JPH11348200A - Manufacturing method of multilayer container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a container having a gas barrier property and capable of separating a thermoplastic resin layer and a barrier layer after use, collecting and reusing the same. SOLUTION: 100 parts by weight of water-soluble ethylene-modified polyvinyl alcohol having a degree of ethylene modification of 1 to 20 mol% and a crosslinking agent of the ethylene-modified PVA of 0.01 to 10%
A method for producing a multilayer container, comprising forming a multilayer sheet obtained by laminating a layer composed of 0 parts by weight and a layer composed of a thermoplastic resin by coextrusion lamination, hot melt lamination, or dry lamination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a container obtained by molding a multilayer sheet made of a thermoplastic resin such as a polyester resin, a polypropylene resin, a polystyrene resin, and a polyamide resin. More specifically, 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, there is a cup manufactured by vacuum forming, pressure forming, or press forming a sheet of a thermoplastic resin such as a polypropylene resin, a polyester resin, and a polystyrene resin.
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 a remedy, a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) having excellent gas barrier properties is formed on the thermoplastic resin layer.
Attempts to stack layers have been made. 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 An object of the present invention is 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. .

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to provide a container having gas barrier properties and which can be recovered and reused.
And water-soluble ethylene-modified polyvinyl alcohol (hereinafter sometimes abbreviated as ethylene-modified PVA) 100
Parts by weight and a crosslinking agent for the ethylene-modified PVA from 0.01 to
Completed the present invention by finding a method for producing a multilayer container characterized by forming a multilayer sheet formed by laminating a layer composed of 100 parts by weight and a layer composed of a thermoplastic resin by coextrusion lamination, hot melt lamination, or dry lamination. I came to.

[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 can be thermally melted, and various thermoplastic resins can be used. Polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE) ), Polystyrene (PS), polyamide (PA)
Etc. are preferably used.

[0008] The ethylene-modified PVA 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, vinyl ester means vinyl acetate, vinyl propionate,
Examples thereof include vinyl formate, vinyl versatate, and vinyl pivalate, and vinyl acetate, which is industrially produced and cost-effective, is usually used. If it is water-soluble,
Α-olefins other than ethylene, ω-hydroxy-α-
Modified with olefin, unsaturated carboxylate, long-chain vinyl ether, unsaturated compound containing polyoxyalkylene group, saturated branched fatty acid vinyl, unsaturated sulfonate, unsaturated compound containing silanol group, unsaturated compound containing amino group, etc. You may. The degree of modification of ethylene is 1 to 20 mol%
Is used, and preferably 5 to 20 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, when the degree of ethylene modification exceeds 20 mol%, the water solubility is remarkably reduced, and it becomes difficult to separate, collect and reuse the thermoplastic resin layer and the barrier layer of the container after use, and the gas barrier property is also reduced.

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 used in the present invention is 200 to 5000 as a viscosity average degree of polymerization (hereinafter simply referred to as degree of polymerization) measured according to JIS K6726.
Is more preferable, and it is more preferable that it is 300-3000. If the degree of polymerization is less than 200, the ethylene-modified PVA layer may be cracked 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 becomes extremely high, and molding becomes difficult.

[0011] The ethylene-modified PVA used in the present invention must be water-soluble. Here, the term "water-soluble" means that when water is added to ethylene-modified PVA to a concentration of 1 to 80% by weight, a solid solution is not observed at a temperature of 5 to 95 ° C and a uniform solution is obtained. Point to.

[0012] The ethylene-modified PVA layer of the multilayer sheet used in the present invention is based on 100 parts by weight of ethylene-modified PVA.
It is necessary to add 0.01 to 100 parts by weight, preferably 0.05 to 80 parts by weight, particularly preferably 0.1 to 50 parts by weight of the ethylene-modified PVA crosslinking agent. If the amount of the crosslinking agent is less than 0.01 part by weight, ethylene-modified PV
A is not sufficiently crosslinked, and the water resistance of the container and the barrier property under high humidity are reduced. On the other hand, when the compounding amount of the crosslinking agent exceeds 100 parts by weight, the strength of the obtained ethylene-modified PVA layer,
Not only may the impact resistance decrease, causing problems such as oozing out of the crosslinking agent, but also it may be difficult to mold the multilayer sheet into a container. Here, the crosslinking agent is an additive capable of crosslinking the above-mentioned ethylene-modified PVA at room temperature or by heating, and specifically, phenol resin, melamine resin, urea resin, polyamide polyurea, dimethylol urea, dimethylol melamine , Polyvalent epoxy compounds, dialdehyde compounds, polyvalent isocyanate compounds,
Aziridine compound, polyamidoamine epichlorohydrin compound, activated vinyl compound, dicarbonate compound, colloidal silica, bentonite, zirconium salt, polyvalent metal salt, boric acid, phosphoric acid, polyacrylic acid, dicarboxylic acid, adipic anhydride, succinic anhydride Products, tetraisopropyl titanate, diisopropoxybis (acetylacetone) titanate, and the like.
In addition, a coupling agent such as 3-glycidopropylmethoxysilane and a radical generator such as peroxide can also be used. Furthermore, the case where sodium dichromate or sodium benzoate is added and crosslinking is performed by UV, electron beam, or radiation is also included.

Among them, zirconium salts, colloidal silica, dialdehyde compounds, polyepoxy compounds, aziridine compounds, polyamidoamine epichlorohydrin compounds and dicarbonate compounds are preferred crosslinking agents. In particular, a system in which colloidal silica is added to ethylene-modified PVA in which silanol groups are further modified by 0.1 to 1 mol%, and ethylene-modified PV in which amino groups are further modified by 0.1 to 5 mol.
A combination of a system in which dialdehyde or a dicarbonate compound is added to A and a system in which polyamidoamine epichlorohydrin is added to ethylene-modified PVA in which unsaturated carboxylic acid is further modified by 0.1 to 5 mol% are preferable.

The ethylene-modified PVA used in the present invention includes:
Various additives other than the cross-linking agent can be appropriately compounded as needed as long as the object of the present invention is not impaired. Examples of additives include plasticizers, antioxidants, processing stabilizers, ultraviolet absorbers, coloring agents, fragrances, lubricants, release agents, antistatic agents,
Known additives such as a reinforcing agent, a bulking agent, and a filler can be used.

The multilayer sheet used in the present invention is composed of 100 parts by weight of the above-mentioned ethylene-modified PVA,
It is a thermoplastic resin multilayer sheet having at least one layer comprising 0.01 to 100 parts by weight of the crosslinking agent of A. There is no particular limitation on the method for producing the multilayer sheet.
A and thermoplastic resin are co-extruded from a T-die by hot melting, and ethylene-modified P is coated on a thermoplastic resin sheet.
A method in which VA is extruded from a T-die by hot melting and then laminated under pressure, and an ethylene-modified PVA sheet is laminated separately after preparing a thermoplastic resin sheet separately and then laminated using heat sealing or an adhesive as necessary. And the like. In particular, a method of separately producing sheets of ethylene-modified PVA and a thermoplastic resin and then laminating (dry lamination method) is preferable. In the case of dry lamination,
This is a preferable production method because a resin having a relatively high melting point and an ethylene-modified PVA can be laminated, and only a specific layer can be stretched. In this case, the ethylene-modified PVA sheet is preferably produced by solvent casting. This molding method is a preferable sheet molding method even in a system containing a cross-linking agent, since molding is easy because of relatively low viscosity, and there is less thermal decomposition and coloring as compared with hot melt molding. Water is suitable as the solvent in this case. In either case, it is desirable to provide an adhesive layer between the thermoplastic resin layer and the ethylene-modified PVA layer so that the adhesiveness 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 layer, and a known adhesive can be used. Further, the ethylene-modified PVA layer is an intermediate layer of the multilayer sheet, that is, the thermoplastic resin layer /
It is preferred that the outermost layer of the multilayer sheet be a thermoplastic resin layer, such as an ethylene-modified PVA layer / thermoplastic resin layer.

The thickness of the multilayer sheet is not particularly limited, but is usually 10 to 5000 μm, and 50 to 300 μm.
Those having a thickness of 0 μm are preferred, and those having a thickness of 100 to 2000 μm are particularly preferred. The thickness of the ethylene-modified PVA layer can be appropriately set according to the desired gas barrier properties.
000 μm, and preferably 3 to 500 μm. The thickness of the adhesive layer is usually 1 to 500 μm,
It is preferably from 300 to 300 μm.

The multilayer container of the present invention is obtained by further molding the above-mentioned multilayer sheet. The molding method is not particularly limited, but is usually molded by vacuum molding, pressure molding, press molding 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, stretching refers to stretching at a temperature not lower than the glass transition temperature of any one of the thermoplastic resins constituting the multilayer sheet and not higher than the melting point, and may be stretched in one direction or may be stretched in two or more directions. You may. 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. The stretching improves the gas barrier properties, water resistance, and transparency of the obtained container.

The multilayer container of the present invention obtained by such a method has excellent gas barrier properties and water resistance, and can be widely used for containers of foodstuffs, beverages, seasonings and pharmaceuticals. Further, the ethylene-modified PVA as the barrier layer can be separated from the thermoplastic resin by a method such as heating in an alkaline aqueous solution, and the container can be collected and reused.

[0019]

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 A container was filled with miso until it was full, and the container was sufficiently 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 The container was immersed in hot water at 80 ° C. for 15 minutes, and the water resistance was evaluated from the degree of elution of the barrier layer. 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 container was immersed in a 10 wt% aqueous solution of sodium hydroxide at 90 ° C.
After immersion for a time, the degree of separation between the thermoplastic resin and the barrier layer was evaluated. 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 A copolymer composed of 7 mol% of ethylene units and 93 mol% of vinyl acetate was saponified to obtain an ethylene-modified PVA having a viscosity average degree of polymerization of 1,000 and a saponification degree of 98.0 mol%. 100 parts of the ethylene-modified PVA, colloidal silica 10
Parts, an ethylene-modified PVA aqueous solution consisting of 500 parts of water,
The extruded product was extruded from a 50 mmφ single screw extruder (manufactured by Plastics Engineering Laboratory) having a 600 mm wide T die at the tip and dried to produce an ethylene-modified PVA film having a thickness of 50 μm. The obtained film was transparent and had a good appearance. In addition, polyethylene terephthalate (hereinafter abbreviated as PET) was extruded using an extruder having a similar T die.
The film was melt-extruded at 80 ° C. to produce a film having a thickness of 200 μm. Takelac A-385 (base agent) / Takenate A-10 (hardener) was applied as a dry lamination adhesive to the obtained PET film at a solid content of 3 g / m ² with a dry laminator using ethyl acetate as a diluent. The ethylene-modified PVA film prepared in
Dry laminating so as to have the composition of adhesive / ethylene-modified PVA / adhesive / PET, 3 types of 470 μm thickness 5
A layer of sheets was obtained. The obtained three-layer, five-layer sheet was treated with 130
After heating to ℃, vacuum forming, 12cm × 12cm × height 7
cm cup-shaped container was obtained. The stretch ratio, gas barrier property, water resistance, and recoverability of the obtained container side were measured. The results are shown in Tables 1 and 2.

Example 2 A cup-shaped container was obtained in the same manner as in Example 1 except that ethylene-modified PVA having a degree of ethylene modification of 13 mol% and a degree of saponification of 97.9 mol% was used. The results are shown in Tables 1 and 2.

Example 3 A cup-shaped container was obtained in the same manner as in Example 1, except that ethylene-modified PVA having a degree of ethylene modification of 3 mol% was used. The results are shown in Tables 1 and 2.

Example 4 A cup-shaped container was obtained in the same manner as in Example 1 except that ethylene-modified PVA having a degree of saponification of 99.6 mol% was used. The results are shown in Tables 1 and 2.

Example 5 A cup-shaped container was obtained in the same manner as in Example 1 except that ethylene-modified PVA having a saponification degree of 93.4 mol% was used. The results are shown in Tables 1 and 2.

Example 6 A cup-shaped container was obtained in the same manner as in Example 1 except that an ethylene-modified PVA having a saponification degree of 88.7 mol% was used. The results are shown in Tables 1 and 2.

Example 7 An ethylene-modified PVA film was prepared using ethylene-modified PVA1
A cup-shaped container was obtained in the same manner as in Example 1 except that the container was prepared using an aqueous solution comprising 00 parts, 0.03 part of colloidal silica and 500 parts of water. The results are shown in Tables 1 and 2.

Example 8 An ethylene-modified PVA film was prepared using ethylene-modified PVA1
A cup-shaped container was obtained in the same manner as in Example 1, except that the container was prepared using an aqueous solution comprising 00 parts, 1 part of colloidal silica, and 500 parts of water. The results are shown in Tables 1 and 2.

Example 9 An ethylene-modified PVA film was prepared using ethylene-modified PVA1
A cup-shaped container was obtained in the same manner as in Example 1 except that the container was prepared using an aqueous solution comprising 00 parts, 30 parts of colloidal silica, and 500 parts of water. The results are shown in Tables 1 and 2.

Example 10 An ethylene-modified PVA film was prepared by using ethylene-modified PVA1
A cup-shaped container was obtained in the same manner as in Example 1 except that the container was prepared using an aqueous solution consisting of 00 parts, colloidal silica 75 parts and water 500 parts. The results are shown in Tables 1 and 2.

EXAMPLE 11 0.2 mol% of vinylmethoxysilane and 7 mol% of ethylene
And a copolymer comprising 92.8 mol% of vinyl acetate were saponified to obtain a silanol group and an ethylene-modified PVA having a viscosity average degree of polymerization of 1,000 and a saponification degree of 97.9 mol%. A cup-shaped container was obtained in the same manner as in Example 1 except that the silanol group and the ethylene-modified PVA were used instead of the ethylene-modified PVA of Example 1. The results are shown in Tables 1 and 2.

Example 12 A copolymer comprising 3 mol% of maleic anhydride units, 7 mol% of ethylene and 90 mol% of vinyl acetate was saponified to obtain a carboxyl having a viscosity average degree of polymerization of 1,000 and a saponification degree of 97.7 mol%. And ethylene-modified PVA were obtained. Example 1 was repeated except that the carboxyl group and the ethylene-modified PVA were used in place of the ethylene-modified PVA of Example 1, and a polyamidoamine epichlorohydrin resin (manufactured by Caimen S-25 Dick Hercules) was used in place of the colloidal silica. Similarly, a cup-shaped container was obtained. The results are shown in Tables 1 and 2.

Example 13 3 mol% of N-vinyl formaldehyde unit and ethylene 7
A copolymer consisting of 90 mol% of vinyl acetate and 90 mol% of vinyl acetate is saponified to give a viscosity average degree of polymerization of 1,000 and a degree of saponification of 98.1
Thus, mol% of primary amino groups and ethylene-modified PVA were obtained.
Example 1 Example 1 was repeated except that the ethylene-modified PVA of Example 1 was replaced with the primary amino group and ethylene-modified PVA, and that the colloidal silica was replaced with a polyamidoamine epichlorohydrin resin (Saimen S-25 manufactured by Dick Hercules). A cup-shaped container was obtained in the same manner as in Example 1. The results are shown in Tables 1 and 2.

Example 14 A cup-shaped container was obtained in the same manner as in Example 1 except that the stretching ratio of the side surface during vacuum forming was 1.1 times. The results are shown in Tables 1 and 2.

Example 15 In Example 1, the multi-layer sheet was provided with no adhesive layer,
A cup-shaped container was obtained in the same manner as in Example 1 except that a 450 μm-thick two-layer, three-layer sheet obtained by dry lamination so as to have a configuration of ET / ethylene-modified PVA / PET was used. The obtained container partially contains a PET layer and ethylene-modified P.
Peeling from the VA layer was observed. The results are shown in Tables 1 and 2.

Example 16 In Example 1, a three-layer three-layer sheet having a thickness of 260 μm obtained by dry laminating a multilayer sheet so as to have a structure of PET / adhesive / ethylene-modified PVA was used. A cup-shaped container was obtained in the same manner as in Example 1, except that the container was vacuum-formed so as to be outside the container. The results are shown in Tables 1 and 2.

Example 17 After blending 100 parts of the ethylene-modified PVA used in Example 1 with 10 parts of colloidal silica, the mixture was heated to 230 ° C. using a 50 mmφ single screw extruder (manufactured by Plastics Engineering Laboratory) having a 600 mm wide T die at the tip. To produce an ethylene-modified PVA film having a thickness of 50 μm. The film was fairly colored. A cup-shaped container was obtained in the same manner as in Example 1, except that the hot-melt extruded film was used as the ethylene-modified PVA film. The results are shown in Tables 1 and 2.

Example 18 A blend of 100 parts of ethylene-modified PVA and 10 parts of colloidal silica, PET, and an adhesive (admer) used in Example 1 were charged into an extruder, and the three resins were fed into a feed block. They were co-extruded from a 600 mm wide T-die at 260 ° C. to obtain three types and five layers of sheets having a structure of PET 200 μm / adhesive layer 10 μm / ethylene-modified PVA 50 μm / adhesive layer 10 μm / PET 200 μm. The sheet was quite colored. 3 kinds 5 obtained
After heating the layer sheet to 130 ° C., vacuum forming and 12 cm
A cup-shaped container having a size of 12 cm and a height of 7 cm was obtained. At this time, the stretching magnification of the side surface was 2.2 times. The results are shown in Tables 1 and 2.

Comparative Example 1 Saponification degree 98.5 mol% instead of ethylene-modified PVA
Was obtained in the same manner as in Example 1 except that the unmodified PVA was used. The results are shown in Tables 1 and 2.

Comparative Example 2 A cup-shaped container was obtained in the same manner as in Example 1 except that ethylene-modified PVA having an ethylene modification degree of 0.5 mol% and a saponification degree of 98.2 mol% was used. The results are shown in Tables 1 and 2.

Comparative Example 3 Ethylene modification degree: 28 mol%, saponification degree: 97.7 mol%
A cup-shaped container was obtained in the same manner as in Example 1 except that ethylene-modified PVA was used. The results are shown in Tables 1 and 2.

Comparative Example 4 A cup-shaped container was obtained in the same manner as in Example 1 except that colloidal silica was not blended. The results are shown in Tables 1 and 2.

Comparative Example 5 The amount of colloidal silica was ethylene-modified PVA100.
A cup-shaped container was obtained in the same manner as in Example 1 except that the amount was 0.005 parts by weight. The results are shown in Tables 1 and 2.

Comparative Example 6 A cup-shaped container was obtained in the same manner as in Example 1, except that the amount of colloidal silica was changed to 120 parts per 100 parts of ethylene-modified. The results are shown in Tables 1 and 2.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

Industrial Applicability The multilayer container of the present invention has excellent gas barrier properties and is suitable for food products (drinks, seasonings, alcohols, etc.).
It can be widely used for containers of medicines and medicines. Also, after use, the thermoplastic resin layer and the barrier layer can be separated, recovered and reused.

Claims (3)

[Claims] 1. An ethylene-modified polyvinyl alcohol having a degree of ethylene modification of 1 to 20 mol% and 100 parts by weight of a water-soluble ethylene-modified polyvinyl alcohol, and a crosslinking agent for the ethylene-modified PVA of 0.01 to 10%.
A method for producing a multilayer container, comprising forming a multilayer sheet obtained by laminating a layer composed of 0 parts by weight and a layer composed of a thermoplastic resin by coextrusion lamination, hot melt lamination, or dry lamination. 2. The method for producing a multilayer container according to claim 1, wherein the lamination method is dry lamination. 3. The method for producing a multilayer container according to claim 1, wherein the multilayer sheet is stretched 1.2 times or more.