1. Txhais thiab muaj nuj nqi ntawm thickener
Cov tshuaj ntxiv uas tuaj yeem ua rau kom cov viscosity ntawm cov xim pleev xim dej yog hu ua thickeners.
Thickeners ua lub luag haujlwm tseem ceeb hauv kev tsim khoom, khaws cia thiab tsim cov txheej txheem.
Lub luag haujlwm tseem ceeb ntawm cov thickener yog ua kom cov viscosity ntawm cov txheej txheem kom tau raws li cov kev xav tau ntawm ntau theem ntawm kev siv. Txawm li cas los xij, qhov viscosity xav tau los ntawm cov txheej txheem sib txawv yog txawv. Piv txwv li:
Thaum lub sij hawm cia, nws yog ntshaw kom muaj viscosity siab los tiv thaiv cov xim los ntawm kev daws teeb meem;
Thaum lub sij hawm tsim kho, nws yog ntshaw kom muaj ib tug nruab nrab viscosity los xyuas kom meej tias cov xim muaj brushability zoo tsis muaj ntau ntau xim staining;
Tom qab kev tsim kho, nws cia siab tias viscosity tuaj yeem rov qab mus rau qhov siab viscosity tom qab lub sijhawm luv luv (txheej txheem txheej txheem) kom tiv thaiv sagging.
Lub fluidity ntawm waterborne coatings yog non-Newtonian.
Thaum cov viscosity ntawm cov xim txo nrog qhov nce ntawm lub zog shear, nws yog hu ua pseudoplastic kua, thiab feem ntau ntawm cov xim yog pseudoplastic kua.
Thaum tus cwj pwm ntws ntawm cov kua dej pseudoplastic muaj feem xyuam rau nws keeb kwm, uas yog, nws nyob ntawm lub sijhawm, nws yog hu ua thixotropic kua.
Thaum tsim cov coatings, peb feem ntau consciously sim ua cov coatings thixotropic, xws li ntxiv additives.
Thaum cov txheej txheem thixotropy yog qhov tsim nyog, nws tuaj yeem daws qhov tsis sib haum xeeb ntawm ntau theem ntawm txheej txheej, thiab ua tau raws li cov kev xav tau ntawm cov viscosity sib txawv ntawm cov txheej hauv kev cia, kev tsim kho theem, thiab ziab theem.
Qee cov thickeners tuaj yeem muab cov xim pleev xim nrog cov thixotropy siab, kom nws muaj viscosity ntau dua thaum so lossis ntawm qhov qis qis (xws li cia lossis tsheb thauj mus los), txhawm rau tiv thaiv cov xim hauv cov xim los ntawm kev teeb tsa. Thiab nyob rau hauv siab shear npaum li cas (xws li txheej txheej), nws muaj viscosity tsawg, yog li ntawd lub txheej muaj txaus txaus thiab theem.
Thixotropy yog sawv cev los ntawm thixotropic index TI thiab ntsuas los ntawm Brookfield viscometer.
TI = viscosity ( ntsuas ntawm 6r / min) / viscosity ( ntsuas ntawm 60r / min)
2. Hom thickeners thiab lawv cov teebmeem ntawm txheej txheej
(1) Hom Nyob rau hauv cov nqe lus ntawm cov tshuaj muaj pes tsawg leeg, thickeners muab faib ua ob pawg: organic thiab inorganic.
Inorganic hom muaj xws li bentonite, attapulgite, aluminium magnesium silicate, lithium magnesium silicate, thiab lwm yam, organic hom xws li methyl cellulose, hydroxyethyl cellulose, polyacrylate, polymethacrylate, acrylic acid los yog methyl Acrylic homopolymer los yog copolymer thiab polyurethane thiab lwm yam.
Los ntawm qhov kev xav ntawm kev cuam tshuam ntawm cov khoom rheological ntawm txheej txheej, thickeners tau muab faib ua thixotropic thickeners thiab associative thickeners. Nyob rau hauv cov nqe lus ntawm kev ua tau zoo, tus nqi ntawm cov thickener yuav tsum tsawg dua thiab cov nyhuv thickening yog zoo; nws tsis yooj yim rau eroded los ntawm enzymes; Thaum qhov kub lossis pH tus nqi ntawm lub cev hloov pauv, viscosity ntawm cov txheej yuav tsis txo qis, thiab cov xim thiab cov muab tub lim yuav tsis flocculated. ; Zoo ruaj khov; dej tuav zoo, tsis muaj qhov pom tseeb foaming tshwm sim thiab tsis muaj kev cuam tshuam rau kev ua haujlwm ntawm cov yeeb yaj kiab txheej.
① Cellulose thickener
Cov cellulose thickeners siv nyob rau hauv coatings yog tsuas yog methylcellulose, hydroxyethylcellulose thiab hydroxypropylmethylcellulose, thiab ob lub tom kawg yog siv ntau dua.
Hydroxyethyl cellulose yog ib yam khoom tau los ntawm kev hloov cov hydroxyl pawg ntawm cov piam thaj hauv cov cellulose ntuj nrog hydroxyethyl pawg. Cov kev qhia tshwj xeeb thiab cov qauv ntawm cov khoom lag luam feem ntau txawv raws li qib kev hloov pauv thiab viscosity.
Cov ntau yam ntawm hydroxyethyl cellulose kuj tau muab faib ua hom dissolution ib txwm, hom dispersion ceev thiab hom kev ruaj ntseg lom. Raws li txoj kev siv kev txhawj xeeb, hydroxyethyl cellulose tuaj yeem ntxiv rau ntau theem hauv txheej txheej txheej txheej. Hom ceev-dispersing tuaj yeem ntxiv ncaj qha rau hauv daim ntawv ntawm cov hmoov qhuav. Txawm li cas los xij, tus nqi pH ntawm lub kaw lus ua ntej ntxiv yuav tsum tsawg dua 7, feem ntau vim tias hydroxyethyl cellulose dissolves maj mam ntawm tus nqi pH tsawg, thiab muaj sijhawm txaus rau cov dej nkag mus rau hauv cov khoom, thiab tom qab ntawd tus nqi pH nce ntxiv kom nws dissolves sai. Cov kauj ruam sib thooj kuj tuaj yeem siv los npaj ib qho kev sib xyaw ntawm cov kua nplaum thiab ntxiv rau txheej txheej txheej.
Hydroxypropyl methylcellulose yog sivyog cov khoom tau los ntawm kev hloov cov pab pawg hydroxyl ntawm cov piam thaj hauv cov cellulose ntuj nrog methoxy pawg, thaum lwm qhov yog hloov los ntawm pawg hydroxypropyl. Nws cov nyhuv thickening yog qhov pib zoo ib yam li ntawm hydroxyethyl cellulose. Thiab nws yog resistant rau enzymatic degradation, tab sis nws cov dej solubility tsis zoo li ntawm hydroxyethyl cellulose, thiab nws muaj qhov tsis zoo ntawm gelling thaum rhuab. Rau saum npoo-kho hydroxypropyl methylcellulose, nws tuaj yeem ncaj qha ntxiv rau dej thaum siv. Tom qab stirring thiab dispersing, ntxiv alkaline tshuaj xws li ammonia dej los kho tus nqi pH rau 8-9, thiab do kom txog thaum tag nrho yaj. Rau hydroxypropyl methylcellulose yam tsis muaj kev kho saum npoo, nws tuaj yeem tsau thiab o nrog dej kub siab tshaj 85 ° C ua ntej siv, thiab tom qab ntawd txias rau chav sov, ces nplawm nrog dej txias lossis dej khov kom yaj tag nrho.
② Inorganic thickener
Hom thickener no feem ntau yog qee cov khoom siv av nplaum, xws li bentonite, magnesium aluminium silicate av nplaum, thiab lwm yam. Nws yog tus cwj pwm nyob rau hauv uas ntxiv rau cov nyhuv thickening, nws kuj muaj cov nyhuv zoo, tuaj yeem tiv thaiv kev poob dej, thiab yuav tsis cuam tshuam cov dej tsis kam ntawm txheej. Tom qab lub txheej yog qhuav thiab tsim rau hauv ib zaj duab xis, nws ua raws li ib tug muab tub lim nyob rau hauv lub txheej zaj duab xis, thiab lwm yam. Lub unfavorable yam yog hais tias nws yuav ho cuam tshuam rau lub leveling ntawm lub txheej.
③ Synthetic polymer thickener
Synthetic polymer thickeners feem ntau yog siv hauv acrylic thiab polyurethane (associative thickeners). Acrylic thickeners feem ntau yog acrylic polymers uas muaj carboxyl pawg. Hauv dej nrog tus nqi pH ntawm 8-10, pawg carboxyl dissociates thiab ua o; Thaum tus nqi pH ntau dua 10, nws yaj hauv dej thiab poob cov nyhuv thickening, yog li cov nyhuv thickening yog rhiab heev rau pH tus nqi.
Lub thickening mechanism ntawm acrylate thickener yog tias nws cov khoom tuaj yeem adsorbed rau saum npoo ntawm cov latex hauv cov xim, thiab tsim cov txheej txheej tom qab alkali o, uas ua rau cov ntim ntawm cov latex ntau ntxiv, cuam tshuam rau Brownian cov lus tsa suab ntawm cov khoom, thiab ua kom cov viscosity ntawm cov xim pleev xim. ; Qhov thib ob, qhov o ntawm cov thickener nce viscosity ntawm theem dej.
(2) Kev cuam tshuam ntawm thickener ntawm txheej txheej
Cov nyhuv ntawm hom thickener ntawm rheological zog ntawm txheej yog raws li nram no:
Thaum tus nqi ntawm cov thickener nce, qhov zoo li qub viscosity ntawm cov xim nce ntxiv, thiab cov viscosity hloov pauv yog qhov pib zoo ib yam thaum raug rau sab nraud shear quab yuam.
Nrog cov nyhuv ntawm thickener, viscosity ntawm cov xim poob sai sai thaum nws raug shear quab yuam, qhia pseudoplasticity.
Siv lub hydrophobically hloov cellulose thickener (xws li EBS451FQ), ntawm qhov siab shear tus nqi, lub viscosity tseem siab thaum tus nqi loj.
Siv associative polyurethane thickeners (xws li WT105A), ntawm tus nqi siab shear, lub viscosity tseem siab thaum tus nqi loj.
Siv acrylic thickeners (xws li ASE60), txawm hais tias qhov zoo li qub viscosity nce sai heev thaum tus nqi loj, qhov viscosity txo qis ntawm qhov siab dua shear.
3. Associative thickener
(1) thickening mechanism
Cellulose ether thiab alkali-swellable acrylic thickeners tsuas tuaj yeem ua rau cov dej tuab, tab sis tsis muaj cov nyhuv thickening ntawm lwm cov khoom hauv cov xim dej, thiab lawv tsis tuaj yeem ua rau muaj kev cuam tshuam loj ntawm cov xim hauv cov xim thiab cov khoom ntawm emulsion, yog li rheology ntawm cov xim tsis tuaj yeem hloov kho.
Associative thickeners yog tus cwj pwm nyob rau hauv uas ntxiv rau thickening los ntawm hydration, lawv kuj thicken los ntawm kev koom tes ntawm lawv tus kheej, nrog dispersed hais, thiab nrog rau lwm yam nyob rau hauv lub system. Lub koom haum no disassociates ntawm siab shear tus nqi thiab re-associates ntawm tsawg shear tus nqi, cia lub rheology ntawm txheej yuav tsum tau kho.
Lub thickening mechanism ntawm associative thickener yog hais tias nws molecule yog ib tug linear hydrophilic saw, ib tug polymer compound nrog lipophilic pawg ntawm ob hnub, uas yog, nws muaj hydrophilic thiab hydrophobic pawg nyob rau hauv cov qauv, yog li nws muaj cov yam ntxwv ntawm surfactant molecules. xwm. Xws li cov molecules thickener tuaj yeem tsis tsuas yog hydrate thiab o kom thicken cov dej theem, tab sis kuj tsim micelles thaum lub concentration ntawm nws cov aqueous tov tshaj ib tug tej yam nqi. Cov micelles tuaj yeem koom nrog cov khoom polymer ntawm cov emulsion thiab cov xim pigment uas tau adsorbed cov dispersant los ua ib qho kev sib txuas ntawm peb-dimensional network qauv, thiab muaj kev sib txuas thiab entangled kom viscosity ntawm lub system.
Dab tsi yog qhov tseem ceeb tshaj yog tias cov koom haum no nyob rau hauv lub xeev ntawm dynamic tshuav nyiaj li cas, thiab cov micelles cuam tshuam tuaj yeem kho lawv txoj haujlwm thaum raug rau sab nraud quab yuam, yog li cov txheej txheem muaj qib theem. Tsis tas li ntawd, txij li cov molecule muaj ob peb micelles, cov qauv no txo cov kev nyiam ntawm cov dej molecules mus rau migrate thiab yog li tsub kom lub viscosity ntawm lub aqueous theem.
(2) Lub luag haujlwm hauv cov txheej txheem
Feem ntau ntawm cov tuab tuab yog polyurethanes, thiab lawv qhov hnyav molecular yog nyob nruab nrab ntawm 103-104 qhov kev txiav txim ntawm qhov loj, ob qhov kev txiav txim siab qis dua li qub polyacrylic acid thiab cellulose thickeners nrog cov txheeb ze molecular hnyav ntawm 105-106. Vim tias qhov hnyav molecular tsawg, qhov ntim tau zoo dua tom qab hydration tsawg dua, yog li nws cov viscosity nkhaus yog flatter dua li cov uas tsis yog-associative thickeners.
Vim tias qhov hnyav molecular tsawg ntawm cov neeg sib koom ua ke thickener, nws cov kev cuam tshuam hauv cov dej theem yog txwv, yog li nws cov nyhuv thickening ntawm cov dej theem tsis tseem ceeb. Nyob rau hauv qhov tsawg shear npaum li cas, lub koom haum hloov dua siab tshiab ntawm molecules yog ntau tshaj li lub koom haum kev puas tsuaj ntawm molecules, tag nrho cov system tuav ib tug inherent suspension thiab dispersion xeev, thiab lub viscosity yog ze rau lub viscosity ntawm dispersion nruab nrab (dej). Yog li ntawd, tus associative thickener ua rau cov xim dej-raws li cov txheej txheem ua kom pom tseeb viscosity qis dua thaum nws nyob hauv thaj tsam qis qis.
Associative thickeners nce lub peev xwm ntawm cov molecules vim yog kev sib koom ntawm cov khoom hauv cov theem dispersed. Nyob rau hauv txoj kev no, xav tau ntau lub zog los rhuav tshem cov kev sib koom ntawm cov molecules ntawm qhov siab shear tus nqi, thiab lub zog shear yuav tsum tau ua kom tiav tib lub shear strain kuj ntau dua, yog li ntawd lub kaw lus nthuav tawm ntau dua shear tus nqi ntawm siab shear tus nqi. Pom tseeb viscosity. Lub siab-shear viscosity siab dua thiab qis qis-shear viscosity tuaj yeem ua rau qhov tsis muaj cov thickeners nyob rau hauv rheological zog ntawm cov xim, uas yog, ob lub thickeners yuav siv tau nyob rau hauv kev sib xyaw ua ke los kho cov fluidity ntawm cov xim latex. Kev ua tau zoo sib txawv, kom ua tau raws li cov kev xav tau ntawm txheej txheej rau hauv cov yeeb yaj kiab tuab thiab txheej zaj duab xis ntws.
Lub sij hawm xa tuaj: Plaub Hlis-28-2024