Hot Melt Vinyl Plastisol
Hot melt plastisols are used for a variety of products which include soft bodied fishing lures, molds, and novelty craft items such as figurines.
Hot melt plastisols may be formulated to include a wide variety of properties; some of which may include the degree of hardness (or softness), clarity, color, mar resistance, feel, or even FDA or medical grade (FDA or medical grade uses raw material approved by the FDA).
Recycling of scrap hot melt plastisols may be possible.
Processing Hot Melts
Hot melts can be processed with a variety of equipment. Most common are the melt pot, microwave, and convection oven. Injection equipment can also be used and is custom made or available through sources listed below.
When processing there are a few important things to keep in mind. Ventilation is a must- the smoke created by the plastisol melting is irritating to the eyes, lungs and mucous membranes. The smoke may contain gasses which are corrosive, especially if some of the vinyl has thermally decomposed (burned). Molten plastisol can cause severe burns so do not get any on you.
1. Heat the liquid plastisol gently to a temperature of 350°F by using a microwave, convection oven or melt pot.
2. Regardless of which method is used to heat the plastisol, you will need to periodically stir it as it melts.
3. The material will change from a white milky looking liquid, to a thick clear gummy paste, then a clear hot liquid.
4. After it gets to the third stage the temperature may be reduced to 315° to 325°F and held there for hours before discoloration from burning will occur.
5. Pour into the mold cavities, (the mold should be warm or the material will not flow to it's extremeties), and allow to air cool. Remove from the molds when cool enough to do so. The plastisol may shrink slightly while cooling.
The process for a melt pot is relatively easy. Pour the plastisol into the pot and turn it on. Turn the mechanical stir unit on at the same time. A temperature control is desirable to have on a melt pot. If a temperature control is not available use a thermometer. When the plastisol gets to the thin runny stage it can be poured into the molds.
Microwaves can be used, but with caution. Test your microwave power first by measuring an amount of plastisol into a glass Pyrex measuring cup. Set your microwave on a particular power and turn on for a few minutes. (ex. 2/3 Cup plastisol for 3 minutes on Hi in our microwave). Take the cup out and stir the plastisol, there should still be some white liquid in there yet. Heat again for another 2 minutes. If the plastisol isn't thin enough to pour, then microwave one minute more at a time until it is ready. Caution- test in your microwave or you may end up with burned plastisol, which is corrosive.
Convection ovens can be used to melt the lure or simple cure it in the molds. If you are melting before pouring make sure to stir the product periodically. Pour into molds when ready.
Generally, special equipment is necessary to injection mold. This equipment requires a tight positive return screw or piston, a liquid tight magazine, and an adequate barrel length for complete fusion (curing). Since fusion occurs along the barrel wall, a long thin diameter barrel heated along its entire length is necessary. A pressure of only 25 to 50 pounds is needed to inject a mold. Melt pots can be attached if barrel length is limited.
Colorants can be added to your plastisol either by the manufacturer or by yourself. Depending on the opacity needed, the amount of pigment needed would be usually 0.05-2% by weight. When the customer adds their own pigment it makes it easy for them to change colors at any time. Dyes can be used, but realize they have the ability to bleed and most of them will. We have a color price list available and offer Custom Color Matching. We also carry glow powders.
Plastcizers are used in plastisol to soften the product. These plasticizers can be added to soften the material even more. Caution should be taken in weighing out or measuring the components carefully. Too much plasticizer will cause hot melts to become tacky.
Hot melt plastisol may be recycled provided that it isn't burned or scorched. Do not try reclaiming the burned portions of scrap. The reclaimed plastisol should be blended with new hot melt plastisol for reuse.