Preparation of a macrocellular acoustic foam

Details Preparation of a macrocellular acoustic foam Preparation of a macrocellular acoustic foam

2001-02-13

2004-04-13

Foelak, Morton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C079S003000, C079S003000, C079S003000

Reexamination Certificate

active

06720363

ABSTRACT:

BACKGROUND OF THE INVENTION
Foams and foamed articles often find utility in acoustic systems for sound absorption and insulation. Such foams, when developed for different market segments (appliance, automotive, building & construction, etc) often need to meet certain acoustic performance requirements and applicable fire test codes. To achieve the desired fire rating, a variety of flame retardants are often added to such foam resin formulations. Unfortunately, the typical flame retardants and other additives added to the formulation cause a number of foam problems. Flame retardants cause poor cell structure and cell collapse due to their effects on the polymer gel viscosity and melt strength. Flame retardants also act as nucleating agents in the foaming process and provide additional nucleation sites, resulting in the formation of a large number of small cells with variable properties. Unfortunately, small cell foam is not as acoustically active as large cell foam for sound absorption.
U.S. Pat. No. 4,277,569 teaches the preparation of flame retardant polyolefin foams for thermal insulation and padding. However, the patent does not describe macrocellular foams or flame retardant macrocellular foams for acoustic applications or their preparation.
Copending U.S. application Ser. No. 60/178,516 filed on Jan. 19, 2000 in the name of Martin Reimers et al., teaches the composition of macrocellular foams useful in sound management and a process to make the same. Copending U.S. application Ser. No. 60/168844 filed on Dec. 3, 1999 in the name of Bharat Chaudhary et al., teaches the use of flame retardants and synergists in the preparation of fabricated articles from substantially random ethylene styrene interpolymers and blends.
However, a significant market need still exists for a large cell, acoustically active foam with good flame retardancy. This disclosure teaches a composition and a method of preparation of such macrocellular acoustic foam having both good flame retardancy and acoustic properties, suitable for several commercial applications. The key to the invention is the selection of a low nucleating foam composition, combining it with a selected flame retardant and extruding the formulation at a specific die pressure. The formulations are based on one or more ethylene or &agr;-olefin homopolymer resins or their blends. The formulation optionally includes, a second polymer component, cell-enlarging agents, and organic or inorganic flame retardant synergists.
BRIEF SUMMARY OF THE INVENTION
One aspect of the present invention is macrocellular acoustic foam comprising:
A) one or more homopolymers of ethylene, one or more C
3
-C
20
&agr;-olefin polymers, or a combination thereof;
B) one or more halogenated flame retardants;
C) optionally, one or more polymers other than that of Component A; and
D) optionally, one or more flame retardant synergists.
Another aspect of the present invention is a process for making macrocellular acoustic foam, such as those described below, comprising subjecting a foamable gel comprising at least one blowing agent and at least one polymeric resin composition to a die pressure greater than the prefoaming critical die pressure but less than or equal to four times that of said prefoaming critical die pressure.
Another aspect of this invention is macrocellular acoustic foams obtainable, or prepared, by the above process of this invention, particularly those comprising;
A) one or more homopolymers of ethylene, one or more C
3
-C
20
&agr;-olefin polymers, or a combination thereof;
B) one or more halogenated flame retardants;
C) optionally, one or more polymers other than that of Component A; and
D) optionally, one or more flame retardant synergists, as such or preferably in the form of an office partition, automotive decoupler, domestic appliance sound insulation, sound proofing panel or machine enclosure.
Another aspect of this invention is the method of using the above macrocellular acoustic foam as an acoustic absorption or acoustic insulation material, particularly in environments in which fire retardancy is required.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Also any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The term “flame retardant” is used herein to indicate a flame retardant which can be any halogen-containing compound or mixture of compounds which imparts flame resistance to the compositions of the present invention.
The term “flame retardant synergist” is used herein to indicate inorganic or organic compounds which enhance the effectiveness of flame-retardants, especially halogenated flame retardants.
The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
The term “macrocellular acoustic foam” is used herein to indicate a foam having an average cell size according to ASTM D3576 of from about 1.5 mm to about 15 mm, with cell sizes of from about 2 mm to about 10 mm being preferred, from about 3 mm to about 10 mm being more preferred, and from about 4 mm to about 8 mm being particularly preferred, and which, at a thickness of 35 mm, has an average sound absorption coefficient (measured via ASTM E-1050 at 250, 500, 1000 and 2000 Hz) of greater than about 0.15, preferably greater than about 0.20, more preferably greater than about 0.25, even more preferably greater than about 0.30.
The term “prefoaming critical die pressure” is best determined empirically by observation of the foaming process, and is defined herein as the minimum die pressure at which popping is heard at the die and the resulting foam takes on a rough surface caused by premature nucleation and expansion of the foam inside the die lip.
Preparation of Foams
Excellent teachings to processes for making ethylenic polymer foam structures and processing them can be found in C. P. Park. “Polyolefin Foam”, Chapter 9, Handbook of Polymer Foams and Technology, edited by D. Klempner and K. C. Frisch, Hanser Publishers, Munich, Vienna, New York, Barcelona (1991), which is incorporated here in by reference.
The present process for making the macrocellular foam involves for the most part a conventional extrusion foaming process. The foam is advantageously prepared by heating an ethylenic polymer material to form a plasticized or melt polymer material, incorporating therein a blowing agent to form a foamable gel, and extruding the gel through a die to form the foam product. Prior to mixing with the blowing agent, the polymer material is heated to a temperature at or above its glass transition temperature or melting point. The blowing agent is optionally incorporated or mixed into the melt polymer material by any means known in the art such as with an extruder, mixer, blender, or the like. The blowing agent is mixed with the melt polymer mater

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