隨著我國節(jié)能減排理念的不斷推廣,鐳射壓印轉移工藝在煙包印刷領域的應用越來越廣,但在煙包生產過程中也經常會出現(xiàn)一些故障。文本中,筆者將結合日程工作中的一些經驗,介紹煙包鐳射壓印轉移工藝的常見問題及解決方法,與業(yè)內同行分享。
鐳射壓印轉移工藝常見問題解析
1.出現(xiàn)皺膜現(xiàn)象
鐳射轉移膜在一定張力下,通過壓合機構將全息圖案轉移到印品表面,在這個過程中,鐳射轉移膜需要經過多根導膜輥,容易出現(xiàn)皺膜現(xiàn)象。主要原因有以下兩點。
?。?)鐳射轉移膜收卷張力過大,使得膜卷兩端張力不一致,從而引起皺膜。此時,需要仔細調整出膜輥、導膜輥、阻尼輥的平衡,比較費時。而且,當下一次重復使用鐳射轉移膜時,張力不一致的方向會反過來,這就需要重新調整設備。常用的方法是在鐳射轉移膜收卷后立即復卷一次,以進一步調整鐳射轉移膜的張力,并對其進行散熱。
?。?)鐳射轉移膜本身沒有質量問題,不合壓不皺膜,一合壓就皺膜。這主要是由于鐳射轉移膜在壓印轉移時壓膜輥兩端的壓力不平衡所致。在這種情況下,需要調整壓膜輥兩端的氣缸壓力,即調節(jié)氣缸行程末端的壓合限位螺絲,因其位于墻板內側,位置比較隱蔽,因此需要用塞尺進行調節(jié),注意及時鎖緊。有的鐳射壓印轉移設備壓膜輥兩端的氣缸壓力可以獨立調整,相對比較方便。
?。?)鐳射轉移膜在各導膜輥處的張力不平衡,造成走膜速度和壓印速度不一致,從而引起皺膜。
2.全息圖案出現(xiàn)針孔、白點現(xiàn)象
這種現(xiàn)象主要表現(xiàn)為針孔、白點位置只有UV光油沒有全息圖案,或既沒有UV光油也沒有全息圖案。具體可分為以下幾種情況。
(1)針孔、白點的位置與形狀比較固定。主要原因:①上光版或網(wǎng)紋輥表面有凹坑,造成印品表面對應位置沒有UV光油,自然就沒有全息圖案;②當使用帶光標的單版避版縫鐳射轉移膜,且UV光油涂布沒有問題時,如果仍然出現(xiàn)這種情況,可能是鐳射轉移膜表面有瑕疵,如鐳射轉移膜每個重復周長對應的位置上本來就沒有全息圖案,壓印轉移后自然就會產生針孔、白點。
?。?)針孔、白點的位置與形狀不固定。主要原因:①鐳射轉移膜質量不穩(wěn)定,在壓印轉移時容易黏掉UV光油,,如使用回收膜制成的OPP鐳射轉移膜就容易出現(xiàn)此類問題;②UV光油的助劑添加不當,或蠟質、硅油、膏類等物質添加過量所致,如有的UV光油生產廠家因為選用的單體不當,為減少UV光油的泡沫,添加了過量的消泡劑,造成壓印轉移時UV光油無法充分進入鐳射轉移膜的網(wǎng)穴;③個別煙包采用UV膠印工藝印刷大面積實地或多色疊印,由于UV油墨固含量較高且瞬間固化,導致印品表面的墨膜不平整,為增強鐳射壓印轉移效果,很多煙包印刷企業(yè)采用了“印刷油墨表面滿版涂布底油+鐳射壓印轉移”的工藝,但是由于底油中可能含有過量的硅油、流平劑等,造成底油在印刷油墨表面的附著力不佳,部分底油在剝離時被鐳射轉移膜帶走(可看到在鐳射轉移膜上有點狀的底油痕跡),從而使得鐳射壓印轉移不*,印品表面出現(xiàn)白點;④UV燈使用時間過長,有效功率不足,使得UV光油不能*固化,部分UV光油在剝離時被鐳射轉移膜帶走,此時應及時更換UV燈,一般國產UV燈的使用壽命約為1000~1500小時;⑤因皺膜引起鐳射壓印轉移不*,使得印品表面產生大面積白點。
?。?)印品拖梢中部、走紙方向上出現(xiàn)條狀的大面積白點或鐳射壓印轉移不*的現(xiàn)象。這主要是由于承印材料嚴重變形所致。如使用低檔灰底白卡紙時,由于車間溫濕度的變化,紙張因吸濕和放濕而產生“荷葉邊”,導致壓印轉移時紙張與鐳射轉移膜之間的空氣不能排盡。解決方法:平衡生產進度,保護承印材料,控制車間溫濕度。
?。?)印品表面局部出現(xiàn)針孔、白點,尤其是印品橫向上,鐳射壓印轉移效果一邊好,一邊差。主要原因有:①壓印輥老化、硬度太低或磨損嚴重,需要重新車磨舊輥或更新新輥,向原廠購買新輥,且一定要注意其橡膠層應為耐紫外線膠型,此外,為延緩壓印輥老化,在設備保養(yǎng)時,切忌勿使用酯類溶劑擦洗壓膜輥(容易造成溶劑殘留),建議使用乙醇擦洗;②如果上光單位采用的是柔性版上光方式,就可能是由于網(wǎng)紋輥壓力沒有調好所致,此時需要重新調整印刷壓力及網(wǎng)紋輥對印刷的壓力;③如果鐳射壓印轉移設備流平段有雜物(如紙皮等),且傳送帶左右張力和速度不一致時,會造成紙張在鐳射壓印轉移設備流平段歪斜,使得壓印轉移時紙張與鐳射轉移膜之間的空氣不能排盡,從而造成上述問題。
?。?)采用同一種UV光油進行鐳射壓印轉移,夏季生產時不出現(xiàn)白點,冬季生產時卻出現(xiàn)白點。這種情況主要出現(xiàn)在北方地區(qū),主要是由于環(huán)境溫度過低導致UV光油中某種材料(如光敏劑、流平劑等)產生結晶。如某流平劑的結晶溫度在10°左右,如果低于10°為半固態(tài),其就不再為液態(tài),這將嚴重影響鐳射壓印轉移的正常進行。解決方法:將UV光油加熱至40°~50°后再使用;使用耐低溫的UV光油;調整UV光油的配方。
?。?)鐳射壓印轉移開始階段出現(xiàn)的針孔、白點較少,后階段出現(xiàn)的針孔、白點越來越多。這多半是由灰塵引起的。因此,在設備保養(yǎng)時,應注意檢查導膜輥上是否有灰塵,并保持勤擦洗。有條件的煙包印刷企業(yè)對車間進行防塵隔離處理,以保持車間環(huán)境潔凈。如果車間內沒有防塵隔離設施,生產時應注意關好車間門窗,每班次至少清洗4次導膜輥,一般在更換鐳射轉移膜時進行。
綜上所述,對針孔、白點問題的控制要點可以概括為“四平”、“四凈”:“四平”是指設備安裝時保持設備前后段水平一致,壓印轉移時保持鐳射轉移膜平整,保持承印材料平整,選擇流平性好的UV光油;“四凈”是指保持上光版(柔性版或凹版)潔凈,保證UV光油過濾干凈,保持導膜輥潔凈,保持車間環(huán)境潔凈。
3.鐳射壓印轉移效果差(如全息圖案表面粗糙、光澤度差)
主要原因:①UV光油涂布量不足(可能是網(wǎng)紋輥線數(shù)過高,網(wǎng)穴深度不夠所致);②UV光油的黏度太低;③為降低成本,在UV光油中添加了過量的溶劑(如酒精),或溶劑使用不當;④鐳射轉移膜的使用次數(shù)太多,其上的網(wǎng)穴不完整,不能形成良好的鐳射效果,造成全息圖案光澤度差;⑤UV光油的低溫下產生結晶。
4.全息圖案發(fā)黃變色
經過鐳射壓印轉移后,煙包表面的全息圖案出現(xiàn)發(fā)黃變色現(xiàn)象(俗稱“黃變”)。這種情況特別容易出現(xiàn)在配置有高功率UV燈的高速鐳射壓印轉移設備上。這主要是由于UV光油配方中的光敏劑選擇不當,如選用了成本較低的Irgacure651光敏劑。解決方法:要求UV光油供應商更換光敏劑(如Irgacure184、Darocur1173等);適當調低UV燈的功率。
5.全息圖案表面產生顆粒狀凸起現(xiàn)象
肉眼一般無法觀察到這種現(xiàn)象,只能借助10倍以上的放大鏡才能觀察到。其實,造成全息圖案表面產生顆粒狀凸起現(xiàn)象的物質是灰塵或幽默顆粒。如果是膠印產品,主要原因是油墨印刷不平整、油墨顆粒粗、墨層過厚。建議在調墨時盡量將色相調深一些,或印刷后在印品表面涂布一層UV底油。如果是凹印產品,可能與紙張橫切時產生的粉塵有關。除了及時更換橫切刀之外,建議在拼版時注意拼版方向,將印品叼口拼在卷筒紙走紙方向前方,在橫切時則以印刷叼口為入刀口,并調整上下橫切刀的間隙。此外,對橫切后的單張紙印品的拖梢切一刀(如1mm),將毛邊切掉,從而大大降低粉塵。
6.先燙印后鐳射壓印轉移時,電化鋁表面的UV光油附著力不佳
這種現(xiàn)象主要表現(xiàn)在用指甲劃過或用3M膠帶粘貼燙印圖案表面時,UV光油脫落。主要原因:①UV光油與電化鋁的匹配性差;②燙印工序與鐳射壓印轉移工序之間的周轉時間過長,燙印后電化鋁表面的涂層發(fā)生氧化。
7.先燙印后鐳射壓印轉移時,燙印邊緣“飛金”多
主要原因:①電化鋁邊緣燙印不實;②電化鋁與UV光油不匹配,UV光油對電化鋁有溶解作用。
解決方法:①調整電化鋁的類型;②對電化鋁與UV光油的匹配性進行測試。簡易的測試方法是選擇2種鐳射壓印轉移效果相差不大的UV光油,將長度和寬度相同的電化鋁放入倒有UV光油的紙杯中,觀察并比較電化鋁在2種UV光油中的溶解時間,優(yōu)先選擇溶解時間長的UV光油做進一步測試。
8.全息圖案表面發(fā)澀,上機包裝不順暢
主要原因:UV光油的固化速度與UV燈功率、生產速度不匹配,導致鐳射轉移膜在壓印轉移后剝離情況不佳;UV光油中的助劑添加不當,如流平劑含量過少,防水霧劑含量過多。
要想確定全息圖案表面的發(fā)澀程度是否不利于煙包上機包裝,可利用摩擦系數(shù)儀測試其表面的摩擦系數(shù)的方法來判斷。特別注意的是,有時全息圖案表面的手感已經很滑,但煙包上機包裝時還是不夠順暢,這主要與UV光油配方中的樹脂種類(如聚氨酯材料)和添加的流平劑種類有關,應要求UV光油供應商配合解決。
9.上機包裝時,煙包折角處的全息圖案易被蹭掉
當煙包表面涂油UV底油時,這種情況特別容易出現(xiàn),因此須調整UV底油和UV光油的匹配性。如果使用水性底油,注意不能添加蠟質、硅油等助劑。如果是凹印產品,建議使用溶劑型UV底油,或使用UV凹印沖淡劑、透明墨、調金油等作為UV底油,因為其與UV光油的匹配性較好。如果是膠印產品,溶劑型UV底油反而不一定合適,因此需要仔細測試UV底油與UV光油的匹配性,墨層較薄的產品不需要涂布UV底油。
Withtheconceptofenergy-savingandemission-reductioncontinuallypopularizedinChina,theHologramImagesTransferringprocessismoreandmorewidelyappliedincigarettepackageprinting,however,someproblemsandmalfunctionsmayfrequentlyoccurontheproductionlineofcigarettepackage.Inthisthesis,theproblemsofcommonoccurrenceintheHologramImagesTransferringprocessandthecorrespondingsolutionsaretobeintroducedbytheAuthor,whosepracticalworkingexperiencesareintegratedintheintroductiontoo,soastoprovidesomevaluableinformationforsharingwithcolleaguesinthesametrade.
AnAnalysis
On
TheProblemsofCommonOccurrence
IntheProcessof
HologramImagesTransferring
Author:JiaoJieming
BengbuJinHuangshanMountainAobanPrintingLimitedCompany
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1.FilmCrinkling
Undercertainstrainstrength,withtheaidofpressingdevice,HolographicTransferringFilmcantransferhologrampatternsontothesurfaceofpressworksheet.Duringthewholeprocess,HolographicTransferringFilmmustgothroughmorethanonefilm-guidingroller,sothatitisliabletooccurfilmcrinkling.Themaincausesare:
?。?)TherewindingtensionofHolographicTransferringFilmistoolarge,makingthetensiononthetwoendsofthefilmrolldifferentfromeachotherandthenthefilmcrinkled.Forthat,itisneededtoadjusttheuniformitiesbetweenfilmoutlet-roller,guiding-rolleranddamping-roller,whichisatime-consumingjob.Furthermore,whenusetheHolographicTransferringFilmforanexttime,theoperationdirectionsoncewithdifferenttensionswillreverse,andthenthesystemhastobereset.Astothis,thenormalsolutionistorewindingtheHolographicTransferringFilmrollonceagainafteritsrewinding,whichcanregulatethetension,andhelptoheat-dissipate.
(2)ThereisnoqualityfaultintheHolographicTransferringFilm,andwithoutembossingpress,filmcrinklingneveroccurs,butoncetheFilmgetsanembossingpress,itcrinkles.Theproblemmainlycausedbythedifferentpressuresonthetwoendsoffilm-pressroller.Inthatcase,thepressureinthecylinderateachendofthefilm-pressrollerneedtoberegulate,thatistoreadjustthelimitingscrewsatthestrokeendofthecylinder,whichlocatedatinnersideofwallplate.Duetoitshard-to-touchlocationpoint,theadjustingshouldbecarryoutwithafeelergaugeanddon’tforgettotimelytightenittothelockingpoint.However,asforsomeHologramimagesTransferringEquipments,thecylinders’pressuresonfilm-pressrollers’endscanbeseparayreadjust,soitisveryconvenienttoregulate.
?。?)IfthetensiononHolographicTransferringFilmattheguiding-rollersisnotthesame,thefilmdeliveringspeedandtransferringspeedwillnotbeevenandthenwillmakefilmcrinkled.
2.Pinholes&whiteflakesonhologrampattern
Atthepositionsofthesepinholes&whiteflakes,thereareonlyUVvarnishingbutnohologrampatternappears,orneitherUVvarnishingnorhologrampatternappears.Specificcasesasfollows:
(1)Pinholeorwhiteflakewithfixedshapeandfixeddistributingposition.Maincauses:1thereisoneormorepitsonthesurfaceofcoatingplateoraniloxroller,sothatonthetransferredsheets’surfacethereisnoUVvarnishingatthepositionresponsivetothepit,thehologrampatterisofcoursemissing.2Ifseam-avoidmarkedHolographicTransferringFilmisadoptedandthespreadcoatingofUVvarnishingisnoproblem,theoccurrenceoftheabovementionedcasemayoriginateformtheflawsonthesurfaceofHolographicTransferringFilm,forexample,thereisnohologrampatternattheresponsivepositionofeachrepeatedperimeteroftheHolographicTransferringFilm,ofcoursePinholeorwhiteflakewillemergeaftertransferring.
?。?)Pinholeorwhiteflakewithunfixedshapeandunfixeddistributingposition.Maincauses:1thequalityoftheHolographicTransferringFilmisnotsteadyandliabletostickoffUVvarnishingduringtransferring,forexample,OPPHolographicTransferringFilmproducedwithrecycledfilmismoreliabletosuchproblem;2additionagentforUVvarnishingwasnotproperlyadded,ortheamountofaddedwax,siliconoil,pastyelementorothersubstanceswastoolarge,makingUVvarnishingcannotsufficientlyenterintothemeshholeofHolographicTransferringFilm;3inthetransferringofsomecigarettepackages,UVoffsetprintinginlargeareaisadoptedandneedtoimplementmulti-coloroverprinting,duetothehighcontentofUVprintinginkanditspropertyofquicksolidification,theink-coatonthesurfaceoftransferredsheetsisoftennotsmooth.Inordertoreinforcethehologramtransferringeffect,manycompanyengagedincigarettepackageprintingadopttheprocessof“printinginksurfacecoatedwithwholeplatebaseoilcoat+hologramimagestransferring”,However,inthebaseoilcoat,thecontentofsiliconoilorflattingagentmaybetoohighthenreducetheadhesivepowerofthebaseoilcoatonthesurfaceofprintingoil,resultingthatsomepeelingoffbaseoilcoatbeentrappedbyHolographicTransferringFilm(baseoilcoatflakescanbeseenonHolographicTransferringFilm),thenmakethetransferringinadequateandwhiteflakesemergeonthetransferredsheets;4theworkingtimeofUVlampistoolong,andtheeffectivepowerofthelampisinsufficient,whichcausetheUVvarnishingcannotsolidifyadequayandsomepeelingoffUVvarnishingentrappedbyHolographicTransferringFilm,insuchacase,theUVlampmustbereplacedassoonaspossible.TheperformancelifeofordinarydomesticUVlampisabout100-1500h;5filmcrinklingcausesinadequatetransferring,resultingthatwhitesflakesemergesinlargearea.
?。?)Inthemiddleoftransferredsheets’tailendandinthedirectionofpaperdelivery,largeareaofwhiteflakesstripesorinadequatetransferringemerged.Themaincauseforthatisseveredeformationofprintingstock.Iflow-gradewhitepaperboardwithgreygroundwasused,duetothetemperaturefluctuationinworkshop,“lotus-leaf-edge”wouldappearonthepaperboardbecauseofmoistureabsorptionanddisabsorption,whichwouldimpedetheexcludingoftheairbetweenpaperboardandHolographicTransferringFilmduringtransferringoperation.Solution:arrangethemanufacturescheduleappropriay,payattentiontotheprotectionofprintingstockandthecontrolsoftemperatureandhumidityinworkshop.
?。?)Pinholesorwhiteflakesemergeonpartareaofthesurfaceoftransferredsheets,especiallyonthetransverseareaofthearticle,thetransferringeffectononesideisgoodwhileontheothersideisnotgood.Maincausesinclude:1thepressrubberrollerwasagedanddegraded,itshardnesswasreducedanditsbodywasheavilyworn.Theoldrollerneedstobereconditionedorreplacedwithanewone.Itisrecommendedtobuyanewrollerformtheoriginalmanufacturer,andmoreattentionshouldbepaidtotheroller’rubberlayer,whichmustbemadeofUV-resistancerubber.Furthermore,inordertodelaytheagingofpressrubberroller,itisrecommendedtouseethanoltocleantheroller,andneveruseesterssolvent(whichisliabletoproduceresidue)ascleanagentinthemaintenanceoftheroller;2Ifflexographicplatewasadoptedinthecoatingunit,andifthepressureofanilox-rollerwasnotadjustedproperly,abovementionedproblemmightbecaused,insuchacase,transferringpressureandanilox-roller’pressureonprintingplateshouldbereadjusted;3ifthereareforeignsubstances(e.g.paperpiece)heldupintheLevelingSectionoftheHologramImagesTransferringEquipment,andthestrainstrengthsandspeedsontheconveyingbelt’sleftandrightsidesarenotthesamewitheachother,thepaperinLevelingSectionwilldeflectandnotlocateatrightplace,whichcanimpedetheexcludingoftheairbetweenpaperandHolographicTransferringFilmduringtransferringoperation,andthencausetheabovementionedproblem.
?。?)WhenadoptingacertainUVvarnishinginHologramImagesTransferring,nowhiteflakesemergeintheproductioninsummer,butintheproductioninwinter,eventhesameUVvarnishingisused,whiteflakesemergenevertheless.SuchaproblemmainlytakesplaceinnorthernChina,andthecrystallizationofsomeaagent(e.g.photosensitizer,flattingagent)inUVvarnishingduetothelowambienttemperatureisthemaincause.Ifthecrystallizationtemperatureofflattingagentisat10℃,oncebelow10℃,theagentwillbeinsemi-solidstateinsteadofliquidstate,andthenhasanegativeinfluenceontheregularoperationofhologramimagestransferring.Solution:heatingtheUVvarnishingtothetemperatureof40℃-50℃beforeputtingitintoservice;onlyadoptinglow-temperature-resistanceUVvarnishing;andrevisingtherecipeofvarnishingtoimprovetheeffect.
(6)Attheinitialstageofhologramimagestransferringoperation,onlyafewofPinholesorwhiteflakesemerge,however,atlaterstages,moreandmorePinholesorwhiteflakeswillemergeandthechiefcauseisdust.Therefore,duringequipmentmaintenance,pleasecarefullycheckifthereisanydustheldupontheguiding-roller,andregularandfrequentwipingandcleaningisalsorequired.Itishighlyrecommendedforprintingenterpriseswithconvenientconditionstoequipworkshopwithdustproofinstallationstokeeptheworkshopno-dustandclean.Ifnodustproofinstallationcanbeequippedinworkshop,thedoorofworkshopshouldbecarefullyclosed,andtheguidingrollershouldbecleanfour(4)timesatleastinoneworkingshift,normallydothecleaningatthesametimeofHolographicTransferringFilmreplacing.
Onthewhole,thekeypointstocopewithpinholesandwhiteflakescanbesummarizedas“fourlevels”and“fourcleans”;,fourlevels:ensuretheforwardpartandrearwardpartkeeplevelwitheachotherwhensettinguptheequipment,keepHolographicTransferringFilmlevelandflatduringtransferringoperation,keepprintingstocklevelandflat,andonlyselectUVvarnishingwithgoodlevel-ability;fourcleans:keeptheplate(flexographicplateorgravureplate)clean,ensureUVvarnishingbecleanlyfiltered,keepguiding-rollercleanandneat,andkeepworkshopclean.
3.Undesirablehologramimagestransferringeffect(e.g.roughhologrampatternsurface,badsurfacegloss)
Maincauses:1theamountofUVvarnishingisinadequate(causes:thenumberofanilox-rollerlinesistoohigh,orthedepthofmeshholeisnotenough);2theviscosityofvarnishingistoolow;3toomuchsolvent(e.g.alcohol)wasaddedintothecoatingforthepurposeofcostreducing,orusethesolventimproperly;4theHolographicTransferringFilmhadbeenusedfortoomanytimesandthemeshholesonitturnedfragmentary,sothatthelaserexposureeffectisnotverygoodthenhasanegativeinfluenceonthesurfaceglossofthehologrampattern;5underlowambienttemperature,theUVvarnishinghadturnedcrystallized.
4.Hologrampatternappearinginchanged,yellowishcolor
Hologrampatternappearsinchanged,yellowishcolorafterembossingandtransferringoperation.(commonlyreferredtoas“changingyellow”).SuchaproblemisespeciallyliabletotakeplaceonHigh-speedHologramImagesTransferringEquipmentwithhighpowerUVlamp.ThatismainlybecausethephotosencitizerintherecipeoftheUVvarnishingwasnotrightlyselected,forexample,thelowprice–lowperformanceIrgacure651wasselected.Solution:requestthesupplieroftheUVglazingoiltoreplacethephotosencitizerwithdesirableones(e.g.Irgacure184,Darocur1173);reducethepoweroftheUVlampproperly.
5.Granularpocksonthesurfaceofhologrampattern
Suchanappearancenormallycannotbeseenbynakedeyewithoutthehelpof10×magnifier.Infact,itisdustandprintinkparticlesthatcausesuchaproblem.
Asforoffsetprinting,themaincauseisthattheprintinginkwasnotprocesseduptoenoughsmoothness,theink’sparticlesarenotfineandtheink-coatistoothick.Itisrecommendedtomakethecolorhueofinkasdarkaspossibleinthepreparationofprintingink,orapplyaUVvarnishingcoatontheprintedarticleafteroperation.
Asforgravureprinting,suchaproblemmaybecausedbythedustcreatedincross-cuttingofpapers.Besidesreplacingthecross-cutter,moreattentionshouldbepaidtothedirectionofpatch-up,thegripperedgefortransferredsheetsshouldbelocatedaheadalongthepaperdeliverydirectionoftheweb,andthenthegripperedgewillbetakenascuttinginletofpaper’scross-cutting,thegapbetweenupperandlowercross-cuttersshouldbereadjustedtoo.Furthermore,theendtailofsinglepieceofarticleshouldgetanadditionalcut(e.g.acutof1mm),sothattheroughedgebecutoffandtheamountofdustbereduced.
6.Asfortransferringafterfoilstamping,UVvanishing’sadhesiveonaluminumsurfacenotverygood
Afingernail-scratch,orapplyinga3Msealingtapeonthesurfaceoffoilstampedpattern,canmaketheUVvarnishingscaledoff.Maincauses:1thecompatibilitybetweenUVvarnishingandaluminumisundesirable.2thetimeintervalbetweenfoilstampingandtransferringwastoolong,thecoatofaluminumsurfacehadbeenoxidizedthroughsuchalongtime.
7.Asfortransferringafterfoilstamping,toomuch“foil-splashing”onfoilstampingpatterns’edge
Maincauses:1thealuminumedgehadnotbeenfoilstampedsturdily;2thealuminumisnotcompatiblewiththeUVvarnishing,andthevarnishinghassomedissolutioneffectonthealuminum.
Solution:1re-selectthealuminumtobeused;2testthecompatibilitybetweenaluminumandUVvarnishing.Asimpletestmethodistoselect2kindsofUVcoatingswithsimilartransferringeffect,thenputaluminumsampleswithsamelengthandwidthintothepapercupsfilledwith2kindsofUVvarnishing,now,examineandcomparethetimelengthforthedissolutionofeachaluminumsampleinoneofthe2papercups,then,theUVvarnishingwithlongerdissolutiontimeshouldbetakenforfurthertest.
8.Thehologrampattern’ssurfaceisunsmoothandnotsuitableforpackagingmachineprocessing
Maincauses:thesolidificationspeedofUVvarnishingisnotcompatiblewiththepowerofUVlampandtheproductionspeed,leadingtheHologramTransferringFilmintoapoorconditionafterhologramimagestransferringoperation;additionagentsforUVvarnishingwerenotproperlyadded,forexample,theamountofflattingagentaddedwastoolittle,whiletheamountofantifoggingagentaddedwastoomuch.
Inordertodeterminewhethertheun-smoothnessofhologrampattern’ssurfaceissuitableforpackagingmachineprocessingornot,africtionmetercanbeused.Pleasenote:sometimeseventhehandfeelofthehologrampatternissmooth,itisstillnotgoodforpackagingmachineprocessing,whichdependingonthetypeofresin(e.g.polyurethane)intherecipeofUVvarnishing,andthetypeofflattingagentaddedinthecoating,sothesupplieroftheUVvarnishingarerequiredtocollaboratetosolutetheproblem.
9.Duringpackagingmachineprocessing,thehologrampatternonthecornersofacigarettecaseiseasytoberubbedoff
SuchaproblemisliabletotakeplaceespeciallywhenthereisUVbasecoatingonthesurfaceofcigarettecase,therefore,thecompatibilitybetweenUVbasecoatingandUVvarnishingisofgreatimportance.Ifaqueousbasecoatingistobeused,pleasedon’tusewaxorsiliconoilasadditionagent.Asforgravureprinting,solvent-bornetypebaseoilisrecommendable,andgravureprintingthinner,PlastisolprintinginkorgoldvanishcanalsobeusedbecauseoftheirgoodcompatibilitywithUVvarnishing.Asforoffsetprinting,onthecontrary,solvent-bornetypebasecoatingisnotrecommendable,therefore,thecompatibilitybetweenUVbasecoatingandUVvarnishingshouldbecarefullytested,andforproduct(article)withathinnerinkcoat,noUVbasecoatingspreadingisneeded.
鐳射壓印轉移工藝常見問題解析
1.出現(xiàn)皺膜現(xiàn)象
鐳射轉移膜在一定張力下,通過壓合機構將全息圖案轉移到印品表面,在這個過程中,鐳射轉移膜需要經過多根導膜輥,容易出現(xiàn)皺膜現(xiàn)象。主要原因有以下兩點。
?。?)鐳射轉移膜收卷張力過大,使得膜卷兩端張力不一致,從而引起皺膜。此時,需要仔細調整出膜輥、導膜輥、阻尼輥的平衡,比較費時。而且,當下一次重復使用鐳射轉移膜時,張力不一致的方向會反過來,這就需要重新調整設備。常用的方法是在鐳射轉移膜收卷后立即復卷一次,以進一步調整鐳射轉移膜的張力,并對其進行散熱。
?。?)鐳射轉移膜本身沒有質量問題,不合壓不皺膜,一合壓就皺膜。這主要是由于鐳射轉移膜在壓印轉移時壓膜輥兩端的壓力不平衡所致。在這種情況下,需要調整壓膜輥兩端的氣缸壓力,即調節(jié)氣缸行程末端的壓合限位螺絲,因其位于墻板內側,位置比較隱蔽,因此需要用塞尺進行調節(jié),注意及時鎖緊。有的鐳射壓印轉移設備壓膜輥兩端的氣缸壓力可以獨立調整,相對比較方便。
?。?)鐳射轉移膜在各導膜輥處的張力不平衡,造成走膜速度和壓印速度不一致,從而引起皺膜。
2.全息圖案出現(xiàn)針孔、白點現(xiàn)象
這種現(xiàn)象主要表現(xiàn)為針孔、白點位置只有UV光油沒有全息圖案,或既沒有UV光油也沒有全息圖案。具體可分為以下幾種情況。
(1)針孔、白點的位置與形狀比較固定。主要原因:①上光版或網(wǎng)紋輥表面有凹坑,造成印品表面對應位置沒有UV光油,自然就沒有全息圖案;②當使用帶光標的單版避版縫鐳射轉移膜,且UV光油涂布沒有問題時,如果仍然出現(xiàn)這種情況,可能是鐳射轉移膜表面有瑕疵,如鐳射轉移膜每個重復周長對應的位置上本來就沒有全息圖案,壓印轉移后自然就會產生針孔、白點。
?。?)針孔、白點的位置與形狀不固定。主要原因:①鐳射轉移膜質量不穩(wěn)定,在壓印轉移時容易黏掉UV光油,,如使用回收膜制成的OPP鐳射轉移膜就容易出現(xiàn)此類問題;②UV光油的助劑添加不當,或蠟質、硅油、膏類等物質添加過量所致,如有的UV光油生產廠家因為選用的單體不當,為減少UV光油的泡沫,添加了過量的消泡劑,造成壓印轉移時UV光油無法充分進入鐳射轉移膜的網(wǎng)穴;③個別煙包采用UV膠印工藝印刷大面積實地或多色疊印,由于UV油墨固含量較高且瞬間固化,導致印品表面的墨膜不平整,為增強鐳射壓印轉移效果,很多煙包印刷企業(yè)采用了“印刷油墨表面滿版涂布底油+鐳射壓印轉移”的工藝,但是由于底油中可能含有過量的硅油、流平劑等,造成底油在印刷油墨表面的附著力不佳,部分底油在剝離時被鐳射轉移膜帶走(可看到在鐳射轉移膜上有點狀的底油痕跡),從而使得鐳射壓印轉移不*,印品表面出現(xiàn)白點;④UV燈使用時間過長,有效功率不足,使得UV光油不能*固化,部分UV光油在剝離時被鐳射轉移膜帶走,此時應及時更換UV燈,一般國產UV燈的使用壽命約為1000~1500小時;⑤因皺膜引起鐳射壓印轉移不*,使得印品表面產生大面積白點。
?。?)印品拖梢中部、走紙方向上出現(xiàn)條狀的大面積白點或鐳射壓印轉移不*的現(xiàn)象。這主要是由于承印材料嚴重變形所致。如使用低檔灰底白卡紙時,由于車間溫濕度的變化,紙張因吸濕和放濕而產生“荷葉邊”,導致壓印轉移時紙張與鐳射轉移膜之間的空氣不能排盡。解決方法:平衡生產進度,保護承印材料,控制車間溫濕度。
?。?)印品表面局部出現(xiàn)針孔、白點,尤其是印品橫向上,鐳射壓印轉移效果一邊好,一邊差。主要原因有:①壓印輥老化、硬度太低或磨損嚴重,需要重新車磨舊輥或更新新輥,向原廠購買新輥,且一定要注意其橡膠層應為耐紫外線膠型,此外,為延緩壓印輥老化,在設備保養(yǎng)時,切忌勿使用酯類溶劑擦洗壓膜輥(容易造成溶劑殘留),建議使用乙醇擦洗;②如果上光單位采用的是柔性版上光方式,就可能是由于網(wǎng)紋輥壓力沒有調好所致,此時需要重新調整印刷壓力及網(wǎng)紋輥對印刷的壓力;③如果鐳射壓印轉移設備流平段有雜物(如紙皮等),且傳送帶左右張力和速度不一致時,會造成紙張在鐳射壓印轉移設備流平段歪斜,使得壓印轉移時紙張與鐳射轉移膜之間的空氣不能排盡,從而造成上述問題。
?。?)采用同一種UV光油進行鐳射壓印轉移,夏季生產時不出現(xiàn)白點,冬季生產時卻出現(xiàn)白點。這種情況主要出現(xiàn)在北方地區(qū),主要是由于環(huán)境溫度過低導致UV光油中某種材料(如光敏劑、流平劑等)產生結晶。如某流平劑的結晶溫度在10°左右,如果低于10°為半固態(tài),其就不再為液態(tài),這將嚴重影響鐳射壓印轉移的正常進行。解決方法:將UV光油加熱至40°~50°后再使用;使用耐低溫的UV光油;調整UV光油的配方。
?。?)鐳射壓印轉移開始階段出現(xiàn)的針孔、白點較少,后階段出現(xiàn)的針孔、白點越來越多。這多半是由灰塵引起的。因此,在設備保養(yǎng)時,應注意檢查導膜輥上是否有灰塵,并保持勤擦洗。有條件的煙包印刷企業(yè)對車間進行防塵隔離處理,以保持車間環(huán)境潔凈。如果車間內沒有防塵隔離設施,生產時應注意關好車間門窗,每班次至少清洗4次導膜輥,一般在更換鐳射轉移膜時進行。
綜上所述,對針孔、白點問題的控制要點可以概括為“四平”、“四凈”:“四平”是指設備安裝時保持設備前后段水平一致,壓印轉移時保持鐳射轉移膜平整,保持承印材料平整,選擇流平性好的UV光油;“四凈”是指保持上光版(柔性版或凹版)潔凈,保證UV光油過濾干凈,保持導膜輥潔凈,保持車間環(huán)境潔凈。
3.鐳射壓印轉移效果差(如全息圖案表面粗糙、光澤度差)
主要原因:①UV光油涂布量不足(可能是網(wǎng)紋輥線數(shù)過高,網(wǎng)穴深度不夠所致);②UV光油的黏度太低;③為降低成本,在UV光油中添加了過量的溶劑(如酒精),或溶劑使用不當;④鐳射轉移膜的使用次數(shù)太多,其上的網(wǎng)穴不完整,不能形成良好的鐳射效果,造成全息圖案光澤度差;⑤UV光油的低溫下產生結晶。
4.全息圖案發(fā)黃變色
經過鐳射壓印轉移后,煙包表面的全息圖案出現(xiàn)發(fā)黃變色現(xiàn)象(俗稱“黃變”)。這種情況特別容易出現(xiàn)在配置有高功率UV燈的高速鐳射壓印轉移設備上。這主要是由于UV光油配方中的光敏劑選擇不當,如選用了成本較低的Irgacure651光敏劑。解決方法:要求UV光油供應商更換光敏劑(如Irgacure184、Darocur1173等);適當調低UV燈的功率。
5.全息圖案表面產生顆粒狀凸起現(xiàn)象
肉眼一般無法觀察到這種現(xiàn)象,只能借助10倍以上的放大鏡才能觀察到。其實,造成全息圖案表面產生顆粒狀凸起現(xiàn)象的物質是灰塵或幽默顆粒。如果是膠印產品,主要原因是油墨印刷不平整、油墨顆粒粗、墨層過厚。建議在調墨時盡量將色相調深一些,或印刷后在印品表面涂布一層UV底油。如果是凹印產品,可能與紙張橫切時產生的粉塵有關。除了及時更換橫切刀之外,建議在拼版時注意拼版方向,將印品叼口拼在卷筒紙走紙方向前方,在橫切時則以印刷叼口為入刀口,并調整上下橫切刀的間隙。此外,對橫切后的單張紙印品的拖梢切一刀(如1mm),將毛邊切掉,從而大大降低粉塵。
6.先燙印后鐳射壓印轉移時,電化鋁表面的UV光油附著力不佳
這種現(xiàn)象主要表現(xiàn)在用指甲劃過或用3M膠帶粘貼燙印圖案表面時,UV光油脫落。主要原因:①UV光油與電化鋁的匹配性差;②燙印工序與鐳射壓印轉移工序之間的周轉時間過長,燙印后電化鋁表面的涂層發(fā)生氧化。
7.先燙印后鐳射壓印轉移時,燙印邊緣“飛金”多
主要原因:①電化鋁邊緣燙印不實;②電化鋁與UV光油不匹配,UV光油對電化鋁有溶解作用。
解決方法:①調整電化鋁的類型;②對電化鋁與UV光油的匹配性進行測試。簡易的測試方法是選擇2種鐳射壓印轉移效果相差不大的UV光油,將長度和寬度相同的電化鋁放入倒有UV光油的紙杯中,觀察并比較電化鋁在2種UV光油中的溶解時間,優(yōu)先選擇溶解時間長的UV光油做進一步測試。
8.全息圖案表面發(fā)澀,上機包裝不順暢
主要原因:UV光油的固化速度與UV燈功率、生產速度不匹配,導致鐳射轉移膜在壓印轉移后剝離情況不佳;UV光油中的助劑添加不當,如流平劑含量過少,防水霧劑含量過多。
要想確定全息圖案表面的發(fā)澀程度是否不利于煙包上機包裝,可利用摩擦系數(shù)儀測試其表面的摩擦系數(shù)的方法來判斷。特別注意的是,有時全息圖案表面的手感已經很滑,但煙包上機包裝時還是不夠順暢,這主要與UV光油配方中的樹脂種類(如聚氨酯材料)和添加的流平劑種類有關,應要求UV光油供應商配合解決。
9.上機包裝時,煙包折角處的全息圖案易被蹭掉
當煙包表面涂油UV底油時,這種情況特別容易出現(xiàn),因此須調整UV底油和UV光油的匹配性。如果使用水性底油,注意不能添加蠟質、硅油等助劑。如果是凹印產品,建議使用溶劑型UV底油,或使用UV凹印沖淡劑、透明墨、調金油等作為UV底油,因為其與UV光油的匹配性較好。如果是膠印產品,溶劑型UV底油反而不一定合適,因此需要仔細測試UV底油與UV光油的匹配性,墨層較薄的產品不需要涂布UV底油。
Withtheconceptofenergy-savingandemission-reductioncontinuallypopularizedinChina,theHologramImagesTransferringprocessismoreandmorewidelyappliedincigarettepackageprinting,however,someproblemsandmalfunctionsmayfrequentlyoccurontheproductionlineofcigarettepackage.Inthisthesis,theproblemsofcommonoccurrenceintheHologramImagesTransferringprocessandthecorrespondingsolutionsaretobeintroducedbytheAuthor,whosepracticalworkingexperiencesareintegratedintheintroductiontoo,soastoprovidesomevaluableinformationforsharingwithcolleaguesinthesametrade.
AnAnalysis
On
TheProblemsofCommonOccurrence
IntheProcessof
HologramImagesTransferring
Author:JiaoJieming
BengbuJinHuangshanMountainAobanPrintingLimitedCompany
----------------------------------------------------------------------
1.FilmCrinkling
Undercertainstrainstrength,withtheaidofpressingdevice,HolographicTransferringFilmcantransferhologrampatternsontothesurfaceofpressworksheet.Duringthewholeprocess,HolographicTransferringFilmmustgothroughmorethanonefilm-guidingroller,sothatitisliabletooccurfilmcrinkling.Themaincausesare:
?。?)TherewindingtensionofHolographicTransferringFilmistoolarge,makingthetensiononthetwoendsofthefilmrolldifferentfromeachotherandthenthefilmcrinkled.Forthat,itisneededtoadjusttheuniformitiesbetweenfilmoutlet-roller,guiding-rolleranddamping-roller,whichisatime-consumingjob.Furthermore,whenusetheHolographicTransferringFilmforanexttime,theoperationdirectionsoncewithdifferenttensionswillreverse,andthenthesystemhastobereset.Astothis,thenormalsolutionistorewindingtheHolographicTransferringFilmrollonceagainafteritsrewinding,whichcanregulatethetension,andhelptoheat-dissipate.
(2)ThereisnoqualityfaultintheHolographicTransferringFilm,andwithoutembossingpress,filmcrinklingneveroccurs,butoncetheFilmgetsanembossingpress,itcrinkles.Theproblemmainlycausedbythedifferentpressuresonthetwoendsoffilm-pressroller.Inthatcase,thepressureinthecylinderateachendofthefilm-pressrollerneedtoberegulate,thatistoreadjustthelimitingscrewsatthestrokeendofthecylinder,whichlocatedatinnersideofwallplate.Duetoitshard-to-touchlocationpoint,theadjustingshouldbecarryoutwithafeelergaugeanddon’tforgettotimelytightenittothelockingpoint.However,asforsomeHologramimagesTransferringEquipments,thecylinders’pressuresonfilm-pressrollers’endscanbeseparayreadjust,soitisveryconvenienttoregulate.
?。?)IfthetensiononHolographicTransferringFilmattheguiding-rollersisnotthesame,thefilmdeliveringspeedandtransferringspeedwillnotbeevenandthenwillmakefilmcrinkled.
2.Pinholes&whiteflakesonhologrampattern
Atthepositionsofthesepinholes&whiteflakes,thereareonlyUVvarnishingbutnohologrampatternappears,orneitherUVvarnishingnorhologrampatternappears.Specificcasesasfollows:
(1)Pinholeorwhiteflakewithfixedshapeandfixeddistributingposition.Maincauses:1thereisoneormorepitsonthesurfaceofcoatingplateoraniloxroller,sothatonthetransferredsheets’surfacethereisnoUVvarnishingatthepositionresponsivetothepit,thehologrampatterisofcoursemissing.2Ifseam-avoidmarkedHolographicTransferringFilmisadoptedandthespreadcoatingofUVvarnishingisnoproblem,theoccurrenceoftheabovementionedcasemayoriginateformtheflawsonthesurfaceofHolographicTransferringFilm,forexample,thereisnohologrampatternattheresponsivepositionofeachrepeatedperimeteroftheHolographicTransferringFilm,ofcoursePinholeorwhiteflakewillemergeaftertransferring.
?。?)Pinholeorwhiteflakewithunfixedshapeandunfixeddistributingposition.Maincauses:1thequalityoftheHolographicTransferringFilmisnotsteadyandliabletostickoffUVvarnishingduringtransferring,forexample,OPPHolographicTransferringFilmproducedwithrecycledfilmismoreliabletosuchproblem;2additionagentforUVvarnishingwasnotproperlyadded,ortheamountofaddedwax,siliconoil,pastyelementorothersubstanceswastoolarge,makingUVvarnishingcannotsufficientlyenterintothemeshholeofHolographicTransferringFilm;3inthetransferringofsomecigarettepackages,UVoffsetprintinginlargeareaisadoptedandneedtoimplementmulti-coloroverprinting,duetothehighcontentofUVprintinginkanditspropertyofquicksolidification,theink-coatonthesurfaceoftransferredsheetsisoftennotsmooth.Inordertoreinforcethehologramtransferringeffect,manycompanyengagedincigarettepackageprintingadopttheprocessof“printinginksurfacecoatedwithwholeplatebaseoilcoat+hologramimagestransferring”,However,inthebaseoilcoat,thecontentofsiliconoilorflattingagentmaybetoohighthenreducetheadhesivepowerofthebaseoilcoatonthesurfaceofprintingoil,resultingthatsomepeelingoffbaseoilcoatbeentrappedbyHolographicTransferringFilm(baseoilcoatflakescanbeseenonHolographicTransferringFilm),thenmakethetransferringinadequateandwhiteflakesemergeonthetransferredsheets;4theworkingtimeofUVlampistoolong,andtheeffectivepowerofthelampisinsufficient,whichcausetheUVvarnishingcannotsolidifyadequayandsomepeelingoffUVvarnishingentrappedbyHolographicTransferringFilm,insuchacase,theUVlampmustbereplacedassoonaspossible.TheperformancelifeofordinarydomesticUVlampisabout100-1500h;5filmcrinklingcausesinadequatetransferring,resultingthatwhitesflakesemergesinlargearea.
?。?)Inthemiddleoftransferredsheets’tailendandinthedirectionofpaperdelivery,largeareaofwhiteflakesstripesorinadequatetransferringemerged.Themaincauseforthatisseveredeformationofprintingstock.Iflow-gradewhitepaperboardwithgreygroundwasused,duetothetemperaturefluctuationinworkshop,“lotus-leaf-edge”wouldappearonthepaperboardbecauseofmoistureabsorptionanddisabsorption,whichwouldimpedetheexcludingoftheairbetweenpaperboardandHolographicTransferringFilmduringtransferringoperation.Solution:arrangethemanufacturescheduleappropriay,payattentiontotheprotectionofprintingstockandthecontrolsoftemperatureandhumidityinworkshop.
?。?)Pinholesorwhiteflakesemergeonpartareaofthesurfaceoftransferredsheets,especiallyonthetransverseareaofthearticle,thetransferringeffectononesideisgoodwhileontheothersideisnotgood.Maincausesinclude:1thepressrubberrollerwasagedanddegraded,itshardnesswasreducedanditsbodywasheavilyworn.Theoldrollerneedstobereconditionedorreplacedwithanewone.Itisrecommendedtobuyanewrollerformtheoriginalmanufacturer,andmoreattentionshouldbepaidtotheroller’rubberlayer,whichmustbemadeofUV-resistancerubber.Furthermore,inordertodelaytheagingofpressrubberroller,itisrecommendedtouseethanoltocleantheroller,andneveruseesterssolvent(whichisliabletoproduceresidue)ascleanagentinthemaintenanceoftheroller;2Ifflexographicplatewasadoptedinthecoatingunit,andifthepressureofanilox-rollerwasnotadjustedproperly,abovementionedproblemmightbecaused,insuchacase,transferringpressureandanilox-roller’pressureonprintingplateshouldbereadjusted;3ifthereareforeignsubstances(e.g.paperpiece)heldupintheLevelingSectionoftheHologramImagesTransferringEquipment,andthestrainstrengthsandspeedsontheconveyingbelt’sleftandrightsidesarenotthesamewitheachother,thepaperinLevelingSectionwilldeflectandnotlocateatrightplace,whichcanimpedetheexcludingoftheairbetweenpaperandHolographicTransferringFilmduringtransferringoperation,andthencausetheabovementionedproblem.
?。?)WhenadoptingacertainUVvarnishinginHologramImagesTransferring,nowhiteflakesemergeintheproductioninsummer,butintheproductioninwinter,eventhesameUVvarnishingisused,whiteflakesemergenevertheless.SuchaproblemmainlytakesplaceinnorthernChina,andthecrystallizationofsomeaagent(e.g.photosensitizer,flattingagent)inUVvarnishingduetothelowambienttemperatureisthemaincause.Ifthecrystallizationtemperatureofflattingagentisat10℃,oncebelow10℃,theagentwillbeinsemi-solidstateinsteadofliquidstate,andthenhasanegativeinfluenceontheregularoperationofhologramimagestransferring.Solution:heatingtheUVvarnishingtothetemperatureof40℃-50℃beforeputtingitintoservice;onlyadoptinglow-temperature-resistanceUVvarnishing;andrevisingtherecipeofvarnishingtoimprovetheeffect.
(6)Attheinitialstageofhologramimagestransferringoperation,onlyafewofPinholesorwhiteflakesemerge,however,atlaterstages,moreandmorePinholesorwhiteflakeswillemergeandthechiefcauseisdust.Therefore,duringequipmentmaintenance,pleasecarefullycheckifthereisanydustheldupontheguiding-roller,andregularandfrequentwipingandcleaningisalsorequired.Itishighlyrecommendedforprintingenterpriseswithconvenientconditionstoequipworkshopwithdustproofinstallationstokeeptheworkshopno-dustandclean.Ifnodustproofinstallationcanbeequippedinworkshop,thedoorofworkshopshouldbecarefullyclosed,andtheguidingrollershouldbecleanfour(4)timesatleastinoneworkingshift,normallydothecleaningatthesametimeofHolographicTransferringFilmreplacing.
Onthewhole,thekeypointstocopewithpinholesandwhiteflakescanbesummarizedas“fourlevels”and“fourcleans”;,fourlevels:ensuretheforwardpartandrearwardpartkeeplevelwitheachotherwhensettinguptheequipment,keepHolographicTransferringFilmlevelandflatduringtransferringoperation,keepprintingstocklevelandflat,andonlyselectUVvarnishingwithgoodlevel-ability;fourcleans:keeptheplate(flexographicplateorgravureplate)clean,ensureUVvarnishingbecleanlyfiltered,keepguiding-rollercleanandneat,andkeepworkshopclean.
3.Undesirablehologramimagestransferringeffect(e.g.roughhologrampatternsurface,badsurfacegloss)
Maincauses:1theamountofUVvarnishingisinadequate(causes:thenumberofanilox-rollerlinesistoohigh,orthedepthofmeshholeisnotenough);2theviscosityofvarnishingistoolow;3toomuchsolvent(e.g.alcohol)wasaddedintothecoatingforthepurposeofcostreducing,orusethesolventimproperly;4theHolographicTransferringFilmhadbeenusedfortoomanytimesandthemeshholesonitturnedfragmentary,sothatthelaserexposureeffectisnotverygoodthenhasanegativeinfluenceonthesurfaceglossofthehologrampattern;5underlowambienttemperature,theUVvarnishinghadturnedcrystallized.
4.Hologrampatternappearinginchanged,yellowishcolor
Hologrampatternappearsinchanged,yellowishcolorafterembossingandtransferringoperation.(commonlyreferredtoas“changingyellow”).SuchaproblemisespeciallyliabletotakeplaceonHigh-speedHologramImagesTransferringEquipmentwithhighpowerUVlamp.ThatismainlybecausethephotosencitizerintherecipeoftheUVvarnishingwasnotrightlyselected,forexample,thelowprice–lowperformanceIrgacure651wasselected.Solution:requestthesupplieroftheUVglazingoiltoreplacethephotosencitizerwithdesirableones(e.g.Irgacure184,Darocur1173);reducethepoweroftheUVlampproperly.
5.Granularpocksonthesurfaceofhologrampattern
Suchanappearancenormallycannotbeseenbynakedeyewithoutthehelpof10×magnifier.Infact,itisdustandprintinkparticlesthatcausesuchaproblem.
Asforoffsetprinting,themaincauseisthattheprintinginkwasnotprocesseduptoenoughsmoothness,theink’sparticlesarenotfineandtheink-coatistoothick.Itisrecommendedtomakethecolorhueofinkasdarkaspossibleinthepreparationofprintingink,orapplyaUVvarnishingcoatontheprintedarticleafteroperation.
Asforgravureprinting,suchaproblemmaybecausedbythedustcreatedincross-cuttingofpapers.Besidesreplacingthecross-cutter,moreattentionshouldbepaidtothedirectionofpatch-up,thegripperedgefortransferredsheetsshouldbelocatedaheadalongthepaperdeliverydirectionoftheweb,andthenthegripperedgewillbetakenascuttinginletofpaper’scross-cutting,thegapbetweenupperandlowercross-cuttersshouldbereadjustedtoo.Furthermore,theendtailofsinglepieceofarticleshouldgetanadditionalcut(e.g.acutof1mm),sothattheroughedgebecutoffandtheamountofdustbereduced.
6.Asfortransferringafterfoilstamping,UVvanishing’sadhesiveonaluminumsurfacenotverygood
Afingernail-scratch,orapplyinga3Msealingtapeonthesurfaceoffoilstampedpattern,canmaketheUVvarnishingscaledoff.Maincauses:1thecompatibilitybetweenUVvarnishingandaluminumisundesirable.2thetimeintervalbetweenfoilstampingandtransferringwastoolong,thecoatofaluminumsurfacehadbeenoxidizedthroughsuchalongtime.
7.Asfortransferringafterfoilstamping,toomuch“foil-splashing”onfoilstampingpatterns’edge
Maincauses:1thealuminumedgehadnotbeenfoilstampedsturdily;2thealuminumisnotcompatiblewiththeUVvarnishing,andthevarnishinghassomedissolutioneffectonthealuminum.
Solution:1re-selectthealuminumtobeused;2testthecompatibilitybetweenaluminumandUVvarnishing.Asimpletestmethodistoselect2kindsofUVcoatingswithsimilartransferringeffect,thenputaluminumsampleswithsamelengthandwidthintothepapercupsfilledwith2kindsofUVvarnishing,now,examineandcomparethetimelengthforthedissolutionofeachaluminumsampleinoneofthe2papercups,then,theUVvarnishingwithlongerdissolutiontimeshouldbetakenforfurthertest.
8.Thehologrampattern’ssurfaceisunsmoothandnotsuitableforpackagingmachineprocessing
Maincauses:thesolidificationspeedofUVvarnishingisnotcompatiblewiththepowerofUVlampandtheproductionspeed,leadingtheHologramTransferringFilmintoapoorconditionafterhologramimagestransferringoperation;additionagentsforUVvarnishingwerenotproperlyadded,forexample,theamountofflattingagentaddedwastoolittle,whiletheamountofantifoggingagentaddedwastoomuch.
Inordertodeterminewhethertheun-smoothnessofhologrampattern’ssurfaceissuitableforpackagingmachineprocessingornot,africtionmetercanbeused.Pleasenote:sometimeseventhehandfeelofthehologrampatternissmooth,itisstillnotgoodforpackagingmachineprocessing,whichdependingonthetypeofresin(e.g.polyurethane)intherecipeofUVvarnishing,andthetypeofflattingagentaddedinthecoating,sothesupplieroftheUVvarnishingarerequiredtocollaboratetosolutetheproblem.
9.Duringpackagingmachineprocessing,thehologrampatternonthecornersofacigarettecaseiseasytoberubbedoff
SuchaproblemisliabletotakeplaceespeciallywhenthereisUVbasecoatingonthesurfaceofcigarettecase,therefore,thecompatibilitybetweenUVbasecoatingandUVvarnishingisofgreatimportance.Ifaqueousbasecoatingistobeused,pleasedon’tusewaxorsiliconoilasadditionagent.Asforgravureprinting,solvent-bornetypebaseoilisrecommendable,andgravureprintingthinner,PlastisolprintinginkorgoldvanishcanalsobeusedbecauseoftheirgoodcompatibilitywithUVvarnishing.Asforoffsetprinting,onthecontrary,solvent-bornetypebasecoatingisnotrecommendable,therefore,thecompatibilitybetweenUVbasecoatingandUVvarnishingshouldbecarefullytested,andforproduct(article)withathinnerinkcoat,noUVbasecoatingspreadingisneeded.
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