Bulk insert query with datetime field

HI,

I'm still struggle to insert bulk insert data with datetime column to database.

Currently i'm using, if any datetime column in database means,   the below codes i use

        $pub_contact_info = array(
           'cc_contact_id'        => $pub_contact_id,
        );
        $this->db->set('cc_created_date', 'NOW()', FALSE);
        $this->db -> insert('ch_contact', $pub_contact_info);

But, in batch insert means, how can i use NOW() in insert_batch() function

Thanks in advance.