AU658701B2

AU658701B2 - Nonwoven, coated substrates and method of applying a coating at high bath concentration and low wet pick-up

Info

Publication number: AU658701B2
Application number: AU29959/92A
Authority: AU
Inventors: Charles Wilson Colman; Cheryl Anne Perkins; John Joseph Sayovitz
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 1991-12-13
Filing date: 1992-12-07
Publication date: 1995-04-27
Anticipated expiration: 2012-12-07
Also published as: ES2093168T3; DE69214609D1; MX9206513A; CA2069839A1; ZA928532B; AU2995992A; EP0546580A1; KR930013307A; DE69214609T2; EP0546580B1; JPH05279950A

Description

S F Ref: 224409

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIRCATION FOR A STANDARD PATENT

ORIGINAL

01 t t t4 i tr 4 4 4 4 Name and Address of Applicant: Kimberly-Clark Corporation 401 North Lake Street Neenah Wisconsin 54956 UNITED STATES OF AMERICA Charles Wilson Colman, Cheryl Sayovitz I I C Actual Inventor(s): Address for Service: Invention Title: Anne Perkins, John Joseph Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Nonwoven, Coated Substrates and Method of Applying a Coating at High Bath Concentration and Low Wet Pick-up 4 4 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845/4 "NONWOVEN, COATED SUBSTRATES AND METHOD OF APPLYING A COATING AT HIGH BATH CONCENTRATION AND LOW WET PICK-UP" Technical Field This invention relates to coated materials and processes for coating fibrous 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 a process for uniformly coating a nonwoven, hydrophobic material with a wetting agent at high bath concentration and low wet pick-up. In addition, it relates to resulting S 15 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.

Background of the Invention Nonwoven, hydrophobic substrates or materials are wel3 known in the art. Many disposable products such as diapers alnd sanitary napkins are constructed with top sheets made of nonwoven, hydrophobic material. The outer surface of these top sheets is typically treated with a wetting agent to allow 25 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 surfac6 treated with a wetting agent are preferred for such applications over top sheets made with a hydrophilic material because the wetting 30 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".

It is desired to apply the wetting agent to the nonwoven material in a uniform concentration for aesthetics i, and to provide uniform wettability to the outer material.

Al 2 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 lo material. 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. 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 of the material.

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Cr C AC C CoS C C [N:\LIBLL]00142:LMM i I~--=PY4 -LL- II--p-M~LL" III*~ )I 3 Summary of the Invention There is disclosed herein a process for uniformly coating a fibrous material, said process comprising the steps of: introducing a coating solution to a first rotating roll, said coating solution containing between 20 and 30 percent by weight of a wetting agent and between 70 and percent by weight of a solvent; and (ii) passing said material through a nip defined between said first roll and a second rotating roll positioned adjacent said first roll, wherein a portion of said coating solution is applied by said first roll to a surface of said material in an amount such that, said wetting agent is applied to said material in an amount of between 0.1 and 0.5 percent by weight of said material, and said solvent is applied to said material in an amount not exceeding 1 percent by weight of said material.

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LIt6 (1 tIt 4i 4 Brief Description of the Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: 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.

Detailed Description of the Invention While the invention will be described in connection with a preferred embodiment and method, it will be understood that we do not intend to limit the invention to that embodiment or method. On the contrary, we intend to cover all alternatives, modifications, and equivalents as may be 25 included within the scope of the invention as defined by the appended claims.

The nonwoven material 18 is preferably a hydrophobic, nonwoven spunbonded web having a basis weight of between about 0.5 and 1.0 ounces per square yard 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; 35 Kinney United States Patent Nos. 3,338,992 and 3,341,394; Lev S* 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 Apel et al. United States Patent No. 4,340,563. Other '7 nonwoven mate are contempli i 'The wE nonwoven mal hydrophilic preferably z 3rials and methods ated for use with itting agent 14 is terial 18 using properties to the "differential" for forming nonwoven materials the present invention.

applied to a surface 50 of the the printer 10 to provide surface 50. The printer 10 is type printer, with the term $44 S .5* 4 *1 4 ea e rrr o er I .25; 41 e it t l t t I K "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. A preferred wetting agent for use with nonwoven materials having a basis weight up to about 0.8 osy is "Triton X-102," available from Union Carbide. "Gemtex SM-33", 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 of between about 0.1 percent to 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 4441r 454 in the art as a 550 (cells per inch) quad, 1. 7 CBM. The gravure roll preferably rotates at a speed of between about 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 oetween about 300 and 1,500 feet per V 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 distance between the transfer roll 111%24 and the gravure roll 38 which defines the nip 39 is preferably between about 1/16 and 1/2 inch to achieve the #4 I t4 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 r611 24 preferably rotates at a rate which advances the material at a line speed of between about 300 and 1,500 feet per minute, *with an optimum line speed of about 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 I hardness of about 90. The backing roll 20 rotates at a rate V which provides the same line speed as the transfer roll 24.

The spacing between the backing roll 20 and the transfer roll which defines the nip 30 is preferably between about 1/4 and 3/4 inch and is optimally about 3/8 inch when coating Aj 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. In order to evaluate the effect of rx~ating 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"1 aqueous solution to a 0.7 osy nonwoven, hydrophobic material. The solution was applied using an "inverted L"1 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 in the cross-direction (Fig. 2) and in the machine-direction f Fig.

3) The representative sample exhibited overall a 5. 0 percent a 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 -direct ion or c3sckle position. Material treated in accordance with 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 spray treatment and treatments requiring secondary drying over steam c"ris.

The printing process of the present invention coats the 340 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 mililiters of runoff; hydrophobic material produces greater than 20 mililiters of runoff. A material having a hydrophilic and hydrophobic surface rapidly 4 allows fluid to pass through and does not allow it to flow back. Thus, such material acts as a "one way valve." It has 7 S been observed that materials having basis weights between and 1.0 osy which are treated in accordance with 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, some of the wetting agent transfers to the untreated side, producing a two-sided hydrophilic material.

S 10 The time required for the wetting agent to transfer to the untreated side being dependent upon the basis weight.

i Materials having a basis weight greater than about 0.85 osy remain one way valves in sheet or roll form. If two sided hydrophilic behavior is desired for materials having a basis S 15 weight in excess of 0.85 osy, a conventional four roll i differential printer (dual printer) may be utilized to apply i the wetting agent to both sides.

Micropore filtration testing of materials treated in 11 I"'t accordance with the invention showed reduced levels of Class i I, Class II and Class III bacteria when compared with I 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 other gram positive cocci, l| Oxidative-Fermentative bacteria, and other gram negative rods.

Class III included Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella sp., and Candida albicans.

S 30 While the control had a total CFU of 17, none of the treated samples exceeded 10 CFU.

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.

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Claims

1. A process for uniformly coating a fibrous material, said process comprising the steps of: introducing a coating solution to a first rotating roll, said coating solution containing between 20 and 30 percent by weight of a wetting agent and between 70 and percent by weight of a solvent; and (ii) passing said material through a nip defined between said first roll and a second rotating roll positioned adjacent said first roll, wherein a portion of said coating solution is applied by said first roll to a lo surface of said material in an amount such that, said wetting agent is applied to said material in an amount of between 0.1 and 0.5 percent by weight of said material, and said solvent is applied to said material in an amount not exceeding 1 percent by weight of said material.

2. The process of claim 1, wherein after said coating solution is transferred to said surface of said material, said material has a tensile strength which is at least percent of the tensile strength of said material before it is coated.

3. The process of claim 1, wherein said fibrous material is a nonwoven material.

4. The process of claim 3, wherein said nonwoven material comprises a nonwoven, hydrophobic material having a basis weight of between 16.95 and 33.9 g/m 2 rll5. The process of claim 1, wherein said nip is formed by positioning said first *roll and said second roll between 6.35 and 19.05 mm apart.

6. The process of claim 1, further comprising using a third roll to apply said coating solution to said first roll. S 5 7. The process of claim 6, wherein said third roll is positioned between 1.5 and ",13 mm apart from said first roll.

8. The process of claim 1, wherein said wetting agent is a surfactant. so's 9. A process for uniformly coating a fibrous, nonwoven material, the process being substantially as hereinbefore described with reference to the accompanying drawings. The process of claim 6 or claim 7, wherein the first roll rotates at a rate which advances the fibrous material at a line speed, and the third roll rotates at a rate equivalent to from 20 to 120 percent of said line speed.

11. A material coated in accordance with the process of any one of the preceding claims.

12. A substrate coated by the process of any one of claims 1, 2 or 4 to 10, the substrate comprising a fibrous material having on at least one side a coating with a i coefficient of variation in surface concentration of 10 percent or less.

13. The coated substrate of claim 12 comprising: i (NALIBLLOJ42:LMM ii a nonwoven material; and (ii) a coating on a surface of said nonwoven material, said coating comprising: a wetting agent applied to said nonwoven material in an amount of between about 0.1 and 0.5 percent by weight of the nonwoven material, and a solvent applied to said nonwoven material in an amount not exceeding about 1 percent by weight of said material.

14. The coated substrate of claim 13, wherein said coated substrate has a tensile strength which is at least 90 percent of the tensile strength of the nonwoven material. The coated substrate of claim 13, wherein said solvent is water.

16. The coated substrate of claim 13, wherein said wetting agent comprises a surfactant.

17. The coated substrate of claim 13, wherein said coating is applied to said surface using a differential printer.

18. The coated substrate of claim 13, wherein said wetting agent provides hydrophilic properties on the coated side of said substrate and the opposite side of said substrate is hydrophobic. Dated 16 February, 1995 L 'Kimberly-Clark Corporation Patent Attorneys for the Applicant/Nominated Person 20 SPRUSON FERGUSON t t I L% c c f e f [N:\LIBLLu !42:LMM i'I j NONNOVEN, COATED SUBSTRATES AND METHOD OF APPLYING A COATING AT HIGH BATH CONCENTRATION AND LOW NET PICK-UP ABSTRACT OF THE DISCLOSURE Nonwoven, hydrophobic fibrous substrates (18) uniformly coated with a wetting agent (14) are disclosed which have improved tensile strength properties over conventional coated, nonwoven substrates. Also disclosed I is a process for applying a high solids content wetting agent (14) to a i substrate (18) in a manner which results in low wet pick-up and 10 eliminates drying requirements. The low wet pick-up reduces degradation r e I 4~ of the tensile strength of the material normally resulting from with the wetting and drying of nonwoven substrates. In one embodiment the untreated side remains hydrophobic producing a "one-way valve" effect. Figure 1 Vo t 4r ch/7662N