Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-06-23
2002-07-09
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S164000, C156S182000, C427S176000, C427S358000, C427S369000
Reexamination Certificate
active
06416613
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods for improving adhesion between substrates and polymers and products made according to such methods. Such methods may produce products in areas as diverse as industrial composite hoses and medical garments.
BACKGROUND OF THE INVENTION
Substrate composite articles having a plurality of layers, especially those used to make garments, air bags and industrial composites, could be vastly improved if there was a method for improving adhesion between substrate and polymer layers; while maintaining the malleability and characteristics of the original substrate. For example, a problem that has long plagued the art has been the inability to construct a long-lasting, durable, reusable medical garment that is breathable and comfortable but impermeable to disease causing microorganisms such as viruses and bacteria. Moreover, industrial composite articles with increased durability, malleability and strength have been sought after by industry leaders for many years. What is needed is a single method of improving adhesion between substrate and polymer layers without adversely affecting desired properties of the original untreated substrate.
Methods for improving adhesion between multiple layers typically involve a combination of surface modification techniques. Several different physical types of surface modification exist. One type of surface modification is to covalently bind a modifier to a surface of a substrate material. Such binding can be achieved in many different ways such as chemical grafting onto the surface of the substrate through condensation or high energy addition reactions, or oxidizing the substrate away leaving a covalently bound modified surface. Covalently bound modifiers are usually the most durable surface modifications. However, such techniques are complicated, expensive and often environmentally hazardous to employ. Another type of surface modification is to cause an association or entrapment of the modifying molecule (or part of the molecule) with the substrate material. This commingling of modifier molecules and substrate relies on molecular attractions such as Van der Waals forces, dipole/dipole interactions, Hydrogen bonding, as well as steric factors to hold the modifier in/on the surface of the substrate. The factors that effect this type of reaction are similar to those that effect thermosol dyeing or blooming. Still another type of surface modification involves the retention of modifier by substrate with only adhesive and cohesive forces between the modifier to the substrate and the modifier to itself respectively. This last technique is the most common type of surface modification in the textile area and is the one in which the present invention makes a dramatic difference in the field of adhesion.
Methods for improving adhesion between substrate and polymer layers have previously come at the expense of other qualities such as durability, malleability, the environment, or performance characteristics. Addressing one aspect of desired qualities usually results in sacrificing other qualities. Conventional treatments for improving adhesion between substrate and polymer layers are typically unable to solve this dilemma and fall into the general categories of (i) surface coatings; (ii) saturations or impregnations; (iii) layers of fibers and/or polymers; (iv) unique chemical compositions; and (v) combinations of the foregoing.
I. Coatings
Coatings can be one or two sided but tend to be step gradients from one surface through the width of the substrate being treated, as opposed to homogeneous materials or continuous gradients. A step gradient has certain intrinsic disadvantages, due mostly to the fact that the coating composition contacts the substrate at one surface, thereby causing a substrate/coating-composition interface. Adhesion at this substrate/coating-composition interface derives mostly from surface forces, less than optimal mechanical interlocking, and sometimes little to no contribution from the cohesive strength of the modifying or coating material. Secondly because of the disparate materials plied together the resultant tactile properties of the composite (i.e.—hand, drape, etc.) are usually distinctly different than the base fabric. Typically, this interface tends to separate upon prolonged washing conditions or upon high stress conditions.
Prior fluorochemical and silicone (See U.S. Pat. Nos. 3,436,366; 3,639,155; 4,472,470; 4,500,584; and 4,666,765) fabric coating treatments evidently can protect only that side of the fabric upon which they are disposed. Such treatments significantly alter the hand, or tactile feel, of the treated side. Prior silicone fabric coatings typically degrade the tactile finish, or hand, of the fabric and give the coated fabric side a rubberized finish which is not appealing for many fabric uses, particularly garments. Coating techniques also encounter durability issues.
Porous webs have been further shown to be surface coated in, for example, U.S. Pat. Nos. 4,478,895; 4,112,179; 4,297,265; 2,893,962; 4,504,549; 3,360,394; 4,293,611; 4,472,470; and 4,666,765. These surface coatings impart various characteristics to the surface of a web, but remain on the surface and do not provide a film over the individual internal fibers and/or yarn bundles of the web. In addition, such coatings on the web surface tend to wash away quickly.
II. Saturation and Impregnation
Prior treatments of webs by saturation or impregnation with a polymer material, such as a silicone resin, polyurethane or neoprene material, are typically accomplished by immersion, using a low viscosity liquid so that the low viscosity liquid can flow readily into the web, and be adsorbed or absorbed therewithin. Immersion applications of one hundred percent (100%) solids, solvent dissolved solids, or aqueous emulsions can be performed by running a fabric through a bath and then drying. Particularly for flexible webs, including fabrics, an immersion application of a liquid or paste composition to the web is achieved, for example, by the so-called padding process wherein a fabric material is passed first through a bath and subsequently through squeeze rollers in the process sometimes called single-dip, single-nip padding. Alternatively, for example, the fabric can be passed between squeeze rollers, the bottom one of which carries the liquid or paste composition in a process sometimes called double-dip or double-nip padding. Usually, one hundred percent (100%) solids applications rely on low molecular weight materials (with viscosity's low enough for processing) that tend to yield a treated substrate with poor mechanical properties or higher molecular weight materials which often do not yield optimal penetration into the substrate. Solvent processing has environmental and economic issues such as removal of the solvent, fate of Volatile Organic Compounds (VOCs), and government permit requirements which are becoming stricter. Solvent and emulsion processing both are thermodynamically driven to yield low surface coverage due to poor substrate wet out (greater than zero contact angle), if the modifier is of a lower surface tension than the substrate (e.g. Durable Water Repellant—DWR). Provided the surface of the substrate is wet out by the modifier these techniques still require removal of the solvent or aqueous media which tends to cause imperfections in the polymer network, manifested as reduced mechanical properties of the modifier/substrate combination.
The silicone resin treated product is typically a rubberized web, or fabric, that is very heavily impregnated with silicone. For example, U.S. Pat. No. 2,673,823 teaches impregnating a polymer into the interstices of a fabric and thus fully filling the interstices. Thus, this patent provides no control of the saturation of the fabric and instead teaches full saturation of the interstices of the fabric. Such a treated web is substantially devoid of its original tactile and visual properties, and instead has the characteristic rubbery properties o
Caldwell James Michael
Patrick Rodney Lane
Gallagher John J.
Heisey David E.
Luce Forward Hamilton & Scripps
Nextec Applications Inc.
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