热灌装技术.doc

Hot-fill closures are hot stuff. Various factors are driving the use of plastic containers and closures for hot-fill applications, including: the continuing migration of beverages and other products from glass to plastic, the increasing use of single-serve sizes, and the proliferationMany hot-fill bottlers continue to use steam to soften caps. However, new hot-fill closure systems are designed to perform without presteaming. There are several advantages to doing without cap steaming, says John Greiner, marketing manager for Alcoa Closure Systems International. First and foremost, you dont have to have one more variable affecting your performance, like a steam box, Greiner says. Secondly, if you were starting from scratch, the cost of installing steam and maintaining the system is an ongoing expense for you. The ongoing expense is indeed something that bottlers want to avoid, says Jim Wilmington, project engineer for Crown Zeller USA. What Im hearing throughout the juice industry is that this is a practice theyre trying to get away from, Wilmington says. They have to have a boiler going, they have to have the gas to heat the boilers, theyve got to continually being boiling water. That view was echoed by Bob Reay, director of marketing for Silgan Closures, whose White Cap division pioneered the use of plastic closures for hot fill. When we introduced the first all-plastic hot-fill vacuum-holding 43-millimeter closure in 1986, the initial customers and most that followed were ones that had previously been running metal closures on glass where the metal closures required heat to soften the plastisol gasket. Therefore, they all had heat available, Reay says. In todays world, many new packers are starting out with plastic closures and dont have or dont want to add heat to their capping lines. Also, some existing packers would like to eliminate heat from their operations. Getting the T-E band to work without pre-steaming is primarily a matter of getting it to slip over the lip of the bottle-known as the A dimension-without having to be softened. Crown Zeller and other manufacturers are accomplishing this by tweaking the resin they use for closures. Certain polypropylene copolymers give just the right degree of flexibility. Another strategy is to tweak the bridges between the T-E band and the cap by altering the number and size of the slits.Crown Zellers BevGuard Plus closure also boasts another improvement in the T-E band: tiny holes in the J-hook, the bottom edge of the band that fits over the lip. When the bottles travel through a cooler bath, the drop in temperature creates a slight vacuum in the headspace. This can suck minute amounts of water into the underside of the cap. The holes drain this water, removing potentially troublesome moisture that could otherwise allow bacteria to breed. Separate seal One step that is often debated in hot-fill applications is whether to use separate induction seals. Some hot-fill bottlers use foil or film induction seals as an added barrier against microbial intrusion, which would compromise the sterility needed for additional shelf life. The key to induction sealing in a hot-fill application is using the right kind of sealing head, or coil-the component that emits a pulse of electromagnetic energy that binds the seal to the bottles lip. Pillar Technologies markets systems with interchangeable coils that can handle a variety of bottle types and sizes with the same base power supply. Both Pillar and Enercon Industries market tunnel sealing heads that allow the container to travel through the sealing head while the electromagnetic pulse is directed to the foil liner for sealing. Enercon is touting capless sealing as a possibility for hot-fill applications. (In most induction sealing, the seal arrives at the bottling plant already inserted into the cap, and the sealing takes place after the cap is applied. Capless sealing refers to a process of attaching the seal to the bottles mouth and then applying the cap.) The big advantage of capless sealing is that it allows the bottles to be cooled before the caps go on. This cuts down on the liability of misapplied caps and the danger of cooling water collecting between the cap and seal. But induction sealing in hot-fill has its detractors. It adds expense and can be perceived by consumers as a nuisance, says Clint Haynes, president of Stress Engineering Services, a consultant engineering firm that specializes in closures. Its been pretty well demonstrated that you can get that seal that you need, and that the foil seal is a little bit of belt and suspenders, Haynes says.Crown Zellers BevGuard Plus closure also boasts another improvement in the T-E band: tiny holes in the J-hook, the bottom edge of the band that fits over the lip. When the bottles travel through a cooler bath, the drop in temperature creates a slight vacuum in the headspace. This can suck minute amounts of water into the underside of the cap. The holes drain this water, removing potentially troublesome moisture that could otherwise allow bacteria to breed. Separate seal One step that is often debated in hot-fill applications is whether to use separate induction seals. Some hot-fill bottlers use foil or film induction seals as an added barrier against microbial intrusion, which would compromise the sterility needed for additional shelf life. The key to induction sealing in a hot-fill application is using the right kind of sealing head, or coil-the component that emits a pulse of electromagnetic energy that binds the seal to the bottles lip. Pillar Technologies markets systems with interchangeable coils that can handle a variety of bottle types and sizes with the same base power supply. Both Pillar and Enercon Industries market tunnel sealing heads that allow the container to travel through the sealing head while the electromagnetic pulse is directed to the foil liner for sealing. Enercon is touting capless sealing as a possibility for hot-fill applications. (In most induction sealing, the seal arrives at the bottling plant already inserted into the cap, and the sealing takes place after the cap is applied. Capless sealing refers to a process of attaching the seal to the bottles mouth and then applying the cap.) The big advantage of capless sealing is that it allows the bottles to be cooled before the caps go on. This cuts down on the liability of misapplied caps and the danger of cooling water collecting between the cap and seal. But induction sealing in hot-fill has its detractors. It adds expense and can be perceived by consumers as a nuisance, says Clint Haynes, president of Stress Engineering Services, a consultant engineering firm that specializes in closures. Its been pretty well demonstrated that you can get that seal that you need, and that the foil seal is a little bit of belt and suspenders, Haynes says.One of the problems with induction sealing is that the foil or film used to make the seal can develop problems that can be hard to trace, Haynes says: They seem simpler but when somebody runs into a problem with film, it is one hell of a problem finding it, because they make a gazillion feet of this thing and actually tracking it down when youre doing your failure investigation is pretty difficult. Liner issues Another vital component of hot-fill closures is the liner on the caps underside. The liner plays two critical roles in the closures performance. It completes the seal, which is especially important in hot-fill, because the products shelf life depends on keeping out microorganisms. And it determines the removal torque. It has been a long-term challenge for all of us closure manufacturers to keep seal integrity with also being able to allow customers to get these closures off, Wilmington says. Maintaining seal integrity without excessive removal torque is largely a function of the closures liner material. Most liners for hot-fill closures are molded in rather than glued, because the heat would attack any adhesive. The most common liner material is thermoplastic elastomer (TPE). As with the closures shell, its a question of tweaking the material to give the right combination of strength and elasticity. I