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Offset printing yog ib txoj kev npaj rau cov duab thiab cov duab uas tsis yog - thaj chaw duab nyob rau tib lub dav hlau ntawm daim ntawv luam ntawv thiab sib txawv tsuas yog los ntawm lawv qhov kev tawm tsam ntawm lub zog ntawm qhov chaw-tshwj xeeb, oleophilicity (ink affinity) thiab hydrophilicity (dej affinity). Cov duab thaj chaw yog oleophilic thiab txais tus cwj mem, qhov chaw uas tsis yog -cov duab yog hydrophilic thiab khaws cov yeeb yaj kiab nyias, cov dej tsis sib xws. Thaum lub sij hawm luam ntawv, lub tshuab dampening ua ntej siv cov tshuaj aqueous dampening rau qhov tsis yog - duab; Tom qab ntawd, tus number case adheres xaiv rau thaj chaw duab oleophilic thiab raug xa mus rau lub substrate ntawm ib daim pam nruab nrab roj hmab. Rau kev ua haujlwm ruaj khov, qhov sib npaug ntawm tus cwj mem zaj duab xis ntawm cov duab duab thiab cov yeeb yaj kiab dej ntawm cov duab tsis yog - yog qhov tseem ceeb. Ib qho kev tsis sib haum xeeb cuam tshuam rau kev luam tawm kev ncaj ncees: tsis txaus dampening ua rau tus number case kis mus rau qhov tsis yog -cov duab ("phaj staining"), thaum dampening ntau dhau ua rau cov number case emulsification, xim desaturation, kev sau npe yuam kev, thiab txo tus number case hloov mus.
Cov nram qab no qhia txog kaum ob feem ntau ntsib cov teeb meem kev ua haujlwm hauv kev luam ntawv offset, nrog rau cov pov thawj -raws li kev kuaj mob thiab cov tswv yim kho kom zoo:
1. Phaj Staining (Dirty Plate)
Phaj staining manifests raws li tus cwj mem tsis xav tso rau ntawm qhov tsis yog - cov duab, ua rau poob ntawm qhov sib txawv, dot nce, ntug qhov muag plooj, thiab coalescence ntawm halftone dots. Nws tuaj yeem nthuav tawm raws li "roj staining" (tsis xwm yeem nthuav dav ntawm thaj chaw duab, distorting contours) lossis "dej staining" (diffuse, low-contrast ink migration hla non-duab zones). Qhov tseem ceeb pab txhawb muaj xws li:
- Kev ua cov phaj tsis txaus, ua rau cov oleophilicity seem nyob rau hauv cov duab tsis yog -;
- Kab mob los yog tus cwj mem -fouled dampening rollers, hloov tus number case rau hauv cov tshuaj dampening;
- Tsis txaus tus number case dej tsis kam los yog ntau dhau dampening tov ntim, txhawb tus number case emulsification thiab tom qab tsiv mus rau hydrophilic aav;
- Kev siv ntau dhau ntawm cov tshuaj ziab kom qhuav los yog surfactants hauv kev tsim cov kua nplaum;
- PH tsawg heev (<4.5) of the dampening solution, accelerating plate corrosion and creating micro-pits that trap ink;
- Ink uas muaj viscosity tsawg heev los yog tshaj -muab, cuam tshuam tus number case-dej tshuav nyiaj li cas;
- Cov ntsiab lus siab ntawm qis -molecular- hnyav additives, txo tus number case cohesion. Kev txo qis suav nrog kev ua kom zoo ntawm cov phaj, ntxuav cov khoom ua kom lub cev tsis zoo, kho cov tshuaj dampening pH (pom zoo ntau yam: 4.8–5.5), kev hloov pauv tus lej rau kev txhim kho cov dej tsis zoo, thiab suav nrog ntau dua - viscosity offset varnishes lossis cov roj toner yog qhov tsim nyog.
2. Teem -tawm (Smudging)
Teem-tawm tshwm sim thaum cov ntawv ntub dej hloov pauv los ntawm cov ntawv luam tawm ntawm ib daim ntawv mus rau sab nraub qaum ntawm daim ntawv uas nyob ib sab hauv pawg xa khoom. Qhov no yog qhov tshwj xeeb tshaj yog nyob rau hauv kev kub ceev ceev-piv txwv li, nyob rau hauv teb offset presses, qhov twg daim ntawv hla dhau lub sij hawm ntawm lub impression cylinders yuav luv li 0.1 vib nas this- tawm lub sij hawm tsis txaus rau thawj zaug number case. Cov txiaj ntsig tseem ceeb kuj suav nrog ntau pawg siab, siab ambient humidity, thiab ink tack tsis txaus. Cov kev kho mob suav nrog kev txo cov kev xav siab, ua kom cov kua nplaum tuab tuab, suav nrog cov khoom siv ntxiv (piv txwv li, micronized paraffin) txhawm rau txhim kho qhov ntog thiab cov txheej txheem thaum ntxov, siv ceev ceev- kom qhuav inks, txo cov av noo ntawm qhov chaw ua haujlwm (lub hom phiaj: 50–55%), thiab ua kom muaj cua txaus.
3. Dej-Induced Tinting (Floating Scum)
Floating scum hais txog cov xim tsis sib xws, faint discoloration thoob plaws tsis yog -cov chaw luam tawm ntawm lub substrate los yog phaj nto, tshwm sim los ntawm ib feem miscibility ntawm tus number case thiab cov tshuaj dampening. Qhov no qhia txog kev sib cais tsis txaus vim qhov tsis zoo ntawm tus number case-dej immiscibility. Kev daws teeb meem yuav tsum tau txhim kho tus cwj pwm dej tsis zoo-piv txwv li, los ntawm kev xaiv ntau dua hydrophobic resins, optimization ntawm pigment deg kho, lossis txo cov kuab tshuaj hydrophilic hauv lub tsheb.
4. Delayed Ink Drying
Delayed drying arises from insufficient catalytic activity of driers (e.g., cobalt or manganese salts), high ambient humidity (>60% RH), los yog tsis tshua muaj ambient kub, tag nrho cov uas impede oxidative polymerization ntawm lub binder. Cov kev kho kom raug suav nrog: ntxiv nrog qhov tsim nyog drier concentrations (thaum zam dhau -catalysis), txo qis cov kua dej ntim, hloov cov pa luam yeeb nrog UV- lossis cua sov- teeb tsa lwm qhov uas ua tau, dehumidifying chav xovxwm, thiab txhim kho qhov cua.
5. Ink Rejection (Ntxuav tawm)
Ink rejection denotes localized tsis ua hauj lwm ntawm number case adhesion ntawm tus number case rau cov menyuam los yog phaj nto, feem ntau tshwm sim raws li streaks los yog voids nyob rau hauv cov ntaub ntawv uas muaj peev xwm. Nws tshwm sim los ntawm ntau tshaj alkalinity (pH> 6.0) ntawm cov tshuaj dampening, uas txhawb kev tsim ntawm insoluble hlau phosphates ntawm hlau rollers, yog li impairing ink receptivity. Cov tshuaj tiv thaiv suav nrog txo cov tshuaj dampening concentration, txo nws cov pH mus rau qhov zoo tshaj plaws (4.8–5.5), thiab qhia tus cwj mem - sib xws diluents los kho rheological compatibility.
6. Plate Desensitization (Duab Fade)
Plate desensitization refers to progressive weakening or loss of image density due to chemical degradation of the oleophilic image layer-commonly triggered by prolonged exposure to highly acidic dampening solutions (pH < 4.5). Acid-induced corrosion erodes lub photosensitive lossis polymerized txheej, nthuav tawm hauv qab hydrophilic substrate. Restoration yuav tsum tau kho tam sim ntawd ntawm dampening tov pH thiab, yog hais tias tsim nyog, phaj reconditioning los yog hloov.
7. Daim ntawv Dusting thiab Pilling
Daim ntawv plua plav cuam tshuam nrog kev tshem tawm ntawm cov fibers saum npoo los yog cov khoom muab tub lim thaum lub tswv yim, uas sib sau rau ntawm daim pam lossis phaj, ua rau mottling, scumming, los yog tsis sib xws ntawm kev nthuav dav. Cov hauv paus hauv paus muaj xws li cov ntawv tsis tshua muaj zog, kev xav ntau dhau, tsis txaus dampening, kev kub ceev ceev, kev siv daim pam nruj heev, lossis kev sib txhuam ntau dhau ntawm daim ntawv-pam interface. Cov kev daws teeb meem suav nrog kev txhim kho kom siab dua -sov- daim ntawv muaj zog, ua kom pom kev zoo siab, zoo -tuning dampening ntim, xaiv qis dua - viscosity inks, txhim kho softer thiab smoother pam vov, txo cov xovxwm ceev, thiab siv cov ntaub ntawv nruj thiab phaj tu cov txheej txheem.
8. Ink Buildup (Roller/Planket Packing)
Ink buildup piav qhia txog kev nce qib ntawm cov kua nplaum, tsis zoo hloov tus cwj mem rau ntawm cov menyuam, phaj, lossis daim pam saum npoo - pov thawj los ntawm cov yeeb yaj kiab tuab, npub, thiab tsis sib xws. Nws feem ntau yog los ntawm tus number case emulsification, uas cuam tshuam kev ncaj ncees ntawm cov ntaub ntawv thiab hloov cov number case rau hauv paste-zoo li pawg nrog cov xim tsis muaj zog. Hauv kev luam ntawv ntau xim, nws kuj tseem yuav tshwm sim los ntawm kev sib tshuam ntawm - chaw nres tsheb viscosity mismatch (xws li, downstream number case dhau viscous), pigment dispersion tsis zoo, cov xim tsis muaj roj nqus, xim xim siab, los yog ntau tus number case ntim. Kev kho muaj xws li hloov tus cwj mem rau kev txhim kho dej tsis kam thiab rheological stability, txo tus number case thiab dampening tov ntim, txo dampening kua acidity, txhim kho daim ntawv zoo, xaiv pigments nrog balanced hydrophobicity thiab dispersibility, thiab siv binders nrog ntau dua molecular hnyav thiab cohesive zog.
9. Dot Gain thiab kab sib kis
Cov dot nce thiab kab sib kis ntau dhau, "greasy" prints nrog widened halftone dots thiab qhov muag plooj. Cov khoom muaj xws li: ink viscosity tsawg dhau; ntau dhau ntawm tus number case oiliness; coupling tus neeg sawv cev nrog elevated acid nqi; dampening kua acidity tsis muaj zog heev; pluag pigment dispersion; number case dej tsis kam siab heev; los yog tsis tsim nyog additive xaiv. Kev kho yuav ua rau muaj kev sib txuas tus neeg sawv cev viscosity, txo qis kev ua kom cov dampening tov ntim, thiab ntxiv dag zog rau dampening kua acidity nyob rau hauv kev nyab xeeb kev ua haujlwm ntau (pH 4.8-5.3).
10. Reduced Solid Density ("Over-sharpening")
Reduced solid ink density-colloquially termed "over-sharpening"-is characterized by progressively lighter tone reproduction and diminished contrast. Nws tshwm sim los ntawm cov kua nplaum ntau dhau los txwv tsis pub hloov pauv kev ua haujlwm lossis cov kua qaub ntau dhau (pH <4.5) ua rau cov duab hauv cheeb tsam, ua rau nws cov hydrophilicity thiab repelling number case. Resolution entails txo tus number case viscosity los ntawm kev tsim nyog diluents thiab kho dampening tov pH nce mus rau qhov zoo tshaj plaws oleophilic cim.
11. Mottle thiab Spots
Mottle yog hais txog qhov tsis yog-cov xim sib txawv ntawm tus number case faib ua qhov tshwm sim tsis xwm yeem lossis lub teeb ci / tsaus nti. Ua rau muaj xws li daim ntawv saum npoo tsis sib xws (piv txwv li, caliper variation, porosity gradients), ink transparency permitting substrate show-through, overpression pressure forcing number into paper valleys, or contamination (xws li, ink droplets adhering to solid plate area, forms snowflake defects{{8}). Cov kev tiv thaiv zoo suav nrog kev siv opaque, dej{10}}cov tshuaj tiv thaiv nrog cov xim pigment loading, txo cov kev xav siab, qhia meej meej, qhov ruaj khov substrates, thiab tswj xyuas cov phaj huv si.
12. Ink Starvation (Streaking)
Ink starvation tshwm raws li qhov sib npaug sib npaug los yog qhov tsis sib xws ntawm cov khoom ntom ntom, feem ntau nrog cov suab nrov tag nrho. Nws qhia tias tus cwj pwm tsis txaus los ntawm tus ciav mus rau lub phaj - feem ntau yog vim tus number case uas muaj nqi ntau dhau los yog thixotropy, incipient gelation, los yog dej paug inducing pigment flocculation. Nruam mechanical agitation ntawm tus ciav cwj mem yog qhov tseem ceeb. Lub sij hawm ntev - kev daws teeb meem suav nrog kev hloov pauv tus cwj mem kom txhim kho cov dej ntws thiab dej tsis kam, lossis kho nrog nruab nrab - mus rau - siab - viscosity binders kom ruaj khov rheology yam tsis muaj kev cuam tshuam kev hloov pauv.