Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-04-25
2003-01-21
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...
C521S060000
Reexamination Certificate
active
06509384
ABSTRACT:
The present invention relates to expandable thermoplastic microspheres comprising a shell and a propellant entrapped therein, a method of their preparation, use of such microspheres as a foaming agent, expandable compositions comprising such microspheres, and articles comprising foamed material containing expanded microspheres.
Expandable thermoplastic microspheres comprising a thermoplastic polymer shell and a propellant entrapped therein are commercially available under the trademark Expancel™ and are used as a foaming agent in many different applications, such as in elastomers, thermoplastic elastomers, polymers, putty, underbody coating, plastisols, printing ink, paper, explosives and cable insulations. Microspheres and their production are also described in detail in, for example, U.S. Pat. No. 3,615,972, EP 486080 JP 87-286534, WO 99/46320 and WO 99/43758.
In such microspheres, the propellant is normally a liquid having a boiling temperature not higher than the softening temperature of the thermoplastic polymer shell. Upon heating, the propellant evaporates to increase the internal pressure at the same time as the shell softens, resulting in significant expansion of the microspheres, normally from about 2 to about 5 times their diameter. The temperature at which the expansion starts is called T
start
, while the temperature at which maximum expansion is reached is called T
max
. When T
max
is exceeded the propellant has been released through the polymer shell to such an extent that the microspheres start to collapse.
It is generally desirable to achieve as high degree of expansion of the microspheres as possible, preferably when included as a foaming agent in thermoplastics, rubber or thermoplastic elastomers. In many applications, for example when included in compositions to be worked at high temperature without risk for unintentional expansion, it is also desirable that T
start
is comparatively high. In many cases is it also advantageous with a high T
max
as the start of collapse of the microspheres during expansion then occurs later.
Thus, it is an object of the present invention to provide thermally expandable microspheres with high values for T
start
and T
max
, and high expansion capability at high temperatures.
It is another object of the invention to provide expandable compositions including thermally expandable microspheres, which compositions can be worked at a comparatively high temperature without unintentional expansion.
It is still another object of the invention to provide foamed materials containing expanded microspheres.
It has been found that these objects can be achieved by microspheres as defined in the appended claims.
More specifically, the invention concerns thermally expandable microspheres comprising a thermoplastic polymer shell and a propellant entrapped therein, wherein said polymer shell is made of a homo- or co-polymer from ethylenically unsaturated monomers comprising more than 85 wt %, preferably more than 92 wt %, more preferably more than 95 wt %, most preferably more than 98 wt % of nitrile containing monomers, or even substantially consisting of nitrile containing monomers, while said propellant comprises at least, suitably more than 50 wt %, preferably more than 55 wt %, more preferably more than about 60 wt % most preferably more than about 70 wt % of isooctane, or even substantially consists of isooctane. The term isooctane as used herein refers to 2,2,4-trimethyl pentane.
Preferably T
start
is within the range from about 80 to about 200° C., more preferably from about 115 to about 200° C., most preferably from about 130 to about 200° C., while T
max
preferably is higher than 190° C., most preferably higher than 200° C. Normally T
max
does not exceed 300° C. The microsphere bulk density after heating to 220° C. is preferably lower than 15 g/l, most preferably lower than 12 g/l.
The nitrile containing monomers used for the polymer shell are preferably mainly selected from one or more of acrylo nitrile, methacrylo nitrile, &agr;-chloroacrylo nitrile, &agr;-ethoxyacrylo nitrile, fumaro nitrile, croto nitrile, most preferably acrylo nitrile, methacrylo nitrile or a mixture thereof. If other ethylenically unsaturated monomers are present, preferably in an amount from 0 to about 5 wt %, most preferably from 0 to about 2 wt %, they are preferably selected from one or more of acrylic esters such as methylacrylate or ethyl acrylate, methacrylic esters such as methyl methacrylate, isobornyl methacrylate or ethyl methacrylate, vinyl chloride, vinylidene chloride, vinyl pyridine, vinyl esters such as vinyl acetate, styrenes such as styrene, halogenated styrenes or &agr;-methyl styrene, butadiene, isoprene, chloroprene. The softening temperature of the polymer shell, in most cases essentially corresponding to its glass transition temperature (T
g
), is preferably within the range from about 80 to about 200° C., more preferably from about 115 to about 200° C. most preferably from about 130 to about 200° C. Preferably the polymer shell constitutes from about 70 to about 90 wt %, most preferably from about 75 to about 85 wt % of the total microsphere.
It may sometimes be desirable that the monomers for the polymer shell also comprise crosslinking multifunctional monomers, such as one or more of divinyl benzene, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol hexa(meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, triallylformal tri(meth)acrylate, allyl methacrylate, trimethylol propane tri(meth)acrylate, trimethylol propane triacrylate, tributanediol di(meth)acrylate, PEG #200 di(meth)acrylate, PEG #400 di(meth)acrylate, PEG #600 di(meth)acrylate, 3-acryloyloxyglycol monoacrylate, triacryl formal or triallyl isocyanate. If present, such crosslinking monomers preferably constitutes from about 0.1 to about 1 wt %, most preferably from about 0.2 to about 0.5 wt % of the total amounts of monomers for the polymer shell.
The propellant may, apart from isooctane, comprise up to totally 50 wt % of one or more of butanes, pentanes, hexanes, heptanes, petroleum distillates or other liquids with a suitable boiling point or boiling point range. Particularly preferred hydrocarbons for use in combination with isooctane are isobutane, isopentane, n-pentane, n-hexane, petroleum ether and n-heptane. Suitably the propellant is liquid at room temperature and has a boiling point at atmospheric pressure below the softening point of the polymer shell. Preferably the boiling point at atmospheric pressure is within the range from about −20 to about 150° C., most preferably from about 20 to about 100° C. It is particularly preferred that the propellant has a boiling point or boiling point range so a temperature above 50° C., more preferably above 60° C., most preferably above 70° C., but preferably not higher than about 150° C., would be required to evaporate at least 50 wt %, preferably at least 80 wt % of the propellant at atmospheric pressure. Preferably the propellant constitutes from about 10 to about 30 wt %, most preferably from about 15 to about 25 wt % of the total microsphere.
Apart from the polymer shell and the propellant the microspheres may comprise further substances added during the production thereof, normally in an amount from about 1 to about 20 wt %, preferably from about 2 to about 10 wt %. Examples of such substances are solid suspending agents, such as one or more of silica, chalk, bentonite, starch, crosslinked polymers, methyl cellulose, gum agar, hydroxypropyl methylcellulose, carboxy methylcellulose, colloidal clays, and/or one or more salts, oxides or hydroxides of metals like Al, Ca, Mg, Ba, Fe, Zn, Ni and Mn, for example one or more of calc
Bjerke Odd
Kron Anna
Sjögren Peter
Akzo Nobel N.V.
Serbin David J.
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