Method of having a plastic container having deep grip recesses

A method of molding a plastic container body having at least one grip recess includes providing a mold assembly having an internal projection that is constructed and arranged to form the grip recess. A low friction surface is provided on at least a portion of the projection in order to reduce friction between the formable plastic material and the projection during the molding process. The low friction surface permits the formable plastic material to stretch with less resistance before it solidifies to the point where additional stretching is not possible. As a result, molding of features that provide resistance to material distribution during molding, such as deep grip recesses, is enabled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of plastic container manufacturing and tooling, and more specifically to processes and mold assemblies for making a plastic container having a deeper grip recess than was conventionally possible.

2. Description of the Related Technology

Plastic containers are typically fabricated using either injection molding or one of two types of blow molding. The blow molding process is characterized by using internal pressure to force a hot, soft plastic preform or parison against a molding surface. Blow molding can be performed using either a reheat stretch blow molding process, which is typical for plastic containers that are fabricated from polyethylene terephthalate (PET), or an extrusion blow molding process, which is typical for containers that are fabricated from such materials as high-density polyethylene and polyolefins.

In the extrusion blow molding process, a molten tube or parison is continuously extruded from an extrusion fixture. A mold assembly that moves at a speed that is substantially equal to the speed of the extruded parison periodically captures portions of the parison, and pressurization is applied to inflate the captured portion of the parison against the interior surfaces of the mold assembly. The mold assembly is typically mounted for motion on either a molding wheel, which moves in a circular path, or on a shuttle, which moves the mold assembly on a substantially straight path.

In either type of blow molding process, the hot formable plastic material begins to cool and harden as soon as it contacts the mold surface. However, to the extent that the shape defined by the internal surfaces of the mold deviates from a cylinder that is equidistant from the longitudinal axis of the parison or preform the formable plastic material will contact some portions of the internal mold surface before others. In cases where the container body is designed to have deep recesses such as grip recesses for receiving a consumers fingers, prominent projections are formed within the mold that the formable plastic material must contact and stretch around in order to reach the portions of mold surface that form the outermost portions of the container sidewall. The friction that is created between the expanding tube of hot, formable plastic material and such internal mold projections has created practical design limitations that have prevented container manufacturers from introducing designs that would otherwise be favorably received by the public.

A need exists for a method of manufacturing a plastic container that permits the formation of a container having features that are deeper and a result of greater stretching of the hot formable plastic material that has been conventionally possible. Moreover, a need exists for a mold assembly that permits container features that are deeper and more extreme than were previously conventionally possible to be molded.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the invention to provide a method of manufacturing a plastic container that permits the formation of a container having features that are deeper and a result of greater stretching of the hot formable plastic material than has been conventionally possible.

It is a second object of the invention to provide a mold assembly that permits container features to be molded that are deeper and more extreme than were previously conventionally possible.

In order to achieve the above and other objects on the invention, a method of making a plastic container having a container body with a grip recess defined therein according to a first aspect of the invention includes providing a mold assembly that defines an internal mold surface. The internal mold surface has a first surface portion that has a first frictional coefficient. The internal mold surface further has a projection that is constructed and arranged to form a grip recess. At least a portion of the projection defines a low friction second surface portion that has a second frictional coefficient that is less than the first frictional coefficient. Formable plastic material is applied against the internal mold surface to form a container body having at least one grip recess. The container body is then removed from the mold.

A mold assembly for forming a plastic container according to a second aspect of the invention includes structure defining an internal mold surface. The internal mold service has a first surface portion that has a first frictional coefficient; and a projection that is constructed and arranged to form a grip recess. At least a portion of the projection defines a low friction second surface portion that has a second frictional coefficient that is less than the first frictional coefficient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular toFIG. 1, a plastic container10includes a finish portion12defining an opening that is in communication with an interior of the container10. Finish portion12preferably has one or more helical threads14defined thereon for receiving a closure.

In the preferred embodiment, plastic container10is fabricated from a material such as polyethylene terephthalate using a standard reheat blow molding process. Alternatively, container10could be fabricated using extrusion blow molding process from a material such as polypropylene, polyethylene or polyolefin.

Plastic container10further preferably includes a neck portion16, a shoulder portion18, a main body portion20and a bottom portion22. In the illustrated embodiment, plastic container10is fabricated as a substantially transparent bottle for packaging a beverage such as liquor.

The main body portion20has an outer surface24that is preferably shaped so as to be substantially cylindrical or substantially round when viewed in transverse cross-section, with the exception of a pair of grip recesses26that are defined therein. The bottom portion22preferably defines the maximum outer diameter of the container10and is preferably substantially round when viewed in transverse cross-section.

Each of the grip recesses26preferably includes a first surface28that extends inwardly from the outer surface24of the main body portion20. Each grip recess26further preferably includes a second surface30that extends inwardly from a more forward location on the outer surface24. A concave recess bottom surface27connects the radially inwardmost portions of the first and second surfaces28,30.

A plurality of ribs32are also preferably defined within the grip recess26for providing additional strength. In the preferred embodiment, each of the ribs32is oriented substantially transversely and extends over a portion of the first surface28, the bottom surface27and the second surface30. In the illustrated embodiment, three ribs32are provided. The ribs32also provide contour to the grip recesses26that conforms with the spaces between a consumers fingers, which creates a feeling of firmness and security in the grip.

Referring now toFIGS. 2-4, a mold assembly40according to the preferred embodiment of the invention includes a mold body42defining an internal mold surface44that is configured to be substantially complementary to the outer surfaces of the desired container shape shown inFIG. 1. The mold assembly has a longitudinal axis51that corresponds to the longitudinal axis of the container10shown inFIG. 1.

The internal mold surface44includes a projection46that is adapted to form one of the grip recesses26shown inFIG. 1. Referring briefly toFIG. 5, which is a transverse cross-section taken along lines5-5inFIG. 2, it will be seen that the projection46includes an apex48, a first side surface50that defines a first angle A1with respect to a first radius extending from the longitudinal axis51and a second side surface52that defines a second angle A2to with respect to a second radius extending from the longitudinal axis51.

In the preferred embodiment, the second angle A2is greater than the first angle A1. Ergonomically, the longer, more oblique second surface30of the grip recess26that is formed by the second surface52provides a stable surface for the consumers fingers to rest and pinch against while gripping the container10. The more radial orientation of the first side surface50, which is not expected to be contacted by a consumer's finger, permits the area of the ground outer surface24of the container10to be maximized. Geometrically, the radial orientation of the first side surface50permits the second side surface52and the apex48to extend for a greater distance in a rightward direction or “deeper” as viewed inFIG. 5, which enhances the stability of the grip.

The relative deepness of the grip and the near radial orientation of the first side surface50is enabled by reducing the frictional engagement between the formable plastic material in the projection46during the molding process, which permits the plastic material to more adequately distribute itself to the portion62that forms the outer surface24of the main body20of the container10. In particular, the frictional reduction permits the material to adequately reach the corner60at the base of the projection46on the side of the first surface50shown inFIG. 5.

In the preferred embodiment, the internal mold surface44and specifically the projection46defines a first surface portion54that has a first frictional coefficient C1with respect to like material. Another portion of the projection46defines a low friction second surface portion56that has a second frictional coefficient C2with respect to like material that is less than the first frictional coefficient C1. The second frictional coefficient C2has static and kinetic values that are both less than the respective static and kinetic values of the first frictional coefficient C1.

The low friction surface portion56in the preferred embodiment includes at least a portion of the apex46, and preferably at least a portion of the first side surface50of the projection46. In the preferred embodiment, the low friction surface portion56includes a coating that is applied to the underlying mold surface by a process such as spraying. Preferably, the coating is a low friction material such as a fluoropolymer. One such coating is commercially available from IMPREGLON under the TEMPCOAT™ brand as code Black966. It is a fluoropolymer coating having a first bonding layer, an intermediate enforcing layer and an upper layer of fluoropolymer material.

Preferably, the second frictional coefficient C2has a static frictional coefficient value at 1000 grams of load that is substantially within a range of about 0.04 to about 0.5, more preferably substantially within a range of about 0.06 to about 0.25 and most preferably substantially within a range of about 0.08 to about 0.15. The second frictional coefficient C2further preferably has a kinetic frictional coefficient value at 1000 grams of load that is substantially within a range of about 0.03 to about 0.45, more preferably substantially within a range of about 0.05 to about 0.23 and most preferably substantially within a range of about 0.07 to about 0.14.

The provision of the second surface portion56speeds the flow of formable plastic material over the apex48, so that it can reach the outer mold surfaces60,62prior to hardening.

In an alternative embodiment, the coating could also have insulative properties, which would maintain a higher temperature at the surface that contacts the formable plastic material during molding. This would also tend to extend the timeframe of flexibility of the plastic material as it progresses to the outer mold surfaces60,62.

It is anticipated that the low friction surface portion56would periodically be inspected for wear or degradation and maintain by replacement or repair as needed to maintain the efficacy of the mold assembly.