NO311435B1 - Thermoplastic elastomer composition and use thereof - Google Patents

Description

FIELD OF THE INVENTION

This invention relates to high-quality thermoplastic elastomers (TPEs) in various colors with good weather resistance and good resistance to permanent compression, and their use.

BACKGROUND OF THE INVENTION

Window seals comprise two main categories, window pane seals and sealing strips. The former is designed for fixed installation, while sealing strips are exposed to frequent compressions and expansions during use. High quality elastomeric materials are required to satisfy these user criteria at different temperatures. Flexible PVC (polyvinyl chloride) has limited application as a thermoplastic elastomer due to its low heat deformation temperature and poor ability to withstand permanent compression (poor "compression set"). Vulcanized elastomers do not have these limitations, but are difficult to produce on equipment intended for thermoplastic materials. They are normally also difficult to flame retardant, are not recyclable and often have poor resistance to oil, chemicals and ozone. Heat-cured rubber must be reinforced with large amounts of carbon black to achieve good mechanical properties, which in turn leads to black products.

Due to its polarity, PVC is miscible with a variety of polymers, and has a long history in compounding. Mixtures of PVC and i) acrylate impact modifying additives or ii) NBR (nitrile butadiene rubber) appeared in 1936 as the first commercial thermoplastic mixtures. Even today, most PVC-based TPEs are mixtures of PVC and unmodified or cross-linked (thermoplastic vulcanizates, TPVs) NBR, made for use in e.g. vehicles, oil-resistant hoses, sealing strips and cable insulation. A major disadvantage of PVC-NBR mixtures is that NBR is unsaturated (contains double bonds) and thus has poor resistance to ozone. Like many other TPEs, they have poor color fastness in light colors and it is therefore necessary to dye them black. There is often a need for TPEs with white or 2 light colours, especially in gaskets for window panes and sealing strips for white hard PVC windows where the color fastness must be as good as for the frame. Therefore, it is highly desirable to obtain high-quality TPEs with good weather resistance in all colors.

The inventors surprisingly found that by replacing NBR with EPDM (ethylene propylene diene monomer), EPR or other polyolefinic elastomers, high-quality TPEs with good weather resistance in all colors could be made. EPDM is resistant to heat, ozone and oxygen, and can withstand a high concentration of filler and oil, while retaining its good physical properties.

Several descriptions of rubber-modified plastics (4-10% by weight of e.g. EPDM) with improved impact resistance at high and low temperatures are already known. These mixtures are nevertheless different from our TPEs, which have a higher EPDM content. One reference describes blends of PVC (0-100 phr) and EPDM with improved tensile properties, using NBR-18 as compatibilizer (EPDM:NBR = 90:10). The tensile properties are far worse than what has been achieved with the present invention. The patent literature describes mixtures of PVC or PVC copolymers with cross-linked NBR (JP61195144, EP353525, GB2271115), cross-linked carboxylated NBR (US4826910) and mixtures of cross-linked NBR (97-70 wt %) and EPDM (3-30 wt %) ( JP07053820, JP07053819). All the compounds have good resistance to permanent compression (low "compression set" value) and good tensile properties, but have the above-mentioned disadvantages of NBR.

PVC and EPDM, EPR or most other polyolefinic elastomers are completely incompatible. It is necessary to use a compatibilizer to obtain a satisfactory mixture. In US Pat. No. 4,442,253 and 4,421,882 describe mixtures of sulfonated EPDM neutralized with amine-terminated polycaprolactone (PCL) and e.g. PVC. Sulphonated EPDM is more expensive than unmodified EPDM and is therefore less commercially attractive. The elongation at break is also poor (10-50%) for these mixtures.

An object of this invention is to create a new "dynamic" TPE (ie a TPE

which is vulcanized during processing) with good color fastness for light colors, where co-extrudability and co-molding with hard PVC are combined with good elastomeric properties over a wide temperature range. This has been achieved by making a TPE comprising 10-70% by weight PVC, homo- or copolymer, 15-70% by weight EPDM and/or EPR and/or other polyolefinic elastomers, 5-50% by weight polycaprolactone (PCL) and/ or in situ polymerized ε-caprolactone, and conventionally known additives for the production of PVC.

The invention further includes the use of this TPE for gaskets for window panes, sealing strips for windows made of hard PVC and other materials, gaskets, sealing strips and scratch strips for car windows, hoses for household and technical use, components for vehicles, special electrical cables such as household and computer cables, O-rings, gaskets and sealing materials.

SUMMARY OF THE INVENTION

The present invention provides a thermoplastic elastomer composition comprising:

(i) from 10-70% by weight PVC, homo- or copolymer,

(ii) from 15-70% by weight of EPDM or EPR, unmodified or modified,

(iii) from 5-50% by weight polycaprolactone (PCL),

(iv) from 0-10 wt% transesterification catalyst,

(v) from 0.05 to 10% by weight of sulfur, peroxy vulcanizing or chemical cross-linking agent,

(vi) from 0.05 to 30% by weight "coagent" for the cross-linking agent,

(vii) from 0-50% by weight of plasticizer and

(viii) from 0.3-6% by weight of stabilizers and processing aids.

DETAILED DESCRIPTION

The thermoplastic vulcanizates produced according to the present invention have good tensile properties, good resistance to permanent compression (low "compression set") and good thermal stability, provided they are produced under correct production conditions.

The PVC used in the present invention can be of any type. This includes but is not limited to copolymers (including graft polymers such as VC (vinyl chloride)A/A (vinyl acetate), VC/VDC (vinylidene chloride), VC/AN (acrylonitrile), VC/P (propylene), VC /E (ethylene), VC/EVA (ethylene/vinyl acetate), VC/TFCE (trifluorochloroethylene), VC/hydroxy-/ethyl-/propyl methacrylate, VC/fumaric acid, VC/maleic anhydride, VC/acrylic acid, VC/methacrylic acid , VC/acrylic or methacrylic acid ester Satisfactory results were obtained with PVC in an amount of 10-70% by weight, preferably 20-50% by weight.

EPDM, EPR or other polyolefin elastomers used in the present invention can be any of those known, including grafted EPDMs and/or EPRs and/or other polyolefin elastomers and mixtures thereof. Suitable monomers for grafting may be, but are not limited to, maleic anhydride, acrylic acids, methacrylic acids, hydroxy methacrylates, silanes, allyl glycidyl ether or butenedial. The amount of EPDM and/or EPR used was 15-70% by weight, preferably 20-50% by weight.

Polycaprolactone or in situ polymerized e-caprolactone is a polyester with all types of end groups. The amount of PCL should be in the range 5-50% by weight, preferably 8-26% by weight.

The elastic properties (resistance to permanent compression, "compression set") are greatly improved by using cross-linking agents. This can be any sulfur-based cross-linking system suitable for steam or pressure curing. This includes, but is not limited to i) mercapto benzothiazole (MBT), tetramethyl thiuram monosulphide and sulphur; ii) zinc oxide, stearic acid, tetramethyl thiuram disulfide (TMTD), MBT and sulphur; iii) MBT, TMTD, tellurium diethyl dithiocarbamate (TEDC) and sulphur; iv) MBT, TMTD, zinc dibutyl dithiocarbamate (ZBDC), TEDC and sulphur; v) ZBDC, tetraethyl thiuram disulfide, zinc dimethyl dithiocarbamate (ZMDC), 4,4-dithio morpholine and sulfur; vi) TMTD, ZBDC, ZMDC, 4,4-dithio morpholine and sulphur. It can also be a peroxy cross-linking agent, that is, any conventionally known peroxide and hydroperoxide with a reasonable half-life, including but not limited to tert-butyl peroxy-3,3,5-trimethylhexanoate, tert-butyl peroxy isopropyl carbonate, cc. a-bis-tert-butylperoxy) diisopropylbenzene, tert-butyl peroxyacetate, dicumyl peroxide, 2,5-dimethyl-2,5-di-tert-butyl peroxy hexane, 1,1-bis-tert-butylperoxy-3,3, 5-trimethylcyclohexane, tert-butyl cumyl peroxide, bis(tert-butyl peroxyisopropyl)benzene, 2,5-dimethyl-2,5-di-tert-butyl peroxy-3-hexyne, n-butyl-4,4- bis-(tert-butylperoxy) valerate, tert-butyl peroxybenzoate and di-tert-butyl peroxide. It may also be an alternative chemical cross-linking agent, including but not limited to poly(ethylene glycol), 1,6-hexanediol, 1,6-hexane diamine, methylene diphenyl diisocyanate, 1,6-hexane diisocyanate, tolylene diisocyanate, di- , tri- or tetraglycidyl ethers, phthalic anhydride, trimellitic acid, iso- or orthophthalic acid. A combination of a chemical cross-linking agent and sulfur or peroxide vulcanizing agents can further improve the compositions. The amount of crosslinking agents should be 0.05-10% by weight or preferably 0.2-4.5% by weight.

In the present invention, a "coagent" can also be used for the crosslinking reagent, which includes but is not limited to diallyl phthalate, dibenzoyl-p-quinone dioxime, triallyl cyanurate, dibenzoyl-p-quinone dioxime, ethylene dimethacrylate, pentaerythritol tri(met )acrylate, trimethylolpropane tri(meth)acrylate, triallyl isocyanurate, pentaerythritol tetramethacrylate, diallyl maleate, ethylene dimethacrylate and N,N'-m-phenylene dimaleimide. The amount of "auxiliary reagent" (coagent) is from 0.05 to 30% by weight, preferably from 0.4 to 10% by weight.

There are no particular restrictions on the plasticizer used. Any plasticizer suitable for making a soft PVC (polyvinyl chloride) product can be used. It can be, but is not limited to, monocarboxylic acid esters, acetates, propionates, butyrates, glycolic acid esters, benzoic acid esters, epoxidized acid esters, phosphates, trimellitic acid esters, polymeric plasticizers, phthalates, citric acid esters, sulfonic acid esters and sulfamides. The amount is 0-50% by weight, preferably 8-23% by weight.

The stabilizers and processing aids used in this invention can be one or more of commercially available, known compositions. Preferred stabilizers include, but are not limited to, stabilizers based on lead, barium/zinc, calcium/zinc, organotin stabilizers, organotin mercaptides and sulfides, metal carboxylate stabilizers, barium/cadmium, and organic-based stabilizers. Costabilizers, such as organic phosphites, epoxy compounds, polyols, antioxidants, 1,3-diketones, dihydropyridine and b-ketocarboxylic acid esters, can also be used. Preferred processing aids include, but are not limited to, fatty alcohols and dicarboxylic acid esters, fatty acid esters of short chain alcohols, (metal salts of) fatty acids and amides, oligomeric fatty acid esters, fatty alcohol fatty esters, waxes, including their esters and soaps, polar polyethylene waxes, non-polar polyolefin waxes , paraffin waxes, fluoropolymers and combinations thereof. The total amount of stabilizers and processing aids used in mixtures in the present invention is 0.3-6% by weight, preferably 1.5-5% by weight.

EXAMPLES

Tensile tests were carried out in accordance with ISO R527. Test for resistance to permanent compression ("compression set") was carried out according to ISO 1856 at 25% compression. Congo Red (measure of thermal stability, "Congo Red") measurements were made at 200 °C in glass tubes (d = 3 mm, h = 3 cm material).

The present invention is illustrated by the following non-limiting examples. The denomination for all the numbers in the tables is phr. Five PVC masterbatches were used:

1: PVC, Hydro Polymers Nordic; 2: Plasticizer, Exxon; 3: Stabilizer, Acros; 4: Stabilizer, Barlocher;

I 5: Stabilizer, Henkel; 6: Costabilizer (epoxidized soybean oil), Henkel; 7: Lubricant, Allied Chemicals Ltd.

Example 1.

Blends with a PCL/EPDM ratio of 1.1 were prepared with and without crosslinking agents and transesterification catalyst. Results are given in table 1.

1: EPDMgMAH, Uniroyal; 2: PCL, Union Carbide; 3: Peroxide, Akzo; 4: Transesterification catalyst/stabilizer, Comtin s.r.l.

The elasticity ("compression set" value) is clearly improved by using a vulcanizing agent or a transesterification catalyst. A combination of both chemicals has the best effect. The tensile strength and elongation at break are clearly improved by using PLC as a compatibilizer.

Example 2.

Mixtures with an increased amount of EPDMgMAH were prepared. The results are given in table 2.

An increased amount of the rubber component has a positive effect on elasticity when a cross-linking agent is used (cf. composition no. 1 & 5 and 4 & 8). The elasticity is further improved by adding a cross-linking "helper reagent" (coagent).

A change in stabilizer to a different Ba-Zn type, tin or lead stabilizer improved the thermal stability but had a small negative effect on the ("Compression Set" value). The best result was achieved with a Ba-Zn stabilizer. The results are given in table 3.

Example 3.

Properties of mixtures where EPDMgMAH has been replaced by unmodified EPDM are given in Table 4.

The elasticity ("compression set" value) became slightly worse (composition no. 10,11 and 14,15). The thermal stability improved, but the tensile strength also deteriorated. EPDMgMAH therefore seems to be a better choice, although pure EPDM also gives TPEs with good elasticity.

Example 4.

Properties of blends of PVC, PCL and EPRgMAH with increasing amounts of an alternative chemical cross-linking agent are given in Table 5.

The "compression set" value is high (worse elasticity) and the morphology is worse than that obtained with peroxy cross-linking agents, but the tensile strength is superior to that obtained for similar mixtures.

Example 5.

Properties of mixtures of PVC, PCL and EPRgMAH with various "auxiliary reagents"

(coagents) are given in Table 6.

EPRgMAH gives TPEs with good elasticity and thermal stability, but poorer tensile strength compared to mixtures with EPDMgMAH (cf. composition no. 8, 10, 11 &21.22).

Example 6.

Two further master batches were used

Properties of mixtures of PVC-g-EVA and EPDM-g-MAH are given in Table 7.

By replacing PVC with a copolymer (PVCgEVA), TPEs with excellent elasticity, thermal properties and tensile strength were obtained.

Claims (8)

1. Thermoplastic elastomer composition characterized in that it comprises 10-70% by weight PVC, homo- or copolymer, 15-70% by weight EPDM and/or EPR and/or other polyolefinic elastomers, 5-50% by weight polycaprolactone (PCL) and/ or in situ polymerized ε-caprolactone, and conventionally known additives for the production of PVC. 2. Thermoplastic elastomer composition according to claim 1, characterized in that it comprises 0-50% by weight of plasticizer, 0.3-6% by weight of stabilizer and conventionally known additives for the production of PVC. 3. Thermoplastic elastomer composition according to claim 1, characterized in that EPDM and/or EPR and/or other polyolefinic elastomers are modified with one or more grafted monomers selected from maleic anhydride, acrylic acid, methacrylic acid, hydroxy methacrylates, silanes or other suitable monomers . 4. Thermoplastic elastomer composition according to claim 1, characterized in that the composition comprises 0.05-10% by weight of sulphur, peroxy vulcanising agent or chemical cross-linking agent. 5. Thermoplastic elastomer composition according to claim 4, characterized in that the composition comprises 0.05-30% by weight auxiliary reagent (coagent) for the cross-linking agent. 6. Thermoplastic elastomer composition according to claim 1, characterized in that it comprises 20-50% by weight of EPDM and/or EPR and/or other polyolefinic elastomers modified with grafted maleic anhydride, acrylic acid, methacrylic acid, hydroxy methacrylates, silanes or other suitable monomers . 7. Thermoplastic elastomer composition according to claim 1, characterized in that the content of PCL is 5-30% by weight. 8. Application of a thermoplastic elastomer composition according to claim 1, for gaskets for window panes, sealing strips for windows made of hard PVC and other materials, gaskets, sealing strips and scratch strips for car windows, hoses for household and technical use, components for vehicles, special electrical cables such as household and computer cables, O-rings, gaskets and sealing materials.