JP7611069B2 - label - Google Patents

Description

This invention relates to roll labels that use polyethylene as the base layer.

Conventionally, various kinds of labels have been attached to bottles for beverages, etc., for the purpose of displaying contents or for decoration. Known types of labels include shrink labels, which are shrunk to fit tightly to the bottle, and roll labels, which are formed into a roll, wrapped around the bottle, cut to a predetermined length, and fixed to the bottle with a hot melt adhesive.
Roll labels made of polypropylene or polyethylene film are known as label substrates, and have the advantage that they can adapt to the flexibility of the bottles to which they are attached (Patent Document 1).
It is also known that when a label uses an opaque white or milky film as a substrate rather than a transparent one, the light-shielding properties, concealment properties, and cosmetic properties can be improved (Patent Documents 2 and 3).

JP 2005-037593 A WO2004/094139 Pamphlet Japanese Patent Application Publication No. 06-102826 JP 2012-177903 A

When wrapping a roll label around a beverage bottle, a hot melt adhesive is generally used.
When a film with low heat resistance, such as a polyethylene film, is used as the label substrate, when the hot melt adhesive is applied, the hot melt adhesive is so hot that wrinkles and curls often occur in the applied area.

To prevent curling, a method has been disclosed in which a nitrocellulose-based coating is applied to the outer surface of a shrink label to prevent curling that occurs during thermal shrinkage (Patent Document 4).

When the above-mentioned white or milky opaque film is used as the label substrate, inorganic substances are often added to the film. This creates minute irregularities on the surface, which tends to reduce the adhesion between the film and these materials when processing such as coating or lamination is performed. This limits the materials that can be used.

Therefore, the objective of this invention is to obtain a roll label that uses a substrate made of polyethylene, which has low heat resistance, and has improved adhesion between the film and the material that improves heat resistance and suppresses the occurrence of wrinkles and curls, even when an opaque white or milky white substrate is used.

This invention solves the above problems by forming a specific coating layer on one side of a base layer made of polyethylene, and the gist of the invention is as follows: [1] to [4]

[1] A label having a coating layer containing nitrocellulose formed on one side of a base layer made of a polyethylene resin, and the coating layer containing an adhesion enhancer to improve adhesion to the base layer in an amount of 0.5% by weight or more and 15% by weight or less relative to the nitrocellulose.
[2] The label described in [1], wherein the adhesion improver is at least one selected from polystyrene-based polymers and fatty acid amides.

[3] A label according to [1] or [2], wherein the coating amount of the coating layer is 0.2 g/m2 or ^more and 7.0 g/m2 ^{or less} in terms of solid content.
[4] The label according to any one of [1] to [3], wherein the surface roughness (Sa) of the base material layer is 0.3 μm or more and 1.0 μm or less.

The label according to this invention has a coating layer containing nitrocellulose, and this coating layer contains an adhesion improver, so even if polyethylene, which has low heat resistance, is used as the label substrate, and even if the substrate is opaque, such as white or milky white, it is possible to improve heat resistance, suppress the occurrence of wrinkles and curls, and improve adhesion between the substrate and the coating layer.

The present invention will be described below.
The present invention relates to a label having a base layer made of a polyethylene resin and a predetermined coating layer formed on one surface of the base layer.

<Base layer>
The base layer may be a film-like material such as a film or sheet made of a polyethylene resin. Examples of the polyethylene resin include ethylene homopolymers such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and ethylene copolymers such as ethylene-propylene copolymers. The ethylene content of the ethylene copolymer is not particularly limited, but is preferably 50% by weight or more when the objective is to exhibit flexibility.

The base layer may be a film-like material having low transparency or being opaque, specifically, a semi-transparent, white or milky white color. Since inorganic substances or the like are generally added to such film-like materials, fine irregularities tend to occur on the surface.
Examples of the inorganic substances include silica, alumina, talc, and titanium oxide.

The degree of transparency of the base layer is closely related to the surface roughness of the base layer, which can be expressed by the arithmetic mean height (Sa), which is an index representing three-dimensional surface properties (surface roughness) and indicates the difference in height from the average plane of each measurement point in a reference area.
The surface roughness (Sa) of this substrate layer is preferably 1.0 μm or less, and preferably 0.8 μm or less. If it is greater than 1.0 μm, sufficient adhesion between the substrate layer and the coating layer may not be obtained even if the present invention is used. Also, it is preferably 0.3 μm or more, and preferably 0.4 μm or more. It may be less than 0.3 μm, but there is a tendency that the adhesion between the substrate layer and the coating layer is good even without using the present invention, and in order to clearly exert the effect of the present invention, 0.3 μm or more is preferable.

The thickness of this base layer is preferably 10 to 80 μm, and more preferably 30 to 50 μm. If the thickness is less than 10 μm, the strength as a label is insufficient. If the thickness is more than 80 μm, handling when attaching to a bottle becomes difficult and there is a disadvantage in terms of cost.
The substrate is formed into a film or sheet by a known method, for example, by heating and melting the constituent resin of the substrate layer, continuously extruding it through a T-die, a circular die or the like, and then cooling it.

<Coat layer>
The coating layer is a layer disposed to prevent the base layer from wrinkling or curling when it is subjected to heat, and contains nitrocellulose as a main resin.
When the surface roughness (Sa) of the substrate layer is large, the coating layer may not adhere well to the substrate layer. Therefore, the coating layer contains an adhesion improver for improving adhesion to the substrate layer.

The adhesion improver is at least one selected from polystyrene-based polymers and acid amide compounds. Examples of the polystyrene-based polymer include polystyrene, which is a homopolymer of styrene, and copolymers of styrene and other monomers, such as styrene-acrylic copolymers.

Examples of the monomer include acrylic monomers and vinyl esters.
Examples of the acrylic monomer include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, and cyclohexyl (meth)acrylate, and (meth)acrylic acid. Examples of the vinyl esters include vinyl acetate.
In this specification, "(meth)acrylic" means "acrylic or methacrylic".

The number average molecular weight of the polystyrene polymer is preferably 50,000 to 400,000, and more preferably 100,000 to 300,000. If the number average molecular weight is within this range, the polymer can fully exert its effect as an adhesion improver.

The acid amides include carboxylic acid amides such as fatty acid amides. Examples of fatty acid amides include stearic acid amide, oleic acid amide, and erucic acid amide.

The content ratio (=addition amount) of the adhesion improver to the nitrocellulose contained in the coating layer is preferably 0.5% by weight or more, and preferably 1% by weight or more. If it is less than 0.5% by weight, the adhesion between the base layer and the coating layer may decrease. Also, it is preferably 15% by weight or less, and preferably 10% by weight or less. If it is more than 15% by weight, there is a risk of problems such as wrinkles and curls occurring easily when exposed to heat.

<Coating of Coating Layer>
The label according to the present invention can be produced by coating the coating layer on the base layer. Specifically, the components constituting the coating layer are dissolved in a solvent such as ethyl acetate, the obtained coating layer liquid is coated on the base layer, and then the label is dried to volatilize the solvent.
The amount of the solvent added to the coating layer is preferably an amount that allows the coating layer liquid to be coated on the base layer. The coating method is not particularly limited, and examples thereof include a bar coater, a gravure coater, a roll coater, and a die coater.
The amount of the coating layer applied to the substrate layer is preferably 0.2 g/m2 or ^more , and more preferably 0.5 g/m2 or ^more , in terms of solid content. If it is less than 0.2 g/ ^m2 , the substrate may wrinkle or curl when heat is applied. Also, it is preferably 7.0 g/ ^m2 or less, and more preferably 5.0 g/m2 or ^less . If it is more than 7.0 g/m2, coating becomes difficult, and even if the coating amount is more than 7.0 g/ ^m2 , the effect is not improved, so there is a possibility that the coating amount will be wasted.

<Label>
The label according to the present invention can be produced by the following method.
First, the coating layer liquid is coated on one surface of the base layer, and then the coating layer liquid is dried to volatilize the solvent, thereby forming a coating layer on one surface of the base layer.
Next, a printing layer is provided on the surface of the base layer on which the coating layer is not formed. This printing layer is a layer for forming a design that explains the product to be put into the bottle to which the label is attached and promotes the desire of the purchaser for the purpose of displaying the contents and decoration. Of this printing layer, the part that displays the design and contents that match the contents of the container (hereinafter, sometimes referred to as the "printed pattern") is formed using ink containing pigments and dyes of each color.
The ink used for this printing layer is not particularly limited, and general inks can be used. Methods for forming such a printing layer include printing using a gravure printer or a flexographic printer. The portion of the printing layer other than the printing pattern is an unprinted portion.

Compared to applying a single-color print to the entire label surface as the printing layer, using a translucent, white, or milky white film-like material for the base layer can partially simplify the printing process and reduce costs.

<Attaching the label according to the present invention to the bottle>
The resulting label is a roll label that is attached to the bottle by a hot melt adhesive.
Specifically, a roll of label is cut to the length of the entire side wall of one bottle, and a hot melt adhesive is melt-applied to the starting and ending portions of the back surface of the label, so that the starting portion is attached to the side wall of the bottle. The label is then wrapped around the side wall of the bottle, and the ending portion is attached on top of the starting portion of the label. This allows the label to be attached so as to cover the side wall of the bottle.

The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples.
First, the raw materials and evaluation methods used in the present examples and comparative examples will be described.

<Ingredients>
[Base layer]
High density polyethylene film...Senba Chemical Industries, Ltd.: New Super Power Pack, containing titanium oxide, milky white, thickness: 40 μm, surface roughness (Sa): 0.5 μm, hereinafter referred to as "HDPE".
Calcium carbonate-containing film... LIMEX (registered trademark), manufactured by TBM, thickness: 25 μm, hereinafter referred to as "LIMEX".
Starch-containing film...Kobayashi Co., Ltd.: Pyriru (registered trademark), thickness: 40 μm, hereinafter referred to as "Pyriru".

[Coat layer]
[Main resin]
Nitrocellulose...Sakata Inx Corporation: XGS-4510 OP Varnish Kai 2, printing varnish, hereinafter referred to as "CN".
[Adhesion improver]
Polystyrene...Kishida Chemical: Reagent, chemical grade, polymerization degree: 2400, hereinafter referred to as "PS".
Styrene-acrylic copolymer... Seiko PMC Co., Ltd.: PE-1304, hereinafter referred to as "PSA".
Erucic acid amide...reagent manufactured by Tokyo Chemical Industry Co., Ltd., purity: >85%, hereinafter referred to as "EA".
Polyacrylic acid...JE-1056 manufactured by Seiko PMC Co., Ltd., hereinafter referred to as "PA".
Polyurethane: Yuriano 3262, manufactured by Arakawa Chemical Industries, Ltd., hereinafter referred to as "PU".

<Evaluation method>
[Surface roughness (Sa)]
A laser microscope (manufactured by Olympus Corporation, "LEXT OLS5000") was used as the measuring instrument, and the measurement was carried out in accordance with ISO25178.

[Coat layer adhesion (Cerropic test)]
A test piece (300 mm x 250 mm) of each Example or Comparative Example was fixed to a 450 mm x 300 mm glass plate with tape so that the coating layer of the test piece was on the surface, and immediately after applying a 24 mm wide cellophane tape (Nichiban Co., Ltd., product name: CT405AP-24) to the coating surface, the tape was peeled off in a direction perpendicular to the glass plate and the peeling of the coating layer was evaluated visually. The evaluation criteria, scoring, and evaluation are as shown below. The coating layer adhesion is preferably evaluated as 3 points or more, and more preferably 4 points or more. This series of operations was repeated three times and the average score was calculated to be an index of the coating layer adhesion.
・1...There is a large area of peeling of the coating layer.
・2...There are spots of coating layer peeling off.
・3... Small dots of coating layer peeling off.
・4...There is slight peeling of the coating layer.
・5...No coating peeling.

[Appearance after heating]
A test piece of each Example or Comparative Example was cut to 70 mm x 50 mm, and the coating layer was heated at a position 5 mm away from the end of the test piece using a heat sealer (Tester Sangyo Co., Ltd., product name: TP-701-B Heat Seal Tester, seal width: 10 mm, pressure: 1 kgf, heating temperature: 130°C, heating time: 0.1 seconds), and the appearance after heating was evaluated visually. The evaluation criteria, scoring, and evaluation are as shown below. The appearance after heating is preferably evaluated as 3 points or more, and more preferably 4 points or more. This series of operations was repeated 3 times, and the average score was calculated and used as an index of the appearance after heating.
・1... Melting, or significant curling or thermal shrinkage is observed.
・2...Significant curling or thermal shrinkage is observed in some areas.
・3...Small curling or thermal shrinkage is observed in some areas.
・4... Slight curling or thermal shrinkage is observed.
・5...No curling or thermal shrinkage is observed.

(Examples 1 to 17, Comparative Examples 1 to 9)
The adhesion improver shown in Table 1 was diluted with tetrahydrofuran to 50% by mass, and the mixture was stirred while being heated to 80° C. until it was completely dissolved.
Next, the adhesion improver dissolved in tetrahydrofuran was mixed with a nitrocellulose-based main resin shown in Table 1, and the mixture was diluted with ethyl acetate so that the total solids concentration was 20% by mass. The mixture was then coated on the surface of a film substrate (size: 300 mm x 250 mm) shown in Table 1 using a bar coater to achieve the coating amount shown in Table 1.
The coated label was then dried at 100° C. for 1 minute in a hot air dryer to produce a label having a coating layer. The above-mentioned tests were carried out using the resulting test piece. The results are shown in Table 1.

Claims (3)

A coating layer containing nitrocellulose is formed on one surface of a base layer made of a polyethylene resin,
The coating layer contains an adhesion improver for improving adhesion to the base layer in an amount of 0.5% by weight or more and 15% by weight or less based on the weight of nitrocellulose,
The adhesion improver is at least one selected from polystyrene-based polymers and fatty acid amides . The label according to claim 1 , wherein the coating layer has a coating amount of 0.2 g/m ² or more and 7.0 g/m ² or less in terms of solid content. The label according to claim 1 or 2 , wherein the surface roughness (Sa) of the base material layer is 0.3 μm or more and 1.0 μm or less.