thymeleaf pattern dd/MM/yyyy

I try to validate an input date to have format dd/MM/yyyy like that :

<input type="date" th:pattern="${date_format}" th:field="*{subscriptionDate}"/>

In my controller, I add an attribute to my model like that :

model.addAttribute("date_format", "dd/MM/yyyy");

But when I submit my form I have this message from my input tag :

Please respect the format