Patent Application
20080118686
This invention relates to a blow molded thermoplastic article and a process for making the article. More particularly, the invention relates to an injection blow molded article that has at least two thermoplastic layers of materials that are different and a process for making the article.
Hollow thermoplastic articles, such as containers, bottles, vials, etc., are typically produced by injection blow molding processes. A conventional injection blow molding process usually includes three main stages of processing, namely, injection molding, blow molding, and ejection. Generally in the first stage, a molten polymer parison is injected onto a core pin that is placed between a top and a bottom injection mold during the first stage to produce a preform. Then in the second stage, the preform is placed between a top and bottom blow mold and gas is injected into the preform through the core pin to produce a hollowed thermoplastic article. Finally, the hollow thermoplastic article is ejected from the core pin.
Hollow thermoplastic articles made via the injection blow molding process have the same material composition at the internal and external surfaces of the article. When a molten polymer is injected through a nozzle into the cavity of the injection mold, material sets up on the inside surfaces of the mold cavity and also on the surface of the core pin which is disposed between the upper and lower mold cavities. The polymer surrounding the core pin eventually becomes the inner layer of the hollow article, and the layer of polymer surrounding the mold cavity surfaces, eventually becomes the outer layer of the hollow article.
Co-injection blow molding processes which employ two or more materials in the injection stage of the process are also well known. For example, two different materials can be melted in separate injection barrels and flow through separate runner systems to the mold. Hollow thermoplastic articles used in the packaging industry benefit greatly by the co-injection process. For example, bottles made for beverage have two or more layers of materials, at least one of which is a gas barrier layer sandwiched between two or more layers having material compositions different than the barrier layer. However, the co-injection process also results in hollow thermoplastic articles that have the same material composition at the internal surface and external surfaces of the article when the injection blow molding process is complete. When a second molten polymer is injected, it flows between the layers formed by the first polymer around the core pin and the mold cavities, and the second polymer becomes a middle layer.
The material properties of the internal and external surfaces of hollow thermoplastic articles, also known as “surface technology” has become increasingly important in several industries. For example, in the healthcare industry, it is often desirable that the internal surface of containers that carry fluids such as, aqueous fluids of pharmaceuticals, or bodily fluids, possess characteristic that are different than the external surface of the container. More specifically, materials which exhibit hydrophobic behavior can prevent water in aqueous solutions from wetting or adhering to the inside surface of the container, thereby ensuring that the concentration of a pharmaceutical dosage maintains consistent. Materials which exhibit hydrophilic behavior can prevent adhesion of proteins to the inside surface of the container. In another example, materials that are hemo-compatible can help prevent platelets of blood from adhering to the surface of the container. Alternatively, a chemically resistant material can be chosen as the interior surface of the container. The material can be specifically chosen to either bind or resist a specific chemical of interest.
In other applications, surface technology can play an important role in aesthetics, for example, where two or more colors are used throughout the part. Therefore, it is desirable to produce a hollow thermoplastic article that has internal and external layers of different material compositions, while utilizing the productivity advantages offered by the injection blow molding process.
The present invention provides for an injection blow molding process for producing a hollow thermoplastic article having at least two layers, an inner layer and an outer layer, each having a material composition that is different.
In one embodiment of the invention, the process for making a hollow thermoplastic article including the steps of placing a sock preform of a first polymer composition about a core pin, injection molding a molten parison of a second polymer composition which is different than the first polymer composition about the sock preform to produce an injection preform having two different material compositions, and blow molding the injection preform to produce a hollow thermoplastic article having an interior surface of the first polymer composition and an exterior surface of the second polymer composition. In another embodiment, the process further includes ejecting the hollow thermoplastic article from the core pin after the blow-molding step.
In another embodiment, the invention provides for a process for making a plurality of hollow thermoplastic articles where at least a portion of each step is carried out simultaneously. A plurality of hollow thermoplastic articles are made by placing a sock preform of a first material composition onto a first core pin, and also injection molding a molten parison of a second material composition onto a second core sock of the first material composition, where the second core sock is supported by a second core pin. The process also includes blow molding an injection preform including an inner layer of the first material composition and an outer layer of a second material composition where the injection perform is supported by a third core pin.
The various embodiments of the present invention can be understood with reference of the following drawings. The components are not necessarily to scale. Also, in the drawings, like reference numerals designate corresponding parts throughout the several views.
The present invention is more particularly described in the following description and examples that are intended to be illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” All ranges disclosed herein are inclusive of the endpoints and are independently combinable. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and/or values.
As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
The term “plurality” as used herein refers to a quantity of two or more.
The term “multi-layer” as used herein refers to at least two layers.
The term “different composition” as used herein refers to the different material or polymer compositions. Two material or polymer compositions can be different if their molecular structures are different, their additives are different, or both, where additives include, but are not limited to, fillers, colorants, components which enhance processing and properties, for example.
Injection blow molding apparatus 100 also includes upper and lower injection molds 140 and 142 disposed above and beneath the second set of core pins, and an injection barrel 144 that feeds molten polymer resin to the injection molds in a step of producing the hollow thermoplastic article, as will be further described. The injection molds receive core pins, for example core pins 120, 122, 124 and 126, respectively, which are disposed between a pair of vertically movable mold clamping plates 146 and 148 adjacent the core supporting wall. Upper and lower injection molds 140 and 142 have a plurality of mold cavities, 150, 152, 154, 156 which shape the injection preforms 121, 123, 125 and 127 during the injection molding stage.
Injection blow molding apparatus 100 also includes upper and lower blow molds 160 and 162 that are attached to clamping plates 164 and 166 along side of the third supporting wall 108. The blow molds receive core pins, for example core pins 130, 132, 134 and 136, respectively, that are disposed between a pair of vertically movable mold clamping plates 164 and 166 adjacent the core supporting wall 108. Upper and lower injection molds 140 and 142 have a plurality of mold cavities, 167, 168, 169, 170 which shape the hollow thermoplastic articles 131, 133, 135, and 137 as they are blow molded to a final product.
Hydraulic cylinders (not shown) can be used for opening and closing injection molds 140, 142 and blow molds 160, 162. A driving motor (not shown) can be used for rotating the turntable 102. The support walls 104, 106, 108, and core pins that extend therefrom, reside at each station for the same period of time. The hollow thermoplastic articles 172, 174, 176 and 178, are the result of the process of a previous cycle in a continuous injection blow molding process.
At the appropriate time, turntable 102 is then rotated counter-clockwise again for approximately 120 degrees, about shaft 109 to advance the core supporting walls 104, 106, 108. Wall 104 is advanced to the adjacent third station in the position shown by that of supporting wall 108 of
Therefore, in a continuous process, at least a portion of each of the steps of loading, injection molding, and blow molding is carried out simultaneously. At the first station a sock preform 111 of a first material is loaded onto a first core pin 110, at the second station a molten parison of a second material composition is injection molded onto a second core sock to produce an injection perform 121 supported by a second core pin 120, and at a third station an injection perform having an inner layer of the first material composition and an outer layer of the second material composition is blow molded to produce a hollow thermoplastic article 137 supported by a third ore pin 136.
Still referring to
It is not necessary, however, that the hollow thermoplastic articles be ejected at the first station where sock preforms are loaded, and thus, in another embodiment, the hollow thermoplastic articles, for example blow molded articles 131, 133, 135 and 137 can be ejected at the third, blow molding station. In such case, after blow molding is completed, the mold plates 164 and 166 are retreated and the cores are drawn out from the blow molds 160, 162 and the hollow products, can be ejected from the core pins.
In an example of a continuous injection blow molding process, the first core pin 110 after receiving the sock perform 111 including a first material composition can be moved from the first station to a position previously occupied by core pin 120 at the second station; and core pin 120, after a second material composition is injection molded onto the sock perform to produce and injection preform, moves to a station previously occupied by core pin 130 at the third station; and core pin 130 after the blow molding step is complete moves to a position at the first station occupied by core pin 110.
In the load stage, injection molding stage, and blow molding stage described above, one is generally labeled a “stage-limiting step” of the continuous process. The stage-limiting step of the process is the step that requires the most time to complete at the various stations. In a continuous injection blow molding process to produce a hollow articles having a single layer, the steps can include, for example, 1) injecting the molten polymer about the core pin to form a perform at a first station, 2) blow molding the perform to produce the hollow article at a second station, and 3) ejecting the hollow article from the core pin at a third station, the injection molding step is often the stage-limiting step, due to the time needed to cool the injection performs prior to blow molding. Also, in many continuous processes, the ejection stage of the process is the shortest. Therefore, in the process of the present invention described above with respect to
The hollow thermoplastic articles produced, for example article 131, can have more than two layers. That is, each of the inner and outer layers 410, 420, or both, can be multi-layered. For example, sock preform which makes up the inner layer 304 of injection preform can be multi-layered and the outer layer of injection preform can be multi-layered. The outer layer can be multi-layered produced via co-injection molding at the injection molding station. For example, two different materials can be melted in separate injection barrels and flow through separate runner systems to the mold. The polymer first injected sets up on the inside surfaces of the mold cavity and also on the surface of the sock preform disposed between the upper and lower mold cavity. When a second molten polymer is injected, it flows between the layer of the first molten polymer surrounding the sock preform and eventually becomes a middle layer of the hollow article, and the second molten polymer surrounding the mold cavity surfaces, becomes the outer layer of the injection preform, and ultimately, the outer layer of hollow article formed during blow molding. The compositions of two or more of the multiple layers can be the same, so long as the material compositions of interior surface and exterior surface of injection preform that ultimately become the interior and exterior surfaces of the hollow article are different compositions.
The processes described above can further include forming the sock preform prior to loading the sock preform on the core pins, for example sock preform 111 of
As stated above, the sock preform can have two or more layers of different material compositions made from a multi-layer sheet or film used during forming. An additional layer in the sheet or film can serve as a tie layer that provides for better adhesion of the molten polymer that is injected onto the sock preform during the injection state. In some cases, the inner layer and the outer layer materials are not compatible at the interface surface and therefore do not adhere well to one another. In such case, a tie layer may be added which is compatible with both the inner and outer layers. In this manner, one of the layers of the sheet or film used to make the sock preform is a material composition having a surface that will be placed into contact with the core pin 111 at the first station of the injection molding apparatus 100 as described above.
Additional layers of the sheet or film can provide additional physical or aesthetic properties, including those of a tie-layer, which are not necessarily required at the internal and external surfaces of the hollow thermoplastic article ultimately produced, and therefore surface management of the internal and external surfaces of the resulting hollow article, a bottle, a container, etc., can be achieved. Bottle 131 appears in
Aesthetic features of the hollow article can also be achieved. For example, the inner and outer layers, as well as any middle layers, may be of a different color. Referring to
Any combinations of materials may be used for the inner layer and outer layer materials as far as they behave like a thermoplastic in undergoing blow molding. Material compositions can include, but are not limited to, polyesters, polycarbonates, polycarbonate-based copolymers; polyesters, such as, for example, amorphous polyester terephthalate (APET), poly(ethylene terephthalate) (PET), poly(propylene terephthalate), poly(butylenes terephthalate) (PBT), poly(clyclohexane dimethanol cyclohexane dicarboxylate), and glycol-modified polyethylene terepthalate (PETG); polyvinylchloride (PVC); polysulfones, including polyethersulfone (PES), and polyphenylsulfone (PPSU); poly(vinyl acetate); polyarylates; polyetherimide (PEI); polyimide; polyamide; polyestercarbonates; polyetherketone; polyolefins, for example, polypropylene, and polyethylene; and polyurethanes. The thicknesses of the inner and outer layers 410, 420 can vary depending upon the desired characteristics of the hollow article. For example, the type of process and material used in forming the sock preform will often dictate the thickness of the inner layer. For example, a thermoformed, sock preform may have a thinner wall thickness than an injection-molded sock preform. Very thin films may be used as the sock preform and both the inner and outer walls 302, 304 of preform 126, for example, will typically shrink in thickness during the blow molding stage. Thus the thickness of inner layer 410 of a completed hollow article 131, can range from 0.1 millimeters to 10 millimeters, in alternative embodiment, from 0.5 millimeter to 1.5 millimeter, and in yet another embodiment from 0.8 millimeters to 1.2 millimeters. Likewise, thin wall thicknesses for the outer layer 304 can be produced by injecting molding molten polymer around the inner layer of sock perform to produce an injection preform. The inner layer 410 (
In another embodiment, additional stations of the injection molding apparatus 100 can present to allow for additional processing steps. For example, the injection molded preform can advance to a conditioning station before advancing to the blow molding station. In such case the injection molded preform is allowed to cool and is then re-heated prior to blow molding. The conditioning stage can allow for a more even temperature distribution of the injection-molded preform before blow molding. Conditioning steps are optional and can depend upon a variety of factors, for example, the geometry of the part, the wall thicknesses and the thermoplastic materials used, as will be appreciated by those of ordinary skill in the art.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
