Patent Grant
7732043
The invention relates to ceiling tile and, more specifically, to a tile construction that provides improved durability and reduction in manufacturing costs by strategic non-uniform distribution of latex binder through the thickness of the tile.
Ceiling tile is frequently manufactured using a felting process to construct a tile or board from a water-based slurry. The slurry, typically, includes a homogeneous mix of all of the raw materials that make up the body proper of the tile. Layers of felted slurry material are pressed into a mat and dried to form a board. Some tiles are constructed from boards that are embossed or patterned before they are completely dry, while others are made from boards that are first dried and then ground to obtain a desired thickness and a smooth finish. Typically, the raw materials include a binder such as latex or starch or a combination of the two that serves to hold the other materials together when the board is dried. Ordinarily, the binder represents a small percentage of the total weight of the board but represents a disproportionately high part of the cost of the materials. The binder content affects board strength and surface hardness. Conventionally, a level of binder content is maintained in the slurry mix to achieve a satisfactory surface hardness and, therefore, acceptable durability.
The invention provides a ceiling tile construction in which binder material has a non-uniform distribution across the thickness of the tile with a relatively high concentration near the finished or visible face of the tile. The disclosed distribution of binder can reduce manufacturing costs while providing a tile with a satisfactory or even superior surface hardness and durability as well as improved noise absorption capability. The tile of the invention can be made by reducing the binder content in the slurry or mix of material to below heretofore standard formulations and, after the mat or tile board is at least preliminarily formed, including on the side of the mat associated with the future visible face of the tile a layer of supplemental water-based latex binder. The coated binder, preferably, is the same material used in the slurry formulation to fix or cement the other materials making up the tile board. The enhanced binder zone at the visible side of the tile can increase the hardness and strength of the product at this side while allowing total binder content to be reduced, reduce final finish coat or paint requirements and increase sound absorption.
The invention comprises mineral wool-based ceiling tile that, in part, is made in a traditional water felting process. In the context of the present invention, the slurry solids typically contain roughly 90% mineral wool and the remainder of solids primarily comprise binder in the form of latex or latex and starch. All together, the solids in the slurry are about 5% of the total weight of the slurry; i.e. a consistency of 5%. Latex is well-known and widely used commercially as a binder. Normally, the latex is disbursed as a water emulsion and coalesces into a solid when the water is driven off. Various formulations for the slurry can be used as desired or necessary. Generally, the following table gives an approximate range of slurry constituents by weight percentage of total solids:
In the felting process, the slurry is deposited on a moving screen and, typically, is dried by gravity, pressure rolls, vacuum, and heat. The solids in the slurry are generally uniformly mixed and distributed and generally remain or are intended to remain in this state as the mat is formed on the screen and is progressively dried. Preferably, the latex used in the slurry is a high Tg binder material cured at relatively high temperature, for example, by exposing the mat to hot air (for example at about 350° F.) and/or infrared heating. A low Tg binder can be used where it provides sufficient strength and hardness of the core.
The invention comprehends a process and article in which the binder distribution across the thickness of the mat is modified so that a greater concentration of the binder exists adjacent the face or ultimate room side of the ceiling tile. It has been discovered that in practicing the invention, the durability of the ceiling tile, its noise reduction coefficient (NRC) and its finish paint requirements can all be improved even while reducing its total binder content and, therefore, reducing its cost of manufacture.
The increased concentration of latex binder at a latex binder enhancement zone, can be produced by conventional coating techniques such as by spraying, roll-coating, flood coating and the like. The binder enhancement zone, when made by a coating process, can be coated before, during, or after the slurry formed mat is dried and/or cured. Prior partial or full curing of the mat can reduce or prevent free migration of the binder material being applied to form the enhancement zone at the face side of the mat. The latex binder in the enhancement zone is typically cured by drying it from its water carrier by exposure to relatively high temperature air, e.g. about 350° F.
The slurry binder can wholly comprise starch or, more preferably, is used in an amount, for example, roughly equal by weight to the latex content. The latex binder enhancement zone or layer preferably uses the same latex material as used in the slurry but, if desired, can be different. The enhancement layer can be applied after the mat is fully cured and can be applied, if the mat or board is to be ground or sanded, after such grinding or sanding.
The latex enhancement zone can reduce manufacturing costs of the tile by allowing the latex content of the slurry to be reduced from that of conventional formulations. With the invention, the effective surface hardness of the face of the finished tile can be even higher than prior art products while the total or net latex usage is less than in such prior art products. The effective hardness of the tile face is measured through any finish material or paint coated and cured on the tile. The increased hardness of the outer face region, either on an absolute basis or as a comparison to prior art product, is reflected in a higher durability of the ceiling tile when it is being handled during installation or during its service life.
The latex enhancement zone is substantially more concentrated on the basis, for instance, of grams per unit of thickness than the remainder of the mat. By way of example, if the slurry carried latex binder content is about 4 or 5% of the weight of the mat distributed over the thickness of the mat proper, the enhancement zone, coated onto the top of the mat, can be about 1% of the total mat weight. Stated otherwise, in this example approximately ¼ to ⅕ of the latex binder content of the finished tile exists at one side of the mat when the latex binder enhancement zone is developed by a coating process. Ordinarily, the top side of the felted mat will be the side made with the supplemental latex binder enhancement zone since, in conventional felting or processing, this is the side which is most accessible. The zone is easily developed on the top of the mat by spraying, roll-coating or the like on the mat production line. When the latex enhanced zone is created by a separate coating process, the latex material used, as mentioned, is preferably the same as used in forming the mat slurry. This commonality affords convenience and cost savings through attendant purchasing, inventory and familiarity.
Ceiling tile of the type under consideration here is normally coated or painted to achieve a color that approaches a true white. This coating typically involves a primer coat and a finish coat of a formulation of a paint type latex with a fast low temperature cure. The invention enables the tile to be coated with less paint while achieving the same or improved whiteness. This effect results from the high concentration of latex binder present in the enhancement zone at the outer surface of the mat made under the principles of the invention which latex binder has a color closer to white than the color of natural mineral wool. The paint required on the face of the dried tile mat or board proper to hide the considerably off-white color of the mineral wool is reduced.
It has been found that the ceiling tile made in accordance with the invention can also exhibit improved sound absorption sometimes technically referenced as noise reduction coefficient (NRC). This phenomena is believed to be the result of using less paint or coating which, apparently, causes less net blocking of the porous surface of the mat and, therefore, promotes greater sound absorption.
The following table sets out an example of a solids formulation of a conventional prior art tile identified by the label “Control” and an example of a formulation of a tile of the invention identified by the label “Trial”.
Formulation/Construction:
Tiles of both formulations/constructions (Control) and (Trial) were tested with the following results:
Coating Coverage, Lab Value and Estimated NRC Value:
Test Run 1
Test Run 2
Test Run 3
Physical Data:
Test Run 1
Test Run 2
Test Run 3
Trial 1, Trial 2 etc. are separate samples of the inventive formulation/constructions.
The tiles (Trial) made according to the invention were coated with finishing material (a latex-based paint) in various quantities of a primer coat and/or a finish coat. Paint grade latex is readily distinguishable on a mechanical strength basis and on an abrasion-resistance basis from a binder type latex material.
Study of the values recorded in the above tables reveals that ceiling tiles fabricated with a latex enhancement zone on the face of the mat according to the invention but with less total latex content can be whiter, capable of greater noise reduction, and more durable than tiles with a conventional formulation (Control).
A Hunter gauge (the source of the HunterG Hrdn's values) is a device used commercially to measure the surface hardness of materials such as wallboard. In general, the higher the Hunter gauge reading, the harder the surface of a product and the greater its durability.
The values L, a, b, are references to a color space method of evaluating the color of a surface wherein pure white is assigned the value of 100 and the lower the absolute value of the a, b values, the less deviation from white to primary colors. The greater the number recorded for NRC, the more a board is capable of absorbing sound.
Other methods can be developed to produce a latex enhancement zone in a ceiling tile mat besides those disclosed herein. For example, it is envisioned that such a zone can be developed in the felting process adjacent the screen by purposely allowing the latex to settle out or by depositing a high latex content onto the screen prior to the formation of the mat proper. Typically, a tile made in accordance with the invention will have a caliper of between about ½ to about ⅞″ and will have a relatively porous interior.
It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3955031 | Jones et al. | May 1976 | A |
| 5320677 | Baig | Jun 1994 | A |
| 5395438 | Baig et al. | Mar 1995 | A |
| 5558710 | Baig | Sep 1996 | A |
| 5911818 | Baig | Jun 1999 | A |
| 5922447 | Baig | Jul 1999 | A |
| 6268042 | Baig | Jul 2001 | B1 |
| 6443256 | Baig | Sep 2002 | B1 |
| 6616804 | Foster et al. | Sep 2003 | B2 |
| 20020096278 | Foster et al. | Jul 2002 | A1 |
| 20030079847 | Howle et al. | May 2003 | A1 |
| 20030118788 | Pearce et al. | Jun 2003 | A1 |
| 20040209071 | Carbo et al. | Oct 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20070056705 A1 | Mar 2007 | US |
