HK1033291A - Spray application of an additive composition to sheet materials - Google Patents

Description

Spraying an additive composition onto a sheet

Technical Field

The present invention relates generally to the application of additive compositions to sheet materials in the manufacture of sheet products such as paper, textiles and flexible sheet materials. More particularly, the invention relates to a method of spraying an additive composition onto sheet material during the manufacture of sheet material products using a pressurized fluid to enhance atomization and a spray formulation having a low volatile solvent content and high viscosity.

Background

Many industrial processes spray liquid compositions containing volatile solvents to achieve application of coatings, adhesives or additives, or spray dry materials. Solvents serve a variety of functions, such as for dissolving various materials, as a carrier medium for emulsions or dispersions, to reduce viscosity for spray application, and to provide suitable flow characteristics after spray application, for example to form a film on a substrate or to penetrate into porous or absorbent materials. However, the organic solvent becomes a major source of air pollution in the workplace and the environment and may cause fire during the manufacturing process.

Therefore, water is often used as a solvent to avoid these problems. However, water may also have its disadvantageous properties, and it is therefore desirable to use it as little as possible in the manufacturing process. Many materials to be sprayed are insoluble in water and thus chemical agents such as surfactants have to be used to emulsify or disperse these materials into water to form a stable form. Water has a low evaporation rate and a high heat of evaporation, resulting in slow and high energy consumption of the product to dry, and must be heated to a temperature that may cause degradation in order to increase the drying rate. Since less water is evaporated during spraying than when volatile organic solvents are used, the viscosity of the spray composition after deposition is often too low to meet the requirements for proper application and therefore its performance is also deteriorated. Furthermore, some substrates are incompatible with water; they degrade by absorbing water, which can result in swelling or reduced cohesion, or the aqueous composition does not wet the substrate properly because the interfacial tension of water is high or the substrate is hydrophobic.

Successful and economical spraying of the composition depends on the spray properties produced by the spraying method, in addition to the volatile solvent and the viscosity characteristics of the spray composition. It is particularly desirable that the spray produced by the spray method has a favourable droplet size, and depending on the application, a narrow droplet size distribution, which means that too large droplets are reduced, which generally results in poor spray quality, but also too small droplets, which will become flying, resulting in insufficient deposition and increased material consumption. It is also desirable that the spray pattern (spray shape) have uniform interior and tapered edges so that the composition can be applied uniformly during spraying. The velocity of the jet should not be too high or too low, or excessively turbulent. The fan jet should be of the appropriate width for a given application and provide good pattern control so that the composition is applied in the desired amounts and locations. It is also desirable that the spray coating process used be capable of atomizing high viscosity compositions so as to minimize or eliminate the use of volatile solvents.

Conventional spray coating methods, such as air spray and airless spray, while each having their advantageous properties, still suffer from disadvantageous characteristics that may limit the applicability of the compositions for application during manufacture. Air spray methods provide a tunable, uniform, feathered fan spray and fine atomization, but they require low viscosity, typically 50 to 100cp (centipoise), and therefore they require the use of high proportions of volatile solvents. Air sprays are again highly turbulent and they generate a very broad droplet size distribution, causing a large proportion of too small droplets to become paint-fly and reduce application efficiency. Airless spray processes can atomize higher viscosity materials with low solvent content, but they typically produce atomized particles that are coarse and have too large droplet sizes to be suitable for many applications. Airless spraying also produces a non-uniform trailing or fishtail-shaped trailing spray pattern, which makes it difficult to achieve uniform application of the composition.

Conventional atomization mechanisms for airless spray coatings are known in the art. Roughly speaking, the material emerges from the nozzle orifice at normal pressure as a liquid film that becomes unstable under the shear induced by its relatively higher velocity than the surrounding air. The wave grows gradually in the liquid film, becomes unstable and breaks up into liquid filaments, which likewise become unstable and break up into droplets. The cohesive and surface tension forces of the collected liquid are overcome by the shear and fluid inertia forces that break it up, and atomization occurs. Often, the liquid film is atomized into droplets after exiting the nozzle orifice by a distance sufficient to be visible to the naked eye. The spray is generally conical in shape with a fan width comparable to the fan width of the nozzle tip. Viscous dissipation greatly reduces the atomization energy, resulting in a coarser atomization for higher viscosities. The terms "liquid film spray" and "liquid film atomization" as used herein refer to a spray, jet or spray pattern (jet shape) in which atomization is by such conventional mechanisms. The liquid film jet is characterized in that it forms a "trailing" or "fish tail" spray pattern in which the material is unevenly distributed in the jet. The effect of surface tension often concentrates more liquid at the edges of the spray and less liquid is distributed in the center, which produces a coarse atomized jet of material that sometimes deviates from the spray. Examples of liquid film spraying are given in figures 4a, 4b, 4c, 4d, 10a, 11a, 12a and 12b of us patent 5,057,342, and figures 3a, 3b, 3c, 9a, 9b and 9c of us patent 5,009,367, which are shown in photographic form.

Supercritical or subcritical compressed fluids, such as carbon dioxide or ethane, can produce a novel airless spray atomization mechanism that produces fine droplet sizes and plume-like spray beams required for high quality coating applications. Without wishing to be bound by theory, it is believed that the formation of such an aerosol is such that: a dissolved compressed fluid, such as carbon dioxide, transitions to a supercritical state when the spray mixture experiences a sudden drop in pressure within the nozzle orifice. This results in a very large driving force for gasification, followed by very fine bubbles of carbon dioxide to convert the solution into a gas-liquid mixture. It is believed that this will change the flow pressure by reducing the sonic velocity of the obstructing fluid to a level equal to the fluid velocity, thus, instead of dropping the pressure to atmospheric pressure, the flow will leave the nozzle orifice at a higher pressure. This will create a pressure zone outside the nozzle orifice where the spray mixture is free to expand to atmospheric pressure. The released carbon dioxide expands and creates an expansion force that overcomes the various liquid forces that would normally bring the fluid streams together. The only factor that constrains the expansion is to shape the jet into a flat or elliptical fan-shaped channel along the cross-section of the outlet. The jet width can be adjusted by changing the pitch of the grooves. This is clearly a different atomisation mechanism, since atomisation occurs at the nozzle orifice, not at a distance from the nozzle. No liquid film was visible at the nozzle orifice. Also, in typical cases, the angle at which the spray exits the nozzle is much wider than in typical airless spray and produces a "plume" with tapered edges as in air spray. This often produces a round, parabolic spray rather than an acute spray shape. Such a jet typically has a fan width that is wider than a conventional airless jet produced with the same nozzle. The terms "decompressed spray" and "decompressed atomization" as used herein refer to a spray, jet, or spray pattern having the characteristics described herein. Examples of decompression sprays can be found in figures 3a, 3b, 3c, 3d, 3e, 10b, 11b, 12c, 12d and 13 of us patent 5,057,342, and figures 4b, 4c, 8 and 9d of us patent 5,009,367, which are shown in photographs.

As the concentration of a supercritical fluid or subcritical compressed fluid, such as carbon dioxide, increases, the spray of liquid film may undergo a transition to a decompressed spray. In the case of suitable concentrations, this transition can also occur with increasing temperature. The transition occurs within a narrow interval of concentration or temperature. As the concentration increases, the film spray initially maintains a generally cone-angle shape and has a relatively constant or slightly increasing width, i.e., the width characteristic obtained when the composition is not sprayed with carbon dioxide, and the average droplet size is also relatively large. But a typical macroscopic liquid film can be observed to recede towards the nozzle aperture. The main source of fogging arises from shear-induced instability caused by interaction with ambient air. The spray shape is controlled mainly by the forces of the liquids. The boundary between the liquid film sections generally appears near the carbon dioxide concentration at the time of disappearance of the liquid film. Later, as the concentration increases, the spray crosses a transition zone where the typical spray pattern will change dramatically, depending on the composition, from a liquid film to a decompressed spray and change its atomization mechanism. Typically, the spray shape and width of the transition zone will vary significantly with small changes in carbon dioxide concentration.

For certain compositions, the spray pattern will collapse abruptly from a flat fan into a narrower, irregular, cone-shaped spray and then expand into a wider, flat, parabolic decompression spray. Sometimes the jet breaks down completely into a single circular jet, or becomes 2, 3 or more jets separated from each other along irregular angles, and finally expands into a decompressed jet. For other compositions, the spray pattern remains generally planar, but the central portion projects outwardly as the spray narrows further, and then retracts gradually as the spray expands to decompress the spray. Sometimes the spray maintains a planar shape, while a decompressed spray pattern is formed that is superimposed on the liquid film spray pattern, which then swirls away. For still other compositions, the pyramidal spray pattern initially largely widens and then changes to a parabolic shape.

The transition zone spray is irregular and often unstable because both the expansion force from the carbon dioxide and the liquid force of the composition do not dominate the atomization and formation of the spray shape, although at this point the atomization has become primarily caused by decompression of the carbon dioxide gas. The different types of spray transition laws are determined by the different surface tensions and the rheological properties of the different compositions.

A decompression spray is formed when the carbon dioxide concentration becomes sufficiently high that the expansion force of the decompression carbon dioxide dominates with increasing outlet pressure. The resulting decompressed spray, while desirably substantially planar, is in most cases parabolic in shape, but in some cases is more nearly conical in shape than it is circular near the nozzle orifice, but may be much wider than the corresponding film spray. Near the edge of the spray, the decompressed spray may have some degree of spray, or the central portion of the spray may have some degree of protrusion, so the spray pattern may protrude. However, at higher decompressed fluid concentrations, these phenomena will generally dissipate and the spray pattern will become more uniform.

In addition to being wider, the planar decompressed spray is generally thicker along the entire spray plane than a corresponding liquid film spray. One of the features of the transition from the liquid film to the decompressed jet is the significant reduction in the mean droplet size of the jet. Us patent 5,057,342 gives examples of the transition from a liquid film to a decompressed spray in its figures 12a-12 d.

Generally, the decompressed spray interval occurs in a region below but already near the solubility limit, thus requiring the proper combination between spray temperature, pressure and carbon dioxide concentration. The solubility limit, and hence the spray conditions required for a depressurized spray, will vary from composition to composition. Spraying of the coating in a region significantly within the two-phase region is avoided since a substantial portion of the organic solvent is generally extracted from the liquid polymer phase to the liquid carbon dioxide phase.

To reduce the release of organic solvents, various aqueous coatings have been developed. However, as mentioned above, the rate of evaporation of water is not high and therefore the amount of water evaporated from the spray is often insufficient. While the spray is depressurized, it has been found that the evaporation of water is enhanced, although less evaporation occurs with less volatile solvents. While not wishing to be bound by theory, it is believed that this high evaporation rate is due to the exceptionally high mass transfer rate during the formation of the decompressed jet, which is caused by the compressed fluid in solution vaporizing at an extremely fast rate. High and medium evaporation rate solvents are affected to a much greater extent by this strong mass transfer condition than are slow evaporating solvents.

Additive compositions are almost uniformly applied in the papermaking process using aqueous solutions, emulsions or dispersions, where water acts as a viscosity reducing agent and volatile solvent. However, the application of additives in the wet end of the papermaking process is generally undesirable because expensive additives will be drained from the wet paper web along with the water, which also creates waste water disposal problems, and the additives applied in the wet end can interfere with the operation of the drying cylinder and tissue creping machine because it can result in a loss of web control. Furthermore, if added at the wet end, it is difficult to control how certain treating agents, such as surface treating agents, are added to the paper product. Thus, it is desirable to apply various additives at the dry end, but the water added along with the aqueous additive composition is detrimental to the dried paper product. For example, when the moisture content exceeds 7%, the paper may be debonded and also have an adverse effect on caliper and tensile strength. For example, beyond a moisture content of 9%, the tensile strength of the tissue may be reduced by as much as 15%. The aqueous composition also penetrates throughout the web, resulting in the additive being dispersed into the interior, rather than residing on the surface that is generally most effective. Since air spray processes for applying aqueous additive compositions require low viscosity for proper atomization, but little evaporation of the water from the spray, the water content of the additive composition deposited on the web must exceed the desired level. However, a reduction in the water content leads to insufficient atomization. One disclosed method for counteracting the addition of excess water is to overdry and heat the web, but this consumes a significant amount of energy and the overdrying or overheating of the web can also have negative effects.

Airless atomization of viscous compositions, such as hot melt, anhydrous, semi-solid, or solid additive compositions, typically results in rough atomization and uneven spray patterns that result in improper application to the surface to which they are applied. Heating the hot melt to high temperatures to further reduce the viscosity can lead to degradation of the sprayed additive composition. Thus, a method using gravure coating or extrusion coating has been disclosed as a preferred application method for applying such a composition.

Similarly, in the manufacture of textile products, it would be advantageous if the applied additive composition, such as a surface treatment, were free of water or could be applied in an amount containing less water than is required using conventional spray coating methods. Such application would enable the composition to be applied more efficiently and effectively without requiring subsequent supplemental drying.

In the manufacture of flexible sheet products, such as plastic films, plastic laminated sheets, plastic reinforced sheets, plastic impregnated sheets, rubber sheets, leather, fiber reinforced sheets, porous sheets, mesh sheets, extruded films, composite sheets, and composite laminated sheets, it is often necessary to apply additives to the sheets to alter or improve the properties of the sheets. However, the use of aqueous additive compositions is often not suitable because the sheet itself is hydrophobic or poorly wetted or is not allowed to dry and is therefore not compatible with water. Similarly, the use of volatile solvents is often undesirable because they are flammable, or because the solvent is not sufficiently evaporated to degrade the sheet product, for example, due to swelling or plasticization caused by solvent absorption or because the processing time is too short. It can be seen that it would be advantageous to be able to spray the additive composition onto a moving flexible sheet without the use of water or volatile solvents, or with a greatly reduced amount of water and/or solvent.

Clearly, there is a need for an improved method of applying an additive composition in the manufacture of sheet products such as paper, textiles and various flexible sheet products which allows the additive composition to be applied in a waterless and reduced application water content form, which does not require volatile solvents, which reduces the atomizing viscosity and which provides improved spray performance and droplet size and ultimately acceptable spray results. In addition to providing various benefits over existing application methods, this new technology allows the development and application of new additives that heretofore have been unavailable for spray application without the use of volatile solvents, either because they are insoluble or non-dispersible or otherwise incompatible with water, or do not allow for adequate atomization using conventional spray application methods.

Summary of The Invention

By means of the present invention, a method has been found which achieves the above-mentioned objects. In accordance with the present invention, the additive composition can be sprayed onto sheet materials during the manufacture of sheet materials such as paper, textile and flexible sheet materials, wherein the additive composition is substantially free of water or volatile organic solvents or both, and can reduce the atomizing viscosity and improve the spray performance and droplet size to achieve the spray. The improved sheet product can be more efficiently manufactured and utilize more expensive additive materials, and produces less waste.

The present invention provides a method of spraying an additive composition comprising at least 1 additive material during the manufacture of a sheet product. In general, the method comprises the steps of:

(1) preparing a liquid mixture comprising the additive composition and a compressed fluid in a closed pressure system;

(2) spraying the liquid mixture through a nozzle orifice to form a spray; and

(3) applying said spray comprising said additive composition to said sheet surface during the manufacture of said sheet product.

In a preferred aspect of the invention, the method employs a decompressive spray of compressed fluid that produces a uniform spray pattern and narrow droplet size distribution, thereby improving application efficiency and quality when the additive composition is applied to a rapidly moving sheet during the spraying step.

The present invention also relates to a method of spraying an additive composition onto a flexible sheet material during the manufacture of a flexible sheet material product, wherein the additive composition is capable of at least adhering to, penetrating into, or being absorbed into the surface or interior of the flexible sheet material.

Detailed Description

The production of the sheet product of the present invention from paper, textiles and flexible sheets will be described in detail below. A sheet is a substantially two-dimensional thin material having a thickness that is much smaller than its length and width.

The additive composition useful in the manufacture of sheet products according to the present invention typically comprises at least 1 additive material which alters or enhances the properties or performance of the product or which it is desired to apply to the sheet during the manufacture of the sheet product. The additives generally include any additive known to those skilled in the art to be suitable for spraying onto the sheet material.

The term "paper product" as used herein is understood to include any sheet material comprising paper fibers, which may also comprise other materials. Suitable paper fibers include natural and synthetic fibers, such as cellulose fibers, various wool fibers used in papermaking, other plant fibers, such as cotton fibers, fibers derived from recycled paper; and synthetic fibers such as rayon, nylon, glass fibers, or polyolefin fibers. The paper product may consist of synthetic fibres only. Natural fibers may be used in combination with synthetic fibers. For example, in the manufacture of paper products, the paper web or paper material may be reinforced with synthetic fibers, such as nylon or fiberglass, or impregnated with non-fibrous materials, such as plastics, polymers, resins, or lotions. The terms "paper web" and "sheet" as used herein should be understood to include paper sheets, paper, and paper materials comprising paper fibers that are being formed or have been formed. The paper product may be a coated, laminated, or composite paper material.

The present invention may also be used to prepare paper products known to those skilled in the art. Such paper products include, but are not limited to, writing paper, printing paper, industrial paper, various tissue papers, paperboard, wrapping paper, paper tapes, paper bags, paper cloths, towels, wallpaper, carpet backing, paper filters, paper felts, decorative paper, disposable liners, garments, and the like.

The invention is particularly applicable in the manufacture of tissue paper products known to those skilled in the art. Suitable tissue products include sanitary napkins, household tissues, industrial tissues, facial tissues, cosmetic tissues, soft tissues, absorbent tissues, pharmaceutical tissues, toilet tissue, paper towels, paper napkins, paper cloths, paper liners, and the like. Common paper products include printing grades (newsprint, catalogues, rotogravure, letterpress, banknote, document, bible, security, ledger, stationery); technical grade (bags, interior lining, corrugated media, construction paper, grease proofing paper, cellophane); and tissue grades (sanitary napkins, towels, condenser paper, wrapping paper).

The tissue may be a felt-pressed tissue, a pattern-densified tissue, or a high-loft, uncompacted tissue. The tissue paper may be creped or uncreped, may be homogeneous or composed of multiple plies, laminated or non-laminated (blended) and single, double or 3 or more plies taken together. Soft and absorbent tissue products are particularly important consumer tissue products.

Paperboard is a thicker, heavier and less flexible paper than ordinary paper. Many hardwood and softwood species undergo mechanical or chemical processing to separate fibers from the wood substrate to produce pulp.

Chemical additives and fillers are used to impart desired physical, optical or electrical properties to the paper product.

Continuous paper machines have experienced a full mechanical race. Cylinder-wire machines use a cylinder of wire-covered wire, which is mounted in a vat containing a fibre slurry. As the cylinder rotates, water drains through the wire into the cylinder and forms a web on the outside. A wet paper web of paper fibers is taken from above and passed through press rolls to remove water, which is then fed into a steam heated drying section.

Fourdrinier machines are common and more complex models. It can produce virtually any grade of paper or paperboard from 1 to 10m width. It consists of a continuous elongated copper mesh supported by a number of drainage means. The fiber slurry or liquid slurry enters from one end and continuously loses water and is formed into a sheet as it moves along the wire, and then is sent to a press and dryer. The slurry, once deposited on the forming wire, is referred to as a paper web. After stock preparation and dilution, the dancer roll discharges the stock evenly across the width of the paper machine into the headbox, where a suitable head discharges the slurry at the correct velocity through a weir onto the moving fourdrinier wire. Wire (copper mesh) is a finely woven continuous belt-like forming medium, made of plastic or metal. The copper wire is fitted around the breast roll at the feed end and around the couch roll at the discharge end. Between the breast roll and the couch roll, the copper wire is supported by a foil and suction boxes for water removal. Machine speeds vary depending on the paper product being produced and the equipment used. The heavy paperboard requires long drying time, so the speed is between 50 and 250 m/min. The very dense paper is difficult to dewater, and the machine speed is in the range of 20-300 m/min. The brown packaging grade paper product is produced at a speed of 200-1000 m/min. The machine for producing newsprint operates at a speed in the range of 800 to 1200 m/mih. The speed of modern tissue machines is limited to 1500-1800 m/min by the limitations of drying capacity and paper product winding, most of which operate at lower speeds, but some operate at speeds up to 2000 m/min.

Virtually all new paper machines are twin fourdrinier wire forming machines because such machines provide more stable high speed operation and better control of forming and dewatering conditions. Water is removed from the slurry under pressure rather than under vacuum. Many large fourdrinier machines are retrofitted to the wet end and a veil unit is added in order to achieve similar advantages in high speed operation, especially for making low basis weight paper product sheets (towels, newsprint). Twin fourdrinier machines are also used to produce fine paper and corrugated media and linerboard grade products. The 2 fourdriniers, with the slurry in between, are wrapped around a drum or a set of support bars or chopping boards. The tension in the outer wire transmits pressure through the slurry to the support structure. The slurry is continuously drained under pressure through one or both of the 2 fourdriniers. In a typical roll twin-wire tissue forming machine, drainage is from one side and is limited to a low basis weight, which is sufficient to allow for smooth drainage of the tissue at very high speeds of 2100 m/min.

The forming unit receives a low consistency slurry fed at a typical value of between 100 and 300kg water/kg solids; whereas the web leaving the couch roll has a consistency of about 4kg water/kg solids. Further water is removed by 1 or more rotating press rolls, which is much more economical than removing water by heating. The paper web is pressed between the surfaces of successive felts, which are a conveyor belt and are porous water receivers. The moisture content of the paper sheet is reduced by pressing to about 1.2-1.9 parts water per part fiber. The final removal of the water must be carried out by evaporative drying, which is costly and constitutes a production limitation. The drying section is typically a series of steam heated drying cylinders. The paper web is typically held against the dryer surface by a fabric. The final moisture content of the dry web is typically in the range of 4 to 10 wt%. The dried web is calendered through a series of nips to reduce caliper and smooth the surface, and then wound onto a paper roll.

Various wet laid felts and nonwovens can also be produced using fourdrinier papermaking machines. Non-cellulosic materials, such as synthetic fibers, may also be included as part or all of the fiber furnish; a water soluble polymer or other binder is used as the binder. Synthetic fibers can be made into paper that is highly resistant to moisture, chemical attack, mechanical abrasion (folding), weathering, and biodegradation.

The chemical agent may be added to the pulp slurry prior to web formation (internal or wet end addition) or to the fully or partially dried formed web (surface or dry end addition). If the additive is not satisfactorily retained on or in the web from the thin stock, it is preferably applied to the web surface. Processing additives can improve the operation of the paper machine. Functional additives can enhance the properties of the paper product, such as fillers, rosin or starch sizing agents, dyes and brighteners, wet strength resins, dry strength additives, pigment coatings to provide a smooth printing surface, polymers to provide mechanical or barrier properties. For certain types of paper or special grades of paper, various machine modifications and ancillary operations may be undertaken. Many paper machines include surface sizing, surface coating, and special calendering capabilities.

The wet strength of paper can be enhanced by natural and synthetic polymers, which have the ability to hydrogen bond, ionically or covalently enhance the hydrogen bonding between cellulose fibers that are destroyed by water when the paper is in the wet state. Papers such as tissue, towel, linerboard, carrier board (carrierboard), and bleached cardboard require wet strength to perform their intended function, which is typically provided by the addition of resinous materials. The primary wet strength resin used is an aminopolyamide-epichlorohydrin resin suitable for tissue and toweling.

While many functional chemicals can be added to the wet end of a paper machine, certain grades of paper are unsatisfactory because the amount of wet end additive trapped by the paper web is too low. This situation requires the application of special chemicals to the paper web being processed in order to achieve satisfactory properties.

Tissue paper includes a wide variety of low basis weight papers. Sanitary and household tissue products include facial tissues, bath tissues, toilet tissues, beauty tissues, handkerchiefs, paper towels, kitchen papers and napkins. It is mainly characterized by softness and water absorption. Paper towels are creped absorbent paper that absorbs water quickly, has a high water holding capacity, and has a high degree of warmth. Industrial tissue includes capacitor, carbonized, and wrapped grade products.

Tissue is generally not produced on conventional paper machines because some tissue-towel products have very low basis weights and others have a loose structure. Although there are a wide variety of types of tissue machines that have been used, the customary arrangement employs a combination of a fourdrinier wire forming section and a so-called "yankee dryer (yankee). Twin fourdrinier machines used in high speed tissue machines are gap roll formers (gap rolls) with drainage areas arranged in a "C" or "S" configuration. An important feature of all tissue-towel forming machines is that the wet paper web is supported throughout the forming, pressing and drying processes. The web is always not under tension prior to drying. Yankee cylinders are large diameter steam heated cylinders that dry the paper web from only one side. The wet paper web is pressed tightly against the highly polished surface. The drying cylinders are enclosed in an air hood, and the drying capacity can be improved by the impact of the high-speed airflow. Percolation drying, i.e. hot air penetration through the web, may be used to obtain a high quality tissue product. The web may or may not be calendered prior to reeling. Certain grades may be calendered on a supercalender after off-line.

The sanitary towel is usually creped just before it leaves the drying cylinder to increase water absorption and softness. Creping breaks the fiber-to-fiber bonds in the web, thereby increasing bulk. Mechanical creping is accomplished by peeling the paper web from the steel cylinder with a sharp doctor blade that is held at an angle to the cylinder surface. The quality of the creped web depends in part on its adhesion/release properties, which in turn depends on the dryer surface coating.

Textile products include cloth and clothing, household textiles such as bedsheets, towels, upholstery, carpets, curtains and wall coverings; and textile products for a variety of industrial uses, such as tire reinforcement, canvas, filter media, conveyor belts, insulation, and reinforcement media in various composite materials.

Textiles are woven, knitted and non-woven fabrics or felted fabrics made from staple fibers (of finite length) and filaments (of continuous length) by a variety of methods. The textile product may be a woven or non-woven product. In woven and knitted fabrics, fibers and filaments are formed into continuous lengths of yarn, which are then interwoven with one another by weaving or crocheted with one another by knitting to form a planar, flexible, sheet-like structure, known as a fabric. Nonwovens are made directly from fibers and filaments by chemical or physical bonding or interlocking of fibers that have been arranged in a planar configuration.

Textile fibers can be classified into the following categories according to their source: naturally occurring fibers, including those with cellulose as a major component (cotton, flax, hemp, jute, ramie, wood), or those composed of protein (wool, mohair, llama, silk); manufactured fibers composed mainly of cellulose or protein derivatives (rayon solvent, lyocell, acetate fibers, triacetate fibers, regenerated protein fibers); synthetic organic polymers (acrylonitrile, aramid, nylon, polyolefin, polyester, spandex, vinylon or vinylon, carbon/graphite, and specialty fibers); or of inorganic material (glass fibres).

Textile finishing processes include a variety of efforts directed to improving the performance of textile products, either for apparel, home use, or for other end uses. Such processing either alters the fiber characteristics or the final properties of the overall textile product. Such modifications may be of chemical or physical nature. Examples of such properties are shrink control, easy care properties, flame retardancy, stain release, smoldering resistance, weathering resistance or static control.

The additive composition which may be used in the process of manufacturing a textile product according to the invention generally comprises at least 1 additive material which is capable of modifying or enhancing the properties or performance of the textile product or which it is desired to apply to the textile material during the manufacture of the textile product.

The term "textile product" as used herein is understood to include any sheet material comprising textile fibres, however it is not limited to textile fibres and may also comprise other materials. Suitable textile fibers generally include those known to those skilled in the art, including, but not limited to, cellulosic fibers, such as cotton or linen; protein fibers, such as wool; cellulose or protein derivative fibers such as rayon and acetate fibers; synthetic organic polymer fibers such as acrylonitrile, aramid, nylon, polyolefin and polyester; inorganic fibers such as glass fibers; and the like. The fibers may be staple or filament and may be in the form of monofilament or multifilament yarns, or in the form of yarns or threads. The textile product may be woven or non-woven or knitted, felted, knotted, bonded or crocheted. It can have a wide variety of textures, finished basis weights, widths, and thicknesses. Suitable textile products include, but are not limited to, cloth, fabric, household textile products, industrial textile products, clothing, apparel, linings, sheets, towels, bandages, upholstery, carpets, curtains, wall coverings, insulation, mats, cloth adhesive tapes, and the like. The textile product may be coated, impregnated, laminated or a composite material. It may be of uniform construction or have a multilayer construction.

It will be appreciated that the invention may also be used to make a product which may be considered both a paper product and a textile product, since it comprises both paper and textile fibres. Such products include, but are not limited to, dryer sheets for softener applications, surgical gowns, industrial coveralls, duct tapes, adhesive tapes, and other composite fiber-based materials and products.

Flexible sheets that can be treated according to the present invention include plastic films, plastic laminated sheets, plastic reinforced sheets, plastic impregnated sheets, rubber sheets, leather, fiber reinforced sheets, porous sheets, mesh sheets, extruded films, composite sheets, and composite-laminated sheets. Suitable plastic films include polyolefin films such as polyethylene and polypropylene; cellophane, cellulose acetate film, and adhesive plastic films and tapes. A flexible sheet is a sheet that can bend and flex, such as when conveyed or wound on a roll. The flexible sheet material may be a porous or continuous film or sheet. It may be a coated, impregnated, laminated or composite material. It may be uniform or multilayered.

The additive composition that may be used in the process of making the flexible sheet product of the present invention generally comprises at least 1 additive material that is capable of at least adhering to, penetrating into, or being absorbed into the surface or interior of the flexible sheet material, which can alter or enhance the properties or performance of the finished flexible sheet product, or which it is desired to apply to the flexible sheet material during the flexible sheet material manufacturing process.

The term "compressed fluid" as used herein is understood to mean a fluid which may be in a gaseous state, a liquid state, or a combination of these 2 states, or a supercritical fluid depending on (i) the particular temperature and pressure at which the fluid is located, (ii) the vapor pressure of the fluid at that particular temperature, and (iii) the critical temperature and critical pressure of the fluid, yet which is in its gaseous state at standard conditions (STP) of 0 ℃ temperature and 1 atm absolute. As used herein, the term "supercritical fluid" is a fluid at a temperature and pressure that determine whether it is above or slightly below its critical point.

Compounds that may be used as the compressed fluid in the present invention include, but are not limited to, carbon dioxide, nitrous oxide, ammonia, xenon, ethane, ethylene, propane, propylene, butane, isobutane, and mixtures thereof. Preferably, the compressed fluid is or can be converted to-environmentally compatible or readily recoverable from the spray environment. The suitability of any of the above-described compressed fluids in the practice of the present invention will depend on the composition used, the application temperature and pressure, and the inertness and stability of the compressed fluid. Nitrous oxide should only be used under safe and stable conditions. Carbon dioxide and ethane are preferred compressed fluids for environmental compatibility and low toxicity. Carbon dioxide is generally the most preferred compressed fluid due in turn to its low cost and nonflammability and wide availability. However, the use of any of the above-described compressed fluids and mixtures thereof should be considered within the scope of the present invention.

As used herein, the terms "additive composition," "additive material," "aqueous additive composition," and "aqueous composition" refer to compositions and materials into which the compressed fluid is not mixed. The additive composition generally comprises more than one additive material. The term "additive material" as used herein refers to a chemical or component or mixture thereof that is applied to the sheet material. The term "sheet product" as used herein refers to a sheet to which the additive composition has been applied.

The term "manufacture" as used herein is to be understood to encompass the manufacture, production, shaping, or fabrication of a sheet product, as well as the alteration, manipulation, transformation, alteration, processing, and modification of such a sheet product.

The term "solvent" as used herein refers to a conventional solvent including water, which is not mixed with a compressed fluid and which is liquid at a temperature of about 25 ℃ and 1 atm absolute.

The method of the present invention can be used to spray apply an additive composition comprising at least 1 additive material in the manufacture of a paper product, such as a tissue paper product, or in the manufacture of a textile product or a flexible sheet product.

The additive materials in the additive composition that can be applied in the method of the present invention include additives that are many in variety to perform a variety of different functions or to provide a variety of different properties to the treated sheet. Additive materials included in additive compositions that provide certain properties or characteristics to sheets treated in accordance with the present invention include, but are not limited to, at least 1 of softeners, lubricants, moisturizers, lotions, pastes, conditioners, absorbents, hydrophilizers, strippers, adhesives, coatings, soaps, sunscreens, surfactants, oils, waxes, polymers, rosins, resins, oleoresins, colorants, dyes, brighteners, hiding agents, ultraviolet light absorbers, flame retardants, antioxidants, vitamins, fragrances, perfumes, deodorants, antimicrobials, disinfectants, drugs, astringents, tackifiers, adhesives, antistatic agents, crosslinkers, plasticizers, curing agents, preservatives, protectants, wetting agents, stabilizers, inhibitors, modifiers, chemicals, and the like. The additive may be a product additive or a processing additive.

Softeners are additive materials that impart sensory softness to the product. Softening additives include a wide variety of silicones, oils, waxes, fatty alcohols and other materials. Emollients are additive materials that have a softening, soothing, tenderizing, covering, lubricating, moisturizing or cleansing effect on the skin. Softener additives include a wide variety of oils, waxes, and fatty alcohols. The hydrophilic agent is an additive material that enhances water absorption, such as a polyol. Examples of such additive materials and their properties to provide to the treated sheet include: fatty alcohols (lubricating, texture, opacity), aliphatic esters (lubricating, improving hand), dimethicone (skin care), powders (lubricating, oil absorbing, skin care), preservatives and antioxidants (product integrity), ethoxylated fatty alcohols (wettability, processing aids), fragrances (consumer appeal) and lanolin derivatives (skin moisturization).

Other additive materials that may be used in the practice of the present invention to achieve various purposes include, but are not limited to: silicones and silicone oils such as dimethicone and alkylmethylpolysiloxane; petroleum-based oils, including mineral oil and petrolatum; animal oils, such as mink oil and lanolin; derivatized lanolin and synthetic lanolin; vegetable oils, such as aloe vera (a1oe) extract and sunflower and avocado oils; natural waxes such as beeswax and carnauba wax; petroleum waxes such as paraffin and ozokerite; silicone waxes, such as alkyl methyl siloxane; synthetic waxes, such as synthetic beeswax and synthetic spermaceti; tallow; fatty alcohols, e.g. C₁₄～C₃₀Carbon chain length alcohols including cetyl alcohol, stearyl alcohol, behenyl alcohol and dodecanol; alkyl ethoxylates, e.g. C with 3-30 oxyethylene units₁₂～C₁₈Ethoxylates of fatty alcohols; fatty acid esters including methyl palmitate, methyl stearate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, ethylhexyl palmitate, lauryl lactate, and cetyl lactate; fatty alcohol ethers such as cetyl glycol and propoxylated fatty alcohols; polyhydroxy fatty acid esters including sorbitan palmitate, sorbitan stearate, sorbitan behenate, monostearate glycerol monopalmitate, monobehenate glycerol, monostearate sucrose and monobehenate sucrose; glycerides, acetoglycerols (acetoglycerolides), and ethoxylated glycerides; phospholipids, such as lecithin; polyhydroxy compounds, such as propylene glycol, glycerol, ethoxylated glycerol, polyglycerol, polyethylene glycol, polypropylene glycol and polyethylene glycol/propylene glycol copolymers; a siloxane diol; such as acrylic, cellulosic, polyester, and vinyl polymers and copolymers; quaternary ammonium compounds, e.g. monoalkyl trimethyl ammonium, benzyl quaternary ammonium, monomethyl trialkyl ammonium, imidazolium quaternaries quaternary ammonium, silicone quaternary ammonium, fatty acid quaternary ammonium, quaternized eggAlbino compounds and quaternized lanolin derivatives; and surfactants, including nonionic surfactants such as nonionic alkyl glycosides, and amphoteric, zwitterionic, anionic and cationic surfactants; a cellulose derivative; a protein; and fluorine compounds and materials.

Siloxanes have been widely used as additives for sheet processing to improve sheet properties and characteristics. Siloxanes, also known as organopolysiloxanes, polyorganosiloxanes, polydiorganosiloxanes, or simply polysiloxanes, are any of a large class of siloxane polymers whose structure consists essentially of alternating silicon and oxygen atoms with various organic groups, hydrogen atoms, or other pendant substituents on the silicon atom. Different properties can be obtained by attaching selected chemical functional groups to the silicon backbone. The siloxane may be liquid, semi-solid, or solid, depending on molecular weight, degree of polymerization, and substituent groups. They may be in the form of fluids, powders, emulsions, solutions, resins, and pastes. Silicones are generally hydrophobic and are available as neat fluids, solutions in organic solvents, or as aqueous emulsions. These emulsions may have a positive, neutral or negative charge. Liquid silicones are sometimes also called silicone oils. The siloxane may have a linear, branched, or cyclic structure, and may be crosslinked. Each substituent group may independently be hydrogen or any alkyl, aryl, alkenyl, alkaryl, aralkyl, cycloalkyl, halocarbyl, or other group. Any of such groups may be substituted or unsubstituted. The groups on any one particular monomeric unit may be different from the corresponding functional groups on its adjacent monomeric units. These groups may independently be another silicon-containing functional group such as siloxanes, polysiloxanes, silanes, and polysilanes. These groups may contain any of a number of functional groups including alcohol, carboxylic acid, aldehyde, ketone, ester, ether, polyether such as ethylene oxide or propylene oxide groups, amine and amide functional groups. One commonly used type of siloxane is polydimethylsiloxane, which may have functional groups capable of hydrogen bonding, such as amino, carboxyl, hydroxyl, ether, polyether, aldehyde, ketone, amide, ester, and mercapto groups, wherein the degree of substitution of the functional groups is generally less than about 20 mole percent, and typically less than about 10 mole percent.

The siloxane may also comprise copolymers and siloxane materials of various other monomers, such as ethylene oxide-dimethylsiloxane copolymers, which may be used as coupling agents. Mixtures of siloxanes may also be used, for example mixtures of functional and non-functional siloxanes, such as mixtures of polydimethylsiloxane and alkylene oxide modified polydimethylsiloxane. Siloxanes may also be used in admixture with other additive materials such as mineral oils. The liquid silicone or any other liquid additive material may be used as a non-volatile solvent to dissolve or disperse other semi-solid or solid additive materials for ease of application.

The intrinsic viscosity of the silicone can vary within wide limits, as long as it is flowable or can somehow be converted to flowable for spraying. This includes viscosities of from about 25cp to about 50,000 cp or more. Preferably, the viscosity is from about 100 to about 5000cp, especially when the silicone is sprayed in neat form, more preferably from about 200 to about 2000 cp. Semi-solid or solid silicones can be heated and melted before application. If desired, high viscosity silicones which are inherently flow resistant may also be used for application, in which case methods such as emulsifying the silicone in water under the action of a suitable surfactant or dissolving it in a volatile solvent such as hexane may be employed. The high viscosity silicone may also be dissolved, emulsified or dispersed in another liquid additive material.

For example, one approach to improving the feel of tissue products is to incorporate silicone additives into the tissue sheet. Silicones are known to provide the desired smooth or silky feel to the tissue surface, thereby improving its sensory softness. The silicone may be applied at some point after the tissue web is formed, before or after drying. Siloxanes have also found considerable use in finishing and improving textile products. They are used as softeners, hydrophobing agents, sizing agents and improve the hand. Linear polysiloxanes containing polyether groups can improve hand and wettability. The siloxane compounds with quaternary ammonium groups reduce static electricity. Siloxanes are also active on the surface of plastics and synthetic fibers.

If desired, at least 1 additive material in the additive composition can be dissolved, emulsified or dispersed in 1 or more volatile solvents. Suitable volatile solvents include, but are not limited to, water; alcohols such as methanol, propanol, butanol and other aliphatic alcohols; ketones such as acetone, butanone, methyl isobutyl ketone, methyl amyl ketone and takoaliphatic ketones; esters, such as methyl acetate, ethyl acetate and other alkyl carboxylates; ethers, such as methyl tert-butyl ether, dibutyl ether and other aliphatic or alkyl aryl ethers; glycol ethers such as ethoxyethanol, butoxyethanol, ethoxy 2-propanol and propoxyethanol; glycol ether esters such as butoxyethoxy acetate and ethyl 3-ethoxy propionate; alkanes such as hexane, heptane, naphtha and mineral spirits; and aromatic hydrocarbons such as toluene, xylene; and the like. Preferably, the additive composition contains only a minor proportion of a volatile solvent, which is present in an amount just sufficient to liquefy the additive to render it flowable for application to the treated sheet. More preferably, the additive composition is substantially free of volatile solvents or water or both. As used herein, the term "substantially free" means less than about 5 weight percent, preferably less than about 2 weight percent, and more preferably less than about 1 weight percent, based on the total weight of the additive composition.

To perform the spraying, the additive composition, whether applied to the sheet material during the manufacture of paper products, textile products, or flexible sheet products, is blended with a compressed fluid in a closed pressure system to form a liquid mixture. The additive composition may be a liquid, semi-solid, or solid prior to mixing with the compressed fluid, so long as it forms a liquid mixture when admixed under pressure with the compressed fluid and is capable of being sprayed. If the additive composition is a liquid, it may be a liquid solution, emulsion, dispersion or suspension. The additive composition may be heated prior to mixing with the compressed fluid, for example to melt or liquefy the semi-solid or solid composition to facilitate blending. The liquid mixture formed by blending with the compressed fluid may be a liquid solution, emulsion, dispersion or suspension. The compressed fluid may be a gaseous, liquid or supercritical fluid phase dissolved or finely dispersed in a liquid mixture. Preferably, the compressed fluid is at least partially dissolved or finely dispersed in the additive composition in a liquid phase.

The liquid mixture of the additive composition and the compressed fluid comprises a compressed fluid in an amount such that the liquid mixture is sprayable. Generally, the amount of compression fluid used should be at least about 5 wt%, preferably at least about 10 wt%, more preferably at least about 15 wt%, even more preferably at least about 20%, and most preferably at least about 25%, based on the total weight of the compression fluid and additive composition. The amount of compressed fluid used will depend on the compressed fluid used, the additive composition and the temperature and pressure employed for spraying. The amount of compressed fluid used, if desired, may exceed its solubility limit in the additive composition, but should not be excessively high, otherwise the excess compressed fluid phase would unduly interfere with the formation of the spray, for example, due to the inability to maintain a good dispersion in the liquid mixture or to provide poor atomization. The use of excess compressed fluid is sometimes advantageous to reduce the spray rate of the additive composition, especially when the additive composition used does not contain a volatile organic solvent. Generally, the compressed fluid content of the liquid mixture will be less than 80% by weight, preferably less than 70%, more preferably less than about 60%. Typically, the liquid mixture will contain from about 25 to about 50% compressed fluid.

The liquid mixture of the additive composition and the compressed fluid has a spray viscosity at the spray temperature and pressure of less than about 300cp, more preferably less than about 150cp, more preferably less than about 100cp, and most preferably less than about 50 cp.

The liquid mixture of the additive composition and the compressed fluid may be prepared in the spray coating apparatus disclosed in the above-mentioned patents, or in other suitable apparatus, in preparation for spraying. The spray coating device may also be UNICARB manufactured by Nordson corporation^System Supply Unit, which is a device used to formulate, mix, heat and pressurize a coating composition with a compressed fluid such as carbon dioxide for coating spray application.

To achieve mixing with the additive composition, particularly with a composition containing the solid additive in dissolved form, the compressed fluid may be heated and the pressure adjusted to a level sufficient to prevent settling of the solids during mixing, for example using the method disclosed in U.S. patent 5,312,862.

The spraying of the liquid mixture is carried out by passing the mixture under pressure through the nozzle orifice of a spraying device to form a spray. While spray pressures of 5000psig and higher can be employed, preferred spray pressures for the liquid mixture are below about 3000psig, more preferably below about 2500 psig. Very low pressures are generally not preferred to create proper atomization. Preferably, however, the spray pressure is greater than about 500psig, more preferably greater than about 800psig, even more preferably greater than about 1000psig, and most preferably greater than about 1200 psig. The pressure employed will depend on the compressed fluid used, its content in the liquid mixture and the nature of the additive composition.

The temperature of the spray of the liquid mixture is preferably less than about 150c, more preferably less than about 100c, and most preferably less than about 80 c. The temperature that can be employed will generally depend on the characteristics of the additive composition, such as stability and heat sensitivity. Preferably, the liquid mixture has a spray temperature of greater than about 25 deg.C, more preferably greater than about 30 deg.C, even more preferably greater than about 40 deg.C, and most preferably greater than about 50 deg.C.

Nozzle orifices, nozzle tips, nozzles and spray guns used in conventional and electrostatic airless and air-assisted airless spray applications are generally suitable for the application of the liquid mixtures of the present invention. The preferred lance, nozzle and nozzle head should not have excessive flow volume between its nozzle orifice and the on-off valve and not impede the wide angles at which the spray exits the nozzle orifice. The most preferred nozzle tip and lance is UNICARB^Nozzle tips and spray guns, manufactured by Nordson corporation or Graco corporation. The preferred nozzle orifice size is from about 0.007 to about 0.025 inch nominal diameter, although smaller or larger nozzle orifice sizes may also be used. The nozzle orifice size is selected to meet the requirements of producing a desired spray rate of the additive composition at a given spray width. Devices and flow designs such as pre-orifices and turbulence promoters for promoting the development of turbulence and flow agitation in the liquid mixture prior to its exit from the nozzle orifice may also be employed. The pre-orifice should preferably not cause an excessive pressure drop in the liquid mixture flow. The pre-orifice can be used to adjust spray beam properties and spray rate.

The spray pattern may be a circular spray, as produced by a circular nozzle orifice, or it may be an elliptical or flat spray, as produced by a channel dug along the nozzle orifice as described above. A wider plume-like flat jet fan is generally preferred. To produce an axisymmetric spray pattern, a preferred nozzle tip design would have mutually orthogonal grooves hollowed out along the nozzle orifice exit. This will produce 2 orthogonal spray sectors that combine to produce an axisymmetric spray pattern.

In the practice of the present invention, the preferred spray conditions for the liquid mixture, i.e., the concentration of compressed fluid in the liquid mixture, the spray temperature and the spray pressure, are such as to produce a decompressed or substantially decompressed spray, which will be referred to as a "decompressed spray" in the following description and claims. These conditions will vary with the additive composition, the compressed fluid and the nozzle head used and therefore they must generally be determined by experimentation. Typically, spraying is carried out at or just below or above the solubility limit. To obtain a sufficiently high solubility, a sufficiently high spray pressure is used. The spray temperature and compressed fluid content are then adjusted to produce a decompressed spray having the desired characteristics to suit the particular spray, such as to suit the desired droplet size. When the compressed fluid concentration exceeds the solubility limit, the excess compressed fluid phase is preferably substantially dispersed in the liquid mixture. Preferably, the excess compressed fluid phase is present as a finely divided liquid phase.

Preferably, the compressed fluid is a supercritical fluid at the temperature and pressure at which the liquid mixture is sprayed.

In order to provide a strong atomisation effect on the spray of the additive composition, the liquid mixture of additive composition and compressed fluid preferably comprises a compressed fluid in an amount such that the liquid mixture forms a liquid compressed fluid phase at the spray temperature used. The spraying pressure is preferably higher than the lowest pressure at which the liquid mixture can form a liquid compressed fluid phase at the spraying temperature used. This technique is disclosed in U.S. patent 5,290,603.

The present invention is not critical to the gas environment in which the spray is formed. However, the pressure in this environment must be substantially lower than the spray pressure in order to achieve sufficient decompression of the compressed fluid to form a decompressed spray. Preferably, the gaseous environment is at or near atmospheric pressure. The environment will typically comprise air, however, other gaseous environments may be used. If the additive composition contains water, it is preferred that the humidity be suitably low to facilitate evaporation of water from the spray.

The average diameter of the spray droplets produced is generally 1 μm or more. Preferably, the droplets have an average diameter of about 5 to about 150. mu.m, more preferably about 10 to about 100. mu.m, even more preferably about 15 to about 70 μm, and most preferably about 20 to about 50 μm.

Decompression of the spray jet produces a uniform atomization with a narrow droplet size distribution, which is desirable for efficient and effective spraying of the additive composition onto the sheet to be treated, particularly when the sheet to be sprayed is in rapid motion in the manufacturing equipment. Not only can the droplet size distribution at the ejection point be narrow, but also the average droplet size can be very uniform along the whole spray pattern, which will narrow the overall droplet size distribution in the whole spray range, so there is no over-atomization or under-atomization in some areas. Non-uniform atomization along the spray pattern is a problem often encountered with air and airless spray methods. The width of the droplet size distribution can be expressed in terms of its span. The span is defined as (D)_0．9-D_0．1)／D_0．5Wherein D is_0．5Is the size that 50% of the droplet volume has a smaller or (larger) size, which is equal to the average droplet size; d_0．1Is 10% of the droplet volume having the smaller size; and D_0．9Droplet volumes that are 10% have larger dimensions. Preferably, the droplet size distribution has a span of less than about 2.0, more preferably less than about 1.8, even more preferably less than about 1.6, and most preferably less than about 1.4. The narrower the span, the smaller the percentage of particles that are too small or too large for a given spray. The desired span will vary with the particular application.

We have found that a narrow droplet size distribution produced by a decompressed spray can be used which is advantageous for spraying the additive composition onto rapidly moving sheets in the manufacture of paper, textile and flexible sheet products, especially when combined with the advantageous spray speed characteristics it possesses. One problem encountered with air spraying rapidly moving sheets that results in poor spray efficiency is the formation of a boundary layer of air along the sheet surface, especially at high speeds. A substantial portion of the droplets produced by the air spray are too small to penetrate the boundary layer of air, and they are carried away by the air stream and become paint-fly. This problem will be exacerbated by the highly turbulent nature of the air spray. Air spraying with a larger average droplet size produces a high proportion of oversized droplets, which produce a poor quality spray and are therefore intolerable.

In contrast, because of the narrow droplet size distribution produced by the decompressed jet, higher average droplet sizes can be used without increasing the proportion of excessively large droplets. In addition, the turbulence of the decompressed spray is significantly less than that of the air spray. Thus, the additive composition can be sprayed efficiently, which will reduce waste generation and application costs. For example, in a direct spray comparison, a decompressed spray with an average droplet size of 35 μm produced an oversized droplet fraction (2% by volume) as a comparable air spray with an average droplet size of 20 μm. Therefore, a depressurized spray will be able to spray the additive composition with much higher efficiency. Again, the composition sprayed with reduced pressure had a viscosity of 2000cp, however, if sprayed with air, the composition had to be diluted with a volatile solvent to a viscosity of 100cp without the use of a reduced pressure spray.

We have also found that in addition to improving spray efficiency, decompression spray improves the coating quality of the additive composition and therefore provides improved products. The uniform atomization and spray pattern can provide more uniform deposition and distribution of the additive composition on the moving sheet. Furthermore, on microporous sheet materials, such as paper and textile products, it has been found that it is desirable to achieve penetration of the spray deposit into the interior of the sheet material. The additive composition is able to penetrate the boundary layer of air but not into the paper substrate itself so that the additive composition remains on the paper surface. This is desirable for many surface treatments, such as the application of softeners, lubricants and lotions, as the additive composition will be more effectively utilized.

Furthermore, penetration of the additive composition into the paper interior can cause undesirable debonding of the sheet and weakening of the cohesion and tensile strength. Because of the lower turbulence produced by the depressurized spray and the generally gentler spray, the weaker paper is stressed less than with air spray and the mechanical integrity is less likely to be compromised. As noted above, the ability to spray viscous additive compositions that are substantially free of water or volatile solvents also provides for superior coating and product quality, which provides a less absorbent or migrating spray to the interior of the sheet material on the surface of the sheet material, such as a tissue product, and results in a smoother, softer surface with less reduction in caliper.

The present invention can also be used to spray relatively dry aqueous additive compositions during the manufacture of paper products or textile products using decompressive spray. In some applications, water is required as a solvent, but it may be desirable to be able to apply a relatively dry additive composition to paper or textile materials. The water content of the aqueous additive composition can be significantly reduced because the depressurized spray can atomize a higher viscosity aqueous additive composition than is possible with air spray. Furthermore, it has been found that decompressing the spray enhances the evaporation of water in the spray and thus allows the aqueous additive composition to be applied to paper or textile sheet material in a relatively dry state even if it has a conventional water content. As disclosed in the above-mentioned us patent 5,716,558, the aqueous composition shows spray drying even a short distance after leaving the nozzle orifice. Thus, with the process of the present invention, it is possible to achieve deposition of the aqueous additive composition in a substantially dry state on paper or textile sheet.

To perform the spraying, the aqueous additive composition, which comprises water and at least 1 additive material that is soluble, emulsified or dispersed in water and may also comprise other ingredients such as suitable surfactants, is blended with a compressed fluid, preferably carbon dioxide or ethane, in a closed pressure system to form a liquid mixture. The compressed fluid is present in the liquid mixture to form a solution, emulsion or gaseous or liquid dispersion, preferably emulsified or finely dispersed therein. We have unexpectedly found that by taking the form of an emulsified or dispersed compressed fluid phase in a liquid mixture, the spray can undergo a transition from a liquid film spray to a decompressed spray with increasing compressed fluid content or temperature, similar to anhydrous compositions having very low solubility for compressed fluids, although the compressed fluid may have very low solubility in aqueous additive compositions. Coupling agents, such as ethylene glycol ethers, propylene glycol ethers, and the like, as well as other coupling materials, may be used to increase the solubility of the compressed fluid in the aqueous additive composition, as disclosed in U.S. patent 5,419,487.

While a viscosity of greater than about 2000cp may be used if a pressure jet is formed, the aqueous additive composition will generally have a viscosity of less than about 2000cp, preferably less than about 1500cp, more preferably less than about 1000cp, and most preferably less than about 700cp at 25℃.

The amount of compressed fluid in the liquid mixture in the aqueous additive composition should be such that the compressed fluid phase remains substantially finely dispersed in the liquid mixture and is capable of producing proper atomization. Preferably, the compressed fluid phase will be converted to a finely dispersed liquid phase at supercritical temperatures and pressures after blending with the aqueous additive composition. The composition may comprise an organic solvent or another ingredient that is miscible with the compressed fluid, thereby enabling the compressed fluid to form a liquid phase. If the content of the compressed fluid is excessively high, a larger aggregate size than desired of the compressed fluid may be formed in the liquid mixture, and it will be relatively difficult to maintain a uniform dispersion state. Thus, although larger amounts may be used, it is preferred that the amount of compressed fluid in the liquid mixture is preferably less than about 40% by weight, more preferably less than about 35%, even more preferably less than about 30%, and most preferably less than about 25%. The amount of compressed fluid present in the liquid mixture is at least the amount that the liquid mixture is capable of forming a compressed spray. The amount required depends on the viscosity and rheological properties of the aqueous additive composition. Preferably, the liquid mixture comprises at least about 4% compressed fluid, more preferably at least about 6% compressed fluid, even more preferably at least about 10% compressed fluid, and most preferably at least about 15% compressed fluid.

The liquid mixture in the aqueous additive composition is preferably sprayed at a temperature above about 40 ℃, more preferably above about 50 ℃, most preferably above about 55 ℃, and a pressure preferably above about 1200psig, more preferably above about 1400psig, which will create a depressurized spray after the mixture flows through the nozzle orifice into an environment suitable for water evaporation, preferably with a low humidity level. One or more jets of dry gas, such as an auxiliary gas stream, may be applied to the depressurized jet to increase the turbulent mixing rate or the temperature or both within the jet, thereby increasing the rate of evaporation of the water. When carbon dioxide is used as the compressed fluid for the aqueous additive composition that is sensitive to lower pH levels, particularly acidic pH values, the pH of the liquid mixture can be controlled to prevent precipitation of the carbon dioxide when mixed with the additive material. The pH can also be controlled using caustic or other alkaline materials, such as ammonia, sodium hydroxide, calcium carbonate, and other salts.

The present invention may be implemented in any commercial paper, textile, or flexible sheet manufacturing system, including the various conversion systems known to those skilled in the art, including the various types of paper machines mentioned above. The additive composition can be applied to sheet material without significantly affecting machine operability, including operating rates. The additive composition may be sprayed directly or indirectly by spraying at any point in the manufacture of the paper, textile or flexible sheet product. The moving paper, textile or flexible sheet material may be unsupported or supported by means known to those skilled in the art during spraying. The additive composition may be sprayed on as the paper, textile or flexible sheet material is transferred from one roll to another. The additive composition may also be sprayed onto the sheet during other operations.

Indirect application methods that may be used in the present invention include, but are not limited to, applying the additive composition from a spray onto at least 1 transfer surface and then ultimately transferring thereto by contact of the transfer surface with moving paper, textiles, or flexible sheets. Preferred transfer surfaces are cylinders or rolls, such as calender rolls or kiss rolls. Other less preferred transfer surfaces are forming wires or fabrics and conveyor belts or materials which are then brought into contact with the moving sheet. If desired, the transfer surface may be heated.

The additive composition is preferably applied by spraying directly onto at least 1 surface of a moving paper, textile or flexible sheet. In the manufacture of paper products or tissue paper products, the additive composition is preferably applied to at least 1 surface of a moving web containing paper fibers. The additive composition may be applied at the wet or dry end of the papermaking operation. Preferably, the additive composition is applied to the moving web after the web has been at least partially dried, more preferably after the web has been substantially dried. If desired, the web may be overdried or heated. In the manufacture of flexible sheet products, the additive composition is preferably applied to at least 1 surface of a moving flexible sheet.

In the practice of the invention, the distance from the nozzle orifice to the moving sheet is not critical. Typically, the sheet will receive a spray of the additive composition at a distance of from about 4 inches to about 24 inches. Preferably about 6 inches to about 18 inches. And most preferably from 8 inches to about 16 inches. The distance used will depend on the particular application. If desired, electrostatic spraying can be used to improve application efficiency, for example, using the methods disclosed in U.S. patent 5,106,650.

Direct spraying on a moving sheet may be by a stationary or reciprocating spray gun or by other means. Multiple spray guns may be provided to produce deposition of a cross-plume spray to achieve uniform coating across the entire width of a moving sheet of material wider than the width of a single spray. For some spray applications, particularly those in which the additive composition is substantially free of volatile solvent, a low spray rate is preferred, for which smaller nozzle opening sizes and wider spray fan shapes are preferred. Pre-orifices may also be used to further reduce the spray rate.

The speed of movement of the paper, textile or flexible sheet during spraying is not sensitive to the practice of the invention. Generally, this speed is the normal speed employed for a particular manufacturing or converting operation. As mentioned above, this speed is generally dependent on the requirements of the product being produced and the equipment used. Preferably, the web is capable of moving at high speeds to improve throughput. Although slower transport speeds may be used, the speed will generally be greater than about 50 m/min, preferably greater than about 100 m/min, more preferably greater than about 150 m/min, and even more preferably greater than about 200 m/min, as appropriate for the particular application. Certain products, such as tissue paper, may be used at very high speeds, for example, above about 1000 m/min.

The application of the additive composition to the moving paper, textile or flexible sheet material is not critical to the practice of the present invention and will generally depend on the particular additive composition being applied and the desired properties and performance of the particular product, as is known to those skilled in the art. The application level of the additive composition is generally balanced between performance and cost. It is generally desirable to use the minimum amount of additive composition required to achieve the desired properties. For example, the amount of softener application required to make a soft tissue should be at least the preferred amount of application that causes a difference in the sensory softness of the paper. The minimum effective application amount will depend on the particular type of sheet being treated and the particular softener being applied. Generally, when the additive composition is applied at less than 0.1% by weight based on the weight of the finished sheet, the softness improvement effect on the tissue paper is minimal, and when it exceeds 5% by weight, the improvement effect on the softness is little or no longer increased and is economically uneconomical. Too high an application level may also leave a detectable residue on the skin.

On the other hand, additives such as lotions, since they contain ingredients intended to be transferred to the skin, are generally applied to the sheet in an amount greater than that used for additives intended to alter the properties of the tissue itself. Typical application levels of the additive composition will range from about 0.1 to about 50 weight percent based on the weight of the sheet, although more or less may be applied. Typically, the application level will be less than about 40%, more specifically less than about 30%, and still more specifically less than about 20%. Many additive compositions are applied at levels of from about 0.1 to about 15%, more specifically from about 0.3 to about 10%. Certain low application rate additive compositions are preferably applied in amounts less than about 5%, more specifically less than about 3%.

The practice of the present invention is not critical to the physical form of the additive composition applied to the paper, textile or flexible sheet material. Preferably, the application of the additive to the sheet is macroscopically uniform. The applied additive composition may take the form of a continuous or discontinuous film or coating, or be a random, discontinuous array of droplets or particles, or be composed of discontinuous droplets or particles. The applied additive composition may be liquid, semi-solid or solid when deposited onto the sheet. The applied additive composition may be absorbed into the sheet or substantially reside on its surface. Preferably, the applied additive composition adheres to the sheet.

If desired, the sheet to which the additive composition has been applied may also be subjected to a post-treatment, such as heating or drying.

While the invention has been described in terms of preferred forms, it will be apparent to those skilled in the art that variations may be applied to the invention as described above without departing from the spirit and scope of the invention. Further, those skilled in the art will appreciate that steps or operations other than those specifically described herein may be used in the manufacture of sheet products.

Example 1

Additive composition comprising modified silicone softener and lotion is sprayed with carbon dioxide as a compressed fluid using UNICARB^System Supply Unit, equipped with UNICARB^A spray gun and a nozzle head comprising an orange-lobe (orange) shaped pre-orifice. 03 to 08, manufactured by Nordson. The liquid mixture was sprayed at a temperature of 60 ℃ and a pressure of 1100 psi. A concentration of 20 wt% carbon dioxide provides a cone angle spray pattern with good atomization. After increasing the carbon dioxide concentration to 25%, a soft plume pattern was formed. After the carbon dioxide concentration was increased to 50%, a decompressed spray with a very good spray pattern and fine atomization was formed. This high level of carbon dioxide achieves uniform mixing with the additive composition and reduces the application rate. The spray application was performed on a tissue sheet and the additive composition was applied in very small but uniform amounts.

Example 2

An additive composition comprising a modified lanolin softener and a lotion was sprayed as a liquid mixture containing 25% carbon dioxide using the same equipment and spray conditions as in example 1. This results in a decompressed spray with an excellent spray pattern, i.e. soft, spread wide, very uniform. The spray application was carried out on a tissue material and the additive composition was applied in very small but very uniform amounts. The carbon dioxide concentration is then increased to 50% whereupon a two-phase liquid mixture is formed. This higher carbon dioxide concentration reduced the spray rate measurement from 76 to 46 g/min. The spray uniformly applies the additive composition to the paper towel product.

Example 3

Using the same equipment as in example 1, the additive composition containing the quaternary ammonium salt was sprayed as a liquid mixture of 20% carbon dioxide at a temperature of 60 ℃ and a pressure of 1100psi to provide good atomization and a uniform spray pattern. After the carbon dioxide concentration was increased to 40% and the pressure reached 1500psi, a two-phase liquid mixture was formed with a slightly wider spray pattern. The additive composition was sprayed on the tissue sheets and in each case a uniform, very small application on the tissue sheets was achieved.

Example 4

Using the same equipment as in example 1, 4 different additive compositions, including (1) a water-absorbent composition containing lecithin, quaternary ammonium, and polyethylene glycol; (2) lanolin; (3) a mixture of quaternary ammonium, surfactant blend and propylene glycol; and (4) silicone oil, all sprayed with 30% carbon dioxide onto fluffy tissue sheets at a temperature of 60 ℃ and a pressure of 1200 psi. In each case, good atomization was exhibited.

Example 5

Hydrophilic anionic sulfosuccinate surfactant, and carbon dioxide as compressed fluid for spraying by using UNICARB^System Supply Unit (manufactured by Graco) equipped with UNICARB^A lance and a nozzle tip comprising a short neck (. 05gpm) pilot orifice. 06-12 manufactured by Nordson. The liquid mixture was sprayed at a temperature of 55 c and a pressure of 1250 psi. Concentrations of more than 25 wt% carbon dioxide result in a very good spray pattern and a finely atomized decompressed spray. Up to 60% carbon dioxide concentration still produces the same effect. This variability in carbon dioxide is used to fine tune the surfactant flow rate and thus actually fine control the application on the nonwoven diaper web. Very small amounts of additives were sprayed onto the fabric and evenly distributed.

Claims (21)

1. A method of spraying an additive composition onto a sheet material during manufacture of a sheet material product, the method comprising:

(1) preparing a liquid mixture comprising an additive composition and a compressed fluid in a closed pressure system, comprising:

(a) an additive composition comprising at least 1 additive material; and

(b) a compressed fluid present in an amount to enable spraying of said liquid mixture, which forms a liquid mixture with said additive composition and which is a gas at standard conditions (STP) of 0 ℃ temperature and 1 atmosphere pressure;

(2) forming a spray by spraying the liquid mixture through a nozzle orifice at a pressure of at least about 500 psi; and

(3) applying said spray containing said additive composition to said sheet to produce a sheet product which is not a release sheet or a water repellent textile product.

2. The method of claim 1, wherein the sheet is paper, textile, or flexible sheet.

3. The method of claim 1, wherein the sheet comprises paper fibers or is paper.

4. The method of claim 1, wherein the sheet comprises paper fibers and the sheet product is tissue paper.

5. The method of claim 4 wherein the tissue product is selected from the group consisting of sanitary napkins, household towels, industrial tissues, facial tissues, beauty tissues, soft tissues, absorbent tissues, pharmaceutical tissues, toilet tissue, paper towels, paper napkins, paper cloths, and paper liners.

6. The method of claim 3, wherein the additive composition is applied to at least 1 surface of a moving web containing the substrate.

7. The method of claim 6, wherein the additive composition is applied to the moving web after the web is at least partially dried.

8. The process of claim 1, wherein the liquid mixture is substantially free of volatile organic solvents and water.

9. The method of claim 1, wherein the liquid mixture is substantially free of water.

10. The method of claim 1, wherein the spray is a decompressive spray.

11. The method of claim 1, wherein the compressed fluid is carbon dioxide or ethane and is a supercritical fluid at the spray temperature and pressure of the liquid mixture.

12. The method of claim 1 wherein said additive material is selected from the group consisting of softeners, emollients, lubricants, moisturizers, lotions, creams, conditioners, absorbents, hydrophilic agents, debonders, surfactants, oils, waxes, silicones, mineral oils, lanolin, derivatized lanolin, aloe vera extract, fatty alcohols, fatty acid esters, polyhydroxy compounds, and quaternary ammonium compounds, and mixtures thereof.

13. The method of claim 1 wherein the additive composition is applied to the sheet material by first applying said additive composition to a surface and then transferring said additive material to said sheet material by contact between said surface and said sheet material.

14. A method of spraying a relatively dry aqueous additive composition onto paper or textile sheet material during the manufacture of paper or textile products, the method comprising:

(1) preparing a liquid mixture comprising an aqueous additive composition and a compressed fluid in a closed pressure system, comprising:

(a) an aqueous additive composition comprising water and at least 1 additive material; and

(b) a compressed fluid present in an amount to enable spraying of said liquid mixture, which forms a liquid mixture with said additive composition and which is a gas at standard conditions (STP) of 0 ℃ temperature and 1 atmosphere pressure;

(2) flowing the liquid mixture through a nozzle orifice into an environment at a temperature of at least about 40 ℃ and a pressure sufficient to form a decompressed jet, wherein at least 1 portion of the water in the liquid mixture evaporates, and wherein the jet comprising the aqueous additive composition is applied to a paper material or a textile material, thereby producing a paper product or a textile product.

15. The method of claim 14, wherein the aqueous additive composition is applied to at least 1 surface of the moving web containing paper fibers after the web has been at least partially dried.

16. A method of spraying an additive composition onto a textile sheet material during manufacture of a textile sheet material product, the method comprising:

(1) preparing a liquid mixture comprising an additive composition and a compressed fluid in a closed pressure system, comprising:

(a) an additive composition comprising at least 1 additive material; and

(b) a compressed fluid present in an amount to enable spraying of said liquid mixture, which forms a liquid mixture with said additive composition and which is a gas at standard conditions (STP) of 0 ℃ temperature and 1 atmosphere pressure;

(2) forming a spray of the liquid mixture by passing the mixture through a nozzle orifice at a pressure of at least about 500 psi; and

(3) applying said jet comprising said additive composition to said textile sheet to produce a textile product which is a non-waterproof textile product.

17. The method of claim 16, wherein the compressed fluid comprises at least 1 supercritical fluid at the temperature and pressure at which the liquid mixture is sprayed.

18. The method of claim 16, wherein the spray is a decompressive spray and the compressed fluid in the liquid mixture is a supercritical fluid at the spray temperature and pressure of the liquid mixture.

19. A method of spraying an additive composition onto a flexible sheet material during manufacture of a flexible sheet material product, the method comprising:

(1) preparing a liquid mixture comprising an additive composition and a compressed fluid in a closed pressure system, comprising:

(a) an additive composition comprising at least 1 additive material capable of at least adhering to, penetrating into, or being absorbed into the surface or interior of the flexible sheet material; and

(b) a compressed fluid present in an amount to enable spraying of said liquid mixture, which forms a liquid mixture with said additive composition and which is a gas at standard conditions (STP) of 0 ℃ temperature and 1 atmosphere pressure;

(2) forming a spray of the liquid mixture by passing the mixture through a nozzle orifice at a pressure of at least about 500 psi; and

(3) applying said spray of said additive composition to at least 1 surface of said flexible sheet to produce a flexible sheet product which is not a release sheet or a water repellent textile product.

20. The method of claim 19, wherein said flexible sheet is selected from the group consisting of plastic film, plastic laminated sheet, plastic reinforced sheet, plastic impregnated sheet, rubber sheet, leather, fiber reinforced sheet, porous sheet, mesh sheet, extruded film, composite sheet, and composite-to-laminate sheet.

21. The method of claim 19, wherein the spray is a decompressive spray.