METHOD OF CONSTRUCTION THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

[0001 ] This application claims the benefit of U.S. Provisional Application Serial No. 61/569,975, filed December 13, 201 1 , and the benefit of U.S. Provisional Application Serial No. 61/703,613, filed September 20, 2012, which are both incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

[0002] This invention relates generally to nonwoven panels, and more particularly to flame retardant, moisture resistant nonwoven structural panels and to their method of construction.

2. Related Art

[0003] It is known to construct structural panels, meaning those capable of functioning as a structural member, such as office divider panels, for example, from fiberglass composites via bonding fiberglass with resin. However, the resins used to construct fiberglass panels include high levels of formaldehyde, which can be harmful to persons, and due to a new regulation CAL1350, which calls for the levels of formaldehydes to be below 0.04ppm, the fiberglass panels are unacceptable. In addition, the fiberglass panels are not environmentally friendly given they have a relatively high carbon footprint in manufacture and are made from materials that are typically not renewable.

[0004] In addition to fiberglass panels, it is known to construct panels including natural fibers bonded with resin. However, the known compositions of these panels are susceptible to water absorption, which can have a deleterious effect on their structural capacity. As such, the natural fiber panels typically fail to meet humidity shock and board stiffness tests required for office divider tackable board applications. Further, these panels are typically constructed via processes that are costly, including requiring multiple coating processes, for example. Accordingly, their costly construction typically renders them cost ineffective, and thus, rules them out for use in many applications. Further yet, natural fiber-based boards typically have a brown color, which is undesirable for visible office panel applications.

SUMMARY OF THE INVENTION

[0005] In accordance with one aspect of the invention, a nonwoven, fire retardant, moisture resistant panel is provided. The panel includes a bonded nonwoven sheet of bast fibers bonded with polymeric binding fibers. Further, the panel includes a single coating of a dried and cured solution. The dried and cured coating includes a binder, a Ph stabilizer and a single flame retardant. The binder is cross-linked with the bast fibers to form a moisture resistant barrier that reduces the moisture absorption of the bast fibers.

[0006] In accordance with another aspect of the invention, the panel meets the requirements of regulation CAL1350 calling for levels of formaldehydes to be below 0.04ppm.

[0007] In accordance with another aspect of the invention, the panel is formed as an office divider panel that passes an ASTM E-84 flame test.

[0008] In accordance with another aspect of the invention, the mixture includes between 50-80 wt% of bast fibers fiber and between 15-50 wt% of polymeric binding fiber.

[0009] In accordance with another aspect of the invention, the bonded nonwoven web is between 150gsm and 1500gsm. [0010] In accordance with another aspect of the invention, the dried and cured coating has between 30gsm and 300gsm dry pickup weight.

[001 1] In accordance with another aspect of the invention, a formaldehyde free scrim layer is bonded to at least one side of the panel.

[0012] In accordance with another aspect of the invention, a method of constructing a nonwoven, fire retardant, moisture resistant panel is provided. The method includes forming a homogenous mixture of bast fibers and polymeric binding fiber; forming a web of the homogenous mixture; melting the polymeric binding fiber and bonding the bast fibers with the material of the polymeric binding fiber to form a bonded nonwoven sheet; saturating the bonded nonwoven sheet in a solution including a binder, a Ph stabilizer and a flame retardant; cross-linking the binder with the bast fibers by drying the saturated, bonded nonwoven sheet and curing the solution; and compressing the nonwoven sheet.

[0013] In accordance with another aspect of the invention, the method includes maintaining the levels of formaldehydes in the panel below 0.04ppm.

[0014] In accordance with another aspect of the invention, the method includes compressing the nonwoven sheet while curing the solution.

[0015] In accordance with another aspect of the invention, the method includes cooling the nonwoven sheet while being compressed.

[0016] In accordance with another aspect of the invention, the method includes using a modified polycarboxylic acid with a polyol for the binder.

[0017] In accordance with another aspect of the invention, the method includes providing the fire retardant as a single fire retardant.

[0018] In accordance with another aspect of the invention, the method includes bonding a formaldehyde free scrim layer to at least one side of the panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other aspects, features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description of presently preferred embodiments and best mode, appended claims and accompanying drawings, in which:

[0020] Figure 1 is a process flow diagram showing the steps of constructing a panel in accordance with one aspect of the invention.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

[0021 ] Referring in more detail to the drawings, Figure 1 illustrates a nonwoven, fire retardant, moisture resistant panel, referred to hereafter as panel 10, 10', 10", constructed in accordance with the invention, as well as a method of construction of the panel 10, 10', 10" in accordance with another aspect of the invention. The panel 10, 10', 10", includes a bonded nonwoven sheet 12 and a dried and cured coating 14 formed from a single solution 16 (Figure

2) that is dried and cured in a single process, thereby minimizing the space requirements and process steps in manufacture. The sheet 12 is formed from a mixture of bast fibers 18 and polymeric binding fiber 20 bonded with one another via a process that melts, at least partially, the polymeric binding fiber 20. The solution 16 includes a solution-based binder, a

Ph stabilizer and a single flame retardant. The binder from the solution 16 is cross-linked with the bast fibers 18 to form an impervious or substantially impervious moisture resistant barrier that greatly reduces the tendency of the bast fibers 18 to absorb moisture.

Accordingly, the structural integrity of the bast fibers 18 and the panel 10, 10', 10", constructed in part therefrom, is maintained in use, even in the presence of moisture, which allows the panel 10, 10', 10" to meet stringent requirements required for office divider tackable board under ASTM E-84 Class A, and further, to pass humidity shock and board stiffness tests. Thus, the panel 10, 10', 10" has a high strength and high stiffness, and as such, is suitable for use as a structural member, such as an office divider panel, for example. Further, the panel 10, 10', 10" is environmentally friendly, in that the materials used to construct the panel 10, 10', 10" can be reclaimed, are renewable, are mostly natural and biodegradable, and further, contain less than 0.04ppm levels of formaldehydes, referred to hereafter as "very low levels of formaldehyde", and thus, the panel 10, 10', 10" is suitable for use in applications needing to pass regulation CAL 1350, which requires formaldehyde contents in office divider boards to contain less than 0.04ppm formaldehyde.

[0022] The bast fibers 18 can be provided from a variety of natural fibers, such as jute, kenaf, hemp, flax or mixture thereof, by way of example and without limitation. The bast fibers 18 are generally provided having a content between about 50-85 wt%, and in one example was provided as 80 wt% kenaf.

[0023] The polymeric binding fiber 20 can be provided from a variety of thermally bonding materials, including polypropylene, polyethylene, copolyesters, nylons, polyactic acid (PLA), and bicomponent fibers (sheath/core fibers, wherein the sheath is typically a low melt polymeric material and the core is a higher temperature polymeric material), by way of example and without limitation. The polymeric binding fiber 20 is generally provided having content between 15-50 wt%, and in the example, was provided as 20 wt% bicomponent, including a polyester core and a modified polyester sheath.

[0024] In the example, the solution-based binder was provided as a modified polycarboxylic acid with a polyol diluted with water. The polyol is used primarily as a crosslinking agent while the modified polycarboxylic acid is compatible with the natural fibers of the bast fibers 18 and forms a good crosslink between the natural fibers and the melted resin of the polymeric binding fiber 20, thereby facilitating formation of an impervious or substantially impervious barrier that greatly reduces the tendency of the bast fibers 18 to absorb moisture.. It is important for the binder to be solution-based, as regular dispersion based latex binders have been found to burn under the ASTM E-84 test method, and thus, do not meet the requirements for a Class A rating. The binder content can range from between 10-20 wt%, and in the example, 14 wt% binder content was used.

[0025] The flame retardant is provided as a single flame retardant and applied in a single process, thereby minimizing the complexity and cost of the manufacture process. The flame retardant can be provided as boron-based, phosphorous-based, or sulfur-based constituent, by way of example. With the polycarboxylic acid having a low Ph, a Ph stabilizer is used to blend the fire retardant in the binder. The fire retardant used in the example was disodium octaborate tetrahydrate, by way of example and without limitation. The amount of fire retardant content can be provided between about 5-25 wt%, and in the example, 15 wt% content was used based on a 30 wt% dry pick-up from the chemical solids.

[0026] The process of constructing the panel 10 includes the following steps: forming a homogenous mixture of bast fibers 18 and polymeric binding fiber 20, shown generally at 22; forming a web 24 of the homogenous mixture 22; heating the web 24 and melting the polymeric binding fiber 20 at least partially and bonding the bast fibers 18 with the melted material of the polymeric binding fiber 20 to form a bonded nonwoven sheet 12; providing a solution 16 including a binder, a Ph stabilizer and a flame retardant; saturating the bonded nonwoven sheet 12 with the solution 16; cross-linking the binder in the solution 16 with the bast fibers 18 by drying the saturated, bonded nonwoven sheet 12; curing the solution and compressing the nonwoven sheet 12, and optionally, if desired to provide enhanced stiffness and change of color from that of the natural fibers, the method further includes bonding a formaldehyde free scrim layer 25 to at least one side (panel 10') or both sides (panel 10") of the sheet 12. [0027] In further detail, the process includes blending the bast fibers 18 and polymeric binding fiber 20 in a mixer and then fine openers until the mixture 22 is homogenous. The homogeneity provides the unifonn distribution of the polymeric binding fiber 20 needed to obtain maximum and uniform stiffness throughout the entirety of the finished panel 10.

[0028] Then, upon forming the homogenous mixture 22 of the bast fibers 18 and polymeric binding fiber 20, the mixture 22 is processed in a web forming machine to create the nonwoven web 24. The weight of the web 24 can be varied from about 150gsm (grams per square meter) up to about 1500gsm, wherein the weight of the sample was formed around 700gsm.

[0029] Then, upon forming the web 24, the web 24 is heated, such as in an oven identified generally at 26, to a temperature suitable to at least partially melt the polymeric binding fiber 20, thereby bonding the bast fibers 18 and polymeric binding fiber 20 together to form the bonded nonwoven sheet 12.

[0030] Then, the bonded nonwoven sheet 12 is saturated with the solution 16, such as by being passed through a bath of the solution 16 identified generally at 28, that includes the solution-based binder, which has a low Ph; a Ph stabilizer to offset the low Ph of the binder, and a flame retardant, as described above, and further being diluted with water, if not used as the Ph stabilizer. The amount of saturation is performed to provide about a 10-40% dry-pickup of the solution 16, wherein the total binder pick-up in the example was about 30% dry pick-up; the total disodium octaborate tetrahydrate pick-up is between about 5-25 wt% based on a 30% dry pick-up from the chemical solids.

[0031 ] Then, the saturated, bonded nonwoven sheet 12 is heated sufficiently to dry the sheet 12 and cure the solution 16, such as in a continuous compression belt oven 30, by way of example and without limitation. During the drying and curing heating process, the water from the solution 16 is first substantially evaporated to leave about 8-10% moisture content in the bonded nonwoven sheet 12. Then, upon achieving the desired moisture content, the temperature is increased to about 180-200 degrees Celsius, at which temperature the binder of the solution 16 is cured and cross-linked with the bast fibers 18. While the binder is curing, the bonded sheet 12 is compressed under a force F to a predetermined finished thickness, such as between a pair of high compression belts 32, by way of example and without limitation. Further, while still being compressed between the belts 32 and upon being fully cured, the resulting panel 10 is cooled, wherein the heating, compression and cooling can all be performed within the continuous compression belt oven 30.

[0032] The cooled and compressed panel 10, if necessary to meet requirements of the intended application, can then be further processed by laminating at least one formaldehyde free scrim layer 25, such as fiberglass or polypropylene, by way of example and without limitation, to one side or both sides of the respective panel 10', 10" via a scrim laminator 34. The resulting finished panel 10, 10', 10" meets the Class A rating for flame as per ASTM E- 84, while the panel 10', 10" also attains enhanced board stiffness, even in the presence of moisture, due to the synergies provided by the solution-based binder, binding fibers 20, and scrim layer(s) 25, and also has a very low formaldehyde content. Of course, if deemed unnecessary for the intended application, the panel 10 can remain free of the scrim layer 25, though this will result in the panel 10 having a diminished strength relative to the panels 10', 10". Throughout the process, the sheet 12 remains a continuous piece of material from the beginning of the process until after compressing, curing and cooling, or if a lamination scrim layer(s) 25, until after lamination. The desired length of panel 10, 10', 10" can be cut via a cutting operation 36, shown as being after compression and after lamination, if performed.

[0033] Many modifications and variations of the present invention are possible in light of the teachings above. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described, and that the scope of the invention is defined by any ultiiTiately allowed claims.