JP2002032024A - Heat shrinkable polyester label having excellent recyclability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat shrinkable polyester label which allows the sure desorption and removal of printing ink under mild conditions. SOLUTION: This heat shrinkable polyester label is a heat shrinklable polyester label formed by providing at least one surface of a base film with a printing layer. This base film consists of a heat shrinkable polyester-base film containing 2 to 20 wt.% polyalkylene glycol unit. The printing layer described above is formed by ink consisting of vehicle resins essentially consisting of a styrene- acrylic copolymer and/or styrene-maleic acid copolymer. An aqueous alkaline solution is brought into contact with such heat shrinkable polyester label, by which the printing layer may be surely desorbed under the mild conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester label excellent in recyclability and a method for removing ink from the label.

[0002]

2. Description of the Related Art Heat-shrinkable polyester labels can be used to protect containers and enhance the printing effect by closely covering various containers such as bottles (including glass and plastic bottles) and cans. Are known.

In recent years, the recycling of plastic resources has been promoted. However, when a heat-shrinkable polyester label having a printed surface is recycled, the ink must be removed in advance. As such a method of detaching ink, Japanese Patent Application Laid-Open No. 11-301885 discloses a method in which a label provided on a polyester-based heat-shrinkable film is dipped in alkaline hot water to remove the ink layer in alkaline water. A method of removing is disclosed. JP-A-11-209677 discloses an alkaline aqueous solution-releasable ink composition containing a urethane-based resin or the like and a styrene-acrylic acid copolymer or the like,
The examples describe an example in which this ink composition was printed on a heat-shrinkable polyethylene terephthalate (PET) film. However, in the examples described in these documents, the ink releasability is not sufficient. In addition, a high-temperature and high-concentration alkaline aqueous solution is required for detachment of the ink.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heat-shrinkable polyester label capable of reliably removing and removing printing ink under mild conditions, and a method for removing ink from the label. Is to provide.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, printed on a base film made of a specific resin with an ink containing a specific resin as a main component of a vehicle resin. In the case of a heat-shrinkable polyester label, it has been found that the printing ink can be easily removed and removed simply by contacting with a low-concentration alkaline aqueous solution at a relatively low temperature, and the present invention has been completed.

That is, the present invention relates to a heat-shrinkable label having a printed layer provided on at least one surface of a base film, wherein the base film contains 2 to 20% by weight of a polyalkylene glycol unit. A heat-shrinkable polyester label comprising a polyester film, wherein the printing layer is formed of an ink containing a styrene-acrylic acid copolymer and / or a styrene-maleic acid copolymer as a main component of a vehicle resin. .
The present invention also provides a method of releasing ink from a label, comprising contacting the heat-shrinkable polyester label with an alkaline aqueous solution to release a printing layer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The base film in the present invention contains 2 to 20% by weight of a polyalkylene glycol unit,
It is preferably composed of a heat-shrinkable polyester film containing 3 to 15% by weight.

Examples of the polyalkylene glycol include polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, polyhexamethylene glycol and the like.
These polyalkylene glycols can be used alone or in combination of two or more. The molecular weight of the polyalkylene glycol unit is not particularly limited, but is preferably 5
It is about 100 to 50,000, more preferably 100
It is about 0 to 30,000.

When the amount of the polyalkylene glycol unit exceeds 20% by weight based on the total weight of the polymer (polyester), the releasability of the ink is improved, but the physical properties (for example, gloss etc.) when used as a label are reduced. Has a negative effect. On the other hand, when it is less than 2% by weight,
Stable ink releasability cannot be obtained.

As the diol component of the polyester constituting the polyester film, in addition to the above-mentioned polyalkylene glycol, for example, ethylene glycol,
Propylene glycol, 1,3-propanediol,
2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2,2
-Diethyl-1,3-propanediol, 2-ethyl-
2-butyl-1,3-propanediol, 2-ethyl-
2-isobutyl-1,3-propanediol, 1,3-
Butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2
4-trimethyl-1,6-hexanediol, 2-ethyl-2,4-dimethyl-1,3-hexanediol,
Aliphatic diols such as 1,8-octanediol, 1,10-decanediol, diethylene glycol, dipropylenediol; 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, Alicyclic diols such as 2,2,4,4-tetramethyl-1,3-cyclobutanediol; 2,2-bis (4 '-. Beta.-hydroxyethoxydiphenyl) propane and bis (4'-. Beta.-hydroxyethoxyphenyl) A) Ethylene oxide adducts of bisphenol compounds such as sulfone; and aromatic diols (including phenols) such as xylylene glycol. These diol components can be used alone or in combination of two or more.

Among the diol components other than the above polyalkylene glycols, aliphatic diols such as ethylene glycol and diethylene glycol and alicyclic diols such as 1,4-cyclohexanedimethanol are preferred.

The dicarboxylic acid component of the polyester constituting the polyester film includes, for example, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and substituted products thereof; 1,4-cyclohexanedicarboxylic acid and the like. Alicyclic dicarboxylic acids; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and substituted products thereof. These dicarboxylic acid components can be used alone or in combination of two or more.

Of the above dicarboxylic acids, terephthalic acid is preferred in terms of heat resistance and versatility. For example, the ratio of terephthalic acid to the total dicarboxylic acid component is 70 to 10
The range is about 0% by weight, preferably about 80 to 100% by weight.

The polyester is prepared by a conventionally known method, for example, a direct esterification method in which a diol component and a dicarboxylic acid component are directly reacted, and an ester exchange method in which an ester such as a methyl ester of a dicarboxylic acid component is reacted with a diol component. Can be manufactured. The heat-shrinkable polyester film can be composed of one or more polyesters.

The base film in the present invention can be produced by a known film forming method. For example, a resin composition containing the above polyester and, if necessary, additives such as a lubricant (titanium dioxide, finely divided silica, kaolin, calcium carbonate, etc.), an antistatic agent, an antioxidant, an ultraviolet absorber, and a coloring agent. The product is formed into a film by extrusion or the like, and then subjected to a stretching treatment to obtain a base film.

The stretching is usually performed by a tenter method. The stretching treatment is performed, for example, by stretching at a temperature of about 70 to 100 ° C. in the width direction (horizontal direction; TD direction) by 2.5 to 5.0 times, preferably about 3.0 to 4.5 times. Will be
Further, if necessary, a stretching process can be performed at a low stretching ratio (for example, about 1.0 to 2.0 times) in the length direction (longitudinal direction; MD direction), for example. Note that heat setting or elongation may be performed before or after the stretching treatment. The base film in the present invention thus includes a uniaxially oriented film stretched in only one direction, and a biaxially oriented film stretched mainly in one direction and slightly stretched in a direction perpendicular to the direction. It is. The base film thus obtained has orientation in the width direction (mainly the direction in which the stretching treatment is performed), and exhibits large heat shrinkability in the direction.

The heat shrinkage of the base film in the main shrinkage direction (warm water: 80 ° C. × 10 seconds) is preferably 30% or more from the viewpoint of shrink adhesion to various containers. The base film may be a single layer or a laminate of two or more layers. The thickness of the base film can be appropriately set in consideration of the application and handling properties, etc., but is generally 10 to 100 μm, preferably 20 to 60 μm.
It is about μm. Further, the surface of the base film may be subjected to a surface treatment such as a corona treatment in order to prevent the ink layer from peeling off before the ink desorption treatment.

The printing layer in the present invention is formed of an ink containing a styrene-acrylic acid copolymer and / or a styrene-maleic acid copolymer as a main component of a vehicle resin. Here, “vehicle” is a general term for a mixture of a resin, a solvent, and a plasticizer, and “vehicle resin” represents only the resin in the vehicle.

The styrene-acrylic acid copolymer may be any copolymer containing styrene and acrylic acid as comonomers, for example, 20 to 40% by weight of styrene, 5 to 15% by weight of methyl methacrylate, and acrylic acid. Copolymers containing 10 to 30% by weight of an alkyl acrylate such as butyl and 10 to 20% by weight of acrylic acid as a monomer component are exemplified. The acid value of the styrene-acrylic acid copolymer is, for example, about 100 to 240, the molecular weight is, for example, about 1600 to 20,000, and the glass transition temperature (Tg)
Is, for example, about 60 to 85 ° C.

Examples of the styrene-maleic acid copolymer include a polymer obtained by copolymerizing styrene with a maleic acid derivative such as maleic anhydride or maleic acid ester, or a derivative thereof (hydrolyzate or the like). Typical examples are styrene-maleic anhydride copolymer, styrene-
And maleic acid monoester copolymer. The acid value of the styrene-maleic acid copolymer is, for example, 180 to 280.
Degree and molecular weight of 2000 to 70000 (preferably 20
00 to 20000), and the glass transition temperature (Tg) is
Preferably it is about 60 to 70 ° C.

[0021] The vehicle resin of the ink used for forming the printing layer may contain a resin other than the styrene-acrylic acid copolymer and the styrene-maleic acid copolymer. As such a resin, a resin used for gravure printing or flexographic printing, for example, urethane resin, acrylic resin, chlorinated polyolefin, polyamide resin, coumarone resin, ketone resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, Examples include urea resin, cellulose resin, ethylene-vinyl acetate resin, polyester resin, chlorinated rubber, and cyclized rubber. The ratio of the styrene-acrylic acid copolymer and / or the styrene-maleic acid copolymer in the resin constituting the vehicle is, for example, about 50 to 100% by weight, preferably 60% by weight.
About 100% by weight. If this proportion is less than 50% by weight, the detachability of the ink when immersed in an alkaline aqueous solution is poor.

As the solvent used for the ink, a solvent usually used for gravure printing or flexographic printing, for example,
Aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane; aromatic hydrocarbons such as toluene and xylene; alcohols such as methanol, ethanol and isopropyl alcohol; esters such as ethyl acetate, isopropyl acetate and butyl acetate Ketones such as acetone and methyl ethyl ketone; glycols such as ethylene glycol and propylene glycol; glycol ethers such as propylene glycol monomethyl ether and propylene glycol monobutyl ether; glycol ether esters such as propylene glycol monomethyl ether acetate; water; No.

The ink may further include, if necessary, a colorant such as a pigment, an extender pigment, a wax, a plastic fine powder,
Additives such as a plasticizer, a weathering agent, an optical brightener, a lubricant, a crosslinking agent, a surfactant, a stabilizer and an antifoaming agent are compounded.

The heat-shrinkable polyester label of the present invention comprises:
The base film can be manufactured by printing a desired image, character, or the like on at least one surface of the base film by a conventional printing method such as gravure printing or flexographic printing to form a print layer. Among the printing methods, gravure printing is preferable.
The printing layer may be either a single layer or a multilayer depending on its design or the like. The thickness of the printing layer can be appropriately selected depending on the application and the like, but is generally about 1 to 10 μm.

After the printing layer is formed, it is cut into a long strip having a desired width, for example, with the printing surface inside, the main orientation direction of the base film becomes the circumferential direction, and After rounding into a cylinder so that the direction perpendicular to the length direction is the length direction, and bonding both ends with a solvent or adhesive,
By cutting to a desired length as required, a cylindrical shrink label can be obtained. This cylindrical shrink label is supplied to an automatic label mounting apparatus, cut into a required length, and then, to be mounted (eg, a plastic or glass bottle such as a PET bottle, etc.) ), The shrink label can be attached to the object by being thermally shrunk by passing through a steam tunnel at about 80 to 100 ° C. or a hot air tunnel at about 100 to 200 ° C.

In the ink detachment method of the present invention, the printing layer is detached by bringing an alkaline aqueous solution into contact with the heat-shrinkable polyester label of the present invention.

The size of the label to be subjected to the ink desorption process can be appropriately set within a range that does not impair the processing efficiency and the like, and may be the same size as when the adherend is attached.
What is crushed or cut into about 10 mm square is used. In addition, the label is usually subjected to the ink detaching process in a state where it is peeled off from the adherend such as a container, but may be subjected to the ink detaching process in a state where it is attached to a container or the like. In the latter case, it is preferable to pulverize or cut a labeled container or the like and then subject it to the above treatment.

The alkaline aqueous solution is not particularly limited, but typical examples thereof include an aqueous solution of an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, an aqueous solution of an alkali metal carbonate such as sodium carbonate, and hydrogen carbonate. An aqueous solution of an alkali metal hydrogencarbonate such as sodium, aqueous ammonia, and the like can be given. The alkaline aqueous solution may contain a small amount of a water-miscible organic solvent as necessary.

The concentration of the alkaline substance in the alkaline aqueous solution can be appropriately selected within a range that does not impair the releasing ability, operability, workability, and the like of the printing layer, and varies depending on the type. %, Preferably 0.3 to 5%
%, More preferably about 0.5 to 3% by weight. In the present invention, there is an advantage that the printing layer is smoothly separated even with a low-concentration alkaline aqueous solution. The pH of the alkaline aqueous solution is, for example, 8 or more, preferably 9 or more.

The treatment temperature with the alkaline aqueous solution is, for example, 1 in consideration of the desorption efficiency of the printed layer, operability, workability, and the like.
Although it can be appropriately selected within the range of 00 ° C. or less, in the present invention, since the print layer has excellent detachability, the print layer can be removed and removed within a short time even at a relatively low temperature of about 40 ° C. to 70 ° C. it can. The processing time is preferably within 30 minutes, particularly preferably within 20 minutes. The amount of the alkaline aqueous solution can be appropriately selected depending on the size of the label and the like, but is generally about 200 to 20,000 parts by weight based on 100 parts by weight of the label.

The method for bringing the heat-shrinkable polyester label into contact with an alkaline aqueous solution is not particularly limited. For example, a method of immersing the label in an alkaline aqueous solution,
A method of spraying an alkaline aqueous solution onto the label is employed. The ink desorption treatment with the alkaline aqueous solution can be performed by any method such as a batch method, a continuous method, and a multi-stage method. The alkaline aqueous solution used for the treatment may be recycled.

The label from which the printed layer has been detached and removed is usually subjected to washing and drying steps, and then recycled. In the case where the label is subjected to the ink desorption treatment together with the adherend such as a bottle, when the base film of the label and the material of the adherend are the same type of polymer as in a PET bottle, these are removed. It can be recovered and reused by melting without separation and pelletizing.
When the base film of the label and the material of the adherend are different polymers, they can be separated by liquid specific gravity separation, wind specific gravity separation, or the like, and can be subjected to a recovery step.

The method of the present invention is widely applicable to the removal of a printed layer of a heat-shrinkable polyester label attached to various adherends such as a plastic container, a glass container and a metal container. It is useful for removing a printed layer of a heat-shrinkable polyester label attached to a plastic container such as a PET bottle, which is highly demanded for recycling.

[0034]

According to the present invention, since printing is performed on a base film made of a specific resin with an ink containing a specific resin as a main component of a vehicle resin, the printing ink can be reliably applied under mild conditions. It can be desorbed and removed.

[0035]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 85 mol parts of terephthalic acid, 10 mol parts of isophthalic acid, 5 mol parts of adipic acid, and 140 mol parts of ethylene glycol were placed in a reaction vessel, and polymerized by a direct polymerization method to complete the esterification step. 450 ppm of antimony trioxide as a polymerization catalyst based on all acid components, and 100 ppm of trimethyl phosphate as a stabilizer based on all acid components.
Further, 5% by weight of polyethylene glycol (weight average molecular weight: 4000) was added to the polymer, and 0.05% by weight of tetrakis [methylene-3- (dodecylthio) propionate] methane was added to the polymer. Was carried out to obtain a polyester resin having an intrinsic viscosity (IV) of 0.78. This resin was supplied to a twin-screw extruder, melt-extruded at 260 ° C. while dehumidifying from a vent port, and formed into a sheet with a T-type die. This sheet was inserted into a tenter oven, stretched 4.5 times in the width direction with hot air at 80 to 85 ° C., and then gradually cooled to produce a heat-shrinkable polyester film having a thickness of 50 μm. The heat shrinkage in the width direction of this film was 35% when soaked in warm water at 80 ° C. for 10 seconds.
An ink containing a styrene-acrylic acid resin as a main component of the vehicle resin was gravure-printed on one surface of the film to prepare a heat-shrinkable polyester label, and printability and recyclability were evaluated by the following methods.

Example 2 Except that 80 mol parts of terephthalic acid, 16 mol parts of isophthalic acid and 4 mol parts of sebacic acid were used as dicarboxylic acids, and polyethylene glycol (weight average molecular weight 3000) was added at 4% by weight to the polymer. A heat-shrinkable polyester film having a thickness of 45 μm was produced in the same procedure as in Example 1. The heat shrinkage in the width direction of this film is 80
It was 37% when soaked in ° C for 10 seconds. An ink containing a styrene-maleic acid resin as a main component was gravure-printed on one surface of the film to prepare a heat-shrinkable polyester label, and printability and recyclability were evaluated by the following methods.

Comparative Example A heat-shrinkable polyester film having a thickness of 50 μm was prepared in the same manner as in Example 1 except that polyethylene glycol was not used. The heat shrinkage in the width direction of this film was 33% when immersed in warm water at 80 ° C. for 10 seconds. On one surface of this film, gravure printing of an ink containing styrene-acrylic acid resin as a main component of a vehicle resin,
A heat-shrinkable polyester label was prepared, and printability and recyclability were evaluated by the following methods.

(Evaluation method) Printability: After adhering Nichiban cellophane tape to the printed surface of the label, it was rapidly peeled off, and the printed peeled state was visually evaluated. Of 10% or less was judged as good, and more than 10% was judged as bad. Table 1 shows the results. Recyclability: Label test pieces (length and width 10cm) at 60 ° C
Was immersed in a 1 L beaker containing a 0.5% by weight aqueous solution of caustic soda, stirred for 15 minutes with a glass rod, and the area of the detached printing ink was visually measured. This measurement was carried out 10 times under the same conditions, and when 80% or more of the detached printing ink was 8 times or more of the test piece surface, it was judged as good, and when it was 7 times or less, it was judged as bad. Table 1 shows the results.

[0040]

[Table 1]

Claims (2)

[Claims] 1. A heat-shrinkable label having a printing layer provided on at least one surface of a base film, wherein the base film comprises two to two polyalkylene glycol units.
The printing layer is formed of an ink containing a styrene-acrylic acid copolymer and / or a styrene-maleic acid copolymer as a main component of a vehicle resin. Heat shrinkable polyester label. 2. A method for removing ink from a label, comprising: contacting the heat-shrinkable polyester label according to claim 1 with an alkaline aqueous solution to remove a printing layer.