EP0594983A1

EP0594983A1 - Method of applying a coating at high bath concentration and low wet pick-up to materials such as nonwovens using a brush spray applicator

Info

Publication number: EP0594983A1
Application number: EP93114164A
Authority: EP
Inventors: Arthur Edward Garavaglia; Cheryl Anne Perkins; Michael David Powers
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1992-10-29
Filing date: 1993-09-03
Publication date: 1994-05-04
Also published as: KR940008750A; MX9306375A; AU4917593A; ZA937704B

Abstract

Nonwoven, hydrophobic fibrous substrates uniformly coated with a wetting agent are disclosed which have improved tensile strength properties over conventional coated, nonwoven substrates. Also disclosed are processes for applying a high solids content wetting agent to a substrate in a manner which results in low wet pick-up and reduces or eliminates drying requirements. The low wet pick-up reduces degradation of the tensile strength of the material normally resulting from the wetting and drying of nonwoven substrates. In one embodiment the untreated side remains hydrophobic producing a "one-way valve" effect. In another embodiment, both sides of the material are treated with direct application to only one side of the material. Disclosed treatment methods include printing and brush spray application. Brush spray application provides the additional advantages of preserving the loft of the material and coating both sides of the material or at least deeply penetrating the material.

Description

Technical Field

This invention relates to coated materials and processes for coating materials. More particularly, this invention relates to nonwoven, hydrophobic materials uniformly coated with a wetting agent and having improved tensile strength. This invention also particularly relates to processes for uniformly coating a nonwoven, hydrophobic material with a wetting agent at high bath concentration and low wet pick-up. Such processes include printing and brush spray application. In addition, the present invention relates to resulting nonwoven fabrics which may be either hydrophilic on both sides or hydrophilic on one side and hydrophobic on the other, in the latter case exhibiting "one-way valve" properties.

Cross Reference

This application is a continuation-in-part of U.S. Patent Application Serial No. 07/806,747 filed on December 13, 1991.

Background of the Invention

Nonwoven, hydrophobic substrates or materials are well known in the art and are often used to make absorbent personal care articles including infant care items such as diapers, child care items such as training pants, feminine care items such as sanitary napkins, and adult care items such as incontinence products. Absorbent personal care products are typically made with multiple layers of nonwoven substrates which layers are treated with wetting agents to render them at least partially hydrophilic. In some cases, it is desirable to make one side of a layer of a personal care item hydrophilic while maintaining the other side hydrophobic and in other cases it is desirable to make both sides of the layer hydrophilic or at least obtain deep penetration of the wetting agent into the layer of material. Top sheets or liners of personal care absorbent articles are often made from initially hydrophobic nonwoven materials which have been treated with a wetting agent on one side. It is the outer surface of these top sheets which is typically treated with a wetting agent to allow fluid to more readily penetrate the outer surface for capture by an underlying absorbent pad. Top sheets made with a hydrophobic material having an outer surface treated with a wetting agent are preferred for such applications over top sheets made with a hydrophilic material because the wetting agent provides hydrophilic properties to the outer surface to improve fluid penetration without compromising the desired hydrophobic properties of the inner surface of the top sheet. The hydrophobic inner surface retains the penetrated fluid and inhibits flow back of the penetrated fluid to the outer surface, thus acting as a "one-way valve".
Other layers of personal care absorbent articles such as surge and absorbent layers are made with both sides rendered hydrophilic and are often made with relatively high loft materials. Such materials are made by separately treating both sides of the material with a wetting agent or treating one side of the material with a large amount of a wetting agent solution so that the wetting agent penetrates to the other side of the material or is transferred to the other side of the material when the material is rolled.
It is desired to apply the wetting agent to the nonwoven material in a uniform concentration for aesthetics and to provide uniform wettability to the outer material. Nonwoven materials, however, typically have irregular surfaces onto which it is difficult to uniformly apply the wetting agent. This is particularly so if a coating solution having a high concentration of wetting agent is used. For these reasons, wetting agents are typically applied by spraying, direct printing, or roller coating a low concentration solution of the wetting agent onto the outer surface of the material. One example of a material treated using conventional techniques is disclosed in United States Patent No. 4,585,449 to Karami.
One disadvantage of coating nonwoven materials using a low concentration solution is that a large amount of the solvent (usually water) is typically "picked-up" by the material. This is more of a problem when it is desirable to penetrate the nonwoven material with a wetting agent or to treat both sides of a nonwoven with a wetting agent because of the large quantities of solution which must be used and is even more of a problem when high loft materials are used because of the thickness of such material and the difficulty in penetrating the material without using large quantities of solution. The wet "pick-up" is removed by drying the coated material to evaporate the solvent. This drying step is detrimental to the strength and softness of the material, as it has been observed that the action of wetting and drying a nonwoven material significantly decreases the tensile strength of the material. Furthermore, a disadvantage of coating a nonwoven material, especially a lofty nonwoven material, with direct printing or roller coating wherein the material is passed through a nip between two rollers is that the rollers compress the material and reduce the loftiness or bulk of the material.
Thus, there is a need in the art for a method of uniformly applying a wetting agent to a nonwoven material which results in a uniform application of the wetting agent on the material without a significant decrease in the tensile strength or loft of the material.

Summary of the Invention

The present invention fills the above needs by providing processes for uniformly applying a high concentration solution of a wetting agent to a substrate such as a nonwoven material. The application of a high concentration solution results in lower wet pick-up by the material, which reduces subsequent drying of the material and the associated loss in tensile strength. This provides a strong, nonwoven material having a uniform coating.
According to a first aspect, the present invention provides a process for coating a material, the process comprising the steps of introducing a coating solution to a first rotating roll, the coating solution containing from about 15 to about 100 percent by weight of a wetting agent compound and from about 85 to about 0 percent by weight of a solvent; and passing the material through a nip defined between the first roll and a second rotating roll positioned adjacent the first roll, wherein a portion of the coating solution is applied by the first roll to a surface of the material in an amount such that the wetting agent is applied to the material in an amount of from about 0.1 to about 0.5 percent by weight of the material, and the solvent is applied to the material in an amount not exceeding about 2 percent by weight of the material.
Another aspect of the present invention provides a coated substrate, comprising a nonwoven material and a substantially uniform coating on a surface of the nonwoven material. The coating comprises a wetting agent applied to the nonwoven material in an amount of from about 0.1 to about 0.5 percent by weight of the nonwoven material and a solvent applied to said nonwoven material in an amount not exceeding about 2 percent by weight of said material.
According to yet another aspect of the present invention, there is provided another process for coating a material, this process comprising the steps of introducing a coating solution to a rotating pick-up roll, the coating solution comprising from about 10 to about 100% by weight of a wetting agent and from about 90 to about 0% by weight of a solvent; contacting the rotating pick-up roll with bristles of a rotating bristle roll and thereby projecting a spray of the coating solution along a path from the rotating pick-up roll; and passing the material through the path of the spray so that a portion of the coating solution is applied to one side of the material in an amount such that the wetting agent is applied to the material in an amount from about 0.1 to about 1% by weight of the material and the solvent is applied to the material in an amount not exceeding 5% by weight of the material. This particular method of the present invention provides the additional advantages of non-compressive coating so that the loft or bulk of the material is preserved and deep penetration of wetting agent solution into the material for deeper hydrophilicity or even two sided hydrophilicity is obtained with direct application of the wetting agent solution to only one side of the material.
According to still another aspect of the present invention, there is provided an apparatus for carrying out the foregoing brush spray method of the present invention.
Thus, it is an object of the present invention to provide an improved coated material and process for coating a material.
A further object of the present invention is to provide a process for coating a material using a high concentration coating solution such that wet pick-up and loss of tensile strength are reduced and drying requirements are reduced and may be eliminated.
A still further object of the present invention is to provide a process for coating a material which does not require drying of the coated material and yet microbiological testing confirms that no unacceptable levels of bacteria are present.
It is also an object of the present invention to provide a process for making a coated material which has improved tensile strength and in one preferred embodiment is hydrophobic on one surface and hydrophilic on the other, exhibiting one-way valve properties.
A further object of the present invention is to provide a process for coating a material so that the coating deeply penetrates the material or even coats both sides of the material with direct application of the coating to only one side of the material.
Still another object of the present invention is to provide a process for coating a lofty material without reducing the loft of the material.

Brief Description of the Drawings

Figure 1 is a perspective drawing of the "inverted L" differential offset printer used to apply a coating to a material in accordance with the present invention.
Figure 2 is a graph showing the percent surface concentration of the wetting agent on the coated material of the present invention as a function of cross-direction position.
Figure 3 is a graph showing the percent surface concentration of the wetting agent on the coated material of the present invention as a function of machine-direction position.
Figure 4 is a graph showing the percent surface concentration of the wetting agent on the coated material of the present invention as a function of gravure roll speed.
Figure 5 is a perspective view of a brush spray applicator for use in applying a coating to a material in accordance with a preferred embodiment of the present invention. A portion of the brush spray applicator is shown in phantom lines so that the rolls are visible.
Figure 6 is a partial schematic side elevation view of the brush spray applicator shown in Figure 5.

Detailed Description of the Invention

While the invention will be described in connection with preferred embodiments and methods, it will be understood that we do not intend to limit the invention to the following embodiments or methods. On the contrary, we intend to cover all alternatives, modifications, and equivalents as may be included within the scope of the invention as defined by the appended claims.
Two methods of applying a coating at high bath concentration and low wet pick-up to materials such as nonwovens are described in detail below. The first method is a printing system 10 which is shown in Fig. 1 and the second method is a brush spray applicator system 100 which is shown in Figs. 5 and 6. The printing system 10 applies a substantially uniform coating of a highly concentrated wetting agent solution with low wet pick-up to a nonwoven material without substantially reducing the tensile strength of the nonwoven material. The brush spray applicator system 100 provides the additional advantages of non-compressive coating so that the loft of the nonwoven material is preserved and deep penetration of wetting agent solution into the nonwoven material for enhanced wettability or even two sided wettability is obtained with direct application of the wetting agent solution to only one side of the material.

THE PRINTING METHOD

The nonwoven material 18 shown in Fig. 1 is preferably a hydrophobic, nonwoven spunbonded web having a basis weight from about 0.5 to about 1.0 ounces per square yard ("osy") although the basis weight is not known to be critical and may be higher, for example, up to 2.5 osy depending on the desired application. Such material is well known in the art and may be prepared in conventional fashion such as illustrated by the following patents: Dorscher et al. United States Patent No. 3,692,618; Kinney United States Patent Nos. 3,338,992 and 3,341,394; Levy United States Patent No. 3,502,538; Hartmann United States Patent Nos. 3,502,763 and 3,909,009; Dobo et al. United States Patent No. 3,542,615; Harmon Canadian Patent No. 803,714; and Appel et al. United States Patent No. 4,340,563. Other nonwoven materials and methods for forming nonwoven materials are contemplated for use with the present invention.
The wetting agent 14 is applied to a surface 50 of the nonwoven material 18 using the printer 10 to provide hydrophilic properties to the surface 50. The printer 10 is preferably a "differential" type printer, with the term "differential" referring to printers wherein the gravure roll speed may be varied with respect to the material or line speed to allow compensation for basis weight changes without changing the gravure roll. The most preferred printer is that which is referred to in the art as an "inverted L" differential offset printer, such as is shown in Fig. 1. The wetting agent 14 is preferably a non-ionic surfactant although other types of surfactants are suitable. A preferred wetting agent for use with nonwoven materials having a basis weight up to about 0.8 osy is "Triton X-102" non-ionic surfactant available from Union Carbide. "Gemtex SM-33" anionic surfactant, available from Finetex Inc., is a preferred wetting agent for use with nonwoven materials having a basis weight in excess of about 0.8 osy, particularly where "one-way valve" properties are not necessary. For certain personal care applications, it has been experienced that a surface concentration of the wetting agent on the material from about 0.1 percent to about 0.5 percent, broadly and, preferably, between about 0.16 percent and 0.38 percent is desired. The "fountainless pan" doctor blade system 44, supplies a uniform application of a solution containing the wetting agent 14 to the gravure roll 38 in a conventional manner. The solution is preferably a high concentration aqueous solution having the wetting agent 14 present in an amount of between about 20 and 100 percent, and most preferably about 25 percent, by weight of the solution.
The gravure roll 38 is preferably a metal roll of a type conventionally used in the printing art, and having a cell pattern known in the art as a "quad" pattern with between about 300 and 700 cells per inch and a cell size of between about 1.5 and 4.0 CBM (cubic billion microns, volume per square inch). The most preferred gravure roll is one known in the art as a 550 (cells per inch) quad, 1.7 CBM. The gravure roll preferably rotates at a speed of between about 20 and 120 percent of the line speed, and most preferably about 60 percent of the line speed (line speed is described below as preferably being between about 300 and 1,500 feet per minute). A graph showing the percent surface concentration of the wetting agent as a function of gravure roll speed for a representative sample is shown in Fig. 4.
The transfer roll 24 is preferably a rubber roll of a type conventionally used in the printing art, and having a durometer hardness of between about 60 and 85. The gravure roll 38 is spaced apart from the transfer roll 24 such that in operation a desired amount of the coating solution transfers to the transfer roll for subsequent application to the nonwoven material. The width of the contact strip located between the transfer roll 24 and the gravure roll 38 which defines the nip 39 is preferably between about 1/16 and 1/2 inch to achieve the desired surface concentration, and is optimally about 3/16 inch when applying the coating solution to nonwoven materials having a basis weight of about 0.7 osy. The transfer roll 24 preferably rotates at a rate which advances the material at a line speed of between about 300 and 1,500 feet per minute. The backing roll 20 is preferably either a metal or rubber roll of a type well known in the printing art, having a durometer hardness of about 90. The backing roll 20 rotates at a rate which provides the same line speed as the transfer roll 24. The width of the contact strip between the backing roll 20 and the transfer roll 20 which defines the nip 30 is preferably between about 1/4 and 3/4 inch and is optimally about 3/8 inch when coating nonwoven materials having a basis weight of about 0.7 osy.
By using the differential printer 10 for coating the nonwoven material 18, the resulting coated material 34 has a more uniform coating of wetting agent and has improved tensile strength over conventionally prepared coated materials. The following Example 1 is designed to illustrate a particular embodiment of the present invention made according to the above disclosed printing method and teach one of ordinary skill in the art the manner of carrying out the printing method of the present invention.

EXAMPLE 1

In order to evaluate the effect of coating a nonwoven material using a high concentration bath or solution, a representative sample was produced by applying a 25 percent by weight "Triton X-102" aqueous solution to a 0.7 osy nonwoven, hydrophobic material. The solution was applied using an "inverted L" differential offset printer producing a line speed of 500 fpm and a gravure roll speed of 300 fpm (60% line speed). The wet pick-up for the representative sample was determined to be about 0.9 percent and the average surface concentration of the wetting agent was about 0.3 percent solids (coat weight). No drying was necessary. This yielded a uniform distribution of about 0.24 grams of coating solution per square yard.
With reference to Figs. 2 and 3, one can see graphically the uniformity of the surface concentration of the wetting agent on the representative sample from Example 1 in the cross-direction (Fig. 2) and in the machine-direction (Fig. 3). The representative sample from Example 1 exhibited overall a 5.0 percent coefficient of variation in surface concentration across the material, and materials of the invention will generally exhibit a coefficient of variation in surface concentration of 10.0 percent or less. Loss in tensile strength for the representative sample was determined (in accordance with RTM-6200) by comparing the tensile strength of treated material with untreated material for the same cross-direction or deckle position. Material treated in accordance with the printing method of the present invention experienced a 5 percent loss in tensile strength. This compares with a typical tensile strength loss of at least 21 percent for coated materials prepared utilizing conventional spray treatments and treatments requiring secondary drying over steam cans.
The printing process of the present invention coats the material from the transfer roll; therefore, only one side of the coated material is hydrophilic, while the other side is hydrophobic. Hydrophilic material is wettable material that produces less than 20 milliliters of runoff; hydrophobic material produces greater than 20 milliliters of runoff. A material having a hydrophilic and hydrophobic surface rapidly allows fluid to pass through and does not allow it to flow back. Thus, such material acts as a "one way valve." It has been observed that materials having basis weights from about 0.5 to about 1.0 osy which are treated in accordance with the printing method of the present invention behave as one way valves when, after treatment, they are not wound up into roll form in a manner that causes contact between opposing sides of the material. It has also been observed that when materials having a basis weight of less than about 0.85 osy are rolled up after application of the wetting agent with the printing system of the present invention, some of the wetting agent transfers to the untreated side, producing a two-sided hydrophilic material. The time required for the wetting agent to transfer to the untreated side being dependent upon the basis weight. Materials having a basis weight greater than about 0.85 osy remain one way valves in sheet or roll form when treated according to the printing method of the present invention. If two sided hydrophilic behavior is desired for materials having a basis weight in excess of 0.85 osy, a conventional four roll differential printer (dual printer) may be utilized to apply the wetting agent to both sides. In addition, the brush spray applicator system 100 described below is effective to treat both sides of materials such as nonwovens.
Micropore filtration testing of materials treated in accordance with the printing method of the invention showed reduced levels of Class I, Class II and Class III bacteria when compared with untreated materials. Class I included Bacillus sp, Corynebacterium, other gram positive rods, mold and yeast (other than Candida albicans). Class II included Staphylococcus sp. (other than S. Aureus), Psuedomonas sp. (other than P. Aeruginosa), Enterobacteriaceae (other than E. Coli and Salmonella sp.), other gram positive cocci, Oxidative-Fermentative bacteria, and other gram negative rods. Class III included Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella sp., and Candida albicans. While the control had a total CFU of 17, none of the treated samples exceeded 10 CFU.

THE BRUSH SPRAY APPLICATION METHOD

A brush spray applicator 100 used in the brush spray application method of the present invention is shown in Figs. 5 and 6 and generally comprises a pick-up roll 103 disposed in a bath container 106 and a bristle roll 109 positioned juxtapositional to the pick-up roll.
The bath container 106 has an elongated trough shape and is open at the top. A weir 112 extends along the length the bath container 106 approximate the rearward side 113 of the container. The weir 112 is spaced slightly from the rearward side 113 of the bath container 106 and controls the height of the bath in the bath container. A fluid outlet 115 extends from the bottom of the bath container 106 between the weir 112 and the rearward side 113 of the container and a fluid inlet 116 extends from the bottom of the bath container between the weir 112 and the forward side 117 of the bath container. The level of the bath in the bath container 106 is kept constant by recirculating the bath in the container. Fluid enters the bath container through the fluid inlet 116, flows over the weir 112, and exits the bath container through the fluid outlet 115. A fluid inlet 116 and outlet 115 may be connected to a fluid source such as a storage tank (not shown).
The pick-up roll 103 and bristle roll 109 extend between L-shaped support panels 118 and 121 which fit against interior sidewalls of the bath container 106. One of the support panels 118 is shown in phantom so that the pick-up roll 103 and bristle roll 109 are visible. The support panels 118 and 121 extend below the upper edge of the weir 112 and above the bristle roll 109. The support panels 118 and 121 each have frontal portions 124 and 127 which extend inwardly along the forward side 117 of the bath container 106. The pick-up roll 103 and bristle roll 109 are rotatably mounted in hubs (not shown) in the support panels 117 and 118. In addition to supporting the pick-up roll 103 and bristle roll 109, the support panels 118 and 121 function as a spray shield to prevent fluid spray from escaping from the ends of the brush spray applicator 100. The support panels 118 and 121 also inhibit air circulation about the pick-up roll 103 and bristle roll 109.
The pick-up roll 103 is positioned to extend partially above the bath container 106 and is partially submerged in the bath in the bath container. The pick-up roll 103 preferably has a shot-peened outer surface 130 for improved liquid pick-up and is crowned to allow for deflection of the pick-up roll and bristle roll 109 along their lengths.
The bristle roll 109 includes a core 133 which extends between the support panels 118 and 121 and an array of bristles 136 extending from the core. The bristles 136 are preferably from 1.2 to 1.75 inches long. The bristle roll 109 is positionable so that the ends of the bristles 136 contact the outer surface 130 of the pick-up roll 103 as the bristle roll rotates. Preferably the bristle roll 109 is adjustable so that the length of the portion of the bristles 136 contacting the outer surface 130 of the pick-up roll 103 is variable. It is also desirable that the bristle roll 109 be adjustable so that the bristle roll 109 can be disengaged from the pick-up roll 103. The dimensions of the bristles 136 and the materials from which the materials are made may vary, but the bristles should be capable of deflecting when contacting the pick-up roll 103 and then have enough resilience to spring to the original shape of the bristles and project fluid from the surface of the pick-up roll to form a spray of atomized fluid droplets.
The degree of interference between the bristles 136 and the outer surface 130 of the pick-up roll 103 is the length of the bristles which extends from the end of the bristles towards the core 133 of the bristle roll 109 and contacts the outer surface of the pick-up roll as the bristles pass over the outer surface of the bristle roll. The degree of interference between the bristles 136 of the bristle roll 109 and the pick-up roll 103 preferably ranges from about 0.01 to about 0.03 inches. The strip of contact along the outer surface 130 of the pick-up roll 103 between the outer surface and the bristles 136 of the bristle roll 109 also may vary but is preferably about 1/2 inch wide.
A spray shield 139 extends between the support panels 118 and 121 and over the bristle roll 109. A rearward shield 142 extends from the rearward edge of the spray shield 139 into the bath container 106 to a level below the upper edge of the weir 112 so that the lower edge of the rearward shield is below the level of the bath in the bath container. The rearward shield 142 also extends between the support panels 118 and 121. An air stripping doctor 145 extends along the rearward side of the pick-up roll 103 and is connected to the rearward shield 142 by air baffles 148. The air stripping doctor 145, air baffles 148 and rearward shield 142 inhibit the circulation of air about the pick-up roll 103 and bristle roll 109.
An upper fluid stripping doctor 151 extends from the forward edge of the spray shield 139 towards the nip between the pick-up roll 103 and bristle roll 109. A series of lower fluid stripping doctors 154, 155 and 156 are mounted on a platform 159 extending from proximate the nip between the pick-up roll 103 and the bristle roll 109 toward the forward side 117 of the bath container 106. The lower fluid stripping doctors 154, 155 and 156 are V-shaped and extend between the sides of the bath container. The lower fluid stripping doctor platform 159 has a vertical leg which extends from proximate the nip between the pick-up roll 103 and bristle roll 109 into the bath container 106 to a lower edge below the upper edge of the weir 112 so that the platform 159 extends into the bath in the bath container. The upper fluid stripping doctor 151 and the lower fluid stripping doctors 154, 155, and 156 control the path and angle of the fluid spray emitted from the nip between the pick-up roll 103 and bristle roll 109 and also aid in inhibiting the circulation of air about the pick-up roll and bristle roll. The upper fluid stripping doctor 151 and the lower fluid stripping doctors 154, 155 and 156 may be set in various positions but preferably are positioned so that the coating solution spray emitted from the nip between the pick-up roll 103 and bristle roll 109 has a spray angle from about 10 to about 20° and most preferably 15°.
As shown in Figure 6, during operation of the brush spray applicator 100, the material to be treated, such as a nonwoven web 165, is passed over rollers 168 and 171 and through the path of fluid spray emitted from the brush spray applicator.
During operation of the brush spray applicator 100, a coating solution is introduced into the bath container 106 through the fluid inlet 116 and as explained above is continuously recirculated so that the weir 112 maintains the bath at a constant level. The pick-up roll 103 and bristle roll 109 are rotated at different speeds by a motor which is not shown. The speeds of the pick-up roll 103 and bristle roll 109 may vary considerably depending on the factors such as the bath viscosity, the nature of the bristles 136 of the bristle roll 109, and the desired rate of application of the coating solution. However, the pick-up roll 103 preferably operated at a speed from about 1.5 to about 15 rpm and the bristle roll is preferably rotated at a speed from about 480 to about 1200 rpm. Preferably, the bristle roll is capable of operating at a velocity sufficient so that the coating solution can penetrate the material being treated, and more preferably, penetrates the material from the one side of the material facing the spray to the opposite side of the material. The line speed of the material being treated can also vary considerably but preferably varies between 135 and 1750 feet per minute.
The nonwoven material 165 is preferably a hydrophobic, nonwoven spunbonded web having a basis weight from about 0.5 to about 1.5 ounces per square yard and higher. Such material is well known in the art and may be prepared in a conventional fashion in accordance with the patents identified above with regard to the nonwoven material 18 shown in Figure 1.
The coating solution applied with the brush spray applicator 100 comprises a wetting agent in the amount from about 10 to 100 percent by weight and a solvent in an amount from about 90 to about 0% by weight. Preferably, the wetting agent is present in the coating solution in an amount from about 10 to about 30% by weight and the solvent is present in the coating solution in an amount from about 90 to 70% by weight. The wetting agent is preferably a surfactant and more preferably non-ionic surfactant. Suitable surfactants include TRITON X-102 available from Union Carbide, Y-12230 Polyalkylene-oxide dimethyl siloxane available from Union Carbide, and Lubrizol 85870 ethoxylated amino sorbitol succinate salt available from the Lubrizol Corporation of Wickliffe, Ohio. Water is a suitable solvent.
The wetting agent is applied to the nonwoven web 165 in an amount from about 0.1 to about 1% by weight of the material and the solvent is applied to the material in an amount not exceeding 5% by weight of the material. When the wet pick-up of the material is not greater than about 2% by weight, the material can be naturally dried at a commercially acceptable rate. However, with a wet pick-up of more than about 2% by weight of the material, the material is dried preferably by passing heated air through the material a process which is commonly known as through-air drying. As with the printing method disclosed above, the brush spray application method preserves the tensile strength of material but also preserves the loft of the material. The material treated with the brush applicator system 100 initially has a first tensile strength, and after the coating solution has been applied to the material and the material has been dried, has a second tensile strength which is at least 85% of the first tensile strength. In addition, materials coated with the brush spray applicator system 100 initially have a first thickness, and after the coating solution has been applied to the material and the material has been dried, the material has a second thickness which is at least 85% of the first thickness.
The following Examples 2-7 are designed to illustrate particular embodiments of the present invention made according to the above-disclosed brush spray application method and teach one of ordinary skill in the art how to carry out the brush spray application method of the present invention. The following Comparative Examples 1 and 2 are designed to illustrate advantages of the present invention. For each of the Examples 2-7, the following conditions were maintained:
The pick-up roll 103 was made of stainless steel with a 100 rms finish and had a 6.375 inch diameter. The pick-up roll 103 was rotated between 2 and 10 rpm. The brush roll 109 had a total diameter of 10 7/16 inches and white nylon bristles that were 1 3/8 inches long with a diameter of 0.012 inches. The bristle roll 109 was rotated at 850 rpm. The degree of interference between the bristles 136 of the bristle roll 109 and the outer surface 130 of the pick-up roll 103 was 0.015 inches and the clearance between the bristle roll and the spray shield 139 was 1/16 inch. The clearance between the upper fluid stripping doctor 151 and the bristle roll was 1/16 inch at the heel and 0.015 inches at the tip. The lower fluid stripping doctors 154, 155, and 156 were located 1/8 inch below the top of the pick-up roll 103. The air baffles 148 were spaced 6 inches apart and the clearance between the air baffles and the bristle roll was 1/32 inch. The bath in the bath container 106 was recirculated between the bath container and a recirculation tank at a rate of 5 gallons per minute. The level of the bath was maintained such that the pick-up roll 103 was submerged 2.25 inches into the bath. The strip of contact between the outer surface 130 of the pick-up roll 103 and the bristles 136 of the bristle roll 109 was about 1/2 inch wide. The resulting spray from the bristle roll 109 was controlled to a 15 degree pattern by the upper fluid stripping doctor 151 and the lower fluid stripping doctors 154, 155 and 156. The nonwoven webs being treated were directed vertically and upwardly with respect to the brush spray applicator system 100 at a distance of 1/4 inches from the outermost portion of the lower fluid stripping doctor platform 159 and 8/14 inches from the nip between the pick-up roll 103 and the bristle roll 109.

EXAMPLE 2

Using the above-described brush spray applicator system 100, a calender point-bonded polypropylene spunbond nonwoven fabric having a basis weight of 0.5 osy and a thickness of 0.007 inches was treated with a bath comprising 25% by weight TRITON X-102 surfactant available from Union Carbide and 75% by weight water. The nonwoven fabric was treated at a line speed of 340 feet per minute and the speed of the pick-up roll was 4.6 rpm. No drying was necessary.

EXAMPLE 3

A calender point bonded polypropylene spunbond nonwoven fabric having a basis weight of 0.7 osy and a thickness of 0.010 inches was treated in accordance with the procedure described in Example 2 except that the pick-up roll speed was 5.6 rpm.

EXAMPLE 4

A calender point bonded polypropylene spunbond nonwoven fabric having a basis weight of 1.0 osy and a thickness of 0.018 inches was treated in accordance with the procedure of Example 2 except that the pick-up roll speed was 7.0 rpm.

The treated fabrics from Examples 2-4 were evaluated and results are shown in Table 1. The web pick-up is shown in percent by weight of the web fabric and is the amount of bath added to the fabric. The surfactant surface concentration (surf. conc.) is the amount of surfactant added to the treated fabric in percent by weight of the treated fabric. The run-off test was performed with the following procedure:
A 5 inch by 15 inch piece of a treated fabric was placed flat on top of an absorbent medium which was positioned at a 30° incline plane. A funnel was placed above the fabric. 100 millimeters of distilled water at 35°C plus or minus 0.6°C was dispensed from the funnel onto the fabric over a time period of 15 seconds plus or minus 1.5 seconds. Any of the distilled water that was not absorbed by the fabric ran off the fabric and was collected. The volume of run-off water was measured.

TABLE 1

	Basis Weight osy	Surfactant Surf. Conc. %	Wet Pick-up-%	Runoff,mls (Treated Side)	Runoff,mls (Untreated Side)
EXAMPLE 2	0.5	0.28	1.1	0.1	0.1
EXAMPLE 3	0.7	0.40	1.6	0.3	0.5
EXAMPLE 4	1.0	0.31	1.2	2.0	3.3

As can be seen from the data in Table 1, despite a wet pick-up of 1.6% by weight or less for each of the fabric samples of Examples 2-4 and having treated only one side of each sample with surfactant, both the treated and untreated sides of the samples were rendered hydrophilic. Because of the low wet pick-up of the samples, no drying was necessary. The coefficient of variation of the surfactant surface concentration for the samples from Examples 2-4 was observed to be less than 10%.

EXAMPLE 5

A calender point bonded polypropylene spunbond nonwoven web having a basis weight of 0.7 osy and a thickness of 0.01 inches was treated with the brush spray applicator system 100 described above. The bath comprised 25% by weight TRITON X-102 surfactant available from Union Carbide and 75% by weight water. The fabric was treated at a line speed of 700 feet per minute and the pick-up roll speed was 4.0 rpm. The resulting fabric required no drying.

EXAMPLE 6

A calender point bonded polypropylene spunbond nonwoven web having a basis weight of 0.7 osy and a thickness of 0.01 inches was treated in accordance with the procedure of Example 5 except that the line speed was 1750 feet per minute and the pick-up roll speed was 7.0.

Treated fabric samples from Examples 5 and 6 were analyzed and the results are shown in Table 2. The properties shown in Table 2 were measured according to the same procedures for obtaining the properties shown in Table 1. The grab tensile was measured according to ASTM D 1682. Like Examples 2-4, the sample fabrics from Examples 5 and 6 were hydrophilic on both the treated side and untreated side with a very low wet pick-up. The samples from Examples 5 and 6 were compared to a Comparative Example 1 (Comp. Ex. 1) which was an untreated calender point bonded polypropylene spunbond nonwoven fabric having a basis weight of 0.7 osy.

TABLE 2

	Basis Weight osy	Surfactant Surf. Conc. %	Wet Pick-up-%	Runoff,mls (Treated Side)	Runoff,mls (Untreated Side)	CD Grab Tensile lbs.
EXAMPLE 5	0.7	0.26	1.0	1.5	1.2	6.37
EXAMPLE 6	0.7	0.30	1.2	0.9	0.7	6.46
Comp. Ex. 1	0.7	0	0	>95	>95	7.29

The data shown in Table 2 is similar to the data shown in Table 1 and the same observations can be made. In addition, however, Table 2 shows that the tensile strengths of samples from Examples 5 and 6 are at least 87% of the tensile strength of the untreated fabric of Comparative Example 1.

EXAMPLE 7

A through-air bonded polypropylene/polyethylene bicomponent spunbond nonwoven fabric having a basis weight of 1.5 osy, a thickness of 0.05 inches, and filaments of 4 denier was treated with the brush spray applicator system 100 described above. The treatment bath comprised 10% by weight Y-12230 polyalkylene-oxide dimethyl siloxane available from Union Carbide, 25% by weight Lubrizol 85870 ethoxylated amino sorbitol succinate salt available from the Lubrizol Corporation of Wickliffe, Ohio, and 65% by weight water. The fabric was treated at a line speed of 135 feet per minute and the speed of the pick-up roll was 3.2 rpm. The fabric was then through-air dried at a temperature of 240°F.

COMPARATIVE EXAMPLE 2

A through-air bonded polypropylene/polyethylene bicomponent spunbond nonwoven fabric having a basis weight of 1.5 osy, a thickness of 0.05 inches, and filaments of 4 denier was treated with a surfactant bath using a conventional nozzle spray apparatus. A treatment bath comprising 0.53% by weight Y-12230 polyalkylene-oxide dimethyl siloxane available from Union Carbide, 1.33% by weight Lubrizol 85870 ethoxylated amino sorbitol succinate salt available from the Lubrizol Corporation of Wickliffe, Ohio with the remainder being water. The fabric was treated at a line speed of 80 feet per minute. The resulting treated fabric was through-air dried at a temperature of 250°F.
Wet and dry samples of treated samples from Examples 7 and Comparative Example 2 were analyzed and the results are shown in Table 3. The same procedures for measuring the properties shown in Table 3 are the same procedures used to obtain the data shown in Table 2. However, the samples of fabric were repeatedly subjected to the run-off test and then washed until the amount of run-off water from the run-off test exceeded 20 milliliters. The number of cycles required for the run-off test to exceed 20 milliliters is shown in Table 3. The fabric samples were washed by submerging the samples in 500 milliliters of water at 25°C and than agitating the samples in the water for 1 minute. The washed samples were then dried in a oven at 200°F for 8 minutes.

The samples from Example 7 and Comparative Example 2 were also subjected to the penetration rate desorption (PRD) test which is as follows:
A 3-inch diameter sample of treated fabric was first weighed and then placed on a screen inside a 2 7/8-inch diameter sample holder so the edges of the sample curled upward along the sides of the sample holder. A 0.103-inch diameter nozzle was positioned 3.5 inches above the center of the sample screen and 100 ml of synthetic urine was deposited on the sample in 6 seconds. The time required for the liquid to completely penetrate the surface was measured and is referred to as the penetration time. After complete penetration of the liquid through the fabric surface, the fabric was removed from the sample holder and weighed. The difference in the weight of the fabric before and after the application of the liquid was calculated as the wet pick-up. The sample was then dried and the procedure was twice repeated. The penetration time and wet pick-up for the samples from Example 7 and Comparative Example 2 are shown in Table 3.

TABLE 3

	Basis Weight osy	Surfactant Surf. Conc. Y-12230,%	Surfactant Surf. Conc. Lubrizol,%	Wet Pick Up %	Wash/Runoff Cycles	PRD Test
						3rd Time (sec)	3rd Pick Up,gm
EXAMPLE 7	1.5	0.4	1.0	4.0	6	7.2	6.44
COMPARATIVE EXAMPLE 2	1.5	0.4	1.0	75	7	7.2	6.02

As can be seen from the data shown in Table 3, the fabric sample from Example 7 treated in accordance with the present invention remained hydrophilic for up to 6 wash cycles despite a wet pick-up of only 4% by weight. The fabric sample from Comparative Example 2 wherein the surfactant was applied with a nozzle spray remained hydrophilic for up to 7 wash cycles but had a wet pick-up of 75% by weight after treatment. The line speed for Example 7 was considerably faster than of Comparative Example 2 because the drying time for the sample from Example 7 was significantly less than that for compared to Example 2 due to the low wet pick-up of the fabric from Example 7. In addition, the PRD data in Table 3 shows that the absorbency of fabric treated with the brush spray and conventional nozzle spray methods are comparable.
The foregoing description relates to preferred embodiments of the present invention, and modifications or alterations may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

A process for coating a material comprising the steps of:
introducing a coating solution to a rotating pick-up roll, the coating solution comprising from about 10 to about 100% by weight of a wetting agent and from about 90 to about 0% by weight of a solvent;
contacting the rotating pick-up roll with bristles of a rotating bristle roll and thereby projecting a spray of the coating solution along a path from the rotating pick-up roll; and
passing the material through the path of the spray so that a portion of the coating solution is applied to one side of the material in an amount such that the wetting agent is applied to the material in an amount from about 0.1 to about 1% by weight of the material and the solvent is applied to the material in an amount not exceeding 5% by weight of the material.
A process as in claim 1 wherein the material comprises a substantially hydrophobic, polymeric, nonwoven fabric.
A process as in claim 2 wherein the material has a basis weight from about 0.5 to about 1.5 ounces per square yard.
A process as in claim 1 further comprising the step of drying the material after the coating solution has been applied to the material.
A process as in claim 4 wherein the drying step includes the step of passing air through the material.
A process as in claim 1 wherein the material initially has a first tensile strength, and after the coating solution has been applied to the material, has a second tensile strength which is at least 85% of the first tensile strength.
A process as in claim 4 wherein the material initially has a first tensile strength, and after the drying step, has a second tensile strength which is at least 85% of the first tensile strength.
A process as in claim 1 wherein the material initially has a first thickness, and after the coating solution has been applied to the material, has a second thickness which is at least 85% of the first thickness.
A process as in claim 4 wherein the material initially has a first thickness, and after the drying step, has a second thickness which is at least 85% of the first thickness.
A process as in claim 1 wherein the wetting agent comprises a surfactant.
A process as in claim 1 wherein the wetting agent is applied in an amount from about 0.1 to about 0.5% by weight of the material and the solvent is applied in an amount not exceeding about 2% by weight of the material.
A process as in claim 1 wherein the wetting agent is present in the coating solution in an amount from about 10 to about 30% by weight and the solvent is present in the coating solution in an amount from about 90 to about 70% by weight.
A process as in claim 1 the coating solution spray is projected towards the material at a spray angle from about 10 to about 20°.
A process as in claim 1 wherein the pick-up roll is rotated at a speed from about 1.5 to about 15 rpm.
A process as in claim 14 wherein the bristle roll is rotated at a speed from about 480 to about 1200 rpm.
A process as in claim 1 wherein the pick-up roll and the bristle roll are positioned relative to one another so the degree of interference between the bristles of the bristle roll and the pick-up roll ranges from about 0.01 to about 0.03 inches.
A process as in claim 15 wherein the pick-up roll and the bristle roll are positioned relative to one another so the degree of interference between the bristles of the bristle roll and the pick-up roll ranges from about 0.01 to about 0.03 inches.
A process as in claim 1 wherein the spray of coating solution is projected with sufficient velocity so that a portion of the wetting agent penetrates the material from the one side of the material to an opposite side of the material.
A process as in claim 1 wherein the spray of coating solution is projected with a velocity effective to treat only one side of the material with the wetting agent.
An apparatus for coating a material comprising:
a rotatable pick-up roll;
a rotatable bristle roll including an array of bristles extending from the bristle roll;
means for introducing a coating solution to the pick-up roll, the coating solution comprising from about 10 to about 100% by weight of a wetting agent and from about 90 to about 0% by weight of a solvent;
means for rotating the pick-up roll;
means for rotating the bristle roll;
means for contacting the rotating pick-up roll with the bristles of the rotating bristle roll and thereby projecting a spray of the coating solution along a path from the rotating pick-up roll; and
means for passing the material through the path of the spray so that a portion of the coating solution is applied to one side of the material in an amount such that the wetting agent is applied to the material in an amount from about 0.1 to about 1% by weight of the material and the solvent is applied to the material in an amount not exceeding 5% by weight of the material.