Paste for screen printing

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Paste development for screen printing

Example: Cathode current collector layer (CCCL) LaSrMnO - type for Solid Oxide Cell applications

Preparation
Preparation via Three Roll Mill

Required equipment and media

  • Laboratory balance
  • Three roll mill
  • Glass dishes or clock glasses (depending on the quantity to be prepared)
  • Spatula or paint knife
  • Suitable paste container
  • Transport medium (binder-solvent mixture)
  • (Spray-dried) powder

The CCCL paste should have a weight ratio of total powder quantity to transport medium of 1 : 1. For this purpose, the spray-dried non-milled LSM powder is weighed into a suitable glass vessel (clock glass or glass dish). Subsequently, the transport medium is weighed in. Both substances are now mixed by hand with a spatula or paint knife until a uniform mixture is obtained. The mixture is now transferred to a three-roll mill, where it is homogenized twice on each of the gap stages (for detailed gap distances and speeds, see Table 1 in the appendix). The paste is then filled into a paste storage container and tight closed. The setting of the required particle size distribution of
d10 = < 2.0; d50 = 6.0 –12.0; d90 = > 12 μm
is adjusted via the gap distance of the three-roll mill. The filled paste container is labeled with the data on the paste and marked with hazard symbols (F, Xi) (here: Powder - CCCL - Year of manufacture - Serial no. - Batch no.; Example: LSM - CCCL - 31 - 03 - SP325).

Characterisation

A check of the grain size distribution is necessary after the production. For this purpose, a small amount of the produced screen printing paste, diluted with ethanol, is placed in a sample vessel. The grain size distribution of the produced screen printing paste is measured. The required grain size distribution is: d10 = < 2.0; d50 = 6.0 -12.0; d90 = > 12 μm. Furthermore, the specific surface area of the dried and calcined paste is determined. For this purpose, 15 g of paste are dried in a quartz crucible in the drying oven and calcined in the sintering furnace. The quartz crucible must be covered during calcination. The following temperature programme is used for this purpose:
3 K min-1 to 400 °C
Hold for 1 h at 400 °C
5 K min-1 up to 20 °C
The calcined powder is then ground and prepared for BET measurement. The viscosity h is determined by means of a viscometer. The target viscosity is 8 - 25 Pa*s at a shear rate of 100 s-1. The paste is now ready for printing and can be stored in an air-conditioned laboratory (18 °C) typically for about twelve months.


Preparation of Transport Medium
Mixing of Transport Medium

Required equipment and media

  • Dispersion drive and dispersion tool
  • Laboratory boy
  • Laboratory glass bottle
  • laboratory stand
  • Lab balance
  • Terpineol (solvent)
  • Ethyl cellulose (binder)


Preparation of Transport Medium

The binder shall have the following composition of terpineol to ethyl cellulose:
94.0 wt% terpineol
6.0 wt% ethyl cellulose
First, the terpineol is weighed into the corresponding laboratory glass bottle. Then the ethyl cellulose is weighed in. The laboratory glass bottle with the initial weight is now clamped in the laboratory stand and secured against tipping or falling. The dispersing tool connected to the dispersing drive (Ultraturrax) is inserted into the laboratory glass bottle with the mixture. Now the Ultraturrax with a rotation of ~ 3000 - 5000 s-1 is started. The heat generated dissolves the ethyl cellulose in the terpineol. Afterwards, the mixed transport medium is removed from the stand holder and labelled with the data on the transport medium and provided with a hazardous substance sticker (F). (here: abbreviation - year of manufacture - serial no.; example: TM - 21 - 03). The transport medium is now ready for mixing the screen printing pastes and can also be stored in an air-conditioned laboratory (18 °C) typically for about twelve months.