Views:128 Author:Vera Publish Time: 2018-08-03 Origin:Site
The methods of improving plastic glossiness include two aspects: one is to improve the surface glossiness of plastic products, which is called brightening modification, and the other is to reduce the surface glossiness of plastic products, which is called extinction modification. The following are the main ways to enhance the brightness of plastics:
The brightening of plastics is to improve the surface gloss or finish of plastic products. Except from reasonable selection of raw materials, the specific brightening methods include adding additives, plastic blending, morphological controlling, controlling the finishing degree of molding equipment, secondary processing and surface coating and so on.
1. Selection of plastic raw materials
The reasonable selection of plastic raw materials is the most basic factor to improve the surface glossiness of plastic products. If the raw material is selected well, it is easy to improve the glossiness; otherwise, it is more difficult.
Plastic raw materials can be divided into two major categories: resin and additive.
2. Selection of resin
The characteristics of resin have great influence on the surface gloss of plastic products, which is the most effective method to control the surface gloss of plastic products. Its impact on the surface gloss of plastic products mainly depends on the following aspects:
1) Varieties of resins
The gloss of the corresponding products varies greatly with the variety of resins. It is generally considered that the gloss of the following corresponding products is better: melamine resin, ABS, PP, HIPS, PA, POM, PMMA and PPO, among which melamine resin and ABS have the most outstanding gloss.
For the same resin, the gloss of the corresponding product is different with different synthetic methods. For example:
a, For PP, the gloss degree of different polymerization methods is as follows: PP-R> homopolymerization PP> block copolymerization PP.
b, For PE, the gloss of three different varieties is as follows: LDPE > LLDPE > HDPE
c, For PVC, the gloss of emulsion PVC resin is higher than suspension PVC resin.
d, For PS resin, the gloss of high impact HIPS is higher than that of GPPS.
2) Properties of resin
For the same resin, with different properties, its glossiness is different. Among the properties of the resin, the following are the main ones that affect the glossiness of plastic:
a, The larger the melt flow rate (MFR) is, the greater the gloss of the product is.
b, The influence of molecular weight: The influence of molecular weight is mainly reflected in the width of molecular weight distribution. The wider the molecular weight distribution, the lower the gloss of the product. This is mainly due to the wide distribution of molecular weight causing the increase of the irregularity of materials.
c, The effect of water absorption. The resin with high water absorption rate has a great influence on the gloss of the corresponding products. For example, (-COOR) and (-CONH2) in the molecule, if they are not dried or not dried thoroughly, water ripples, bubbles, silver wire, stripes, wool defects and so on will be produced on the surface of the product, so that the surface gloss will be greatly reduced.
3. Selection of additives
Of all the additives for plastics, fillers have the greatest effect on glossiness, and plasticizers, stabilizers and flame retardants have less influence.
Effect of fillers
The effects of fillers on gloss can be divided into the following aspects:
a, varieties of fillers
The effects of different filler varieties on gloss are different. Almost all fillers except glass beads will reduce the gloss of the fillers, but by different degrees.
The order of influence of several fillers on the gloss of filling products is as follows: metal salt > glass fiber < talc powder < mica
b, shape of fillers
The influence of the glossiness of filler products varies according to the microcosmic shape of filler particles. And the order of influence is as follows: globular < granular < needle-shaped < flake.
c, Particle size of filler
The smaller the size of the filler is, the lower the gloss of the filler is. In addition, the dispersion of distribution of the filler is different, and the effect on the gloss of the filled products is different. The influence law is: the wider the distribution of the filler, the lower the gloss of the filler surface. This is mainly because the bigger the difference of the size of the filler is, the surface is more convex and uneven, and the incident light is more likely to generate diffuse reflection.
d, filling amount of filler
The surface gloss of the filler product decreases with the increase of filler. Taking CaCO3 filled PP system as an example, when CaCO3 filling is 5%, the surface gloss of the filled product is 50%. When the CaCO3 fill is 15%, the gloss of the filling product drops to 32%.