Method for producing a glass mat

Details Method for producing a glass mat Method for producing a glass mat

1999-10-29

2001-09-18

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S222000, C524S492000, C524S493000, C524S494000

Reexamination Certificate

active

06291552

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to glass mats and their method of manufacture. In particular, the invention relates to a wet-aid method of making a glass mat, particularly abundled glass mat, and the mats formed by this method. Such mats may be formed into a variety of products, such as roofing shingles, composite articles, polyurethane foam headliners, and employed in reinforced plastics applications such as boat hulls and food service trays.
BACKGROUND OF THE INVENTION
Glass fiber mats are used as reinforcing elements for roofing shingles, flooring, and wall coverings, as well as in the formation of molded parts using polymer resins. The fiberglas s mat industry typically uses 1.25 inch fiberglass fibers to make mats. These fiberglass fibers are generally coated with a sizing agent, typically an antistatic compound, such as a cationic softener, and formed into mats.
The two most common methods for producing glass fiber mats from such fibers involves wet-aid and dried processing. Typically, in a dry-lid process, fibers are chopped and air blown onto a conveyor, and a binder is then applied to form a mat. Dry-laid processes may be particularly suitable for the production of highly porous mats having bundles of glass fibers. However, such dry-laid processes tend to produce mats that do not have a uniform weight throughout their surface areas. This is particularly true for lightweight dry-aid mats having a basis weight of 200 g/m
2
or less. In addition, the use of dry-chopped input fibers can be more expensive to process than those used in a wet-laid process, as the fibers in a dry-laid process are typically dried and packaged in separate steps before being chopped, which may not be necessary in wet-laid processes.
In a wet-laid process, an aqueous solution, often referred to in the art as “white water”, is formed into which the glass fibers are dispersed. The white water may contain dispersants, viscosity modifiers, defoaming agents or other chemical agents. Chopped, fibers are then introduced into the white water and agitated such that the fibers become dispersed, forming a slurry. The fibers of the slurry may then be deposited onto a moving screen, whereupon a substantial portion of the water is removed-to form a web. A binder is then applied to the web and the resulting mat is dried to remove the remaining water and to cure the binder. The resulting non-woven mat is an assembly of dispersed glass filaments.
The white water and resulting slurry can play a major role in achieving the desired fiber distribution within the glass fiber mats. For example, the type and charge of the glass fibers, the dispersant, and/or the viscosity modifiers in the white water can affect the level of dispersion of the fibers. Further, the level of dispersion of the fibers during processing has a significant effect on the porosity, tensile strength and tear strength of the finished glass mat.
Wet-laid processes have employed nonionic viscosity modifier systems, which may contain a cationic viscosity modifier, or anionic viscosity modifier systems. For example, U.S. Pat. No. 4,869,932 proposes treating glass fibers with low molecular weight watersoluble anionic vinyl polymers for use in a white water having a long-chain anionic viscosity modifier, to prevent precipitates from interfering with the white water formulation. In contrast, U.S. Pat. No. 4,526,914 relates to a white water dispersant system employing a cationic surfactant, a viscosity modifier system having a cationic viscosity modifier and 0 to 90% of a nonionic cellulosic viscosity modifier.
Previous systems have not proven entirely satisfactory for controlling the dispersion of fibers and subsequent formation of glass mats with controlled porosity, particularly for bundled or structured glass mats. For example, wet-laid processes containing an anionic polyacrylamide viscosity modifier have been used to make mats with highly dispersed fibers, such as for roofing mats, but are not suitable for making bundled or structured glass mats.
Accordingly, there is a need for a wet-laid process for making glass mats which is economical and allows better control of fiber-fiber interactions. More particularly, there is a need for an improved wet-laid process for making bundled or structured glass fiber mats having a high porosity and a uniform weight.
SUMMARY OF THE INVENTION
The invention answers the need for an economical wet-laid method for producing high quality fibrous glass mats. The invention accomplishes this by providing control of both the dispersion of glass fibers and subsequent bundling of the fibers through the use of oppositely charged viscosity modifiers. By properly sequencing the addition of the oppositely charged viscosity modifiers, the glass fibers may be dispersed in the white water and then attracted together to form bundles. Electrostatic forces generated by the viscosity modifiers first disperse the glass fibers, then attract the fibers back together in a controlled manner, so that glass mats, particularly those with high porosity and uniform weight, may be produced more efficiently and with better control than previously done.
More specifically, the invention provides for a method of making a fibrous glass mat, preferably a bundled glass mat. The method involves forming a glass mat by first dispersing glass fibers in a white water that contains a dispersant and a charged viscosity modifier to form a slurry. An oppositely charged viscosity modifier may then be added to the slurry. The water may then removed from the slurry to form a glass mat. The mats of the invention may contain uniformly dispersed glass fibers or bundles of glass fibers, depending upon the desired end use.
The invention also relates to a slurry. Generally, a slurry of the invention contains glass fibers, a positively charged or cationic viscosity modifier, a negatively charged or anionic viscosity modifier, a surfactant, and water. Typically, the cationic viscosity modifier is present in an amount ranging from about 100 parts per million (ppm) to about 1000 ppm, or about 0.01 to about 0.1 weight percent of the slurry. The anionic viscosity modifier is present in an amount of about 1 to about 35 weight percent by weight of the cationic viscosity modifier, or about 0.0001 to about 0.035 weight percent of the slurry.
The invention is discussed in more detail below.


REFERENCES:
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patent: 4869932 (1989-09-01), Romberger
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patent: 5518586 (1996-05-01), Mirous
patent: 5977232 (1999-11-01), Arkens et al.
patent: WO 98/11299 (1998-03-01), None
patent: WO 99/45198 (1999-09-01), None

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