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1、.附录1 中文译文共射注塑成型技术简介和背景注塑挤压成型法是大规模生产塑料制品最卓越的生产工艺。它是一种非常通用的生产方法。注塑成型允许生产几何形状非常复杂和几何尺寸非常小的塑料制品。例如，一次性照相机的外壳就是通过注塑成型的方法生产出来的。像这一类塑料制品的几何性状经常包括着几条复杂的曲线、筋板、孔洞、圆柱型的凸台和其他一些复杂结构。到目前为止，为了进一步增强注塑成型法的有效性，扩大其适用范围和增加收益率，注塑成型法的新的应用和改良被不断发展。共射注塑成型技术（Co-injection Molding）于是开始出现。现在主要有两种类型的联合注塑成型技术。第一种被成为双色成型法。双色成型法的工
2、艺过程是先向模具中注射进一种树脂材料，然后抽回模具的一部分零件（增加型腔空间）或将已成型的制品转入到一个更大的型腔，并使其充分冷却后，注射进第二种树脂材料。这种技术被用来生产像计算机的按键和汽车的双色尾灯之类的制品。第二种技术则更为普通，用第二种技术生产出来的制品通常包含不同的肤层材料和芯层材料。就像我们所熟知的“夹心三明治”一样，因为芯层材料被包围在肤层材料之间。夹芯成型技术是将两种不同的塑料原料同时或者快速依次通过同一个浇口的有效注塑成型方法。一种塑料原料用来形成制品的内部结构，另外一种塑料原料组成制品的表面。通过组合两种不同的塑料原料可以获取原本传统注塑成型方法所无法提供的好处。图1一个
3、共射注塑机的结构夹芯注塑成型技术在1969年被申请成为专利。它的最初发明目的是用来代替结构泡沫塑料的生产工艺。传统的结构泡沫塑料的生产需要抛光和上色这样的后续处理工艺。夹芯注塑成型技术可以一个由实体表面包围的单元核来获的很好的表面光滑度。这项生产工艺在1975年进入商业应用。夹芯注塑成型生产过程由一台拥有两套彼此独立的注塑控制单元的注塑机来完成。为了使两种不同的塑料原料在注塑成型过程中通过同一个浇口，必须使用同一个喷嘴和一个转换装置。图1说明了一个共射注塑成型注塑机的结构。因为夹芯注塑成型技术与双色注塑成型技术相比更为普通和具有代表性，接下来将重点讨论夹芯注塑成型技术。共射注塑成型技术（Co-
4、injection Molding）的生产过程第一种使两种不同的塑料注射进同一塑料制品成为可能的方法是按照以下的顺序来完成的。这是使用同一个浇流道来完成的。图2说明了了共射注塑成型生产过程中的生产步骤。图2共射注塑成型的生产步骤。起初，向模具型腔内注射进肤层材料，但并不是完全填充满整个型腔。这就是我们所知道的“短射”。接下来的第二步向模具型腔注入芯层材料。同时一个冷凝层（肤层）开始在模具的型腔壁上形成。在接下来的一个阶段内，被注射进型腔内的芯层材料几乎完全充满制品。产生此种现象的原因是：在注塑过程中形成的喷射流将影响已经存在着的、且处于熔融状态的肤层材料，将处在模具型腔中间的肤层材料推向模具型
5、腔表面，从而受冷产生制品的肤层。一旦模具被完全填充之后,少量的肤层材料被注射进浇道去清除掉浇道中的芯层材料，以防止在下一注射周期开始时浇道中的芯层材料被注射进制品的表面。单一浇道注塑成型法产生的问题是：在喷嘴转换时将发生注射停滞，从而在制品表面上留下熔接线。另外这种注塑方法很难使芯层材料在制品中均匀分布。由于这些原因，单一浇道注塑成型法通常被用来生产芯层为泡沫塑料的厚壁制品。图3 利用两个同心注射通道进行的共射注塑成型另外一种有效的共射注塑成型方法是同时向模具型腔注射进两种原料。入图3所示。这种方法使用具有两个同心流道的喷嘴。同时注射在保持溶流前锋稳定的流动速率方面具有明显的优势，可以帮助避免
6、在制品的表面产生冲模流动痕迹，破坏制品的光滑表面。肤层材料和芯层材料在制品中所占的比例和分布情况基于这两种原料的使用情况。主要因素包括两种材料的黏度比值和体积比值。但是模具的几何形状和注塑生产过程的工艺情况（比如，注射速度）同样也会对肤层/芯层材料的所占比例和分布产生影响。图4说明了两种不同材料的黏度比值对肤/芯层的分布影响。图4 两种不同材料的黏度比值对肤/芯层的分布影响黏度比值对芯层在肤层中渗透长度和厚度的一致性起到了十分重要的作用。为了制品内部获得厚度较厚且均匀的芯层，可以通过模具中注了比肤层材料黏度稍厚的芯层材料来实现。肤层/芯层材料的黏度比值在决定最终产品的机械特性方面同样具有十分重
7、要的意义。如果注塑过程中肤/芯层材料体积设置了一个不恰当的比例（既用量比例的不恰当），将造成芯层的材料打破肤层而流向制品的表面。这种芯层材料打破肤层而流向制品表面的现象是共射注塑成型中的常见缺陷。除了体积比例因素外，同时也基于注塑过程中的参数设置，比如注塑速度、芯层和肤层的注塑时间、熔体温度和模具温度。图5说明了在一个连续共射注塑成型的案例中芯层和肤层材料的熔体长度与芯层材料打破肤层现象发生地点之间的关系。图形被分为四个部分：1）肤层材料被注射进型腔。2）肤层材料停止注射，芯层材料被注射进型腔。3）芯层熔流前锋肤层熔流前峰，但芯层熔流没有打破肤层熔流（两种材料开始混合）。4）芯层熔流前锋打破肤
8、层熔流前峰（芯层材料将在制品表面出现）。图5芯层和肤层材料的熔体长度与芯层材料打破肤层现象发生地点之间的关系5）图6说明了模具设计对于芯层材料的分布影响。当芯层材料被注射进型腔时，如果型腔的任何部分已经被肤层材料完全填充，那么芯层材料是不可能被注射进模具型腔的。芯层材料无法穿透肤层到达其内部因为已经没有空间来放置芯层材料。基于这个原因，平衡流动在共射注塑成型中是十分重要的。图6 模具设计对于芯层材料的分布影响共射注塑成型技术的优点和缺点使用共射注塑成型法进行生产具有许多的优点。使用共射注塑成型技术的主要原因之一是工业界对于日益增长的回收塑料的再利用。回收利用废塑料是一项非常困难和昂贵的工作。许
9、多公司开始试图使用共射注塑成型技术来解决这个难题。他们将回收的废塑料作为芯层原料，而使用新塑料作为肤层原料。这项技术可以有效减少对资源的使用、减少回收利用的费用，从而减少废弃塑料对环境做出贡献。另为，使用共射注塑成型技术可以同时获得几种材料特性。最为普通的材料结合有实心的芯层和实心的肤层，或者实心的肤层和发泡的芯层。实心的芯层和实心的肤层的结合产生一系列的增强特性：减少了材料使用但增强了硬度，获得了良好的表面光洁度并了刚度，表面是柔软的但内部确实硬的。实心的肤层和发泡的芯层同样十分普遍。其主要思想是获得空心泡沫结构的好处并避免其缺点。一个空心泡沫结构的芯层减少了材料的使用，降低了制品的重量和拥
10、有高强度。空心泡沫结构的通常缺点是表面的光洁度，传统的做法是对它们进行抛光和油漆。用共射注塑成型技术获得的实心的肤层和发泡的芯层，原本额外的处理工序不再需要并且能够提供很好表面光洁度。共射注塑成型技术的最大缺点是必须使用复杂的注塑成型机。而共射注塑成型注塑成型机与传统的普通注塑成型机相比过于昂贵。事实上，共射注塑成型技术使用的一些特殊设备比传统的注射成型设备贵出了50%-100%。由于出奇昂贵的价格，注射成型技术并没有获得很大范围的接受。到1996年为止，也不到100台注塑成型设备具有共射注塑成型能力。然而，随着经济增长的需要和以环境保护角度出发的资源利用使使用共射注塑成型技术成为一种选择。B
11、emis公司正在利用共射注塑成型技术生产座便器。许多自动车公司正在利用共射注塑成型技术解决汽车生产过程中造成的大量的废弃塑料。*;附录2 英文原文Introduction and Background:Along with extrusion, injection molding is the most prominent process for mass-producing plastic products. It is a very versatile operation. Injection Molding allows for very complicated geometries a
12、nd small dimensions. For example, the casing for disposable cameras is made via injection molding. The geometry for those pieces include several complicated curves, ribs, holes, protruding cylinders, and other elements. Even so, new applications and modifications of injection molding are being devel
13、oped to increase the usefulness, applicability, and profitability of injection molding. One such emerging technology is that of co-injection molding.There are two main types of co-injection molding. The first is referred to as two color molding. In two-color molding a part is molded using one resin,
14、 and then a second resin is molded into the first once it is sufficiently cooled after some part of the mold retracts or the part rotates to a second larger cavity. This technology is used in products such as computer keys and multi-colored automotive taillights. The second, and more common, type of
15、 co-injection molding involves the injection of a skin material and a core material. This is also known as “sandwich molding” because the core material is sandwiched in between the skin material. Sandwich molding is a variation of injection molding in which two different plastics are either simultan
16、eously or in rapid sequence injected through the same gate. One material makes up the core of the product and the other makes up the skin. Through the combination of two different materials several benefits can be extracted that traditional injection molding can not supply by itself. Figure 1: Sandw
17、ich molding machine with a common nozzle and a switchieadThe sandwich injection molding process was patented in 1969. It was first invented to be an alternative to the structural foam process. Traditionally structural foam needed post-processing operations such as polishing and painting. The sandwic
18、h molding process could use a cellular core with a solid skin to obtain a good surface finish. The process has been commercially used since 1975. The sandwich molding process is achieved by a machine that has two separate and individually controlled injection units. Since the two materials are injec
19、ted through the same gate, they must have a common injection nozzle and a switching head. Figure 1 illustrates a sandwich molding machine. The sandwich molding process is more common than the two-color process, so the rest of this paper will focus on sandwich molding (referred to just as co-injectio
20、n molding throughout the rest of the report).The Co-injection Molding Process:The first possibility for injecting the two materials is to do so sequentially. This is achieved using one channel. Figure 2 illustrates the steps in the sequential co-injection process. Initially, a shot of the skin mater
21、ial is injected into the mold but does not completely fill it. This is known as a “short shot.” In the next step the core material is injected. A frozen layer begins to form at the cold mold walls. In the next stage, a shot of the core material is injected to almost completely fill the part. The phe
22、nomena known as the fountain flow effect of polymer inside the mold will cause the skin material that is still in the melt phase near the center of the mold thickness to be pushed out against the mold walls creating the skin layer. Once the mold is almost filled, a small amount of skin material is i
23、njected to purge the core material from the spruce to eliminate any possibility for it to show up at the surface of the next shot. The problem with the one-channel method is that stagnation occurs at the switch-over which results in a “hesitation line” in the shape of a dull ring. Also, it is diffic
24、ult to achieve a uniform distribution of the core material. For this reason, the one-channel method is usually reserved for thick-walled parts with a foam core.Figure 1: Illustrations of the stages in sequential co-injection molding through a single nozzleThe other possible co-injection method is si
25、multaneous injection of the two materials. This method utilizes nozzles with concentric flow channels such as those shown in figure 3. Simultaneous injection has the advantage of maintaining a constant flow-front velocity which helps to avoid flow marks and differences in gloss.Figure 2: Concentric
26、injection channels used for simultaneous co-injection moldingThe ratio and distribution of the skin and core material depends on the materials used. The primary factors are the viscosity ratio of the two materials and the volume ratio, but it is also affected by mold geometry and the processing cond
27、itions (i.e. injection speed). Figure 4 illustrates the effect that viscosity ratio can have on the skin/core distribution. It plays an important effect in determining the thickness uniformity and length of core penetration. The most uniform thickness distribution can be achieved by injecting a core
28、 that has a slightly higher viscosity than the skin. The viscosity ratio also had a significant effect on the mechanical properties of the final product. Using an improper volume ratio can give rise to the core material breaking through the skin material to the surface of the product.Figure 4: Illus
29、trating the effects of the viscosity ratio on the thickness distribution of the core materialThe breakthrough phenomenon is a common defect in co-injection molding. Besides the volume ratio it is dependent on the processing conditions such as injection speed, injection time of the core and skin mate
30、rials, melt temperature and mold temperature. Figure 5 illustrates the relationship between flow length of both the skin and core materials for a sequential co-injection molding process for a case where the breakthrough phenomenon occurs. The graph is divided into four regions: 1) the skin material
31、is injected, 2) the skin injection stops and the core material is injected, 3) the core flow front reaches the skin flow front but does not break through (the two material advance together), 4) the core flow front breaks through the skin flow front (the core material will appear at the surface of th
32、e product.Figure 5: Flow length relationship with injection time for core and skin when breakthrough occursFigure 6: Illustrating the effects of mold cavity geometry on the core material distributionThe affect of mold design on core distribution is illustrated by figure 6. The core will not penetrat
33、e any part of the mold that has already been completely filled by the skin material when the core is injected. It cannot penetrate the skin material because there is no room to displace it. For this reason, a balanced flow is very important in co-injection molding.Advantages and Disadvantages:There
34、are many advantages to using the co-injection molding process. One of the main factors driving co-injection technology is the growing need for recycling in industry. Recycling wasted plastic is very difficult and costly to do. In order to solve this problem, many companies are attempting to use co-i
35、njection where recycled plastic is used as the core material and virgin material is used as the skin material. This technique can significantly reduce material and recycling costs along with the environmentally friendly reduction of waste. Also, some beneficial material properties can be achieved wi
36、th through the use of co-injection molding. The most common combinations of materials used are a solid skin and solid core, or a solid skin and a foam core. The solid skin and solid core combination can create a number of enhanced properties: high rigidity with reduced material costs, good surface f
37、inish with increased rigidity, and flexible surface with rigid core. The solid skin and foam core combination is also very common. The main idea is to provide the benefits of foam without the disadvantages. A foam core reduces material usage, has lower part weight, and has high strength. The usual d
38、rawback of foam is the surface finish, and traditionally they have been polished and painted. With a solid skin co-inject with the foam, the extra processing is eliminated and can provide a good surface finish.The main disadvantage of the co-injection process is the complicated machinery that is nec
39、essary. This causes co-injection machines to be much more expensive than tradition injection molding machines. In fact, the special equipment necessary can be up to 50% to 100% more expensive than traditional injection molding equipment. Due to this drastic price increase, co-injection molding has n
40、ot gained widespread acceptance. As of 1996, there were fewer than 100 processors with co-injection capability However, the increasing need for economic and environmentally friendly use of material is making co-injection molding an attractive option. One company that currently utilizes co-injection molding is Bemis, a company that makes toilet seats. Many automotive companies are investigating the use of co-injection molding due to the large amount of plastic that is wasted in the automobile manufacturing process.