Top plate for cooking device, production method therefor, and method for assessing charring

2:

• The cooker top plate according to claim 1, wherein a surface of the coating film has an arithmetic mean height Sa of not less than 0.4 nm and not more than 10 nm measured with a size of a measurement view field of 316.77 μm×237.72 μm and a resolution of 640 pixels×480 pixels.

3:

• The cooker top plate according to claim 1, wherein a water contact angle of a surface of the coating film is not less than 80 degrees.

4:

• The cooker top plate according to claim 1, wherein the glass substrate is made of a borosilicate glass or a low-expansion crystallized glass.

5:

• The cooker top plate according to claim 1, wherein the glass substrate has an average coefficient of linear thermal expansion of not more than 40×10−7/° C. at 30° C. to 380° C.

6:

• The cooker top plate according to claim 1, wherein the coating film contains a hydrolytic condensate of a trifunctional alkoxide represented by the following formula (2):
• in the formula (2), R1 represents an alkyl group having 1 to 6 carbon atoms, a phenyl group or a vinyl group and R represents an alkoxy group.

7:

• The cooker top plate according to claim 6, wherein the R1 of a compound represented by the formula (2) is a methyl group.

8:

• The cooker top plate according to claim 1, wherein a pencil hardness of the cooker top plate measured from a side thereof where the coating film is located is not less than 9H.

9:

• The cooker top plate according to claim 1, wherein when a sample for char sticking evaluation is made by dropping an evaluation liquid onto a surface of the coating film and heating the liquid and an image of the sample for char sticking evaluation is taken from a side of the glass substrate opposite to the coating film, an area ratio of a char sticking portion determined from the taken image is not more than 70%.

10:

• The cooker top plate according to claim 1, wherein when the cooker top plate undergoes a heat resistance test under conditions at a temperature of 350° C. for 24 hours, a change in water contact angle of a surface of the coating film between before and after the heat resistance test is less than three degrees.

11:

• The cooker top plate according to claim 1, wherein a surface of the cooker top plate located on a side thereof having the coating film is a cooking surface on which a cooking utensil is to be placed.

12:

• The cooker top plate according to claim 1, wherein
• a printed layer having a pattern is provided on the principal surface of the glass substrate, and
• the coating film is provided to cover the printed layer on the principal surface of the glass substrate.

13:

• The cooker top plate according to claim 12, wherein the pattern is a dotted, grid, striped or ring-shaped pattern.

15:

• The method for producing a cooker top plate according to claim 14, wherein the R1 of the compound represented by the formula (2) is a methyl group.

18-21. (canceled)

22:

• The char sticking evaluation method according to claim 17, wherein in the measurement step a char sticking area ratio is determined as a ratio of the area of the char sticking portion to an area of an entire region where the sample for char sticking evaluation is provided.

23:

• The char sticking evaluation method according to claim 22, wherein in the measurement step whether the plate-shaped material is a non-defective product or a defective product is determined from the char sticking area ratio.

24:

• A cooker top plate having a char sticking area ratio of not more than 70% determined by the char sticking evaluation method according to claim 16.