Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
1998-04-23
2002-02-05
Nguyen, Nam (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C425S272000, C425S275000
Reexamination Certificate
active
06344163
ABSTRACT:
STATEMENT REGARDING FEDERAL SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thin film glove and cot-like article constructed of PVC and more specifically to an article which is approximately 0.0015 to 0.006 inches in thickness throughout (plus or minus 0.0005 inches) a major portion of its extent. The article comprising an elongated hollow article which is open at one end and closed at its opposite end. The open end may include a rolled portion defining a reinforcement bead about the open end of the article. The invention also includes an apparatus for making these articles as well as the method of manufacture carried out by the apparatus.
2. Description of Related Art
The following prior U.S. Patents disclose articles which are coated through the use of methods which are similar in general construction and which are formed, in some cases, by somewhat similar methods:
1,773,418
2,009,629
2,128,827
2,146,293
2,233,555
2,482,418
3,146,873
3,278,991
3,530,825
4,275,864
4,655,280
U.S. Pat. No. 1,773,148, dated Aug. 19, 1930, to Yervant H. Kurkjian, discloses rotating a core in a rubber solution. U.S. Pat. No. 2,009,629, dated Jul. 30, 1935, to E. F. Mechlin, discloses dipping an article to be coated and then spinning the coated articles to throw off excess dip material by centrifugal force.
U.S. Pat. No. 2,128,827, dated Aug. 30, 1938, to F. L. Killian, discloses forming rubber goods (finger cots and gloves) by dipping and then rotating and tilting to obtain reasonably constant thickness.
U.S. Pat. No. 2,146,293, dated Feb, 7, 1939, to J. R. Gammiter, discloses forming rubber goods (finger cots) by dip process.
U.S. Pat. No. 2,233,555, dated Mar. 4, 1941, H. Reisinger, discloses forming rubber goods (finger cots) by dip process.
U.S. Pat. No. 2,482,418, dated Sep. 20, 1949, to W. L. Jenkins, discloses using a high-frequency electrostatic field for drying and vulcanizing shaped, hollow rubber goods.
U.S. Pat. No. 3,146,873, dated Sep. 1, 1964, to John R. Johnson, discloses spinning a dipped article after dipping to detear.
U.S. Pat. No. 3,278,991, dated Oct. 18, 1966, W. V. Peterneill et al, discloses a dip conveyor for forming gloves (apparently not providing any means to spin for the purpose of detearing).
U.S. Pat. No. 3,530,825, dated Sep. 29, 1970, to Peter Antonissen, discloses rotating a coated article about each of two axes angularly displaced at least 30° (preferably 90°) relative to each other.
U.S. Pat. No. 4,275,864 dated Jun. 30, 1981, to Les W. Richards, and U.S. Pat. No. 4,655,280, dated Apr. 7, 1987, to Katsuhiko Takahashi, disclose improvements in interior cooling of molds.
However, the articles and methods disclosed by the above-noted patents are not equivalent to the article of the instant invention or the method utilized informing the article.
SUMMARY OF THE INVENTION
The articles of the instant invention include PVC gloves and PVC finger cots and other cot-like articles.
When forming the articles of the instant invention, elongated male molds are carried on an endless conveyor and successively dipped into a vinyl plastisol while the molds are rotated at a slow speed (20-30 RPM) about their longitudinal axes. Thereafter, the molds are removed from the plastisol and rapidly spun (1,000-1,200 RPM) about longitudinal axes thereof to spin off excess plastisol. Then, the molds move through a heating oven or chamber (for generally 45 seconds) while being rotated at slow speed and the exteriors and interiors of the molds are heated by rapid heated air flow and/or infra-red heating in order to rapidly increase the exterior temperature of the molds as well as the plastisol article thereon to approximately 275-400° F. The molds then move from the heating chamber and into a cooling chamber while the molds are being rotated at slow speed and the exteriors and interiors of the molds are subject to rapid flow of cooling air in order to quickly reduce the temperature of the molds and the articles thereon to approximately 120° F. Thereafter, the article molds and articles thereon are moved to the next station at which the open ends of the articles are rolled to form reinforcing beads thereon. Thereafter the artricles are powdered and are removed from the molds and the molds. The molds then continue through the next dipping, spinning, heating and cooling steps.
The importance of forming the articles (gloves and finger cots as well as other finger cot-like articles) of polyvinyl chloride (PVC) includes the utilization of a less expensive product in forming the articles, using a material to form the articles which allows excess material spun from the molds to be collected and returned to the vat of material into which the molds are dipped and using a material which may be “cured” more quickly. In addition, the utilization of PVC as opposed to latex rubber enables greater wall thickness control of the finished articles. The use of PVC in forming the articles of the instant invention by the disclosed method allows wall thickness control of approximately plus or minus 0.0005 inches throughout the entire article. Furthermore, although it is generally necessary to heat the coating and the molds to approximately 370° F., depending upon the compound of the plastisol utilized, fusion temperature or cure may be reached between 275° F. and to 400° F. Still further, it is only necessary for the forms to spend between 15 and 45 seconds in the heating chamber and even less time in the cooling chamber. Also, it is pointed out that the air heating of the exterior of the molds could be augmented by radiant heat energy, infra-red energy, or, as an additional option, infra-red energy alone may be utilized to heat the mold exteriors sufficiently to effect a cure of the article thereon, although this type of heating may not be desirable in some instances. If infra-red heating is utilized, inasmuch as the PVC material, in the thin-wall thickness desired, is relatively transparent, not only the article coating on the mold is heated by infra-red energy, but the mold surfaces inside the coating will be heated by infra-red energy.
Vinyl plastisols are dispersions of special fine particle size polyvinyl chloride resins in plasticizing liquids. In addition to the resins and plasticizers, heat or light stabilizers, color pigments, flame retardants, blowing agents, or many other additives may be included as determined by the intended product. Plastisols are fused with heat in relatively thick section without concern for solvent or water blistering; they are commonly referred to as 100% solids material.
Plastisols are liquid at room temperature. Depending upon the compound, they can be poured pumped or sprayed or cast. As a plastisol is heated, fusion takes place and it is converted in to a tough, homogeneous mass with excellent abrasion, aging, corrosion, and electrical resistance.
Fusion requirements vary from compound to compound. Minimum fusion temperature is the temperature at which the ultimate physical properties are obtained. It is necessary to bring the entire mass of plastisol and adjacent surfaces up to that temperature. The minimum fusion temperature of plastisol usually is 350° F., although lower temperature fusion plastisols are available.
The main object of this invention is to provide a hollow, thin wall PVC article of substantially constant wall thickness utilizing a method of manufacture which substantially eliminates wastage of the material of which the article is formed and allows the article to be formed in considerably less time that which is required to form similar articles of latex rubber. In this manner, the quality of the product is improved, wastage of material of which the article is formed is eliminated, and the time required to form the article is substantially reduced. This enables many times the number of articles to be formed utilizing a generally similar manufacturing method than similiar articles formed of latex rubber.
Another object of this invention is to provide a PVC glove or cot-like a
Nguyen Nam
Nguyen Thu Khanh T.
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