Method for producing a wet-laid fiber mat

Abstract

A method is provided for forming a wet-laid nonwoven glass fiber mat comprised of a plurality of bundles of fibers. The method includes the steps of adding chopped fibers to an aqueous slurry containing a sufficient amount of a suitable hydrophobic agent to cause the fibers to form a plurality of bundles. The fibers are then formed into a mat which may be used in a number of reinforcement applications. A method is also provided for modifying the components in the water slurry to produce mats comprising either bundles of fibers or dispersed fibers.

Description

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY [0001] The present invention relates to a process for producing a non-woven fiber mat, and more particularly, to a wet-laid process for forming a glass fiber mat comprised of small bundles of glass fibers. BACKGROUND OF THE INVENTION [0002] Two main techniques utilized for producing glass fiber mats are wet-laid processing and dry-laid processing. Typically, in a wet-laid process, an aqueous slurry containing dispersed fibers and a variety of other components such as surfactants, viscosity modifiers, defoaming agents, or other chemical agents is prepared and sufficiently agitated to disperse the fibers throughout the slurry composition. The aqueous slurry is then deposited onto a moving screen, chain or fabric that retains the majority of the fibers while allowing a substantial portion of the water to be removed and thereby form a fiber web supported by the upper surfaces of the screen. [0003] A binder composition may then be applied to t...

AI Technical Summary

Benefits of technology

[0012] The present invention provides an economically competitive process capable of producing lightweight glass fiber mats which are both relatively uniform in weight and are comprised of primarily of bundles of relatively short fibers and which exhibits an open, porous structure suitable for and compatible with use in the production of reinforced molded parts with highly viscous resin compositions. The present process provides a wet-laid glass fiber mat utilizing a conventional aqueous slurry composition, thereby avoiding the difficulties associated with the inclusion of the hydrophobic agent, while still promoting the organization of the fibers into discrete bundles of closely associated multiple fibers arranged in a substantially parallel relationship. The resulting mat may comprise small or large bundles of fibers, is of a substantially uniform weight, and has a generally porous structure.

[0013] In particular, the process according to the present invention uses WUCS that have been treated with a modified size composition that promotes the formation of the fiber bundles within the slurry without the difficulties associated with adding a hydrophobic agent directly to the slurry composition. Then, as in the conventional processes, the slurry will be applied to a supporting and porous conveyor through which the majority of the water will be removed to form a fiber web. The fiber web will then typically be transferred to another downstream conveyor for application of a binder composition, after which it will be dried and the binder cured to form the finished fiber mat product.

[0016] The method of the present invention provides an advantage over prior processes in that the size composition used to treat the chopped fibers prior to their distribution in the aqueous slurry which tends to cause or promote bundle formation within the slurry may be easily modified to form mats comprising primarily dispersed fibers (i.e., having substantially no fiber bundles). This can be done without having to drain the aqueous slurry from the machine or mixing tank in which the fibers are processed, which results in a substantial savings in time and cost.

[0019] When the formation of mats with bundled fibers is no longer desired, the method may include the step of modifying the size composition that is being applied to the fibers before chopping to reduce or suppress the tendency of the fibers to form bundles in the slurry. A mat comprising primarily dispersed fibers may then be produced by removing water from the fibers to form a web and applying a binder.

Problems solved by technology

However, conventional dry-laid processes tend to produce mats are of a less uniform weight when compared with mats produced by a wet-laid process, i.e., different areas of the mats have different weights and / or fiber densities.

At lower basis weights below about 300 g / m2, the relatively poor small-scale weight uniformity of the air-laid process mat becomes increasingly apparent in terms of uneven distribution of the fibers.

As a result, machine productivity is also sacrificed because the conveyor speed cannot be increased in proportion to the reduction in bias weight of the mat without further degrading the uniformity.

In addition, processes utilizing dry-chopped input fibers tend to be more expensive than those utilizing wet-chopped input fibers because the fibers in a dry-laid process are dried and packaged in separate steps before being chopped offline, while size can be applied directly to the manufactured fibers shortly before they are chopped to form the chopped fibers that will be added to the aqueous slurry.

However, because such mats still include a number of dispersed fibers in addition to the fiber bundles, they have proven generally unsuitable for applications in which higher porosities are desired or necessary.

This result is particularly undesirable in reinforcement applications because the longer fibers tend to be visible in the final molded product and detract from the product's appearance.

Although this method improved the uniformity and porosity of the resulting fiber mat, it was difficult to control on a commercial scale and the addition of the hydrophobic agent was associated with certain negative effects on subsequent products.

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