Plastic Caps Knowledge

February 24, 2010

Hot runner system in plastic injection process

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A hot runner system is one of ideal injection molding equipments that can create injection molded products of a uniform density, free from all mold runners, flash, and gate stubs. The plastic material in the hot runner mold keeping molten status when not for injection production. The hot runner system is making especially for injection molded plastic products with great complexity, like plastic closure of PP or PE cap and lid, PET plastic parts, ABS components and so on. 32 Cavities hot runner cap mould.24 Cavities connector mould

Connector mold system is a sophisticated mould system which applied in plastic injection molding industry for a long time. By using its male and female contractors mounted in a movable mold thus create plastic products for people’s daily life and industries, from a small plastic screw to medium size bucket and auto body as a large.

Major cap product of our company comprises: Buittress cap, Child resistant closure, Dispensing cap, Dome cap/jar seal, Flip-top jar cover, Phenolic polyseal cone liner, Poly/pulp and foil liner, PP Teflon liner cap, Sprayer cap, Spice cap, Spout cap and Tamper event caps and more.

The considerations for plastic injection molding

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Plastic Injection Molding Most plastic components on the market today are injection molded. An injection molded plastic part is created using an injection molding machine, which works by melting plastic pellets, and injecting them into a mold.

Designing plastic caps & plastic closures is a complex process, and the manufacturing end of it must be taken into account during the design phase. There are three elements of an injection molded plastic part, the nominal wall, projections, and holes and recesses.

The nominal wall refers to the wall thickness. The wall thickness throughout the part should not vary by more than 10 percent. Varying wall thicknesses in the injection molded plastic part are one of the main causes of flawed product. In designing the part, one wishes to avoid excessively thick walls, simply because thick walls use more plastic, and are more expensive to produce. However, there is a limit as to how thin the part can be as well. The strength of the part is a function of the thickness, and the final use of the product will determine the desired strength. Some specialized injection molded plastic caps & plastic closures require reinforcement with glass or carbon fibers.

A projection is an element of the plastic caps & plastic closures that projects out of the nominal wall, such as reinforcement ribs. The ribs must not be thicker than the nominal wall, or else sink marks may result.

Recesses and holes also are a major design element, The location of any holes or recesses may significantly affect the part’s overall strength. Trying to create a hole in the side of a part is especially challenging, and the need for side holes should be minimized in the initial design.

Another design factor for plastic closures & plastic caps is the corners of the part. How the plastic enters and fills the mold is of great concern. Since melted plastic is a fluid, fluid dynamics will dictate the design as well, to a large extent. When flowing into the mold, the plastic may have to go around corners. The plastics will flow better if corners are rounded. The plastics will pull against a sharp corner during the cooling process, and a flawed part may result. Creating a low stress design with smooth transitions will result in a stronger part that is less likely to crack or break.

What is TPE materials

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TPE stands for Thermo Plastic Elastomer. It is a range of polymers (plastics) that can be processed (moulded or extruded) like a plastic when over their melt temperature, but exhibit properties of thermoset rubber. the advantage to using TPE over thermoset rubber, is that it can be easily re-moulded and re-worked whereas rubber cannot.

TPE can be soft, stretchy, and flexible, or hard and rigid depending on the mixture of crystalline and amorphous polymers used.

Thermoplastic Elastomers (TPEs) are a class of polymers that, within their design limits, behave like thermoset rubber but that, above their melt or softening temperatures, are melt processable via thermoplastic processing methods and, unlike thermoset rubber, can be easily reprocessed and remolded. The ability to process these materials with thermoplastic methods allows for design and fabrication freedom that thermoset rubber does not offer.

All TPEs are composed of crystalline and amorphous domains. Some are blends or alloys of crystalline and amorphous polymers, some are block co-polymers comprised of blocks of crystalline and amorphous domains along the same polymer chain. It is the crystalline domains that act as the “heat-fugitive cross-links” that give TPEs their thermoplastic character and the amorphous domains that give them their elastomeric character. The crystalline domains are typically referred to as the “hard” phase and the amorphous domains as the “soft” phase. While both phases contribute to the overall physical and mechanical properties of a TPE, some key properties may be associated with one phase or the other thereby guiding the selection or design of a TPE compound.

“Hard Phase” — The plastic properties:

Processing temperatures
Continuous use temperature
Tensile strength
Tear strength
Chemical and fluid resistance
Adhesion to inks, adhesives, and over-molding substrates
“Soft Phase” — The elastomeric properties:

Lower service temperature limits
Hardness
Flexibility
Compression set and tensile set
Industry has typically rated the various TPE technologies on a cost vs. performance basis. This is a convenient way of classifying materials but it can be very misleading because performance should be defined by the requirements of the application, rather than a standard property set, and the performance — price curve will vary depending upon the performance criteria of interest. In our section Choosing the Correct TPE, we list some of the criteria that plstic industries use to narrow down and select the best TPE for an application.

Blow modling process for plastic products

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There are basically four types of blow molding used in the production of plastic bottles, jugs and jars. These four types are: extrusion blow molding, injection blow molding, stretch blow molding and reheat and blow molding. Extrusion blow molding is perhaps the simplest type of blow molding, whereby a hot tube of plastic material is dropped from an extruder and captured in a water cooled mold. Once the molds are closed, air is injected through the top or the neck of the container; just as if one were blowing up a balloon. When the hot plastic material is blown up and touches the walls of the mold the material “freezes” and the container now maintains its rigid shape. There are various types of shuttle, reciprocating and wheel style machines for the production of extrusion blown bottles. Shuttle or reciprocating type machines can be used for small, medium and high volume production with wheel machines being the most efficient for huge volume production of certain resins.

Injection blow molding is part injection molding and part blow molding. With injection blow molding, the hot plastic material is first injected into a cavity where it encircles the blow stem, which is used to create the neck and establish the gram weight. The injected material is then carried to the next station on the machine, where it is blown up into the finished container as in the extrusion blow molding process above.

Injection blow molding is generally suitable for smaller containers and absolutely no handleware. Extrusion blow molding allows for a wide variety of container shapes, sizes and neck openings, as well as the production of handleware. Extrusion blown containers can also have their gram weights adjusted through an extremely wide range, whereas injection blown containers usually have a set gram weight which cannot be changed unless a whole new set of blow stems are built. Extrusion blow molds are generally much less expensive than injection blow molds and can be produced in a much shorter period of time.

Many people have heard about stretch blow molding in conjunction with P.E.T. bottles commonly used for water, juice and a variety of other products. There are two processes for stretch blow molded P.E.T. containers. In one process, the machinery involved injection molds a preform, which is then transferred within the machine to another station where it is blown and then ejected from the machine. This type of machinery is generally called injection stretch blow molding (ISBM) and usually requires large runs to justify the very large expense for the injection molds to create the preform and then the blow molds to finish the blowing of the container. This process is used for extremely high volume (multi-million) runs of items such as wide mouth peanut butter jars, narrow mouth water bottles, liquor bottles etc.

Another stretch blow process is commonly called reheat and blow (RHB). In this process, a preform is injection molded by an outside vendor. There are a number of companies who produce these “stock” preforms on a commercial basis. Factories buy the preforms and put them into a relatively simple machine which reheats it so that it can be blown. The value of this process is primarily that the blowing company does not have to purchase the injection molding equipment to blow a particular container, so long as a preform is available from a stock preform manufacturer. This process also allows access to a large catalog of existing preforms. Therefore, the major expense is now for the blow molds, which are much less expensive than the injection molds required for preforms.

There are, however, some drawbacks to this process. If you are unable to find a stock preform which will blow the container you want, you must either purchase injection molds and have your own private mold preforms injection molded, or you will have to forego this process. For either type of stretch blow molding, handleware is not a possibility at this stage of development. The stretch blow molding process does offer the ability to produce fairly lightweight containers with very high impact resistance and, in some cases, superior chemical resistance.

Whether using the injection stretch blow molding process or the reheat and blow process, an important part of the process is the mechanical stretching of the preform during the molding process. The preform is stretched with a “stretch rod.” This stretching helps to increase the impact resistance of the container and also helps to produce a very thin walled container.

The extrusion blow molding process allows for the production of bottles in a wide variety of materials, including but not limited to: HDPE, LDPE, PP, PVC, BAREX?, P.E.T., K Resin, P.E.T.G., and Polycarbonate. As noted above, a wide variety of shapes (including handleware), sizes and necks are available. Injection blow molding allows for the production of bottles in a variety of materials, including but not limited to: HDPE, LDPE, PP, PVC, BAREX?, P.E.T., and Polycarbonate.

Besides the P.E.T. noted above for stretch blow molding, a number of other materials have been stretch blown, including polypropylene. As time goes on and technology moves forward, more materials will lend themselves to stretch blow molding as their molecular structures are altered to suit this process.

The decision as to which process will be used is based upon the desired appearance (clear or not), whether chemical or impact resistant is desired, and the desired cost/benefit relationship. The ultimate choice of materials and processes is also based upon the cost of the tooling involved and the sizes of the production runs. Some materials lend themselves to certain types of decorating better than others and some to certain types of decorating to the exclusion of others.

Listed below are representative brands of some types of the machinery we have discussed above. This list is not all-inclusive and you will find additional brands by looking through this and other packaging industry journals and magazines.

For shuttle extrusion type machines Bekum, Battenfeld/Fischer, and Hayssen are probably the best known in the United States. For injection blow molding machines JOMAR is a well known brand. For stretch blow and reheat and blow type machines there are Sidel, Nissei and other machines produced by Johnson Controls and others. For wheel machines you might wish to contact Johnson Controls or Wilmington Machinery.

The approach for recycle different types of plastic

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The confusion over what we can and cannot recycle continues to confound consumers. Plastics are especially troublesome, as different types of plastic require different processing to be reformulated and re-used as raw material. Some municipalities accept all types of plastic for recycling, while others only accept jugs, containers and bottles with certain numbers stamped on their bottoms.

What is the deal with plastics recycling these days? The following description will explain what the different numbers molded onto the bottom of plastic containers stand for.

Recycling by the numbers
The symbol code we’re familiar with—a single digit ranging from 1 to 7 and surrounded by a triangle of arrows—was designed by The Society of the Plastics Industry (SPI) in 1988 to allow consumers and recyclers to differentiate types of plastics while providing a uniform coding system for manufacturers.

The numbers, which 39 U.S. states now require to be molded or imprinted on all eight-ounce to five-gallon containers that can accept the half-inch minimum-size symbol, identify the type of plastic. According to the American Plastics Council, an industry trade group, the symbols also help recyclers do their jobs more effectively.

Easy plastics to recycle
The easiest and most common plastics to recycle are made of polyethylene terephthalate (PETE) and are assigned the number 1. Examples include soda and water bottles, medicine containers, and many other common consumer product containers. Once it has been processed by a recycling facility, PETE can become fiberfill for winter coats, sleeping bags and life jackets. It can also be used to make bean bags, rope, car bumpers, tennis ball felt, combs, cassette tapes, sails for boats, furniture and, of course, other plastic bottles.

Number 2 is reserved for high-density polyethylene plastics. These include heavier containers that hold laundry detergents and bleaches as well as milk, shampoo and motor oil. Plastic labeled with the number 2 is often recycled into toys, piping, plastic lumber and rope. Like plastic designated number 1, it is widely accepted at recycling centers.

Plastics less commonly recycled
Polyvinyl chloride, commonly used in plastic pipes, shower curtains, medical tubing, vinyl dashboards, and even some baby bottle nipples, gets number 3. Like numbers 4 (wrapping films, grocery and sandwich bags, and other containers made of low-density polyethylene) and 5 (polypropylene containers used in Tupperware, among other products), few municipal recycling centers will accept it due to its very low rate of recyclability.

Another useful plastic to recycle
Number 6 goes on polystyrene (Styrofoam) items such as coffee cups, disposable cutlery, meat trays, packing “peanuts” and insulation. It is widely accepted because it can be reprocessed into many items, including cassette tapes and rigid foam insulation.

Hardest plastics to recycle
Last, but far from least, are items crafted from various combinations of the aforementioned plastics or from unique plastic formulations not commonly used. Usually imprinted with a number 7 or nothing at all, these plastics are the most difficult to recycle and, as such, are seldom collected or recycled. More ambitious consumers can feel free to return such items to the product manufacturers to avoid contributing to the local waste stream, and instead put the burden on the makers to recycle or dispose of the items properly.

Why you must stop to use plastic bags

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What’s so bad about plastic bags?
Plastic bags are not biodegradable. They clog waterways, spoil the landscape, and end up in landfills where they may take 1,000 years or more to break down into ever smaller particles that continue to pollute the soil and water.

Americans throw away almost 100 billion plastic bags every year, and only 1 percent to 3 percent are ever recycled.

Plastic bags also pose a serious danger to birds and marine mammals that often mistake them for food. Thousands die each year after swallowing or choking on discarded plastic bags.

Finally, producing plastic bags requires millions of gallons of petroleum that could be used for transportation or heating.

Consider a personal ban on plastic bags
Some businesses have stopped offering their customers plastic bags, and many communities are either considering a ban on plastic bags or have already implemented one.

Can we recycle plastic bottle closures, plastic caps and plastic lids

Filed under: Uncategorized — admin @ 7:11 am

Everyone knows we should recycle metal, glass and plastic cans and bottles, but what about all the lids, tops and caps? I see people recycling plastic bottles, for example, with their caps on, but I’ve always been told to thrown them out. Is that wrong?  Many recycling centers do not accept plastic lids, tops and caps. They are usually made of a different plastic than the containers they accompanied and can contaminate the recycling stream while also jamming equipment and injuring workers.

Many municipal recycling programs throughout the United States still do not accept plastic lids, tops and caps, even though they take the containers that accompany them. The reason is that lids typically are not made from the same kind of plastic as their containers, and therefore should not be mixed together with them.

Recycling Plastic Lids and Caps May Pose Dangers to Workers
Also, plastic caps and lids can jam processing equipment at recycling facilities, and the plastic containers with tops still on them may not compact properly during the recycling process. They can also present a safety risk for recycling workers.

Plastic Lids and Plastic Containers Don’t Mix
“Just about any plastic can be recycled,” says Signe Gilson, Waste Diversion Manager for Seattle-based CleanScapes, one of the West Coast’s leading “greenc solid waste and recycling collectors, “but when two types are mixed, one contaminates the other, reducing the value of the material or requiring resources to separate them before processing.”

Most Communities Ask Consumers to Discard Plastic Lids and Caps
Some recycling programs do accept plastic caps and lids, but usually only if they are off their containers completely and batched separately. Given the many potential issues, however, most recyclers would rather avoid taking them altogether. Thus, it is hard to believe but true: In most locales, the responsible consumers are the ones who throw their plastic caps and lids into the trash instead of the recycling bin.

Metal Lids and Caps Can Sometimes Be Recycled
As for metal caps and lids, they, too, can jam processing machines, but many municipalities accept them for recycling anyway because they do not cause any batch contamination issues. To deal with the potentially sharp lid of any can you are recycling (such as a tuna, soup or pet food can), carefully sink it down into the can, rinse it all clean, and put it in your recycling bin.

“Most plastic bottles are baled for transport, and if they don’t crack when baled the ones with tightly fastened lids can explode when the temperature increases,” Gilson says.
Buying in Bulk Means Fewer Plastic Lids and Caps to Process
Of course, the best way to reduce all kinds of container and cap recycling is to buy in large rather than single-serving containers. Does the event you’re holding really require dozens and dozens of 8- to 16-ounce soda and water bottles, many of which will get left behind only partly consumed anyway? Why not buy large soda bottles, provide pitchers of (tap) water, and let people pour into reusable cups?

The same kind of approach can be taken with many if not all of the bottled and canned grocery items we buy routinely for our homes. If more people bought in bulk, apportioning out of fewer, larger containers, we could take a huge bite out of what goes into the waste stream.

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