Ethylene-acrylic copolymer having excellent long-term adhesive force and method for preparing same

Abstract

The ethylene-acrylic acid copolymer according to the present invention has a zero shear viscosity ([eta] 0) and a storage modulus (G ') in specific ranges, thereby having the effect of being able to maintain initial high adhesive properties for a long period of time.

Description

TECHNICAL FIELD

[0001] The present invention relates to an ethylene-acrylic acid copolymer and a method for preparing the same, and more particularly, to an ethylene-acrylic acid copolymer which can stably maintain an initial high adhesive force for a long time and a method for preparing the same. BACKGROUND

[0002] An ethylene-acrylic acid copolymer (EAA) is a high value-added chemical product and is used in various fields, and is mainly used as a functional adhesive resin, for example, as an adhesive for a thin packaging material such as an aluminum foil for milk packaging, a detergent, etc.

[0003] However, the ethylene-acrylic acid copolymer requires a high pressure apparatus in a preparation process, and requires a high level of technical ability, for example, requires production of a product at a high acidity, etc. For example, copolymerization of an ethylene monomer and a carboxylic acid monomer is performed using a high pressure radical copolymerization system, specifically, through a high pressure autoclave reactor or a tubular reactor.

[0004] In particular, when the ethylene-acrylic acid copolymer is coated and heat-adhered to the surface of a high molecular film, paper, a metal foil, and a fabric, etc., it initially has excellent adhesive properties, but has a limitation in that the adhesive force is reduced over time.

[0005] Therefore, there is a need to research an ethylene-acrylic acid copolymer which can stably maintain an initial high adhesive property for a long time after adhesion. SUMMARY

[0006] (1) Technical problem to be solved

[0007] The present invention relates to an ethylene-acrylic acid copolymer which can maintain an initial high adhesive property for a long time and a method for preparing the same.

[0008] (2) Technical solution

[0009] The present invention can provide an ethylene-acrylic acid copolymer, the ethylene-acrylic acid copolymer having a zero shear viscosity (η0) of 3800 Pa·s or more at 170℃, and a storage modulus (G') of 90 Pa or more at a loss modulus (G'') of 500 Pa at a cross over frequency of 0.01-20 Hz at 170℃.

[0010] As one embodiment, in an ethylene-acrylic acid copolymer in which the logM value of the maximum dw / dlogM satisfies the following Formula 1, the weight average molecular weight of the ethylene-acrylic acid copolymer having a cumulative concentration fraction of 0.75 or more can be 220,000 g / mol or more.

[0011] [Formula 1]

[0012] 4.2 ≤ logM ≤ 4.8

[0013] (the logM can refer to a logarithmic value of a molecular weight M of an ethylene-acrylic acid copolymer as a horizontal axis of a molecular weight distribution curve measured by gel permeation chromatography, and a maximum peak value of dw / dlogM, which differentiates a concentration fraction w with a logarithmic value of a molecular weight logM, can be present in the range of the logM.)

[0014] As one embodiment, the mass average molecular weight / number average molecular weight (Mw / Mn) of the ethylene-acrylic acid copolymer can be 6 or more, and the Z average molecular weight / mass average molecular weight (Mz / Mw) can be 3.9 or more.

[0015] As one embodiment, the mass average molecular weight (Mw) of the ethylene-acrylic acid copolymer can be 90000 g / mol or more, the number average molecular weight can be 17000 g / mol or more, and the Z average molecular weight (Mz) can be 400000 g / mol or more.

[0016] As one embodiment, the content of an acrylic acid structural unit in the ethylene-acrylic acid copolymer can be 1 to 30% by weight of the total weight of the copolymer.

[0017] As one embodiment, the melt index (190°C / 2.16 kg, ASTM D1238) of the ethylene-acrylic acid copolymer can be 5 to 15.

[0018] As one embodiment, the ethylene-acrylic acid copolymer can be produced by polymerizing monomers at a temperature of 150 to 350°C and a pressure of 1000 to 5000 bar (bar).

[0019] As one embodiment, an adhesive can be provided, the adhesive including the ethylene-acrylic acid copolymer.

[0020] As one embodiment, an adhesive can be provided, the adhesive forming an adhesive layer between an aluminum metal sheet and a low-density polyethylene sheet and performing co-extrusion lamination, and a time required for the laminated sheet to lose adhesion in a citric acid aqueous solution (3% by weight) at 45°C is 14 days or more.

[0021] As one embodiment, a laminated sheet can be provided, in which an adhesive including the ethylene-acrylic acid copolymer forms an adhesive layer between a metal sheet and a polymer sheet.

[0022] As one embodiment, a package can be provided, which is formed of a laminate including the laminated sheet, and which has a fluid containing space.

[0023] (III) Beneficial Effects

[0024] The ethylene-acrylic acid copolymer according to the present application has the effect that the initial high adhesion property can be maintained for a long period of time. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a graph measuring the change in dw / dlogM and the cumulative concentration fraction according to logM of the ethylene-acrylic acid copolymer of the present application. DETAILED DESCRIPTION

[0026] Hereinafter, the ethylene-acrylic acid copolymer having excellent long-term adhesion and a method for preparing the same according to the present application will be explained in detail.

[0027] Unless otherwise defined, the technical and scientific terms used in the present specification have the meanings commonly understood by one of ordinary skill in the art to which the present application pertains, and the description below skips the explanation of the well-known functions and configurations that can unnecessarily make the gist of the present application unclear.

[0028] The singular forms of the terms used in the present specification can be interpreted as including the plural forms unless otherwise specified.

[0029] The numerical range used in the present specification includes the lower limit value and the upper limit value and all values within the range, the increments logically deduced from the form and width of the defined range, all values defined therein, and all possible combinations of the upper limit and lower limit of the numerical range defined in different forms from each other. In the specification of the present application, values other than the numerical range that can occur due to experimental error or rounding of numbers are also included in the defined numerical range unless otherwise defined.

[0030] The "comprising" or "including" recited in the present specification is an open-ended recitation with the same meaning as the expressions "having," "containing," "including," and the like, and does not exclude elements, materials, or processes not further listed.

[0031] In the present specification, the unit used without special mention indicates weight.

[0032] The term "layer" or "film" recited in the present specification means that each material forms a continuum and has a dimension of thickness that is relatively small compared to the width and length. Therefore, the term "layer" or "film" in the present specification should not be interpreted as a two-dimensional flat plane.

[0033] Ethylene-acrylic acid copolymer (EAA) is a high value-added chemical product and is widely used in various fields. In particular, when ethylene-acrylic acid copolymer is coated and adhered on the surface of adherends having various surface materials such as high molecular films, paper, metal foils, and fabrics, it has excellent initial adhesion, and thus is mainly used for adhesive applications. However, the existing ethylene-acrylic acid copolymer has a limitation in that the initial adhesion is lost over time after being adhered to the adherend. Therefore, there is a serious problem in that the storage, transportation, and the like of the product on which the adhesion is completed need to be managed, and as time passes, a great influence on the quality of the product is required, and thus a high cost is required.

[0034] As described above, the existing known ethylene-acrylic acid copolymer has a problem in that the long-term adhesion is significantly low. Therefore, the present application redefines the elements that affect the long-term adhesion of ethylene-acrylic acid copolymer, and by targeting the numerical range of the zero shear viscosity and the storage modulus, which are specific elements, that can maximize the long-term adhesion, the present application provides an ethylene-acrylic acid copolymer having an extremely excellent long-term adhesion compared to the existing ethylene-acrylic acid copolymer.

[0035] As a method of significantly improving the long-term adhesion characteristics of ethylene-acrylic acid copolymer, the ethylene-acrylic acid copolymer according to the present application can have a zero shear viscosity (η0) of 3800 Pa·s or more at 170℃, and a storage modulus (G') of 90 Pa or more when the loss modulus (G'') of the ethylene-acrylic acid copolymer measured at a crossover frequency of 0.01-20 Hz at 170℃ is 500 Pa.

[0036] As one example, the ethylene-acrylic acid copolymer according to the present application can have a lower limit of the zero shear viscosity (η0) of 3800 Pa·s or more, 3900 Pa·s or more, 4000 Pa·s or more, 4100 Pa·s or more, 4200 Pa·s or more, 4300 Pa·s or more, 4500 Pa·s or more, 4600 Pa·s or more, 4700 Pa·s or more, 4800 Pa·s or more, 4900 Pa·s or more, 5000 Pa·s or more, and an upper limit of 6000 Pa·s or less, 5500 Pa·s or less, 5200 Pa·s or less, but is not limited thereto.

[0037] The lower limit of the storage modulus (G') of the ethylene-acrylic acid copolymer according to the present application can be 90 Pa or more, 91 Pa or more, 92 Pa or more, 93 Pa or more, 94 Pa or more, 95 Pa or more, 96 Pa or more, and the upper limit can be 100 Pa or less, 99 Pa or less, but is not limited thereto.

[0038] Thereby, excellent initial adhesion properties to adherends having various surface materials can be maintained for a long period of time, and in particular, long-term adhesion properties between an aluminum metal surface and a polyethylene film surface can be further improved.

[0039] The zero shear viscosity is denoted by η0, and is the viscosity at which the flow of a material substantially stops. The zero shear viscosity can refer to a representative value calculated by extrapolation from the melt viscosity measured according to the change in shear rate at a specific temperature using a rheometer. In the present application, the zero shear viscosity can refer to the viscosity value calculated when the shear rate converges to 0 according to the melt viscosity data measured at a temperature of 170°C in the crossover frequency region of 0.01-20 Hz.

[0040] Further, the storage modulus is denoted by G', and is a measure of the amount of stored energy, i.e., the elastic component of a substance. The loss modulus is denoted by G", and is a measure of the amount of energy lost in the form of heat, and is the viscous component of a substance. In the present application, the storage modulus can refer to the storage modulus at a loss modulus (G") of 500 Pa measured at 170°C in the crossover frequency region of 0.01-20 Hz. The zero shear viscosity and the storage modulus are properties of a polymer defined in advance, and a more specific measurement method can be referred to the following embodiments or a publicly known document.

[0041] As one example, in an ethylene-acrylic acid copolymer in which the logM value at the maximum dw / dlogM satisfies the following Formula 1, the weight average molecular weight of the ethylene-acrylic acid copolymer in which the cumulative concentration fraction is 0.75 or more can be 220,000 g / mol or more.

[0042] [Formula 1]

[0043] 4.2 ≤ logM ≤ 4.8

[0044] The logM refers to the logarithmic value of the molecular weight M of the ethylene-acrylic acid copolymer measured by gel permeation chromatography as the horizontal axis of the molecular weight distribution curve, and dw / dlogM in which the concentration fraction w is differentiated by the logarithmic value of the molecular weight logM has a maximum peak in the range of the logM.

[0045] Reference Figure 1The ethylene-propylene acid copolymer of the present application is described based on data measured by gel permeation chromatography using polystyrene as a conversion standard.

[0046] In a differential molecular weight distribution curve in which the horizontal axis is a logarithmic value of a molecular weight M and the vertical axis is a differential value dw / dlogM of a logarithmic value of a molecular weight logM with respect to a concentration fraction w, the ethylene-propylene acid copolymer is a copolymer in which a proportion of a high molecular weight is high, which includes a chromatogram in a form having a shoulder in a high molecular region. Further, the ethylene-propylene acid copolymer is a copolymer in which (1) a value of dw / dlogM is maximum in a range of 4.2≤logM≤4.8, and (2) a weight average molecular weight of a high molecular having a cumulative concentration fraction of 0.75 or more is 220000 g / mol or more.

[0047] The lower limit of the weight average molecular weight of the high molecular having a cumulative concentration fraction of 0.75 or more can be 220000 g / mol or more, 230000 g / mol or more, 240000 g / mol or more, 260000 g / mol or more, and the upper limit can be 400000 g / mol or less, 380000 g / mol or less, 350000 g / mol or less, 300000 g / mol or less, 280000 g / mol or less, but is not limited thereto.

[0048] The lower limit of the mass average molecular weight / number average molecular weight (Mw / Mn) of the ethylene-propylene acid copolymer can be 6 or more, 6.1 or more, 6.2 or more, 6.3 or more, 6.4 or more, 6.5 or more, and the upper limit can be 8 or less, 7 or less, but is not limited thereto.

[0049] The lower limit of the Z average molecular weight / mass average molecular weight (Mz / Mw) of the ethylene-propylene acid copolymer can be 3.9 or more, 4.0 or more, 4.1 or more, and the upper limit can be 6 or less, 5 or less, but is not limited thereto.

[0050] The lower limit of the mass average molecular weight (Mw) of the ethylene-propylene acid copolymer can be 90000 g / mol or more, 100000 g / mol or more, 110000 g / mol or more, and the upper limit can be 200000 g / mol or less, 150000 g / mol or less, but is not limited thereto.

[0051] The lower limit of the number average molecular weight of the ethylene-propylene acid copolymer can be 17000 g / mol or more, 17100 g / mol or more, 17200 g / mol or more, and the upper limit can be 20000 g / mol or less, 19000 g / mol or less, but is not limited thereto.

[0052] The lower limit of the Z-average molecular weight (Mz) of the ethylene-acrylic acid copolymer can be 400,000 g / mol or more, 410,000 g / mol or more, 420,000 g / mol or more, 440,000 g / mol or more, 450,000 g / mol or more, 460,000 g / mol or more, 470,000 g / mol or more, and the upper limit can be 600,000 g / mol or less, 500,000 g / mol or less, 490,000 g / mol or less, but is not limited thereto.

[0053] The ethylene-acrylic acid copolymer according to the present application can have a long chain branching structure, and the proportion of high molecular weight in the molecular weight distribution can be high, and the entanglement between the high molecular chains can be more. As one example, the copolymer having such a structural feature satisfies the average molecular weight and the molecular weight distribution in the above range at the same time, so that the reduction of the adhesion force over time can be significantly delayed, and the above long-term adhesion force can be further improved.

[0054] The zero shear viscosity and the storage modulus can be controlled by adjusting various preparation conditions in the preparation method of the ethylene-acrylic acid copolymer. As one example, by adjusting the polymerization pressure, the polymerization temperature, the use amount of the initiator, and the like, an ethylene-acrylic acid copolymer having a controlled zero shear viscosity and storage modulus can be provided.

[0055] The ethylene-acrylic acid copolymer according to the present application can be prepared by a preparation method including a polymerization step of copolymerizing monomers including an ethylene monomer and an acrylic acid comonomer to prepare an ethylene-acrylic acid copolymer, at this time, the polymerization can be performed under high temperature and high pressure conditions.

[0056] As one example, the monomers can be polymerized to prepare an ethylene-acrylic acid copolymer at a temperature of 150-350℃ or 180-300℃. In addition, the ethylene-acrylic acid copolymer can be prepared by polymerizing the monomers at a pressure of 1000-5000 bar or 1500-4000 bar.

[0057] The ethylene-acrylic acid copolymer according to the present application can include an acrylic acid structural unit and an ethylene structural unit, the content of the acrylic acid structural unit can be 1-30 wt%, 3-25 wt%, or 7-15 wt% of the total weight of the copolymer. When the above range is satisfied, the initial high adhesion property can be achieved, and by satisfying the zero shear viscosity and the storage modulus in the above range, the initial high adhesion property can be maintained for a long time.

[0058] The melt index (190°C / 2.16 kg, ASTM D 1238) of the ethylene-acrylic acid copolymer according to the present application is not greatly limited, but can be, for example, 5 to 15, 5 to 10, or 5 to 9, but is not limited thereto.

[0059] Hereinafter, the polymerization process is described as one specific example.

[0060] The polymerization step according to one example of the present application can include a supply step in which a compressed material formed by secondary compression of a mixture using a secondary compressor as a high-pressure compressor is supplied to a reactor, the mixture including ethylene monomers that are once compressed by a primary compressor and monomers containing acrylic acid comonomers. In addition, the polymerization step can further include a circulation step in which unreacted residues separated from a discharge material discharged from the reactor are separated and supplied again to the front end of the primary compressor or the secondary compressor. Herein, the "discharge material" is a material discharged after an ethylene-acrylic acid polymerization reaction inside a reactor in a process of producing an ethylene-acrylic acid copolymer, and can include an ethylene copolymer and unreacted residues. In addition, the "unreacted residues" are materials other than the ethylene-acrylic acid copolymer in the process of producing the ethylene-acrylic acid copolymer, and specifically, can include unreacted ethylene monomers, unreacted acrylic acid comonomers, solvents, initiators, other additives, etc.

[0061] Specifically, the supply step can include a first supply step in which ethylene monomers are supplied and a second supply step in which acrylic acid comonomers are supplied. In describing the supply process of the reactants, the ethylene monomers supplied in the first supply step are compressed by the primary compressor to generate a once-compressed material. Thereafter, a mixture including the acrylic acid comonomers supplied in the second supply step and the once-compressed material is secondary-compressed using a high-pressure compressor as a secondary compressor to generate a secondary-compressed material. The generated secondary-compressed material is supplied to the reactor, and the ethylene monomers and the acrylic acid comonomers in the secondary-compressed material are copolymerized in the reactor to synthesize the ethylene-acrylic acid copolymer.

[0062] The inside of the reactor is provided with a stirrer for mixing the reactants and the products, and the stirrer shaft has a baffle that divides the inside of the reactor into an upper reactor and a lower reactor. The ethylene monomers and the acrylic acid comonomers are supplied to the upper reactor and the lower reactor, respectively. However, the presence or absence and the number of the baffle that divides the inside of the reactor do not limit the polymerization process of the ethylene-acrylic acid copolymer.

[0063] The circulating step can include a first circulating step in which the effluent discharged from the reactor is separated by a high-pressure separator, and unreacted residue is supplied to the front end of the secondary compressor. In addition, the circulating step can include a second circulating step in which the substance separated from the high-pressure separator is secondarily separated by a low-pressure separator, and unreacted residue is supplied to the front end of the primary compressor.

[0064] Specifically, in the first circulating step, impurities can be removed by discharging the impurities to the outside through a filter that can filter and separate unreacted residue, and the impurities other than the unreacted residue can also be removed by filtering and separating. In the second circulating step, the effluent from which the unreacted residue is separated by primary filtering can be secondarily filtered, and the separated residual unreacted residue can be supplied to the primary compressor.

[0065] As one exemplary embodiment, the reaction temperature of the upper portion of the reactor can be adjusted to be at least 10°C lower than the reaction temperature of the lower portion of the reactor, and preferably, the temperature difference is 12 to 15°C.

[0066] In the polymerizing step, the polymerization can be polymerization caused by an initiator, and for example, can be radical polymerization. Accordingly, the compressed material supplied to the reactor can further include an initiator, and specifically, can further include a radical initiator, and the polymerization can be performed by causing reactions between the respective monomers under the radical initiator. As one example, the polymerization can be performed by an initiator mixed solution including a radical initiator and a dilution solvent. The use content of the initiator can be an extent to initiate radical polymerization, and for example, 0.001 to 1 parts by weight of the initiator can be used with respect to 100 parts by weight of the total monomers. In addition, the use content of the dilution solvent can also be appropriately adjusted, and for example, 5 to 1000 parts by weight of the dilution solvent can be diluted and used with respect to 1 part by weight of the initiator. The initiator mixed solution can be supplied to the upper portion of the reactor and the lower portion of the reactor, respectively. However, this is merely described as one specific example, and should not be construed as limiting the present application thereto.

[0067] As one example, the radical initiator can be any one or two or more selected from peroxyl organic peroxides including peroxide carbonate, peroxide dicarbonate, peroxide ester, and peroxide ketal, as long as the radical initiator can cause radical polymerization of the ethylene monomer and the acrylic acid comonomer. However, this is merely described as one specific example, and should not be construed as limiting the present application thereto.

[0068] The dilution solvent can use a known initiator dilution solvent, for example, when using a paraffin-based solvent as a dilution solvent, more preferably, when using Isopar-H in a paraffin-based solvent as a dilution solvent, it is possible to more accurately control the zero shear viscosity and storage modulus while achieving the above-mentioned effects.

[0069] In one example of the present application, the compressed material supplied to the reactor can further include a chain transfer agent. As a non-limiting example, the chain transfer agent can use aliphatic hydrocarbons and olefin-based hydrocarbons such as isobutane, propylene, butene, hexane, cyclohexane, octane, etc. compounds; ketone-based compounds such as acetone, methyl ethyl ketone, diethyl ketone, dipentyl ketone, etc.; aldehyde-based compounds such as formaldehyde, acetaldehyde, propionaldehyde, etc.; and alcohol-based compounds such as methanol, ethanol, propanol, butanol, etc. When using a chain transfer agent, the use content of the chain transfer agent is not too limited, for example, 0.1-20 parts by weight of the chain transfer agent can be used with respect to 100 parts by weight of the total monomer. However, this is merely described as an example and should not be interpreted as limiting the present application thereto.

[0070] As described above, the ethylene-acrylic acid copolymer according to the present application is used for an adhesive use, and the present application can provide an adhesive including the ethylene-acrylic acid copolymer.

[0071] The adhesive according to one example of the present application can further include an additive, and when further including an additive, the content of the additive can be 0.01-10 parts by weight or 0.05-5 parts by weight with respect to 100 parts by weight of the ethylene-acrylic acid copolymer. As an example, the additive can include any one or two or more selected from pigments, dyes, antifoaming agents, preservatives, thickeners, modifiers, humectants, nucleating agents, anti-blocking agents, processing aids, ultraviolet stabilizers, neutralizing agents, lubricants, surfactants, tackifiers, plasticizers, antioxidants, colorants, reinforcing agents, blowing agents, and flame retardants, etc. However, this is merely described as a specific example and should not be interpreted as limiting the present application thereto.

[0072] The adhesive, i.e., the ethylene-acrylic acid copolymer according to the present application can be used for adhesive use for various objects such as sterilization packaging of milk packaging and the like, aluminum foil laminates and the like, and specifically, exhibits high adhesive properties in adherends having various surface materials such as polymeric films, paper, metal foils, and fabrics. In particular, the present application can achieve relatively higher initial adhesive properties and higher long-term adhesive properties in adhesion between metal surfaces, adhesion between polymeric films, or adhesion between metal surfaces and polymeric films. As one example, the adhesive properties between an aluminum metal sheet surface and a polyethylene sheet surface can be more excellent. In the case of the adhesive according to one example, in a severe condition in which a laminated sheet in which the adhesive forms an adhesive layer between an aluminum metal sheet and a low-density polyethylene sheet and is co-extrusion laminated is put in a citric acid aqueous solution (3% by weight) at 45°C, the time required for loss of adhesive force can be 14 days or more or 15 days or more. When the zero shear viscosity and the storage modulus in the above-mentioned range are not satisfied, the time required for loss of adhesive force can be 12 days or less, which is significantly reduced by about 25% or more.

[0073] As one example, the present application can provide a laminated sheet in which the adhesive, i.e., the ethylene-acrylic acid copolymer forms an adhesive layer between a metal sheet and a polymeric sheet. In addition, the present application can provide a package formed of a laminate including the laminated sheet, and the package has a fluid containing space.

[0074] Hereinafter, the present application is described in detail by way of examples, but the scope of the rights of the present application is not limited to the following examples.

[0075] [Example 1]

[0076] <Preparation of Ethylene-Acrylic Acid Copolymer>

[0077] Ethylene monomer was supplied to the front end of the primary compressor at an average flow rate of 900 kg / hour, compressed in the primary compressor, and supplied to the secondary compressor at a pressure of 200 bar, and acrylic acid comonomer was supplied to the secondary compressor at an average flow rate of 500 kg / hour. An initiator mixed solution was supplied to the inside of the reactor at an average flow rate of 53 L / hour, the inside temperature of the upper portion of the reactor was adjusted to 234°C, the inside temperature of the lower portion of the reactor was adjusted to 248°C, and the pressure was adjusted to 2175 bar, thereby inducing a polymerization reaction. Among them, the initiator mixed solution used was a mixed solution in which an initiator (tert-butyl peroxyacetate) was diluted to 10% by weight in a dilution solvent (Isopar-H, ExxonMobil Corp.). In addition, the effluent discharged from the reactor was supplied to a high-pressure separator, and the effluent in which the unreacted residue was once separated by the high-pressure separator was supplied to a low-pressure separator, and the unreacted residue was twice separated. After the unreacted residue was twice separated in the low-pressure separator, an ethylene-acrylic acid copolymer was obtained, at this time, the content of acrylic acid in the ethylene-acrylic acid copolymer was 8.2% by weight.

[0078] <Measurement of physical properties of ethylene-acrylic acid copolymer>

[0079] The zero shear viscosity (η0), storage modulus, average molecular weight, polydispersity index, and molecular weight distribution of the prepared ethylene-acrylic acid copolymer were measured by the following method, and the long-term adhesion of the ethylene-acrylic acid copolymer was measured, and the results are shown in Table 1 below.

[0080] 1. Measurement of zero shear viscosity, storage modulus

[0081] The ethylene-acrylic acid copolymer was aged for more than 3 weeks under constant temperature and humidity conditions (temperature: 25°C, relative humidity: 45%) after preparation. Then, the above aged ethylene-acrylic acid copolymer was physically pressed using a hot press at 160°C for 10 seconds, thereby preparing a sample having a diameter of 2.5 cm and a thickness of 2 mm. After that, the rheological viscosity data of the storage modulus of the sample were obtained using an ARES G2 machine. Among them, the sample was loaded into the ARES G2 machine at 170°C, and the sample holder was placed in a state in which the thickness was reduced to 1 mm for 20 minutes to remove air bubbles, and then the rheological data of the storage modulus were measured, and the measurement was performed in the cross-over frequency region of 0.01-20 Hz. Then, the storage modulus (G') at the time when the loss modulus (G'') was 500 Pa was calculated from the rheological data.

[0082] Further, the zero shear viscosity (η0) of the ethylene-acrylic acid copolymer is a viscosity calculated by regression of the data using the Cross model, calculating the viscosity at which the crossover frequency converges to 0.

[0083] 2. Measurement of average molecular weight, polydispersity index, molecular weight distribution

[0084] The average molecular weight, polydispersity index, and molecular weight distribution of the ethylene-acrylic acid copolymer were measured using gel permeation chromatography (GPC). At this time, for the ethylene-acrylic acid copolymer, it is difficult to find a suitable combination of solvents and columns due to the difference in polarity between ethylene and acrylic acid, and it is also difficult to address the mutual reaction of the hydrogen bond of the pure copolymer and the acid group of the GPC column. In order to avoid such interaction, the acid group of the copolymer can be esterified, methylated, silylated, and the ethylene-acrylic acid copolymer can be silylated for GPC analysis. At this time, the temperature at the time of measurement was 160°C, chlorobenzene was used as a solvent, and the molecular weight was calculated using polystyrene as a standard sample.

[0085] <Evaluation of long-term adhesion of ethylene-acrylic acid copolymer>

[0086] A laminated sheet (Al / EAA / LDPE multi-layer) in which the adhesive formed an adhesive layer between an aluminum metal sheet and a low-density polyethylene sheet and was co-extrusion laminated was put into a container filled with a citric acid aqueous solution (3 wt%) at 45°C and sealed. Then, the container was left under a constant temperature condition at 45°C, and then the time required for loss of adhesion was measured using a peel tester (TA Instrument), and the results are shown in Table 1 below.

[0087] [Examples 2 to 5]

[0088] Ethylene-acrylic acid copolymers were prepared by the same method as Example 1, except that the ethylene-acrylic acid copolymers were prepared by adjusting the pressure, temperature, and content of the initiator so that the prepared ethylene-acrylic acid copolymers had different values of zero shear viscosity (η0) and storage modulus (G') shown in Table 1 below. Then, the zero shear viscosity (η0), storage modulus, and long-term adhesion of the prepared ethylene-acrylic acid copolymers were measured by the same method as Example 1, and the results are shown in Table 1 below.

[0089] Specifically, the same method as in Example 1 was used, except that in Example 2, the pressure, temperature, and flow rate of the initiator were adjusted to 2180 bar, 232°C in the upper part of the reactor, 244°C in the lower part of the reactor, and 53 L / hour of the initiator mixed solution, respectively, in Example 3, the pressure, temperature, and flow rate of the initiator were adjusted to 2200 bar, 235°C in the upper part of the reactor, 248°C in the lower part of the reactor, and 42 L / hour of the initiator mixed solution, respectively, in Example 4, the pressure, temperature, and flow rate of the initiator were adjusted to 2225 bar, 235°C in the upper part of the reactor, 248°C in the lower part of the reactor, and 45 L / hour of the initiator mixed solution, respectively, and in Example 5, the pressure, temperature, and flow rate of the initiator were adjusted to 2160 bar, 235°C in the upper part of the reactor, 249°C in the lower part of the reactor, and 33 L / hour of the initiator mixed solution, respectively.

[0090] [Comparative Examples 1 to 4]

[0091] The same method as in Example 1 was used, except that an ethylene-acrylic acid copolymer having a zero shear viscosity (η0) and a storage modulus (G') not within the numerical range of the zero shear viscosity (η0) and the storage modulus (G') proposed in the present application was prepared by controlling the pressure, temperature, and content of the initiator. The zero shear viscosity (η0), storage modulus, and long-term adhesion of the prepared ethylene-acrylic acid copolymer were measured by the same method as in Example 1, and the results are shown in Table 1 below.

[0092] The results of the zero shear viscosity, storage modulus at a loss modulus of 500 Pa, average molecular weight (Mw, Mn, Mz), molecular weight distribution, polydispersity index (PDI), and long-term adhesion (adhesion retention time) of the ethylene-acrylic acid copolymers of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0093] [Table 1]

[0094]

[0095] Referring to Table 1, in the examples in which the zero shear viscosity (η0) at 170°C is 3800 Pa-s or more and the storage modulus (G') at 500 Pa of the loss modulus (G'') measured at a cross-over frequency of 0.01 to 20 Hz at 170°C is 90 Pa or more, the adhesive force retention time is 15 days or more. On the other hand, in the comparative examples in which the zero shear viscosity (η0) is less than 3800 Pa-s and the storage modulus (G') is less than 90 Pa, the adhesive force retention time is 12 days or less. Thus, it can be confirmed from Table 1 that the long-term adhesive force of the examples satisfying the zero shear viscosity (η0) and the storage modulus (G') in the specific ranges is 30% or more superior to that of the comparative examples not satisfying the zero shear viscosity (η0) and the storage modulus (G') in the above ranges. Furthermore, when comparing Comparative Example 3 and Comparative Example 4 based on the examples, it can be seen that excellent long-term adhesive force effects can be achieved only when the zero shear viscosity (η0) in the specific range and the storage modulus (G') in the specific range are both satisfied, and that when either of the two is not satisfied, the above effects cannot be achieved. Furthermore, it can be confirmed from Table 1 that in Example 1 having excellent long-term adhesive force effects, the weight average molecular weight of the high molecular having a cumulative concentration fraction of 0.75 or more is 262169 g / mol, and that the molecular weight of the high molecular region is considerably high compared to Comparative Example 2 (weight average molecular weight: 213892 g / mol) not having such a weight average molecular weight.

[0096] Furthermore, in Example 1 and Example 2, it was confirmed that the physical properties such as the zero shear viscosity, the storage modulus at 500 Pa of the loss modulus, etc. were maintained even after 350 days using an Advanced Rheometric Expansion System (ARES) for measurement.

Claims

1. An ethylene-acrylic acid copolymer having a zero shear viscosity η0 at 170°C of 3800 Pa-s or more, and a storage modulus G' at a loss modulus G" of 500 Pa measured at a cross-over frequency of 0.01 to 20 Hz at 170°C of 90 Pa or more.

2. The ethylene-propylene acid copolymer of claim 1, wherein, In the ethylene-acrylic acid copolymer in which the logM value at the maximum dw / dlogM satisfies the following formula 1, the weight average molecular weight of the ethylene-acrylic acid copolymer having a cumulative concentration fraction of 0.75 or more is 220,000 g / mol or more, [Formula 1] 4.2 ≤ logM ≤ 4.8 The logM refers to a logarithmic value of a molecular weight M of an ethylene-acrylic acid copolymer as an abscissa of a molecular weight distribution curve measured by gel permeation chromatography, and dw / dlogM in which a concentration fraction w is differentiated by a logarithmic value of a molecular weight logM has a maximum peak value in the range of the logM.

3. The ethylene-propylene acid copolymer of claim 1, wherein, The mass average molecular weight / number average molecular weight, that is, Mw / Mn, of the ethylene-acrylic acid copolymer is 6 or more, and the Z average molecular weight / mass average molecular weight, that is, Mz / Mw, is 3.9 or more.

4. The ethylene-propylene acid copolymer of claim 3, wherein, The mass average molecular weight Mw of the ethylene-acrylic acid copolymer is 90,000 g / mol or more, the number average molecular weight is 17,000 g / mol or more, and the Z average molecular weight Mz is 400,000 g / mol or more.

5. The ethylene-propylene acid copolymer of claim 1, wherein, The content of an acrylic acid structural unit in the ethylene-acrylic acid copolymer is 1 to 30% by weight of the total weight of the copolymer.

6. The ethylene-propylene acid copolymer of claim 1, wherein, The ethylene-acrylic acid copolymer has a melt index of 5 to 15 measured according to ASTM D 1238 at 190°C / 2.16 kg.

7. The ethylene-propylene acid copolymer of claim 1, wherein, The ethylene-acrylic acid copolymer is produced by polymerizing monomers at a temperature of 150 to 350°C and a pressure of 1000 to 5000 bar.

8. An adhesive comprising the ethylene-acrylic acid copolymer according to any one of claims 1 to 7.

9. The adhesive of claim 8, wherein, The time required for the adhesive to lose adhesion in a 3% by weight aqueous citric acid solution at 45°C is 14 days or more in a laminated sheet in which the adhesive forms an adhesive layer between an aluminum metal sheet and a low-density polyethylene sheet and is co-extrusion laminated.

10. A laminated sheet in which the adhesive according to claim 8 forms an adhesive layer between a metal sheet and a polymer sheet.

11. A package formed of a laminate including the laminated sheet according to claim 10, and having a fluid containing space.

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