Docstoc

Speeding up the development

Document Sample
Speeding up the development Powered By Docstoc
					  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:                  01/2009
  Seite/Page:




                        Speeding up the development

  During production of LCD colour monitors and                          quality applications such as TVs. They give a better
  televisions, coloured coatings are applied and                        viscosity reduction and more stable pigment dispersion.
  selectively removed ("developed") after UV exposure.                  But their drawbacks are their inferior developing properties
  It is shown that faster development can be obtained by                compared to the polyester polyurethane graft copolymers.
  using highly soluble dispersants and by formation of                  A new generation of acrylic block copolymers with better
  a salt between dispersant and the acid groups of the                  developing properties has therefore been created [3].
  binder.
                                                                        Test coatings use a simplified formulation
  Novel dispersants can give faster LCD screen production               A typical colour resist formulation contains an organic
  Bernd Göbelt*                                                         solvent, such as methoxypropyl acetate (MPA) or
  Sabine Johann                                                         butyldiglycol acetate, pigment, dispersant, a binder that
  Johanna Dettmer                                                       usually contains carboxylic acid, a multifunctional acrylic
  Markus Rößner                                                         monomer, photoinitiator and other additives such as
  Progress in the development of new and better electronic              surfactants.The multifunctional acrylic monomer and the
  devices such as computers or monitors has been driven                 photoinitiator are low molecular weight components that are
  by faster and more efficient computer chips. Less                     easily soluble or emulsified in water, and for this evaluation
  obviously, this development has also been assisted by the             the test formulation has therefore been simplified, using only
  performance of chemical components which may not come                 the pigment concentrate, consisting of the solvent, pigment,
  into mind when one thinks about electronic devices.                   dispersant and binder, to emphasise the differences in
  In the field of LCD monitors or televisions, the image is             the developing properties of the coatings derived from the
  generated with a colour filter and a liquid crystal layer that is     dispersant.
  oriented in an electrical field and "switches on and off" the         The pigment concentrates were prepared by grinding with
  light behind distinct areas of the colour filter. The colour filter   zirconia beads in a shaker. For the developing tests, the
  itself is a pigmented coating on a glass panel. It assembles          glass panels were spin-coated with pigment concentrates
  the three colours red, green and blue in a pixel pattern.             which had been further diluted with methoxypropyl acetate,
  This filter consists essentially of the coating matrix, pigment       to give a coating film with a thickness of about 0.2 µm after
  and dispersant. The dispersant is needed to form and                  drying for 24 hours at room temperature. An aqueous 0.1
  stabilise the pigment dispersion in the pigment paste and             weight % solution of KOH was used as the developer.
  the liquid coating. But in this field the dispersant has to
  meet additional requirements. For example, it should not              Time for coating to dissolve is measured
  influence electronic properties such as the voltage holding           For the developing test, the glass panel was put into a glass
  ratio (which influences image quality), and it has to support         beaker with developer solution. During the test, the solution
  the manufacturing process of the colour filter.                       was stirred. The break time ts was measured (defined as the
                                                                        time when the dissolution or release of the coating started).
  Dispersants are critical to colour resist formulation                 As the binder and the developer as well as the dispersant
  The colour filter pattern is produced by a photolithographic          influence the developing properties of the colour resist, the
  procedure. In this process, the whole glass panel is coated           break times are given only in a relative sense:
  with the liquid colour resist by spin or slide coating. After         : no release of the coating from the glass panel
  drying the coating, the pixel pattern of the colour is created        (+) : long break time
  by UV curing certain parts of the panel using a photo-mask            + : average value of break time
  and removing the non-cured coating with a developer a                 ++ : shorter break time
  basic aqueous solution that also contains surface-active              +++ : much shorter break timeThe binder is a
  substances.                                                           benzylmethacrylate-methacrylic acid copolymer with 20
  In this step the colour resist has to become water-soluble.           weight% of methacrylic acid. For this study the following
  The dispersant must not adversely influence this developing           pigments were chosen:
  step, for example by lengthening the process time or by               ››› Pigment red PR 254, "Irgaphor Red BT-CF" from Ciba
  causing a scum to form on the panel (coating particles left on        Speciality Chemicals, a diketo-pyrrolo-pyrrole pigment;›››
  the panel). Therefore, the choice of dispersant is important          Pigment green PG 36, a phthalocyanine pigment from
  in achieving the required developing properties.                      BASF ("Heliogen Green CF 9365");
  Dispersants used for colour resists can be divided into               ››› Pigment violet PV 23 "RL-COF02 LV 3101" from Clariant,
  two groups: polyester polyurethane graft copolymers [1]               with a dioxazine chromophore.
  and linear polyacrylate block copolymers [2]. The acrylic             Dispersants 1-4 are described in table 1. Dispersants 1-3
  block copolymers are made by controlled radical or ionic              are methacrylic block copolymers containing a B block that
  polymerisation technologies.                                          consists of tert-aminoalkyl methacrylate and/or quaternary
  As these technologies provide better control of the                   ammonium alkyl methacrylate. The A blocks are a mixture
  polymeric structure compared to the urethane chemistry,               of alkyl and aralkyl methacrylates. Dispersant 4 is a
  polyacrylate block copolymers are used mainly for high-



  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:                 01/2009
  Seite/Page:



  graft copolymer with polyether side chains and quaternary           the three-component complex of the dispersant with the
  ammonium groups attached to the main chain.                         pigment and the binder. In the developing step, the KOH
                                                                      reacts with the other carboxylic groups of the binder and
  Developing behaviour follows two patterns                           makes this complex more water-soluble than the pigment/
  The components of the colour resist formulation are not             dispersant complex.
  normally water-soluble. The driving force to solubilise the         To prove this concept, dispersants 1-3 were selected.
  dried colour resist film in the aqueous developer is the            Dispersant 1 contains only quaternary ammonium salts as
  neutralisation reaction of the acidic binder with the KOH           pigment-affinic groups. These groups make the dispersant
  of the developer. After neutralisation, the binder becomes          water-soluble but do not form a salt with the binder. By
  water-soluble.The coating is released from the glass panel          contrast, dispersant 3 contains only aminic groups. Due
  in two different ways. Ideally, the coating should become           to the less polar nature of the tertiary amines, 3 is not
  completely soluble in the developer. The coating dissolves          water-soluble. The water-soluble dispersant 2 contains both
  and coloured streaks are formed in the developer solution.          pigment-affinic groups amines and quaternary ammonium
  Another type of dissolution behaviour is peeling. The               salts.
  coating is released in small pieces. Depending on the               The results in table 2 support the theory of salt formation
  coating formulation, the coating is released in smaller or          of the binder and the dispersant. The dispersant 1 with
  larger pieces. Often scum spots of coating is left on the           ammonium groups gives a coating that cannot be released
  glass panel. Examples of the removal process are shown              from the glass panel. The coatings with the aminic
  in figures 1 and 2.                                                 dispersants 2 and 3 peel off in the developing step. The
                                                                      coatings with 2 and 3 have almost the same break time for
  Dispersant solubility controls development speed                    coating peel-off. The difference between them is the amount
  The coating with dispersant 1 was insoluble in the                  of scum. The coating with 3 is released quickly, giving a
  developing step an unexpected finding, since the polymer            coating-free glass panel. Dispersant 2 with the quaternary
  itself is water-soluble (table 2). A closer look at the polymeric   ammonium salts gives scum.
  structure gives an explanation for the poor dissolution
  behaviour of this formulation. Dispersant 1 is an AB                Similar behaviour confirmed with other pigments
  block copolymer with a binder-compatible A block that               The concept of salt formation having been proved in this
  consists of different alkyl methacrylates and a B block of          way, the other pigments PV 23 and PG 36 were used to
  polymethacrylates having quaternary ammonium salts in               show that the complex formation of the dispersant with the
  the side chains.                                                    binder and the pigment is a general concept independent of
  The water solubility of 1 results from these quaternary             the type of pigment. The results obtained in the developing
  ammonium groups in the B block. The A block itself is not           test with violet are not very different from those with the PR
  water-soluble. The pigment-affinic groups are attached to           254 pigment (table 3).
  the pigment surface, and the binder-compatible A block of           The coating with 1 is not released from the glass panel.
  the additive forms a shell around the pigment particle. As          The coatings with 2 and 3 peel off the glass substrate. The
  the outside of this shell is water-insoluble, the pigment-          coating with 3 shows the shortest break time. In general, the
  dispersant complex is therefore not dispersible in water,           break times ts with PV 23 are shorter than with PR 254. For
  which adversely affects the developing properties of the            PG 36, all the coatings are released from the glass panels
  coating on the glass panel.One approach to improving                including the coating with dispersant 1. The break times of
  developing speed is to design a water-soluble resin-                the coatings with dispersants 2 and 3 are much shorter than
  compatible block, providing a water-soluble shell on the            the break time of the coating with dispersant 1 (table 3).
  pigment dispersant complex. This has been achieved in               Scum was obtained for the dispersants 1 and 2 with the
  dispersant 4. This is a graft copolymer with polyether              quaternary ammonium groups, as was observed for PR
  side chains as the resin-compatible part of the dispersant          254. In addition, the peeled-off pieces of coating in the
  and the quaternary ammonium groups attached to the                  developer solution are smaller for the coating with 3 than
  backbone. When this is used, the coating peels off in a very        the pieces of the coating with 2 and 1, showing the better
  short time. This very fast developing property can be used          solubility of the coating with 3 relative to the coating with 2
  advantageously in a dispersant combination with a slowly            and 1.
  developing dispersant such as polymer 1. By changing the
  ratio of the two additives, the developing speed of the resist      Addition of acids enhances solubility
  coating can be adjusted, as can be seen in table 2.                 The interaction of the aminic dispersant with the acidic
                                                                      binder improves the solubility of the resist coating in
  Binder-dispersant interaction is also important                     the developer. Therefore, addition of acids to the resist
  Another concept takes advantage of the interaction of the           formulation should also have the same effect and should
  pigment-affinic groups of the dispersant with the acidic            further shorten the break time.
  groups of the binder. For this purpose the dispersant has           To demonstrate this effect, two acidic dispersants were
  to have aminic groups, as they are capable of forming               selected. A phosphoric acid ester with a water-soluble
  ammonium salts with the carboxylic acids of the binder and          polyether chain and its corresponding carboxylic acid
  of interacting with the pigment surface. The idea is to form        counterpart (indicated as dispersants 5 and 6 respectively)
  a complex of pigment, dispersant and binder as shown in             were added to the millbase before grinding. Both acids
  figure 3.                                                           were used in combination with dispersant 2 in a ratio to
  Parts of the aminic groups or other pigment-affinic groups          obtain one-to-one salt formation with acid value equal to
  such as the quaternary ammonium salts are attached to               amine value. Post-addition of 5 and 6 to the mill base after
  the pigment surface. Other aminic groups form a salt with           grinding is an alternative procedure.Both acids 5 and 6
  the acidic groups of the binder. These interactions generate



  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:              01/2009
  Seite/Page:



  influence the developing properties of the coating in the
  same direction and give roughly the same break time (table
  4). In comparison with the control experiment the coating
  containing only dispersant 2 the addition of both the acids
  leads to a shorter break time and faster coating peel-off.

  Several options for speeding up development
  To obtain good developing properties of the colour
  resist, the choice of the binder, the developer, the
  pigment and the dispersant play a role. The newly
  developed dispersants give more opportunities to adjust
  the developing properties.They improve these properties
  in different ways depending on the chemical structure of
  the dispersant. The selection of a water-soluble, resin-
  compatible part in the dispersant can shorten the break
  time, as was shown with dispersant 4.
  The choice of dispersants with aminic pigment-affinic
  groups leads to another mechanism for improving the
  developing properties by forming a three-component
  complex with the acidic binder and the pigment.
  Further addition of an acidic dispersant shortens the
  developing time of the colour resist once again.

  REFERENCES
  [1] US 4 647 647, US 4 762 752, US 4 795 796, US
  4 942 213 [2] F. Kother, B. Göbelt, European Coatings
  Journal 2006, 5, 22-29 [3] B. Göbelt, S. Johann, J. Dettmer,
  proceedings of the conference COSI 2008, Noordwijk,
  2008, 96-98

  Results at a glance
  »› The production of LCD colour monitors and televisions
  requires the application of a coloured coating which is
  UV cured in selective areas, with the uncured areas
  being later removed ("developed") to provide the required
  pixel pattern.»› A key component in the formulation is
  the dispersant, which must both stabilise the pigment
  dispersion and assist in the developing process.»› Several
  dispersants of differing chemical structure were used in
  formulations to determine how quickly and cleanly they
  could be removed by the alkaline developer solution. Both
  the solubility of the dispersant and its ability to form a
  salt with the acid groups of the binder affect the speed of
  removal. Mixing an acidic dispersant with an amine type
  can assist in salt formation.»› The results obtained were
  confirmed with three different pigments of different colours
  and composition.

  * Corresponding Author
  Dr. Bernd GöbeltByk-Chemie GmbHTel. +49 281 670 691
  bernd.goebelt@altana.com




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:            01/2009
  Seite/Page:




      Polymer              tS                       Developing behaviour

      2                    +                        Peeling type

      2+5                  ++                       Peeling type

      2+6                  ++                       Peeling type




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:             01/2009
  Seite/Page:




      Polymer        Weight ratio of    tS                Developing
                     dispersants                          behaviour

      1                                 –                 No release

      4                                 +++               Peeling type

      1+4            7:3                ++                Peeling type

      1+4            3:7                +++               Peeling type

      2                                 +                 Peeling type

      3                                 +                 Peeling type




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:             01/2009
  Seite/Page:




      Polymer        Pigment            tS                Developing
                                                          behaviour

      1              PV 23              –                 No release

                     PG 36              (+)               Peeling type

      2              PV 23              +                 Peeling type

                     PG 36              ++                Peeling type

      3              PV 23              ++                Peeling type

                     PG 36              ++                Peeling type




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:            01/2009
  Seite/Page:




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:            01/2009
  Seite/Page:




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:            01/2009
  Seite/Page:




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
  Quelle/Publication: European Coatings Journal
  Ausgabe/Issue:            01/2009
  Seite/Page:




  .




Vincentz Network +++ Plathnerstr. 4c +++ D-30175 Hannover +++ Tel.:+49(511)9910-000

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:5
posted:12/13/2012
language:English
pages:10