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Application of plasma treatment machine in surface modification of materials等離子處理機在材料表麵改性中的應用

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Application of plasma treatment machine in surface modification of materials等離子處理機在材料表麵改性中的應用

發布日期:2018-06-30 作者:www.tonertimes.com 點擊:

  低溫等離子體中粒子的能量一般約為幾個至幾十電子伏特,大於聚合物材料的結合鍵能(幾個至十幾電子伏特),完全可以破裂有機大分子的化學鍵而形成新鍵;但遠低於高能放射性射線,隻涉及材料表麵,不影響基體的性能。處於非熱力學平衡狀態下的低溫等離子體中,電子具有較高的能量,可以斷裂材料表麵分子的化學鍵,提高粒子的化學反應活性(大於熱等離子體),而中性粒子的溫度接近室溫,這些優點為熱敏性高分子聚合物表麵改性提供了適宜的條件。  

一、形成裝置及影響因素 

   選擇適宜的放電方式可獲得不同性質和應用特點的等離子體,通常,熱等離子體是氣體在大氣壓下電暈放電產生,冷等離子體由低壓氣體輝光放電形成。熱等離子體裝置是利用帶電體尖端(如刀狀或針狀尖端和狹縫式電極)造成不均勻電場,稱電暈放電,使用電壓和頻率、電極間距、處理溫度和時間對電暈處理效果都有影響。電壓升高、電源頻率增大,則處理強度大,處理效果好。但電源頻率過高或電極間隙太寬,會引起電極間過多的離子碰撞,造成不必要的能量損耗;而電極間距太小,會有感應損失,也有能量損耗。處理溫度較高時,表麵特性的變化較快。處理時間延長,極性基團會增多;但時間過長,表麵則可能產生分解物,形成新的弱界麵層。 

   冷等離子體裝置是在密封容器中設置兩個電極形成電場,用真空泵實現一定的真空度,隨著氣體愈來愈稀薄,分子間距及分子或離子的自由運動距離也愈來愈長,受電場作用,它們發生碰撞而形成等離子體,這時會發出輝光,故稱為輝光放電處理。輝光放電時的氣壓大小對材料處理效果有很大影響,另外與放電功率,氣體成分及流動速度、材料類型等因素有關。 

   等離子刻蝕機不同的放電方式、工作物質狀態及上述影響等離子體產生的因素,相互組合可形成各種低溫等離子體處理設備。 

等離子刻蝕機

二、在表麵改性中的應用 

   低溫等離子體技術具有工藝簡單、操作方便、加工速度快、處理效果好、環境汙染小、節能等優點,在表麵改性中廣泛的應用。 

1. 表麵處理 

   通過低溫等離子體表麵處理,材料表麵發生多種的物理、化學變化,或產生刻蝕而粗糙,或形成致密的交聯層,或引入含氧極性基團,使親水性、粘結性、可染色性、生物相容性及電性能分別得到改善。 

   用幾種常用的等離子體對矽橡膠進行表麵處理,結果表明N2、Ar、O2、CH4-O2及Ar-CH4-O2等離子體均能改善矽橡膠的親水性,其中CH4-O2和Ar-CH4-O2的效果更佳,且不隨時間發生退化。英國派克製筆公司將等離子體技術用於控製墨水流量塑料元件的改性工藝中,提高了塑料的潤濕率。 

   上述表明,用低溫等離子體在適宜的工藝條件下處理PE、PP、PVF2、LDPE等材料,材料的表麵形態發生的顯著變化,引入了多種含氧基團,使表麵由非極性、難粘性轉為有一定極性、易粘性和親水性,有利於粘結、塗覆和印刷。 

   塑料、橡膠、纖維等高分子材料在成形過程中加入的增塑劑、引發劑及殘留單體和降解物等低分子物質很容易析出而匯集於材料表麵,形成無定形層,使潤濕性等性能變差。尤其對醫用材料,低分子物滲出會影響到生物機體的正常功能。低溫等離子體技術可在高分子材料表麵形成交聯層,成為低分子物滲出的屏障。    

2. 表麵聚合 

   大多數有機物氣體在低溫等離子體作用下,聚合並沉積在固體表麵形成連續、均勻、無針孔的超薄膜,可用作材料的防護層、絕緣層、氣體和液體分離膜以及激光光導向膜等,應用於光學、電子學、醫學等許多領域。 

   以聚甲基丙烯酸甲酯或聚碳酸酯塑料均可製成價廉且易於加工的光學透鏡,但其表麵硬度太低,易產生劃痕。采用有機氟或有機矽單體,采用低溫等離子體聚合技術在透鏡表麵沉積出10nm的薄層,可改善其抗劃痕性和反射指數。國外還有等離子體化學氣相沉積技術應用於塑料窗用玻璃、汽車百葉窗和氖燈、鹵天燈的反光鏡的報道。 

   等離子體聚合膜具有多種性能,可使同樣的基材應用於很多領域。在金屬和塑料上塗類金剛石碳耐磨塗料的化學氣相沉積技術是把含碳氣體導入等離子體中,該塗層耐化學藥品、無針孔、不滲透,能防止各種化學藥品侵蝕基材。同樣還可將減摩塗料塗於擋風玻璃雨刮器上,或將低摩塗層塗於計算機磁盤上以降低磁頭磁撞。 

   等離子聚乙烯膜沉積於矽橡膠表麵後,矽橡膠對氧氣的透過係數明顯降低。由含氮單體製備反滲透膜,Z高可阻出98%的食鹽。生物體內的緩釋藥物一般采用高分子微囊,亦可采用等離子體聚合技術在微囊表麵形成反滲透膜層。 

等離子體聚合物膜在傳感元件上的應用研究表明,放電功率等因素對膜電阻值有較大影響。用各種乙烯基單體和Ar輝光放電處理織物,其疏水性及染色性能在極短時間裏便有改善。 

3. 表麵接枝 

   以等離子體接枝聚合進行材料表麵改性,接枝層同表麵分子以共價鍵結合,可獲得優良、耐久的改性效果。美國曾將聚酯纖維進行輝光放電等離子體處理與丙烯酸接枝聚合,改性後纖維吸水性大幅度提高,同時抗靜電性能也有改善。白敏冬等用Ar等離子體處理尼龍綢表麵,引入丙烯酸,接枝聚合使尼龍綢抗靜電性增強。低溫等離子體接枝改性毛織物原料及成品,可改善毛絨表麵性能、增強著色性、軟化織物、降低縮水率,且毛織物本體不受影響。滌綸纖維堅固耐穿,但其結構緊密、吸水性差、難染色,王雪燕等用低溫氮等離子體引發丙烯酰胺對滌綸織物進行接枝改性,接枝後滌綸織物的上染百分率、染色深度及親水性都有明顯提高。 

   低溫等離子體對醫用材料表麵處理,可引入氨基、羰基等基團,生物活性物質與這些基團接枝反應可固定於材料表麵。用等離子體處理聚丙烯膜,引入氨基,再通過共價鍵接枝,固定上葡萄糖氧化酶,經測定,接枝率分別達52μg/cm2和34μg/cm2。 

     The energy of particles in low-temperature plasma is about several to dozens of electron volts, which is larger than the bond energy of polymer materials (several to dozens of electron volts). It can break the chemical bond of organic macromolecules and form new bond completely. However, it is far lower than high-energy radioactive rays, which only involves the surface of materials and does not affect the performance of matrix. In the non thermodynamic equilibrium low temperature plasma, electrons have high energy, can break the chemical bonds of the molecules on the surface of the material, improve the chemical reaction activity of the particles (greater than that of the thermal plasma), and the temperature of the neutral particles is close to room temperature, which provides suitable conditions for the surface modification of the thermal sensitive polymer. 

    1. Forming device and influencing factors.

       Plasma with different properties and application characteristics can be obtained by choosing appropriate discharge mode. Generally, hot plasma is produced by corona discharge of gas at atmospheric pressure, while cold plasma is formed by glow discharge of low-pressure gas. The hot plasma device uses the tip of the charged body (such as knife or needle tip and slit electrode) to create an uneven electric field, which is called corona discharge. The use voltage and frequency, electrode spacing, treatment temperature and time have an impact on the corona treatment effect. With the increase of voltage and power frequency, the treatment intensity is high and the treatment effect is good. However, if the power frequency is too high or the electrode gap is too wide, it will cause excessive ion collision between the electrodes, resulting in unnecessary energy loss; if the electrode gap is too small, there will be induction loss and energy loss. When the treatment temperature is higher, the change of surface properties is faster. If the treatment time is prolonged, the polar groups will increase, but if the treatment time is too long, the decomposition products may be produced on the surface, forming a new weak interface layer. In the cold plasma device, two electrodes are set in the sealed container to form an electric field, and a certain degree of vacuum is achieved by using a vacuum pump. With the gas becoming thinner and thinner, the molecular spacing and the free movement distance of molecules or ions become longer and longer. Under the action of the electric field, they collide to form a plasma, which will emit glow, so it is called glow discharge treatment. In addition, it is related to discharge power, gas composition, flow rate and material type. Different discharge mode, working material state and the above factors that affect the production of plasma can be combined to form a variety of low-temperature plasma processing equipment.

2、 The application of low temperature plasma technology in surface

        1. Surface treatment:

       Through low-temperature plasma surface treatment, a variety of physical and chemical changes take place on the surface of the material, or etching and rough, or forming a dense cross-linking layer, or introducing oxygen-containing polar groups, so that the hydrophilicity, cohesiveness, dyeability, biocompatibility and electrical properties are improved respectively. The surface of silicone rubber was treated by several kinds of plasma. The results showed that N2, AR, O2, ch4-o2 and ar-ch4-o2 plasma could improve the hydrophilicity of silicone rubber, among which ch4-o2 and ar-ch4-o2 had better effect and did not degrade with time. The plasma technology is used in the modification process of plastic components to control ink flow by Parker pen company in the UK, which improves the wettability of plastics. The above results show that the surface morphology of PE, PP, PVF2, LDPE and other materials changes significantly when treated with low temperature plasma under suitable process conditions, and a variety of oxygen-containing groups are introduced to make the surface change from nonpolarity and difficult viscosity to a certain polarity, easy viscosity and hydrophilicity, which is conducive to bonding, coating and printing. Plasticizers, initiators, residual monomers and degradation products and other low molecular substances added in the forming process of polymer materials such as plastics, rubber and fibers are easy to separate out and gather on the surface of the material, forming an amorphous layer, making the wettability and other properties worse. Especially for medical materials, low molecular exudation will affect the normal function of biological body. Low temperature plasma technology can form cross-linking layer on the surface of polymer materials, and become the barrier of low molecular exudation. 

     2. Surface polymerization: 

        Most organic gases are polymerized and deposited on the solid surface under the action of low-temperature plasma to form a continuous, uniform, pinhole free ultrathin film, which can be used as the protective layer, insulating layer, gas and liquid separation membrane of materials, laser photoconductive membrane, etc., and applied in many fields such as optics, electronics, medicine, etc. The cheap and easy to process optical lens can be made of PMMA or polycarbonate plastic, but its surface hardness is too low, which is easy to produce scratches. The scratch resistance and reflection index of the lens can be improved by depositing a thin layer of 10nm on the surface of the lens with organic fluorine or organosilicon monomer and low temperature plasma polymerization technology. There are also reports abroad on the application of plasma chemical vapor deposition technology to the mirrors of glass for plastic windows, automobiles shutters, neon lamps and halogen lamps. Plasma polymerized film has many properties, which can make the same substrate applied in many fields. The chemical vapor deposition technology of diamond-like carbon wear-resistant coating on metals and plastics is to introduce the carbon containing gas into the plasma. The coating is resistant to chemicals, no pinholes, no penetration, and can prevent all kinds of chemicals from eroding the substrate. It can also apply antifriction coating to windshield wipers or low friction coating to computer disks to reduce head magnetic impact. When the plasma polyethylene film is deposited on the surface of silicone rubber, the permeability of silicone rubber to oxygen decreases obviously. The reverse osmosis membrane was prepared from nitrogen-containing monomers, which could block 98% salt at most. In vivo, polymer microcapsules are generally used for sustained-release drugs, and plasma polymerization technology can also be used to form reverse osmosis film on the surface of microcapsules. The study on the application of plasma polymer film to the sensor shows that the discharge power and other factors have a great influence on the film resistance. The hydrophobicity and dyeing properties of fabrics treated with various vinyl monomers and AR glow discharge were improved in a very short time.

3. Surface grafting

    The surface of the material was modified by plasma grafting polymerization, and the grafted layer was covalently bonded with the surface molecules, which could obtain excellent and durable modification effect. In the United States, polyester fibers were treated by glow discharge plasma and grafted with acrylic acid. The water absorption and antistatic properties of the modified fibers were greatly improved. The surface of nylon silk was treated by Ar plasma, acrylic acid was introduced, and the antistatic property of nylon silk was enhanced by graft polymerization. The raw materials and finished products of wool fabric modified by low temperature plasma grafting can improve the surface properties of wool, enhance the coloring, soften the fabric, reduce the shrinkage, and the body of wool fabric is not affected. The polyester fiber is strong and durable, but its structure is tight, its water absorption is poor, and it is difficult to dye. Wang Xueyan et al. Initiated by low temperature nitrogen plasma, acrylamide grafted polyester fabric. The dye uptake, dyeing depth and hydrophilicity of the grafted polyester fabric are obviously improved. 

     Groups such as amino group and carbonyl group can be introduced into the surface treatment of medical materials by low temperature plasma. The polypropylene membrane was treated by plasma, amino group was introduced, then grafted by covalent bond, glucose oxidase was fixed on the membrane. The grafted rate was 52 μ g / cm2 and 34 μ g / cm2, respectively.

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