Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Reexamination Certificate
2001-01-17
2003-06-24
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
C264S051000, C264SDIG006
Reexamination Certificate
active
06582633
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparation of light weight objects comprising a step of calendering, extrusion, blow or injection moulding a resin of one or more of polypropylene, polystyrene and HD (high density) polyethylene and, admixed therein, thermally expandable microspheres.
BACKGROUND OF THE INVENTION
Many kinds of objects are produced by calendering, extrusion, blow or injection moulding polypropylene, polystyrene or HD polyethylene resins. However, it is difficult to produce light weight objects of high quality from high melting resins without losing mechanical strength or getting a bad surface finish or sink marks.
DE Patent Specification No. 19531631 discloses that thermoplastic foam can be produced by extrusion or injection moulding bulk plastics like HD polyethylene together with gas- or liquid filled microspheres expanding on heating. It is regarded as necessary to add 5-50 wt % of soft and/or low melting plastic or unvulcanised rubber before the extrusion, blow or injection moulding.
JP laid open patent application, Laid Open No. 1998-152575 discloses extrusion or injection moulding of thermoplastic resins mixed with thermoexpandable microspheres to obtain a foamed product.
However, working polypropylene, polystyrene or HD polyethylene according to the above described processes does generally not give satisfactory low density. Furthermore, discoloration is a serious problem, particularly when the objects are intended to be white.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved process for producing light weight objects by calendering, extrusion, blow or injection moulding polypropylene, polystyrene or HD polyethylene resins into which thermally expandable micro spheres have been admixed.
According to the invention it has surprisingly been found that objects of low density and with no or only minor discoloration can be obtained if the resin contains a certain kind of thermally expandable microspheres. Thus, the invention concerns a process for preparation of light weight objects comprising calendering, extrusion, blow or injection moulding a resin of polypropylene, polystyrene, HD polyethylene or copolymers thereof and, admixed therein, thermally expandable microspheres including a thermoplastic polymer shell encapsulating a propellant, at a temperature sufficient to result in expansion of the microspheres, wherein said polymer shell is made of a homo- or co-polymer from ethylenically unsaturated monomers comprising more than 80 wt %, suitably more than 85 wt %, preferably more than 92 wt %, most preferably more than 98 wt % of nitrile containing monomers, or possibly even substantially consisting of nitrile containing monomers. The propellant preferably 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.
It has been found possible to achieve good results even if the content of thermally expandable microspheres is comparatively low, for example from about 0.2 to about 20 wt %, preferably from about 0.5 to about 10 wt %, most preferably from about 1 to about 5 wt % of the resin.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Thermally expandable microspheres are known in the art and described in detail in, for example, U.S. Pat. No. 3,615,972, EP 466080, JP laid open patent application, Laid Open No. 87-286534, WO 99/46320 and WO 99/43758, which documents hereby are incorporated by reference. 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.
For the present invention it is, however, important that the thermoplastic polymer shell of the expandable microspheres comprises a sufficiently high amount of nitrile containing monomers. It is also highly favourable if the boiling point of the propellant is comparatively high.
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, fumarc 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, although it is most preferred to only use non halogen containing monomers. The softening temperature of the polymer shell, normally 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, triailyiformal 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.
Preferred propellants are selected from liquids or combination of liquids with a boiling point or boiling point range so a temperature exceeding 50° C. would be required to evaporate 50 wt % of the liquid at atmospheric pressure. Examples of such liquids are isooctane, 2,4-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, cyclohexane, heptane and isomers or combinations thereof. Liquids with lower boiling point may be included, but preferably only in combinations with one or more other liquids so the resulting boiling point or boiling point range becomes sufficiently high.
It is particularly favourable if the propellant preferably comprises isooctane, suitably in an amount of more than 50 wt %, preferably more than 55 wt %, more preferably more than about 60 wt % most preferably more than about 70 wt % of, or possibly even substantially consists of isooctane. The propellant may further comprise, preferably up to totally 50 wt %, of one or more o
Bjerke Odd
Elfving Klas
Kron Anna
Sjögren Peter
Akzo Nobel N.V.
Kuhns Allan R.
Serbin David J.
LandOfFree
Process for producing objects does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing objects, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing objects will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3127753