Improvements in brushes and synthetic bristles

Abstract: Said bristle being formed preferably from a synthesized polymer, a co-polymer, or an alloy or mixture of synthetic polymers. A synthetic bristle manufactured by injecting a blowing agent into a melt of polymer prior to extrusion and subsequent drawing. This provides a synthetic bristle, particularly suited for paint brushes, which has the properties of natural bristles, such as an irregular surface texture for paint retention, whilst retaining also the desirable characteristics of synthetic bristles, such as good water and abrasion resistance.

Description: This invention relates to an improvement in brushes, an improvement in synthetic bristles used in brushes, and methodology for producing such improved synthetic bristles. It is useful to first discuss the improvements in synthetic bristles. In mankind's long history of utilizing natural materials, considerable application has been made of relatively coarse hairs, filaments and fibres of animal and vegetable origin. "Bristle" is a common term for these materials, although the term is often restricted to mean animal hair, and even more specifically, sometimes to the hair of the swine. In the context of this disclosure, we use the term "bristle" in its broadest sense to cover all naturally derived filamentatious material which can be used to make the flexible brushing portion of a brush. We further define a brush as a device, composed of a multiplicity of bristles, in which at least a proportion of the bristles are synthetic bristles falling within the scope of the claims in the present Specification. As will be recognized by those skilled in the art, Amalon is a mixture of polyolefin and nylon, and Esterlon is a mixture of polyester and nylon. Since the development of the first truly synthetic bristle (nylon) as an adaptation of synthetic fibre technology after World War II, a number of other synthetic bristle adaptations have been developed and commercially employed. These synthetics have displaced natural bristles in some brush applications. However, natural bristles are still important materials in the brush industry because the synthetics developed to date have not been completely satisfactory substitutes. On the other hand, some of the synthetics provide certain superior properties to the natural bristles for some applications (e.g. improved water resistance and abrasion resistance). One aim of this invention is to provide synthetic bristles which have not only the aforementioned benefits of such synthetics, but also many of the attributes of natural bristles never before available in synthetic versions. A second aim of this invention is to provide a synthetic bristle superior to conventional synthetics in terms of polymeric material utilization efficiency. A third aim is to provide a synthetic bristle which is opaque, or nearly opaque, to light without requiring pigmentation or by using significantly less pigmentation than conventional synthetics. Natural bristle materials, whether of vegetable or animal origin, result from organic growth processes wherein elongated cellular formations build upon one another to form essentially rod-like structures of sufficient resilience and integrity to serve the functional needs required in brushes for painting, powdering, scrubbing, sweeping and the like. It is the cellular wall formation that provides structural character to these natural bristles along with the complex chemical makeup of the specific bristle. Some natural bristles are essentially tapered in that one end (the butt end) of the bristle is larger than the other (tip end). Still others are not tapered or have very little of this tendency. Natural bristles are always irregular in shape along their length, and have scale-like outer surfaces. Some of these are naturally split at the end, forming tiny fingers which are useful in brush performance. Synthetic bristles are available in tapered or untapered form, and in cross-sectional profiles of solid round, hollow round, ribbed, S-shaped and other shapes dependent on extrusion technology. All synthetics to date require physical splitting of the ends (flagging) where this is deemed desirable in brushes. Our improved synthetic bristles are designed in both tapered and untapered form, and in all the extrusion shapes as other synthetics. The result of this improvement is to provide synthetic bristles which combine the appearance and physical properties associated with natural bristles with chemical and physical properties associated with the polymeric materials used in their composition. Furthermore, these improved synthetic bristles, by virtue of their cellular structure, are less dense than other synthetics made from the same polymers. For example, such bristles may possess only 70 to 75% of the weight of, (though not limited to this range), synthetics made in the same cross-sectional profile from the same base polymer. This benefit provides more efficient utilization of the base polymer and desirably lighter weight bristles. These improved synthetic bristles are more easily split or flagged than synthetics of the same cross-sectional profile. US-A-4 010 308 describes a two- or three-material coated fibre in which the backbone comprises a glass fibre to which a coating is applied; and Example XII thereof describes the use of this coated fibre in a brush. However, this is an expensive way of producing a brush bristle, and the incorporation of carbon black in the bristle makes it unsuitable for the application of, say, white paint. Another form of synthetic bristle is described in US-A-3 411 979 (FR-A-1 508 433) , but this too has certain limitations. The invention as defined in the claims starts from US-A-3 411 979 (FR-A-1 508 433), and the preambles of the independent claims 1 and 7 are based on what is shown in this prior art. The advantages of the invention are given by the characterising features of claim 1 (product) and the characterising features of claim 7 (method). The invention is illustrated more or less diagrammatically in the accompanying Figures wherein, Figure 1 is a schematic view of a conventional mode of producing synthetic bristles; Figure 2 is a schematic view of the new mode of producing synthetic bristles described herein; Figure 3 is a side view, with a portion sectioned, of a solid bristle of the present invention; Figure 4 is a right end view of the solid bristle of Figure 3; Figure 5 is a side view, with a portion sectioned, of a hollow bristle of the present invention; and Figure 6 is a right end view of the hollow bristle of Figure 5. To explain our improvements in brushes, it is important to provide some basic brush design background. We have defined a brush as a device, composed of a multiplicity of bristles attached to a handle and designed primarily for painting, powdering, scrubbing, sweeping and the like. While any brush may perform all of these tasks outlined to some degree, use experience and refinement have led to more specific brush designs for each of these applications. For example, the shapes of the handles are generally different and may be expressly designed for these different functions of painting, powdering, sweeping and scrubbing, as well as refined within each function, especially as related to the specific task. Hence, scrubbing brush handles usually take different forms from painting brush handles, but tooth scrubbing brushes usually also are different in design from floor scrubbing brushes, and brushes designed for sash painting normally have different shaped handles from wall painting brushes. Bristles used in brushes also are selected or designed for the particular application of the brush. In general, we define bristles as being relatively coarse hairs, filaments and fibres which possess sufficient resilience and integrity to provide the function required of a brush. Experience has shown that of these functions, scrubbing requires the most resilient bristles and painting the least resilient with artists brushes being the softest. Sweeping usually requires an intermediate resilience. Resilience is a function of the bristle's cross-sectional area relative to its length as well as the flexural properties of the bristle material substance. It should also be recognized that different practical methods have evolved for atttaching the bristles to the handles for these different functional brushes. Staple setting of bristle tufts is a commonly employed method for many designs of scrubbing and sweeping brushes. Strip binding is another method which is widely used. Twisted wire techniques are also used, especially when circular brushes are desired (such as bottle scrubbing brushes). The primary method used to make painting brushes is called ferrule setting wherein a bristle mixture is bound in a metal band with an adhesive setting material. The adhesive applied in liquid form penetrates within the interstices between the bristles, and if the bristle's cross-section is so designed, within the bristle itself. With this background, our improvements in brushes are more easily understood. One such embodiment is improved paint brushes as explained below: Two paint brushes were constructed, using a standard formulation in one case, and an experimental formulation in the other. The difference was substitution in the experimental brush of 40% by weight of our improved cellular synthetic bristle for a like amount of a commercial synthetic bristle. Both synthetics were of tapered form; of polyester material; and of the same physical size. The two brushes were determined to have the same flexural stiffness when compared in a special device designed for that purpose. Painting tests were then performed using a special machine which allowed both brushes to be compared in painting performance simultaneously using the same painting surface over a range of angles of address to the surface, and a range of displacements of the brush to the surface. The paint out results were compared in both the wet and dried states. It was clear to the three test observers that the experimental brush produced superior paint out results over the complete range of testing using Glidden Latex Spred Satin Paint. This experimental brush was also tested against a commercial brush formulated of natural animal bristle using Tru-Test Alkyd Semi-Gloss enamel (7174 color). The experimental brush provided clearly superior painting results. Still another test comparison was made to a commercial brush which contained approximately 50% natural bristle and 50% synthetic polyester bristle. This test also applied the Tru-Test Alkyd Semi-Gloss enamel and again the experimental brush produced superior painting results with the same number of painting strokes on the test machine. Another test comparison was made to a commercial brush made from all polyester synthetic bristles. This brush was considered an outstanding performing brush. When both brushes simultaneously applied Dutch Boy Latex 73-11 Semi-Gloss paint, the experimental brush was so superior that only three strokes were required to produce the quality of paint film that the commercial brush produced in four brush strokes. We postulate that the superior results observed are derived from the use of our improved synthetic bristle because of its several unique properties previously described. Also, because the improved bristle uses less resin material than offset bristles, the resulting brushes are more economical to produce. Still another advantage is the superior holding character in the ferrule setting process when compared to other synthetics. This is a significant benefit since it reduces the probability of bristle shedding onto the painting surface. We attribute this benefit to the scale-like surface on the bristle which improves the attachment of the adhesive to the bristle. We have previously described our improved synthetic bristles. The following disclosure describes the methodology we teach for producing these bristles. Synthetic bristles are conventionally produced by first melting an appropriate resin, thermoplastic polymer, co-polymer, alloy or mixture, in combination with certain additives to add opacity, color, and to minimize thermal degradation. Such materials are often pre-compounded in major constituents such as pelletized special grade resins, and pelletized colorants and additives. Standard practice is to melt the resin and additive mixture to a temperature appropriate to the resin grade for hot melt extrusion through a group of small diameter orifices in a head. A group of small diameter filaments emerge from the extrusion head and are carried forward through take up rolls, water baths (or other liquids) and controlled temperature zones, see Figure 1. One function of this take-up system is to orient the essentially random molecular structure into an essentially axially aligned structure within each filament. This process, which elongates the filaments and reduces their diameters, is sometimes called drawing, and provides linear integrity to the filaments. These filaments are later cut to length. When the filament to length ratio is such that the resulting cut section has suitable resilience properties for use in a brush as a substitute for natural bristle as previously described, it is a synthetic bristle. By design of the orifices in the extrusion head, a variety of bristle cross-sectional shapes are commercially produced. For example, X-shapes, triangular, round, and even hollow shapes are formed as taught by others. In addition, sections may be cut so that tapered synthetic bristles are produced having a thick end and a thin end, and simulating in this respect naturally tapered bristle grown by hogs or swine. The invention comprises including, in the extrusion melt or process, certain other additives; sometimes called foaming or blowing agents, including nucleating materials, which are designed to create tiny gaseous bubbles at random within the extruding filaments. It should be noted that the use of blowing agents in plastic parts manufactured by extrusion, injection and compression moulding and other conventional plastic fabricating processes is well known as disclosed for example in the articles "Extruding Thermoplastic Foams", Modern Plastics Encyclopedia, Christopher Eaton, 1986 - 1987, pp. 243, 244 and "Foaming Agents", Modern Plastics Encyclopedia, Raymond Shute, Modern Plastics Encyclopedia, 1986 - 1987, pp. 150-154. See Figure 2. As these filaments are drawn in the next stage of the process, tiny elongated cells are formed within the filament structure (see Figure 3). The bubbles or bubble craters occurring near the filament surface(s) cause indentations and roughness at the filament surface which is scale-like in character, and which can be controlled in the extrusion portion of the process. Furthermore, the random occurrence and random size of the bubbles within the filaments form a somewhat irregular shape as opposed to the true, uniform shape resulting from conventional technology.

Claims: A synthetic bristle suitable for use in brushes, the bristle being composed throughout its length of a melted synthetic material selected from the group consisting essentially of synthetic polymers, co-polymers or alloys, whereby a plurality of cells resulting from the action of gas bubbles of a blowing agent added to the melted synthetic material form void spaces in the bristle and are randomly distributed throughout the entire cross-sectional area of the bristle and throughout its length, characterised in that : (a) the bristle has a substantially uniform cross-sectional shape throughout its length; and (b) the exterior of the bristle has an irregular scale-like surface finish derived from randomly-located craters formed when a gas bubble ruptures the exterior surface and randomly-located peaks formed by the action of gas bubbles which are near, but do not rupture, the exterior surface. A synthetic bristle according to claim 1, characterised in that the synthetic material of the bristle is selected from the group consisting essentially of (a) polyester, (b) nylon, and (c) polyolefin. A synthetic bristle according to claim 1 or claim 2, characterised in that all cells within the bristle are oriented in a direction generally parallel to the longitudinal axis of the bristle. A synthetic bristle according to any one of claims 1-3, characterised in that the bristle is substantially circular in cross-section. A brush composed of a plurality of bristles, characterised in that at least a proportion of the bristles are synthetic bristles as claimed in any one of claims 1-4. A brush according to claim 5, characterised in that at least 40% of the bristles in the brush are bristles as claimed in any one of claims 1-4. A method of producing a brush bristle which comprises melting one or more materials selected from the group consisting of (a) a synthesized polymer, (b) a co-polymer, (c) an alloy, or (d) a mixture of synthetic polymers, to a temperature appropriate for a hot melt extrusion through small-diameter orifices and adding blowing agent material to the melted synthetic material(s) to create gaseous bubbles throughout the entire mass of the latter in its subsequent extruded form in order to generate a multiplicity of randomly-located cells resulting from the action of the blowing agent within and throughout the synthetic material, characterised by drawing the synthetic material(s) to form a bristle which has a substantially uniform cross-sectional shape throughout its length and to elongate the cells in the direction of the axis of the bristle throughout its length, the blowing agent also creating a scaly exterior surface on the bristles derived from randomly-located craters formed when bubbles generated by the blowing agent material rupture the exterior surface and randomly-located peaks formed from the action of gas bubbles which are near, but do not rupture, the exterior surface. A method according to claim 7, characterised in that the bristles are substantially circular in cross-section.

Inventors: BURNS FREDRICK BRANDT, BURNS, FREDRICK BRANDT
Applicants: NEWELL OPERATING CO, NEWELL OPERATING COMPANY
Application year: 1988
Main classification: A46D1
IPC codes: A46D1