Antiblock Agents Selection

Role of Anti-block Agents

Anti-block agents, also referred to as anti-slip agents, assist in minimizing surfaces from interacting with one another either through adhesion or other forces. These materials form barriers between surface layers and modify the frictional properties of the surface.

Anti-block/anti-slip agents can be applied internally or in several cases, applied on the surface. Without an appropriate anti-block or anti-slip agent, depending on nomenclature use, polymers and molded part quality and performance can be severely impacted.

Anti-block agents can be used individually or formulated into a liquid or polymer master batch. Further, these materials may affect polymer specific aspects like:

Friction
Clarity or optical properties
Antistatic properties
Hardness and
Other material/surface characteristics

Common areas of use include polymer systems that are inherently soft and tacky both as fibers and films. The more crystalline polymers are fairly tack-free as fibers though as films, static attraction forces may result in product performance issues.

Another area is injection molding where it is critical that the polymer can be easily removed from the die. Without a release agent & an anti-block agent, the surface of the polymer can be easily damaged resulting in poor quality parts and rejected products.

Let's explore the types of anti-blocking agents and how to choose the correct type for your desired application.

Types of Antiblocking Agents

#1 Waxes: Paraffinic

These materials are produced from petroleum refining. The waxes are typically termed microcrystalline, as these are very small crystals making them fairly flexible and thin.

Benefits	Limitations
Wide range of melting points	Selection of material dependent on processing temperature
Inert with little interaction to bulk material	Melting during the process may alter the effectiveness
Good thermal stability	Less effective in external use

EO/PO materials

Versatile synthetic materials prepared from ethylene and propylene oxide. Ratio changes of EO and PO allows a wide diversity of materials from liquids to hard crystalline type waxes to be generated.

Benefits	Limitations
Wide range of compositions and molecular weights	Variable effectiveness in use
Easy to use due to wide solubility parameters	Hard to use in internal applications
Generally useful in more crystalline polymers PE, PP PET, PA	Minor effect in highly amorphous polymers
Good dispersion assists with other anti-blocks	Minor effect in highly amorphous polymers

#2 Fatty Acid Soaps

These are the typical anti-block materials used for fibers, less so for films and injection molding applications. The soaps are formed by the reaction of the respective acid (or mixed acids) with an alkaline material. Most commonly used internally are Ca, Mg and Zinc salts formed from stearic acid. These are generally cost-effective for most polymer applications. Sodium and preferred potassium salts are widely used for external application end-uses.

Benefits	Limitations
Easy to produce cost-effectively	Solubility for internal uses can be problematic
Choice of inorganic salts allow good performance	Calcium and magnesium soaps are difficult to apply for external use where liquid media is commonly used for applications
Calcium and magnesium offer the preferred anti-block agents for most applications	Sodium tends to be more abrasive and Zinc has been questioned on total effectiveness and potential toxicity issues during processing
Calcium salts for internal uses are generally preferred, zinc in special applications	Calcium and magnesium soaps can be difficult to apply for external use as liquids are normally used to facilitate dispersion and application
Magnesium salts are preferred for external uses
Good thermal stability
Sodium and potassium salts are normally used externally for crystalline polymers

#3 Fatty Acid Amides

Amides display very good anti-block properties with most polymers. They are widely used with PVC and other tackier polymers as well as extruded polymer films. Easily made from a variety of amines and fatty acids, compatibility, optical effects, thermal stability and other physical properties can be adjusted. Higher molecular weight amides are preferred for their thermal stability in extrusion. Behenic, erucic acids and several di-acids amides for internal use in films and fibers predominate offerings available.

Benefits	Limitations
Good compatibility with most polymers	External uses are more difficult to formulate
Variety of compounds are available for customized uses	Stability of polymer can be affected by the chemical structure of amide
Good to exceptional thermal stability	Primary use for films can be highly regulated
Useful in combinations with other anti-block agents	Limited range of materials available for use in film packaging, FDA and EU regulations
Functional as a dispersant for other anti-blocks, especially mineral-based

#4 Silicones

These unique materials offer only limited uses as anti-block agents. High costs inhibit their uses for commodity (low cost) polymers. Silicones are available as a masterbatch formulation with other anti-blocks and their use is defined by their wetting properties and inertness to other materials. Elastomeric fibers make heavy use of silicones, high molecular weight PSMD fluids, to assist in minimizing surface-surface contact.

Benefits	Limitations
Good compatibility with all polymers, especially spandex	Cost ineffective
Good wettability for superior surface coverage of the anti-block effect	Limited needs for most polymer fiber and films
Modified silicones can provide antistatic and softening effects	Modified silicones tend to yellow many polymers, with aminosilicones yellowing in fairly short time intervals
	Hard to formulate with other anti-blocks

#5 Silicates

Silicates are the largest naturally occurring mineral class widely used for anti-block/anti-slip applications. Calcium, aluminum and magnesium are most commonly favored. Talc, a magnesium silicate, is used both internally and externally. Calcium and aluminum silicates find their main use for internal compounding due to their structure and hardness.

Particle size control is very good for these minerals with a newer milling process, offering improved size reduction for superior use versus cost performance. This minimizes the negative impact on polymer properties by an equal performance at less loading.

Additionally, improvements have been realized by the availability of nano-scale materials, like halloysite, a commonly occurring aluminum silicate nanotube. Better anti-blocking effects are demonstrated in fibers and films at far lower loading levels than previously seen.

Benefits	Limitations
Easily obtained materials at low cost	High loading can degrade the final product
Several types used widely with considerable end-use data	Poor particle size control can lead to surface imperfections
Very effective in extrusion of fibers, films and injection molding	Silicates are composed of six sub-classes; several contain asbestos-type minerals co-existing in the ore
Masterbatches for most polymers are readily available to control loading and minimize the impact on bulk polymer	Talc, a member of the Phyllosilicate sub-class, is often found with deposits of asbestos-related minerals
Particle size can be precisely controlled for optimizing performance and bulk polymer properties	Talc, deemed considerably safe, is under increased scrutiny, is external use where excessive prolonged contact or dust inhalation may exist.
Newer nano-scale particle size offering show better anti-block character at lower levels	Toxicity concerns has been raised especially for inhalation of nanoscale materials
Calcium and aluminum silicates are slightly favored versus talc

Selecting Antiblocking Agents

Various classes of polymers tend to have soft, pliable and tacky character. These systems are normally older polymers of lower molecular weight providing very flexible properties, i.e. Polyethylene chloride [PVC] and copolymers which have large substantial amorphous non-crystalline regions, i.e. polyurethanes, represented by elastic polymers like spandex.

These materials rely heavily on the use of anti-blocking agents to maximize their use by minimizing physical interactions of two adjacent surfaces. Films of these inherent tacky polymers and the more crystalline polymers, PET, PP, PE, PA generate fairly substantial static interactions during preparation and require additives that are applied either externally or more generally via internal compounding by a master batch approach.

Anti-block materials tend to be semi-solids or solids though externally used ones can be liquid in form. These materials exhibit a range of properties that need to be profiled for end-uses. While primarily for minimizing surface contact and adhesive forces, they can alter the coefficient of friction, optical properties, optical clarity, polymer character, and other physical and chemical properties.

Importance of Particle Size

Many of the current systems, whether mineral-based or synthetic, have one feature of importance when considering for use. Particle size can make a significant impact on performance and other properties.

Quality and consistency are very important when dealing with solids, especially high melting ones that are unlikely to melt during processing. The smaller the particle size, the greater the surface area affected and potentially lower levels needed for optimum results. This translates into cost savings and efficiencies in managing a process.

With improvements in milling procedures, particle size management in precipitation methods and other unique material handling operations improved and uniform quality control for anti-blocking materials is now available.

Finally, considerable research and commercial availability of nano-scale particles for many materials that have anti-block potential are now new improvements to use, utility and overall effectiveness for higher quality with minimal downsides.

These materials are either mineral-based or synthetic compounds of a wide variety. The more commonly used ones are provided in the selection guide tables below.

Selection of Anti-block Agents for PVC & Elastomers

Polymer Class	PVC Type				Elastomers (like Spandex)
Polymer Class	Internal Use (2)	Application Ease (3)	External Use	Application Ease (3)	Internal Use (2)	Application Ease (3)	External Use	Application Ease (3)
Waxes
Paraffinic/ microcrystalline	3	4	2		0		2
EO/PO	2	3	2		0		1
Fatty Acid Soaps
K, Na	0	0	0		2-	0	2-	0
Ca	5	4	2		1	1	0	0
Mg	2	4	4		1	4+	2+	2+
Zn	1	4	1		1	1	0	0
Fatty Acid Amines (6)
Primary	4-	4	2	3	2	2	0	1
Secondary	4	4	2	3	2	2	1	1
Surface Active Silicones
PDMS	1	n/a	1		n/a	n/a	3+	5
Amino	0	n/a	0		n/a	n/a	4	5
Phosphates	0	n/a	0		n/a	n/a	2+	5
Silicates
Talc (mg) (solid)	0	3	2	2	1	1	4	2+
Hydrosilicates (CA, Mg, Al) (solid)	2	4	0	2	1	3	2	1-
Material Selector: View All Slip/Anti-block/ Anti-tack Agents for PVC Polymer »

Selection of Anti-block Agents for Films & Rubber

Polymer Class	Films ( PET, PA, PE, PP, Aramids)				Rubber
Polymer Class	Internal Use (2)	Application Ease (3)	External Use	Application Ease (3)	Internal Use (2)	Application Ease (3)	External Use	Application Ease (3)
Waxes
Paraffinic/ microcrystalline	4+	5	3	3	4	4	3	4
EO/ PO	2	5	3+	4	0	0	0	0
Fatty Acid Soaps
K, Na	0	0	4	5	n/a
Ca	3	5	2	3	4	4	3	3
Mg	4	5	1	0	4	4	4	3
Zn	3+	5	0	0	4	4	2	3
Fatty Acid Amines (6)
Primary	3	4	2	2	n/a	n/a	n/a	n/a
Secondary	4	4	3	2	n/a	n/a	n/a	n/a
Surface Active Silicones
PDMS	1	2	3	4	n/a	n/a	n/a	n/a
Amino	1	1-	3+	4	n/a	n/a	n/a	n/a
Phosphates	1	1-	2	4	n/a	n/a	n/a	n/a
Silicates
Talc (mg) (solid)	4	5	n/a	n/a	3	3	4	3
Hydrosilicates (CA, Mg, Al) (solid)	3+	5	n/a	n/a	3	3	4	3
Legends for tables above Anti-block and anti-slip agents tend to be synonymous by name as effects of materials are similar Normal process temperatures for this class of polymer Overall ease to apply internally or externally (formulated or individually): For Aramids, the internal application is very difficult Normal Internal Application via polymer masterbatch compounding Normal Internal Application via rubber compounding, external just as a release agent in the tire mold Work both as friction modifier and anti-block. Secondary systems internally offer higher thermal stability but lower migration to surface rates and are preferred for films

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Antiblocking Agents: Types & Selection Process