探索UV有机硅离型剂化学机理

Exploring the Chemistry Behind Silicone-Based Release Additives

Thorsten Schierle

The need for certain release properties can be found in numerous everyday applications, as well as in industrial applications.1 Depending on the nature of these applications, different levels of the release effect are desired, and demands regarding durability of the release effect vary substantially. Therefore, it makes sense to take a closer look at the specialty additives that create this effect.

In the first section of this article, the chemical background of this additive class is explained. The second section explains the mode of action in typical release additive applications and the basic effects of different types of silicone-based release additives. Finally, the basic formulation principles are explained.

Chemical Background

The most simple route to a silicone-based release additive is to obtain polydimethylsiloxane (PDMS) from dichlorodimethylsilane (Figure 1), which is readily available via the Müller-Rochow synthesis2 on industrial scale, via a hydrolysis-condensation reaction (Figure 2).3

FIGURE 1 » Synthesis of dichlorodimethylsilane via the Müller-Rochow synthesis.

Synthesis of dichlorodimethylsilane via the Müller-Rochow synthesis

FIGURE 1 ? Synthesis of dichlorodimethylsilane via the Müller-Rochow synthesis.

Synthesis of polydimethylsiloxane via a hydrolysis-condensation reaction

FIGURE 2 ? Synthesis of polydimethylsiloxane via a hydrolysis-condensation reaction.

The obtained PDMS typically consists of 30-50 repeating units. For further fine-tuning of the polymer, equilibration processes are utilized. Under the influence of catalysts, the PDMS polymers are forced into a condensation (water removal) reaction; this yields a PDMS polymer with a higher number of repeating units (Figure 3).4

FIGURE 3 » Condensation reaction of polydimethylsiloxanes

The condensation reaction is terminated by the addition of “end cappers,” such as  (H3C)3Si-O-Si(CH3)3. Thus, the number of repeating units and the molecular weight of the PDMS are controlled (Figure 4). Alternatively, the termination of the condensation may also be established with mono-functional chloroalkylsilanes (Figure 5).5

FIGURE 4 » Termination of the condensation reaction of polydimethylsiloxanes via “end cappers”.

FIGURE 5 » Termination of the condensation reaction of polydimethylsiloxanes via mono-functional chloroalkylsilanes.

The PDMS obtained via these synthesis routes are noncrosslinkable. This results in a migration tendency mainly influenced by the molecular weight of the molecule, the compatibility of the PDMS with the coating formulation and the coating formulation itself. The most basic way to modify the molecular weight was described in the previous section. The compatibility of silicone release additives can be modified by changing two parameters: the length of the siloxane chain and the degree of organic modification. Regarding the former, the release effect increases as the length of the siloxane chain increases. At the same time, the compatibility decreases. Regarding the latter, the compatibility increases as the degree of organic modification increases. Furthermore, the better the polarity of the organic modification matches the polarity of the coating formulation, the higher the compatibility.To obtain crosslinkable siloxanes, acrylate functionalities are introduced into the polymer.6 In principle, two main options for the modification are possible:modification at the backbone of the polymer chain, which yields comb-like structures modification at the ends of the polymer chain, which leads to a a,w-modification (Figure 6)

FIGURE 6 » Polydimethylsiloxane with α,ω-modification (organic modification in blue, acrylate groups in purple).

The influence of adequate organic modification on the compatibility is quite apparent when comparing mixtures of modified PDMS/water and pure PDMS/water. The mixture of water with pure PDMS looks turbid, while mixtures of water with adequately 

modified PDMS remain clear. Figure 7 illustrates this effect.

FIGURE 7 » Mixtures of water with pure PDMS (left) and adequately modified PDMS (right).

As explained in the first section, silicone release additives can be separated into two groups: noncrosslinkable and crosslinkable release additives. In a standard release coating, the noncrosslinkable release additive is partially at the top of the coating surface (Figure 8). When, for example, a label is placed on this coating, the noncrosslinkable release additive migrates (over time) into the glue layer; thus, the release effect is influenced negatively (Figure 9).

FIGURE 8 » Coating film with noncrosslinkable release additive, covered by adhesive tape.

FIGURE 9 » Coating film with noncrosslinkable release additive, covered by adhesive tape; migration of release additive into the glue layer.

If a crosslinkable release additive is used, most of the additive molecules will be permanently anchored due to the crosslinking of the double bonds of the attached acrylate groups. When, for example, a label is placed on this coating, the crosslinked release additive molecules remain in place and do not migrate into the glue layer; thus, the release effect maintains a high level of performance for a prolonged time (Figure 10).

FIGURE 10 » Coating film with anchored crosslinkable release additive, covered by adhesive tape.

Formulation Approach

Crosslinkable release additives are important when long-lasting release effects are required in printing applications. As explained in the previous section, the ability to incorporate the release additive permanently into the coating or ink layer via the crosslinkable acrylate groups offers a major benefit when durability is desired. The acrylate groups form a network with the binder upon radiation curing, thus minimizing the tendency of the additive to migrate. In this way, longer-lasting surface effects can be achieved.Typical applications for crosslinkable release additives include:Wipe-off applications (such as the scratch-off section of a lottery ticket);Peel-off application (such as label release or easy-opening packaging);Anti-blocking applications (such as blocking prevention in stacked packaging).In a formulation, the main goal is to level out release properties and maintain a smooth surface. A common approach includes using a combination of radiation-curing additives. Typically, additives that yield good leveling properties are combined with additives that yield excellent release properties. Depending on the formulation and on the polarity of the system, 

different combinations and ratios of the radiation-curing additives are necessary. The most common approach is to first choose the appropriate release additive, then choose the appropriate combination partner to achieve the desired leveling. 

Figure 11 illustrates the release effect of various additives. Therefore, if maximal release is desired, Rad 2800 is the product of choice.

FIGURE 11 » Comparison of the release effect of different TEGO Rad additives.

About Radiation-Curing Additives

Radiation-curing additives are a range of modified silicone-based additives with organic modification. They bear acrylate groups, thus they are crosslinkable, which equips them with unique properties. Depending on the silicone character and on the degree of organic modification, they improve slip, substrate wetting and anti-cratering, scratch resistance, and leveling. Furthermore, some of them have release and defoaming properties.

Summary 

The radiation-curing additives are unique because they can be crosslinked into the coating; the resulting glide and release effects are particularly durable. With conventional additives, the release effect is markedly weaker and less permanent because the additives are not crosslinked into the coating.

References

1   Gl?ckner et. Al. Radiation Curing Coatings and Printing Inks; Hannover: Vincentz Network, 2008 (1), p 142ff.

2   Koerner et. al. Silicones; Essen: Vulkan Verlag, 1991 (1) p. 9-15.

3   Brook. Silicon in Organic, Organometallic and Polymer Chemistry; New York: Wiley & Sons, 2000 (1), p. 258ff.

4   Brook. Silicon in Organic, Organometallic and Polymer Chemistry; New York: Wiley & Sons, 2000 (1), p. 261ff.

5   Klotzenburg; et al. Polymere; Berlin: Springer, 2014 (1), p. 204f.

6   Gl?ckner et. Al.: Radiation Curing Coatings and Printing Inks; Hannover: Vincentz Network, 2008 (1), p 98f.

This article has also appeared in PPCJ and Boytürk magazines.

以下为中文翻译：

探索有机硅离型助剂背后的化学机理

作者：Thorsten Schierle，应用技术、油墨、数据和新应用 部总监，赢创资源能效公司，德国埃森   |  发表于：2017-04-12 

许多日常应用及工业用途中都发现需要具备一定的离型性能1。根据这些用途的性质，需要达到离型效果也不同，并且有关离型效果的持久性

的要求也在增加。因此，仔细研究能产生这种效果的特殊助剂意义重大。

本文第一部分解释了这种类别助剂的化学背景。第二部分解释了在典型的离型助剂用途中的作用模式和基于不同类型有机硅离型助剂的基本作

用。最后，解释了基本的配制原理。

化学背景

制备有机硅离型助剂的最简单的路线是从二氯二甲基硅烷（图1）得到聚二甲基硅氧烷（PDMS）

（图1），可在工业规模上通过Müller-Rochow合成法2方便地制得，或通过水解-缩合反应制备（图2 ）3。

所获得的PDMS通常由30-50个重复单元组成。为了进一步对聚合物进行微调，利用平衡工艺，在催化剂的影响下，PDMS聚合物被迫进行缩合（

脱水）反应。这样能得到具有更多数量重复单元的PDMS聚合物（图3）4。

通过加入“封端剂”，例如（H3C）3Si-O-Si

（CH3）3来终止缩合反应。从而控制重复单元的数量和PDMS的相对分子质量（图4）。或者也可以使用单官能团的氯烷基硅烷来使缩合终止（

图5）5。

通过这些合成路线得到的PDMS是不可交联的。这导致了迁移的倾向，它的迁移倾向会受分子的相对分子质量、PDMS与涂料配方及涂料配方本身

的兼容性的影响。前面部分描述的是最基本的改变相对分子质量的方法。通过改变硅氧烷离型助剂的下列两个参数能改变助剂的相容性：硅氧

烷链的长度和有机改性的程度。关于前者，随着硅氧烷链的长度增加，离型效果提高。同时，相容性降低。关于后者，相容性随着有机改性程

度的增加而增加。此外，有机改性的极性与涂料配方的极性匹配得越好，相容性越高。

为获得可交联的硅氧烷，将丙烯酸酯官能团引入聚合物中6。原则上，可用于改性的有两种主要选择：

? 在聚合物链的主链上进行改性，得到梳状结构；

? 在聚合物链的末端进行改性，得到α、ω-改性（图6）。

当比较改性的PDMS/水和纯的PDMS/水的混合物时发现，进行充分的有机改性对相容性的影响是相当明显的。水与纯PDMS的混合物看起来是混浊

的，而水与充分改性的PDMS的混合物保持清澈。图7说明了这种效果。

作用模式

如第一部分中所解释的，有机硅离型助剂可以分成两组：不可交联的和可交联的离型助剂。在标准的离型涂层中，不可交联的离型助剂部分在

涂层表面的上部（图8）。例如，当将标签置于该涂层上时，不可交联的离型助剂随时间迁移进入胶层；因此，离型效果受到负面影响（图9）

如果使用可交联的离型助剂，由于与所附带的丙烯酸酯基团双键的交联作用，大多数助剂分子将被永久锚定。例如，当将标签置于该涂层上时

，交联的离型助剂分子保持在原位而不会迁移进入到胶层中。优异的离型效果可长时间保持（图10）。

配制方法

印刷中如需要持久的离型效果，可交联的离型助剂则尤显重要。如前面部分所解释的，当需要持久性时，通过可交联的丙烯酸酯基团将离型助

剂永久地加入涂层或油墨层中非常重要。在辐射固化时，丙烯酸酯基团与基料形成网络结构，从而将助剂迁移的趋势最小化。采用这种方式，

可获得更持久的表面效果。

可交联的离型助剂的典型用途包括：

? 刮除用途（例如彩票的刮开部分）；

? 剥离用途（如标签剥离或易打开的包装）；

? 抗粘连用途（如堆叠包装中的防止粘连）。

在配方中，主要目标是平衡离型性能并保持表面光滑。常见的方法包括使用辐射固化助剂的组合。通常，将具有良好流平性能的助剂与具有优

异脱模性能的助剂组合使用。根据配方和体系的极性，必须使用不同的辐射固化助剂的组合和比例。最常用的方法是首先选择合适的离型助剂

，然后选择合适的组合助剂来获得所需要的流平性。图11给出了各种助剂的脱模效果。因此，如果需要最佳的脱模效果，Rad2800是可以选择

的产品。

关于辐射固化助剂

辐射固化助剂是一系列经过有机改性的有机硅助剂。它们带有丙烯酸酯基团，因此它们是可交联的，这赋予它们独特的性能。根据有机硅特性

和有机改性的程度，它们能提高滑爽性、基材润湿性和抗开裂、耐划伤的性能以及流平性。此外，它们中的一些具有离型和消泡性能。

概述

辐射固化助剂是独特的，因为它们可以获得交联涂层；所得到的爽滑和离型效果特别持久。对于常规助剂，由于助剂不能与涂层进行交联，离

型效果明显较弱，更不持久。

参考文献

Gl?ckner et. Al. Radiation Curing Coatings and Printing Inks; Hannover: Vincentz Network,2008(1),p 142ff.

Koerner et. al. Silicones; Essen: Vulkan Verlag,1991(1)p.9-15.

Brook. Silicon in Organic, Organometallic and Polymer Chemistry; New York: Wiley & Sons, 2000 (1),p.258ff.

Brook. Silicon in Organic, Organometallic and Polymer Chemistry; New York: Wiley & Sons, 2000 (1),p.261ff.

Klotzenburg; et al.Polymere; Berlin: Springer, 2014 (1),p.204f.

Gl?ckner et. Al.: Radiation Curing Coatings and Printing Inks; Hannover: Vincentz Network, 2008 (1),p 98f.

本文也在PPCJ和Boytürk杂志上刊登过。

本人专注于离型研究。欢迎各位加入以下联系方式和我讨论技术问题，或者索要分享原稿：

一，微信，手机号-高家乐：15995870029