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                                                                     Exhibit 3.1
                                 AMENDED AND RESTATED
                             CERTIFICATE OF INCORPORATION
                                          OF
                             ROTONICS MANUFACTURING INC.
                             ---------------------------


    Rotonics Manufacturing Inc., a corporation organized and existing under 
the laws of the State of Delaware, hereby certifies as follows:

    1.   The name of the Corporation is Rotonics Manufacturing Inc.  Rotonics
Manufacturing Inc. was originally incorporated under the name of Pentron
Corporation, and the original Certificate of Incorporation was filed with the
Secretary of State of the State of Delaware on September 10, 1986.

    2.   Pursuant to Sections 242 and 245 of the General Corporation Law of the
State of Delaware, this Amended and Restated Certificate of Incorporation
restates and integrates and further amends the provisions of the Certificate of
Incorporation of this Corporation.

    3.   The text of the Certificate of Incorporation as heretofore amended or
supplemented is hereby restated and further amended to read in its entirety as
follows:

    ARTICLE ONE.  NAME.  The name of the Corporation is "Rotonics Manufacturing
Inc."

    ARTICLE TWO.  REGISTERED OFFICE.  The address of the registered office of 
the Corporation in the State of Delaware is 1013 Centre Road, in the City of 
Wilmington, County of New Castle.  The name of its registered agent at such 
address is United States Corporation Company.

    ARTICLE THREE.  PURPOSES.  The purpose of the Corporation is to engage in
any lawful act or activity for which corporations may be organized under the
General Corporation Law of the State of Delaware.


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    ARTICLE FOUR.  CAPITAL STOCK.

     A.  AUTHORIZED CAPITAL.  The Corporation is authorized to issue one (1)
class of shares of stock to be designed "Common Stock".  The total number of
shares of Common Stock which the Corporation is authorized to issue is Twenty
Million (20,000,000), each share to have a par value of $.01.  Each outstanding
share of Common Stock as of this date is to remain as one share of Common Stock.

    ARTICLE FIVE.  LIMITATION OF LIABILITY AND INDEMNIFICATION OF DIRECTORS.

         A.   ELIMINATION OF CERTAIN LIABILITY OF DIRECTORS.   Each director of
the Corporation shall not be personally liable to the Corporation or its
stockholders for monetary damages for breach of fiduciary duty as a director,
except for liability (i) for any breach of such director's duty of loyalty to
the Corporation or its stockholders, (ii) for acts or omissions not in good
faith or which involve intentional misconduct or a knowing violation of law,
(iii) under Section 174 of the General Corporation of the State of Delaware, or
(iv) for any transaction from which such director derived any improper personal
benefit.  If the General Corporation Law of the State of Delaware is amended
after filing this Certificate of Incorporation with the Delaware Secretary of
State so as to authorize corporate action further eliminating or limiting the
personal liability of directors, then the liability of each director of the
Corporation shall be eliminated or limited to the fullest extent permitted by
the General Corporation Law of the State of Delaware, as so amended.


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    Any repeal or modification of the foregoing paragraph by the stockholders
of the Corporation shall not adversely affect any right or protection of a
director of the Corporation existing at the time of such repeal or modification.

         B.   INDEMNIFICATION AND INSURANCE.

              (1)  RIGHT TO INSURANCE.  Each person who was or is made a party
or is threatened to be made a party to or is involved in any action, suit or
proceeding, whether civil, criminal, administrative or investigative
(hereinafter a "proceeding"), by reason of the fact that he or she, or a person
of whom he or she is the legal representative, is or was a director or officer
of the Corporation, or is or was serving at the request of the Corporation, as a
director, officer, employee or agent of another corporation or of a partnership,
joint venture, trust or other enterprise, including service with respect to
employee benefit plans, whether the basis of such proceeding is alleged action
in an official capacity as a director, officer, employee or agent or in any
other capacity while serving as director, officer, employee or agent, shall be
indemnified and held harmless by the Corporation to the fullest extent
authorized by the General Corporation Law of the State of Delaware, as the same
exists or may hereafter be amended (but, in the case of any such amendment, only
to the extent that such amendment permits the Corporation to provide broader
indemnification rights than said law permitted the Corporation to provide prior
to such amendment), against all expense, liability and loss (including
attorneys' fees, judgments, fines, ERISA excise taxes or penalties and amounts
paid or to be paid in settlement) reasonably incurred or suffered by such person
in connection therewith and


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such indemnification shall continue as to a person who has ceased to be a
director, officer, employee or agent and shall inure to the benefit of his or
her heirs, executors and administrators; PROVIDED, HOWEVER, that the Corporation
shall indemnify any such person seeking indemnification in connection with a
proceeding (or part thereof) initiated by such person only if such proceeding
(or part thereof) was authorized by the Board of Directors of the Corporation.
The right to indemnification conferred in this Section B shall be a contract
right and shall include the right to be paid by the Corporation the expenses
incurred in defending any such proceeding in advance of its final disposition;
PROVIDED, HOWEVER, that if the General Corporation Law of the State of Delaware
requires, the payment of such expenses incurred by a director or officer in his
or her capacity as a director or officer (and not in any other capacity in which
service was or is rendered by such person while a director or officer,
including, without limitation, service to an employee benefit plan) in advance
of the final disposition of a proceeding, shall be made only upon delivery to
the Corporation or an undertaking, by or on behalf of such directors or officer,
to repay all amounts so advanced if it shall ultimately be determined that such
director is not entitled to be indemnified under this Section or otherwise.  The
Corporation may, by action of its Board of Directors, provide indemnification to
employees and agents of the Corporation with the same scope and effect as the
foregoing indemnification of directors and officers.

              (2)  NON-EXCLUSIVITY OF RIGHTS.  The right to indemnification and
the payment of expenses incurred in defending a proceeding in advance of its
final


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disposition conferred in this Section B shall not be exclusive of any other
right which any person may have or hereafter acquire under any statute,
provision of this Certificate of Incorporation, Bylaw, agreement, vote of
stockholders or disinterested directors or otherwise.

              (3)  INSURANCE.  The Corporation may maintain insurance, at its
expense, to protect itself and any director, officer, employee or agent of the
Corporation or another corporation, partnership, joint venture, trust, or other
enterprise against any such expense, liability or loss, whether or not the
Corporation would have the power to indemnify such person against such expense,
liability or loss under the Delaware General Corporation Law.

    ARTICLE SIX.  MANAGEMENT OF BUSINESS.  The business and affairs of the
Corporation shall be managed by or under the direction of the Board of Directors
and the directors need not be elected by ballot unless required by the Bylaws of
the Corporation.

    ARTICLE SEVEN.  BYLAWS.  In furtherance and not in limitation of the powers
conferred by stature, the Board of Directors and the stockholders of the
Corporation are each expressly authorized to adopt, amend or repeal the Bylaws
of the Corporation.

    ARTICLE EIGHT.  AMENDMENTS.  The Corporation reserves the right to amend
and repeal any provision contained in this Certificate of Incorporation, and to
take other corporate action to the extent and in the manner now or hereafter
permitted or prescribed by the laws of the State of Delaware.  All rights herein
conferred are granted subject to this reservation.


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         4.   This Amended and Restated Certificate of Incorporation was
submitted to the stockholders of the Corporation for their approval at the
annual meeting of Stockholders, and at such meeting the necessary number of
shares as required by statute were voted in favor of the Amended and Restated
Certificate of Incorporation.

         5.   This Amended and Restated Certificate of Incorporation was duly
adopted in accordance with the provisions of Sections 242 and 245 of the General
Corporation Law of the State of Delaware.

    IN WITNESS WHEREOF, Rotonics Manufacturing Inc. has caused this Amended 
and Restated Certificate of Incorporation to be signed by Sherman McKinniss, 
its President, and attested by E. Paul Tonkovich, its Secretary, on 
this 11th day of February, 1997.

ATTEST:                           ROTONICS MANUFACTURING INC.



/s/ E. Paul Tonkovich             By: /s/ Sherman McKinniss
------------------------------       -----------------------------
E. Paul Tonkovich                    Sherman McKinniss
Secretary                            President



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