JP5530668B2 - Adhesive sheet for printing - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive sheet for printing, and more specifically, has a coating layer for printing on one surface of a biaxially stretched base material sheet for improving adhesion to printing ink, and the other side. A pressure-sensitive adhesive sheet for printing having a pressure-sensitive adhesive layer on the surface, and as the base material sheet, at least one surface of a core layer made of a polypropylene layer in order to improve adhesion with the above-described printing coat layer or pressure-sensitive adhesive layer Further, the present invention relates to a pressure-sensitive adhesive sheet for printing having a specific skin layer and excellent sheet physical properties.

  Plastic sheets have been used as substrates for printing adhesive sheets used for various printing. In general, when the substrate of the pressure-sensitive adhesive sheet for printing is a plastic sheet, a coating layer for printing is provided on the surface of the substrate sheet in order to improve the adhesion with ink. In recent years, the demand for flexographic printing has increased in the printing industry. In addition, as a flexographic ink, UV (ultraviolet curable) ink is mainly used. However, flexographic printing has a larger amount of ink than normal offset printing, so when flexographic printing is performed using UV ink, the adhesion to the adhesive sheet substrate is low, and the ink shrinks due to ink shrinkage. There was a problem that dropout occurred. Accordingly, there has been a demand for a printing pressure-sensitive adhesive sheet that can follow the shrinkage associated with curing of the UV ink and has excellent adhesion to the UV ink even when flexographic printing is performed using the UV ink.

Polypropylene resin stretched sheets, on the other hand, are used for packaging for food packaging, clothing packaging, pharmaceutical packaging, miscellaneous goods packaging, etc., for laminates for building materials, plywood, metal plates, etc. and for molding various decorative plates It is used as a mold release material or for book covers, cosmetic boxes, food cases, etc.
Among the stretched sheets of polypropylene resin, the biaxially stretched polypropylene sheet has characteristics such as excellent heat resistance, tensile strength, impact resistance strength, gas permeability, and waist strength. However, in this biaxially stretched polypropylene sheet, as the stereoregularity is increased by stretching, the crystallinity and orientation are remarkably increased, so the sheet physical properties such as rigidity are improved, but the stress during stretching is When it becomes high, there arises a molding problem such as stretching breakage.
When a polypropylene resin stretched sheet having such properties is used as a substrate sheet for a printing pressure-sensitive adhesive sheet, a printing pressure-sensitive adhesive sheet having excellent heat resistance and mechanical properties can be obtained, but as the stereoregularity increases. , The above-mentioned problem of stretching breakage and the problem that curved surface followability deteriorates arise. In addition, a stretched sheet of polypropylene resin generally has a problem of poor adhesion to a printing ink or a pressure-sensitive adhesive layer, and a solution to these problems is required.

  In place of the above-described polypropylene resin stretched sheet, printing adhesive sheets using various base materials have been proposed. For example, a printing film in which an elastic layer is provided on a substrate is disclosed (for example, see Patent Document 1). Also, a skin layer made of a thermoplastic resin such as ethylene-vinyl acetate is provided on both surfaces of a core layer made of either polyethylene, polypropylene or propylene copolymer, and an adhesive layer is provided on one surface thereof. An adhesive label for printing is disclosed (for example, see Patent Document 2).

JP 2002-264265 A Japanese Patent No. 2859140

Although the said patent document 1 is following the hardening shrinkage | contraction of UV ink and has described the adhesive sheet for printing from which the adhesiveness of a base material and UV ink is obtained, the problem of the stretch | stretching of a base film, a curved surface, etc. No mention is made of the three-dimensional followability.
Moreover, in the adhesive label for printing described in the above-mentioned Patent Document 2, according to the study by the present inventors, for example, in order to improve the adhesion with the printing ink on the skin layer, a coating layer for printing is provided. When a flexographic printing is performed using UV ink and a printing adhesion test is performed, adhesion between the skin layer and the coating layer for printing is sufficiently obtained, but the skin layer is broken (hereinafter referred to as cleavage). I understood that.
The present invention has been made under such circumstances, and is provided with a skin layer capable of suppressing the occurrence of cleavage, and has excellent sheet physical properties and adhesion to a coating layer for printing and an adhesive layer. An object of the present invention is to provide a printing pressure-sensitive adhesive sheet excellent in the quality.

  As a result of intensive studies to achieve the above object, the present inventors have a coating layer for printing on one side of a base sheet that has been biaxially stretched, and an adhesive layer on the other side. In the pressure-sensitive adhesive sheet for printing, the object is achieved by providing, as the base material sheet, a skin layer having a plane orientation coefficient measured by a predetermined method in a specific range on at least one side of a core layer made of a polypropylene layer. I found out that I could do it. The present invention has been completed based on such findings.

That is, the present invention
(1) A printing adhesive sheet having a printing coat layer on one surface of a biaxially stretched substrate sheet and an adhesive layer on the other surface, wherein the substrate sheet is a polypropylene layer on at least one surface of a core layer consisting of, plane orientation coefficient is measured by the following method have a skin layer in the range of from 0.0120 to 0.0132, the coated printing layer is provided on the skin layer The printing coat layer is made of an acrylic resin, and the skin layer contains a propylene-ethylene copolymer and silica particles ,
<Measurement method of plane orientation coefficient>
Based on JIS K 7105, the refractive indexes MDn, TDn, and ZDn in the MD (longitudinal) direction, TD (width) direction, and ZD (depth) direction are measured with an Abbe refractometer, respectively. Using the result, the plane orientation coefficient (fn) is calculated by the following equation.
fn = (MDn + TDn) / 2−ZDn
(2) The adhesive sheet for printing as described in the above item (1), wherein the binder resin used for forming the coating layer for printing has a glass transition temperature in the range of 30 to 95 ° C.
(3) The polypropylene constituting the core layer is homopolypropylene, and the pressure-sensitive adhesive sheet for printing as described in (1) or (2) above, and (4) the skin layer has a thickness of 0.5 to 2 The pressure-sensitive adhesive for printing according to any one of (1) to (3) above, which is a propylene-ethylene copolymer layer having a thickness of 0.0 μm and an ethylene unit content of 0.5 to 5% by mass. Sheet,
Is to provide.

  According to the present invention, the biaxially stretched substrate sheet has a printing coat layer for improving the adhesion to the printing ink on one surface and the pressure-sensitive adhesive layer on the other surface. In order to improve the adhesiveness with the above-mentioned printing coat layer and pressure-sensitive adhesive layer as a base sheet, a specific skin layer is provided on at least one surface of a core layer made of a polypropylene layer. The pressure-sensitive adhesive sheet for printing having excellent sheet physical properties can be provided.

It is a cross-sectional schematic diagram of an example of the adhesive sheet for printing of this invention. It is a cross-sectional schematic diagram of the example from which the adhesive sheet for printing of this invention differs.

The printing pressure-sensitive adhesive sheet of the present invention is a printing pressure-sensitive adhesive sheet having a printing coat layer on one side of a biaxially stretched substrate sheet and having a pressure-sensitive adhesive layer on the other side. The material sheet has a skin layer having a plane orientation coefficient measured by a method described later in a range of 0.0120 to 0.0132 on at least one side of a core layer made of a polypropylene layer.
[Base material sheet]
The substrate sheet in the pressure-sensitive adhesive sheet for printing of the present invention is a biaxially stretched product of a laminated sheet in which a skin layer having a specific property is provided on at least one side, preferably both sides, of a core layer made of a polypropylene layer.

(Polypropylene layer)
The core layer composed of the polypropylene layer in the biaxially stretched substrate sheet is preferably a crystalline homopolypropylene layer from the viewpoint of sheet physical properties.
The homopolypropylene constituting the crystalline homopolypropylene layer can be evaluated for stereoregularity by measuring cold xylene solubles.
<Method for measuring cold xylene solubles>
After dissolving 0.5 g of a polypropylene film sample in 100 ml of boiling xylene and allowing to cool, the polypropylene component dissolved in the filtrate after recrystallization in a constant temperature water bath at 20 ° C. for 1 hour is obtained by liquid chromatography. Quantify (X (g)).
Using the precision value (X0 (g)) of 0.5 g of the sample, the following formula is used.
Cold xylene soluble content (mass%) = (X / X0) × 100
It shows that it is inferior to stereoregularity, so that this cold xylene soluble content is large.
In the present invention, as a homopolypropylene, from the viewpoint of balance such as sheet physical properties, stretchability, and three-dimensional followability of the pressure-sensitive adhesive sheet for printing, the cold xylene soluble content is in the range of 2.2 to 3.3 mass%. Some are preferred.

The homopolypropylene preferably has a melt index M I (temperature 230 ° C., load 21.18 N) in the range of 1.3 to 3.5 g / 10 min from the viewpoint of sheet physical properties.
Such crystalline homopolypropylene can be obtained by homopolymerizing propylene using a Ziegler-Natta type catalyst or a metallocene catalyst.
In the present invention, the thickness of the homopolypropylene layer is preferably in the range of 30 to 90 [mu] m, more preferably in the range of 40 to 75 [mu] m, in order to sufficiently exhibit the function as the core layer.

  The polypropylene layer can contain a stabilizer such as an antioxidant, a chlorine scavenger, an antistatic agent, a slipping agent and the like as long as the object of the present invention is not impaired. Examples of the stabilizer include hindered phenols, hindered amines, phosphites, tocopherols, and lactones. Furthermore, examples of the chlorine scavenger include calcium stearate and hydrotalcite. Antistatic agents include alkylmethyl dibetaine, alkylamine diethanol and / or alkylamine ethanol ester and / or alkylamine diethanol diester, and slip agents include aliphatic amides such as stearic acid amide and erucic acid amide, lauric acid Examples include diethanolamide, alkyldiethanolamine, aliphatic monoglyceride, and aliphatic diglyceride.

(Skin layer)
In the biaxially stretched substrate sheet of the present invention, a skin layer is provided on at least one side, preferably both sides, of the core layer composed of the polypropylene layer described above. This skin layer is a layer provided in order to improve the adhesion between the pressure-sensitive adhesive layer, metal vapor deposition layer or printing coat layer provided thereon and the core layer comprising the polypropylene layer, and its thickness Is usually about 0.3 to 3.0 μm, preferably 0.5 to 2.0 μm.
The skin layer needs to have a plane orientation coefficient measured by the following method in the range of 0.0120 to 0.0132.
<Measurement method of plane orientation coefficient>
Based on JIS K 7105, the refractive indexes MDn, TDn, and ZDn in the MD (longitudinal) direction, TD (width) direction, and ZD (depth) direction are measured with an Abbe refractometer, respectively. Using the result, the plane orientation coefficient (fn) is calculated by the following equation.
fn = (MDn + TDn) / 2−ZDn
If the plane orientation coefficient is less than 0.0120, the surface of the base sheet may be roughened, or the haze of the base sheet may be increased and the base sheet may become cloudy. On the other hand, when it exceeds 0.0132, when a printing coat layer is provided thereon and an adhesion test is performed on the printing coat layer, cleavage occurs in the skin layer.

The orientation coefficient of the skin layer is adjusted by controlling the stereoregularity of the skin layer according to the content of ethylene units in the propylene-ethylene copolymer preferably used as the following skin layer and the stretching temperature described later. can do.
In the present invention, the skin layer is preferably a propylene-ethylene copolymer layer having an ethylene unit content in the range of 0.5 to 5% by mass from the viewpoint of preventing cleavage of the skin layer. is there. The propylene-ethylene copolymer may be a random copolymer or a block copolymer, but a block copolymer is preferable from the viewpoint of preventing cleavage of the skin layer.

The skin layer can contain a known heat stabilizer, antioxidant, chlorine scavenger and the like in order to impart stability of the propylene-ethylene copolymer. These are as described for the polypropylene layer.
The skin layer can contain an anti-blocking agent. Examples of the blocking inhibitor include inorganic particles such as silicon oxide, calcium carbonate, aluminum oxide, and titanium oxide, and crosslinked resin particles such as crosslinked polymethyl methacrylate, benzoguanamine resin, and crosslinked polystyrene. The average particle size of these antiblocking agents is preferably 1.0 to 6.0 μm. The content is preferably about 300 to 5,000 mass ppm, more preferably 800 to 3,000 mass ppm.

(Manufacture of base sheet)
The method for producing a base material sheet according to the present invention will be described by taking as an example a laminated sheet in which skin layers are provided on both surfaces of a core layer made of a polypropylene layer, but it is of course not limited to the production method.
Extruder I, II, III Extruder equipment comprising three extruders and a joining device for forming a resin sheet of three layers by joining the resin composition extruded from each extruder The resin composition 2 constituting the skin layer 2 from I, the resin composition 1 constituting the core layer 1 from the extruder II, and the resin composition 3 constituting the skin layer 3 from the extruder III are respectively melt extruded and the skin layer 2 The molten sheet consisting of / core layer 1 / skin layer 3 is extruded from the die, cooled while being pressed with air pressure on a cooling drum of about 15 to 60 ° C., and further led to a water bath of about 15 to 70 ° C. to be sufficiently cooled and solidified. Get a cooling sheet.
Subsequently, the cooling sheet is heated to about 130 to 160 ° C. while being brought into contact with a metal roll, and then stretched in the longitudinal direction about 3 to 6 times between rolls having a difference in peripheral speed to obtain a uniaxially oriented sheet. Next, the uniaxially oriented sheet is gripped with a clip and introduced into a hot air oven, preheated to about 150 to 180 ° C., then stretched about 7 to 12 times in the width direction, and subsequently about 0 to 10% in the width direction. Perform heat fixation while allowing relaxation.
In the present invention, from the viewpoint of preventing cleavage of the skin layer, in the biaxial stretching treatment of the base material sheet, after stretching 4.4 to 5.2 times at 135 to 145 ° C. in the longitudinal direction, 166 in the width direction. It is preferable to stretch 8 to 10 times at ˜178 ° C.
The biaxially oriented sheet obtained by stretching in the longitudinal direction and the width direction in this way improves the adhesion with the below-mentioned printing coat layer provided thereon and the pressure-sensitive adhesive layer provided on the opposite surface. For this purpose, one or both surfaces can be subjected to surface treatment as desired. The obtained base material sheet is wound after the surface of the biaxially oriented sheet is subjected to surface treatment after trimming the clip edge gripped by the clip.
As this surface treatment method, for example, surface roughening treatment such as sandblasting or solvent treatment, or surface oxidation treatment such as corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, ozone / ultraviolet irradiation treatment, etc. A preferable means for the surface treatment is a method of performing corona discharge treatment after substituting the atmosphere air with a mixed gas of nitrogen gas and carbon dioxide gas.
In this way, a biaxially stretched product of the resin laminated sheet in which the skin layer 2 and the skin layer 3 are provided on both surfaces of the core layer 1, respectively, and the surface-treated skin layer 2 and the skin layer 3 are provided. A material sheet can be obtained.

[Coat layer for printing]
In the pressure-sensitive adhesive sheet for printing of the present invention, a printing coat layer for imparting printability is provided on one surface of the biaxially stretched substrate sheet obtained as described above.
The coating layer for printing is used to improve adhesion with UV (ultraviolet curable) ink used as flexographic ink and normal oxidation polymerization type ink, and also to improve thermal transfer printability. It is a layer to be provided.
The material constituting the coating layer for printing is not particularly limited as long as it has good adhesion to the base sheet and can form a printing layer with good adhesion of the printing ink. Various things can be used. Examples of such materials include acrylic resins, styrene resins, cross-linked polyester urethane resins, polyester resins, cured resins of active energy ray curable compounds, polyurethane resins, polyol resins, polyvinyl alcohol, and polyvinylpyrrolidone. , Cellulose derivatives, acetate derivatives, polyvinyl chloride resins, polyimide resins, latex resins, starch, gelatin, vegetable protein, casein, gum arabic, albumin and other organic binders, surface roughening agents as desired, concrete Silica, zirconia, clay, talc, kaolin, diatomaceous earth, alumina, titania, zeolite, calcium carbonate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium phosphate, glass and other inorganic powders, acrylic resins, Urethane resins, vinyl chloride resins, benzoguanamine resins, benzoguanamine / melamine / formaldehyde condensate, ion exchange resins, urea resins, those containing organic powders such as polystyrene resins. These coating layer forming materials for printing can be appropriately selected according to the type of resin constituting the base sheet. When the pressure-sensitive adhesive sheet is required to be transparent, this printing coat layer is also transparent.
The method for coating the material on the substrate sheet is not particularly limited, and conventionally known methods such as a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, and the like can be used.

As the binder resin used in the coating layer for printing, it is preferable to use a resin having a glass transition temperature (hereinafter sometimes referred to as “Tg”) in the range of 30 to 95 ° C. If this Tg is less than 30 ° C., the resulting pressure-sensitive adhesive sheet for printing is inferior in blocking resistance. On the other hand, if Tg exceeds 95 ° C., the printability of the pressure-sensitive adhesive sheet for printing tends to deteriorate. The preferable range of Tg is 40 to 85 ° C.
Furthermore, the thickness of the coating layer for printing is about 40 to 450 nm. When the thickness is less than 40 nm, the printability is lowered. On the other hand, when it exceeds 450 nm, the blocking resistance tends to be lowered. A preferred thickness is 60 to 350 nm.

[Preparation of adhesive sheet for printing]
In the printing pressure-sensitive adhesive sheet of the present invention, the above-mentioned printing coat layer is provided on one surface of the base sheet, and in order to form this printing coat layer, first the printing coat layer is formed. A forming coating solution is prepared.
(Coating liquid for coating layer formation for printing)
As a coating liquid for forming a coating layer for printing for forming the coating layer for printing, a material constituting the coating layer for printing described above in an appropriate solvent, a photopolymerization initiator used as necessary, and various types A coating liquid in which an additive such as an organic or inorganic pigment, a colorant, a plasticizer, an antioxidant, a light stabilizer, a dispersant, a crosslinking agent, a leveling agent, or a surface roughening agent is dissolved or dispersed. Can be used.

<Solvent>
The solvent used in the coating liquid for forming a coating layer for printing is not particularly limited. For example, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, and cyclohexanone, toluene And aromatic hydrocarbon solvents such as xylene.
The solid content concentration in the coating liquid for forming a coating layer for printing is not particularly limited as long as it is a concentration that allows coating, but is usually about 1 to 10% by mass, preferably 2 to 5% by mass.

(Formation of coating layer for printing)
First, the coating liquid for forming a coating layer for printing prepared as described above has a dry film thickness of 40 on one surface of a base sheet by, for example, a gravure roll method, an air knife method, a wire bar coating method, or the like. It coats so that it may become about -450nm, It is made to dry and the coating layer for printing is formed.

In the printing pressure-sensitive adhesive sheet of the present invention, a pressure-sensitive adhesive layer may be directly provided on the opposite side of the substrate sheet on which the printing coating layer is provided, or a metal vapor deposition layer is provided, and this metal You may provide an adhesive layer through a vapor deposition layer.
(Metal vapor deposition layer)
This metal vapor deposition layer is a layer provided in order to give a concealment effect etc. to a printing layer.
The metal species to be vapor-deposited is not particularly limited as long as it can be vaporized or cluster ionized and can be removed in vacuum. For example, aluminum, zinc, copper, nickel, chromium, tin, iron Gold, silver, etc. are exemplified, and these two or more may be mixed or laminated for vapor deposition. These metal species may be partially or wholly oxidized when the metal layer is formed on the skin layer surface or after the metal layer is formed.
Although there is no restriction | limiting in particular in the thickness of this metal vapor deposition layer, Usually, it is about 10-80 nm. As the metal species, aluminum is preferable from the viewpoint of durability and economy.

(Adhesive layer)
In the pressure-sensitive adhesive sheet for printing of the present invention, as the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer provided directly or via a metal vapor deposition layer on the side of the base sheet on the side where the printing coat layer is provided. There is no particular limitation, and any one conventionally used for the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for printing can be appropriately selected and used. For example, an acrylic adhesive, a rubber adhesive, a silicone adhesive, a polyurethane adhesive, a polyester adhesive, and the like can be used. These pressure-sensitive adhesives may be emulsion type, solvent type, or solventless type. The thickness of the pressure-sensitive adhesive layer is usually 1 to 300 μm, preferably about 5 to 100 μm.
Among the various pressure-sensitive adhesives, acrylic pressure-sensitive adhesives are preferable from the viewpoint of weather resistance and the like.
The pressure-sensitive adhesive layer formed using this acrylic pressure-sensitive adhesive contains an acrylic resin having a weight average molecular weight of about 300,000 to 2,000,000, preferably 500,000 to 1,500,000 and is crosslinked. It is suitable that it is a layer. When the weight average molecular weight is in the above range, a printing pressure-sensitive adhesive sheet having a balance between the pressure-sensitive adhesive force and the holding power can be obtained.
In addition, the said weight average molecular weight is the value of polystyrene conversion measured by the gel permeation chromatography (GPC) method.

As the acrylic resin contained in the acrylic pressure-sensitive adhesive, a (meth) acrylic acid ester copolymer is used. As this (meth) acrylic acid ester-based copolymer, a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms, a monomer having a functional group having an active hydrogen, and optionally used. Preferred examples include copolymers with other monomers.
Here, examples of the alkyl (meth) acrylate alkyl ester having 1 to 20 carbon atoms in the alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth) acrylic. Butyl acid, pentyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, (meth) Examples include dodecyl acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, and the like. These may be used alone or in combination of two or more.

  On the other hand, examples of monomers having a functional group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-methacrylic acid 2- Hydroxyl group-containing monomers such as hydroxybutyl, (meth) acrylic acid hydroxyalkyl ester such as 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; acrylamide, methacrylamide, N-methylacrylamide, N An amide group-containing monomer such as methyl methacrylamide, N-methylol acrylamide, N-methylol methacrylamide; monomethylaminoethyl (meth) acrylate, monoethylaminoethyl (meth) acrylate, monomethylaminopropyl (meth) acrylate, Monoethyl (meth) acrylate Examples thereof include monoalkylaminoalkyl (meth) acrylates such as aminopropyl; ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid and citraconic acid. These monomers may be used independently and may be used in combination of 2 or more type.

Examples of other monomers used as desired include vinyl esters such as vinyl acetate and vinyl propionate; olefins such as ethylene, propylene and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; styrene Styrene monomers such as α-methylstyrene; diene monomers such as butadiene, isoprene and chloroprene; nitrile monomers such as acrylonitrile and methacrylonitrile; N, N-dimethylacrylamide, N, N— And N, N-dialkyl-substituted acrylamides such as dimethylmethacrylamide. These may be used alone or in combination of two or more.
In the acrylic pressure-sensitive adhesive, the (meth) acrylic acid ester copolymer used as a resin component is not particularly limited with respect to the copolymerization form, and may be any of random, block, and graft copolymers. .

In the present invention, this (meth) acrylic acid ester copolymer may be used alone or in combination of two or more.
The acrylic pressure-sensitive adhesive is preferably subjected to a crosslinking treatment, and the crosslinking agent used for the crosslinking treatment is not particularly limited, and any one of those conventionally used as a crosslinking agent in an acrylic pressure-sensitive adhesive can be arbitrarily selected. Those can be appropriately selected and used. Examples of such a crosslinking agent include polyisocyanate compounds, epoxy compounds, melamine resins, urea resins, dialdehydes, methylol polymers, metal chelate compounds, metal alkoxides, metal salts, and the like. Is preferably used.
In this invention, this crosslinking agent may be used individually by 1 type, and may be used in combination of 2 or more type. Further, the amount used depends on the kind of the crosslinking agent, but is usually 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the (meth) acrylic ester copolymer. It is selected in the range of mass parts.
In addition, a tackifier, an antioxidant, an ultraviolet absorber, a light stabilizer, a softener, a silane coupling agent, a filler, and the like can be added to the acrylic pressure-sensitive adhesive as desired.

In the pressure-sensitive adhesive sheet for printing of the present invention, the pressure-sensitive adhesive layer may be provided by directly applying the pressure-sensitive adhesive layer coating liquid on the surface of the base sheet opposite to the surface having the coating layer for printing. The pressure-sensitive adhesive layer with a release material is formed by forming a pressure-sensitive adhesive layer on the surface of the release material that has been subjected to the release treatment and bonding the pressure-sensitive adhesive layer to the surface of the substrate opposite to the coating layer for printing. May be formed. Various methods can be used as the method for forming the pressure-sensitive adhesive layer without any particular limitation. For example, air knife coater, blade coater, bar coater, gravure coater, roll coater, roll knife coater, curtain coater, die coater, knife Examples include coaters, screen coaters, Mayer bar coaters, and kiss coaters.
In order to protect the pressure-sensitive adhesive layer, a release material is temporarily attached to the pressure-sensitive adhesive layer surface until normal use.
The release material is not particularly limited as long as the surface has releasability, and any material can be used. For example, a release layer is provided on the surface of a paper substrate or a film substrate. And the like are preferred. As the paper substrate, various paper materials such as polyethylene laminated paper, polypropylene laminated paper, clay-coated paper, resin-coated paper, glassine paper, and high-quality paper can be used. Examples of the film substrate include various resin films such as polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, and polyacrylate. In addition, a film or synthetic paper in which a filler such as a filler is added to a film base or a paper base can be used. If necessary, the surface of the base material bonded to the pressure-sensitive adhesive layer may be subjected to a peeling treatment.
Examples of the release treatment include formation of a release agent layer made of a release agent such as a silicone resin, a long-chain alkyl resin, and a fluorine resin. The thickness of the release material is not particularly limited and may be appropriately selected.
In the printing pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer may be applied to the entire surface of the skin layer, or may be applied in the form of fine lines, lattices, or dots. It is also possible to provide in a surface shape in which a large number of small circular portions not applied are formed, and the form of this layer can be freely selected depending on the application.

The printing pressure-sensitive adhesive sheet of the present invention thus produced is excellent in adhesion and printability of inks of different brands such as UV (ultraviolet curable) type and oxidation polymerization type, and is also excellent in thermal transfer printability. It has the features such as. In particular, it is characterized by excellent adhesion and printability with UV (ultraviolet curable) ink used as flexographic ink.
1 and 2 are cross-sectional schematic views of different examples of the printing pressure-sensitive adhesive sheet of the present invention. The printing pressure-sensitive adhesive sheet 10 shown in FIG. 1 has a skin layer 2 and a skin layer 3 on both surfaces of the core layer 1. Furthermore, the coating layer 4 for printing is provided on the skin layer 2, and the adhesive layer 5 is provided on the skin layer 3.
On the other hand, the printing pressure-sensitive adhesive sheet 20 shown in FIG. 2 has a skin layer 2 and a skin layer 3 on both surfaces of the core layer 1, and further a printing coat layer 4 is provided on the skin layer 2. It has the structure where the aluminum vapor deposition layer 6 and the adhesive layer 5 were provided in order on the top.
On the printing coating layer 4 in the printing adhesive sheet 10 shown in FIG. 1 and the printing adhesive sheet 20 shown in FIG. 2, a flexographic printing layer using, for example, UV (ultraviolet curable) ink is applied. be able to. Further, a release material (not shown) is usually stuck on the pressure-sensitive adhesive layer 5.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Various characteristics in each example were measured according to the following methods.
(1) Thickness of each layer It measured using the dial gauge type thickness meter (JIS B 7509, measuring element 5 mm diameter flat type).
(2) Cold xylene soluble content of polypropylene layer <Method for measuring cold xylene soluble content>
The polypropylene layer is shaved, and about 0.5 g of polypropylene as a sample is dissolved in 100 ml of boiling xylene, allowed to cool, and then recrystallized in a constant temperature water bath at 20 ° C. for 1 hour to dissolve in the filtrate. System components are quantified by liquid chromatography (X (g)).
It calculated | required with the following formula | equation using the exact value (X0 (g)) of the sample.
Cold xylene soluble content (mass%) = (X / X0) × 100
(3) Ethylene unit content of resin used for skin layer According to the method described in the section of “(i) Random copolymer” on page 256 of Polymer Analysis Handbook (1985, published by Asakura Shoten) Were determined.
(4) Measurement of melt index M I method JIS K 7210 polypropylene test method shown in (1999) (230 ℃, 21.18N ), polyethylene test method (190 ° C., 21.18 N) was measured in accordance with.
(5) Plane orientation coefficient of skin layer <Measurement method of plane orientation coefficient>
Based on JIS K 7105, the refractive indexes MDn, TDn, and ZDn in the MD (longitudinal) direction, TD (width) direction, and ZD (depth) direction are measured with an Abbe refractometer, respectively. Using the result, the plane orientation coefficient (fn) is calculated by the following equation.
fn = (MDn + TDn) / 2−ZDn

(6) Performance of printing pressure-sensitive adhesive sheet (a) Printability of UV curable ink (a) UV seal printing adhesion On the surface of the coating layer for printing of the printing pressure-sensitive adhesive sheet, UV ink [manufactured by T & K TOKA Corporation, trade name Using “BEST CURE UV161 Black S”], printing was performed with a printing machine (trade name “RI Tester” manufactured by Akira Seisakusho Co., Ltd.), and UV irradiation (high pressure mercury lamp) was performed to obtain an image.
(B) Adhesion to UV flexographic printing Using UV ink [manufactured by T & K TOKA Co., Ltd., trade name “Flexo White HT-2”] on a pressure-sensitive adhesive sheet for printing, a flexographic printing machine [manufactured by Merchandy, trade name “MA” -2200 "printing speed 20 m / min], flexographic printing was performed, UV irradiation (metal halide lamp 3 kW) was performed, and a printed image was obtained. The cell of the anilox roller of the flexographic printing machine is a turtle shell type # 200, and the cell capacity is 16 cm ³ / m ² .
Next, in accordance with JIS K 5600-5-6, 10 × 10 squares of 1 mm each grid are prepared on the printed layer of each printed adhesive sheet, and cellophane tape [manufactured by Nichiban: CT24] is attached. When the tape was peeled, the number of squares peeled out of 100 squares was examined.
(B) Whether or not the skin layer is cleaved In UV flexographic printing adhesion evaluation, when cellophane tape [manufactured by Nichiban Co., Ltd .: CT24] is attached and the tape is peeled off, the skin layer is checked for breakage (cleavage). Confirmed.
○: No cleavage.
Δ: Partially cleaved but acceptable level.
X: Cleavage entirely.
(C) Blocking resistance After the base material sheet on which the printing coat layer is formed is allowed to stand for 1 week in an environment of 23 ° C. and 50% RH, the printing coat layer surface of the base sheet and the printing coat layer are formed. After overlapping the five uncoated surfaces, each was sandwiched between glass plates. Next, a load of 80 g / cm ² was applied in an environment of 60 ° C. and 95% RH or in an environment of 70 ° C. and 30% RH and left for 7 days. Thereafter, the film was allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH, and then the overlapped film was peeled off, and the adhesion to the coated surface for printing was determined according to the following criteria.
○: There is no adhesion to the surface on which the printing coat layer is not formed.
X: The surface on which the coating layer for printing is not formed and the surface of the coating layer for printing adhere to each other, and it is impossible to remove both by hand, or both can be removed by hand, but after peeling Changes are observed on the surface of the coating layer for printing.
(D) Haze of base material sheet Based on JIS K 7105 (1981), the average value of 5 points of data measured using a haze meter manufactured by Suga Test Instruments Co., Ltd. was defined as the haze of the base material sheet. The haze of the base sheet is desirably 3.0% or less from the viewpoint of the transparency of the base sheet. The cloudiness of the base material sheet was confirmed visually.
○: No cloudiness.
Δ: White turbidity is observed but acceptable level.
X: It becomes cloudy.
(E) Glass transition temperature (Tg) of the binder resin used to form the coating layer for printing
The binder resin used to form the coating layer for printing is applied to a release film (OPP) so that the dry thickness is 30 μm, dried in a hot air dryer at 120 ° C. for 1 hour, and then 5 mm × 30 mm strip shape The measurement sample piece was cut out. The obtained sample piece for measurement was measured using a dynamic viscoelasticity measuring apparatus [manufactured by TA Instruments, product name “Q-800”], frequency: 11 Hz, temperature rising rate: 3 ° C./min. The temperature dependence data of the storage elastic modulus (E ′) was measured.
Subsequently, based on JIS K7121, the intermediate glass transition temperature was calculated | required from the obtained temperature dependence data.

  In the following Examples 1 to 6 and Comparative Examples 1 and 2, the resin b1, the resin b2, and the resin b3 used as the skin layer 2 and the skin layer 3 are the first stage when polymerizing the propylene-ethylene copolymer. In this reactor, ethylene monomers are introduced and polymerized and dispersed in polypropylene, and the ethylene unit contents are 1% by mass, 2% by mass and 4% by mass, respectively. Moreover, 1000 mass ppm of [Mizusawa Chemical Industry Co., Ltd. product, "Silton JC-20"] (silica particle) is added to resin b1, resin b2, and resin b3, respectively as an antiblocking agent. The resin a used as the core layer is a polypropylene resin having an ethylene unit content of 0% by mass, a melt index MI of 2.1 g / 10 min, and a cold xylene soluble content of 2.8% by mass.

Example 1
(1) Preparation of biaxially stretched substrate sheet As a layer configuration of the substrate sheet, a laminated sheet composed of three polypropylene resin layers is formed and the characteristics are evaluated.
As the core layer 1, resin a, and as the skin layer 2 and skin layer 3, resin b1 were prepared.
Each of these resins is melt-extruded using three single-screw extruders and extruded from the die as a three-layer laminated sheet composed of skin layer 2 / core layer 1 / skin layer 3. The molten sheet discharged from the die is cooled while being pressed on a cooling drum at 25 ° C. with air pressure, and further led to a water bath at 25 ° C. to be sufficiently cooled and solidified to obtain a cooling sheet. Subsequently, the cooling sheet is heated to 140 ° C. while being in contact with a metal roll, and then stretched 4.8 times in the longitudinal direction between rolls having a difference in peripheral speed to obtain a uniaxially oriented sheet. Next, the uniaxially oriented sheet was gripped with a clip and introduced into a hot air oven, preheated to 175 ° C., and then stretched 9.0 times in the width direction to obtain a biaxially oriented laminated sheet.
Next, both surfaces of this biaxially oriented laminated sheet are subjected to a corona discharge treatment of 23 W / m ² / min at a sheet temperature of 60 ° C. in a mixed gas atmosphere of nitrogen and carbon dioxide (volume ratio of carbon dioxide 10%). Thus, a biaxially stretched substrate sheet was produced. In this base material sheet, the core layer had a thickness of 48 μm, the skin layers 2 and 3 had a thickness of 1 μm and 1 μm, respectively, and the total thickness was 50 μm.
(2) Formation of printing coat layer On one surface (skin layer 2) of the substrate sheet obtained in (1) above, an acrylic resin [manufactured by Dainichi Seika Co., Ltd., trade name “ "VM-D" Tg 66 ° C] 100 parts by mass (solid content 27.5% by mass), isocyanate crosslinking agent [manufactured by Nippon Polyurethane Industry Co., Ltd., trade name “Coronate L”] and 900 parts by mass of toluene, A coating solution consisting of 900 parts by weight of methyl ethyl ketone and 90 parts by weight of cyclohexanone was applied by bar coating and dried at 90 ° C. for 1 minute to form a coating layer for printing. The thickness after drying of the coated printing layer spectroscopic ellipsometer [J.A.Woolla m Co., Ltd. under the trade name "M-2000"] was measured by, was 200nm.
(3) Production of printing pressure-sensitive adhesive sheet A film of metal aluminum is formed on the surface (skin layer 3) of the base material sheet obtained in (2) above where the coating layer for printing is not provided with a crucible vapor deposition machine. Was deposited to be 50 nm. On the other hand, an acrylic adhesive [trade name “PAT1E”, manufactured by Lintec Co., Ltd.] is applied to the release treatment surface of a release material [trade name “SP-8LK”, manufactured by Lintec Co., Ltd.] obtained by peeling the polyethylene laminated paper with a silicone release agent. Was dried to form an adhesive layer having a thickness of 20 μm. Next, the pressure-sensitive adhesive release material was stuck so that the pressure-sensitive adhesive layer faced the aluminum vapor deposition layer, and the pressure-sensitive adhesive layer was transferred to prepare a pressure-sensitive adhesive sheet for printing having the configuration shown in FIG.
The performance evaluation results of this pressure-sensitive adhesive sheet for printing are shown in Table 1. The performance evaluation was performed at a stage where the pressure-sensitive adhesive layer (3) was not provided. (Hereinafter the same)

Examples 2, 3, 5, 6
In the production of the base sheet of Example 1 (1), the same operation as in Example 1 was performed except that the resin constituting the skin layer 2 was changed to b2 and the width direction stretching temperature was changed as shown in Table 1. A pressure-sensitive adhesive sheet for printing was prepared and performance evaluation was performed. The results are shown in Table 1.
Example 4
In the production of the base sheet of Example 1 (1), the same operation as in Example 1 was performed except that the resin constituting the skin layer 2 was changed to b3 and the width direction stretching temperature was changed as shown in Table 1. A pressure-sensitive adhesive sheet for printing was prepared and performance evaluation was performed. The results are shown in Table 1.

Comparative Example 1
In the production of the base material sheet in Example 1 (1), the same operation as in Example 1 was performed except that the stretching temperature in the width direction was changed as shown in Table 1, and a pressure-sensitive adhesive sheet for printing was produced. The performance was evaluated. The results are shown in Table 1.
Comparative Example 2
In the production of the base sheet of Example 1 (1), the same operation as in Example 1 was performed except that the resin constituting the skin layer 2 was changed to b2 and the width direction stretching temperature was changed as shown in Table 1. A pressure-sensitive adhesive sheet for printing was prepared and performance evaluation was performed. The results are shown in Table 1.

From Table 1, in Examples 1-6, except for Example 5, cleaving does not occur in the skin layer in printability evaluation, and Example 6 shows white turbidity, but is at an acceptable level and has good printability. It turns out that it is an adhesive sheet for printing. Example 5 was partially cleaved, but it was an acceptable level, the performance was the same as that of the other examples, and it was found that the printing adhesive sheet had good printability.
On the other hand, as in Comparative Example 1, when the surface orientation coefficient of the skin layer is too low, cleavage does not occur in the skin layer in printability evaluation, but the base sheet has a high haze, and the base sheet becomes cloudy. It turns out that the external appearance as an adhesive sheet is bad and printing performance is inferior.
As in Comparative Example 2, it can be seen that if the surface orientation coefficient of the skin layer is too high, the UV flexographic printing adhesion is poor and cleavage occurs in the skin layer in printability evaluation.

  The pressure-sensitive adhesive sheet for printing according to the present invention is provided with a skin layer capable of suppressing the occurrence of cleavage on at least one surface of a core layer made of a polypropylene layer, and is in close contact with a coating layer for printing or a pressure-sensitive adhesive layer. And blocking properties are good. Further, the coating layer for printing can improve the adhesion with UV (ultraviolet curable) ink used as flexographic ink.

DESCRIPTION OF SYMBOLS 1 Core layer 2, 3 Skin layer 4 Coat layer for printing 5 Adhesive layer 6 Aluminum vapor deposition layer 10, 20 Adhesive sheet for printing

Claims (4)

A printing pressure-sensitive adhesive sheet having a printing coat layer on one surface of a biaxially stretched substrate sheet and a pressure-sensitive adhesive layer on the other surface, the core sheet comprising a polypropylene layer on at least one surface layer, the surface orientation coefficient measured by the following methods have a skin layer in the range of 0.0120 to 0.0132, the coated printing layer is provided on said skin layer, The pressure-sensitive adhesive sheet for printing, wherein the printing coat layer is composed of an acrylic resin, and the skin layer contains a propylene-ethylene copolymer and silica particles .
<Measurement method of plane orientation coefficient>
Based on JIS K 7105, the refractive indexes MDn, TDn, and ZDn in the MD (longitudinal) direction, TD (width) direction, and ZD (depth) direction are measured with an Abbe refractometer, respectively. Using the result, the plane orientation coefficient (fn) is calculated by the following equation.
fn = (MDn + TDn) / 2−ZDn   The pressure-sensitive adhesive sheet for printing according to claim 1, wherein the binder resin used for forming the printing coat layer has a glass transition temperature in the range of 30 to 95 ° C.   The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the polypropylene constituting the core layer is homopolypropylene.   The skin layer is a propylene-ethylene copolymer layer having a thickness of 0.5 to 2.0 µm and an ethylene unit content of 0.5 to 5% by mass. The pressure-sensitive adhesive sheet for printing described in 1.

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