Patent Application
20130087298
The present invention pertains to a sensor sheet or wipe for detecting surface conditions. In particular, the invention pertains to an indicator disposed on a web or substrate to create a sensor wipe, wherein the sensor wipe can indicate a surface condition of an article such as pH, microbial contamination and the like.
Convenient monitoring of surface conditions in industrial or commercial settings can be challenging. For example, because bacteria can thrive within certain pH range, it is desirable to test the pH of certain surfaces such as those used for food preparation. It may also be desirable to test the pH of other surfaces where it is important to maintain a particular pH.
Typically, pH is measured with a pH meter, which is not feasible for testing surface areas of a substantial size such as a counter top or even human skin. Sometimes, the pH varies over an area, so testing a few small areas within the total area may not provide results that adequately represent the actual surface pH. Further, pH test strips are not feasible for testing the pH of a surface because they can only make effective contact with a relatively small flat surface.
Wipes are capable of swiping large expanses of surfaces, which do not necessarily have to be flat. Some pH indicator dye(s) may be incorporated into a wipe so that when the wipe contacts a surface, it changes color to indicate the pH of such surface. However, one drawback to conventional pH indicating wipes is dye leaching. Traditional wipes when made with pH indicator dyes may leave residual pH indicator dye on any surface to which they make contact, resulting in not only a problem with cleanliness, but possible regulatory problems in industrial settings. Further, because of the leaching problem, such wipes may only be used once. If rinsed with water, the indicator dye is diluted to the point where it cannot effectively detect a surface pH.
Other types of contaminants may be detected with various wipes having indicator dyes other than pH indicator dyes. However, like the pH dyes, to make them non-leachable on wipes requires the extra step of adding a leaching inhibitor to the substrate.
It is therefore desirable to provide a sensor wipe that does not leach indicator dye. It is also desirable to not rely on a leaching inhibitor so as to manufacture the sensor wipe as efficiently as possible. For certain industrial applications, it may be desirable to provide a sensor wipe that can be used multiple times before disposal.
In accordance with one embodiment of the present disclosure is a method of manufacturing sensor wipes or sheets. The manufacturing steps include: immobilizing an indicator dye onto paper-making fibers; preparing a pulp slurry by combining the indicator fibers with an aqueous solution; creating a web from the pulp slurry; hydroentangling or coforming the web with a synthetic polymer; and converting the hydroentangled or coformed web to create a plurality of sensor sheets.
In accordance with another embodiment of the present disclosure is a method of manufacturing pH indicating sensor wipes sheets. The manufacturing steps include: immobilizing a pH indicator dye onto cellulose fibers to create indicator fibers; preparing pulp by combining the indicator fibers with a pulp solution; preparing a web comprising indicator fibers; and hydroentangling or coforming the web with a polymer.
Other features and aspects of the present invention are set forth in greater detail below.
Reference now will be made in detail to various embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations.
As used herein, the term “spunbonded filaments” refers to small diameter continuous filaments which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, eductive drawing and/or other well-known spunbonding mechanisms. The production of spun-bonded nonwoven webs is illustrated in patents such as, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al. The disclosures of these patents are hereby incorporated by reference.
The present invention is a nonwoven substrate made in accordance with a method of immobilizing an indicator dye to a cellulose fiber, and then incorporating the fiber into a nonwoven substrate. The resulting nonwoven substrate may be used to make sensor wipes or sheets used to test the pH or other characteristics of surfaces or even liquids. Because no dye leaching occurs, a sensor wipe that has been in contact with an acidic or basic surface may be rinsed in water or buffer solution to restore it to a neutral pH, allowing the sensor wipe to be used multiple times prior to disposal.
The method of the present invention generally includes saturating cellulosic fibers with one or more dyes having reactive groups capable of forming a bond with the fibers such that immobilizes the dye onto the fibers. The saturated fibers are used in a process to make a nonwoven, such as a hydroentangling or coforming process.
Because the fibers are mechanically defiberized during the hydroentangling or coforming process, it is quite unexpected that the chemical bonds between the cellulosic fibers and the dye(s) are maintained and not disrupted in a way that causes leaching. One advantage associated with the method of the present invention is that a post-modification step can be eliminated over other known processes for manufacturing sensor wipes.
In general, any suitable fibrous web may be used to make substrates in accordance with the present disclosure. For example, in one embodiment, the web can be a tissue product, such as a bath tissue, a facial tissue, a paper towel, an industrial wiper and the like. These products typically have a bulk of at least 3 cc/g. The tissue products may contain one or more plies.
Fibers suitable for making tissue webs comprise any natural or synthetic cellulosic fibers including, but not limited, to nonwoody fibers, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, ramie, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and woody or pulp fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as eucalyptus, maple, birch, and aspen. Pulp fibers can be prepared in high-yield or low-yield forms and can be pulped in any known method, including kraft, sulfite, high-yield pulping methods and other known pulping methods. Fibers prepared from organosolv pulping methods can also be used, including the fibers and methods disclosed in U.S. Pat. No. 4,793,898, issued to Laamanen et al.; U.S. Pat. No. 4,594,130, issued to Chang et al.; and U.S. Pat. No. 3,585,104. Useful fibers can also be produced by anthraquinone pulping, exemplified by U.S. Pat. No. 5,595,628 issued to Gordon et al.
Any known bleaching method can be used. Chemically treated natural cellulosic fibers can be used such as mercerized pulps, chemically stiffened or crosslinked fibers, or sulfonated fibers. To maintain the best mechanical properties of the papermaking fibers, it is desirable that the fibers be relatively undamaged, largely unrefined or only lightly refined. While recycled fibers can be used, virgin fibers are generally useful for their optimal mechanical properties and lack of contaminants.
Mercerized fibers, regenerated cellulosic fibers, cellulose produced by microbes, rayon, and other cellulosic material or cellulosic derivatives can be used. Suitable papermaking fibers can also include recycled fibers, virgin fibers, or mixes thereof. In certain, to have high bulk and good compressive properties, the fibers may have a Canadian Standard Freeness of at least 200, more specifically at least 300, more specifically still at least 400, and most specifically at least 500.
Other papermaking fibers that can be used in the present disclosure include paper broke or recycled fibers and high yield fibers. High yield pulp fibers are those papermaking fibers produced by pulping processes providing a yield of about 65% or greater, more specifically about 75% or greater, and still more specifically about 75% to about 95%. The term “yield” as used herein is the resulting amount of processed fibers expressed as a percentage of the initial wood mass. Such pulping processes include bleached chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP), pressure/pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulfite pulps, and high yield Kraft pulps, all of which leave the resulting fibers with high levels of lignin. High yield fibers are well known for their stiffness in both dry and wet states relative to typical chemically pulped fibers.
In one aspect of the present disclosure, an indicator dye having a charge can be immobilized onto tissue fibers to produce the indicator-containing fibers. The indicator-containing fibers can be provided as pulp sheets (wet or dry) or an aqueous pulp slurry that may be combined with select tissue making fibers prior to forming a tissue sheet in a conventional manner, as described herein.
The immobilization can be achieved by many methods such as chemical bonding, physical absorption, or by using a carrier such as a polymer or a particle. In one desirable embodiment, a highly charged porous material can effectively immobilize an oppositely charged indicator. For example, the fibers described supra have been found to be suitable charged materials to immobilize negatively charged indicators.
In one aspect of the present disclosure, partially neutralized weak acids or bases and/or charged polymer surfactants are deposited on cellulosic fibers to create a surface charge to which a dye can bond. The fibers are subsequently dried. An immobilization solution that contains ion-responsive charged polymeric surfactants is then deposited on the fibers which are again dried. Prior to making a web for hydroentangling/conforming, at least one indicator dye such as a pH indicator solution is then deposited on the fibers, making them ready to be made into pulp slurry.
Other methods of immobilizing dye (e.g. azo dye) on fibers are presented in U.S. Pat. No. 4,029,598 issued to Neisus et al., which is incorporated herein by reference to the extent it is consistent with the present disclosure.
Suitable pH indicator dyes may transfer from one hue or color intensity to another, or from colorless to colored. Desirably, the pH indicator can be any color changing dye that changes color in the pH range from about 1 to about 14 and which is stable, non-leaching, and safe to handle. Certain pH ranges may be of particular interest depending on what microbe is being detected. For instance, the pH range may be from about 4 to 10, 3 to 11 and 5 to 9. For household applications, it may be desirable to detect microbes at a pH range of 10 to 11. Other ranges are contemplated.
Desirably, the pH indicator is reversible so that when it is incorporated into a nonwoven web, the end product such as a wipe can be neutralized and used again.
Such commercially available pH indicators include, but are not limited to, Alizarin (C.A.S. No. 72-48-0), Alizarin Yellow (C.A.S. No. 584-42-9), Alizarin Red S(C.A.S. No. 130-22-3), Basic Fushsin (C.A.S. No. 569-61-9), Brilliant Yellow (C.A.S. No. 3051-11-4), Bromochlorophenol Blue (C.A.S. No. 102185-52-4), Bromocresol Green (C.A.S. No. 76-60-8), Bromocresol Purple (C.A.S. No. 115-40-2), Bromophenol Blue (C.A.S. No. 115-39-9), Bromothymol Blue (C.A.S. No. 34722-90-2), Chlorophenol Red (C.A.S. No. 4430-20-0), Chrysoidin (C.A.S. No. 532-82-1), Congo Red (C.A.S. No. 573-58-0), o-Cresolphthalein (C.A.S. No. 596-27-0), Cresol Red (C.A.S. No. 1733-12-6), Ethyl Orange (C.A.S. No. 62758-12-7), m-Cresol Purple (C.A.S. No. 2303-01-7), Methyl Orange (C.A.S. No. 547-58-0), Methyl Red (C.A.S. No. 493-52-7), Mordant Orange I (C.A.S. No. 2243-76-7), Neutral Red (C.A.S. No. 553-24-2), Nile Blue A (C.A.S. No. 3625-57-8), Nitrazine Yellow (C.A.S. No. 5423-07-4), 3-Nitrophenol (C.A.S. No. 554-84-7), 4-Nitrophenol (C.A.S. No. 100-02-7), Phenolphthalein (C.A.S. No. 77-09-8, Phenol Red (C.A.S. No. 143-74-8), Rosolic Acid (C.A.S. No. 603-45-2), Thymol Blue (C.A.S. No. 76-61-9), Thymolphthalein (C.A.S. No. 125-20-2), and Xylenol Blue (C.A.S. No. 125-31-5. Additional suitable pH indicators or dyes are disclosed in U.S. Pat. No. 4,029,598 entitled “Non-Bleeding Indicator and Dyes Therefor”, issued Jun. 14, 1977 to Neisius et al., which is hereby incorporated by reference. As disclosed therein, particularly suitable dyes include: 4-anilino-3″-azobenzene, which turns deep purple in the pH range of 0-4.5; 4-anilino-3′-azobenzene, which turns deep purple in the pH range of 0-3; and a 1:1:3 weight ratio of a mixture of 4-anilino-3-azobenzene, 2-(2,4-dinitrophenylazo)-4-napthol-sulphonic acid, and 4-methylamido-2-dimethylaminobenzene sulfonic acid, which turns from yellow to green in the pH range of 2-3.
In another aspect of the present disclosure, other suitable dyes include: 1) redox dyes which may be useful for measuring the oxidation state of the environment, 2) metal sensitive dyes which may be useful in microbial control, 3) amino acid detection dyes which may be useful in odor control, microbial control and cleaning applications, and 4) explosives detection dyes which may be useful for security applications.
Redox dyes can detect an environment in which microbes will grow. A low redox measure indicates that odors may be produced by the microbes, whereas a high redox measure indicates that odor is inhibited. High redox measures also indicate conditions that inhibit the growth of obligate anaerobes, and conditions that favor the growth of aerobes. Low redox measures indicate conditions that limit the growth of anaerobes.
Redox dyes are also useful for understanding the impact of conditions for spore germination. A low redox measure indicates anaerobic spore germination e.g. Clostridia. A high redox measure indicates aerobic spore germination, e.g. aerobic bacilli. High redox conditions are indicative of poor stability of oxygen sensitive materials. Examples of pH independent Redox dyes are shown in Table 1.
Examples of pH dependent Redox dyes are shown in Table 2.
Other redox dye examples include Nile Blue, Toluidine Blue, metal-organic complexes (e.g. phenanthroline), true organic redox systems (e.g. Methylene blue) Azodyes, Tetrazolium dyes and Alamar blue.
Metal and cation binding dyes are useful in understanding conditions that might inactivate biocides. When in contact with skin, these dyes can be used to find calcium, sodium and potassium levels of the body. Further, these dyes may be used to define safety problems, such as high levels of lead in an environment.
Examples of metal and cation sensitive dyes include the following. Ca/Mg examples: Fluorescent Ca/Mg dyes: mag-fura-2, magnesium green, fura-2, and fluo-3,1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid (IX) (metal-ion EDTA). Metal ion examples: Solochrome Dark Blue or Eriochrome blue black R (metal-ion EDTA) sodium 1-(2-hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate and Cu dye Pyrocatechol Viole t, Calcon also known as Solochrome Dark Blue or Eriochrome blue black R or sodium 1-(2-hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate, Eriochrome Red B or sodium salt of 4-(2-hydroxy-4-sulpho-1-naphthylazo)-3-methyl-1-phenyl-2-pyrazolin-5-one (IX), Fast Sulphon Black F, 2-hydroxy-1-(2-hydroxy-4-sulpho-1-naphthylazo)-3-naphthoic acid, Pyrocatechol Violet Pyrocatechol sulphone phthalein (VII); Catechol violet. Variamine Blue B.
Protein detection dyes can be used to measure proteins on a surface. This can be important for infection control, and wipes having such dyes immobilized theron may be used in both residential and commercial settings such as hospitals and clinics. Examples of amino acid detection dyes include Blue fluorescent dye-protein and Bromphenol blue.
Explosives sensitive dyes can be used in security applications. Examples of explosive sensitive dyes include p-dimethylaminocinnamaldehyde and p-dimethylaminobezaldehyde.
The quantity of indicator fibers in a nonwoven substrate of the present disclosure (based on the dry weight of fiber in the nonwoven substrate), may be from about 0.1 to about 100 dry weight percent, more specifically from about 0.1 to about 50 dry weight percent, more specifically from about 0.1 to about 25 dry weight percent, and still more specifically about 10 to about 20 percent dry weight percent. The proper amount will depend, at least in part, upon the pH color change range of the chosen pH indicator.
One process for producing a nonwoven substrate of the present invention is by hydroentangling cellulosic fibers and synthetic fibers. Referring to
Water is removed from the suspension of pulp fibers to form a uniform layer of pulp fibers 118.
The pulp fibers may be any high-average fiber length pulp, low-average fiber length pulp, or mixtures of the same. The high-average fiber length pulp typically have an average fiber length from about 1.5 mm to about 6 mm. Exemplary high-average fiber length wood pulps include those available from the Kimberly-Clark Corporation under the trade designations Longlac 19, Coosa River 56, and Coosa River 57.
The low-average fiber length pulp may be, for example, certain virgin hardwood pulps and secondary (i.e. recycled) fiber pulp from sources such as, for example, newsprint, reclaimed paperboard, and office waste. The low-average fiber length pulps typically have an average fiber length of less than about 1.2 mm, for example, from 0.7 mm to 1.2 mm.
Mixtures of high-average fiber length and low-average fiber length pulps may contain a significant proportion of low-average fiber length pulps. For example, mixtures may contain more than about 50 percent by weight low-average fiber length pulp and less than about 50 percent by weight high-average fiber length pulp. One exemplary mixture contains 75 percent by weight low-average fiber length pulp and about 25 percent high-average fiber length pulp.
The pulp fibers used in the present invention may be unrefined or may be beaten to various degrees of refinement. Small amounts of wet-strength resins and/or resin binders may be added to improve strength and abrasion resistance. Useful binders and wet-strength resins include, for example, Kymene 557 H available from the Hercules Chemical Company and Parez 631 available from American Cyanamid, Inc. Cross-linking agents and/or hydrating agents may also be added to the pulp mixture. Debonding agents may be added to the pulp mixture to reduce the degree of hydrogen bonding if a very open or loose nonwoven pulp fiber web is desired. One exemplary debonding agent is available from the Quaker Chemical Company, Conshohocken, Pa., under the trade designation Quaker 2008. The addition of certain debonding agents in the amount of, for example, 1 to 4 percent, by weight, of the composite also appears to reduce the measured static and dynamic coefficients of friction and improve the abrasion resistance of the continuous filament rich side of the composite fabric. The de-bonder is believed to act as a lubricant or friction reducer.
A continuous filament nonwoven substrate 120 is unwound from a supply roll 122 and travels in the direction indicated by the arrow associated therewith as the supply roll 122 rotates in the direction of the arrows associated therewith. The nonwoven substrate 118 passes through a nip 24 of a S-roll arrangement 126 formed by the stack rollers 128 and 130.
The nonwoven substrate 120 may be formed by known continuous filament nonwoven extrusion processes, such as, for example, known solvent spinning or melt-spinning processes, and passed directly through the nip 116 without first being stored on a supply roll. The continuous filament nonwoven substrate 120 is preferably a nonwoven web of continuous melt-spun filaments formed by the spunbond process. The spunbond filaments may be formed from any melt-spinnable polymer, co-polymers or blends thereof. For example, the spunbond filaments may be formed from polyolefins, polyamides, polyesters, polyurethanes, A-B and A-B-A′ block copolymers where A and A′ are thermoplastic endblocks and B is an elastomeric midblock, and copolymers of ethylene and at least one vinyl monomer such as, for example, vinyl acetates, unsaturated aliphatic monocarboxylic acids, and esters of such monocarboxylic acids. If the filaments are formed from a polyolefin such as, for example, polypropylene, the nonwoven substrate 120 may have a basis weight from about 3.5 to about 70 grams per square meter (gsm). More particularly, the nonwoven substrate 120 may have a basis weight from about 10 to about 35 gsm. The polymers may include additional materials such as, for example, pigments, antioxidants, flow promoters, stabilizers and the like.
One important characteristic of the nonwoven continuous filament substrate is that it has a total bond area of less than about 30 percent and a uniform bond density greater than about 100 bonds per square inch. For example, the nonwoven continuous filament substrate may have a total bond area from about 2 to about 30 percent (as determined by conventional optical microscopic methods) and a bond density from about 250 to about 500 pin bonds per square inch.
Although pin bonding produced by thermal bond rolls is possible, the present disclosure contemplates any form of bonding which produces good tie down of the filaments with minimum overall bond area. For example, a combination of thermal bonding and latex impregnation may be used to provide desirable filament tie down with minimum bond area. Alternatively and/or additionally, a resin, latex or adhesive may be applied to the nonwoven continuous filament web by, for example, spraying or printing, and dried to provide the desired bonding.
The pulp fiber layer 118 is then laid on the nonwoven substrate 120 which rests upon a foraminous entangling surface 132 of a conventional hydraulic entangling machine. It is preferable that the pulp layer 118 is between the nonwoven substrate 120 and the hydraulic entangling manifolds 134. The pulp fiber layer 118 and nonwoven substrate 120 pass under one or more hydraulic entangling manifolds 134 and are treated with jets of fluid to entangle the pulp fibers with the filaments of the continuous filament nonwoven substrate 120. The jets of fluid also drive pulp fibers into and through the nonwoven substrate 120 to form the composite material 36.
Alternatively, hydraulic entangling may take place while the pulp fiber layer 118 and nonwoven substrate 120 are on the same foraminous screen (i.e., mesh fabric) where the wet-laying took place. The present invention also contemplates superposing a dried pulp sheet on a continuous filament nonwoven substrate, rehydrating the dried pulp sheet to a specified consistency and then subjecting the rehydrated pulp sheet to hydraulic entangling.
The hydraulic entangling may take place while the pulp fiber layer 118 is highly saturated with water. For example, the pulp fiber layer 118 may contain up to about 90 percent by weight water just before hydraulic entangling. Alternatively, the pulp fiber layer may be an air-laid or dry-laid layer of pulp fibers.
Hydraulic entangling a wet-laid layer of pulp fibers is desirable because the pulp fibers can be embedded into and/or entwined and tangled with the continuous filament substrate without interfering with “paper” bonding (sometimes referred to as hydrogen bonding) since the pulp fibers are maintained in a hydrated state. “Paper” bonding also appears to improve the abrasion resistance and tensile properties of the high pulp content composite fabric.
The hydraulic entangling may be accomplished utilizing conventional hydraulic entangling equipment such as may be found in, for example, in U.S. Pat. No. 3,485,706 to Evans, the disclosure of which is hereby incorporated by reference. The hydraulic entangling of the present invention may be carried out with any appropriate working fluid such as, for example, water. The working fluid flows through a manifold which evenly distributes the fluid to a series of individual holes or orifices. These holes or orifices may be from about 0.003 to about 0.015 inch in diameter.
In the hydraulic entangling process, the working fluid passes through the orifices at a pressures ranging from about 200 to about 2000 pounds per square inch gage (psig). At the upper ranges of the described pressures it is contemplated that the composite fabrics may be processed at speeds of about 1000 feet per minute (fpm).
The fluid impacts the pulp fiber layer 118 and the nonwoven substrate 120 which are supported by a foraminous surface which may be, for example, a single plane mesh having a mesh size of from about 40×40 to about 100×100. The foraminous surface may also be a multi-ply mesh having a mesh size from about 50×50 to about 200×200. As is typical in many water jet treatment processes, vacuum slots 138 may be located directly beneath the hydro-needling manifolds or beneath the foraminous entangling surface 132 downstream of the entangling manifold so that excess water is withdrawn from the hydraulically entangled composite material 136.
While not being held to a particular theory of operation, it is believed that the columnar jets of working fluid which directly impact pulp fibers laying on the nonwoven continuous filament substrate work to drive those fibers into and partially through the matrix or nonwoven network of filaments in the substrate. When the fluid jets and pulp fibers interact with a nonwoven continuous filament web having the above-described bond characteristics (and a denier in the range of from about 5 microns to about 40 microns) the pulp fibers are also entangled with filaments of the nonwoven web and with each other. If the nonwoven continuous filament substrate is too loosely bonded, the filaments are generally too mobile to form a coherent matrix to secure the pulp fibers. On the other hand, if the total bond area of the substrate is too great, the pulp fiber penetration may be poor. Moreover, too much bond area will also cause a splotchy composite fabric because the jets of fluid will splatter, splash and wash off pulp fibers when they hit the large non-porous bond spots. The specified levels of bonding provide a coherent substrate which may be formed into a pulp fiber composite fabric by hydraulic entangling on only one side and still provide a strong, useful fabric as well as a composite fabric having desirable dimensional stability.
In one aspect of the invention, the energy of the fluid jets that impact the pulp layer and substrate may be adjusted so that the pulp fibers are inserted into and entangled with the continuous filament substrate in a manner that enhances the two-sidedness of the fabric. That is, the entangling may be adjusted to produce high pulp fiber concentration on one side of the fabric and a corresponding low pulp fiber concentration on the opposite side. Alternatively, the continuous filament substrate may be entangled with a pulp fiber layer on one side and a different pulp fiber layer on the other side to create a composite fabric with two pulp-rich sides. In that case, hydraulically entangling both sides of the composite fabric is desirable.
After the fluid jet treatment, the composite fabric 136 may be transferred to a non-compressive drying operation. A differential speed pickup roll 140 may be used to transfer the material from the hydraulic needling belt to a non-compressive drying operation. Alternatively, conventional vacuum-type pickups and transfer fabrics may be used. If desired, the composite fabric may be wet-creped before being transferred to the drying operation. Non-compressive drying of the web may be accomplished utilizing a conventional rotary drum through-air drying apparatus shown in
It may be desirable to use finishing steps and/or post treatment processes to impart selected properties to the composite fabric 136. For example, the fabric may be lightly pressed by calender rolls, creped or brushed to provide a uniform exterior appearance and/or certain tactile properties. Alternatively and/or additionally, chemical post.
Turning now to the drawings and referring first to
In accordance with one aspect of the present invention, the primary gas stream 10 is merged with a secondary gas stream containing individualized wood pulp fibers so as to integrate the two different fibrous materials in a single step. The individualized wood pulp fibers typically have a length of about 0.5 to 10 millimeters and a length-to-maximum width ratio of about 10/1 to 400/1. A typical cross-section has an irregular width of 30 microns and a thickness of 5 microns. Thus, in the illustrative arrangement a secondary gas stream 14 is formed by pulp sheet divellicating apparatus of the type described and claimed in U.S. Pat. No. 3,793,678, entitled “Pulp Picking Apparatus with Improved Fiber Forming Duct.” This apparatus comprises a conventional picker roll 20 having picking teeth for divellicating pulp sheets 21 into individual fibers. The pulp sheets 21 are fed radially, i.e., along a picker roll radius, to the picker roll 20 by means of rolls 22. As the teeth on the picker roll 20 divellicate the pulp sheets 21 into individual fibers, the resulting separated fibers are conveyed downwardly toward the primary air stream through a forming nozzle or duct 23. A housing 24 encloses the picker roll 20 and provides a passage 25 between the housing 24 and the picker roll surface. Process air is supplied to the picker roll in the passage 25 via duct 26 in sufficient quantity to serve as a medium for conveying the fibers through the forming duct 23 at a velocity approaching that of the picker teeth. The air may be supplied by any conventional means as, for example, a blower.
It has been found that, in order to avoid fiber floccing, the individual fibers should be conveyed through the duct 23 at substantially the same velocity at which they leave the picker teeth after separation from the pulp sheets 21, i.e., the fibers should maintain their velocity in both magnitude and direction from the point where they leave the picker teeth. More particularly, the velocity of the fibers separated from the pulp sheets 21 preferably does not change by more than about 20% in the duct 23. This is in contrast with other forming apparatus in which, due to flow separation, fibers do not travel in an ordered manner from the picker and, consequently, fiber velocities change as much as 100% or more during conveyance.
In order to maintain the desired fiber velocity, the duct 23 is positioned such that its longitudinal axis is substantially parallel to the plane which is tangent to the picker roll 20 at the point at which the fibers leave the influence of the picker teeth. With this orientation of the duct 23, fiber velocity is not changed by impingement of fibers on the duct walls. Thus, where the pulp sheets 21 are radially fed to the picker in a plane which is substantially parallel to the primary air stream, the plane which is tangent to the picker roll 20 at the point of contact with the pulp sheets is perpendicular to the primary air stream. Accordingly, since for the schematic embodiment illustrated in
The width of the duct is approximately equal to the height of the picker teeth on the roll 20, the passage between the picker teeth and the picker roll housing 24 being very small. With such a duct width, the velocity of the process air supplied through the process air duct 26 remains substantially constant in its travel with the picker and thence through the duct 23. Furthermore, because the velocity of the process air approaches that of the picker teeth, which in turn is about the same as the velocity of the separated fibers, the process air causes no substantial variations in fiber velocity in the duct 23. With duct widths approximately equal to the height of the picker teeth, e.g., no more than about 1.5 times the tooth height, air velocities in the forming duct 23 of at least 70% of the picker tooth velocity are useful in the illustrated apparatus.
Duct length and transverse width, i.e., the width in a direction along the picker roll axis, are also important in order to achieve an optimum web. Preferably, the duct length should be as short as the overall equipment design will allow. For the apparatus schematically illustrated in
As illustrated in
The capacity of the air stream which attenuates the polymeric microfibers and entrains surrounding air is always larger than the volume of air used to introduce the pulp fibers. The primary air jet typically increases in volume flow more than five-fold before the maximum jet velocity has decreased to 20% of its initial value. However, the pulp fibers are introduced early in the zone of diffusion of the microfiber jet in order to expose the fiber mixture to the intense small-scale turbulence in this area of the diffusion zone, and to mix the fibers while the polymeric microfibers are in a soft nascent condition at an elevated temperature. In the later stages of diffusion of the microfiber jet, the scale of turbulence becomes large compared to the fiber entanglements, and the energy in turbulence is continuously decreasing. The combination of a high-intensity and small-scale turbulence field provides maximum mechanical containment of the small pulp fibers within the matrix of microfibers.
Deceleration of the high-velocity gas stream carrying the microfibers frees the microfibers from the drawing forces which initially form them from the polymer mass. As the microfibers relax they are better able to follow the minute eddies and to entangle and “capture” the relatively short wood pulp fibers while both fiber types are dispersed and suspended in a gaseous medium. The resulting combination is an intimate mixture of wood pulp fibers and polymeric microfibers integrated by physical entrapment and mechanical entanglement while suspended in space. It is preferred to initiate the combining action while the microfibers are still in a softened state at an elevated temperature.
Attenuation of the microfibers occurs both before and after the entanglement of these fibers with the pulp fibers. The total attenuation is from a fiber diameter of about 0.015 inch (which is a typical diameter for the die apertures) to about 5 microns (0.0002 inch) or less. Most of the attenuation occurs within about three inches of the die face, before the air velocity in the fiber stream drops below about 250 feet/second. Since the wood pulp fibers are typically introduced into the microfiber stream about one inch from the die face, attenuation of the microfibers may continue after the merger with the pulp fibers. Due to their extremely small cross-section, the polymeric microfibers are at least 50 to 100 times more flexible than conventional textile fibers made from the same polymer, and are even more flexible and conformable when freshly formed and hot.
Because the microfibers are much longer, thinner, limper and more flexible than the wood pulp fibers, the microfibers twist around and entangle the relatively short, thick and stiff pulp fibers as soon as the two fiber streams merge. This entanglement interconnects the two different types of fibers with strong, persistent inter-fiber attachments without any significant molecular, adhesive or hydrogen bonds. In the resulting matrix the microfibers retain a high degree of flexibility, with many of the microfibers being spaced apart by engagement with the comparatively stiff pulp fibers. The entangled pulp fibers are free to change their orientation when the matrix is subjected to various types of distorting forces, but the elasticity and resiliency of the microfiber network tends to return the pulp fibers to their original positions when the distorting forces are removed. A coherent integrated fibrous structure is formed solely by the mechanical entanglement and interconnection of the two different fibers.
The microfibers and the nature of their anchorage to the wood pulp fibers provide yielding “hinges” between the fibers in the final structure. The fibers are not rigidly bonded to each other, and their connection points permit fiber rotation, twisting and bending. At even moderate microfiber contents, the structure is capable of providing textile-like properties of “hand” and drape, and is conformable while retaining a degree of elasticity and resiliency. Even when wet with water, which softens the wood pulp fibers, the material exhibits flexural resiliency and a wet strength comparable to its dry strength.
The wood pulp fibers are preferably distributed uniformly throughout the matrix of microfibers to provide a homogeneous material.
In order to convert the fiber blend in the integrated stream 15 into an integral fibrous mat or web, the stream 15 is passed into the nip of a pair of vacuum rolls 30 and 31 having foraminous surfaces that rotate continuously over a pair of fixed vacuum nozzles 32 and 33. As the integrated stream 15 enters the nip of the rolls 30 and 31, the carrying gas is sucked into the two vacuum nozzles 32 and 33 while the fiber blend is supported and slightly compressed by the opposed surfaces of the two rolls 30 and 31. This forms an integrated, self-supporting fibrous web 34 that has sufficient integrity to permit it to be withdrawn from the vacuum roll nip and conveyed to a wind-up roll 35 (not shown).
The containment of the wood pulp fibers in the integrated fibrous matrix, and the other characteristics noted above, are attained without any further processing or treatment of the airlaid web. However, if it is desired to improve the strength of the composite web 34, it maybe embossed either ultrasonically or at an elevated temperature so that the thermoplastic microfibers are flattened into a film-like structure in the embossed areas. This film-like structure functions to hold the pulp fibers more rigidly in place in the embossed areas. Thus, in the illustrative process of
This process permits utilization of all the advantages of a melt-blowing process for forming a fibrous mat, while at the same time permitting integration of the melt-blown microfibers with different amounts and types of wood pulp fibers that can be selected to provide the final product with a variety of different combinations of desired properties that cannot be realized by the use of a melt-blowing process alone. Consequently, this process can be used to produce different materials that are especially tailored for a wide variety of different applications. By using the process of this invention to integrate wood pulp fibers with the microfibers produced by the melt-blowing operation, the liquid retention and absorbency characteristics of a cellulosic mat can be improved to a level that makes the mat perfectly suitable for use as a wipe. The composite fabric can be modified by secondary thermal treatments such as hot calendering, embossing or spot bonding.
A wide variety of thermoplastic polymers are useful in forming the melt-blown microfibers, so that materials can be fashioned with different physical properties by the appropriate selection of polymers or combinations thereof. Among the many useful thermoplastic polymers, polyolefins such as polypropylene and polyethylene, polyamides, polyesters such as polyethylene teraphthalate, and thermoplastic elastomers such as polyurethanes are anticipated to find the most widespread use in the preparation of the materials described herein.
The picker roll shown in the illustrative arrangement is preferred for producing the secondary air stream containing the wood pulp fibers. However, other devices may be used to generate secondary air streams containing additional fibrous and/or particulate materials, including synthetic fibers such as staple nylon fibers and natural fibers such as cotton, flax, jute and silk. If desired, the wood pulp fibers and an additional material may be carried in a single secondary air stream.
In order to achieve a particular combination of properties in the final fibrous web, there are a number of variables in both the primary and secondary air streams that can be controlled along with the composition and basis weight of the web. Process parameters susceptible to control in the primary gas stream are the gas temperature; the gas velocity, which is preferably in the sonic range within the die; the polymer extrusion rate, which is preferably in the range of 0.25 grams per hole per minute; the polymer temperature; and the ratio of air to polymer (mass flow rates) which is preferably in the range of 10/1 to 100/1. Variables that can be controlled in the secondary gas stream are the gas flow rate and velocity of the picker roll; the gas velocity which is preferably in the sub-sonic range, e.g., 50-250 feet per second; and the fiber size which is typically on the order of 3.0 millimeters in length. The relationship between the primary and secondary gas streams can also be controlled, and it is generally preferred that the ratio of the gas velocities in the primary and secondary streams be in the range of from 5/1 to 10/1. The relative percentages of the materials introduced by the primary and secondary gas streams may vary over a wide range, but it is typical for the polymeric microfiber to comprise from about 1% to 80% by weight of the final mat. The angle between the primary and secondary gas streams at the point of their merger may also be varied, but it is generally preferred to have the two streams come together perpendicular to each other. Similarly, the particular point at which the two streams are merged, relative to the melt-blowing die in the upstream direction and foranimous forming surface in the downstream direction, may be varied.
In one desired aspect of the invention, the nonwoven polymer comprises polypropylene, and the ratio of indicator fibers to the polypropylene is 80:20. It is also contemplated that the ratio of indicator fibers to the polypropylene is 75:25. It is further contemplated that the ratio of indicator fibers to the polypropylene is 95:5. Other polymers may be substituted for the polypropylene, and other ratios ratio of indicator fibers to a polymer range from 95:5 to 70:20.
Several hand-sheet samples having a basis weight of 60 gsm were formed using a standard hand-sheet former. Each hand sheet contained 0 percent to 98 percent blend by dry-weight of wood fibers obtained from KLEENEX brand tissue samples, and 2 percent to 100 percent indicator pulp by dry-weight. Indicator pulp was made by chemically bonding the pH indicator dye bromothymol blue to wood fibers.
The hand sheets were hydroentangled with polypropylene spunbond (0.35 osy/12 gsm) to form a nonwoven substrate. Sets of nonwoven substrate samples were air-dried and subsequently insulted with different pH buffer solutions having one of the following pH levels: 3, 4, 5, 6, 7, 8 and 9.
As can be seen in
By comparing
Referring to
After an initial insult, the sample shown in 4B was insulted with an acid buffer solution to test the reversibility of the color change. A rapid color reversal was noted (see
While the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.
