WO2013071218A1

WO2013071218A1 - Thin-walled injection molded container

Info

Publication number: WO2013071218A1
Application number: PCT/US2012/064601
Authority: WO
Inventors: Paul William HAVENS; Christopher NAVRATIL; Kirk D. MORROW
Original assignee: Alltrista Plastics, Llc
Priority date: 2011-11-11
Filing date: 2012-11-12
Publication date: 2013-05-16

Abstract

A container is produced with less material compared to blow-molded containers by using an injection molding process using a plastic material, such as polypropylene, having a melt flow index of at least about 100 and a material flow length to wall section ratio of at least about 350 to 1. Because injection molding can hold tighter tolerances than blow-molding, water tight seals can be formed between containers and lids without the need for supplemental sealing materials.

Description

THIN- WALLED INJECTION MOLDED CONTAINER

BACKGROUND AND SUMMARY

Plastic canisters for holding and/or dispensing products such as moistened towelettes are typically blow-molded as an open cup-shaped container and fitted with a separate snap-on lid. Because of the limitations of the blow-molding process, the wall section thickness of such canisters must be thicker than desired because of the inability of the blow-molding process to produce uniform wall sections. This can become a problem if one attempts to reduce the material thickness of the container walls so as to produce a more sustainable product using less plastic material. That is, when trying to reduce the wall sections of a typical blow-molded cup- shaped container, the wall sections can become excessively thin to the point where holes may appear in the wall section. In addition, the stacking strength of such thin-walled blow-molded containers can be compromised.

Another limitation with blow-molded containers is the accuracy of the fitment of a canister to its closure or lid. Because of the relatively poor dimensional tolerances inherent with blow-molding processes, it is difficult to achieve a water tight fit. In this case, a second or third sealing surface, or an additional form of a heat sealed or adhesively sealed film is required covering the open mouth of the container. Loss of moisture through the seal between the cap and container can present a problem when the contents of the container must be kept moist, such as in the case of moist towelettes used for hand wipes and the like. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a bottom perspective view of a thin wall container molded in accordance with one embodiment of this disclosure;

Figure 2 is a front elevation view of Figure 1;

Figure 3 is an axial elevation view in section taken along section line 3-3 of Figure 2; Figure 4 is a partial enlarged view of region 4 of Figure 3;

Figure 5 is a view of Figure 4 with a cap hermetically mounted over the mouth of the containers without supplemental sealing; and

Figure 6 is a top plan view of Figure 2.

In the various views of the drawings, like reference numbers denote like or similar parts. DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

In order to avoid the disadvantages noted above, the method disclosed herein has been developed to produce an injection molded thin-walled canister which can use 30% less material than equivalent sized blow-molded containers. This is achieved by designing evenly uniform wall sections on the order of .016 - .022 inches thick and using vertical or longitudinal ribs on the inner walls of the containers to improve the stacking strength as well as enhance and facilitate the manufacturing process. In one example, the part weight for a particular container for holding wet or moist towelettes is less than 48 grams with a length of, for example, 8 inches high, 4 inches in diameter and with a wall thickness of 0.020 inches.

An additional feature of the container constructed in accordance with this disclosure is the ability to incorporate a lid stabilizing ring adjacent to the rim or open mouth of the container. The profile of the lid stabilizing ring not only provides strength and rigidity to the container, but also forms a positive water-tight seal with a complementary plastic lid.

The design of the container neck with a stabilizing sealing ring having a smooth finish and precision configuration provides a close, high precision fitment against a closure cap so as to minimize moisture loss from within the closed container. This is important when the container is used for holding moistened articles or articles which should be protected from evaporation.

Various types of lids can be adapted for use with the subject container with various mating container neck designs. Such lids include wet-wipe lids, paper towel dispensing lids, snap-on lids or even screw lids. The particular lid design is not critical as long as the lid snugly and elastically engages the lid stabilizing ring with a tight biased interference fit.

A relatively narrow seal ring feature on the stabilizing ring, as discussed below, reduces material surface area contact and allows for increased contact pressure between the container and lid and provides improved EVAP test results over previous designs which are far superior to current blow-molded products. The sharp edges on the top and bottom of the seal ring ensure and maintain a good grip or "bite" against a surrounding lid.

The container according to this disclosure can be adapted for receiving dry goods and other products at the same fill rates and at the same speeds on filling lines as prior blow-molded containers.

One aspect of the present disclosure is the adoption of a molding machine having a container mold cavity with a 450:1 material flow length to wall section ratio. Lower ratios have also been achieved in injection molding in accordance with this disclosure, such as at least about 350:1 to 400: 1. These ratios are far beyond anything applicable to blow-molded canisters due to the limitation of the blow-molding process which has stretch length to wall thickness ratios with upper limits around 2:1 and 3:1.

Tolerances with the present injection molded method can be held within +/- .005 inch unlike blow-molded products with tolerances of +/-.020 inch. Moreover, multiple form factors are achievable by injection molding products according to this disclosure. These forms include tapered designs and nestable designs allowing for improved packaging densities which are significantly better than straight edge wall designs such as produced with blow-molding. For example, oval containers such as ice cream containers, square containers such as tissue box containers, rectangular containers such as cereal box containers and cylindrical containers such as chewing gum containers are all easily achievable with the injection molding process in accordance with this disclosure. These forms are difficult to achieve with blow-molding processes.

In order to achieve the advantages noted above using an injection molding process, ultrahigh melt flow index (MFI) material is used. For example, in order to achieve the results noted above, a melt flow index greater than about 100 MFI for polypropylene materials is used. In contrast, conventional injection molding processes use melt flow index materials ranging from about 5.0 - 30 MFI. This is over an order of magnitude below that used in accordance with the subject disclosure. By using an ultrahigh MFI of at least about 100 or greater than 100 with a polypropylene material, a 100% recyclable container (including the lid or closure) is achievable. In this injection molding scenario, using the ultra high flow materials, one may achieve greater than a 5% reduction in plastic weight as compared to similar blow-molded containers.

For example, a polypropylene nucleated copolymer material having the following characteristics may be used: MFI of at least about 100-150 g/10 min, specific gravity 0.90 g/cm , flexural modulus 230 MPa, temperature deflection @ 66 psi = 224° F, and Optimal Melt Temperature Range 450°-500° F.

Using plastic materials with an MFI of greater than 100 results in a very high flow rate material having a very low viscosity. This requires the shut offs on mold tooling to be very tight in order to eliminate flash. The mold tooling may include a part filling stabilization feature that allows for the molding of thin walls. A very high fill rate may be used with the subject disclosure such that a container or part fills a mold in under 0.2 seconds. For example, an injection speed of plastic material at up to 1000 mm/second can be used to carry out the injection molding process. The material is fed directly through a direct gate with no material waste and a straight injection is used including injection compression, vacuum venting and air ejection.

An example of a container formed in accordance with this disclosure is shown in Figures 1 through 6. These containers can have a length of 8", an open mouth diameter of 4" and a wall thickness of 0.020"-0.022". The drawings are of reduced size but are drawn proportionally to scale.

In order to achieve the advantages noted above using an injection molding process for thin-walled containers and canisters, a special injection molding machine meeting specific requirements must be used. One non-limiting example of an injection molding machine meeting these requirements includes a closed loop control system, a minimum injection speed capability of 20 in./sec, a valve gate control system, a barrier flight screw design, and an open cylinder head.

In addition, the mold used in such an injection molding machine must meet the following specific design requirements. One non-limiting example of a mold meeting these requirements includes: a full stainless steel frame, a valve gate hot runner system with a minimum gate diameter of 0.060 in., a moldmax/beryllium copper core top with vent ring for ejection, geometric steel tolerances maintained at +/- 0.0001 in., a radial core/cavity interlock system with adjustable pads, core deflection stabilization, core and cavity cooling meeting a Reynolds number of 10,000, and temperature rise on cooling circuits not exceeding 3°F.

Examples of special execution designs of injection molding machines meeting the above molding machine requirements and having molds meeting the above mold design requirements include those made by Netstal-Maschinen AG of Switzerland and Husky Injection Molding Systems of Bolton, Ontario, Canada.

The resulting ultra thin-walled injection molded container not only reduces material content but provides for greater dimensional accuracy. Because of this greater dimensional accuracy, tighter tolerances can be maintained between a container body and its closure cap to form a water tight seal, such that the use of a secondary film seal or tamper evident film is not required, but can be used for additional sealing if desired. Moreover, the tapered side walls facilitate nesting of these containers for improved shipping density. Straight walls for maximum load bearing may also be utilized in the range of form factors. While a MFI material of 100 to 150 is adequate, higher MFI materials can be used advantageously.

As seen in Fig. 1, a container 10 is formed in accordance with the method and apparatus noted above. The container 10 includes a substantially cylindrical or tubular thin wall 12 having a slight conical taper or draft diverging from a bottom portion 14 to a top portion 16. Bottom portion 14 is formed with a circular recessed portion 18 and an annular chamfered or rounded edge portion 20. A radially inwardly and upwardly stepped or tapered frustoconical portion 22 extends from a bottom wall 23 to the circular recessed portion 18. The top portion 16 is formed with an annular edge 24 surrounding a circular open mouth portion 26 (Fig. 6). As seen in Fig. 4, the top portionl6 is formed with an annular lid stabilization ring 30 having a wall thickness greater than the wall thickness of the tubular wall 12. The stabilizing ring 30 provides strength and rigidity to the top portion 16 so that a biased watertight hermetic seal can be formed between the stabilizing ring 30 and a closure cap 32 (Fig. 5).

As further seen in Fig. 4, the stabilizing ring 30 is formed with an annular upper sharp edge corner portion 34 and an annular lower sharp edge corner portion 36. A thin annular planar surface sealing portion 38 extends between the upper and lower sharp edge portions 34, 36. Surface portion 38, along with the sharp edge portions 34, 36 are configured and formed with tight tolerances to sealingly engage the inner surface of a sealing closure cap 32 and form a tight waterproof hermetic seal. The thin sealing portion 38 is dimensioned with a small surface area to generate a high contact pressure against the closure cap 32.

The outer diameter of the stabilizing ring 30 along the vertical planar surface portion 38 is greater than the inner diameter of the closure cap 32 so that a biased sliding resilient interference fit is formed therebetween. As seen in Fig. 5, the annular wall 40 of the circular cap 32 presses radially inwardly against the sealing portion 38 in the direction of arrow 42 as it is deflected radially outwardly while sliding against the seal portion 38.

In order to facilitate the positioning of the cap 32 over the sealing ring 30 with a simple sliding press fit, an upper annular ramped portion 44 extends radially inwardly and upwardly from the upper sharp edge 34 to the annular edge 24. A lower annular ramped portion 46 extends radially inwardly and downwardly from the lower sharp edge 36 into a more mildly tapered thick wall portion 48. Wall portion 48 tapers radially inwardly and downwardly into the thin- walled tubular wall portion 12. As seen in Figs. 3 and 6, a series of evenly spaced support or strengthening ribs 50 extends radially along the inner surface of the bottom wall 23 from the recessed portion 18 around the rounded portion 20 and vertically or axially at least up over a portion of the inner wall of the tubular thin wall 12. Ribs 50 provide strength and rigidity to the container 10 and provide the needed strength and rigidity for automated stacking of a series of containers nested one within another.

It will be appreciated by those skilled in the art that the above thin-walled injection molded container is merely representative of the many possible embodiments of the invention and that the scope of the invention should not be limited thereto, but instead should only be limited according to the following claims.

Claims

CLAIMS What is claimed:

1. An injection molded container comprising an injection molded plastic material having a melt flow index (MFI) of at least about 100 and a flow length to wall section ratio of at least about 350 to 1.

2. The container of claim 1, wherein said container comprises a tubular wall portion, a top portion, a bottom portion, a lid stabilizing ring on said top portion having at least one annular sharp edge portion for forming a tight seal with a closure cap.

3. The container of claim 2, wherein said at least one annular sharp edge portion comprises an annular upper sharp edge portion and an annular lower sharp edge portion.

4. The container of claim 3, wherein said lid stabilizing portion further comprises an annular planar surface portion extending between said upper and lower sharp edge portions.

5. The container of claim 4, wherein said lid stabilizing portion further comprises an upper annular ramped portion extending radially inwardly and upwardly from said annular upper sharp edge portion.

6. The container of claim 4, wherein said lid stabilizing portion further comprises a lower annular ramped portion extending radially inwardly and downwardly form said annular lower sharp edge portion.

7. The container of claim 2, wherein said top portion comprises a first radial wall thickness and wherein said tubular wall portion comprises a second radial wall thickness less than said first wall thickness.

8. The container of claim 2, further comprising a plurality of strengthening ribs formed along a portion of said tubular wall portion.

9. The container of claim 8, wherein said tubular wall portion comprises an inner wall portion and wherein said strengthening ribs are formed on said inner wall portion.

10. The container of claim 1, wherein said tubular wall portion comprises a wall thickness maintained within a tolerance of plus or minus 0.005 inch.

1 1. The container of claim 1, wherein said plastic material comprises polypropylene having an optimal melt temperature range of 450° to 500° F.

12. The container of claim 3 further comprising a cap press fit onto said stabilizing ring with a sliding interference fit.

13. The container of claim 12, wherein said cap forms a biased watertight seal against said stabilizing ring.

14. The container of claim 13, wherein said watertight seal is formed exclusively between said cap and said stabilizing ring without additional sealing material.

15. A method of forming a thin- wall container, comprising:

providing a plastic material with a melt flow index of at least about 100; providing an injection molding machine comprising straight injection, injection compression, vacuum venting and air ejection; and

injecting said plastic material into a mold cavity in said injection molding machine having a flow length to wall section ratio of at least about 350 to 1.

16. The method of claim 15, further comprising filling said mold cavity with said plastic material in less than 0.2 seconds.

17. The method of claim 16, further comprising injecting said plastic material into said mold at a speed of at least 20 inches per second.