Checkbox in html using php

I am creating a table in which each cell should have a checkbox.The layout of table is coming fine but in each cell I am getting blank instead of a checkbox like this http://ift.tt/1TObWRj Below is the php code

  <?php
  $j=0;
  for($k=0;$k<3;$k++)
  {
      if($k==0)
      {
          echo "<tr id="."spanDate".">";
          for($i=0;$i<8;$i++)
          {
             if($i==0)
                echo "<td><input type='checkbox' name='time' value='" . ($i+1) . "'></td>";
            else
                echo "<td><input type='checkbox' name='time" . $j . "' value='" . ($i+1) . "'></td>";
            $j++;
          }
          echo "</tr>";
      }
      else
      {
          echo "<tr id="."spanDate".$k.">";
          for($i=0;$i<8;$i++)
          {
             if($i==0)
                echo "<td><input type='checkbox' name='time' value='" . ($i+1) . "'></td>";
            else
                echo "<td><input type='checkbox' name='time" . $j . "' value='" . ($i+1) . "'></td>";
            $j++;
          }
          echo "</tr>";
      }

  }
?>