Heat sealable, non-woven padding has been used particularly in automobile manufacture. Particularly in the side or door panels, sun visors, and other areas of decorative fabric is laid over a thickness of non-woven padding which carries a thermoplastic binder. The non-woven padding, in turn, may be placed on a backing of cardboard or the like. When, a dielectric or radio frequency (R.F.) sealing apparatus may be used to place seal lines into the stack of fabric padding and backing, so that the fabric bulges out in areas between the seal lines in a resilient and decorative manner.
For example, the latex-bonded, non-woven paddings which are Product Numbers 147a or 6131-x of the Fiber Bond Corporation of Michigan City, Ind. They are illustrative of a type of padding which has been sold to the auto industry for several years for the purpose described above. A vinyl latex binder is applied to non-woven padding, which padding is produced by an airlaid, garnet or carding process. The latex emulsion is applied to a fibrous web which is so produced by a spraying or saturation method. The web is then dried to remove water, and heated to fuse the latex, resulting in a fibrous pad which can adhere to many fabrics and to cardboard backing upon R.F. sealing.
One deficiency of non-woven padding, and their binders, of the prior art is that the adhesion upon heat sealing of such padding to knitted or other loose weave fabrics which are not coated with a binder leaves something to be desired. The high temperature flow characteristics of such vinyl binders is not very high, so that adhesion to such loose weave fabrics by mechanical entrapment of the fibers in the fabric is not very good. Thus when the prior art non-woven padding is R.F. sealed to such fabrics at typical bonding temperatures of 275.degree.-325.degree. F., they lack low melt viscosities, and do not form a strong mechanical bond with the fabrics. Their bonding capabilities are based more upon physical interaction on the molecular level with the materials of fabrics or binders in the fabrics, so that the prior art pads do adhere well for example to supported vinyl fabric or to woven fabric with latex adhesive on the back, but not well to uncoated knit fabrics and the like.
Also, the non-woven padding with latex binders exhibits certain difficulties in meeting certain environmental heat aging tests, because the vinyl polymer will soften and creep under stress to a point to where bond failures can occur, for example, at temperatures of 85.degree.-93.degree. C. Latex polymers that are formulated to give better bonding with uncoated, loose-weave fabrics, may rapidly lose their strength and fail cohesively at elevated test conditions of 85.degree. C. and the like. Conversely, if a latex polymer is used which does not soften appreciably at 85.degree.-93.degree. C., it will not melt sufficiently at practical bonding temperatures used in R.F. sealing to produce good mechanical bonds for good mechanical adhesion to uncoated fabrics.
Additionally, the Sackner Company, a subsidiary of Bemis Manufacturing Company of Grand Rapids, Mich., sells a product Number 151a, which is a composite pad. Lines of thermoplastic polyamide or polyester powder are laid on fibrous pads and fused. Following this, the lines of fused powder can be used in R.F. sealing to fabric.
Such a product is undesirably expensive due to the need to apply the polyamide or polyester powder in lines across the face of padding and then to fuse it. Thereafter the plastic lines must be fused once again by R.F. sealing, for example, for bonding to fabric and the like. As a further disadvantage besides cost, the fused polyamide or polyester can break off as the pad is handled so that portions fall off of the pad. Likewise fused powder will fall off of the pad as well, which will result in the inconvenience of undesirable powder flying around, and a possible loss of bonding capabilities due to loss of material from the fused lines.
Accordingly, there is a need for an improved binder for fibrous padding which can be inexpensive, yet which can provide reliable, effective bonding to a larger variety of fabrics than the latex bonded pads of the prior art, so that the auto industry and other groups can make use of padding manufactured in accordance with this invention with a wide and varying selection of fabrics, without concern that there will be a bonding failure in the final product.