The main reasons for poor gloss of Plastic parts are: mold, injection molding process, raw materials, etc. PTJ elaborates on this issue as follows, please correct me if it is wrong!

1.Injection mold

• 1. If the mold cavity is poorly processed, such as scars, micro-holes, abrasion, roughness, etc., it will inevitably reflect on the plastic parts and make the plastic parts poorly shiny. For this, the mold must be carefully processed to make the cavity surface more Small roughness, chrome plating can be polished if necessary.
• 2. If there are oil stains, water stains on the surface of the cavity, or too much release agent, the surface of the plastic part will be dark and dull. For this, the oil and water stains should be removed in time, and the release agent should be used in a limited amount.
• 3. If the demolding angle of the plastic part is too small, it is difficult to demold, or the force is too large during demolding, so that the surface of the plastic part has the best gloss. For this, increase the demolding angle.
• 4. If the mold exhaust is poor, too much gas will stay in the mold, which will also cause poor gloss. For this, check and correct the mold exhaust system.
• 5. If the cross-sectional area of the gate or runner is too small or suddenly changes, the shear force will be too large when the melt flows in it, and it will flow in turbulent dynamics, resulting in poor gloss. For this, the gate and runner should be appropriately enlarged Cross-sectional area.

2. Injection molding process

• 1. If the injection speed is too low, the surface of the plastic part is not dense and the gloss is poor. For this, the injection speed can be appropriately increased.
• 2. For thick-walled plastic parts, if the cooling is not sufficient, the surface will be hairy and the gloss will be dark. For this, the cooling system should be improved.
• 3. If the holding pressure is insufficient and the holding time is too short, the density of the plastic part is insufficient and the gloss is poor. For this, the holding pressure and holding time should be increased.
• 5. If the melt temperature is too low, the fluidity will be poor, which will easily lead to poor gloss. For this, the melt temperature should be appropriately increased.
• 6. For plastic parts made of crystalline resin, such as PE, PP, POM, etc., uneven cooling will cause poor gloss. For this, the cooling system should be improved to make it evenly cooled.
• 7. If the injection speed is too high and the gate cross-sectional area is too small, the area around the casting will be dark and poor gloss. For this, the injection speed can be appropriately reduced and the gate cross-sectional area can be increased.

3.Raw materials

• 1. The large difference in the particle size of the raw materials makes it difficult to plasticize uniformly and the gloss is poor. For this, the raw materials should be sieved.
• 2. Too much recycled materials or nozzle materials are added in the raw materials, which will affect the uniform plasticization of the melt and cause poor gloss. For this, the amount of recycled materials or nozzle materials should be reduced.
• 3. Some raw materials will decompose and change color during temperature adjustment and cause poor gloss. For this, materials with better temperature resistance should be used.
• 4. The content of moisture or volatile matter in the raw materials is too high, which volatilizes into gas when heated, and condenses in the cavity and melt, resulting in poor gloss of the plastic parts. For this, the raw materials should be pre-dried.
• 5. The dispersibility of some additives is too poor and the gloss of the plastic parts is poor. For this, the additives with better flow properties should be used.
• 6. The raw materials are mixed with foreign matter, miscellaneous materials or incompatible materials, and they cannot be uniformly mixed and melted with the raw materials, resulting in poor gloss. For this, these miscellaneous materials should be strictly excluded in advance.
• 7. If the amount of lubricant is too small, the fluidity of the melt will be poor, and the surface of the plastic part will not be dense, resulting in poor gloss. For this, the amount of lubricant should be appropriately increased.

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Link to this article：How can ABS injection molded parts increase brightness?

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