provide more space to tag field in odoo

def get_tag_value(self, cr, uid, ids, field_name, arg, context=None):
    res = {}
    for record in self.browse(cr, uid, ids, context=context):
        tags = record.tag_ids
        if tags:
            res[record.id] = ', '.join(map(lambda val: val.name, tags))
        else:
            res[record.id] = False
    return res

_columns = {
    'tag_value': fields.function(get_tag_value, type='char', 
    string='Tag'),
}