Flame attenuated fiberglass

Details Flame attenuated fiberglass Flame attenuated fiberglass

2001-07-12

2002-06-04

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S036000

Reexamination Certificate

active

06399525

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention pertains to fiberglass products prepared from glass compositions suitable for a process involving flame attenuation. The glass fibers exhibit good biosolubility and excellent moisture resistance.
2. Description of the Related Art
Fiberglass has a myriad of uses, including the reinforcement of polymer matrix composites; preparation of thermoformable intermediate products for use as headliners and hoodliners in vehicles; air and water filtration media; and sound and thermal insulation products. The preparation and/or subsequent processing of such materials often involves handling steps which result in cut or broken fibers which may be inhaled. As it is impractical or impossible to remove such fibers from the body, it has become important to create glass compositions which exhibit high degrees of biosolubility, i.e. which are rapidly solubilized in biological fluids.
If high biosolubility were the only factor which need be considered, a solution to the biosolubility problem would be rapidly attained. However, in addition to being biosoluble, glass fibers must also possess a number of other physical and chemical characteristics. For example, in many applications such as in battery separators, high chemical (e.g. acid) resistance is required. As can be readily imagined, high chemical resistance and high biosolubility are largely conflicting characteristics.
Glass fibers must also be strong and moisture-resistant. If moisture weakens glass fibers appreciably, their applicability to many uses suffers. Weakened glass fibers not only possess less than desired tensile strength and modulus, but also break and fracture more easily, thus increasing the risk of inhalation, etc. By the same token, moisture resistant glass fibers which have low strength to begin with also do not fulfill many requirements. For example, building insulation is shipped in compressed form. If the glass fibers of the insulation product are weak or brittle, many fibers will be broken during compression, not only increasing the number of small fibers which are bioavailable, but also producing an inferior product which may not recover a sufficient amount of its pre-compressed thickness. Strong fibers which are not moisture resistant also exhibit a great deal of breakage, especially under humid storage, as illustrated hereinafter. Finally, glass fibers must be prepared from glass compositions which can be economically processed.
The two principle methods of glass wool fiber production are the pot and marble process and the centrifugal or “rotary” process. In the latter, molten glass enters a centrifugal spinner from the forehearth of a glass melting furnace. As the centrifugal spinner rotates, relatively large diameter glass strands stream from orifices located in the spinner's periphery. These large diameter strands immediately contact an intense hot gas jet produced by burners located around the spinner. The hot gas attenuates the large diameter strands into fine, elongated fibers, which may be collected on a moving belt.
The primaries exiting the pot from the pot and marble process are flame attenuated rather than hot gas attenuated, thus exposing the glass fibers to higher temperatures than in the rotary process. These higher temperatures cause a loss of the more volatile compounds of the glass composition from the outside of the fibers, resulting in a “shell” which has a different composition than the fiber interior. As a result, the biosolubility of glass fibers prepared from pot and marble fiberglass is not the same as that derived from the rotary process. As glass fibers must necessarily dissolve from the fiber ends or the cylindrical exterior, a more highly resistant shell will dramatically impede the dissolution rate. Fibers having such a shell, which are flame attenuated, are also prepared by the rod method or direct melt method. These latter methods involve conveying raw materials, in any form, to an orifice or bushing to form primaries, which are then flame attenuated, as in the pot and marble method.
While flame attenuated fibers exhibit excellent chemical and moisture resistance due to this core/sheath structure, biosolubility of the fibers desirably should be improved. The industry would find useful a fiberglass which exhibited excellent moisture resistance as well as good biosolubility.
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that glass fibers of enhanced biosolubility may be prepared from glass compositions suitable for flame attenuation processing, which have well defined formulations. The fibers have a core/sheath structure where the outer shell (sheath) has a different composition than the core portion (fiber interior), and are prepared from a composition comprising:
SiO
2
66- 69.7
Al
2
O
3
 0- 2.2
RO
 7-18
R
2
O
 9- 20
B
2
O
3
 0- 7.1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The glass composition of the glass fibers of the present invention must fall within the following range of composition, in mol percent:
SiO
2
66- 69.7
Al
2
O
3
 0- 2.2
RO
 7-18
R
2
O
 9- 20
B
2
O
3
 0- 7.1
where R
2
O is an alkali metal oxide and RO is an alkaline earth metal oxide. R
2
O is preferably Na
2
O in most substantial part, while RO may be MgO and/or CaO, preferably both, in a molar ratio of MgO/CaO of 1:3 to 3:1, more preferably 2:3 to 3:2.
At the same time, the HTV and liquidus of the overall composition must be suitable for glass fiber processing. It is preferred that the subject invention glasses have HTV and liquidus which are suitable for production of glass fibers in the pot and marble process. Such glass generally must have an HTV (10
3
poise) of 1800° F. to 2100° F., preferably 1900° F. to 2000° F., and exhibit a liquidus which is minimally about 350° F., preferably 425° F., and more preferably 500° F. or more lower than the HTV. These characteristics are necessary to prepare glass fibers economically on a continuous basis.
It has been found that flame attenuated glass of high biosolubility, while yet maintaining other necessary physical properties such as chemical resistance and moisture resistance, is obtained when the compositions of the present invention are observed.
Preferably, the biosoluble fiberglass of the subject invention has a composition which falls within the following ranges (in mol percent):
SiO
2
66- 69.0
Al
2
O
3
 0-2.2
RO
 7-16
R
2
O
 9- 19
B
2
O
3
 3- 7.1.
Most preferably, the biosoluble glass fibers of the subject invention have a composition which falls within the following most preferred range:
SiO
2
66- 68.25
Al
2
O
3
 0- 2.2
RO
 7-13
R
2
O
 9-18
B
2
O
3
 4- 7.1.
With respect to the performance characteristics of the glass fibers of the subject invention, it is preferred that the ratios of C(acid), C(bio) and C(moist), defined as follows:
C(acid)=[SiO
2
]/([Al
2
O
3
]+[B
2
O
3
]+[R
2
O]+[RO])
C(bio)=[SiO
2
]/([Al
2
O
3
])/[B
2
O
3
]+[R
2
O]+[RO])
C(moist)=([SiO
2
]+[Al
2
O
3
]+[B
2
O
3
])/([R
2
O]+[RO]).
are such that C(acid) is greater than or equal to 1.95, and more preferably greater than or equal to 2.00; C(bio) is less than or equal to 2.30, more preferably less than equal to 2.23, most preferably less than or equal to 2.20; and that C(moist) is greater than or equal to 2.40, more preferably less than or equal to 2.50, and most, preferably greater than or equal to 2.60. It is most desirable that C(acid) and C(moist) be as high as possible. For example, C(moist) values of 3.00 or greater are particularly preferred. It should be noted also, that the various C-ratios are independent in the sense that a more preferred glass need not have all “more preferred” C-ratios.
Acid resistance may be measured by battery industry standard tests. For example, a typical test involves addition of 5 grams of no

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