Textiles: manufacturing – Textile product fabrication or treatment – Fiber entangling and interlocking
Reexamination Certificate
2000-12-11
2003-05-20
Vanatta, Amy B. (Department: 3765)
Textiles: manufacturing
Textile product fabrication or treatment
Fiber entangling and interlocking
C028S111000, C028S115000
Reexamination Certificate
active
06564437
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention involves improvements in fiber glass mats that are used as reinforcements in thermoplastic composite materials.
Composites of fiber glass reinforcements and thermoplastic matrix materials can be formed by various molding techniques such as compression molding or stamping. The resulting composites can be used in a wide variety of products where a combination of strength and light weight are desired.
The configuration and type of reinforcement significantly effect the physical characteristics of the composite, such as tensile strength, flexural strength, and impact performance. Preferred reinforcement configurations may vary considerably for different molding processes and molding conditions. One known method of varying the physical configuration of a mat is by needling. Needling has several effects on a mat that are beneficial for high flow thermoplastic laminating applications. These include consolidating the mat to enhance mat strength, modifying loft, and rupturing and opening fiber glass bundles to individual filaments. The rupturing and opening functions improve the ability of the glass fiber reinforcement to flow along with the polymeric matrix material when the laminate is molded. In other words, the fiber glass reinforcement has sufficient mobility to be displaced into features of the molded product during the molding process. This, in turn, improves the appearance of the molded composite products. However, known needling techniques are not able to achieve optimization of all of these factors in a single mat. Needling from only one side of a mat is good for strengthening the mat, but it is difficult to achieve sufficient opening of the mat for improved flow without over-punching the mat and sacrificing strength.
Needling a fiber glass mat is known to produce spikes of fibers protruding from the original surface of the mat. U.S. Pat. No. 4,335,176 (Baumann) discloses needling a fiber glass mat through its thickness from one side whereby one side of the mat has more fiber spikes than the other side. The differential is produced by the orientation of barbs on the needles. Because the mat is needled from one side, the number of needle punches is necessarily uniform throughout the mat. The patent discloses assembling two of these mats for lamination.
U.S. Pat. No. 4,885,205 (Wahl et al.) discloses symmetrically needling a mat from both sides so as to reduce needle penetration depth. The objective is to improve appearance of the laminate by reducing the height of the fiber spikes above the original mat surface due to the needling. The emphasis of the disclosure is on making the needling symmetrical on both sides, both in needle penetration depth and needle penetration density. While some improvements are possible with this approach, it has been found difficult to balance tensile strength with good appearance of the molded product using mats made by the method of this patent.
U.S. Pat. No. 5,580,646 (Jansz et al.) discloses needling a mat on both sides, wherein the needling depth or needle type differs from one side to the other. Needle punch density is the same on both sides. The asymmetric mats that are produced are intended to be laminated in pairs. When high flow properties are produced by this method, it has been found that loft is higher than desirable for some applications.
It would be desirable if certain properties of a fiber glass mat could be enhanced for improved thermoplastic composite molding performance with less compromise in other desirable properties as is incurred with prior art approaches.
SUMMARY OF THE INVENTION
It has now been found that a fiber glass mat intended for use in reinforcing thermoplastic composites can be provided with a surprisingly advantageous combination of properties by means of a novel needling configuration. The mats of the present invention have a unique combination of good strength, controlled loft, and an enhanced degree of openness for flow during molding. This combination of advantageous properties has been discovered to be attainable by needling the mat from both sides, wherein the needling density (i.e., the number of needle punches per area of mat surface) on one side of the mat differs from that on the other side. The amount of the needling density difference may vary depending upon the desired effect and the details of a particular mat construction and needling operation. Any appreciable difference may be significant, but generally significant advantages are observed when the needle punch density on one side exceeds that on the other side of the mat by more than 5 percent, preferably more than 10 percent. Particularly good results have been obtained by the inventors with preferred commercial mat embodiments when the needling density on one side of the mat is at least 20 percent greater than that on the opposite side of the mat. Optionally, further variations may be used in the needling parameters from one side to the other, such as the needle type and/or needle penetration depth, to achieve further refinements in the mat characteristics. It is particularly advantageous to vary the needling penetration depth in conjunction with the needling density difference. The combination of needling at a relatively deep penetration at relatively low density on one side and needling at a relatively low penetration at relatively high density on the opposite side has been found to be particularly advantageous in achieving improved openness of the mat structure without undue loss of strength.
After needling, the mat may be laminated with thermoplastic resin to form a stampable composite sheet in the usual manner. Unlike some of the prior art, it is not necessary to use two reinforcement mats with the present invention.
Other properties are generally sought after with fiber glass reinforcements including good permeability for impregnation by the thermoplastic matrix material and the ability to yield composite products with good surface smoothness and mechanical properties such as tensile, flexural and compressive strength, tensile and flexural modulus and stiffness. These desirable properties need not be sacrificed in order to attain the advantages of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention involves fiber glass reinforcement mats, for which the general manufacturing techniques are well known in the art. The glass fibers used in the mats of the present invention are also those conventionally used in the art. The following description of the fiber forming and mat forming operations are merely examples of processes that may be used for these steps and are included for the sake of completeness of the disclosure of the best mode of carrying out the invention. Additional information regarding these conventional aspects of the invention may be found in K. Loewenstein,
The Manufacturing Technology of Continuous Glass Fibres
, 3rd Ed. (1993).
The mat is comprised of fibers of known glass compositions based upon oxides such as silica selectively modified with other oxide and non-oxide compounds. Useful glass fibers can be formed from any type of fiberizable glass composition known to those skilled in the art, and include those prepared from fiberizable glass compositions commonly known as “E-glass,” “A-glass,” “C-glass,” “D-glass,” “R-glass,” “S-glass,” as well as E-glass derivatives that are fluorine-free and/or boron-free. Most reinforcement mats comprise glass fibers formed from E-glass. Such compositions and methods of making glass filaments therefrom are well known to those skilled in the art and a more detailed description is not necessary. Further information may be found in Loewenstein (supra), pages 30-44, 47-60, 115-122, and 126-135, which are hereby incorporated by reference.
Commercially produced glass fibers generally have nominal filament diameters ranging from 5.0 to about 35.0 micrometers, and most commonly produced E-glass fibers have a nominal filament diameter of 9.0 to 30.0 micrometers. The present invention may employ any of t
Meng Jian
Thimons Thomas V.
Millman Dennis G.
PPG Industries Ohio Inc.
Siminerio Andrew C.
Vanatta Amy B.
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