Controlling the mixing quality of 2K adhesives by means of electrical capacitance tomography – Part I: necessary polymer characteristics

Figures & data

Figure 1. Roadmap of the publication.

Table 1. Overview of investigated adhesives and associated mixing/processing conditions, all values taken from manufacturer’s technical data sheet (TDS).

Adhesive	Mixing ratio by weight (resin: hardener)	Pot life [min]	Filler materials
EPX_A1	2.00: 1	90	titanium dioxide, silanes
EPX_A2	3.45: 1	120	Silica, quartz
EPX_B1	0.58: 1	60	Unfilled
EPX_B2	2.37: 1	85	Unfilled
EPX_B3	0.60: 1	Oven cured	Minerals
EPX_B4	2.22: 1	45	Aluminium hydroxide
EPX_B5	1.65: 1	15	Minerals
EPX_C1	2.00: 1	60	–
PUR_A1	100: 100	30	–
PUR_B1	100: 17	5	–
PUR_B2	100: 55	4	–
PUR_B3	100: 70	10	–
PUR_B4	100: 10	30	silan terminated
PUR_C1	100: 94	<0.2	Antistatic
PUR_C2	100: 65	<0.2	Antistatic
PUR_D1	100: 58	<0.2	–

Figure 2. Developed permittivity measurement device (PMD) with (1) base frame, (2) movable stamp, (3) stainless steel electrodes, and (4) precision shims.

Table 2. Measuring range of PMD for determination of permittivity, ε_PMD, in dependency of adhesive layer thickness/shim height.

Capacitance range [pF]	Adhesive layer thickness/shim height [mm]
	0.5	0.7	1.0
1–10	0.7	0.983	1.4
10–100	7	9.83	14
100–1000	70	98.3	140

Figure 3. Illustration of PMD measurement procedure (herein for a correctly mixed 2K-EPX), all measurements performed at RT.

Table 3. Dielectrics of known permittivity taken from literature^[21] and used for the PMD validation.

Dielectric	Permittivity, ε, at RT and 1 Mhz	Shim height [mm]	Repetitions per shim	Number of measurements
Acetone	21.1	0.5; 0.7; 1.0	3	9
Ethanol	25.4	0.5; 0.7; 1.0	3	9
Isopropyl	20.3	0.5; 0.7; 1.0	3	9
Methylethylketone	18.5	0.5; 0.7; 1.0	3	9
Water	79.7	0.5; 0.7; 1.0	3	9
			Σ	45

Table 4. Experimental programme of unmixed and mixed adhesive components.

	Mixtures	Shim heights [mm]		Repetitions per component/shim/mixture	Number of measurements
Components
Each adhesive	–	0.7; 1.0		3	12
					Σ = 192
Mixed adhesives
EPX_A1	11	0.7; 1.0		3	66
EPX_A2	11	0.7; 1.0		3	66
EPX_B1	11	0.7; 1.0		3	66
PUR_C1	11	0.7; 1.0		3	66
					Σ = 264

Table 5. Assumed values and constants for the analytical considerations to be inserted in the equations of W as well as L&R.

Mixing ratio [hardener: resin]	εECT-H [const.]	Permittivity hardener, εH	Shape coefficient, u (W)	Shape coefficient, k (L&R)
1:1	0.13	5	∞	1
1:5	0.13	5	∞	1
1:10	0.13	5	∞	1

Figure 4. Determined permittivities of reference dielectrics measured with the developed PMD in comparison to known values from literature, values indicate arithmetic mean out of three repetition measurements, all measurements performed at RT.

Figure 5. Determined capacities of reference dielectrics measured with the developed PMD (see section 2.2.2) in comparison to theoretical values calculated acc. to equation 5(5) ${\epsilon }_{\mathrm{P}\mathrm{M}\mathrm{D}}=\frac{({\mathrm{C}}^{\ast }-{\mathrm{C}}_{\mathrm{p}})}{{\epsilon }_0}\cdot \frac{\mathrm{d}}{\mathrm{A}}$(5) , all measurements performed at RT.

Figure 6. Results of PMD permittivity measurements for the 2K-EPX adhesives, all measurements performed at RT.

Figure 7. Results of PMD permittivity measurements for the 2K-PUR adhesives, all measurements performed at RT.

Figure 8. Dependency between experimentally determined permittivity, ε_PMD, of mixed adhesive components and mixing ratio for the adhesives EPX_A1 (left) and EPX_A2 (right) along with resulting fitting curve and associated shape coefficients of W as well as L&R; crosses indicate arithmetic mean of measured values (triple determination), all measurements performed with PMD (see section 2.2) at RT.

Figure 9. Dependency between experimentally determined permittivity, ε, of mixed adhesive components and mixing ratio for the adhesives EPX_B1 (left) and PUR_C1 (right) along with resulting fitting curve and associated shape coefficients of Was well as L&R; crosses indicate arithmetic mean of measured values (triple determination), all measurements performed with PMD (see section 2.2) at RT.

Table 6. Characteristic values of the permittivity-mixing-ratio-function of the representative ECT-suitable adhesives investigated, all values determined at RT.

Adhesive	εR	εH	εtarget	Shape coefficient u (W)	Shape coefficient k (L&R)	εECT-R	εECT-H
EPX_A1	9.0	13.7	10.1	0	–1	0.095	0.090
EPX_A2	5.7	25.5	7.2	0.125	–0.5	0.169	0.154
EPX_B1	10.6	5.6	6.9	0	–1	0.092	0.097
PUR_C1	16.6	8.2	10.9	0	–1	0.196	0.203

Figure 10. Dependency of the ECT-index on the mixing ratio and the permittivity difference.

Dortmund Data Bank. Retrieved February 1, 2022 www.ddbst.com.

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