Cross-Reference to Related Applications

The present application is related to th following co-pending applications of the present invention filed on even date herewith:

"Tamper-Evident, Reclosable, Plastic Lid";

"Reclosable, Tamper-Evident Plastic Lid for a Container Having a Circular Wall"; and

"Plastic Container with Integral Tamper- Evident, Reclosable Lid".

The present method relates to the formation of plastic member from a rigid plastic material where th plastic member comprises first and second sections that ar integrally secured together along a tear line that enable ready separation of the two sections. More specifically the method is usable to form a plastic member such as container lid or integral lid and container that has rupturable portion in the lid. The tear line formed by th present method enables separation and removal of th rupturable portion of the lid to enable access to th contents of a container.

While such rupturable portions have been forme from various thermoplastic materials such as polyethylen or polypropylene, problems remain relative to lids s

formed or the processes for their formation. I polyethylene members, for example, the formation of a tear line between two integral sections of a plastic componen is easily achieved by filling one cavity with molte plastic to form one section and causing the molten plasti material to flow across a constriction, to form a tea line, with the molten plastic then filling another cavit to form a second section. With the use of low densit polyethylene material, such flow across a constriction in mold cavity to form a tear line can be effected, but th resultant product does not provide the desired hig resistance to moisture passage and oxygen permeability i containers or lids for foodstuffs, and the like. Also, lid formed from polyethylene is relatively pliable an removing and replacing such a lid on a container withou detection is possible and undesirable.

In order to overcome the objections that ar present with polyethylene or other pliable types of plasti containers or lids, it has been proposed to form a lid fro polypropylene. The use of a polypropylene polymer or othe rigid type of polymer provides problems relative to th formation of a tear line between two sections of a plasti member formed from such polymers. When these more rigi type polymers are molded, a problem exists in that th molten plastic material does not flow across a constricte cavity between two sections of a plastic member unless th contriction is so large as to not serve as a satisfactor tear line. Thus, by using a constriction between tw sections of a plastic member, formation of a first sectio and flow across a constricted area to form a ^" satisfactor tear line, and finally flow of the molten plastic materia through the tear line to form the second section cannot b effected. The constricted cavity, in order to effect flo of the rigid plastic material thereacross, must be of width such that the thickness of the web between the tw

sections is too great to serve as a tear line f separation of the two sections.

It has previously been proposed to form a plast member that has two sections interconnected by a tear li where a weld between two supplies of molten plasti material is effected at the tear line. Such processes hav however, used sequential molding steps. In U.S. 3,499,57 for example, a method using sequential molding steps i described where a tear portion and a remaining portion ar welded together along a rupturable weld line of fuse material of both portions. This sequential molding proces is described for use in forming a lid, where t confronting movable mold bodies are closely spaced define two separated lid portions with a small g therebetween and, after molding of the two separated li portions, the confronting mold bodies are moved slightl apart due to pressure buildup, and the gap is filled wit plastic to connect the two lid portions together by tearable weld line. More specifically, a flash-fusing o the edges of two portions is effected using heated flowabl synthetic thermoplastic material, such as polyethylene polystyrene, etc.

In U.S. 4,448,324, a method of manufacturing container element is disclosed which comprises injectio molding a first injection molded portion, and subsequentl injection molding a second portion so as to form a wel zone between the first and second injected molded portion in an area of direct contact between the first and secon portions. This method involves sequentially molding t parts, with injection molding of the second part carrie out so that the molecule chains of the plastic materia essentially are broken in the weld zone and/or so that th temperature of the plastic material in the first and secon parts is maintained at a lower level than required fo complete fusing together. The sequential, multi-step

molding process is used to make container closures with a tear-out portion and preferably closures of a composite type where a thin metal foil and plastic material composite is used. It is an object of the present invention to provide a method for formation of plastic members from rigid plastic materials that have first and second sections interconnected along a tear line which provides an easy and clean separation of the two sections. It is another object of the present invention to provide a method for formation of a lid, or container having an integral lid, from a rigid plastic material, tha has a rupturable portion thereon to enable separation of portion thereof along a tear line to provide access to th contents of a container while also providing a tamper evident feature for the container.

It is a further object of the present inventio to provide a method for formation of a lid, or containe having an integral lid, which has a closure membe integrally formed therewith from a rigid plastic material, with a rupturable portion on the lid which enable separation of a portion thereof along a tear line t provide access to the contents of the container an resealing of the-container by the integral closure member. Summary of the Invention

A rigid plastic member having first and secon sections integrally secured together across a tear line i formed by simultaneously injection molding the first an second sections in spaced mold cavities, that ar interconnected through a constricted cavity, to fill bot the first and second cavities and continuing injection o the supplies of molten plastic to the first and secon cavities to simultaneously force plastic material from bot the cavities into the constricted cavity to caus coalescence of the supplies of plastic material in th

constricted cavity and form a weld between the supplies o plastic material which comprises the tear line of th finished plastic member. The plastic material is a rigi plastic having a tensile modulus and flexural modulus i excess of 100 x 10^ p.s.i. (pounds per square inch) and melting point above 140°C.

In a preferred embodiment of the present method an article such as a rigid plastic lid or integra container and lid is formed, having a planar membe integrally secured to a surrounding peripheral membe across a. tear line, in a recess formed by the periphera member, the article having a rupturable portion comprisin the planar member that can be removed from the remainder o the lid. In a most preferred embodiment, the lid o integral container and lid has a closure member integrall formed with the surrounding peripheral member across narrowed hinge line.

Description of the Drawings Figure 1 is a schematic of a cross-sectional vie of mold portions forming the cavities for use in th present method;

Figure 2 is a view similar to Figure 1 showin the initial flow of two supplies of molten plastic materia into the mold cavities to form first and second sections o a plastic member;

Figure 3 is a view similar to Figure 2 showin the mold cavities for forming the first and second section filled with molten plastic, and confronting supplies o plastic material adjacent the constricted cavity, nea completion of the formation of the plastic member;

Figure 4 is an enlarged view of the constricte cavity, and adjacent portions of the first and secon cavities, showing simultaneous flow of the two supplies o molten plastic therein to weld together and form the tea

line between the first and second sections of the plasti member; and

Figure 5 is a cross-sectional view of a plasti lid produced according to the present method. Detailed Description

The present method is for forming a plasti member, such as a lid or container with integral lid, tha has first and second sections of a predetermined thicknes that are integrally secured together along a tear line that has a thickness less than the first and secon sections, from a rigid plastic material. In the formatio of rigid plastic lids or containers with an integral lid the plastic material preferably also has sufficient oxyge and moisture barrier properties, as well as environmenta stress crack resistance. Where an integral closure membe is provided on the plastic member, the plastic materia should, while having the necessary rigidity, also posses properties for formation of an integral hinge between th closure member and plastic member. The plastics usable in the present method ar those having a tensile modulus in excess of about 100 x 10 p.s.i. according to ASTM D638, a flexural modulus in exces of about 100 x 10 ³ p.s.i. according to ASTM D790, and melting point or glass transition temperature in excess o about 140°C. Examples of such plastic material are polypropylene homopolymer, copolymers thereof having up t about 6 percent of a comonomer such as ethylene, an preferably less than about 3 percent of such a comonomer or ethylene and a termonomer such as butene -1, pentene - or hexene -1, the total thereof being less than about 6 an preferably less than 3 percent. Other plastic having th desired properties include a nylon polymer such as nylon or nylon 6/6, a polymethyl pentene polymer, or polycarbonate.

While the present method is usable to for various plastic articles or members having first and secon sections integrally secured together across a tear line the method is especially useful in formation of a plasti lid for a container or an integral container and li composite, and the following description will refer t formation of a plastic lid.

The drawings illustrate the present method fo use in forming a plastic lid that has a first sectio comprising a planar member and a second section tha comprises a peripheral wall section, with a planar web o tear line extending from the inner wall of the periphera wall section coplanar with the planar member. The first an second sections are secured together through a weld line. Referring now to Figures 1 to 4, the presen method is illustrated. A mold 1 includes separable mol portions, upper mold portion 3, upper mold side portion and lower mold portion 7 which together form a composit mold cavity 9. Ejector pins 11 are provided to remove molded product from the mold after formation according t the present method. The composite mold cavity 9 comprises first mold cavity 13 for formation of a first section 15 o a molded plastic member 17, and a second mold cavity 19 fo formation of a ^' second section 21 of a molded plastic membe 17, which second mold cavity 19 may have a sub-section 23. A constricted mold cavity 25 is provided between first mol cavity 13 and second mold cavity 19 for formation of a tea line 27 between the first and second sections 15 and 21 o the molded plastic member 17. In the present method, the plastic member i formed from at least two separate streams of molten plasti which enter the mold cavity. There are thus provided first gate 29, illustrated as a central gate, and at leas one other second gate 31, illustrated as a side gate, whic feed molten plastic to the mold cavity 9. Molten plasti

from a source, not shown, may be fed to the first and second gates 29 and 31 through a common inlet 33 to the mold 1.

As illustrated in Figure 2, a first supply of molten plastic material 35 is injected through first gate 29, such as a valve gate, to the first mold cavity 13 at about the central portion thereof. At the same time, a second supply 37 of molten plastic material is injected from the second gate 31, such as an edge gate, to the second mold cavity 19. Continual injection of the first and second supplies 35, 37 of molten plastic material is carried out, as shown in Figure 3, with the valve gate 29 substantially filling the first mold cavity 13, forming the first section of the plastic member, while the edge gate 31 substantially fills the second mold cavity 19, with the two supplies 35 and 37 adjacent the constricted mold cavity 25, one on each side of the constricted mold cavity 25. Further continual injection completely fills both the mold cavities 13 and 19 and simultaneously forces molten plastic from opposite directions into the constricted cavity 25, where the two supplies of molten plastic material 35, 37, as illustrated in Figure 4, meet, coalesce, and weld together to form a weld line w that comprises tear line 27 of the plastic.member -formed. With the use of rigid plastic material in the present process, it has been found that the thickness o the tear line is a critical feature. The tear line, or wel line, that is formed between the first and second section must have a thickness of between 0.002 to 0.007 inch, whil the width of the tear line can vary between 0.001 to 0.02 inch in size. The thickness and width of the tear line is of course, controlled by the dimensions of the constricte cavity 25. If the constricted cavity has a depth of les than about 0.002 inch, the flow of rigid plastic materia from the first and second sections into the constricte

cavity cannot be effected simultaneously, while a depth greater than about 0.007 inch will produce a weld line tear line that is too difficult to tear and/or leave undesirable jagged edges along the tear line. Th corresponding length of the constricted cavity is thu between 0.001 and 0.025 inch ^' to produce the desired widt of the tear line. A correlation exists between th thickness and width of the resultant weld line in that th larger the thickness of the weld line in the range that i used, the larger the width of the weld line, within th respective range, that is required, i.e., a weld line o about 0.007 inch thick would require a width of about 0.02 inch, while a thickness of about 0.002 inch requires width at the lower range thereof, or about 0.001 inch. An example of this type of plastic member 1 having a first section 17, a second section 21, and tea line 27, is a lid 41 that can be formed using the presen process as illustrated in Figure 5. A tamper-evident reclosable, plastic lid 41 formed from rigid polymer has first section or planar member 43 corresponding to firs mold cavity 13 and a second section or peripheral wal member 45 with an integral subsection or closure member 4 hingedly secured thereto through hinge 49 corresponding t second mold cavity 19. A tear line 51 is provided betwee planar member 43 and peripheral wall member 45, which tea line corresponds to the constricted mold cavity 25. Wit the closure member 47 in closed position, parallel to th planar member 43, a double seal is provided by the lid 41 When access through the lid 41 is desired, the plana member is removed by tearing the same along the tear lin 51 and removing it from the peripheral wall section 45. Th planar member extends across a recess 53 provided by th peripheral wall section 45, while securing means such a downwardly extending spaced walls 55 depend from th peripheral wall section 45 to enable securement of the li

41 to the upper edges of a container (not shown) . When th lid has an integral closure member molded therewith throug an integral hinge 49, the hinge 49 cannot be less tha about 0.008 in thickness since flow across the section o the mold cavity to form the hinge is very difficult, whil a hinge thickness of greater than about 0.012 inch woul not provide the requisite pliability and hinge actio needed. While the lid 41 is illustrated as a separate ite for securement to a container, it is also possible to us the present method to form a plastic container with a integral, tamper-evident, reclosable, plastic lid that has tear out portion by molding a downwardly extendin container wall in lieu of the downwardly extending space walls 55 shown. In formation of an integral container an lid, a plurality of the side gates should be used.

The present method thus enables the production o a plastic member having two sections connected togethe along a tear line from a rigid plastic material, and i especially useful in the formation of rigid plastic lids o containers having integral lids.