TWI838625B - Ethylene vinyl ester based copolymer saponified pellets and film containing the same - Google Patents

Abstract

The instant disclosure relates to an ethylene vinyl ester based copolymer saponified pellet and a film formed therefrom. The ethylene vinyl ester based copolymer saponified pellet has an ethylene content of 24~35 mole%, and the pellets have a tubidity of less than 300 NTU when dissolved in a 60% (w/w) methanol aqueous solution; or the pellet has an ethylene content of 36~48 mole%, and the pellets have a tubidity of less than 200 NTU when dissolved in a 80% (w/w) methanol aqueous solution. The present invention controls the amount of aggregates by controlling the turbidity of the ethylene vinyl ester based copolymer saponified pellet dissolved in methanol aqueous to reduce the amount of gel produced after film formation.

Description

Ethylene-vinyl ester copolymer saponified pellets and films thereof

The present invention relates to a saponified ethylene-vinyl ester copolymer, in particular, pellets of the saponified ethylene-vinyl ester copolymer having a specific turbidity when dissolved in a methanol aqueous solution. The present invention also discloses a film formed from the pellets of the saponified ethylene-vinyl ester copolymer.

Ethylene-vinyl ester copolymers, such as ethylene vinyl alcohol copolymer (EVOH) resins, are widely used in multilayers for preserving perishable items. For example, EVOH resins and multilayers are commonly used in the food packaging industry, medical equipment and consumables industry, pharmaceutical industry, electronics industry, and agrochemical industry. EVOH resins are often used to be added to multilayers as a unique layer to act as an oxygen barrier layer.

It is known that EVOH pellets/granules formed from EVOH resin often contain a large amount of aggregates, which causes the film formed from the EVOH pellets to produce a large amount of gel and have poor quality.

The inventors have found that the poor quality of EVOH films is caused by uneven mixing or insufficient addition of polymerization inhibitors in the EVOH production process, a large amount of aggregates in EVOH pellets, the amount of gel in the EVOH film and/or the high oxygen permeability (also referred to as oxygen permeability in this article) of the EVOH film.

In view of the continuing need for a membrane that can provide ethylene-vinyl ester copolymer saponified pellets with a low gel content and a low oxygen transmission rate (OTR).

The present invention relates to an ethylene-vinyl ester copolymer saponified pellet, wherein the ethylene content of the pellet is 24-35 mole%, and the turbidity of the pellet in a 60% (w/w) methanol aqueous solution is less than 300 NTU; or the ethylene content of the pellet is 36-48 mole%, and the turbidity of the pellet in a 80% (w/w) methanol aqueous solution is less than 200 NTU. In some cases, the ethylene-vinyl ester copolymer saponified pellet has an ethylene content of 24-35 mole%, and the turbidity of the pellet in a 60% (w/w) methanol aqueous solution is 0.5-120 NTU; or the ethylene content of the pellet is 36-48 mole%, and the turbidity of the pellet in a 80% (w/w) methanol aqueous solution is 0.5-120 NTU. The ethylene-vinyl ester copolymer saponified pellet can be used to prepare a membrane or a multilayer structure.

Additionally or alternatively, the pellets include a polymerization inhibitor in an amount of 1 to 850 ppm. In a preferred embodiment, the pellets include a polymerization inhibitor in an amount of 5 to 650 ppm. The polymerization inhibitor is a conjugated polyene. The polymerization inhibitor may be sorbic acid, cinnamic acid, 1,3-hexadiene or myrcene. According to at least one embodiment, the addition of the polymerization inhibitor is mixed by a mixer, which is a dynamic mixer or a static mixer. In some embodiments, the length to radius ratio of the mixer is 1.3 to 65 L/D.

According to at least one embodiment, the ethylene-vinyl ester copolymer saponified pellets have an ethylene content and a saponification degree, wherein the ethylene content is about 24 to about 48 mole %, and the saponification degree is 99.5 mole % or higher.

In addition, according to at least one embodiment, the ethylene-vinyl ester copolymer saponified pellets may further have a boron content of 10-450 ppm. In some cases, in addition to the boron content of 10-450 ppm, the ethylene-vinyl ester copolymer saponified pellets may also contain alkali metals, lubricants, alkaline earth metals, salts thereof and/or mixtures thereof.

In other aspects of the present invention, a film formed from the above-mentioned ethylene-vinyl ester copolymer saponified pellets is provided. In some preferred embodiments, the oxygen transmission rate (OTR) of the film is less than 3.4 cm ³ *20 μm/m ² *24Hr*atm at 23°C and 65% relative humidity according to ISO 14663-2.

Additionally or alternatively, the present invention provides a film formed from the ethylene-vinyl ester copolymer saponified pellets as described above, wherein the number of gels in the film is less than 1180/m ² . In some cases, the number of gels in the film is less than 600/m ² .

According to at least one embodiment, the multi-layer structure includes: (a) at least one layer formed by the ethylene-vinyl ester copolymer saponified pellets as described above; (b) at least one polymer layer; and (c) at least one adhesive layer. The polymer layer can be, for example, selected from the group consisting of a low-density polyethylene layer, a polyethylene grafted maleic anhydride layer, a polypropylene layer, and a nylon layer. The adhesive layer is a tie layer.

It was unexpectedly discovered that in the manufacturing process of ethylene-vinyl ester copolymer saponification products, a large amount of initiator is added during polymerization to react, and the polymerization output contains a large amount of initiator, and an inhibitor is added to terminate the reaction. At this time, if the inhibitor is added sufficiently and the polymerization output is mixed evenly with the inhibitor, the reaction can be terminated without generating aggregates, and the ethylene-vinyl ester copolymer saponification product will not generate gel after film formation; if the inhibitor is added insufficiently or the polymerization output is mixed unevenly with the inhibitor, the reaction cannot be terminated, and the reaction will continue to generate aggregates, and the ethylene-vinyl ester copolymer saponification product will generate gel after film formation. In view of this, the inventors believe that no matter how the polymerization conditions and inhibitor addition conditions are changed, as long as the turbidity of the ethylene-vinyl ester copolymer saponified pellets dissolved in methanol water is ensured to be within a certain range, it means that the content of aggregates in the ethylene-vinyl ester copolymer saponified pellets is low, thereby achieving the goal of reducing the amount of gel produced after film formation and lowering the oxygen permeability.

The present invention provides an ethylene-vinyl ester copolymer saponified product, specifically, for example, ethylene vinyl alcohol copolymer (EVOH), the ethylene-vinyl ester copolymer saponified product can be in the form of particles/pellets, films, fibers, etc. The ethylene-vinyl ester copolymer saponified product described herein is formed into one or more pellet forms and/or shapes through granulation. Although the ethylene-vinyl ester copolymer saponified product is described throughout the present invention as being formed into one or more ethylene-vinyl ester copolymer saponified product pellet forms through granulation, the ethylene-vinyl ester copolymer saponified product can be processed into the form of beads, cubes, chips, shavings, etc.

In some cases, the ethylene-vinyl ester copolymer saponified product is in the form of pellets having a specific turbidity, particularly an ethylene content of 24-35 mole%, and a turbidity of the pellets in a 60% (w/w) methanol aqueous solution of less than 300 NTU; or an ethylene content of 36-48 mole%, and a turbidity of the pellets in an 80% (w/w) methanol aqueous solution of less than 200 NTU. The ethylene-vinyl ester copolymer saponified product pellets can be used to prepare membranes.

The ethylene content of the pellets is between 24 and 35 mole%, and the turbidity of the pellets in a 60% (w/w) methanol aqueous solution is, for example, less than 300 NTU, less than 275 NTU, less than 250 NTU, less than 225 NTU, less than 200 NTU, less than 175 NTU, less than 150 NTU, less than 125 NTU, less than 100 NTU, less than 75 NTU, less than 50 NTU, less than 25 NTU, less than 20 NTU, less than 15 NTU, less than 10 NTU or less than 1 NTU. The pellets have an ethylene content of 36-48 mole%, and the turbidity of the pellets in 80% (w/w) methanol aqueous solution is less than 200 NTU, for example, less than 200 NTU, less than 175 NTU, less than 150 NTU, less than 125 NTU, less than 100 NTU, less than 75 NTU, less than 50 NTU, less than 25 NTU, less than 20 NTU, less than 15 NTU, less than 10 NTU or less than 1 NTU. In a preferred embodiment, the ethylene-vinyl ester copolymer saponified pellets have an ethylene content of 24-35 mole%, and the pellets have a turbidity of 0.5-120 NTU when dissolved in a 60% (w/w) methanol aqueous solution, for example: 0.5-120 NTU, 0.5-100 NTU, 0.5-80 NTU, 0.5-60 NTU, 0.5-40 NTU, 0.5-20 NTU, 1-120 NTU, 1-100 NTU, 1-80 NTU, 1-60 NTU, 1-40 NTU, 1-20 NTU, 5-120 NTU, 5-100 NTU, 5-80 NTU, 5-60 NTU, 5-40 NTU, 5-20 NTU, 10-120 NTU, 10-100 NTU, 10-80 NTU, 10-60 NTU, 10-40 NTU, 10-20 NTU, 25-120 NTU, 25-100 NTU, 25-80 NTU, 25-60 NTU, 25-40 NTU, 50-120 NTU, 50-100 NTU or 50-80 NTU; or its ethylene content is 36-48 mole%, and the turbidity of the pellets dissolved in 80% (w/w) methanol aqueous solution is 0.5-120 NTU, for example: 0.5-120 NTU, 0.5-100 NTU, 0.5-80 NTU, 0.5-60 NTU, 0.5-40 NTU, 0.5-20 NTU, 1-120 NTU, 1-100 NTU, 1-80 NTU, 1-60 NTU, 1-40 NTU, 1-20 NTU, 5-120 NTU, 5-100 NTU, 5-80 NTU, 5-60 NTU, 5-40 NTU, 5-20 NTU, 10-120 NTU, 10-100 NTU, 10-80 NTU, 10-60 NTU, 10-40 NTU, 10-20 NTU, 25-120 NTU, 25-100 NTU, 25-80 NTU, 25-60 NTU, 25-40 NTU, 50-120 NTU, 50-100 NTU, or 50-80 NTU.

The formation of aggregates in EVOH pellets may be affected by complex factors such as EVOH with low ethylene content, EVOH with high polymerization degree, EVOH with high ethylene content, or EVOH with dehydration crosslinking. Although not limited by any specific theory, the inventors believe that as long as the turbidity value of ethylene-vinyl ester copolymer saponified pellets dissolved in methanol water is within the desired range, the content of aggregates in the ethylene-vinyl ester copolymer saponified pellets can be ensured to be low, thereby reducing the amount of gel produced after film formation and lowering the oxygen permeability.

The ethylene-vinyl ester copolymer saponified pellets have an ethylene content. For example, the ethylene content of the EVOH may be about 24 to about 48 mole%, about 20 to about 50 mole%, about 25 to about 45 mole%, about 28 to about 42 mole%, or about 30 to about 40 mole%. The ethylene content is, for example, 24 mole%, 25 mole%, 26 mole%, 27 mole%, 28 mole%, 29 mole%, 30 mole%, 31 mole%, 32 mole%, 33 mole%, 34 mole%, 35 mole%, or any two of the above values; or, for example, 35 mole%, 36 mole%, 37 mole%, 38 mole%, 39 mole%, 40 mole%, 41 mole%, 42 mole%, 43 mole%, 44 mole%, 45 mole%, 46 mole%, 47 mole%, 48 mole%, or any two of the above values.

Additionally or alternatively, the EVOH resin composition 100 may have a saponification degree of 90 mole% or more, preferably 95 mole% or more, preferably 97 mole% or more, and preferably 99.5 mole% or more.

The ethylene-vinyl ester copolymer saponified pellets include a polymerization inhibitor in an amount of 1-850 ppm, for example, 1-850 ppm, 1-800 ppm, 1-750 ppm, 1-700 ppm, 1-650 ppm, 1-600 ppm, 1-550 ppm, 1-500 ppm, 1-450 ppm, 1-400 ppm, 1-350 ppm, 1-300 ppm, 1-250 ppm, 1-200 ppm, 1-150 ppm, 1-100 ppm, 1-50 ppm, 5-850 ppm, 5-800 ppm, 5-750 ppm, 5-700 ppm, 5-650 ppm, 5-600 ppm, 5-550 ppm, 5-500 ppm, 5-450 ppm, 5-400 ppm ppm, 5~350 ppm, 5~300 ppm, 5~250 ppm, 5~200 ppm, 5~150 ppm, 5~100 ppm, 5~50 ppm, 50~850 ppm, 50~800 ppm, 50~750 ppm, 50~700 ppm, 50~650 ppm, 50~600 ppm, 50~550 ppm, 50~500 ppm, 50~450 ppm, 50~400 ppm, 50~350 ppm, 50~300 ppm, 50~250 ppm, 50~200 ppm, 50~150 ppm, 50~100 ppm, 10~850 ppm, 10~800 ppm, 10~750 ppm, 10~700 ppm, 10~650 ppm, 10~600 ppm, 10~550 ppm, 10~500 ppm, 10~450 ppm, 10~400 ppm, 10~350 ppm, 10~300 ppm, 10~250 ppm, 10~200 ppm, 10~150 ppm, 10~100 ppm, 10~50 ppm, 100~850 ppm, 100~800 ppm, 100~750 ppm, 100~700 ppm, 100~650 ppm, 100~600 ppm, 100~550 ppm, 100~500 ppm, 100~450 ppm, 100~400 ppm, 100~350 ppm, 100~300 ppm, 100~250 ppm, 100~200 ppm, 300-850 ppm, 300-800 ppm, 300-750 ppm, 300-700 ppm, 300-650 ppm or 300-600 ppm. In a preferred embodiment, the ethylene-vinyl ester copolymer saponified pellets include a polymerization inhibitor, the content of which is 5-650 ppm. The polymerization inhibitor is a conjugated polyene, which can be, for example: 2,3-Dimethyl-1,3-butadiene, 2-tert-butyl-1,3-butadiene, 1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene, 2-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1,4-diphenyl-1,3-butadiene, 1-methoxy-1,3-butadiene, 2-methoxy-1,3-butadiene, 1-ethoxy-1 ,3-butadiene, 2-ethoxy-1,3-butadiene, 2-nitro-1,3-butadiene, chloroprene, 1-chloro-1,3-butadiene, 1-bromo-1,3-butadiene, isoprene, tropone, ocimene, fulvene, ferrandrene, myrcene, farnesene, phllandrene, cembrene, sorbic acid, sorbic acid esters, sorbic acid salts and other sorbic acids, abietic acid The conjugated diene is composed of a conjugated structure of two carbon-carbon double bonds, such as 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostearic acid, tung oil, cholecalciferol, etc. The conjugated triene is composed of a conjugated structure of three carbon-carbon double bonds. The conjugated polyene can also be used in combination of two or more. Preferred conjugated polyenes are sorbic acids such as sorbic acid, sorbic acid esters, sorbic acid salts, cinnamic acid, 1,3-hexadiene or myrcene.

The polymerization inhibitor is added by mixing with a mixer, which is a dynamic mixer, a general static mixer or a Noritake static mixer. In order to achieve a better mixing effect, the mixer has a specific length and diameter ratio, for example: 1~70 L/D, 1~65 L/D, 1~60 L/D, 1~50 L/D, 1~40 L/D, 1~30 L/D, 1~20 L/D, 1~10 L/D, 1.3~70 L/D, 1.3~65 L/D, 1.3~60 L/D, 1.3~50 L/D, 1.3~40 L/D, 1.3~30 L/D, 1.3~20 L/D, 1.3~10 L/D, 5~70 L/D, 5~65 L/D, 5~60 L/D, 5~50 L/D, 5~40 L/D, 5~30 L/D, 5~20 L/D, 5~10 L/D, 20~70 L/D, 20~65 L/D, 20~60 L/D, 20~50 L/D, 20~40 L/D, 40~70 L/D, 40~65 L/D, 40~60 L/D, 40~50 L/D or 60~70 L/D.

The ethylene-vinyl ester copolymer saponified pellets may contain boron compounds and/or boric acid and/or cinnamic acid and/or alkali metals and/or conjugated polyenes and/or lubricants and/or alkaline earth metals in some cases. The above substances can give the ethylene-vinyl ester copolymer saponified pellets better properties. The above substances are common substances usually present in ethylene-vinyl ester copolymer saponified pellets, making them have better properties. If the content of the above conjugated polyene structure compound is 1 to 30,000 ppm per unit weight of the ethylene-vinyl ester copolymer saponified pellets, coloring after heating can be further suppressed and thermal stability is more excellent. If the content of the alkali metal compound or alkaline earth metal compound per unit weight of the ethylene-vinyl ester copolymer saponified pellets is 1-1000 ppm in terms of metal, the long-term operation moldability can be further improved. If the content of the lubricant per unit weight of the ethylene-vinyl ester copolymer saponified pellets is 1-300 ppm, the processability can be further improved.

Additionally or alternatively, according to other aspects of the present invention, the ethylene-vinyl ester copolymer saponified pellets may have a boron content of 10 to 450 ppm. Without being limited to any particular theory, it is believed that adding a boron compound to the ethylene-vinyl ester copolymer saponified pellets to have a boron content of 10 to 450 ppm reduces or eliminates sticking during extrusion through a screw extruder and further improves film thickness uniformity and flexibility. In some cases, the boron content of the ethylene-vinyl ester copolymer saponify pellets may be 10 to 450 ppm, 10 to about 400 ppm, 10 to about 350 ppm, 10 to about 300 ppm, 10 to about 275 ppm, 10 to about 250 ppm, 10 to about 225 ppm, 10 to about 200 ppm, 10 to about 175 ppm, about 20 to 450 ppm, about 20 to about 400 ppm, about 20 to about 350 ppm, about 20 to about 300 ppm, about 20 to about 275 ppm, about 20 to about 250 ppm, about 20 to about 225 ppm, about 20 to about 200 ppm, about 20 to about 175 ppm, about 60 to 450 ppm, about 60 to about 400 ppm, ppm, about 60 to about 350 ppm, about 60 to about 300 ppm, about 60 to about 275 ppm, about 60 to about 250 ppm, about 60 to about 225 ppm, about 60 to about 200 ppm, about 60 to about 175 ppm, about 100 to 450 ppm, about 100 to about 400 ppm, about 100 to about 350 ppm, about 100 to about 300 ppm, about 100 to about 275 ppm, about 100 to about 250 ppm, about 100 to about 225 ppm, about 100 to about 200 ppm, about 100 to about 175 ppm, about 140 to 450 ppm, about 140 to about 400 ppm, about 140 to about 350 ppm, about 140 to about 300 ppm, about 140 to about 275 ppm ppm, about 140 to about 250 ppm, about 140 to about 225 ppm, about 140 to about 200 ppm, about 180 to about 450 ppm, about 180 to about 400 ppm, about 180 to about 350 ppm, about 180 to about 300 ppm, about 180 to about 275 ppm, about 180 to about 250 ppm, about 180 to about 225 ppm, about 220 to 450 ppm, about 220 to about 400 ppm, about 220 to about 350 ppm, about 220 to about 300 ppm, about 220 to about 275 ppm.

In some cases, the boron compound may include boric acid or a metal salt thereof. Examples of metal salts include, but are not limited to, calcium borate, cobalt borate, zinc borate (e.g., zinc tetraborate, zinc metaborate), aluminum potassium borate, ammonium borate (e.g., ammonium metaborate, ammonium tetraborate, ammonium pentaborate, ammonium octaborate), cadmium borate (e.g., cadmium orthoborate, cadmium tetraborate), potassium borate (e.g., potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, potassium octaborate), silver borate (e.g., silver metaborate, silver tetraborate), copper borate (e.g., copper (II) borate, copper metaborate, copper tetraborate), sodium borate (e.g., sodium metaborate, sodium diborate, tetraborate), and the like. The present invention also includes the following: a) sodium borate (e.g., sodium pentaborate, sodium hexaborate, sodium octaborate), b) lead borate (e.g., lead metaborate, lead hexaborate), c) nickel borate (e.g., nickel orthoborate, nickel diborate, nickel tetraborate, nickel octaborate), e) barium borate (e.g., barium orthoborate, barium metaborate, barium diborate, barium tetraborate), d) bismuth borate, d) magnesium borate (e.g., magnesium orthoborate, magnesium diborate, magnesium metaborate, trimagnesium tetraborate, pentamagnesium tetraborate), d) manganese borate (e.g., manganese (I) borate, manganese metaborate, manganese tetraborate), d) lithium borate (e.g., lithium metaborate, lithium tetraborate, lithium pentaborate), salts thereof, or combinations thereof. Borate minerals such as borax, boraxite, boraxite, boraxite, boraxite/suanite and szaibelyite may be included. Among them, borax, boric acid and sodium borate (such as sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate and sodium octaborate) are preferably used.

On the other hand, the present invention provides a film formed by the ethylene-vinyl ester copolymer saponified pellets as described above. Suitable methods and equipment for preparing films formed by ethylene-vinyl ester copolymer saponified pellets may include methods and equipment that are easily understood by a person of ordinary skill in the art. The film preferably has highly uniform gas barrier properties. The gas barrier properties of the film can be evaluated by measuring the oxygen transmission rate (OTR) of the film. The gas barrier properties of the film can be measured using an OX-TRAN Model 2/21 oxygen transmission rate tester (manufactured by mocon) in accordance with ISO 14663-2 method. In certain embodiments, the film has an oxygen vapor transmission rate of less than 3.4, such as less than 3.4, less than 3, less than 2.8, less than 2.6, less than 2.4, less than 2.2, less than 2, less than 1.8, less than 1.6, less than 1.4, less than 1.2, less than 1, less than 0.8, less than 0.6 or less than 0.4, at 23°C and 65% relative humidity according to ISO 14663-2. 14663-2 At 23°C and 65% relative humidity, the oxygen permeability of the membrane is 0.05~3, for example: 0.05~3, 0.05~2.7, 0.05~2.5, 0.05~2.3, 0.05~2.1, 0.05~1.9, 0.05~1.7, 0.05~1.5, 0.05~1.3, 0.05~1.1, 0.05~0.9, 0.05~0.7, 0.05~0.5, 0.1~3, 0.1~2.7, 0.1~2.5, 0.1~2.3, 0.1~2.1, 0.1~1.9, 0.1~1.7, 0.1~1.5, 0.1~1.3, 0.1~1.1, 0.1~0.9, 0.1~0.7, 0.1~0.5, 0.3~3, 0.3~2.7, 0.3 ~2.5, 0.3~2.3, 0.3~2.1, 0.3~1.9, 0.3~1.7, 0.3~1.5, 0.3~1.3, 0.3~1.1, 0.3~0.9, 0.3~0.7, 0.3~0.5, 0.5~3, 0.5~2.7, 0.5~2.5, 0.5~2.3, 0.5~2.1, 0.5~1.9, 0.5~1. 7, 0.5~1.5, 0.5~1.3, 0.5~1.1, 0.5~0.9, 1~3, 1~2.7, 1~2.5, 1~2.3, 1~2.1, 1~1.9, 1~1.7, 1~1.5, 1.2~3, 1.2~2.7, 1.2~2.5, 1.2~2.3, 1.2~2.1, 1.2~1.9, 1.2~1.7 or 2~3.

In another aspect, the present invention provides a film formed from the pellets of ethylene-vinyl ester copolymer saponification product as described above. In certain embodiments, the number of gels in the film is less than 1180/m ² , for example, less than 1180/m ² , less than 1000/m ² , less than 900/m ² , less than 800/m ² , less than 700/m ² , less than 600/m ² , less than 700/m ² , less than 500/m ² , less than 400/m ² , less than 300/m ² , less than 200/m ² or less than 100/m ² . Preferably, the number of gels in the film is less than 600/ ^m2 , less than 550/ ^m2 , less than 500/ ^m2 , less than 450/ ^m2 , less than 400/ ^m2 , less than 350/ ^m2 , less than 300/ ^m2 , less than 250/ ^m2 , less than 200/ ^m2 , less than 150/ ^m2 or less than 100/ ^m2 .

In another aspect, the present invention provides a multi-layer structure having at least one layer formed by the pellets of the ethylene-vinyl ester copolymer saponified product of the present invention; at least one polymer layer; and at least one adhesive layer. The polymer layer can be selected from a low-density polyethylene layer, a polyethylene grafted maleic anhydride layer, a polypropylene layer, a nylon layer, and a combination thereof. The adhesive layer can be a tie layer, such as ARKEMA OREVAC 18729 from ARKEMA.

The following non-limiting embodiments of various aspects of the present invention are provided mainly to illustrate various aspects of the present invention and the benefits achieved .

The following provides a non-limiting method for preparing EVOH particles formed from an EVOH resin composition. Seven non-limiting example EVOH resin compositions (Examples EVOH 1-7) and eight comparative example EVOH resin compositions (Comparative Examples EVOH 1-8) were prepared according to methods similar to those disclosed below. However, the specific methods for preparing Example EVOH 1-7 and Comparative Examples EVOH 1-8 will generally differ from the methods disclosed below in one or more aspects.

Ethylene, vinyl acetate (VAM), methanol and initiator are added to a reactor and polymerized under specific conditions. A large amount of initiator is added during the polymerization to react. The polymerized material contains a large amount of initiator. Inhibitor is added to terminate the reaction. After polymerization, the ethylene-vinyl acetate copolymer (hereinafter referred to as "EVAC") solution is mixed with the polymerization inhibitor using a special mixer. After mixing, the solution is stripped, alkalized, granulated and dried to make EVOH granules/pellets.

Specifically, ethylene-vinyl acetate copolymer with a specific ethylene content is saponified with a saponification degree of 99.5% to prepare EVOH polymer. Subsequently, EVOH is dissolved in a solution containing methanol and water (ratio 70:30). Afterwards, the EVOH solid content of the solution is 41 wt.%, and the solution is placed at 60°C.

The solution of methanol, water and EVOH is then pelletized by underwater pelletization. Specifically, a pump is used to pump the solution of methanol, water and EVOH into a feed pipe at a flow rate of 120 L/min, and then fed into an input pipe with a diameter of 2.8 mm, and cut using a rotary knife at 1500 rpm. 5°C water is added to cool the EVOH pellets. Subsequently, the EVOH pellets are centrifuged to separate the EVOH particles. The separated EVOH particles are washed with water, and then dried using 3 different dryer combinations (as shown in Table 1) to obtain EVOH pellets. Example 2

The Example EVOH pellets 1-7 were used to form films according to the following method. The Example EVOH pellets 1-7 and the Comparative Example EVOH pellets 1-8 were fed into a single-layer T-die casting extruder (optical control system MEV4) to prepare films. The thickness of the films formed by the Example EVOH pellets 1-7 and the Comparative Example EVOH pellets 1-8 was 20 μm. The temperature of the extruder was set to 220°C, and the temperature of the mold (i.e., the T-die) was set to 230°C. The rotation frequency of the screw was 7 rpm (rotations/minutes). Example 3

Example EVOH pellets 1-7 and comparative example EVOH pellets 1-8 were evaluated to determine the properties of these EVOH pellets and the films formed therefrom. As described above, Example EVOH pellets 1-7 and comparative example EVOH pellets 1-8 were prepared according to a method similar to the method described in Example 1 above. However, the method for preparing EVOH pellets 1-8 differed from the prepared EVOH pellets in the following aspects: ●  Experimental changes in polymerization reaction: polymerization temperature, polymerization pressure, VAM/methanol ratio; ●  Experimental changes in inhibitor addition: inhibitor and initiator addition ratio, inhibitor type; ●  Experimental changes in mixing polymerization output with inhibitor: mixer form, mixer length; ●  Experimental changes in stripping, alkalization, and filtering after water addition: whether to filter.

The experimental process variables are summarized in Table 1.

Table 1 Parameter variables Range of variables Inhibitor dosage (ppm) 10~1000 Types of inhibitors added Conjugated polyenes Inhibitor Mixture Type Dynamic mixer or static mixer Mixer length (L/D) 1.3~65 Mixer pressure drop (KG/cm ² ) 0.02~1.2 Polymer viscosity (cp) 420~1500 Reaction pressure (KG/cm ² ) 28~70 Reaction temperature 40~90℃ Methanol/VAM ratio 5~60 Initiator dosage (ppm) 50~500 Discharge solid content (%) 10~70

The turbidity value of the EVOH pellets in methanol aqueous solution was further evaluated. Films were formed from Example EVOH 1-7 and Comparative Example EVOH 1-8, respectively, in a manner similar to that described in Example 2, and the films were analyzed for evaluation of gel number and oxygen permeability.

Table 2 provides the polymerization conditions, inhibitor addition conditions and an overview of some properties (i.e., EVOH inhibitor content, turbidity in methanol water) of Example EVOH Pellets 1-4 and Comparative Example EVOH Pellets 1-4; Table 3 provides the polymerization conditions, inhibitor addition conditions and some properties of Example EVOH Pellets 5-7 and Comparative Example EVOH Pellets 5-8, as well as the gelation conditions and oxygen permeability of the films formed by Example EVOH 1-7 and Comparative Example EVOH 1-8.

Table 2 Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Polymerization conditions Ethylene content (%) 27 twenty four 32 35 32 29 27 35 Reaction temperature 50℃ 90℃ 40℃ 70℃ 30℃ 100℃ 60℃ 80℃ Reaction pressure (kg/cm ² ) 32 28 39 43 39 35 32 43 Methanol/VAM(%) 20 5 60 40 70 40 0 50 Initiator dosage (ppm) 200 100 500 400 600 5 1000 10 Discharge solid content (%) 40 70 10 20 0 40 80 30 Inhibitor addition conditions Inhibitor dosage (ppm) 150 1000 100 40 200 200 10 40 Inhibitor addition amount/initiator addition amount 0.75 10 0.2 0.1 0.33 40 0.01 4 Type of inhibitor Sorbic acid Sorbic acid Cinnamic acid 1,3-Hexadiene Sorbic acid Lauric acid Butadiene Hexene Inhibitor Addition Mixing Type Dynamic mixer Static mixer Static mixer Noritake Static Mixer Static mixer Dynamic mixer No mixer Batch Bucket Mixing Mixer length (L/D) 65 20 1.3 20 30 1000 X X Pressure drop 0.6 1.2 0.02 0.1 0.01 0.5 X 0.5 Polymer viscosity (cp) 600 1500 1000 420 100 800 5400 400 Whether to filter X X X O X X O X Filter size X X X 20 X X 100 X Methanol water ratio (%) 60 60 60 60 60 60 60 60 Technical Features EVOH inhibitor content (ppm) 130 580 5 20 110 210 0 10 EVOH methanol water turbidity 0.5 35 18 120 315 450 718 321 Membrane efficacy EVOH film gel quantity 75 432 120 82 Unable to form film 1342 2464 1765 EVOH film OTR 0.3 0.1 0.35 0.6 Unable to form film 4.1 10.1 6.3

table 3 Embodiment 5 Embodiment 6 Embodiment 7 Comparison Example 5 Comparative Example 6 Comparison Example 7 Comparative Example 8 Polymerization conditions Ethylene content (%) 36 44 48 48 36 38 44 Reaction temperature 60℃ 80℃ 40℃ 30℃ 50℃ 100℃ 50℃ Reaction pressure (kg/cm ² ) 44 60 70 70 44 32 60 Methanol/VAM(%) 30 20 50 70 0 20 50 Initiator dosage (ppm) 50 100 350 200 1000 100 500 Discharge solid content (%) 25 60 60 0 40 90 40 Inhibitor addition conditions Inhibitor dosage (ppm) 10 20 200 200 10 10000 5 Inhibitor addition amount/initiator addition amount 0.5 0.2 0.57 1 0.01 100 0.01 Type of inhibitor Sorbic acid Myrcene 1,3-Hexadiene Sorbic acid Hexene Sorbic acid Cinnamic acid Inhibitor Addition Mixing Type Static mixer Dynamic mixer Dynamic mixer Static mixer Dynamic mixer Batch Mixer No mixer Mixer length (L/D) 40 5 55 60 0.65 X X Pressure drop 0.8 0.04 1 0.02 0.1 3.6 2.1 Polymer viscosity (cp) 900 1100 1200 130 1000 4200 1300 Whether to filter X X O X X O O Filter size X X 100 X X 20 100 Methanol water ratio (%) 80 80 80 80 80 80 80 Technical Features EVOH inhibitor content (ppm) 15 10 150 150 0 1200 410 EVOH methanol water turbidity 0.5 12 70 220 412 513 240 Membrane efficacy EVOH film gel quantity 210 110 240 1180 1385 1962 1762 EVOH film OTR 1.2 0.8 2.4 4.1 5.4 4.3 3.4

In order to evaluate the turbidity of Example EVOH 1-7 and Comparative Example EVOH 1-8, about 2.5 g of EVOH sample was weighed and placed in a 250 mL conical flask, and 84 g of methanol water (50.3 g of methanol plus 33.6 g of water) was prepared. The prepared methanol water was added to the 250 mL conical flask, and the solvent and sample in the conical flask were heated and refluxed for 2 hours until dissolved (heating plate temperature 450°C). After dissolution, the heating plate was lowered to 60°C, and then the solution was tested according to the ISO 7027 method, and the measuring instrument was Turbidimeter HI98703. According to the above method, after adding EVOH pellets to methanol/water, the solution becomes turbid because the trace aggregates in the EVOH particles are insoluble in methanol/water. The amount of aggregates can be analyzed using a turbidity meter.

The gelation of the films formed from Example EVOH 1-7 and Comparative Example EVOH 1-8 was evaluated. After the EVOH was processed into a single-layer film, the amount of gel in the single-layer film was analyzed using FSA-100, mainly analyzing gels below 100 μm in size.

The oxygen transmission rate (OTR) of the film formed from Example EVOH 1-7 and Comparative Example EVOH 1-8 was evaluated. After the EVOH was processed into a single-layer film, the gas barrier property was tested by OTR. The test method was based on ISO 14663-2. The test conditions were 23°C/65%RH. The measuring instrument was OXTRAN 2/21, manufactured by Mocon. The unit was cm ³ *20 μm/m ² *24Hr*atm.

The results show that Example EVOH 1-4 has an ethylene content of 24% to 35%, and the number of gels in the film formed by Example EVOH 1-4 (75 to 432/m ² ) is much lower than the number of gels in the film formed by Comparative Example EVOH 1-4 (1342 to 2464/m ² ). This shows that no matter how the polymerization conditions and inhibitor addition conditions change, EVOH with an ethylene content of 36% to 48% can achieve the expected effect at a methanol-water ratio of 60%, as long as the methanol water turbidity is ensured to be less than 300 NTU.

Example EVOH 5-7 has an ethylene content of 36% to 48%, and the number of gels in the film formed from Example EVOH 5-7 (110 to 240/m ² ) is much lower than the number of gels in the film formed from Comparative Example EVOH 5-8 (1180 to 1962/m ² ). This shows that no matter how the polymerization conditions and inhibitor addition conditions change, EVOH with an ethylene content of 36% to 48% can achieve the desired effect at a methanol-water ratio of 80%, as long as the methanol-water turbidity is ensured to be less than 200 NTU.

According to the results of the examples, the causes of the formation of aggregates are quite complex and may be affected by the mixer type, mixer length, inhibitor addition amount, inhibitor addition type, reaction temperature, reaction pressure, methanol/VAM ratio, etc. The size of the aggregates produced varies greatly, and even the use of filters cannot effectively remove the aggregates. As can be seen from Comparative Examples EVOH 3, 7 and 8, even if a 20 or 100 μm mesh filter is used for filtering during the preparation of EVOH, the amount of gel in the film formed by Comparative Examples EVOH 3, 7 and 8 is still quite high, which exceeds the expected range of the present invention. Although not limited by any particular theory, the present invention has found that the turbidity of the prepared EVOH dissolved in methanol water is controlled within a specific range, indicating that it is EVOH in which the inhibitor and the polymer are well mixed, the content of aggregates in the EVOH is low, and the amount of gel after subsequent film making is small.

In addition, the oxygen permeability of the film formed by Example EVOH 1-7 is about 0.1~2.4 cm ³ *20 μm/m ² *24Hr*atm, and the oxygen permeability of the film formed by Comparative Example EVOH 1-8 is about 3.4~10.1 cm ³ *20 μm/m ² *24Hr*atm. The test results of the present invention show that as long as the turbidity of the prepared EVOH dissolved in methanol water is controlled within a specific range, the oxygen permeability of the film formed by the EVOH can be reduced. As shown in Tables 2 and 3, the turbidity of Comparative Example EVOH 1-8 dissolved in methanol water exceeds the expected range described herein, and the test results show that the films formed by Comparative Example EVOH 1-8 all have higher oxygen permeabilities (about 3.4~10.1 cm ³ *20 μm/m ² *24Hr*atm). The EVOH film with low oxygen vapor permeability can be used to produce various films, sheets and packaging containers with high oxygen barrier properties.

In summary, the ethylene-vinyl ester copolymer saponified pellets of the present invention have a specific turbidity value in methanol water, especially when the ethylene content is 24-35 mole%, and the turbidity of the pellets dissolved in 60% (w/w) methanol water solution is less than 300 NTU; or when the ethylene content is 36-48 mole%, and the turbidity of the pellets dissolved in 80% (w/w) methanol water solution is less than 200 NTU. In the production process of ethylene-vinyl ester copolymer saponified pellets, if the inhibitor is not added enough or the polymerization output and the inhibitor are not mixed evenly, a large amount of gel will be generated after film formation. In view of this, the inventors have found that no matter how the polymerization conditions and inhibitor addition conditions are changed, as long as the turbidity value of the ethylene-vinyl ester copolymer saponified pellets dissolved in methanol water is within the desired range, the content of aggregates in the ethylene-vinyl ester copolymer saponified pellets can be ensured to be low, thereby achieving the goal of reducing the amount of gel produced after film formation and lowering the oxygen permeability.

Herein, all ranges provided are intended to include each specific range within the given range and the combination of sub-ranges between the given ranges. In addition, unless otherwise specified, all ranges provided herein include the endpoints of the ranges. Thus, the range 1-5 specifically includes 1, 2, 3, 4 and 5, as well as sub-ranges such as 2-5, 3-5, 2-3, 2-4, 1-4, etc.

All publications and patent applications cited in this specification are incorporated herein by reference, and each individual publication or patent application is specifically and individually indicated as incorporated herein by reference for any and all purposes. In the event of any inconsistency between this document and any publication or patent application incorporated by reference, this document controls.

As used herein, the terms "including", "having" and "comprising" have an open, non-limiting meaning. The terms "a", "an" and "the" should be understood to cover the plural as well as the singular. The term "one or more" means "at least one" and thus can include a single feature or a mixture/combination of features.

Except in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients and/or reaction conditions may in all cases be modified by the term "about," meaning within ±5% of the indicated number. The terms "substantially free" or "substantially free" as used herein refer to less than about 2% of a particular feature. All elements or features that are affirmatively described herein may be negatively excluded from the scope of the claims.

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Claims (16)

An ethylene-vinyl ester copolymer saponified pellet, wherein the ethylene content is 24-35 mole%, and the pellet has a turbidity of less than 300 NTU when dissolved in a 60% (w/w) methanol aqueous solution; or the ethylene content is 36-48 mole%, and the pellet has a turbidity of less than 200 NTU when dissolved in an 80% (w/w) methanol aqueous solution; and the pellet contains a polymerization inhibitor, the content of which is 1-850 ppm. For example, the ethylene-vinyl ester copolymer saponified pellets described in Item 1 of the patent application have an ethylene content of 24-35 mole%, and the pellets have a turbidity of 0.5-120 NTU when dissolved in a 60% (w/w) methanol aqueous solution; or the ethylene content of the pellets has an ethylene content of 36-48 mole%, and the pellets have a turbidity of 0.5-120 NTU when dissolved in an 80% (w/w) methanol aqueous solution. The ethylene-vinyl ester copolymer saponified pellets as described in item 1 of the patent application, wherein the polymerization inhibitor content is 5-650ppm. As described in item 1 of the patent application, the ethylene-vinyl ester copolymer saponified pellets, wherein the polymerization inhibitor is a conjugated polyene. The ethylene-vinyl ester copolymer saponified pellets as described in item 1 of the patent application, wherein the polymerization inhibitor is sorbic acid, cinnamic acid, 1,3-hexadiene or myrcene. As described in Item 1 of the patent application, the ethylene-vinyl ester copolymer saponified pellets, wherein the polymerization inhibitor is added by mixing through a mixer, and the mixer is a dynamic mixer or a static mixer. Ethylene-vinyl ester copolymer saponified pellets as described in Item 6 of the patent application, wherein the ratio of the length to the diameter of the mixer is 1.3~65 L/D. The ethylene-vinyl ester copolymer saponified pellets as described in Item 1 of the patent application have a boron content between 10-450ppm. The ethylene-vinyl ester copolymer saponified pellets as described in Item 1 of the patent application further contain one or a combination of a group consisting of an alkali metal, a lubricant and an alkaline earth metal. As described in Item 1 of the patent application, the ethylene-vinyl ester copolymer saponified pellets have a saponification degree greater than 99.5 mol percent. An ethylene-vinyl ester copolymer film is formed from ethylene-vinyl ester copolymer saponified pellets as described in any one of claims 1 to 10. The ethylene-vinyl ester copolymer film as described in claim 11, wherein the oxygen vapor transmission rate of the film is less than 3.4 cm ³ *20 μm/m ² *24 Hr*atm at 23°C and 65% relative humidity according to ISO 14663-2. The ethylene-vinyl ester copolymer film as claimed in claim 11, wherein the number of gels in the film is less than 1180/ ^m2 . The ethylene-vinyl ester copolymer film as claimed in claim 11, wherein the number of gels in the film is less than 600/ ^m2 . A multi-layer structure comprising: (a) at least one layer formed by ethylene-vinyl ester copolymer saponified pellets of any one of claims 1 to 10; (b) at least one polymer layer; and (c) at least one adhesive layer. A multi-layer structure as described in claim 15, wherein the polymer layer is selected from the group consisting of a low-density polyethylene layer, a polyethylene grafted maleic anhydride layer, a polypropylene layer and a nylon layer, and the adhesive layer is a tie layer.