Dip molding is a process in which plastic components, parts, and products are manufactured by dipping a mold into melted plastic, allowing the mold to set, and removing the mold from the hardened plastic
Manufacturers use dip molding to mold parts for both protective and decorative applications. Manufacturers like dip molding because, depending on the temperature, the dip speed and time, and the rate in which the plastic is removed from the plastisol, they can achieve different wall thicknesses. Plus, dip molding is a highly versatile and cost-efficient way to make sure products have an attractive finish, and reliable protection from the elements.
Dip molding is popular in a wide range of industries, such as healthcare, medical device, electronics, consumer, sports and recreation, food and beverage, sanitation and retail. Common Items that are made using dip molding include small plastic products (plastic plugs, plastic bottle caps, etc.), sports equipment, gloves, plastic closures, plastic bags, and handles and grips for appliances.
Dip molding has been around in some form another for some time. For example, before the 20th century, artisans used a form of dip molding during hot wax candle creation. However, the practice of modern dip molding didn’t take off until the 1930s in the UK and the USA. What brought on this sudden change was World War II. Manufacturers were churning out plastic polymer parts for the war effort as quickly as possible. When they discovered that, with dip molding, they could mold tool handles, containers and other plastic shapes even faster, they jumped at the process.
For much of its existence, plastic dip molding was performed with either a PVC coating or natural latex. This changed in 1993, when the FDA published their findings about Americans and latex allergies. They found that between 2% and 10% of the American population suffered from a latex allergy. With this knowledge, the dip molding industry had to evolve and use new materials. Some of the materials they turned to included: polyurethane, nitrile rubber, SBR (styrene butadiene rubber) and neoprene. (PVC dip molding remained popular.) This announcement also led to the creation of latex-free gloves.
Today, plastic molding and plastic dip molding are more popular than ever. Researchers still seek to create more diverse and environmentally-friendly polymer blends, so that they can use dip molding for even more applications. They also seek to make it more efficient and less expensive.
The most commonly used materials for dip molding are: plastisol, latex, neoprene, urethane, and epoxy.
Plastisol, a vinyl (PVC) compound, is unique, because it is already liquid at room temperature and permanently hardens once exposed to heat. Because it requires less energy to undergo manufacturing, liquid plastisol is the ideal choice of material for the vinyl dip molding process. To protect outdoor applications from the sun’s damaging rays, manufacturers can add an UV coating to a plastisol dip part.
Latex as a raw material can be derived from nature, or it can be synthesized. It is known to be non-toxic and inexpensive. However, it was discovered in the late ‘80s that some people had begun developing an allergy to its powder, so latex is far less popular that it once was.
Neoprene, sometimes called polychloroprene, is a synthetic polymer. It is flexible, non-toxic, ozone resistant and chemical resistant. It works well as a latex substitute.
Urethane, or polyurethane, is durable, stable when exposed to light and highly resilient.
Epoxy exhibits the following qualities: temperature resistance, chemical resistance, mechanical strength, heat resistance and electrical insulation.
The dip molding process involves dipping a mold into a liquid material and then curing or solidifying the material to form the desired product. Here’s an overview of the typical steps involved in the dip molding process:
The first step is to prepare the mold. Molds can be made from various materials, including metal, ceramic, or even certain types of plastic. The mold must be clean and free from any contaminants or residues that might affect the quality of the final product.
The material used for dip molding depends on the desired characteristics of the final product. Common materials include latex, PVC (polyvinyl chloride), neoprene, and various types of plastics. The material is typically in liquid form, such as a latex emulsion or plastisol.
The mold is immersed or dipped into the liquid material. The speed and angle of immersion can impact the thickness and uniformity of the coating. A controlled withdrawal speed helps to achieve an even coating thickness.
Gelation and Fusion
After the mold is dipped, it is then slowly removed from the material, allowing excess material to drain off. The remaining coating on the mold is then subjected to gelation or fusion, depending on the material being used.
In the case of latex and some other materials, the coated mold is heated to a point where the material solidifies or “gels” on the surface of the mold. The mold is usually heated using hot air or other heating methods.
For plastisol and similar materials, gelation is not sufficient. Instead, the coated mold is heated to a higher temperature, causing the material to fully fuse and form a solid layer.
Multiple Dips and Coatings
(Optional): Depending on the thickness and desired properties of the final product, the dipped mold may undergo multiple dips and coatings. Between each dip, the coating may be heated to promote adhesion and create a uniform build-up.
For certain materials like latex or rubber, curing is necessary to achieve the final mechanical properties. The coated mold is usually placed in an oven or subjected to other curing methods to complete the transformation of the material into a more robust and elastic state.
Once the material has cured or solidified, the product can be removed from the mold. In some cases, the mold may need a release agent to facilitate easy de-molding.
Trimming and Finishing
After de-molding, the product may undergo additional trimming or finishing processes to remove any excess material or imperfections, ensuring the final product meets the required specifications.
Manufacturers must take several considerations into account when performing dip molding and producing dip molded items to ensure the quality, efficiency, and safety of the process. First and foremost, material selection is critical. Different materials have unique properties and curing requirements, so choosing the appropriate material for the specific application is vital. Manufacturers must also carefully design the molds, considering the complexity of the desired product and ensuring proper mold release to facilitate de-molding. Controlling the dipping process, including immersion speed, angle, and withdrawal speed, is essential to achieve uniform coating thickness and avoid defects like air bubbles or drips. Temperature and curing time must be carefully monitored during the gelation or fusion process to ensure the material solidifies or fuses correctly. Quality control measures, including inspection and testing, should be implemented to identify any defects or inconsistencies in the final product. Additionally, manufacturers must comply with safety regulations and ensure proper ventilation and personal protective equipment (PPE) for workers handling the materials and during the curing process. Regular maintenance of equipment and molds is necessary to ensure consistent and reliable production. By addressing these considerations, manufacturers can optimize the dip molding process and produce high-quality dip molded items that meet the required specifications and customer expectations.
Depending on the exact process, manufacturers may use a number of different machines to dip mold your parts. Some of the most common ones are detailed below.
In this oven, manufacturers preheat the mandrel or another dipping tool in preparation for the dip molding process. It often features a blower, which boosts heat transfer and air turbulence.
Mandrels are metal molds used to shape the interior of a dip molded product. They are usually made from aluminum or steel, though they may also be made from other metal alloys. Once the plastic part has hardened around the mandrel, manufacturers remove it. Manufacturers can customize mandrels by mounting them directly onto a dip molding machine arm, or by adding multiple mandrels to a bar inside a master rack.
A master rack is a steel or aluminum frame. Featuring indentations or pins placed to hold adapter bars in place, this is where manufacturers hang or rest mandrels. Master racks are designed for the dip molding machine with which they work.
The dip tank holds the molten polymer in which the mandrels will be dipped. The tank, or bath, often agitates to assist the process.
Cure ovens dry and solidify the dip molded plastic part. They feature heaters or high temperature fans, like blowers, to speed up the process.
Overhead Dip Station
Overhead dip stations feature two axes, a vertical axis and a horizontal axis, upon which parts, tools or racks can be moved from the machine to the dip tanks. Overhead dip stations allow for manufacturers to dip multiple mandrels at the same time. They can also perform multiple color dips or multiple grade dips.
Automatic Rack Transfer System (ARTS) Station
ARTS stations are machinery used mainly during rotational molding with rotary dip molding machines. They streamline the process and make it easier to load, unload and reload mandrels without having to remove the racks. They also make more space for cooling and priming metal parts.
Variations and Similar Processes
Another process used in fabricating the aforementioned plastic products is known as dip coating. Dip coating involves partially or fully coating products with a protective material. Like dip molding, the dip coating process involves dipping molds into melted plastic material. Most often, this is a plastisol coating.
While dip molding creates a product from a mold, dip coating provides a protective layer on a pre-existing product. Products such as wire racks, wire forms, or plastic-coated fences are fully coated. Other items such as tool handles, grips, and electrical connectors only require a partial coating. Dip coating can be used for both protective and decorative purposes. For example, while some plastic coatings can be used for better comfort and grip, other coatings can add an element of design to the product.
Depending on the technique, these plastic coatings can be made in a wide range of colors, textures, and levels of hardness. Aside from improving the product’s appearance, dip coating provides insulation and protection. For example, plastic coating can provide electrical insulation for components such as electrical wires, jumper cables, and extension cords. In addition to electrical insulation, plastic coating can be applied to fences and wires to extend their lifespan and protect them from corrosion. Also, plastic coating aids in noise reduction, vibration dampening, and it reduces sharp edges on metal parts, eliminating the need for deburring.
During plastic injection molding, manufacturers use a mold and a molten polymer mixture to create a product. They force the liquid plastic into a mold cavity with a screw plunger or a ram. Inside the mold cavity, the plastic spreads until it touches all of its contours. Then, it cools and solidifies. Sometimes, injection molding also involves extra clamping in order to add compression. In this case, it’s known as injection compression molding. Manufacturers choose custom plastic injection molding for its efficiency, low cost, low wastage and durable mold product results.
Blow molding is a process used to make hollow plastic parts, especially plastic bottles. During blow molding, manufacturers form molten plastic into a parison, which is a tube-shaped piece of plastic with a hole at one end. They then clamp the parison into a mold and blow compressed air into it through the hole. This pressure causes the plastic to swell until it reaches the interior border of the mold. There, it takes on its shape, cools and hardens. After it cools and hardens, manufacturers can open up the mold and eject the new plastic product. Blow molding is mostly valued for its low tooling costs and fast production rates.
Dip molding is a versatile manufacturing process that offers numerous advantages, making it suitable for various applications. One of the primary benefits of dip molding is its cost-effectiveness, especially for smaller production runs. The equipment required for dip molding is relatively simple and less expensive than the complex machinery needed for injection molding or blow molding. This makes it an attractive option for companies looking to produce custom-made or low-volume products without incurring significant upfront costs.
Another significant advantage of dip molding is its ability to create seamless and flexible designs. Since the material adheres closely to the mold surface during the dipping process, it forms a continuous and uniform coating. This seamless construction is particularly desirable for products like gloves and coatings for handles, where comfort, durability, and a smooth surface are crucial factors.
Dip molding also excels in producing complex shapes with consistent wall thickness. The close adherence of the material to the mold surface allows for the accurate replication of intricate details, enabling manufacturers to create products with a high level of design complexity and precision. This capability is especially valuable for items like custom grips, caps, and other molded components with intricate features.
Moreover, dip molding supports a wide range of materials, including latex, rubber, plastics, and PVC. Each material has its own unique properties, such as elasticity, chemical resistance, and thermal resistance. This variety of materials allows manufacturers to select the most suitable material for the intended application, ensuring that the final product meets specific performance requirements.
Compared to injection molding, dip molding offers several advantages. For instance, dip molding is more cost-effective for smaller production runs. Changing the design or dimensions of a product in dip molding is relatively easy and requires less tooling modification compared to the more time-consuming and expensive process of changing molds in injection molding. Additionally, dip molding can produce products with more intricate and complex designs, which may be challenging to achieve using injection molding.
Likewise, dip molding outperforms blow molding in certain aspects. The seamless construction achieved through dip molding sets it apart from blow molding, where products often have visible seams where the mold halves meet. Additionally, dip molding is well-suited for smaller production runs and prototypes, whereas blow molding is more efficient for large-scale production due to the cost of mold tooling. Furthermore, dip molding accommodates complex shapes better and supports a broader range of materials, making it a versatile choice for various applications.
In conclusion, dip molding offers a cost-effective, flexible, and versatile manufacturing process suitable for producing seamless, intricate, and complex products. Its ability to work with different materials and create custom designs makes it ideal for various industries, ranging from medical and industrial to consumer goods and beyond.
Things to Consider
Plastic dip molding is a popular molding service. For that reason, you will find that there are countless companies out there vying for your business. While competition can help you get better prices, it can also create an overwhelming number of choices. Among those choices are some good and some not-so-good manufacturers, and you may find it hard to discern which ones are which.
To help you out, we’ve curated a list of industry leading dip molding service providers that you can trust. When you’re ready, take some time to browse their profiles. As you do so, keep in mind your specifications and requirements. From among our list, choose three or four plastic product companies to whom you’d like to speak. Then, reach out to each of them to discuss your project. Don’t forget to go over your budget, timeline, standard requirements and delivery preferences. Once you’ve done that, compare and contrast their answers. Choose the provider that you believe will provide you with the best service and the best products.
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Dip Molding Informational Video