Fabric Coating Process and Product Thereof

The present invention relates to rainwear products which have superior durability, breathability and "handle". Notably, these products are substantially wind-resistant and water-repellent.

Generally, water-repellency and wind-resistance depend upon the characteristics of a fabric and the fiber from which it is constructed. Unbleached cotton and linen fabrics have inherent water-repellency because natural waxes are present. But, scoured and bleached cotton and linen fabrics, as well as rayon fabrics, are hydrophilic; that is, absorb water. Wool has some initial repellency, but it eventually absorbs water.

A synthetic fiber may resist water absorption, and yet fabrics composed of that fiber can be thoroughly wetted by water. What occurs is that water coating the surface of each fiber fills voids between fibers of the fabric. Because a fiber is hydrophobic, does not mean that fabrics made from them are water-repellent. In fact, voids which lie between fibers can act like capillaries to enhance the spreading and wicking of water. Consequently, fabrics are generally treated with special finishes to impart desirable characteristics.

Conventional finishes form a coating over the fabric surface. Typical finishes comprise paraffins, natural and synthetic rubber, as well as a variety of resins. Canvas illustrates such coated fabrics. Unfortunately, those finishes increase the weight of the product by approximately 50 to 90 percent. Moreover, the coated product is neither porous, durable nor soft.

Silicone and certain fluorinated polymers are also popular coating materials. However, these coatings are either not durable or not aesthetic. Moreover, both water and wind, for example, in a driving rain, can penetrate fabrics coated with these materials due to the porosity of the fabric and the force at which water and wind contact the fabric.

The present invention discloses a superior formulation, method of application and product thereof which overcomes the disadvantages of the prior art noted above and which is substantially wind-resistant and water-repellent.

According to the present invention, a unique chemical formulation is disclosed which, when applied to a fabric, results in a product that is substantially wind-resistant and water-repellent. The formulation comprises two critical components, namely, a silicone polymer and a tin catalyst. More specifically, the first component is a poly dimethyl siloxane compound having a concentration between about 93 to about 99% by weight. Siloxane compounds are manufactured by Dow Corning. The second component consists of a tin catalyst like dibutyl tin diacetate or preferably dibutyl tin dilaurate, both of which are manufactured by Dow Corning. The concentration of the tin catalyst should be between about 0.5 to about 1.5% by weight.

Optionally, the formulation includes an acid like glacial acetic acid manufactured by Industrial Chemical and an aromatic solvent like xylol manufactured by Amsco. The optional ingredients perform the function of extending the shelf life of the formulation once the polymer and tin catalyst are mixed. The concentration ranges for the acid and solvent are 0.0 to about 1.5% by weight and 0.0 to about 5.0% by weight, respectively.

A method is also taught for applying the formulation to a substrate such as fabrics used in manufacturing raincoats. The method comprises three basic steps. One step includes depositing the formulation on a substrate, uniformly distributing it across the width of the substrate and curing the product. Another step comprises dipping the substrate in a bath of silicone or hydrofluorocarbon solution and removing excess solution. The other treatment can be performed either before or after the first mentioned step. The last step comprises compressing the multicoated fibers of the substrate from the first two steps. This results in a product which is superior to those of the prior art. Specifically, the fabric is porous, durable, and has a good handle. More importantly, the product is substantially wind-resistant and water-repellent. Over all, it overcomes the disadvantages of the prior art noted above.

As previously mentioned, the formulation of the subject invention comprises two critical components as well as two optional components. The formulation listed below, along with the range of concentration for each of the components, is a typical formulation within the purview of the subject invention:

The preferred formulation is:

The poly dimethyl siloxane component is critical to the formulation. A suitable siloxane is manufactured by Dow Corning. Typically, the viscosity of the siloxane is between 20,000 to 40,000 centipoise at 25.degree. C. The silicone content is about 30% by weight.

Regarding the critical tin catalyst component, suitable catalysts are dibutyl tin diacetate, dibutyl tin dilaurate, and dibutyl tin octoate. The tin content of such catalysts are important. Dow Corning manufactures suitable catalyst under the trade names XY 170 (dibutyl tin dilaurate) and XY 176 (dibutyl tin diacetate). The tin content is 8.7% by weight and 33.4% by weight for the respective Dow Corning catalysts. That concentration of tin is contained within the concentration range of 0.5 to 1.5% by weight of the catalyst component.

The two remaining components are optional and function to reduce the viscosity of the formulation. More importantly, they increase the life of the formulation so that it is more suitable for commercial applications. Typically, the acid is acetate acid. Other acids are also suitable. The aromatic solvent is typically xylol. Other solvents, such as toluene, are suitable. Both the acid and solvent pass to the atmosphere during processing.

As previously mentioned, the method comprises three basic steps. One step is directed to the application of the unique formulation. The formulation is deposited upon a surface of a taut substrate, which continuously passes beneath the point of deposition. The formulation can be applied to one or both sides of the substrate. However, application to one side is preferred. Multiple depositions or coatings are within the purview of the subject invention. A conventional floating doctor blade, having a thickness of about 0.25 to 0.40, is used to uniformly spread the formulation across the width of the substrate. Thereafter the substrate and deposited formulation are cured in an oven having a temperature of about 300.degree. F. That conventional oven may have two stages with the first stage at 300.degree. F., while the second stage is at 325.degree. F. The purpose of the first mentioned step is to impart both wind-resistance and water-repellency to the finished substrate.

The viscosity of the formulation is typically between about 20,000 to about 100,000 centipoise as measured with a Brookfield Viscometer. A preferred range of viscosity is between about 20,000 and about 40,000 centipoise. If the viscosity is lower than 20,000 centipoise, the formulation will run through the substrate and stiffen it. If the viscosity is higher than about 100,000 centipoise, it becomes difficult to uniformly coat the surface of and penetrate the substrate.

Another step in the method comprises padding the substrate in a bath containing a silicone or a hydrofluorocarbon solution along with the attendant removal of excess solution. Typical silicone and hydrofluorocarbon solutions appear below:

A very thin coat of either solution is applied and produces an add-on weight to the finished product of about 0.05 to about 0.1 oz./square yard. The solution is dried for three minutes at about 250.degree. F. and cured for about two minutes at 340.degree. F. This other procedure can be applied either before or after application of the first step. If the solution is applied prior to the application of the formulation, a silicone solution is preferred. The purpose of this padding technique is to impart greater water-repellency to the substrate. The substrate is padded on both of its sides.

The last step in the method comprises compressing the substrate. For example, if a fabric is used, it is compressed or shrunk by conventional techniques about 1/10 of 1% in its width. Its length is compressed by a similar amount. The purpose of this step is to give the treated substrate a suitable handle.

The add-on weight to the substrate, after application of the method just described, should be between about 0.4 to about 0.8 oz./square yard. Significant is the fact that present invention is directed to coating fibers rather than coating the surface of a substrate constructed from these fibers.

Typical substrates used in the subject of the invention are polyester-cotton combinations at various percent mixtures, natural fiber fabrics, synthetic materials, and combinations of natural and synthetic materials. Some fabrics are not acceptable, such as canvas and taffeta. The density of such fabrics varies between about 3.0 to about 6.0 oz./square yard. The fabric must be closely woven or tight, that is, have a thread count of at least about 90 threads per inch in the warp and at least about 68 threads per inch in the weft or fill. A typical fabric would have a thread count of 106.times.70 threads per inch, i.e. warp.times.weft. A thread count less than those noted above allows the formulation to pass through the substrate.

The following examples illustrate the formulation, method of application and a product of the present invention. Although manufacture of rainwear material is described below, that manufacture is merely illustrative of the preferred product and is not considered to limit the present invention.

A number of formulations are described in the examples. The initial viscosity of each formulation is about 20,000 centipoise. The physical properties of the rainwear material manufactured in each example are also described. Several properties were evaluated, but each property pertains to characteristics essential for outerwear clothing that repels rain. A brief discussion of the most important of these follows along with the procedure used to evaluate the property.

Probably the most important of these tests is the Rain Test which measures the resistance of fabrics of penetration of water. A typical testing apparatus comprises an eight-foot water column which is connected to a spray nozzle facing a test sample that is stretch over a hoop. The specimen is backed by a weighed blotter and is sprayed for five minutes. Thereafter, the blotter is again weighed to ascertain any increase in weight caused by penetration of water through the sample. An increased weight of five grams is acceptable. An increased weight of about one gram is excellent.

Another test used to check rainwear is the Hydrostatic Pressure Test, sometimes called the Suter Test. It measures the resistance of fabrics to the penetration of water under static pressure such as that found in a driving rain. A water column is used; and like the Rain Test, water impinges on a sample stretched over a hoop. The first few drops of water penetrating the fabric signals completion of the test. The result is reported to the nearest centimeter of water column height.

Water vapor transmission is determined by using a special metal cup into which is measured about 90 mls of distilled water. The test sample is clamped over the cup and the level of the water is within about 20 mm of the fabric sample. The apparatus, including cup, water and sample, is weighed. After 24 hours in a conditioned atmosphere, the cup is re-weighed to determine loss of water which penetrated the sample. The data is reported in grams/hr./square meter. A number of 25-35 is considered ideal.

A polyester-cotton fabric having a thread count of 106 threads per inch by 70 threads per inch was tested. The fabric sample was processed according to the method detailed above. Specifically, a formulation was deposited on the sample. The formulation comprised:

That formulation was deposited on the fibrous substrate and evenly spread over one of its surfaces. The sample was then cured at about 300.degree. F. Then the sample was padded with the hydrofluorocarbon composition described in detail above. Excess solution was removed. The sample was dried for about three minutes at 250.degree. F. and then cured for about two minutes at 340.degree. F. That sample was then compressively shrunk using the conventional technique described above. The finished product containing multicoated fibers was analyzed. Pertinent physical properties are described below:

Example I was repeated except the formulation differed:

The physical properties of the resulting product were:

Example II was repeated except that the concentration of the acetic acid was reduced. The formulation appears below:

The physical properties of the product resulting from using the above formulation was substantially identical to those obtained in Example II. The decrease in the concentration of acetic acid merely decreased the shelf life of the formulation and increased its viscosity all in relation to the formula used in Example II.

Example II was again repeated except that a different catalyst was used. The formulation appears below:

The physical characteristics of the product manufactured using this formulation were substantially identical to those of Example II.

Example II was repeated on a commercial scale. Approximately 120 yards of sample were processed. Formula used was as follows:

The physical characteristics of the product are as follows:

This example utilizes the preferred formulation of the subject invention, Example I was repeated except that the fabric was padded with a silicone solution described in detail above instead of the hydrofluorocarbon solution. This example was operated at a commercial scale with approximately 6000 yards of fabric being manufactured. The formulation used in this commercial scale operation was:

The physical properties of the commercial product described above were as follows:

It is not intended to limit the present invention to the specific embodiments described above. It is recognized that other changes may be made in the formulation and method of application specifically described herein without deviating from the scope and teaching of the present invention. It is intended to encompass all other embodiments, alternatives, and modifications consistent with the present invention.