Plastic Caps and Plugs
Plastic caps and plugs are two distinct ways for sealing the ends, tops, and openings of tubes and containers. Caps are placed over the opening, and plugs are placed in the opening. Due to the many varieties of...
Please fill out the following form to submit a Request for Quote to any of the following companies listed on
This article presents will present detailed information about plastic coatings and dip molded plastics. Read further to learn more about:
Plastic coating is the application of liquid polymers or plastic onto the surface of a workpiece through dipping/immersion. The result is a thick plastic finish for protective and decorative purposes. This gives the material additional resistance against scratches, wear, corrosion, and external elements. It makes a metal piece more durable, and gives it longer service life. Plastic coatings serve as convenient and protection for end-users by providing surfaces for gripping and insulation.
Plastic coating is usually seen in hand tools, handles, and grips. Pliers are a typical example of a hand tool with plastic coating. With the plastic coating applied on the handle, compression or bending of a rigid material is convenient to the user and more efficient while preserving the hand tool itself. Other applications that benefit from its rigidity are shopping carts, baskets, forceps, covers, caps, plugs, and much more.
Plastic coatings are also known to be heat and electrical insulators. They can also be seen in many hand tools such as tongs and spatulas, serving as additional protection when handling hot objects. Plastic coatings also serve as insulation in electronic components such as wires, cables, digital meter probes, and so forth.
The process of casting a plastic material into a pre-existing metal piece is called dip molding. The metal that is coated acts as the mold that the plastic or polymer adheres to during the process. The portion (or sometimes the whole piece) to be dipped or immersed is treated and preheated before it is lowered directly into the liquid polymer. The liquid polymer adheres to the metal and hardens upon cooling.
The process of dip molding is similar to dip coating; except that dip molding has an additional demolding or unloading step. Dip molding creates single, hollow, and double-walled parts. This eliminates the need for additional downstream processes such as trimming and deflashing. By having fewer subtractive secondary operations, the process saves raw materials. Some dip molded plastic products are latex gloves, fashion and costume accessories, cups, plastic closures, and recreational equipment parts.
The most common polymers used as coating materials are plastisol, latex, neoprene, polyurethane, and epoxy. A notable desired characteristic of a polymer is that the polymer mixture must be readily available in liquid form at room temperature without needing additional processing. Also, before the liquid polymer is considered for dip coating and dip molding processes, it must be viscous enough to be able to resist flowing off the surface of the mold; hence, the polymer settles on the surface until it is cured.
Plastisol is the most commonly used polymer in dip molding and dip coating processes. It is composed of fine polyvinyl chloride (PVC) resins suspended in a liquid plasticizer. When exposed to heat, it solidifies into a soft, flexible, and rubber-like material upon cooling. Plastisol coating is known for its toughness, excellent corrosion resistance, and impact resistance. It has high dielectric strength, which makes it suitable for electrical applications. Colorants are added to customize the finish of the end product.
Latex is an emulsion of very small polymer particles (30-40% of which are rubber particles). It is the raw material for rubber production, which may be natural or synthetic. This polymer is readily available and non-toxic. However, according to some studies, some individuals develop allergic reactions once it degrades into powder, decreasing its popularity.
Neoprene is produced by the polymerization of chloroprene and is a substitute for latex. It is known for its chemical resistance and flexibility.
Polyurethane is composed of urethane (or ethyl carbamate) groups joined by carbamate links. It is known for its flexibility and high resiliency to deformation.
Epoxy is a thermosetting polymer that forms high-strength, and chemical, and thermal-resistant coatings once the polymeric chains have been cross-linked.
As mentioned in the previous chapters, dip coating and dip molding have the same operating concept. In this chapter, the procedures in both processes will be discussed.
Pre-treatment steps are important to properly apply the plastic coating to the metal substrate. These steps are critical for both processes.
The pre-treatment of a dip coating process is more delicate than dip molding processes since the polymer is intended permanently cover the metal, which acts as the mold. The steps are as follows:
Impurities interfere with the adhesion of the polymer to the mold or part. An impurity acts as a weak regions where damage can initiate and propagate.
Oils and greases on the surface of the metal substrate act as impurities that decrease water resistance and prevent proper adhesion and deposition of the plastic coating. Oils and greases are removed by means of alkali washes, acidic washes, or thermal degreasing.
For coating previously coated parts, the old coat is thoroughly removed before the new coat is applied.
Aside from cleaning the surface, additional properties can be imparted to produce desirable characteristics. These characteristics may be helpful in the dip coating process itself or the end-use of the product.
Phosphating (or phosphate conversion) is the process of applying a thin phosphate layer before plastic coating. The phosphate layer gives additional corrosion resistance to the substrate for cases where damage to the plastic coating is inevitable. Common phosphate layers used in dip coating are zinc phosphate, iron phosphate, and tricationic phosphate.
Shot peening is done by striking a surface with round particles, inducing cold working. This introduces compressive residual stress on the surface of the substrate to strengthen and relieve any residual stress. Residual stress causes microcracks that may be induced in the proceeding processes.
Blasting modifies the surface of the substrate by inducing microscopic holes. This increases the surface area to which the primer, undercoat, and plastic coating can stick. Common types of blasting processes used are sand, metal grit, glass bead blast, plastic bead blasting, and so on.
De-embrittlement is a heat treatment process that removes the hydrogen diffused into the metal substrate, which increases the risk of brittle fracture under stress. The diffused hydrogen is introduced during the preceding pre-treatment steps, such as acidic washes and phosphate application.
The following are applied on the surface of the substrate to improve coating quality:
Primers serve as a preparatory coating layer that increases the adhesion between the substrate and plastic coating. It also gives additional protection to the substrate being coated.
Undercoats are additional coatings that give special characteristics to the finished part, such as UV and scratch resistance. Undercoats are generally not used on their own and typically serve their function when coupled with the main plastic coating.
For the dip molding process, a layer of mold release agent is applied or fixed on the surface of the mold to aid in removing the molded part. Silicone and permanent polytetrafluoroethylene (PTFE) are the most widely used mold release agents.
Once the pre-treatment steps are done, the mold is dried to remove moisture. Retained moisture causes expansion brought on by heat introduced in the succeeding steps. This results in void or bubble formation.
The mold is heated in an oven to a predetermined temperature and time. The heating temperature is one of the parameters determining the coating thickness of the part. The quality of heat distribution depends on the design of the mold and airflow within the oven. It is important to heat the mold uniformly to ensure consistent coating thickness distribution within the material.
The heated mold is partially or fully immersed in the liquid polymer. The polymer attaches to the surface of the mold. The exterior dimensions of the mold assume the internal space of the part. Dwell time or the duration in which the mold is submerged in the liquid polymer, is also one of the parameters that determine the final coating thickness of the part. Longer dwell times produce thicker coatings.
The rate of immersing and withdrawing the mold is also a critical parameter to consider, depending on the properties of the liquid polymer used. These rates are determined by the manufacturers during the optimization phase. As a rule of thumb, these rates must be slow in order to control the flow of the liquid polymer, and obtain a smooth finish. Withdrawing the mold too quickly after the dwell time will result in surface irregularities. However, if the mold is immersed and withdrawn too slowly, the resulting coat will be too thick.
More advanced factories use a fluidized bed of fine polymer powder to replace the conventional liquid polymer solution. The concept is similar to the conventional method; the fine polymer powder melts and adheres to the heated surface of the mold once it comes in contact.
The excess liquid polymer is allowed to drain from the surface of the mold. Multiple dipping steps may be performed to achieve a desired thicker coating, or a special coating may be applied.
The coating is cured in an oven to set the polymer more thoroughly and completely evaporate the excess moisture, solvents, and additives. In this step, the final mechanical properties of the polymer such as rigidity and flexibility are acquired. In thermosetting polymers, the curing step allows the polymeric chains to become completely cross-linked.
The cured coating is cooled by dipping in a water tank, where the water temperature is between 122-1112° F (50 - 600° C), or by means of forced or natural air convection. The rate of cooling is not considered a critical parameter compared to other types of molding.
The finished parts are removed from the frame. In the case of a dip molding operation, the plastic coating is removed from the mold manually or by mechanical means. This separates a single part from its batch. The result is a finished plastic component or part.
The dip molded plastic or the plastic coating may undergo additional finishing steps such as notching, punching, printing, and decorating.
Due to the similarities between the dip coating and dip molding processes, they share almost the same machinery. In a dip coating or dip molding operation, several machines and components are used to produce the dip molded plastic. The following are the equipment and apparatuses involved in an industrial dip coating and dip molding process set-up.
This is where the mandrel or metal to be coated is heated in preparation for the dipping process. The preheat oven uses blowers or fans to assist in the forced convection (hot air circulation) inside the chamber.
The mold tool used in a dip molding operation is called a mandrel. It is a custom-made male mold containing the three-dimensional form of the part to be molded. The external figure of the mandrel will create the interior space of the finished part. As mentioned, in the case of a dip coating operation, the piece of metal to be coated also acts as the mold or mandrel. The mandrel can be fabricated from a solid metal block that is shaped by machining, cast aluminum from a wood pattern, or formed sheet aluminum.
The mandrels are transported along the process, and dipped into a tank of polymer solution. Then, they are rested before curing by means of a carrier frame. This frame contains multiple mandrels and may be attached to a mechanical arm digitally controlled by computer software to improve molding cycle time.
The dipping tank is where the polymer solution is contained and the mandrels are dipped. The solution bath is often agitated to ensure uniform temperature and concentration. De-aeration equipment is used to remove air and moisture from the mixture. Before the solution is transferred to the dipping tank, an offline tank equipped with a mixer is usually utilized to blend the resin, additives, and colorant.
This is where heat treatment after molding takes place in order to settle the plastic coating. Similar to a pre-heat oven, it also utilizes forced convection to circulate hot air inside the chamber.
Several set-up configurations involving the same set of equipment were made in order to improve production efficiency. Some of them are:
Multiple mechanical arms containing the carrier frames are attached to a rotating wheel, like a carousel. Each arm is indexed as the wheel slowly rotates while the mandrels are submerged into varying depths.
The frames containing the mandrels are transported throughout the process using a precision conveyor. This allows continuous production mode of the dip coating or dip molding process. The pre-heat and cure ovens are placed on opposite sides of the polymer solution tank. Each oven has an entrance and exit doors to allow movement of the frames. Additional dipping tanks for special coatings may be added to the set-up.
Dip coating and dip molding are advantageous to some manufacturers due to the simplicity of their concept and flexibility. Below are some benefits of utilizing these methods:
Since no shrinkage is developed during these processes, the desired internal dimension can be obtained accurately. As mentioned earlier, the rate of cooling is not a critical parameter to be controlled compared to other types of molding.
Dip coating and dip molding readily produce seamless, double-walled parts. The seams resulting from joining two components produce stress points that significantly decrease the durability of the part.
Through dip plastic casting, it is possible to manufacture large plastic components through dip molding by enclosing large metal pieces. If a similar large plastic were to be produced in an injection or blow molding process, it would require large tooling; and become an expensive operation. The only limitation in dip molding is the size of the tool, the capability of the pre-heat and cure ovens, and the capacity of the polymer solution tank.
Dip coating and dip molding also have the ability to form complicated designs with severe undercuts and angles.
The designer can readily put additional details on the end product since the tooling material is easy to modify. Varying coating materials and thickness can be produced using the same tooling depending on how the polymer solution is formulated.
Dip coating and dip molding are ideal for short orders and laboratory-scale production because the set of equipment involved in these processes is simple, unlike in injection and blow molding, which require sophisticated machinery and a large amount of floor space. Also, the tooling for dip molding is inexpensive since it does not operate on high pressures.
In dip coating and dip molding, the excess solution drips back to the dipping tank, allowing it to be reused. In other types of molding, excess polymer material comes in the form of cut-outs and runners, which require additional processing in order to be recycled. Dip coating is more advantageous than spray coating. Compared to the spray method, some of the spray coatings will be transferred to the surrounding walls of the coating chamber or equipment, thus being wasted.
However, there are some limitations in using these processes in which other molding methods have the advantage. The following are the disadvantages:
Though the internal dimensions produced are accurate, it is difficult to obtain a precise coating thickness since it is heavily dependent on a number of variables: dwell time, the temperature of the tooling, rate of immersion, withdrawal of the tooling in the polymer solution, and properties of the polymer solution. It also makes a good coating thickness distribution difficult to achieve.
Dip molding is a slow process because it requires undergoing long heating, dipping, and cooling cycles.
Plastic coatings have become a common part of the production of goods. They are used by manufacturers to enhance the appearance of cars, tools, appliances, sports equipment, and banisters. The adaptability and versatility of plastic coatings make them an easy addition to products. Essentially, the use of plastic coatings has become a necessity in the modern era to ensure the longevity and durability of commercial and industrial items.
The need for plastic coatings can be described by three words - longevity, Durability, and Safety. In the present day market, producers are constantly searching for ways to extend the life of a product as well as guarantee that it is safe and reliable. These essential factors are at the heart of the introduction of new products, from creation and design to marketing and distribution.
Many years ago, when customers purchased a new product, they knew the product would eventually need replacement. It was a principle that producers relied on to maintain their market share. As technology has advanced and products have become more complex and expensive, the focus of customers has changed, and they demand that what they purchase last. In response to the change in the paradigm, producers have developed methods to extend the useful life of products.
With the improvement in the design and capabilities of components has come a group of exceptionally strong plastic polymers that have been adapted to meet the configuration and structure of modern devices. In many ways, they are the reason that televisions last for years and computers have unequaled durability in stressful conditions. Used as coatings, these polymers form a protective shield around commercial and industrial tools to help enhance and improve their longevity.
In the world of commerce and home appliances, consumers rely on protective coatings to protect them from being injured by an uncovered corner or exposed edge. In the industrial world, where there are complex, dangerous, and intricate tools, protective plastic coatings have the vital job of keeping workers safe from hazardous materials and equipment. Safety walls, gates, and enclosures, coated in plastic form a shield and keep workers from harm.
Additionally, there are several advantages to plastic-coated tools for use with moving parts, electrical circuits, and controls. A fundamental rule of modern manufacturing is safety for workers, which is improved with the use of tools coated in plastic.
Vibrations are a natural consequence of the operation of heavy machinery and industrial equipment. Facilities work diligently to reduce and suppress vibrations for the production of devices produced for longetivity. A major part of the effort is plastic coatings that prevent machinery from making contact as well as decreasing vibrations.
Regardless of the many attempts to reduce the amount of noise in production operations, noise is still a major part of manufacturing due to the necessary force required to produce so many products. In addition to attempting to limit vibrations, plastic coatings are also used to suppress noise as separators, gaskets, shields, controls, and enclosures.
The reduction of friction in an industrial process can improve efficiency and the smooth completion of various production operations. Friction creates wear on equipment, abrasions, and EMFs, each of which can be damaging to equipment. Applying plastic coatings to various aspects of a process drastically reduces friction to improve safety and increase productivity.
Modern industrial machinery is manufactured with some type of insulation for the protection of workers and products. Plastic coatings, due to their durability, ease of installation, and longevity, are widely used. A coating of plastic reduces EMFs, protects from contact between metal components, and ensures the smooth operation of equipment.
The simple application of protective plastic coatings offers added protection and value to industrial processes. It is an investment that reduces the wear, damage, and eventual replacement of critical machinery and significantly improves worker safety.
Plastic caps and plugs are two distinct ways for sealing the ends, tops, and openings of tubes and containers. Caps are placed over the opening, and plugs are placed in the opening. Due to the many varieties of...
Blow molding is a type of plastic forming process for creating hollow plastic products made from thermoplastic materials. The process involves heating and inflating a plastic tube known as a parison or preform. The parison is placed between two dies that contain the desired shape of the product...
Industrial coatings are a type of substance that is spread over a surface of various derivatives like concrete or steel. They are engineered chemically to give protection over industrial products that include pipelines and...
Plastic bottles are bottles made of high or low-density plastic, such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polycarbonate (PC), or polyvinyl chloride (PVC). Each of the materials mentioned has...
Thermoforming is the process of heating thin plastic sheets to its forming temperature and stretching it over a mold which takes its shape. After cooling and setting of the molded plastic sheet, each part will be separated from its batch to form a single unit or product...