Soft water-permeable polyolefins nonwovens having opaque characteristics

Abstract: A method for making nonwoven material containing polyolefin filaments and having an increased degree of opacity, characterized in that at least about 25% of the total weight of the filaments in the nonwoven web are polyolefin filaments that have a delta "Δ" or diamond cross-sectional configuration, an initial spun denier not exceeding about 24 dpf, and a final drawn denier of not less than about 1 dpf is disclosed.

Description: This invention relates to a method for nonwoven fabrics containing polyolefin filaments having particular cross-sectional configurations. The chemical inertness, low allergenic properties, high tensile strength and low melting point of polyolefin fiber and filaments makes them useful in nonwoven fabrics from which personal contact products such as cover-stock for diapers can be made, as described, for instance, in U.S. Patents 4,112,153, 4,391,869, 4,573,987, and 4,578,066. EP-0 296 572 A2 published after the priority date discloses nonwoven fabrics containing not less than about 25 %, based on total web weight of the non-woven fabric, of polyolefin filaments having a Δ-cross-sectional configuration, and initial spun denier not exceeding about 4.4 dtexpf (4 dpf) and a final drawn denier of not less than about 1.1 dtexpf (1 dpf ). Such materials must be cost-competitive, retain substantial cross directional (CD) strength and toughness, and have a soft surface "feel". However, an effective combination of such properties is difficult to achieve in nonwovens with existing technology and using conventional synthetic fibers, as described in the said patents. In particular, softness is usually gained at the expense of cross directional strength and a substantial increase in cost. In the case of personal-contact products, such as diaper cover-stock, and other covering purposes, it is also desirable to enhance certain non-functional esthetic properties, such as opacity and stain-masking ability. In order to achieve such properties, including a preferred degree of opacity of 32%-45%, it is even more difficult to provide an acceptable balance of properties, particularly with chemically inert polyolefins such as polypropylene. Colorants and brighteners have been used as spun melt components to enhance opacity and stain-masking ability, but they cause additional problems such as leaching, allergenic reactions and increased cost. A method for making nonwoven fabrics containing polyolefin filaments that increases its opacity while reducing the need for high concentrations of colorants is therefore needed. According to the invention, a method for making nonwoven fabrics as defined in claim 1, is provided herewith. In a second and third aspect, the invention refers to a nonwoven fabric according to claims 12 and 21. Preferred embodiments can be found in the claims being dependent thereupon. Generally, by the method of the instant invention, one can achieve an opacity within the range of 32%-45% or even higher, depending upon the balance of interdependant properties selected for the final product. It is possible to obtain nonwoven fabrics in a wide range of weights, from heavy to as light as 12 to 36 g/m² (10-30 gm/yd²) and having substantially improved opacity and stain-hiding properties without substantial sacrifice in other areas. The production techniques for obtaining the various polyolefin cross-sectional configurations, and the conventional methods for producing the nonwoven material itself, are well known in the art and are not part of the present invention. Thus, conventional techniques for bonding the filaments to form nonwoven fabrics, such as spun bonding, needle punching and thermal or sonic bonding techniques may be used. However thermal bonding is generally the most effective fabrication technique to obtain a wide range of weights at low cost. In the method according to the invention, the web of filaments can comprise, in addition to the polyolefin filaments of diamond cross sections, other types of conventionally used filaments such as other polyolefin filaments or rayon filaments, including filaments having various known cross-sectional configurations, such as delta "y", "x", "o" (round), oval, square, and rectangular configurations, including blends of such filaments with fibrillated film (such as polyolefin film). The particular combination and amount of filament of diamond configuration within the limits required according to the invention, will depend substantially upon the degree of opacity desired in combination with other properties, such as strength and a soft or velvety feel. Preferably, the proportion of diamond cross-sectional configuration to another cross-sectional configuration is about 50%, with the other 50% configuration preferably being round. Also preferably, the diamond cross-sectional polyolefin filament have a preferred initial spun denier within a range of about 2.2 to 4.4 dtex pf (2.0-4.0 dpf) and a final drawn denier correspondingly within the range of about 1.1 to 3.3 dtex pf (1.0-3.0 dpf), more preferably 2.1 to 2.7 dtex pf (1.9-2.5 dpf), in order to retain both strength and softness. Preferably, for a combination of softness and cross-dimensional strength, polyolefin filaments having both delta and diamond cross-sectional configurations are used. The desired combination may be supplied by a uniform blend in a single web or laminated group of webs of uniform composition, or by a plurality of homogeneous webs individually differing in the blend of filaments used. Preferably, the filaments used vary from about 2.5-7.6 cm in length. Longer filaments naturally produce higher cross directional tensile strength, and mixtures of long and short filaments within the above range tend to provide optimum toughness. For example, a 50:50 mixture of 2.5 cm diamond with longer (e.g. 3.8cm-5cm) round cross-sectional filament is preferred for providing both strength and a velvet-like feel. The following examples and table further illustrate the present invention. Example 1 A. Delta cross-sectional isotactic polypropylene filament of 4.4 dtex pf (4.0 dpf) spun denier is produced in a conventional manner by melt spinning at 290°C using PRO-FAX R 6501 polypropylene polymer (commercially available from Hercules Incorporated of Wilmington, Delaware), degraded in the usual way with .025% Lupersol® to an MFR (Melt Flow Rate) (ASTM D 1238-82) value of 16 and spun, using a 700 hole delta spinnerette to obtain a final drawn denier of 2.3 dtex pf (2.1 dpf). Crimped (10 crimps/cm) bundles are then cut into 2.54 cm length, collected, and compressed into bales for later testing. B. Round cross-sectional polypropylene filament of 2.8 dpf spun denier is similarly produced in a conventional manner by melt spinning PRO-FAX R 6501 polypropylene polymer degraded to an MFR value of 13, spun at 290°C to obtain a final drawn denier of 2.3 dtex pf (2.1 dpf), crimped as before, cut into 5.1 cm (2 inch) lengths, collected, compressed and baled for later testing. C. Delta cross-sectional polypropylene of 2.9 dtex pf (2.6 dpf) spun denier is produced by melt spinning at 285°C, using PRO-FAX® 6301 (commercially available from Hercules Incorporated of Wilmington, Delaware), and finally drawn to 2.45 dtex pf (2.2 dpf), crimped as before, cut into 5.1 cm (two inch) bundles, collected, compressed, and baled for later testing. D. Delta cross-sectional fiber of Example 1 A (2.1 dpf denier) is crimped as before and cut into 3.8 cm (1.5 inch) bundles collected and compressed into bales for later testing. E. Round cross-sectional fiber of 3.1 dtex pf (2.8 dpf) spun denier is drawn to 2.3 dtex pf (2.1 dpf) as in Example I B, crimped as before and cut into 3.8 cm bundles, collected, and compressed into bales for later testing. F. Staple cut fiber of delta and round cross-sectional configuration treated as described in C. and B. supra is combined in a homogeneous ratio of 50-to-50 parts by weight, collected, compressed and baled for later testing. G. Round cross-sectional polypropylene filament of 1.5 dpf is produced in the manner of Example 1 B by melt spinning PRO-FAX® 6501 polypropylene polymer degraded to an MFR value of 12 at 285°C and drawn to obtain a final drawn denier of 1.1 dtex pf (1 dpf), crimped as before, cut into 3.8 cm (1.5 inch) lengths, collected, compressed and baled for later testing. H. Delta cross-sectional polypropylene of 1.7 dtex pf (1.5 dpf) spun denier is produced the manner of Example I C by melt spinning PRO-FAX® 6501 at 285°C and drawn to 1.1 dtex pf (1.0 dpf), crimped as before, cut into 3.8 cm bundles, compressed, and baled for later testing. I. Round cross-sectional polypropylene filament of 8.0 dpf is produced from the same melt and in the manner of Example I B, spun to obtain a 6.7 dtex pf (6 dpf) final denier, crimped crimped as before, cut into 3.8 cm lengths, collected, compressed, and baled for later testing. Example 2 A. Baled 2.5 cm crimped polypropylene staple of delta cross-sectional configuration as described in Example I A is broken, and formed into two identical homogeneous webs in a conventional manner, and the webs superimposed in machine direction as they are transferred onto a continuous fiber glass belt, and thermally bonded, using a hot diamond-patterned calendar at 165°C and 276 kPa (40 psi) roll pressure to a obtain a nonwoven weighing 24 g/m² (20gm/yd²). The resulting material, identified as NW-1, is then cut into convenient dimensions for conventional testing purposes and test results reported in Table I below B. Baled 5 cm crimped polypropylene staple of round cross-sectional configuration as described in Example I B is broken, and formed into two identical homogeneous webs in a conventional manner, the webs being superimposed in machine direction as they are transferred onto a continuous fiber glass belt, and thermally bonded as in Example 2 A, using a hot diamond-patterned calendar to obtain a semi-opaque nonwoven weighing 24 g/m² (20gm/yd²). The resulting material, identified as NW-2, is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported as control in Table I below. C. The 2.5 cm and 5 cm crimped staple of delta and round configuration of Examples I A and I B is added to separate openers and conveyed into separate cards to form two homogeneous webs with a 25/75 weight ratio of 2.5 cm (1") delta 5.1 cm (2") round in a conventional manner, the webs being transferred onto a continuous fiber glass belt, and thermally bonded as before, using a hot diamond-patterned calendar to obtain a nonwoven material weighing 24.8 g/m² (20.7gm/yd²). The resulting material, identified as NW-3, is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported in Table I below. D. The 2.5 cm and 5 cm crimped staple of Examples I A and I B is added to separate openers, broken, conveyed into separate cards, and formed into two homogeneous webs having a 50/50 ratio of 2.5 cm delta/5 cm round in a conventional manner, the webs being superimposed in machine direction as they are transferred onto a continuous fiber glass belt, and thermally bonded as before, using a hot diamond-patterned calendar to obtain a nonwoven material weighing 24.8 g/m² (20.7gm/yd²). The resulting material, identified as NW-4, is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported in Table I below. E. The 2.5 cm and 5 cm crimped staple of Examples I A and I B is added to separate openers, broken and conveyed into separate cards and formed into two identical homogeneous webs of 2.5 cm delta/5 cm round of 75/25 weight ratio in a conventional manner, the two webs being superimposed in machine direction, transferred onto a continuous fiber glass belt, and thermally bonded as before, using a hot diamond-patterned calendar to obtain a nonwoven material weighing 23.1 g/m² (19.3gm/yd²). The resulting material, identified as NW-5, is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported in Table I below. F. Baled combined 5 cm crimped staple of 50:50 delta:round cross-sectional configuration by weight, as described in Example I F (1 B and 1 C) is broken and formed into two identical mixed fiber webs in the same general manner as before, the webs being superimposed in machine direction, transferred onto a continuous fiber glass belt, and thermally bonded as before, using a hot diamond-patterned calendar to obtain a nonwoven material weighing 22.8 g/m² (19.1gm/yd²). The resulting material identified as NW-6 is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported in Table I below. G. Baled 3.8 cm crimped staple of drawn 2.1 dpf delta cross-section, as described Example I D is broken and formed into a web in the same manner as before. A second web is then prepared using 3.8 cm crimped staple of 2.1 dpf circular cross-section as described in Example IE is broken and formed into a web of equal weight in the same manner as before. The two webs, consisting of different fiber cross-section are superimposed in a machine direction, transferred onto a continuous fiber glass belt, and thermally bonded as before, using a hot diamond-patterned calendar to obtain a nonwoven material weighing 21.5 g/m² (18gm/yd²). The resulting material identified as NW-7 is then cut into convenient dimensions for testing purposes, standard tests run, and test results reported in Table I below. H. Baled 3.8 cm (1.5") polypropylene staple of round cross-sectional configuration (extruded 1.5 dpf drawn 1 dpf) as described in Example 1 G is broken and formed into two identical homogeneous webs, the webs being superimposed in machine direction as they are transferred onto a continuous fiber glass belt then thermally bonded, using a hot diamond-patterned calendar at 165°C and 276kPa (40 psi) roll pressure to obtain a nonwoven weighing 24 g/m² (20gm/yd²). The resulting nonwoven, identified as NW-8, is then cut into convenient dimensions for testing purposes, and test results reported in Table I below as a control. I. Baled 3.8 cm polypropylene staple of delta cross-sectional configuration drawn to 2.1 dpf from Example 1D, and round cross sectional configuration from 1E, are combined in the manner of Example 2 G supra to obtain an opaque nonwoven weighing about 24 g/m² (20gm/yd²). The resulting material, identified as NW-9, is then cut into convenient dimensions for testing purposes and test results reported in Table I below as a control. J. Baled 3.8 cm polypropylene staple of round cross-sectional configuration and a drawn 6.6 dtex pf (dpf of 6) from Example 1 I is broken and formed into two identical homogeneous webs in the manner of as in Example 2 H, to obtain a nonwoven, identified as NW-10, is then cut into convenient dimensions for testing purposes, and conventional test results reported in Table I below as a control. Example 3 A. Diamond cross-sectional isotactic polypropylene filament of 6.6 dtex pf (6.0 dpf) spun denier is obtained in a conventional manner by melt spinning at 290°C. using PRO-FAX R 6501 polypropylene polymer, degraded, spun and processed in the manner of Example 1 A to obtain a final drawn 2.3 dtex (denier of 2.1), then cut to 2.5 cm length, baled, and stored for later use. B. Delta cross-sectional isotactic polypropylene filament having a 2.9 dtex pf (2.6 dpf) spun denier, is produced in the manner described in Example 1 C to a drawn 2.3 dtex (denier of 2.1), then cut into 5 cm bundles and baled for later testing. C. Round cross-sectional isotactic polypropylene filament of 3.1 dtex pf (2.8 dpf) spun denier is produced as described in Example 1 B to a drawn 2.3 dtex (denier of 2.1) then cut into 5 cm bundles and baled for later testing. Example 4 Three test nonwoven samples are prepared as follows: A. Nonwoven test strips are prepared by conventionally producing homogeneous webs varying in weight within a range of about 12 to 18 g/m² (10-15 gm/yd²), using filaments of diamond cross-section configuration from Example 3 A. Random combinations of two homogeneous webs, thus produced, are superimposed in machine direction onto a continuous fiber glass belt and bonded using a diamond-patterned calendar at 165°C and 276kPa (40 psi). The resulting nonwoven test materials are cut, weighed and tested for opacity using a Diano Match Scan II color spectrometer, and the results reported in Table II below as S-1, S-2 and S-3. B. Nonwoven test strips are prepared by producing homogenous webs varying in weight within a range of about 12 to 18 g/m² (10-15 gm/yd²) using the filaments of round cross-sectional configuration reported in Example 3 C. Random combinations of two homogeneous webs, thus produced, are superimposed in machine direction onto a continuous fiber glass belt and bonded using a diamond-patterned calendar at 165°C. and 276kPa. The resulting nonwovens are cut, weighed and tested for opacity using a Diano Match Scan II Color Spectrometer, and the results reported in Table II below as S-10, S-11 and S-12. C. Nonwoven test strips are prepared by conventionally producing homogeneous webs varying in weight from about 12 to 18 g/m² (10-15 gm/yd²) using filaments of delta cross-sectional configuration reported in Example 3 B. Random combinations of two homogenous webs thus produced are superimposed in machine direction onto a continuous fiber glass belt and bonded using a diamond-patterned calendar at 165°C and 276kPa. The resulting nonwovens are cut, weighed and tested for opacity as before and test results reported in Table II as S-4, S-5 and S-6. D. Nonwoven test strips are prepared by producing homogenous webs of diamond and of delta cross-sectional configuration as in Examples 3 A and 3 B supra. Webs of different fiber cross section are randomly chosen, superimposed in machine direction, and bonded to obtain test nonwovens having 50:50% by weight of diamond:delta-fiber content, then the nonwoven is cut, weighed and tested as before. Test results are reported in Table II below as S-7, S-8 and S-9. Sample Fiber Content Cross-Section Configuration Nonwoven wt (gm/yd²) g/m² (2 webs) Opacity % S-1 100% Diamond (20.0)23.9 37.0 S-2 100% Diamond (21.5)25.7 37.5 S-3 100% Diamond (26.0)31.1 40.5 S-4 100% Delta (20.1)24.0 41.0 S-5 100% Delta (21.5)25.7 42.2 S-6 100% Delta (26.0)31.1 46.0 S-7 50% Diamond) (20.0)23.9 40.5 50% Delta ) S-8 50% Diamond) (21.5)25.7 41.0 50% Delta ) S-9 50% Diamond) (26.0)31.1 44.0 50% Delta ) S-10 100% Round (20.2)24.2 28.0 S-11 100% Round (21.5)25.7 29.5 S-12 100% Round (26.2)31.3 34.0

Claims: A method for making nonwoven material containing polyolefin filaments comprising assembling a web of filaments, including the polyolefin filaments and bonding the filaments, to form a nonwoven material, characterized in that at least 25 % of the total weight of the filaments in the web are polyolefin filaments having a diamond cross-sectional configuration, an initial spun denier not exceeding 26.6 dtexpf (24 dpf), and a final drawn denier of not less than 1.1 dtexpf (1 dpf). A method for making nonwoven fabrics as claimed in claim 1, further characterized in that the polyolefin filaments have an initial spun denier not exceeding 4.4 dtexpf (4 dpf) and a final drawn denier of not less than 1.1 dtexpf (1 dpf). A method for making nonwoven fabrics as claimed in claim 1, further characterized in that the polyolefin filament has an initial spun denier not exceeding 6.6 dtexpf (6 dpf). A method for making nonwoven fabrics as claimed in claim 2, further characterized in that the polyolefin filament has an initial spun denier within the range of 2.2 to 4.4 dtexpf (2.0-4.0 dpf) and a final drawn denier above 2.1 dtexpf (1.9 dpf). A method for making nonwoven fabrics as claimed in claim 4, further characterized in that the polyolefin filaments have a final drawn denier above 2.8 dtexpf (2.5 dpf). A method for making nonwoven fabrics as claimed in any of the preceding claims, further characterized in that the polyolefin filaments are comprised of a mixture of filaments with diamond and round cross-sectional configuration. A method for making nonwoven fabrics as claimed in any of the preceding claims, further characterized in that the polyolefin filaments are comprised of a mixture of filaments with delta and diamond cross-sectional configuration. A method for making nonwoven fabrics as claimed in any of the preceding claims, further characterized in that at least 50 % of the polyolefin filaments are comprised of a mixture of filaments with diamond cross-sectional configuration and the remaining filaments have a round cross-sectional configuration. A method for making nonwoven fabrics as claimed in any of the preceding claims, further characterized in that the filaments used vary from 2.5-7.6 cm in length. A method for making nonwoven fabrics as claimed in claim 9, further characterized in that the nonwoven fabrics comprise 2.5 cm-long polyolefin filaments of diamond cross-sectional configuration and 3.8-5 cm-long round cross-sectional filaments. Nonwoven fabrics containing polyolefin filaments, characterized in that at least 25 % of the total weight of the filaments in the web are polyolefin filaments having a diamond cross-sectional configuration, an initial spun denier not exceeding 26.6 dtexpf (24 dpf), and a final drawn denier of not less than 1.1 dtexpf (1 dpf). A nonwoven fabric as claimed in claim 11, further characterized in that the polyolefin filaments have an initial spun denier not exceeding 4.4 dtexpf (4 dpf)and a final drawn denier not exceeding 6.6 dtexpf (6 dpf). A nonwoven fabric as claimed in claim 11, further characterized in that the polyolefin filaments have an initial spun denier not exceeding 6.6 dtexpf (6 dpf). A nonwoven fabric as claimed in claim 12, further characterized in that the polyolefin filaments have an initial spun denier within the range of 2.2 to 4.4 dtexpf (2.0 to 4.0 dpf) and a final drawn denier above 2.1 dtexpf (1.9 dpf). A nonwoven fabric as claimed in claim 14, further characterized in that the polyolefin filaments have a final drawn denier above 2.8 dtexpf (2.5 dpf). A nonwoven fabric as claimed in any of claims 11 to 15, further characterized in that the polyolefin filaments are comprised of a mixture of filaments with diamond and round cross-sectional configurations. A nonwoven fabric as claimed in any of claims 11 to 15, further characterized in that the polyolefin filaments are comprised of a mixture of filaments with delta and diamond cross-sectional configuration. A nonwoven fabric as claimed in any of claims 11 to 17, further characterized in that at least 50 % of the polyolefin filaments are diamond cross-sectional filaments, the remaining filaments having a round cross-sectional configuration. A nonwoven fabric as claimed in any of claims 11 to 18, further characterized in that the filaments used vary from about 2.5 to 7.6 cm in length. A nonwoven fabric as claimed in claim 19, further characterized in that the nonwoven fabric comprises 2.5 cm long polyolefin filaments of diamond cross-sectional configuration and 3.8 to 5.0 cm long polyolefin filaments of round cross-sectional configuration. A nonwoven fabric containing polyolefin filaments is characterized in that it contains not less than about 25 %, based on total web weight of the nonwoven fabric, of polyelefin filaments having a delta cross-sectional configuration, an initial spun denier of more than 4.4 but not exceeding 26.6 dtexpf (4 to 24 dpf). A nonwoven fabric as claimed in claim 21, further characterized in that it contains a blend of delta and round filaments. A nonwoven fabric as claimed in claim 22, further characterized in that it contains a blend of a uniform blend of 25 % to 75 % of delta filaments and 75 % to 25 % of round filaments. A nonwoven fabric as claimed in claim 22, further characterized in that it contains a blend of 50 % of each of the delta and round filaments. A nonwoven fabric as claimed in claim 23 or 24, further characterized in that the delta filaments have an initial spun denier not exceeding 6.6 dtexpf (6 dpf) and a final drawn denier within the range of 1.1 to 3.3 dtexpf (1 to 3.0 dpf). A nonwoven fabric as claimed in claim 25, further characterized in that the delta filaments have a final drawn denier within the range of 2.1 to 2.8 dtexpf (1.9 to 2.5 dpf). A nonwoven fabric as claimed in any of claims 21 to 26, further characterized in that the filaments in the nonwoven fabric are from about 2.54 to 7.62 cm in length. A nonwoven fabric as claimed in claim 27, further characterized in that it comprises a 50 : 50 mixture by weight of 2.54 cm delta filaments and 3.81 cm to 5.04 cm round filaments. A nonwoven fabric as claimed in any of the preceding claims, further characterized in that it has an opacity within the range of 32 % to 45 %. A nonwoven fabric as claimed in any of the preceding claims, further characterized in that all the delta and diamond filaments are polypropylene filaments. A nonwoven fabric as claimed in any of the preceding claims, further characterized in that the filaments of the nonwoven fabric are bonded by thermal bonding.

Inventors: MODRAK JAMES P, ROBERTS OWEN P, MODRAK, JAMES P., ROBERTS, OWEN P.
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1989
Main classification: D04H1
IPC codes: D04H1, D04H3