MXPA06005764A - A preform of a plastic container particularly for packaging foodstuffs - Google Patents

Abstract

This invention relates to the preform to produce a plastic container for packaging foodstuffs, and especially to blow mould thin-walled containers which can be hermetically closed with a metal lid by double seaming. The preform (1) includes a body (4) and a convex hemispherical bottom (6). The body (4) has a conical shape that flares towards a cylindrical neck (2) surrounded by a flange (3) that terminates in a thickened rim (5). Preferably, the angle (alpha) at which the internal body surface (4) flarestowards the cylindrical neck is greater than the angle (beta) at which the external body surface (4) opens upwards, and the thickness (g2) of the cylindrical neck (2) is less than the thickness (g3) of the bottom (6).

Description

A PREFORM OF A PLASTIC CONTAINER PARTICULARLY DESIGNED FOR PACKAGING FOODS The Field of the Invention The invention relates to the preform of a plastic container particularly designed to pack food. This preform is formed using conventional injection molding machinery and used to form plastic containers, such as cans, to pack food, and especially to thin-walled, blow-molded containers that can be sealed with a metal lid secured to the container when sewing the flange of the lid in filling machines, without deforming the flange or the cylindrical neck under it. The state of the art Polish patent application No. P 336 680 A1 relates to a plastic preform designed to form thin-walled containers. The preform has a threaded neck and a cylindrical body finished with a hemispherical convex bottom. The diameter of the body of this preform is from 0.5 to 0.85, and the thickness of the body wall is 0.08 to 0.18, of the diameter of the neck. It has been known for some time how to form thin-walled containers finished with a flange by blow-molding the conventional preform and then cutting the upper portion of the container including a threaded neck. In this way immense quantities of fragments are produced, which results in the complete process being highly anti-economic. In addition, this method leaves a lot of uncertainty about the reliability of the closure, including its tightness and resistance to pressure inside the container. The edge of the flange of the container can be grooved by cutting operations and its thickness can vary along the circumference, which is normal since the flange is blow molded as part of the side wall of a larger container. In order that the closure of the plastic container be airtight under pressure, it would be better if the container were formed from the preform molded by injection by a stretch blow molding process. EP 0482652B1 discloses a cylindrical preform with a flat bottom, wherein the bottom is much thinner than the walls of the preform that gradually separate slightly. Due to the fact that the flow of material is hindered, it is impossible to achieve the thickness of the flange that is below 0.3 mm. The flange of the preform is uniform and has no thickened edge. WO-A 83/01766 discloses a preform, which is generally cylindrical in shape and tapers slightly in the downward direction; its walls and bottom have the same thickness. The rim is uniform and does not have a thickened edge. It has been noted in the document that it is impossible for someone to achieve a good degree of orientation of the material on the flange of such preform; hence, its resistance is insufficient for the good quality connection between the metal lid and the container. The optimal solution for the cylindrical neck and flange is to be as close as possible to the dimensions of a metal container, while maintaining the best possible strength parameters. In this form, the container formed from the preform by a blow molding stretch process can be efficiently closed by sewing a metal lid, thereby providing a reliable closure for carbonated beverages under pressure. This invention brings us closer to solving this problem. SUMMARY OF THE INVENTION The preform in question to form plastic containers has a conical shape with a convex hemispherical bottom. The body of the preform protrudes towards a cylindrical neck surrounded by a radially outwardly extending rim terminated in a thickened rim. The opening angle of the inner conical surface of the body is greater than the opening angle of the external conical surface of the body; from here that, the bottom is the thickest part of the body of the container and the cylindrical neck is significantly thinner than the bottom. The inflow of material into the neck space and then into the rim is easy. This is due to the fact that the bottom at the injection point is relatively thick, the walls are tilted properly and their thickness tapers in a favorable manner. The flow velocity of the material in the mold is relatively high during the forming process with the result that the time taken by the material to reach the peripheries of the preform, including the flange, is short and a decline in the temperature of the material Flowing is much smaller, which allows proper filling and orientation and ensures a much better flange strength. In this way, it is possible that the thickness of the flange is less than 0.3 mm, which is required for the good quality seam of the metal cover. The best sewing quality is achieved when there is a gradual change in the thickness between the cylindrical neck and the flange and the transition between these two elements is arched. Preferably, the ratio of the thickness of the flange to the thickness of the cylindrical neck should be approximately 0.8. Furthermore, in order to ensure that the metal lid of the container fits snugly on the edge of the rim, it is desirable that the angle between the rim and the cylindrical neck be 180 ° -?, Where? it is within a range of 60 ° to 90 °, and more preferably equal to 78 °. In order for the sewing operation to ensure a good connection quality between the pressurized container and the metal lid, the rim should end in a thickened annular rim showing on one or both sides of the end of the rim. The height of the thickened annular edge should vary from 1.1 to 2.0 of the thickness of the flange. The rim in the view in axial section may also have a rectangular edge whose height is generally equal to the thickness of the rim. Such rims can be used in containers where there is no internal pressure involved. In such a case, the angle? it is preferably 90 °. BRIEF DESCRIPTION OF THE DRAWINGS The present invention has been described in greater detail in the following figures. It is considered that these figures illustrate the most efficient version of the preform. Figure 1 shows an axial sectional view of the preform. Figure 2 shows an enlarged image of the flange of the preform with an annular thickened edge of double side. Figure 3 shows an enlarged image of the flange of the preform with an annular thickened edge on one side on top of the flange. Figure 4 shows an enlarged image of the flange of the preform with an annular thickened rim on one side below the rim. Figure 5 shows an enlarged image of the flange of the preform with the edge of the rectangular flange. The most efficient version As shown in Figure 1, the preform 1 of the plastic container particularly designed to pack food, includes a body 4 with a convex hemispherical bottom part 6. The body 4 has a conical shape that opens upwards and ends with a cylindrical neck 2 surrounded by a rim 3 extending radially outwardly terminated in a thickened edge 5. The angle a in which the inner body surface 4 opens upwards is greater than the angle ß in which the surface 4 of the external body opens upwards. In the axial sectional view, the internal radius R2 of the bottom 6 of the body 4 is smaller than the corresponding external radius R1. The thickness of the body 4 gradually decreases starting from the bottom 6; therefore the thickness g2 of the cylindrical neck 2 is significantly smaller than the thickness g3 of the bottom 6. The thickness of the rim g1 is less than 0.3 mm.

Figure 2 shows an enlarged edge 5 of the rim 3 of the preform 1 that deviates from the cylindrical neck at an angle of 180 ° -?, Where? It is within a range of 60 ° to 90 °. The flange 3 ends in an annular thickened edge 5a on both of its sides. The height h of the thickened edge 5a varies from 1.1 to 2.0 of the thickness g1 of the flange. Figure 3 shows an enlarged edge 5 of the rim 3 of the preform 1 that deviates from the cylindrical neck at an angle of 180 °-?, Where? It is within a range of 60 ° to 90 °. The flange 3 ends in an annular thickened edge of one side 5b on the upper part thereof. The height h of the thickened edge 5b varies from 1.1 to 2.0 of the thickness g1 of the flange. Figure 4 shows an enlarged edge 5 of the rim 3 of the preform 1 that deviates from the cylindrical neck at an angle of 180 °-?, Where? It is within a range of 60 ° to 90 °. The flange 3 ends in an annular thickened edge of one side 5c below it. The height h of the thickened edge 5c varies from 1.1 to 2.0 of the thickness g1 of the flange. Figure 5 shows an enlarged edge 5 of the rim 3 of the preform 1 that deviates from the cylindrical neck at an angle of 180 ° -?, Where? It is within a range of 60 ° to 90 °. The flange 3 ends in a rectangular edge 5d whose height h is generally equal to the thickness g1 of the flange. The preform 1 as shown in Figure 1 with outer diameter D1 and height H is made of polyethylene terephthalate (PET), a thermoplastic material specifically designed to pack food. When the preform in question is used to mold a thin-walled container by screed, the diameters D1 and D2 of the cylindrical neck 2 and the flange 3 do not change. The relatively small flange thickness allows a better adjustment of the metal cap in the first stage of the double seam process. The thickening of the edge of the flange facilitates the clamping of the preform during the blow molding operation and allows the additional clamping of the metal cap against the body of the pressurized container in the second stage of the double-seam process,

Claims (2)

1. CLAIMS 1. A preform of a plastic container designed particularly for packaging food comprising a conical shaped container body with a convex hemispherical bottom, projecting towards a cylindrical neck, characterized in that the body of a single layer in which the The external diameter of the cone as measured at the point of connection with the cylindrical part is equal to the external diameter of the cylindrical part, wherein the cylindrical part ends with a flange terminated by a thickened edge. 2. The preform according to claim 1 is characterized in that the thickness of the flange as measured at a distance of about 0.5 mm from the end of the flange is less than 0.25 mm (preferably about 0.20 mm) and that the The thickness of the wall is less than or equal to the thickness of the wall of the cylindrical neck 3. The preform according to claim 1 is characterized in that the edge of the rim has an annular thickening in the upper part and below it, whose height varies from 1.1 to 2.0 of the thickness of the flange 4. The preform according to claim 1 is characterized in that the edge of the flange has a thickening of a side similar to a ring on the upper part thereof, whose height varies from 1.1 to 2.0 of the thickness of the flange 5. The preform according to claim 1 is characterized in that the edge of the flange has a thickening of a side similar to a ring below it, whose height a varies from 1.1 to
2. 2.0 of the thickness of the flange. SUMMARY This invention relates to the preform for producing a plastic container for packaging food, and especially for blow-molding thin-walled containers that can be hermetically sealed with a metal lid by double stitching. The preform (1) includes a body (4) and a hemispherical convex bottom (6). The body (4) has a conical shape protruding towards a cylindrical neck (2) surrounded by a ridge (3) ending in a thickened edge (5). Preferably, the angle (a) in which the internal surface of the body (4) protrudes towards the cylindrical neck is greater than the angle (ß) in which the outer surface of the body (4) opens upwards, and the thickness (g2) of the cylindrical neck (2) is smaller than the thickness (g3) of the bottom (6). FIG. 1