Análise Estática de Imagens de partículas de toner

Toners are colorants for electrostatic printing processes. Toner is a very fine powder consisting of 5 to 30 μm particles. Due to the very small particle size, the powder is flowable and behaves like a liquid. Toner is composed of synthetic resin, pigments, magnetizable metal oxides and various auxiliary substances.

Toners are mainly used in photocopying machines and laser printers to create a print image on paper. Laser toner cartridges for use in copiers and printers come in sets of cyan, magenta, yellow and black (CMYK), allowing a very large variety of colors to be generated by mixing (Fig. 1).

The demands placed on the toner are very high: On the one hand, it must meet the requirements with regard to the printing result, on the other hand, the toner should adhere to as many materials as possible, except for the device itself (fixing rollers). Furthermore, it must meet the technical requirements of the device, must not accept moisture and must remain consistent in its consistency until use.

To ensure these consistent material properties, precise characterization of particle size and particle shape with an according particle analyzer is crucial.

Figura 1:
Left: Typical toner cartridges for use in laser printers. Right: Toner samples submitted for analysis in a Microtrac laboratory, from left to right: black liquid, black powder, yellow liquid and yellow powder.

Analisador de tamanho e formato de partículas Camsizer M1

Learn more about the Static Image Particle Analyzer used in this application note.

CAMSIZER M1 Entre em contato!

Solução Análise Estática de Imagens com o CAMSIZER M1

O CAMSIZER M1 adota o princípio de medição por análise de imagem estática para determinar o tamanho de partículas e seu formato em um intervalo de 0,5 μm a 1500 μm. O analisador baseia-se num potente microscópio cuja estrutura e software são otimizados para análise automatizada de partículas.

Para análise de imagem estática (cf. ISO 13322-1), a amostra deve ser posicionada em um slide de objeto ou outro suporte e é movida por um porta-amostra para ser fotografada passo a passo por uma câmera de 18,1 mergapíxels. A amostra se mantém estática durante a captação da imagem, o que assegura imagens de alta qualidade e riqueza de detalhes.

Até seis diferentes aumentos e o preciso porta-amostras com precisão de posição de <3 μm assegura ótimas condições de medição ao longo de todo o intervalo de medição. Os resultados são apresentados como distribuições de tamanho e formato com uma variedade de parâmetros de medição configuráveis. O software do Particle X-Plorer permite a apresentação e análise posterior de qualquer partícula unitária registrada.

For the sample preparation of dry powders, such as toner particles, the M-Jet module is available, see Fig. 2 on the right.

Análise Estática de Imagens com o CAMSIZER M1

Sample Preparation

Black toner and yellow toner, both as powder and as suspension have been submitted for analysis (four samples altogether, Fig. 1, right). As preparation for the analysis the two suspensions, two drops each were placed on a slide and covered with a coverslip. For the undiluted samples, about 10% of the image area was covered by the particles, as a result of which many overlays were detected (Fig 3, left). The samples were therefore diluted until a covered area of 0.5 - 1% was reached. For the diluted samples, almost all particles are well separated from each other, the effect of the overlays can therefore be neglected (Fig. 3, right). The two powder-like toner samples have been dispersed on a glass slide with the M-Jet module (70 kPa pressure).

Análise Estática de Imagens de partículas de toner - Figura 3a

Análise Estática de Imagens de partículas de toner - Figura 3b

Figura 3:
Left: Toner particles in liquid, original concentration -> many agglomerates. Right: Toner particles in liquid, diluted -> particles separated. CAMSIZER M1 images, 20 x magnification

The toner particle samples were measured with the CAMSIZER M1 with the size definitions x_{c min} (width), x _area (circle equivalent diameter) and x_{Fe max} (length). Simultaneously the shape of particles is detected. The instrument was set up for transmitted light and 20 x magnification. Additional tests have been made with 50 x magnification. A detailed description of the size and shape definitions can be found in the appendix.

	Analysis time	Number of particles	Field size	Number of images
Yellow liquid	7 min 24 s	17 737	15.0 x 8.8	1017
Black liquid	7 min 0 s	11 697	12.1 x 10.3	961
Yellow dry	16 min 9 s	41 373	17.1 x 18.5	2426
Black dry	27 min 14 s	30 603	16.3 x 35.1	4384

Table 1:
Typical measurement conditions for toner particle samples wet / dry at 20 x magnification.

Resultados

In the following diagrams the size distribution is expressed by:

Cumulative distribution Q₃
Frequency distribution q₃

20 x or 50 x magnification?

Fig. 4 shows a comparison between analysis at 20 x and 50 x magnification. The results are almost identical. Therefore, it is reasonable to measure with the lower magnification because this results in significantly shorter analysis time.

Análise Estática de Imagens de partículas de toner - Figura 4

Figura 4:
Graphs of the black dry toner particles sample, size definition X_{c min}. with 20 x (red) and 50 x magnification (blue).

Repeatability

The yellow liquid sample has been measured three times (Fig. 5). The repeatability of the results is excellent.

Análise Estática de Imagens de partículas de toner - Figura 5

Figura 5:
Three consecutive measurements of the yellow toner liquid sample. Size definition x_{c min} with magnification 20 x. First measurement: red curve, second measurement: green curve, third measurement: blue curve. Some agglomerates appear as the measurements proceed and the toner sample slowly dries (oversize particles in the third measurement).

Dry samples

Fig. 6 shows a comparison of the size distribution for the two dry powders. The black powder is slightly larger than the yellow powder.

Análise Estática de Imagens de partículas de toner - Figura 6

Figura 6:
Graphs of dry yellow toner particles sample (red) and dry black toner particles sample (blue) size definition x _{c min.}

Liquid samples

Fig. 7 shows a comparison of the size distribution for the two dry powders. Again, the black powder is slightly larger than the yellow powder.

Análise Estática de Imagens de partículas de toner - Figura 7

Figura 7:
Graphs of the liquid toner samples, size definition x _{c min.} 20 x magnification. Yellow toner liquid sample (red) and black toner liquid sample (blue)

Particle Size results: Overview

Table 2 shows the percentiles of the Q3 distribution at 10 %, 50% and 90 % (d10, d50, d90) for all three size definitions x_{c min}, x_area and x_{Fe max}
The results for the wet and dry measurement of each color are almost identical. It is therefore possible to measure toner in wet or dry mode. However, the concentration of the liquid must not be too high. Dry sample preparation with the M-Jet works equally well as a wet dispersion.

x_{c min}	Yellow liquid	Black liquid	Yellow dry	Black dry
D10 [µm]	4.37	4.78	4.05	4.25
D50 [µm]	5.69	6.31	5.21	5.75
D90 [µm]	7.27	7.85	6.79	7.44

x_area	Yellow liquid	Black liquid	Yellow dry	Black dry
D10 [µm]	4.88	5.45	4.55	5.09
D50 [µm]	6.29	7.03	5.85	5.58
D90 [µm]	7.78	8.47	7.59	8.17

x_{Fe max}	Yellow liquid	Black liquid	Yellow dry	Black dry
D10 [µm]	5.09	5.99	4.70	5.73
D50 [µm]	6.98	7.91	6.55	7.61
D90 [µm]	8.81	9.80	9.12	9.76

Table 2:
d10, d50 and d90 of all four samples, 20 x magnification, size definition x _{c min}, x _areaand x _{Fe max}

Comparison with Laser Diffraction

Laser diffraction is an established method to measure the particle size distribution in a range from below 100 nm up to 2 mm. It is a very versatile technique, however, the reported size is always based on a sphere model, no information about shape, length or width of the particles is available.

Resolution, sensitivity and accuracy are better for image analysis. Fig. 8 shows a comparison between CAMSIZER M1 x_{c min}, x_area and x_{Fe max} with a laser diffraction result. The Q3 curve from laser diffraction is between x_cmin and x_{Fe max} and wider than xarea. This is very typical for the correlation between laser and image analysis.

Análise Estática de Imagens de partículas de toner - Figura 8

Figura 8:
Graphs of dry black toner sample CAMSIZER M1, x _{c min}(red), x _area (green) and x _{Fe max} (blue) and laser diffraction (black *). The distribution obtained from laser diffraction is wider than the CAMSIZER M1 result. Laser diffraction calculates particle size based on a sphere model. The result is therefore between the width and length measurement of the CAMSIZER M1.

Particle Shape Analysis

Simultaneously with the size measurement, the CAMSIZER M1 detects particle shape. The result of the shape analysis can be presented as a cumulative distribution (Q3). Round, isometric or spherical particles will plot on the right side of the diagram, more elongated, angular or non-spherical particles plot on the left side. Fig. 9 and 10 show the aspect ratio and the roundness of a yellow and black toner sample as Q3 distribution. Shape analysis reveals that the yellow toner is more spherical than the black toner.

Análise Estática de Imagens de partículas de toner - Figura 9

Figura 9:
Shape graphs of the yellow liquid toner (red) and black liquid toner (blue). Shape parameter aspect ratio (b/l); X_{c min} divided by x_{Fe max.}

Análise Estática de Imagens de partículas de toner - Figura 10

Figura 10:
Shape graphs of yellow liquid toner (red) and black liquid toner (blue). Shape parameter roundness (RDNS_C).

Toner Particles Evaluation

All particle images acquired during the measurement are saved and can be used for later evaluation. The Particle X-Plorer software offers many possibilities to evaluate images or individual particles. Filter options are available to browse for particles with selected characteristics. In the following, particle examples of both toner samples are presented. Note that all relevant particle size and particle shape data is displayed right next to the according image.

Análise Estática de Imagens de partículas de toner - Figura 11

Figura 11:
Example images of the yellow liquid toner sample. All relevant data is displayed next to the particle image. Agglomerates (bottom row) can be easily identified by the low circularity or convexity of the particle. If required, these may be excluded from the evaluation.

Análise Estática de Imagens de partículas de toner - Figura 12a

Análise Estática de Imagens de partículas de toner - Figura 12b

Figura 12:
Example particles of the black liquid toner sample.

Summary

A análise do tamanho das partículas e a análise do formato das partículas de todas as quatro amostras de toner foram realizadas com o analisador estático de imagens CAMSIZER M1. As amostras líquidas foram diluídas (2-3 gotas em 20 ml de água deionizada). Os pós secos foram dispersos em uma lâmina com o módulo de dispersão M-Jet. O tamanho médio de partículas está entre 5,21 μm e 6,31 μm e as partículas de toner amarelo são ligeiramente menores que as partículas de toner preto.

Os aglomerados podem ser ignorados na medição usando um filtro de formato com base no parâmetro convexidade (convexidade das partículas < 0,97 ignorada). A repetibilidade é excelente, conforme mostrado na Fig. 5. Os resultados podem ser confirmados por análise de difração de laser (Fig. 8). A análise do formato das partículas revela que as partículas de toner amarelo são mais compactas, têm maior circularidade e maior proporção de aspecto do que as partículas de toner preto. Uma ampliação de 20 vezes é suficiente para caracterizar as partículas de toner. A medição com ampliação de 50 vezes é possível, mas levará a um tempo de medição mais longo se o mesmo número de partículas for analisado.