JPH11198225A - Laminate stretching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve gas barrier properties, transparency, tensile strength and a draw ratio by a laminate consisting of a saponified ethylene-vinyl acetate copolymer layer and a thermoplastic resin layer is drawn while being irradiated with microwaves. SOLUTION: As EVOH of a saponified ethylene-vinyl acetate copolymer EVOH layer, a substance in which an ethylene content is 10-60 mole % and the degree of saponification of a vinyl acetate component is 90 mole %. is used. A polyolefin resin and others are used as the thermoplastic resin of a thermoplastic resin layer. Both layers are coextruded to form a laminate. The laminate is drawn while being irradiated with microwaves. First, the undrawn laminate is drawn longitudinally in the first drawing process and then is drawn crosswise in the second drawing process to obtain a biaxially oriented laminate. Since the EVOH laminate is drawn while being irradiated with microwaves, gas barrier properties, transparency, tensile strength, and others improve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for stretching a laminate of a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) layer and a thermoplastic resin layer.

[0002]

2. Description of the Related Art Heretofore, EVOH has been widely used for various packaging applications by taking advantage of its gas barrier properties. However, usually, EVOH is laminated with various thermoplastic resins and practically used as a laminate. That is the fact. Such a laminate is generally subjected to uniaxial or biaxial stretching in order to improve the strength of the laminate, impart tearability, improve gas barrier properties, and the like. At the time of stretching, attempts have been made to increase the stretching temperature or to add a plasticizer in order to increase the stretchability.

[0003]

However, according to a detailed study by the inventor, if the stretching temperature is too high during stretching, the laminated thermoplastic resin layer such as a polyolefin resin crystallizes and the transparency is lowered. Loss, also, when using an additive such as a plasticizer, often has an adverse effect such as a decrease in the interlayer adhesion of the laminate, without using an additive such as a plasticizer, does not cause a decrease in transparency There is a demand for a stretching method capable of performing high stretching.

[0004]

Accordingly, the present inventor has conducted intensive studies in view of the above circumstances, and as a result, the laminate comprising the EVOH layer and the thermoplastic resin layer is stretched while being irradiated with microwaves. Not to mention gas barrier properties,
High draw ratio (1.5 to 8) excellent in transparency, tensile strength, etc.
The present invention has been found that a laminate of (2) is obtained.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The stretching method of the present invention will be specifically described below. The laminate used in the present invention is EV
It is composed of an OH layer and a thermoplastic resin layer, and the EVOH used for the EVOH layer is not particularly limited,
Ethylene content 10-60 mol%, preferably 20-60
Mol%, more preferably 25 to 55 mol%, and the saponification degree of the vinyl acetate component is 90 mol% or more, preferably 95 mol% or more. When the ethylene content is less than 10 mol%, the water resistance is insufficient. On the other hand, if it exceeds 60 mol%, the gas barrier property is undesirably lowered. 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. In the EVOH used in the present invention, if necessary, an antioxidant, a lubricant, an anti-blocking agent,
Coloring agents, antistatic agents, ultraviolet absorbers and the like can also be added.

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. Further, as the thermoplastic resin used for the thermoplastic resin layer, linear low-density polyethylene,
Low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-propylene copolymer, ethylene-acrylate copolymer, polypropylene, propylene
α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, homo- or copolymer of olefin such as polybutene, polypentene, or homo- or copolymer of these olefins with unsaturated carboxylic acid or ester thereof Broadly defined polyolefin resin such as graft-modified resin, polystyrene resin, polyester, polyamide, copolymerized polyamide, polyvinyl chloride, polyvinylidene chloride, acrylic resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene And chlorinated polypropylene. Among them, a polyolefin resin, a polyamide resin, a polyester resin, and a polystyrene resin are preferably used.

Using the above EVOH and thermoplastic resin,
In producing a laminate including an EVOH layer and a thermoplastic resin layer, a known method can be employed.For example, an EVOH layer and a thermoplastic resin layer are produced in advance, and both are formed of an organic titanium compound. Isocyanate compound,
A method of laminating using a known adhesive such as a polyester compound, a method of forming a laminate by melt co-extrusion of EVOH and a thermoplastic resin, and a method of extrusion coating are exemplified. In the present invention, when the obtained laminate is stretched while being irradiated with microwaves, it has the greatest feature in stretching, 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 preferred. If the time is less than 1 second, the effect of irradiation cannot be expected. If the time exceeds 300 seconds, the EVOH is heated too much and improvement in stretch orientation cannot be expected. More preferably, it is 2 to 180 seconds. For stretching, uniaxial,
Although not limited to any of biaxial (simultaneous and sequential) and blow stretching, biaxial (sequential) stretching will be described here.

[0010] In the present invention, microwave irradiation is performed in the first step.
The stretching can be performed in either the next (MD direction) stretching step or the second (TD direction) stretching step or in both steps. Here, a case where microwave irradiation is performed in both steps will be described. First, the laminate before stretching is the first
The next (MD direction) stretching step is performed. The first (M
For the stretching in the D direction), a known method can be used. In the present invention, the surface of the laminate is irradiated with the above-described microwave at the time of such stretching. Or the left and right) may be attached with the microwave generator as described above. The temperature of the laminate at this time is 100 to
It is also preferable to adjust the temperature to 160 ° C.
If the temperature is lower than 0 ° C., it is difficult to sufficiently stretch the thermoplastic resin in the outer layer. On the other hand, if the temperature exceeds 160 ° C., the thermoplastic resin in the outer layer melts or crystallizes, which is not preferable. Although the stretching ratio at this time is not specified, in the present invention, a high stretching ratio can be used.
1.5 to 8 times (more preferably 2 to 8 times) in the direction D)
It is preferred that the film be stretched to

The above-mentioned first (MD direction) stretched laminate is then stretched in the transverse direction in the second (TD direction) stretching step. )
The stretching can be performed in the same manner as in the stretching. Although the stretching ratio at this time is not particularly specified, such a laminate is placed horizontally (T
1.5 to 8 times (more preferably 2 to 8 times) in the direction D)
It is preferred that the film be stretched to Usually, such secondary stretching is performed by a tenter method in which both ears of the laminate are sandwiched by clips, but may be performed by a generally known method. Also,
Usually, heat setting is further performed. Heat setting is 120 ° C under tension
Heating the laminate at a temperature 5 ° C. lower than the melting point of the laminate for several seconds to several minutes.

In this way, a biaxially stretched laminate is obtained. In the case of uniaxial stretching, it may be performed according to the above.
When the layer structure of the laminate of the present invention is A, the EVOH layer is B, and the thermoplastic resin layer is B.
/ A / B, A / B / A, B / A / B / A, B / A / B /
It is also possible to adopt a laminate structure such as A / B.

Thus, the (stretched) laminate obtained by the stretching method of the present invention is excellent in appearance characteristics, gas barrier properties, etc., and therefore, is suitable for packaging films, sheets, tubes, foods, pharmaceuticals, agricultural chemicals and industrial chemicals. It is very useful for applications such as bags, containers, and retort containers. In addition, the stretching method of the present invention uses E
It is also a useful method for stretching a VOH monolayer.

[0014]

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 Polypropylene [manufactured by Nippon Polychem, "Novatech PP"
EG8]] layer (100 μm thickness) / adhesive resin [Mitsui Petrochemical Co., Ltd., “Admer QF500”] layer (30 μm)
/ EVOH [ethylene content 32 mol%, saponification degree 9
9.8 mol%] layer (30 μm thick) / adhesive resin [same as above] layer (30 μm) / polypropylene [same as above] layer (100 μm
Thickness) was sequentially biaxially stretched and heat-set under the following conditions to obtain a biaxially stretched laminate.

[Primary stretching (longitudinal stretching) conditions] Microwave frequency 2.45 GHz Power of microwave generator 1 kW Microwave irradiation time 15 seconds Stretcher Roll type stretcher Stretching temperature 140 ° C. Stretching ratio in longitudinal direction 3 .6 times film thickness after stretching 75 μm [Secondary stretching (transverse stretching) conditions] Microwave frequency Same as above Power of microwave generator Same as above Microwave irradiation time Same as above Stretching machine Tenter stretching machine Stretching temperature 140 ° C Lateral direction Stretch ratio 3.9 times Film thickness after stretching 17 μm Film width after stretching 800 mm [Heat setting conditions] Temperature 160 ° C. Time 5 seconds Regarding gas barrier properties, transparency and tensile strength of the obtained biaxially stretched laminate, The evaluation was performed as follows.

(Gas barrier property) Oxygen permeability (cc / m ² · day · atm) under conditions of 20 ° C. and 65% RH
Was measured. (Transparency) The haze value was measured. (Improvement of tensile strength) Under the conditions of 20 ° C. and 65% RH,
In accordance with ASTM-D-882 and 1922, the tensile strength in the longitudinal direction and the transverse direction was measured, and the tensile strength of the film stretched without irradiation with microwaves (stretch ratio: 3 × 3 times) was measured. Then, it was examined whether or not the tensile strength was improved from a film stretched while irradiating microwaves in both the longitudinal and transverse directions.

Example 2 A biaxially stretched laminate was obtained in the same manner as in Example 1 except that the stretching conditions were changed as described below, and the evaluation was performed in the same manner. [Primary stretching (longitudinal stretching) conditions] Microwave frequency 2.45 GHz Power of microwave generator 1.3 kW Microwave irradiation time 20 seconds Stretching machine Roll stretching machine Stretching temperature 140 ° C Longitudinal stretching magnification 4. Eight times Thickness after stretching 60 μm [Secondary stretching (transverse stretching) conditions] Microwave frequency Same as above Power of microwave generator Same as above Microwave irradiation time Same as above Stretching machine Tenter stretching machine Stretching temperature 140 ° C Lateral stretching Magnification 5.2 times Film thickness after stretching 14 μm Film width after stretching 800 mm

Example 3 A biaxially stretched laminate was obtained in the same manner as in Example 1 except that the stretching conditions were changed as described below, and the same evaluation was performed. [Primary stretching (longitudinal stretching) conditions] Microwave frequency 2.45 GHz Power of microwave generator 0.2 kW Microwave irradiation time 5 seconds Stretching machine Roll stretching machine Stretching temperature 150 ° C Longitudinal stretching magnification 3. 5 times film thickness after stretching 80 μm [Secondary stretching (transverse stretching) conditions] Microwave frequency Same as above Power of microwave generator Same as above Microwave irradiation time Same as above Stretching machine Tenter type stretching machine Stretching temperature 150 ° C. Lateral stretching Magnification 3.8 times Film thickness after stretching 18 μm Film width after stretching 800 mm

Example 4 In Example 1, an ethylene content of 4 was used as EVOH.
A biaxially stretched laminate was obtained in the same manner except that EVOH having 4 mol% and a saponification degree of 99.8 mol% was used, and was similarly evaluated.

Example 5 In Example 1, a layer of polypropylene [Novatech PPEG8, manufactured by Nippon Polychem Co., Ltd.] (100 μm thick)
Adhesive resin [Mitsui Petrochemical Co., Ltd., "Admer QF50
0 "] layer (30 μm) / EVOH [ethylene content 32
Mol%, saponification degree 99.8 mol%] layer (30 μm thickness) /
A biaxially stretched laminate was obtained in the same manner as above except that a laminate of the adhesive resin [same as above] layer (30 μm) / low-density polyethylene layer (100 μm thickness) was obtained and evaluated in the same manner.

Example 6 In Example 1, nylon [Novami, manufactured by Mitsubishi Chemical Corporation]
d 1020 ″] layer (50 μm thick) / EVOH [ethylene content 32 mol%, saponification degree 99.8 mol%] layer (50
μm thickness) / Nylon [Mitsubishi Chemical's Novamid 102
0 ”] layer (50 μm thick), the stretching temperature in the first stretching is 130 ° C., the longitudinal stretching ratio is 4.5 times, and the film thickness after stretching is 45 μm. Stretching temperature of 1
30 ° C., transverse stretching ratio 5.2 times, film thickness after stretching 15 μm
m, and heat-fixing was performed at 170 ° C. for 7 seconds to obtain a biaxially stretched laminate, which was similarly evaluated.

Example 7 The same laminate as in Example 1 was subjected to uniaxial stretching and heat setting under the following conditions to obtain a uniaxially stretched laminate, which was evaluated in the same manner as in Example 1. [Primary stretching (longitudinal stretching) conditions] Microwave frequency 2.45 GHz Power of microwave generator 1.8 kW Microwave irradiation time 10 seconds Stretching machine Roll stretching machine Stretching temperature 150 ° C Longitudinal stretching magnification 7. 8 times Thickness after stretching 35 μm Width of film after stretching 400 mm [Heat setting conditions] Temperature 160 ° C. Time 5 seconds

Comparative Example 1 In Example 1, stretching was performed without performing microwave irradiation at the time of stretching. However, high stretching could not be performed, and network streaks were generated in the laminate. Table 1 shows the evaluation results of the examples.

[0024]

Table 1 Gas barrier properties Transparency Improvement of tensile strength (oxygen permeability) (Haze value) Example 1 3.4 1.6 Strength improvement was observed {2 4.1 1.4 Same as above} 5.2 1.8 Same as above ４ 4 7.4 1.6 Same as above ５ 5 4.8 1.5 Same as above 〃 6 1.4 1.1 Same as above ７ 7 1.7 1.5 Same as above Comparative example 1> 10 35 Strength decreased Note) The unit of gas barrier property is cc / m ² · day · atm

[0025]

According to the present invention, since the EVOH laminate is stretched while being irradiated with microwaves, it is possible to obtain a stretched laminate having a high stretching ratio and excellent gas barrier properties, transparency, tensile strength, and the like. It is very useful as a packaging material for foods, pharmaceuticals, agricultural chemicals, industrial chemicals and the like.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 9:00

Claims (4)

[Claims] 1. A method for stretching a laminate, comprising stretching a laminate comprising a saponified ethylene-vinyl acetate copolymer layer and a thermoplastic resin layer while irradiating microwaves. 2. The laminate according to claim 1, wherein the saponified ethylene-vinyl acetate copolymer has an ethylene content of 10 to 60 mol% and a saponification degree of the vinyl acetate component of 90 mol% or more. Body stretching method. 3. The resin according to claim 1, wherein the thermoplastic resin is any one of a polyolefin resin, a polyamide resin, a polyester resin, and a polystyrene resin.
Or the stretching method of the laminate according to 2. 4. The stretching ratio is 1.5 to 8 in the machine direction (MD).
The stretching method according to any one of claims 1 to 3, wherein the stretching ratio is 1.5 to 8 times in the transverse (TD) direction.