Editing Cathode-ray tube (section)

====Screen manufacture====
Early color CRTs did not have a black matrix, which was introduced by Zenith in 1969, and Panasonic in 1970.<ref name="auto55"/><ref name="auto39">{{Cite web|url=https://patents.google.com/patent/US5081394A/en|title=Black matrix color picture tube|accessdate=18 December 2022}}</ref><ref name="auto95"/> The black matrix eliminates light leaking from one phosphor to another since the black matrix isolates the phosphor dots from one another, so part of the electron beam touches the black matrix. This is also made necessary by warping of the shadow mask.<ref name="auto94"/><ref name="auto103"/> Light bleeding may still occur due to stray electrons striking the wrong phosphor dots. At high resolutions and refresh rates, phosphors only receive a very small amount of energy, limiting image brightness.<ref name="auto97"/>

Several methods were used to create the black matrix. One method coated the screen in photoresist such as dichromate-sensitized polyvinyl alcohol photoresist which was then dried and exposed; the unexposed areas were removed and the entire screen was coated in colloidal graphite to create a carbon film, and then hydrogen peroxide was used to remove the remaining photoresist alongside the carbon that was on top of it, creating holes that in turn created the black matrix. The photoresist had to be of the correct thickness to ensure sufficient adhesion to the screen, while the exposure step had to be controlled to avoid holes that were too small or large with ragged edges caused by light diffraction, ultimately limiting the maximum resolution of large color CRTs.<ref name="auto103"/> The holes were then filled with phosphor using the method described above. Another method used phosphors suspended in an aromatic diazonium salt that adhered to the screen when exposed to light; the phosphors were applied, then exposed to cause them to adhere to the screen, repeating the process once for each color. Then carbon was applied to the remaining areas of the screen while exposing the entire screen to light to create the black matrix, and a fixing process using an aqueous polymer solution was applied to the screen to make the phosphors and black matrix resistant to water.<ref name="auto39"/> Black chromium may be used instead of carbon in the black matrix.<ref name="auto103"/> Other methods were also used.<ref>{{Cite web|url=https://patents.google.com/patent/KR100728490B1/en|title=photo-sensitive compound and photo-resist resin composition for forming black matrix of CPT containing effective amount thereof|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US5840450A/en|title=Method for forming a black matrix on a faceplate panel for a color CRT|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US6022651A/en|title=Black matrix and a phosphor screen for a color cathode-ray-tube and production thereof|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/DE19655045C2/en|title=Water-soluble photocurable resin compsn. useful in black matrix punch|accessdate=18 December 2022}}</ref>

The phosphors are applied using [[photolithography]]. The inner side of the screen is coated with phosphor particles suspended in PVA photoresist slurry,<ref>{{cite journal |last1=Lakatos |first1=Andras I. |title=Introduction |journal=Journal of the Society for Information Display |date=2000 |volume=8 |issue=1 |pages=1 |doi=10.1889/1.1985254 |s2cid=57611617 }}</ref><ref>{{Cite book|url=https://books.google.com/books?id=aAQBIuPrudQC&q=crt+phosphor+photolithography&pg=PA94|title = Cathodoluminescence and Photoluminescence: Theories and Practical Applications|isbn = 9781420052732|last1 = Ozawa|first1 = Lyuji|date = 3 October 2018| publisher=CRC Press }}</ref> which is then dried using infrared light,<ref>{{Cite magazine|title=Assembly line for lower-priced TV <!--http://www.earlytelevision.org/pdf/life_12-28-59.pdf-->|date=28 December 1959|magazine=Life Magazine}}</ref> exposed, and developed. The exposure is done using a "lighthouse" that uses an ultraviolet light source with a corrector lens to allow the CRT to achieve color purity. Removable shadow masks with spring-loaded clips are used as photomasks. The process is repeated with all colors. Usually the green phosphor is the first to be applied.<ref name="auto6"/><ref>{{cite web |url=http://www.earlytelevision.org/pdf/recent_improvements_in_the_21axp22_color_kinescope.pdf |archive-url=https://web.archive.org/web/20201101112452/http://www.earlytelevision.org/pdf/recent_improvements_in_the_21axp22_color_kinescope.pdf |archive-date=2020-11-01 |url-status=live |title= Recent Improvements in the 21AXP22 Color Kinescope|date=1956 |website=www.earlytelevision.org |access-date=2020-12-11}}</ref><ref name="auto47">{{Cite web|url=https://patents.google.com/patent/US6614160B1/en|title=Fluorescent screen of color CRT and fabricating method thereof|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US5256463A/en|title=Method for manufacturing color phosphor surface|accessdate=18 December 2022}}</ref> After phosphor application, the screen is baked to eliminate any organic chemicals (such as the PVA that was used to deposit the phosphor) that may remain on the screen.<ref name="auto39"/><ref>{{Cite web |url=https://patents.google.com/patent/US3515553A/en|title=Photolithographic deposition of phosphors on faceplate of crt using spraying of photosensitive pva-phosphor suspension in plural layers |website=Google Patents |date=26 September 1951}}</ref> Alternatively, the phosphors may be applied in a vacuum chamber by evaporating them and allowing them to condense on the screen, creating a very uniform coating.<ref name="auto26"/> Early color CRTs had their phosphors deposited using silkscreen printing.<ref name="auto90"/> Phosphors may have color filters over them (facing the viewer), contain pigment of the color emitted by the phosphor,<ref>{{cite journal |last1=Ohno |first1=K. |last2=Kusunoki |first2=T. |title=ChemInform Abstract: Effect of Ultrafine Pigment Color Filters on Cathode Ray Tube Brightness, Contrast, and Color Purity. |journal=ChemInform |date=5 August 2010 |volume=27 |issue=33 |pages=no |doi=10.1002/chin.199633002 }}</ref><ref name="auto8"/> or be encapsulated in color filters to improve color purity and reproduction while reducing glare.<ref name="auto47"/><ref name="auto14"/> Such technology was sold by Toshiba under the Microfilter brand name.<ref>{{cite web | url=https://books.google.com/books?id=QVZ3k_kTQ-oC&dq=toshiba+microfilter+tube&pg=PA30 | title=PC Mag | date=26 September 1995 }}</ref> Poor exposure due to insufficient light leads to poor phosphor adhesion to the screen, which limits the maximum resolution of a CRT, as the smaller phosphor dots required for higher resolutions cannot receive as much light due to their smaller size.<ref>{{Cite web|url=https://patents.google.com/patent/US6013978A/en|title=Method for producing phosphor screens, and color cathode ray tubes incorporating same|accessdate=18 December 2022}}</ref>

After the screen is coated with phosphor and aluminum and the shadow mask installed onto it the screen is bonded to the funnel using a glass frit that may contain 65–88% of lead oxide by weight. The lead oxide is necessary for the glass frit to have a low melting temperature. Boron oxide (III) may also present to stabilize the frit, with alumina powder as filler powder to control the thermal expansion of the frit.<ref>{{Cite web|url=https://patents.google.com/patent/US6583079B1/en|title=CRT frit capable of sealing a CRT bulb at a relatively low temperature and in a short time|accessdate=18 December 2022}}</ref><ref name="auto81"/><ref name="auto50"/> The frit may be applied as a paste consisting of frit particles suspended in [[amyl acetate]] or in a [[polymer]] with an alkyl methacrylate [[monomer]] together with an organic solvent to dissolve the polymer and monomer.<ref name="auto57">{{cite web |url=https://data.epo.org/publication-server/pdf-document?pn=0889010&ki=A1&cc=EP |title=Sealing glass paste for cathode ray tubes patent applicatrion|date=1999 |website= data.epo.org|format=PDF|access-date=2020-12-11}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US5281560A/en|title=Non-lead sealing glasses}}</ref> The CRT is then baked in an oven in what is called a Lehr bake, to cure the frit, sealing the funnel and screen together. The frit contains a large quantity of lead, causing color CRTs to contain more lead than their monochrome counterparts. Monochrome CRTs on the other hand do not require frit; the funnel can be fused directly to the glass<ref name="auto104"/> by melting and joining the edges of the funnel and screen using gas flames. Frit is used in color CRTs to prevent deformation of the shadow mask and screen during the fusing process. The edges of the screen and the edges of funnel of the CRT that mate with the screen, are never melted.<ref name="auto6"/> A primer may be applied on the edges of the funnel and screen before the frit paste is applied to improve adhesion.<ref>{{Cite web|url=http://scienceon.kisti.re.kr/srch/selectPORSrchPatent.do?cn=USP1988114788471|title=Sealing for CRT components|publisher=Zenith Electronics Corporation|date=November 21, 1986|website=ScienceON}}</ref> The Lehr bake consists of several successive steps that heat and then cool the CRT gradually until it reaches a temperature of 435–475&nbsp;°C<ref name="auto57"/> (other sources may state different temperatures, such as 440&nbsp;°C)<ref>{{cite web |url=https://patentimages.storage.googleapis.com/pdfs/US5355051.pdf |archive-url=https://web.archive.org/web/20201031225810/https://patentimages.storage.googleapis.com/pdfs/US5355051.pdf |archive-date=2020-10-31 |url-status=live |title=Patent data |website=patentimages.storage.googleapis.com |access-date=2020-12-11}}</ref> After the Lehr bake, the CRT is flushed with air or nitrogen to remove contaminants, the electron gun is inserted and sealed into the neck of the CRT, and a vacuum is formed on the CRT.<ref>{{Cite web|url=https://patents.google.com/patent/US3658401A/en|title=Method of manufacture of cathode ray tubes having frit-sealed envelope assemblies|accessdate=18 December 2022}}</ref><ref name="auto75"/>