Negotiation/discount is usually used in combination (repurchase of B/L for funding at debtor/exporter etc.) See: http://www.geocities.co.jp/HeartLand-Ayame/5161/tradeexport1...

Actually, I believe ”買い取り銀行に持ち込み” is the whole phrase here which is "taking (the documents) to the negotiating bank."

買い取り銀行 is the negotiating bank

This is about getting documents such as the bill of lading, invoice, etc. as specified in the letter of credit and taking them to the negotiating bank which has to accept the letter of credit and its conditions to make payment.

Here's a definition of negotiating bank:
http://www.intracen.org/tfs/docs/glossary/ne.htm
Negotiating bank:
In a letter of credit, the bank which accepts the documents for examination and, if these are found in order, credits the due amount to the beneficiary.

or: purchase of the shipping documents

In documentary credit, usually the beneficiary's bank which agrees to pay the beneficiary by purchasing a negotiable instrument (importer's or buyer's draft). Also called accrediting party.
http://www.businessdictionary.com/definition/negotiating-ban...
Negotiating Bank - The bank that reviews the documents required in the letter
of credit for compliance with its terms and remits payment to the beneficiary.
The bank may be specifically named in the letter of credit, or may be a bank
chosen by the seller.
http://www.creditmanagementworld.com/glossary/letterofcredit...

「持ち込み買取」という便利なタームは有りませんが、輸出入の実務経験からすると上記の表現が妥当ではないかと考えます。
買取銀行の英訳は、negotiation bankが定訳とおもいますが、ここでの買取はすばりpaymentとしたほうが分かりやすいと思います。

Bank guarantees in international trade: the law and practice of ... - Google ブック検索結果
Roeland I. V. F. Bertrams - 2004 - Business & Economics - 562 ページ
By definition, guarantees payable upon submission of third-party documents are independent guarantees and they can be ... which has issued a documentary credit , that the seller has not tendered the shipping documents, or not in time. ...
books.google.co.jp/books?isbn=9041122435...
L/C payable upon good receipt | Letter of Credit Forum - [ このページを訳す ]
投稿 4 件 - 3 人の編集者 - 最新の投稿: 2008年11月14日
I understand the above case as " he being the supplier of the goods has agreed upon the follwings payments terms. 30 percent down and 70 after submission of shipping documents." Now the applicant has amended the payment ...
letterofcreditforum.com/lcfbackup/.../lc-payable-upon-good-receipt - キャッシュ
Owner Operators: - [ このページを訳す ]
*Regular Pay - Payment is made within 30 days of receipt of all original shipping and receiving document------ Whether we get paid or not!! *Upon submission of the NECESSARY DOCUMENTS concerning a trip of Owner Operator, including all ...
www.eclipsetrans.com/owner_operator.htm - アメリカ合衆国 - キャッシュ
Shantaram Sapre's Blog - Accounting for Entreprenuers: November 2010 - [ このページを訳す ]
The last shipment date should be the as per the period agreed upon between the seller and the buyer to ship the goods through a carrier. ... The requirements for submission of shipping documents should be thoroughly reviewed. ...
shantaram-sapre.blogspot.com/2010_11_01_archive.html - キャッシュ
Essentials of Letters of Credit - [ このページを訳す ]
Other courts require payment upon substantial compliance with documentary requirements. ... credit in favor of the exporter, payable upon presentation of the seller,s draft, bill of lading and other shipping documents specified in the credit. ... The vendor is entitled to payment upon submission of proper documents. By presenting its draft and demand for payment, the vendor represents that all ...
www.coveringcredit.com/business_credit_articles/.../art015.... - キャッシュ