JPH044130A - Transparent in-mold label - Google Patents

Abstract

PURPOSE:To prevent a label from generating a deformation or blister, by specifying opaqueness and the tensile modulus of elasticity of the label. CONSTITUTION:The subject label is constituted of a resin film havingopaqueness of not exceeding 10% and the tensile modulus of elasticity of 2000-6000 kg/cm<2>. This resin film is formed of at least one kind of polymer selected out of a propylene-ethylene copolymer containing 80-95 wt.% propylene and 20-5 wt.% ethylene or propylene-butene copolymer containing the 80-85 wt.% propylene and 20-5 wt.% butene or a propylene-etylene-butene copolymer containing the 80-95 wt.% propylene, the 0.5-12 wt.% ethylene and the 2-10 wt.% butene.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] <Industrial Application Field> The present invention relates to a transparent in-mold label that prevents label blistering.

<Conventional technology> Conventionally, in order to manufacture a synthetic resin molded article with a transparent label by integral molding, it has been necessary to use an unstretched extruded film of crystalline polypropylene or a crystalline polypropylene film formed by a casting method. As a material layer, a heat-sensitive adhesive resin layer such as low-density polyethylene or ethylene/vinyl acetate copolymer is directly extruded laminated to the base material layer, or a low-melting point resin such as polyvinyl acetate or ethylene/vinyl acetate copolymer is used. A transparent label obtained by coating with a solution dissolved in a solvent using a gravure coater or the like and drying is inserted into the inner wall of a mold in advance, and then a molding resin such as polypropylene or polyethylene resin is placed in the mold. Direct supply, injection molding, hollow molding, in-mold bead foam molding, and other methods were used. Furthermore, when attaching a label to a polypropylene or polyethylene sheet, a differential pressure molding method (vacuum molding, pressure molding) in which the sheet is heated and molded using a differential pressure has been carried out using substantially the same method.

<Problem to be solved by the invention> A transparent label is used in which a base layer is such an extruded crystalline polypropylene film or a crystalline polypropylene film obtained by a casting method, and an ethylene resin film is laminated as an adhesive layer. When trying to decorate a polypropylene hollow container, the polypropylene parison temperature should be set to 230°C or higher, and the mold cooling water temperature should be set to 10°C.
A good product could not be obtained unless the temperature was above ℃.

In addition, for such a label, it is essential that the polyethylene hollow container has the same parison temperature and mold cooling water temperature conditions as the polypropylene hollow container.

In general, considering the conditions for increasing the speed of blow molding of polyethylene (melting point 119 to 135° C.) containers and production costs, it is desirable to lower the parison temperature and shorten the cooling time.

However, at a parison temperature of about 180 to 210°C that can satisfy such high-speed conditions, the adhesive strength between the label and the hollow container is low when using a label made of the biaxially stretched polypropylene film or cast film. It was low and I couldn't get anything practical.

[Summary of the invention]

Summary> In view of the above problems, the inventors of the present invention have conducted extensive research and found that the tensile modulus (ASTM-D638) of labels made of crystalline polypropylene film is approximately 8.50.
Due to the high pressure of 0 to 9,000 kg/c, when the molten parison expands and adheres to the label, the surface of the parison is curved, so the pressure of the parison applied to the label differs depending on the location, making it stronger in some areas. There are adhesive parts and weak adhesive parts, and when the container formed from the parison is cooled, crystalline polypropylene and crystalline polyethylene have a large dimensional shrinkage rate of 1.5 to 3%. It has been found that this shrinkage stress causes peeling in weakly bonded areas, causing blistering.

However, in order to lower the tensile modulus of the label, it is necessary to use foamed labels or synthetic paper (Japanese Patent Laid-Open No. 58-1979
Publication No. 69015 and European Published Patent No. 2549
23 specification) is used, the label itself has appropriate compressibility even if the label contains a stretched film because it contains many fine voids inside, and when attached to the inner wall of the mold, the The surface temperature of the mold is difficult to conduct heat to the label surface, which prevents the label surface temperature from decreasing and prevents label deformation and blistering. However, these labels are opaque, and transparent It is not a proper label.

In addition, for transparent labels, printing is often applied to the adhesive side of the label that is attached to the container to improve gloss and protect the printing, so when using opaque labels, such printing may not be readable. It had the following drawbacks.

On the other hand, conventional crystalline polypropylene has an opacity of 10
% or less transparent labels do not have minute voids like the synthetic paper mentioned above, so the label itself is hard, and it also has high heat conduction, so the label surface can become hot or cold, and the adhesive layer on the label surface due to the molten resin. The range of conditions for melting and sticking the resin in +1 hours is narrow. For example, in order to lower the melt viscoelasticity of the parison and make it easier to expand, the temperature of the parison is set to 230° C. or higher. However, if the temperature of the parison is increased too high, the parison will draw down and the hollow container will tend to have uneven thickness, so the temperature can only be raised to 240° C. at most.

Therefore, as a result of further research, the inventor of the present invention found that if the tensile modulus of the label itself is set to 2,000 to 6,000, a molded product with a label that does not cause label deformation or blister formation can be obtained. The present invention was completed based on these findings.

That is, the transparent in-mold label of the present invention has an opacity of 10% or less and a tensile modulus of 2. 000-6
．． 000 kg/c-.

Effect> Since the transparent in-mold label of the present invention is formed with the elastic modulus of the label reduced to 2,000 to 6,000 kg/c-, mold shrinkage after molding of polypropylene or polyethylene moldings is avoided. Since the label itself can be easily deformed while being attached, peeling of the label does not occur, and a label with strong adhesive strength can be obtained.

Therefore, even in the molding processing conditions for polypropylene and polyethylene, it is possible to set the resin temperature to a lower temperature side, or to lower the cooling temperature of the mold to shorten the molding cycle, which greatly improves productivity. It is possible to produce an integral molded product with a label attached thereto, which has an excellent appearance with little blister generation on the label of the resulting molded product, and has excellent adhesion between the label and the container.

[Detailed description of the invention]

[I] In-mold label 1) Structure The transparent in-mold label of the present invention may have a single layer or a two or more layer structure. However, if the resin forming the container and the material resin forming the label are of the same type, a single layer may be used, but if the material forming the label and the material forming the container are different types, heat-sensitive It has a structure of at least two layers, a base material layer and an adhesive layer. Moreover, the base material layer can also be formed as a multilayer structure of two or more layers.

(a) Base layer The material used for the single-layer label, or the base layer for labels with two or more layers, contains 80 to 97% by weight of propylene and 2 to 20% by weight of ethylene. ,
Random or block copolymers containing two or three types of butene-1 in an amount of 1 to 12% by weight, or a mixture thereof, can be mentioned.
Propylene-ethylene copolymer containing 20-5% by weight of ethylene, 80-95% by weight of propylene
% by weight, propylene-butene-1 copolymer containing 20-5% by weight of butene-1, 80-95% by weight of propylene and 0.9% by weight of ethylene. 5 to 12% by weight, butene-1 to 2
Propylene, ethylene, butene containing ~10% by weight
1 copolymer or a mixture thereof.

In addition, as monomers constituting these copolymer components,
In addition to the above propylene, ethylene, and butene-1, small amounts (0.5% to 5% by weight) of hexane-1 and pentene-1
Random or block copolymers containing one or more α-olefins such as , 4-methylpentene-1 and the like can be used.

Such a base material layer may be multilayered; however, in this case as well, a multilayer film is used in which the thickness of the base material layer accounts for 50% or less of the total thickness of the label.

If the base material layer has a multilayer structure, especially the layer on the side opposite to the adhesive layer described below, or if it has a three-layer structure, the center layer may be a polypropylene homopolymer or a polypropylene copolymer containing less than 5% by weight of ethylene or butene-1a-2. It may also be made of resin.

The thickness of these base layers is generally 50 to 250 μm, preferably 50 to 120 μm, and the opacity (J I 5-P8
138) is preferably 1096 or less.

(b) Adhesive layer When the in-mold label of the present invention is formed of two or more layers, the material used as the adhesive layer is 10°C or higher, preferably 15 to 100°C higher than the melting point of the molded material to be adhered. A thermoplastic resin having a low "C" melting point of 70-155"C, preferably 80-130"C is used.

For example, when the molded material to be bonded is a polypropylene resin, an ethylene resin such as low density polyethylene, ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, or a metal salt thereof is used. .

These thermosensitive resin adhesive layers are formed by extrusion lamination on the base material layer, or by coating a liquid obtained by dissolving these adhesive resins in a solvent using a gravure coater and drying.

In addition, when the molding material to be bonded is a polyethylene resin, an ethylene/vinyl acetate copolymer, an ethylene/acrylic acid copolymer, or a metal salt thereof, which has a lower melting point than the polyethylene resin, is used. .

These adhesive layers are embossed during lamination, and gravure patterns are applied during gravure coating to ensure good air escape between the label and the molten resin and prevent blistering. It is desirable to apply a coating method that leaves a residue on the surface.

In addition, the thickness of such an adhesive layer is generally 0.5μ ~
20μ, preferably 1μ to 15μ.

(e) Lamination When the label has a structure of two or more layers, an adhesive layer is laminated on the base layer. Lamination is generally carried out by extrusion lamination, gravure coating, or other methods.

(2) Printing There is a method in which printing is performed before the adhesive layer is provided on the base material layer and an adhesive layer is provided thereon, and a method in which printing is performed on the surface of the base material layer opposite to the adhesive layer.

Further, it is preferable that the printing layer surface of this base layer is previously subjected to corona discharge treatment or coated with an anchor coating agent such as polyethyleneimine, an antistatic agent, etc. in order to improve printing suitability.

Printing includes gravure printing, offset printing, flexo printing,
Printing can be performed on the adhesion layer side or on the opposite side using a printing method such as screen printing.

Detailed explanation of the invention In the case of labels, the same color as the color of the molded product is used as the label material, and is often printed on the side of the base material layer on which the adhesive layer is laminated. Since the printed surface is on the inside of the label, there are advantages such as the fact that when the product is made into a product, the printing ink does not fall off due to rubbing between the molded products or the box in which the molded products are placed.

(3) Label The transparent in-mold label thus formed has an opacity (J I 1-P8138) of 10% or less and a tensile modulus of 2,000 to 6. 000
kg/c-, so the label can easily cope with the shrinkage of the product after the molded product is molded and pasted, while the label itself is pasted. The label is firmly adhered to the surface of the molded product, making it difficult to peel off, and the label will not be deformed or blistered.

If the tensile modulus is less than 2,000 kg/c-, printing becomes difficult or it becomes difficult to automatically feed the label into a mold using a suction pad. On the other hand, the tensile modulus is 6
,000kg/c-, printing processability and label independence improve, but except for some container molding conditions, blistering occurs frequently, and processing conditions with good productivity (resin or mold High-speed production is not possible due to low cooling temperatures.

Furthermore, if the opacity (J 15-P8138) exceeds 1%, even beautiful printing becomes unclear, reducing the practicality of the label.

(II) Adhesion Molding methods used to integrally mold and adhere the transparent in-mold label of the present invention include generally known blow molding methods, injection molding methods, differential pressure molding methods, and in-mold It is based on a bead foam molding method, a press molding method, etc., and can be carried out in the same manner as known molding methods.

Specifically, in the case of the blow molding method, after inserting the label in advance with the adhesive layer side facing inside the inner wall surface of the mold, a parison of polypropylene resin or polyethylene resin melt-kneaded by an extruder is inserted into the mold. 180℃~23
After hanging at a temperature of 0°C and sealing one end by clamping the parison, 0.0°C is placed inside the parison. The parison is expanded by introducing compressed gas of 5-10 kg/cd G, preferably 2-5 kg/cd G.

As a result, the outer surface of the parison is pressed against the inner wall of the mold, and the parison is molded into a shape that follows the shape of the mold. After the parison is brought into contact and the resin of the adhesive layer of the label is melted to fuse the parison and the adhesive layer of the label, it is cooled and the mold is opened to obtain a blow-molded container with a label.

[Experimental Example] The transparent in-mold label of the present invention will be specifically described below with reference to Examples and Comparative Examples.

Example 1 Production of label base material layer (la) A polypropylene random copolymer with a melt flow rate (MFR) of 4f/10 minutes, 5% by weight of ethylene, and 95% by weight of propylene was placed in the die of an extruder set at 250°C. The film was extruded to a thickness of about 0.1 mm, and then cooled to 30°C to obtain an unstretched film.

Printing and production of adhesive layer (lb) After corona discharge treatment was applied to both sides of the base layer (A), an aqueous solution containing an acrylic antistatic agent and polyethyleneimine was applied at a coating amount of 0.1 g/nf. I applied it as desired. On one side of this base material layer (A), the contents of the container, the product name, the ingredients,
After printing the manufacturer, distributor, etc. with gravure ink, the printed surface is further coated with a coating amount of 3g using a gravure coater.
/rrr using a gravure roll to apply a solvent-type heat-sensitive adhesive (trade name: Toyo Morton Co., Ltd. Atcoat 33P5) containing ethylene/vinyl acetate copolymer as the main component.
After drying, a printed film with an adhesive layer was obtained.

Table 1 shows the physical properties of this film.

Manufacture of a label A label was manufactured by cutting the above-mentioned film into a length of 7C++* and a width of 901111.

Manufacture of Labeled Hollow Containers The label 1 was placed in a mold 3 of a molding machine 2 for manufacturing hollow molded containers shown in FIG. After fixing the label 1 to the inner wall 3a of the mold by a reduced pressure action, the polypropylene "Mitsubishi Norvenon MA-6J" manufactured by Mitsubishi Yuka Co., Ltd. (melting point -164°C,
MFR-0.8g/10 minutes) was extruded from the die 4 at a temperature of 210°C as a parison 5 with an inner diameter of 2C)+m and a wall thickness of 3mm, and after this parison 5 was sandwiched between the molds 3, it was extruded from the nozzle 6. Pressure 3. 5 kg/cm2 of compressed air is supplied into the parison 5 for blow molding, and the outer surface 5a of the parison 5 presses the label 1 to melt the adhesive layer 1b surface of the label 1, thereby attaching the label 1 to the parison 5. After the fusion, the mold 3 was cooled to 10°C to solidify the molded body, and the mold was opened, and the diameter of the body to which the label 1 was attached was 60+ m.
A hollow container with a height of 200 cities (wall thickness of 1 dragon) was obtained.

Furthermore, using the same method, high-density polyethylene manufactured by Mitsubishi Yuka ■ (
HDPE) r Mitsubishi Polyethylene BZ53A” 18
At a parison temperature of 0°C, Mitsubishi Yuka side paper manufacturing density polyethylene (LDPE) r Mitsubishi Polyethylene ZE41J was 155
It was carried out at a parison temperature of 0.degree. C. to obtain labeled hollow containers.

Table 1 shows the results of testing the obtained labeled hollow containers for the occurrence of blisters, the capsule shape of the label, and the adhesive strength of the label.

Note that these tests were conducted by the following method.

For each blister measurement container, 5 points are given for those with blister formation or no blisters on the attached label, 4 points are given for those with blister formation on less than 10% of the label area, and 4 points are given for those with blister formation on 10% or more of the label area.
Items with blisters occurring in less than 20% of the area are classified as 3.
A total of 20 points for containers, with 2 points for containers with blisters on an area of 20% or more but less than 50%, and 1 point for containers with blisters on an area of 50% or more. It was evaluated by

Adhesion strength between label and container The portion of the container to which the label was attached was cut to a width of 15 mm, and the peel strength of the label was measured using a tensile tester.

Examples 2 to 4 and Comparative Example 1.2 A polypropylene resin film having the composition shown in Table 1 was produced as the base layer 1a by the same method as the label base layer film of Example 1, and other adhesive layers were A label was produced using the same printing method as in Example 1. Table 1 shows the physical property values of the label and the test results of the labeled hollow container.

Example 5 Production of label base material layer (la) Polypropylene homopolymer (A) with a MFR of 4 g/10 minutes was supplied to an extruder set at 250°C, and a separate extruder set at 250°C MFR4g/1 for extruder
A propylene-ethylene-butene-1 ternary random copolymer consisting of 85% by weight of propylene, 10% by weight of ethylene, and 15% by weight of butene is supplied, and both resins discharged from both extruders are A three-layer film is extruded in the die, with a polypropylene homopolymer as an intermediate layer and the propylene-ethylene-butene-1 terpolymer laminated on the front and back surfaces, and then, It was cooled to 30°C using a cooling roll to obtain a label base material with a three-layer structure. At this time, the thickness of the intermediate layer was 30 μm, and the thicknesses of the layers on both sides were each 30 μm, yielding a label base material with a total thickness of 90 μm.

Production of adhesive layer (1b) An ethylene/methyl acrylate copolymer resin (melting point 90 ℃) was laminated using an extruder set at 200°C to a thickness of 15 μm. 2 at the same time as laminating
The adhesive layer was cooled using a gravure-type embossing roll with 00 lines, and the surface of the adhesive layer was embossed. Table 1 shows the physical properties of this film.

Printing and label production After cutting the film into 636 squares vertically and 470 square meters horizontally, offset printing is performed on the opposite side to the embossed surface using a sheet-fed offset printing machine, and then 70 squares vertically and 90 mm horizontally.
A label was obtained by cutting it to the desired size.

This labeling was carried out in the same manner as in Example 1 to obtain a labeled hollow container. The results are shown in Table 1.

Example 6 A label was obtained in the same manner as in Example 5, except that the composition of the resin used in the base layer of Example 5 was changed to a propylene/ethylene binary random copolymer resin having the composition shown in Table 1.

This label was applied in the same manner as in Example 1 to obtain a labeled hollow container. The results are shown in Table 1.

Example 7 A propylene-ethylene binary random copolymer containing 98% by weight of propylene with a MFR of 4 g/10 min and 2% by weight of ethylene was fed into an extruder set at 250°C, and the extruder and another 250"C Propylene 9 into the extruder set to
Propylene containing 5% by weight and 5% by weight of ethylene.
The ethylene binary random copolymer is supplied, and both resins discharged from both extruders are supplied to one die, extruded in the die into a sheet shape, and then cooled to 30°C to form two layers. A structured film was obtained.

Next, the adhesive layer produced in Example] was laminated on the propylene/ethylene binary random copolymer resin layer side containing 95% by weight of propylene and 5% by weight of ethylene, but the same as in Example 1. I got the label using this method.

A hollow container was obtained by applying this label in the same manner as in Example 1. The results are shown in Table 1.

[Brief explanation of the drawing]

Figure m1 is a sectional view of a molding machine used in the method for manufacturing a labeled blow-molded container according to an example of the present invention. DESCRIPTION OF SYMBOLS 1... Label, 1a... Base material layer, 1b... Adhesive layer, 6... Nozzle, 2... Molding machine for blow molded container manufacturing, 3... Mold, 3a... Mold inner wall, 4... die,
5...Parison, 5a...Outer surface of the parison.

Claims (1)

[Claims] 1. Opacity is 10% or less and tensile modulus is 2,000
A transparent in-mold label characterized by being a resin film of ~6,000 kg/cm^2. 2. The resin film is a propylene/ethylene copolymer containing 80 to 95% by weight of propylene and 20 to 5% by weight of ethylene, or a propylene/butene copolymer containing 80 to 95% by weight of propylene and 20 to 5% by weight of butene. At least one polymer selected from a copolymer or a propylene/ethylene/butene copolymer containing 80 to 95% by weight of propylene, 0.5 to 12% by weight of ethylene, and 2 to 10% by weight of butene. The transparent in-mold label according to claim 1.