The part becomes more rigid as it cools in the mold. Even an essentially rigid material might be successfully ejected from the mold if this function is performed while the part is still soft. 

However, the part must also be rigid enough to withstand the force of ejection without enduring permanent distortion.

The point at which the cap is cool enough to eject, yet warm enough to strip off the core, will vary according to the means of ejection employed.

Ejector pins provide very localized forces at the base of the cap. An ejector plate creates an ejection force which is distributed uniformly across the base of the cap. Therefore the cap can be ejected in a softer condition with the use of a stripper plate.

That results in a cycle reduction on the order of 30%, however, the stripper plate adds a significant increment of cost to the tooling.

The amount of force required to eject the part can also be attained through the use of interrupted threads on the bottle cap. By breaking the continuity of the thread, the amount of material which must be stretched to permit removal of the cap from the mold is significantly reduced.

The determining factor in how deep a thread can be stripped is its strain rate.

Continue to Bottle Cap Case Study

The bottle cap will be presumed that it must be made of acrylic for appearance reasons because this polymer can provide a very high level of gloss.

Acrylic is an amorphous thermoplastic with a very low rate of strain. In this case, too low to permit the part to be stripped off the mold. Therefore, the cap would need to be turned off the core of the mold.

Challenges to turn the part off the core

In order to turn the part off the core, an unscrewing mechanism must be employed. There are several ways to go about this, however, all of them incur significant additional cost.

Furthermore, the space required for the mechanism limits the number of cavities which can be placed within a mold base. If the platens of the molding machine have sufficient space, a larger mold base can be used. However, if the mold was already sized to the limits of the platen, the number of cavities will need to be reduced or a larger molding machine will be required.

Either way, fewer bottle caps will be produced with each molding cycle and the machine cost for each cap will be increased, thus reducing the efficiency of the production. 

The machine cost will also be increased by the longer cycle necessitated by the time required for the unscrewing mechanism to function. Thus, a cap produced in an unscrewing mold will always have a greater machine cost increment than one which is stripped off a core—all other elements being equal.

A solution for lower production quantities

There is another method for producing internal threads which are too rigid to be stripped off a mold. That involves a core mechanism which collapses.

Such “collapsing cores” are patented and there is an added cost for this mechanism. Molds utilizing these cores cycle nearly as fast as stripper plate molds and the mechanisms require a moderate amount of additional space.

However, these molds are reported to have higher maintenance costs than the other types of molds and are generally thought of as a solution for applications with lower production quantities.

In conclusion, the details of the part design are dependent on the decisions reached as a whole. Clearly the thread design will be dependent on the determination of whether the cap is to be turned or stripped off the core or whether a collapsing core is to be used instead. When appearance is of greater importance than molding efficiency, esthetic requirements may be the determining factor.

The melt coloring of plastics is one of the most functional value added features a resin producer, compounder, or parts fabricator can impart to their products. It not only provides desired appearance properties that help sell the product, but it can also enhance several other properties, such as stability toward UV light. In addition, melt coloring usually eliminates the need for a separate, off-line, painting step. Overall manufacturing costs can thereby be reduced.

Once the color system is incorporated into the plastic matrix, however, it becomes an integral part of the material and may alter the engineering, performance, and processing properties in ways not considered during the design and formulation of the new material. Coloring, frankly, is usually viewed as the end-users problem, and the ball lands in the court of the color formulator.

This specialist (who is usually untrained in the finer points of polymer science) is then left with the task of navigating through what often seems to be an obstacle course of known and unpredicted interactions while trying to give the end-user an economical color package that will meet the product’s appearance requirements.

The task is even more critical in the case of high performance polymer blends and alloys, whose highly valued engineering and performance properties are often sensitive to small compositional changes.

THE MAJOR CLASSES OF COLORANTS

The colorants used in plastics fall into two very broad categories: pigments and dyes. Pigments are defined as colorants which do not dissolve in the plastic matrix of interest, whereas dyes are colorants that do go into solution. Pigments therefore reside as a separate phase.

Consequently, there are phase boundaries to consider, and these can be crucial to the end-user.

INORGANIC PIGMENTS

Inorganic pigments are metal salts and oxides which can predictably impart color to a substrate. Most of these pigments have an average particle size of about 0.2-1.0 microns. The manufacturers take great pains to eliminate agglomerates with particle sizes above 5 microns.

With few exceptions, inorganic pigments are inexpensive raw materials. Because of their relatively low color strength they are not always the best value. 

Some good properties which many inorganic pigments share are:

• easy to disperse (relatively little work is required to break down the pigment,

coat it with the plastic, and distribute it uniformly);

• good heat and weather resistance;
• little, if any, reactivity.

Make note of this: COLOR SELLS! If you want a new high performance thermoplastic alloy or blend to reach the widest number of appropriate end user markets, you have to be able to color it in a cost effective manner that does not harm its performance properties.

Barriers to cost effective coloring include: 

• the material’s inherent color and opacity;

• chemical incompatibility with one or more polymeric or compatibilizer components;

• physical incompatibility with one or more polymeric components (many materials will not physically accept dyes, e.g.);

• stringent heat stability and/or weathering requirements. Of these barriers, the one that is most overlooked is the first.

Many of the new thermoplastic materials coming into the marketplace are blends and alloys that are specifically engineered to provide a combination of the properties of the individual polymers.

Often these materials combine crystalline and amorphous polymers with an impact modifier. The products of these marriages often contain a maze of phase boundaries that result in light scattering (milkiness) equivalent to as much as 0.5% titanium dioxide.

Obtaining high chroma colors (e.g., some electrical code colors or even a jet black) in the presence of this inherent milkiness becomes an expensive proposition. Often so much color has to be added to the material formulation that critical material properties are affected – a double whammy, cost and performance.

There are 4 principle elements to a successful plastic product: material selection, part design, tooling, and processing. Typically, product designers are effective part designers but have limited background in the other disciplines. 

This leads to products which are more expensive than necessary and difficult to manufacture—which also increases the cost. 

Many companies have solved this problem through the use of multidisciplinary design teams. However, team members report that such teams can be dysfunctional, often due to the fact that team members’ schedules are difficult to synchronize or a lack of availability of required skills.

Ideally, the part designer would know enough about these other disciplines to be able to design with them in mind. That utopian situation could create the ultimate in efficient product design—the holistic design approach.

Bottle cap example.

A closure for a bottle

An example of this type of thinking would be the case of a closure for a bottle containing cosmetics. In order to protect the contents, the closure must seal the opening.

Typically, that seal is created with a seal ring or liner which is clamped down with force provided by screw threads, thus creating what is generally known as a bottle cap.

Process selection is simplified because the process of choice for most bottle cap applications is injection molding.

Compression and transfer molding are possibilities, however, they are slower than injection molding and are rarely used for thermoplastic materials. Therefore, they would only be considered if the material of choice turned out to be a thermoset.

Example of cosmetic bottle caps

In the case of a cosmetic bottle cap, the most extreme temperatures it is likely to encounter will be in transit or washing prior to application. This limits the range to that which is readily accommodated by most thermoplastics without deformation.

However, thermal expansion will need to be considered as the cap cannot loosen enough to break the seal at elevated temperatures nor contract enough to crack at low temperatures.

Furthermore, it must not fail due to stress relaxation over time nor impart an odor of its own to the contents. For a cosmetic application, there may also be an appearance requirement of a high-gloss surface.

Most importantly, it must withstand the chemical attack of the contents. While resin manufacturers typically perform limited tests for resistance to various chemical compounds, they cannot do this when the composition of the exposure is a secret such as with a cosmetic.

The manufacturer is expected to conduct such tests privately.

There is another element of material selection for a bottle cap which involves the tool building and processing disciplines. It derives from the fact that the decision must be made as to whether the threads are to be stripped off the core, turned off the core or the core is to be collapsed to permit ejection.

The tool for the former will be far less expensive and the mold will operate at a much faster rate of speed. However, the material must be one which is flexible enough to strip off the mold, yet rigid enough to perform its other functions.

The problem is created by the fact that the formation of a thread creates plastic at a point inside the largest diameter of the hardened core as shown in the picture below

As the force of ejection pushes on the base of the cap to remove it from the core, it must be flexible enough to expand off the core as illustrated below

Anti-blocking agents roughen the surface of the film to create a spacing effect.

Self-adhesion is an undesirable situation when using LLDPE and LDPE film.

Anti-blocking additives like other plastic raw materials are melted into the thermoplastics directly or in use of a masterbatch.

Therefore, an anti-blocking additive is developed to make a slight surface roughness. By doing so, the additive prevents the film from sticking to itself.

Daily use items such as grocery bags, shipping bags and a lot of packaging applications are incorporating antiblocking agents and slip agents into PE films.

LLDPE and LDPE are the 2 most common polymers extruded into a film. HDPE is also common, but it is being used less than LLDPE and LDPE.

Why use PE resins in film packaging?

Well, simply because PE resins are low cost and weight, high toughness, and have many optical properties.

4 criteria are used in the selection of an antiblocking agent, as shown in the infographic below:

The inorganic materials dominate the antiblocking agents market.

The four major types of antiblocking agents are:

1. Diatomaceous earth
2. Talc
3. Calcium carbonate
4. Synthetic silicas and silicates

A majority of inorganic additives suppliers provide the market with fillers and extenders as their primary additive products. Those additives can also be used as antiblocking agents in PE films. However, only a few filler and extender suppliers promote their products for this end use.

1. Slip agents.

Slip agents or slip additives are the terms used by industry for those modifiers that impart a reduced coefficient of friction to the surface of finished products.

Slip agents can significantly improve the handling qualities of polyolefins and, to a lesser extent, PVC, in film and bag applications. They help speed up film production and ensure final product quality.

Fatty acid amides, the primary chemical type used as slip agents, are similar to migratory antistatic agents and some lubricants with a molecule which has both a polar and non- polar portion.

These additives migrate to the surface and form a very thin molecular layer that reduces surface friction.

Slip agents are typically employed in applications where surface lubrication is desired—either during or immediately after processing. To accomplish this, the materials must exude quickly to the surface of the film.

To function properly they should have only limited compatibility with the resin. Slip agents, in addition to lowering surface friction, can also impart the following characteristics:

• Lower surface resistivity (antistatic properties)
• Reduce melt viscosity
• Mold release

Slip agents are often referred to as lubricants. However, they should not be confused with the lubricants which act as processing aids.

While most slip agents can be used as lubricants, many lubricants cannot be used as slip agents since they do not always function externally.

The major types of slip agents include:

• Fatty acid amides (primarily erucamide and oleamide s Fatty acid esters
• Metallic stearates
• Waxes
• Proprietary amide blends

Antiblock and slip agents can be incorporated together using combination masterbatches which give the film extruder greater formulation control.

Suppliers

Because of the different chemical composition of anti-blocking and slip agents, few companies are involved in both. A few of Vietnam’s companies fully developed anti-blocking and slip agents listed below.

 

Flame retardants are in a unique position among plastics additives in that they are both created by regulations and yet are threatened by other regulations. They are expensive and lower the physical properties of the plastics in which they are employed.

On the other hand, environmental and toxicity concerns now have regulators looking at the important halogenated and antimony-based synergist flame retardants that have been developed over the years. Any regulations which limit the use of such products will again change the industry and force producers to develop a new generation of products.

Flame retardant overview

Flame-retardant additives for plastics are essential safety materials. The transportation, building, appliance, and electronic industries use flame retardants in plastics to prevent human injury or death and to protect property from fire damage.

Fundamentally, flame retardants reduce the ease of ignition smoke generation and the rate of burn of plastics. Flame retardants can be organic or inorganic in composition and typically contain either bromine, chlorine, phosphorus, antimony, or aluminum materials.

The products can be further classified as being reactive or additive. Reactive flame retardants chemically bind with the host resin. Additive types are physically mixed with a resin and do not chemically bind with the polymer.

Flame retardants are used at loading levels from a few percents to more than 60% of the total weight of a treated resin. They typically degrade the inherent physical properties of the polymer, some types significantly more than others.

Resin formulators and compounders must select a flame retardant that is both physically and economically suitable for specific resin systems and the intended applications.

It is common to formulate resins with multiple flame-retardant types, typically a primary flame retardant plus a synergist such as antimony oxide, to enhance overall flame-retardant efficiency at the lowest cost. Several hundred different flame-retardant systems are used by the plastics industry because of these formulation practices.

Driving forces

In addition to cost and performance demands, the plastics market for flame retardants is driven by a number of competing forces ranging from fire standard legislation and toxicity regulations to price situations, performance, and other market factors.

These combined factors have resulted recently in significant shifts in demand for the major types of flame retardants.

Further, large numbers of new flame retardants have emerged, designed for both traditional and specialty niche markets.

Recent acquisitions, joint ventures, and alliances by flame- retardant producers have also created constant change in this market. The largest area of activity is in non-halogenated flame retardants because of environmental concerns associated with the halogen-based products.

Down the road, the need and the market exist for non-halogenated approaches to the flame retarding of plastics. All the major flame retardant companies, including those making halogenated types, are working in the area.

Viable, non-halogenated flame-retardant products do exist, but customers are reluctant to sacrifice the cost/performance advantage of brominated products. Organic phosphate, inorganic phosphorus, melamine salts, and inorganic metal hydrate approaches seem to be the major directions being followed to develop non-halogenated alternatives.

Suppliers

MTB has 2 kinds of ABS Flame Retardant Compounds:

• Non-halogen
• Halogen

 

 

 

 

 

The packaging is the biggest market for additives.

The output of plastic packaging depends strongly on the population, people’s average income, and expenditure.

We need plastic packaging mostly for the food and beverage industry. Therefore, the increase in the population and the average income will have a positive effect on the demands of plastic packaging as well as additives.

Packaging industry

Foreign market

Asia has the rapid growth in the consumption of plastic packaging.

The first reason is that Asia has the highest and most developing population rate. Researchers forecast that Asia is going to reach 4,3 billion people in 2022. Moreover, the population growth rate and GDP growth rate are “gold rate” and desirable.

Besides, Europe and North America consume plastic packaging a lot. While those 2 regions have a quite low population density, they have a good source of income and their consumption habits of plastic packaging were established a long time ago (since 1950).

Flexible packaging makes up 59% of the total consumption of plastic packaging.

Flexible packaging is made from PE and PP resins by blow molding. The consumption of flexible packaging and bottle packaging is forecasted to decrease a little bit due to the increase in people’s awareness of the environment.

Food packaging and bottle packaging made up for 93% in 2,400 billion of packaging products in 2018. The demand for food packaging will reach 1,788 billion products in 2022.

Asia is the main and most potential market for the plastic packaging industry.

As I said before, Asia has the gold growth rate of population and average income.

Another reason is that many developed countries are moving towards “green life”, minimizing the use of single-use plastic products.

Vietnam

The development in the non-alcohol beverage market will drive the plastic packing industry in a new chapter.

The demand for plastic packaging products mainly depends on the growth of food production, the beverage industry, and household income and expenditure in general.

According to BMI, household spending will be about VND 3.3 million billion in 2019 VND and 4.7 million billion VND in 2022. Of which, spending on food and non-alcoholic beverages will still account for a large proportion, about 20% of total household expenditure.

The growth of food and non-alcoholic beverages is expected to grow by 11.8% and 12% per year, respectively, from 2019 to 2022. This is the main driving force for the growth of food processing and beverage industries.

Main Additives used

Materials/Resins

The 5 most popular additives used in the packaging industry are anti-blocking and slip agents, anti-fogging agents, the usual heat and light stabilizers, and pigments.

Oxygen scavengers are also getting popular in food packaging.

PE is the dominant packaging polymer, it is used in very high-volume shopping bags, rubbish sacks, and food packaging. HDPE is the most essential, especially in Europe.

PP is used more in the specialized role of industrial goods.

Polyethylene naphthenate is being promoted in the form of thin, flexible film with good barrier properties.

Specific additives for packaging industries

Social habits change, people’s expenditure habits change. The increasing popularity of hanging out with premade meals and microwaveable containers leads to a remarkable increase in using food packaging; therefore, increasing the use of additives.

The technology to premade and packaged food requires special additives.

Plastic bottles and containers have undergone considerable changes in recent years due to increased interest in barrier layers.

Consumers also like bottles to have a wide mouth. PVC has been defeated as a bottle material by PET.

Adding an impact modifier creates a favorable condition for PET to gain competitive advantages over polycarbonate in manufacturing larger bottle sizes.

Moreover, PE clarifying additives allows you to produce cheaper and cleaner packaging.

Anti-fogging agents are used in flexible PVC food wrapping. UV absorbers used in transparent bottles to protect the contents and the polymer.

People are considering to stop using single-use plastic in many packaging applications. Due to litter issues, the fast-food industry is criticized a lot. Several countries have banned single-trip shopping bags.

Non-woven and multi-trip packages are trendy.

 

Additives are essential. Plastics are not plastics anymore without additives. Plastics on their own have many properties that make them ideal for creating durable consumer goods. Plastic additives help to enhance these features and add new features that are often needed to assist in the processing, manufacture, and final uses.

Additives solve problems

Melting temperature and sticking to machines are problems in the process of extrusion.

Additives are added to the plastic to help deal with it. Process aids help the pigments in the plastic to dissolve in the liquid around them.

Lubricant is used with plastic, which becomes very sticky when melted. It reduces friction between particles and construction machines. In the antioxidant process, additives are used to protect plastics from excessive heat, which can often lead to breakage or adversely have a significant effect on product color.

The problem of dissolving plastic in heat when it melts is called heat stabilizer. All of this helps make the manufacturing process more accessible and cheaper.

Extra items can also be used for purely aesthetic reasons. Pigment binders serve a variety of practical and aesthetic purposes. Plastic made to match the color of other large product parts, such as in automobiles, or they can be colored to attract the attention of consumers.

Additives bring more values to plastic products

Practical use includes the manufacture of opaque plastics to protect lightly sensitive materials, such as milk bottles or medicine containers. The pellets are added to the plastic before melting and mixing for the plastic to be dyed expertly.

Different compounds and blends combine to create different colors and light properties. Carbonic black and titanium oxide are two common pigment additives. Carbon black light-reducing plastics look black, while titanium oxide blocks light and blends the plastic with white.

Reduce the frequency of product replacements and maintenance

Another beneficial use of additives in plastics is to add value to final products. This will ultimately save money for consumers who need to reduce the frequency of product repairs or replacements.

Impact modifiers have been combined to improve crack resistance. It is useful for durable plastic products. Light stabilizers and UV absorbers enhance durability. They protect the plastic from the negative effects of the sun and extend plastic life. Without such additives, plastic products are more likely to be useless in a short time.

Increase the safety level for end-users

Additives to make plastic more economically beneficial and more durable. Additives also contribute to the safety of end-users. Many additives mentioned above make the products safer.

For example, flame retardant is suitable for extrusion coating and other high-temperature applications. It exhibits good thermal and UV stability and also does not adversely affect sealability in films.

Save money and energy  

Plastic additives make plastics more environmentally-friendly. Plastic parts are perfect alternatives to metal parts in cars. It is not only lighter but can also take less energy to produce.

Besides, additives save your money. For example, mineral fillers boost the thermal conductivity of plastics; therefore, they cool down and heat up quicker than normal. What does that mean to you? It means shorter mold cycle times and more articles produced at a lower cost. 

0.5p/molding may not sound remarkable. However, if you produce several injection moldings every few seconds, you will be surprised at how much you save after a year. There is a wide variety of additives available to help reduce costs that mention below.

10 common types of additives

MTB has developed successfully 10 types of additives that will enhance your products and save cost-effectively:

• Weather Stabilizer
• Anti-Aging
• Anti-Fog
• Anti-static
• Flame retardant
• Desiccant / Humidity absorber
• Anti-Blocking Slip
• Anti-blocking and Slip
• Processing Aid
• Odor scavenger

 

 

 

 

Main function of polymer additives.

Normally, manufactures choose additives used in plastics materials based on their intended performance over a chemical basis. For more convenience, MTB classifies additives into 8 groups with similar applications and functions.

Functions	Additives
Polymerization/chemical modification aids	Accelerators Chain growth regulators Compatibilizers Cross-linking agents Promoters
Improvement in processability and productivity (transformation aids)	Flow promoters Plasticizers Processing aids Release agent Surfactants Thixotropic agents Wetting agents Defoaming and blowing agents
Increased resistance to degradation during processing application	Acid scavengers Biostabilisers Light/UV stabilizers Metal deactivators Processing/thermal stabilisers
Improvement/modification of mechanical properties	Compatibilizers Cross-linking agents Fibrous reinforcements (glass, carbon) Fillers and particle reinforcements Impact modifiers (elastomers) Nucleating agents Plasticizers or flexibility
Improvement of product performance	Antistatic agents Blowing agents EMI shielding agents Flame retardants Friction agents Odour modifiers Plasticisers Smoke suppressants
Improvement of surface properties	Adhesion promoters Anti Fogging agents Antistatic agents Antiwear additives Coupling agents Lubricants Slip and anti blocking agents Surfactants Wetting agents
Improvement of optical properties	Nucleating agents Optical brighteners Pigments and colorants
Reduction of formulation cost	Diluents and extenders Particulate fillers

Generally speaking, the main applications of additives are to reduce cost and alter polymer properties. In the past, manufacturers just sought to have one or two particular material improvements. However, in present, with the strong and fast development of R&D departments, multifunctional additives are born. Now, we can combine several different additive functionalities together. For example, EuP processing aid and flame retardant in cross-linked epoxies.

Common concerns over additives

There are some typical concerns about additive technology raised by plastics manufacturers and producers. MTB takes the application of injection moulding of polyamides as an example.

However, the appropriate addition of chain extenders and nucleating agents, release agents…etc can tackle the problems without much effort. The benefits of additives are obvious. Additives are not simply a kind of optional ingredient, but an essential factor to plastics producers and manufacturers’ success.

Main technology concerns

Short cycle times Better mould release Plate-out and deposits on moulds and plastics surfaces Feeding problems Increased dimensional stability, less shrinkage Processing protection against depolymerisation and yellowing Better melt flow Improved surface of glass-reinforced parts Better strength of flow lines in moulded parts Higher molecular weight Rise of impact strength and elongation at break

Understand customer’s concern, MTB has developed 10 types of additives that will enhance your products and save cost effectively:

1. Weather Stabilizer
2. Anti-Aging
3. Anti-Fog
4. Anti-static
5. Flame retardant
6. Desiccant / Humidity absorber
7. Anti-Blocking
8. Slip Anti-blocking and Slip
9. Processing Aid
10. Odor scavenger

Contact us for more information and get a solution for optimizing your business.