JPH0316269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite container for retort foods such as dessert foods such as fruit jelly, coffee jelly, and water jelly, and canned foods.
The object of the present invention is to provide a container that has excellent durability, beautiful appearance, and rigidity, and is particularly useful for dessert foods that are enjoyed as a luxury item.

Conventionally, retort food containers have been made of thermoplastic resin having gas barrier properties, such as polyethylene terephthalate film, in order to impart heat-sealing properties to a sheet laminated with a low-melting point resin film, or further laminated with aluminum foil. A bag-like product made from a sheet is used. However, since these bag-like products lack rigidity, they can currently only be used to package retort pouch foods such as instant curry and soup. Furthermore, since it does not easily change shape, it is not suitable for packaging foods that require rigidity and firmness in the container, such as dessert foods that require retort sterilization.

For this reason, aluminum containers and tin containers are currently the mainstream packaging containers for the above-mentioned dessert foods.

However, aluminum containers are not only difficult to print on, but also have poor impact resistance and are easily dented.

On the other hand, tin containers have the disadvantage that only simple printing is possible and the material costs are high.

To obtain a cup-shaped container with elaborate multicolor printing on the outer surface, the outer surface of the pre-formed container is
A blank with multicolor printing such as offset printing may be attached with adhesive. However, retort containers are sterilized at 110 to 130°C in the retort pot after the contents are filled into the container and covered, and then cooled with water spray, so during this sterilization and cooling,
This conventional method is impractical for retort containers because the blank often swells or peels off from the container body.

The present inventors fixed a thermoplastic resin film such as polyvinyl chloride, polypropylene, polyethylene, etc. printed with letters and designs in a mold by electrostatic adhesion or vacuum pressure, which is the conventional practice, and then fixed the film made of the same material as these films. A method for producing a thermoplastic synthetic resin molded product on which a blank is pasted or painted by contacting a melted thermoplastic resin with a film under pressure or reduced pressure, and then cooling the melted material (Japanese Patent Publication No. 1986-
No. 5036, No. 38-26119, No. 40-12988, No. 46-
9959, Publication No. 48-12865, etc.), we focused on the fact that the adhesion between the blank and the container body is strong, and the material of the blank is made of a thermoplastic resin film with high water resistance. When this blank pasting technique was applied to retort containers, the following problems were discovered.

In conventional blank pasting methods (including labels), the blank material and the molding resin for hollow, injection, etc. are the same resin, so the blank melts during molding and the edges of the printed letters and images become blurred. It often becomes unclear. Conventional blank film printing happens to be gravure printing or flexo printing, and these printing methods can print only large and simple designs and letters, so overall there is only a slight blurring of the print due to melting of the blank during molding. The reality was that it was overlooked as there was no practical problem.

Therefore, it is desired to develop a plastic blank that can be printed with delicate characters and patterns in multiple colors and that can be attached during molding.

The resin forming the container body is a thermoplastic resin with excellent gas barrier properties, such as polycarbonate and polyethylene terephthalate.
If these are used alone, the cost of the container will be high.

One possible solution to the above drawbacks is to use, for example, a thermoplastic resin film that can be used for offset printing as the blank material.
Offset printing is useful as a printing technique because it allows delicate characters and patterns to be printed in multiple colors, but it has the disadvantage that it cannot be applied to conventional plastic films.

In recent years, synthetic papers with paper-like layers made of stretched polypropylene films or polyethylene films containing inorganic fillers have been proposed or commercially available as synthetic papers (Japanese Patent Publications No. 46-40794, No. 54-31030, British Patent No. 1090059) There are also synthetic papers that can be offset printed.

If this offset printable synthetic paper is fixed in a mold as a blank, and the same material resin as the blank is used, low-pressure molding such as blow molding or pressure molding is performed at a pressure of 1 to 8 kg/cm ² as in the past. , the blank shrinks during molding and wrinkles occur, resulting in only defective products. This is because the label is a stretched film, so the external stress stored during stretching becomes shrinkage stress, and when it comes into contact with molten resin during blow molding or other molding, the heat causes the blank to shrink.

The present inventors manufactured various blanks in order to prevent the occurrence of wrinkles when using this stretched film as a material for blanks, and as a result of studying the method of attaching the blanks, the inventors developed a method using polypropylene containing an inorganic filler. Using a blank made of a composite sheet containing at least a stretched film as a paper-like layer and a thermoplastic resin film having a melting point 15° C. or more lower than the melting point of the polypropylene as a back layer, and
It was discovered that wrinkles could be prevented by using a composite sheet with a thermoplastic resin film with a relatively low melting point as the back layer for forming the container body, and by bonding the blank to the container body using vacuum pressure. Ta.

The above problem can be solved by using a composite sheet of heat-resistant and rigid polypropylene and gas barrier resin as a molding sheet in order to reduce the amount of expensive gas barrier resin used.

That is, this invention uses a stretched polypropylene film containing 8 to 65% by weight of inorganic fine powder with offset printing on the surface as a paper-like layer,
A composite sheet with at least two layers, the back layer being a thermoplastic resin film with a thickness of 1 to 30 microns that has a melting point 15°C or more lower than that of the polypropylene that forms the surface opposite to the paper-like layer. A blank with a wall thickness of 30 to 300 microns is inserted so that the paper layer side of the blank is in contact with the mold, and then on top of the mold is placed at least (a) a polypropylene base film and (b) a polyamide film. , a resin film layer with low gas permeability selected from polyester, saponified ethylene/vinyl acetate copolymer, and polyvinylidene chloride, and (c) having a melting point 15°C or more lower than the melting point of the polypropylene, and supplying a molding composite sheet melt having a back layer made of a thermoplastic resin film that is compatible with the thermoplastic resin constituting the back layer of the blank so that the back layer side faces the mold; The object of the present invention is to provide a cup-shaped composite container for retort food in which blanks are integrally laminated on the outer surface, obtained by molding using vacuum and/or compressed air.

In carrying out this invention, the simplest structure of the multilayer blank material before offset multicolor printing contains 8 to 65% by weight of inorganic filler, preferably 20 to 55% by weight. The paper-like layer is a stretched polypropylene film with a wall thickness of 1 to 30 microns (μ), preferably 3 to 10 μ, and a density of 0.91 to 0.97 g/
cc polyethylene, preferably density 0.935-0.960
The thickness of the back layer is 30~300μ, preferably 150~
It is a composite sheet with a 250μ two-layer laminated structure.

Such a composite sheet is produced by melting and kneading polypropylene containing an inorganic filler and the polyethylene in separate presses, and then feeding them into the same die.
After laminating in a die, coextrude into a sheet, cool to 40-80℃, then reheat to 134-164℃, preferably 145-160℃, 3.5-10 times in the vertical and horizontal directions, respectively, simultaneously or sequentially. It is obtained by biaxially stretching and, if necessary, annealing the resulting stretched film at 165 to 168°C for 5 to 60 seconds.

In addition, polypropylene film containing an inorganic filler in advance is coated using the difference in circumferential speed of the roll group.
The polyethylene film is melt-laminated on the film obtained by longitudinally stretching 3.5 to 7 times at 134 to 155°C, and once cooled to 50 to 80°C,
It is obtained by reheating to 155-164°C, preferably 155-164°C, and then stretching 4-10 times in the transverse direction using a tenter. In this method for manufacturing a multilayer sheet as well as in the method for manufacturing a composite sheet having three or more layers to be described later, the annealing treatment is performed as necessary after stretching.

When the composite sheet has three or more layers, it can be manufactured in various ways. For example, (A) inorganic fine powder of 8 to 65
Polypropylene containing % by weight, (B) polypropylene, (C) density 0.91 to 0.97 g/cc, preferably 0.935 to
Each of the 0.970 g/cc polyethylene was melted and kneaded using separate extruders, the melt was transferred to one die, and the film consisting of (B) was laminated in the die so as to form an intermediate layer. , coextruded laminated sheet, (A)
It is produced by simultaneous or sequential biaxial stretching at a temperature lower than the melting point of polypropylene. Further, after longitudinally stretching a coextruded sheet of polypropylene (B) and polyethylene (C) in advance, a sheet of the polypropylene composition (A) is laminated on the surface side of the polypropylene sheet (B) of this coextruded sheet,
It can also be obtained by subsequent transverse stretching. Furthermore, by melt-laminating a sheet of the polypropylene composition of (A) and a sheet of polyethylene of (C) on each side of the polypropylene sheet of (B), which has been longitudinally stretched in advance, and then stretching the sheet transversely. can get.

When coextruding the polyethylene layer and the polypropylene layer, a coextruded sheet with uniform thickness distribution can be obtained by containing 5 to 25% by weight of polyethylene on the polypropylene layer side.

Among these multilayer sheets, from the viewpoint of offset printability, it is preferable that the paper-like layer of polypropylene containing 8 to 65% by weight of inorganic fine powder is oriented only in one axis direction. By stretching, cracks are generated on the surface with the inorganic fine powder as the nucleus, and the adhesion and drying properties of the printing ink are improved. Biaxially stretched orientation increases the chances of inorganic fine powder falling off, and deep cracks formed by uniaxial stretching may disappear with further stretching, resulting in offset printability inferior to uniaxially oriented films. .

Further, the number of layers is preferably three or more including a biaxially oriented polypropylene film layer as an intermediate layer. This biaxially oriented polypropylene film gives stiffness to the blank and facilitates paper feeding during sheet offset printing.

The wall thickness of the blank used in this invention is 30~
The thickness of the back layer is 300μ, preferably 150 to 250μ, and the thickness of the back layer is 1 to 30μ, preferably 3 to 20μ.
If the wall thickness of the blank is thinner than 30μ, paper feeding and offset printing will be difficult. Furthermore, shrinkage of the blank may occur during molding. If the wall thickness exceeds 300μ, it is economically disadvantageous. The thickness of the polyethylene film for the back layer needs to be 1μ or more in order for the polyethylene film to be melted by the heat of molten polyethylene during differential pressure forming such as vacuum forming or pressure forming, and for the molded product and blank to firmly adhere to each other. Moreover, if it exceeds 30 μm, the blank will curl, making offset printing difficult and making it difficult to fix the blank to a mold, which is not preferable.

In the above blank description, polyethylene was used as an example of a thermoplastic resin having a melting point 15°C or more lower than that of polypropylene, but instead of polyethylene, ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer Combined metals (Na,
It is also possible to use salts (Zn, K, etc.).

Although the blank is a wall plate partially connected to a bottom plate, the present invention also includes a sheet-like label. Furthermore, it goes without saying that the composite sheet used to create the blank can be printed in multiple colors not only by offset printing but also by methods such as gravure printing and flexo printing.

Next, the molding sheet will be described. This molding sheet is a multi-layer structure sheet, and has at least the following (a)
It has three layers of ~(c).

(a) Polypropylene base layer film (b) Gas barrier resin film (c) Low melting point thermoplastic resin back layer film for melt bonding to the blank.

In addition, an adhesive film layer is provided, if necessary, for adhesion between these layers or for facilitating heat sealing between the container body and the lid.

The polypropylene base layer film (a) above is used to impart rigidity to the container, and contains homopropylene polymer (melting point 163-167°C), propylene as the main component (95 mol% or more), and ethylene,
Copolymer with olefin such as butene-1 (melting point
142-161°C) is used. If necessary, 0.5 to 20% by weight of a gas barrier resin, a low melting point resin, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, etc. may be blended to improve adhesion with other layers. Furthermore,
Pigments such as titanium oxide are used to add beauty to containers.
It may be added in an amount of 0.5 to 5% by weight. Generally, the polypropylene base film is used so as to account for 40 to 95% of the wall thickness of the sheet for differential pressure molding.

The resins that provide the gas barrier film (b) include polyamides such as nylon 6; polyesters such as polyethylene terephthalate; saponified EVA (ethylene/vinyl acetate copolymer with an ethylene content of 25 to 50 mol%, is 93%
It is preferable to saponify it so that the above results are obtained);
Examples include polyvinylidene chloride. This gas barrier resin film has a thickness of 1 to 100% of the thickness of the forming sheet.
Used to account for 50%.

As the low melting point resin (c), a thermoplastic resin having a melting point 15° C. lower than the melting point of the polypropylene (a) is used. The resin is polyethylene,
Examples include metal (Zn, Na, Li, K) salts of ethylene/vinyl acetate copolymer and ethylene/acrylic acid copolymer, and these must be compatible with the thermoplastic resin that forms the back layer of the blank. is necessary. Polyethylene is preferred in terms of cost and odorlessness. The thickness of the film in (c) is 2 to 20 mm thick than the sheet.
%.

If the adhesion between these layers is poor, use adhesive resins such as maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, maleic anhydride grafted ethylene/vinyl acetate copolymer, or metal salts of ethylene/acrylic acid copolymer. Use. Regarding such products, maleic anhydride-modified polyolefin resins are sold by Mitsubishi Yuka Co., Ltd. under the trade name Modic, and metal salts of the latter copolymers are sold by DuPont under the trade name Surlyn.

The method for manufacturing a multilayer molding sheet is as follows:
In addition to the method of manufacturing by melt-kneading the resins forming each layer using separate extruders, then supplying the melt to one die, laminating them within the die, and coextruding them, there are also methods such as outside-die lamination method, tandem method, etc. Of course, it can also be manufactured using a method.

The wall thickness of this molding sheet is 200 microns to 2 mm.
Preferably it is 400-1000 microns.

The present invention will be explained in more detail below based on the accompanying drawings.

The molding of the composite container, that is, the cup-shaped container 1, is carried out using a mold 4 in which a blank 2 with a wall plate 8 and a bottom plate 9 partially connected shown in FIG. The molten sheet 3 for molding is introduced ~10 cm upward, and differential pressure molding is carried out under a pressure of 1.5 to 7 Kg/cm ² or a reduced pressure of 2 to 600 mmHg, or a combination of both (see Figure 2). ).
During this molding, the blank 2 comes into contact with the melt of the thermoplastic resin 3c such as polyethylene, which is the layer (c) of the molding sheet 3, but the paper-like layer 2a side of the blank 2 on which the offset printing 10 is applied is in contact with the mold 4. Since the paper-like layer 2a is cooled in contact with the paper layer 2a, the surface of the paper-like layer 2a does not melt. That is, multicolor printing does not lose its clarity. Further, since the blank 2 is attached to the cup-shaped container 1 under pressure and in a state where the polypropylene of the paper-like layer 2a of the blank 2 is not entirely melted, shrinkage of the blank 2 is prevented.
Note that 2b is a low melting point synthetic resin film, and 3a is a polypropylene base film. (See Figure 3) The temperature of the molten sheet depends on the type of gas barrier resin 3b used (b), but is generally 140 to 260°C.

After differential pressure molding, a cup-shaped container 1 is formed by trimming.
is collected as a product and then sent to the filling process.

After filling the container with the contents 7, the lid 5 is heat-sealed to the rim portion 6 of the container 1, then sterilized in a retort pot at 110 to 130°C for 10 to 60 minutes, and sprinkled with water at 20 to 60°C. A cooled retort food sealed container is obtained (see Figure 4).

According to this method of attaching a blank, the blank can be firmly attached to the molded article without problems such as heat shrinkage or unclear printing, even though the blank uses a stretched film.

Furthermore, since polypropylene, which is highly water and chemical resistant, is used as the blank material, the blank will not peel off due to water sprinkling even if the container obtained by implementing the present invention is used as a retort food container.

The composite container of the present invention obtained by this molding method has the following advantages.

1. It is more economical than tin containers or aluminum retort containers.

2. It is lighter than tin containers and has excellent logistics suitability.

3. Unlike aluminum containers, the container will not dent due to impact.

4. A rigid container whose shape and dimensions can be freely changed can be obtained.

5. Since the container itself can be printed in multiple colors, it is possible to obtain a retort container that has both retort suitability and fashionability.

Hereinafter, this invention will be explained in more detail with reference to Examples. However, the present invention is not limited to this embodiment, and any embodiments may be included within the scope of the present invention as long as they do not exceed the gist thereof. Note that parts and percentages in the examples are based on weight.

Example of manufacturing synthetic paper 1 (B). Mitsubishi Yuka Co., Ltd.'s polypropylene "Mitsubishi Noblen MA-6" (trade name, melting point = 164℃) 87 parts, Mitsubishi Yuka Co., Ltd.'s high-density polyethylene "Yukalon Hard"
EY-40” (product name, melting point = 134℃, density 0.950g/
After melt-kneading a composition consisting of 10 parts of cc) and 3 parts of fired clay using an extruder, 250
The sheet was extruded at a temperature of 50°C and the sheet was cooled to a temperature of about 50°C.

Next, after heating this sheet to about 153℃,
A uniaxially stretched film was obtained by stretching 4 times in the longitudinal direction using the difference in peripheral speed between the roll groups.

Separately, (A). A mixture consisting of 57 parts of polypropylene "Mitsubishi Noblen MA-3" (trade name, melting point 163°C) manufactured by Mitsubishi Yuka Co., Ltd. and 43 parts of calcined clay, and (C). High-density polyethylene "Yukalon Hard EY-40" (melting point 134
℃) are melt-kneaded using two separate extruders, and the molten material of (A) is melted through two dies at a temperature of 250℃, and the polyethylene of (C) is formed into a sheet at a temperature of 230℃. A three-layer sheet was obtained by extruding each film and laminating it on the front and back surfaces of the uniaxially stretched film.

After cooling this three-layer sheet to 60℃, approx.
The film was reheated to a temperature of 163°C, stretched 8 times in the transverse direction using a tenter, and then passed through an oven set at 165°C to set the heat.
℃, and the edges were slit to obtain an intermediate biaxially stretched base layer film with a thickness of 62 microns, a surface layer uniaxially stretched film made of the composition of (A) with a wall thickness of 20 microns, and (C A composite stretched film (1) having a thickness of 8 microns in the back layer made of polyethylene was obtained.

Blank production example Synthetic paper (composite stretched film) obtained in the above production example
After corona discharge treatment on the paper-like layer side, an acrylic antistatic agent solution ST- manufactured by Mitsubishi Yuka Co., Ltd.
1300 was applied and dried.

Next, the edges of the composite stretched film were slit, and the composite stretched film was further cut into a width of 50 cm using a knife cutter perpendicular to the film flow direction, and the cut composite stretched film was stored in a sheet stocker.

Multicolor offset printing was performed on the paper-like layer surface of the cut sheet-like synthetic paper according to each purpose, and then punching was performed to obtain a blank.

Example of manufacturing sheet for molding 1 (a) Polypropylene “Mitsubishi Noblen MA-8”
(trade name manufactured by Mitsubishi Yuka Co., Ltd., melting point 164℃), a mixture of 90 parts of maleic anhydride-modified polypropylene "Modic", (b) polyethylene terephthalate "ARNITE"
A200" (trade name manufactured by AKZO) and (c) high-density polyethylene "Yukalon Hard EY-40" are each melt-kneaded in separate extruders, then the melts are supplied to one die, and inside the die ( After laminating in the order of c) / (a) / (b) / (a) / (c), coextrusion (248°C) is carried out, and then cooled to form a 5-layer sheet with a wall thickness of 800 microns (each wall thickness is
35/350/30/350/35 microns).

Example 2 (a) Mixture of 95 parts of polypropylene MA-8 and 5 parts of TiO ₂ , (b) Saponified ethylene/vinyl acetate copolymer "EVAL" (trade name manufactured by Kuraray), (c) Low density polyethylene "Yukalon"LK-30'' (trade name manufactured by Mitsubishi Yuka Co., Ltd., melting point 119℃) and (d) adhesive resin ``Modic'' were melt-kneaded using separate extruders, and then the melts were fed into one die. , within the die (c)／(d)／
(b) / (d) / (a) / (d) / (c) were laminated in the order, coextruded and cooled to obtain a sheet with a 7-layer structure (thickness 50/
20/50/20/690/20/50 microns).

Examples 3-5 Instead of EVAL as the resin in (b), nylon-6
"Novamid 1040 (trade name) manufactured by Mitsubishi Kasei, or vinylidene chloride-vinyl chloride copolymer "K Flex (trade name) manufactured by Kureha Chemical Industries", or linear thermoplastic polyester "Vylon 200 (trade name) manufactured by Toyobo Co., Ltd." The wall thickness was 900 mm in the same manner as in Example 2 above except that
A sheet with a seven-layer structure of microns was obtained.

Examples 1 to 5 The blank with offset printing obtained above was punched out, and the diameter of the bottom plate was 53 mm and the height of the peripheral wall was 28 mm.
A blank with a height of .

After fixing 16 of these blanks in the cavity of the lower mold of a vacuum mold with the printing side in contact with the cavity surface of the mold, the melted sheets obtained in Examples 1 to 5 above (140 to 260°C ) was guided 5 cm above the mold using a compressed air vacuum forming machine manufactured by Uniku.
Plug assist molding was performed by reducing the pressure (60 mmHg) and supplying compressed air of 4 kg/cm ² G from the upper mold side for 10 seconds, followed by trimming to mold 16 cup-shaped containers at once. The average wall thickness of the containers was 550-600 microns.

There is no fading of the blank print on any of the products.
Further, no deformation of the blank was observed. Further, the adhesion strength between the container body and the blank was strong, and the blank could not be peeled off by hand.

Heat resistance, water resistance Pour the contents (approximately 93°C) into a container printed in multiple colors using the blank obtained in the above example, then heat the lid with a four-layer structure of polyethylene terephthalate/Modic/aluminum foil/polyethylene. A sealed container was obtained by sealing.

The thus obtained sealed container was placed in a retort pot and sterilized at 120° C. for 60 minutes, and then water was sprinkled to cool the container.

No deformation or discoloration was observed in any of the containers. Moreover, no peeling between the blank and the container was observed.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a blank, FIG. 2 is a sectional view showing one of the steps of forming a composite container of the present invention, and FIG. 3 is a partially cutaway sectional view of a composite container showing an embodiment of the present invention. FIG. 4 is a cross-sectional view of a sealed container filled with contents. In the figure, 1... Composite container (cup-shaped), 2
... Blank, 2a ... Paper-like layer, 2b ... Low melting point synthetic resin film, 3 ... Sheet for molding, 3a ...
...Polypropylene base film, 3b...Gas barrier resin, 3c...Thermoplastic resin.

Claims (1)

[Claims] 1. The blank is integrally thermally bonded to the container, obtained by molding a thermoplastic synthetic resin composite sheet heated using compressed air and/or vacuum onto the inner surface of a blank inserted into a mold. In a composite container with a structure that
The blank has a paper-like layer made of a polypropylene stretched film containing 8 to 65% by weight of inorganic fine powder, and the surface opposite to this paper-like layer (the back surface).
A composite sheet having at least a two-layer structure having a back layer of a film of 1 to 30 microns thick of a thermoplastic resin having a melting point 15° C. or more lower than the melting point of the polypropylene constituting the polypropylene; The composite sheet consists of (a) a polypropylene base film and (b) polyamide, polyester, ethylene, etc.
(c) a resin film layer with low gas permeability selected from saponified vinyl acetate copolymer and polyvinylidene chloride; and (c) a back layer of the blank, which has a melting point 15° C. or more lower than the polypropylene. It is a molding composite sheet having at least a back layer made of a thermoplastic resin film that is compatible with the thermoplastic resin that constitutes the blank, and the bonding is performed by thermally bonding the back layer of the blank and the back layer of the molding composite sheet. Composite container for retort food with a built-in structure. 2. The composite container for retort food according to claim 1, wherein the paper-like layer side of the blank is printed in multiple colors. 3. The blank has a paper-like layer made of a uniaxially stretched film and a polypropylene 2 film between the paper-like layer and the back layer.
3. The composite container for retort food according to claim 1 or 2, which is a blank having a structure having a base material layer made of an axially stretched film. 4. The composite container for retort food according to claim 1, 2, or 3, wherein the thermoplastic resin constituting the back layer of the blank is polyethylene. 5. The composite for retort food according to claim 1, 2, 3, or 4, wherein the thermoplastic resin constituting the back layer of the composite sheet for molding is polyethylene. container.