The surface of a weaving bobbin which comes into contact with the yarn that is wound around it must be extremely smooth so that the yarn will not be caught and broken during the weaving process. In addition to being smooth, the surface of the bobbin must also be wear resistant since many of the yarns used in modern weaving technology are extremely abrasive. Wood bobbins are normally produced by cutting blocks of wood to an initial rough size and then mechanically reducing the bobbin blank to its ultimate desired dimension, as by turning or the like. Due to the inherent shortcomings of the mechanical shaping operation, only clear, straight grained wood could be used in the production of bobbins. Thus, forming woods or grains such as curly, bird's-eye, etc., or heartwood would result in surface imperfections that could only be made useful through the application of a multiplicity of surface coats. It was not possible to provide an adequate surface finish, whether a varnish or an enamel, with the application of a single layer of protective material. Although it is known to apply surface finishes containing from about 20 to 25 percent solids, this being the maximum heretofore permissible, it has not been possible to apply surface coating of acceptable viscosity, which contained the percentage of solids necessary to impart surface protection to the bobbin with a single application.
Surface finishes other than varnish or enamel that have a high solids content have been tried but they are not suitable as a bobbin finish due to the lack of hardness, tackiness, solid yarn withdrawal characteristics or they require curing conditions that are incompatible with wood or wood bobbins.
USPTO Backgrounds
USPTO Backgrounds