Identification of common plastic printing materials for screen printing

Screen printers are often asked

Print on many types of substrates, and customers can only say that it is "plastic", "white", "polymer material" and other information when providing materials, so the screen printer can only figure out what it is. Material and choose the right ink for it. The purpose of this article is to introduce common plastics and POP materials.

Styrene

Styrene is widely used in indoor posters and can be found everywhere in retail stores and exhibition showrooms. It can also be used to make bottles and packaging boxes. Styrene is hard, brittle, and thermoplastic. It is sensitive to solvents. If excessive amounts of solvent are used, it will crack. Thin styrene can be torn apart and the sound is harsh. When a large roll of styrene trembles, the sound is like thunder.

Styrene can also be identified by a simple solvent test. Styrene will soften when it meets ketone and aromatic solvents, and a few drops of screen cleaner on styrene will become significantly softer after a few minutes. Touching the softened surface with a gloved fingertip will produce fine plastic stripes. A few drops of aromatic hydrocarbon can also soften styrene.

Styrene can also be identified by the combustion test. When the styrene is lit, the flame is orange, crackling, releasing a thick black smoke, which will continue to burn when the styrene is removed from the blowtorch.

Polypropylene

Polypropylene is a thermoplastic rigid and hard material with good durability, suitable for making signs, containers / bottles, packaging boxes and film lamination. Common polypropylene is a grooved sheet with different shapes. The bottom of the polypropylene container is marked with recycling mark Code 5 or PP. Other products such as cups and pens are not marked with recycling mark.

Polypropylene is cleanly cut, can float in water, and can be bent repeatedly without tearing or damage.

Because polypropylene is very solvent-resistant, solvent testing does not tell much. Burning tests can provide a lot of information. The flame is blue with yellow, and there is no smoke. When the polypropylene is removed from the torch, it will continue to burn. The softened plastic is transparent. Like other polyolefin polymers, polypropylene has no ignition point, and the flame of polypropylene burning cannot spread quickly.

Polyethylene

Polyethylene is commonly used in containers, solvent-resistant water pipes and packaging boxes. It also has a leaflet form. There are many types of polyethylene: high density, low density, rigid leaflets, flexible polyethylene for flags, etc. Substrate suppliers generally provide roll and sheet-type polyethylene.

Polyethylene is light, strong, and particularly solvent-resistant. It has a waxy feel, which makes it distinguishable from polypropylene. The polyethylene sheet has stretch before tearing. Polyethylene is cut like polypropylene and can float in water. The results of the solvent and combustion tests are identical to polypropylene.

In order to get the ideal ink viscosity, proper printing process is essential. Container decorators flame the bottles online before printing, and banner printers usually use corona discharge to pretreat the material.

Ethylene

Vinyl substrates are the most widely used plastics in screen printing, and can be used for signs, adhesive paper, decals, bottles, labels, advertising posters, and so on. Commonly used by screen printers are pressure-sensitive vinyl, electrostatic vinyl, rigid PVC, expanded PVC board, vinyl flag material, polished vinyl, friction-resistant vinyl, and many others. Ethylene can be roughly divided into flexible and rigid, and can be subdivided according to the purpose of use.

Flexible vinyl includes oil-containing flexibilizers, which makes the material flexible and stretchable. The flexibilizer contained in ethylene is not a strict component of ethylene. The presence of flexibilizers can usually be detected by olfaction, and it can also be seen from the oil film on the surface that the odor of many flexibilis is discriminatory and sweet for many people. The longer the life of ethylene, the stronger the smell of the flexibilizer. Hard vinyl has no flexibility, so it has no odor.

Ethylene softens with cyclohexanone instead of aromatic solvents. Flame test Ethylene showed a bright greenish flame, releasing dirty black smoke. It immediately goes out when removed from the fire. Vinyl film is difficult to tear, cut and clean. [next]

Polycarbonate and polyester

Polycarbonate and polyester films are generally used for membrane switch panels, instrument panels, labels and nameplates. Both materials are transparent and matte. There are important differences between polycarbonate and polyester, and it is important for screen printers to distinguish them because their differences affect printing, die cutting, embossing, and other operations.

Screen printers who are often in contact with these two materials can distinguish them by their feelings, possibly through sound, touch, appearance or tearing.

The simplest is chemical testing. Polyester is resistant to solvents and polycarbonate is not. Knowing this, a drop of cyclohexanone on polycarbonate will soften significantly after 15min ~ 30min, while polyester is not affected.

Polycarbonate burning test will find it difficult to ignite, there is crackling sound when burning, orange flame, smell, black smoke. Polycarbonate is carbonized during the combustion process, and will continue to burn when removed from the fire. It is cut cleanly, and it becomes soft when it meets cyclic ketone, but not when it meets aromatic solvents.
The polyester burning test will find that it burns quickly, with a bluish yellowish flame. When it is moved from the fire and continues to burn, the polyester mentioned above is very resistant to solvents.

test

The initial test starts with observation. Only when necessary, chemical tests for solvents and combustion are carried out. Through processing performance, it is possible to clarify a variety of plastics without the need for further chemical tests.

The first step is to record the color, texture, and feel. The feel includes roughness, smoothness, texture, fibrousness, waxiness, and oiliness. Smell the plastic to determine whether there is an odor, odor may be a softener. Shake it to hear the sound, is it easy to bend? Or is it crisp? Can you tear it away easily? Cut a small piece of material to see if it is neat or burred. Put it in the water to see if it floats or sinks.
Further tests are solvent experiments and combustion experiments. When performing these tests, they should be in a well-ventilated environment, and operators must wear gloves and protective glasses when testing any industrial chemicals.

The simple and easy solvent test is to drop a drop of solvent on the material, put it for 30 minutes, and then touch the drop of solvent with the tip of a gloved finger to check whether the plastic softens or swells. The common solvents used for testing are ketone solvents and aromatic hydrocarbon solvents. Most thermoplastics are not resistant to solvents, but the common solvent-resistant materials for screen printing include polypropylene, polyethylene, and polyester.

For flame test or burning test, use clean flame from alcohol lamp or propane torch. Use a pair of clamps or small tweezers to clamp a small piece of plastic to the flame. Observe the color and the appearance of the flame. The color indicates the type of plastic. Remove the plastic from the spray gun and observe whether the material continues to burn or extinguish itself.

Another method of flame test is to take a 30cm long copper wire, peel off a few centimeters of insulating material at one end, and heat the bare copper wire on the spray gun until it glows red and all impurities have burned out. On the plastic, it melts some plastic and covers the copper wire. Move the copper wire wrapped with plastic to the spray gun. Observe the flame color, styrene is orange, vinyl is bright green, and other plastics have their own color characteristics. .

If it is inconvenient for screen printers to perform these tests, they can contact the ink supplier, and the ink manufacturer provides a complete test service and technical service for distinguishing substrates.

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