Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-09-14
2001-11-13
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S070000, C525S079000, C525S085000, C525S086000
Reexamination Certificate
active
06316527
ABSTRACT:
BACKGROUND
The present invention relates to compositions containing a blend of a styrene-acrylonitrile resin (hereafter referred to as “SAN”) and certain modifiers which provides an improved balance of impact resistance and optical clarity to SAN alone. More specifically, the present invention concerns a resin blend containing a styrene-acrylonitrile resin having from 19 to 35 weight percent acrylonitrile (hereafter referred to as “AN”) and a modifier which contains a rubbery core, an intermediate hard stage, and a shell containing a hydroxyl group or another functional group which acts in a similar manner as the hydroxyl group.
SAN resins (e.g., copolymers derived from units of styrene and acrylonitrile monomers) exhibit various excellent properties such as resistance to temperature, chemicals, and burning and also exhibit clarity, moldability, and low cost compared to other transparent resins such as polycarbonate (“PC”) and polymethylmethacrylate (“PMMA”). However, SAN is currently underutilized as a transparent engineering resin compared to PC and PMMA primarily because it has low elongation at break values and poor impact performance. A SAN resin composition having improved elongation at break values and impact strength while maintaining good clarity would therefore provide a low-cost transparent engineering resin.
Many methods have been proposed to improve the elongation at break and impact strength of SAN resins. Various techniques wherein rubbery polymers or rubber-containing polymers are mixed with SAN have been developed to improve the impact resistance of SAN and thermoplastic materials. One attempt has been made to incorporate a butadiene-based rubbery component into SAN to improve its impact resistance to prepare the so-called acrylonitrile-butadiene-styrene (“ABS”) resins. Even when these methods are implemented, however, ABS resins are typically opaque due to the refractive index mismatch and relatively large domain sizes of the SAN and butadiene-rubber phases; typical commercial-grade SAN resins have refractive indices in the range of from 1.56 to 1.58 whereas the refractive index of polybutadiene is about 1.52.
Another attempt has been to blend in certain core-shell polymers comprising a core made of rubbery polymer and a shell, around the core, made of a glassy polymer are excellent agents for improvement of impact strength of SAN where clarity is not an object. However these methods usually involve incorporating by melt-blending some sort of rubbery component having a rather larger domain size and a relatively low (mismatched) refractive index which results in tougher, yet resin compositions which are still opaque. As an example are the addition of methacrylate-butadiene-styrene (“MBS”) modifiers, such as PARALOID® EXL-2600 (Rohm and Haas Company), which are known in the art as core-shell polymer particles containing a rubbery polymeric core based on polybutadiene and a hard polymeric shell derived from methyl methacrylate units. Unfortunately such MBS modifiers have refractive indices of about 1.54 and also form opaque blends with SAN resins.
When these prior art methods are used, the SAN resin composition generally exhibits poor clarity due to the refractive index mismatch with the modifier Even when these prior art core-shell modifiers are added to SAN resins and found to produce enhanced elongation at break values, the clarity of SAN resins is destroyed.
McKee et al., U.S. Pat. No. 4,393,164 teaches a transparent, impact-resistant thermoplastic molding material produced from SAN resin and MBS modifiers, but requires from 15 to 70 parts by weight of additional costly PMMA so that the refractive index difference between the MBS modifier and combination of SAN and PMMA is less than 0.005. Thus there is a need for low-cost core-shell modifiers that are compatible with SAN and which have a refractive index in the range of 1.56 to 1.58 so that there is no need to additionally blend in an additional resin such as PMMA to reduce the refractive index in order to prepare engineering resin blends having a good balance of toughness and clarity.
Carson et al., U.S. Pat. No. 5,321,056 teaches modifiers which produce transparent, high notched Izod impact strength blends with amorphous aromatic polyesters. Carson et al. reports that when low concentrations of certain hydroxyalkyl (meth)acrylates are copolymerized with aromatic vinyl monomers to form the shell of core-shell modifiers having RI's in the 1.55 to 1.58 range, very high notched Izod impact strengths are obtained with amorphous polyesters at 30% or lower modifier loadings, and preferably at from 5 to 20% loadings. Although Carson provides for significantly improved impact strength of clear, amorphous aromatic polyester, Carson does not teach or suggest that such modifiers are useful in transparent to translucent SAN resins.
The object of the present invention is to provide SAN blend compositions having improved toughness (impact strength and elongation at break) when they are processed into objects while retaining their clarity. Another object of the present invention is to provide a composition which will overcome the breakage problem when brittle SAN articles are ejected from injection molding equipment. A still further object is to provide transparent to translucent injection molded SAN articles.
STATEMENT OF INVENTION
In the present invention, the elongation at break value of SAN resins is increased substantially by the addition of small amounts of certain core-shell modifiers which disperse very readily in SAN resins. Additionally, the present invention provides a modified SAN resin composition having an improved balance of impact resistance and optical properties over previously known compositions. Specifically, the present invention provides a SAN resin composition which will overcome the breakage problem when brittle SAN articles are ejected from injection molding equipment. These and other objects as will become apparent from the following disclosure are achieved by the present invention.
The modified SAN resin composition of this invention is a blend of (I) at least one SAN resin and (II) at least one core-shell modifier having (A) a rubbery core such as a copolymer containing a diolefin, preferably a 1,3-diene, (B) an intermediate stage comprised mainly of a hard polymer such as a polymer containing a vinyl aromatic monomer, and (C) a shell comprised mainly of a vinyl aromatic monomer (such as styrene), and hydroxyalkyl (meth)acrylate or, in the alternative, another functional monomer which acts in a manner similar to the hydroxyalkyl (meth)acrylate).
The modified SAN resin composition of the present invention comprises:
(I) from 70 to 99 parts of at least one SAN resin having a refractive index of from 1.56 to 1.58; and
(II) from 1 to 30 parts of at least one core-shell modifier comprising
(A) from 15 to 85 parts of a core comprising
(1) from 40 to 60 percent by weight of units derived from at least one vinyl aromatic monomer,
(2) from 20 to 60 percent by weight of units derived from at least one 1,3-diene,
(3) up to 10 percent by weight of units derived from at least one copolymerizable vinyl or vinylidene monomer, and
(4) up to 5 percent by weight of units derived from at least one graft-linking or cross-linking monomer;
(B) from 10 to 50 parts of an intermediate stage comprising at least 25 percent by weight of units derived from at least one vinyl aromatic monomer; and
(C) from 5 to 35 parts of an outer shell comprising (1) from 2 to 40 percent by weight of units derived from at least one hydroxyalkyl (meth)acrylate,
(2) from 60 to 98 percent by weight of units derived from at least one vinyl aromatic monomer,
(3) up to 25 percent by weight in the shell of units derived from one or more copolymerizable vinyl or vinylidene monomer, and
(4) up to 5 percent by weight of units derived from at least one graft-linking or cross-linking monomer;
the at least one core-shell modifier having a refractive index in the range of from 1.56 to 1.58.
A further variation of the modified SAN resin compositi
Chiquet Yannick Jean Yvon
Meyer Jean-Philippe Gaëton
Trinchero Fabrizio
Mullis Jeffrey
Rohm and Haas Company
Rosedale Jeffrey H.
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