关于塑料退火

关于退火为了改善成型品的尺寸稳定性，有时需要进行退火工序。

那么，应在何时、何温度、用多长时间进行退火，以及退火有哪些要注意的事项呢？此次，介绍一下正确的退火条件和方法。

■尺寸稳定性的改善——首先，何谓后收缩？象本公司“夺钢”（POM树脂）及Duranex（PBT树脂）那样的所谓结晶性塑料，一经冷却固化，其分子就进行规则有序排列，所以体积有很大收缩。

这种收缩的程度一般用成型收缩率的值来表示。

但是，成型品中有序排列的分子所占的比例（称之为结晶度）并非100%。

在高分子材料中，由于分子过长，运动受限制，所以必然剩有未结晶化的部分，叫做非结晶部分。

这种非结晶部分会因使用环境温度的增高等原因而发生结晶，使体积进一步收缩，这种现象叫做“后收缩”。

图1、后收缩情况（附加说明）即使是非结晶树脂也会发生体积收缩，但它与结晶性树脂相比其数值要小。

这种后收缩的大小受成型条件（模具温度）和树脂的使用环境温度所左右。

图2表示了以模具温度40℃和80℃进行成型的成型品，分别在80℃和120℃环境下一定时间静置后的后收缩率。

从图中可以看出：模具温度越低、静置温度越高，后收缩率就越大。

图2、夺钢M90-44（50mm正方形平板、点浇口φ1.0、板厚1mm）时数据库：自M90-44的收缩率中选出(English)另外,后收缩率的大小因树脂的种类和品级制品而异。

下表中列出了各代表品级制品的值，请参照。

表1、各代表性品级制品的后收缩率树脂.品级制品后收缩率成型品成型条件静置条件夺钢（POM）M90S 0.31%(FD)0.30%(TD)120mm正方形平板板厚2mm侧浇口4*2t机筒200℃模具60℃保压60MPa温度100℃时间24 hrDuranex（（PBT）33000.1%(FD)0.03%(TD)120mm正方形平板板厚2mm侧浇口4*2t机筒310℃模具60℃保压60 MPa温度80℃时间2hrFortron （PPS）1140Al 0.01%(FD)0.03%(TD)80mm正方形平板板厚2mm侧浇口4*2t机筒310℃模具150℃保压60 MPa温度150℃时间2 hrVectra（LCP）A150B 0.0%(FD)0.1%(TD)80mm正方形平板板厚3mm侧浇口4*2t机筒300℃模具140℃保压59 MPa温度150℃时间3 hr■尺寸稳定性的改善——最佳退火温度和时间？改善尺寸稳定性亦即减少后收缩率的方法有两个方面。

（1）充分提高成型时的模具温度如果提高模具温度，则会促进成型品的结晶化，所以，可相应地减少后收缩。

下页汇总了后收缩率数据，请一并参照。

成型时的模具温度高于制品的使用环境温度时，几乎所有制品均不需要退火。

（2）进行退火退火是将成型品在高温环境下放置一定时间，预先促进其结晶化的方法。

换言之，就是事前人为地使其进行后收缩，以达到使用环境温度下的稳定状态。

如上所述，使用环境温度越高、模具温度越低，后收缩就越大。

所以，退火温度必须根据使用环境温度而改变。

一般认为，以使用环境温度+10~20℃的退火温度为宜。

譬如：使用环境温度为80℃时，退火温度应为90~100℃。

另外，虽然定为+20℃，但是仅就退火而言，可以高于这一温度。

然而，温度过高时有可能会产生其它（变色等）问题，所以，还须注意温度不能过高。

退火时间一般建议在3小时左右。

但是，厚度薄的成型品有时无须3小时即可。

模具温度高时也可使用较少的时间。

所以，为避免浪费，最好按照不同的时间，分别测定实际成型品的尺寸，从而确定必要且充分的退火时间。

另外，可在任何时候进行退火。

成型后立即退火和放置若干日后退火，效果相同。

■退火时注意事项（1）玻璃纤维增强材料应注意异向性与成型收缩率相同，后收缩率也有异向性。

它还因成型品的厚度和浇口的位置、形状而异。

（2）嵌入品不得退火嵌入品绝对不可进行退火。

否则，会大大损坏制品性能和减少制品寿命。

对嵌入成型品进行退火使之进行后收缩时，有可能在熔合纹处造成破坏、或在与嵌入物的界面处因应力松弛而产生间隙。

（3）过多的退火原则上不宜进行过高温度和过长时间的退火。

否则，可能会产生变色、分解和表面膨胀等问题。

建议对使用的材料和制品进行实际的退火与尺寸测定，从而找出退火的最佳条件。

After-Shrinkage of M90-44Magnify for your click at a graph.These data are the typical values obtained undervarying conditions prescribed by applicablestandards and test methods, and are not minimumstandard material values.[Test specimen] 120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200MoldTemp:60 Annealing Time:Horizontal Annealing Temp.50 Holding Pressure:60MPa Direction:In the graph [Test specimen] 120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200 MoldTemp:60 Annealing Time:Horizontal Annealing Temp.65 Holding Pressure:60MPa Direction:In the graph120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200MoldTemp:60 Annealing Time:Horizontal Annealing Temp.80 Holding Pressure:60MPa Direction:In the graph[Test specimen] 120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200 MoldTemp:80 Annealing Time:Horizontal Annealing Temp.65 Holding Pressure:60MPa Direction:In the graph 120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200MoldTemp:80 Annealing Time:Horizontal Annealing Temp.50 Holding Pressure:60MPa Direction:In the graph[Test specimen] 120 x 120mm Flat Plate Thickness:2mm Side Gate:4w x 2t[Condition] Cylinder Temp.:200MoldTemp:80 Annealing Time:Horizontal Annealing Temp.80 Holding Pressure:60MPa Direction:In the graph50 x 50mm Flat Plate Thickness:1mm Pin Point Gate:1mm[Condition] Cylinder Temp.:200 Mold Tem:In the graph Annealing Time:Horizontal Annealing Temp.:In the graphHolding Pressure:75MPa [Test specimen] 50 x 50mm Flat Plate Thickness:3mm Pin Point Gate:1mm[Condition] Cylinder Temp.:200 Mold Tem:In the graph Annealing Time:Horizontal Annealing Temp.:In the graphHolding Pressure:75MPa 50 x 50mm Flat Plate Thickness:2mm Pin Point Gate:1mm[Condition] Cylinder Temp.:200 Mold Tem:In the graph Annealing Time:Horizontal Annealing Temp.:In the graphHolding Pressure:75MPa*** Test method ***The data shown in this home page are based on our accumulated experience and laboratory data, and not alwaysdirectly applicable to your products used under different conditions. Therefore, we can not guarantee that the contents of this home page are directly applicable as they are to the specific condition in our customers, and we appreciate your final decision on the use of these data.Evaluation method for after-shrinkage1.Apparatus•Two molds are used , each of which has a plaque-shaped cavity with different dimensions as shown below.(1)120mm x 120mm (2)50mm x 50mmType(1) is side-gated and type(2) is pinpoint-gated. The sizes of the gates are shown in the figures.•Ordinary-type injection molding machines with the clamping force of about 150 tons and 75 tons are used for the mold of type(1) and type(2) respectively.•,A three-dimensional measuring apparatus is used for the measurement of dimensions.2.M olding condition•Cylinder temperatures shown in the figures represent those at the nozzle and the metering zone.•,Injection speed is fixed at the screw-forward speed of about 16.7mm/sec or about 1m/min.•,Mold temperatures shown in the figures are actually measured at the surface of the cavity with a contact-type thermocouple thermometer.•,Dwell time is strictly maintained above the gate-sealing time , although actual time is variable depending on the kind of materials and the type of molds.•,Cooling time is fixed at 10sec.3.Measuring method for dimensions•The moldings are aged at 23and 50%RH for 24hrs.•The dimensions at the center of the thickness are measured by a three-dimensional measuring apparatus. For the moldings of type(1), the length in the directions of both flow and perpendicular toflow is measured.•After that, the moldings are annealed at the temperature indicated in the figures for the time also indicated in the figures.•After the annealing process, the moldings are aged at 23and 50%RH for 24 hrs.•The dimensions at the center of the thickness are measured by a three-dimensional measuring apparatus. For the moldings of type(1) , the length in the directions of both flow and perpendicular toflow is measured.•After-shrinkage is calculated from the dimensions before and after the annealing , according to the followingequation.4.NoteThe data shown in this home page are based on our accumulated experience and laboratory data,and not always directly applicable to your products used under different conditions. Therefore, wecan not guarantee that the contents of this home page are directly applicable as they are to thespecific condition in our customers, and we appreciate your final decision on the use of these data.塑料制品的调湿处理：塑料制品的调湿处理，主要是对聚酰氨类（尼龙）原料制品。