Querying Advanced Custom Fields

Try using a meta_query in your $args. You are far more flexible this way. For the full reference of the possibilities check the Codex

$args = array( 
    'post_type' => 'Product', 
    'posts_per_page' => -1, 
    'orderby' => 'title', 
    'order' => 'ASC', 
    'meta_query' => array(
       array(
           'key' => 'product_type',
           'value' => 'Paper',
           'compare' => '=',
       )
    )
);