Impact resistant blend of polybutylene terephthalate resin and OSA graft copolymer

Blend of polybutylene terephthalate resin and a graft copolymer of styrene and acrylonitrile on olefin copolymer rubber (e.g., EPDM) has high impact strength, provided the blend contains at least 25% of the graft.

This invention relates to an impact resistant blend of polybutylene 
terephthalate (PBT) resin and a graft copolymer of styrene and 
acrylonitrile on olefin copolymer rubber (OSA). 
My copending application (Ser. No. 423,397, filed Sept. 24, 1982, discloses 
high impact three-component blends of (a) polyester resin, (b) 
polycarbonate resin, and (c) graft copolymer of EPDM type rubber with at 
least one polar monomer. The present invention is based on the discovery 
that certain two-component blends consisting essentially of polybutylene 
terephthalate resin and olefin copolymer graft provide high impact 
strength along with other desirable properties in an economical manner.

U.S. Pat. No. 3,919,353, Castelnuovo et al., Nov. 11, 1975, discloses 
impact resistant blends of polyester and rubber-resin graft copolymers. 
EPDM grafted with common ethylenically unsaturated monomers is disclosed 
although polybutadiene is the preferred elastomer and all examples use MBS 
(polybutadiene grafted with styrene-methyl methacrylate). The elastomer is 
crosslinked. Twenty-two out of twenty-three examples employ polyethylene 
terephthalate (PET, which is outside the scope of this invention.) In the 
example (No. 23) employing polybutylene terephthalate (PBT) the notched 
impact is only 2.8 ft-lb/in (15 kg-cm/cm). The modifier level (i.e., the 
grafted elastomer) is 3-30%. 
U.S. Pat. No. 4,260,690, Binsack et al., Apr. 7, 1981, discloses a blend of 
polyester and melt-polymerized rubber-resin graft, including 
ethylene/propylene rubber grafted with various monomers. Binsack et al do 
not distinguish among the various graft monomers that are shown, and the 
notched impact strengths of the blends given in the examples are 
relatively low (3.0-4.5 kJ/m.sup.2 =0.7-1.1 ft-lb/in). These materials 
have notched impacts at best only slightly higher than that of unmodified 
PBT (0.6 ft-lb) and clearly point away from the very high impact obtained 
in the present invention with styrene-acrylonitrile graft. Binsack et al 
discloses 1-30% grafted monomers in the modifier and up to 40% total 
modifier (graft copolymer) in the final blend. The present invention, in 
contrast, is directed to the use of 35-60% styrene-acrylonitrile in the 
graft and 25-55% modifier (graft) level in the final blend. 
U.S. Pat. No. 4,172,859, Epstein, Oct. 30, 1979, discloses blends of 
polybutylene terephthalate, polycarbonate resin and an impact modifier. 
The impact modifier comprises various monomers, combinations of which can 
include EPDM. 
Various other blends based on polyester resin, polycarbonate resin, or 
graft copolymer rubber-resin materials have also been proposed (e.g., U.S. 
Pat. Nos. 3,591,659; 4,022,748; 4,034,013; 4,034,016; 4,044,073; 
4,096,202; 4,257,937; and 4,280,949). 
In accordance with the present invention high impact blends are prepared by 
mixing polybutylene terephthalate resin with 25% or more of an olefin 
rubber graft copolymer. Addition of less than 25% graft affords no 
significant impact improvement. 
In my previously mentioned copending application Ser. No. 423,397, directed 
to high impact blends of polybutylene terephthalate, polycarbonate, and 
grafted EPDM, high impact is achieved at lower elastomer (EPDM graft) 
levels than in the present two-component blends. Comparing the two 
systems, high impact two-component blends of the invention tend to be 
somewhat softer but nevertheless have a highly useful balance of 
properties and are remarkably economical. 
The polybutylene terephthalate component of the blend of the invention is 
thermoplastic resinous poly(1,4-butylene terephthalate) and is described 
for example in U.S. Pat. Nos. 2,465,319; 3,047,539; 4,257,937 and 
4,280,949. 
The graft copolymer component of the composition of the invention is termed 
OSA and is based on an olefin copolymer rubber spine, usually a copolymer 
of ethylene and propylene (EPR), whether a binary copolymer containing 
only ethylene and propylene (saturated EPM) or a copolymer of ethylene and 
propylene and another monomer, as in such unsaturated terpolymers as 
ethylene-propylene-non-conjugated diene terpolymers (EPDM, wherein 
ethylidene norbornene, dicyclopentadiene and hexadiene are examples of the 
third monomer), or terpolymers containing other monomers such as phenyl 
norbornene. 
The graft copolymer is made by graft copolymerizing styrene and 
acrylonitrile on the olefin copolymer rubber spine in accordance with 
conventional practice as described for example in U.S. Pat. No. 4,202,948, 
Peascoe, May 13, 1980, or by the extrusion mass grafting method described 
in application Ser. No. 441,122 of Paul D. Andersen, filed Nov. 12, 1982. 
For purposes of the invention the amount of styrene and acrylonitrile in 
the graft copolymer ranges from 35 to 60% by weight, based on the total 
weight of monomers plus rubber spine. The ratio of styrene to 
acrylonitrile may range from 90:10 to 60:40, by weight. 
It will be understood that in practice the product of the graft 
copolymerization process is actually a mixture of true graft of resin on 
rubber along with a certain amount of separate, ungrafted resin (that is, 
the grafting efficiency is not 100%). If desired, additional separately 
prepared styrene-acrylonitrile resin may be added to the graft copolymer 
composition. 
To prepare the blends of the invention the polybutylene terephthalate resin 
and the graft copolymer are mixed together at elevated temperature in 
conventional plastics mixing equipment, such as a twin screw 
extruder-mixer. 
One desirable mixing procedure is a two-step compounding process involving 
first working the graft copolymer without the polybutylene terephthalate, 
under shearing and fluxing conditions, for example in a twin screw 
extruder-mixer. This disperses the olefin copolymer rubber within the 
resin contained in the graft copolymer composition, to form an "inverted" 
composition in which the olefin copolymer rubber is the discontinuous 
phase. The second step involves fluxing the inverted graft component with 
the polybutylene terephthalate component under lower shear conditions, for 
example in a single screw extruder. 
In commercial practice the foregoing two steps can be combined in one 
extrusion operation, using an extruder having a first and second feed 
port. A section of the extruder downstream of the first feedport can be 
used to shear (invert) the graft copolymer and a section downstream of the 
second feedport can be used to mix the graft with the polybutylene 
terephthalate. 
The inverted graft composition may also be pelletized and tumble blended 
with polybutylene terephthalate pellets to form a physical mixture which 
can be fed into an injection molding machine or an extruder. In this case 
the plasticizing screw of the injection or extrusion machine can perform 
the second stage of the mixing during fabrication. 
The table below shows the composition and properties of a number of blends 
of the invention. For comparison, a number of blends outside the scope of 
the invention are also shown. Composition 1 is a control containing no 
graft copolymer. Blends 2-6 use a graft copolymer of styrene and 
acrylonitrile on EPDM as the modifier; of these only blends 4, 5 and 6, 
containing 30% or more of modifier, come within the invention. Blends 2 
and 3, containing smaller amounts of graft copolymer, have poor impact 
strength and are outside the invention. Comparison blends 7-11 contain a 
graft copolymer of styrene and methyl methacrylate on EPDM; all of these 
fail to achieve high impact strength regardless of the level of modifier. 
Likewise, comparison blends 12-15 containing a graft copolymer of methyl 
methacrylate on EPDM have poor impact strength at all graft levels tested. 
The graft copolymer used in blends 2-6 is a graft of 50 parts of 
styrene-acrylonitrile (72:28 ratio) on 50 parts of an EPDM based on 
ethylidene norbornene; E/P ratio 60/40; iodine number 20; ML-4 68 at 
125.degree. C. 
The graft copolymer used in blends 7-11 is a graft of 50 parts of 
styrene-methyl methacrylate (50:50 ratio) on 50 parts of the same EPDM as 
previously described. 
The graft copolymer used in blends 12-15 is a graft of 50 parts of methyl 
methacrylate on 50 parts of the same EPDM. 
The table indicates the amounts, in parts by weight, of the various grafts 
and of polybutylene terephthalate resin (PBT), which is a commercial 
material (Valox 310; trademark), employed in making the blends, which were 
mixed in accordance with the two-stage procedure described above. The 
grafts were first fluxed in a 53 mm Werner and Pfleiderer twin-screw 
extruder mixer equipped with a strand die and pelletizer. The pelletized 
grafts were the fluxed with the PBT in a one inch single screw extruder. 
Specimens for mechanical property testing were cut from 1/8 inch injection 
molded plaques. 
In the table, NIRT indicates the notched Izod impact strength in foot 
pounds per inch of notch, at room temperature. NI -20.degree. F. incidates 
the notched Izod impact strength at -20.degree. F. Rockwell-R indicates 
the hardness. 
The data in the table indicate that the styrene-acrylonitrile graft (S/ACN) 
is specific in producing very high impact strength in blends where PBT is 
the only other component. The other EPDM grafts, namely styrene/methyl 
methacrylate (S/MMA) and methyl methacrylate (MMA) are effective (in the 
absence of a polycarbonate resin). 
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IMT MODIFIED PBT 
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 
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GRAFT 
S/ACN 10 20 30 40 50 
S/MMA 10 20 30 40 50 
MMA 20 30 40 50 
PBT 100 
90 80 70 60 50 90 80 70 60 50 80 70 60 50 
NIRT 0.6 
1.3 
1.9 
16.7 
19.3 
19.2 
0.9 
0.9 
1.2 
1.3 
1.4 
1.0 
1.2 
1.5 
2.3 
NI -20.degree. F. 
0.4 
0.7 
0.8 
1.0 
1.6 
1.7 
0.5 
0.7 
0.6 
0.7 
0.7 
0.7 
0.7 
0.6 
0.8 
Rockwell-R 
119 
113 
108 
96 87 70 116 
107 
93 78 63 108 
95 84 69 
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