilized.
14 is bonded as described above to give a two layer nonwoven 318.

Discussing the embodiments described in connection with FIGS. 2 and 3, where a first deposited web is bonded and then a second deposited web is placed thereon,
It should be noted that the bond pattern used when the two webs are brought together must be selected in view of the bond pattern already used for the first deposition web.
At this time, it is desirable that the second coupling pattern does not overlap the first pattern. Therefore, if the second binding pattern is the same as the first, the patterns should be staggered. However, from the perspective of web softness, it has a second bond pattern that is different from the first pattern,
In particular, it is preferable to set the occupancy rate lower than the point rate on the surface of the first web. Of course, the final bond pattern of the first deposited web will be the sum of the first and second bond patterns. Therefore, also from this point, it is advantageous that the occupancy rate of the second coupling pattern is low.

It should be noted that, from a descriptive point of view, the term first deposited web means the web that was first formed in the production line, or in other words, the web that was previously made and wound. Is. Also, as used herein, particularly in the claims, the "first web".
It should also be noted that the terms and "second web" are optional designations and do not necessarily indicate their order of formation. The stacking order of the webs and especially the order of the polymers used depends on the end use of the textile fabric.

One advantage of the present invention is that the first deposited web may have a higher bond pattern occupancy than the second deposited web. Thus, the first deposited web can have sufficient tensile strength, while the second deposited web can have greater softness. This is advantageous, for example, for non-woven webs for disposable diapers, in which the second deposited web is used to increase the "body side" softness of the diaper, while the first deposited web is higher in the liner. It can provide tensile strength.

Also, according to a preferred embodiment, it is desirable to first bond a polyethylene web having originally high flexibility to increase its tensile strength. In general, the order in which these two webs are deposited can be selected to place each web on the side most suitable for bonding as well as addition of the wetting agent.

FIG. 4 is a bottom perspective view of a spinneret plate 41 having two bulge-shaped orifices 42. Polymer is extruded through these orifices 42. The monofilament thus made has a shape with two bulges,
It has a "dogbone" or "dumbbell" cross section. The present inventors have found that one of the layers of the multilayer nonwoven fabric is a nonwoven web made of bilobed monofilaments, which is a particularly advantageous nonwoven fabric.

In the non-woven fabric of the present invention, either the first or the second deposited web can be made of bilobed monofilaments, and these two swollen shaped spinneret plates are
It can be provided on any of the forming machines of FIGS.
For the following reasons, it is currently preferred to provide the second forming machine of the above apparatus with two bulge shaped spinneret plates. That is, it is presently preferred to have a monofilament with a cross-section in the shape of two bulges in the second deposited web.

The spinneret plate of the other former may have any predetermined shaped orifice. 2 in one layer of non-woven fabric
Due to having the monofilament shaped in one bulge, some improvement is achieved regardless of the shape of the monofilament in the other layers. Of course, orifices of circular cross section are most common, and the use of circular monofilaments in one layer of the nonwoven fabric of the present invention is also included in the present invention. Further, in some embodiments, it is desirable that each of the two layers be a monofilament shaped with two bulges. Presently, the most preferred shape of the cross section of the other web, i.e. the two non-bulging monofilaments, is referred to as the Y-shape. FIG. 6 shows a Y-shaped orifice for making such a filament.

The spinneret plate 41 is made slightly larger than the width of the web to be made. The preferred width of the web will vary depending on the intended end use. For example, non-woven fabrics made for use as disposable diaper liners are advantageously about 31.75 cm (about 12.5 inches) wide.

The orifices are arranged in the spinneret plate at predetermined intervals and their number is selected to provide a predetermined filament density in the web. Currently, it is preferred to have about 30 to about 100 orifices in the spinneret plate per inch of web width. Most preferably, the number of orifices is about 85 per inch of web width. For example, about 30.48 cm (12 inches) spinneret, or about 30.48 cm wide
Most preferably for forming (12 inch) webs, there are 1020 orifices.

FIG. 5 is an enlarged view showing a preferable arrangement of the two orifices 42 of the spinneret plate 41. It is not known whether the size and proportion of the two bulge-shaped orifices are critical, but these give a monofilament with a two bulge-shaped cross section according to the invention. In general, the preferred arrangement of orifices is as follows. The smallest dimension is the thickness "a" of the strip. The diameter "b" of the portions 25, 26 of substantially circular cross section is about twice the thickness "a".
The length "c" of the orifice 24 is about 10 times the thickness "a". In the most preferred embodiment, the thickness "a" is 0.215 mm,
The diameter "b" is 0.430 mm and the length "c" is 2.15 mm. Obviously, these dimensions as well as their mutual proportions can be varied in each embodiment depending on factors such as the type of polymer extruded, the properties, the desired properties of the nonwoven, etc.

As already mentioned, the preferred spacing between the orifices depends on the density of the nonwoven to be made. In the most preferred embodiment, the spacing "d" between the orifices is 7.25 mm. Also, the preferred orientation of the orifices is such that all orifices are parallel to each other and their length "c" is aligned with the direction of movement of belt 17 (ie, the machine direction).

FIG. 6 is an enlarged bottom view of the Y-shaped orifice of the spinneret plate. The inventors have observed that the monofilament made with this orifice maintains a Y-shaped cross section even after stretching. Further, the present inventors have found that a non-woven web made of a monofilament having such a Y-shaped cross section has higher rigidity than a web made of a monofilament having a cross section having a circular shape or two bulges. I learned that it has low softness. However, the inventors have also found that a web made of Y-shaped monofilaments has a higher tensile strength than a web made of circular monofilaments. As noted above, the two non-bulging layers are most preferably polyethylene Y-shaped monofilament webs. this is,
Generally, it is desirable for obtaining a fabric having both high softness and high tensile strength.

FIG. 7 illustrates a cross section of a monofilament nonwoven web 71 having two bulge shapes. The nonwoven web may be either the first or second deposited web in the above method. Moreover, this web becomes a part of the multilayer nonwoven fabric of the present invention. Most preferably, the bilobed monofilament is made of polypropylene. As will be appreciated, this web comprises a large number of continuous monofilaments 72, which are oriented in a completely chaotic manner relative to each other. It is desirable that the monofilaments be highly looped and weighted in the web. These properties are affected by factors such as the density of the monofilaments deposited, the rate at which the monofilaments are deposited.

As can be seen, each monofilament of this web 71 has a cross section with two bulges. It is unclear whether the dimensions of the cross section of these two bulges are critical or not, but the basic characteristics of such cross section exist. That is, the cross section of the monofilament includes a substantially rectangular portion having an enlarged portion, typically circular in cross section, at each of its furthest ends.

As described above, it is extruded from the spinneret plate 41 and then stretched. As a result, they typically have dimensions smaller than the dimensions of orifice 42. This size reduction depends on factors such as the type and properties of the extruded polymer, the cooling rate of the monofilament, the drawing force applied to the monofilament, and the like. In the preferred embodiment using polypropylene, the monofilaments typically terminate in a cross sectional length in the range of about 30 to about 60 microns. Most preferably, this end length is about 60 microns, although this will vary with the particular properties of the nonwoven web.

FIG. 8 is a view similar to FIG. 7, except that the illustrated monofilament has a Y-shaped cross section. As noted above, in the most preferred embodiment one of the nonwoven webs has a monofilament of this type and is made of polyethylene.

FIG. 9 shows a cross section of the disposable diaper 91.
The non-woven liner 92 is located on the surface side of the diaper 91 which is arranged so as to contact the body of the infant. Liner as shown
92 consists of two layers 93 and 94. In the most preferred embodiment, the bodyside layer 93 comprises polypropylene monofilaments having a cross-section with two bulges.
The other layer 94, on the other hand, comprises polyethylene monofilaments having a Y-shaped cross section. In addition, layer 94 can include two bulge-shaped or cylindrical monofilaments. The main part of the diaper consists of a layer 95 of absorbent material such as fluffed cellulose pulp. Naturally, this layer 95 is for absorbing water. In addition, a moisture impermeable layer 96 is included.

An important property of liner 92 is its softness. In particular, considering the comfort of the infant, the liner 92 is extremely flexible and soft to the touch, which is an important property.
The present inventors have made a significant improvement in softness over conventional non-woven liners made of monofilaments having a circular cross-section by including a layer on the body side containing two bulging cross-sections of monofilaments. I was a little surprised to know that I showed my degree. Furthermore, the use of polypropylene or polyethylene shows an even further improved softness compared to conventional non-woven liners.

The test used by the present inventors to evaluate the softness of a non-woven fabric is “Smeltnik Stiffn
In this test, a non-woven test piece is placed on top of an open cylinder. A hemispherical probe with a diameter slightly smaller than this cylinder diameter is then dropped from the standard altitude. Then, the non-woven fabric is pushed into the cylinder.At this time, the distance that the probe penetrates into the cylinder is measured and recorded as an index of the softness of the non-woven fabric, that is, flexibility or draper suitability. The non-woven diaper liner has a probe penetration distance of 155 m into the cylinder.
Although the m was recorded, a non-woven diaper liner made of the same material and a monofilament having a cross-section with two bulge shapes recorded 370 mm. Thus, it has been shown that the softness of the nonwoven is significantly increased.

Another aspect of softness that is particularly important in diaper liners is "feel" or softness on contact. Although no special tests of this property have been performed by the present inventors at this time, the present inventors and others have found that non-woven webs made of monofilaments with two bulge-shaped cross sections. It was observed that the softness of touch was increasing. This web is preferably placed on the body side of the diaper 91.

Another property of non-woven liners as well as nonwovens is generally tensile strength, or tear resistance. This property has been measured by the present inventors with a device in which a nonwoven fabric test piece is sandwiched between a pair of jaws and then the jaws are pulled. The force required to break this fabric is recorded as the grab tensile strength. This test is performed by orienting the cloth between the jaws so that the force is applied parallel to the direction in which the cloth is installed (machine direction: MD), or by applying a force perpendicular to the direction in which the web lies (cross direction: CD). It can be carried out by orienting the cloth so as to hang. All tensile strength values reported herein are intended to represent machine direction (MD) strength.

The inventors were satisfied with the knowledge that non-woven fabrics having one layer of non-woven web made of monofilaments with two bulge-shaped cross sections exhibit high tensile strength. Without wishing to be bound by any particular theory, it is generally believed that this high tensile strength is due to the increased contact area between the filaments when the filaments are thermally bonded as described above. Similarly, as noted above, the tensile strength of multilayer nonwovens increases when the first deposited web has a high proportion of bonded area. Further, the tensile strength is improved when two bulge-shaped webs and a Y-shaped web are used in a multilayer nonwoven fabric, which is attributed to an increase in contact area due to thermal bonding. Seem.

Another property of particular importance when using the web as a liner for disposable diapers is the wettability of the liner. Depending on the diaper design, it is usually desirable to make the liner at least partially wettable to facilitate moisture transfer to the absorbent layer. Furthermore, it is even more desirable to provide a wettability gradient in the liner to exclude water from the wearer. In particular, it is most preferred to provide a body-side layer having a lower wettability than the "transfer" layer, i.e. a layer in contact with the absorbent. In this way, moisture flows into the absorbent layer more easily than it returns to the wearer.

Many polymers suitable for making nonwoven webs are hydrophobic. Notably, the two most preferred polymers, polyethylene and polypropylene, are completely hydrophobic.
Therefore, it is desirable to go through a process for increasing the wettability of the nonwoven web made from these polymers.

It is known in the art that wetting can be increased by the addition of wetting agents such as surfactants. In particular,
Cationic, anionic as well as nonionic surfactants can be added to make the material wettable. In a preferred embodiment of the present invention, the polypropylene monofilament becomes wettable by adding a nonionic surfactant thereto. This treatment can be carried out by mixing the surfactant with the polymer and then extruding it, ie by "internal addition". The wetting agent is preferably mixed with the polymer in an amount of up to about 5% based on the weight of the polymer. Furthermore, when using polymers such as polypropylene, it is advantageous to heat the nonwoven at some stage to transfer the wetting agent to the monofilament surface. This heating process used to transfer the internally added wetting agent to the surface of the monofilament
r) in U.S. Pat. Nos. 3,973,068 and 4,070,218, the entire disclosures of which are hereby incorporated by reference. Naturally, the heating temperature of the web must be below the melting point of the monofilament.

One of the advantages of the present invention is that the wettability gradient described above can be formed by adding a predetermined amount of wetting agent to the polymer in the nonwoven web of the transfer layer. This web of the bodyside layer may be humectant-free, slightly humectant added or less effective humectant added.

Another advantage of the present invention is that when the wetting agent is internally added to the polyethylene filament, there is no need to subsequently heat the filament to transfer the surfactant to the surface. This is because the heating step can be eliminated,
It is advantageous when a polyethylene web is used as the transfer layer.

As an alternative to this internal addition, it is also possible to apply the wetting agent as a solution to the nonwoven web after it has been formed (external application). This application can be carried out by dipping either or both non-woven webs in a solution of wetting agent, followed by evaporation of the solvent to leave a certain amount of surfactant on the web surface. It is also desirable to heat the web to remove solvent more rapidly. Further, the surfactant solution can be applied to the web by a spraying method or a gravure printing method. In either case, evaporation of the solvent can be accelerated by heating the web. Of course,
This evaporation is preferably completed before the web is wound on the take-up roll. In all three external coating methods, the surfactant is added in an amount of up to 5% by weight of the web.

In connection with internal application, it is preferable to selectively apply a wetting agent to provide a gradient in wettability. This can be done by applying a wetting agent to either or both of the webs prior to bonding them. This can also be done by using different materials for each web so that the humectant is more effective when applied to the transfer layer than when applied to the bodyside layer.

The inventors have observed that a Y-shaped monofilament is better as a moving layer than when using a monofilament having a shape with two bulges or a circular shape. It is generally believed that this is due to the increased bulk, or reduced density, of webs made of Y-shaped monofilaments. For this reason Y-shaped monofilaments will be provided with a larger surface for absorption of moisture.

Yet another important property for nonwovens for liners is their opacity or hiding power. It is known in the art to add small amounts of titanium dioxide to polymer melts to increase the opacity of nonwovens. The inventors have found that the non-woven fabric made according to the present invention has a high opacity, which has two bulging shapes and / or which can reflect a large amount of light.
It was also found that this is due to an increase in the surface occupancy of the Y-shaped monofilament.

FIG. 10 shows a cross section of a typical sanitary article, such as a women's napkin 101. As shown, the pad comprises a non-woven wrap 102, which wraps around the absorbent section 105. This wrap is made of 2 non-woven webs 1
It consists of 03 and 104. Most of the desirable properties for non-woven liners for disposable diapers are desirable for non-woven wraps for sanitary products as well. In particular,
It is important for the present invention to provide a nonwoven web with high softness, i.e., drivability and smoothness on contact. There, it is also desirable to have a monofilament web of two bulges on the body side of the article as well. Also, increasing the wettability of the wrap 102 is of particular importance, and it is most preferred to have a wettability gradient. This can be done by adding wettability to one or both of the webs in the wrap, according to the method as described in connection with the diaper liner above.

Example 1 Example 1 was carried out using an apparatus as described above with reference to FIG. In particular, the web width is about 30.48 cm (12 inches), and the first spinning plate has 50 orifices with two bulges per 1 inch width.
The spinneret plate has two bulge shaped orifices, 50 per inch wide. Polypropylene was extruded from the spinneret at a melt temperature of about 237.8 ° C (about 460 ° F). About 237.8 ° C (about 460 ° F) polypropylene
Extruded from the second spinneret at a melt temperature of The basis weight of the first deposited web was 0.4 ounces / (yard) ² .
The basis weight of the second deposited web was 0.4 ounces / (yard) ² . These two webs are about 22.5% of the web area
Bonded in the pattern shown in Figure 11a with a bonded area of. The binder roll temperature was about 270 ° F (132.2 ° C).

Smeltonic stiffness test (SST) of the resulting non-woven fabric
The value was 160 mm. Further, with respect to the cloth of this example, a grab tensile strength was measured by placing a web test piece between grippers that pull in the opposite direction. The force required to tear the web was about 13 pounds in the direction it was lying, or the machine direction (MD).

Example 2 was carried out in the same manner as Example 1. The apparatus used was that described in connection with FIG. The first deposited web is about 132.2 ° C (about 270 ° F) and the bonding area is about 2
2.5% were bound in the pattern shown in Figure 11a. Second
Of the above web was placed on the first deposited web and then bonded with a bond area of about 3%. This first deposited web was made wettable by gravure printing with a nonionic surfactant solution.

The obtained cloth has an SST value of 200 mm and an MD tensile strength of about 4.54 kg (10
It was £). In addition, tests were conducted to determine the "runoff" value of this fabric. This test is about 20.3 of the web
It consists of placing a 2 to 25.4 cm (8 to 10 inch) test strip on an absorbent vat. This bat and web angle
Oriented at 45 °. Then 100 ml of water from the bottom about 15.
Poured onto a cloth at a point of 25 cm (6 inches). The amount of water absorbed from the bottom and flowing out was measured and recorded. In Example 2, this value was 5.5 ml.

Example 3 was carried out as Example 2 except that the first layer was not bonded and the second layer was placed on top of it. The resulting fabric had an SST value of 315 mm, MD tensile strength of about 30.48 cm (12 inches), and an outflow value of 3.0 ml.

Example 4 was carried out in the same manner as Example 2. In this example, the first deposited web was bonded at about 121.1 ° C. (250 ° F.) and then the second web was placed thereon. The two webs were bonded to give a bond area of about 6.6%. The resulting fabric had an SST value of 430 mm, an MD tensile strength of about 3.632 kg (8 lbs) and an outflow value of 2.9 ml.

Example 5 was carried out in the same manner as Example 2. However, the cross section of the first deposited web was Y-shaped, and it contained an internally added surfactant. About 12 webs
Bonded together at 6.7 ° C (260 ° F). The generated cloth is SS
It exhibited a T value of 300 mm, a MD tensile strength of about 2.724 kg (6 lbs), and an outflow value (with a Y-shaped layer as the moving layer) of 22.5 ml.

Example 6 shows that the first deposited web had round monofilaments and the second deposited web had a basis weight of 0.5 ounces /
(Yard) The same procedure as in Example 5 was performed except that the number was ² . The resulting fabric had an SST value of 220 mm, an MD tensile strength of about 4.086 kg (9 pounds) and an outflow value of 71 ml.

Example 7 was carried out in the same manner as Example 2. However, the basis weight of each of the first and second deposited layers is 0.5 oz /
(Yard) ² The monofilament of the first layer was Y-shaped and contained the internally added surfactant. The second layer was extruded from a spinneret plate with 30 orifices per inch. The final binding temperature was about 280 ° F (137.8 ° C). The resulting fabric had an SST value of 230 mm, an MD tensile strength of 12 pounds, and an outflow value of 30 ml.

Example 8 was carried out in the same manner as Example 11. About 190.6 ℃
Extrusion was from a second spinneret with a Y-shaped orifice at a melt temperature (about 375 ° F). The basis weight of the second deposited layer was 0.6 ounces / (yard) ² . The two webs were bonded at about 225 ° F (193 ° C) with a bond area of about 24%. The resulting web had an SST value of 325 mm and an MD tensile strength of about 4.313 kg (9.5 lbs).

Example 9 was carried out using the apparatus as described above with reference to FIG. In particular, the web width was about 30.48 cm (12 inches) and the first spinneret plate had 50 orifices per inch width. About 237.8
It was extruded from the first spinneret through two bulge-shaped orifices at a melt temperature of 460 ° C. Polyethylene was extruded from the second spinneret through a Y-shaped orifice at a melting point of about 375 ° F (190.6 ° C). The basis weight of the first deposited web was 0.4 ounces / (yard) ² . Second deposited web has 0.6 ounces /
(Yard) It was ² . The two webs were bonded in the pattern shown in Figure 11c with a bond area of about 24% of the web area. The temperature of the binder roll was about 225 ° F (107.2 ° C).

The SST value of the obtained cloth was 325 mm. Further, with respect to the cloth of this example, a web test piece was placed between grippers for pulling in the opposite direction, and the grab tensile strength was measured. The direction in which this web is lying (machine direction: MD)
The force required for tearing was about 4.313 kg (9.5 pounds).

Example 10 was performed in the same manner as Example 9, but with a bond temperature of about 112.8 ° C (235 ° F). SST value of the obtained cloth is 80m
m and MD tensile strength is about 4.767 kg (10.5 lb)
Met.

Example 11 was carried out in the same manner as Example 9. Each of the polypropylene and polyethylene webs had a basis weight of 0.5 ounces / (yard) ² . The two webs were bonded together with a bond area of about 9%. Emboss roll is 110
Maintain at ℃ (230 ℃), anvil or smooth roll about 1
The temperature was maintained at 29.4 ° C (about 265 ° F). The resulting cloth is SST
The value was 390 mm, and the MD tensile strength was about 1.816 kg (4 lbs).

Example 12 was carried out as in Example 11, but with the layers and the bonding temperature reversed. That is, polyethylene was placed first, followed by polypropylene. Also, about the embossing roll
129.4 ° C (about 265 ° F) and 110 ° C anvil roll
(230 ° F). The resulting fabric had an SST value of 550 mm (probably due to the more slippery polyethylene web placed at the bottom, i.e. in contact with the cylinder), and MD tensile strength of about 2.27 kg (5 lbs). .

Example 13 was carried out in the same manner as Example 11. However, the web was bonded with a bonding area of about 6%. The resulting fabric has an SST value of 5
It exhibited a 50 mm and MD tensile strength of about 1.362 kg (3 lbs).

Example 14 was carried out in the same manner as Example 12. However, the polypropylene web had monofilaments with a Y-shaped cross section and the web was bonded with a bond area of about 22.5%. The obtained cloth has an SST value of 145 mm and an MD tensile strength of about 3.
Had 178 kg (7 lbs).

Example 15 was performed in the same manner as Example 9, except that the polypropylene layer was bonded at about 132.2 ° C (about 270 ° F) and then polyethylene was placed thereon and bonded in a bonding pattern of about 22.5%. It was The resulting fabric had an SST value of 185 mm and an MD tensile strength of about 3.178 kg (7 lbs).

Although the present invention has been described above according to its specific embodiments, it will be apparent to those skilled in the art in light of the numerous alternatives, modifications and variations in light of the above list. In particular, although the nonwoven webs of the present invention have been described in the context of disposable diaper liners and wraps for sanitary products, other forms of products, such as surgical and other disposable garments, industrial wipers, etc., are of course also included. To be done. Furthermore, while all the described embodiments include only two layers of nonwoven web, it should be understood that nonwoven fabrics having three or more layers are within the scope of the invention. It is therefore to be understood that all such alternatives, modifications and variations are intended to be within the spirit of the invention and the following claims.
In the claims that follow, the terms first and second are arbitrary and independent of the order of formation or the position of the web.

[Brief description of drawings]

FIG. 1 is a schematic view of a preferred manufacturing apparatus for a multilayer nonwoven fabric of the present invention, FIG. 2 is a schematic view of another manufacturing apparatus for a multilayer nonwoven fabric of the present invention, and FIG. 3 is a schematic view of the present invention. Fig. 4 is a schematic view of still another manufacturing apparatus of the non-woven fabric of Fig. 4, which is provided with two bulge-shaped orifices for extruding monofilaments having two bulge cross sections. 5 is a bottom perspective view of the spinneret plate shown in FIG. 5, and FIG. 5 is an enlarged bottom view of an orifice having two two bulges of the spinneret plate shown in FIG. FIG. 7 is a bottom view of an orifice having three bulges in the spinneret plate, and FIG. 7 is a partial sectional view of a monofilament nonwoven web having two bulges. FIG. 8 shows a monofilament having a cross section with three bulges. FIG. 9 is a partial cross-sectional view of a Lament nonwoven web, FIG. 9 is a partial cross-sectional view of a disposable diaper made of the nonwoven liner of the present invention, and FIG. 10 is a nonwoven of the present invention. FIG. 11 is a partial cross-sectional view of a sanitary wrap made from wraps, FIGS. 11a-11c showing various patterns of cyclic thermal bonding that can be applied to the nonwoven fabrics of the present invention. (Main reference numbers) 11,12 …… Web forming machine, 13 …… First web, 14 …… Second web, 15 …… Belt, 18 …… Two-layer non-woven fabric, 19,20… Compression roll, 21 ...... Spinneret box, 22,23 …… Spinneret plate, 24,25 …… Monofilament, 26,27 …… Cooling chamber, 28,29 …… Drawing nozzle, 111 …… First forming machine, 112 …… 2 forming machine, 113,114 …… nonwoven web, 115 …… belt, 118 …… nonwoven fabric, 119,120,219,220 …… compressing roll, 221,222 …… bonding roll, 123 …… winding roll, 301 …… roll, 312 …… forming machine , 313,314 …… nonwoven web, 315 …… belt, 318 …… nonwoven fabric, 319,320 …… compression roll, 321,322 …… bonding roll, 323 …… winding roll, 41 …… spinneret plate, 42 …… orifice, 71 …… Nonwoven fabric, 72 …… monofilament, 81 …… woven fabric, 82 …… monofilament, 91 …… diaper, 92 …… la Trainer, 93, 94 ...... nonwoven web, 95 ...... absorbent layer, 101 ...... napkins, 102 ...... nonwoven lap, 103, 104 ...... nonwoven webs, 105 ...... absorber layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Robert John Ferran Woodstock Canterbury Lane, Georgia, USA 1116 (72) Inventor Lin Sunwoon United States Appleton East Florida Avenue, Wisconsin 1009 (56) References JP-A-55 -116848 (JP, A) JP 59-67043 (JP, A) JP 57-121657 (JP, A) JP 59-157366 (JP, A)

Claims (16)

(57) [Claims] 1. A first nonwoven web comprising a first plurality of monofilaments or fibers of a first thermoplastic, the monofilaments having a cross-sectional shape with two bulges, and the first. Adjacent to and bonded to the nonwoven web of
A second nonwoven web comprising a second plurality of monofilaments or fibers of the thermoplastic material of claim 1. 2. The multilayer nonwoven fabric according to claim 1, wherein the first and second thermoplastic materials are independently selected from the group consisting of polyolefins. 3. The multilayer nonwoven fabric according to claim (2), wherein the polyolefin in the first nonwoven web is polyethylene. 4. The multilayer nonwoven fabric according to claim 2, wherein the polyolefin of the second nonwoven web is polypropylene. 5. The multilayer nonwoven fabric according to claim 2, wherein the monofilaments or fibers of the second non-woven web have higher wettability than the first non-woven web. 6. The multilayer nonwoven fabric according to claim 1, wherein the monofilaments or fibers of the second nonwoven web have a cross section having three bulges. 7. The multilayer nonwoven fabric according to claim 4, wherein the monofilaments or fibers of the second nonwoven web have a cross section with three bulges. 8. The multilayer nonwoven fabric according to claim 6, wherein the monofilament of the second nonwoven web has higher wettability than the monofilament of the first nonwoven web. 9. A multilayer nonwoven according to claim 1 wherein each of the nonwoven webs contains some interfilamentary bonds to stabilize the webs. . 10. A multi-layer nonwoven fabric according to claim (2), wherein the polyolefin in one of the nonwoven webs is an ethylene-propylene copolymer. 11. A first plurality of substantially similarly prepared continuous and substantially randomly deposited monofilaments of a first thermoplastic polymer, the monofilaments having two bulges. A first non-woven web having a cross-section, a second adjacent to and connected with the first non-woven web
A second non-woven web comprising a plurality of substantially similarly made continuous and substantially randomly deposited second thermoplastic polymer monofilaments; Having a plurality of intermittent densified regions with heat-induced filament bonding over most of the thickness of one non-woven web, the densified regions being distributed as a discontinuous pattern, between the patterns A non-woven textile product, characterized in that it provides an unbonded filament span. 12. The non-woven fiber product according to claim 11, wherein the densified region occupies about 5 to about 30% of the area. 13. The second non-woven web has a greater wettability than the first non-woven web.
The non-woven fiber product according to the item. 14. A thermoplastic polymer is extruded from a spinneret having a plurality of orifices to form a discontinuous monofilament, the monofilament is stretched, and the monofilament is laminated substantially randomly on a carrier belt or the like. A method for producing a non-woven article, comprising the steps of forming a web and stabilizing the web by inter-filament bonding, using a spinneret having an orifice having two bulges to form a first non-woven web. 2 monofilaments inside
A method for producing a non-woven article, comprising forming a second non-woven web which is formed so as to have a cross section having two bulges and which is bonded to the first non-woven web. 15. The filament-to-filament bond is formed by passing the web between two counter-rotating rolls, at least one of which is heated and at least one of which has a relief pattern. To form a plurality of periodic densified regions with bond of heat-induced filaments over most of the thickness of the article, the densified regions being the relief pattern of at least one of the rolls. The method of claim 14 wherein the method is distributed as a periodic pattern corresponding to, and the periodic pattern provides an unbonded filament span therebetween. 16. The method of claim 14 wherein the first and second thermoplastic materials are each independently selected from the group consisting of polyolefins.