How Screen Printing Plastic and Other Materials Works
Learn more about the process of screen printing and the materials that can be screen printed.
What is screen printing? Screen printing is pressing ink through a stenciled mesh screen to create a printed design. It’s a widespread technique used in a wide range of different industries. The process is sometimes called serigraphy or silk screen printing, but these names refer to essentially the same method. Screen printing can be used on almost any type of substrate, even with substrates that have uneven or round surfaces. This article looks at the different materials that can be used with the screen printing method, specifically plastic.
Screen printing is traditionally used with fabric and paper materials. One of the biggest screen printing applications is printing t-shirts with designs on them in the textile industry. It can print graphics and designs on fabrics such as silk, cotton, polyester, and organza. Silk screen printing is well known, but any form of fabric that requires some form of printing can be used in screen printing. Different inks work with various materials, including ceramics, wood, glass, metal, and plastic.
Screen printing can be used on paper in marketing and advertising. These industries use posters, flyers, and other forms of advertising promotional items that require graphics. Since advertising requires limited edition printing, it uses screen printing because printing electronically or digitally on a small scale is much higher than screen printing.
The following plastic substrates of plastic products are mainly used for screen printing.
Polyvinyl chloride (PVC) has the advantages of bright color, anti-break, acid and alkali resistance, and low price. However, the addition of some materials during PVC production is usually toxic, so PVC products can’t be used for food containers.
ABS resin plastic is an engineering plastic widely used in televisions, calculators, and other products in recent years. It is characterized by easy process and forming. Polyethylene plastics are commonly used and can be made into various finished products by extrusion, injection molding, and other molding processes.
Polypropylene has been one of the essential varieties of plastic suitable for all molding methods. It can be processed to all kinds of pipes, boxes, containers, films, and fibers, etc.
Different screen printing methods exist, but they all use the same basic techniques. The screen is composed of mesh stretched over a frame. The mesh could be a synthetic polymer, such as nylon, and a more delicate and smaller aperture for the mesh is used for a design that needs more detail. The mesh has to be mounted on a frame under tension for the mesh to operate. The frame holding the mesh could be made of materials such as wood or aluminum, depending on the machine’s complexity or the artisan procedure. The tension of the mesh may be tested using a tensiometer.
A stencil is created by blocking off parts of the screen in the negative image of the desired design. The open spaces are where the ink appears on the substrate. Before printing, the frame and screen must undergo the pre-press process, in which an emulsion is ‘scooped’ across the mesh.
After this mixture has dried, it is selectively exposed to ultra-violet light through a film printed with the required design. The exposure hardens the emulsion in the exposed areas but softens the unexposed parts. They are then washed away using a water spray, creating a clean space in the mesh in the same shape as the desired image, which will allow passage of inks. It is a positive process.
The surface supporting the fabric is commonly called a pallet in fabric printing. It is coated with a wide pallet tape that protects the pallet from any unwanted ink leaking through and potentially staining the pallet or shifting unwanted ink onto the next substrate.
A screen printing machine in operation.
Screen printing is a secondary processing for almost all kinds of plastic surfaces compared to other substrates. Secondary processing can be necessary to compensate for these shortcomings and improve the appearance of plastic products. Nowadays, screen printing has been able to print on plastic products with different surface textures, hardnesses, and shapes, and is widely used to decorate plastic packaging films and plastic containers.
The ink for plastic printing is different from the ink used for paper, and the two cannot be mixed. To adapt inks for most plastic surfaces, plastic resins such as polyamide, synthetic solvents, organic solvents, and colorants are used to mix the plastic printing inks.
All screen printing requires a substrate and a framed screen with the graphic process. The silkscreen mesh on the screen frame can be conveyed through the ink, and the non-image area of the mesh can not. Therefore, when printing on plastic, the ink is poured at one end of the screen printing screen, and a squeegee presses the ink film to the other end of the screen. The ink is then scraped through the screen mesh onto the plastic substrate to create desired image and characters.
Some plastic parts may require additional supplies other than the right ink. Large signs large pallets, for example. A vacuum pallet can ensure any flat substrates like signs and posters stay where they’re supposed to while printing. Because items printed with air dry inks must be laid out to fuller cure, they’ll need extra storage space while they dry. A drying rack may ensure that they’re not taking up too much shop space.
Digital printing uses a specialized fabric printer like an inkjet computer printer to transfer an image directly onto a textile. However, it differs from screen printing because a digital printer transfers the design directly onto the product. In addition, because there’s no stencil, multiple colors can be applied simultaneously instead of in separate layers, meaning this technique is frequently used to print intricate or very colorful designs.
Unlike screen printing, there’s minimal setup required, which means that digital printing is a more cost-effective option for printing small batches of clothing or single items. However, as the colors are printed using CMYK-style dots of color rather than solid ink blocks, it doesn’t provide the same intensity of color as with screen printing. Texturized effects cannot be created with a digital printer, either.
Inks of various colors that are used in screen printing.
In recent years, printed electronics technology has had an increased demand for thin-film coating for thinner electronic devices with higher density internal structures, thick film coating for improving circuit insulation, coating of highly viscous material in ultrafine lines, improved printing position accuracy for supporting miniaturization of electronic devices. As a result, screen printing has evolved and developed to satisfy these demands.
Different plastics have different plastic applications. Plastic screen printing using polypropylene is used on boxes, plastic bags, posters, and banners. Polycarbonate is used for DVDs, CDs, bottles, lenses, signs, and displays. Polyethylene terephthalate’s common uses include bottles and backlit displays. Polystyrene is often used for foam containers, and ceiling tiles. Polyvinyl chloride’s uses include credit cards, gift cards, and construction applications.
On top of the most common synthetic and oil-based plastic products, there are also “bioplastics,” that are made from organic materials. Plastic materials can differ widely even within the same category, so it’s essential to pay attention to the properties of the substrate before printing. Because the properties of plastic materials vary widely, thorough testing is crucial before beginning printing on plastic.
Screen printing is an effective technique that finds use in a variety of applications. We hope that this article has brought clarity to how the process works and has explained some of its use with plastic materials.
If you are interested in screen printing or other part marking services, contact Xometry to get your free, no-obligation quote. You can also learn more about the different types of part marking technologies by exploring our Ultimate Guide to Direct Part Marking. In that guide, you will find our guidelines around each process and further information on the types of markings we perform and what we'll do in case of missing information to ensure your order gets to you on time while remaining to your specifications.
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