KR20210149558A - Meltblown absorbent fibers and composites - Google Patents

Abstract

Absorbent fibers are made from melt processable polymers. Absorbent composites include absorbent fibers in addition to natural fibers and superabsorbent materials. A method for making superabsorbent fibers and absorbent composites is also disclosed. Absorbents are useful in disposable personal care absorbent products such as diapers, training pants, feminine pads, adult incontinence products, and professional health care products for absorbing and retaining fluids.

Description

Meltblown absorbent fibers and composites

The present invention relates to an absorbent material having improved absorbency. More particularly, the present invention relates to absorbent fibers made from melt processable polymers and absorbent composites comprising such absorbent fibers. The present invention also relates to absorbent fibers and methods of making absorbent composites.

U.S. Patent Nos. 5,280,079 (issued Jan. 18, 1994 to Allen et al.), 5,147,956 (issued Sep. 15, 1992 to Allen), 4,962,172 (issued Oct. 9, 1990 Allen et al.) et. is described. However, the absorbent fibers described herein are made by a solution spinning process. In addition, the water-soluble polymers used to form the fibers are non-melt processable. In addition, superabsorbent staple fibers are commercially available from Camelot Superabsorbent Ltd, Calgary, Canada, under the trade name FIBERDRI (registered trademark), an isobutylene-maleic anhydride copolymer based absorbent fiber, Grimsby, UK. It is commercially available under the trade designation OASIS(R) 101, a sodium polyacrylate based absorbent fiber, available from Technical Absorbents, Inc. These commercially available superabsorbent fibers are also prepared by solution spinning of non-melt processable water-soluble polymers. The staple fiber is produced by a textile fiber dry spinning process. They can be introduced into the absorbent core through an air laying process, but do not form bonds with other components of the core, such as superabsorbent particles and fluff fibers. The absorbent core from the process is not a stabilized structure. A need exists for absorbent fibers and absorbent composites comprising the absorbent fibers that can be manufactured with high productivity and low cost. There is also a need for stabilized absorbent composites that can exhibit improved dry and wet integrity. There is also a need for a method of making absorbent fibers and absorbent composites with high productivity and low cost.

Absorbent fibers currently supplied commercially are made by solution spinning processes, for example solution dry spinning used for making textile fibers or solution blowing spinning processes used for making nonwovens. The solution spinning process is initiated with an aqueous polymer solution. The polymer solution is then spun into fibers and crosslinked to form water-swellable, water-insoluble fibers. However, the solution spinning process is low in productivity and expensive due to the presence of an excess of water in the polymer solution. For this reason, absorbent fibers are not widely used as absorbent materials in disposable personal care absorbent products. Some polymers can be processed into different shapes or forms when the temperature is above a certain temperature and can be referred to as 'melt processable'. Other polymers decompose rather than melt upon reaching certain elevated temperatures and may be referred to as 'non-melt processable'. Fibers made from melt processable polymers such as polyethylene (PE) or polypropylene (PP) are widely used in the nonwoven industry due to their low cost. However, these polymers cannot be used in absorbent composites for disposable personal care absorbent articles because of their high hydrophobicity, which makes them non-wetting and poor fluid handling properties such as absence of wicking.

In one embodiment of the present invention, the absorbent fibers comprise melt-processable water-soluble polymers that are meltblown and then crosslinked to form water-swellable but water-insoluble absorbent fibers. The absorbency underzero load value of the resulting absorbent fiber is at least about 5 grams of fluid (g/g) per gram of fiber. Melt processable water-soluble polymers include nonionic homopolymers such as polyethylene oxide, polypropylene oxide, hydroxy propyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, polyethylene imine, polyvinyl amine, polyvinyl alcohol, poly (ethylene oxide-co-propylene oxide), polyacrylic acid, polyacrylamide, and combinations thereof. In addition, melt processable water soluble polymers include at least one ionic and one nonionic monomer, such as sodium acrylate (used in commercially available superabsorbent materials) and methyl methacrylate (currently commercially available melt processable polymers). used in ) may be a copolymer of monomers. In another embodiment of the invention, the absorbent composite comprises hydrophilic fibers (such as wood pulp fluff, cotton, downy, other cellulosic fibers, regenerated cellulosic fibers, natural fibers or modified or spun staple fibers, and hydrophilic synthetic fibers such as For example, those sold under the trade name HYDROFIL (registered trademark) by Allied Corporation of Morristown, NJ and combinations thereof) and commercially available superabsorbent materials including meltblown melt processable water soluble polymers do. The polymers are crosslinked to form absorbent fibers that are water swellable but water insoluble. The resulting absorbent composite is superabsorbent such that it exhibits a zero load absorption value of at least 5 grams of fluid per gram of composite (g/g) and a zero load absorption value of at least about 10 g/g to about 50 g/g. may be As described in the above embodiments, melt processable water-soluble polymers are nonionic homopolymers such as polyethylene oxide, polypropylene oxide, hydroxy propyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, polyethylene imine, polyvinyl. amines, polyvinyl alcohol, poly(ethylene oxide-co-propylene oxide), polyacrylic acid, polyacrylamide, and combinations thereof, or at least one ionic and one nonionic monomer, such as sodium It may be a copolymer of monomers of acrylate and methyl methacrylate. In either embodiment, the crosslinking agent may be sprayed onto the surface of the meltblown fibers. The crosslinking agent must have at least two functional groups capable of reacting with functional groups on the surface of the melt processable polymer. In order to initiate the crosslinking reaction, a post-treatment such as heat treatment, microwave irradiation, electron beam (e-beam) irradiation, ultraviolet (UV) irradiation, steam treatment or steam treatment is necessary. The present invention also relates to an absorbent comprising the steps of melting a melt processable water soluble polymer, extruding the polymer, spinning the polymer to form fibers, adding a crosslinking agent and curing the resulting fiber. It relates to a method of making fibers and absorbent composites.

Absorbents are useful in disposable personal care absorbent products such as diapers, training pants, feminine pads, adult incontinence products, and professional health care products for absorbing and retaining fluids. Absorbents or superabsorbents are often combined with water insoluble fibers to make absorbent composites for use in the absorbent core of disposable personal care absorbent articles according to methods known in the art. Particulate superabsorbents are widely used as superabsorbent materials in disposable personal care absorbent products. However, superabsorbent particles are sometimes difficult to use because they do not exist stationary during the manufacture of the disposable personal care absorbent article and thus can be displaced in the disposable personal care absorbent article. The use of absorbent or superabsorbent fibers in place of superabsorbent particles in disposable personal care absorbent products can provide improved product integrity, better retention, reduced product volume and improved absorbency, for example, rapid fluid absorption and fluid dispensing. It is potentially advantageous because In addition, the use of fibers can provide thinner, softer products that provide improved product properties, such as better body conformability, reduced gel migration, and effective simplification of the absorbent article manufacturing process.

The present invention relates to absorbent fibers made from melt processable polymers and to absorbent composites comprising such absorbent fibers. The absorbent composite may also be used in the absorbent core of a disposable personal care absorbent article. Absorbent composites are useful in absorbent articles, such as diapers, training pants, swimwear, adult incontinence articles, feminine hygiene articles, and absorbent medical articles. The present invention also relates to absorbent fibers and methods of making absorbent composites. 1 is an exploded perspective view of a diaper; Referring to FIG. 1 , the disposable diaper 10 includes an outer cover 12 , a body-side liner 14 , and an absorbent core 40 positioned between the body-side liner 14 and the outer cover 12 . include The absorbent core 40 may include absorbent fibers or absorbent composites according to the present invention. The bodyside liner 14 and outer cover 12 are made of conventional non-absorbent materials. 'Non-absorbent' means that the material has an absorbent capacity of not more than 5 g of 09% aqueous sodium chloride solution per gram of material, excluding pockets filled with superabsorbent. The bodyside liner 14 is made of a material with high liquid permeability. The layer functions to transport liquid from the wearer to the absorbent core 40 . Suitable liquid-permeable materials include porous woven materials, porous non-woven materials, porous films, open-celled foams and cottons. Other examples of suitable bodyside liner materials include any flexible porous sheet of polyolefin fibers such as polypropylene, polyethylene or polyester fibers, spunbonded polypropylene, webs of polyethylene or polyester fibers, webs of rayon fibers, bonded carded webs of synthetic or natural fibers or combinations thereof. U.S. Patent No. 5,904,675, issued May 18, 1999 to Laux et al., incorporated herein by reference, provides further examples of suitable surge materials. The layer may also be a plastic film in which voids are present. Suitable cottons include certain air-formed thermochemical and chemothermomechanical wood pulps. The dimensions of the different layers of the article 10 may be different depending on the size and body type of the wearer. The outer cover material 12 must be breathable to water vapor. In general, the water vapor transmission rate (MVTR) of the outer cover 12 is at least about 300 g/m 2 -24 hours, preferably at least about 1000 g/m 2 -24 hours or at least about 3000 g/m 2 -24 hours. A waist elastic member 26 , a fastening tape 28 and a leg elastic member 30 are attached to the outer cover 12 . The leg elastic members 30 generally have a carrier sheet 32 and individual elastic strands 34 . The diaper of Figure 1 is representative of one basic diaper embodiment. It is possible to vary the design and material of the diaper parts differently. For example, methods and materials for making the diaper embodiment shown in FIG. 1 are set forth in greater detail in US Pat. No. 5,509,915, issued Apr. 23, 1996 to Hanson et al., which is incorporated herein by reference, have. Possible modifications to the diaper shown in FIG. 1 are set forth in US Pat. Nos. 5,509,915 and 5,364,382, issued Nov. 15, 1994 to Latimer et al. According to one embodiment of the present invention, the absorbent fibers comprise melt-processable water-soluble polymers that are meltblown and then crosslinked to form water-swellable but water-insoluble absorbent fibers. Suitable melt processable water-soluble polymers are nonionic homopolymers such as polyethylene oxide, polypropylene oxide, hydroxyl propyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, polyethylene imine, polyvinyl amine, polyvinyl alcohol, poly (ethylene oxide-co-propylene oxide), polyacrylic acid, polyacrylamide, and combinations thereof. Some modifications may be necessary to improve their melt processability. Such modifications include, but are not limited to, addition of minor proportions of additives, blends and/or comonomers. The modified polyvinyl alcohol used herein is commercially available from Nippon Gohsei, Osaka, Japan. Although nonionic water-soluble and melt processable polymers are absorbent, they are not superabsorbent because of the lack of ionic charges on their macromolecular chains. Particulate superabsorbent materials on the market today are made of ionic polyacrylates. However, pure ionic water-soluble polymers are generally not melt-processable. Other melt processable water-soluble polymers may be copolymers of ionic and nonionic monomers. Suitable monomers for the copolymer include ionic monomers such as sodium acrylate commercially available from Aldrich Chemical Co, Milwaukee, Wis., and nonionic monomers such as methyl meta available from Aldrich Chemical Company. acrylates. In order to achieve both water solubility and melt processability of the copolymer, the proportion of monomers on a dry weight basis is important. Preferably, the ratio of monomers on a dry weight basis should be from about 30:70 to about 70:30. Polymerization to form the copolymer can be carried out according to conventional methods known in the art. Because of the addition of the ionic comonomer, the water-soluble melt processable copolymer absorbs greater than the nonionic homopolymer. Whether homopolymer or copolymer, the molecular weight of the polymer is important. The molecular weight of the polymer must be at least about 10,000 to have high fluid absorption. However, the molecular weight of the polymer cannot exceed about 1,000,000 because meltblowing equipment cannot handle excessively high viscosities. Suitable polymers have a molecular weight of about 50,000 to 1,000,000, preferably about 100,000 to 1,000,000, or about 100,000 to 500,000. After fiber formation, the fiber is still water soluble. A solution comprising a crosslinking agent is sprayed onto the surface of the meltblown fibers to form water-swellable but water-insoluble fibers either immediately or after the curing step, depending on the nature of the crosslinking agent used. Suitable crosslinking agents may be reactive or latent. The reactive crosslinking agent will crosslink the fibers in the spinning process. Latent crosslinking agents do not crosslink the fibers and usually require a certain activation energy, such as heating, to trigger crosslinking. It is preferred that the crosslinking agent has at least two functional groups capable of reacting with hanging functional groups on the melt processable polymer. Suitable crosslinking agents include diols, polyols, diamines, polyamines, dicarboxylic acids, polycarboxylic acids, dialdehydes, polyaldehydes, butanediol, diethylene triamine, citric acid, glutaric dialdehyde and ethylene glycol diglycidyl ether. , trivalent or tetravalent metal ions, and combinations thereof. Suitable functional groups on the crosslinker depend on the melt processable polymer. For example, when polyvinyl alcohol is used as the melt processable polymer, suitable functional groups on the crosslinker include carboxylic acid groups (forming ester linkages with hydroxyl groups on polyvinyl alcohol), aldehyde groups (with hydroxyl groups on polyvinyl alcohol) and form acetal linkages) or epoxy groups (form ether linkages with hydroxyl groups on polyvinyl alcohol). However, if the melt processable polymer has different types of functional groups, such as amino or carboxylic acids or other groups, suitable functional groups on the crosslinker will be different. For example, if the polymer has a carboxylic acid functional group, suitable functional groups on the crosslinker include a hydroxyl group (forming an ester linkage with the carboxylic acid group on the polymer), an amino group (forming an amide linkage with the carboxylic acid group on the polymer) or Contains trivalent or tetravalent metal ions (forming ionic bonds with carboxylic acid groups on the polymer). An example of a commercially available crosslinking agent is KYMENE®, available from Hercules Incorporated of Wilmington, Del. KYMENE® contains functional groups capable of reacting with hydroxyl groups on polyvinyl alcohol. KYMENE® is widely used to crosslink cellulosic fibers. However, the chemical composition is patented. When a latent crosslinking agent is used, a post-treatment process is required to initiate the crosslinking reaction. The post-treatment process includes heat treatment, microwave irradiation, e-beam irradiation, UV irradiation, steam treatment or steam treatment. According to another embodiment of the present invention, an absorbent composite comprises a melt-processable water-soluble polymer that is meltblown with hydrophilic fibers and a commercially available superabsorbent material to form a coform material. The polymers are crosslinked to form absorbent fibers that are water swellable but water insoluble. Any of the homopolymers or copolymers described above having a molecular weight of about 10,000 to 1,000,000 may be suitable for the melt processable water-soluble polymer of this embodiment of the present invention. The superabsorbent material may be any commercially available superabsorbent material, such as superabsorbent particles or superabsorbent fibers. Examples of commercially available particulate superabsorbents include SANWET® IM 3900 and SANWET® IM-5000P available from Hoescht Celanese, Potsmouth, Va., from Midland, Michigan, USA. DRYTECH® 2035 available from the Dow Chemical Co. and FAVOR® SXM 880, SXM 9543 available from Stockhausen, Greensboro, NC. Any of the above commercially available superabsorbent staple fibers may be suitable as superabsorbent fibers. The hydrophilic fiber is preferably wood pulp fluff sold under the trade designation Coosa CR 1654 by US Alliance Forest Products Corporation, Coosa Pine, Alabama. The resulting absorbent composite, which is a coform material, as shown in Figures 2A-2C, comprises absorbent fibers 36 made of polyvinyl alcohol in this case, hydrophilic fibers, in this case wood pulp fluff 38, and in this case supernatant. and superabsorbent material 39 which is an absorbent particle. The invention also includes methods of making absorbent fibers and absorbent composites. In FIG. 3 , hopper 50 contains pellets of a melt processable water soluble polymer. The single or twin screw extruder 52 melts the pellets by means of a conventional heating device to form a melt extrudable composition, which is melted by the action of a rotating extruder screw (not shown) located within the extruder 52 . It is extruded through a blowing die (54). The extrudable composition is fed through a die 54 . Die 54 and the gas feed circulated therethrough are heated by conventional apparatus (not shown). In addition to the spinning die diameter, the air speed can also be adjusted to adjust the fiber diameter. To produce a nonwoven material comprising only the absorbent fibers of the present invention, a solution comprising a crosslinking agent is sprayed onto the gaseous fiber stream 56 by a sprayer presented by stream 60 . The absorbent fibers are then conveyed by vacuum 67 onto a forming wire 64 comprising a belt 66 and rollers 68 to form the nonwoven material followed by air drying and post-crosslinking to initiate the crosslinking reaction. It can be treated with a treatment process. The use of a vacuum box 67 under the forming wire 64 may help the fibers form a uniform web on the forming wire 64 . The post-treatment may be heat treatment, microwave treatment, e-beam irradiation, UV irradiation, steam treatment or steam treatment. The nonwoven material is then wound on a winder 70 and collected. To prepare the absorbent composite of the present invention which is a coform material, the gas-containing fiber stream 56 is converted into a second gas stream comprising individualized hydrophilic fibers, preferably wood pulp fibers, to incorporate the different fiber materials in one step ( 58) is fused with The solution comprising the crosslinking agent is sprayed onto the gaseous fiber stream (56) by an atomizer presented by stream (60). The superabsorbent material may be added concurrently with the hydrophilic fibers and crosslinker via an additional gas stream 62 . The integrated gas stream is then conveyed by vacuum 67 onto a forming wire 64 comprising a belt 66 and rollers 68 to air form the coform. Air may be supplied by any conventional means, for example a blower (not shown). Any of the melt processable polymers, superabsorbent materials, hydrophilic fibers and crosslinking agents described above may be used to prepare absorbent fibers and/or absorbent composites. After coform material formation, the coform material is dried and subjected to a post-treatment process to initiate a crosslinking reaction. This post treatment is sometimes referred to as 'curing'. The treatment may be any one of heat treatment, microwave treatment, e-beam irradiation, UV irradiation, steam treatment, or steam treatment. The coform material is then wound on a winder 70 and collected. When heat treatment is used as a post-treatment process for coform materials, sometimes undesirable discoloration of coform materials occurs. For example, if a coform material comprising wood pulp fibers is thermally cured at a temperature greater than 140° C. for a time greater than 2 hours, the cured coform material will have a dark yellow to brown color due to oxidation of the wood pulp fibers. . The discoloration will also occur if the meltblown fibers are made of polyvinyl alcohol. Effective methods of minimizing or eliminating discoloration include (1) lowering the curing temperature by using a catalyst or low temperature curable crosslinker, (2) curing the coform material using different curing methods, such as microwave irradiation or e-beam irradiation, (3) the use of different types of melt processable polymers, such as hydroxy propyl cellulose, (4) the use of self-crosslinkable polymers, such as silane grafted polyethylene oxide, with moisture-induced self-crosslinking capacity. and (5) the use of antioxidants. During the manufacture of the coform material, during fiber spinning and water spraying in the superabsorbent material/wood pulp fluff/superabsorbent fiber mixing zone can help increase the interfiber or superabsorbent interparticle bonding. Thus, the concentration of cross-linking agent can play an important function in controlling the structure and integrity of absorbent composites. If more water is required, a more dilute crosslinker solution can be prepared and vice versa. On the other hand, the concentration of the crosslinking agent affects the shell thickness of the surface of the crosslinked fibers, the lower the concentration, the thicker the crosslinked surface shell layer is formed.

Claims (2)

An absorbent fiber having an absorbency under zero load of at least about 5 g/g comprising a melt processable water soluble polymer and a crosslinking agent. 2. The method of claim 1, wherein the polymer is polyethylene oxide, polypropylene oxide, hydroxyl propyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, polyethylene imine, polyvinyl amine, polyvinyl alcohol, poly(ethylene oxide-co-propylene oxide) ), polyacrylic acid, polyacrylamide, and combinations thereof.