Patent Application
20190062959
This invention relates generally to high temperature polymer materials and, more particularly, to high temperature fabrics made from polymer filaments for use in various articles, such as belting and tray liners.
Polyphenylene sulfide (PPS) is used in chemical and heat resistant products. When PPS is drawn as a filament, whether as a monofilament or as part of a multifilament yarn, the filament will shrink at elevated operating temperatures, such as by 15% or more, depending on grade and filament manufacturing process, and application operating temperature. Furthermore PPS monofilament generally can have a ‘roughness’ after weaving that limits use in applications such as steam bulking and heat setting of yarns, various food applications, etc. There is a continuing need for improved monofilament materials for belting and other articles.
A general object of the invention is to provide improved polymer fabrics that can be used as a substrate with higher temperature resistance and/or dimensional stability in various fabricated parts for high temperature and/or liquid applications. The invention provides, at least in part, a fabricated part for a high temperature operation including a non-metallic substrate formed of a polymer fabric of woven non-absorbent polymer filaments, wherein the substrate is heat-resistant and heat set at a temperature that is above a predetermined operating temperature of an intended operation of the fabricated part. As used herein, references to the term “non-metal” or “non-metallic” are to be understood to refer to an element or material being devoid of metal.
In embodiments of this invention, the polymer filament includes a high temperature chain extended or cured polymer material, desirably obtained by the heat setting. “Heat setting” according to embodiments of this invention involves keeping the material at the setting temperature for a period of time such that a curing and/or crosslinking process occurs. This is discernable by a color change in the fabric and the heat set material of this invention has increased dimensional stability (little to no shrink) at the in-use temperature after being subjected to the curing temperature again.
The heat setting of the substrate according to this invention provides benefits such as pre-shrinking the polymer fabric and/or curing or chain extending the polymer material to impart higher heat resistance. Heat setting the substrate above the intended operating temperature, or the temperature of the intended use, allows for heat resistance and dimensional stability at that operating temperature. Without wishing to be bound by theory, curing PPS with heat in the presence of oxygen results in property changes that are a result of molecular chain extension and formation of molecular chain branches via an oxygen ion bonded between the aromatic rings of PPS. The curing increases the molecular weight, resulting in some thermoset-like properties, including good thermal stability, dimensional stability, and resistance to harsh chemical environments. However, PPS is a thermoplastic and does not suffer from many of the shortcomings of thermosets. For example, whereas PPS monofilament belting is known to shrink during high temperature use, the substrate and articles of this invention are pre-shrunk or thermally stabilized via the heat setting such that the product will not fail due to shrinkage or other destabilization in the operation at, for example, 212° F. (100° C.) and higher.
In embodiments of this invention, the substrate is formed by heat setting a polymer fabric (e.g., a fabric of polymer monofilaments or multifilaments) at the temperature that is above the predetermined operating temperature of the operation for a predetermined time period, to obtain the polymer substrate. The heat setting can be performed is any suitable method that preshrinks/thermally stabilizes the fabric and/or otherwise imparts dimensional stability. In one embodiment of this invention, the substrate is formed by winding the polymer fabric with a non-stick layer to form wound material layers, and heating the wound material layers to the heat setting temperature, such as in a batch oven, for a sufficient time. In another embodiment, the substrate is formed by calendaring the polymer fabric at or above the heat setting temperature, such as using heated calendar rolls.
The fabricated parts of this invention include endless belts, trays, bakeware or cookware. Exemplary endless belts include conveyor belts for, without limitation, steam treatment, article washing, oven drying, baking, or deep frying. The conveyor belts desirably include an edge material strip along or over the opposing ends and/or longitudinal edges of the belt. The edge material can be a thermoplastic, a fiber-reinforced material, or a silicone material capable of withstanding the predetermined operating temperature. Trays, such as cooking or baking sheets, can be formed from a piece of fabric and an edge material along or over all side or peripheral edges. The tray can be an insert for a cooking device designed to be placed in an oven used for dehydration, baking, or pressing. Other articles include thermoformed articles stamped from the substrate, such for cooking, washing, and/or drying food, plant material, or parts or articles (e.g., can washing).
The invention further provides an apparatus with a heating device configured to operate at a predetermined operating temperature, and a non-metallic endless belt as described above extending through the heating device. In embodiments of this invention, the heating device includes microwave, steam, and/or a heated liquid. The apparatus can be, for example, a washing apparatus, a drying oven, a deep fryer, or a yarn treatment apparatus.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.
The present invention provides a monofilament fabric having dimensional stability and temperature resistance, and method for making. The monofilament fabric is desirably woven, and can be formed as a mesh with a plurality of mesh openings between the woven monofilament strands.
The polymer filaments (monofilaments or multifilaments) of this invention can be formed of suitable polymer material, such as polyphenylene sulfide (PPS), polyaminde-imide (PAI), polyphenylene sulfone (PPSU), polyethersulfone (PES), polyethylene (PE), liquid-crystal polymers (LCP), and/or polyether ether ketone (PEEK). The polymer material can include additives to impart additional properties. Inclusion of chopped or milled fiberglass within the polymer materials and within the individual filaments can be used to increase strength or stiffness, thereby not requiring separate, continuous fiberglass reinforcement of the substrate or fabric as a whole. The opposing ends and/or edges 30 and 32 of the substrate 20 each include an edge material strip 36, such as formed of a thermoplastic or silicone material, and optionally fiber-reinforced, capable of withstanding the predetermined operating temperature of the intended use of the substrate 20.
In embodiments of this invention, the substrate 20 is heat set at a heat setting temperature to obtain improved stability and/or temperature resistance. Heat setting according to this invention provides benefits such as curing or chain extending of the polymer material, and/or preshrinking the polymer fabric. In embodiments of this invention, the polymer fabric of the substrate is heat set at a temperature that is greater than a predetermined operating temperature of the intended use of the resulting fabricated part including the substrate. The higher temperature preshrinks/heat stabilizes the fabric before the substrate is put into use, thereby reducing or eliminating shrinkage and rupture during use, particularly at temperatures above 180° F. (82° C.). In embodiments of this invention, the substrate shrinks less than 2% during treatment. However, even 1% shrinkage during use can result, for example, in an endless belt prematurely failing on the conveyor rollers.
If the operating temperature of the final product is too close to, or higher than, the heat setting temperature, then the substrate fabric will likely still shrink, neck, distort, and/or sometimes even elongate during use. The heat setting temperature is above the glass transition temperature of the polymer, and in embodiments of this invention the heat setting temperature is least 15° over the predetermined operating temperature, and preferably at least 25°, and desirably at least 50° over the predetermined operating temperature. For embodiments including PPS monofilament, the heat setting temperature is desirably 212° F. (100° C.) or above, more desirably at least 250° F. (121° C.), for at least 15 minutes, and preferably at least 30 minutes, and desirably at least one hour.
Heat setting can be performed by any suitable heating apparatus. In embodiments of this invention, the heat setting is done in combination with a process to further provide stability and/or reduce roughness.
After heat setting, the monofilament fabric can be further processed according to the intended use. The mesh can be spliced or cut into the necessary length/shape, and include necessary edge materials, such as described above in
The monofilament fabric/mesh of this invention is useful in forming many articles for use. In embodiments of this invention, the monofilament fabric can be formed into conveyor belts, such as shown in
In addition to an endless belt, the monofilament fabric/mesh can be cut and edged as needed to form a sheet, tray, or other fabricated part.
The food support 80, which can be formed, for example, as a cooking basket/tray or a planar cooking sheet, and is useful for placing and removing food items from, and holding food items while in, an oven. The food support of this invention is desirably durable for multiple heating cycles, high temperature and water/oil resistant, easy to clean, stain resistant, and dissipates heat quickly; all while desirably not having any or much effect on the cooking of food. The food support can include a tight weave as a more solid bottom substrate sheet, such as to prevent liquids from dripping on heating elements, or a more open mesh substrate sheet to allow hot air through. The thickness of the substrate and/or the size of the mesh openings provide the ability to cook different food items and provide, for example, the desired food browning, toasting and/or heating characteristics.
The temperature-resistant materials of this invention are also non-absorbent, non-wicking, and resistant to chemicals, steam, and wet conditions, thereby making them particularly useful in numerous applications. Exemplary uses for the belting or other articles made according to this invention include, without limitation, food processing (drying, cooking (oven or microwave)), washing and/or drying of parts or materials (e.g., cans, plant materials (hemp, tobacco, etc.)), yarn bulking/heat setting, high-temperature insulation manufacture, non-woven manufacture, textile drying/shrinking/lamination, screen printing, industrial microwave/RF application, dehydration/drying, bacon cooking, doughnut and corn dog production, pasta belting and pasta screen, extruding corn puffs, and manufacturing pet food.
The counterband holds a bundle of yarn in place as the conveyor carries it through the oven and any yarn cooler. There are several places and mechanisms by which the yarn can become displaced or snagged, which reduces the production efficiency of the entire system. At each end of a steam chamber of the heat setting oven, there is a set of pinch rollers 116 that squeeze the yarn between the counterband 112 and the conveyor belt 118. The rollers 116 substantially seal the chamber at both ends, preventing the pressurized steam from escaping. As the rollers are constantly exposed to the steam and moisture, the counterband also keep the yarn from sticking to the rollers 116.
The monofilament fabrics of this invention can also be thermoformed (i.e., heat pressed) into shaped articles. Due to the temperature resistance, microwave safe, and non-stick capabilities, the monofilament materials are particular suitable for use in or forming cookware or bakeware. Exemplary thermoformed articles include, without limitation, cooking sheets, bread pans, and trays and baskets, particularly for use in high speed ovens.
The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.
As a control, a fabric material was heat processed using conventional methods of running the material in a tenter frame through an infrared oven set to 210° C. (410° F.), such that the filament/yarn in the fabric did not reach the actual oven set-point temperature. This process was then followed by the material being calendared at 220° C. (428° F.) using a heated steel two roll calendar. A piece of this material 10″×218.5″ was then placed into a conventional oven set at 220° C. (428° F.) for 8 hours to simulate use. The material was a dull yellow in color after processing. When removed and measured, the material lost 3.75% in the width and 4.75% in the length and the material had changed color to a dull amber color.
Another piece of fabric 11.875″×1142″ that went through the heat setting and calendaring process above was rolled up a layer of PTFE coated fiberglass fabric between each layer of PPS monofilament fabric like displayed in
Thus, the invention provides a non-absorbent polymer fabric substrate having many uses in heated and/or wet environments. By heat setting the polymer fabric of the substrate at a temperature above the intended use temperature, the substrate is preshrunk and stabilized for belting applications at higher temperatures than generally thought.
The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.
While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
This application claims the benefit of U.S. Provisional Patent Application, Ser. No. 62/551,563, filed on 29 Aug. 2017. The co-pending parent application is hereby incorporated by reference herein in its entirety and is made a part hereof, including but not limited to those portions which specifically appear hereinafter.
| Number | Date | Country | |
|---|---|---|---|
| 62551563 | Aug 2017 | US |
