The main reason for the yellowing of PVC pipes is that the amount of stabilizer is not enough or the grade is not good, and there should be redness. It is possible that a particularly poor quality stabilizer was used.
But in most cases, the problem is caused by unbalanced lubrication, too little lubrication, especially too little external slip, and excessive plasticization causes discoloration and brittleness of the pipe.
You can add some titanium dioxide to see if it can cover it. If not, try adding stabilizer or replace it. If it is calcium-zinc stabilizer, pay more attention to the adjustment of slip agent.
In addition, lubricants affect plasticization, calcium carbonate is added with whitening agents, etc., and there is PVC resin. Under the same other conditions, poorly used PVC will become yellower and require more stabilizers. .
Under normal circumstances, one would think of the problem of stabilizers. In fact, when the stability is sufficient, lubrication is also a very important factor. In addition, if the calcium powder gets damp, it will also affect the plasticization.
The stabilizer is generally considered first, but the solution to the problem can generally be started by adjusting the lubrication system appropriately. Excluding the problem of stabilizers, focus on slip agents and dynamic balance. The stabilizers mentioned in the industry generally do not contain antioxidants. But calcium and zinc stabilizers generally contain antioxidants.
The background color of rutile is reddish, while the background color of anatase is blue. Rutile is better, but more expensive.
Whether it is rutile or anatase titanium dioxide, in the visible wavelength range (400-700nm), they have high reflectivity to light, so they have good whiteness. However, in the ultraviolet wavelength range less than the visible light range, such as 300-400 nanometers, the performance of the two different crystal types of titanium dioxide is very different.
For rutile titanium dioxide (red line) in the very lethal UV-A band (350-400nm), its reflectivity to ultraviolet rays is much lower than that of blue anatase titanium dioxide. In other words, it is The absorption rate of ultraviolet rays is much higher than that of blue anatase titanium dioxide.
Under this circumstance, the ultraviolet light that the organic resin around the film-forming substance has to share is much less, so the life of these organic substances will be longer. This is why what we usually call rutile-type titanium self-powder is much better than anatase-type weather resistance, these characteristics are innate.
During extrusion, the background color of the titanium dioxide type affects the color of the product. In the later use, the difference of the ultraviolet absorption of the titanium dioxide affects the weather resistance of the product and thus affects its color. In fact, rutile type titanium dioxide is only slightly yellower than anatase type and is not yellowish. The problem lies in the possibility of stabilizers. It may also be the use of composite stabilizers. At present, there are some domestic manufacturers of composite stabilizers. In order to reduce the cost, a lot of lubricants are added and the amount of active ingredients is reduced. The stability is slightly insufficient under the same amount.
The temperature is too high, the compression ratio of the mold is too large, the amount of stabilizer added is not enough, the lubrication system is problematic, the stability of the resin itself is not enough, the calcium powder tide, the gap between the screw and the barrel is problematic, the shear is too large, and there are many reasons. Actual situation investigation!!
0.1 stearic acid is added to promote plasticization
And 0.3 parts of titanium dioxide, mainly to cover up the problem of background color
The appearance of the made pipe is very white, and the color light is reddish