JP2001162678A - Method for producing multi-layer container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multi-layer container which has good gas-barrier properties and can be recovered/recycled with a thermoplastic resin layer separated from a barrier layer after being used. SOLUTION: In a method for producing the multi-layer container, a multi- layer sheet obtained by dry-laminating a water-soluble ethylene-modified polyvinyl alcohol resin layer 1-19 mole % in ethylene-modification degree and a thermoplastic resin layer is thermoformed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a container for thermoforming a multilayer sheet obtained by dry laminating a thermoplastic resin layer and a water-soluble ethylene-modified polyvinyl alcohol-based resin layer. More particularly, the present invention relates to a method for producing a container having gas barrier properties and capable of separating a thermoplastic resin layer and a barrier layer after use, and recovering and reusing the container.

[0002]

2. Description of the Related Art In recent years, thermoplastic resin containers have been widely used as containers for foodstuffs, beverages, pharmaceuticals and the like. For example, a sheet of a thermoplastic resin such as polypropylene, polyester resin, and polystyrene resin is vacuum formed, pressure-formed,
Examples include a cup manufactured by press molding. The thermoplastic resin container is frequently used for various purposes because of its light weight, workability, ease of handling, and the like.

However, in applications where gas barrier properties are required, for example, containers such as food cups, the thermoplastic resin molded products obtained in this way often have insufficient gas barrier properties. . As an improvement measure, an attempt has been made to laminate a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) layer having excellent gas barrier properties on the thermoplastic resin layer. That is, a molded article having three or more types of laminated structures such as a thermoplastic resin layer / EVOH layer / thermoplastic resin layer has been studied. For example, a method of forming a sheet having a three-layer structure of a thermoplastic resin layer / EVOH layer / thermoplastic resin layer has been used.

However, commercially available EVOH is insoluble in water because the degree of ethylene modification exceeds 20 mol%.
A container having an EVOH layer has a problem that, after being used, it is difficult to separate the thermoplastic resin and the EVOH layer, and it is difficult to reuse the container. After use, the thermoplastic resin layer and the barrier layer are separated. A container that can be collected and reused has been desired.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a container having a gas barrier property and capable of separating a thermoplastic resin layer and a barrier layer after use, and recovering and reusing the container. is there.

[0006]

An object of the present invention is to provide a water-soluble ethylene-modified polyvinyl alcohol resin (hereinafter sometimes abbreviated as ethylene-modified PVA) layer having a degree of ethylene modification of 1 to 19 mol% and a thermoplastic resin. This is achieved by providing a method for producing a multilayer container for thermoforming a multilayer sheet obtained by dry laminating layers.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The thermoplastic resin used in the present invention is not particularly limited as long as it is heat-fusible and has water resistance, and various thermoplastic resins can be used, and polyethylene terephthalate (PET), polypropylene ( P
P), polyethylene (PE), polystyrene (PS),
Polyamide (PA) or the like is preferably used.

The ethylene-modified PVA resin used in the present invention is a water-soluble polymer obtained by copolymerizing a vinyl ester and ethylene by a conventional method and then saponifying the copolymer.
Here, the vinyl ester includes vinyl acetate, vinyl propionate, vinyl formate, vinyl versatate, vinyl pivalate, and the like. Vinyl acetate that is industrially produced and has a cost advantage is usually used. If the resulting modified PVA is water-soluble, other monomers such as α-
Olefin, ω-hydroxy-α-olefin, unsaturated carboxylate, long-chain vinyl ether, unsaturated compound containing polyoxyalkylene group, saturated branched fatty acid vinyl, unsaturated sulfonate, unsaturated compound containing silanol group, containing amino group It may be modified with an unsaturated compound or the like. It is important that the degree of modification of ethylene is 1 to 19 mol%, preferably 3 mol% or more, more preferably 5 mol%.
As described above, it is optimally at least 7 mol%, and the upper limit is preferably at most 18 mol%, more preferably at most 15 mol%, optimally at most 13 mol%. If the degree of ethylene modification is lower than 1 mol%, sufficient gas barrier properties cannot be exhibited, particularly under high humidity. On the other hand, if the degree of ethylene modification exceeds 19 mol%, the water solubility significantly decreases,
It becomes difficult to separate, collect, and reuse the thermoplastic resin layer and the barrier layer of the container after use.

The degree of saponification of the ethylene-modified PVA used in the present invention is preferably 80 mol% or more.
It is more preferably at least 0 mol%, particularly preferably at least 95 mol%. If the degree of saponification is lower than 80 mol%, the barrier properties of the obtained container are significantly reduced.

The degree of polymerization of the ethylene-modified PVA resin used in the present invention is 200 to 50 as a viscosity average degree of polymerization (hereinafter simply referred to as degree of polymerization) measured according to JIS K6726.
00, more preferably 300 to 3000. If the degree of polymerization is less than 200, the ethylene-modified PVA-based resin layer may be broken or its appearance may be damaged when an impact such as dropping is applied to the obtained container. On the other hand, when the degree of polymerization exceeds 5,000, the viscosity of the ethylene-modified PVA-based resin becomes extremely high, so that hot melt molding becomes difficult.

The ethylene-modified PVA resin used in the present invention must be water-soluble. Here, the term "water-soluble" means that water is added to an ethylene-modified PVA resin,
It means that at a temperature of 95 ° C., no solid matter is observed and a homogeneous solution is obtained at any concentration of t%.
Here, “uniform” does not necessarily have to be transparent.

The ethylene-modified PVA-based resin used in the present invention may contain various additives, if necessary, as long as the object of the present invention is not impaired. Examples of additives include known additives such as plasticizers, antioxidants, processing stabilizers, ultraviolet absorbers, coloring agents, fragrances, lubricants, release agents, antistatic agents, reinforcing agents, extenders, and fillers. . Particularly, plate-like clay such as montmorillonite, swellable synthetic mica, and the like are preferably used.

The multilayer sheet used in the present invention is a multilayer sheet having one or two or more layers of the above-mentioned ethylene-modified PVA resin and one or two or more thermoplastic resin layers. It is important that the multilayer sheet is obtained by dry lamination, and as a lamination method, a method of laminating an ethylene-modified PVA-based resin and a thermoplastic resin under pressure and the like is general. By dry laminating, the thermoplastic resin layer and the barrier layer, ethylene-modified P
The separation and recovery of the VA-based resin layer is improved, and the humidity dependence of the barrier layer is reduced. When a multilayer sheet is obtained by laminating, an adhesive layer can be provided between the thermoplastic resin layer and the ethylene-modified PVA-based resin layer so that the adhesion between the thermoplastic resin and the ethylene-modified PVA becomes good.
The adhesive used for the adhesive layer is not particularly limited as long as it improves the adhesiveness between the thermoplastic resin layer constituting the multilayer sheet and the ethylene-modified PVA-based resin layer, and a known adhesive can be used. Further, it is desirable that the ethylene-modified PVA-based resin layer is an intermediate layer of the multilayer sheet. That is, a multilayer sheet in which thermoplastic resin layers are provided on both sides of an intermediate ethylene-modified PVA layer, such as a thermoplastic resin layer / ethylene-modified PVA-based resin layer / thermoplastic resin layer, is preferable. When the outermost layer of the multilayer container is a thermoplastic resin layer, the resulting multilayer container has improved surface water resistance, handleability, and the like.

The thickness of the multilayer sheet is usually 10 to 5000
μm is used, preferably 50 to 3000 μm, and particularly preferably 100 to 2000 μm.
The thickness of the ethylene-modified PVA-based resin layer can be appropriately set according to the desired gas barrier properties, but is usually 1 to 1000 μm.
And preferably from 3 to 500 μm. The thickness of the adhesive layer is usually 1 to 500 μm, and 3 to 300 μm.
m, more preferably 5 to 100 μm.

The multilayer container of the present invention is obtained by thermoforming the above-mentioned multilayer sheet. The thermoforming method is not particularly limited, but is usually formed by vacuum forming, pressure forming, press forming or the like. Here, it is desirable that at least a part of the multilayer sheet is stretched 1.2 times or more, preferably 2.0 times or more before or during the forming. Here, the term “stretching” refers to stretching at a temperature not lower than the glass transition temperature and not higher than the melting point of the thermoplastic resin constituting the multilayer sheet, and may be stretched in one direction or in two or more directions. The stretching ratio is indicated by a value obtained by dividing the thickness of the original multilayer sheet by the thickness of the container after molding. By stretching, the gas barrier properties of the obtained container,
Water resistance and transparency are improved.

The multilayer container of the present invention obtained by such a method has excellent gas barrier properties and can be widely used for containers of foodstuffs, beverages, seasonings and pharmaceuticals. Further, since the ethylene-modified PVA-based resin as the barrier layer is water-soluble, it can be separated from the thermoplastic resin with hot water or steam, and the container can be collected and reused.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In the examples, “%” and “parts” are based on weight unless otherwise specified. The method for measuring and evaluating the characteristic value is as follows.

(1) Method of measuring characteristic values (1-1) Degree of polymerization and degree of saponification Measured according to JIS K6726.

(2) Evaluation method (2-1) Gas barrier property A container was filled with miso until it was full, and the container was purged with dry nitrogen and sealed. 30 ° C, 65% RH in a constant temperature and humidity chamber
The gas barrier property was evaluated from the degree of discoloration of the miso after standing for 0 days. The evaluation result is shown by the following display. ◎: extremely good (no discoloration) ○: good (no discoloration) △: slightly poor (slightly discolored) ×: bad (very discolored)

(2-2) Water resistance 1 ml of water was dropped on the surface of the container and rubbed with a finger to evaluate the water resistance from the degree of elution of the surface. The evaluation result is shown by the following display. ◎: extremely good (no elution at all) ○: good (almost no elution) △: slightly poor (slightly eluted) ×: poor (very eluted)

(2-3) Recoverability The multilayer container was pulverized and immersed in hot water at 95 ° C. for 2 hours to evaluate the degree of separation between the thermoplastic resin layer and the barrier layer. The evaluation result is shown by the following display. ：: Very good (barrier layer is completely eluted and very easy to separate) ○: Good (barrier layer is slightly eluted but easy to separate) △: Slightly poor (barrier layer is hardly eluted and ×: poor (barrier layer is not eluted at all and cannot be separated)

Example 1 An aqueous solution containing 15% by weight of ethylene-modified PVA having a viscosity-average degree of polymerization of 1,000, a degree of ethylene modification of 7 mol%, and a degree of saponification of 98.0 mol% has a T-die having a width of 600 mm at its tip.
It was extruded from a mmφ single screw extruder (manufactured by Plastics Engineering Laboratory) and dried to produce a cast film having a thickness of 50 μm. In addition, polyethylene terephthalate (hereinafter P
(Abbreviated as ET) in the same manner using an extruder having a T die.
The film was melt-extruded at 80 ° C. to produce a film having a thickness of 200 μm. Takelac A-385 (base) / takenate A as dry lamination adhesive on PET film
-10 (curing agent) was applied with a solid content of 3 g / m ^{2 using a} dry laminator using ethyl acetate as a diluent, and the ethylene-modified PVA film prepared earlier was subjected to PET / adhesive /
Dry lamination was performed so as to have a configuration of ethylene-modified PVA / adhesive / PET to obtain a sheet of three types and five layers having a thickness of 470 μm. The resulting three-layer, five-layer sheet was heated to 130 ° C., and then subjected to pressure forming to obtain a cup-shaped container having a size of 12 cm × 12 cm × 7 cm. The stretch ratio, gas barrier properties, water resistance, and recoverability of the container were measured. Table 1 shows the results.

Examples 2 to 5 A cup-shaped container was obtained in the same manner as in Example 1 except that the modified PVA had different degrees of ethylene modification and saponification. Table 1 shows the results
Shown in

Examples 6 and 7 Cup-shaped containers were obtained in the same manner as in Example 1 except that the stretching ratio in the pressure forming was different. Table 1 shows the results.

Example 8 Instead of a three-layer, five-layer sheet, a three-layer, 260 μm-thick three-layer sheet obtained by dry lamination to have a structure of PET / adhesive / ethylene-modified PVA was used. Example 1 except that the layer was formed so as to be on the outside
To obtain a cup-shaped container. Table 1 shows the results.

Example 9 An adhesive layer was not provided in place of the three-layer five-layer sheet.
A cup-shaped container was obtained in the same manner as in Example 1 except that dry lamination was performed so as to have a structure of PET / ethylene-modified PVA / PET, and a 450 μm-thick two-layer three-layer sheet was used. Table 1 shows the results.

Comparative Example 1 A cup-shaped container was obtained in the same manner as in Example 1 except that unmodified PVA was used instead of ethylene-modified PVA. Table 1 shows the results
Shown in

Comparative Example 2 A cup-shaped container was obtained in the same manner as in Example 1, except that the degree of ethylene modification was 0.5 mol%. Table 1 shows the results.

Comparative Example 3 A cup-shaped container was obtained in the same manner as in Example 1 except that the degree of ethylene modification was 28 mol%. Table 1 shows the results.

[0030]

[Table 1]

[0031]

The multilayer container obtained by the present invention has excellent gas barrier properties, and can be widely used for food (drinks, seasonings, alcohols, etc.) and pharmaceutical containers.
Also, after use, the thermoplastic resin layer and the barrier layer can be separated, recovered and reused.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4F100 AK01B AK01C AK04A AK21A AK42 AL06A BA02 BA03 BA06 BA10B BA10C BA13 CB01 DA01 EC182 EH012 EJ372 GB16 GB23 GB66 JB09A JB16B JB16C JD02 JL16 YY04 A10AA AA AA AA AA AAC A AH55 MA02 MB01 MB22 MG01 MG04 MG07 MG12 MG22

Claims (3)

[Claims] A multilayer sheet obtained by dry laminating a water-soluble ethylene-modified polyvinyl alcohol-based resin layer and a thermoplastic resin layer having a degree of ethylene modification of 1 to 19 mol% and thermoforming. Container manufacturing method. 2. The multilayer container according to claim 1, wherein the multilayer sheet is a multilayer sheet obtained by dry laminating an ethylene-modified polyvinyl alcohol-based resin layer as an intermediate layer and thermoplastic resin layers on both sides of the intermediate layer. Production method. 3. The method for producing a multilayer container according to claim 1, wherein the multilayer sheet is stretched 1.2 times or more before or during thermoforming.