FLUORINE-FREE HYDROPHOBIC AND OLEOPHOBIC NONWOVEN

Abstract

The invention relates to fluorine-free hydrophobic and oleophobic nonwoven for use, for example, in automotive engine bays, and a method for making such nonwoven.

Claims

1. A method for making a nonwoven fabric having hydrophobic and oleophobic properties, the method comprising the following steps: providing a nonwoven fabric comprising fibers; providing an aqueous colloidal solution comprising nanoscale SiO.sub.2-particles, which is formed from an aqueous precursor solution comprising a SiO.sub.2-producing substance; and applying the colloidal solution onto the nonwoven fabric to form a hydrophobic and oleophobic finish on fibers of the fabric and thereby impart hydrophobic and oleophobic properties.

2. The method of claim 1, wherein the fibers are carded fibers.

3. The method of claim 1, wherein the fibers comprise 50 wt % to 100 wt % synthetic fibers.

4. The method of claim 1, wherein the SiO.sub.2-producing substance is a silicon alkoxide.

5. The method of claim 1, wherein the solvent of the aqueous precursor solution is water or a mixture of alcohol and water.

6. The method of claim 1, wherein the aqueous precursor solution comprises a hydrolysis and condensation catalyst.

7. The method of claim 1, wherein the solids content in the colloidal solution is between 0.1 and 15 wt %.

8. The method of claim 1, wherein the colloidal solution is applied onto the surface of the nonwoven fabric by spray application, coating or by foaming.

9. The method of claim 1, wherein the amount of colloidal solution applied to the nonwoven fabric is between 0.1 g/m.sup.2 and 5 g/m.sup.2.

10. A nonwoven fabric comprising a surface having a hydrophobic and oleophobic properties, wherein the nonwoven fabric comprises fibers and wherein a hydrophobic and oleophobic finish is present on fibers of the fabric, thereby imparting hydrophobic and oleophobic properties to the fabric, wherein the finish comprises a continuous or interrupted porous SiO.sub.2-containing layer of nanoscale thickness.

11. The nonwoven fabric of claim 10, wherein the layer has a thickness of 10 to 300 nm.

12. The nonwoven fabric of claim 10, wherein the surface free energy of the surface having a hydrophobic and oleophobic properties is 24 mN/m or lower.

13. The nonwoven fabric of claim 10, wherein the porous SiO.sub.2-containing layer comprises structural elements from SiO.sub.2, RSiO.sub.1.5, and/or R.sub.2SiO, where RH, alkyl, aryl, epoxy-alkyl, or aminoalkyl.

14. An automotive article, said article comprising the nonwoven fabric according claim 10.

15. The method of claim 1, wherein the fibers are carded fibers and providing the nonwoven fabric includes carding and laydown of the carded web on a conveyor of a production line.

16. The method of claim 1, wherein the fibers are carded fibers and providing the nonwoven fabric includes carding and laydown of the carded web on a conveyor of a production line involving cross-laying the carded web.

17. The method of claim 1, wherein the fibers comprise 50 wt % to 100 wt % synthetic fibers and formed from polypropylene, polyethylene, polyethylene terephthalate, polyacrylate, polyacrylonitrile, polyamide, or a mixture thereof.

18. The method of claim 1, wherein the SiO.sub.2-producing substance is a silicon alkoxide that is selected from one or more of a tetraalkoxysilane, an alkyltrialkoxysilane, a dialkyldialkoxysilane, or any mixture thereof, preferably alkyltriethoxysilanes or aminopropyltriethoxysilanes.

19. The method of claim 1, wherein the solids content in the colloidal solution is between 1 and 7 wt %.

20. The method of claim 1, wherein the amount of colloidal solution applied to the nonwoven fabric is between 0.5 g/m.sup.2 and 2 g/m.sup.2.

Description

[0027] Further details and advantages of the invention will become apparent from the working examples and figures described in the following. In the figures:

[0028] FIG. 1: shows a production line for carrying out a method of the invention;

[0029] FIG. 2: visual results for the inventive fluorine-free treatment;

[0030] FIG. 3: a microscopic image of the surface-facing fibers of a 30 wt % viscose and 70 wt % polyester nonwoven fabric on which the inventive fluorine-free treatment has been carried out; and

[0031] FIG. 4: a microscopic image of the surface-facing fibers of a 30 wt % viscose and 70 wt % polyester nonwoven fabric before the inventive fluorine-free treatment has been carried out.

EXAMPLE 1-COLLOIDAL SOLUTION PREPARATION

[0032] Production of an aqueous colloidal solution comprising nanoscale SiO.sub.2-particles in a first embodiment:

[0033] 100 ml tetraethoxysilane, 400 ml water and 200 ml 0.01 N hydrochloric acid as a polycondensation catalyst are mixed at ambient temperature (20 C.) and stirred continuously (approx. 5 hours). The result is an aqueous silica sol-gel, with a solids content of approx. 4.5% and with an average particle size of 6 nm.

EXAMPLE 2-COLLOIDAL SOLUTION PREPARATION

[0034] Production of an aqueous colloidal solution comprising nanoscale SiO.sub.2-particles in a second embodiment:

[0035] 40 ml tetraethoxysilane, 40 ml aminopropyltriethoxysilane, 20 ml 3-methacryloxypropyltrimethoxysilane and 400 ml water are mixed at ambient temperature (20 C.), wherein the SiO.sub.2-forming precursors in the order tetraethoxysilane, aminopropyltriethoxysilane and 3-methacryloxypropyltrimethoxysilane after in each case 3 hours stirring are added to the solvent H.sub.2O. Then, while stirring, the 200 ml 0.01 N hydrochloric acid carboxylic acid as a polycondensation catalyst is titrated. The result is an aqueous silica sol-gel with a solids content of approx. 6% and with an average particle size of 6 nm.

EXAMPLE 3-PRODUCTION

[0036] FIG. 1 illustrates a production line 100 that can be used for carrying out a method of the invention for making a hydrophobic and oleophobic nonwoven fabric.

[0037] The production line 100 comprises a number of stations subsequently arranged. The first station 110 is for fiber preparation and comprises means like a hopper feeder or the like for enabling a uniform feed of staple fibers to carding machine 120. From the carding machine 120, a perforated conveyor belt travels through the subsequent spunlacing station 130, which is followed in-line by a first drying station 140, a foam-application station 150 and a second drying station 160 before the finished dried nonwoven fabric is wound up onto a roll.

[0038] The carding machine 120 and subsequent spunlacing station 130 can be configured as generally known in the art. The fibers of the fibrous web formed from the laydown in station 120 can be conveyed on the conveyor belt at high speed of, for example, 5 meters per minute and 25 meters per minute, and be mechanically bonded by means of high energy water jets.

[0039] Next in line is the first drying oven 140, which dries the fabric that is wet from spunlacing.

[0040] Next in line is the foam-application station 150, which is representative for the key step of the inventive process. The nonwoven fabric enters the foam-application station 150 at unchanged travel speed. The foam-application station 150 comprises a foam application system suitable to uniformly apply at a rate sufficient high to apply between 0.1 and 2 gram per square meter dry content of the colloidal solution comprising nanoscale SiO.sub.2-particles.

[0041] The foam-application station 150 is followed by a drying station 160, which comprises a drying oven through which the chemistry loaded nonwoven fabric travels with unchanged speed for drying under elevated temperature. In a final in-line step, the dried nonwoven fabric is wound up to form large rolls of meters in width and up to kilometres in length. The rolls can be stored in a warehouse, shipped to different locations, and unwound for further processing.

EXAMPLE 4-PRODUCT TEST

[0042] A carded and spunlaced polymer fiber (100% PET) nonwoven fabric has been prepared.

[0043] For the inventive samples, an amount of 1.03 g/m.sup.2 of a colloidal solution of the invention based on solids content of SiO.sub.2 was spray-applied to the fabric and the fabric was dried in an oven (hot air 190 C.) for 15 minutes.

[0044] Reference samples comprised untreated samples and samples treated by a standard C6 fluoro chemical.

[0045] During the tests, carried out according to ISO 14419, 5 drops of 0.5 ml each of different liquids were deposited on the surface. The result was recorded after 10 seconds. The results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Surface tension Negative C-6 fluoro Fluorine-free Liquid (mN/m) reference chemical treatment Distilled water 72 Not OK OK OK Liquid no. 3 27.3 Not OK OK OK (n-hexadecane) Liquid no. 4 26.4 Not OK OK OK (n-tetradecane) Liquid no. 5 24.7 Not OK OK OK (n-dodecane) Liquid no. 6 23.5 Not OK OK OK (n-decane) Liquid no. 7 21.4 Not OK OK OK (n-octane) Liquid no. 8 19.8 Not OK Not OK Not OK (n-heptane)

[0046] Visual results for the inventive fluorine-free treatment are shown in FIG. 2. As apparent, the liquids 1 to 7, i.e. even liquids with a surface tension down to 20 mN/m, did not penetrate into the fabric due to the oleophobic properties imparted by the inventive treatment.

[0047] A microscopic image of the surface-facing fibers of the nonwoven fabric on which the inventive fluorine-free treatment has been carried out is shown in FIG. 3. A comparative picture of the same type of nonwoven, before the treatment has been carried out, is shown in FIG. 4.

[0048] The comparison demonstrates the result of the inventive treatment, namely the nanoscale modified silica surface hierarchy on the nonwoven fabric fibers, which is produced by means of a sol-gel process. This structure imparts a surface tension around 20 mN/m and is thus both hydrophobic and oleophobic.