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Homogeneous PVC Profiles' Aging & Discoloration

Time : 2021-11-15 Hits : 4

In recent years, color plastic doors and windows  have developed rapidly.Because of the lowest production cost, full color homogeneous profiles are still widely used in some areas. Practice had proven that the weather resistance of the entire color profile was not only related to the dosage of anti-aging additives in the formula, but also to the structure of the color masterbatch and the color system. The specific problems needed to be analyzed. They could not be generalized. This paper focuses on the analysis and demonstration of the effects of the colorant structure, color, particle size and addition on the aging performance of full base color plastic profiles (including PVC/PVC two-color co-extrusion). At the same time, it also analyzed and studied the color difference phenomenon occurring during the production of full color plastic special-shaped materials. At the same time, it proposed effective measures to improve the weather resistance of full color plastic special-shaped materials and prevent their color change during production.

Influence of PVC colorant material structure and color system on aging performance

Colorants are substances that give polymers a variety of bright colors. Colorants used in PVC plastics are mainly pigments. The coloring ability, transparency or opacity, and coloring strength of a pigment is usually the nature of the pigment, independent of the PVC plastic formulation.However, other properties of the pigment, such as thermal stability, light stability, mobility, outdoor durability and insulation, will be affected by the formulation and processing conditions. Therefore, it is necessary to consider the applicable pigments at first and then the problem of color matching and uniform dispersion.

The forming process of plastic profile is generally required to have strong coloring power, stable performance, no serious discoloration, easy dispersion, no decomposition, good mixing with PVC resin, no trace ions (such as Fe) that can cause polymer degradation, no precipitation from the profile to the surface layer and migration to other articles in contact with it, no impact on the internal physical and chemical properties of the profile, excellent heat resistance and weather resistance, high light fastness, insoluble in water, no absorption of ultraviolet outside to make the profile temperature rise, etc. In summary, there are four main items:

(1) Can meet people's color requirements;

(2) Does not affect the normal plastic extrusion of plastic profiles;

(3) Does not affect the requirements for chemical and physical properties of plastic profiles;

(4) Has good weather resistance, and can meet the requirements of doors and windows in outdoor use for a long time without discoloration and aging.

At present, there are many manufacturers producing colorants for plastics in China. But Few are really for the plastic door and window profiles. Many factory-produced colorants are difficult to meet the requirements of long-term outdoor use of plastic doors and windows,anti-aging performance. In order to improve the weather resistance of colorants, it is necessary to understand the pigment structure and color system and other factors.

1. Effect of the color of the PVC colorant on weather resistance

The weather resistance of colorants is also related to color. The red profile or the colored profile added with red pigment is the most easy to fade. The molybdenum complex red in the red panel, pig liver profile and olive grey profile is red first, and the molybdenum complex red is very fast. Light yellow profile skin has been nearly turbid white, basically can not see the yellow base. Although the sky-blue profile skin aging,a thin layer of dark gray skin, but can still see the sky-blue base. Better not to use light red or light yellow. Colors such as iron red, zinc white, zinc barium white, iron yellow, mineral violet, copper pow pigment, etc. have promoting effect on polychloroethylene dehydrochlorination and should not be used. Improper use of carbon black will also promote thermal aging in hard polyvinyl chloride. PVC profiles will decompose and release HCI during extrusion production, which may cause color change of weak acid resistance colorants. For example, ultramarine will dissociate sulfur and fade under acidic conditions. Therefore, effective heat stabilizers should be selected to minimize the dehydrochlorination reaction of polyvinyl chloride.

2. Effect of PVC Colorant Pigment Structure on Weather Resistance


Colorants can be roughly divided into inorganic and organic pigments. The general inorganic pigment is represented by titanium dioxide and carbon black. The organic pigment is represented by macromolecular red. The metallic luster pigment is represented by gold and copper. The fluorescent pigment is represented by fluorescent whitening agent and the pearlescent pigment is represented by pearl powder.

PVC-U plastic profiles shall not be used together with colorants containing iron, cobalt, manganese and zinc plasma as much as possible to prevent metal ions contained in the pigments from accelerating the decomposition of PVC products and causing phase transformation. Sulfide colorants such as cadmium red and cadmium yellow, etc. will release hydrogen sulfide during decomposition of colorants in the heat processing of PVC-U plastic materials using lead salt as stabilizer, and react with lead to generate black lead sulfide, turning the profiles into gray.

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