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There is no denying that plastic filler materials are one of the most essential factors in retaining cost-effectiveness for plastic firms. Let’s take a look at 4 most common plastic filler materials in the plastic industry to better acknowledge the benefits of these magical materials.

Plastic filler materials are known as one of the key factors leading to the revolution of the plastic industry. The volume of plastic filler consumption reached approximately 33 billion tons in 2016. Countries which record the largest number of plastic beads materials exported include Asian countries such as China, Japan, Korea,…, followed by North America and Europe.

The use of plastic filler materials have brought various benefits to plastic firms, in which the most important is cost reduction and mechanical properties enhancement.

1. What are plastic filler materials?

For a long time, primary plastic has been seen as the only way for many manufacturers who wish to manufacture plastic products. At that time, plastic production was extremely unstable and risky due to the uncertainty of oil, which is the main source of all types of plastic worldwide. As such, for a large number of companies, especially those who depend completely on foreign market, plastic production has never been an easy task, as they are usually put into a struggling situation when primary plastic’s price gets higher or delivery is late as a consequence of the unexpected.

That’s the reason why the plastic filler materials are born. Technically, they are particles added to plastic production to cut cost as well as supporting in enhancing some properties of end-products. Plastic filler materials are divided into two groups:

• The inorganic (also known as mineral) fillers such as calcium carbonate (limestone), magnesium silicates (talc), calcium sulfate, mica, calcium silicate, barium sulfate and kaolin (China clay).
• The organic plastic fillers such as tree bark flour, nut flours, chicken feathers, and rice hulls.

Normally, the inorganic filler materials are more prefered in industrial production as their simple molecular composition makes them more easily to be processed. Therefore, in this article, we would like to go deeply into the inorganic ones.

2. The most commonly used plastic filler materials

As mentioned, there is a wide variety of plastic filler materials and their uses completely depend on the characteristics of end-products as well as the standard requirements. These listed below are the top 4 most widely used in the plastic industry.

Calcium carbonate (CaCO3)

Calcium carbonate is a substance which is most commonly found in the form of rocks or limestone. It is also the main component of eggshells, snail shells, seashells and pearls. In the plastic industry, calcium carbonate is also widely used as one of the plastic filler materials. It improves mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity) when being added to PVC. Polypropylene is another resin that uses calcium carbonate at the proportion of 20 – 40% as it strengthens the rigidity – an important requirement when plastic is exposed to high temperature. Most importantly, this matter helps significantly decrease the overall production cost, which often accounts for up to 60% of product’s price. Compared to primary plastic, CaCO3 is more reasonable and less fluctuating, thus degrading the uncertainty for the business.

Magnesium silicates (talc)

Talc is a clay mineral, composed of hydrated magnesium silicate and made of three main components including magie, silic and oxi. In nature, talc is a common metamorphic mineral in metamorphic belts that contain ultramafic rocks, such as soapstone (a high-talc rock), and within whiteschist and blueschist metamorphic terranes. It is widely used in the plastic industry as one of the effective plastic filler materials to enhance durability, thermal resistance, anti UV and anti aging ability. The combination between talc and plastic resins creates talc filler masterbatch, which is widely prefered thanks to its mechanical properties enhancement and processability as it requires no changes in the manufacturing equipment, thus saving a large amount of expense for plastic firms.

Besides, talc can also be added into compounds (tailor-made materials to serve for a specific plastic product) to enhance end-products properties such as rigidity, modulus bending, flexural strength as well as decreasing the level of shrinkage, warping and improving the conductivity and surface rigidity.

Sodium sulfate (NaSO4)

Sodium sulfate is another well-known substance which is widely used as a plastic filler. Sodium sulfate’s fomular is NaSO4 and mostly found in the form of decahydrate (known as mirabilite mineral or Glauber’s salt). NaSO4 is commonly known for its high solubility in water and it rises more than tenfold between 0 °C to 32.384 °C. One outstanding advantage of sodium sulfate is its transparency (more clear than calcium carbonate) and its reasonable price (cheaper than barium sulfate). Therefore, sodium sulfate is widely used as one of the plastic filler materials.

The use of sodium sulfate significantly improves the transparency and glossiness of plastic products. Also, it reinforces end-products mechanical properties with excellent dispersion, high tenacity and strong stability. Furthermore, sodium sulfate is highly recommended thanks to its eco-friendly components, which barely pose any threats on our environment.

Barium sulfate (BaSO4)

Barium sulfate is an inorganic compound that is odorless and insoluble in water. It is commonly used as a plastic filler to increase the density of the polymer in vibrational mass damping applications. In polypropylene and polystyrene plastics, it is commonly used as a filler with a proportion of 70%.

However, one disadvantage of barium sulfate is the relatively high price compared to other plastic filler materials. The more transparency required, the larger proportion of BaSO4 needed, thus costing plastic firms a greater amount of production expense. That more or less raises hesitation from customers’ view as they are looking for an alternative solution for primary plastic to address the cost’s problem, not to get another burden.

 3. Which plastic filler materials to choose?

As such, there is a large number of plastic filler material for plastic firms to use. However, the challenging part is how to choose a suitable one for your companies. These criteria below may simplify your decision making process:

What are your end-products? This should be the first priority for any firms who wish for a plastic filler. What are your products used for? What are their standard requirements? Which mechanical properties do you expect? That information definitely gives you a clue on which should be the right plastic filler material.

Are you on a budget? Of course, you are searching for plastic fillers with a view to saving on production cost. However, even the price of plastic fillers varies from the lowest like calcium carbonate to the highest like barium sulfate. Therefore, positioning a range of acceptable prices is necessary.

Quality and reliability should never be underestimated. A famous manufacturer who owns a good reputation is undoubtedly more trustworthy than an unknown one, especially those experienced in the market can give you valuable advices on appropriate products.

Blowing film is one of the most popular methods of film manufacture. However, it’s not an easy mission to choose the right blowing film resin because each product requires specific properties, which leads to different input materials. So how exactly do we find the correct ones? Let’s hammer out in this article!

1. What is blowing film?

Blowing film (also known as the Tubular film) is one of the most common methods of film manufacture. To initiate the process, materials mixture is entered into the extruder through a hopper. After being melted, it goes through an annular slit die and is formed as a thin tube. The tube is then cooled by the air ring and continues moving upwards until it passes through nip rolls, where it is flattened. This lay-flat tube is then taken back down via more rollers. The edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels.

2. What is blowing film technology used for?

Blowing film is widely used in many applications to create various products, ranging from simple monolayer films for bags to very complex multilayer structures used in food packaging. Some products of this process include:

• Industrial films and bags
• Agricultural and construction films
• Barrier films
• Stretch films
• PVC cling films
• Laminating films
• Can liners
• High barrier small tube systems.

3. Why need to consider blowing film resin ?

As mentioned above, there are many types of films which are the outputs of the blowing film process. However, each product has some particular properties regarding adhesion, stiffness, toughness, formability, thickness,…thus requiring mindful choices of input resins to ensure that end products can meet all standard requirements.

Besides, the choice of resins is also about the production cost problem as raw material cost accounts for up to 80% of the overall cost of making film. Therefore, making the right decision on the input resins also helps plastic manufacturers save a large amount of expense.

4. Most common blowing film resin

Polyethylene (PE)

All types of PE are chemically identical: a wide range of processing and product properties results from different forms of branching, crystallinity levels and densities.

• PE is the basis of most co extruded blown film structures
• Used in sealant layers and in-forming film bulk
• Often blended together to optimize property profiles, processability and cost
• Excellent chemical resistance

High-density PE (HDPE)

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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.