Applicator, applicator set, degree of cleanliness determination method, and degree of cleanliness determination system

1. An applicator comprising:

a marker composition containing retroreflective particles and a dispersion medium, a blending ratio of the retroreflective particles being from 50 to 90 mass % on the basis of the total marker composition; wherein the dispersion medium comprises a water-soluble polymer, and

an applicator body capable of retaining the marker composition;

wherein an exposed part of the applicator body is capable of delivering the marker composition to a surface of an application target surface to be cleaned.

2. The applicator of claim 1 , wherein the applicator body is porous.

3. The applicator of claim 1 , wherein the applicator body has interconnected cells in the interior of the applicator body.

4. The applicator of claim 3 , wherein the cell count of the interconnected cells is 15 to 100 cells per 25 mm.

5. The applicator of claim 1 , further comprising:

a retention body for retaining the applicator body so that at least part of the applicator body is exposed;

and a lid body detachably attached to the retention body, for hermetically sealing the exposed part of the applicator body.

6. An applicator set comprising a plurality of the applicators of claim 1 ,

each applicator respectively comprising:

a retention body for retention of the applicator body, the retention body retaining the applicator body so that at least part of the applicator body is exposed,

and a lid part detachably attached to the retention part of another applicator, the lid part being capable of hermetically sealing the exposed part of the applicator body of the other applicator.

7. The applicator set of claim 6 , wherein a single applicator among the plurality of applicators is capable of being distinguished from the other applicators.

8. A method for determining a degree of cleanliness, the method comprising:

applying the marker composition to a surface to be cleaned using the applicator according to claim 1 ;

cleaning the surface;

irradiating light onto the surface;

sensing a reflected light from the retroreflective particles; and

determining a degree of cleanliness based on the result of sensing of the reflected light.

9. A system for determining a degree of cleanliness, the system comprising:

the applicator according to claim 1 ;

a sensing means for sensing reflected light from retroreflective particles based on image data showing a condition of a surface to be cleaned; and

a determination means for determining of degree of cleanliness of the surface to be cleaned based on results of sensing the reflected light obtained by the sensing means.

10. The applicator of claim 1 , wherein the marker composition further comprises water, wherein the water is present in the marker composition at 3-25% by weight.

11. The applicator of claim 1 , wherein the marker composition further comprises an alcohol, wherein the alcohol is present in the marker composition at 4-16% by weight.

12. The applicator of claim 1 , wherein the marker composition further comprises a humectant, wherein the humectant is present in the marker composition at 0.1-2% by weight.

13. The applicator of claim 1 , wherein the marker composition further comprises a pH adjusting agent.

14. The applicator of claim 1 , wherein the marker composition further comprises a surfactant.

15. The applicator of claim 14 wherein the marker composition, when dried, retains its water-dispersibility.