SCRATCH AND ABRASION RESISTANT IONOMERS FOR PROTECTIVE FORMULATIONS

Abstract: Ethylene copolymer compositions that are useful for fabricating films and molded articles are disclosed. These compositions contain a combination of metal ions providing superior scratch and abrasion resistance than the individual composition containing only a single metal ion. These compositions comprise a copolymer of ethylene and 10-30 % by weight of acrylic acid or methacrylic acid which is neutralized from 10-99.9 % with a combination of at least two ions selected from the group consisting of Na, Zn, Li, Mg and Ca in a specific ratio. The compositions are useful for packaging abrasive goods and as transparent top layers for floors, wall covers or sporting goods.

Description: TITLE Scratch and Abrasion Resistant Ionomers for Protective Formulations FIELD OF THF. INVENTION The present invention relates to ethylene copolymer compositions that are useful for fabricating films, sheets and molded articles of scratch/abrasion resistant material. More particularly, the ethylene copolymer compositions of the present invention can be used as protective coatings or layers on wear and scratch- exposed objects for example as wear layers on floor tiles or as protective layers for skis or other wear and scratch exposed objects such as seal layers in packaging structures that contain hard, abrasive objects such as dry soup mixes or the like. BACKGROUND OF THE INVENTION Ionomers are thermoplastic resins that contain metal ions in addition to organic-chain molecules. Ionomers have solid-state properties characteristic of cross-linked polymers and melt-fabricability properties characteristic of uncrosslinked thermoplastic polymers : see for example US Patent 3,262,272. Major applications of ionomers are in the areas of packaging and for sporting goods. As disclosed in US Patent 3,262,272, it is not essential that only one metal ion be employed in the formation of the ionomers, and more than one metal ion may be preferred in certain applications. Nevertheless, commercially available ionomers such as that available from DuPont under the Trademark SURLYN are neutralized with a single metal ion, commonly zinc or sodium. Indeed, the only improved property actually attributed to combinations of different ions and which has led to a specific application is improved resilience. This is a very important property for golf balls and blends of ionomers have been disclosed specifically for golf ball applications. So far where problems of scratching a surface or a film made of an ionomer film or sheet arose, these problems had to be overcome by crosslinking these ionomers by external crosslinking agents such as organic compounds or epoxy and formaldehyde functionalities. Patent publications WO 95/11333, US 3,264,269, and US 3,317,631 treat this problem and claim solutions to it. WO 95/11333 claims composition made up of ethylene carboxylic acid ionomers and polyfunctional polymerisable olefinic compounds comprising a polyfunctional acrylic or methacrylic ester that provide sufficient crosslinking in order to achieve the scratch resistance necessary to use these ionomers in wear resistant floor tile applications. The disadvantage of such composition is however the manner of production which implies compounding and extruding at elevated temperature where part of the reaction already takes place. Therefore these reactions are difficult to control. US 3,317,631 describes thermosetting compositions based on ethylene carboxylic acid copolymers and melamine formaldehyde resins giving essentially a thermoset polymer without possibility of thermoplastic processability. US 3,264,269 teaches a process for crosslinking polymers containing carboxyl groups which comprises imbibing a shaped article of the polymer in a diisocyanate. The disadvantages of this process are its 2-step nature (processing plus imbibing) combined with the toxic nature of diisocyanates. SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-indicated disadvantages by providing property enhancements to ionomers comparable to those achieved with the previous crosslinking routes (such as higher scratch resistance) while still allowing thermoplastic processability, non toxicity and by using a one step process. The present invention provides a thermoplastic composition for producing a film or sheet or molded articles of abrasion and scratch-resistant transparent material, in particular for application as a protective transparent coating or layer on abrasion and scratch-exposed objects, comprising a copolymer of ethylene and 10-30% by weight of an α,β-unsaturated C3 -C8 carboxylic acid, particularly acrylic acid or methacrylic acid, that is neutralized with more than one metal ion. The copolymer may further contain an acrylate, and may be processed by e.g. extruding or casting a sheet or blowing a film, or injection molding a molded article. The ionomer compounds are well known to those familiar with the art but contain a combination of two different metal ions in a given ratio, instead of only one metal ion as those polymers that are commercially available. According to the invention a combination of compounds of at least two ions (ion, and ion 2 ) selected from the group consisting of Na, Zn, Li, Mg and Ca is used, each ion type providing at least 5% of the neutralization of the acid functionality in the copolymer. To achieve the advantageous effects of the invention, it has been discovered that the two ions must be present in a ratio, called the equivalent ratio, at a value close to one and in any event in the range from 0.3 to 2.5, preferably between 0.6 and 1.5. The "equivalent ratio" ion, to ion 2 is defined as: wt% ion, x ( " valence ion,) x Mw 2 Mw, wt% ion 2 x (valence ion 2 ) where Mw, and Mw 2 represent the molecular weights of the neutralizing compounds containing ion, and ion 2 respectively. The ethylene copolymer composition of the present invention overcomes the aforementioned problems of scratching by providing a means of superior crosslink surprisingly obtained by different metal ion combinations without the addition of external crosslinking agents, and yields sheets and molded articles having a superior abrasion and scratch resistance from the very beginning. Additionally and surprisingly it was discovered that these ionomers containing two ions such as Zn and Mg show an unexpected clarity and an improved penetration resistance to stiff objects such as needles etc. The transparency of these mixed ionomer compositions is much higher than the transparency of a highly neutralized Zn ionomer and is even higher than that of a highly neutralized Na ionomer, the clearest commercially available ionomers on the market. DETAILED DESCRIPTION OF THE INVENTION The thermoplastic copolymers used in the present invention are known. They are copolymers of ethylene and an α,β-unsaturated C3 -Cs carboxylic acid. Acrylic and methacrylic acids are preferred acid comonomers. The copolymer can be from about 10 to 99.9% neutralized with more than one metal ion type selected from sodium, zinc, lithium, magnesium, and calcium. Such neutralized ethylene acid copolymers are known in the art as 'ionomers'. Typically, neutralization will be from 10-70%. Preferably the copolymer has from about 35 to about 70% of the carboxylic acid groups ionized by neutralization with more than one metal ion selected from sodium, zinc, lithium, magnesium, and calcium, advantageously zinc/magnesium in the specified amounts providing an equivalent ratio close to 1 , or in any event in the range from 0.3 to 2.5. Ionomers and their methods of manufacture are described in US Patent No. 3,264,272. Suitable ionomers for use in preparing compositions according to the present invention are commercially available under the trademark SURLYN from the DuPont Company. In the framework of this invention we have surprisingly found that whereas combinations of ions were previously known to improve only the resilience, the combination of different ions (in our specific preferred case Zn and Mg) considering equal viscosity and composition of the remainder of the compound unexpectedly leads to superior scratch and abrasion resistance, clarity and penetration resistance compared to ionomers of similar composition and viscosity but being neutralized with a single ion (Zn, Mg or Na) only, or when neutralized by two ions such as to provide an equivalent ratio below 0.3 or above 2.5. This translates to significantly improved scratch resistance in particular after an aging period of 4 weeks between the test and the molding of a plaque. The advantages of this improvement can be manifold in various applications. Primarily this is important for applications where the aforementioned ionomers are employed as a scratch resistant surface layer and eliminates the need for external crosslinking agents in order to achieve the same improvement. Such applications include transparent flooring wear layers and top layers for skis. Other applications can be found where these materials are used as inner layers in flexible film packaging and where very abrasive stiff/hard packaging goods are packaged such as bones in meat packaging, or dried soup or noodle mixes. The employment of a scratch-resistant sealing layer can largely increase the shelf life and reduce the leaker rate during transportation or storage through reduction of film penetration. BRIEF DESCRIPTION OF DRAWINGS The invention will be further described with reference to the following Examples and the accompanying drawing wherein Fig. 1 graphically illustrates the measured scratch resistance for Examples according to the invention and comparative Examples. Examples All Ionomers used are based on ethylene acid copolymer with approximately 15wt% methacrylic acid ("MAA"). Master Batches: The acid copolymers used in the master batches CS1 and CS2 are based on 10wt% MAA for CS1 and 5wt% MAA for CS2 and have a melt-flow index MFI (190°C/2.16kg) of 500. CS 1 Ethylene methacrylic acid copolymer masterbatch 45% ZnO CS2 Ethylene methacrylic acid copolymer masterbatch 50wt% MgOH2 Ionomers used: Ionomers II and 16 are control ionomers available commercially under the Trademark SURLYN from E. I. du Pont de Nemours and Company. Ionomer 12 is a specially prepared Zn-neutralized control ionomer with low melt flow index. Ionomers 13, 14 and 15 are Zn-Mg neutralized ionomers according to the invention. The weight percentages of the neutralizing agents and the MFI (melt flow index 190°C/2.16kg) of the ionomers are shown in Table I. TABLE 1 %ZnO %Mg(OH)2 MFI 11 4.2 - 0.7 (control ionomer) 12 4.42 - 0.45 (control ionomer) 13 2.12 1.55 0.47 14 2.06 1.55 0.4 15 2.07 1.55 0.64 16 - 2.8 0.7 (control ionomer) The Examples described below were run by preparing a sheet of the respective resin or the resin plus masterbatch blend on a laboratory 2-roll mill and pressing the so-obtained ionomer resin sheet in a hydraulic press into plaques of the dimensions 100x100x3 mm. These plaques were then tested after 1 month, for scratch resistance using a scratch-resistance tester by Eirichsen according to ISO 1518, where a weight between 0.1 and 2 kg is applied onto a needle which is drawn over the surface of the plaque. This apparatus measures the weight in Newton at which a scratch mark is visible on the surface. A Taber abrasion test according to ASTM D3389 was also run. This test indicates the weight loss in g/2000 revolutions, average of two samples. A wheel with H-18 roughness was used, with a 250g weight on each arm. The weight was checked and wheel cleaned every 500 revolutions. Flex Modulus was measured according to ASTM D790 and hardness according to ASTM D2240. Composition of Examples Table 2a indicates the composition of the control ionomers Cl to C7 and of Examples 1 to 4 according to the invention in terms of the corrected amount of methacylic acid (MAA), the % neutralization for the Zn and Mg ions, and the total % neutralization. TABLE 2a Example MAA Zn neut Mg neut Total corrected* % % neut % Cl 14.74 60 0 60 C2 14.72 67 0 67 C3 14.69 73 0 73 C4 14.73 63 0 63 C5 14.69 60 10 70 C6 14.65 61 20 81 C7 14.72 0 56 56 EX1 14.74 59.9 39.9 99.8% EX2 14.72 30 31 62 EX3 14.72 30 31 61 EX4 14.72 30 31 61 * Assumes nominal MAA of 15wt% in base resin and 10 and 5wt% MAA, respectfully, in Zn and Mg concentrates. Table 2b shows the ionomer and additive (masterbatch or Magnesium hydroxide) included in each control ionomer Cl to C7 and in Examples 1 to 4 according to the invention, as well as the calculated weight % of the Zn and Mg ions and the Zn/Mg equivalent ratio for those ionomers with 2 ions. TABLE 2b wt%Zn wt%Mε Zn/Mε eq. ratio Ex Ionomer CSl CS2 (wt%) (wt%) (wt%) Cl 100 11 3.36 - C2 99 12 1 3.72 - C3 98 11 2 4.08 - C4 100 12 3.53 C5 99 11 1 3.36 0.21 6 C6 98 11 2 3.36 0.42 3 C7 100 16 1.17 0 Exl 98 11 2% Mg(OH) 2 3.36 0.83 1.5 Ex2 100 13 1.69 0.64 0.99 Ex3 100 14 1.83 0.7 0.98 Ex4 100 15 1.66 0.63 0.99 Table 2b thus represents the composition of the various examples and comparative examples taking into account the composition of the ionomer mentioned in Table 1 and the information about the master batches CSl and CS2. Using the molecular weight of ZnO and Mg(OH) 2 respectively we have calculated the weight % of Zn and Mg in the respective compounds and the above-defined "equivalent ratio of Zn Mg" taking account of the valences and molecular weight (Mw) of the mixed ions. Results Table 3 shows the results, namely the scratch resistance (SCR) measured as the weight in Newton after which a scratch mark is visible after 4 weeks at room temperature, the Abrasion (ABR) measured by the Taber test in g/2000 revolutions, the Stiffness (STF), i.e. the flex modulus in Mpa, the shore hardness (HRD) and viscosity (VIS), which is the melt flow index MFI (190°C/2.16kg). TABLE 3 HRD VIS Ex Ionomer CSl CS2 Wt Taber Flex Hardness MFI wt% wt% N g/2000 MPa D g/io min Cl 11 12 0.143 51.3 65 0.7 C2 11 1 8 0.6 C3 11 2 9 0.5 C4 12 10 0.45 C5 11 1 10 1.5 C6 11 2 10 1.3 C7 16 N/A 0.156 39.2 65 0.7 Exl 11 2% Mg(OH) 2 18 0.11 Ex2 13 18 0.4 Ex3 14 16 0.075 46.1 65 0.47 Ex4 15 17 0.069 49.4 65 0.64 Table 3 presents results that have been obtained on ionomers with identical chemical composition but which have been neutralized either with Zn or Mg alone or combined. II and 16 represent control ionomers that are neutralized solely by Zn or Mg ions. 13, 14, 15 are ionomers according to the invention that contain both Mg and Zn ions. As can be seen Mg Ions provide less stiffness than Zn Ions (lower flex modulus), but abrasion resistance and scratch resistance is the same. A combined neutralization (Ex3, Ex4) provides an intermediate flexural modulus as expected. Surprisingly, however, scratch and abrasion properties of ionomers that contain both Mg and Zn ions are unexpectedly synergistically improved even in those cases where the fluidity is similar to those ionomers that contain only a single ion (C4, C7). It can be seen (C2; C3 and C5;C6) that by adding Zn or Mg concentrate to Zn ionomers alone provides only minor or no improvement compared to the control II. This only leads to small increases in Mg concentration and an equivalent ratio far away from the value 1 , namely a value 6 for C5 and a value 3 for C6. This may be due to the fact that the Mg ions are introduced together with a masterbatch containing an acid copolymer with 10% methacrylic acid only and a high MFI of 10. Repeating the experiment with Mg(OH)2 powder, thus eliminating the negative influence of the masterbatch improves the situation, Example 1, where equivalent ratio is 1.5. The use of a combination of Zn/Mg ions leading to very low MFI (about 0.5) and an equivalent ion ratio close to 1 gives a synergistic effect and leads to far improved scratch resistance expressed by a higher number (Examples 3 and 4) as well as a higher abrasion resistance tested by the Taber Abrasion test. As shown by comparative Example C4, a low MFI Zn ionomer (without Mg incorporated), or as shown by comparative Example C7 a Mg ionomer (ionomer 16) with a MFI of 0.7, when compared to the mixed ionomer (15) with almost identical MFI, does NOT improve the scratch resistance even after aging or Taber Abrasion resistance. The improved scratch resistance is graphically represented in Fig. 1 which illustrates the measured weight at which a scratch mark appears for the comparative Examples and the Examples according to the invention, after an aging period of 4 weeks.

Claims: Claims: 1. A composition for producing a film or sheet or molded articles of abrasion and scratch-resistant material, comprising a copolymer of ethylene and 10- 30% by weight of an α,β unsaturated C 3 -C 8 carboxylic acid neutralized from 10-99.9%) with a combination of compounds of at least two ions (ion, and ion 2 ) selected from the group consisting of Na, Zn, Li, Mg and Ca, with an equivalent ratio (ion, : ion 2 ) in the range from 0.3 to 2.5, each ion type providing at least 5% of the neutralization of the acid functionality in the copolymer, said equivalent ratio being defined as wt% ion, x (valence ion,) x Mw, Mw, wt% ion 2 x (valence ion 2 ) where Mw, and Mw 2 represent the molecular weights of the neutralizing compounds containing ion, and ion 2 respectively. 2. The composition according to claim 1 where the ions are Zn and Mg, the Zn:Mg equivalent ratio is in the range 0.6 to 1.5 and the neutralization is between 50 and 99%. 3. The composition of claim 1 which has a melt flow index (190°C/2.16kg) between 0.1 and 2. 4. A film, sheet or body of abrasion and scratch-resistant transparent material formed from the composition according to claim 1 , which material has a durable abrasion or scratch resistance of at least 15 Newton measured according to the standard ISO 1518. 5. The composition according to claim 1 transformed into a transparent protective scratch-resistant film or sheet on a scratch-exposed object. 6. The composition according to claim 5 which is a sheet used as a transparent scratch-resistant layer on flooring/sporting good applications. 7. The composition according to claim 4 which is a film used as packaging film for dry abrasive goods.

Inventors: HAUSMANN KARLHEINZ, POWELL RICHARD JAMES, HAUSMANN, KARLHEINZ, POWELL, RICHARD, JAMES
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1999
Main classification: C08F8
IPC codes: B65D65, C08F8, C08J5, C08L23