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Semi-Cured Phenolic Sheet: Paper Dipped in Phenol Resin and Part-Cured at 120-130 °C (Lucas, Western Electric, US 1,470,990)
Paper soaked in phenol resin is dried, then cured only part of the way, so the resin is stiff but not yet hard. Lucas did this before the final hot press so the press would not squeeze the resin out of the fibres.
Result: a dry, partly cured phenolic sheet that a later coat of phenolic resin can still bond into.
Source: Lucas, US 1,470,990 (Western Electric, 1923). Stopping before his final hot press is ours. Not given: the solvent in his resin, paper grade, mercerising strengths. Picture drawn by Youblob.
Intermediate
1 hour
Instructions
1
1
Dip the paper in phenol resin
Dip the paper in phenol resin
Run the paper through a bath of phenol resin of specific gravity about 0.970: about 2 minutes for plain paper, 1 minute or less if mercerised first. Ours: Liquid Bakelite as the resin; Lucas does not say how it was thinned.
Materials for this step:
Paper1 as required
Liquid Bakelite (Phenol-Formaldehyde Condensation Product)1 as requiredTools needed:
Prepreg Impregnating Line
Hydrometer2
2
Optional: mercerise the paper first
Optional: mercerise the paper first
For faster, fuller soaking, first pass the paper through caustic soda, squeeze, wash in water, neutralise in an acid, wash again and dry. Strengths and the acid: not given.
Tools needed:
Lye (Sodium Hydroxide)Prepreg Impregnating Line3
3
Dry at about 90 °C
Dry at about 90 °C
Dry the soaked paper in an oven at about 90 °C, just long enough to dry it.
Tools needed:
Drying Oven4
4
Part-cure at 120-130 °C
Part-cure at 120-130 °C
Pass the dry paper through a curing oven at 120-130 °C for about 10 minutes (Lucas's description; his claim 4 says 125 °C for about 10 seconds). The resin sets as stiff as the fibres, but does not harden through.
Tools needed:
Curing Oven5
5
Dip again for 10-15 seconds and dry
Dip again for 10-15 seconds and dry
Dip the part-cured paper in phenol resin again for 10-15 seconds, then dry at about 90 °C until it can be wound on a reel. Stop here: the sheet is semi-cured. Lucas's next step, stacking and hot pressing, cures it fully.
Materials for this step:
Liquid Bakelite (Phenol-Formaldehyde Condensation Product)1 as requiredTools needed:
Prepreg Impregnating LineDrying OvenMaterials
2- 1 as requiredPlaceholder
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Tools Required
5- Placeholder
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