KR102247231B1 - Ethylene vinyl acetate and molded article produced therefrom - Google Patents

Abstract

In the present invention, the content of vinyl acetate is 15 to 30% by weight, the melt index (measured with a load of 2.16 kg at 125°C according to ASTM D1238) is 2.5 to 5.5 g/10min, and the molecular weight distribution (PDI) and the content of long chain branches (LCB) meets the relationship of 3.012*PDI+3.950≦LCB≦2.143*PDI+11.343, and relates to an ethylene vinyl acetate copolymer and a molded article made therefrom.

Description

Ethylene vinyl acetate copolymer and molded article manufactured therefrom {ETHYLENE VINYL ACETATE AND MOLDED ARTICLE PRODUCED THEREFROM}

The present invention relates to an ethylene vinyl acetate copolymer having a high content of vinyl acetate, low melt index, and sufficient tensile strength.

Ethylene vinyl acetate is a copolymer of ethylene and vinyl acetate. Depending on the content of vinyl acetate, the range of use is very wide, from hard materials to soft materials such as hot melt adhesives. Compared to polyethylene, it has low crystallinity, low temperature characteristics and impact resistance. It has this excellent feature.

In addition, ethylene vinyl acetate has a thermoplastic polymer or rubbery character, has excellent electrical insulation and voltage resistance, and has excellent transparency, barrier properties, adhesion, and UV properties. It is widely used for tapes, adhesives, various sheets, and the like, and has recently been expanding its use area with a protective film for photovoltaic devices such as solar cells.

In general, the ethylene vinyl acetate copolymer can be prepared by injecting ethylene and vinyl acetate into an autoclave reactor or a tubular reactor at an appropriate ratio into the reactor, and polymerizing under high temperature/high pressure conditions. At this time, if the amount of vinyl acetate input to the reactor increases, some vinyl acetate may act as a chain transfer agent, and eventually the molecular weight of ethylene vinyl acetate decreases and the melt index (MI) increases, resulting in tensile strength and There is a limit to the deterioration of the same mechanical properties.

Therefore, in the case of the existing ethylene vinyl acetate copolymer with a high vinyl acetate content, it has excellent flexibility and elasticity, but causes a problem of deteriorating mechanical properties and workability, so it is used for wires, foaming, compounds, etc. There was a limit.

Accordingly, there is still a need for research on an ethylene vinyl acetate copolymer having sufficient tensile strength while maintaining a high content of vinyl acetate required for ethylene vinyl acetate for use in wires, foaming, compounds, and the like.

The present invention is to provide an ethylene vinyl acetate copolymer having a low melt index and sufficient tensile strength while containing a high content of vinyl acetate.

In the present invention, the content of vinyl acetate is 15 to 30% by weight,

A melt index (measured at 125° C. with a load of 2.16 kg according to ASTM D1238) of 2.5 to 5.5 g/10 min,

The molecular weight distribution (PDI) and the content of long-chain branches (LCB; based on 10,000 carbon atoms) satisfy the relationship of 3.012*PDI+3.950≤LCB≤2.143*PDI+11.343, to provide an ethylene vinylacetate copolymer.

In addition, the present invention provides a molded article made from the ethylene vinyl acetate copolymer.

Hereinafter, an ethylene vinyl acetate copolymer and a molded article prepared therefrom according to a specific embodiment of the present invention will be described in more detail.

According to one embodiment of the invention, the content of vinyl acetate is 15 to 30% by weight,

A melt index (measured at 125° C. with a load of 2.16 kg according to ASTM D1238) of 2.5 to 5.5 g/10 min,

An ethylene vinylacetate copolymer is provided, wherein the molecular weight distribution (PDI) and the content of long chain branches (LCB; based on 10,000 carbon atoms) satisfy the relationship of 3.012*PDI+3.950≤LCB≤2.143*PDI+11.343.

The ethylene vinyl acetate copolymer of this embodiment comprises vinyl acetate in a relatively high content of about 15 to 30% by weight, or about 20 to 30% by weight, or about 25 to 30% by weight, or about 27 to 30% by weight. , It can exhibit excellent flexibility, elasticity, transparency, heat seal properties, and blending properties.

In addition, the ethylene vinyl acetate copolymer has a low melt index (measured by a load of 2.16 kg at 125° C. according to ASTM D1238) of about 2.5 to 5.5 g/10min. In general, when the content of vinyl acetate in the ethylene vinyl acetate copolymer increases, some vinyl acetate may act as a chain transfer agent, and eventually the molecular weight of ethylene vinyl acetate decreases and the melt index (MI) increases, Although there is a limit in which mechanical properties are deteriorated, the ethylene vinyl acetate copolymer of one embodiment contains vinyl acetate in an amount of about 15% by weight or more, but by controlling the polymerization conditions to have a low melt index, mechanical properties such as tensile strength It can also be maintained excellently.

In addition, the ethylene vinyl acetate copolymer satisfies the relationship of 3.012*PDI+3.950≤LCB≤2.143*PDI+11.343 in molecular weight distribution (PDI) and long-chain branch content (LCB; based on 10,000 carbon atoms). In this case, the content of the long-chain branch of the ethylene vinyl acetate copolymer refers to the content of the long-chain branch having 15 to 25 carbon atoms per 10,000 carbon atoms, and size exclusion chromatography (SEC) is used in multi-angle light scattering (MALS). ) The value measured using SEC-MALS (multi angle light scattering) in combination with detection can be calculated by the following method.

First, using the SEC-MALS analysis method, it is possible to derive the Radius of gyration value (Rg), that is, the Rg-M relationship for each molecular weight (M) of the ethylene vinyl acetate copolymer.In theory, the branched polymer (b) at the same molecular weight is It is smaller than the linear polymer (l), and using an arbitrary linear polymer sample as reference data, calculate the branching index (g) through the following equation:

[Equation 1]

And, using the calculated g value, based on the Zimm-stockmayer equation of Equation 2, the branch number (B) for each molecular weight is calculated:

[Equation 2]

And, using the branch number (B) value for each molecular weight, a long chain branch (LCB) per 10,000 carbon atoms is calculated based on Equation 3 below:

[Equation 3]

In Equation 3, C is the number of carbons, and Ci is the polymer concentration of the i-th molecular weight (Mi).

The ethylene vinyl acetate copolymer of the embodiment that satisfies this relationship, in particular, increases the ratio of the highly crystalline region and the crystallinity of the copolymer, so that the ratio of long-chain branches may be low, and the molecular weight distribution may be narrowed. As such, the ethylene vinyl acetate copolymer has a low content of long-chain branches and a narrow molecular weight distribution, and thus may exhibit improved tensile strength at the same vinyl acetate content.

In addition, the ethylene vinyl acetate copolymer may have a long-chain branch content of about 15 to 25, preferably about 16 to 24, and more preferably about 17 to 23 per 10,000 carbon atoms. The content of the long-chain branch is related to the tensile strength of the ethylene vinyl acetate copolymer, and as in the copolymer of the embodiment, when the content of the long-chain branch is small and the molecular weight distribution is narrow, it has high tensile strength, It can be very preferably used in applications such as foaming and other compounds.

In addition, the ethylene vinyl acetate copolymer may have a molecular weight distribution (PDI) of about 4 to 5.5. The molecular weight distribution (PDI) refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw/Mn), and if the molecular weight distribution is less than 4, it is not possible to increase the line speed in the extrusion molding process, so that the ease of processing is It decreases, and when the molecular weight distribution exceeds 5.5, mechanical properties may decrease.

In addition, the weight average molecular weight (Mw) of the ethylene vinyl acetate copolymer may be about 50,000 to 100,000 g/mol.

The molecular weight distribution (PDI) and the weight average molecular weight were measured using SEC-MALS (multi angle light scattering) in the same manner as the content of the long chain branch described above.

Meanwhile, the ethylene vinyl acetate copolymer of the embodiment may be prepared by polymerizing an ethylene monomer and a vinyl acetate monomer in an autoclave reactor in the presence of a low temperature initiator and a high temperature initiator.

In addition, the polymerization step may be performed at a pressure of 1,800 bar or more by controlling (the maximum temperature at the bottom of the reactor)-(input gas temperature) of the autoclave reactor at 130 to 170°C.

As can be seen through the following examples, etc., the content of vinyl acetate described above by using two or more initiators including a low-temperature initiator and a high-temperature initiator together, and adjusting polymerization conditions such as temperature and pressure of each part of the reactor. , Melt index and molecular weight distribution-it is possible to prepare ethylene vinyl acetate that satisfies the content relational formula of long chain branches.

If two or more initiators including a low-temperature initiator and a high-temperature initiator are not used, or the polymerization conditions are different, the final produced ethylene vinyl acetate does not have a low melt index within the above-described range, or a molecular weight distribution and a long chain It is possible that the content of the branch does not meet the specific relationship described above.

A more detailed description of the method for producing ethylene vinyl acetate according to the embodiment is as follows.

Ethylene vinyl acetate copolymer can be prepared in an autoclave or tubular reactor.In general, ethylene vinyl acetate prepared in an autoclave reactor has a wide molecular weight distribution, and ethylene vinyl acetate prepared in a tubular reactor. Is characterized by a narrow molecular weight distribution, and it is common to select and manufacture a reactor according to the application.

However, in the case of using an autoclave reactor in which back-mixing takes place, since it is possible to maintain a uniform and high reaction temperature, higher vinyl than in the case of using a tubular reactor in which mixing occurs by turbulent plug flow. There is an advantage of producing an ethylene vinyl acetate copolymer having an acetate content.

Therefore, the manufacturing method of the embodiment is a method of controlling polymerization conditions such as temperature and pressure in the reactor using an autoclave reactor, and has a narrow molecular weight distribution and mechanical properties such as tensile strength even when the autoclave reactor is used. This excellent ethylene vinyl acetate copolymer can be produced.

More specifically, the manufacturing method of the embodiment includes the step of polymerizing an ethylene monomer and a vinyl acetate monomer in an autoclave reactor in the presence of a low temperature initiator and a high temperature initiator.

In the following specification, the low-temperature initiator refers to an initiator capable of initiating and/or accelerating the reaction between the ethylene monomer and the vinyl acetate monomer at a temperature of 100 to 160°C, and the high-temperature initiator refers to the reaction at 160°C to 230°C. It refers to an initiator capable of initiating and/or accelerating at a temperature of.

In general, when only one initiator is used in the manufacture of an ethylene vinyl acetate copolymer, the initiator cannot react when the operating temperature is too low, and when the reaction temperature is too high, the initiator is decomposed before polymerization of the copolymer, resulting in an initiator efficiency. Fall or run away reactions can occur.

Therefore, when using a mixture of a low-temperature initiator and a high-temperature initiator as an initiator, as in the method for producing the ethylene vinyl acetate copolymer of the above embodiment, the operating temperature range (for example, (the highest temperature at the bottom of the reactor)-(injection By widening the gas temperature)), the production of ethylene vinyl acetate having a narrow molecular weight distribution can be increased.

In addition, the low-temperature initiator and the high-temperature initiator may be mixed and used in a weight ratio of about 5:95 to 90:10, preferably about 20:80 to 70:30.

The low-temperature initiator has a characteristic capable of initiating a polymerization reaction at a temperature lower than a general high-pressure radical polymerization reaction temperature, for example, DIPND (1,4-di (2-neodecanoylperoxyisopropyl) benzene), CUPND (Cumylperoxy neodecanoate). , SBPC(Di(sec-butyl) peroxydicarbonate), NBPC(Di(n-butyl)peroxydicarbonate), EHP(Di(2-ethylhexyl) peroxydicarbonate), TAPND(Tert-amylperoxyneodecanoate), and TBPND(Tert-butyl peroxyneodecanoate) One or more compounds selected from the group may be used.

In addition, the high-temperature initiator has a characteristic capable of initiating a polymerization reaction at a temperature higher than a general high-pressure radical polymerization reaction temperature, for example, TAPPI (Tert-amylperoxy pivalate), TBPPI (Tert-butylperoxy pivalate), INP ( Di(3,5,5-trimethylhexanoyl) peroxide), TAPEH (Tert-amylperoxy 2-ethylhexanoate), TBPEH (Tert-butylperoxy 2-ethylhexanoate), TBPIB (Tert-butylperoxy-isobutyrate), TBPIN (Tert-butylperoxy-3, At least one compound selected from the group consisting of 5,5-trimethylhexanoate) and TBPA (Tert-butylperoxyacetate) may be used.

In addition, the low-temperature initiator and the high-temperature initiator may be used by diluting the initiator stock solution in a hydrocarbon solvent in an amount of 20 to 80 wt%, preferably 30 to 70 wt%. At this time, as the hydrocarbon solvent, for example, one or more selected from the group consisting of n-decane, n-octane, iso-dodecane, and iso-octene may be used, or an Isopar-based solvent, which is a commercial product of a mixture of hydrocarbons, may be used. .

In addition, the polymerization step is performed by controlling the pressure of the autoclave reactor, the temperature of the input gas, the maximum temperature at the bottom of the reactor, and the maximum temperature at the top of the reactor. Can be reduced, the molecular weight distribution can be narrowed, and the tensile strength can be increased.

The temperature of the input gas of the autoclave reactor refers to an average of the temperature measured between a portion divided for distribution of the input gas to each stage of the reactor and a portion connected to the reactor. In addition, the maximum temperature at the bottom of the reactor and the maximum temperature at the top of the reactor mean the temperatures measured by the thermocouple installed at the lowest position of the reactor and the highest end of the reactor, respectively.

In particular, the (highest temperature at the bottom of the reactor)-(input gas temperature) of the autoclave reactor is a reaction condition related to the conversion rate, which is the rate at which the monomer is converted to a polymer, the molecular weight distribution of the polymerized copolymer, and the content of short and long chain branches. By controlling the (highest temperature at the bottom of the reactor)-(input gas temperature) at about 130 to 170°C, preferably at about 130 to 165°C, an ethylene vinyl acetate copolymer having mechanical properties such as more excellent tensile strength is obtained. It can be prepared with conversion rate.

In addition, the temperature of the input gas may be about 10 to 60 ℃, preferably about 20 to 50 ℃. When the temperature of the input gas is lower than 10℃, it is difficult to control the polymerization heat of the autoclave, which is an adiabatic reactor, and a lost reaction may occur. When the temperature of the input gas is higher than 60℃, the polymerization conversion rate is lowered and thus the production cost is reduced. It is not desirable.

In addition, the maximum temperature at the bottom of the autoclave reactor may be about 170 to 230°C, preferably about 180 to 220°C. When the maximum temperature at the bottom of the reactor is lower than 170°C, the polymerization conversion rate is lowered, which is not preferable in terms of production cost, and when the maximum temperature at the bottom of the reactor is higher than 230°C, the run away reaction is caused by the problem of thermal stability of the vinyl acetate monomer. Can occur.

In addition, the maximum temperature at the top of the autoclave reactor may be about 120 to 180°C, preferably about 130 to 170°C. When the maximum temperature at the top of the reactor is lower than 120℃, it is difficult to control the reaction temperature and a lost reaction may occur. When the maximum temperature at the top of the reactor is higher than 180℃, the amount of initiator for polymerization of the target polymer increases. It is not desirable in terms of production cost.

In addition, the polymerization step may be carried out at a pressure of about 1800 bar or more, preferably about 1800 to 2000 bar. When the pressure in the reactor is low, less than 1800 bar, the amount of initiator for the polymerization of the target polymer increases, which is not preferable in terms of production cost, and when it is higher than 2000 bar, it is difficult to control in terms of polymerization stability, resulting in a lost reaction or a run away reaction. This can happen.

And, in the manufacturing method of the ethylene vinyl acetate copolymer of the embodiment, the vinyl acetate monomer is included in about 15 to 30 parts by weight, preferably about 26 to 30 parts by weight, based on 100 parts by weight of the sum of the ethylene monomer and the vinyl acetate monomer. can do.

Meanwhile, according to another embodiment of the present invention, a molded article manufactured from the ethylene vinyl acetate copolymer may be provided. As described above, the content of the vinyl acetate is 15 to 30% by weight, the melt index (measured with a load of 2.16 kg at 125°C according to ASTM D1238) is 2.5 to 5.5 g/10min, and the molecular weight distribution (PDI) and long chain Ethylene vinyl acetate copolymer in which the branch content (LCB) satisfies a specific relationship has excellent processability and improved tensile strength, and thus has a wider application field compared to molded products made of conventional ethylene vinyl acetate used in the past.

In addition to the ethylene vinyl acetate according to the present invention, the molded article is at least one selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, optical brighteners, ultraviolet absorbers, pigments, and dyes, if necessary. It may further include.

As an example of the manufacturing method of the molded article, after mixing ethylene vinyl acetate and other additives according to the present invention well using a mixer, extruding with an extruder to produce pellets, drying the pellets and then injecting them into an injection molding machine. It may include steps.

According to the present invention, an ethylene vinyl acetate copolymer having a low melt index and sufficient tensile strength can be provided while containing a high content of vinyl acetate.

The invention will be described in more detail in the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

Examples and Comparative Examples

An ethylene vinyl acetate copolymer was prepared in an autoclave reactor under the process conditions shown in Table 1 below, and Comparative Example 2 is a commercially available ethylene vinyl acetate copolymer product (ELVAX 265, Dupont).

Process conditions Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 VA content (wt%) 28.1 27.9 28.1 27.6 27.4 27.3 Initiator TBPND, TBPPI EHP, TBPND, TBPPI EHP, TBPND, TBPPI EHP, TBPND, TBPPI EHP, TBPND, TBPPI - Pressure (bar) 1880 1880 1940 1940 1940 - Maximum temperature at the bottom of the reactor-Input gas temperature (℃) 165 155 144 140 171

Experimental example

The physical properties of the ethylene vinyl acetate copolymers of Examples 1 to 4 and Comparative Examples 1 to 2 prepared above were measured by the following method, and are shown in Table 2.

(1) MI (melting index): Using MI-4 manufactured by Goeffert, it was calculated by correcting the measurement result (A) using a 2.16 kg weight at 125° C. according to ASTM D1238. The correction formula is as follows:

[Equation 4]

logMI=0.9394+(0.9174*logA)

(2) LCB: Using the SEC-MALS (multi angle light scattering) analysis method, it is possible to derive the Radius of gyration value (Rg), that is, the Rg-M relationship for each molecular weight (M) of the ethylene vinyl acetate copolymer. Branched polymer (b) at the same molecular weight is smaller than that of Linear polymer (l), and using an arbitrary linear polymer sample as reference data, the branching index (g) was calculated through Equation 1 below:

[Equation 1]

And, using the g value calculated as described above, based on the Zimm-stockmayer equation of Equation 2, the branch number (B) for each molecular weight was calculated:

[Equation 2]

Next, using the branch number (B) value for each molecular weight, a long chain branch (LCB) based on 10,000 carbon atoms was calculated based on Equation 3 below:

[Equation 3]

In Equation 3, C is the number of carbons, and Ci is the polymer concentration of the i-th molecular weight (Mi).

(3) Molecular weight distribution (PDI), weight average molecular weight (Mw): It was measured using SEC-MALS (multi angle light scattering).

(4) Tensile strength: A polymer sample was prepared in the form of a sheet of 2 mm thick using a hot press equipment, and then measured according to ASTM D638 using a UTM equipment.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 MI(g/10min) 5.2 5.3 4.2 3.2 5.0 3.1 LCB/10 ⁴ C 22.1 21.6 20.6 18.4 25.4 25.0 PDI 5.3 5.1 4.6 4.2 5.9 6.1 Tensile strength (kg/㎠) 120 120 140 185 110 180

Referring to Table 2, the ethylene vinyl acetate copolymer according to the present invention has a low melt index, and unlike Comparative Examples 1 and 2, although the content of vinyl acetate is 27% by weight or more, the molecular weight distribution (PDI) and long chain It can be seen that the content of the branch satisfies the relationship 3.012*PDI+3.950≤LCB≤2.143*PDI+11.343.

As described above, the ethylene vinyl acetate copolymers of Examples 1 to 4 in which the molecular weight distribution (PDI) and the content of the long-chain branch satisfies a specific relational expression have a high crystallinity of the copolymer and the ratio of the high-crystalline region, so the content of the long-chain branch Since this is low and the molecular weight distribution is narrow, it is possible to exhibit more improved tensile strength at the same vinyl acetate content.

Claims (5)

The content of vinyl acetate is 15 to 30% by weight,
Melt index (measured at 125° C. with a load of 2.16 kg according to ASTM D1238) is 2.5 to 5.5 g/10 min,
An ethylene vinyl acetate copolymer having a molecular weight distribution (PDI) and a long chain branch content (LCB; based on 10,000 carbon atoms) satisfying the relationship of 3.012*PDI+3.950≤LCB≤2.143*PDI+11.343.
The method of claim 1,
Molecular weight distribution (PDI) is 4 to 5.5, ethylene vinyl acetate copolymer.
The method of claim 1,
The content of long-chain branches (LCB; based on 10,000 carbon atoms) is 15 to 25 per 10,000 carbon atoms, ethylene vinyl acetate copolymer.
The method of claim 1,
The weight average molecular weight is 50,000 to 100,000 g/mol, ethylene vinyl acetate copolymer.
A molded article produced from the ethylene vinyl acetate copolymer of any one of claims 1 to 4.