METHOD AND APPARATUS FOR MANUFACTURING A THIN WALLED BARRIER ARTICLE

Abstract: The present invention relates to a method and apparatus for manufacturing a thin-walled body shielding article, such as a glove that is particularly well suited for medical applications. Broadly stated, the method consists of forming by sequential injection moulding a pre-form. The pre-form is then expanded to a final shape by blow-moulding.

Description: METHOD AND APPARATUS FOR MANUFACTURING A THIN WALLED BARRIER ARTICLE FIELD OF THE INVENTION The invention relates to a method and apparatus for manufacturing a thin walled body shielding article, such as a glove particularly well suited for medical applications. In a specific embodiment the method is a two-step process. During the first step a pre-form approximating the shape of the final article is formed by injection moulding. The second step consists of expanding the pre-form to its final three- dimensional configuration. The expansion distends the pre-form to reduce its wall thickness at levels that cannot be practically achieved by injection moulding alone. BACKGROUND OF THE INVENTION Natural rubber latex (NRL) gloves are extensively used in the medical profession, particularly where a healthcare worker may come in contact with body fluids such as human blood. Indeed, these gloves constitute an efficient mechanical barrier preventing contact between the skin and biological fluids and thus help prevent transmission of serious diseases such as AIDS and Hepatitis among others. The traditional method for manufacturing latex gloves is to use a dipped form that has the shape of a human hand. The form is plunged briefly into a body of latex to coat the form uniformly. The form is removed from the bath and the latex film is allowed to cure. This method is efficient and cost effective and for that reason it has gained wide acceptance in the industry. However, latex gloves have many drawbacks. Perhaps, the most serious one is the sensitivity to natural rubber latex protein, or to chemical accelerators used to cross link NRL, observed in a number of individuals in the population. When a person oversensitive to latex protein or accelerators wears traditional gloves, he or she develops a skin reaction that may be more or less severe depending upon the degree of over sensitivity. Thus, there is a need in the industry to develop a method and an apparatus for manufacturing thin-walled body shielding articles from many synthetic materials that are less susceptible to create undesirable skin reactions than latex. OBJECTIVES AND STATEMENT OF THE INVENTION An object of the invention to provide a novel method for manufacturing a thin- walled body shielding article. Another object of the invention is to provide a method for manufacturing a thin- walled body shielding article that can be carried out by using materials less susceptible to create undesirable skin reactions than latex. A further object of the invention is to provide a novel apparatus for manufacturing a thin-walled body shielding article. Another object of the invention is to provide an apparatus for manufacturing a thin-walled body shielding article from materials less susceptible to create undesirable skin reactions than latex. As embodied and broadly described therein, the invention provides a method for manufacturing a thin-walled body shielding article, said method comprising the steps of: - flowing liquid synthetic material in a lamellar cavity to form at least a portion of a pre-form; - distending the pre-form for causing the pre-form to acquire a predetermined three-dimensional configuration. As embodied and broadly described herein, the invention also provides an apparatus for manufacturing a thin-walled body shielding article, said apparatus comprising: - a mould cavity for forming a pre-form, at least a portion of said mould cavity being shaped as a lamella; - a delivery port opening in said portion of said mould cavity shaped as a lamella for introducing in said portion liquid synthetic material; - means for distending the pre-form formed in said mould cavity to a predetermined three-dimensional configuration. In a most preferred embodiment the mould cavity that forms the parison is provided with a sequential injection system that can introduce liquid synthetic material at different sites of the cavity. The injectors are grouped into banks actuated in a timed relationship to fill different portions of the mould cavity sequentially. As an example, the bank associated with the portion of the cavity near the finger tips part of the pre-form is actuated first. The liquid synthetic material is introduced in the cavity and flows toward the portion of the mould cavity forming the base of the fingers. When the fluid front reaches the second injectors bank that may be located say near the finger base portion, the second injectors bank is activated to introduce fluid in that area. The incoming liquid cannot flow backwards (countercurrent to the liquid form the first injectors bank) since the mould cavity is filled in that region. Thus, the only possibility for the liquid is to progress forward. This cycle is repeated until the entire mould cavity has been filed. This process has one important advantage. The use of a sequential injection system allows to manufacture a pre-form that is very close to the final three- dimensional shape of the body shielding article, by using reasonably low injection pressures. For example, in the case of a surgical glove, all the fingers, palm and wrist portions of the glove have acquired their near final shape. If the liquid were introduced in the mould through a single port, the pressure that would be required to cause the liquid to fill the entire mould at a rate sufficiently high to prevent premature curing, would be extremely high to be practical and perhaps not even attainable with current technology. As a final stage of the manufacturing process, the pre-form needs to be distended to reach the predetermined three-dimensional configuration of the body shielding article. The expansion required is not necessarily a major dimensional change, but enables to reduce the thickness of the moulded material to a value that is difficult to attain solely with injection moulding. Most preferably the expansion is made by blow moulding the pre-form against the surface of a mould cavity shaped as the body shielding article. Other methods of expansion can also be used without departing from the spirit of the invention, namely introducing high pressure media other than gas in the parison, such as liquid for example. Mechanical expansion can also be used, although this alternative is not very practical for applications where complex three-dimensional shapes must be manufactured, such as gloves for instance. The body shielding article that can be manufactured by the above method and apparatus may be a glove, a condom or any other structure designed to cover wholly or in part the human body. In a most preferred embodiment, the body shielding article is disposable which means that it is intended to be discarded after a single use. The notion of a throwaway article, however, is not critical to the invention since it may very well be envisaged to produce the body shielding article, such as a glove that could deliver a satisfactory performance over several use cycles. A variety of synthetic materials can be used with the method and apparatus of the present invention to manufacture the body shielding article. The choice of a particular material depends upon the special use or purpose of the body shielding article and can be based on the following factors namely cost, puncture resistance, skin sensitivity among many others. It is within the reach of a person skilled in the art to select the proper material for the intended application. In a most preferred embodiment, the body shielding article has a thickness in the range from about 0.002 to about 0.020 inch and it is made of co-polymer material. BRIEF DESCRD?TION OF THE DRAWINGS Figure 1 is a perspective view of a protective glove in accordance with the present invention; Figure 2 is a schematical view of a manifold and a plurality of injectors to illustrate the principle of sequential injection moulding; Figures 3-6 are sectional views of a mould cavity and an associated injection system for sequentially filling the cavity, the various figures showing the progress of the fluid front in the cavity as injectors are progressively opened; Figure 7 is a perspective view of a core used in a mould cavity for injection forming a pre-form; Figure 8 is a top plan view of the mould for injection moulding the parison, the core shown in Figure 8 being illustrated in the dotted line; Figure 9 is a cross-sectional view taken along lines 9-9 in Figure 9, showing the mould in the closed position; Figure 10 is a cross-sectional view also along lines 9-9 but showing the mould in the opened position with the pre-form formed on the core; and Figure 11 is a vertical longitudinal cross-sectional view of a blow moulding station where the injection-moulded pre-form is expanded in size to acquire a predetermined three-dimensional configuration. In the drawings, preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for the purpose of illustration and as an aid to understanding, and are not intended as a definition of the limits of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS With reference to the annexed drawings the present invention provides a novel method and apparatus for manufacturing a body shielding device such as a glove, shown in Figure 1 that is particularly well suited for medical applications or for any other use where a mechanical barrier must be provided over one's hand to avoid contact between contaminated body fluids or other dangerous products and the human skin. The glove is made of a continuous and resilient film-like layer having a thickness in the range from about 0.003 to about 0.020 inches, or 0.004 to 0.008 inches. The materials of choice are thermal plastic elastomers which will flow in processing such as styrenic polymers and copolymers, polyurethanes, vinyls, metalocene catalyzed polyolifins, and alloys and blends such as silicones. The apparatus and method used for manufacturing the glove in accordance with the present invention will now be described in connection with figures 2 to 11. In a most preferred embodiment, the glove is manufactured by a two-stage process. The first stage is an injection molding operation that forms a pre-form that approximates the final shape of the glove. At the next stage the parison is expanded to acquire the final three-dimensional configuration of the glove. The expansion process reduces the wall thickness to levels that cannot be practically achieved by injection molding alone. The injection molding stage is a sequential injection operation that allows to produce relatively thin articles while avoiding the necessity of a setup operating at extremely high feed pressures. Figure 2 illustrates the principle of sequential injection molding. The mold cavity illustrated by the crosshatched area is supplied with liquid synthetic material from four individual injectors 18, 20, 22, and 24. The injectors are connected to a common manifold structure 26 supplied with pressurized liquid synthetic material from a suitable source. Each injector is electrically controlled to selectively enable the flow of synthetic material in the mold cavity. By operating the injectors in a timed relationship all the regions of the mold cavity can be filled while maintaining the feed pressure at reasonable levels. Figure 3 illustrates the mold cavity at time tl where the injector 18 is opened while the injectors 20, 22, and 24 are closed. The pressurized liquid flows through the injector 18 and progresses forward in the direction identified by the arrow 28. When the liquid front reaches the injector 20, which occurs at time t2 the injector 20 is opened. The fluid injected in the mold cavity through injector 20 cannot flow backwards, toward injector 18 since that portion of the cavity is already full. Thus, the only pathway available for the liquid is to progress forward toward injectors 22 and 24. The remaining portion of the mold cavity is filled in a similar manner by sequentially opening injectors 22 and 24 at times t3 and t4, respectively. This is shown at figures 6 and 7. Referring back to figure 2, the crosshatched area identifies the pressure gradient developed as the injection through the manifold 26 proceeds. The zones that are lightly crosshatched show high pressure while the zones that are more heavily hatched designate lower pressure regions. It will be noted that the feed pressure is relatively high near each injector and progressively diminishes away from the injector, reaching a low level immediately before the next injector in line. The ability of the sequential injection molding process to limit the feed pressure in the mold at comparatively low levels allows to use this method for the manufacture of thin-walled articles. The present invention takes advantage of this characteristic and applies the sequential injection molding for producing a pre-form that later is expanded to reach the desired three-dimensional configuration of the glove. The apparatus for carrying out the sequential injection molding process is illustrated at figures 7, 8, 9, 10 and 11. With reference to figure 9, the apparatus includes a mold designated comprehensively by the reference numeral 30. The mold includes a core 32, best shown at figure 7, that has the shape of a human hand. The core 32 is somewhat smaller than the dimension of the final glove because the parison formed on the core 32 will be expanded later. The mold 30 further includes a pair of mating mold halves 34 and 36 that enclose the core 32, defining with the core 32 a three dimensional lamellar void area that can be filled with synthetic material. The mold is filled by a plurality of injectors grouped into banks. This feature is best shown at figures 8 and 9. The first injector bank 40 includes a group of four injectors formed near the finger tips of the core 32. A second injector bank 42 is provided at the base of the fingers. The second injector bank also includes four injectors. The third injector bank 44, also formed of four injectors is placed on the upper palm surface of the core 32, also extending over the thumb area. Finally, a fourth injector bank 46 is provided between the injector banks 42 and 44. The fourth injector bank includes only two injectors. The four banks of injectors 40 - 46 are provided on the mold half 34 and an identical group of injector banks, configured in the same way but being the mirror image of the injector banks 40 - 46, is provided on the mold half 36. The injector banks on the mould half 36 will be designated with the same reference numerals used for the injector banks 40 - 46 followed by the suffix "a". The molding operation of the pre-form begins by opening the banks 40 and 40a of injectors. For reference this operation occurs at time tl. The flow of liquid synthetic material that may or may not be loaded with platelets (depending upon the specific application) fills the portion of the lamellar void area 38 located at the finger tips of the core. The fluid front progresses toward the injector banks 42 and 42a. When the liquid reaches those injector banks they are opened (this operation occurs at time t2). The injector banks 46 and 46a, and 44 and 44 a are then sequentially opened at times t3 and t4, respectively, to complete the molding operation. The next step of the operation is to part the mold halves 34 and 36. The core 32 on which is formed the pre-form 48 is then transferred to a blow molding station illustrated at figure 12. In essence, the blow molding operation consists of subjecting the pre-form to a pressure differential that causes expansion of the synthetic material to reduce the wall thickness. To develop the pressure differential the core 32 is provided with a network of channels 50 that open at the surface of the core. All the channels connected with a main supply conduit 52 extending in the wrist region of the core. After the injection molding operation is completed, the core 32 and the pre-form 48 are inserted in a mold 54 comprising an upper mold half 56 and a lower mold half 58. The cavity defined by the mold halves 56 and 58 determines the final three-dimensional shape of the glove. By comparison to figure 10, it will become apparent that this mold cavity is somewhat larger than the cavity used for forming the pre-form 48. When the core 32 and the pre-form 48 have been inserted in the mold 54, and the mold halves 56 and 58 have been closed, compressed air supplied from a suitable source (not shown in the drawings) is delivered to the main conduit 52 and distributed through the individual passages 50. The air pressure differential developed across the parison causes the synthetic material to expand and conform to the topography of the mold 54. This expansion causes the synthetic material to stretch uniformly, thus providing the requisite wall thickness. As discussed earlier, the wall thickness of the glove after the blow molding operation is completed is in the range of about 0.002 and about 0.020 inches. Note that the air injected through the main conduit 52 may be heated to ease the expansion of the parison. An important element of the blow molding operation is the degree of curing of the pre-form material when the pressure differential is established. If the pre-form is at an advanced curing stage, the expansion may not produce the desired effect of permanently stretching the material. Thus, the transfer from the injection molding station to the blow molding station must be effected sufficiently rapidly. Also, the synthetic material chosen for manufacturing the glove should be selected in accordance with a maximum allowable curing rate. The slower the curing rate, the easier it becomes to blow mold the pre-form, however this also reduces mold cycle times as it takes longer for a product to be completed. While the present inventive principle has been described in the context of a method and apparatus for manufacturing a glove for medical applications, it should be noted that the invention is not limited only to the manufacture of such articles. The present process and apparatus may be used to form various body shielding devices, other than gloves. A specific example is condoms. Applications of the product and methods of the present invention for sanitary and other healthcare uses can be accomplished by any technique as is presently or prospectively known to those skilled in the art. Thus, it is intended that the present application covers the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.

Claims: ΓN THE CLAIMS 1. A method for manufacturing a thin- walled body shielding article, said method comprising the steps of: - flowing liquid synthetic material in a lamellar cavity of a mould to form at least a portion of a pre-form; - distending the pre-form for causing the pre-form to acquire a predetermined three-dimensional configuration. 2. A method for manufacturing a thin-walled body shielding article as defined in claim 1, comprising the step of subjecting the pre-form to a pressure differential to cause the pre-form to expand and reduce a wall thickness of the preform at least at a certain location thereof. 3. A method for manufacturing a thin-walled body shielding article as defined in claim 2, comprising the steps of: - removing the pre-form from said mould; - placing said pre-form in a blow-moulding cavity having a topography corresponding to a three-dimensional configuration of said body shielding article; - establishing said pressure differential in said moulding cavity across the pre-form to cause the pre-form to conform to the topography of said moulding cavity. 4. A method for manufacturing a thin walled body shielding article as defined in claim 1, comprising the step of injecting in a timed relationship liquid synthetic material in a plurality of sites in said lamellar cavity. 5. An apparatus for manufacturing a thin walled body shielding article, said apparatus comprising: - a mould cavity for forming a pre-form, at least a portion of said mould cavity being shaped as a lamella; - a delivery port opening in said portion of said mould cavity shaped as a lamella for introducing in said portion liquid synthetic material; - means for distending the pre-form formed in said mould cavity to a predetermined three-dimensional configuration. 6. An apparatus as defined in claim 5, wherein said means for distending the pre-form to a predetermined three-dimensional configuration includes means for blow moulding the pre-form. 7. An apparatus as defined in claim 6, wherein said means for blow moulding the pre-form includes: - a blow-moulding cavity having a topography corresponding to a three-dimensional configuration of the body shielding article; - means for establishing a pressure differential in said blow-moulding cavity to cause the pre-form to conform to a topography of said blow- moulding cavity. 8. An apparatus as defined in claim 5, comprising a plurality of injectors for supplying liquid synthetic material to said mould cavity, said injectors being capable of being actuated in a timed relationship for injecting liquid synthetic material in said mould cavity at different instants in time. 9. An apparatus as defined in claim 5, comprising a core on which the preform is formed, said core including a network of pathways for supplying fluid allowing to subject the pre-form to a pressure differential. 10. A thin-walled body-shielding article manufactured by the method defined in claim 1. 11. A thin- walled body-shielding article as defined in claim 10, wherein said body-shielding article is a glove. 12. A thin-walled body shielding article as defined in claim 11, wherein said glove has a wall thickness in the range from about 0.002 to about 0.020 inch.

Inventors: ENGBERG KATHLEEN, HUGHES GARY, PESAVENTO MODESTO, ENGBERG, KATHLEEN, HUGHES, GARY, PESAVENTO, MODESTO
Applicants: JOHNSON & JOHNSON MEDICAL, JOHNSON & JOHNSON MEDICAL, INC.
Application year: 1997
Main classification: B29C49
IPC codes: A41D19, B29C45, B29C49