Process for producing flow-in closure sealing gaskets from hot melt compositions

• US 4,085,186 A
• Filed: 12/05/1975
• Issued: 04/18/1978
• Est. Priority Date: 12/05/1975
• Status: Expired due to Term

• Current Assignee: Morton Coatings, Inc.
• Original Assignee: CPL Corporation
• Inventors: Rainer, William C.
• Primary Examiner(s): Thurlow, Jeffery R.
• Application Number:
  US05/637,851
• Time in Patent Office: 865 Days
• Field of Search: 264/268, 264/267, 264/299, 264/322, 260/880 R, 260/878, 260/879, 260/876 B
• US Class Current: 264/268
• CPC Class Codes: B29C 70/80 Moulding sealing material into closure members placing sealings in closures B21D51/46
• CPC Class Codes: B29K 2031/04 Polymers of vinyl acetate, e.g. PVAc, i.e. polyvinyl acetate
• CPC Class Codes: B29K 2096/04 Block polymers
• CPC Class Codes: B29K 2105/0085 Copolymers

Abstract

A hot melt composition for forming flowed-in closure liners or gaskets having a viscosity and resulting flow properties suitable for use in high speed, liner forming operations. The composition comprises between 20 and 55 percent of a thermoplastic elastomer chosen from the group consisting of block copolymers of the type having the general formula A-B-A or of the type having a plurality of chains of the general formula B-A radiating from a central hub. A is a thermoplastic segment, preferably polystyrene, and B is an elastomeric segment, preferably polybutadiene, polyisoprene, or polyethylene-butylene. The other ingredients in the composition may be extenders, antioxidants, fillers, pigments, lubricants, etc. as desired.

An in-situ molded crown liner, ring-seal bottle cap gasket, roll-on closure liner, CT (screw) cap gasket, lug cap gasket, and snap-on cap gasket, made from the composition and containing no PVC, are disclosed.

A hot melt process for producing liners is also disclosed which is characterized by the steps of providing a hot melt composition which cools to a coherent elastomeric mass, heating the composition to cause it to flow, depositing a metered amount of the molten liquid composition from a dispensing nozzle into a closure shell, shaping the composition to the desired shape, and cooling the formed liner.

Claims

1. Process for producing a gasket in a closure to thereby render the closure capable of sealing a container, said process being characterized by the steps of:

(a) providing a vinyl chloride free, elastomeric hot melt composition having a viscosity index less than about 40 meter-grams torque at 175°

C and being capable of retaining a given shape when cooled;

(b) heating the composition to cause it to flow;

(c) depositing a metered amount of the flowable, heated composition from a nozzle into a closure shell;

(d) shaping the composition in the closure shell to form a gasket; and

(e) cooling the shaped gasket.

2. The process of claim 1 wherein the hot melt composition comprises between about 20 to about 55 percent of a thermoplastic elastomer chosen from the group consisting of:

(a) triblock copolymers of the type having the general formula ABA, wherein A is a thermoplastic segment of a polymerized alkenyl aromatic compound of average molecular weight within the range of about 2,000 to about 30,000 and wherein B is an elastomeric segment of polymerized diene selected from the class consisting of conjugated diene hydrocarbon compounds formed from monomers having four to eight carbon atoms and elastomeric copolymers of ethylene with butylene, said elastomeric segment having an average molecular weight within the range of 10,000 to 200,000, the total polymerized alkenyl aromatic compound content constituting from about 15 to about 65 percent by weight of the triblock molecule; and

(b) radial block copolymers of the type having a plurality of chains having the general formula BA wherein B is linked to a central hub and is an elastomeric segment of a polymerized diene selected from the class consisting of conjugated diene hydrocarbon compounds formed from monomers having four to eight carbon atoms and elastomeric copolymers of ethylene with butylene, said elastomeric segment having an average molecular weight within the range of about 10,000 to about 200,000, and A is a thermoplastic segment of a polymerized alkenyl aromatic compound of average molecular weight within the range of about 2,000 to about 30,000, the total polymerized alkenyl aromatic compound content constituting between about 20 to about 50 percent by weight of the radial block copolymer molecule.

3. The process of claim 1 wherein, in said heating step, the composition is heated to between 160°

C and 210°

C.

4. The process of claim 1 wherein the closure shell is heated.

5. The process of claim 1 wherein said shaping step is effected by contacting the composition in the closure shell with a die.

6. The process of claim 5 wherein the die is cooled.

7. The process of claim 1 wherein the hot melt composition comprises a blend of a polyethylene and at least one member of the class consisting of copolymers of ethylene/vinyl acetate and terpolymers of acid/ethylene/vinyl acetate.