WITH EXTENDED LIFE AND METHOD OF MANUFACTURING THEREOF

FIELD OF THE INVENTION

The present invention relates to dipping molds and more particularly to dipping molds having longer life, and a method for salvaging used dipping molds using a green approach.

BACKGROUND OF THE INVENTION

Rubber gloves such as examination, surgical or industrial gloves, and many other elastic articles such as condoms, are manufactured in a multi-step process. Clean dipping molds, referred to herein as dipping molds, in the form of hands are dipped into a coagulant bath to help the latex mixture, of the next step, to adhere to the dipping mold and help ensure the latex is distributed evenly. The dipping molds covered with coagulant are then dipped into a latex mixture and will eventually travel through a series of ovens to dry the latex mixture formed on the molds. The dipping molds then are put through a leaching line to remove residual chemicals and water-soluble proteins from the surface of the gloves. Next, the latex gloves are stripped off the dipping molds.

The dipping molds can then be reused in the next dipping cycle. But before that the dipping molds must be cleaned to ensure there is no dirt or other debris on the molds. Failure to properly clean the dipping molds would cause the final glove product to possibly have defects like holes or uneven thickness. To clean the dipping molds, they are dipped into an acid bath followed by rinsing with clean water. The dipping molds are then dipped into an alkaline bath to neutralize residual acid, and again rinsed in clean water. The dipping molds are then brushed to ensure their surfaces are consistent in order to eliminate pin holes forming on the latex gloves.

Traditionally, dipping molds have been made from ceramic/porcelain as that is one of the cheapest and easiest materials to make the molds from. Dipping molds made from aluminium and thermoplastics are also known, though ceramic remains the industry standard.

From the process steps outlined above, it can be seen that the dipping molds undergo tremendous physical and chemical stresses during each cycle run. These include thermal expansion and contractions and chemical erosion. These conditions particularly affect dipping molds made of ceramic material, making their working life relatively short. Among the the normal degradation problems affecting ceramic dipping molds are pitting, hairline cracks, non removable dirt, stain, defective beading, pleating and fragility. If dipping molds with such defects are used for making gloves the result is unacceptable defective gloves with holes, tears and uneven thickness. The average lifespan of a typical ceramic dipping mold is less than 12 months, which is unacceptably short. This short lifespan, coupled with the millions of glove molds used around the world, results in thousands of unusable dipping molds being generated and discarded each day. The current practice is to simply discard the used molds. This results in huge wastage, environmental problems, and unacceptable carbon footprint. The short lifespan also results in the need for high quantity of replacement molds, and this results in high energy requirement generated from gas combustion as ceramic molds have to be heat treated a part of their manufacturing process. The resulting carbon footprint is therefore substantial and very damaging to the environment.

The problem is not as acute with aluminium and thermoplastic dipping molds as they have better lifespans. However, aluminium and thermoplastic dipping molds are minimally used in the industry due to their higher cost. So, discarded dipping molds pose a serious problem especially to the environment. There is therefore a need in the industry for a means of reducing or obviating the above problem of dipping mold wastage. With ceramic glove mold, the discarded molds cannot be recycled and reformed into new molds. So the discarded molds just end up in landfills without having any positive economic or environmental benefit unlike many other industrial materials that can be readily recycled. The ceramic used for dipping molds is a non-renewable resource as it generally contains natural components such as special clay, feldspar and alumina. Despite the drawbacks of using ceramic as the preferred material for dipping molds, it is still the most attractive material from a cost point of view. So any solution should take this into account. There are therefore generally two problems to be solved, the first being to extend the life new ceramic, or other material, dipping molds, and the second being to re-use the discarded dipping molds.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a dipping mold made out of existing material but which has a much longer lifespan.

It is another objective of the present invention to provide a means to extend the lifespan of unusable or discarded dipping molds, i.e. to effectively reuse worn out dipping molds, thereby providing an environmentally-friendly approach to solving the problem of pollution originating from discarded dipping molds.

It is yet another objective of the present invention to provide a means to effectively extend the lifespan of unusable or discarded dipping molds. It is still yet another objective of the present invention to provide a green technology solution to the serious problem of discarded dipping molds. It is still yet another objective of the present invention to provide a method for making a dipping mold with extended life.

The above objectives are attained by the present invention that comprises a former core that is encased within an outer coating of durable material. The former core may be made of ceramic. The durable material constituting the outer coating may include any one or a combination of: Nylon™, polyethylene, polypropylene, PVDF (polyvinylidene difluoride), PEEK (polyether ether ketone) and a fluoropolymer, or it may be made of epoxies and the coating may be texturised. If Nylon™ is used for the outer coating it may suitably be Nylon 11™.

With regard to the objective of providing a dipping mold made from existing material but which has a much longer lifespan, new ceramic formers are used as the former core. In this way the ceramic former core is protected by the durable material constituting the outer coating of Nylon™, polyethylene, polypropylene, PVDF, PEEK, a fluoropolymer, or a combination thereof, or epoxies and the coating texturised, forming the dipping mold of the present invention. Such a dipping mold would have a much greater lifespan due to the durability of the outer coating. With regard to the objective of providing a dipping mold made from unusable or discarded dipping molds, used or discarded ceramic formers are used as the former core. In this way the used ceramic former core is protected by the durable material constituting the outer coating of Nylon™, polyethylene, polypropylene, PVDF, PEEK, a fluoropolymer, or a combination thereof, or epoxies and the coating texturised, forming the dipping mold of the present invention. Such a dipping mold would have a much greater lifespan due to the durability of the outer coating.

The former core may be dipping molds made from aluminium or a thermoplastic, which may be new or used. Likewise, the outer coating may include any one or a combination of: Nylon™, polyethylene, polypropylene, PVDF, PEEK and a fluoropolymer , or it may be made of epoxies and the coating may be texturised. If Nylon™ is used for the outer coating, it may suitably be Nylon 1 1™. Depending on the former core, the dipping mold of the present invention may be used to make gloves or any other encasing elastic article.

The present invention also provides a method for making a dipping mold with extended life, comprising encasing a former core with an outer coating of durable material. The former core may be ceramic, aluminium or thermoplastic or any other material, and the outer coating may include any one or a combination of: Nylon™, polyethylene, polypropylene, PVDF, PEEK and a fluoropolymer, or it may be made of epoxies and the coating may be texturised. If Nylon™ is used for the outer coating, it may suitably be Nylon 11™. The former core may be a new glove dipping mold or a used one. Where the former core is a used new dipping mold, as necessary, cleaning the used glove dipping mold may precede encasing it with the outer coating of durable material. The coating of the former core with an outer coating of durable material can be effected in any way such as electrostatic spray coating or fluidized dip coating. If electrostatic spray coating, the former core is pre-heated prior to the coating.

It is within the scope of the present invention that more than one outer coating may be applied to the former core. One of the advantages of the dipping mold of the present invention is that it permits the re-use or salvaging of worn out dipping molds, thus reducing the need for new dipping molds the manufacture of which is very energy intensive. This is especially true when the dipping mold is made of ceramic where high temperature is required in its manufacture and other resources such as special clay, feldspar and alumina which all cause large carbon footprint.

Another advantage of the dipping mold of the present invention, when a thermoplastic is used as the coating, is that it is relatively economical to make as it requires minimal heat. Normally for thermoplastic coating the temperature is below 300 °C for 1 hour, whereas a temperature of more than 1,000 °C for 15 hour, typically using liquid petroleum gas, is needed in the ceramic mold making process. It has thus been broadly outlined the features of the invention in order that the detailed description thereof of the preferred embodiment that follows may be better understood, and in order that the present contribution to the art may be better appreciated.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawing and descriptive matter in which there are illustrated preferred embodiments of the invention. The drawing is merely illustrative in nature and should not be construed as limiting the invention in any way.

Figure 1 is a cross section view of the long-lasting dipping mold of the present invention.

In describing the preferred embodiments of the invention, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. Combination of the various embodiments of the present invention as described herein may also be used depending on specific facility requirements.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, the dipping mold with extended life of the present invention comprises a former core (1) that is encased within an outer coating (2) of durable material. The former core (1) may be constituted of ceramic, aluminium or thermoplastic material or any other material, and the outer coating may include any one or a combination of: Nylon™ including Nylon 11™., polyethylene, polypropylene, PVDF, PEEK and a fluoropolymer, or it may be made of epoxies and the coating may be texturised. The present invention also provides a method for making a dipping mold with extended life, comprising encasing a former core (1) with an outer coating (2) of durable material.

Typically the said method involves a number of steps for best results. Using the making of elastic gloves such as examination, surgical or industrial gloves as an example, firstly a suitable worn out used glove dipping mold is chosen as the former core (1). Due to the rigours of the glove making process, it will normally have pits, surface abrasions, fungal molds, stains, etching and other defects. The used glove dipping mold itself may be constituted of ceramic, aluminium, thermoplastic or other material, but the most practical is used ceramic molds are they are available in large quantities and at very reasonable cost since they are essentially waste products. For best results, the former core (1) must have a higher melting temperature than the outer coating (2). Depending on the type of defects of the chosen former core (1), it is cleaned using an appropriate cleaning technique or combination thereof which may include washing with a cleaning solution, rinsing, drying, mechanical brushing, or sand blasting with alumina media suitably of 60 to 100 mesh size range at 2 to 5 bar air pressure.

The outer coating (2) of durable material is selected according to requirement. The material choice of the outer coating (2) may be Nylon™ including Nylon 11™, polyethylene, polypropylene, PVDF, PEEK and a fluoropolymer, or combination thereof, and may suitably be in powder form, or epoxies. The outer coatings made from these material may be texturised to enable better glove formation. The encasing of the former core (1) with the outer coating (2) of durable material may be achieved via various application methods such as electrostatic spray coating, plastic dip coating or fluidized bed coating.

Where the outer coating (2) is applied using the electrostatic spray coating method, the used former core (1) is first heated but to a temperature not exceeding the melting temperature of the outer coating (2) material. The outer coating (2) material, in powder form, is then electrostatically charged and sprayed evenly. To build the thickness of the outer coating (2), multiple cycles of spraying may be executed up to the required thickness. Once the coating process is complete, the coated former is place in a hot air oven where air draft, preferably starting from low draft, gradually builds up the temperature to the meting temperature of the outer coating material causing it to fuse and resiliency adhere to the surface of the former core (1) underneath. Typically a residence time of 1 hour or less is sufficient. For various coating material, a temperature range of 180 °C to 300 °C is sufficient. A thickness of the outer coating (2) is suitably between 0.2 to 0.5 mm for rendering the used former core (1) with a significantly extended life.

Where the outer coating (2) is applied using the fluidized bed method, the used former core (1) is likewise first heated but to a temperature above the melting temperature of the outer coating (2) material. The heated former core (1) is then immersed into a powder bath of the coating material contained in a vessel with bottom perforations through which air is blown to agitate the suspended powder coating material, whereupon a layer of coating material will adhere, melt and form an even coating encasing the former core (1). The process may be repeated to achieve the required thickness of the outer coating (2).

Irrespective of the method by which the outer coating (2) is applied to the former core (1), the outer coating (2) may then be conditioned to render it amenable to the glove making process. This may involve surface texturing which may be by way of air or shot blasting with abrasive media such as alumina of suitable mesh size to attain the desired surface roughness required to optimize the wetting or pick-up of process liquids or coagulant solution in the glove making process.

Any embodiment of the invention described herein is only meant to facilitate understanding of the invention and should not be construed as limiting the invention to that embodiment only.

INDUSTRIAL APPLICABILITY

The dipping mold with extended life of the present invention and the related method find ready industrial application in the glove making industry. Depending on the shape of the former, the invention is also suitable for the condom and balloon making industries and other industries where thin elastic articles are made.