HOT MELT ADHESIVE COMPOSITIONS

Abstract: A hot melt adhesive includes (a) from 15 to 80 wt% of a polymer derived from ethylene and an ethylenically unsaturated ester, the ester derived units being from 20 to 40 wt% of the total and the polymer having an MI from 100 to 6000 and having from 0 to 10 alkyl branches per 1000 backbone C-atoms; (b) from 20 to 70 wt% of a compatible tackifier resin; and (c) from 0 to 30 wt% of a compatible oil or wax the weight percentages of (a), (b) and (c) being calculated on the total weight of the formulation. Improved heat resistance can be obtained at low viscosities.

Description: Hot melt adhesive compositions. The invention relates to hot melt adhesive compositions for use especially but not exclusively in sanitary (diaper) end uses. Background of the invention The use of medium melt index ethylene vinylacetate polymers in hot melt adhesive blends is known from EP-A-78122. A range of vinyl acetate contents of from 11 to 40 % is used together with a high melt index of from 700 to 10000. A range of different transfer agents is disclosed for use providing the high melt index. EP-A-271254 disclosed hot melt formulations including ethylene vinyl acetate acrylic acid terpolymers having a melt viscosity of from 3000 mPa.s to 7000 mPa.s. at a temperature of 190-.C. The terpolymers may contain from 5 to 20 wt% of vinylacetate. AU 2995689 discloses the use of an ethylene vinylacetate copolymer having a melt index from 700 to 10000 and from 5 to 40 wt% of VA with less than 10 alkyl branches per 1000 backbone C-atoms as asphalt modifier. There is a need for improved hot melt formulations which have a better balance fluidity cohesion strength and thermal resistance to permit spray application yet give good bond strength and endurance. It has been found that by selecting particular low branched, high VA ethylenevinylacetate polymers a good balance of properties can be provided, superior particularly in applications such as a multi-line adhesive in diaper constructions where different panels have to adhere to another. Summary of the invention The invention provides a hot melt adhesive composition including (a) from 15 to 80 wt% of a polymer derived from ethylene and an ethylenically unsaturated ester, the ester derived units being from 20 to 40 wt % of the total and the polymer having an MI of from 100 to 6000 and having from 0 to 10 alkylbranches per 1000 C-atoms; (b) from 20 to 70 wt% of a compatible tackifier resin; and (c) from 0 to 30 wt% of a compatible oil or wax the weight percentages of (a) , (b) and (c) being calculated on the total weight of the formulation. The polymer may be a co- or terpolymer with additional functional groups. It is preferred that the polymer is an EVA copolymer. It is further preferred to have an ester derived content of from 25 wt%, especially from 30 wt% up to 35 wt % so as to obtain a flexible formulation with good compatibility characteristics. The ester may also be methyl acrylate or is homologues or methacrylate equivalents. It is preferred that the melt index is from 200 to 1000 and especially from 300 to 800. The polymer may be made by the process described in EP-A-78122 but preferably using an aldehyde, particularly acetaldehyde, as a chain transfer agent for increasing the MI. The tackifiers are preferably compatible hydrogenated, low colour tackifiers. Advantageously hydrogenated petroleum resins are used derived from a C5/C6 olefin or diolefin feed stream and a C9 aromatic compound containing feed stream by thermal or catalytic (Friedel-Crafts) polymerisation. It is preferred, in order that compatibility can be optimised to provide a resin having an aromaticity of from 0 to 50 % preferably from 10 to 40 wt%. With good compatability high tackifier amounts can be incorporated preferably from 35 to 65 wt%. Preferably the tackifiers have a Mn of from 200 to 1300 and a Mw/Mn of from 11 to 25 as determined by GPC. The oils and waxes are used optionally to lower the viscosity of the overall formulation to a level suitable for application. As these ingredients reduce generally reduce tack they are used in minimal amounts. The oils may be naphthenic oils, polybutenes, liquid resins, paraffinic oils etc. The overall viscosity of the formulation is preferably from 300 to 15000 mPa.s at 180°C. Amounts of the ingredients and melt indices are selected so as to produce the desired viscosity. Examples Different MI EVA'S were prepared using acetaldehyde as the transfer agent. Properties of the products are listed below in Table 1. Table 1 Polymer 1 2 3 4 5 6 The MI was determined according to ASTM 1238D using condition E i.e. a load of 2,1 kg at 190 -ΪC The number of alkyl branches per 1000 C backbone atoms is less than 10 as determined by proton NMR. These polymers were made into a formulation for sanitary uses by blending with tackifier and oil and other usual ingredients such as filler and anti-oxidant stabilizer. Table 2 shows the composition and associated results. Runs 3, 6, 7, 10 are not according to the invention and are for comparative purpose. Apart from polymers 1 to 6, the key to the ingredients is as follows ; E-5300 hydrogenated dicyclopentadiene resin Escorez (RTM) Escorene (RTM) MV02528 a 25 Meltindex, 28% VA ethylene vinylacetate polymer Vestoplast (RTM) 708 C2/C3/C4 amorphous poly-A-olefin Parapol (RTM) 2225 Polybutene polymers produced by Parapol (RMT) 1300 Exxon Chemical Primol (RTM) 352 paraffinic/naphtenic oil Irganox (RTM) 1076 antioxidant Table 2 10 Formulations Escorez 5300 35 35 35 50 50 50 30 50 50 50 Properties 1 2 3 4 5 6 7 8 9 10 Viscosity 180 degC 3880 1515 1620 . 2945 1985 2650 3375 1460 1520 1775 (mPa.s) Softening point 73.2 70.5 61 67.5 73 69.5 91 67.5 70 67 (degC) Cloud point (degC) 115 105 145 >200 170 190 >200 170 110 135 Hot shear ( in/degC) 20/60 1/60 1/50 5/60 29/60 12/60 2/50 4/60 3/70 13/60 T-peel PE/N C multiline (g/cm) at 23 degC 2.25 1.40 0.6 0.8 0.7 0.5 0.2 0.4 jerking at 40 degC 0.5 0.5 0.2 - 0.15 0.3 0.45 0.5 0.4 Similar formulations can also be used advantageously for woodworking applications. Details of the composition and properties for such end-use are set out in Table 3. Formulation of the invention shows superior heat resistance as measured with hot shear shaft test and similar adhesive properties at lower HMA blend viscosity than formulation using regular EVAs. SUBSTITUTESHEET TABLE 3 Formulations ECR 340 10 10 10 10 10 10 10 10 Dertopoline P 15 15 15 15 15 15 15 15 UL 40028 45 25 Polymer 1 45 Polymer 5 45 Escorene UL 15028 45 Escorene UL 8720 45 Polymer 3 45 UL 8705 45 UL 00728 CaC03 BaS04 Irganox 1076 Saft (degC) Horniflex 71 75 83 73 78 79 Linoplex 72 75 82 73 79 80 Eiche 69 75 85 71 72 75 Ageing at 180 degC - 2 hours colour skinning % - 25 hours colour skinning % - 50 hours colour skinning % Runs 1, 4 and 8 are not according to the invention and are for comparative purposes It can be seen that the invention permits formulations to be prepared which are in many ways competitive with formulations based on propylene/butene copolymer and regular EVAs. The formulation of the invention of superior compatibility, lower cloud point, better adhesive performance as measured with T-peel test, of higher tensile strength, and secant modulus, good elongation and higher heat resistance, obtained at lower HMA blend viscosity.

Claims: CLAIMS 1. A hot melt adhesive composition including (a) from 15 to 80 wt% of a polymer derived from ethylene and an ethylenically unsaturated ester, the ester derived units being from 20 to 40 wt% of the total and the polymer having an MI from 100 to 6000 and having from 0 to 10 alkyl branches per 1000 backbone C-atoms. (b) from 20 to 70 wt% of a compatible tackifier resin; and (c) from 0 to 30 wt% of a compatible oil or wax the weight percentages of (a) , (b) and (c) being calculated on the total weight of the formulation. 2. A formulation according to claim 1 or claim 2 in which the polymer is present in an amount of from 25 to 60 wt%. SUBSTITUTESHEET 3. A formulation according to any of the preceding claims in which the tackifier is a hydrogenated or non-hydrogenated petroleum resin derived from catalytic or thermal polymerisation of dicyclopentadiene, its isomers, olefins such as 2-methyl butene; 1,2 methylbutene-2 cyclopentadiene 1,3; C9 such as indene, vinyltoluene; aromatics such as styrene, terpenes such alpha-pinene, delta-3-carene said resin having an aromaticity of from 0 to 50%. 4. A formulation according to claim 4 in which the tackifier is present in an amount of from 20 to 70% preferably from 35 to 65 wt%. 5 ' . A formulation according to any of the preceding claims having a viscosity of from 200 to 20000 mPa.s at 180 e , preferably from 500 to 10000 mPa.s. SUBSTITUTESHEET

Inventors: FAISSAT MICHEL LOUIS, FAISSAT, MICHEL, LOUIS
Applicants: EXXON CHEMICAL LTD, EXXON CHEMICAL LIMITED
Application year: 1991
Main classification: C09J123
IPC codes: C08L23, C08L101, C09J123