Inserting new record to a table is not successful

Hi everyone,
My table “list” is consisted of one field, datetime type.
The following code is to add a new record to that table:


<!doctype html>
<html lang=en>
<head>
<title>Insert Date</title>
<meta charset=utf-8>
</head>
<body>
<?php
date_default_timezone_set('xxx');
$dbcon = @mysqli_connect ('xxx', 'xxx', 'xxx', 'xxx')
OR die ('Could not connect to MySQL: ' . mysqli_connect_error () );
mysqli_set_charset($dbcon, 'utf8');
if (isset($_POST['exam_date']))
{
$myDate = trim($_POST['exam_date']);
$q = "INSERT INTO list (exam_date) VALUES ($myDate)";
$result = @mysqli_query ($dbcon, $q);
?>
<form action="to_forum.php" method="post">
<input id="exam_date" name="exam_date" type="datetime"
value="<?php echo date('d-m-y H:i:s'); ?>">
<input id="submit" type="submit" name="submit" value="Send">
</form>
</body>
</html>

Having clicked “submit” with default date in the input box, no new record is added. Could anyone help me please with adding a record to that table?
Thanks !