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Intermittent Jolts of Galactic UV Radiation Mutagenetic Effects

Intermittent Jolts of Galactic UV Radiation Mutagenetic Effects
Intermittent Jolts of Galactic UV Radiation Mutagenetic Effects

a r X i v :a s t r o -p h /0104209v 1 11 A p r 2001Intermittent Jolts of Galactic UV Radiation:Mutagenetic E?ects

by

John Scalo,J.Craig Wheeler,and Peter Williams

University of Texas,Austin,Texas,USA

ABSTRACT We estimate the frequency of intermittent hypermutation events and disruptions of planetary/satellite photochemistry due to ultraviolet radiation from core collapse supernova explosions.Calculations are presented for planetary systems in the local Milky Way,including the important moderating e?ects of vertical Galactic structure and UV absorption by interstellar dust.The events are particularly frequent for satellites of giant gas planets at ~>5-10AU distance from solar-type parent stars,or in the conventional habitable zones for planets orbiting spectral type K and M parent stars,with rates of signi?cant jolts about 103?104per Gyr.The steep source spectra and existing data on UVA and longer-wavelength radiation damage in terrestrial organisms suggest that the mutational e?ects may operate even on planets with ozone shields.We argue that the mutation doubling dose for UV radiation should be much smaller than the mean lethal dose,using terrestrial prokaryotic organisms as our model,and that jolts may lead to important real-time evolutionary episodes if the jolt durations are longer than about a week,corresponding to several hundred generation times,or much less if the equivalent of mutator genes exist in extraterrestrial organisms.Longer-term phylogenetic e?ects are likely if atmospheric photochemical disturbances lead to niche creation or destruction in relevant habitats.

I.Introduction

Genetic diversity provided by mutagenesis is the raw material for natural selection and evolution.A signi?cant fraction of current-day mutation is due to error-prone,light-mediated DNA damage repair of cyclobutane pyrimidine dimers induced by ultraviolet radiation (e.g.Alpen 1998,Jagger 1985).The near-universality of specialized mechanisms for DNA repair,including repair of speci?cally radiation-induced damage,from prokaryotes to humans (see Nickolo?&Hoekstra 1998a,b),suggests that the Earth has always been subject to damage/repair events above the rate of intrinsic replication errors.The antiquity of several of prokaryotes possessing a variety of radiation repair pathways suggests that the mechanisms developed very early in the development of life.It is clear that early organisms were subjected to signi?cant ultraviolet radiation because anaerobic bacteria show intrinsic resistance to UV damage and use photoreactivation DNA repair

of UV damage(Rambler&Margulis1980),showing that most life did not evolve in the deep oceans.Any shielding or other UV-avoidance tactic,whether in surface waters(see Sagan1973, Cleaves&Miller1998)or on the Earth’s surface(see Garcia-Pichel1998)must have only served to moderate,but not obliterate,the solar UV?ux.Additional evidence for early exposure to sunlight can be found in Brock et al.(1999)and in Xiong et al.(2000).

Lateral gene transfer is now believed to be a primary source of genetic diversity,and hence evolutionary driving force,in eubacteria and archaea(see Ochman et al.2000,Doolittle1999). The mechanisms involved in lateral gene transfer are often the same as those involved in the repair of DNA damage due to UV and ionizing radiation,suggesting a connection.Similar processes are involved in meiosis.These considerations open the possibility that radiation may have been the dominant generator of genetic diversity in the terrestrial past and on any extraterrestrial and extrasolar planets and satellites harboring life based on a genetic code.An excellent general review of the role of UV radiation in the development of early life can be found in Rothschild(1999) We argue here that intermittent cosmic radiation can a?ect evolution through this variety of radiation-active mechanisms,restricting the present discussion to ultraviolet(UV)radiation.We also argue that such radiation can a?ect evolution indirectly through the creation and destruction of niches during intermittent disturbances of planetary photochemistry.

Sagan(1973)was among the?rst to discuss the potentially far-reaching e?ects of UV radiation on the?rst life forms.Even earlier,Sagan&Shklovskii(1966)suggested that supernova explosions could intermittently a?ect biological activity on the Earth.They pointed out that the UV and especially cosmic ray?uxes from supernovae could have been catastrophic for some organisms,but could have also been”favorable for evolution.”Since then,a number of authors have suggested terrestrial biological e?ects due to supernovae and related phenomena(see Rudermann1974, Crutzen and Bruhl1996,Collar1996,Dar,Laor&Shaviv1996,Ellis&Schram1995,Ellis,Fields &Schramm1996).Nearly all this work focused on the possible relation of Galactic events to mass extinctions.Little attempt was made to estimate the rates at which signi?cant events should have occurred as a function of?ux or?uence,their potential for mutagenesis,or the signi?cance of such events for life on other planets,satellites of giant planets,or extrasolar planets.

In the present paper,we concentrate on the200-300nm spectral region because DNA action spectra for many types of alterations peak at260nm and decline rapidly at larger and smaller wavelengths.Shorter wavelengths are relevant to atmospheric chemistry,as discussed below. Many cosmic sources have spectra that rise rapidly at longer wavelengths.The increased?ux

at larger wavelengths may compensate for the reduction in magnitude of biological sensitivity

at these wavelengths,making the UVB,UVA(320-400nm),and even the blue region of the spectrum potentially rich in biological a?ect.If so,then even planets with no ozone shielding will be susceptible to potential mutagenesis by UV events.

II.Core-collapse Supernovae

Here we report results for one type of event:UV radiation from core-collapse(Type II) supernovae(SNe).Core collapse SNe produce UV radiation by two separate phenomena.First,

there is a prompt hard UV radiation burst due to shock breakout,which is found in all numerical and analytical theoretical models(e.g.Falk1978,Ensman&Burrows1992,Matzner&McKee 1999).We estimate that such events typically produce about1047erg in hard UV photons, predominantly shortward of200nm,for about a day or less.The subsequent UV emission as the explosion progresses to the more protracted light curve phase,lasting2-3months while the outer hydrogen envelope expands and becomes transparent,has been computed only roughly. We estimate a UV energy release of again about1047erg or larger for the light curve phase, from both theory and observation,but with a luminosity of about1041erg s?1,compared to the shock breakout luminosity of a few times1044erg s?1.Thus both phenomena may give similar total UV energies(and hence?uences at a given distance from a particular planetary/satellite system),but with very di?erent spectra,luminosities(and hence?uxes),and timescales.There are uncertainties in these numbers,but they are small(less than a factor of10)compared to the uncertainties in the mutation doubling dose(§IIIA).

The issue of luminosities and timescales is crucial.Both shock breakout and light curve UV will be equally capable of a?ecting atmospheric chemistry(apart from di?erences in spectral distribution compared to photolysis cross sections).The smaller?uxes of the light curve UV compared to the shock breakout UV means that the former will be less capable of dominating the UV?ux of the parent star.As discussed below,the duration of the explosion is also crucial with regard to evolutionary e?ects.

III.Frequency of Signi?cant Events

A.Critical UV Fluence for Mutational Evolution

For high-energy(ionizing)photons or particles,the major mutational lesions are also those leading to lethality(e.g.double-strand breaks).The situation is very di?erent for UV mutagenesis, a fact that has apparently been overlooked in the astrobiological literature.Forλ~<310nm(UVC and UVB),bipyrimidic photoproducts,most importantly cylclobutane pyrimidine dimers,are the dominant contributors to UV mutation(see Friedberg et al.1995for a comprehensive discussion; also Chandrasekhar&Van Houten2000).These photoproducts dominate the mutation rate because they are repaired by error-prone photoreactivation and speci?cally bypassed by the SOS response,but are rarely lethal,thanks to accurate nucleotide excision and other repair pathways, leading to a potentially very small mutation doubling dose.The best-studied prokaryotic systems(E.coli and B.subtilis)exhibit signi?cant lethality at?uences around104erg cm?2 (e.g.Dose et al.1997),although signi?cant variations occur,both smaller(e.g.Asad et al. 2000)and larger(e.g.spores,Dose et al.1996;the likely Archaean thermophile Chloro?exus aurantiacus under anoxic conditions,Pierson et al.1993;and the extreme radiation resistance of D.radiodurans,see Battista1997).We can estimate a lower limit to the UV mutation doubling dose(MDD)for E.coli bacteria as follows.Drake(1991)found that among lower organisms the spontaneous mutation rate per genome is surprisingly constant(compared to the mutation rate per base pair,which varies by orders of magnitude).We therefore de?ne the MDD(erg cm?2)as the

spontaneous mutation rate per genome,SMR G,divided by the number of mutations per organism per unit?uence(erg cm?2),multiplied by the number of germline genome copies per organism, which is one for prokaryotes.Drake et al.(1998)estimate a spontaneous mutation rate per base pair per generation for E.coli lac I as about5.4x10?10.The genome size is4.6x106bp,yielding SMR G≈2.4x10?3.According to Hamkalo(1972),the dose at254nm to produce an average of one thymine dimer per E.coli DNA is≈0.1erg cm?2,so the number of thymine dimers produced per(erg cm?2)is≈10.This gives an MDD of only~2x10?4erg cm?2.This is a lower limit, since not all thymine dimers lead to mutation.Correction for cyclobutane dimers repaired by nucleotide excision repair(NER)and other essentially error-free repair pathways will be discussed in detail elsewhere;we estimate an order of magnitude correction factor of102,giving MDD~0.02 erg cm?2if we ignore timescale constraints on these repair paths.Our small UV MDD is also consistent with the fact that a single chain break or cross link is2-3orders of magnitude more likely to cause lethality than a single thymine dimer(Rahn1972).Another way to see this is that the number of lesions per cell per lethal D37dose is4x105for thymine dimers in E.coli,but only about100for single strand breaks(Ward et al.1997).These results strongly suggest that the mutation doubling dose for microorganisms due to UV radiation may be much smaller than the lethal dose.This is in contrast to the MDD for ionizing radiation,where the MDD is typically 0.1-0.3times the lethal dose.The low MDD for UV combined with the likely in?uence of UVB, UVA,and blue light leads us to suspect that UV may be the dominant contributor to mutagenesis on extraterrestrial planets,whether or not a UVC screening agent exists.

Although we realize that extrapolation to other organisms(especially extraterrestrial ones!) is dangerous,these results strongly suggest that the mutation doubling dose for microorganisms due to UV radiation may be much smaller than the lethal dose.Given all the uncertainties, we adopted F cr=600erg cm?2(closer to the lethality dose than to the estimated MDD)for both terrestrial and extraterrestrial microorganisms as a conservative?ducial estimate,with the understanding that this value is subject to order of magnitude uncertainties.

For the atmospheric attenuation of Archaen(pre-ozone)atmospheres,we adopt Cockell’s (1998)calculations of absorption and scattering in CO2+N2atmospheres,giving an attenuation factor of about3in the200-300nm region.This is clearly a lower limit,since there may exist signi?cant non-ozone UV shields,including aerosols.Adopting an attenuation factor of3means that the required?ducial?uence above the atmosphere is F cr=2x103erg cm?2.

B.Recurrence Rates

We have calculated the mean time between cosmic events that generate a?uence in excess of an estimated critical?uence(erg cm?2)required for mutagenesis for a variety of astronomical phenomena.The average frequency of biologically and atmospherically signi?cant events is surprisingly large.Assume that the Galactic events in question occur at a rate per unit volume, S.Then the frequency of events at a distance D is

f=(4π/3)SD?3,(1)

where D is the distance of the event.The mean time between events is T=1/f.The distance from the event is related to the?uence F received in a given wavelength interval by F=E/4πD2,where E is the total energy of the event in that wavelength interval.Solving for D and substituting in f above gives for the mean time between events at?uence level F:

T=(6π1/2/S)(F/E)3/2=3.2x1056S?1[F/E]3/2yr,(2) where the event rate S is expressed in units of yr?1pc?3and F and E are in cgs units.Taking an average Galactic Type II supernova rate S=1.5x10?13yr?1pc?3(Capellaro et al.1997)and a total200-300nm energy release of1047erg as discussed above,T SN=0.067F cr3/2yr,and F cr is the critical?uence.

The order of magnitude formula for the mean interevent time,Eq.2,is a severe underestimate at small?uences(or?uxes)because it neglects the density gradient perpendicular to the Galactic plane and the e?ect of interstellar dust extinction.Both of these e?ects eliminate a large number of very distant SNe.To correct for this,we assumed an exponential vertical distribution of Galactic dust and of SNe progenitors,with a scale height of60pc(see Binney&Merri?eld1988). For dust extinction we adopt3mag per kpc path length in the200-300nm spectral region(Binney &Merri?eld1988)with a scaling to the200-300nm spectral region based on Table21.6in Cox (2000).We neglect the radial density gradient of the Galaxy because its scale length(~5kpc)is so much larger than the scale lengths for vertical thinning and extinction.

The results are shown in Fig.1,where the mean time between events of given or larger UV ?uence is shown.The short-dashed and long-dashed lines show the e?ects of vertical structure and dust extinction separately,while the solid line represents the combined e?ects.The dotted line corresponds to the homogeneous unattenuated approximation(eq.2).Notice that this

plot is independent of any assumption about the planetary/satellite atmosphere(?uences are above-atmosphere),location in the local Galaxy,type of parent star,or selection of critical?uence. The e?ects of vertical structure and extinction reduce the mean recurrence time by only a factor of two or so for very large received?uences(above the atmosphere)of105erg cm?2,which nevertheless should occur roughly every5million years.We conclude that all planets in any planetary system have been subjected to extremely large UV?uences(far above the lethality limit) about a thousand times.For the smaller?uences required for mutagenesis in the example we have used for an Archaean atmosphere(2000erg cm?2)the recurrence time is increased drastically by the e?ects of Galactic structure and dust extinction relative to the simple estimate,but is still small,about2x105yr.This corresponds to about20,000such events above the2000erg cm?2level during the history of the solar system.Considering that we may have underestimated the mutagenic sensitivity of even present-day micro-organisms because of the mutation/lethality disparity discussed earlier,this number could be much larger.As we show next,not all of these events are relevant,depending on the distance of the planet from,and spectral type of,the parent star,whose?ux must be exceeded by the Galactic event if there is to be any signi?cant e?ect.

Fig.1.—Time between receptions of a?uence in the200-300nm spectral region equal to or greater than that shown,for any position in the solar neighborhood,due to shock breakout and light curve events from core collapse supernovae.Long-dashed line:only e?ect of vertical Galactic structure included;short-dashed line,only e?ect of Galactic dust extinction included;solid line:both vertical structure and extinction included;dotted line:homogeneous no-extinction approximation(eqn.2). The top horizontal axis shows a similar result,but for bolometric?uxes due to shock breakout events in core collapse supernovae.The inset letters show where to read o?the present-day solar 200-300nm?uxes at the position of each of the planets indicated,using the top horizontal scale. For atmospheric photochemistry the relevant wavelengths are smaller than for biological a?ect,and the planetary?uxes should be reduced by a factor of about?ve(inset letters shifted to left by this factor).

IV.Fluxes and Atmospheric Chemistry

The Galactic UV events are only relevant if the?ux from the Galactic event exceeds the background parent star?ux.Shown on the upper horizontal axis of Fig.1are the received bolometric?uxes for shock breakout from SNe(~1044erg s?1)while the inset indicates the?ux from the present-day Sun at the distances of the various planets.Events exceeding the solar?ux by a signi?cant factor should have occurred several times even during the history of the Earth,

but only occur frequently(more than thousands of times)for Jupiter and beyond.Alternatively,

for extrasolar planets orbiting K and M spectral type stars,the e?ects are frequent even in the traditional habitable zone,because the fraction of the photospheric?ux in the UV should be smaller by roughly an order roughly of magnitude for these stars(see Kasting1997,Cockell1999), and the recurrence time involves this?ux to the3/2power.

UV jolts exceeding the UV?ux of the Sun that are important for photochemistry should occur much more often than those important for mutagenesis.If the background solar UV?ux at wavelengths below the photolysis thresholds of most photochemically important molecules is taken to be103erg cm?2s?1at1AU(the thresholds are almost all in the100-200nm range,see for example Gri?th et al.1998),then,for a planet or satellite at a distance R AU from the Sun (in units of AU),a random SN breakout will exceed this?ux with an average time interval T SN ~107/R AU3,adopting L=1011L⊙for the average UV breakout event.More detailed calculations including the e?ects of vertical Galactic structure and dust extinction are shown in Fig.1(?uxes given on top horizontal axis).The corresponding positions of the Solar?ux at the distances of the planets should be shifted to the left by a factor of?ve or so to account for the smaller Solar?ux below the photolysis thresholds relative to the200-300nm?ux used in the plot.

This result indicates that atmospheric photochemistry must have been signi?cantly perturbed about102-103times during the history of the solar system,even at1AU.For the Jovian planets and their satellites,the number of such jolts is much larger,by a factor of order103,because of the lower solar background at larger heliocentric distances.In the latter case,photochemically signi?cant jolts(λ~<100?200nm)must occur roughly every105yr!Photochemistry of the outer planets and their satellites has likely been disturbed at least50,000times during the history of the solar system.The frequency would again be roughly103/2times larger for cooler parent stars than the sun because of the order of magnitude decrease in UV?ux.

V.Evolutionary Change?

In order for a transient mutagenic event to result in evolutionary consequences,the mutation must not only be passed on to a subsequent generation on an individual basis,it must also persist for a su?ciently large number of generations that?xation occurs;all members of the population must come to possess that mutation.Only if the mutation?xates and is adaptive in terms of the stress caused by the enhanced radiation?ux(or the environmental changes wrought by the radiation)will the episodic cosmic events have evolutionary signi?cance.The duration of peak UV ?ux from a core collapse SN in the200-300nm spectral region is estimated to be from a day to a week.A week corresponds to several hundred bacterial regeneration times,assuming a typical generation time of103sec.For comparison,a similar statement for humans would imply that evolutionary change is possible over about2x104yr.

Are such rapid?xations possible?Microorganisms apparently possess great facility for rapid evolution compared to multicelled macroscopic organisms.Experimental evidence for rapid evolutionary bursts in microbial populations is now abundant(e.g.Elena,Cooper,&Lenski1996, Coyne&Charlesworth1996).Most relevant to the present paper are the experiments by Ewing

(1995,1997)in which radiation resistance was increased in the presence of increasingly stronger X-ray and UV doses,and with timescales that correspond to hundreds of generations.Although the time between exposures was many orders of magnitude smaller than would occur for cosmic events,it is still signi?cant that the total exposure time for appreciable adaptation was only about 10hr.Obviously the question is complex,but there is probably su?cient evidence to argue for widespread mutation?xation due to Galactic radiation events with durations in excess of a week. For this reason,the enhanced cosmic ray?ux due to the(later)passage of the supernova remnant near the planetary system in question may play a more important role,since the duration could be many centuries or longer.

Mutator genes,which act to increase the spontaneous mutation rate in response to environmental stresses,is an extremely active area of research(see Boe et al.2000,Lieber2000), especially because of its potential relevance to carcinogeneisis(Cairns1998,2000),and may be expected to play a signi?cant role in the response to a sudden elevation of the UV?ux.The idea that stress-inducible processes exist that operate only when high mutation rates are advantageous is supported by several recent identi?cations of mutator genes and their associated mutases(see Radman1999,Masutani et al.1999,Friedberg&Gerlach1999).Among the most intriguing results is that of Sniegowski et al.(1987)who observed spontaneously arising mutator genes in E. coli adapting to a new environment.Several authors have suggested that adaptive evolution by mutator genes interacting with an unpredictable environment may be bene?cial to bacterial cells and populations;the same speculation could be made for extraterrestrial microbial organisms if they are genetic code lifeforms.

There is also the possibility for“adaptive mutations”in which bene?cial mutations occur within a single generation,i.e.during the resting state of a cell.The prevalence and mechanisms of this phenomenon are still controversial over a decade after their putative discovery(see Foster 1999for a review).An optimistic theoretical interpretation of adaptive mutation is given by Koch(1993),who argued persuasively that bacteria have evolved in such severely?uctuating environments that they have evolved a“catastrophe kit”to deal with sudden environmental changes.The components of such a kit include the development of metabolically inactive states (e.g.sporulation),activation of previously evolved but silent genes,increasing rates of mutation under stress,and activation of exogenous gene transfer(transformation,conjugation,plasmid transmission).We suggest that frequent intermittent blasts of radiation from cosmic sources may have played a pivotal role in the development of this toolkit.If adaptive mutation is possible in an enhanced radiation environment,then the timescale argument discussed above is irrelevant,and the evolutionary consequences of Galactic radiation sources become much more likely,even for events of very small duration,as long as the frequency of high-?ux and high-?uence doses is large enough.

We acknowledge extremely useful conversations and correspondence with Charles Cockell, Andrew Karam and Peter H¨o?ich.This work was supported by NSF Grant9907582.

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4真空电镀的生产工艺

真空电镀的生产工艺 一﹑真空电镀的概念 真空电镀即真空蒸发镀膜﹐其原理是在高度真空条件下(1.3×10-2~1.3×10-1Pa) 使金属铝片受热蒸发并附于(塑料)工件表面﹐形成一层金属膜的方法﹒真空电镀的特点: 1>真空镀膜所获得的金属膜层很薄(一般为0.01~0.1um),能够严格复制出啤件 表面的形状 2>工作电压不是很高(200V)﹐操作方便﹐但设备较昂贵﹒ 3>蒸镀锅瓶容积小﹐电镀件出数少﹐生产效率较低﹒ 4>只限于比钨丝熔点低的金属(如铝﹑银﹑铜﹑金等)镀饰﹒ 5>对镀件表面质量要求较高﹐通常电镀前需打底油来弥补工件表面缺陷﹒ 6>真空镀膜可以镀多种塑料如﹕ABS﹑PE﹑PP﹑PVC﹑PA﹑PC﹑PMMA等 ﹒ 二﹑真空电镀工艺流程 工艺流程图

重要工序工艺说明 1)待镀啤件:真空电镀对啤件要求特别高,如: a)要求啤件表面清洁,无油渍﹑污渍. b)要求啤件表面粗糙度尽可能低. c)啤件内应力要尽可能低﹐内外转角要倒圆角﹒啤塑时要用较低的注射压 力﹐较高的 模温﹑料温﹐以及尽可能慢的注射速度﹒ d)啤件外型应利于获得均匀的镀层﹐如较大平面中间要微突起(突起度约 0.1~0.15mm/cm) e)啤件壁厚要适当﹐太薄的件易变形使镀层附着力不好﹐太厚的件易缩水 使外观受影响﹒一般来讲﹐薄壁不宜小于0.9mm﹐厚壁不宜超过3.8mm﹒ f)注塑缺陷如缩水﹑夹水纹﹑气纹﹑气泡等均会影响电镀外观质量﹐必须 严格控制其程度﹐为此要求注塑时采用﹕ i> 充分的原料烘干 ii> 不使用脱模剂(尤其是硅烷类) iii> 适当的注塑模温﹐较高料温 iv> 尽可能少加入或不加入水口料(减低材料中挥发物含量) g)若啤件有台阶或凹位﹐应预先设计必要的斜度过渡﹒ h)如有盲孔﹐应设计孔深不超过孔径一半﹐否则对孔底镀层应不作要求. i) 如有“V”形槽﹐要求其宽度与深度比应大于3﹒ 2)脱脂 脱脂作用﹕清除啤件表面尘垢﹑油污﹐保证镀膜有足够的附着力﹒ 脱脂剂﹕现时生产中使用的是有机溶剂脱脂﹐有机溶剂的选择原则是不伤害塑件表面而能迅速挥发为佳﹐所以因塑料品种而异﹐以下情况提供塑料

真空镀膜工艺流程

真空镀膜工艺流程-标准化文件发布号:(9456-EUATWK-MWUB-WUNN-INNUL-DDQTY-KII

真空镀膜工艺流程 一、真空镀膜的工艺流程大致可用以下的方框图表示: 二、具体说明如下: 1、表面处理:通常,镀膜之前,应对基材(镀件)进行除油、除尘等预处理,以保证镀件的整洁、干燥,避免底涂层出现麻点、附着力差等缺点。对于特殊材料,如PE(聚乙烯)料等,还应对其进行改性,以达到镀膜的预期效果。 2、底涂:底涂施工时,可以采用喷涂,也可采用浸涂,具体应视镀件大小、形状、结构及用户设备等具体情况及客户的质量要求而定。采用喷涂方法,可采用SZ-97T镀膜油;采用浸涂方法,可采用SZ-97、SZ-97+1等油,具体应视镀件材料而定。 3、底涂烘干:SZ-97镀膜油系列均为自干型漆,烘干的目的是为了提高生产效率。通常烘干的温度为60-70oC,时间约2小时。烘干完成的要求是漆膜完全干燥。 4、镀膜:镀膜时,应保证镀膜机的真空度达到要求后,再加热钨丝,并严格控制加热时间。同时,应掌握好镀膜用金属(如铝线)的量,太少可能导致金属膜遮盖不住底材,太多则除了浪费外,还会影响钨丝寿命和镀膜质量。 5、面涂:通常面涂的目的有以下两个方面:A、提高镀件的耐水性、耐腐蚀性、耐磨耗性;B、为水染着色提供可能。SZ-97油系列产品均可用于面涂,若镀件不需着色,视客户要求,可选用911、911-1哑光油、889透明油、910哑光油等面油涂装。 6、面涂烘干:通常面涂层较底涂层薄,故烘干温度较低,约50-60oC,时间约1~2小时,用户可根据实际情况灵活把握,最终应保证面涂层彻底干燥。如果镀件不需着色,则工序进行到此已经结束。 7、水染着色:如果镀件需要进行水染着色,则可将面漆已经烘干的镀件放进染缸里,染上所需颜色,之后冲洗晾干即可。染色时要注意控制水的温度,通常在 60~80oC左右,同时应控制好水染的时间。水染着色的缺点是容易褪色,但成本较低。

塑胶电镀中真空电镀的做法

塑胶电镀中真空电镀的做法 常见的塑胶电镀工艺有两种:水电镀和真空离子镀. 真空离子镀,又称真空镀膜.真空电镀的做法现在是一种比较流行的做法,做出来的产品金属感强,亮度高.而相对其他的镀膜法来说,成本较低,对环境的污染小,现在为各行业广泛采用. 真空电镀适用范围较广,如ABS料、ABS+PC料、PC料的产品.同时因其工艺流程复杂、环境、设备要求高,单价比水电镀昂贵. 现对其工艺流程作简要介绍:产品表面清洁--〉去静电--〉喷底漆--〉烘烤底漆--〉真空镀膜--〉喷面漆--〉烘烤面漆--〉包装. 一般真空电镀的做法是在素材上先喷一层底漆,再做电镀.由于素材是塑料件,在注塑时会残留空气泡,有机气体,而在放置时会吸入空气中的水分. 另外,由于塑料表面不够平整,直接电镀的工件表面不光滑,光泽低,金属感差,并且会出现气泡,水泡等不良状况.喷上一层底漆以后,会形成一个光滑平整的表面,并且杜绝了塑料本身存在的气泡水泡的产生,使得电镀的效果得以展现.真空电镀可分为一般真空电镀、UV真空电镀、真空电镀特殊.工艺有蒸镀、溅镀、枪色等. 水电镀因工艺较简单,从设备到环境得要求均没有真空离子镀苛刻,从而被广泛应用. 但水电镀有个弱点,只能镀ABS料和ABS+PC料(此料镀的效果也不是很理想).而ABS 料耐温只有80℃,这使得它的应用范围被限制了.而真空电镀可达200℃左右,这对使用在高温的部件就可以进行电镀处理了.像风嘴、风嘴环使用PC料,这些部件均要求耐130℃的高温.另,一般要求耐高温的部件,做真空电镀都要在最后喷一层UV油,这样使得产品表面即有光泽、有耐高温、同时又保证附着力. 两种工艺的优缺点: A、简单来说,真空电镀不过UV油,其附着力很差,无法过百格TEST,而水电镀的明显好于真空电镀!因此,为保证真空电镀的附着力,均需后续进行特殊的喷涂处理,成本当然高些. B、水电镀颜色较单调,一般只有亮银和亚银等少数几种,对于闪银、魔幻蓝、裂纹、水滴银等五花八门的七彩色就无能为力了. 而真空电镀可以解决七彩色的问题. C、水电镀一般的镀层材质采用“六价铬”,这是非环保材料.对于“六价铬”有如下的要求:欧盟: 76/769/EEC:禁止使用; 94/62/EC:<100ppm; ROHS:<1000ppm 如此严格的要求,国内一些厂家已开始尝试使用“三价铬”来替代“六价铬”;而真空电镀使用的镀层材质广泛、容易符合环保要求. 简单一点,就是在真空状态下将需要涂覆在产品表面的膜层材料通过等离子体离化后沉积在工件表面的表面处理技术. 它有真空蒸发镀,溅射镀,离子镀等,获得这些沉积方法的途径有多种:电加热、离子束、电子束、直流溅射、磁控溅射、中频溅射、射频建设、脉冲溅射、微波增强等离子体、多弧等等很多种方法,可以根据的需求和经济技术条件考虑选用的涂层设备. 相对于传统的湿发电镀,真空电镀具有以下优点: 1.沉积材料广泛:可沉积铝、钛、锆等湿法电镀无法沉积的低电位金属,通以反应气体和合金靶材更是可以沉积从合金到陶瓷甚至是金刚石的涂层,而且可以根据需要设计涂层体系. 2.节约金属材料:由于真空涂层的附着力、致密度、硬度、耐腐蚀性能等相当优良,沉积的镀层可以远远小于常规湿法电镀镀层,达到节约的目的. 3.无环境污染:由于所有镀层材料都是在真空环境下通过等离子体沉积在工件表面,没有溶液污染,所以对环境的危害相当小. 但是由于获得真空和等离子体的仪器设备精密昂贵,而且沉积工艺还掌握在少数技术人员手中,没有大量被推广,其投资和日常生产维护费用昂贵.但是随着社会的不断进步,真空电镀的优势会越来越明显,在某些行业取代传统的湿法电镀是大势所趋.

真空电镀及工艺流程

真空电镀及工艺流程 真空蒸镀法就是在高度真空条件下加热金属,使其熔融、蒸发,冷却后在塑料表面形成金属薄膜得方法。常用得金属就是铝等低熔点金属。 加热金属得方法:有利用电阻产生得热能,也有利用电子束得. 在对塑料制品实施蒸镀时,为了确保金属冷却时所散发出得热量不使树脂变形,必须对蒸镀时间进行调整。此外,熔点、沸点太高得金属或合金不适合于蒸镀。置待镀金属与被镀塑料制品于真空室内,采用一定方法加热待镀材料,使金属蒸发或升华,金属蒸汽遇到冷得塑料制品表面凝聚成金属薄膜。 在真空条件下可减少蒸发材料得原子、分子在飞向塑料制品过程中与其她分子得碰撞,减少气体中得活性分子与蒸发源材料间得化学反应(如氧化等),从而提供膜层得致密度、纯度、沉积速率与与附着力。通常真空蒸镀要求成膜室内压力等于或低于10—2Pa,对于蒸发源与被镀制品与薄膜质量要求很高得场合,则要求压力更低(10—5Pa)。 镀层厚度0、04-0、1um,太薄,反射率低;太厚,附着力差,易脱落。厚度0、04时反射率为90%,真空离子镀,又称真空镀膜、真空电镀得做法现在就是一种比较流行得做法,做出来得产品金属感强,亮度高.而相对其她得镀膜法来说,成本较低,对环境得污染小,现在为各行业广泛采用. 真空电镀适用范围较广,如ABS料、ABS+PC料、PC料得产品、同时因其工艺流程复杂、环境、设备要求高,单价比水电镀昂贵、现对其工艺流程作简要介绍:产品表面清洁—-〉去静电--〉喷底漆—-〉烘烤底漆——〉真空镀膜--〉喷面漆-->烘烤面漆-—〉包装、 一般真空电镀得做法就是在素材上先喷一层底漆,再做电镀.由于素材就是塑料件,在注塑时会残留空气泡,有机气体,而在放置时会吸入空气中得水分.另外,由于塑

真空镀膜的工艺详解

真空镀膜 真空镀膜是一种产生薄膜材料的技术。在真空室内材料的原子从加热源离析出来打到被镀物体的表面上。其工艺流程一般如下: 1、表面处理:通常,镀膜之前,应对基材(镀件)进行除油、除尘等预处理,以保证镀件的整洁、干燥,避免底涂层出现麻点、附着力差等缺点。对于特殊材料,如PE(聚乙烯)料等,还应对其进行改性,以达到镀膜的预期效果。 2、底涂:底涂施工时,可以采用喷涂,也可采用浸涂,具体应视镀件大小、形状、结构及用户设备等具体情况及客户的质量要求而定。采用喷涂方法,可采用SZ-97T镀膜油;采用浸涂方法,可采用的SZ-97、SZ-97+1等油,具体应视镀件材料而定。参见产品展示中各产品的适应范围。 3、底涂烘干:我公司生产的SZ-97镀膜油系列均为自干型漆,烘干的目的是为了提高生产效率。通常烘干的温度为60-70℃,时间约2小时。烘干完成的要求是漆膜完全干燥。 4、镀膜:镀膜时,应保证镀膜机的真空度达到要求后,再加热钨丝,并严格控制加热时间。同时,应掌握好镀膜用金属(如铝线)的量,太少可能导致金属膜遮盖不住底材,太多则除了浪费外,还会影响钨丝寿命和镀膜质量。 5、面涂:通常面涂的目的有以下两个方面:A、提高镀件的耐水性、耐腐蚀性、耐磨耗性;B、为水染着色提供可能。深展公司生产的SZ-97油系列产品均可用于面涂,若镀件不需着色,视客户要求,可选用911、911-1哑光油、889透明油、910哑光油等面油涂装。 6、面涂烘干:通常面涂层较底涂层薄,故烘干温度较低,约50-60℃,时间约1~2小时,用户可根据实际情况灵活把握,最终应保证面涂层彻底干燥。如果镀件不需着色,则工序进行到此已经结束。 7、水染着色:如果镀件需要进行水染着色,则可将面漆已经烘干的镀件放进染缸里,染上所需颜色,之后冲洗晾干即可。染色时要注意控制水的温度,通常在60~80℃左右,同时应控制好水染的时间。水染着色的缺点是容易褪色,但成本较低。各种水染色粉我公司有配套销售。 8、油染着色:若镀件需进行油染着色,则镀膜后视客户要求,直接用SZ-哑光色油、SZ-透明色油浸涂或喷涂,干燥后即可。油染的色泽经久不褪,成本较水染略高。

浅谈水性木器漆配方的解决方案

浅谈水性木器漆配方的解决方案 深圳威诺华是一家专业的水性涂料原材料供应商,通过近6年的水性木器漆配方研发,逐步解决了一系列困绕水性木器漆性能的技术瓶颈,为广大的配方工程师在实际配方应用问题中提供了切实可行的解决方案和独到的应用价值,具体如下: 1、glaze仿古擦色: 主要问题集中体现在擦拭效果差,开放时间短,干燥时间长,层间附着力差等问题。针对上述问题,威诺华新推出了系列水性格瑞斯擦色剂,包括红、黄、黑、棕四色,完全克服了上述问题,达到甚至超过了溶剂型格瑞斯的仿古擦色效果,简单调配颜色即可使用。 2、高固透明腻子: 实木全封闭式透明涂装对透明腻子的要求非常高,乳液由于固体份太低,常需加入大量填料以增加固含,但常用的水性填料如滑石粉、碳酸钙、硫酸钡等透明度太差,石英粉、硅微粉透明度好,但硬度太高,打磨性差,应用于溶剂型木器涂料的透明粉大多呈酸性,水解稳定性差,加入会破坏乳液的稳定性,而威诺华引入中国市场的透明填料MINEX-7可克服上述所有不足,既使加入30%以上仍能保证腻子优异的透明度,特殊的针状结构还可以提供极好的填补性和防塌陷性。

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