FISH, Boris (Nahalal 4, Hadera, 38236, IL)
OLY, Shuky (Bialik 9, Rishon Lezion, 75268, IL)
FISH, Boris (Nahalal 4, Hadera, 38236, IL)
| CLAIMS: 1. A method for making an item in a mold-press, comprising: a) substantially isolating an upper mold surface of an upper mold part of the mold- press inside a PIMC spraying booth by engaging said upper mold part with said spraying booth so that an outer rim of an aperture of said spraying booth is intimately encircled by a mold seam area of said upper mold surface; b) while said upper mold surface is substantially isolated inside said spraying booth, electrostatically applying a layer of PIMC resin powder to said upper mold surface; c) disengaging said spraying booth from said upper mold part so as not to interfere with mold closing; d) placing a charge of plastic thermoset resin on a lower mold surface of a lower mold part of the mold-press; e) activating the mold-press to close said mold, bringing said upper mold surface and said lower mold surface together so as to spread said plastic thermoset resin charge to fill the volume between said upper and lower surfaces of said mold and to contact said applied PIMC resin powder with a surface of said plastic thermoset resin charge; f) subsequent to 'e', allowing said spread thermoset resin to cure, opening said mold to separate the upper and lower mold surfaces, and removing said cured thermoset resin as the item. 2. The method of claim 1, wherein the gap between said outer rim of said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.2 mm while said upper mold surface is substantially isolated inside said spraying booth. 3. The method of claim 1, wherein the gap between said outer rim said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.15 mm while said upper mold surface is substantially isolated inside said spraying booth. 4. The method of claim 1, wherein the gap between said outer rim said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.1 mm while said upper mold surface is substantially isolated inside said spraying booth. 5. The method of any of claims 1 to 4, further comprising, prior to the activation of the mold-press to close said mold, placing fittings on said lower mold surface. 6. The method of any of claims 1 to 5, further comprising, while said spraying booth engages said upper mold part, evacuating excess PIMC resin powder from said spraying booth. 7. The method of any of claims 1 to 6, prior to the spreading of said plastic thermoset resin charge, allowing the applied PIMC resin powder to at least partially cure on said upper mold surface. 8. The method of any of claims 1 to 7, wherein said disengaging of said spraying booth is prior to substantial partial curing of said applied PIMC resin powder. 9. The method of any of claims 1 to 7, wherein said disengaging of said spraying booth is subsequent to substantial partial curing of said applied PIMC resin powder. 10. The method of any of claims 1 to 9, wherein said charge of plastic thermoset resin is selected from the group consisting of thermoset polyesters, epoxy, acrylics, polyphenols, TGIC polyester and urethane polyester. 11. The method of any of claims 1 to 10, wherein said charge of plastic thermoset resin comprises a polyester resin. 12. The method of any of claims 1 to 11, wherein said charge of plastic thermoset resin comprises fibers. 13. The method of any of claims 1 to 11, wherein said charge of plastic thermoset resin is substantially devoid of fibers. 14. The method of any of claims 1 to 13, wherein said PIMC resin powder is selected from the group consisting of epoxy, polyester, polyester TGIC, epoxy-polyester hybrids, urethane polyester, polyvinylidene fluoride, acrylic, polyvinyl chloride, polyolefms and nylon. 15. The method of any of claims 1 to 13, wherein said PIMC resin powder comprises a polyester resin. 16. A PIMC device, comprising: a) a mold-press suitable for compression molding of thermosets including a mold having least two mold parts: i. an upper mold part with an upper mold surface; and ii. a lower mold part with a lower mold surface said mold-press configured to close said mold by moving said upper mold part and said lower mold part together to a closed state and apart to an open state; b) a PIMC spraying booth configured to reversibly engage said upper mold part, so that when said spraying booth engages said upper mold part an outer rim of an aperture of said spraying booth is intimately encircled by a mold seam area of said upper mold surface so as to substantially isolate said upper mold surface inside said spraying booth; and c) an electrostatic sprayer with at least one nozzle configured for electrostatic application of PIMC resin powder to said upper mold surface when substantially isolated inside said spraying booth. 17. The device of claim 16, wherein when said upper mold surface is substantially isolated inside said spraying booth, the gap between said outer rim of said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.2 mm. 18. The device of claim 16, wherein when said upper mold surface is substantially isolated inside said spraying booth, the gap between said outer rim of said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.15 mm. 19. The device of claim 16, wherein when said upper mold surface is substantially isolated inside said spraying booth, the gap between said outer rim of said aperture of said spraying booth and said mold seam area of said upper mold part is an average of not more than about 0.1 mm. 20. The device of any of claims 16 to 19, further comprising a spraying booth moving mechanism, configured to move said spraying booth to engage said upper mold part, to maintain said spraying booth engaged for a sufficient time and to disengage said spraying booth from said upper mold part. 21. The device of any of claims 16 to 20, wherein said at least one nozzle is configured to apply a substantially even coating of PIMC resin powder to substantially the entire said upper mold surface substantially simultaneously when said spraying booth is engaged with said upper mold part. 22. The device of any of claims 16 to 20, wherein said at least one nozzle is configured to move inside said spraying booth when said spraying booth is engaged with said upper mold part, allowing application of a substantially even coating of PIMC resin powder to substantially the entire said upper mold surface. 23. The device of any of claims 16 to 22, said at least one nozzle configured to move in and out of said spraying booth. 24. The device of any of claims 16 to 22, said at least one nozzle contained inside said spraying booth. 25. The device of any of claims 16 to 24, further comprising a PIMC resin powder evacuation assembly functionally associated with said spraying booth, configured for evacuating PIMC resin powder suspended inside said spraying booth when the spraying booth is engaged with said upper mold part. 26. A method of making a PIMC spraying booth, comprising: a) preparing an upper aperture part including an outer rim configured to be intimately encircled by a mold seam of a corresponding upper mold part; and b) securing said upper aperture part to a lower enclosure part of the spraying booth. 27. A method of making a PIMC spraying booth, substantially as described in the specification. 28. A mold suitable for compression molding of thermosets, comprising: a) an upper female mold part; and b) an lower male mold part. 29. A mold, substantially as described in the specification. 30. A PIMC spraying booth for use with a compression mold, substantially as described in the specification. |
RELATED APPLICATION
The present application gains priority from U.S. Provisional Patent Application No. 61/170,280 filed 17 April 2009, which is included by reference as if fully set forth herein.
FIELD AND BACKGROUND OF THE INVENTION
The invention, in some embodiments, relates to the field of powder in-mold coating of thermosets and more particularly, but not exclusively, to a method for performing powder in- mold coating that in some embodiments provides results superior to prior methods.
Thermosets are plastic materials that start as semi-fluid masses of low molecular weight resin compositions that cure (polymerize) upon application of heat. Typical thermosets are thermoset polyesters, epoxy, acrylics, TGIC polyester and urethane polyester.
A popular method of fashioning items from thermosets, especially flat or curved items, is compression molding using a mold-press. A plastic charge of a thermoset resin is loaded onto an upwardly facing female mold surface of a lower part of a mold of the mold-press, as sheets cut to an appropriate size (SMC - sheet molding compound) or as a suitable mass of resin (BMC - block molding compound). The mold-press is activated moving the downwardly facing male mold surface of an upper part of the mold of the mold-press towards the female mold surface against the charge of resin. The pressure applied on the resin charge forces the resin to spread outwards and entirely fill the volume between the female and male surfaces of the mold parts. After the resin has sufficiently cured, the mold parts are moved apart and the formed item removed from the mold.
In some instances fibers such as glass fibers are placed together with the resin charge in the mold to make glass-reinforced thermoset. Typically, glass-reinforced thermoset is made using SMC including sheets of glass fibers together with sheets of thermoset resin. Glass- reinforced thermoset is relatively cheap and simple to make, and provides strong and esthetic items at a reasonable price.
Compression molded thermosets, especially glass-fiber reinforced polyesters, are a popular choice for the production of enclosures for outdoor use such as junction enclosures, control enclosures, and cabinets for power distribution, telecommunication, cable and telephony.
Generally, a number of panels corresponding to the sides of the enclosure are individually made by compression molding with embedded fittings (typically of metal, such as nuts) and the panels assembled together to make the enclosure. A typical such panel 10 is depicted in Figure 1. Panels such as 10 for making enclosures have a number of characteristics that influence how compression molding manufacture is implemented.
The outside of enclosures should be smooth and substantially featureless, to simplify maintenance, for durability and for esthetic reasons, so the outer surface (e.g., 12) of a panel should be smooth and featureless. Consequently, the inner surface (e.g., 14) of a panel bears necessary features such as reinforcing ribs and struts (e.g., 16) and fittings 18. As a result, in compression molding of such panels, the male mold part corresponds to the inner surface of the panel while the female mold part corresponds to the outer surface of a panel. To make the manufacturing process efficient the lower mold part of the mold of the mold-press bears an upwardly facing male mold surface while the upper mold part of the mold of the mold-press bears a downwardly facing female mold surface. Fittings, required for example, for assembly of the enclosure or for mounting equipment in the enclosure are placed on the upwardly facing mold surface of the lower mold part. A plastic charge (usually SMC sheets) of thermoset resin and glass fibers is placed on the upwardly facing mold surface. The mold-press is activated, lowering the upper mold surface to press and force the thermoset resin and fibers to spread outwards in the volume between the upper and lower mold surfaces of the mold. After the resin is sufficiently cured, the mold parts are moved apart and the panel separated from the mold surfaces. The fittings are embedded in the lower surface of the resulting panel, the surface fashioned by the lower male mold surface. The enclosure is then assembled from the separate panels.
As the inside of an enclosure is hidden from view and protected from the elements, it is unnecessary and therefore economically undesirable to modify the inner surfaces of the component panels, for example by painting. On the other hand, it is generally desirable to have the option to provide the outside of such enclosures and therefore the outside surface of the component panels with a desirable color. Painting requires an additional production step, extra care during handling and transport to ensure that the paint coating is not damaged, and periodic repainting of the enclosure.
Further, during normal use the outside of such enclosures is exposed to contact with objects that may lead to scratching and staining of the outer surfaces of the component panels.
Further, during normal use, the outside of such enclosures is exposed to the elements including sunlight, hot / cold cycles, wind-borne abrasives as well as chemical pollutants. One of the common results of exposure to the elements is fiber blooming where the outside surfaces of the enclosure are eroded so that the glass fibers become apparent. Not only is fiber blooming esthetically undesirable, there is also a public health and safety issue that potentially arises when a person rubs against the exposed glass fiber.
It is therefore desirable to treat the outer surfaces of fiber-reinforced thermoset items to impart a desired color, to increase hardness and to reduce fiber blooming. It is critical that such treatment be cheap so as not to significantly increase the price of the final produced item.
SUMMARY OF THE INVENTION
Some embodiments of the invention relate to methods for performing powder in-mold coating (PIMC) that, in some aspects, have advantages over known methods. Some embodiments of the invention relate to devices for performing PIMC. Some embodiments relate to items coated with PIMC.
According to an aspect of some embodiments of the invention there is provided a method for making an item in a mold-press, comprising: a) substantially isolating an upper mold surface of an upper mold part of the mold- press inside a PIMC spraying booth by engaging the upper mold part with the spraying booth so that an outer rim of an aperture of the spraying booth is intimately encircled by a mold seam area of the upper mold surface; b) while the upper mold surface is substantially isolated inside the spraying booth, electrostatically applying a layer of PIMC thermoset resin powder to the upper mold surface; c) disengaging the spraying booth from the upper mold part so as not to interfere with mold closing; d) placing a charge of plastic thermoset resin on a lower mold surface of a lower mold part of the mold-press; e) activating the mold-press to close the mold, bringing the upper mold surface and the lower mold surface together so as to spread the plastic thermoset resin charge to fill the volume between the upper and lower surfaces of the mold and to contact the applied PIMC resin powder with a surface of the plastic thermoset resin charge; f) subsequent to 'e', allowing the spread thermoset resin to cure, opening the mold to separate the upper and lower mold surfaces, and removing the cured thermoset resin as the item.
In some embodiments, while the upper mold surface is substantially isolated inside the spraying booth, the gap between the outer rim of the aperture of the spraying booth and the mold seam area of the upper mold part is an average of not more than about 0.2 mm, in some embodiments not more than about 0.15 mm, and in some embodiments even not more than about 0.1 mm.
According to an aspect of some embodiments of the invention there is also provided a PIMC device, comprising: a) a mold-press suitable for compression molding of thermosets including a mold having least two mold parts: i. an upper mold part with an upper mold surface; and ii. a lower mold part with a lower mold surface the mold-press configured to close the mold by moving the upper mold part and the lower mold part together to a closed state and apart to an open state; b) a PIMC spraying booth configured to reversibly engage the upper mold part so that when said spraying booth engages said upper mold part an outer rim of an aperture of the spraying booth is intimately encircled by a mold seam area of the upper mold surface so as to substantially isolate the upper mold surface inside the spraying booth; and c) an electrostatic sprayer with at least one nozzle configured for electrostatic application of PIMC resin powder to the upper mold surface when substantially isolated inside the spraying booth.
In some embodiments, when the upper mold surface is substantially isolated inside the spraying booth, the gap between the outer rim of the aperture of the spraying booth and the mold seam area of the upper mold part is an average of not more than about 0.2 mm, in some embodiments not more than about 0.15 mm and in some embodiments even not more than about 0.1 mm.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. In case of conflict, the specification, including definitions, will control.
As used herein, the indefinite articles "a" and "an" mean "at least one" or "one or more" unless the context clearly dictates otherwise.
BRIEF DESCRIPTION OF THE FIGURES
Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying figures. The description, together with the figures, makes apparent how embodiments of the invention may be practiced to a person having ordinary skill in the art. The figures are for the purpose of illustrative discussion of embodiments of the invention and no attempt is made to show structural details of an embodiment in more detail than is necessary for a fundamental understanding of the invention. For the sake of clarity, some objects depicted in the figures are not to scale.
In the Figures: FIG. 1 (prior art) is a schematic depiction of a component panel of an enclosure made using compression molding of a thermoset plastic;
FIGS. 2 A, 2B and 2C are schematic depictions of an embodiment of a PIMC device useful for implementing some embodiments of the invention;
FIGS. 3 A and 3B are schematic depictions of embodiments of PIMC-spraying booths useful in implementing some embodiments of the invention;
FIGS. 4 A, 4B and 4C are schematic depiction of an embodiment of a PIMC device useful for implementing some embodiments of the invention;
FIG. 5 is a schematic depiction of a spraying booth comprising an upper aperture part and a lower enclosure part; FIG. 6 is a schematic depiction of a stage in preparation of an outer rim of an aperture of a spraying booth having the required gap size;
FIGS. 7 A and 7B (prior art) schematically depict a traditional mold design; and
FIGS. 8A, 8B and 8C schematically depicts an embodiment of an upper mold part (Figure 8A), the upper mold part engaged with a spraying booth (Figure 8B); and the upper mold part with a corresponding lower mold part (Figure 8C).
DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
Some embodiments of the invention relate to methods for performing PIMC that, in some aspects, have advantages over methods known in the art. Some embodiments of the invention relate to devices for performing PIMC. Some embodiments relate to items coated using PIMC.
The principles, uses and implementations of the teachings of the invention may be better understood with reference to the accompanying description and figures. Upon perusal of the description and figures present herein, one skilled in the art is able to implement the teachings of the invention without undue effort or experimentation.-
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth herein. The invention is capable of other embodiments or of being practiced or carried out in various ways. The phraseology and terminology employed herein are for descriptive purpose and should not be regarded as limiting.
As noted above, compression molded thermoset plastics, especially glass-fiber reinforced thermosets, especially polyesters, are a popular choice for the production of items, such as enclosures, for outdoor use. However, as noted above, there is a desire to impart color to, to increase hardness of and to reduce fiber blooming of the outside surfaces of such enclosures.
A potential solution for imparting the component panels of such an enclosure with a chosen color, increased hardness for scratch, impact and stain resistance as well as reduced fiber blooming is powder in mold coating (PIMC). In PIMC, dry powdered thermoset resin (including additives such as pigments) is sprayed using an electrostatic spray gun on an upwardly facing lower female mold surface so that the PIMC resin powder adheres by electrostatic attraction to the lower mold surface in a thin, uniform layer.
The lower mold surface is heated so that the PIMC resin powder melts and partially cures on the lower mold surface (typically for about 10 seconds). A resin charge is placed on the upwardly facing mold surface in the usual way and the mold parts brought together. Inside the mold, during the curing process, the PIMC resin powder chemically bonds to the surfaces of the item. When separated from the mold, the surfaces of the item are covered with an integrally formed PIMC layer of uniform thickness (generally 150 - 250 micrometers) having desired properties.
In reality, there are a number of significant challenges in implementing PIMC that relate to excess PIMC resin powder. It is difficult to isolate the PIMC resin powder to the mold and often metal surfaces in an entire work area are eventually undesirably coated with PIMC resin powder. PIMC resin powder accumulates on the mold seams of the mold parts, and must be removed before the mold parts are brought together. Practically speaking, this means that often an otherwise automated or semi-automated process must be stopped every few press cycles to allow cleaning of the mold seams.
Since the entire work area becomes coated with PIMC resin powder and since every few press cycles the production process must be stopped for mold seam cleaning, it is too expensive to practically implement PIMC of component panels of enclosures.
An additional challenge in implementing PIMC relates to the difficulties of applying PIMC to a downwardly facing upper mold surface, for example, to allow PIMC of component panels of enclosures. Aspects of some embodiments of the invention relate to methods and devices that allow the practical implementation of PIMC, for example of component panels of enclosures and similar items. Specifically, some embodiments of the invention reduce contamination of the work place and reduce mold seam coating by PIMC resin powder. As a result, the work place remains cleaner and there is reduced down-time required for mold seam cleaning.
Method of Powder In-MoId Coating
According to an aspect of some embodiments of the invention, there is provided a method for making an item (especially a thermoset item, in some embodiments a component panel of an enclosure) in a mold-press, comprising: a) substantially isolating an upper mold surface of an upper mold part of the mold- press inside a PIMC spraying booth, by engaging the upper mold part with the spraying booth so that an outer rim of an aperture of the spraying booth is intimately encircled by the mold seam area of the upper mold surface; b) while the upper mold surface is substantially isolated inside the spraying booth, electrostatically applying a layer of PIMC resin powder (especially thermoset PIMC resin powder) to the upper mold surface; c) disengaging the spraying booth from the upper mold part so as not to interfere with mold closing; d) placing a charge of plastic thermoset resin on the lower mold surface of the lower mold part of the mold-press; e) activating the mold-press to close the mold, bringing the upper mold surface and the lower mold surface together so as to spread the plastic thermoset resin charge to fill the volume between the upper and lower surfaces of the mold and to contact the applied PIMC resin powder with a surface of the plastic thermoset resin charge; f) subsequent to 'e', allowing the spread thermoset resin charge to cure, opening the mold to separate the upper and lower mold surfaces, and removing the cured thermoset resin as the thermoset item.
The placing of the charge of plastic thermoset resin 'd' may be performed at any suitable time. In some embodiments, the placing is prior, during or subsequent to the engaging of the upper mold part with the spraying box. In some embodiments, the placing is prior, during or subsequent to the disengaging of the upper mold part from the spraying box.
Generally, the upper mold surface is a downwardly facing mold surface and the lower mold surface is an upwardly facing mold surface. Generally, electrostatic application of the PIMC resin powder is performed with the help of an electrostatic sprayer, for example a commercially available corona-type spray gun, e.g., from Larius SrI, Calolziocorte, LC, Italy.
By "intimately encircles" is meant that while the upper mold surface is substantially isolated inside the spraying booth, the gap between the outer rim of the aperture of the spraying booth and the mold seam area of the upper mold part of the mold-press is very small. In some embodiments, while the upper mold surface is substantially isolated inside the spraying booth the gap between the outer rim of the aperture and the mold seam area around the periphery of the aperture when engaging the upper mold part is on the average not more than about 0.2 mm, not more than about 0.15 mm and even not more than about 0.1 mm.
When the outer rim of the aperture of the spraying booth is intimately encircled by the mold seam area of the upper mold surface and the upper mold surface is substantially isolated inside the spraying booth (so that other components of the press mold and other portions of the upper mold part including the mold seam area are not contained inside the spraying booth), sprayed PIMC resin powder that does not coat the upper mold surface cannot pass the booth aperture / upper mold seam area interface. The upper mold seam area of the upper mold surface remains substantially clean and free of PIMC resin powder, and substantially no
PIMC resin powder escapes the confines of the spraying booth to cover surfaces in the work area. Since the mold seam area remains free of PIMC resin powder, it is not necessary to intermittently stop the molding process to clean the mold seam area.
In the art, PIMC resin powder is applied to a lower mold surface, amongst other reasons, because it is relatively simple and easy to direct the nozzle of an electrostatic sprayer downwards. In contrast , when PIMC resin powder is applied to an upper mold surface such as when implementing the teachings of some embodiments of the invention, it is necessary to have a relatively complex assembly or mechanism such as a robot to maintain the spraying booth engaged with the upper mold part during the application of the PIMC resin powder, and to disengage from the upper mold part quickly and cleanly to avoid over- or under-curing of the applied PIMC resin powder prior to mold closing.
Despite this, application of PIMC resin powder to an upper mold surface in accordance with some embodiments of the invention, for example for the manufacture of component panels of enclosures, allows for a produced item having an improved outer surface and the simple installation of fittings.
Further, it has been found that it is easier to achieve a high-quality PIMC surface with fewer rejects, that is to say, the method is more robust and less sensitive to spray parameters than methods known in the art where PIMC resin powder is applied to a lower mold surface. Without wishing to be held to any one theory, it is believed that the increased ease of achieving a high-quality PIMC surface results, at least in part, from the isolation of the upper mold surface inside the spraying booth, together with the upward application of the PIMC resin powder to the upper mold surface that allows excess PIMC resin powder to drop from the upper mold surface and reduces accumulation of PIMC resin powder at the interface between the mold seam area of the rim of the aperture of the spraying booth.
In some embodiments, during and/or subsequent the application of the PIMC resin powder layer, while the upper mold part is substantially isolated in the spraying booth, excess PIMC resin powder is evacuated from the spraying booth, for example by generating air flow inside the spraying booth (e.g., by applying suction). In some embodiments, such excess PIMC resin powder is discarded. In some embodiments, such excess PIMC resin powder is recovered for reuse, for example, using a filter, cyclone precipitator or electrostatic precipitator. In some embodiments, the inner surfaces and even substantially the entire spraying booth are fashioned of a material or materials to which PIMC resin powder does not substantially electrostatically adhere for example are fashioned from a material such as wood, plastic, paper, cardboard or polyvinylchloride. In some such embodiments, PIMC resin powder that does not coat the upper mold surface of the upper mold part falls to the bottom of the spraying booth to be easily recoverable or, if applicable, is evacuated from the spraying booth.
In some embodiments, the inner surfaces of the spraying booth are fashioned of a material or materials to which PIMC resin powder electrostatically adheres, such as a metal. In some such embodiments, some PIMC resin powder that does not coat the upper mold surface of the upper mold part adheres to the inner walls of the spraying booth.
Similar to the known in the art, in some embodiments prior to closing the mold and spreading the plastic thermoset resin, the PIMC resin powder is allowed to at least partially cure on the upper mold surface.
In some embodiments, the time required to disengage the spraying booth from the upper mold part and move the spraying booth out from between the two mold parts so as not to interfere with mold closing is not more than the time required or sufficient partial curing of the PIMC resin powder. Thus, the disengaging and moving of the spraying booth does not substantially effect the cycle time. Additionally, in some embodiments it is advantageous during at least part of the time required for the partial curing, to maintain the spraying booth engaged with the upper mold part to allow non-adhering PIMC resin powder to settle in the spraying booth so that during the disengaging, PIMC particles are not attracted to the mold seam area of the upper mold surface.
In some embodiments, the disengaging of the spraying booth from the upper mold part is prior to substantial partial curing of the applied PIMC resin powder.
In some embodiments, the disengaging of the spraying booth from the upper mold part is subsequent to substantial partial curing of the applied PIMC resin powder. In such embodiments, the process of disengagement of the spraying booth from the upper mold part cleanly tears the film formed by the partially cured layer of PIMC resin powder.
In some embodiments the downwardly facing mold surface is the female mold surface and the upwardly facing mold surface is the male mold surface. That said, in some embodiments, the downwardly facing mold surface is the male mold surface and the upwardly facing mold surface is the female mold surface
In some embodiments, for example when making component panels of enclosures, fittings are placed in the appropriate places of the mold parts prior to activation of the mold- press so that the fittings are embedded in the thermoset item. Fittings are preferably placed in the appropriate location on the (upwardly facing) lower mold surface of the lower mold part. In such a way, the fittings rest on the mold and exceptionally complex means are not required to keep the fittings from falling, for example, as would potentially occur if the fittings are placed on the (downwardly facing) upper mold surface of the upper mold part.
The charge of plastic thermoset resin may be in any suitable form. Suitable such thermoset resins are commercially available. In some embodiments the charge of plastic thermoset is supplied as sheets (SMC - sheet molding compound). In some embodiments the charge of plastic thermoset is supplied as suitable mass (BMC - bulk molding compound). In some embodiments where the thermoset item to be made is a component panel of an enclosure, the charge of plastic thermoset resin is supplied as sheets.
The charge of plastic thermoset resin may be of any suitable composition, for example thermoset polyesters, epoxy, acrylics, polyphenols, TGIC polyester and urethane polyester, especially polyesters. In some embodiments, the charge of plastic thermoset resin includes fibers, for example glass fibers. In some embodiments, the charge of plastic thermoset resin is substantially devoid of such fibers. In some embodiments where the thermoset item to be made is a component panel of an enclosure, the charge of plastic is a thermoset resin including polyester, preferably including fibers, especially glass-fibers so that the resulting panel is of glass-reinforced polyester.
Any suitable composition of thermoset PIMC resin powder may be used in implementing the invention. Suitable PIMC resin powders are commercially available, for example, from Synres-Almoco b.v., a subsidiary of Raschig GmbH, Hoek van Holland, The Netherlands. In some embodiments (and depending on the desired finished item surface properties and the nature of the charge of thermoset resin) the thermoset PIMC resin powder is selected from the group consisting of epoxy, polyester, polyester TGIC, epoxy-polyester hybrids, urethane polyester, polyvinylidene fluoride, acrylic, polyvinyl chloride, polyolefms and nylon. In some embodiments where the thermoset item to be made is a component panel of an enclosure, the thermoset PIMC resin powder is suitable for coating polyester or glass- reinforced polyester, and is preferably chosen to increase surface hardness and to improve weatherability. A typically suitable PIMC resin powder is PIMC- 1241 from Synres-Almoco b.v. a subsidiary of Raschig GmbH, Hoek van Holland, The Netherlands. Details and parameters for implementing the method, including process parameters such as choice of type and amounts of materials, spray settings, temperatures, press settings, rates of mold opening and closing, are substantially similar to known PIMC parameters and are easily determined by a person having ordinary skill in the art upon perusal of the description herein.
Device for Powder In-MoId Coating
Embodiments of the method of the invention may be implemented using any suitable device or combination of devices. A particularly suitable device for implementing some embodiments of the method is a PIMC device of the invention. According to an aspect of some embodiments of the invention there is provided a
PIMC device, comprising: a) a mold-press suitable for compression molding of thermosets including a mold having least two mold parts: i. an upper mold part with an upper mold surface; and ii. a lower mold part with a lower mold surface the mold-press configured to close the mold by moving the upper mold part and lower mold part together to a closed state and apart to an open state; b) a PIMC spraying booth configured to reversibly engage the upper mold part, so that when said spraying booth engages said upper mold part an outer rim of an aperture outer rim of the spraying booth is intimately encircled by the mold seam area of the upper mold surface so as to substantially isolate the upper mold surface inside the spraying booth when engaging the upper mold part; and c) an electrostatic sprayer with at least one nozzle configured for electrostatic application of PIMC resin powder to the upper mold surface when substantially isolated inside the spraying booth.
By "intimately encircles" is meant that when the upper mold surface is substantially isolated inside the spraying booth, the gap between the outer rim of the aperture of the spraying booth and the mold seam area of the upper mold part of the mold is very small. In some embodiments, when the upper mold surface is substantially isolated inside the spraying booth, the gap between the outer rim of the aperture of the spraying booth and the mold seam area of the upper mold part is an average of not more than about 0.2 mm, not more than about 0.15 mm and even not more than about 0.1 mm.
In some embodiments, the inner surfaces of the spraying booth and even the entire spraying booth are fashioned of a material or materials to which PIMC resin powder does not substantially electrostatically adhere (materials that can be electrostatically charged), for example are fashioned from a material such as wood, plastic, paper, cardboard or polyvinylchloride.
In some embodiments, the inner surfaces of the spraying booth are fashioned of a material or materials to which PIMC resin powder electrostatically adheres.
In some embodiments, the PIMC device includes a spraying booth moving mechanism configured to automatically or semi-automatically move the spraying booth to engage the upper mold part, maintain the spraying booth in an engaged state for the desired period of time and to disengage the spraying booth from the upper mold part. In some embodiments, such mechanism is a suitable robot, for example an appropriately modified robot available from ABB Robotics Ltd., Zurich, Switzerland.
In some embodiments, a PIMC device includes an excess PIMC resin powder container. During operation, excess PIMC resin powder that accumulates at the bottom of the spraying booth is emptied into the excess PIMC resin powder container, for example a spraying booth moving mechanism is used to tip the contents of the spraying booth into the container.
In some embodiments for making component panels of enclosures, the downwardly facing mold surface is the female mold surface and the upwardly facing mold surface is the male mold surface. In some embodiments, the downwardly facing mold surface is the male mold surface and the upwardly facing mold surface is the female mold surface
In some embodiments, the mold-press of the PIMC device is configured so that the lower mold part is static and the upper mold part moves downwards to bring the mold to the closed state and upwards to bring the mold to an open state. In some embodiments, the mold- press is configured so that the upper mold part is static and the lower mold part moves upwards to bring the mold to the closed state and downwards to bring the mold to an open state. In some embodiments, the mold-press is configured so that both the upper mold part and the lower mold part both move, moving together to bring the mold to the closed state and moving apart to bring the mold to an open state.
Any suitable electrostatic sprayer may be used in implementing the invention. Suitable electrostatic sprayers are commercially available, for example commercially available corona type spray guns, e.g., from Larius SrI, Calolziocorte, LC, Italy.
In some embodiments, the at least one nozzle is configured to apply a substantially even coating of PIMC resin powder to substantially the entire upper mold surface substantially simultaneously when the spraying booth is engaged with the upper mold part. In some such embodiments, the at least one nozzle is static during application of the PIMC resin powder to the upper mold surface.
In some embodiments, the at least one nozzle is configured to apply PIMC resin powder to only a part of the upper mold surface at any one time. In some such embodiments, the at least one nozzle is configured to move inside the spraying booth when the spraying booth is engaged with the upper mold part, allowing application of a substantially uniform coating of PIMC resin powder to substantially the entire upper mold surface. During application of PIMC resin powder, the electrostatic sprayer is moved inside the spraying booth to apply PIMC resin powder to the entire upper mold surface. In some embodiments, moving of the at least one nozzle is performed automatically or with the help of a robot to ensure that PIMC resin powder is uniformly applied to the entire upper mold surface.
In some embodiments, the at least one nozzle of the electrostatic sprayer is configured to move in and out of the spraying booth, as desired. For example, in some such embodiments, the at least one nozzle is mounted on the arm of a robot and the spraying booth includes a window. In some such embodiments, when the spraying booth engages the upper mold part, the robot moves the at least one nozzle into the spraying booth through the window to apply PIMC resin powder to the upper mold surface. Subsequently, the at least one nozzle is removed from the spraying booth through the window and the spraying booth disengaged from the upper mold part.
In some embodiments, the at least one nozzle is contained inside the spraying booth and is configured to move together with the spraying booth, for example throughout the process of engaging the upper mold part and disengaging from the upper mold part.
In some embodiments, a PIMC device further comprises an evacuation assembly functionally associated with the spraying booth, configured for evacuating PIMC resin powder suspended inside the spraying booth when the spraying booth is engaged with the upper mold part. In some such embodiments, the evacuation assembly is configured to evacuate powder through a duct in fluid communication with the inside of the spraying booth. Suction applied by the evacuation assembly draws suspended PIMC resin powder out of the spraying booth. In some embodiments, the spraying booth also includes a gas inlet that allows gas such as air to enter the spraying booth when the evacuation assembly is being operated. Generally, the evacuation assembly is operated during and/or subsequent to application of PIMC resin powder to the upper mold surface. Excess PIMC resin powder in the spraying booth that does not settle at the bottom of the spraying booth is evacuated by the evacuation assembly through the duct. In some embodiments, the evacuated PIMC resin powder is discarded. In some embodiments, the evacuated PIMC resin powder is recovered, for example with the help of a component such as a filter, cyclone precipitator or electrostatic precipitator for reuse.
In some embodiments, a PIMC device as described above is configured for substantially manual use and includes appropriate manual controls, as well known in the field of compression molding. A disadvantage of manual use is that the spraying booth is preferably engaged with the upper mold part throughout the electrostatic application of the PIMC resin powder and the upper mold part is preferably carefully removed quickly enough so that the applied PIMC resin powder does cure too much (for example, to an extent that adhesion of the resin powder to the plastic thermoset resin charge is substantially adversely effected) prior to mold closing. In some embodiments, a PIMC device as described above is configured for semiautomatic or substantially automatic use, as well known in the field of compression molding. In some such embodiments, a PIMC device is provided with one or more robots to perform the required tasks semi-automatically or substantially automatically.
As is known in the art, a lower mold part of a mold-press is generally provided with ejectors, components that release a cured item from the mold while an upper mold part is generally devoid of such ejectors. Since according to embodiments of the invention PIMC resin powder is applied to the upper mold part, in some embodiments, there is no need for special modification of ejectors for implementing the invention. In some embodiments where the upper mold part is provided with ejectors, it is preferred that the ejectors be non-contact ejectors, e.g., air valve ejectors, to reduce the chance of marking or damaging a produced PIMC-coated surface.
An embodiment of the method will be described with reference to PIMC device 20 schematically depicted in Figures 2 A, 2B and 2C.
PIMC device 20, substantially entirely depicted in Figure 2A, comprises a mold-press 22 for compression molding of thermosets and a spraying assembly 24. Mold-press 22 comprises a mold with a female upper mold part 26 having a downwardly facing female upper mold surface 28 and a male lower mold part 30 having an upwardly facing male lower mold surface 32. Mold-press 22 is configured to close the mold to a closed state by moving upper mold part 26 down towards lower mold part 30, and to open the mold to an open state by moving upper mold part 26 up and away from lower mold part 30. In Figure 2A, the mold is depicted in an open state.
Spraying assembly 24 comprises a spraying booth 34 mounted on a spraying booth moving mechanism 36, with an integrated electrostatic sprayer 38 (see Figures 2B and 2C), an evacuation assembly 40 and an excess PIMC resin powder container 42.
Excess PIMC resin powder container 42 is an open-topped container accessible to spraying booth moving mechanism 36 for collecting recovered PIMC resin powder.
Spraying booth 34, substantially an enclosure made of wood with an open upper aperture 44, is schematically depicted from above in Figure 2B and in side cross section engaged with upper mold part 26 in Figure 2C.
Components of electrostatic sprayer 38 including nozzle 46 are seen inside of spraying booth 34. Electrostatic sprayer 38 (e.g., a modified corona type spray gun) is integrated with and moves together with spraying booth 34. Nozzle 46 of electrostatic sprayer
38 is contained inside spraying booth 34, but is configured to move inside spraying booth 34 on X-Y table 48 in a controlled fashion (control wires not depicted) to evenly-apply PIMC resin powder to upper mold surface 28 when spraying booth 34 is engaged with upper mold part 26.
Evacuation assembly 40 includes a pump (not depicted) configured to draw air from inside spraying booth 34 through duct 50 in fluid communication with the inside of spraying booth 34 and an air inlet 52 to allow air to enter the inside of spraying booth 34. When the pump of evacuation assembly 40 is activated, PIMC resin powder suspended inside spraying booth 34 is evacuated from inside spraying booth 34 through duct 50 to be discarded or recovered.
Spraying booth 34 is configured to reversibly engage upper mold part 26 through upper aperture 44. Upper aperture 44 of spraying booth 34 includes an outer rim 54 having a shape substantially similar to that of a mold seam area 56 of upper mold part 26. Outer rim 54 is slightly smaller than mold seam area 56, so that when spraying booth 34 engages upper mold part 26, outer rim 54 is intimately encircled by mold seam area 56 and that a gap 58 between outer rim 54 and mold seam area 56 is an average of not more than about 0.1 mm. As a result, when spraying booth 34 engages upper mold part 26, upper mold surface 28 is substantially isolated inside spraying booth 34 from mold seam area 56, other components of PIMC device 20, and the surroundings.
For use for preparing an item such as a component panel of an enclosure, mold-press 22 is prepared in the usual way. For example, the temperatures of the various components are set to the usual values for a desired PIMC resin powder and desired thermoset resin charge. A charge of plastic thermoset resin (SMC or BMC, with or without reinforcing fibers, for example a thermoset including polyester) is placed on lower mold surface 32 of lower mold part 30 in the usual way. If necessary, fittings such as nuts, bolts and the like are placed in the appropriate positions on lower mold surface 32 of lower mold part 30.
Spraying booth moving mechanism 36 is activated to substantially isolate upper mold surface 28 inside spraying booth 34, substantially as depicted in Figure 2C, by engaging upper mold part 26 with spraying booth 34 so that outer rim 54 of upper aperture 44 of spraying booth 34 is intimately encircled by mold seam area 56 of upper mold part 26.
While upper mold surface 28 is substantially isolated inside spraying booth 34, electrostatic sprayer 38 is activated so thermoset PIMC resin powder (e.g., a PIMC resin powder comprising a polyester) is applied to upper mold surface 28 through nozzle 46. Nozzle 46 applies the PIMC resin powder to only a part of upper mold surface 28 at any one time. X-Y table 48 is used to move nozzle 46 inside spraying booth 34 to ensure that PIMC resin powder is applied evenly to the entirety of upper mold surface 28.
As discussed above, the isolation of upper mold surface 28 inside spraying booth 34 and the intimate encirclement of outer rim 54 of upper aperture 44 of spraying booth 34 by mold seam area 56 ensures that mold seam area 56 remains substantially clean of PIMC resin powder, and that substantially no PIMC resin powder contaminates components of PIMC device 20 or the surroundings. Spraying booth moving mechanism 36 maintains spraying booth 34 engaged with upper mold part 26 for a required time (typically in the order of 5 to 10 seconds) to allow substantial partial curing of the applied PIMC resin powder on upper mold surface 28. As a result, the applied PIMC resin powder melts, spreads to form a layer and begins to cure into a film while spraying booth 34 is still engaged with upper mold part 26.
When a sufficient degree of substantial partial curing is achieved, spraying booth moving mechanism 36 disengages spraying booth 34 from upper mold part 26. The disengaging cleanly tears the film of partially cured PIMC resin powder. As the PIMC resin powder is already partially cured, there is no migration of PIMC resin powder to mold seam area 56. Spraying booth moving mechanism 36 withdraws spraying booth 34 from between upper mold part 26 and lower mold part 30 so as not to interfere with mold closing.
Mold-press 22 is activated in the usual way to close the mold, bringing upper mold surface 28 and lower mold surface 32 together, spreading the plastic thermoset resin charge in the usual way to fill the volume between upper mold surface 28 and lower mold surface 32 to form the desired item from the thermoset resin. While spreading, the upper part of the thermoset resin charge contacts the partially-cured applied PIMC resin powder on upper mold surface 28 in the usual way.
In the usual way, the mold is maintained in a closed state allowing the thermoset resin to cure and to react with the partially-cured PIMC resin powder on upper mold surface 28. In the usual way, the layer of partially-cured PIMC resin powder becomes integrally formed with the thermoset resin to form a PIMC surface on the cured thermoset resin.
In the usual way, when the thermoset resin is substantially cured, the mold is opened by separating upper mold surface 28 from lower mold surface 32, and the cured thermoset resin is removed from the mold as the desired thermoset item. While spraying booth 34 is engaged with upper mold part 26 and during the application of PIMC resin powder to upper mold surface 28, the pump of evacuation assembly 40 is operated. Air enters the inside of spraying booth 34 through air inlet 52 and is drawn into duct 50, thereby evacuating excess PIMC resin powder resin from inside spraying booth 34. In some embodiments, usually in accordance with operator discretion, evacuation is suspended when application of PIMC resin powder resin is completed. In some embodiments, usually in accordance with operator discretion, evacuation is continued during the period of time allowed for partial curing of the applied PIMC resin powder on the upper mold surface and suspended proximal to the time when it is desired to disengage spraying booth 34 from upper mold surface 28. While spraying booth 34 is engaged with upper mold part 26 and during the application of PIMC resin powder to upper mold surface 28, excess PIMC resin powder that does not adhere to upper mold surface 28 and that is not evacuated by evacuation assembly 40 settles and accumulates at the bottom of spraying booth 34. While the mold is closed, spraying booth moving mechanism 36 tips spraying booth 34 over excess PIMC resin powder container 42 so that excess PIMC resin powder falls thereinto to be collected.
In some embodiments, a spraying assembly such as 24 is devoid of an evacuation assembly such as 40. In some such embodiments, excess PIMC resin powder settles and accumulates at the bottom of spraying booth 34, and can be collected in an excess PIMC resin powder container such as 42.
In the embodiment discussed above, spraying booth 34 remained engaged with upper mold part 26 for sufficient time allowing substantial partial curing so that the applied PIMC resin powder forms a film. In some embodiments, a spraying booth is disengaged from an upper mold part soon after application of the PIMC resin powder and prior to substantial partial curing of the applied PIMC resin powder.
In Figures 2, electrostatic sprayer 38 is integrated with spraying booth 34 and moves together with spraying booth 34 while nozzle 46 of electrostatic sprayer 38 is configured to move inside spraying booth 34 to evenly apply PIMC resin powder to upper mold surface 28 when engaged with upper mold part 26. In some embodiments, such as depicted in Figure 3A, nozzles 46 of electrostatic sprayer 38 are fixed in position and static inside spraying booth 34, but are arranged in a way to evenly apply PIMC resin powder to substantially the entire upper mold surface 28 substantially simultaneously when engaged with upper mold part 26.
In some embodiments, such as depicted in Figure 3B, electrostatic sprayer 38 is separate from spraying booth 34, but is configured to move into and out of spraying booth 34 for application of PIMC resin powder. In Figure 3B, electrostatic sprayer 38 is mounted on an independent robot arm 60. When spraying booth 34 is engaged with an upper mold part 26, robot arm 60 maneuvers nozzle 46 of electrostatic sprayer 38 into spraying booth 34 through an elongated window 62 in the side of spraying booth 34 sealed with a brush seal and moves nozzle 46 inside spraying booth 34 to evenly apply PIMC resin powder to upper mold surface
28. When application of PIMC resin powder is complete, robot arm 60 withdraws nozzle 46 from spraying booth 34 out through window 62.
In the embodiments depicted above, spraying booth 34 and electrostatic sprayer 38 are mounted on robots to automatically or semi-automatically, quickly and accurately engage spraying booth 34 with upper mold part 26 for the required length of time and to control electrostatic sprayer 38 to evenly apply PIMC resin powder to upper mold surface 28. In some embodiments, other mechanisms are used to engage a spraying booth with an upper mold part and to control an electrostatic sprayer. An additional PIMC device useful for implementing some embodiments of the method, PIMC device 64, is schematically depicted in Figures 4A, 4B and 4C.
PIMC device 64, substantially entirely depicted in Figure 4A, comprises a mold-press 22 for compression molding of thermosets and a spraying assembly 24.
Like in PIMC device 20 discussed above, mold-press 22 comprises a mold with a female upper mold part 26 having a downwardly facing upper mold female surface 28 (not depicted) and a male lower mold part 30 having an upwardly facing lower mold male surface 32. In Figure 4A, the mold is depicted in an open state.
Spraying assembly 24, schematically depicted in detail in Figures 4B and 4C, comprises a spraying booth 34 mounted on a spraying booth moving mechanism 36, with an integrated electrostatic sprayer 38 and a duct 50 of an evacuation assembly.
Spraying booth 34, substantially an enclosure made of wood with an open upper aperture 44, is schematically depicted (with a side cut out) in Figure 4C in proximity of upper mold part 26.
Spraying booth moving mechanism 36 is configured to move spraying booth 34 between upper mold part 26 and lower mold part 30 by sliding spraying booth 34 like a drawer along rails 68. Once upper aperture 44 is properly positioned below mold seam area
56 of upper mold part 26, actuators 70 lift spraying booth 34 upwards, thereby engaging upper mold part 26 with spraying booth 34 so that outer rim 54 of upper aperture 44 is intimately encircled by mold seam area 56 of upper mold surface 28, substantially isolating upper mold surface 28 inside spraying booth 34.
Components of electrostatic sprayer 38 including nozzle 46 are seen inside of spraying booth 34. Electrostatic sprayer 38 is integrated with and moves together with spraying booth 34. Electrostatic sprayer 38 is mounted on X-Y table 48 which is outside spraying booth 34. Nozzle 46 of electrostatic sprayer 38, mounted on arm 60, is contained inside spraying booth 34. Arm 60 of electrostatic sprayer 38 passes through elongated window 62 (sealed, for example, with a brush seal (not depicted)) on the side of spraying booth 34 into spraying booth 34. X-Y table 48 is under control of a robot (control wires not depicted) to evenly apply PIMC resin powder to upper mold surface 28 when spraying booth 34 is engaged with upper mold part 26. The evacuation assembly includes a pump configured to draw air from inside spraying booth 34 through duct 50.
Spraying booth 34 is configured to reversibly engage upper mold part 26 through upper aperture 44. Upper aperture 44 includes an outer rim 54 having a shape substantially similar to that of mold seam area 56 of upper mold part 26. Outer rim 54 is slightly smaller than mold seam area 56, so that when spraying booth 34 and upper mold part are engaged, outer rim 54 is intimately encircled by mold seam area 56. As a result, when spraying booth
34 is engaged with upper mold part 26, upper mold surface 28 is substantially isolated inside spraying booth 34 from mold seam area 56, other components of PIMC device 64 and the surroundings.
Implementation of embodiments of the method of the invention using PIMC device 64 is substantially analogous to the described hereinabove.
Embodiment of a spraying booth In some embodiments, a spraying booth as described herein comprises two parts: a lower enclosure part and an upper aperture part which are substantially immovably engaged to constitute the spraying booth. Such an embodiment is depicted in Figure 5, spraying booth 72 comprising an upper aperture part 74 and a lower enclosure part 76 including clips 78 configured to reversibly substantially immovably engage upper aperture part 74 to lower enclosure part 76.
A lower enclosure part such as 76 is substantially an open-topped box including other components of the spraying booth as described above including components such as duct 50, elongated window 62, brush seals, components of an electrostatic sprayer and the like. A lower enclosure part such as 76 is also configured to substantially immovably engage an upper aperture part such as 74 to the open top of the lower enclosure part, for example, with the help of clips 78.
The upper aperture part such as 74 is substantially a frame 82 having a size and shape that matches the open top of the lower enclosure part and is substantially immovably engageable to the lower enclosure part. An upper aperture part defines an outer rim 54 having a size and shape to be intimately encircled by a mold seam area of a respective upper mold surface.
One stage of an embodiment of making an outer rim 54 of an aperture 44 of an upper aperture part 74 of a spraying booth such as 72 is schematically depicted in Figure 6. A female upper mold part 26 is placed upside-down so that an upper female mold surface 28 faces upwards. A mold seam area 56 is covered with a thin (having a thickness corresponding to the desired gap 58, e.g., not more than about 0.2 mm, not more than about 0.15 mm and in some embodiments even not more than about 0.1 mm thick) protective layer 80 (for example of sheet wax available, for example, from Freeman Mfg. and Supply Co., OH, USA). A frame 82 (e.g., of wood) is set on top of upper mold part 26, frame 82 defining an aperture approximately (preferably slightly larger) that of the circumference of mold seam area 56. Sheets of a material 84 (see below) that adhere to frame 82 but not to protective layer 80 are adhered to the inner part of the aperture of frame 82 and covering protective layer 80 around the entire circumference of mold seam area 56 to define an incipient outer rim 54 of upper aperture 44 of the spraying booth. Sufficient sheets are placed (depending in the nature if the sheets, e.g., to a thickness of between about 2 mm and about 10 mm) so that the produced outer rim 54 will be sufficiently strong. For example, in some embodiments, the sheets of material are adhesive curable sheets such as air-curable epoxy-impregnated glass fiber sheets.
When outer rim 54 is completed (e.g., if applicable, the curable sheets making up the incipient outer rim have cured to constitute a completed rim) the thus-made upper aperture part 74 (comprising frame 82 and cured sheets 84) is separated from upper mold part 26. Upper mold part 26 is cleaned of protective layer 80.
The thus-made upper aperture part 74 is then substantially immoveable engaged to a lower enclosure part. For example, in some embodiments, the upper mold part is properly placed in a mold press (upper mold surface facing downwards), the lower enclosure part is properly secured to the respective spraying booth moving mechanism and the upper aperture part is loosely placed on the open top of the lower enclosure part. The spraying booth moving mechanism is activated to slowly bring the lower enclosure part and upper aperture part to proximity with and to engage the upper mold part. The position of the upper aperture part is adjusted so that the outer rim of the upper aperture part is intimately encircled by the mold seam area of the upper mold surface. While the outer rim is intimately encircled by the mold seam area of the upper mold, the upper aperture part is substantially immoveable engaged to the lower enclosure part.
Mold seam area and venting channels
One of the challenges in PIMC in compression molding of thermosets relates to venting channels. When a mold closes on a charge of plastic thermoset resin, the plastic thermoset resin spreads to fill the volume between the upper and lower mold surfaces. Air trapped between the mold parts is displaced by the spreading resin and either escapes or is compressed inside the resin, producing defects.
A prior art mold design is depicted in cross section in Figures 7A and 7B, including an upper male mold part 30 and a lower female mold part 26 where the gap (e.g., 0.05 mm) between mold parts 26 and 30 constitutes a venting channel 86. When the mold is brought to a closed state, the thermoset resin charge 88 spreads, displacing air outwards through venting channel 86. As depicted in Figure 7B, when applying PIMC to such a mold, it is known to place a mask 90 on top of lower female mold part 26 to cover mold seam area 56 while applying PIMC resin powder. Despite the use of mask 90, at least some PIMC resin powder is attracted upwards into a gap 92 between the outer rim of mask 90 and seam area 56. During closure of the mold, some of the PIMC layer is mechanically sheared off and blocks venting channel 86.
A possible solution (recommended, for example, in "Framework and process guidelines for Powder in-Mould Coating" dated October 2004 by Synres-Almoco bv, a subsidiary of Raschig GmbH, Hoek van Holland, The Netherlands) is to increase the size of the venting channel in the region where the PIMC is applied (bordering the mold seam area), typically to between about 0.5 mm to about 0.7 mm. The increase of size allows some PIMC to enter the venting channel without blocking the venting channel. Such a solution is inappropriate when the upper mold part is female: in some instances spreading resin drips downwards due to the force of gravity, blocking the large venting channel. Further, such a solution is inappropriate when the spreading resin includes reinforcing fibers: a venting channel larger than about 0.3 mm allows entry of the reinforcing fibers into the flash formed inside the venting channels. It then becomes very difficult and expensive to remove the flash.
Some embodiments described herein, especially some embodiments where PIMC resin powder is applied to an upper mold surface, especially an upper female mold surface, overcome some of the challenges associated with venting channels.
Such an embodiment is depicted in Figures 8A, 8B and 8C. It is important to note that, for clarity, some features are not drawn to scale. The actual scale of the various features is clear to a person having ordinary skill in the art upon perusing the accompanying description.
In Figure 8A is schematically depicted in cross section a portion of an embodiment of a female upper mold part 26, including a downwardly facing upper mold surface 28 and a mold seam area 56. Mold seam area 56 has a diameter slightly larger than that of the adjacent upper mold surface 28, the difference 94 typically between about 0.03 mm and about 0.07 mm, in some embodiments between about 0.04 mm and about 0.06 mm, in some embodiments about 0.05 mm. Height 96 of the larger diameter portion of mold seam area 56 is any suitable height, typically between about 10 mm and about 30 mm, in the embodiment depicted in Figure 8 A being 20.5 mm. In some embodiments, such as the embodiment depicted in Figure 8A, the mold seam area is discontinuous with the female mold surface. In some embodiments, the discontinuity is greater than about 70°, in some embodiments greater than about 80°, and in some embodiments, the discontinuity is even greater than about 85°. In the embodiment depicted in Figure 8 A, discontinuity 97 is about 90°. In some embodiments, such as the embodiment depicted in Figure 8 A, the mold seam area adjacent to the female mold surface is substantially parallel (in some embodiments, within 5% of parallel) to the mold axis (the axis along which the mold parts move together and apart).
In Figure 8B, upper female mold part 26 is depicted engaged with spraying booth 34 where outer rim 54 of aperture 44 of spraying booth 34 is intimately encircled by mold seam area 56 of upper mold part 26. Gap 58 between outer rim 54 and mold seam area 56 is not more than about 0.2 mm (in Figure 8B, about 0.1 mm). The height 98 of outer rim 54 is slightly greater than the height of mold seam area 56, typically the difference 100 being between about 0.2 mm and about 1.5 mm (in Figure 8B, about 0.5 mm). Protrusion 102 of spraying booth 34 that defines outer rim 54 is thick enough to be sufficiently strong, typically between about 2mm and about 10 mm (in Figure 8B, about 5 mm).
As height 98 of outer rim 54 is greater than that of mold seam area 56, a part of outer rim 54 protrudes beyond mold seam area 56 (in Figure 8B, by about 0.5 mm) and defines a gap 104 (in Figure 8B of about 0.05 mm) between upper mold surface 28 and outer rim 54. When PIMC resin powder is applied to upper mold surface 28 when engaged with spraying booth 34 as depicted in Figure 8B, PIMC resin powder is electrostatically attracted to exposed portions of upper mold surface 28. When the PIMC resin powder is approximately the same or smaller than gap 104, some PIMC resin powder also enters gap 104 in between upper mold surface 28 and the upper portion of outer rim 54. For example, when gap 104 is about 0.05 mm as in Figure 8B, fine PIMC resin powder (for example 0.05 mm diameter powder that produces a fine PIMC finish) is attracted thereinto to cover the masked portions of upper mold surface 28 without substantial deposition of PIMC resin powder on mold seam area 56. Without wishing to be held to any one theory, in some embodiments the height of the outer rim of the spraying booth is such that when the spraying booth and female mold part are engaged, a portion of the female mold surface is masked by the outer rim of the spraying booth (in some embodiments, the portion being between about 0.2 mm and about 1.5 mm high, in Figure 8B about 0.5 mm), thereby assisting in preventing substantial PIMC resin powder deposition on the mold seam area, even though PIMC resin powder is deposited on substantially the entire female mold surface: sufficient PIMC resin powder is drawn by electrostatic attraction to cover the portion of the female mold surface masked by the outer rim of the spraying booth. Without wishing to be held to any one theory, in some embodiments the degree of discontinuity of the mold seam area with the female mold surface (as discussed above, in some embodiments, greater than about 70°, in some embodiments greater than about 80°, and in some embodiments, greater than about 85°) of the female mold prevents applied PIMC resin powder from being electrostatically drawn past the discontinuity to the mold seam area. Without wishing to be held to any one theory, it is believed that in some embodiments the degree of discontinuity together with the masking of a portion of the female mold surface by the outer rim of the spraying booth assist in preventing substantial deposition of PIMC resin powder on the mold seam area.
Without wishing to be held to any one theory, in some embodiments the size of the gap between the female mold surface and the outer rim of the spraying booth (in Figure 8B, gap 104 is about 0.05 mm; in some embodiments the gap is not greater than about 0.2 mm, in some embodiments not greater than about 0.15 mm, in some embodiments not greater than about 0.1 mm) makes passage of applied PIMC resin powder into the gap difficult. Applied PIMC resin powder drawn by electrostatic attraction into the volume between the outer rim of the spraying booth and the female mold surface is initially deposited close to the upper tip of the outer rim, constituting a bottleneck to the passage of additional PIMC resin powder subsequently applied. In some such embodiments, such a bottleneck assists in preventing substantial deposition of PIMC resin powder on the mold seam area.
Without wishing to be held to any one theory, it is believed that in some embodiments the size of the gap between the female mold surface and the outer rim of the spraying booth together with the masking of a portion of the female mold surface by the outer rim of the spraying booth assist in preventing substantial deposition of PIMC resin powder on the mold seam area. Without wishing to be held to any one theory, it is believed that in some embodiments the size of the gap between the female mold surface and the outer rim of the spraying booth together with the degree of discontinuity of the mold seam area with the female mold surface assist in preventing substantial deposition of PIMC resin powder on the mold seam area. Without wishing to be held to any one theory, it is believed that in some embodiments the size of the gap between the female mold surface and the outer rim of the spraying booth together with the masking of a portion of the female mold surface by the outer rim of the spraying booth and together with the masking of a portion of the female mold surface by the outer rim of the spraying booth assist in preventing substantial deposition of PIMC resin powder on the mold seam area.
As discussed above, depending on the embodiment, subsequent to application of a PIMC resin powder layer spraying booth 34 is disengaged from upper mold part 26 before substantial curing of the deposited PIMC resin powder or after substantial curing of deposited PIMC resin powder.
In Figure 8C, the mold comprising upper mold part 26 and lower mold part 30 is depicted in a closed state. Volume 106 in which thermoset resin is molded is seen between upper mold surface 28 and lower mold surface 32. The diameter of lower mold surface 32 is slightly smaller than the diameter of mold seam area 56 of upper mold part 26 so that the gap between mold parts 26 and 30 constitutes a venting channel 86. Width 108 of venting channel is generally less than about 0.2 mm and even less than about 0.1 mm (in Figure 8C, about 0.05 mm). Penetration 110 of lower mold part 30 into upper mold part 26 (as determined by the mold press mechanism) is slightly less than height 96 of mold seam area 56 to define an "inlet" 112 into venting channel 86, generally less by between about 0.2 mm and about 0.8 mm (in Figure 8C, penetration 110 is about 20 mm while height 96 is about 20.5 mm so that the height difference ("inlet" 112) is about 0.5 mm). As a result, venting channel 86 remains clear and unobstructed during molding. In some embodiments, such as the embodiment depicted in Figure 8C, no substantial part of the female mold on which PIMC resin powder is applied is a part of venting channel 86. As a result, venting channel 86 remains clear and unobstructed. In some embodiments, this allows venting channel 86 to be sufficiently small so that few if any reinforcing fibers present in the thermoset resin charge are found in the flash, making flash removal of molded item simple.
In some embodiments, such as depicted in Figure 8C, "inlet" 112 into venting channel 86, defined by discontinuity 97 of mold seam area 56 with female mold surface 28, the periphery of male mold surface 32 and penetration 110 of male mold part 30 into female mold part 28 is at an angle greater than greater than about 70° (in some embodiments greater than about 80°, and in some embodiments, greater than about 85°, in Figure 8C about 90°) to the mold axis.
Female Mold Part Mold parts are traditionally made of either steel or nickel-coated aluminum. There are many advantages for having mold parts of nickel-coated aluminum (for example, the thermal expansion coefficient of aluminum, unlike steel, is very similar to that of fiber-reinforced polyester) it is exceptionally advantageous to have an upper (moving) mold part of aluminum. As an aluminum mold part is lighter than a steel mold part, the press that moves the mold part is smaller and lighter and replacement of the aluminum mold part is much simpler.
However, nickel-coated aluminum mold parts are of limited use for the compression molding of fiber-reinforced thermosets. During compression molding, the glass fibers slowly abrade the protective nickel layer exposing the aluminum metal. Titanium oxide that is commonly present in thermoset resin compositions chemically reacts with the aluminum, reducing the lifetime of the mold part.
It has been found that when implementing the teachings of the invention, it is possible to extend the lifetime of the upper female mold part. It is currently believed that the applied PIMC layer protects the nickel surface of the mold from abrasion and/or contact with titanium oxide in the thermoset resin.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.
Section headings are used herein to ease understanding of the specification and should not be construed as necessarily limiting.