SAPONIFIED ETHYLENE-VINYL ESTER COPOLYMER PELLET AND METHOD FOR PRODUCING SAME

Abstract

Provided is an EVOH resin pellet which is capable of reducing the occurrence of fish eyes in a melt molded article of an EVOH resin. The occurrence of fish eyes in a melt molded article such as a film that is produced by melt molding using pellets is able to be suppressed by setting the abundance of a conjugated polyene in a surface portion of the pellet to an intended amount or more.

Claims

1. A saponified ethylene-vinyl ester-based copolymer pellet comprising a saponified ethylene-vinyl ester-based copolymer and a conjugated polyene, wherein an amount of the conjugated polyene determined by a below method is 30 ppb or more: 20 g of the saponified ethylene-vinyl ester-based copolymer pellets being agitated at room temperature for 10 minutes in 30 mL of liquid containing distilled water and methanol at a mix ratio of 1:1 in volume, and analyzing an amount of the extracted conjugated polyene.

2. The saponified ethylene-vinyl ester-based copolymer pellet according to claim 1, wherein a ratio of the amount (SC) of the conjugated polyene determined by the method described in claim 1 to a total amount (TC) of the conjugated polyene contained in the saponified ethylene-vinyl ester-based copolymer pellet, SC/TC, is 0.015% by weight or more.

3. The saponified ethylene-vinyl ester-based copolymer pellet according to claim 1, wherein the total amount of conjugated polyene contained in the saponified ethylene-vinyl ester-based copolymer pellet is from 0.1 to 10000 ppm.

4. The saponified ethylene-vinyl ester-based copolymer pellet according to claim 1, wherein the conjugated polyene is at least one selected from the group consisting of sorbic acid, sorbic acid ester, and sorbic acid salt.

5. A method for producing a saponified ethylene-vinyl ester-based copolymer pellet comprising, contacting a saponified ethylene-vinyl ester-based copolymer pellet with a treatment liquid containing a conjugated polyene to obtain a saponified ethylene-vinyl ester-based copolymer pellet in which an amount of conjugated polyene is 30 ppb or more measured by a method below: 20 g of the saponified ethylene-vinyl ester-based copolymer pellets being agitated at room temperature for 10 minutes in 30 mL of liquid containing distilled water and methanol at a mix ratio of 1:1 in volume, and analyzing an amount of the extracted conjugated polyene.

6. The producing method according to claim 5, wherein the saponified ethylene-vinyl ester-based copolymer pellet is a porous pellet.

7. The producing method according to claim 5, wherein the saponified ethylene-vinyl ester-based copolymer pellet is a pellet obtained by pelletizing an alcohol solution containing the ethylene-vinyl ester-based copolymer.

8. The producing method according to claim 5, further comprising adding a conjugated polyene as a polymerization inhibitor in production of ethylene-vinyl ester-based copolymer.

9. The producing method according to claim 5, wherein the treatment liquid contains at least one selected from the group consisting of boron compound, acetic acid, and acetate.

10. A method for reducing fish eye in a melt molded article of comprising a saponified ethylene-vinyl ester-based copolymer comprising employing either a plurality of saponified ethylene-vinyl ester-based copolymer pellets or mixture of the saponified ethylene-vinyl ester-based copolymer pellet and an optional other thermoplastic resin pellet as a raw material for the melt-molded article, wherein an amount of a conjugated polyene in the saponified ethylene-vinyl ester-based copolymer pellet is 30 ppb or more measured by the below method: 20 g of the saponified ethylene-vinyl ester-based copolymer pellets being agitated at room temperature for 10 minutes in 30 mL of liquid containing distilled water and methanol at a mix ratio of 1:1 in volume, and analyzing an amount of the extracted conjugated polyene.

11. A saponified ethylene-vinyl ester-based copolymer pellet comprising a saponified ethylene-vinyl ester-based copolymer and a conjugated polyene, wherein the total amount of conjugated polyene contained in the saponified ethylene-vinyl ester-based copolymer pellet is from 0.1 to 10000 ppm, and wherein an amount of the conjugated polyene determined by a below method is 30 ppb or more: 20 g of the saponified ethylene-vinyl ester-based copolymer pellets being agitated at room temperature for 10 minutes in 30 mL of liquid containing distilled water and methanol at a mix ratio of 1:1 in volume, and analyzing an amount of the extracted conjugated polyene.

12. The saponified ethylene-vinyl ester-based copolymer pellet according to claim 11, wherein a ratio of the amount (SC) of the conjugated polyene determined by the method described in claim 11 to a total amount (TC) of the conjugated polyene contained in the saponified ethylene-vinyl ester-based copolymer pellet, SC/TC, is 0.015% by weight or more.

13. The saponified ethylene-vinyl ester-based copolymer pellet according to claim 12, wherein the conjugated polyene is at least one selected from the group consisting of sorbic acid, sorbic acid ester, and sorbic acid salt.

Description

EXAMPLE

[0104] The invention will be specifically explained with examples below, but these examples do not limit the invention as long as it does not exceed the gist of the invention.

[0105] The term part(s) in Examples is on the basis weight unless otherwise indicated.

<Measurement and Evaluation Method>

(1) Preparation of the Analyte Solution for Determining Total Amount (TC) of Conjugated Polyene Contained in Pellet

[0106] EVOH resin pellet were frozen and pulverized to powder. 1 g of the powder and 8 mL of solvent for extraction (distilled water:methanol=1:1 in volume ratio) were put in a measuring flask (10 mL) and extracted in ultrasound bath for 60 minutes. The solvent for extraction was further added in the measuring flask up to 10 mL. Thereafter the obtained solution was filtrated with filter having a pore size of 0.45 m to obtain an analyte solution for determining TC.

(2) Preparation of Analyte Solution for Determining Amount (SC) of Conjugated Polyene Contained in a Surface Portion of Pellet

[0107] 20 g of EVOH resin pellets were supplied for extraction with solvent (distilled water:methanol=1:1 in volume ratio). The extraction is conducted by agitating the EVOH resin pellets in 30 mL of the solvent at room temperature for 10 minutes. The obtained solution was concentrated up to 2 mL and filtrated with a filter having a pore size of 0.45 m. The obtained filtrate was used as an analyte solution for determining SC.

(3) Quantitative Determination of Conjugated Polyene

[0108] The above prepared analyte for quantitative determination of the amount of conjugated polyene was analyzed by LC-UV analysis under the conditions below. The amount of the conjugated polyene (sorbic acid or sodium sorbate) was determined based on the values of detected peak area and the calibration curve of the standard solution prepared below.

[Preparation of Calibration Curve]

[0109] Weighing 50 mg of sodium sorbate in 50 mL of measuring flask and dissolving it in methanol-ultra pure water mixed solvent (ratio of methanol:ultra-pure water=50:50) were carried out to prepare 50 mL solution as an original standard solution having a concentration of 1000 g/mL. This original standard solution was diluted with the methanol-ultra pure water mixed solvent step by step to prepare a plurality of standard solutions differing in their concentration. A calibration curve was created by conducting LC-UV analysis of these standard solutions.

[0110] Thus created calibration curve was also utilized in the case of employing sorbic acid as a conjugated polyene. Since the signal intensity for one molecule of sorbic acid is identical to that of sodium sorbate, the amount of the sorbic acid was computed by multiplying the value of molecular weight of sorbic acid divided by molecular weight of sodium sorbate.

[Conditions for LC-UV Analysis]

[0111] LC system: Agilent 1260/1290 (Agilent)
Ultraviolet spectrophotometer: Agilent 1260 Infinity equipped with diode array detector (from Agilent)
column filler: Cadenza CD-C18 3 m (from Imtact)
column tube: 3 mm in inner diameter and 100 mm in length
column temperature: 40 C.
Mobile phase A: acetonitrile (5 vol %) aqueous solution containing formic acid (0.05 vol %)
Mobile phase B: acetonitrile (95 vol %) aqueous solution containing formic acid (0.05 vol %)
Time chart: [0112] 0.0.fwdarw.5.0 min, B %=30% [0113] 5.0.fwdarw.8.0 min, B %=30%.fwdarw.50% [0114] 8.0.fwdarw.10.0 min, B %=50% [0115] 10.0.fwdarw.13.0 min, B %=50%.fwdarw.30% [0116] 13.0.fwdarw.15.0 min, B %=30%
Flow rate: 0.2 mL/min
UV/Vis detected range of wavelength: 190 to 400 nm
Measured wavelength: 262 nm

(4) Fish Eye

[0117] The prepared EVOH resin pellets were fed to a 40 mm single screw extruder equipped with barrel, adapter and die all set at 210 C., to form into a film 30 m thick. The film was evaluated with respect to fish eye.

[0118] The fish eyes having a diameter of 200 m or more, a diameter of 100 to 190 m, and diameter less than 100 m per 100 cm.sup.2 of the produced films (except films Nos. 1 and 2) were counted respectively by an inspection apparatus for film. Counting was conducted at 10 points per 50 m long in film. The average value of the 10 counted points were determined.

[0119] When it comes to the inspection apparatus for film, FSA-100 (from OCS) for No. 1, DT-300F (from Disc Inspection Technology Co., Ltd.) for No. 2, and TEC EYE (from LINE SENSOR CAMERA EXCEL) for Nos. 3 to 6 were used respectively. We confirmed that either inspection apparatus was warranted for the same accuracy for inspection of fish eyes having the above-mentioned size.

<Production of EVOH Resin Pellet>

No. 1:

[0120] 500 parts of vinyl acetate, 100 parts of methanol, 0.0585 part of acetyl peroxide (per vinyl acetate), and 0.015 part of citric acid (per vinyl acetate) were supplied in a polymerization vessel equipped with cooling coil. Air in the vessel was replaced with nitrogen gas and thereafter with ethylene. Subsequently blowing pressurized ethylene gas into the vessel up to 40 kg/cm.sup.2 in the pressure of ethylene. Under the condition of pressurized ethylene gas, the polymerization was initiated by elevating the temperature to 67 C. with agitating the solution in the vessel. At the time that the rate of polymerization arrived at 60 wt %, i.e. 6 hours after the initiation, sorbic acid 0.0525 part (relative to the charged amount of vinyl acetate) was added to produce ethylene-vinyl acetate copolymer having an ethylene unit content rate of 32.5 mol %. The resulting solution containing the produced ethylene-vinyl acetate copolymer was fed into a distillation column and gaseous methanol was introduced from the bottom of the distillation column, thereby removing unreacted vinyl acetate and obtaining methanol solution of ethylene-vinyl acetate copolymer. Saponification was carried out by feeding methanol solution containing 0.007 equivalent weight of sodium hydroxide, as a result, a methanol solution having a concentration of 30 wt % EVOH resin and 70 wt % methanol. The resultant EVOH resin had a saponification degree of 99.7 mol %.

[0121] Thus obtained methanol solution of EVOH resin was extruded in a form of strand in a cooling water. The strand-shaped extrudate, which was hydrous porous body, was cut with cutter to obtain a porous pellet with 3.8 mm in diameter and 4 mm in length. The porous pellet contained EVOH resin in a concentration of 35 wt %.

[0122] The porous pellets was rinsed for 1 hour with a treatment liquid for rinsing. With respect to 100 parts of porous pellets, 300 parts of the treatment liquid for rinsing which contained sodium acetate 0.1 part, acetic acid 0.1 part, boric acid 0.003 part (in terms of boron), and sorbic acid 0.0008 part. The concentration of sorbic acid in the treatment liquid for rinsing was 2.7 ppm. Such rinsing operation was repeated five times. Next, thus rinsed porous pellet was dried at 110 C. for 8 hours in blowing nitrogen gas having oxygen content of 0.5 vol % or less. The resultant EVOH resin pellet contained 0.15 part of volatile matter, 0.06 part of sodium, and 0.015 part of boric acid (in terms of boron) with respect to 100 parts of EVOH resin. The EVOH resin pellet had MFR of 3.8 g/10 minutes (210 C., load of 2160 g). The resultant EVOH resin pellet, i.e. conjugated polyene-holding EVOH resin pellet, was evaluated with respect to amounts of conjugated polyene (TC and SC) and fish eye according to the evaluation method described earlier. The evaluation results are shown in Table 1.

No. 2:

[0123] The same manner of operation as No. 1 was conducted to produce a porous pellet of EVOH resin except that a composition of treatment liquid for rinsing the porous pellet of EVOH resin was changed. The composition of the treatment liquid for rinsing contained 0.1 part of sodium acetate, 0.1 part of acetic acid, and 0.003 part of boric acid (in terms of boron) per 100 parts of porous pellets.

[0124] The obtained EVOH resin pellet was evaluated with respect to the amounts of conjugated polyene (TC and SC) and fish eye according to the evaluation method described earlier. The evaluation results are shown in Table 1.

Nos. 3 to 6:

[0125] The EVOH resin pellet having an increased amount of conjugated polyene was produced by spraying an aqueous solution having a concentration of sodium sorbate indicated in Table 1 against the surface of the EVOH resin pellet No. 1. The amounts of conjugated polyene (TC and SC) contained in the produced EVOH resin pellet were indicated in Table 1. The produced EVOH resin pellet was evaluated with respect to fish eye. The evaluation results are shown in Table 1.

TABLE-US-00001 TABLE 1 No. 1 2 3 4 5 6 Treatment Amount of sobic acid added in 0.0525 0.0525 0.0525 0.0525 0.0525 0.0525 for adhering polymerization conjugated (part/100 parts of vinyl acetate) polyene Amount of sorbic acid contained 0.0008 0 0.0008 0.0008 0.0008 0.0008 in 300 parts of rinsing liquid for pellets part/100 parts of pellets) Amount of sodium sorbate in 56 660 4000 56000 aqueous solution of sodium sorbate for spray (ppm) EVOH Total amount of conjugated 150 150 280 280 300 570 resin pellet polyene (TC: ppm) Ambulance of conjugated polyene 39 21 180 790 20000 290000 in surface portion (SC: ppb) Rate of ambulance of conjugated 0.026 0.014 0.064 0.28 6.7 51 polyene in surface portion (SC/TC: wt %) EVOH Fish eyes having 200 m or more 0 2 0 0 0 0 resin film in diameter (count) Fish eyes having 100-190 m in diameter (count) 1 12 1 1 1 3 Fish eyes having less than 100 m in diameter (count) 1 1 1 11

[0126] It is understood from Table 1 that EVOH resin pellets Nos. 1 and 3-6, respective of which had 30 ppb or more of conjugated polyene in a surface portion (SC), achieved to suppress the occurrence of fish eye of 200 m or more in diameter as well as minute fish eye less than 200 m in diameter. On the other hand, EVOH resin pellet No. 2, which had a total amount (TC) of conjugated polyene almost equal to that of the above pellets but had less than 30 ppb in the amount (SC) contained in a surface portion, insufficiently suppressed the occurrence of fish eyes.

[0127] A rinsing operation with a rinsing liquid containing conjugated polyene (sorbic acid) could slightly increase the amount (SC) of conjugated polyene (sorbic acid) contained in a surface portion with almost no affecting the total amount (TC) of conjugated polyene as shown in No. 1. EVOH resin pellet No. 1 exhibited the production of the EVOH resin pellet having an amount contained in a surface portion (SC) adjusted to 30 ppb or more.

[0128] Nos. 3 to 6 exhibited that the increase of the amount (SC) of conjugated polyene (sorbic acid and sodium sorbate) in a surface portion (SC) without significant increase of the total amount (TC) of the conjugated polyene could be achieved by spraying the solution containing the conjugated polyene against the surface of pellet, which was not accompanied with troublesome operations. However, in the case of SC above 25000 ppb (25 ppm) and the ratio of SC to TC, (SC/TC) above 10 wt %, minute fish eye less than 200 m in diameter tended to occur increasingly (No. 6).

INDUSTRIAL APPLICABILITY

[0129] The EVOH resin pellet of the invention could avoid the occurrence of fish eyes and therefore could provide a wrapping material capable of satisfying strict requirements for the appearance of film. Moreover, the inventive method for producing EVOH resin pellet can produce EVOH resin pellets utilizing the facilities for manufacturing in exist and merely changing the composition of rinsing liquid or treatment liquid for pellets, therefore being capable of producing the EVOH resin pellets of the invention without troublesome operations.