Five factors of shrinkage warpage of plastic products

The warpage is that the plastic part is not formed according to the designed shape, but the surface is twisted, and the warpage of the plastic part is caused by the uneven shrinkage of the formed plastic part. If the entire plastic part has a uniform shrinkage, the deformation of the plastic part will not warp, but will only shrink the size; however, due to factors such as molecular chain/fiber alignment, mold cooling, plastic part design, mold design and forming conditions, etc. The interaction effect, to achieve low shrinkage or uniform shrinkage is a very complicated job.

So what are the factors that affect the shrinkage warpage of plastic products?

1. Related to the crystallinity of plastics

There are two kinds of thermoplastics: crystalline and amorphous. The crystalline molecular chains are arranged neatly, stably and tightly. During cooling and solidification, there are nucleation to grain formation. The amorphous plastic molecular chains are disorderly sorted. , there is no crystal nucleus and grain growth process, just the “freezing” of free macromolecular chains

2, related to the type of pigment

Organic pigments may act as nucleating agents in the molding of plastic products to promote the crystallization process. Generally, pigments with symmetric molecular structure have large shrinkage effects, such as Pigment Red 254, Pigment Blue 15:1, Pigment Blue 15:3, 酞Cyanine 7 and so on, while inorganic pigments have little effect on shrinkage, such as titanium dioxide, which is negligible.

3, related to the shape of the pigment

The crystal state of the pigment is various, and the particles have a needle shape, a rod shape, a spherical shape, and the like. If it is needle-like or rod-shaped, the length direction is easily aligned in the flow direction of the resin, so that shrinkage occurs, and the inorganic pigment is usually spherical crystal, which direction is the same in the spherical direction, and there is no problem of alignment, so the inorganic pigment usually does not shrink. The problem of warping. Therefore, the shrinkage rate of the crystalline plastic during injection molding is generally larger than that of the amorphous plastic, and the thermosetting plastic has almost no effect, that is, the shrinkage warpage only occurs in the crystalline plastic.

4, related to the particle size of the pigment

The same type of pigment, different manufacturers have different processes, the particle size of the produced pigment is different, and the particle size also affects the shrinkage warpage. When the particle size is large to a certain extent or small to a certain extent, the molding shrinkage is small. This is not a good description, nor a unified standard. It can only be tested in practical applications. In general, even if the same type of pigment, the deformation of this factory is serious, maybe another factory will shrink. The warpage is very slight.

5, related to the molding temperature of the pigment

When molding plastics, it is necessary to melt the plastic at a temperature. This molding temperature varies with the type of plastic and different processing methods. For example: Pigment Brown 23, Pigment Red 149 will significantly affect the shrinkage of HDPE plastic at a processing temperature of 220 °C. The increase is adversely affected; while the pigment yellow 13 is in HDPE, if the processing temperature is too low, the shrinkage effect of plastic products in Dongguan increases, so there is no law to follow. In addition to testing according to the production process, there seems to be no other solution. Program.