JP3016443B2 - Method for producing multilayer sheet for draw-formed container - Google Patents

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 multilayer sheet for a draw-formed container, and more particularly, to a method for producing the above-mentioned multilayer sheet by recycling a scrap containing a polyester resin and a polyvinylidene chloride resin. About.

[0002]

2. Description of the Related Art Vinylidene chloride resin has an oxygen barrier property,
It is known that they have excellent water vapor barrier properties and that their performance is less dependent on temperature, and are widely used as packaging materials as gas barrier materials.

For this reason, conventionally, food packaging, especially cups,
Tray, as a container used for hermetic sterilization packaging of food in the form of pouches, etc., a vinylidene chloride resin is combined with a propylene resin having excellent mechanical properties and heat resistance to form a multilayer sheet, which is formed by drawing. Containers are used.

However, in the case of the above container,
Because propylene resin has the property of adsorbing or permeating the flavor components of the contents, to improve these disadvantages,
For the purpose of preserving the flavor of food and other contents and preventing the transfer of container odor to the contents, for example, a method of using polyester for the innermost layer of a container has been proposed as disclosed in Japanese Patent Application No. 2-42197. ing.

[0005]

On the other hand, when a sheet-formed container is usually manufactured, 20 to 50% of the sheet is necessarily scrapped, and its effective use in the art is reduced in cost, saving resources and preventing pollution. Is required from the perspective of Therefore, even in the sheet-formed container using the vinylidene chloride-based resin as described above, it is possible to reuse the scrap present in the form of a mixture of the above-mentioned vinylidene chloride-based resin and other resins used as necessary such as a propylene resin. In the case of such recycling, it is necessary to expose the vinylidene chloride-based resin to a high temperature. At this time, there is a problem that coloring, foaming, deterioration of physical properties, etc. are caused by thermal decomposition as a dehydrochlorination reaction. Had occurred.

Accordingly, it has been proposed to limit the resins which can be used together with the vinylidene chloride resin to those which can be processed at a relatively low temperature, as disclosed, for example, in JP-A-1-48551.

However, when the polyester is used as the innermost layer of the container from the viewpoint of maintaining the flavor of the contents as described above, since the melting temperature of the polyester is relatively high, the scrap containing the vinylidene chloride resin and the polyester is processed at the processing temperature of the polyester. And it was difficult to obtain a multilayer sheet in which the above-mentioned scrap-containing layer, the vinylidene chloride-based resin layer and the polyester layer were laminated by a co-extrusion method.

Accordingly, it is an object of the present invention to recycle scrap containing vinylidene chloride resin and polyester,
Eliminates drawbacks such as coloring, foaming, and deterioration of physical properties of vinylidene chloride resin that occur when producing multilayer sheets for draw-formed containers, and is excellent in gas barrier properties, flavor retention, and prevention of transfer of container odor. An object of the present invention is to provide a sheet manufacturing method.

[0009]

Means for Solving the Problems As a result of intensive studies by the present inventors, the object of the present invention is to provide at least a layer containing a mixed resin layer obtained by melt-extruding a mixture containing at least polyester and polyvinylidene chloride. A method for producing a multilayer sheet, comprising laminating a vinylidene-based resin layer and a polyester resin layer with the polyester resin layer as an outermost layer, wherein the mixed resin layer contains a condensed phosphate. It has been found that this can be achieved by a sheet manufacturing method.

Hereinafter, the present invention will be described in more detail.

The mixed resin layer constituting the multilayer sheet of the present invention contains at least polyester and polyvinylidene chloride, and preferably contains polypropylene resin. The processing temperature of such a mixed resin layer is 230 ° C. or higher, preferably 230 to
250 ° C is required. That is, at a processing temperature of less than 230 ° C., the melt dispersion is insufficient, and the obtained sheet may be cracked or have a reduced strength.

[0012] The mixture used in the mixed resin layer is preferably a trimming which is mostly generated during sheet production or sheet drawing, that is, scrap of the sheet. In the present invention, the resin forming the mixed resin layer may be composed of only scrap, or an unprocessed propylene resin or the like may be newly added. These scraps are pulverized, a propylene resin or the like is added as necessary, and a condensed phosphate is further added. Then, the mixture is heated and melt-extruded to form a mixed resin layer. Such a mixed resin layer may be formed by co-extrusion as necessary, as a shaped layer having a propylene resin layer on one or both surfaces.

As the above-mentioned condensed phosphate, pyrophosphate, tripolyphosphate, tetrapolyphosphate, trimetaphosphate, tetrametaphosphate, hexametaphosphate and the like are used. It is preferably used. In particular, sodium pyrophosphate is optimally used.

These condensed phosphates are preferably used in an amount of 10 to 200 parts by weight based on 100 parts by weight of the vinylidene chloride resin in the mixed resin layer.

It is considered that the above-mentioned condensed phosphates suppress foaming by trapping hydrogen chloride released from polyvinylidene chloride by heating and by preventing a chain reaction in the dehydrochlorination reaction.

Hereinafter, the present invention will be described more specifically with reference to the drawings.

FIG. 1 is a sectional view showing a preferred example of a multilayer sheet obtained by the production method of the present invention. According to FIG. 1, a multilayer sheet according to the present invention is a propylene resin containing an inorganic or organic white or colored pigment on both surfaces of a mixed resin layer 1b containing polyester, polyvinylidene chloride resin, propylene resin and condensed phosphate. The shaping layer 1 provided with the resin layers 1a and 1c, and the vinylidene chloride-based resin layer 2 and the polyester layer 3 are laminated on the propylene resin layer 1c side of the shaping layer. That is, both surfaces of the mixed resin layer 1b are sandwiched by the propylene resin layers 1a and 1c and laminated by a co-extrusion method, and a single-layer or multi-layer vinylidene chloride previously formed at an appropriate processing temperature is added thereto. The films or sheets of the system resin layer 2 and the polyester layer 3 are laminated by a dry lamination method, an extrusion lamination method, an extrusion simultaneous lamination method, or the like.
According to such a method, the multilayer sheet of the present invention can be obtained without deteriorating the thermal decomposition performance of the vinylidene chloride-based resin layer serving as the gas barrier layer.

The vinylidene chloride-based resin layer is for imparting oxygen barrier properties to the resulting container to prevent the contents from being oxidized and deteriorated. The vinylidene chloride-based resin layer is composed of vinylidene chloride, vinyl chloride, acrylic ester and methacrylic ester. It is preferable to use a film made in advance of a copolymer comprising at least one selected monomer.

In order to effectively obtain the oxygen barrier effect, it is desirable to use a stretched film, and the stretching ratio is preferably 1.5 to 4 times in length and 1.5 to 4 times in width. The resin layer preferably has a thickness of 9 μm or more in order to maintain oxygen barrier properties, and when the thickness is 200 μm or more, there is no difference in effect depending on the thickness.

As the vinylidene chloride resin used for the vinylidene chloride resin layer, for example, Saran UB film manufactured by Asahi Kasei Corporation can be used.

The polyester layer forms the innermost layer of the container and prevents the permeation and adsorption of the fragrance components of the contents such as foods. As the polyester layer, a layer prepared in advance as a film is preferably used, and its thickness is preferably 9 to 100 μm. 100 when thickness is less than 9μm
In any case exceeding μm, it is often difficult to form the polyester layer stably without damaging the polyester layer.

As such a polyester, a copolymer of a polybasic acid component and a polyhydric alcohol component can be used. The main component of the polybasic acid component is preferably terephthalic acid. Examples of polybasic acids that can be used as accessory components together with terephthalic acid include isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid,
Aromatic carboxylic acids such as diphenylsulfone dicarboxylic acid and diphenyl ether dicarboxylic acid; alicyclic carboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid; aliphatic carboxylic acids such as adipic acid, sebacic acid and azelaic acid; Oxy acids such as -β-hydroxyentoxybenzoic acid, p-oxybenzoic acid and α-oxycapnic acid; trimellitic acid, trimesic acid, 3,3 ′,
Examples thereof include aromatic polybasic acids such as 5,5'-tetracarboxyphenyl; aliphatic polybasic acids such as butanetetracarboxylic acid; and oxycarboxylic acids such as tartaric acid and malic acid.

The main component of the polyhydric alcohol component of the polyester is preferably ethylene glycol. Polyhydric alcohols that can be used as an accessory component together with ethylene glycol include propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentyl Glycol, diethylene glycol, 1,1-cyclohexane dimethylol, 1,4-cyclohexane dimethylol, 2,2-bis (4-β-hydroxyethoxyphenyl) propane, bis (4-β-hydroxyphenyl) sulfonecyclohexanediol, , 4-bis (β-hydroxyethoxy) benzene, 1,3-bis (hydroxyethoxy) benzene, fluorochrysin,
1,2,4,5-tetrahydroxybenzene, glycerin, trimethylolmethane, trimethylolpropane,
Pentaerythol and the like can be exemplified.

The propylene resin preferably used in the mixed resin layer 1b and optionally used in the propylene resin layers 1a and 1c in the present invention includes polypropylene and a propylene-ethylene copolymer.

The white or colored pigment which can be contained in the propylene resin layer is used for the purpose of coloring the sheet molding container and concealing the colored mixture layer from the external appearance. Hidden inorganic or organic pigments used in the above can be used, and titanium white (titanium dioxide) is preferably used as the white pigment.

In the present invention, the shaping layer 1 including the mixed resin layer desirably has a thickness of 300 to 3000 μm. 30
If it is less than 0 μm, cracking or uneven thickness may occur during drawing, or deformation of the container may occur during heat sterilization. In addition, the strength of the container may be insufficient, and it may be difficult to maintain its shape. On the other hand, when it exceeds 3000 μm, drawing often becomes difficult.

The shaping layer is composed of a propylene resin layer / a mixed resin layer /
In the case of a propylene resin layer, the thickness ratio of each resin layer is arbitrary, but the thickness ratio of the mixed resin layer to the propylene resin layer on one side is 0.4 due to the scrap utilization efficiency and the hiding effect by the propylene resin layer. -4 is desirable, and the thickness ratio of the mixed resin layer to the total thickness of the propylene resin layers on both sides is desirably 0.2-2.

The multilayer sheet of the present invention can be drawn and used as a container. The drawing is a method in which a multilayer sheet is pressed against a mold while being softened by heating and formed. The heating of the multilayer sheet can be carried out by a known method such as an infrared heater.

The method of drawing is a method of pressing against a shape, a method of pressing against a mold by vacuum suction from the mold side (vacuum forming method), and a method of pressing against a mold by applying compressed air from the opposite side of the mold (compression forming method). , A method of pressing a male mold (plug) from the opposite side of the mold and pressing it against the mold (plug molding method), a method of using these together, etc.
It can be carried out by any of these methods. Further, in the present invention, it is necessary to use a polyester layer on the inner surface of the container in order to prevent permeation and adsorption of the fragrance component of the contents.

[0030]

EXAMPLES Example 1 A polyester film (F-8 manufactured by Toray) was prepared in advance.
6, thickness 16 μm), a vinylidene chloride resin film (Saran UB manufactured by Asahi Kasei Corporation, thickness 25 μm), and an unstretched polypropylene film (Toray Synthetic Trefan 3931, thickness 30 μm) were sequentially dry-laminated to obtain a laminated film (A).

Next, a blended resin (PP) obtained by mixing titanium white with 3% by weight of propylene resin is melt-extruded from a T-die and the unstretched polypropylene film surface of the laminated film (A) is thermally laminated at the same time. I got a sheet.

Next, this sheet was heated to about 170 ° C., and a round container having a diameter of 90 mm and a height of 55 mm was formed by a pneumatic forming method with plug assist. At this time, the effective utilization rate of the sheet was about 55% (the scrap generation rate was about 45%).

The generated scrap was pulverized by a pulverizer, and a propylene resin masterbatch containing 50% by weight of anhydrous sodium pyrophosphate was added to the scrap by 10%.
% By weight. Using this mixture as a mixed resin layer, three layers of PP / mixed resin layer / PP (thickness ratio 1: 2: 1) were co-extruded,
The laminated film (A) is simultaneously heat-laminated to a total thickness of 1.5 m.
m multilayer sheet was formed. The co-extrusion was performed so that the extrusion temperature of the mixed resin layer was 235 ° C. The extrusion processing temperature referred to here is a temperature generally referred to as a resin temperature, which is measured by inserting a resin thermometer into a resin flow path at the extruder tip.

A cup was formed from the obtained multilayer sheet in the same manner as described above. When the above operation was repeated 10 times, no foaming or deterioration of the mixed resin layer (foaming of the vinylidene chloride-based resin in the mixed resin layer, kogation) was observed at all. In addition, there were no problems with regard to the mechanical performance (compression strength, drop impact strength), physical performance (color, gas barrier property, content taste) and hygiene of the cup obtained from each operation.

Comparative Example 1 In Example 1, the amount of the propylene resin masterbatch containing 50% by weight of anhydrous sodium pyrophosphate added to the mixed resin layer was changed from 10% by weight to 1% by weight, and a cup was formed in the same manner as in Example 1. Then, after performing the same operation,
During the co-extrusion of the mixed resin layer, hydrogen chloride gas foaming was observed from the mixed resin layer.

Comparative Example 2 A cup was molded in the same manner as in Example 1 except that the extrusion temperature of the mixed resin layer was changed to 220 ° C., and the same operation was performed. Unmelted polyester remained in the mixed resin layer of the cup, and the container appearance and mechanical performance were insufficient.

[0037]

As described above, according to the production method of the present invention, the coloring of the vinylidene chloride resin generated when the scrap containing the vinylidene chloride resin and the polyester is reused to produce the multilayer sheet for the draw-formed container is produced. It is possible to provide a multilayer sheet for a draw-formed container which eliminates defects such as foaming, deterioration of physical properties and the like, and is excellent in gas barrier properties, flavor retention and transfer of container odor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a multilayer sheet obtained by a production method of the present invention.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B29K 27:00 67:00 105: 26 B29L 9:00 (56) References JP-A-1-148551 (JP, A) JP Hei 3-75120 (JP, A) JP-A-1-269528 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 47/00-47 / 96 B29C 51/00-51/46

Claims (1)

(57) [Claims] 1. A multilayer sheet in which at least a vinylidene chloride-based resin layer and a polyester resin layer are laminated on a layer containing a mixed resin layer obtained by melt-extruding a mixture containing at least polyester and polyvinylidene chloride, with the polyester resin layer as the outermost layer. The method for producing a multilayer sheet for a draw-formed container, wherein the mixed resin layer contains a condensed phosphate.