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脂環(huán)族環(huán)氧樹脂：熱固化應(yīng)用篇
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更新日期： 2020-6-22 |
常用的環(huán)氧固化劑花樣繁多，固化技術(shù)也多種多樣 (熱固化、微波固化、光固化等)，但大多數(shù)適于光固化的環(huán)氧樹脂不一定適于熱固化，當(dāng)然也有光固和熱固都行的，但是這樣的體系比較少，脂環(huán)族環(huán)氧樹脂就是其中一例。在上一期內(nèi)容中，我們介紹了脂環(huán)族環(huán)氧樹脂的光固化應(yīng)用篇。本期我們將重點(diǎn)講述脂環(huán)族環(huán)氧樹脂的
另一大優(yōu)勢——熱固化應(yīng)用篇。
A wide variety of epoxy curing agents and curing technologies (thermal curing, microwave curing, UV curing, etc.) can be commonly used. Most of the UV curable epoxy resins are not suitable for thermal curing. Very few epoxy compounds, such as cycloaliphatic epoxy resins, are both UV curable and thermal curable. In the previous article, we introduced the UV curing application of cycloaliphatic epoxy resins. In this article, we will focus on another great advantage of cycloaliphatic epoxy resins —
thermal curing application.
環(huán)氧樹脂通常作為涂料、復(fù)材和膠黏劑等材料的基體，廣泛應(yīng)用于建筑、電子電氣、航空航天等領(lǐng)域。一個完整的環(huán)氧樹脂體系一般由四種成分組成，包括環(huán)氧樹脂、改性劑、流動性調(diào)節(jié)劑和其他成分 (顏料、溶劑、消泡劑、流平劑、增粘劑等) 。但實(shí)際應(yīng)用時，不一定要這四種成分都具備，但樹脂成分必須包括固化劑，可見固化劑的重要性。
Epoxy resin is generally used as a substrate of coatings, composites, adhesives and other materials. It is widely used in construction, electrical and electronic, aerospace and other fields. A complete epoxy resin system is generally composed of four parts, including epoxy resin, modifier, flowability regulator and some others (such as pigment, solvent, defoamer, leveling agent, tackifier, etc.). In fact it is not necessary to have all these four parts, but the resin part must include the very important curing agent.
脂環(huán)族環(huán)氧樹脂的主要熱固化方式即酸酐固化。酸酐固化劑常用的為六氫苯酐、甲基四氫苯酐、氯乙酸酐等。它的揮發(fā)性小，毒性小，對皮膚的刺激性也小。而且它的使用期長，操作也方便。通常酸酐類固化速度較慢，但固化物剛性好。
The thermal curing agent for cycloaliphatic epoxy resins is mostly anhydride type. Commonly used anhydride type curing agent can be hexahydrophthalic anhydride (HHPA), methyl tetrahydrophthalic anhydride (MTHPA), chloroacetic anhydride, etc. It is less volatile, less toxic or less irritant to skin. It can be easily operated and used for a long time. Generally anhydride curing agent has low curing speed, but the cured material can provide good rigidity.
主要酸酐分類：
1. 順酐>苯酐>四氫苯酐>甲基四氫苯酐
2. 六氫苯酐>甲基六氫苯酐
3. 甲基納迪克酸酐
4. 均苯四甲酸二酐
5. 改性酸酐
6. 酸酐分子中負(fù)電性取代基則活性增強(qiáng)
Main anhydride classification:
1. Cis-butenedioic anhydride > o-Phthalic anhydride > tetrahydrophthalic anhydride > methyl tetrahydrophthalicanhydride
2. Hexahydrophthalic anhydride > methylhexahydrophthalic anhydride
3. Methyl-5-norbornene-2,3-dicarboxylicanhydride
4. Pyromellitic Dianhydride
5. Modified anhydride
6. Anhydride with electronegative substituent for increased reactivity
脂環(huán)族環(huán)氧樹脂的固化物具有以下特點(diǎn)：
①較高的壓縮與拉伸強(qiáng)度；
②長期暴置在高溫條件下仍能保持良好的力學(xué)性能；
③耐電弧性、耐紫外光老化性能及耐氣候性較好。
Characteristics of cycloaliphatic epoxy resin curing material:
①Higher compression and tensile strength.
②Maintain good mechanical performance when exposed at high temperature for a long time.
③Strong arc resistance, good UV-aging properties and excellent weatherability.環(huán)氧樹脂/酸酐體系由于粘度低，使用壽命長，固化放熱量小，收縮率低，固化產(chǎn)物的耐熱性高和力學(xué)性能優(yōu)良而在國民經(jīng)濟(jì)的各個領(lǐng)域得到了極為廣泛的應(yīng)用。通常環(huán)氧樹脂/酸酐體系在低溫下固化速率非常緩慢，只能在高溫時才能固化，當(dāng)封裝電子元器件時，過高的溫度會損壞元器件，因此，有時需要用催化劑降低固化溫度，同時加快固化速率。
Cycloaliphatic epoxy resin/anhydride system has been widely used in various fields of the national economy due to its low viscosity, long service life, low curing heat, low shrinkage rate, strong heat resistance and excellent mechanical properties of curing products. The epoxy resin/anhydride system usually cures very slowly at low temperature and it can only be cured at high temperature. When electronic components are encapsulated, excessive temperatures may damage components, so catalysts are sometimes needed to reduce the curing temperature while speeding up the curing rate.
酸酐固化環(huán)氧樹脂體系具有優(yōu)異的機(jī)械物理性能和高溫穩(wěn)定性能。
Anhydride-cured epoxy resin system possesses outstanding mechanical/physical properties and high-temperature stability.
酸酐的熱固化反應(yīng)分為無促進(jìn)劑和有促進(jìn)劑存在兩種情況。
The thermal curing reaction by anhydrides is divided into two types: with promoter and without promoter.
當(dāng)無促進(jìn)劑存在時，首先是環(huán)氧樹脂中的羥基使酸酐開環(huán)，生成單酯和羧酸：
When in the absence of promoter, the hydroxyl group of the epoxy resin makes anhydride open ring to produce monoester and carboxylic acid.
羧酸對環(huán)氧基加成，生成二酯和羥基：
The carboxylic acid is added to the epoxy group to produce diester and hydroxyl group.
酯化生成的羥基與環(huán)氧基發(fā)生醚化反應(yīng)：
The hydroxyl group obtained from esterification will react with epoxy group by etherification.
如此開環(huán)-酯化-醚化反應(yīng)不斷進(jìn)行下去，直至環(huán)氧膠黏劑交聯(lián)熱固化。
As such, the ring opening-esterification-etherification reaction continues until the epoxy glue is cross-linked and thermally cured.
當(dāng)有路易斯堿 (如叔胺)促進(jìn)劑存在時，叔胺進(jìn)攻酸酐，生成羧酸鹽陰離子；此羧酸鹽陰離子與環(huán)氧基反應(yīng)生成烷氧陰離子；烷氧陰離子與別的酸酐反應(yīng)，再生成羧酸鹽陰離子。反應(yīng)依次進(jìn)行下去，逐步進(jìn)行加成聚合，而使環(huán)氧樹脂固化。有促進(jìn)劑存在時，酸酐熱固化反應(yīng)生成的全是酯鍵，未發(fā)現(xiàn)有醚鍵生成。酸酐在促進(jìn)劑存在時的熱固化反應(yīng)按如下歷程進(jìn)行。
When in the presence of Louis alkali (e.g., tertiary amine) promoter, tertiary amine will attack anhydride to produce carboxylate anion. The carboxylate anion reacts with epoxy group to produce alkoxide anion. Then the alkoxide anion reacts with another anhydride to produce another carboxylate anion. Addition polymerization is gradually done for curing of epoxy resins. When the promoter exists, anhydride is thermally cured and reacted to produce ester bond rather than ether bond. Please find the thermal curing mechanism of anhydride in the presence of the promoter as follows,
叔胺進(jìn)攻酸酐生成羧酸鹽陰離子：
The tertiary amine attacks anhydride to produce carboxylate anion.
羧酸鹽陰離子與環(huán)氧基反應(yīng)生成烷氧陰離子：
The carboxylate anion reacts with epoxy group to produce alkoxide anion.
烷氧陰離子與另一個酸酐反應(yīng)生成羧酸鹽陰離子：
The alkoxide anion reacts with another anhydride to produce another carboxylate anion.
在促進(jìn)劑存在時，環(huán)氧樹脂的熱固化速度也受體系內(nèi)羥基濃度的支配。因此，添加促進(jìn)劑對液態(tài)環(huán)氧樹脂非常有效，120～150℃即能完成熱固化反應(yīng)。
When the promoter exists, the thermal curing speed of epoxy resin depends on the concentration of hydroxyl group in system. Hence, it is extremely effective for liquid epoxy resins to add with the promoter. The thermal curing reaction can be done at a temperature range from 120℃ to 150℃.
脂環(huán)族環(huán)氧樹脂 (環(huán)氧化脂環(huán)烯烴化合物) 是含有兩個脂環(huán)環(huán)氧基的低分子化合物。本身不是聚合物，但是與固化劑作用后能生成性能優(yōu)異的三維體型結(jié)構(gòu)的聚合物。
Cycloaliphatic epoxy resin (also called oxirane) is a low-molecular compound with two oxirane functional groups. It is not a polymer in itself, but it can react with the curing agent to create a high-performance, three-dimensional structured polymer.
脂環(huán)族環(huán)氧化合物的耐熱性、力學(xué)性能及耐候性好，尤其是粘度小，適用期長，特別適用于濕法層壓成型和纏繞成型制造高強(qiáng)度耐熱復(fù)合材料。
Cycloaliphatic epoxy compounds have many advantages, including low viscosity, long service life, good weatherability, strong heat resistance and excellent mechanical properties. They are especially suitable for use in manufacturing of high-strength and heat-resistant composites by wet type laminating and winding technique.
脂環(huán)族環(huán)氧化合物還可作塑料模具中的樹脂組分，所得的固化物耐熱性好，有較好的機(jī)械強(qiáng)度，體積收縮率小，精確度較高，適合做精密鑄模和模具。比起金屬模具，它具有易于加工、價格低、重量輕、利于模塑操作等優(yōu)點(diǎn)。
The cycloaliphatic epoxy compound can also be used in the resin part of the plastic mold. It shows strong thermal resistance after curing. Due to good mechanical strength, low volume shrinkage ratio and high precision, it is suitable for use in precision molds and dies. When compared with metal molds, it shows advantages of easy processing, low price, light weight, convenient molding operation, etc.
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