Introduction: The application of plastic products is quite extensive, with various colors and vibrant colors on the market, loved by the public. So, how is the coloring of injection molding products processed? What factors cause product fading? This article briefly describes the methods of plastic coloring and fading factors, which can be referenced by purchasing friends:

Coloring Methods

The coloring method has a great relationship with the colorant used and is closely related to the plastic’s properties, molding parameters, and the additives used. For example, pearlescent powder can be added, and talcum powder can be added to make PET transparent color become opaque color (adding some color powder for color adjustment). The formation of water ripples is related to the amount of pearlescent powder added.

1.Pigment Coloring

Pigments generally fall into three categories: inorganic pigments, organic pigments, and dyes.

Inorganic pigments

They have good temperature resistance and weather resistance, but the disadvantages are poor coloring power and poor dispersibility. It is mainly mineral refining, with a temperature resistance of over 300 degrees, and is not suitable for transparent and bright colors.

Organic pigments

They have poor temperature resistance and good dispersibility, and can be used for elastomers. Petrochemical refining;

Dyes

They have good temperature resistance, the best dispersibility, and high vividness. The disadvantage is that they are more prone to migration, and are not suitable for elastomers.

Advantages

Good dispersibility, suitable for small-batch plastic processing, low cost, saving the consumption of manpower and material in the process of coloring masterbatch and coloring paste.

Disadvantages

Not suitable for film blowing, spinning products, using pigment coloring, because the pigment powder is evenly distributed in the resin to be colored, so its dispersibility is better.

2.Coloring with Color Masterbatch

Coloring with color masterbatch employs a certain process and corresponding equipment, and under the effect of the additive, pigments (or dyes) are mixed into the carrier. Through heating, plasticization, stirring, and cutting actions, the molecular structure of the pigments and the carrier resin become thoroughly combined and eventually made into particles similar in size to resin particles.

Advantages

It improves the environmental pollution problem caused by the flying pigments, and makes it easy to change color during use without special cleaning of the extruder hopper. It is targeted and has simple color matching and easy quantification. Compared to batch resin dry-coloring and then molding, using color masterbatch can reduce the aging of resin performance caused by secondary processing of plastic products, and is beneficial for improving the service life of plastic products. During processing, pigments are fully blended and combined with the carrier resin under the effect of the additive. When used, it is placed in the raw resin at a certain ratio, and its compatibility is significantly better than pigment coloring.

Disadvantages

The dispersion is poor, and because the amount added is small, the processing time for plastic products is short, and it is limited by the screw length ratio of the extruder. The dispersion of the color masterbatch is often worse than that of pigments. The cost is high, with an additional manufacturing process, and the coloring cost is higher than that of pigment coloring; it has high performance requirements for the color masterbatch, and when the performance of the carrier in the color masterbatch and the coloring resin is different, the surface of the plastic products often shows undispersed points, color spots, and patterns. Therefore, the use of color masterbatch is limited by its compatibility and dispersion.

Coloring with Color Slurry Color slurry is a semi-finished product made by dispersing pigments and fillers in paint. According to its application, it can be divided into coating color slurry, tape color slurry, papermaking color slurry, textile color slurry, machinery color slurry, toy color slurry, etc.

3. Pigment coloring

Pigment is a semi-finished product made by dispersing pigments and fillers in the paint. According to the use, it can be classified into paint pigment, tape pigment, papermaking pigment, textile pigment, mechanical pigment, toy pigment, latex product pigment, etc.

Advantages

Easy to use, can be directly used for molding and board coloring in the processing technology; generally, it has good high-temperature resistance, easy storage, and no precipitation; it can reduce the dust pollution problem in the use of color powder, and also solve the insufficient compatibility and dispersibility of color masterbatch, the amount of pigment used can be easily controlled in use, reducing the color difference, improving the coloring power and color and brightness; environmental-friendly type meets the requirements of EU REACH and other regulations.

Disadvantages

At present, the biggest restriction in the development of pigments is the high quality of pigments in the production process of domestic pigments, which requires high quality in both process and raw materials, and the cost is higher than that of color masterbatch and color powder; the screw may slip when a large amount is added; if stored for a long time, it will precipitate, it is better to stir before use.

4.”Oil Dyeing”

Oil dye is a liquid pigment concentrate without a resin carrier. Currently, oil dyes are mainly used on bottle preforms in China.

Advantages:

-Low addition ratio, usually transparent series 0.10.5%, pearl/solid color series 0.33.0%; -Excellent dispersion, more uniform and consistent color, more brilliant color, and higher gloss of products;

-Stable color, reducing coloring defects;

-The material only undergoes one high-temperature process, keeping the original resin physical properties unaffected;

-Best inventory management, only a small space is needed to store oil dyes, saving three-quarters of storage space compared to masterbatch;

-Reducing the pressure of overall inventory and operating capital;

-Simple and low-cost oil dye addition equipment, simple and fast color change process, increasing production scheduling freedom, saving personnel time, machines and energy losses;

-Suitable for all polyolefins (such as PP/PE), polystyrene resin (PS), PET resin, and other engineering resins.

Disadvantages:

-Anti-static agents cannot be added to oil dyes, resulting in dust resistance for products on shelves or in storage; -Shelf life of oil dye products is shorter than that of masterbatch products;

-Oil dyes require a dedicated oil dye addition equipment, an oil dye metering pump, to supply the dye to the injection molding machine to produce the desired color products.

Fading Factors

Plastic colored products may fade due to various factors. The fading of plastic colored products is related to the lightfastness, oxidation resistance, heat resistance, acid-base resistance, and properties of the resins used. Here is a detailed analysis of the factors causing fading of plastic coloring:

1 Lightfastness

The lightfastness of the dye directly affects the fading of the product. Outdoor products exposed to strong light, the lightfastness (sun resistance) level of the dye used should be high.

2 Oxidation resistance

Oxidation resistance of the resin and dye used directly affects the aging and fading of plastic colored products.

3 Heat resistance

Heat resistance is related to the thermal stability of the resin and dye used.

4 Acid-base resistance

Acid-base resistance directly affects the stability of the color of plastic colored products and affects the aging and fading of plastic colored products.