3. Too much or too little stabilizer
The role of the stabilizer is to inhibit degradation or to react with the released hydrogen chloride and to prevent discoloration during processing of the polyvinyl chloride.
Stabilizers vary by type, but in general, excessive use delays the plasticizing time of the material, resulting in less plasticization of the material as it exits the mold, and there is no complete fusion between them. The molecules in the formulation system.
Its intermolecular structure is not strong.
When the equivalent is too small, relatively low molecular substances in the formulation system may degrade or decompose (also referred to as excessive plasticization), and the stability of the intermolecular structure of each component may be destroyed.
Therefore, the amount of stabilizer also affects the impact strength of the profile. Too much or too little results in a reduction in profile strength and a tendency to make the profile brittle.
4, excessive use of external lubricants
The external lubricant is less soluble in the resin and promotes slippage between the resin particles, thereby reducing frictional heat and retarding the melting process. This effect of the lubricant is early in the process (ie, external heating and frictional heat generated internally).
The resin is the largest before the resin is completely melted, and the resin in the melt loses its identifying properties.
External lubricants are classified into pre-lubrication and post-lubrication, and over-lubricated materials exhibit poor shape under various conditions. If the lubricant is used improperly, it may cause flow marks, low yield, turbidity, poor impact, and rough surface.
, poor adhesion, poor plasticization, etc.
In particular, when the equivalent is too large, the compactness of the profile is poor, the plasticization property is poor, and the impact property is poor, resulting in the profile becoming brittle.
5, hot mixing feed sequence, temperature setting and curing time are also decisive factors for profile performance
There are many component formulas in PVC-U. The order of addition should be beneficial to the action of each additive, which is beneficial to increase the dispersion speed and avoid adverse synergistic effects. The order of the additives should help to improve the adjuvant.
The synergistic effect of the reagent overcomes the effect of phase elimination, so that the auxiliary agent which should be dispersed in the PVC resin completely enters the inside of the PVC resin.
The typical lead salt stabilization system recipe sequence is as follows:
a.
When running at low speed, add PVC resin to the hot mixing tank;
b.
Stabilizer and soap are added at 60 ° C under high speed operation;
c.
At 80 ° C, high speed operation, adding internal lubricants, pigments, impact modifiers, processing aids;
d.
Adding a lubricant such as wax at a high speed of about 100 ° C;
e.
Adding filler at high speed operation at 110 °C;
f.
The material is cooled in a cold mixing tank at a low speed of 110 ° C - 120 ° C;
g.
When the temperature of the mixture was cooled to about 40 ° C, the material was discharged and sieved.
The above feeding sequence is more reasonable, but in the actual production process, according to the equipment and various conditions, most manufacturers add other additives in addition to the resin.
There is also a light active calcium carbonate added together with a main component or the like.
This requires the company's technical staff to develop their own processing technology and feeding sequence according to the characteristics of the company.
In general, the hot mixing temperature is about 120 ° C, the temperature is too high
When the material is low, the gelation and the mixture are not uniform. Above this temperature, some substances may decompose and volatilize, and the dry mixed powder is yellow.
The mixing time is generally 7-10 minutes to achieve compaction, homogenization and partial gelation.
The cold mixture is usually below 40 ° C and the cooling time requirement is very short. If the temperature is above 40 ° C and the cooling rate is slow, the prepared dry mixture will be less dense than conventional.
The curing time of the dry mixture is usually 24 hours. When the time is longer than this, the material easily absorbs water or agglomerates. Below this time, the structure between the molecules is unstable, resulting in large fluctuations in the profile size and wall thickness during the extrusion process.
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If the above link is not enhanced, the quality of the profile product will be affected. In some cases, the outline will be very fragile. (to be continued)