JPH11254523A - Production of saponified ethylene/vinyl acetate copolymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce an EVOH film excellent in film thickness accuracy and film strength. SOLUTION: Raw material pellets comprising a saponified ethylene/vinyl acetate copolymer are extruded on a casting roll in a molten state from a T-die by an extrusion molding machine to obtain an unstretched film which is, in turn, biaxially stretched to produce a saponified ethylene/vinyl acetate copolymer film. In this method, a heat exchanger is provided between the extrusion molding machine and the T-die and the resin temp. difference (ΔT) between the inlet and outlet of the heat exchanger is regulated to a range represented by the formula: (230-0.9×Y)/96<=ΔT<=(230-0.9×Y)/4 [wherein Y is the ethylen content (mol.%) of raw material resin pellets].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a saponified ethylene-vinyl acetate copolymer film. Hereinafter, the saponified ethylene-vinyl acetate copolymer is abbreviated as EVOH.

[0002]

2. Description of the Related Art Heretofore, EVOH films have been frequently used in various packaging applications by utilizing their gas barrier properties. Such an EVOH film is produced by extruding a raw resin pellet from a T-die onto a casting roll by an extruder to obtain an unstretched film, and then biaxially stretching the unstretched film.

[0003] Incidentally, EVOH has too strong crystallinity, and strongly exhibits oriented crystallization during longitudinal stretching, which is the primary stretching. For this reason, in the production of a biaxially stretched EVOH film, the film is not uniformly stretched during the secondary stretching, that is, the film is not stretched uniformly, and stretch unevenness occurs, and the film is likely to break frequently. In order to solve such a problem, Japanese Patent Publication No. 60-26697 discloses an E having a specific density.
A method is described in which an unstretched film of VOH is stretched at 50 to 130 ° C. while adjusting the water content to 3.5% by weight or less.

[0004]

However, even in the case of the above method, the film still breaks at the time of stretching, making it difficult to manufacture the film stably, the film thickness of the stretched film to be inferior in accuracy, and the desired physical properties. May not be obtained. The present invention has been made in view of such circumstances,
Its purpose is to provide an EV with excellent film thickness accuracy, film strength, etc.
An object of the present invention is to provide a stable production method of an OH film.

[0005]

That is, the gist of the present invention is to melt-extrude a raw resin pellet comprising a saponified ethylene-vinyl acetate copolymer from a T-die onto a casting roll by an extruder to form an unstretched film. Obtained, then, in a method for producing a saponified ethylene-vinyl acetate copolymer film by biaxially stretching the unstretched film,
Ethylene, wherein a heat exchanger is provided between the extruder and the T-die, and a resin temperature difference (ΔT) at an inlet and an outlet of the heat exchanger is adjusted within a range of the following formula (1). -A method for producing a saponified vinyl acetate copolymer stretched film.

[0006]

(230−0.9 × Y) / 96 ≦ ΔT ≦ (230−0.9 × Y) / 4 (1) (in the formula (1), Y is the ethylene content of the raw material resin pellets) (Mole%).)

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the raw material resin (pellet) used in the present invention will be described. In the present invention, the ethylene content is usually 10
ＯＨ60 mol%, preferably 20 to 60 mol%, more preferably 25 to 55 mol%, and EVOH having a degree of saponification of the vinyl acetate component of usually 90 mol% or more, preferably 95 mol% or more is used. . In the case of EVOH having an ethylene content of less than 10 mol%, the water resistance of the obtained film is insufficient, and EVO having an ethylene content of more than 60 mol%
In the case of H, the gas barrier property of the obtained film decreases. In the case of EVOH having a degree of saponification of less than 90 mol%, the obtained film has insufficient water resistance.

In particular, the sum of the contents of Na and K metals is 0.01
EVOH in the range of ３０30 ppm is preferably used.
The sum of the above metal contents is preferably 0.1 to 10 ppm. EVO having a sum of the above metal contents of less than 0.01 ppm
In the case of H, coloring (yellowing) may occur at the time of extrusion, and in the case of EVOH exceeding 30 ppm, the frequency of gel generation increases, and as a result, the film tends to break during stretching. . Other metals are not particularly limited, but the content of 5 to 300 ppm of Ca and / or 5 to 200 ppm of Mg is preferable in order to exhibit the effect of suppressing the generation of a gel.

[0009] The EVOH used in the present invention may be variously modified as required, or may be a mixture of modified EVOH and unmodified EVOH. Examples of the modified EVOH include various modified EVOs listed in Table 1 below.
H.

[0010]

Table 1 (1) Modification E with propylene, isobutene, etc.
VOH (2) at least one of α-olefins having 3 to 30 carbon atoms
EVOH modified with at least one species or the olefin with ethylene (3) Modification E by graft polymerization of acrylate
VOH (4) Modified E obtained by saponifying a terpolymer composed of (meth) acrylate-ethylene-vinyl acetate
VOH (5) Modified EVOH obtained by modifying the hydroxyl group of EVOH with a cyanoethyl group (6) Modified E containing a polyester graft obtained by depolymerizing a polyester and vinyl alcohol
VOH (7) Modified EV obtained by saponifying a copolymer of vinyl acetate-ethylene-silicon-containing olefinically unsaturated monomer
OH (8) Modified EVO obtained by saponifying a terpolymer of pyrrolidone ring-containing monomer-ethylene-vinyl acetate
H (9) Modified EVOH obtained by saponifying a terpolymer of acrylamide-ethylene-vinyl acetate (10) Modified EVOH obtained by saponifying a terpolymer of allyl acetate-ethylene-vinyl acetate (11) Modified EVOH obtained by saponifying a terpolymer composed of isopropenyl acetate-ethylene-vinyl acetate (12) Modified EVOH obtained by adding a polyether component to the terminal of EVOH (13) Polyether component Modified EVOH added in the form of a graft as a branch polymer of EVOH (14) Modified EVOH in which an alkylene oxide is added to EVOH

Further, the EVOH used in the present invention may be an α-olefin other than those described above, an unsaturated carboxylic acid or a salt thereof, a partial alkyl ester, a complete alkyl ester, a nitrile, an amide, an anhydride, an unsaturated sulfonic acid or a salt thereof. Such a comonomer may be included.

Also, 0.1 parts by weight of EVOH is 0.1 part by weight.
If necessary, the following general resins may be blended within the range of 150 parts by weight.

[0013]

[Table 2] (1) Polyamide resin and its modified resin (2) Polyolefin resin and its modified resin (3) Polyester resin and its modified resin (4) Polystyrene resin and its modified resin (5) Polyvinyl alcohol resin and its modified resin (6) Polyurethane resin and its modified resin (7) Polymethymethacrylate resin and its modified resin

Next, the formation of an unstretched EVOH film will be described. In the present invention, the raw resin pellets are melt-extruded from a T-die onto a casting roll by an extruder to obtain an unstretched film. As the extruder, a general screw-type extruder is used. As the types of screw type extruders, single screw extruders,
Any of a twin screw extruder (rotating in the same direction or different directions) and the like may be used. The melting temperature is 10 to 80 from the melting point of EVOH.
° C, preferably 20 to 60 ° C, is selected. However, as long as the kneading of the resin is sufficient, the temperature is preferably set to a lower value in order to suppress the generation of gel.

By the way, as the size of the screw type extruder increases, the shear heat generated during melting in the extruder increases, and the resin temperature rises above the control temperature. In addition, the residence time up to the exit of the T-die increases with the scale-up. As a result, a gel is easily generated, and the film breaks during stretching.

Therefore, in the present invention, a heat exchanger is provided between the extruder and the T-die, and the resin temperature difference (ΔT) between the inlet and the outlet of the heat exchanger is calculated by the following equation (1). Adjust to a range. That is, in the present invention, the above-mentioned gel generation is suppressed by lowering the temperature after the EVOH is completely melted.

[0017]

(230−0.9 × Y) / 96 ≦ ΔT ≦ (230−0.9 × Y) / 4 (1) (in the formula (1), Y is the ethylene content of the raw resin pellets) (Mole%).)

The difference between the resin temperatures at the inlet and outlet of the heat exchanger (Δ
When T) is smaller than the lower limit value of the above formula (1), not only does it have no meaning as a heat exchanger, but also the residence time of the molten resin becomes longer, so that the gel is more likely to be generated, and the stretching time during stretching is rather high. Film breakage trouble occurs. When the resin temperature difference (ΔT) is larger than the upper limit of the above formula (1), not only the resin viscosity at the outlet of the heat exchanger becomes too high to make extrusion difficult, but also in an extreme case. The solidification of the molten resin begins on the heat exchanger wall.

The type of the heat exchanger is not particularly limited, but a multi-tube type heat exchanger is preferable from the viewpoint of heat exchange efficiency. Resin temperature difference between inlet and outlet of heat exchanger (Δ
As a method of controlling T), a method of controlling the temperature of the cooling heat medium based on the molten resin temperature and the resin pressure measured at the inlet and the outlet of the heat exchanger is preferable.

In addition to the heat exchanger, a filter such as a disk type or a pole type is provided between the extruder and the T-die for adjusting the flow rate and pressure and removing foreign matters, if necessary. Alternatively, a thermogenizer for maintaining the temperature may be provided.

For molding on a casting roll,
An electrostatic pinning method, an air knife method, a vacuum chamber method, or the like is applied. The raw resin melt-extruded from the T-die is brought into close contact with a casting roll maintained at a temperature of usually 60 ° C. or lower, preferably 40 ° C. or lower, quenched, and becomes an unstretched film.

The unstretched film is subjected to a longitudinal stretching step. Prior to the stretching, the film is immersed in a warm bath at 40 ° C. or higher to improve the stretchability. May be adjusted.

Next, the biaxial stretching of the EVOH unstretched film will be described. In the present invention, a uniaxially stretched film is obtained by stretching an unstretched film in the longitudinal direction under the conditions of a temperature range of 50 to 70 ° C. and a stretching ratio of 2.5 to 4.0 times by a roll type stretching machine. Then, the above uniaxially stretched film is stretched in the transverse direction by a tenter type transverse stretching machine under the conditions of a temperature range of 60 to 120 ° C. and a stretching ratio of 2.5 to 5.0 times, to form a biaxially stretched film. In addition, the above method of heat-setting the biaxially stretched film in a temperature range having a lower limit of 110 ° C and an upper limit of 5 ° C lower than the melting point of the raw material resin is preferably applied.

The above-mentioned roll-type stretching machine is composed of a plurality of rolls and a plurality of nip rolls capable of controlling the temperature and controlling the speed, and by changing the linear speed of the low-speed roll and the high-speed roll in one or more stages, The longitudinal stretching ratio of the film can be variously changed.

In the above-mentioned longitudinal stretching, when the stretching temperature (film temperature) is lower than 50 ° C., the stretching stress tends to be too high and the film tends to be broken.
If it exceeds, the film sticks to the stretching roll,
Even if it does not adhere, crystallization proceeds rapidly, so that the next transverse stretching becomes difficult, which may cause the film to break. In the above longitudinal stretching, if the stretching ratio is less than 2.5 times, the desired orientation cannot be imparted to the finally obtained film, and if the stretching ratio exceeds 4.0 times, The film is easily broken. The heating of the film is preferably performed by a roll of a roll-type vertical stretching machine.

The above-mentioned tenter type transverse stretching machine is disclosed in, for example, Japanese Utility Model Publication No. 46-19426 and Japanese Patent Publication No. 55-30977.
JP, JP-B-56-32089, JP-B-56-32089
No. 36853, which is well known to those skilled in the art. The transverse stretching ratio can be variously changed by adjusting the interval between tenters at which both ends in the film width direction are gripped.

In the above transverse stretching, the stretching temperature is 70 ° C.
If less than, the stretching stress is too high and the film is easily broken, and if the stretching temperature exceeds 120 ° C., the orientation effect by stretching cannot be sufficiently obtained, and the mechanical strength is weak and the thickness accuracy is poor. Tend to be obtained only. Further, in the above transverse stretching, if the stretching ratio is less than 2.5 times, the desired orientation cannot be imparted to the finally obtained film, and if the stretching ratio exceeds 5.0 times, The film is easily broken. The film may be heated by any method such as a hot air oven, a heater type oven or a combination of both.

The above-mentioned heat setting is performed to improve the dimensional stability of the biaxially stretched film. When the heat setting temperature is lower than the above lower limit temperature (110 ° C.), the heat setting becomes insufficient. Holes may break and break. Heat setting is
It may be performed in any state of the film in a tensioned state or a relaxed state, or in a state in which both are combined. The relaxation rate is preferably 10% or less. The heating of the film can be performed in the same manner as in the case of the transverse stretching.

The transfer time of the uniaxially stretched film obtained in the above-mentioned longitudinal stretching step to the transverse stretching step (transport time to the transverse stretching start position) is preferably as short as possible, for example, within 5 seconds. Is preferred. With such a short transfer,
By suppressing the progress of orientation and crystallization associated with longitudinal stretching, film breakage, which is a concern during transverse stretching, is effectively prevented.
Further, since the transverse stretching step is performed at a stretching temperature higher than that in the longitudinal stretching step, it is preferable to preheat the film to a necessary temperature during the transfer.

Next, the layer constitution of the biaxially stretched film in the present invention will be described. The biaxially stretched film according to the present invention obtained by the above method is used as it is, that is, used as a single-layer film or as a laminate having at least one film. Such a laminate is
It is obtained by laminating another substrate (film or sheet) on one or both sides of a biaxially stretched EVOH film.

As the above laminating method, for example,
Using a known adhesive such as an organic titanium compound, an isocyanate compound or a polyester compound, the EVOH 2
A method of laminating the axially stretched film and another base material may, for example, be mentioned.

Further, the above-mentioned substrate (film or sheet)
Examples are linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-
Homo- or copolymers of olefins such as propylene copolymer, ethylene-acrylate copolymer, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms), polybutene and polypentene; Graft-modified olefin homo- or copolymers with unsaturated carboxylic acids or esters thereof,
Polystyrene resin, polyester resin, polyamide resin, copolyamide resin, polyvinyl chloride resin, polyvinylidene chloride resin, acrylic resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene, EVOH ( EVOH 2 layers or more). Further, paper, metal foil, woven cloth, nonwoven cloth, metal cotton strip, woody surface, etc. can also be used.

The layer structure of the laminate is such that the layer of the biaxially stretched film of EVOH is represented by A (A1, A2,...) And the other base material is represented by B (B1, B2,...). , A / B, B / A / B, A / B / A, A1 /
A2 / B, A / B1 / B2, B2 / B1 / A / B1 / B
Any combination such as 2 is possible.

Further, the biaxially stretched film according to the present invention comprises:
Other materials can be coated into a composite film.

Examples of the coating material include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-propylene copolymer, and ethylene-acrylic acid. Ester copolymer, polypropylene, propylene-α-olefin (C 4-20
Α-olefin) copolymers, polybutenes, homo- or copolymers of olefins such as polypentene, graft-modified polyolefin resins of these olefins homo- or copolymers with unsaturated carboxylic acids or esters thereof, polystyrene resins, Polyester, polyamide,
Copolymerized polyamide, polyvinyl chloride, polyvinylidene chloride, acrylic resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene, EVOH, etc., and further represented by metal, silicon, etc. Inorganic substances and the like can be used. As a coating method,
In addition to a method of applying and drying a solution of a coating substance, a vapor deposition method and the like are appropriately selected and applied.

The 2 according to the present invention produced as described above
Axial stretched films, their laminates and composite films are excellent in appearance characteristics, gas barrier properties, etc., and are therefore used in the fields of food, pharmaceuticals, agricultural chemicals, and industrial chemicals for packaging films, sheets, tubes, bags, containers, and retort containers. It is suitably used for such purposes.

[0037]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In the following examples, “parts” and “%” mean on a weight basis unless otherwise specified.

Examples 1 to 6 and Comparative Examples 1 to 3 EVOH described in Table 7 was supplied to a single-screw extruder having the specifications shown in Table 3 and passed through a heat exchanger having the specifications shown in Table 4 to obtain Table 5. Melt extrusion was performed using a T-die with the specifications shown. Table 6 shows the main processing and stretching conditions.

[0039]

<Single screw extruder> Screw inner diameter: 65 mm L / D: 28 Screw compression ratio: 3.8 Extrusion temperature: C1 (210 ° C.) / C2 (220
° C) / C3 (230 ° C) / C4 (230 ° C) / C5 (2
20 ℃)

[0040]

[Table 4] <Heat exchanger: Multi-tube heat exchanger (installed in a static mixer)> Number of tubes: 6 Heat exchanger length: 500 mm Heat medium for cooling: "Barrel Therm 40" manufactured by Matsumura Oil Co., Ltd.
0 "

[0041]

[Table 5] <T die: coat hanger type> Die width: 450mm Die temperature: 220 ° C

The EVOH melt-extruded from the T-die was
Rapidly cooled on a 600 mm diameter casting roll cooled to 0 ° C.
m). Next, after continuously performing longitudinal stretching by a roll stretching machine, transverse stretching by a tenter stretching machine, and heat setting for a treatment time of 5 seconds, the humidity is adjusted to EV according to the present invention.
An OH biaxially stretched film was obtained.

The obtained EVOH biaxially stretched film (film after 3 hours of stretching treatment) was subjected to ASTM-D-
882 and 1922, tensile strength in the machine direction and transverse direction (Ts; kg / mm) under the conditions of 20 ° C. and 65% RH.
² ) was measured. Further, the above-mentioned stretching treatment was continuously performed for 8 hours, and the number of breaks (including holes) at that time was examined to evaluate the continuous stretchability. Table 8 shows the results.

[0044]

[Table 6] (EVOH biaxially stretched film production conditions)

[0045]

[Table 7] (EVOH raw materials)

[0046]

[Table 8] (Evaluation results)

[0047]

According to the present invention described above, a stable method for producing an EVOH film having excellent film thickness accuracy and film strength is provided, and the industrial value of the present invention is remarkable.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Ninomiya 2-13-1 Muroyama, Ibaraki-shi, Osaka Inside the Central Research Laboratory of Nippon Gosei Chemical Industry Co., Ltd. (72) Inventor Kuniyasu Kato 2 Kamiya, Ogaki-shi, Gifu Chome 80 Nippon Gohsei Chemical Industry Co., Ltd. Ogaki Plant Ogaki Film Factory

Claims (4)

[Claims] 1. An unstretched film is obtained by melt-extruding a raw resin pellet comprising a saponified ethylene-vinyl acetate copolymer from a T-die onto a casting roll by an extruder, and then biaxially stretching the unstretched film. In a method for producing a saponified ethylene-vinyl acetate copolymer film, a heat exchanger is provided between an extruder and a T-die, and a resin temperature difference between an inlet and an outlet of the heat exchanger (Δ
A method for producing a saponified ethylene-vinyl acetate copolymer film, wherein T) is adjusted to fall within the range of the following formula (1). (230−0.9 × Y) / 96 ≦ ΔT ≦ (230−0.9 × Y) / 4 (1) (in the formula (1), Y is the ethylene content of the raw material resin pellets) (Mole%).) 2. A raw material resin pellet having an ethylene content of 1
2. The composition according to claim 1, wherein the saponification degree is 0 to 60 mol% and the saponification degree is 90% or more.
Production method described in 1. 3. The production method according to claim 1, wherein the sum of the Na and K metal contents of the raw resin pellets is in the range of 0.01 to 30 ppm. 4. A uniaxially stretched film is obtained by stretching a non-stretched film in a longitudinal direction under a condition of a temperature range of 50 to 70 ° C. and a stretching ratio of 2.5 to 4.0 by a roll type stretching machine. ,
Next, the above uniaxially stretched film is stretched in the transverse direction by a tenter type transverse stretching machine in a temperature range of 60 to 120 ° C. and a stretching ratio of 2.5 to 5.0 times to form a biaxially stretched film. The method according to any one of claims 1 to 3, wherein the biaxially stretched film is heat-set in a temperature range having a lower limit of 110 ° C and an upper limit of 5 ° C lower than the melting point of the raw material resin.