(1)Cleanliness
Orignally filters were produced for filtration,so cleanliness of the membrane itself was no issue, and filter manufacturer did not care for remaining particles on filter membranes.
ISO 16232 and VDA Vol.19 give clear instructions about the blank value, which is the limit of contaminaion of the cleanliness analysis equipment itself. Filters are of course part of the analysis equipment and thus contribute to the blank value.
In cleanliness analysis, filter cleanliness is of importance and should be specified.

JOMESA met this challenge since 2015 by cleaning, lasercutting and packing the filters in a cleanroom class 7 (ISO 14644).JOMESA controls cleanliness of filter production with a dedicated optical (JOMESA HFD) and SEM (JOMESA PSE) systems.

 

(2)Porosity
SEM images of typical filter membranes

Foamed membrane: Cellulose 0.8µm poresize	Closed Mesh Filter	Open Mesh Filter, 20µm poresize

Open mesh filters (> 15µm poresize) can be easily measured by image analysis.They can be used to separate different particle sizes:Mesh filters with 20µm holes (pores) size mesh will allow all particles smaller than 20µm to pass and hold back all particles larger.

Different closed mesh fabrics, defined by their weaving pattern (Binding key) and filament diameters are often misleading called 1µm, 5µm and 10µm or similar.

„1µm“ Binding key:30-01 07-01-03	„5µm“ Binding key:20-04 04-01-01	„10µm“ Binding key:20-03 03-01-01

※JOMESA definition and test of closed mesh filtration

	A defined amount of dirt liquid is poured through a closed mesh filter.
	The mesh filter is analyzed how many particles in the range from 5 to 15µm is on the filter (how many the mesh filter hold back).
	The filtered liquid is poured through a Cellulose 0.8µm poresize filter.
	The Cellulose filter is analyzed how many particles in the range from 5 to 15µm is on the filter (how many particles the mesh filter let pass).
Weaving pattern and filament diameter have no significant influence on filtration. The ration of heldback/pass through depents on filtration condition (pressure).

 

(3)Chemistry and Mechanical Properties.
ISO 16232:2018 and VDA 19.1 classifiy filters for microscopic filter analysis in 2 classes: Foamed and Mesh Filters

Filter material		Medium (test or final rinsing liquid)
		Aqueous neutral cleaner	Isopropanol	Ethanol (spirit)	Aliphatic hydrocarbons (cold cleaners)	Ketones (Acetone)
Foamed membrane	Cellulose nitrate	+	–	–	+	–
	Cellulose acetate	+	+	–	+	–
	Polyamide/Nylon	+	+	+	+	+
Mesh	Polyester	+	+	+	+	+
	Polyamide/Nylon	+	+	+	+	+
+ suitable, – unsuitable

Because of their chemical stability (see above table), PET and Polyamide filters are suitable for all rinsing liquids used.
Because of quicker filtration processes, mesh filters are preferred against foamed filters.

Polymer	Melting Temperature	Moisture Regain (20 deg C, 65%rel.Hum.)	Recommended drying temperature
Polyamide 6.6 (Nylon)	approx. 240 deg C	4.5%	70 deg C
Polyester PET	approx. 250 deg C	0.2%	90 deg C

Because of hygroscopic and thermal advantages PET filters are mostly used in cleanliness analysis applications.

From the woven fabric, filtermembranes can be produced in two ways:

Cold stamped Cold-stamping is a process, where particlulate contamination cannot be avoided.

Laser cut

Due to cleanliness requirements and to avoid entangling with environment, JOMESA offers only Laser cut filtermembranes.

Nylon (Polyamid) Filter Membranes, Laser cut

Polyester (PET) Filter Membranes, Laser cut

Closed Mesh Filters, Laser Cut

Article Code	SEM Image	Binding key	Filtration Specification	Cleanliness Specification
NY-47L-1		30-01 07-01-03	50% (+-25%) of particles 5 to 15µm are held back by the mesh filter 80% (+-20%) of particles larger 15µm are held back by the mesh filter	No particle > 200µm Max 3 particles between 50 and 200 µm Max. 300 particles between 5 and 50 µm
PE-47L-5 NY-47L-5		20-04 04-01-01
PE-47L-10		20-03 03-01-01

Open Mesh Filter, Laser Cut

Article Code	SEM Image	Binding key	Pore Size Specification	Cleanliness Specification
PE-47L-15		20-02 02-01-03	15µm x 15µm +- 5µm	No particle > 200µm Max 3 particles between 50 and 200 µm Max. 300 particles between 15 and 50 µm
PE-47L-20		20-02 02-01-01	20µm x 20µm +- 7µm	No particle > 200µm Max 5 particles between 50 and 200 µm Max. 50 particles between 25 and 50 µm
PE-47L-50		20-02 02-01-01	50µm x 50µm +- 10µm	No particle > 200 µm Max. 20 particles > 50µm
PE-47L-100		20-02 02-01-01	100µm x 100µm +- 15µm	Max. 5 particles > 100µm
PE-47L-150		20-02 02-01-01	150µm x 150µm +- 15µm	Max. 5 particles > 150µm
PE-47L-200		20-02 02-01-01	200µm x 200µm +- 10µm	Max. 5 particles > 200µm

(All product specifications are subject to modifications without prior notice)