GB2262939A

GB2262939A - Thermoplastic compositions

Info

Publication number: GB2262939A
Application number: GB9127153A
Authority: GB
Inventors: Loon Achiel Josephus Maria Van; Ilse Lydia Marcella Simo Meyer
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1991-12-20
Filing date: 1991-12-20
Publication date: 1993-07-07
Also published as: GB9127153D0

Abstract

A thermoplastic composition comprises a reaction product of (a) an acid group containing polymer derived from at least ethylene and at least 10 wt% of a copolymerisable acid group containing comonomer; and (b) an amorphous polyamide having an amino number of less than 70 and substantially one neutralisable amine group per molecule. The composition provides a combination of adhesive, impact resistance, and thermoplastic behaviour appropriate for metal hot melt coating applications. The comonomer is preferably acrylic or methacrylic acid. The polyamide preferably has a ring and ball softening point of 110 DEG C to 170 DEG C and is suitably derived from a difunctional primary amino and a dimeric acid. The composition may be prepared by high shear blending and extruding at a temperature of at least 180 DEG C, so as to condense the polyamide onto the acid group containing polymer.

Description

THERMOPLASTIC COMPOSITIONS Field of invention The invention relates to thermoplastic compositions. The invention relates particularly but not exclusively to melt coating composition for metal surfaces to provide an anti-corrosive or anti-impact damage effect for use for example as car body undercoating.

Background of invention Numerous prior art documents show adhesive mixtures derived at least in part from an acid group containing copolymer and a polyamide (See : DE 2741928 Allied Chemical ; GB 2075991 Raychem ; JP-57123274 Toyo Ink ; JP-01085754-A Ube Industries US 4517340 Raychem ; WO-8600631 Dow ; JP-61296079-A Ube Industries ; EP 212085 Allied Corp ; JP-63115736-A Kishimoto).

Some prior art documents suggest for such compositions the use of polyamide derived from naturally occurring carboxylic acids of non-linear structure (See : JP 51047927 Nippon Paint JP 55090575 Toyo Ink ; JP 01289886-A Ueno.

US 4018733 Raychem discloses a hot melt composition with an acid group containing polymer and a polyamide having an amine number of 70 to 400. High amine numbers indicate reactive polyamides which tend to cross-link. The polyamide is present in an amount of at least 40 wt %. To obtain the desired adhesive properties at least 3 parts of tackifier are used per 100 parts of acid polymer and polyamide combined.

The mixture is complex and is a blend ; the mixture is prone to processing difficulties if overheated and perhaps defensive in low temperature characteristics.

JP 61002781-A Sumitomo Electrical uses at least 30 wt % of a polyamide of low amine content (0.5 to 15 amine value) in combination with less than 30 wt % of an acid group containing polymer and as an essential component from 5 to 30 wt % of a block copolymer. The polyamide is the reaction product of a dimer acid and a diamine component.

WO-8700190-A Minnesota Mining and Manufacturing Co. discloses a thermosetting i.e. crosslinking adhesive for use in sealing. The polyamide has an amine number above 70. About 95 to 80 wt % of the composition remains crosslinked; less than 40 wt % is the acid group containing polymer.

It is amongst the objects of the invention to provide a thermoplastic composition derived at least in part of an acid group containing polymer and a polyamide which has an improved balance of processability (i.e. low viscosity when molten) ; thermal stability ; adhesion and low temperature stress resistance.

Summary of Invention The invention provides a thermoplastic composition including a reaction product of (a) an acid group containing polymer derived from at least in part ethylene and at least 10 wt% of a copolymerisable acid group containing comonomer ; and (b) an amorphous polyamide having an amine number of less than 70 and substantially one neutralisable amine group per molecule.

Preferably the amount of (a) is at least 60 wt % of (a) + (b). Preferably the overall composition having a Brookfield (at 190 0C) viscosity of less than 30 Pa.s.

Suitably (a) + (b) forms a predominant amount of the composition, preferably at least 80 wt%.

The product is basically an acid group containing polymer modified by condensing a minor proportion of polyamide to provide a readily processed, resilient and high temperature (over 1000 C) resistant material. The low viscosity variants provide processability for coating, spraying or extrusion.

The condensed product can be stored in a heated condition without appreciable cross-linking.

Preferably the comonomer is acrylic acid (AA) or methacrylic acid (MAA) and optionally units derived from a copolymerisable ethylenically unsaturated ester are present in the polymer ; the acid group containing polymer has a Brookfield viscosity (190 0C) of from 5 to 20 Pa.s suitably less than 15; the amorphous polyamide has an amine number of less than 30 especially less than 20 and optionally an acid number of from 1 to 10. Suitably the overall compound has a Brookfield viscosity (190 C) of less than 30 Pa.s preferably less than 20 Pa.s. The proportion of (a) based on (a) + (b) is preferably at least 70 wt %, especially at least 80 wt %.

At least 5 wt %, preferably at least 10 wt % of the polyamide is used.

Typical acid group containing polymers include EAA, EMAA and terpolymers such as E-VA-AA and E-MA-AA.

Suitably, the composition is substantially free of solvents contains less than 3 wt % of tackifier ; and/or contains less than 5 wt % of an elastomer component such as rubber.

Advantageously, the amorphous polyamide is derived has a ring and ball softening point of from 110 to 1600C, has a linear structure and a molecular weight between 5 to 10 000 g/mole.

It is difunctional primary amine and an dimeric acid.

Typical amorphous polyamides may include products selected from the Euremelt range (Registered Trade Mark) produced by Schering A.G. and Macromelt (Registered Trade Mark) produced by Henkel A.G.

In a coated form the composition may provide improved characteristics as defined herein such as a cold bend temperature of -40 C and an acceptable vertical flow after 24 hours at 1400C.

The composition can be made on conventional high shear mixing equipment.

A stay at over 200"C for a controlled period helps to ensure completion of the condensation reaction. The reaction can be accompanied by controlled de-watering to ensure completion of condensation. If kept at such an elevated temperature for too long the composition can lose water by intra-molecular reaction and lose adhesion in the process.

The product can be pelletized under water.

Articles may be made of metal having adhered thereto a coating of a composition having a thickness of from 25 to 2500 micron meter.

The composition may be melted and sprayed, extruded or coated.

Examples An ethylene acrylic acid copolymer, obtainable from Exxon (EX 194), containing 12.5 wt % of acrylic acid and having a Brookfield viscosity at 190 0C of 6.3 Pa s and an amorphous polyamide, obtainable from Schering Euremelt 2145, having an amine- and acid number typically around 7, a Brookfield viscosity at 1900C of 8.5 Pa s and a softening point between 135 and 1450C were mixed. A slightly yellow, transparent product with a Brookfield viscosity of 8.2 Pa s (1900C) and an acid- and amine number of 79 and 0.13 respectively, resulted.

These two components were mixed in a twin-screw co-rotating extruder ZSK-25 from Werner and Pfleiderer at a throughput level of 7 kg/h, a screwspeed of 180 revolutions/min with a barrel temperature in the reaction zone of 210 0C. The extruder was equipped with two venting ports : one operating at atmospheric pressure, the other operating at 190 mbar.

The venting ports are used to evaporate water formed by reaction. A reaction product is obtained which is pelletised giving free flowing, dry, non-sticky pellets containing 679 ppm of water.

Standard epoxy-dipped (ED) coated steel plates were coated with a layer of 500 micron of the reaction product. To coat the plates, a 3 mm thick plaque is pressed according to ASTM D 1928. This plaque is pressed onto the ED-coated plate to form a layer with a thickness of 500 micron at a pressure of 0 bar for 15 sec, 200 bar for 15 sec and 400 bar for 15 sec with the upper press-plate having a temperature of 180"C and the lower plate having a temperature of 1000C. After pressing, the press is opened and the plate is allowed to cool for 3 minutes.

The following tests are performed on these plates (1) water immersion (2) vertical flow (3) gravel resistance (1) For the water-immersion test, the coated panels resulting after the gravel-resistance test are used.

The plates are put in a water bath at 550C for seven days. The rust-formation is observed in areas impacted by the gravel, for signs of delamination and possible rust penetration under the coating.

(2) Vertical flow is measured by placing the coated panels in a hot air oven in a vertical position starting at 1000C. Every 30 minutes, the temperature is increased by 100C till 1400C. The formation of dripmarks at the edge and flow within the layer is checked each time before raising the temperature. At 1400C the performance of the plate is checked after 30 minutes, after 90 minutes and after 24 hours.

(3) For the measurement of the gravel-resistance the method ASTM 3170 is used.

Apart from these tests on coated plates, the following characteristics are measured on the pellets of the reaction product or a film ( 4) Low temperature flexibility ( 5) Brookfield viscosity ( 6) Hardness (shore D) ( 7) Ring and Ball Temperature ( 8) Water Vapour Transmission ( 9) Water content (10) Mettler Drop point (11) Acid Number (12) Amine Number (4) To measure the low temperature performance a film of 400 micron is bent over a cylinder with a diameter of two and a half cm in a refrigerated space at different temperatures. Five strips are tested. The number of strips that can be bent in a controlled manner without breaking are reported.

(5) Brookfield viscosity : a Brookfield viscosimeter model DVII with a spindle RV-SC4-27 is used. The viscosity is measured at 1900 C, the spindle is turning at 50 to 100 rounds/minute and the reading after 20 minutes is reported.

(6) Hardness is tested in accordance with ASTM D 2240 on a shore durometer. The instrument indicates the hardness of the specimen based on the indentation of a needle in the specimen under specified conditions.

(7) Ring and Ball temperature : standard ring and ball test conditions (ASTM E 2867).

(8) Water Vapour Transmission is tested using the ASTM F 372 method.

( 9) The water content is measured using a Dupont 903 Moisture Evolution Analyzer with an oven temperature of 110 0C over a time period of 30 minutes.

(10) The drop point is determined using a Mettler Drop Point Apparatus. The sample is heated to about 20"C above its melting point to form a pourable liquid. The sample cups are placed on glass slides and filled with the molten sample. The furnace of the instrument is then preheated to a temperature of about 20"C below the expected dropping point. When the sample is equilibrated in the furnace, the sample is heated at a rate of 20C/min. The heating continues until drops are being formed. The temperature at which a drop of the material cuts a lightbeam 19 mm under the sampleholder is recorded.

(11) The acid number is determined based upon DIN 16945.

(12) The amine number is determined based upon DIN 53402.

The procedure described previously was repeated with different starting materials. The EAA was replaced by EMAA (EX 937 of EXXON CHEMICAL) as acid group containing polyolefin. EUREMELT 2140, 2147 and 2148 from Schering were used in place of EUREMELT 2145 as polyamides.

Characteristics of the starting materials were EMAA (EX 973) : 13 wt % of methylacrylacid (MAA) and a Brookfield at 1900C viscosity 6.3 Pa.s

I I I I - I Euremelt Softening i Brookfield Acid No. | Amine No.

Point (190 C) viscosity I I I I 2140 135 - 145 17.4 2 max 9 max 2145 138 - 148 8.5 7 max 7 max 2147 140 - 150 40 - 50 2148 140 - 150 40 - 50 Tables 1 and 1B give an overview of the results obtained.

Different ratios of the polyolefines and the polyamides were used as shown in the Table 2 for comparative purposes.

TABLE 1 A : Selection of blends

Run Acid Type Ratio No. of Through Viscosity H2O Hard- Ring No. Type Poly- of Venting put (190 C) ness and Cont. amide E (M) AA Ports Ball Polymer PA wt%wt% kg/h Pa s ppm Shore C D 1 EX 194 2145 15/85 2 7 8.2 722 (EAA) 2 EX 194 2145 15/85 2 7 8.2 3 EX 194 2145 5/95 1 7 6.9 347 38.2 99.4 4 EX 194 2145 10/90 1 7 7.6 449 36.2 104.8 5 EX 194 2145 15/85 1 7 8.2 679 36.7 123.9 6 EX 194 2145 20/80 1 7 8.8 763 33.8 129.4 7 EX 194 2145 30/70 1 7 8.0 35.7 137.3 8 EX 194 2145 15/85 1 10 8.1 831 9 EX 194 2140 15/85 1 7 9.8 638 10 EX 194 2147 15/85 1 7 24.0 1,163 11 EX 194 2148 15/85 1 7 16.6 900 12 EX 937 2145 15/85 1 7 16.1 531 TABLE 1 B : PROPERTIES MEASURED ON COATED ED PANELS

Run Drop Cold Bend Drip / Time Layer / Time No. Point -41 -38 Flow ( C) ( C) (0C) (0C/h) (hours) ( C) (hours) 3 117.3 3/5 5/5 110 4 118.1 5/5 140 1.5 140 1.5 5 141.9 5/5 140 1.5 140 24 6 152.6 4/5 5/5 140 24 7 155.2 4/5 5/5 8 5/5 140 24 140 24 9 0/5 120 10 120 120 11 120 110 12 > 140 > 140 TABLE 2 : PROPERTIES MEASURED IN PELLETISED END PRODUCT

Run Ratio Brook- Acid R & B Main Hard- Drop Cold No. EX 194 : field No. Tg ness point Bend EUREMELT viscos. -41 2145 | (190 C) | | | | | | ( C) (wt%/wt%) (Pa.s) ( C) ( C) ShoreD ( C) (No/5) 13 100: 0 6.3 92 97.4 45 37.3 119.6 5/5 3 95: 5 6.9 87 99.4 51 38.2 117.3 3/5 4 90: 10 7.6 83 104.8 50 36.2 118.1 5/5 8 85: 15 8.2 79 123.9 48 36.7 141.9 5/5 6 80: 20 8.8 74 129.4 46 33.8 152.6 4/5 7 70: 30 8.0 66 137.3 45 35.7 155.2 4/5 14 0:100 6.1 6.3 > 140 85 42.5 5/5 Analysis of Runs 1 to 14 Table 1 shows that runs 4 to 7 using 5 to 30 wt % of the low amine number polyamide gave low viscosities ; considerable elevation in drop point and high temperature layer vertical flow as well as good cold bend properties.

Table 2 shows comparatively how the reaction products enable the EAA to be upgraded efficiently in performance by including minor amounts of suitable polyamides.

Increasing Ring and Ball temperatures and drop points resulted from increasing levels of polyamide indicating a better high temperature performance.

The best results for the cold bend test emerge from runs 4 and 5. The low temperature performance may suffer from very high amounts of polyamide. Thus higher amounts (towards 30 wt%) of polyamide improve ring and ball and drop point but the cold temperature properties decline.

Claims

1. Thermoplastic composition including a reaction product of (a) an acid group containing polymer derived from at least ethylene and at least 10 wt% of a copolymerisable acid group containing comonomer; and (b) an amorphous polyamide having an amine number of less than 70 and substantially one neutralisable amine group per molecule.

2. Composition according to Claim 1, in which the comonomer is acrylic acid or methacrylic acid and optionally units derived from a copolymerisable ethylenically unsaturated ester are present in the polymer ; the acid group con taining polymer has a Brookfield viscosity of less than 20 Pa.s, suitably less than 15 Pa.s and from 5 Pa.s; the amorphous polyamide has an amine number of less than 30 especially less than 20 and optionally an acid number of from 0 to 10; the overall compound viscosity is less than 30 Pa.s preferably less than 20 Pa.s and/or the proportion of (a) based on (a) + (b) is at least 70 wt % preferably at least 80 wt % and at least 5 wt % preferably 10 wt % is used of the polyamide.

3. Composition according to Claim 1 or Claim 2 in which the composition is substantially free of solvents ; contains less than 3 wt % of tackifier ; and/or contains less than 5 wt % of an elastomer component such as rubber.

4. Composition according to claim any of the preceding claims in which the amorphous polyamide has a ring and ball softening point of from ll00C to 1700C and is derived from a difunctional primary amine and a dimeric acid.

5. Composition according to any of the preceding claims in which the composition has a cold bend temperature as defined herein of less than -40 C and vertical flow (as defined herein) starting only after 24 hours at 1400.

6. Process for preparing thermoplastic composition according to any of claims 1 to 5 in which the components (a) and (b) are high shear blended and extruded at a temperature of at least 180 0C so as to condense the polyamide onto the acid group containing polymer.

7. An article including a metal layer and adhered thereto a coating of a composition according to any of claims 1 to 5 having a thickness of from 25 to 2500 micron.

8. A process for preparing an article according to Claim 7 which includes melting the composition and spraying it in molten form against an optionally heated metal surface.