Use drupal_add_css with the option 'browsers'.

drupal_add_css(
  path_to_theme() . '/ie.css',
  array(
    'browsers' => array(
      'IE' => 'lte IE 9',
      '!IE' => FALSE
    )
  )
);

Use drupal_add_css with the option 'browsers'.

drupal_add_css(
  path_to_theme() . '/ie.css',
  array(
    'browsers' => array(
      'IE' => 'lte IE 9',
      '!IE' => FALSE
    )
  )
);

You should add this function call in your theme's template.php file through template_preprocess_html like this:

function MYTHEME_preprocess_html(&$vars){
  drupal_add_css(
      path_to_theme() . '/css/ie.css',
      array(
        'browsers' => array(
          'IE' => 'lte IE 9',
          '!IE' => FALSE
        )
      )
    );
}