CN1321142C

Movatterモバイル変換

Info

Publication number: CN1321142C
Application number: CNB2005100197805A
Authority: CN
Inventors: 朱传方; 吴小峰; 万婷
Original assignee: Central China Normal University
Current assignee: Central China Normal University
Priority date: 2005-11-11
Filing date: 2005-11-11
Publication date: 2007-06-13
Anticipated expiration: 2025-11-11
Also published as: CN1772785A

Abstract

一种二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法。本方法是直接应用二羟基聚二烃基硅氧烷代替部份聚酯或聚醚二元醇与异佛尔酮二异氰酸酯或甲苯二异氰酸酯或4，4′-二苯基甲烷二异氰酸酯，二羟甲基丙酸，以及甘油或三羟甲基丙烷或1，4-丁二醇，在溶剂氮甲基吡咯烷酮、丙酮或丁酮或乙酸乙酯的存在下，以二月桂酸二丁基锡作催化剂，得到二羟基聚二烃基硅氧烷改性的水性聚氨酯预聚体；经碱中和，加水剪切乳化，再加乙二胺扩链，得到含固量在30wt%-40wt%的聚氨酯乳液。所得水性聚氨酯乳液固含量高，附着力、耐候性、耐水性和光泽度良好，耐磨性优异。该水性聚氨酯乳液适宜于用作织物，塑料，皮革等的油墨；适当调节硬度，也可用于涂料领域。The invention discloses a preparation method of waterborne polyurethane modified by dihydroxy polydihydrocarbyl siloxane. This method is to directly apply dihydroxy polydihydrocarbyl siloxane to replace part of polyester or polyether diol and isophorone diisocyanate or toluene diisocyanate or 4,4'-diphenylmethane diisocyanate, dihydroxy Methylpropionic acid, and glycerol or trimethylolpropane or 1,4-butanediol, in the presence of the solvent nitrogen methylpyrrolidone, acetone or methyl ethyl ketone or ethyl acetate, with dibutyltin dilaurate as a catalyst, A water-based polyurethane prepolymer modified by dihydroxy polydihydrocarbyl siloxane is obtained; alkali neutralization, water shear emulsification, and ethylenediamine chain extension are added to obtain a polyurethane emulsion with a solid content of 30wt%-40wt%. The obtained aqueous polyurethane emulsion has high solid content, good adhesion, weather resistance, water resistance and gloss, and excellent abrasion resistance. The water-based polyurethane emulsion is suitable for use as ink for fabrics, plastics, leather, etc.; it can also be used in the field of coatings with proper hardness adjustment.

Description

Translated fromChinese

二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法Preparation method of waterborne polyurethane modified by dihydroxy polydihydrocarbyl siloxane

技术领域：Technical field:

本发明是一种二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，特别是直接应用二羟基聚二烃基硅氧烷代替部份聚酯或聚醚二元醇与脂肪族二异氰酸酯或芳香族二异氰酸酯制备成水性聚氨酯乳液的方法。该乳液主要应用于作油墨、涂料、粘合剂。The present invention is a preparation method of water-based polyurethane modified by dihydroxy polydihydrocarbyl siloxane, especially directly using dihydroxy polydihydrocarbyl siloxane to replace part of polyester or polyether diol and aliphatic diisocyanate Or aromatic diisocyanate is prepared into the method of aqueous polyurethane emulsion. The emulsion is mainly used as ink, coating and adhesive.

背景技术：Background technique:

水性聚氨酯是近代发展起来的高分子材料，因以水为分散介质，与溶剂型聚氨酯相比，价格低，使用安全，无环境污染，因此广泛应用于印刷、涂料、造纸、皮革涂饰等行业。Water-based polyurethane is a polymer material developed in modern times. Because water is used as the dispersion medium, compared with solvent-based polyurethane, it is cheaper, safer to use, and has no environmental pollution. Therefore, it is widely used in printing, coatings, papermaking, leather finishing and other industries.

水性聚氨酯液用于皮革涂饰时，其流平性好，成膜性能好，遮盖力强，粘结牢固，涂层耐寒、耐热、耐磨，富有弹性。用于织物涂层整理聚氨酯涂层具有涂层薄、弹性好，手感软，耐溶剂、耐低温、耐磨、防水透湿等优点。When the water-based polyurethane solution is used for leather finishing, it has good leveling property, good film-forming performance, strong hiding power, firm bonding, and the coating is cold-resistant, heat-resistant, wear-resistant and elastic. The polyurethane coating used for fabric coating and finishing has the advantages of thin coating, good elasticity, soft touch, solvent resistance, low temperature resistance, abrasion resistance, waterproof and moisture permeability, etc.

胶粘剂水性聚氨酯主要用作木材加工、织物和植绒、复合薄膜的粘合。Adhesive water-based polyurethane is mainly used for wood processing, fabric and flocking, and bonding of composite films.

水性聚氨酯涂料是涂料品种中除了用作家具漆，电泳漆、电沉积涂料、建筑涂料、纸张涂料、玻璃纤维涂料外，还可用作航天航空、舰船、光纤、军工等部门的特殊专用涂料。Water-based polyurethane coatings are not only used as furniture paints, electrophoretic paints, electrodeposition paints, architectural paints, paper paints, and glass fiber paints, but also as special paints for aerospace, ships, optical fibers, and military industries. .

对于水性聚氨酯合成主要是用异氰脲酸与聚酯二元醇、聚醚二元醇、聚碳酸酯二元醇如：Eur.Pat.Appl.EP 1241199 A1 18 Sep 2002，14 pp.PCTInt.Appl.WO2002012407 A1 14 Feb 2002，59pp、Eur.Pat.Appl.EP 1172389A1 16 Jan 2002，7 pp专利中主要是以聚酯二元醇与聚-2-丁烯二元醇制成水性聚氨酯涂料，；Ger.Offen.DE 10112390 A1 2 Oct 2002，10 pp.应用丙烯酸改性水性聚氨酯是通过异佛儿酮二异氰酸酯与多元醇，丙烯酸衍生物等作用得到的分散液用于制硬度高的膜的涂料，其含固量在30％。For the synthesis of waterborne polyurethane, isocyanuric acid and polyester diol, polyether diol, polycarbonate diol are mainly used, such as: Eur.Pat.Appl.EP 1241199 A1 18 Sep 2002, 14 pp.PCTInt. Appl.WO2002012407 A1 14 Feb 2002, 59pp, Eur.Pat.Appl.EP 1172389A1 16 Jan 2002, 7 pp patents are mainly water-based polyurethane coatings made of polyester diol and poly-2-butene diol, ; Ger.Offen.DE 10112390 A1 2 Oct 2002, 10 pp. Application of acrylic modified water-based polyurethane is a dispersion liquid obtained by the action of isophorone diisocyanate, polyols, acrylic acid derivatives, etc. for the production of films with high hardness The coating has a solid content of 30%.

CN 2001-115056 20 Jun 2001.所制备的丙烯酸环氧改性水性聚氨酯是通过甲苯二异氰酸酯、异佛儿酮二异氰酸酯与多元醇，环氧树脂、丙烯酸衍生物作用得到的分散液用作涂料的基料。CN 2001-115056 20 Jun 2001. The prepared acrylic epoxy modified water-based polyurethane is used as a coating through the dispersion liquid obtained by the action of toluene diisocyanate, isophorone diisocyanate and polyol, epoxy resin and acrylic acid derivatives Binder.

A.Anand Prabu，M.Anagar(Progress in organiccoating，2004，29，236-243)，报导了合成环氧改性的水性聚氨酯后应用含氨基的硅氧烷扩链，用以提高水性聚氨酯(PU)的机械性能。A.Anand Prabu, M.Anagar (Progress in organiccoating, 2004, 29, 236-243), reported the application of amino-containing siloxane chain extension after the synthesis of epoxy-modified water-based polyurethane to improve water-based polyurethane (PU ) mechanical properties.

发明内容：Invention content:

本发明的目的是提供一种二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法。该方法制备的二羟基聚二烃基硅氧烷改性的水性聚氨酯可用于油墨；涂料和粘合剂。The purpose of the present invention is to provide a kind of preparation method of the waterborne polyurethane modified by dihydroxy polydihydrocarbyl siloxane. The dihydroxyl polydihydrocarbyl siloxane modified waterborne polyurethane prepared by the method can be used for printing ink, coating and adhesive.

硅氧键具有良好的耐候性、成膜性能、提高膜的硬度和润湿性及低温流动性。The silicon-oxygen bond has good weather resistance, film-forming properties, improves the hardness and wettability of the film, and low-temperature fluidity.

本发明是在制备水性聚氨酯中应用直接加入异氰酸酯代替部份聚酯或聚醚多元醇，然后按常规的方法制备得到含固量30wt％-40wt％的二羟基聚二甲基硅氧烷改性的水性聚氨酯乳液。The present invention uses directly adding isocyanate to replace part of polyester or polyether polyol in the preparation of water-based polyurethane, and then prepares a modified dihydroxypolydimethylsiloxane with a solid content of 30wt%-40wt% according to a conventional method. water-based polyurethane emulsion.

本发明的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备步骤为：第1、采用异佛尔酮二异氰酸酯或六亚甲基二异氰酸酯或甲苯二异氰酸酯，二羟基聚二烃基硅氧烷或聚酯二元醇或聚醚多元醇或聚碳酸酯二元醇、以及二羟甲基丙酸，在溶剂氮甲基吡咯烷酮、丙酮或丁酮或乙酸乙酯的存在下，以二月桂酸二丁基锡作催化剂，加热进行反应，直至检测游离异氰酸基质量含量＜0.5％，将预聚物冷却降温至40±2℃，得二羟基聚二烃基硅氧烷改性的水性聚氨酯预聚体；The preparation steps of the waterborne polyurethane modified by dihydroxy polydihydrocarbyl siloxane of the present invention are: 1st, adopt isophorone diisocyanate or hexamethylene diisocyanate or toluene diisocyanate, dihydroxy polydihydrocarbyl siloxane Alkanes or polyester diols or polyether polyols or polycarbonate diols, and dimethylolpropionic acid, in the presence of solvent nitrogen methylpyrrolidone, acetone or methyl ethyl ketone or ethyl acetate, dilauryl Dibutyltin dibutyltin as a catalyst, heated for reaction until the mass content of free isocyanate groups < 0.5%, and cooled the prepolymer to 40±2°C to obtain a water-based polyurethane prepolymer modified by dihydroxy polydihydrocarbyl siloxane Polymer;

第2、用三乙胺中和步骤1得到的二羟基聚二烃基硅氧烷改性的水性聚氨酯预聚体；The 2nd, the aqueous polyurethane prepolymer that obtains with triethylamine and the dihydroxy polydihydrocarbyl siloxane modification that step 1 obtains;

第3、在步骤2进行完后的二羟基聚二烃基硅氧烷改性的聚氨酯预聚体中，加入其预聚体质量1-1.2倍的去离子水进行剪切乳化；3. In the polyurethane prepolymer modified by dihydroxy polydihydrocarbyl siloxane after step 2, add deionized water with 1-1.2 times the mass of the prepolymer for shear emulsification;

第4、在步骤3剪切乳化后的二羟基聚二烃基硅氧烷改性的聚氨酯水性分散体中，加入其分散体质量0.4％-1.0％的乙二胺扩链剂，即得到一种阴离子盐，其固含量为30％-40％的水分散体二羟基聚二烃基硅氧烷改性的水性聚氨酯；The 4th, in step 3 shear emulsified after the dihydroxy polydihydrocarbyl siloxane modified polyurethane aqueous dispersion, add the ethylenediamine chain extender of its dispersion mass 0.4%-1.0%, promptly obtain a kind of Anionic salts, aqueous dispersions of dihydroxypolydihydrocarbylsiloxane-modified waterborne polyurethanes with a solid content of 30% to 40%;

在其预聚中，异氰酸酯基与羟基的摩尔比为1.3/1-1.6/1，二羟甲基丙酸与多元醇的摩尔比为1.0/1-2.0/1，二羟基聚二甲基硅氧烷的含量为所有二元醇的5wt％-30wt％，反应时间为4-8小时，反应温度为55℃-80℃。In its prepolymerization, the molar ratio of isocyanate group to hydroxyl group is 1.3/1-1.6/1, the molar ratio of dimethylol propionic acid to polyol is 1.0/1-2.0/1, dihydroxy polydimethylsiloxane The content of oxane is 5wt%-30wt% of all glycols, the reaction time is 4-8 hours, and the reaction temperature is 55°C-80°C.

本发明所用的二羟基聚二甲基硅氧烷具有下列结构式：The dihydroxypolydimethylsiloxane used in the present invention has the following structural formula:

其中的n为3-50，R是C₁-C₄的脂肪族烃基或不饱和的碳碳双键。分子量Mw在300-3000之间。Where n is 3-50, R is a C₁ -C₄ aliphatic hydrocarbon group or an unsaturated carbon-carbon double bond. The molecular weight Mw is between 300-3000.

本发明所述的聚酯二元醇为聚己二酸酯二醇、聚ε-己内酯二醇或聚碳酸酯二元醇。The polyester diol described in the present invention is polyadipate diol, polyε-caprolactone diol or polycarbonate diol.

本发明所述的聚醚多元醇是聚氧化丙烯二醇、聚氧化乙烯二醇、聚氧化丁烯二醇、聚四氢呋喃或聚四氢呋喃-氧化丙烯二醇。The polyether polyol of the present invention is polyoxypropylene diol, polyoxyethylene diol, polyoxybutylene diol, polytetrahydrofuran or polytetrahydrofuran-oxypropylene diol.

本发明的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法的优选条件为：预聚反应温度为56±1℃，反应时间6.5±0.2小时。The preferred conditions for the preparation method of the dihydroxypolydihydrocarbylsiloxane-modified waterborne polyurethane of the present invention are: the prepolymerization reaction temperature is 56±1° C., and the reaction time is 6.5±0.2 hours.

本方法制备的二羟基聚二烃基硅氧烷改性的水性聚氨酯分散液与一种水性聚丙烯酸酯类的树脂，或一种水性环氧树脂，或一种水性环氧改性的聚丙烯酸酯类的树脂共混，构成水性涂料，或水性油墨。The dihydroxy polydihydrocarbyl siloxane modified water-based polyurethane dispersion prepared by the method and a water-based polyacrylate resin, or a water-based epoxy resin, or a water-based epoxy-modified polyacrylate A class of resins are blended to form water-based coatings or water-based inks.

具体实施方案：Specific implementation plan:

实施例1Example 1

在250ml装有温度计、回流冷凝管、搅拌、滴液漏斗的四口烧瓶中，加入异佛尔酮二异氰酸酯16g，二羟基聚二甲基硅氧烷(Mn＝800)5g，聚碳酸酯二醇(Mn＝1000)，17g，聚己二酸酯二醇(Mn＝2000)3g，二羟甲基丙酸3g，N-甲基吡咯烷酮5g以及催化剂0.2g，丙酮5g，在70℃反应直至检测游离异氰酸基含量＜wt0.5％，得到聚氨酯预聚体，将此预聚体降温至40℃，加2.8g三乙胺中和，加去离子水60g，剪切后，加乙二胺1.2g扩链，最后减压抽挥发物得固含量在40wt％的聚氨酯乳液。In a 250ml four-neck flask equipped with a thermometer, reflux condenser, stirring, and dropping funnel, add 16g of isophorone diisocyanate, 5g of dihydroxy polydimethylsiloxane (Mn=800), polycarbonate di Alcohol (Mn=1000), 17g, polyadipate diol (Mn=2000) 3g, dimethylol propionic acid 3g, N-methylpyrrolidone 5g and catalyst 0.2g, acetone 5g, react at 70 ℃ until Detect the content of free isocyanate groups < wt0.5% to obtain a polyurethane prepolymer, cool the prepolymer to 40°C, add 2.8g of triethylamine for neutralization, add 60g of deionized water, after shearing, add ethyl alcohol 1.2 g of diamine was chain-extended, and finally the volatile matter was pumped under reduced pressure to obtain a polyurethane emulsion with a solid content of 40 wt%.

实施例2Example 2

在250ml装有温度计、回流冷凝管、滴液漏斗的四口烧瓶中，加入甲苯二异氰酸酯(TDI)17g，二羟基聚二甲基硅氧烷(Mn＝800)5g，聚碳酸酯二醇(Mn＝1000)16g，聚己二酸酯二醇(Mn＝2000)3g，二羟甲基丙酸3.3g，N-甲基吡咯烷酮5g以及催化剂0.2g，丙酮10g，在56℃反应直至检测游离异氰酸基含量＜wt0.5％，降温冷却至40℃，2.8g三乙胺中和，得到PU预聚体。加去离子水60g，剪切后，加乙二胺1.5g扩链，最后减压抽挥发物得固含量在38wt％的聚氨酯乳液。In a 250ml four-necked flask equipped with a thermometer, a reflux condenser, and a dropping funnel, 17g of toluene diisocyanate (TDI), 5g of dihydroxypolydimethylsiloxane (Mn=800), polycarbonate diol ( Mn=1000) 16g, polyadipate diol (Mn=2000) 3g, dimethylol propionic acid 3.3g, N-methylpyrrolidone 5g and catalyst 0.2g, acetone 10g, react at 56 ℃ until free to detect The free isocyanate content is less than 0.5% by weight, the temperature is lowered to 40°C, and 2.8g of triethylamine is neutralized to obtain a PU prepolymer. Add 60 g of deionized water, after shearing, add 1.5 g of ethylenediamine to extend the chain, and finally extract volatile matter under reduced pressure to obtain a polyurethane emulsion with a solid content of 38 wt%.

实施例3将方案1中的聚碳酸酯二醇由聚氧化丙烯二醇代替，聚氧化丙烯二醇(Mn＝1000)16g。Example 3 The polycarbonate diol in scheme 1 was replaced by polyoxypropylene diol, polyoxypropylene diol (Mn=1000) 16g.

实施例4将方案1中的聚碳酸酯二醇由聚氧化乙烯二醇代替，聚氧化乙烯二醇(Mn＝1000)18g，二羟基聚二甲基硅氧烷(Mn＝800)5g改为二羟基聚二甲基硅氧烷(Mn＝2000)3g。Example 4 The polycarbonate diol in Scheme 1 is replaced by polyoxyethylene diol, polyoxyethylene diol (Mn=1000) 18g, dihydroxypolydimethylsiloxane (Mn=800) 5g is changed to Dihydroxypolydimethylsiloxane (Mn=2000) 3g.

实施例5将方案1中的聚碳酸酯二醇与聚己二酸酯二醇全由聚四氢呋喃代替，聚四氢呋喃(Mn＝2000)20g。Example 5 The polycarbonate diol and polyadipate diol in scheme 1 were all replaced by polytetrahydrofuran, polytetrahydrofuran (Mn=2000) 20g.

由本发明经过加入二羟基聚二甲基硅氧烷改性所得的聚氨酯水分散体的固含量可达到38％以上，其附着力、耐候性、耐水性、光泽度与未改性水性聚氨酯相同外，其耐磨性能、耐热性能、硬度均高于未改性水性聚氨酯。该分散体可喷涂、刷涂、辊涂；可用于皮革、织物、塑料等的油墨印刷。The solid content of the aqueous polyurethane dispersion obtained by adding dihydroxypolydimethylsiloxane modification in the present invention can reach more than 38%, and its adhesion, weather resistance, water resistance, and gloss are the same as those of unmodified water-based polyurethane. , its wear resistance, heat resistance and hardness are all higher than those of unmodified waterborne polyurethane. The dispersion can be sprayed, brushed, and rolled; it can be used for ink printing on leather, fabrics, plastics, etc.

Claims

Translated fromChinese

1、一种二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，其特征是步骤为：1, a kind of preparation method of the waterborne polyurethane of dihydroxy polydihydrocarbyl siloxane modification, it is characterized in that the step is:

第1、采用异佛尔酮二异氰酸酯或六亚甲基二异氰酸酯或甲苯二异氰酸酯，二羟基聚二烃基硅氧烷或聚酯二元醇或聚醚多元醇或聚碳酸酯二元醇，以及二羟甲基丙酸，在溶剂氮甲基吡咯烷酮、丙酮或丁酮或乙酸乙酯的存在下，以二月桂酸二丁基锡作催化剂，加热进行反应，直至检测游离异氰酸基质量含量＜0.5％，将预聚物冷却降温至40±2℃，得二羟基聚二烃基硅氧烷改性的水性聚氨酯预聚体；1. Using isophorone diisocyanate or hexamethylene diisocyanate or toluene diisocyanate, dihydroxy polydihydrocarbyl siloxane or polyester diol or polyether polyol or polycarbonate diol, and Dimethylolpropionic acid, in the presence of solvent nitrogen methylpyrrolidone, acetone or methyl ethyl ketone or ethyl acetate, with dibutyltin dilaurate as a catalyst, heating and reacting until the mass content of free isocyanate groups is detected <0.5 %, cooling the prepolymer to 40±2°C to obtain a waterborne polyurethane prepolymer modified by dihydroxy polydihydrocarbyl siloxane;

第4、在步骤3剪切乳化后的二羟基聚二烃基硅氧烷改性的聚氨酯水性分散体中，加入其分散体质量0.4％-1.0％的乙二胺扩链剂，即得二羟基聚二烃基硅氧烷改性的水性聚氨酯；The 4th, in step 3 shear emulsification after the dihydroxy polydihydrocarbyl siloxane modified polyurethane aqueous dispersion, add the ethylenediamine chain extender of its dispersion quality 0.4%-1.0%, obtain dihydroxy Polydihydrocarbyl siloxane modified waterborne polyurethane;

在其预聚中，异氰酸酯基与羟基的摩尔比为1.3/1～～1.6/1，二羟甲基丙酸与多元醇的摩尔比为1.0/1～～2.0/1，二羟基聚二甲基硅氧烷的含量为所有二元醇的5wt％～～30wt％，反应时间为4～～8小时，反应温度为55℃～～80℃。In its prepolymerization, the molar ratio of isocyanate group to hydroxyl group is 1.3/1~~1.6/1, and the molar ratio of dimethylol propionic acid to polyol is 1.0/1~~2.0/1. The content of siloxane is 5wt%-30wt% of all dihydric alcohols, the reaction time is 4-8 hours, and the reaction temperature is 55°C-80°C.

2、如权利要求1所述的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，其特征在于所述的二羟基聚二烃基硅氧烷具有下列结构式：2. The preparation method of dihydroxy polydihydrocarbyl siloxane modified water-based polyurethane according to claim 1, characterized in that said dihydroxy polydihydrocarbyl siloxane has the following structural formula:

其中的n为3-50，R是C₁-C₄的脂肪族烃基或不饱和的碳碳双键，分子量Mw在300-3000之间。Where n is 3-50, R is a C₁ -C₄ aliphatic hydrocarbon group or an unsaturated carbon-carbon double bond, and the molecular weight Mw is between 300-3000.

3、如权利要求1所述的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，其特征在于所述的聚酯二元醇为聚己二酸酯二元醇、聚ε-己内酯二醇或聚碳酸酯二元醇。3. The preparation method of the water-based polyurethane modified by dihydroxy polydihydrocarbyl siloxane as claimed in claim 1, wherein said polyester diol is polyadipate diol, polyε- Caprolactone diol or polycarbonate diol.

4、如权利要求1所述的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，其特征在于所述的聚醚多元醇是聚氧化丙烯二醇、聚氧化乙烯二醇、聚氧化丁烯二醇、聚四氢呋喃或聚四氢呋喃-氧化丙烯二醇。4. The preparation method of the waterborne polyurethane modified by dihydroxy polydihydrocarbyl siloxane as claimed in claim 1, wherein said polyether polyol is polyoxypropylene glycol, polyoxyethylene glycol, poly Butylene oxide, polytetrahydrofuran or polytetrahydrofuran-oxypropylene glycol.

5、如权利要求1所述的二羟基聚二烃基硅氧烷改性的水性聚氨酯的制备方法，其特征在于步骤(1)的预聚反应温度为56±1℃，反应时间6.5±0.2小时。5. The preparation method of dihydroxy polydihydrocarbyl siloxane modified water-based polyurethane according to claim 1, characterized in that the prepolymerization reaction temperature in step (1) is 56±1°C, and the reaction time is 6.5±0.2 hours .