FLOORING UNDERLAYMENT MATERIAL, AND RELATED METHODS AND SYSTEMS

A material for making an underlayment of a floor includes a thermoplastic polymer that has a thickness and a microstructure. The microstructure includes a plurality of closed cells, each cell containing a void and each cell having a maximum dimension extending across the void within the cell that is less than or equal to 200 micrometers long. The microstructure also includes a density that is greater than or equal to 0.18 grams per cubic centimeter.

BACKGROUND

Floor coverings generally require an underlayment that is installed between the floor covering, which is the finished topmost flooring layer, and the subfloor, which is the unfinished base that structurally supports the floor covering and the underlayment that lie on top of it. The underlayment may be attached to the subfloor with adhesives, staples, nails, and suchlike, or it may rest unaffixed to the subfloor. In the latter case, the underlayment is used in floating floor systems and applications whereby both the floor covering and underlayment lie on top of the subfloor without being secured to the subfloor such that they are said to “float” detachedly above the subfloor. These types of flooring systems are very flexible since they are easier to install and uninstall; are more convenient to repair, including local spot repairs, and at a lower cost; and can be relocated to some other part of the house or building.

The underlayment is essential to a quality floor covering and often serves multiple functions. The underlayment layer may smooth out the irregular surfaces of the unfinished subfloor to ensure that the floor covering at the top remains uniformly even and smooth. The underlayment can cushion the floor covering by imparting a certain amount of resiliency and pliability that lessen the floor's impact on a person's knees and joints. In general, the thicker the underlayment, the more resiliency or cushioning it provides. The underlayment may also function as an insulating material that provides a barrier to heat entering and leaving through a floor, to noise, to moisture, and even to liquid.

Unfortunately, though, many current underlayment layers often interfere with the subfloor's support of the floor covering and do not themselves replace that support to the floor covering. As a result, the condition of floor covering often worsens when the floor covering is subjected to excessive or continuous loads or pressures. For example, LVT (luxury vinyl tile) floor coverings tend to be weakest at the joints where the tiles interlock with each other. With a thick underlayment layer (i.e., greater than 1.5 mm) and a compressive load or pressure applied to the floor covering, the cushioning effect of the thick underlayment creates uneven stress across the floor tiles, thereby making the weaker points of the tiles at the joints more susceptible to bending, breaking, and deteriorating. Although a thinner underlayment layer may better support the LVT against uneven stress across the floor tiles because it is less pliable or resilient, the thinner underlayment layer is also less effective at preventing or even reducing the transmission of noise, moisture, or liquid through the floor.

Thus, there is a need for an underlayment that provides pliability or resiliency; that serves as a barrier to noise, moisture, and liquid; and that does not compromise the subfloor's support of the floor covering.

SUMMARY

In an aspect of the invention, a material for making an underlayment of a floor includes a thermoplastic polymer that has a thickness and a microstructure. The microstructure includes a plurality of closed cells, each cell containing a void and each cell having a maximum dimension extending across the void within the cell that is less than or equal to 200 micrometers long. The microstructure also includes a density that is greater than or equal to 0.18 grams per cubic centimeter.

With a microstructure that has very small closed cells, or bubbles, and a density greater than or equal to 0.18 grams per cubic centimeter, a compressive strength of the thermoplastic material may be generated that does not interfere with the sub-floor's support of the floor covering, i.e., that effectively or more evenly transfers the loading experienced by the floor covering to the sub-floor. In addition, the closed cells, or bubbles, of the microstructure provide an effective barrier against noise, moisture, and liquid travelling through the floor, and thus help keep noise generated above the floor from being heard below the floor and vice-versa, as well as mitigate damage to the sub-floor or other portions of the structure that moisture and liquid may cause.

In another aspect of the invention, a method for making a floor underlayment material includes: 1) infusing a thermoplastic material with a gas; 2) heating the gas-infused thermoplastic material to a temperature that is at least the glass-transition-temperature of the gas-infused thermoplastic material, to nucleate closed cells in the gas-infused thermoplastic material, wherein each closed cell has a void and a maximum dimension extending across the void; 3) maintaining the temperature to allow the closed cells to grow in size such that the maximum dimension of the void of each of the closed cells is less than or equal to 200 micrometers; and 4) cooling the gas-infused thermoplastic material to stop the growth of the closed cells such that the density of the material is equal to or greater than 0.18 grams per cubic centimeter.

DETAILED DESCRIPTION

FIG.1is a cross-sectional view of a floor10, according to an embodiment of the invention. The floor10includes a sub-floor12that is mounted to a plurality of floor joists14(only two shown), an underlayment16, and a floor covering18. Here the floor covering18is a luxury vinyl tile (LVT), but in other floor systems the floor covering18may be linoleum, or any other desired floor covering such as laminate, hardwood, carpet, porcelain, and/or stone. The underlayment16(discussed in greater detail in conjunction withFIG.2) includes a thermoplastic polymer that has a microstructure20(only a portion shown inFIG.1for clarity) that extends the length of the underlayment16in the directions along the length of the joists14and along the length between the joists14(seeFIG.2). The microstructure20includes a plurality of closed cells, each cell containing a void and each cell having a maximum dimension extending across the void within the cell that is less than or equal to 200 micrometers (μm) long. The microstructure20also has a density that is greater than or equal to 0.18 grams per cubic centimeter.

With a microstructure20that has very small closed cells, or bubbles, and a density greater than or equal to 0.18 grams per cubic centimeter, a compressive strength of the thermoplastic material may be generated that does not interfere with the support that the sub-floor12provides the floor covering18, i.e., that effectively or more evenly transfers the loading experienced by the floor covering18to the sub-floor12. In addition, the closed cells, or bubbles, of the microstructure20provide an effective barrier against noise, moisture, and liquid travelling through the floor10, and thus help keep noise generated above the floor10from being heard below the floor10and vice-versa, as well as mitigate damage to the sub-floor12or other portions of the structure that moisture and liquid may cause.

The underlayment16may have any desired thickness and may be mounted to the sub-floor12in any desired manner. For example, in this and other embodiments, the thickness of the underlayment ranges between 0.5 millimeters (mm) and 2.0 mm; and the underlayment “floats” on top of the sub-floor12, that is, the underlayment16is not fastened to the sub-floor12, but rather is simply placed on top of the sub-floor12. Adjacent sheets of underlayment16, and the walls and/or thresholds (not shown) that define the boundary of the floor10, hold the underlayment16in the desired position over the sub-floor12. Likewise, the floor covering18may be mounted to the underlayment16in any desired manner. Here again, in this and other embodiments the floor covering18“floats” on top of the underlayment16. In other embodiments, the underlayment16may be mounted to the sub-floor12and/or the floor covering18may be mounted to the underlayment16with any conventional adhesive and/or nails, staples, or screws.

Still referring toFIG.1, the thermoplastic polymer included in the underlayment16may be any desired thermoplastic polymer that provides the mechanical properties, such as compression strength, desired. For example, the thermoplastic polymer may be any amorphous or semi-crystalline thermoplastic. In this and other embodiments, the thermoplastic polymer included in the underlayment16is polyethylene terephthalate (PET). In other embodiments, the thermoplastic polymer included in the underlayment16includes one or more of the following polymers: polyolefins such as polypropylene (PP) and polyethylene (PE), thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), polystyrene, polycarbonate, acrylonitrile-butadiene-styrene, glycol modified PET, polyethylene, polypropylene, NORYL (a blend of polyphenylene oxide and polystyrene), and polyvinyl chloride. The underlayment16may also be fabricated from recycled polymer materials, including recycled polyethylene terephthalate and mixed recycled plastics.

FIG.2is a cross-sectional view of the underlayment16shown inFIG.1that shows the microstructure20of the underlayment's thermoplastic polymer, according to an embodiment of the invention. The microstructure20of the underlayment's thermoplastic polymer includes many closed cells22(only 6 labeled inFIG.2for clarity)—about 108or more per cubic centimeter (cm3)—with each closed cell containing a void. The size of each closed cell22is less than or equal to 200 μm long at its maximum dimension that extends across the void. Because the geometry of each closed-cell is rarely, if at all, a perfect sphere, the size of each closed cell is arbitrarily identified as the length of the longest chord that extends through the void within the closed cell. For example, the size of an oblong cell would be the length of the longest chord that extends in the same direction as the cell's elongation, and the size of a sphere would be the length of the sphere's diameter.

In this and other embodiments, the many closed cells22included in the microstructure20are uniformly dispersed throughout the thickness of a layer24which forms a portion of the thickness of the underlayment16. And, the size of each of the closed cells22included in the layer24ranges between 5 and 50 μm long at its maximum dimension that extends across the void. In other embodiments, the size of each of the closed cells22in the microstructure20may be smaller than 5 μm long at its maximum dimension that extends across the void; or each may be larger than 50 μm long at its maximum dimension that extends across the void.

More, other embodiments are also possible. For example, the closed cells22may not be uniformly dispersed throughout the thickness of the layer24. For another example, the microstructure20may include more than one layer24of closed cells22, with the closed cells22of each of the layers24having the same size (seeFIG.5), or with each layer24having closed cells22having a size that is different than the closed cells22of each of the other layers24.

The microstructure20may also include a region or layer that does not include any closed cells22. For example, in this and other embodiments the microstructure20also includes two layers26that do not have any cells (open or closed), and that are located above and below the layer24. Each layer26has a thickness that is equal to the thickness of the other layer26, and is much less than the thickness of the layer24, which effectively makes the layers26a solid skin of the underlayment16. Because these two layers26do not include any cells, they provide a barrier against moisture and liquid in addition to the barrier that the layer24of closed cells22provides against moisture and liquid, especially when the underlayment “floats” in the floor10(FIG.1). Here, the layers26are integral to the layer24—i.e., not a separate layer that is laminated to the layer24, or co-extruded with the layer24—which helps prevent delamination of the layers26from the layer24during transportation, installation, and use.

FIG.3is a schematic view of a process for generating the microstructure20(FIG.2) that the underlayment16includes, according to an embodiment of the invention. The microstructure20may be generated by any desired process that provides the thermoplastic polymer the desired size of the closed cells22with the desired density (apparent density of the underlayment16). For example, in this and other embodiments the microstructure20is generated by a solid-state microcellular foaming process. More specifically, the process for generating the microstructure20in the thermoplastic polymer30includes dissolving into the polymer30(here shown as a film rolled around a drum32, but may be a block or thin sheet) a gas34that does not react with the polymer30. The process also includes making the polymer30with the dissolved gas thermodynamically unstable at a temperature that is or close to the glass transition temperature of the polymer30with the gas34dissolved in it—the temperature at which the polymer30is easily malleable but has not yet melted. With the temperature at or near the glass transition temperature, bubbles of the gas34can nucleate and grow in regions of the polymer30that are thermodynamically unstable—i.e., supersaturated. When the bubbles have grown to a desired size, the temperature of the polymer30is reduced below the glass transition temperature to stop their growth, and thus provide the polymer30with a microstructure20having bubbles, i.e., closed-cells22, whose size may be less than or equal to 200 μm long.

In the process, the first step36is to dissolve into the polymer30any desired gas34that does not react with the polymer30. For example, in this and certain other embodiments of the process, the gas34may be carbon dioxide (CO2) because CO2is abundant, inexpensive, and does not react with PET. In other embodiments of the process, the gas may be nitrogen and/or helium. Dissolving the gas34into the polymer30may be accomplished by exposing the polymer30for a period of time to an atmosphere of the gas34having a temperature and a pressure. The temperature, pressure, and period of time may be any desired temperature, pressure, and period of time to dissolve the desired amount of gas34into the polymer30. The amount of gas34dissolved into the polymer30is directly proportional to the pressure of the gas34and the period of time that the polymer30is exposed to the gas34at a specific temperature and specific pressure, but is inversely proportional to the temperature of gas34. For example, in this and certain other embodiments, the temperature may be 72° Fahrenheit, the pressure may be 800 pounds per square inch (psi), and the duration of the period may be 10 hours. This typically saturates the polymer30with the gas34. In other embodiments, the pressure may range between 500 psi and 1000 psi, and the duration of the period may range between 4 hours and 24 hours.

Because the layers of the rolled polymer film30that lie between adjacent layers or between a layer and the drum32are substantially unexposed to the atmosphere when the roll is placed in the atmosphere, a material38is interleaved between each layer of the rolled polymer film30, before gas34is dissolved into the polymer30at step36. This allows each layer of the rolled polymer film30to be exposed to the atmosphere of gas34. In this and certain other embodiments, the material38includes a sheet of cellulose, and is disposed between each layer of the polymer film30by merging the sheet with the film and then rolling the combination into a single roll40. The material38exposes each layer of the polymer film30by allowing the gas34to easily pass through it. After the gas34has saturated the polymer film30, the material38may be removed from the roll42and saved as a roll44for re-use.

The next step46in the process includes exposing the polymer film30with the dissolved gas34to an atmosphere having less pressure than the one in the first step36to cause the combination of the polymer film30and the gas34dissolved in the polymer film30to become thermodynamically unstable—i.e., the whole polymer or regions of the polymer to become supersaturated with the dissolved gas34. For example, in this and certain other embodiments, the reduction in pressure may be accomplished by simply exposing the polymer film30to atmospheric pressure, which is about 14.7 psi, in the ambient environment.

When the combination of the polymer film30and the dissolved gas34becomes thermodynamically unstable, the dissolved gas tries to migrate out of the film30and into the ambient environment surrounding the film30. Because the dissolved gas34in the interior regions of the polymer film30must migrate through the regions of the polymer film30that are closer to the film's surface to escape from the polymer film30, the dissolved gas in the interior regions begins to migrate after the dissolved gas34in the surface regions begins to migrate, and takes more time to reach the ambient environment surrounding the polymer film30than the dissolved gas34in the film's regions that is closer to the film's surface. Thus, before heating the polymer film30to a temperature that is or is close to its glass transition temperature, one can modify the concentration of dissolved gas34in regions of the polymer film30by exposing the polymer film30to an atmosphere having less pressure than the one in the first step36for a period of time. Because the concentration of dissolved gas34depends on the amount of gas that escapes into the ambient environment surrounding the polymer film30, the concentration of dissolved gas34is inversely proportional to the period of time that the film30is exposed to the low-pressure atmosphere before being heated to its or close to its glass transition temperature.

In this manner, an integral skin, such as the layer26of the microstructure20(FIG.2), may be formed in the polymer film30when the film30is heated to a temperature that is or is close to its glass transition temperature. For example, in this and certain other embodiments, the roll42of polymer film30and interleaved material38can remain in a thermodynamically unstable state for a period of time before removing the material38from the roll42and heating the polymer film30. This allows some of the gas dissolved in the region of the film30adjacent the film's surface to escape. With the gas absent from this region of the film30, this region becomes more thermodynamically stable than the regions that are further away from the film's surface. With a sufficient amount of thermodynamic stability in the region, bubbles or closed cells22won't nucleate in the region when the film30is heated close to its glass transition temperature. Consequently, closed cells22(FIG.2) can be omitted from this region of the polymer film30, leaving a solid portion of the microstructure20that is integral to the closed cell portion24of the microstructure20, such as the skin or layer26of the microstructure20(FIG.2). Because the thickness of the layer26depends on the absence of dissolved gas34in the region of the film30, the thickness of the layer26or solid skin portion is directly proportional to the period of time that the film30spends in a thermodynamically unstable state before being heated to or substantially close to its glass transition temperature. In this and certain other embodiments, the thickness of the integral skin ranges between 5-200 μm.

The next step48in the process is to nucleate and grow bubbles in the polymer30to form closed cells22(FIG.2) and achieve a desired apparent density for the polymer film30. Bubble nucleation and growth begin about when the temperature of the polymer film30is or is close to the glass transition temperature of the polymer film30with the dissolved gas34. The duration and temperature at which bubbles22are nucleated and grown in the polymer30may be any desired duration and temperature that provides the desired apparent density. For example, in this and certain other embodiments, the temperature that the PET polymer30is heated to is approximately 190°-280° Fahrenheit, which is about 30°-120° Fahrenheit warmer than the glass transition temperature of the polymer without any dissolved gas34. The PET film30is held at approximately 190°-280° Fahrenheit for approximately 30 seconds. This provides an apparent density of the thermoplastic polymer with the closed-cell microstructure of about 0.31 grams per cubic centimeter. If the PET film30is held at 190°-280° Fahrenheit for a period longer than 30 seconds, such as 120 seconds, then the bubbles grow larger, and thus the size of resulting closed cells22are larger. This may provide an apparent density of the closed-cell microstructure of about 0.138-0.26 grams per cubic centimeter. If the PET film30is held at 190°-280° Fahrenheit for a period shorter than 30 seconds, such as 10 seconds, then the bubbles remain small, and thus the size of resulting closed cells22are smaller. This may provide a relative density of the closed-cell microstructure of about 0.552 grams per cubic centimeter.

To heat the polymer film30that includes the dissolved gas34, one may use any desired heating apparatus. For example, in this and certain other embodiments, the PET film30may be heated by a roll fed flotation/impingement oven, such as the oven disclosed in U.S. patent application Ser. No. 12/423,790, titled ROLL FED FLOTATION/IMPINGEMENT AIR OVENS AND RELATED THERMOFORMING SYSTEMS FOR CORRUGATION-FREE HEATING AND EXPANDING OF GAS IMPREGNATED THERMOPLASTIC WEBS, filed 14 Apr. 2009. This oven suspends and heats a polymer film that moves through the oven, without restricting the expansion of the film.

The next step50in the process includes reducing the temperature of the heated polymer30, and thus the malleability of the polymer30that occurs at or near the glass transition temperature, to stop the growth of the bubbles and establish the closed cells22. The temperature of the heated polymer30may be reduced using any desired technique. For example, in this and certain other embodiments, the polymer film30may be left to cool at ambient room temperature—i.e., simply removed from the heating apparatus. In other embodiments, the heated polymer film30may be quenched by drenching it with cold water, cold air, or any other desired medium.

Other embodiments of the process are possible. For example, the polymer film30can be heated to a temperature that is or close to its glass transition temperature when the polymer film30is initially exposed to an atmosphere that causes the gas dissolved in the polymer film30to become thermodynamically unstable. This allows one to make a film that does not include a solid skin layer26or includes a solid skin layer26having a minimal thickness.

By modifying and controlling the parameters of the process for generating the microstructure of the underlayment's thermoplastic polymer, one can generate a variety of different microstructures20in the underlayment's thermoplastic polymer, which allows one to form an underlayment16that has a variety of desired characteristics. For example, one can generate a microstructure20that includes closed cells that are around 5 μm in size, and has an apparent density that is 0.18 grams per cubic centimeter. Or, one can generate a microstructure20that includes closed cells that are around 5 μm in size, and has an apparent density that is 0.3 grams per cubic centimeter. Likewise, one can generate a microstructure20that includes closed cells that are around 200 μm in size, and has an apparent density that is 0.18 grams per cubic centimeter. Or, one can generate a microstructure20that includes closed cells that are around 200 μm in size, and has an apparent density that is 0.3 grams per cubic centimeter.

Each ofFIGS.4A-4Cis a graph that shows compressive stress data for two, different underlayments60and62for a floor, each according to an embodiment of the invention.FIG.4Ashows compressive stress data of each of the two underlayments60and62for easy comparison. The data labeled64corresponds to the compressive stress and compressive strain experienced by the underlayment60. The data labeled66corresponds to the compressive stress and compressive strain experienced by the underlayment62.FIG.4Bshows the compressive stress strain curve of the underlayment60. AndFIG.4Cshows the compressive stress strain curve of the underlayment62.

In this and certain other embodiments, the underlayment60is 0.6 mm thick, and includes a PET thermoplastic polymer whose microstructure20(FIG.2) includes closed cells22(FIG.2) whose size is less than 200 μm, and has a density of 0.18 grams per cubic centimeter. And, the underlayment62is 1.25 mm thick, and includes a PET thermoplastic polymer whose microstructure20(FIG.2) includes closed cells22(FIG.2) whose size is less than 200 μm, and has a density of 0.28 grams per cubic centimeter. As can be seen inFIGS.4A-4C, the thicker and more dense underlayment62can experience a compressive stress of 1.3 megapascals (MPa) or 5,928 Newtons (N) before its thickness is reduced 10% or to 1.13 mm; while the thinner and less dense underlayment60can experience a compressive stress of 0.62 megapascals (MPa) or 283 Newtons (N) before its thickness is reduced 10% or to 0.54 mm. Similarly,FIG.4Bshows the response of the underlayment60to a variety of different compressive stresses ranging from 0.0 MPa to 2.75 MPa; andFIG.4Cshows the response of the underlayment62to a variety of different compressive stresses ranging from 0.0 MPa to 6.1 MPa.

FIG.5is a cross-sectional view of another underlayment70for a floor that shows a microstructure72of the underlayment's thermoplastic polymer, according to another embodiment of the invention. The microstructure72is similar to the microstructure20(FIG.2) of the underlayment16(FIG.2), except that the microstructure72includes two regions or layers74having closed cells76(only four labeled for clarity), and three regions or layers78that does not include any closed cells76. In this and other embodiments, the underlayment70may be formed by fusing or otherwise attaching two underlayments16together to form an underlayment70that is thicker than each of the underlayments16. In this manner, One can easily obtain an underlayment70whose thickness is greater than 1.5 mm, such as 6 mm or more.