Abstract:
A molding composition including a thermoplastic processable polyamide, an elastomer, and an epoxy having a plurality of epoxide groups.

Description:
This application is a continuation of application Ser. No. 07/463,779, filed Jan. 8, 1990, now abandoned, which is a continuation of application Ser. No. 219,996, filed Jul. 15, 1988, now abandoned. 
    
    
     The present invention is directed to impact-resistant and rigid polyamide compositions, more specifically such compositions which provide a high measure of rigidity and dimensional stability. 
     BACKGROUND OF THE INVENTION 
     Polyolefins have poor compatibility with a polyamide matrix. As a result, it is difficult to obtain blends which are both processable and practical and various expedients have been adopted in an attempt to solve this problem. 
     British Patent 998439 (German 1,241,606) teaches achieving high impact resistance by mixing two polyolefins into the rigid polyamides. In order to overcome the incompatibility problem, the olefins have unsaturated carboxylic acids grafted thereon. 
     Swiss Patent 649566 seeks to solve the same problem by introducing polyolefins based upon ethylene, propylene, and 1,4-hexadiene or 2,5-norbornadiene. These materials are activated by the introduction of α, β unsaturated dicarboxylic acids, anhydrides, or esters. Thus, the high bending E-modulus of the polyamide is modified by the unsaturated additives. Molded shapes prepared from such compositions have good impact and notched bar impact properties and high ductility. However, they are not sufficiently rigid, nor are they dimensionally stable. In other words, they have a great tendency to creep, which makes them unsuitable for many uses. 
     Another approach to the same problem is the introduction of core/shell polymers or grafted copolyolefins into rigid amorphous copolyamides. Such compositions are disclosed in U.S. Pat. Nos. 4,410,661 and 4,536,541. However, mixtures of the foregoing type exhibit substantial and undesirable shrinkage at elevated temperatures, even after only a short period of time. Therefore, shapes produced from such compositions are unsuitable for any use wherein exposure to elevated temperatures is involved. 
     A narrower improvement is shown in German 3,436,362, wherein rigid polyamides derived from terephthalic acid, isophthalic acid and alkanediamines form the basic material. To this is added copolymers of ethylene and/or acrylates to which carboxyl groups are grafted. 
     European Patent 27,198 teaches the addition of a core/shell polymer as a modifier of impact resistance. Acrylic acid derivatives are grafted onto a polybutadiene or butadiene/styrene core. This improves the impact resistance, but results in a substantial loss in stiffness. The patent teaches compensating for this loss by the addition of glass fibers. 
     U.S. Pat. No. 4,180,494 teaches the impact-resistance modifiers of the present invention, and German 3,339,000 teaches the use of similar core/shell polymers in conjunction with polyamides. However, molded shapes of this character are usually unsatisfactory, as they are not dimensionally stable. In particular, they tend to creep and to be highly susceptible to shrinkage under heat. 
     British Patent 1,069,176 seeks high thermal and dimensional stability for molded shapes by the addition of cross-linking diepoxides. 
     British 1,376,537 and German 2,144,687 introduce epoxide resins into plastomeric materials. These are substantially dimensionally stable and rigid; however, their impact-resistance is insufficient. Moreover, the presence of a high concentration of fillers and reinforcing agents produces a high density which, in many cases, is to be avoided. 
     Thus, there is a substantial need for polymeric materials which are impact-resistant, rigid, and dimensionally stable. In addition, such materials should be capable of simple injection molding. Such materials are used as casings and other protective parts in machines, vehicle bodies, etc. 
     BRIEF DESCRIPTION OF THE INVENTION 
     It is, therefore, desirable to provide molding compositions which are impact-resistant, rigid, dimensionally stable, without an excessive increase in density. Such products should have minimal creepage and shrinkage. 
     In accordance with the present invention, the foregoing requirements are met by the use of thermoplastic, processable polyamide compositions which contain an elastomer impact resistance modifier and an epoxide having more than one epoxide group. 
     In particular, it has been found that the combination of the epoxy compound and the impact resistance modifier in the polyamide produces a synergistic effect. The amount of modifier can be substantially reduced without impairing the desired impact properties. As a result, an improved relationship between resistance and rigidity can be obtained. Moreover, cost savings can also be realized. The shapes made from the foregoing materials are particularly stable and have minimal shrinkage when subjected to elevated temperatures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Polyamides which have been used as molding materials are generally useful in the present invention. 
     For example, specific mention is made of semicrystalline and amorphous copolyamides, e.g. those made from diamines and acidic monomers. Suitable diamines include hexamethylene diamine and its derivatives, mono and dicycloaliphatic diamines and derivatives thereof (especially of the alkylated bis(4-aminocyclohexyl)methane type) etc. The acids comprise isophthalic acid and terephthalic acid which may be substituted by other aromatic or aliphatic dicarboxylic acids. 
     Polyamide 6; polyamide 6,6; polyamide 6,10; polyamide 11; polyamide 12; and polyamide 6,12 have all been found to be suitable. Typical ether amides are reaction products of H 2  N--(R--O) n  R--NH 2  with dicarboxylic acids. The ether ester amides have ester linkages in addition to the --NH--CO-- linkages. The foregoing materials are preferably used in amounts of at least 40% by weight of the total molding composition. 
     The molding compositions preferably contain at least 3% by weight of the impact resistance modifying material, based upon the total molding composition. More preferably, 5 to 30% by weight is used and 10 to 20% by weight is most desirable. 
     Such modifiers include copolymers of α olefins which are activated by subsequent grafting with an unsaturated copolyolefin, preferably an α-unsaturated acid, and most preferably 1.0 mol % of an unsaturated dicarboxylic acid. This results in a maximum of 2.0 mol % carboxylic groups; ethylene is not more than 90 mol %, the rest preferably comprising propylene and/or 1-butene. Also, core/shell polymers are suitable. Preferably, these comprise a copolyolefin core which contains a butadiene or acrylate, and a shell of grafted vinyl compounds, e.g. acrylates. The metallic salts of the grafted copolymers (Ionomers) are not recommended because of the decrease in the number of adhesion sites. 
     Epoxy compounds suitable for use in the present invention are those which have at least two epoxy groups. Preferably, these are terminal, i.e. located at the ends of the molecule. Of special desirability are those epoxies having more than one glycidyl ether group in the molecule. They increase the molecular weight by linking the polyamide molecules. Very small amounts are sufficient; often an optimum can be found at less than 1% by weight, based on the total molding composition. It is preferred to use 0.05 to 5% and most preferred to use 0.1 to 1.0%, based on the molding composition. Polymeric epoxy compounds containing at least two epoxy groups or glycidyl groups in each molecule are also useful in the present invention. 
     Diglycidyl ethers having the formula Y--O--X--O--Y have been found especially advantageous. Y is an epoxide carrying radical and X is a divalent radical taken from the class consisting of alkyl having 2 to 10 carbons and aralkyl having 7 to 20 carbons. Those which are derivatives of neopentyl glycol and/or bisphenol A are deserving of particular mention. 
     Preparation of the compositions of the present invention is substantially conventional. The ingredients are premixed in the usual types of apparatus; such as, vibrating mixers, stirring mixers, mills, or phase mixers. Processing takes place in the melted form using screw machines such as extruders or plasticorders. These devices produce the compositions as granulates, strands, etc. which are then formed in injection molding machines or extruders in the usual manner. 
     Of course, normal additives, such as stabilizers, pigments, lubricants, emulsifiers, release agents, colorants, flame retardants, mineral or metallic fillers, reinforcing agents, etc. can all be included as needed. 
    
    
     EXAMPLES 
     The polyamide starting material was mixed sequentially with the impact resistance modifier and the epoxy compound. The combination was homogenized on a Werner Pfleiderer ZSK 30 two-phase extruder at 220° to 290° C. Thereupon, extrusion took place to yield a strand which was comminuted to form a uniform granulate. The granulate was dried under nitrogen at 80° to 90° C. and a vacuum of 30 to 50 mbar. Test bodies were then prepared using an Arburg extruder (type 320-210-250) and the various properties of the test bodies were measured. 
     The results are shown in Tables I to V herein. Some of the samples contain no epoxy and constitute comparisons with the prior art. The compositions set forth in Tables I to IV contain copolyolefin modifiers derived from ethylene, propylene, 1-butene modified with maleic acid anhydride. Table V displays the results of tests using the core/shell polymer. The melt viscosities are in Pas at 270° C. and 122.6N. 
     The impact and notch resistances were measured according to DIN 53453 dry at 23° C. No break is indicated by nb. The bending E modulus and the limit bending stress were determined in accordance with DIN Norm 53452 and the shrinkage values in the longitudinal direction are in accordance with DIN tension bars 53445/3. They were measured after storage for 24 hours in a circulating air oven at 100° C. and, in another test, for 1 hour at 140° C. The shrinkage values were determined for DIN tension bars 53445/3 after dry storage for 24 hours after injection molding. The values are given in percentages. 
     In Tables I, V and VI, polyamide 6 (melting point 221° C.) was used. In Table II, an amorphous polyamide which is the reaction product of hexamethylenediamine and isophthalic acid was the starting material. It had a glass transition temperature of 140° C. 
     Table III shows the results of the use of Grilamid TR 55 (T g  155° C.) which is also described in U.S. Pat. No. 4,356,300. Table IV describes the use of polyamide 12 having a melting point of 178° C. All the foregoing polyamides are commercial products of EMS-Chemie AG of Domat/Ems, Switzerland. 
     The preferred epoxy compound of Tables I to V is neopentyl diglycidyl ether, also known as 2,2&#39;-(2,2-dimethyl-1,3-propanediyl)-bis(oxymethylene)bisoxirane. In Table II, test (1), 1,4-butanediglycidyl ether was used. Table VI shows the use of the diglycidyl ether derived from bisphenol A. G1302, a product of EMS-Chemie AG, has a molecular weight of 385. 
     
                                           TABLE I__________________________________________________________________________Polyamide 6 - moulding materials with impact-resistance-modifier derivedfrom dicarboxylic acids-grafted copolyolefines__________________________________________________________________________                     5    6    7     2         4     Impact                          Notch                               Bending     Impact-          3    Melt  Resis-                          Impact                               E Modu-1    Resis-          Digly-               Viscos-                     tance                          Resist                               lus0    Poly-     tance          cidyl               ity   23° C./                          23° C./                               23° C./Test amid-     modifier          ether               (270°/                     dry  dry  dryNo.  wt. %     wt. %          wt. %               122.6N)                     kJ/m2                          kJ/m2                               N/mm2__________________________________________________________________________(a)  PA 6  0   0     350  nb    6.0 2000A28  100pure(b)  PA 6  0   0.4  `403  nb    4.1 2645E 500699.6(c)  PA 6 15   --    578  nb   35.4 1203E 517985(d)  PA 6 15   0.2  1363  nb   38.1 1950E 517884.8(e)  PA 6 15   0.4  1342  nb   44.7 1940E 500584.6(f)  PA 6 15   0.5  1032  nb   53.3 1870E 548784.5(g)  PA 6 12   0.5  1177  nb   32   2160E 518087.5(h)  PA 6 10   1.0  6071  nb   39   1243E 491389.0(i)  PA 6 10   3.0  &gt;10000                     nb   69.5 2625E 479687.0(k)  PA 6 20   0.4   681  nb   14.3 1667E 500773.6                      (-40°)                          50.4(e)  75   20   5.0  &gt;10000                     nb   nb   2045E 4575(l)  77.7   19.4          2.9  2065  nb   66.6 2039E 4574                    nb   30.6(E 3752)                  (-20°)                          (-20°)(m)  80   20   --    136  nb   42   1517A 28NZ__________________________________________________________________________         10        128    9   Elon-             11    Exten-Limit     Yield         gation             Tensile                   sion                       13     140    Bending     Stress         at  Strength                   at  Shrinkage                              ShrinkageTest Stress     23° C./         Yield             23° C./dry                   Break                       after  afterNo.  N/mm2     dry %   N/mm2 %   24 h/100° C.                              1 h/140° C.__________________________________________________________________________(a)  100  85  10  55     10 -0.36  -0.75A28pure(b)  109  --  --  --    --  -0.22  -0.32E 5006(c)  84     57.3         7.0 42      17.2                       -0.38  -0.47E 5179(d)  83     56.3         7.8   65.3                   264 -0.30  -0.36E 5178(e)  79.6 --  --  --    --  -0.28  -0.35E 5005(f)  80   --  --  --    --  --     --E 5487(g)  90   42  7.3   53.3                   144 -0.16  -0.33E 5180(h)  91.3 --  --  --    --  --     --E 4913(i)  104  --  --  --    --  --     --E 4796(k)  68.6                   -0.28  -0.40E 5007(e)  77.7 --  --  --    --  --     --E 4575(l)  79.6 --  --  --    --  --     --E 4574(E 3752)(m)  62   45  5   50    150 -0.47  -0.58A 28NZ__________________________________________________________________________ 
    
     
                                           TABLE II__________________________________________________________________________Amorphous copolyamide (type XE 3038) derived from hexamethylenediamine/isophthalicacid with impact-resistance-modifier (impact-resistance-modifier as inTable I)__________________________________________________________________________                   5    6   7     2        4    Impact                        Notch                            Bending     Impact-          3   Melt Resis-                        Impact                            E Modu-                                 8 1   Resis-          Digly-              Viscos-                   tance                        Resist                            lus  Limit0     Poly-     tance          cidyl              ity  23° C./                        23° C./                            23° C./                                 BendingTest  amid-     modifier          ether              (270°/                   dry  dry dry  StressNo.   wt. %     wt. %          wt. %              122.6N)                   kJ/m2                        kJ/m2                            N/mm2                                 N/mm2__________________________________________________________________________(a) A2771 100  0   0   1755 40% nb                         1.5                            2960 166XE 3038                 60% 60(b)   99.7      0   0.3 2643 40% nb                         1.6                            3120 125E 6248                  60% 58(c)   86.8     13   0.2 2643 nb   47.0                            2350 114E 6248(d) E4471 85  15   --  --   nb   38  1991   100.3E 6603(e)   84.8     15   0.2 2994 nb   51.3                            2238 110E 5864(f)   84.7     15   0.3 3407 nb   49.2                            2241 112E 5864(g)   84.6     15   0.4 4440 nb   49.9                            2288 114E 5866(h)   80  20   --  4027 nb   42.2                            1880  93E 5275(i)   79.9     20   0.1 4801 nb   43.6                            1920  92E 6753(k)   79.8     20   0.2 --   nb   45.6                            2110 102E 6601(l)   84.7     15   0.3 4130 nb   47.1                            2299 114E 5867__________________________________________________________________________                   13     14     10        12  Longi- Longi-                                15 9   Elon-         11    Exten-                   tudinal                          tudinal                                % Yield     gation         Tensile               sion                   Shrink-                          Shrink-                                Injection0     Stress     at  Strength               at  age    age   ShrinkageTest  23° C./     Yield         23° C./dry               Break                   after  after afterNo.   dry %   N/mm2 %   24 h/100° C.                          1 h/140° C.                                24 h__________________________________________________________________________(a) A2771 110  10.5         70    62  0.0132  -0.332                                +0.218XE 3038(b)   --  --  --    --  -0.33  -1.1E 6248(c)   73  8   55    25  -0.05   -0.54E 6248(d) E4471 --  --  --    --  +.17   -2.0-4.0E 6603(e)   68  9   55    46  -0.092 -3.8E 5864(f)   70  7   57    61  -0.07  -3.1  +0.315E 5864(g)   70  7   54    25  -0.03  -2.6E 5866(h)   65  7   56    65  +0.188 -5.0-8.0                                -0.5-0.E 5275(i)   --  --  --    --  +0.02  -3.9  +0.374E 6753(k)   67    6.5         56     8  -0.071  -2.36E 6601(l)   70    8.5         53    18  -0.04  -3.6E 5867__________________________________________________________________________ 
    
     
                                           TABLE III__________________________________________________________________________Amorphous Copolyamide TR55 (impact-resistance-modifier as in Table__________________________________________________________________________I)                   5    6   7     2        4    Impact                        Notch                            Bending     Impact-          3   Melt Resis-                        Impact                            E Modu-                                 8 1   Resis-          Digly-              Viscos-                   tance                        Resist                            lus  Limit0     Poly-     tance          cidyl              ity  23° C./                        23° C./                            23° C./                                 BendingTest  amid-     modifier          ether              (270°/                   dry  dry dry  StressNo.   wt. %     wt. %          wt. %              122.6N)                   kJ/m2                        kJ/m2                            N/mm2                                 N/mm2__________________________________________________________________________(a)   100  0   0   1200-1500                   nb    5.0                            2100 118TR55(b) E5428 99.7      0   0.3 2189 nb    5.26                            2160 --E5716 99.7      0   0.3 1241 nb    5.09                            2080 119(c)   99.6      0   0.4 1446 nb    5.03                            2190 --E 5482(d)   90  10   --  1516 nb   21.9                            1730 101F3-55(e)   89.7     10   0.3 3511 nb   23.8                            1860 98E 6180(f)   85  15   --  1454 nb   30.9                            1737 89F3-56(g)   84.6     15   0.4 2601 nb   34.9                            1780 88E 5255(h)   80  20   --  1755 nb   37.7                            1504 77F3-57(i)   79.6     20   0.4 2815 nb   40.2                            1800 95E 7287__________________________________________________________________________                   13     14     10        12  Longi- Longi-                                15 9   Elon-         11    Exten-                   tudinal                          tudinal                                % Yield     gation         Tensile               sion                   Shrink-                          Shrink-                                Injection0     Stress     at  Strength               at  age    age   ShrinkageTest  23° C./     Yield         23° C./dry               Break                   after  after afterNo.   dry %   N/mm2 %   24 h/100° C.                          1 h/140° C.                                24 h__________________________________________________________________________(a)   75   8  60    30  -0.07  -0.09 0.8-1.0TR55(b) E5428 --  --  --    --  --     --E5716 80  11  55    24(c)   --  --  --    --  -0.16  0.4E 5482(d)   64  20  54    33  -0.30  -1.3  -0.5F3-55(e)   64  10  50    50  -0.08  -0.36 -0.36E 6180(f)     50.7     21  48    36  -0.50  -1.2  -0.53F3-56(g)   60  10  52    82  -0.23  - 0.98E 5255(h)   21  22  44    36  -0.58  -2.6  -0.69F3-57(i)   68  18  57    28   -0.073                          -0.24 -0.40E 7287__________________________________________________________________________ 
    
     
                                           TABLE IV__________________________________________________________________________Polyamide 12 with impact-resistance-modifier (impact-resistance-modifieras in Table I)__________________________________________________________________________                     5    6    7     2         4     Impact                          Notch                               Bending     Impact-          3    Melt  Resis-                          Impact                               E Modu-1    Resis-          Digly-               Viscos-                     tance                          Resist                               lus0    Poly-     tance          cidyl               ity   23° C./                          23° C./                               23° C./Test amid-     modifier          ether               (270°/                     dry  dry  dryNo.  wt. %     wt. %          wt. %               122.6N)                     kJ/m2                          kJ/m2                               N/mm2__________________________________________________________________________Gril-100  --   --         nb   14.4 1256amid(a) L25(b)   99.75     --    0.25               1853  nb   15.6 1420E6413(c)  99.6 --   0.4  --    nb   23.2 1680E5254(d)  91.7  8   0.3  3698  nb   72.8 1350E6424(e)  89.7 10   0.3  3089  nb   65.3 1290E6423(f)  86.0 10   4.0  &gt;10000                     nb   nb   2243E3535(g)  90   10   --    320  nb   nb    380E3536__________________________________________________________________________                        13     14        10        12    Longi- Longi-    8    9   Elon-            11    Exten-                        tudinal                               tudinal    Limit    Yield        gation            Tensile                  sion  Shrink-                               Shrink-0   Bending    Stress        at  Strength                  at    age    ageTest    Stress    23° C./        Yield            23° C./dry                  Break after  afterNo. N/mm2    dry %   N/mm2 %     24 h/100° C.                               1 h/140° C.__________________________________________________________________________Gril-    64   44  9   47    178   +0.25  +0.9amid(a) L25(b) 65   45  7   44    126   +0.20   +0.82E6413(c) 72   50  7   60    153   +0.13  +0.5E5254(d) 60   40  8   44    120   -0.14  +0.8E6424(e) 57   38  10  46    140   -0.24  -0.6E6423(f) 122  --  --  --    --    --     --E3535(g) 58   38  23  42    280   -0.36   +1.15E3536__________________________________________________________________________ 
    
     
                                           TABLE V__________________________________________________________________________Polyamide 6 with impact-resistance-modifier derived from core-sheathpolymers__________________________________________________________________________                    5    6     7     2         4    Impact                         Notch Bending     Impact-          3    Melt Resis-                         Impact                               E Modu-1    Resis-          Digly-               Viscos-                    tance                         Resist                               lus0    Poly-     tance          cidyl               ity  23° C./                         23° C./                               23° C./Test amid-     modifier          ether               (270°/                    dry  dry   dryNo.  wt. %     wt. %          wt. %               122.6N)                    kJ/m2                         kJ/m2 N/mm2__________________________________________________________________________(a)  100  --   --   350  nb    4.0  2000A28 pure(b)  91.6  8   0.4  372  nb    7.3  2570E 5253(c)  89.6 10   0.4  454  nb   14.4  2360E 5004(d)  84.6 15   0.5  --   nb   18.5  2380E 5223(e)  75   25   --   434  nb   38    1572A28 NT(f)  74.6 25   0.4  2394 nb   60% nb                               1698E 5008                        40% 50(h)  72   25   3.0  5369 nb   42.8  2005E 4572(i)  70   25   5.0  --   nb   nb    1974E 5473__________________________________________________________________________                       13     14         10        12  Longi- Longi-8    9   Elon-             11    Exten-                       tudinal                              tudinalLimit     Yield         gation             Tensile                   sion                       Shrink-                              Shrink-0    Bending     Stress         at  Strength                   at  age    ageTest Stress     23° C./         Yield             23° C./dry                   Break                       after  afterNo.  N/mm2     dry %   N/mm2 %   24 h/100° C.                              1 h/140° C.__________________________________________________________________________(a)  100  83  10  55    30  -0.36  -0.75A28 pure(b)  106  73  7   54    10  -0.28  -0.48E 5253(c)  97 ` --  --  --    --  -0.40  -0.50E 5004(d)  91   63  7   51    123 -0.42  -0.34E 5223(e)  66.2 45  5   40    110 -0.65  -0.57A28 NT(f)  69.6 --  --  --    --  -0.48  -0.39E 5008(h)  78.5 --  --  --    --  --     --E 4572(i)  76.8 --  --  --    --  --     --E 5473__________________________________________________________________________ 
    
     
                                           TABLE VI__________________________________________________________________________Polyamide 6 with impact-resistance-modifier (C elastomeric copolyolefinetype) and diglycidyl ether              4    5    6     2        Melt Impact                        Notch                             7              10        12     Impact-          3   Viscos-                   Resis-                        Impact                             Bending                                  8    9    Elon-                                                 11   Exten-1    Resis-          Digly-              ity  tance                        Resist                             E Modu-                                  Limit                                       Yield                                            gation                                                 Tensile                                                      sion0    Poly-     tance          cidyl              (270°/                   23° C./                        23° C./                             lus  Bending                                       Stress                                            at   Strength                                                      atTest amid-     modifier          ether              122.6N)                   dry  dry  23° C./                                  Stress                                       23° C./                                            Yield                                                 23° C./dry                                                      BreakNo.  wt. %     wt. %          wt. %              kJ/m2                   kJ/m2                        N/mm2                             dry  N/mm2                                       dry  %    N/mm2                                                      %__________________________________________________________________________A28NZ80%  20   --  136  nb   42   1517 62   45   5    50   150E771684.2%     15   0.8%              814  nb   44.4 1951 78   56   6    62   150          G1302E771879.2%     20   0.8%              2808 nb   53.8 1760 69   48   7    51   135          G1302__________________________________________________________________________