Patent Application
20060118999
The present invention relates to a method of preparing a coated molded article by means of in-mold coating. The method involves the use of a mold apparatus that includes: a rotatable core having at least one molding surface; a first die and a second die each having an internal surface; and at least two separate mold cavities. The second die has a reversibly slidable portion having an internal surface that defines substantially the internal molding surface of the second die. A plastic molded article is formed in a first mold cavity defined in part by the first die, the core is rotated, and a coating is applied to the plastic molded article in a separate second mold cavity that is defined in part by the slidable portion of the second die. The slidable portion of the second die is moved towards the core causing the coating to be spread over the surface of the molded article. The present invention also relates to a mold apparatus.
Molded plastic articles are utilized in a number of areas, such as, interior and exterior components of motor vehicles (e.g., automobiles, trucks and aircraft), housings for electronic devises and lenses (e.g., ophthalmic lenses and lenses for motor vehicle head lights and break lights). For purposes of improved aesthetic appearance and/or physical properties (e.g., smoothness, weatherability and/or photochromaticity) it may be desirable to apply a coating or coatings to the surface of a molded plastic article.
Coatings may be applied to the surface of a molded plastic article after removal of the article from the mold in which it is formed. The post-mold (or extra-mold) application of coatings to molded plastic articles typically results in the formation of coatings that suffer from deficiencies such as, poor appearance due to, for example, poor wetting of the plastic surface, and a lack of electrical and/or thermal conductivity of the molded plastic article.
The in-mold application of coatings to molded plastic articles is known. Relative to post-mold applications, the in-mold application of coatings to molded plastic articles provides advantages including: improved smoothness of the coating (due to the coating surface being defined by the interior surface of the mold); improved uniform thickness of the coating; and improved adhesion of the coating to the molded plastic article (e.g., due the cure of thermosetting coatings within the mold and/or mold pressures that serve to drive a portion of the coating into the surface of the molded plastic article).
The in-mold application of coatings to molded plastic articles typically involves (e.g., as described in U.S. Pat. Nos. 4,081,578, 4,668,460, and 5,387,750) first forming a molded article in a mold, partially opening the mold to form a space between the molded article and an interior surface of the mold, introducing a coating composition into the mold, curing the coating within the mold, and removing the coated article from the mold. Such in-mold coating methods typically suffer from inefficiencies, such as low product formation rates due to a single mold being used for both molding and coating operations. That is, a subsequent plastic molded article can not be formed until the in-mold coating steps are completed. In addition, with such prior in-mold coating methods, adjusting the temperature under which the coating is formed is typically limited, because the same mold is used for both formation of the molded plastic article and formation of the coating layer.
International Application Publication No. WO 03/049929 A1, published under the Patent Cooperation Treaty, discloses a method of applying an ultraviolet light curable paint to molded parts using a turnable mold. WO 03/049929 A1 does not disclose shaping or forming the surface of the paint by contact thereof with an internal mold surface.
United States Patent Application No. US 2003/0197307 (the '307 application) discloses a method for injection molding and successive decoration molding of a molded product. The '307 application discloses the use of a mold apparatus having two separate mold cavities each having fixed volumes.
It would be desirable to develop additional methods of preparing coated molded plastic articles by in-mold coating processes. It would be desirable that such newly developed in-mold coating methods provide, for example, improved product formation rates, and an independence of temperature between the molded article and coating formation steps. In addition, it would be desirable to develop new mold apparatuses that may be used to prepare in-mold coated plastic articles.
In accordance with the present invention, there is provided a method of preparing a coated molded article comprising:
(A) providing a mold apparatus comprising,
(B) engaging at least said first die with said core and forming said first mold cavity;
(C) introducing plastic material into said first mold cavity to form an uncoated molded article having a second surface that abuts the molding surface of said core which defines said first mold cavity, and having a first surface that is substantially opposed to said second surface;
(D) disengaging at least said first die from said core;
(E) rotating said core with said uncoated molded article on said molding surface of said core, and aligning the first surface of said uncoated molded article with the internal surface of said second die;
(F) engaging said second die with said core such that the internal surface of said second die and the first surface of said uncoated molded article together define an intermediate second mold cavity, said intermediate second mold cavity having a volume;
(G) introducing a coating composition into said intermediate second mold cavity;
(H) moving said reversibly slidable portion of said second die towards said core, thereby reducing the volume of said intermediate second mold cavity and causing said coating composition introduced into said intermediate second mold cavity to spread over at least a portion of said first surface of said uncoated molded article, thereby forming a coated molded article;
(I) disengaging at least said second die from said core;
(J) removing said coated molded article from said core; and
(K) optionally rotating said core such that one of said molding surfaces of said core is aligned with the internal surface of said first die, and repeating steps (B) through (J).
In further accordance with the present invention, there is provided a method of preparing a coated molded article comprising steps (A) through (E) and (I) through (K) as described above, but in which steps (F) through (H) are as follows:
(F) engaging said second die with said core such that,
(G) introducing a coating composition between said internal surface of said second die and said first surface of said uncoated molded article, said internal surface of said second die being concurrently separated from said first surface of said uncoated molded article thus forming an intermediate second mold cavity having a volume, the volume of said intermediate second mold cavity being greater than the volume of said initial second mold cavity; and
(H) moving said reversibly slidable portion of said second die towards said core, thereby reducing the volume of said intermediate second mold cavity and causing said coating composition residing in said intermediate second mold cavity to spread over at least a portion of said first surface of said uncoated molded article, thereby forming a coated molded article.
In further accordance with the present invention there is provided a mold apparatus as described in step (A) above.
The features that characterize the present invention are pointed out with particularity in the claims, which are annexed to and form a part of this disclosure. These and other features of the invention, its operating advantages and the specific objects obtained by its use will be more fully understood from the following detailed description and accompanying drawings.
Unless otherwise indicated, all numbers or expressions, such as those expressing structural dimensions, process conditions, etc. used in the specification and claims are understood as modified in all instances by the term “about.”
In
In the method of the present invention there is provided a mold apparatus. With reference to the drawing figures, the mold apparatus 1 includes a first die 11, which has an internal surface 14, a second die 17 having an internal surface 20, and a reversibly rotatable core 29 having at least one molding surface (e.g., 32 and 35). The second die 17 includes a reversibly slidable portion 23 having an internal surface 26. The internal surface 26 of slidable portion 23 substantially defines the internal surface 20 of second die 17. Preferably, the internal surface 26 of slidable portion 23 and the internal surface 20 of second die 17 are one and the same. As used herein and in the claims, with regard to the dies of the molding apparatus (e.g., first die 11 and second die 17), the term “internal surface” means an internal molding surface for forming a molded article (in the case of first die 11) or a coated molded article (in the case of second die 17).
The components of the mold apparatus of the present invention may be fabricated from suitable materials that are known to the skilled artisan. Typically, the components of the mold apparatus (e.g., the first die, second die, slidable portion of the second die, and the rotatable core) are fabricated from metals, such as steel, e.g., tool steel. The molding surfaces of the core and the internal surfaces of the first and second dies may each independently be polished steel surfaces, stainless steel surfaces, plated nickel surfaces or nickel/polytetrafluoroethylene surfaces.
The first die 11 and the second die 17 are each reversibly and separately/independently engageable with core 29, and accordingly core 29 is reversibly and independently engageable with each of first die 11 and second die 17. Engagement of first die 11 and second die 17 with core 29 may be achieved by means of first die 11 and second die 17 each being reversibly and independently moveable towards and/or away from core 29 (core 29 being substantially stationary relative to lateral movement). Alternatively, only one of first die 11 and second die 17 may be moved towards or away from core 29, while the other die remains engaged with or disengaged from core 29.
As used herein and in the claims with regard to the first die, second die and core, the term “engaged with” and similar terms means that a die (e.g., first die 11) and the core (e.g., core 29) are moved/positioned into an abutting relationship with each other such that a mold cavity is formed or potentially formed (e.g., first mold cavity 38 and second mold cavity 41).
In a preferred embodiment, first die 11 is maintained substantially stationary relative to lateral movement, and second die 17 and core 29 are each reversibly and independently moveable (laterally) towards and/or away from first die 11. In a particularly preferred embodiment of the present invention, first die 11 is maintained substantially stationary, and second die 17 and core 29 are laterally reversibly moveable in unison towards first die 11. For example, core 29 is moved towards and engaged with first die 11 thus forming first mold cavity 38, and concurrently second die 17 is moved towards and engaged with core 29 thus forming second mold cavity 41.
The reversible movement of second die 17, core 29 and first die 11 relative to each other may be achieved by art recognized methods. For example, each of second die 17 and core 29 may be movably fixed to rails (not shown) and reversibly moved by hydraulically driven drive arms (not shown).
The core of the molding apparatus of the present invention has at least one molding surface (e.g., 1, 2, 3, 4, 5, 6, 7 or 8 molding surfaces). As used herein and in the claims with reference to the core, the term “molding surface” and similar terms means a core surface upon which a molded plastic article may be formed. In the embodiment represented by mold apparatus 1 of the drawing figures, core 29 has two molding surfaces 32 and 35. A core having at least two molding surfaces allows for the simultaneous (or nearly simultaneous) performance of multiple operations. For example, a mold apparatus according to the present invention that includes a core having three or four molding surfaces (not shown) may be used to simultaneously perform plastic article molding, in-mold coating, molded article surface treatment and molding surface cleaning operations. In addition, a mold apparatus according to the present invention that includes a core having three or four molding surfaces (not shown) may be used to simultaneously perform plastic article molding, and the in-mold application of multiple coatings compositions, such as primer coatings, base coatings, clear coatings and hard-coatings compositions. With mold apparatus 1 of the drawing figures, which has two molding surfaces 32 and 35, plastic article molding and in-mold coating operations may be performed simultaneously.
Core 29 of mold apparatus 1 may be rotated by methods that are known to the skilled artisan. For example, core 29 may be rotated by means of a shaft or shafts (not shown) extending outwardly from core 29 coextensively along longitudinal axis 104 (of
In addition to the first and second dies, the scope of the present invention is inclusive of a mold apparatus that includes additional dies, e.g., third and/or fourth dies (not shown) that are each separately and reversibly movable towards and engageable with the rotatable core. Such additional dies may be configured in accordance with first die 11 and/or second die 17. For example, an additional die configured in accordance with first die 11 allows for the formation of a coated molded article that includes a multilayered plastic molded article (e.g., having layers of different thermoplastic and/or thermosetting materials). Alternatively, or in addition thereto, an additional die configured in accordance with second die 17 (i.e., having a reversibly slidable portion) allows for the formation of a coated molded article having a multi-layered coating (e.g., having a primer-coat layer and a top-coat layer).
The first, second and optional further dies may be positioned around the core at any degree (e.g., at 45°, 90° or 180°) relative to each other. First die 11 and second die 17 of mold apparatus 1 of the drawing figures are oriented in such a way as to be substantially opposed one from the other (i.e., oriented substantially 180° relative to each other). In addition, molding surfaces 32 and 35 of core 29 are substantially opposed to each other (i.e., oriented substantially 180° relative to each other).
When first die 11 is engaged with core 29, the interior surface 14 of first die 11 and one of the molding surfaces (e.g., molding surface 32) of core 29 together define a first mold cavity 38. The first mold cavity 38 has a volume, and is configured to define a plastic molded article that may be formed therein.
When second die 17 is engaged with core 29, the interior surface 20 (i.e., interior surface 26 of reversibly slidable portion 23) of second die 17 and one of the molding surfaces of core 29 (e.g., molding surface 35) together define a second mold cavity 41 having a volume. The molding surface of core 29 that defines the second mold cavity may be the same or different than the molding surface of the core that defines the first mold cavity. If the core has only one molding surface, then the first and second mold cavities would be defined by the same molding surface of the core. With mold apparatus 1 of the drawing figures, first mold cavity 38 is defined in part by molding surface 32 of core 29, and second mold cavity 41 is defined in part by molding surface 35 of core 29.
Alternatively, if core 29 is rotated through 180°, first mold cavity 38 would be defined in part by molding surface 35 of core 29, and second mold cavity 41 would be defined in part by molding surface 32 of core 29.
The volume of second mold cavity 41 is reversibly reduced by the movement of reversibly slidable portion 23 of second die 17 toward core 29. More particularly, as slidable portion 23 is moved towards core 29, internal surface 26 of slidable portion 23 (which substantially defines internal surface 20 of second die 17) moves closer to molding surface 35 of core 29. Still more particularly, and with reference to
The slidable portion 23 of second die 17 may be reversibly moved towards core 29 by means of art recognized methods. With reference to
The first die includes at least one first die port (or passage) that provides fluid communication with the first mold cavity. A first material (e.g., a thermoplastic or thermosetting plastic material) may be passed through the first die port into the first mold cavity. With reference to
The second die includes at least one second die port (or passage) that provides fluid communication with the second mold cavity (and also an intermediate second mold cavity as will be discussed further herein). A second material (e.g., a coating composition) may be introduced into the second mold cavity through the second die port. With reference to
The first and second dies may each independently and optionally include additional passages (not shown). Such additional passages may be used for the introduction of additional materials (e.g., co-reactants), or the same materials injected at different points, into the respective mold cavities. Additional passages may also be used to allow gasses (e.g., volatile blocking groups liberated from unblocked isocyanate groups) to escape from the respective mold cavities.
In an embodiment of the present invention, the reversibly slidable portion of the second die further includes at least one masking extension that extends beyond the internal surface of the reversibly slidable portion of the second die towards the core. The masking extension is configured to abut a portion of the first surface of an uncoated molded article residing within the second mold cavity (as will be discussed in further detail herein). The masking extension may be a stationary masking extension or a reversibly retractable masking extension. With reference to
The molding apparatus of the present invention may further include separate means (e.g., first and second means) for separately controlling the temperatures of the first and second mold cavities. With reference to
The first mold cavity 38 and the second mold cavity 41 (and correspondingly intermediate second mold cavity 53) may be maintained at different temperatures (including different rates of temperature increase and/or decrease) by means of the separate temperature controlling means 3 and 5. Such separate control of temperature is desirable when different temperatures are required for injection of plastic material into first mold cavity 38, and the introduction of a coating composition into (and optional curing thereof in) intermediate mold cavity 53, as will be discussed in further detail herein. The temperatures at which the first, second and intermediate second mold cavities are maintained may be selected from those related temperatures as discussed in further detail herein. For example, the first mold cavity may be maintained at a temperature of from 2° C. (35° F.) to 163° C. (325° F.), or more typically 16° C. (60° F.) to 93° C. (200° F.); while the second mold cavity and/or intermediate second mold cavity are maintained at a temperature of from 38° C. (100° F.) to 177° C. (350° F.), or more typically 66° C. (150° F.) to 149° C. (300° F.).
In the method of the present invention and with reference to
The molded article may optionally include at least one integrally formed plastic extension, which for example, facilitates handling of the molded article during further production steps. Such integrally formed plastic extensions may be later removed from the molded article (e.g., by cutting them off).
Molded article 44 of
The molding surface (e.g., 32) of core 29 and internal surface 14 of first die 11 that together define first mold cavity 38 may each independently include surface features (e.g., impressions and/or raised portions) (not shown) that serve to provide the uncoated plastic molded article formed therein with surface features and/or extensions (not shown). For example, imprinting surface roughness features (not shown) into the first surface 50 of molded plastic article 44 may improve the adhesion of the in-mold coating subsequently applied thereto. Forming molded plastic article 44 with extensions (not shown) on its second surface 47 may be desirable for purposes of attaching the molded article to another structure, e.g., the support structure of an automotive dash board.
The plastic material may be introduced into first mold cavity 38 under conditions of elevated pressure and in a metered amount by known means. For example, a piston (not shown) may be included between reservoir 92 and conduit 89, which serves to introduce a metered amount of plastic material into first mold cavity 38. The pressure at which the plastic material is introduced into first mold cavity will depend in part on the viscosity of the plastic material, e.g., a higher viscosity plastic material will typically require a higher injection pressure. In an embodiment of the present invention, a thermoplastic material (e.g., thermoplastic polycarbonate), is introduced into first mold cavity at an injection pressure of from 1000 psi to 50,000 psi, and more typically at a pressure of from 10,000 psi to 20,000 psi.
The thermoplastic material that is introduced into the first mold cavity, to form the uncoated molded article, may be selected from thermosetting plastic materials and/or thermoplastic materials. As used herein and in the claims, the term “thermosetting plastic material” and similar terms means plastic materials having a three dimensional crosslinked network resulting from the formation of covalent bonds between chemically reactive groups, e.g., active hydrogen groups and free isocyanate groups. In addition, as used herein and in the claims the term “thermosetting” is inclusive of thermal curing (e.g., curing at abient or elevated temperatures) and/or curing my means other than thermal, e.g., by means of actinic light.
Thermosetting plastic materials that may be introduced into the first mold cavity to form the uncoated molded article, include those known to the skilled artisan, e.g., crosslinked polyurethanes, crosslinked polyepoxides, crosslinked polyesters and crosslinked polycarbonates (e.g., formed from allyl functional carbonate monomers and oligomers). Of the thermosetting plastic materials, crosslinked polyurethanes are preferred. The uncoated molded article may be fabricated from crosslinked polyurethanes by the art-recognized process of reaction injection molding. In the present invention, reaction injection molding typically involves injecting separately, and preferably simultaneously, into the first mold cavity: (i) an active hydrogen functional component (e.g., a polyol and/or polyamine); and (ii) an isocyanate functional component (e.g., a diisocyanate such as toluene diisocyanate, and/or dimers and trimers of a diisocyanate such as toluene diisocyanate). Alternatively, the active hydrogen functional component and the isocyanate functional component may be injected into the first mold cavity together through a single injection port or head (e.g., a reaction injection mixing head), as is known to the skilled artisan. The filled first mold cavity may optionally be heated to ensure and/or hasten complete reaction of the injected reactive components.
As used herein and in the claims, the term “thermoplastic material” means a plastic material that has a softening or melting point, and is substantially free of a three dimensional crosslinked network resulting from the formation of covalent bonds between chemically reactive groups, e.g., active hydrogen groups and free isocyanate groups. Examples of thermoplastic materials that may be introduced into the first mold cavity to form the uncoated plastic molded article include, but are not limited to, thermoplastic polyurethane, thermoplastic polyurea, thermoplastic polyimide, thermoplastic polyamide, thermoplastic polyamideimide, thermoplastic polyester (e.g., polyethylene terephthalate and polybutylene terephthalate), thermoplastic polycarbonate, thermoplastic polysulfone, thermoplastic polyketone, thermoplastic polyalkylenes (e.g., thermoplastic polyethylene and thermoplastic polypropylene), thermoplastic acrylonitrile-butadiene-styrene and thermoplastic compositions containing one or more such recited thermoplastic materials.
Of the thermoplastic materials that may be introduced into the first mold cavity, thermoplastic polycarbonates are preferred. The uncoated plastic molded article (e.g., article 44) may be fabricated from thermoplastic materials by the art-recognized process of injection molding, in which a molten stream of thermoplastic material (e.g., molten thermoplastic polycarbonate) is injected into the first mold cavity, which may be optionally heated. A preferred thermoplastic material that may be introduced into the first mold cavity to form the uncoated molded article is thermoplastic polycarbonate, e.g., MAKROLON thermoplastic polycarbonate, commercially available from Bayer MaterialScience LLC.
The thermosetting plastic materials and/or thermoplastic materials that may be introduced into the first mold cavity, may optionally be reinforced with a material selected from glass fibers, glass beads, carbon fibers, nano-tubular carbon fibers, boron fibers, metal fibers and combinations thereof. The reinforcing fibers, and the glass fibers in particular, may have sizings on their surfaces to improve miscibility and/or adhesion to the plastics into which they are incorporated, as is known to the skilled artisan. Glass fibers are a preferred reinforcing material in the present invention. If used, the reinforcement material (e.g., glass fibers) is typically present in the thermosetting plastic materials and/or thermoplastic materials that are introduced into the first mold cavity in a reinforcing amount (e.g., in an amount of from 5 percent by weight to 60 percent by weight, based on the total weight of the uncoated molded plastic article).
The plastic material introduced into the first mold cavity to form the uncoated molded article may further contain one or more functional additives other than or in addition to the reinforcing materials. Additives that may be present in the plastic material from which the uncoated molded article is formed include, but are not limited to, antioxidants, colorants, e.g., pigments and/or dyes, mold release agents, fillers (e.g., calcium carbonate and barium sulfate), ultraviolet light absorbers, fire retardants and mixtures thereof. Additives may be present in the plastic material from which the uncoated molded article is formed in functionally sufficient amounts, e.g., in amounts independently from 0.1 percent by weight to 10 percent by weight, based on the total weight of the plastic material.
With reference to
With reference to
In the next step, second die 17 is engaged with core 29. With reference to
When second die 17 is engaged with core 29 so as to form intermediate second mold cavity 53, first die 11 may optionally also be engaged with core 29 to reestablish first mold cavity 38. In
A coating composition is next introduced into intermediate second mold cavity 53 from second reservoir 101 through conduit 98 and second die port 95. Typically, the coating composition is introduced into intermediate second mold cavity 53 in an amount such that intermediate second mold cavity 53 is less than totally filed therewith, as represented in
More particularly, coating composition 56 is introduced into intermediate mold cavity 53 through second die port 95 and initially strikes a facing surface of tab 116. The coating formed on tab 116 typically includes surface defects (e.g., commonly referred to as injection coating defects) (not shown). When tab 116 is later removed from coated molded article 59 (
The coating composition introduced into the second mold cavity in the method of the present invention may be selected from thermoplastic and/or thermosetting coating compositions. Thermoplastic coating compositions may include one or more of those thermoplastic polymers recited previously herein with regard to the thermoplastic material introduced into the first mold cavity (e.g., thermoplastic polyurethane and/or thermoplastic polycarbonate).
Preferably, the coating composition introduced into the second mold cavity is a thermosetting (or curable) coating composition that is capable of at least being partially cured (polymerized or cross-linked) therein. The thermosetting or curable coating composition may be selected from one-component compositions or two-component coating compositions that are known to the skilled artisan. One-component coating compositions include, for example, reactants having blocked isocyanate groups and reactants having active hydrogen groups. Two-component coating compositions include, for example: reactants having unblocked (or freely reactive) groups, such as free isocyanate groups and oxirane groups; and reactants having active hydrogen groups, such as hydroxyl, thiol, primary and secondary amines, or carboxylic acid groups. The reactants/components of a two-component coating composition are typically mixed together prior to injection into the mold, or are injected separately into the mold in such a way as to result in mixing upon injection. The coating compositions may include resins having backbones selected from, for example, polyethers (or polyepoxides), polyesters, polycarbonates, polyurethanes, poly(meth)acrylates and combinations thereof. Coating compositions that may be used in the method of the present invention include, but are not limited to, those described in U.S. Pat. Nos. 4,081,578, 4,293,659, 4,331,735, 4,366,109 and 4,668,460, the pertinent disclosures of which are incorporated by reference herein.
In an embodiment of the present invention, the coating composition introduced into the second mold cavity includes monomers and/or oligomers having terminal and/or pendent ethylenically unsaturated groups that are cured by free radical polymerization initiated by, for example, heat activated peroxide initiators or ultraviolet light. More particularly, the coating compositions typically include urethane components having terminal and/or pendent acrylate groups. In an embodiment of the present invention, the coating composition includes: the reaction product of a multi-functional isocyanate (e.g., toluene diisocyanate, methylene di-phenyl isocyanate, isophorone diisocyanate or condensates thereof) and a hydroxyl functional acrylate (e.g., 2-ethylhydroxy acrylate); a radical polymerization initiator (e.g., di-tertiary butyl peroxide); and optionally other multi-functional ethylenically unsaturated components (e.g., mono- and poly-alkyleneglycol diacrylates, such as diethylene glycol diacrylate). The coating composition may also include the reaction product of an epoxide (oxirane) functional material (e.g., the reaction product of trimethylol propane and epichlorohydrin) and a hydroxyl functional acrylate (e.g., 2-ethylhydroxy acrylate).
Thermosetting coatings introduced into the second mold cavity are at least partially cured, and are preferably substantially fully cured within the mold before removal of the coated molded plastic article there from. If cured by the application of actinic light (e.g., ultraviolet light), the second die typically must be fitted with a window to allow the introduction of such actinic light therein. If cured by means of free radical polymerization, the application of heat is typically required to activate the radical polymerization initiator. While two-component coating compositions do not necessarily require elevated temperatures to achieve cure, the application of heat is typically employed to accelerate the cure process. In general, with thermosetting coating compositions: cure times of 10 seconds to 60 minutes, typically 10 seconds to 2 minutes, and more typically 30 seconds to 30 minutes; and cure temperatures of 38° C. (100° F.) to 177° C. (350° F.) or 66° C. (150° F.) to 149° C. (300° F.), are employed.
The coating composition that is introduced into the second mold cavity may include additives. Classes of additives that may be included in the coating composition include, but are not limited to: static colorant pigments (e.g., inorganic and/or organic pigments); conductive pigments (e.g., conductive carbon blacks, carbon fibers and metallic pigments); photochromic materials; fillers (e.g., clays and talcs); ultraviolet light absorbers; thermal stabilizers; flow control agents; thickeners; and combinations thereof. The amount of additives included in the coating composition may vary widely. Typically, the coating composition contains from 0.1 to 50 percent by weight, more typically 0.1 to 20 percent by weight of additives, based on the total weight of the coating composition.
Static colorant pigments (e.g., TiO2) do not appreciably change color upon exposure to ultraviolet (UV) light. Photochromic materials or substances (e.g., photochromic dyes and/or pigments) reversibly change color upon exposure to UV light, as is known to the skilled artisan. Examples of photochromic substances that may be included in the coating composition include art-recognized inorganic and organic photochromic substances. Examples of organic photochromic substances that may be used include, but are not limited to, spiro(indoline)naphth-oxazines, spiro(indoline)benzoxazines, chromenes (such as benzopyrans and naphthopyrans), organo-metal dithizonates (e.g., mercury dithizonates), fulgides (e.g., 3-furyl and 3-thienyl fulgides), fulgimides (e.g., 3-furyl and 3-thienyl fulgimides) and combinations thereof. The use of photochromic substances in the coating composition results in a coated molded article having photochromic properties, such as photochromic ophthalmic lenses, photochromic sun lenses and photochromic glazings (e.g., automotive and architectural windows).
The coating composition is introduced into the intermediate second mold cavity (or between the internal surface of the second die and the second surface of the uncoated molded plastic article) in an amount at least sufficient such that the coated molded plastic article has a coating thickness that provides a desired level of properties (e.g., smoothness, weatherability, scratch resistance and/or photochromaticity). Generally, the coating composition is introduced into the intermediate second mold cavity (or between the internal surface of the second die and the first surface of the uncoated molded plastic article) in an amount such that the coated molded plastic article has a coating thickness of 0.1 to 50 mils (2.54 to 1270 μm), typically from 0.5 to 20 mils (12.7 to 508 μm), and more typically from 0.5 to 3 mils (12.7 to 76.2 μm).
A portion of the first surface of the uncoated molded article may be masked prior to coating of the molded article within the mold apparatus (e.g., before introduction of the coating composition into intermediate second mold cavity 53). Masking a portion of first surface 50 of molded article 44 may be achieved by means that are known to the skilled artisan (e.g., contact masking means, such as masking tapes). For example, when the mold apparatus is opened, core 29 may be rotated to an intermediate position (not shown) to allow for the application of a mask to first surface 50 of molded article 44. Alternatively, slidable portion 23 of second die 17 may include a masking extension (e.g., reversibly retractable masking extension 119) as discussed previously herein with reference to
With reference to
After introduction of the coating composition into intermediate second mold cavity 53, slidable portion 23 of second die 17 is moved towards core 29, and the volume of intermediate second mold cavity 53 is reduced. The reduction in the volume of intermediate second mold cavity 53 results in the coating composition introduced therein to spread over at least a portion of, and preferably over the whole of, first surface 50 of uncoated molded article 44. See
Slidable portion 23 is moved towards core 29 in such a way as to subject the introduced coating 56 to a pressure that is at least sufficient to result in spreading of coating 56 over first surface 50 of molded article 44. In moving slidable portion 23 towards core 29, the introduced coating 56 may be subjected to a pressure of from 5 psi to 30,000 psi, typically from 100 psi to 10,000 psi, and more typically from 1000 psi to 7000 psi.
When slidable portion 23 of second die 17 is moved towards core 29 to spread the introduced coating composition 56 over first surface 50 of molded article 44, second die port 95 is typically plugged or otherwise occluded (not shown). Plugging of second die port 95 prevents the coating composition 56 from being pushed back up through conduit 98 into second reservoir 101 by the movement of slidable portion 23 towards core 29. Effective plugging of second die port 95 may be achieved by a piston (not shown) in conduit 98 or second reservoir 101.
In an embodiment of the present invention, the uncoated molded article includes a molded-in seal. A surface of the slidable portion of the second die abuts the molded-in seal of the uncoated molded article. The abutting relationship between the molded-in seal and the surface of the slidable portion serves to substantially seal the intermediate second mold cavity, thus preventing a coating composition introduced therein from escaping from the cavity and coating unwanted portions of, for example, the molded article, the core and/or the second die. As used herein and in the claims with regard to the molded article, the term “molded-in” means a feature, such as a seal, that has been formed concurrently with the mold formation of the molded article. As such, the molded-in seal comprises plastic material, and is substantially integral and continuous with the plastic material of the molded article. In an embodiment of the present invention, the molded-in seal comprises the same plastic material as that of the uncoated molded article. Alternatively, the molded-in seal may be comprise a different plastic material from that of the uncoated molded article, and may be formed in mold cavity separate from that of the first mold cavity (not shown).
With reference to
After slidable portion 23 of second die 17 has been moved towards core 29 causing the coating 56 to spread over at least a portion of first surface 50 of uncoated molded plastic article 44, the coating is at least partially cured (if it is a thermosetting coating composition). After a period of time that is at least sufficient to spread and/or cure the coating composition, at least second die 17 is disengaged from core 29, and the coated molded plastic article 59 is removed from core 29, e.g., as depicted in
After formation of the coated molded article and disengagement of the second die from core, the slidable portion of the second die may optionally be moved to an initial position. For example, with reference to
Prior to removal of coated molded article 59, core 29 may be rotated to an intermediate position between first die 11 and second die 17. For example, with general reference to
In an embodiment of the present invention, the molding surface defining the first mold cavity and the surface defining the second mold cavity are different/separate molding surfaces of the core. As such, the first mold cavity may be formed concurrently with the intermediate second mold cavity, which allows for the concurrent performance of in-mold coating and molded article formation steps (e.g., the concurrent performance of method steps B and F with steps C and G as recited previously herein). More particularly, and with reference to
With reference to
In an embodiment of the present invention, the intermediate second mold cavity is not formed prior to the introduction of the coating composition, but rather is formed upon introduction of the coating composition into the mold. When the second die (e.g., 17) is engaged with the core (e.g., 29), the second surface of the plastic molded article (e.g., first surface 50) may substantially abut the internal surface (e.g., 20) of the second die. Alternatively, the internal surface of the second die and the second surface of uncoated molded article may together define an initial second mold cavity having a volume. The volume of the initial second mold cavity is typically less than the volume of the second mold cavity.
As the coating composition is introduced between the internal surface of the second die and the second surface of the molded article, the internal surface of the second die (i.e., the internal surface of the slidable portion) is concurrently separated from the second surface of the uncoated molded article thus forming the intermediate second mold cavity. The slidable portion of the second die may be held (or maintained) at a pressure (a positive or neutral pressure) that is lower than the positive pressure at which the coating composition is introduced between the internal surface of the second die and the second surface of the molded article. The greater positive pressure of the introduced coating composition accordingly causes the slidable portion and its internal surface to move away from the second surface of the uncoated molded article (and the core) and to form the intermediate second mold cavity. The volume of the resulting intermediate second mold cavity is greater than the volume of the initial second mold cavity. The positive pressure under which the coating composition is introduced between the internal surface of the second die and the second surface of the uncoated molded article is generally from 5 psi to 30,000 psi, typically from 100 psi to 10,000 psi, and more typically from 1000 psi to 7000 psi. After introduction of the coating composition is complete, the slidable portion of the second die is moved back towards the core, the volume of the intermediate second mold cavity is reduced and the introduced coating is spread over the second surface of the uncoated molded article, as described previously herein.
Alternatively, as the coating composition is introduced between the internal surface of the second die and the second surface of the molded article (which are in either abutting relationship or together defining the initial second mold cavity), the slidable portion of the second die may itself be concurrently moved away from the core by means other than the pressure of the introduced coating composition. For example, concurrent with the introduction of the coating composition, the slidable portion of the second die may be pulled away from the core by a reversible drive arm (e.g., drive arm 74). The slidable portion of the second die may be pulled away from the core (and the second surface of the molded article) at a rate that is at least commensurate with the rate at which the coating composition is introduced between the interior surface of the second die and the second surface of the molded article.
The method of the present invention may be used to prepare numerous types of coated molded plastic articles. Classes of coated molded articles that may be prepared by the method of the present invention include, but are not limited to, lenses, ophthalmic lenses, sunshade lenses, glazings, interior (passenger compartment) motor vehicle components (e.g., interior panels and dash board components), exterior motor vehicle components (e.g., exterior panels), motor vehicle engine-compartment components (e.g., filter housings and fuel injection housings), architectural panels (e.g., office walls and cubicle dividers) and housings for electronic devices (e.g., business/office machines, computer housings, portable phones and pagers). Coated lenses that may be prepared according to the present invention include, for example, lenses for lights such as motor vehicle head lamps, break lights, turn signal lights and landing lights on aircraft. Coated glazings that may be prepared according to the present invention include, for example, architectural windows, motor vehicle windows and aircraft windows.
As described previously herein, the coating composition may include a photochromic material, in which case the coated molded article prepared by the method of the present invention is a photochromic coated molded article. Photochromic molded articles that may be prepared by the present method include, but are not limited to photochromic ophthalmic lenses, photochromic sun shade lenses (i.e., non-corrective photochromic sunglasses or spectacles), and photochromic glazings, such as photochromic architectural windows, photochromic motor vehicle windows and photochromic aircraft windows. Photochromic coated molded articles prepared in accordance with the present method may have an underlying molded article fabricated from thermoplastic polycarbonate.
The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention except insofar as and to the extent that they are include in the accompanying claims.
