JPH11291245A - Drying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the extrusion-stability of a product without the development of whitening and void and the abnormality of its transparency and shape by a method wherein a saponified ethylene-vinyl acetate copolymer is dried by being irradiated with microwaves. SOLUTION: A saponified ethylene-vinyl acetate copolymer EVOH employed has an ethylene content of 10-60 mol.% and the degree of saponification of 90 or more mol.%. The preferable water content of the dried EVOH, microwaves are irradiated. The above drying method can also be employed for drying after the processing of the EVOH pellets with various aqueous solutions or the molding of the EVOH product as well as at the manufacturing of the EVOH. Thus, since no phenomena such as the development of whitening or voids occurs in the dried EVOH, the resultant EVOH is excellent in transparency, non-deformation or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for drying a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH).

[0002]

2. Description of the Related Art Conventionally, EVOH has been widely used in various packaging applications, etc. by making use of characteristics such as transparency, antistatic property, oil resistance, solvent resistance, gas barrier property, and fragrance retention property.
In the production of such EVOH, usually, a copolymer of ethylene and vinyl acetate is saponified in a slurry state, and then extruded into a coagulation bath in a strand form and cut.
Generally, it is then dried to produce a product in the form of pellets. Also, since EVOH is a resin that easily absorbs moisture, if its storage state is poor, it absorbs moisture, and EVO absorbs moisture.
When H is formed into a film with an extruder or the like, foaming or the like occurs, and a good molded product cannot be obtained, and drying of EVOH is important. At present, hot air having a temperature close to 100 ° C. is usually used for drying them.

[0003]

However, in the above-mentioned method using hot air, a phenomenon such as whitening of EVOH or generation of voids is observed, and new improvement of the drying method is desired.

[0004]

Accordingly, the present inventor has conducted intensive studies in view of such circumstances, and as a result, has found that the above problems can be solved by irradiating EVOH with microwaves and drying. The invention has been completed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The EVOH used in the present invention is not particularly limited, but has an ethylene content of 10 to 60 mol%, preferably 20 to 60 mol%, more preferably 25 to 55 mol%,
A vinyl acetate component having a degree of saponification of at least 90 mol%, preferably at least 95 mol% is used.
If the amount is less than 0 mol%, the water resistance becomes insufficient. On the other hand, if it exceeds 60 mol%, the gas barrier property decreases, which is not preferable.
On the other hand, if the saponification degree is less than 90 mol%, the water resistance becomes insufficient, which is not preferable.

[0006] The EVOH may be variously modified, if necessary, or may be a mixture of the modified EVOH and the EVOH. As the modified EVOH, for example, modified EVOH with propylene, isobutene, etc., having 3 carbon atoms
At least one α-olefin having from 30 to 30 carbon atoms or 3 carbon atoms
Saponified terpolymer comprising modified EVOH, modified EVOH obtained by graft polymerization of at least one α-olefin of at least 30 and ethylene and acrylic acid ester, and (meth) acrylate-ethylene-vinyl acetate Modified EVOH, a modified EVOH obtained by modifying the hydroxyl group of EVOH with a cyanoethyl group, a modified EVOH containing a polyester graft obtained by depolymerizing a polyester with vinyl alcohol, a vinyl acetate-ethylene-silicon-containing olefinically unsaturated monomer EVOH obtained by saponifying a monomeric copolymer, modified EVOH obtained by saponifying a terpolymer comprising a pyrrolidone ring-ethylene-vinyl acetate, acrylamide-
Modified EVOH obtained by saponifying a terpolymer of ethylene-vinyl acetate, modified EVOH obtained by saponifying a terpolymer of allyl acetate-ethylene-vinyl acetate, isopropenyl acetate-ethylene-acetic acid Modified EVO obtained by saponifying vinyl terpolymer
H, modified EVOH in which a polyether component is added to the terminal of EVOH, modified EVOH in which a polyether component is added in a graft form as a branch polymer of EVOH, and modified EVOH in which an alkylene oxide is added to EVOH.

EVOH contains comonomer other than the above, such as α-olefins, unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides, unsaturated sulfonic acids or salts thereof. You can be there.

The water content of the EVOH to be dried is not particularly limited, but is preferably 0.3 to 60% by weight.
If the water content is less than 0.3% by weight, the drying treatment is meaningless. If the water content is more than 60% by weight, excessive microwave irradiation is required, and as a result, E is increased.
VOH may cause deterioration, which is not preferable. In the present invention, when drying the EVOH as described above, it has the greatest feature in performing irradiation treatment with microwaves, and such a method will be described.

In the present invention, in order to irradiate microwaves, for example, a microwave generator having a commercial frequency of 2.45 GHz and a power of 0.1 to 2 kW may be used. , 1-300
Seconds are preferable. If the time is less than 1 second, the effect of irradiation cannot be expected. If the time exceeds 300 seconds, EVOH may be excessively heated and deteriorated. More preferably, 2
~ 180 seconds. The microwave intensity at this time is 4 to 40 Mrad (further 5 to 25 Mra
If d) is less than 4 Mrad, drying takes a long time and is not practical.
OH is not preferable because it may cause deterioration.

[0010] The drying method of the present invention comprises the steps of:
Can be used not only during the production (drying of the pellets), but also after the pellets are treated with various aqueous solutions or after the molded article is molded with EVOH.

[0011] Thus, EVOH dried by the drying method of the present invention does not show any phenomena such as whitening or void generation during the drying process, and thus has no transparency or abnormal shape (deformation). Is excellent, and
Because of excellent extrusion stability, such EVOH is used for food,
Various packaging materials such as pharmaceuticals, industrial chemicals, and agricultural chemicals (films,
It is useful for applications such as sheets, containers, etc.) and fibers.

[0012]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” mean on a weight basis unless otherwise specified. Example 1 EVOH with a water content of 40% [ethylene content 29 mol%,
(Saponification degree 99.8 mol%) (5 cm × 5 cm
× 200 μm) was irradiated with a microwave (20 Mrad) having a frequency of 2.45 GHz, and dried until the water content became 0.3%. When the surface of the EVOH film after the drying treatment was visually observed, neither whitening nor generation of voids was observed.

Example 2 EVOH having a water content of 30% [ethylene content 29 mol%,
A microwave (3 mm in diameter, 2 mm in length, 6 mm in length) having a frequency of 2.45 GHz (3
(0 Mrad) and dried until the water content was 0.5%. When the EVOH pellets after the drying treatment were visually observed, neither whitening nor generation of voids was observed.

Example 3 A dry treatment was performed in the same manner as in Example 1 except that the microwave was changed to 30 Mrad, and the same evaluation was performed. However, neither whitening nor generation of voids was observed.

Example 4 EVOH having a water content of 20% [ethylene content 46 mol%,
A microwave (2.45 GHz frequency) was added to a pellet (diameter 2 mm, length 4 mm) having a saponification degree of 99.8 mol%.
(0 Mrad) and dried until the water content was 0.5%. When the EVOH pellets after the drying treatment were visually observed, neither whitening nor generation of voids was observed.

Example 5 In Example 1, an ethylene content of 44 was used as EVOH.
The same drying treatment was carried out, except that the product having a molar percentage of 98 mol% and a saponification degree of 98 mol% was used, and the same evaluation was carried out.

COMPARATIVE EXAMPLE 1 In Example 1, instead of microwave irradiation, 15
A resin composition was obtained in the same manner except that hot air at 0 ° C. was used, and evaluation was performed in the same manner. As a result, a void was generated in the film and whitening occurred.

[0018]

According to the present invention, since the EVOH is dried by microwave irradiation, it is excellent in that there is no whitening phenomenon, no generation of voids, no transparency and no abnormal shape (deformation). , Excellent extrusion stability,
It is very useful as a packaging material for agricultural and industrial chemicals.

Claims (3)

[Claims] 1. A drying method comprising irradiating a microwave to a saponified ethylene-vinyl acetate copolymer. 2. The drying method according to claim 1, wherein the water content of the saponified ethylene-vinyl acetate copolymer is 0.3 to 60% by weight. 3. The saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the ethylene content is 10 to 60 mol% and the saponification degree of the vinyl acetate component is 90 mol% or more. Drying method.