JP2020183503A - Adhesive composition and adhesive sheet - Google Patents

Abstract

To provide an adhesive composition capable of producing an adhesive sheet having excellent adhesive force and holding power with improved productivity.SOLUTION: The adhesive composition contains an organic solvent type adhesive (A) containing an adhesive resin (A1) and hydrophobized cellulose nanofibers (B). The adhesive resin (A1) contains an acrylic resin. The acrylic resin is a copolymer having a constituent unit (a1) derived from an alkyl (meth)acrylate and a constituent unit (a2) derived from a functional group-containing monomer.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

Adhesive sheets are used for fixing parts and temporary fixing in various industrial fields such as OA equipment, home appliances, and automobiles, but in addition to that, they are used for labels and masking for displaying various information. It is used in a wide variety of ways.
These adhesive sheets are required to have various characteristics depending on the intended use, but in many cases, adhesive strength and holding power are required. In order to obtain a pressure-sensitive adhesive sheet having good adhesive strength and holding power, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is often formed from a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive resin and a cross-linking agent.

On the other hand, when focusing on the manufacturing process of the pressure-sensitive adhesive sheet, when the pressure-sensitive adhesive composition containing a cross-linking agent is used, the pressure-sensitive adhesive layer formed by applying and drying the pressure-sensitive adhesive composition needs to undergo an aging step. There is. In addition, it is necessary to pay attention to the pot life (pot life) of the pressure-sensitive adhesive composition.
Therefore, from the viewpoint of productivity, a non-crosslinking adhesive composition that does not require an aging step and does not need to consider pot life (pot life), a long pot life, and a low cross-linking agent content. Adhesive compositions are also required.
For example, Patent Document 1 describes an acrylic copolymer having a (meth) acrylate monomer, a polar group-containing monomer, and a constituent unit derived from a monomer having a glass transition temperature of 20 ° C. or higher as a homopolymer in a predetermined content ratio. A pressure-sensitive adhesive composition containing the above-mentioned main agent is disclosed.
Patent Document 1 describes that the pressure-sensitive adhesive composition does not use a cross-linking agent, but can realize a pressure-sensitive adhesive tape having suitable adhesive strength and holding power at room temperature and high temperature.

Japanese Unexamined Patent Publication No. 2013-116935

However, the adhesive strength of the adhesive tape specifically disclosed in the examples of Patent Document 1 is as low as 16 N / 25 mm at the maximum value. Further, regarding the measurement condition of the holding force, the load is as small as 100 g, and the holding force under the condition of the load of about 1 kg has not been studied.
That is, the adhesive tape described in Patent Document 1 still has room for improvement in terms of improving adhesive strength and holding power.

An object of the present invention is to provide a pressure-sensitive adhesive composition capable of producing a pressure-sensitive adhesive sheet having excellent adhesive strength and holding power with improved productivity.

The present inventors have found that the above problems can be solved by using hydrophobicized (oil-based) cellulose nanofibers.

That is, the present invention relates to the following [1] to [11].
[1] A pressure-sensitive adhesive composition containing an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1) and hydrophobic cellulose nanofibers (B).
[2] The pressure-sensitive adhesive composition according to the above [1], which comprises blending an organic solvent-type pressure-sensitive adhesive (A) with an organic solvent dispersion containing hydrophobic cellulose nanofibers (B).
[3] In the above [1] or [2], the content of the hydrophobic cellulose nanofibers (B) is 0.1 to 30 parts by mass with respect to 100 parts by mass of the total amount of the adhesive resin (A1). The pressure-sensitive adhesive composition described.
[4] The pressure-sensitive adhesive composition according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive resin (A1) contains an acrylic resin.
[5] The above-mentioned [4], wherein the acrylic resin is a copolymer having a structural unit (a1) derived from an alkyl (meth) acrylate and a structural unit (a2) derived from a functional group-containing monomer. Adhesive composition.
[6] Any one of the above [1] to [5], wherein the content of the adhesive resin (A1) is 50 to 99.95% by mass with respect to the total amount of the active ingredient of the pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition according to one.
[7] The above-mentioned [1] to [6], wherein the content of the surfactant is less than 0.001 part by mass with respect to 100 parts by mass of the total amount of the adhesive resin (A1). Adhesive composition.
[8] The pressure-sensitive adhesive composition according to any one of the above [1] to [7], wherein the gel fraction is 10% by mass or less.
[9] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above [1] to [8].
[10] The adhesive sheet according to the above [9], which has an adhesive strength of 10 N / 25 mm or more.

By using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive sheet having excellent adhesive strength and holding power can be produced with improved productivity.

It is sectional drawing of the adhesive sheet which shows an example of the structure of the adhesive sheet of this invention.

In the present invention, the "active ingredient" refers to a component contained in the pressure-sensitive adhesive composition excluding an organic solvent as a diluting solvent. When the pressure-sensitive adhesive composition contains a small amount of water, the "active ingredient" refers to the component excluding the organic solvent and water.
The mass average molecular weight (Mw) is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method, and specifically, a value measured based on the method described in Examples.

In the present invention, for example, "(meth) acrylic acid" means both "acrylic acid" and "methacrylic acid", and other similar terms are the same.
Further, with respect to a preferable numerical range (for example, a range such as content), the lower limit value and the upper limit value described stepwise can be combined independently. For example, from the description "preferably 10 or more, more preferably 30 or more, preferably 90 or less, more preferably 60 or less", "preferable lower limit value (10)" and "more preferable upper limit value (60)" Can be combined to make "10 or more, 60 or less", in other words, "10 to 60".

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention contains an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1) and hydrophobic cellulose nanofibers (B).
Here, the hydrophobic cellulose nanofiber (hereinafter referred to as hydrophobic CNF) is treated with a hydrophobic surface treatment by a cellulose nanofiber (hereinafter referred to as CNF) in which a hydrophobic group is introduced on the surface and a surface treatment agent. Means CNF. Further, CNF is a material produced by finely loosening natural cellulose such as plant fiber to the nano level. Details will be described later.
The pressure-sensitive adhesive composition of the present invention contains a hydrophobic CNF (B) to provide a pressure-sensitive adhesive layer capable of increasing the cohesive force of the formed pressure-sensitive adhesive layer, improving the holding power, and maintaining a high pressure-sensitive adhesive force. Can be formed.
The reason is that the hydrophobized CNF (B) forms a three-dimensional network structure in the formed pressure-sensitive adhesive layer, so that the cohesive force can be enhanced, thereby exhibiting a high holding force, and It is presumed that the adhesive strength can be maintained high.
Therefore, the pressure-sensitive adhesive composition of the present invention can be a pressure-sensitive adhesive composition having a low content of a cross-linking agent or a non-cross-linking type pressure-sensitive adhesive composition containing no cross-linking agent.

As described above, the non-crosslinkable pressure-sensitive adhesive composition does not require an aging step and does not need to consider pot life (pot life), so that it improves productivity in manufacturing a pressure-sensitive adhesive sheet. There is an advantage in. In addition, the non-crosslinked pressure-sensitive adhesive composition is also excellent in terms of safety because it does not require the addition of highly reactive components or catalysts such as heavy metals. Further, a pressure-sensitive adhesive composition having a low content of a cross-linking agent also has a longer pot life than a pressure-sensitive adhesive composition having a high content of a cross-linking agent, which is advantageous for improving productivity and has high reactivity. It is also possible to reduce the amount of components and catalysts used.
Further, the pressure-sensitive adhesive layer formed from the non-crosslinking type pressure-sensitive adhesive composition or the pressure-sensitive adhesive composition having a low content of the cross-linking agent has a lower gel content than the pressure-sensitive adhesive composition having a high content of the cross-linking agent. Since it is easily dissolved in an organic solvent, if a residue adheres to the adherend after peeling, the residue can be easily removed by applying the organic solvent to the adherend. Moreover, since the gel fraction is low, it is easy to dissolve and recycle.

The gel fraction of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of one aspect of the present invention is preferably 15% or less, more preferably 10% or less, still more preferably 8% or less, still more preferably 6% or less. Is.
In the present specification, the method for forming the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition and the gel fraction of the pressure-sensitive adhesive layer mean values formed and measured by the methods described in Examples described later. ..

Further, in the pressure-sensitive adhesive composition of one aspect of the present invention, the content of the cross-linking agent is preferably 100 parts by mass based on the total amount of the pressure-sensitive adhesive resin (A1) when high productivity improvement and high safety are required. Is less than 0.001 parts by mass, more preferably less than 0.0001 parts by mass, still more preferably less than 0.00001 parts by mass, even more preferably 0 parts by mass, that is, it is even more preferably free of a cross-linking agent.
When it is desired to reduce the amount of the resin component used while making it possible to crosslink the resin component by using a cross-linking agent, the content of the cross-linking agent is preferably 0 with respect to 100 parts by mass of the total amount of the adhesive resin (A1). 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.5 parts by mass or more, and preferably less than 5 parts by mass, more preferably less than 2.5 parts by mass, still more preferably. It is less than 2 parts by mass.

Further, in the pressure-sensitive adhesive composition of one aspect of the present invention, the hydrophobized CNF (B) is easily hydrophobized in the pressure-sensitive adhesive resin (A1) and the organic solvent-type pressure-sensitive adhesive (A). Compared with the case of using no CNF, it is advantageous in the quality stability of the pressure-sensitive adhesive composition, and more CNF can be uniformly dispersed in the pressure-sensitive adhesive. As a result, it is also advantageous to reduce the amount of the cross-linking agent used. Further, since the hydrophobized CNF (B) is likely to be uniformly dispersed in the adhesive resin (A1) and the organic solvent type adhesive (A), transparency is imparted to the entire composition even if a large amount of CNF is contained. The use of the composition can be expanded.

The pressure-sensitive adhesive composition according to one aspect of the present invention may contain a general additive for a pressure-sensitive adhesive, which will be described later, as the organic solvent-type pressure-sensitive adhesive (A).
However, in the pressure-sensitive adhesive composition of one aspect of the present invention, the total content of the pressure-sensitive adhesive resin (A1) and the hydrophobized CNF (B) is based on the total amount (100% by mass) of the active ingredients of the pressure-sensitive adhesive composition. It is preferably 60% by mass or more, more preferably 65% by mass or more, further preferably 70% by mass or more, and preferably 100% by mass or less.
Hereinafter, each component contained in the pressure-sensitive adhesive composition of the present invention will be described in detail.

<Organic solvent type adhesive (A)>
The pressure-sensitive adhesive composition of the present invention contains an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1).
The organic solvent type pressure-sensitive adhesive (A) is a pressure-sensitive adhesive containing a pressure-sensitive adhesive resin (A1) and an organic solvent, and is distinguished from an emulsion-type pressure-sensitive adhesive.
Since the pressure-sensitive adhesive composition of the present invention contains the organic solvent-type pressure-sensitive adhesive (A), a pressure-sensitive adhesive layer having excellent water resistance can be formed.
Further, in the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition obtained by blending the hydrophobicized CNF (B) with the organic solvent-type pressure-sensitive adhesive (A), the hydrophobicized CNFs (B) are likely to come close to each other from the viewpoint of free energy. , Hydrophobicized CNF (B) facilitates the formation of a three-dimensional network structure. As a result, the formed pressure-sensitive adhesive layer has a high cohesive force, and easily develops a high holding power while maintaining a high adhesive force.

It is preferable that the pressure-sensitive adhesive composition of one aspect of the present invention does not substantially contain an emulsion-type pressure-sensitive adhesive (that is, a water-dispersible pressure-sensitive adhesive composition).
In the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition obtained by blending a hydrophobic CNF with an emulsion-type pressure-sensitive adhesive, a dispersoid composed of a pressure-sensitive resin contained in the emulsion-type pressure-sensitive adhesive and water as a dispersion medium are used. When the hydrophobic CNF, which is a highly elastic body, is adsorbed on the interface of the material, the adhesive force at the interface with the adherend tends to decrease. In addition, the cohesive force tends to decrease, and the holding force tends to be inferior.

For the above reasons, it is preferable that the pressure-sensitive adhesive composition of one aspect of the present invention does not substantially contain an emulsion-type pressure-sensitive adhesive. Therefore, the content of the surfactant required for preparing the emulsion-type pressure-sensitive adhesive is The smaller the number, the more preferable.
In the pressure-sensitive adhesive composition of one aspect of the present invention, the content of the surfactant is preferably less than 0.001 part by mass, more preferably 0.0001 with respect to 100 parts by mass of the total amount of the pressure-sensitive adhesive resin (A1). It is even more preferably less than parts by mass, more preferably less than 0.00001 parts by mass, even more preferably 0 parts by mass, that is, it does not contain a surfactant.

The pressure-sensitive adhesive composition according to one aspect of the present invention contains a pressure-sensitive adhesive resin (A1) and an organic solvent as an organic solvent-type pressure-sensitive adhesive (A), as well as an additive for a pressure-sensitive adhesive, as long as the effects of the present invention are not impaired. It may be contained.

[Adhesive resin (A1)]
The adhesive resin (A1) used in one aspect of the present invention may be a polymer having adhesiveness by itself and having a mass average molecular weight (Mw) of 10,000 or more.
The mass average molecular weight (Mw) of the adhesive resin (A1) used in one aspect of the present invention is preferably 10,000 or more, more preferably 20,000 or more, still more preferably 30,000 or more, from the viewpoint of improving the adhesive strength. It is preferably 2 million or less, more preferably 1.5 million or less, still more preferably 1 million or less.

In the pressure-sensitive adhesive composition of one aspect of the present invention, from the viewpoint of providing a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing cohesive force, improving holding power, and maintaining high pressure-sensitive adhesive force, an adhesive resin ( The content of A1) is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, based on the total amount (100% by mass) of the active ingredient of the pressure-sensitive adhesive composition. It is more preferably 80% by mass or more, preferably 99.95% by mass or less, more preferably 99.90% by mass or less, still more preferably 99.50% by mass or less, still more preferably 99.00% by mass. It is as follows.

Examples of the adhesive resin (A1) used in one embodiment of the present invention include rubber resins such as acrylic resins, urethane resins, and polyisobutylene resins, polyester resins, olefin resins, silicone resins, and polyvinyl ethers. Examples include based resins.
These adhesive resins (A1) may be used alone or in combination of two or more.
When these adhesive resins (A1) are copolymers having two or more kinds of constituent units, the form of the copolymer is not particularly limited, and block copolymers, random copolymers, and the like. And a graft copolymer may be used.

Among these, a pressure-sensitive adhesive that facilitates the formation of a three-dimensional network structure by hydrophobized CNF (B), enhances cohesive force to improve holding power, and can form a pressure-sensitive adhesive layer capable of maintaining high adhesive strength. From the viewpoint of the composition, the adhesive resin (A1) used in one aspect of the present invention preferably contains an acrylic resin.

From the above viewpoint, the content ratio of the acrylic resin in the adhesive resin (A1) is usually 50% by mass or more, preferably 50% by mass or more, based on the total amount (100% by mass) of the adhesive resin contained in the adhesive composition. It is 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still more preferably 90% by mass or more, and preferably 100% by mass or less.

(Acrylic resin)
Acrylic resins suitable as the adhesive resin (A1) used in one aspect of the present invention include, for example, a polymer containing a structural unit derived from an alkyl (meth) acrylate having a linear or branched alkyl group, and a cyclic resin. Examples thereof include polymers containing a structural unit derived from (meth) acrylate having a structure.

The mass average molecular weight (Mw) of the acrylic resin is preferably 10 from the viewpoint of forming a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing cohesive force, improving holding power, and maintaining high adhesive force. 10,000 or more, more preferably 200,000 or more, still more preferably 250,000 or more, still more preferably 300,000 or more, and preferably 1.5 million or less, more preferably 1.2 million or less, still more preferably 1 million or less. More preferably, it is 900,000 or less.

From the viewpoint that the hydrophobized CNF (B) facilitates the formation of a three-dimensional network structure, enhances the cohesive force, improves the holding force, and can form an adhesive layer capable of maintaining a high adhesive force. As the acrylic resin used in one embodiment of the present invention, a structural unit (a1) derived from an alkyl (meth) acrylate (a1') (hereinafter, also referred to as "monomer (a1')") and a functional group-containing monomer ( An acrylic copolymer having a structural unit (a2) derived from a2') (hereinafter, also referred to as "monomer (a2')") is preferable.

The number of carbon atoms of the alkyl group contained in the monomer (a1') is preferably from the viewpoint of forming a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing cohesive force, improving holding power, and maintaining high adhesive force. Is 1 or more, more preferably 2 or more, still more preferably 4 or more, and preferably 24 or less, more preferably 12 or less, still more preferably 8 or less, still more preferably 6 or less.
The alkyl group contained in the monomer (a1') may be a straight chain alkyl group or a branched chain alkyl group.

Examples of the monomer (a1') include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and tridecyl (). Examples thereof include meta) acrylate and stearyl (meth) acrylate.
These monomers (a1') may be used alone or in combination of two or more.

From the viewpoint of forming a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing the cohesive force to improve the holding power and maintaining a high adhesive force, the content of the structural unit (a1) is the acrylic copolymer. It is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, and preferably 80% by mass or more, based on all the constituent units (100% by mass) of. Is 99.9% by mass or less, more preferably 99.0% by mass or less, still more preferably 97.0% by mass or less, still more preferably 95.0% by mass or less.

Further, in one aspect of the present invention, the structural unit (a1) contained in the alkyl-based copolymer is an alkyl (meth) acrylate having an alkyl group having the same carbon number as that of the above-mentioned monomer (a1'). It is preferable to include the derived structural unit (a11).
Further, in one aspect of the present invention, from the viewpoint of forming a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer in which the adhesive strength is maintained high and the holding power is further improved, the constituent unit (a11) in the constituent unit (a1) is formed. ) Is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass, based on the total amount (100% by mass) of the constituent unit (a1) of the acrylic copolymer. It is more than that, and it is preferably 100% by mass or less.

Examples of the functional group contained in the monomer (a2') include a hydroxy group, a carboxy group, an amino group, an epoxy group and the like.
That is, examples of the monomer (a2') include a hydroxy group-containing monomer, a carboxy group-containing monomer, an amino group-containing monomer, an epoxy group-containing monomer, and the like.
These monomers (a2') may be used alone or in combination of two or more.
Among these, the hydroxy group-containing monomer is used as the monomer (a2') from the viewpoint of forming a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing cohesive power, improving holding power, and maintaining high adhesive power. And carboxy group-containing monomers are preferred.

Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-hydroxybutyl ( Hydroxyalkyl (meth) acrylates such as meta) acrylate and 4-hydroxybutyl (meth) acrylate; unsaturated alcohols such as vinyl alcohol and allyl alcohol can be mentioned.

Examples of the carboxy group-containing monomer include ethylenically unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; ethylenically unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, maleic acid, and citraconic acid, and their anhydrides. , 2- (Acryloyloxy) ethyl succinate, 2-carboxyethyl (meth) acrylate and the like.

From the viewpoint of making a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of increasing the cohesive force to improve the holding power and maintaining a high adhesive force, the content of the structural unit (a2) is the acrylic copolymer. 0.1% by mass or more, more preferably 1.0% by mass or more, still more preferably 3.0% by mass or more, still more preferably 5.0% by mass, based on all the constituent units (100% by mass) of. % Or more, preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 30% by mass or less, still more preferably 20% by mass or less.

The acrylic copolymer may further have a structural unit (a3) derived from a monomer (a3') other than the monomer (a1') and (a2').
However, in the acrylic copolymer, the content of the structural units (a1) and (a2) is preferably 70% by mass or more with respect to the total structural units (100% by mass) of the acrylic copolymer. It is more preferably 80% by mass or more, further preferably 90% by mass or more, still more preferably 95% by mass or more, and preferably 100% by mass or less.

Examples of the monomer (a3') include olefins such as ethylene, propylene and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; diene monomers such as butadiene, isoprene and chloroprene; cyclohexyl (meth) acrylates, It has a cyclic structure such as benzyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and imide (meth) acrylate. (Meta) Acrylate; Examples thereof include styrene, α-methylstyrene, vinyltoluene, vinyl formate, vinyl acetate, acrylonitrile, (meth) acrylamide, (meth) acrylonitrile, (meth) acryloylmorpholine, and N-vinylpyrrolidone.

[Additives for adhesives]
The pressure-sensitive adhesive composition according to one aspect of the present invention may further contain a tackifier and an additive for a pressure-sensitive adhesive as the organic solvent-type pressure-sensitive adhesive (A) as long as the effects of the present invention are not impaired.
The tackifier is a compound in the oligomer region having a molecular weight of 100 to 10,000, which can be mixed with the adhesive resin (A1) and has a function of further improving the adhesive performance of the adhesive resin (A1). ..
Examples of the tackifier include rosin-based resin, hydride-based resin, terpene-based resin, hydride-based terpene-based resin, styrene-based resin, and penten, isoprene, piperin, 1,3-produced by thermal decomposition of petroleum naphtha. C5-based petroleum resin obtained by copolymerizing C5 distillates such as pentadiene, C9-based petroleum resins obtained by copolymerizing C9 distillates such as inden and vinyl toluene produced by thermal decomposition of petroleum naphtha, and these. Examples thereof include hydride petroleum resin obtained by hydrogenating petroleum resin.
Examples of adhesive additives include antioxidants, softeners (plasticizers), rust inhibitors, pigments, dyes, reaction retarders, reaction accelerators (catalysts), UV absorbers, fungicides, and fungicides. Examples include agents, antibacterial agents, bactericides, antistatic agents and the like.
These tackifiers and tackant additives may be used alone or in combination of two or more.

When the pressure-sensitive adhesive composition of one aspect of the present invention contains a pressure-sensitive adhesive, the content thereof is preferably 100 parts by mass of the pressure-sensitive adhesive resin (A1) from the viewpoint of appropriately ensuring the required adhesiveness. Is 5 parts by mass or more, more preferably 7 parts by mass or more, further preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, and preferably 70 parts by mass or less, more preferably 60 parts by mass or less. It is more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less.
When an additive for a pressure-sensitive adhesive is contained, the content of each additive for a pressure-sensitive adhesive is appropriately selected according to the type of the additive, but is preferably 0 with respect to 100 parts by mass of the pressure-sensitive adhesive resin (A1). It is .001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less.

[First organic solvent]
The organic solvent type pressure-sensitive adhesive (A) used in one aspect of the present invention contains an organic solvent together with the pressure-sensitive adhesive resin (A1). The organic solvent used together with the adhesive resin (A1) may be referred to as a first organic solvent.
The first organic solvent is appropriately selected in consideration of its solubility in the adhesive resin (A1) to be used. For example, toluene, ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), methyl isobutyl ketone, methanol. , Ethanol, isopropyl alcohol (IPA), n-butanol, t-butanol, s-butanol, acetone, acetylacetone, cyclohexanone, n-hexane, cyclohexane and the like.
These organic solvents may be used alone or as a mixed solvent in which two or more kinds are used in combination.

The concentration of the active ingredient of the organic solvent-type pressure-sensitive adhesive (A) used in one embodiment of the present invention is preferably 1% by mass from the viewpoint of improving the handleability of the obtained pressure-sensitive adhesive composition and imparting excellent coatability. As mentioned above, it is more preferably 10% by mass or more, further preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less.

<Hydrophobic cellulose nanofiber (B)>
The pressure-sensitive adhesive composition of the present invention contains a hydrophobized CNF (B).
As described above, the hydrophobized CNF (B) means a CNF having a hydrophobic group introduced into the surface and a CNF that has been hydrophobized with a hydrophobizing agent. By containing the hydrophobized CNF (B), even if the amount of the cross-linking agent used is small or the cross-linking agent is not added, the cohesive force of the formed pressure-sensitive adhesive layer is enhanced to improve the holding power, and the holding power is high. An adhesive layer capable of maintaining adhesive strength can be formed.

CNF is hydrophilic in nature, but is hydrophobized (hydrophobicized) by introducing a hydrophobic group or surface-treating with a hydrophobizing agent, and toluene, ethyl acetate, butyl acetate, MEK, IPA, cyclohexanone, acetone. , Ethanol and other organic solvents, and other organic solvents compatible with these solvents will be uniformly dispersed. Therefore, in the case of non-hydrophobicized CNF, even if it is mixed with an organic solvent, it will be phase-separated or aggregated and become cloudy, whereas in the case of hydrophobic CNF, it will not become cloudy even if it is mixed with an organic solvent. Disperse evenly.

The pressure-sensitive adhesive composition using the hydrophobized CNF (B) can increase the holding power at high temperature. This is presumed to be due to the following reasons. When the temperature of the pressure-sensitive adhesive composition rises, the pressure-sensitive adhesive resin acts to shorten the time until the pressure-sensitive adhesive resin undergoes cohesive failure and falls off from the adherend (that is, acts to reduce the holding power). On the other hand, CNF has low temperature dependence, and even if the temperature rises to about 200 ° C., there is almost no change in morphology. Further, since the CNF is hydrophobized, the CNF can be uniformly dispersed in the organic solvent type pressure-sensitive adhesive (A). In this way, the presence of the hydrophobic CNF (B) maintains the cohesive force over the entire pressure-sensitive adhesive composition even at high temperatures, and as a result, suppresses a decrease in the holding power of the pressure-sensitive adhesive composition even if the pressure-sensitive adhesive resin (A1) softens. As a result, it is presumed that the holding power of the pressure-sensitive adhesive composition can be made difficult to decrease even at high temperatures.

Various conventionally known methods can be used for the hydrophobizing treatment for hydrophobizing (oil-forming) CNF. The following methods are typical examples.
(1) A part of the hydroxyl group of CNF by carrying out reactions such as esterification (acylation) (alkyl esterification, composite esterification, β-keto esterification, etc.), alkylation, tosylation, epoxidation, and arylation. Or replace all with hydrophobic groups. Of these, esterification is preferable, and in the esterified hydrophobic CNF, part or all of the hydroxyl groups of cellulose are carboxylic acids such as acetic acid, acetic anhydride, propionic acid, butyric acid, or halides thereof (particularly chlorides). ) Is acylated.
(2) CNF is modified with a carboxy anion by an oxidation treatment using an N-oxyl compound such as TEMPO. Further, an organic onium compound having an onium structure such as organic ammonium and organic phosphonium is added and reacted to make CNF hydrophobic.
(3) One selected from silane-based coupling agents, titanate-based coupling agents, aluminum-based coupling agents, silicone oils, fluorooils, silicone resins, fluororesins, acrylic resins, and inorganic powders treated with these. CNF is surface treated using two or more as hydrophobizing agents. Of these, silane-based coupling agents are preferable. In the silane coupling agent, CNF is hydrophobized by dehydration condensation reaction with the hydroxyl group on the fiber surface to form a strong covalent bond.
(4) The surface of a metal or ceramic raw material is coated by a physical vapor deposition method (PVD method) such as vacuum deposition, ion plating, or sputtering, a chemical vapor deposition method (CVD method), or a plating method such as electroless plating or electrolytic plating. , CNF is made hydrophobic by physical modification.

Among these, the method (2) above is particularly preferable. When the method (2) above is used, the degree of hydrophobicity can be adjusted by changing the length of the alkyl chain of the organic onium compound.

Whether or not CNF is hydrophobized, or the degree of hydrophobization can be measured by various methods. For example, an organic solvent containing CNF to be measured is applied to an appropriate support and dried to form a CNF film, and distilled water is dropped onto the CNF film to measure the contact angle to measure the degree of hydrophobicity of CNF. Can be measured. The degree of hydrophobicity of CNF can also be measured by a method such as dispersing CNF in an organic solvent such as toluene at a predetermined concentration and examining the degree of precipitation of CNF after a certain period of time.
When the degree of hydrophobicity of CNF is confirmed by measuring the contact angle with water, it can be specifically measured by the method described in Examples.
If the contact angle with water is 40 ° or more and 150 ° or less, it can be determined that CNF is hydrophobized.
The contact angle of the hydrophobized CNF with water is preferably 45 ° or more, more preferably 50 ° or more, and preferably 120 ° or less, more preferably 100 ° or less, still more preferably 80 ° or less, still more preferably. Is 60 ° or less.

The pressure-sensitive adhesive composition of the present invention is formed by blending a hydrophobized CNF (B) with an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1), but from the viewpoint of productivity. , It is preferable that the organic solvent type pressure-sensitive adhesive (A) is blended with an organic solvent dispersion liquid containing a hydrophobic CNF (B).
The content of the hydrophobized CNF (B) in the organic solvent dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass, based on the total amount (100% by mass) of the organic solvent dispersion. % Or more, more preferably 1% by mass or more, still more preferably 3% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, still more preferably. Is 8% by mass or less.
When the content of the hydrophobic CNF (B) in the organic solvent dispersion is 0.1% by mass or more, the amount of the organic solvent type pressure-sensitive adhesive (A) added to the pressure-sensitive adhesive composition does not become too large. Therefore, the content of the organic solvent does not become excessive, and it is easy to adjust the viscosity to be suitable for coating. Further, when the content of the hydrophobized CNF (B) is 30% by mass or less, an organic solvent dispersion containing the hydrophobized CNF (B) can be easily prepared.

As the organic solvent (second organic solvent) used together with the hydrophobized CNF (B), the same one as the above-mentioned first organic solvent used for the organic solvent type pressure-sensitive adhesive (A) can be used. In particular, from the viewpoint of compatibility, it is preferable to use toluene, ethyl acetate, butyl acetate, MEK, or IPA. The first organic solvent and the second organic solvent may be of different types or of the same type.

The method of adding the hydrophobized CNF (B) to the second organic solvent is not limited to this, but for example, a dispersion liquid in which a cellulosic raw material such as pulp is dispersed in an aqueous dispersion medium is used. Prepared, as described later, through denaturation treatment of cellulosic raw material, hydrophobization treatment of modified cellulosic raw material, defibration of hydrophobized cellulosic raw material, etc. until hydrophobized CNF (B) is produced. A method of solvent-substituting the aqueous dispersion medium with a second organic solvent can be used at any one of the above steps and at least one of the steps after the hydrophobized CNF (B) is produced.
The method of solvent replacement is not limited to this, but for example, an organic solvent is added to the aqueous dispersion and mixed, the solid content is filtered off, and the obtained solid content is added to a new organic solvent. If necessary, a method of repeating filtration and addition to an organic solvent can be used. As the organic solvent to be used, the target organic solvent may be used from the stage of addition to the aqueous dispersion. In addition, a hydrophilic organic solvent is used at the stage of addition to the aqueous dispersion, an organic solvent having properties similar to the target organic solvent is used after filtration, and finally the target organic solvent is used. The type of organic solvent may be changed step by step.

The content of the hydrophobized CNF (B) is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and further preferably 1.0 part by mass with respect to 100 parts by mass of the adhesive resin (A1). More than parts, more preferably 3.0 parts by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less, still more preferably 15 parts by mass or less. is there. The content of the hydrophobized CNF (B) is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 25 parts by mass, still more preferably, with respect to 100 parts by mass of the adhesive resin (A1). It is 1.0 to 20 parts by mass, more preferably 3.0 to 15 parts by mass.
When the content of the hydrophobic CNF (B) is 0.1 parts by mass or more, it is easy to form a three-dimensional network structure of the hydrophobic CNF (B) in the formed adhesive layer, and the cohesive force is enhanced. A pressure-sensitive adhesive layer having excellent adhesive strength and holding power can be formed even at a high temperature of about 80 ° C.
On the other hand, when the content of the hydrophobized CNF (B) is 30 parts by mass or less, it is easy to maintain good adhesiveness of the obtained pressure-sensitive adhesive composition even if CNF which is a highly elastic body is added. Therefore, for example, when the base material is provided on one surface of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition, the adhesiveness between the pressure-sensitive adhesive layer and the base material can be improved.

Further, in the pressure-sensitive adhesive composition of one aspect of the present invention, the content of the hydrophobized CNF (B) is preferably 0.05% by mass with respect to the total amount (100% by mass) of the active ingredient of the pressure-sensitive adhesive composition. % Or more, more preferably 0.10% by mass or more, still more preferably 0.50% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less. is there.
When the content of the hydrophobized CNF (B) is 0.05% by mass or more, it is easy to form a three-dimensional network structure, so that the cohesive force is increased, the holding force is improved, and the adhesive force can maintain a high adhesive force. It can be a pressure-sensitive adhesive composition capable of forming a layer. Further, when the content of the hydrophobic CNF (B) is 30% by mass or less, it is difficult for the viscosity to increase due to the entanglement of the hydrophobic CNF, so that the coated surface formed from the obtained pressure-sensitive adhesive composition is uniform. It becomes easy to make a flat surface. The haze value of the pressure-sensitive adhesive composition is maintained at a low value even if the content of the hydrophobic CNF (B) increases. Therefore, if the content of the hydrophobic CNF (B) is within the above range, The transparency of the pressure-sensitive adhesive composition is ensured.

Examples of the raw material of CNF for obtaining hydrophobized CNF (B) include wood-derived kraft pulp or sulfite pulp; kraft pulp or sulfite pulp crushed with a high-pressure homogenizer, a mill, or the like; Microcrystalline kraft powder purified by chemical treatment such as hydrolysis; Bast fiber pulp such as kozo, ganpi, and sansho; Cellulosic raw material derived from plants such as cotton pulp, kenaf, hemp, rice, bacas, and bamboo; Examples include cellulosic materials.

If a large amount of lignin remains in these raw materials, the oxidation reaction of the raw materials may be hindered. Therefore, cellulosic raw materials obtained by removing lignin from these raw materials are preferable.
Further, it is also possible to use the above-mentioned cellulosic raw material finely divided by a dispersion device such as a high-speed rotary type, a colloid mill type, a high pressure type, a roll mill type, an ultrasonic type, a wet high pressure or an ultrahigh pressure homogenizer, or the like.

The above-mentioned treatment for hydrophobizing the CNF may be performed at the time of defibrating the cellulosic raw material, before defibration, or after defibration.

The above-mentioned cellulose-based raw material can be made into cellulose nanofibers by defibrating and converting into nanofibers.
As a specific method, a dispersion containing CNF can be obtained by preparing a dispersion in which the cellulosic raw material is dispersed in a dispersion medium such as water, and then applying a shearing force to the cellulosic raw material. ..
When the above-mentioned hydrophobization treatment is performed when defibrating the cellulosic raw material, for example, a dispersion liquid in which the cellulosic raw material is dispersed in an aqueous dispersion medium is subjected to the hydrophobization treatment while at the same time applying a shearing force to the cellulosic raw material. By doing so, a dispersion of hydrophobized CNF can be obtained.
When the above-mentioned hydrophobization treatment is performed before the defibration of the cellulosic raw material, for example, the cellulosic raw material is hydrophobized by using an aqueous dispersion of the cellulosic raw material to disperse the cellulosic raw material. After obtaining the liquid, a shearing force can be applied to the hydrophobized cellulosic raw material to obtain a dispersion of hydrophobized CNF.
When the above-mentioned hydrophobization treatment is performed after the defibration of the cellulosic raw material, after the defibration of the cellulosic raw material, a hydrophobizing agent is added to make the defibrated cellulose hydrophobic, and the hydrophobized cellulose is re-dissolved. By defibrating, a dispersion of hydrophobized CNF can be obtained.

The procedure for producing the hydrophobized CNF organic solvent dispersion is as follows. For example, an aqueous dispersion containing CNF that has been subjected to a modification treatment such as TEMPO oxide CNF is prepared, the solvent is replaced from the aqueous dispersion medium with an organic solvent, the hydrophobic treatment is performed by the various methods described above, and then further. By performing the re-defibration treatment, a dispersion liquid in which the hydrophobized CNF (B) is dispersed in an organic solvent can be obtained.
The solvent substitution may be performed at any stage before the hydrophobization treatment, during the hydrophobization treatment and after the hydrophobization treatment, and at any stage before, during, or after the defibration of the cellulosic raw material. You may go.

As a method of applying a shearing force to a cellulosic raw material, after adding the cellulosic raw material to a dispersion medium such as water, a device such as a high-speed rotary type, a colloid mill type, a high pressure type, a roll mill type, or an ultrasonic type is used. A method of applying a shearing force is preferable.
At this time, the pressure applied to the dispersion is preferably 50 MPa or more, more preferably 100 MPa or more, and further preferably 140 MPa or more.
From the viewpoint of applying a strong shearing force to the cellulosic raw material under such a high pressure, it is preferable to apply the shearing force using a high-pressure device, and it is more preferable to use a wet high-pressure or ultra-high-pressure homogenizer. ..

The organic solvent dispersion containing the hydrophobic CNF (B) can be easily prepared by adding the hydrophobic CNF (B) to the second organic solvent and stirring the mixture.

<Preparation method of adhesive composition>
The method for preparing the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is an organic solvent containing a hydrophobized CNF (B) in an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1) and an organic solvent. It is preferable to mix and prepare the dispersion.
The above-mentioned additive for a pressure-sensitive adhesive used as needed may be added to the organic solvent-type pressure-sensitive adhesive (A) in advance together with the pressure-sensitive adhesive resin (A1), and contains a hydrophobized CNF (B). It may be blended with an organic solvent dispersion.
After blending the organic solvent dispersion, it is preferable to stir sufficiently so that the hydrophobized CNF (B) is uniformly dispersed in the solution.

<Concentration of active ingredient of adhesive composition and content of organic solvent>
The concentration of the active ingredient of the pressure-sensitive adhesive composition according to one aspect of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and particularly preferably 20% by mass or more. Further, it is preferably 60% by mass or less, more preferably 50% by mass or less, and further preferably 40% by mass or less.
In the pressure-sensitive adhesive composition of one aspect of the present invention, the total content of the organic solvent for preparing the organic solvent-type pressure-sensitive adhesive (A) and the organic solvent for preparing the organic solvent dispersion of the hydrophobized CNF is preferably 20% by mass. As mentioned above, it is more preferably 25% by mass or more, further preferably 30% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less.
In the pressure-sensitive adhesive composition of one aspect of the present invention, 1% by mass or less of water may be contained. When the pressure-sensitive adhesive composition contains water, the concentration of the active ingredient is represented by the concentration of the component of the pressure-sensitive adhesive composition excluding the organic solvent and water. The preferable numerical range of the active ingredient concentration in this case is the same as the above-mentioned numerical range.
The total content of the active ingredient concentration, the organic solvent for preparing the organic solvent type pressure-sensitive adhesive (A), the organic solvent for preparing the organic solvent dispersion of the hydrophobic CNF, and the water contained in some cases should be within the above range. Since the prepared pressure-sensitive adhesive composition is less likely to cause liquid phase separation, a uniform pressure-sensitive adhesive layer can be formed.

[Structure of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention may have a pressure-sensitive adhesive layer formed from the above-mentioned pressure-sensitive adhesive composition of the present invention.
FIG. 1 is a cross-sectional view of the pressure-sensitive adhesive sheet showing an example of the structure of the pressure-sensitive adhesive sheet of the present invention.
Examples of the pressure-sensitive adhesive sheet according to one aspect of the present invention include a base-based pressure-sensitive adhesive sheet 1a having a pressure-sensitive adhesive layer 12 on at least one surface of the base material 11, as shown in FIG. 1 (a).
In the configuration of the pressure-sensitive adhesive sheet 1a with a base material, as shown in FIG. 1B, the pressure-sensitive adhesive sheet 1b with a base material may be obtained by further laminating the release material 13 on the pressure-sensitive adhesive layer 12.

Further, as the pressure-sensitive adhesive sheet of one aspect of the present invention, as shown in FIG. 1 (c), the structure is such that the double-sided pressure-sensitive adhesive sheet 1c with a base material has the pressure-sensitive adhesive layers 12a and 12b on both sides of the base material 11, respectively. May be.
The double-sided pressure-sensitive adhesive sheet 1c shown in FIG. 1C may have a structure in which a release material is laminated on the pressure-sensitive adhesive layers 12a and 12b, respectively.

Further, as the pressure-sensitive adhesive sheet of one aspect of the present invention, as shown in FIG. 1D, a group having a structure in which the pressure-sensitive adhesive layer 12 is sandwiched between two release materials 13a and 13b without using a base material. A materialless adhesive sheet 1d may be used.
The release materials 13a and 13b of the base-less adhesive sheet 1d may be made of the same type of material or different types of materials, but the release force of the release material 13a and the release material 13b are different. It is preferable that the material is adjusted so as to be used.
As the pressure-sensitive adhesive sheet without a base material, there is also an pressure-sensitive adhesive sheet having a structure in which a pressure-sensitive adhesive layer is provided on one surface of a release material that has been peeled on both sides and wound in a roll shape.

The thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to one aspect of the present invention is appropriately set according to the use of the pressure-sensitive adhesive sheet, but is preferably 1 μm or more, more preferably 3 μm or more, still more preferably 5 μm or more. Further, it is preferably 100 μm or less, more preferably 70 μm or less, and further preferably 50 μm or less.

<Base material>
The base material contained in the pressure-sensitive adhesive sheet according to one aspect of the present invention is appropriately selected according to the use of the pressure-sensitive adhesive sheet, and is, for example, a paper base material such as high-quality paper, art paper, coated paper, and glassin paper; these paper bases. Laminated paper with a thermoplastic resin such as polyethylene laminated on the material; metal foil such as aluminum foil, copper foil and iron foil; porous material such as non-woven fabric: polyolefin resin such as polyethylene resin and polypropylene resin, polybutylene terephthalate resin and polyethylene Examples thereof include a resin film or sheet containing one or more resins such as a polyester resin such as a terephthalate resin, an acetate resin, an ABS resin, a polystyrene resin, and a vinyl chloride resin.

The base material used in one aspect of the present invention may be a single-layer film or sheet, or may be a multi-layer film or sheet which is a laminate of two or more layers.
Further, the resin film or sheet may be unstretched, or may be stretched in a uniaxial direction or a biaxial direction such as vertical or horizontal.
Further, the resin film or sheet may contain an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a slip agent, an antiblocking agent, a colorant and the like in addition to the above-mentioned resin.

When the base material is a resin film or sheet, the surface of the base material is subjected to surface treatment such as an oxidation method or an unevenness method, if necessary, from the viewpoint of improving the adhesion between the base material and the pressure-sensitive adhesive layer. Is preferable.
Examples of the oxidation method include a corona discharge treatment method, a plasma treatment method, a chromium acid oxidation (wet), a flame treatment, a hot air treatment, an ozone / ultraviolet irradiation treatment, and the like.
In addition, examples of the unevenness method include a sandblasting method and a solvent treatment method.
These surface treatments are appropriately selected according to the type of the base material, but the corona discharge treatment method is preferable from the viewpoint of improving the adhesion to the pressure-sensitive adhesive layer and operability. Further, the surface of the base material may be subjected to a primer treatment.

Further, depending on the type of the base material, a sealing layer may be provided on the surface of the base material on the side where the pressure-sensitive adhesive layer is laminated. In addition to preventing the adhesive composition from penetrating into the base material, this sealing layer is used to further improve the adhesion between the base material and the pressure-sensitive adhesive layer, or the base material is paper and is too flexible. In some cases, it is provided to impart rigidity.
For example, the sealing layer is mainly composed of a styrene-butadiene copolymer, an acrylic resin, a polyester resin, a polyurethane resin, a polystyrene resin, a polyvinyl alcohol resin, etc., and clay, silica, carbon dioxide, etc., if necessary. It can be formed from a composition containing a filler such as calcium, titanium oxide, or zinc oxide.

The thickness of the base material is appropriately selected depending on the use of the pressure-sensitive adhesive sheet, but is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 20 μm or more, and preferably 250 μm or less, more preferably 200 μm. Below, it is more preferably 150 μm or less.

[Release material]
As the release material contained in the pressure-sensitive adhesive sheet of one aspect of the present invention, a release sheet that has been subjected to double-sided release treatment, a release sheet that has been subjected to single-sided release treatment, or the like is used, and a release agent is applied onto a substrate for the release material. Things etc. can be mentioned.

Examples of the base material for the release material include papers such as high-quality paper, glassin paper, and kraft paper; polyester resin films such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin, and olefins such as polypropylene resin and polyethylene resin. Plastic films such as resin films; etc. may be mentioned.

Examples of the release agent include silicone-based resin; olefin-based resin; rubber-based elastomer such as isoprene-based resin and butadiene-based resin; long-chain alkyl-based resin; alkyd-based resin; and fluorine-based resin.

The thickness of the release material is not particularly limited, but is preferably 10 μm or more, more preferably 25 μm or more, still more preferably 35 μm or more, and preferably 200 μm or less, more preferably 170 μm or less, still more preferably 100 μm or less. Even more preferably, it is 80 μm or less.

[Manufacturing method of adhesive sheet]
The method for producing the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and the pressure-sensitive adhesive composition of the present invention is applied onto a base material or a release material to form a coating film, and the coating film is dried to adhere. Examples thereof include a manufacturing method having a step of forming a drug layer.

Since the pressure-sensitive adhesive composition of the present invention contains hydrophobic CNF (B), a pressure-sensitive adhesive layer having high cohesive force is formed even if the pressure-sensitive adhesive composition does not contain a cross-linking agent or the content of the cross-linking agent is small. be able to.
Therefore, when the pressure-sensitive adhesive composition used as the material for forming the pressure-sensitive adhesive layer is a non-crosslinked type, it is not necessary to go through an aging step after forming the pressure-sensitive adhesive layer.

Examples of the method for applying the pressure-sensitive adhesive composition onto the base material or release material include a spin coating method, a spray coating method, a bar coating method, a knife coating method, a roll coating method, a roll knife coating method, a blade coating method, and a die coating method. Examples include the method and the gravure coat method.

As a specific manufacturing method, as a manufacturing method of the pressure-sensitive adhesive sheet 1a with a base material as shown in FIG. 1A, for example, the pressure-sensitive adhesive composition is directly applied to one surface of the base material 11 and dried. A method of forming and manufacturing the pressure-sensitive adhesive layer 12 can be mentioned.
Further, as a method for producing the adhesive sheet 1b with a base material as shown in FIG. 1B, for example, the adhesive composition is directly applied on the peeling surface of the release material 13 and dried to dry the adhesive layer 12. After forming the above, the surface of the exposed pressure-sensitive adhesive layer 12 and the base material 11 are bonded to each other for production, or the pressure-sensitive adhesive composition is directly applied onto the base material 11 and dried to dry the pressure-sensitive adhesive layer 12. A method of manufacturing by laminating the peeling-treated surface of the peeling material 13 on the surface of the exposed pressure-sensitive adhesive layer 12 after forming the above.
Further, as a method for producing the double-sided pressure-sensitive adhesive sheet 1c with a base material as shown in FIG. 1 (c), for example, the pressure-sensitive adhesive composition is directly applied to both sides of the base material, dried, and the pressure-sensitive adhesive layer 12a. After forming a method of forming 12b and preparing two release materials, directly applying the adhesive composition on the release-treated surface of each release material, and drying to form an adhesive layer. Examples thereof include a method in which the pressure-sensitive adhesive layers 12a and 12b formed on the two release materials are bonded to both surfaces of the base material 11 for production.
Then, as a method for producing the base-less pressure-sensitive adhesive sheet 1d as shown in FIG. 1D, for example, the pressure-sensitive adhesive composition is directly applied to the peeling-treated surface of one release material 13a, dried, and the pressure-sensitive adhesive layer 12 is dried. A method of manufacturing by laminating another release material 13b on the surface of the exposed pressure-sensitive adhesive layer 12 after forming the above.

[Physical properties and uses of adhesive sheets]
The adhesive strength of the pressure-sensitive adhesive sheet according to one aspect of the present invention to a stainless steel plate is preferably 10 N / 25 mm or more, more preferably 12.5 N / 25 mm or more, still more preferably 15 N / 25 mm or more, still more preferably 17 N / 25 mm or more. , More preferably 18 N / 25 mm or more.
In this specification, the adhesive strength of the adhesive sheet to the stainless steel plate is a value measured in accordance with JIS Z0237: 2000, and more specifically, a value measured based on the method described in Examples. Is.

The elapsed time (holding power) of the adhesive sheet according to one aspect of the present invention until it is completely peeled off from the stainless steel plate as an adherend when a load of 1 kg is applied, which is measured under the conditions described in Examples described later. At 40 ° C., preferably 30,000 seconds or longer, more preferably 35,000 seconds or longer, further preferably 40,000 seconds or longer, and at 80 ° C., preferably 1,000 seconds or longer, more preferably 1 , 500 seconds or more, more preferably 2,000 seconds or more.
Further, from the viewpoint of ensuring sufficient holding power even in a high temperature environment, the holding power RT ₁ (second) of the pressure-sensitive adhesive composition containing the hydrophobic CNF at 40 ° C. is the pressure-sensitive adhesive composition to which the hydrophobic CNF is not added. A pressure-sensitive adhesive composition containing a hydrophobic CNF, preferably 1.2 times or more, more preferably 1.4 times or more, still more preferably 1.6 times or more, with respect to RT _{1 in} a product, at 80 ° C. The holding power RT ₂ (seconds) is preferably 1.2 times or more, more preferably 1.5 times or more, still more preferably 2. times, with respect to RT ₂ in the pressure-sensitive adhesive composition to which the hydrophobic CNF is not added. It is 0 times or more.

As described above, the pressure-sensitive adhesive sheet according to one aspect of the present invention tends to improve transparency because the hydrophobized CNF (B) is easily dispersed in the pressure-sensitive adhesive resin. Therefore, the pressure-sensitive adhesive sheet of one aspect of the present invention is suitable for applications requiring light transmission. For example, when the pressure-sensitive adhesive sheet needs to be attached to an accurate position of an adherend, it is covered through the pressure-sensitive adhesive sheet. It can be attached while checking the position of the body. The pressure-sensitive adhesive sheet of one aspect of the present invention can also be used for optical applications. In order to impart good transparency to the pressure-sensitive adhesive sheet, the haze value after the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached to the PET substrate is preferably 25% or less, more preferably 20% or less, still more preferably 10. % Or less, more preferably 5% or less. For the haze measurement, a value measured according to JIS K7136 2000 with a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH 5000") can be adopted.
The haze of the adhesive sheet can be specifically measured by the method described in Examples.

The adhesive sheet of the present invention has excellent adhesive strength and holding power.
Therefore, the adhesive sheet of the present invention can be used not only for fixing or temporarily fixing various parts, but also for various purposes such as labeling for displaying various information and masking.
More specifically, it is suitable for applications such as masking tape for signboards, wallpaper, tape for attaching to skin, medical members, and tape for toys.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to the following examples. The physical property values in the following production examples and examples are values measured by the following methods.

<Mass average molecular weight (Mw)>
It was measured under the following conditions using a gel permeation chromatograph device (manufactured by Tosoh Corporation, product name "HLC-8020"), and the value measured in terms of standard polystyrene was used.
(Measurement condition)
-Column: "TSK guard volume HXL-L""TSK gel G2500HXL""TSK gel G2000HXL""TSK gel G1000HXL" (all manufactured by Tosoh Corporation) are connected in sequence.-Column temperature: 40 ° C.
-Development solvent: tetrahydrofuran-Flow velocity: 1.0 mL / min

Examples 1-3, Comparative Example 1
After preparing an organic solvent type pressure-sensitive adhesive containing an adhesive resin and an organic solvent with the types and blending amounts shown in Table 1, the organic solvent dispersion liquid containing the hydrophobic cellulose nanofibers and the organic solvent shown in Table 1 is adhered. Each of the pressure-sensitive adhesive compositions was prepared by adding to the agent and stirring thoroughly until uniform.
Then, the prepared pressure-sensitive adhesive composition is applied onto one surface of a polyethylene terephthalate (PET) film having a thickness of 50 μm, which is a base material, to form a coating film, and the coating film is heated at 100 ° C. for 2 minutes. It was dried to form a 25 μm thick pressure-sensitive adhesive layer.
Next, a release-treated surface of a light release film (manufactured by Lintec Corporation, product name "SP-PET38131", thickness: 38 μm), which is a release material, is laminated on the exposed surface of the formed pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet with a base material was prepared by laminating the base material, the pressure-sensitive adhesive layer, and the release material in this order.

Further, the base material is changed to a heavy-release film (manufactured by Lintec Co., Ltd., product name "SP-PET382150", thickness: 38 μm), which is a release material, and the above-mentioned is applied on the release-treated surface of the heavy-release film. A baseless pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive layer having a thickness of 25 μm by the same method, then laminating a light-release film, and then laminating a heavy-release film, a pressure-sensitive adhesive layer, and a light-release film in this order. Was also made.

The details of each component used in the preparation of the pressure-sensitive adhesive composition are as follows.
<Adhesive resin>
Acrylic resin (1): Acrylic copolymer (BA / AAc = 90/10 (mass ratio)) obtained by copolymerizing a raw material monomer composed of n-butyl acrylate (BA) and acrylic acid (AAc). ), Mw = 700,000.

<Hydrophobicized cellulose nanofiber organic solvent dispersion>
-CNF (1): Chemically modified, manufactured by Nippon Paper Co., Ltd., concentration 1.3%, average diameter (thickness) = 3.8 nm, average length = 0.7 μm, average aspect ratio = 184. Weigh 100 g of cellulose nanofibers (carboxyl group amount 1.4 mmol / g) and 100 g of ion-exchanged water in a 500 ml beaker, add hydrochloric acid to adjust the pH to 2.5, and then wash thoroughly with water. An acid-type carboxylated TEMPO-oxidized CNF was obtained. 200 g of acetone was added to this acid-type carboxylated TEMPO oxidized CNF, the mixture was stirred for 30 minutes, and the mixture was recovered by filtration. By repeating the operation of adding acetone, stirring and filtering three times, an acetone-dispersed CNF in which the solvent was replaced by acetone was obtained. 200 g of toluene was added to this acetone-dispersed CNF, and the mixture was stirred for 30 minutes and recovered by filtration. By repeating the operation of adding toluene, stirring and filtering three times, a toluene-dispersed CNF in which the solvent was replaced with toluene was obtained. The mass ratio of CNF in the slurry was 7.0 wt%. A hydrophobizing agent (JEFFAMINE (registered trademark) M-2005 (manufactured by HUNTSMAN, molecular weight 2000)) was added to the obtained toluene-dispersed CNF to adjust the solid content concentration in the dispersion to 7.5% by mass. The amount of the hydrophobizing agent added was 1 equivalent with respect to the amount of carboxyl groups. This dispersion was defibrated with an ultra-high pressure homogenizer (150 MPa) to produce a toluene dispersion of CNF to which a hydrophobic agent was bound.

<Degree of hydrophobicity of CNF>
A CNF dispersion containing the CNF to be measured (here, a hydrophobic CNF toluene dispersion) is applied onto a PET sheet using an applicator and dried at 120 ° C. for 2 minutes to obtain a CNF having a thickness of 3 μm. A film was formed.
After allowing to stand for 24 hours in a 23 ° C. 50% RH environment, 2 ml of pure water is dropped on the surface of the CNF membrane, and the static contact angle 1 second after the drip is set to the fully automatic contact angle. The static contact angle with water was measured by measuring using a meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DM-701").
As a result, the contact angle of CNF contained in this dispersion was 51.9 °, and it was confirmed that it was hydrophobized.
For comparison, a commercially available TEMPO oxide CNF aqueous dispersion (product name "Serenpia TC-01A", manufactured by Nippon Paper Industries, Ltd.), average diameter (thickness) = 3.8 nm, average length = 0.7 μm A similar measurement was carried out using a chemically modified cellulose nanofiber (aqueous dispersion containing 1% by mass of carboxy group amount 1.4 mmol / g) having an average aspect ratio of 184, and the contact angle was found. It was 35.2 °.

Various physical property values of the pressure-sensitive adhesive sheets produced in Examples and Comparative Examples were measured based on the following methods. These results are shown in Table 1.

<Haze of adhesive layer>
The baseless adhesive sheet produced in Examples and Comparative Examples was sandwiched between two PET films (Product name "Cosmo Shine A4100" manufactured by Toyobo Co., Ltd., thickness 50 μm) with the easy-adhesion side of the PET film inside. The haze value was measured according to JIS K7136 2000 using a haze meter (“NDH 5000” manufactured by Nippon Denshoku Industries Co., Ltd.). In the measurement, 0 point correction was performed using the measured values in the case of only two PET films.

<Gel fraction of adhesive layer>
After cutting the base-free pressure-sensitive adhesive sheet produced in Examples and Comparative Examples into a size of 80 mm in length × 80 mm in width, the light release film and the heavy release film were removed, and only the pressure-sensitive adhesive layer was taken out. Then, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200) whose mass was measured in advance to prepare a test sample. After allowing the test sample to stand in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 24 hours, the mass of the test sample is weighed with a precision balance, and the mass of the polyester mesh is removed from the measured value before immersion. The mass of only the pressure-sensitive adhesive layer was calculated. The mass of the measured pressure-sensitive adhesive layer was defined as M ₁ .
The test sample was then immersed in ethyl acetate at room temperature (23 ° C.) for 168 hours.
After immersion, the test sample was taken out, and the test sample was dried in an oven at 80 ° C. for 12 hours and then allowed to stand for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 50%. The mass of the test sample after drying was weighed with a precision balance, and the mass of the adhesive layer after immersion and drying was calculated by removing the mass of the polyester mesh from the measured values. The mass of the measured pressure-sensitive adhesive layer was defined as M ₂ .
From the value of the mass M ₁ of the pressure-sensitive adhesive layer before immersion and the value of the mass M ₂ of the pressure-sensitive adhesive layer after immersion, the gel fraction of the pressure-sensitive adhesive layer was calculated by the following formula.
-Gel fraction (mass%) = (M ₂ / M ₁ ) x 100

<Adhesive strength>
A test piece was obtained by cutting the pressure-sensitive adhesive sheet with a base material produced in Examples and Comparative Examples into a size of 300 mm in length × 25 mm in width. In an environment of 23 ° C. and 50% RH (relative humidity), the light release film of the test piece was removed, and the surface of the exposed adhesive layer was attached to a stainless steel plate (SUS304 360 polishing) in the same environment. It was allowed to stand underneath for 24 hours.
After standing, the adhesive force when the test piece was peeled from the stainless steel plate was measured at a tensile speed (peeling speed) of 300 mm / min by a 180 ° peeling method based on JIS Z0237: 2000.

<Holding power>
The pressure-sensitive adhesive sheet with a base material produced in Examples and Comparative Examples was cut into a size of 25 mm in length × 100 mm in width and used as a test piece. In an environment of 23 ° C. and 50% RH (relative humidity), the light release film of the test piece was removed, and the surface of the exposed adhesive layer was made of a stainless steel plate (SUS304, 360 polishing) as an adherend. The sticking surface was 25 mm in length × 25 mm in width. At the time of this attachment, a roller weighing 2 kg was used and reciprocated 5 times to be pressure-bonded to the adherend.
After sticking, let stand for 20 minutes, then move it into a constant temperature layer at a temperature of 40 ° C., attach a 1 kg weight to the adhesive sheet so that a load is applied in the vertical direction, and the adhesive sheet slips off and completely from the adherend. The elapsed time RT ₁ (seconds) until it peeled off was measured.
After the application, the mixture was allowed to stand for 20 minutes, then transferred to a constant temperature layer at a temperature of 80 ° C., and the elapsed time RT ₂ (seconds) until the adherend was completely peeled off was measured by the same procedure as described above. did.
It can be said that the longer these elapsed times are, the more excellent the adhesive sheet is in holding power. In the column of holding force in Table 1, "cf" means that the adhesive sheet was coagulated and broken and peeled off from the adherend.

The pressure-sensitive adhesive sheets produced in Examples 1 to 3 had good adhesive strength, and also showed higher holding power than Comparative Example 1 at both 40 ° C. and 80 ° C. In addition, as the content of the hydrophobized CNF increased, the holding power tended to increase particularly at high temperatures.
Further, the pressure-sensitive adhesive sheets prepared in Examples 1 to 3 all had a small haze value, indicating that the hydrophobized CNF was well dispersed in the pressure-sensitive adhesive. In addition, through these adhesive sheets, the characters on the other side of the adhesive sheet could be visually recognized.
Furthermore, the pressure-sensitive adhesive sheets produced in Examples 1 to 3 all have a small gel fraction, and unlike the pressure-sensitive adhesive in which the pressure-sensitive adhesive resin is crosslinked with a cross-linking agent, the amount of components easily soluble in an organic solvent is very large. Nevertheless, good adhesive strength and holding power could be imparted.

1a, 1b, 1c, 1d Adhesive sheet 11 Base materials 12, 12a, 12b Adhesive layers 13, 13a, 13b Release material

Claims (10)

A pressure-sensitive adhesive composition containing an organic solvent-type pressure-sensitive adhesive (A) containing a pressure-sensitive adhesive resin (A1) and hydrophobic cellulose nanofibers (B). The pressure-sensitive adhesive composition according to claim 1, wherein the organic solvent-type pressure-sensitive adhesive (A) is blended with an organic solvent dispersion containing hydrophobicized cellulose nanofibers (B). The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the hydrophobized cellulose nanofibers (B) is 0.1 to 30 parts by mass with respect to 100 parts by mass of the total amount of the pressure-sensitive adhesive resin (A1). .. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive resin (A1) contains an acrylic resin. The pressure-sensitive adhesive composition according to claim 4, wherein the acrylic resin is a copolymer having a structural unit (a1) derived from an alkyl (meth) acrylate and a structural unit (a2) derived from a functional group-containing monomer. .. The pressure-sensitive adhesive according to any one of claims 1 to 5, wherein the content of the pressure-sensitive adhesive resin (A1) is 50 to 99.95% by mass with respect to the total amount of the active ingredient of the pressure-sensitive adhesive composition. Composition. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, wherein the content of the surfactant is less than 0.001 part by mass with respect to 100 parts by mass of the total amount of the pressure-sensitive adhesive resin (A1). The pressure-sensitive adhesive composition according to any one of claims 1 to 7, wherein the gel fraction is 10% by mass or less. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 8. The adhesive sheet according to claim 9, which has an adhesive strength of 10 N / 25 mm or more.