The present invention relates to the manufacture of glass articles and, more particularly, to improved hot and cold end coatings and the vitreous articles having an improved abrasion resistant surface which are produced thereby including glassware, glass and glazed surfaces. Vitreous surfaces have, especially immediately following the formation of the surface, high free energy. The nature of the surface makes it highly susceptible to damage by being contacted with other surfaces and/or atmospheric influences. A large part of the sensitivity which vitreous surfaces exhibit to contact with other surfaces is thought to occur due to the high coefficient of friction between vitreous surfaces and other surfaces, including vitreous surfaces, which are generally encountered in a glass production line and in the subsequent filling and packaging line. This high coefficient of friction, which may exceed one (1), will result in high forces being generated on the vitreous surface at the point of contact with other surfaces regardless of the relative directional components between the surfaces. Such forces may cause fracture or abrasion of the surface, giving rise to a substantially weakened structural integrity for the underlying article.
As is well known in the art, the problems of abrasion and fracture to glassware have been mitigated by various surface treatments applied to the glass substantially immediately following formation of the article or at least prior to packing.
One basic facet of such treatments is the surface treatment of the glass, prior to annealing, with various metallic compounds which pyrolytically decompose upon contact with the heated, freshly formed glass to form metallic oxide surface layers on the glass. Such metallic oxide coatings are frequently called "hot end" coatings because they are applied after the formation of the glassware and prior to its entrance into the annealing lehr. Such metallic coatings are frequently formed from tin oxide or titanium dioxide to provide a measure of abrasion resistance. In themselves, however, such metallic oxide coatings do not provide an adequate measure of scratch resistance or surface lubrication and have been combined with outer coatings of a lubricating film of, for example, polymeric material. The outer lubricating films of polymeric material are applied at the "cold end" of the lehr. Such combined coatings of metal oxide and lubricating films provide a desirable measure of scratch resistance and a lubricated glass surface.
Although hot end coatings do not, in themselves, provide sufficient abrasion resistance and lubricity for subsequent ware handling, they do provide an important degree of protection to glass surfaces while in the hot end of a glass production line. The newly formed glass articles are especially susceptible to damage from contact with other surfaces. As the glass surfaces are still near their forming temperature during their travel through the hot end, contact between them may cause seizure and extensive damage to the surfaces. Furthermore, the outer surfaces cool much quicker than the inner glass thereby experiencing high tensile forces. As is well known in the art, the strength of glass is greatly reduced when in tension, and abrasions or fractures have a much greater propensity to propagate thereby seriously reducing the structural strength of the glass article. The subsequent annealing of the glass articles relieves the tensile forces and places the outer surface in compression providing a much stronger article which has greater resistance to abrasion. Such annealing will not, however, repair or remedy flaws produced during the hot end travel of the glassware. Therefore, although hot end coatings cannot in themselves provide a sufficient degree of protection for glass surfaces during later travel and handling, it is desirable that they provide a significant degree of protection from the generation of irreversible flaws and damage when the hot glass surface is in its especially delicate state during its travel through the hot end of a glass production line.
There are many difficulties with the present methods of using hot end metallic oxide coatings. The coatings are expensive; they require special equipment; and they result in air pollution and/or corrosion from their by-products. A number of efforts have been made to provide scratch resistance and lubricity to glass surfaces without the use of such metallic coatings. Such efforts have included spraying the heated glassware during its manufacture and while it is at a temperature of 300.degree. to 500.degree. F., with a polymerizable monomeric system or a low molecular weight polymer in the absence of a solvent or other volatile unreactive diluent, as set forth in U.S. Pat. No. 3,713,867. Another such effort has included forming a protective surface coating by an emulsion of hard wax on the surface of the glassware while it is at the temperature of from about 175.degree. to 212.degree. F., as set forth in U.S. Pat. No. 3,997,693.
Other efforts to provide increased scratch resistance and lubricity have included applying onto glassware, which has been previously coated with an inorganic metallic oxide coating as set forth above, an aqueous dispersion of ionomeric polymer and colloidal silica in the form of discrete particles rather than as a continuous film, as set forth in U.S. Pat. No. 3,984,608. Another suggestion is to provide plastic-coated bottles with hard, smooth, friction-reducing surfaces such as those provided by spherical glass beads embedded in or attached to the plastic covering, as set forth in U.S. Pat. No. 3,924,767.
It is a principal object of the present invention to provide improved glass surfaces which have desirable scratch resistance and lubricity and are capable of manufacture from hot and cold end coatings which are inexpensive, do not require special equipment and do not result in air pollution or corrosion from their by-products.
It is a further object of the present invention to eliminate the need for metallic oxide coatings in the hot end of a commercial glass line.
It is a further object of the present invention to provide an improved method of applying a particulate dry coating material to an article.
It is a further principal object of the present invention to provide a hot end coating which self-heals any damage occurring during travel through the hot end of a glass manufacturing line.
It is a further object of the present invention to produce scratch resistant and lubricious glass surfaces which meet the commercial standards of the glass industry.
It is a further object of the present invention to provide a hot end coating which coacts with a cold end coating to retain and present a boundry layer lubricant at the vitreous substrate surface.
It is a further object of the present invention to provide a vitreous substrate having an exterior structure which substantially reduces the severity of fractures and plastic deformation occasioned by contact with other or like surfaces.
It is a further object of the present invention to provide an energy efficient and inexpensive method of producing such an exterior structure.