JPH0482102B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a blow-molded container with a label, and more specifically, the present invention relates to a method for manufacturing a blow-molded container with a label. , relates to a method of forming a container side surface by in-mold label operation with excellent adhesion and peeling resistance. (Prior art) Attaching a label that indicates the contents to a blow-molded container has an important meaning in terms of packaging technology because it increases the commercial value of the packaged product and stimulates consumers' desire to purchase it. There is. It has been known for a long time to apply labels to blow-molded containers by in-mold label operation.The label to be affixed to the inner surface of the cavity of a molding die is held by means such as vacuum suction, and the label is applied inside the mold. A method of blow-molding a plastic parison is generally employed (for example, Japanese Patent Laid-Open No. 61-202818). JP-A No. 60-89327 discloses that during the above-mentioned in-mold label operation, the film has a laminated structure of a synthetic resin film layer and a metal foil having an adhesive layer on the outer surface, and the heat shrinkage temperature of the film is higher than that of the adhesive. It is described that a label having a temperature equal to or higher than the softening temperature of (Problems to be Solved by the Invention) However, when a plastic film label is applied to a blow-molded container by an in-mold label operation, wrinkles and blisters occur on the label, resulting in the appearance of the attached label. In addition, the adhesion between the label and the outer surface of the container is insufficient, and there is also a tendency for the label to peel off or fall off the container when the container is stored or transported. In order to give the label a metallic luster and improve its decorative properties, labels using metal foil and printing on it are widely used. It has been found that when the label is applied to the side surface of a blow-molded container using an in-mold label operation, the above-mentioned wrinkles and blisters are particularly noticeable. SUMMARY OF THE INVENTION It is therefore an object of the present invention to eliminate the above-mentioned drawbacks that occur when applying a label with a metal layer to the side surface of a blow-molded container that is being formed by an in-mold label operation, and to prevent scaly and wrinkles on the outer surface of the label. To provide a method for attaching a label having a metallic luster and an excellent decorative effect, with excellent adhesion and peeling resistance. (Means for Solving the Problems) According to the present invention, a single-layer to multi-layer plastic parison or sheet is blow-molded using a blow mold with a label affixed to the inner surface of the cavity, and the label is bonded to the side wall surface. In the method for manufacturing a hollow container with a label, the label is heated at a temperature (T ₁ ) 30°C lower than the melting point or softening point of the plastic that makes up the surface of the container.
A method is provided which is characterized in that it uses a laminate of at least one layer of a stretched plastic film having a heat shrinkage rate greater than the molding shrinkage rate of the plastic, a thin layer of metal and a thermoplastic adhesive. In the present invention, the label is defined by the stretched plastic film contained therein according to the formula R _S = L ₁ − L ₂ /L ₁ ×100 (1) where L ₁ is the length of the label film peeled from the container. , L ₂ represents the length when this label film is equilibrated at the above temperature (T ₁ ), and the residual equilibrium shrinkage rate (R _S ) defined as is 0.5 to 100.
%, especially 1 to 50%, is preferred. In addition, the metal thin layer is
It is preferable to have a thickness of 150000 Å. (Function) When manufacturing a blow-molded container, a plastic parison in a molten or softened state is expanded in a mold by blowing pressurized fluid, and the expanded plastic comes into contact with the cavity surface of the mold.
By cooling, it is molded into the shape of a container, and finally the mold is opened and the container is taken out. In an in-mold label operation, the label is held against the interior surface of the cavity and the expanded molten plastic parison contacts the label to develop a thermal bond prior to blow molding the parison. The present invention uses a laminate of a plastic film layer, a metal layer, and a thermoplastic adhesive layer as a label, and performs an in-mold label operation. The base material is a stretched plastic film that has a heat shrinkage rate higher than the molding shrinkage rate of the plastic at a temperature (T ₁ ) lower than 30°C, and a thin layer of metal is provided, generally having a thickness of 50 to 150,000 Å. It is characterized by its use, and as a result, it is possible to obtain a labeled hollow container with no blisters or wrinkles on the outer surface of the label and excellent adhesion between the container and the label and excellent peeling resistance. In the present invention, the melting point or softening point of plastic primarily means the melting point for plastics (crystalline polymers) that have a clear internal melting point, and the softening point for plastics that do not have a clear melting point. shall be. It is generally believed that plastic films that are thermally treated with improved dimensional stability, such as stretched and heat-set films, will give satisfactory results both in terms of adhesion and thermal stability. ing. However, when attaching a label based on such a stretched heat-set film to a blow-molded container using the in-mold labeling method, wrinkles, blisters, etc. may occur on the outer surface of the label, and the appearance characteristics may deteriorate. First, the adhesion to the container and the peeling resistance are lower than those adhered outside the mold. The reason for this is that the density of plastic is lower in the molten state than in the solid state at room temperature, and therefore the molded container shrinks considerably in the solid state at room temperature compared to the state in which it is attached to a label (in the molten state). This is thought to be due to the occurrence of In the present invention, by using, as the basic film of the label, a stretched plastic film having a higher heat shrinkage rate than the molding shrinkage rate of the plastic constituting the outer surface of the container at the temperature _T1 , It is possible to retain heat shrinkability in the label so that the residual equilibrium shrinkage rate (R _S ) is within a certain range, which keeps the outer surface of the label smooth and improves its adhesion to the container. It was extremely successful. Furthermore, the molding shrinkage rate of plastic is
It is proposed in ASTMD955, while the thermal shrinkage rate of the film can be determined by JIS C2318 (heating is T ₁ and heating time is 30 minutes). Generally, the degree of heat shrinkage of a plastic film depends on the degree of molecular orientation imparted by stretching and the degree of heat fixation of this orientation. That is, in general, the greater the degree of molecular orientation, the greater the degree of thermal contraction, and the greater the degree of thermal fixation of molecular orientation, the smaller the degree of thermal contraction. Thus, by adjusting the degree of molecular orientation of the stretched film used for the label, or by further adjusting the degree of heat setting, the degree of heat shrinkage of the film can be adjusted to a desired range. It is also important in the present invention that the metal is provided in the form of a thin layer, generally with a thickness of 50 to 150,000 Å, in particular 100 to 90,000 Å. In other words, when the thickness of the metal layer becomes thicker than the above upper limit, as in the case of ordinary metal foil, the metal layer cannot follow the shrinkage of the film base, and the label after being pasted will also develop blisters and wrinkles. However, according to the present invention, by reducing this thickness, the metal layer can also follow the shrinkage of the base film, and it is recognized that the occurrence of blisters and wrinkles can be eliminated. However, if the thickness of the metal layer falls below the above lower limit, metallic luster cannot be obtained, so it is preferable to keep the thickness within the above range. The metal layer is
It can be provided as a vapor deposited layer or can be used as a very thin metal foil. (Preferred embodiment of the invention) A first example showing an example of a laminate label used in the present invention
In the figure, the label 1 consists of a laminate of a stretched plastic film basic layer (outer layer) 2, a printing ink layer 3 applied to the back side, a thin metal foil 4 and a thermoplastic adhesive layer 5. The plastic film base 2 is uniaxially or biaxially stretched, and has a heat shrinkage rate greater than the molding shrinkage rate of the plastic at a temperature (T ₁ ) 30°C lower than the melting point or softening point of the plastic forming the outer surface of the container. This shows that. Thermoplastic adhesive resins are those that can be thermally bonded to the plastic being molded by fluid injection. This label 1 is made by printing a stretched plastic film and applying a known adhesive or adhesive primer to the metal foil in such a position that the printing ink layer and the metal foil face each other. It is formed by laminating and then applying a thermoplastic adhesive to the metal foil. In FIG. 2 showing another example of a laminate label,
This label 1a consists of a laminate of a stretched plastic film outer layer 2, a printing ink layer 3 applied to the back side thereof, a stretched plastic film intermediate layer 6 having a metal vapor deposited layer 4a on its surface, and a thermoplastic adhesive inner layer 5. . Both stretched plastic films 2, 6 must have the properties mentioned above. By performing metal vapor deposition on a stretched plastic film, the metal layer can be made sufficiently thin within a range that provides metallic luster. This label 1a is made by printing on a stretched plastic film and applying metal vapor deposition to the stretched plastic film, with the printing ink layer and the metal vapor deposition layer facing each other, and applying an adhesive or an adhesive primer to the stretched plastic film. It is formed by laminating the metallized film through the film and applying a thermoplastic adhesive to the metal-deposited film side. Further, the laminate label may have a layered structure as shown in FIG. 3. In FIG. 3, this label 1b is a laminate of a stretched plastic film outer layer 2, a printing ink layer 3 applied to the back side thereof, a stretched plastic film intermediate layer 6 having a metal vapor deposited layer 4a on the surface, and a hot melt adhesive inner layer 5. It is made up of Double-stretched plastic film 2,
6 must have the characteristics described above. This label 1b is made by pasting together a printed stretched plastic film and a vapor-deposited stretched plastic film using an adhesive, with the printed ink layer facing the stretched film. It is formed by applying an adhesive primer to the metallized layer and then applying a thermoplastic adhesive thereon. In FIG. 4 for explaining the in-mold label operation, in step A, prior to blow molding the plastic parison, the blow molds 7a and 7b are in an open state, and the cavity surface 8 of at least one of them is Apply label 1 in advance. That is, the cavity surface 8 has a portion that supports the label 1, a vacuum suction mechanism 9 is provided in this portion, and the label 1 is held on the cavity surface 8 by a suction. In this case, the label is positioned such that the plastic film base 2 is on the outside and the hot melt adhesive resin layer 5 is on the inside. The application and fixing of the label 1 to the cavity surface 8 is not limited to suction, but can also be carried out, for example, by electrostatic electricity. Next, in step B, the molten plastic parison 11 is extruded from the die 10, the blow molds 7a and 7b are closed, and pressurized gas is blown into the closed parison 11. In step C, the parison expanding in the mold is held on the mold surface and pressed against the label 1 to bring them into close contact, and the expanded parison comes into contact with the mold surface and is cooled, forming the labeled container 12. becomes. Blow molding includes direct blow molding using horizontal rotary blow molding machines, vertical rotary blow molding machines, etc., as well as any blow molding methods such as injection blow molding, two-stage blow molding, sheet forming, and stretch blow molding. It can be done by method. In the present invention, the plastics constituting the container and label base film include, for example, crystalline polypropylene, crystalline propylene-ethylene copolymer, crystalline polybutene-1, crystalline poly-4-
Polyolefins such as methylpentene-1, low-, medium- or high-density polyethylene; aromatic vinyl polymers such as polystyrene, styrene-butadiene copolymer; halogenated vinyl polymers such as polyvinyl chloride and vinylidene chloride resin; Nitrile polymers such as acrylonitrile-styrene copolymer and acrylonitrile-styrene-butidiene copolymer; polyamides such as nylon 6, nylon 6,6, para- or meta-xylylene adipamide; polyethylene terephthalate, polytetramethylene terephthalate, etc. Examples include polyesters; various polycarbonates; and thermoplastic resins such as polyacetals such as polyoxymethylene. Blow-molded containers can have a single-layer or multi-layer structure, such as containers made of a single layer of polyolefin or polyethylene terephthalate, or inner and outer layers made of polyolefin or polyethylene terephthalate, with a gas barrier thermoplastic resin between them. Examples include multilayer containers in which the intermediate layer is provided with .
As a gas barrier resin, the ethylene content is
Gas barrier resins known per se such as 50 to 20 mol% ethylene-vinyl alcohol copolymer; xylylene group-containing polyamides; gas barrier polyesters; high nitrile group-containing polymers; vinylidene chloride resins can be used. can. When there is no adhesiveness between the inner and outer layers and the intermediate layer, adhesive resins such as acid-modified olefin resins, various copolyamides, and various copolyesters may be contained between them. Examples of molding shrinkage rates (ASTM D955) of various resins constituting hollow containers are shown in Table 1 below.

[Table] The stretched film used for the label is formed from the thermoplastic resin listed above, but the heat shrinkage rate at temperature T ₁ is higher than the molding shrinkage rate shown in Table 1 above for the resin constituting the container. More preferably, the type of resin and the degree of stretching are determined so that the residual equilibrium shrinkage rate (R _S ) of formula (1) falls within the above-mentioned range. This stretched film is generally 20
It is preferable to have a thickness of 300 μm to 300 μm, particularly 50 to 150 μm. As the metal layer, a foil or vapor deposited layer of a metal with metallic luster, such as aluminum, tin, or copper, is used. The foil generally has a thickness of 1 to 15 μm, especially 5 to 15 μm.
9μm is used, while in the case of vapor deposited layer,
The thickness of the foil used is equal to or less than that of the above-mentioned foil. Lamination of printed stretched film substrate and metal foil, or laminated printed stretched film substrate and metallized film can be performed using urethane adhesive, epoxy adhesive, or depending on the film substrate, acid-modified olefin resin adhesive. This can be done using Examples of thermoplastic adhesives that can be used include vinyl acetate-based adhesives such as vinyl acetate polymers, vinyl acetate-acrylic acid ester copolymers (acrylic esters include ethyl acrylate, butyl acrylate, and diacrylic acid). - ethylhexyl, etc.), vinyl acetate-ethylene copolymer (containing 10 to 50% by weight of ethylene) alone or in combination.
Some resin components contain a mixture of more than one type. Acrylic adhesives include ethyl acrylate,
Mainly composed of butyl acrylate, 2-ethylhexyl acrylate, and methacrylate,
Some have a copolymer with styrene, acrylonitrile, etc. as a resin component. Ethylene-based adhesives include ethylene-vinyl acetate copolymer (with a vinyl acetate content of 5 to 50% by weight), ethylene-acrylic acid copolymer, and ethylene-acrylic ester copolymer (with an acrylic ester content of 5 to 50% by weight). (5 to 40 wt%), polyethylene or ethylene-vinyl acetate copolymer graft polymerized with unsaturated acids such as acrylic acid, methacrylic acid, maleic acid, etc., low-density polyethylene, etc., either alone or in combination. Those containing a mixture of the above, and one or more of these resins, rosin resin, terpene resin, petroleum resin, styrene resin, ester gum, coumaron resin, chlorinated paraffin, vinyl chloride resin, and nitrocellulose. Some resin components contain 5 to 50% by weight of Further, there are thermoplastic polyamide adhesives, thermoplastic polyester adhesives, thermoplastic polyurethane adhesives, etc., and mixtures of resin components of two or more of the above adhesives can also be used. The thermoplastic adhesive resin is generally preferably provided on the metal foil or film to a thickness of 1 to 40 μm, particularly 3 to 15 μm. The method of the present invention is particularly effective for performing in-mold labeling operations on hollow containers whose outer surface is made of an olefin resin such as polypropylene. In this case, the stretched film base of the label is made of an olefin resin such as polypropylene. It is particularly suitable to use a stretched film of. (Effects of the Invention) According to the present invention, when producing a labeled hollow container by in-mold labeling operation, a label having a stretched film having a certain heat shrinkability as a base and containing metal in the form of a thin layer can be used. This makes it possible to maintain a certain equilibrium shrinkage rate on the attached label, thereby improving the appearance characteristics of the label by preventing wrinkles and blisters from occurring on the label while maintaining a metallic luster. It has also become possible to improve the adhesion and peeling resistance between the label and the outer surface of the container. Additionally, by performing in-mold labeling operations, the troublesome adhesive application and label pasting operations can be omitted, making it possible to streamline the container manufacturing process. (Example) The present invention will be explained with the following example. Example 1 Made of ethylene-propylene copolymer with a melting point of 137°C, with a thickness of 100 μm, the heat shrinkage rate of MD at T ₁ (melting point of the plastic forming the outer surface of the container -30°C), that is, 127°C is 14%. , TD heat shrinkage rate is 3.0%
One side of a biaxially stretched film was printed, and an acrylic polyol and an isocyanate anchoring agent were coated thereon, and aluminum was then vacuum-deposited to a thickness of 500 Å. Next, a primer was applied to this aluminum vapor-deposited surface, and a sealant made of a blend of ethylene-acrylic acid copolymer and rosin resin was applied thereon. Next, an oval-shaped label with a length of 90 mm and a width of 60 mm is punched out from the obtained label base material, and the molding shrinkage rate is 1.2% and the melting point is 157°C by the process shown in Figure 4.
It was attached to the surface of a bottle made of ethylene-propylene copolymer. In this case, the molten resin temperature of the ethylene-propylene copolymer parison is 210℃,
The blow mold temperature was 8°C. The appearance of the in-mold label bottle thus obtained was very good, and no wrinkles were observed on the label. Furthermore, the adhesive strength between the label and the bottle was measured and found to be 650 g/15 mm. Furthermore, considering hot filling, we measured the adhesive strength at 85℃.
The weight was 300g/15mm, and the heat resistance was also sufficient. On the other hand, the film of the label of the resulting in-mold label bottle was peeled off and heat treated at T ₁ =127° C. for 2 hours to measure the residual equilibrium shrinkage rate, which was found to be MDD 12%. Example 2 Biaxial stretching with a thickness of 100 μm made of an ethylene-propylene copolymer with a melting point of 137°C and a heat shrinkage rate of MD of 14% and TD of 3.0% at T ₁ = 127°C. One side of the film was printed, a urethane adhesive was applied thereto, a 6 μm aluminum foil was laminated, and a primer was further applied to the surface of the aluminum foil. A sealant made of a blend of ethylene-vinyl acetate copolymer and rosin resin was applied thereon. Next, an oval-shaped label with a length of 90 mm and a width of 60 mm is punched out from the obtained label base material, and the molding shrinkage rate is 1.2% and the melting point is 157°C by the process shown in Figure 4.
It was attached to the surface of a bottle made of ethylene-propylene copolymer. In this case, the molten resin temperature of the ethylene-propylene copolymer parison is 210℃,
The blow mold temperature was 8°C. The appearance of the in-mold label bottle thus obtained was very good, and no wrinkles were observed on the label. Furthermore, the adhesive strength between the label and the bottle was measured and found to be 310 g/15 mm width. On the other hand, the film of the label of the obtained in-mold label bottle was peeled off and heat treated at T ₁ =127° C. for 2 hours to measure the residual equilibrium shrinkage rate, which was found to be MD 12.5%. Example 3 A stretched film made of an ethylene-propylene copolymer with a melting point of 137°C and having a thickness of 50 μm and a heat shrinkage rate of 48% for MD and 0% for TD at T ₁ = 127°C. This stretched polypropylene film, which is printed on one side and laminated with an aluminum-deposited stretched polypropylene film via a urethane-based binder so that the aluminum-deposited side faces the printed side, has a melting point of 158°C. The thickness is 20μm, and the heat shrinkage rate at T ₁ = 127℃ is
The MD is 6.0%, the width is 1.0%, and the thickness of the aluminum vapor deposition layer is 600 Å. Then, a sealant made of a blend of ethylene-vinyl acetate copolymer and rosin resin was applied to the film side of the aluminum-deposited film. An in-mold label bottle was molded in the same manner as shown in Example 1 using the above materials. The resulting bottle had a good appearance with no wrinkles. When the adhesive strength between the label and the bottle was measured, it was 350 g/15 mm width. The label film of the obtained in-mold label bottle was peeled off and heat treated at T ₁ =127° C. for 2 hours, and the residual equilibrium shrinkage rate of the 50 μm stretched ethylene-propylene film was MD41%. On the other hand, the residual equilibrium shrinkage rate of the stretched polypropylene film of 20 μm was MD 2%. Examples 4 and 5 Comparative Example 1 Heat at T ₁ = 127°C with a thickness of 100 μm consisting of a blend of ethylene-propylene block copolymer with a melting point of 155°C, ethylene-propylene random copolymer with a melting point of 142°C, and polyethylene with a melting point of 125°C Shrinkage rate
A label was made in the same manner as in Example 1 or 2 using a stretched film with an MD of 37% and a TD of 0%, and a polypropylene in-mold label bottle was similarly molded. The results are shown in Table 1 as Examples 4 and 5 and Comparative Example 1. In the case of Comparative Example 1 in which the aluminum metal layer was thick, wrinkles occurred.

[Table] * Label shrinkage rate is the shrinkage rate of the label attached to the bottle compared to the label before being attached.
** The melting point of the PP used to form the bottle is
157℃.
*** Sealant is a blend of EVA and rosin resin.
Example 6 Made of ethylene-propylene copolymer with a melting point of 137°C, 100 μm thick, MD has a heat shrinkage rate of 4.0% and TD has a heat shrinkage rate of 1.5% at T ₁ = 105°C 2
One side of the axially stretched film is printed, acrylic polyol and isocyanate anchoring agent are applied on top of that, and then aluminum is applied on top of that.
Vacuum deposited to a thickness of 500 Å. Next, a primer was applied to this aluminum-deposited surface, and a sealant made of a blend of ethylene-vinyl acetate copolymer and rosin resin was applied thereon. Next, an oval-shaped label with a length of 90 mm and a width of 60 mm is punched out from the obtained label base material, and the molding shrinkage rate is 2.5% and the melting point is 135°C by the process shown in Figure 2.
It was attached to the surface of a bottle made of high-density polyethylene. In this case, the molten resin temperature of the high-density polyethylene parison is 200℃, and the blow mold temperature is 8℃.
It was hot. The appearance of the in-mold label bottle thus obtained was very good, and no wrinkles were observed on the label. In addition, the adhesive strength between the label and the bottle was 380 g/15 mm width. On the other hand, the residual equilibrium shrinkage rate was measured by peeling off the label of the obtained in-mold label bottle and heat-treating it at T ₁ = 105°C for 2 hours.
MD was 1.5%. Comparative Example 2 One side of biaxially oriented polyethylene terephthalate with a melting point of 256°C, a thickness of 50 μm, and a heat shrinkage rate of MD 0.5% and TD 0% at T ₁ = 105°C was printed, and acrylic was printed on it. Polyol and isocyanate-based anchoring agents were applied, and aluminum was then vacuum-deposited to a thickness of 500 Å. Next, a primer was applied to this aluminum-deposited surface, and a sealant made of a blend of ethylene-vinyl acetate copolymer and rosin resin was applied thereon. Next, an oval-shaped label with a length of 90 mm and a width of 60 mm is punched out from the obtained label base material, and the molding shrinkage rate is 2.5% and the melting point is 135°C by the process shown in Figure 2.
It was attached to the surface of a bottle made of high-density polyethylene. In this case, the molten resin temperature of the high-density polyethylene parison is 200℃, and the blow mold temperature is 8℃.
It was hot. The thus obtained in-mold label bottle suffered from peeling at the end of the label some time after molding. In addition, the residual equilibrium shrinkage rate was measured by peeling off the label of the obtained in-mold label bottle and heat-treating it at T ₁ = 105°C for 2 hours.
MD was 0%.

[Brief explanation of the drawing]

1 to 3 are diagrams showing examples of cross-sectional structures of labels used in the present invention, and FIG. 4 is a diagram illustrating in-mold label operation, where reference numbers 1, 1a, and 1b are labels, 2 3 is a stretched plastic film substrate, 3 is a printing ink layer,
4, 4a are metal layers, 5 is an adhesive layer, 6 is a stretched plastic film intermediate layer, 7 is a blow mold, 8
9 represents a cavity surface, 9 represents a vacuum suction mechanism, 10 represents a die, 11 represents a parison, and 12 represents a labeled container.

Claims (1)

[Scope of Claims] 1. A method for producing a labeled hollow container, which comprises blow-molding a single-layer or multi-layer plastic parison or sheet using a blow mold with a label affixed to the inner surface of the cavity, and bonding the label to the side wall surface. As a label, the temperature (T ₁ ) is 30°C lower than the melting point or softening point of the plastic that makes up the outer surface of the container.
A method comprising using a laminate of at least one plastic stretched film having a heat shrinkage rate greater than the molding shrinkage rate of the plastic, a thin metal layer and a thermoplastic adhesive layer. 2 The label is made of stretched plastic film with the formula R _S = L ₁ − L ₂ /L ₁ ×100 where L ₁ is the length of the label film peeled from the container, and L ₂ is the length of the label film peeled off from the container at the temperature ( The residual equilibrium shrinkage rate (R _S ), defined as the length when equilibrated at T ₁ ), is between 0.5 and 100.
%. 3. A method according to claim 1, characterized in that the thin metal layer has a thickness of 50 to 150,000 Å. 4. The method of claim 1, wherein the laminate has a layer structure of an outer layer of plastic stretched film, an intermediate layer of metal foil, and an inner layer of thermoplastic adhesive. 5 The laminate includes an outer layer of plastic stretched film,
2. The method of claim 1, comprising a metallized plastic stretched film interlayer and a thermoplastic adhesive inner layer.