JP6559489B2 - Easy-release adhesive composition - Google Patents

Description

 The present invention relates to an easily peelable adhesive composition.

  An adhesive is used when a label or the like is attached to the container or a poster is attached to the wall. In some cases, the labels or posters need to be peeled off for recycling or re-sealing the container. In the case of peeling, it becomes a problem that the adhesive remains on the base material such as a container or a wall. Therefore, an adhesive that can be easily peeled is required.

  As such an adhesive that can be easily peeled off, a thermoplastic resin having a glass transition temperature of less than 50 ° C., a tackifier, a solid plasticizer, a melting point of 150 ° C. or lower and an acid value of 2 or higher. And an easily peelable thermosensitive adhesive (Patent Document 1) containing resin waxes having a glass transition temperature of 50 ° C. or higher and an average particle size of 10 μm or less, (A) a tackifying resin (B) aqueous A resin emulsion, (C) a release-type aqueous hot-melt adhesive composition containing a release agent (Patent Document 2), a starch-based adhesive, and a non-starch-based adhesive having an adhesive strength of 2.45 N or more alone An adhesive for container labels (Patent Document 3) having an adhesive strength of greater than 0.78N and less than 2.65N is disclosed.

JP 11-35920 A JP 2003-286470 A JP 2008-81592 A

  However, the adhesive requires treatment such as immersion in water (Patent Document 1) and energy irradiation (Patent Document 2) for peeling. Moreover, in the case of an adhesive that emphasizes peelability that does not require treatment, there is a problem that the adhesive strength is insufficient (Patent Document 3).

  Accordingly, an object of the present invention is to provide an easily peelable adhesive composition that has high adhesive strength, does not require special treatment for peeling, and does not cause the adhesive to remain on the base material.

The present invention provides the following [1] to [3].
[1] An easily peelable adhesive composition comprising cellulose nanofibers.
[2] The easily peelable adhesive according to [1], wherein the cellulose nanofiber has a number average fiber diameter of 2 nm to 500 nm, a fiber aspect ratio of 50 or more, and a cellulose I-type crystal structure. composition.
[3] The easily peelable adhesive composition according to [1] or [2], wherein the cellulose nanofiber is anion-modified.

   The easily peelable adhesive composition of the present invention has high adhesive strength, does not require special treatment for peeling, and has the effect that the adhesive does not remain on the substrate.

  Next, embodiments of the present invention will be described in detail.

  The cellulose nanofiber of the present invention is a fiber obtained by defibrating a cellulose raw material to nano size.

  The cellulose nanofibers of the present invention preferably have a number average fiber diameter of 2 nm to 500 nm, a fiber aspect ratio of 50 or more, and a cellulose I-type crystal structure.

  The number average fiber diameter of the cellulose nanofibers is 2 nm or more and 500 nm or less, but preferably 2 nm or more and 150 nm or less, more preferably 2 nm or more and 100 nm or less, and particularly preferably 3 nm or more and 80 nm or less from the viewpoint of adhesive strength. is there. If the number average fiber diameter is less than 2 nm, the strength of the fiber itself may decrease and the adhesive strength may decrease. If the number average fiber diameter exceeds 500 nm, the surface area of the fiber increases and the adhesive strength increases. There is a risk of becoming smaller.

  The maximum fiber diameter of the cellulose nanofibers is preferably 1000 nm or less, particularly preferably 500 nm or less, from the viewpoint that the cellulose nanofiber does not remain on the substrate.

  The number average fiber diameter and the maximum fiber diameter of the cellulose nanofiber can be measured, for example, as follows. That is, an aqueous dispersion of fine cellulose having a solid content of 0.05 to 0.1% by weight was prepared, and the dispersion was cast on a carbon film-coated grid that had been subjected to a hydrophilization treatment. (TEM) observation sample. In addition, when the fiber of a big fiber diameter is included, you may observe the scanning electron microscope (SEM) image of the surface cast on glass. Then, observation with an electron microscope image is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Then, after obtaining an observation image that satisfies this condition, two random axes, vertical and horizontal, per image are drawn on this image, and the fiber diameter of the fiber that intersects the axis is visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope, and the fiber diameter values of the fibers intersecting with each of the two axes are read (thus, at least 20 × 2 × 3 = 120). Information on the fiber diameter of the book is obtained). The maximum fiber diameter and the number average fiber diameter are calculated from the fiber diameter data thus obtained.

  The cellulose nanofiber has an aspect ratio of 50 or more, preferably 100 or more, more preferably 200 or more. If the aspect ratio is less than 50, the strength of the fiber itself may be reduced and the adhesive strength may be reduced.

The aspect ratio of the cellulose nanofibers can be measured, for example, by the following method, that is, a TEM that has been subjected to negative staining with 2% uranyl acetate after the cellulose nanofibers have been cast on a carbon film-coated grid that has been hydrophilized. From the image (magnification: 10,000 times), the number average fiber diameter and fiber length of the cellulose nanofibers were observed. That is, the number average fiber diameter and fiber length were calculated according to the methods described above, and the aspect ratio was calculated according to the following formula (1) using these values.

The cellulose nanofiber is a fiber obtained by refining a naturally-derived cellulose raw material having an I-type crystal structure. That is, in the process of biosynthesis of natural cellulose, nanofibers called microfibrils are first formed almost without exception, and these form a multi-bundle to form a higher order solid structure.

  The cellulose constituting the cellulose nanofiber has an I-type crystal structure, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, in the vicinity of 2 theta = 14-17 ° and 2 theta = 22-23 °. It can be identified by having typical peaks at two nearby positions.

  The cellulose nanofiber can be produced by a known method, specifically as follows.

  For example, it can be obtained by suspending natural cellulose in water and treating it with a high-pressure homogenizer or a grinder to make it fine.

  Natural cellulose is not particularly limited as long as it is cellulose derived from plants, animals, or microorganisms. Kraft pulp or dissolving pulp derived from conifers or hardwoods, cotton linter, lignocellulose with low cellulose purity, wood flour, plant cellulose, bacterial cellulose Etc.

  The cellulose nanofiber may be bacterial cellulose produced by bacteria. Examples of the bacterium include Acetobacter genus, and more specifically, Acetobacter aceti, Acetobacter subsp., Acetobacterxylinum, and the like. It is done. By culturing these bacteria, cellulose is produced from the bacteria. Since the obtained product contains bacteria and cellulose nanofibers (bacterial cellulose) that are produced from the bacteria and are connected to the bacteria, the product is removed from the medium, washed with water, or treated with alkali. By removing the bacteria, water-containing bacterial cellulose that does not contain bacteria can be obtained.

  The cellulose nanofiber is preferably anion-modified. Specifically, examples of the anion-modified cellulose include oxidized cellulose, carboxymethyl cellulose, polyvalent carboxymethyl cellulose, and long-chain carboxycellulose. Of these, oxidized cellulose is preferred because of excellent hydroxyl group selectivity on the fiber surface and mild reaction conditions.

  Carboxymethyl cellulose is also preferred from the viewpoint of versatility and safety.

  The oxidized cellulose uses natural cellulose as a raw material, uses an N-oxyl compound as an oxidation catalyst in water, and reacts with a co-oxidant to oxidize the natural cellulose to obtain reactant fibers, removing impurities. Thus, it can be obtained by a production method including a purification step of obtaining a reactant fiber impregnated with water and a dispersion step of dispersing the reactant fiber impregnated with water in a solvent.

  In the oxidized cellulose, it is preferable that the hydroxyl group at the C6 position of each glucose unit in the cellulose molecule is selectively oxidized and modified to become one of an aldehyde group, a ketone group, and a carboxyl group. The carboxyl group content (carboxyl group amount) is preferably in the range of 1.2 to 2.5 mmol / g, more preferably in the range of 1.5 to 2.0 mmol / g, from the viewpoint of dispersibility in water.

  The carboxyl group amount of the oxidized cellulose is measured by, for example, preparing 60 ml of a 0.5 to 1% by weight slurry from a cellulose sample obtained by accurately weighing the dry weight, and adjusting the pH to about 2.5 with a 0.1 M hydrochloric acid aqueous solution. Then, 0.05M sodium hydroxide aqueous solution is dripped and electrical conductivity measurement is performed. The measurement is continued until the pH is about 11. The amount of carboxyl groups can be determined from the amount of sodium hydroxide consumed in the neutralization step of the weak acid with a gentle change in electrical conductivity (V) according to the following formula (2).

In addition, adjustment of a carboxyl group amount can be performed by controlling the addition amount and reaction time of the co-oxidant used at the oxidation process of a cellulose nanofiber so that it may mention later.

  The oxidized cellulose is preferably reduced with a reducing agent after the oxidative modification. As a result, part or all of the aldehyde group and the ketone group are reduced to return to the hydroxyl group. Note that the carboxyl group is not reduced. And, by the reduction, the total content of aldehyde groups and ketone groups as measured by the semicarbazide method of the cellulose nanofiber is preferably 0.3 mmol / g or less, particularly preferably 0 to 0.1 mmol / g. , Most preferably substantially 0 mmol / g. Thereby, it becomes what was excellent in the storage stability of an easily peelable adhesive composition.

The oxidized cellulose is oxidized using a co-oxidant in the presence of an N-oxyl compound such as 2,2,6,6-tetramethylpiperidine (TEMPO), and an aldehyde group generated by the oxidation reaction. It is preferable that the ketone group is reduced with a reducing agent because the cellulose nanofiber can be easily obtained. Also, reduction with the reducing agent, the is by hydrogenation sodium borohydride (NaBH _4), more preferable from the viewpoint.

  Measurement of the total content of aldehyde groups and ketone groups by the semicarbazide method is performed, for example, as follows. Specifically, 50 ml of a semicarbazide hydrochloride 3 g / l aqueous solution adjusted to pH = 5 with a phosphate buffer is accurately added to the dried sample, sealed, and shaken for 2 days. Next, 10 ml of this solution is accurately collected in a 100 ml beaker, 25 ml of 5N sulfuric acid and 5 ml of 0.05N potassium iodate aqueous solution are added and stirred for 10 minutes. Thereafter, 10 ml of 5% potassium iodide aqueous solution was added, and immediately titrated with a 0.1N sodium thiosulfate solution using an automatic titrator. From the titration amount and the like, according to the following formula (3), The amount of carbonyl groups (total content of aldehyde groups and ketone groups) can be determined. Semicarbazide reacts with an aldehyde group or a ketone group to form a Schiff base (imine), but does not react with a carboxyl group. Therefore, it is considered that only the aldehyde group and the ketone group can be quantified by the above measurement.

In the oxidized cellulose, the hydroxyl group at the C6 position of each glucose unit in the cellulose molecule on the fiber surface is selectively oxidized and modified to become one of an aldehyde group, a ketone group and a carboxyl group. Whether or not only the hydroxyl group at the C6 position of the glucose unit on the cellulose nanofiber surface is selectively oxidized can be confirmed by, for example, a ¹³ C-NMR chart. That is, a 62 ppm peak corresponding to the C6 position of the primary hydroxyl group of the glucose unit, which can be confirmed by a ¹³ C-NMR chart of cellulose before oxidation, disappears after the oxidation reaction, and instead a peak derived from a carboxyl group or the like (178 ppm) The peak of is a peak derived from a carboxyl group). In this way, it can be confirmed that only the C6 hydroxyl group of the glucose unit is oxidized to a carboxyl group or the like.

  Moreover, the detection of the aldehyde group in the said oxidized cellulose can also be performed, for example with a Faring reagent. That is, for example, after adding a Fering reagent (a mixed solution of sodium potassium tartrate and sodium hydroxide and an aqueous solution of copper sulfate pentahydrate) to a dried sample, the supernatant is obtained when heated at 80 ° C. for 1 hour. When blue and cellulose nanofiber parts are amber, it can be judged that aldehyde groups have not been detected, and when the supernatant is yellow and cellulose fiber parts are red, it can be judged that aldehyde groups have been detected. it can.

  The cellulose nanofibers obtained by defibrating the oxidized cellulose are preferably produced by (1) an oxidation reaction step, (2) a reduction step, (3) a purification step, (4) a dispersion step (a refinement treatment step), etc. Specifically, it is preferable to manufacture by the following steps.

(1) Oxidation reaction step After natural cellulose and an N-oxyl compound are dispersed in water (dispersion medium), a cooxidant is added to start the reaction. During the reaction, a 0.5 M aqueous sodium hydroxide solution is added dropwise to maintain the pH at 10 to 11, and the reaction is regarded as completed when no change in pH is observed. Here, the co-oxidant is not a substance that directly oxidizes a cellulose hydroxyl group but a substance that oxidizes an N-oxyl compound used as an oxidation catalyst.

  The natural cellulose means purified cellulose isolated from cellulose biosynthetic systems such as plants, animals, and bacteria-producing gels. More specifically, softwood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, non-wood pulp such as straw pulp and bagasse pulp, bacterial cellulose (BC), cellulose isolated from sea squirt, seaweed Cellulose isolated from can be mentioned. These may be used alone or in combination of two or more. Among these, soft wood pulp, hardwood pulp, cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as straw pulp and bagasse pulp are preferable. The natural cellulose is preferably subjected to a treatment for increasing the surface area such as beating, because the reaction efficiency can be increased and the productivity can be increased. In addition, if the natural cellulose that has been stored after being isolated and purified and not dried (never dry) is used, the microfibril bundle is easily swollen. This is preferable because the number average fiber diameter after the crystallization treatment can be reduced.

  The dispersion medium of natural cellulose in the reaction is water, and the concentration of natural cellulose in the reaction aqueous solution is arbitrary as long as the reagent (natural cellulose) can be sufficiently diffused. Usually, it is about 5% or less based on the weight of the reaction aqueous solution, but the reaction concentration can be increased by using a device having a strong mechanical stirring force.

  Examples of the N-oxyl compound include compounds having a nitroxy radical generally used as an oxidation catalyst. The N-oxyl compound is preferably a water-soluble compound, more preferably a piperidine nitroxyoxy radical, especially 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) or 4-acetamido-TEMPO. preferable. The N-oxyl compound is added in a catalytic amount, preferably 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l.

  Examples of the co-oxidant include hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogen acid or a salt thereof, hydrogen peroxide, a perorganic acid, and the like. These may be used alone or in combination of two or more. Of these, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are preferable. And when using the said sodium hypochlorite, it is preferable to advance reaction in presence of alkali bromide metals, such as sodium bromide, from the point of reaction rate. The addition amount of the alkali metal bromide is about 1 to 40 times mol, preferably about 10 to 20 times mol for the N-oxyl compound.

  The pH of the aqueous reaction solution is preferably maintained in the range of about 8-11. The temperature of the aqueous solution is arbitrary at about 4 to 40 ° C., but the reaction can be performed at room temperature (25 ° C.), and the temperature is not particularly required to be controlled. In order to obtain a desired amount of carboxyl group and the like, the degree of oxidation is controlled by the amount of co-oxidant added and the reaction time. Usually, the reaction time is completed within about 5 to 120 minutes, at most 240 minutes.

(2) Reduction step It is preferable that the oxidized cellulose further undergoes a reduction reaction after the oxidation reaction. Specifically, fine oxidized cellulose after the oxidation reaction is dispersed in purified water, the pH of the aqueous dispersion is adjusted to about 10, and the reduction reaction is performed with various reducing agents. As the reducing agent used in the present invention, a general reducing agent can be used, and preferred examples include LIBH ₄ , NaBH ₃ CN, NaBH _{4 and the} like. Of these, NaBH ₄ is preferable from the viewpoint of cost and availability.

  The amount of the reducing agent is preferably in the range of 0.1 to 4% by weight, particularly preferably in the range of 1 to 3% by weight, based on the fine oxidized cellulose. The reaction is usually carried out at room temperature or slightly higher than room temperature, usually 10 minutes to 10 hours, preferably 30 minutes to 2 hours.

  After completion of the reaction, the pH of the reaction mixture is adjusted to about 2 with various acids, and solid-liquid separation is performed with a centrifuge while sprinkling purified water to obtain cake-like fine oxidized cellulose. Solid-liquid separation is performed until the electric conductivity of the filtrate is 5 mS / m or less.

(3) Purification step Next, purification is performed for the purpose of removing unreacted co-oxidant (such as hypochlorous acid) and various by-products. At this stage, the reactant fibers are usually not dispersed evenly to the nanofiber unit. Therefore, by repeating the usual purification method, that is, washing with water and filtration, the reactant fibers are highly purified (99% by weight or more). Use water dispersion.

  As the purification method in the purification step, any apparatus can be used as long as it can achieve the above-described object, such as a method using centrifugal dehydration (for example, continuous decanter). The aqueous dispersion of reactant fibers thus obtained is in the range of approximately 10 wt% to 50 wt% as the solid content (cellulose) concentration in the squeezed state. Considering the subsequent dispersion step, if the solid content concentration is higher than 50% by weight, it is not preferable because extremely high energy is required for dispersion.

(4) Dispersion process (miniaturization process)
The reaction fiber (water dispersion) impregnated with water obtained in the purification step is dispersed in a dispersion medium and subjected to a dispersion treatment. With the treatment, the viscosity increases, and a dispersion of cellulose nanofibers that has been refined can be obtained. Thereafter, the cellulose nanofibers may be dried as necessary. Examples of the method for drying the cellulose nanofiber dispersion include spray drying, freeze drying, and vacuum drying when the dispersion medium is water. When the dispersion medium is a mixed solution of water and an organic solvent, a drying method using a drum dryer, a spray drying method using a spray dryer, or the like is used. The cellulose nanofiber dispersion may be used in the state of dispersion without drying.

  Dispersers used in the dispersion step include a homomixer under high-speed rotation, a high-pressure homogenizer, an ultra-high pressure homogenizer, an ultrasonic dispersion processor, a beater, a disk type refiner, a conical type refiner, a double disk type refiner, a grinder, and the like. Use of a powerful and beating-capable device is preferable in that a more efficient and advanced downsizing is possible, and a water-containing lubricant composition can be obtained economically advantageously. Examples of the disperser include a screw mixer, paddle mixer, disper mixer, turbine mixer, disper, propeller mixer, kneader, blender, homogenizer, ultrasonic homogenizer, colloid mill, pebble mill, and bead mill grinder. It can be used. Further, two or more types of dispersers may be used in combination.

  Carboxymethyl cellulose, which is one of the anion-modified cellulose nanofibers, can be produced by the following method using the cellulose raw material. That is, cellulose is used as a raw material, and the solvent is 3 to 20 times lower alcohol, specifically methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, etc. Or a mixture of two or more and water. In addition, the mixing ratio of a lower alcohol is 60-95 mass%. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per glucose residue of cellulose. Cellulose is formed by mixing cellulose, a solvent, and a mercerizing agent. The reaction temperature at this time is 0 to 70 ° C., preferably 10 to 60 ° C., and the reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, the etherification reaction is carried out by adding 0.05 to 10-fold mol of carboxymethylating agent per glucose residue. The reaction temperature at this time is 30 to 90 ° C., preferably 40 to 80 ° C., and the reaction time is 30 minutes to 10 hours, preferably 1 hour to 4 hours.

  Cellulose nanofibers can be obtained by defibrating the carboxymethylcellulose with a high-pressure homogenizer or the like. A high-pressure homogenizer is a device that pressurizes a fluid with a pump and ejects it from a very delicate gap provided in a flow path. It is possible to emulsify, disperse, defibrate, grind, and make ultrafine particles by using total energy such as collision between particles and shear force due to pressure difference.

  The treatment conditions with the homogenizer of the present invention are not particularly limited, but the pressure conditions are 30 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more. In addition, prior to defibration / dispersion treatment with a high-pressure homogenizer, carboxymethyl cellulose can be pretreated using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer as necessary. is there.

  In this invention, it is preferable that the carboxymethyl substitution degree per glucose unit of carboxymethylcellulose is 0.02 or more and 0.50 or less. By introducing a carboxymethyl substituent into cellulose, the celluloses are electrically repelled. For this reason, the cellulose which introduce | transduced the carboxymethyl substituent can be nano-defibrated easily. In addition, when the carboxymethyl substituent per glucose unit is smaller than 0.02, nano-defibration cannot be sufficiently performed, and the adhesive strength may be reduced. On the other hand, if the carboxymethyl substituent per glucose unit is larger than 0.50, it swells or dissolves, so that it cannot be obtained as a nanofiber and the adhesive strength may be lowered. The easily peelable adhesive composition of the present invention is an aqueous solution in which the cellulose nanofibers and other additives are dispersed in water.

Although content of the said cellulose nanofiber in the easily peelable adhesive composition of this invention is not specifically limited, 0.01 mass% or more and 10.0 mass% or less are preferable, and 0.1 mass% or more and 2 mass% or less are more preferable. . If content of a cellulose nanofiber is 0.01 mass% or more and 10 mass% or less, the applicability | paintability of an easily peelable adhesive composition will be excellent.
Other additives can be added to the easily peelable adhesive composition of the present invention as long as the effects of the present invention are not impaired.

  Examples of the other additives include plastic resins and rubbers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antioxidants, anti-blocking agents, flow improvers, mold release agents, flame retardants, and colorants. , Inorganic neutralizers, hydrochloric acid absorbents, fillers, conductive agents, antifoaming agents, viscosity modifiers and the like.

  The easily peelable adhesive composition of the present invention can be produced by adding various additives to the aqueous dispersion of cellulose nanofibers as necessary and mixing them by a known stirring technique.

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples. In the examples, “%” means mass basis unless otherwise specified.

[Production of Cellulose Fiber A1 (for Examples)]
50 g of softwood bleached kraft pulp (NBKP) was dispersed in 4950 g of water to prepare a dispersion having a pulp concentration of 1% by mass. This dispersion was treated 30 times with serendipeater MKCA6-3 (manufactured by Masuko Sangyo Co., Ltd.) to obtain cellulose fiber A1.

[Production of Cellulose Fiber A2 (for Examples)]
100 g of softwood pulp was placed in a mixed solution of 435 g of isopropanol (IPA), 65 g of water and 9.9 g of NaOH, and stirred at 30 ° C. for 1 hour. To this slurry system was added 23.0 g of an IPA solution of 50% monochloroacetic acid, and the mixture was heated to 70 ° C. and reacted for 1.5 hours. The obtained reaction product was washed with 80% methanol, then substituted with methanol and dried to produce carboxymethylated cellulose fibers. Next, pure water was added to the cellulose fiber to dilute it to 2%, and the fiber was treated once with a high-pressure homogenizer (manufactured by Sanwa Engineering, H11) at a pressure of 100 MPa to produce cellulose fiber A2.

[Production of Cellulose Fiber A3 (for Examples)]
After adding 150 ml of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO to 2 g of softwood pulp, and thoroughly stirring and dispersing, 13 wt% sodium hypochlorite aqueous solution (co-oxidant) was added to the pulp 1. The reaction was started by adding sodium hypochlorite so that the amount of sodium hypochlorite was 12 mmol / g with respect to 0 g. Since the pH decreased with the progress of the reaction, the reaction was continued until no change in pH was observed while dropping a 0.5N aqueous sodium hydroxide solution so that the pH was maintained at 10-11 (reaction time: 120 minutes). ). After completion of the reaction, 0.1N hydrochloric acid was added for neutralization, followed by purification by repeated filtration and washing to obtain cellulose fibers having oxidized fiber surfaces. Next, pure water was added to the cellulose fiber to dilute it to 2%, and the fiber was treated once with a high pressure homogenizer (manufactured by Sanwa Engineering Co., H11) at a pressure of 100 MPa to produce cellulose fiber A3.

[Production of Cellulose A′1 (for Comparative Example)]
According to the production of cellulose fiber A3, except that regenerated cellulose is used instead of the raw conifer pulp, and the addition amount of the sodium hypochlorite aqueous solution is 27.0 mmol / g with respect to 1.0 g of regenerated cellulose. Thus, cellulose A′1 was produced.
About each cellulose obtained as mentioned above, each characteristic was evaluated according to the following reference | standard. The results are also shown in Table 1 below.

〔Crystal structure〕
Using an X-ray diffractometer (Rigaku Corporation, RINT-UltIma3), the diffraction profile of each cellulose fiber was measured, and at two positions near 2 theta = 14-17 ° and 2 theta = 22-23 °. When a typical peak was observed, the crystal structure (type I crystal structure) was evaluated as “present”, and when no peak was observed, it was evaluated as “none”.

[Number average width of shorter width]
The number average width of cellulose was observed using a transmission electron microscope (TEM) (manufactured by JEOL Ltd., JEM-1400). That is, from the TEM image (magnification: 10000 times) negatively stained with 2% uranyl acetate after each cellulose fiber was cast on a hydrophilized carbon film-coated grid, The number average width of was calculated.

〔aspect ratio〕
From the TEM image (magnification: 10000 times) that was negatively stained with 2% uranyl acetate after the cellulose was cast on a hydrophilic membrane-coated carbon film grid, the number average width and the long width of the short width of cellulose The number average width of was observed. That is, the number average width of the shorter width and the number average width of the longer width are calculated according to the methods described above, and the aspect ratio is calculated according to the following formula (1) using these values. .

From the results shown in Table 1, the celluloses A1 to A3 for Examples all had a cellulose I type crystal structure within the range where the number average width of the shorter width was 2 to 500 nm.

[Example 1]
The cellulose fiber A1 was diluted to 0.1% with pure water. This was applied to high-quality paper (adhesive) cut to 5 cm × 5 cm, and bonded to high-quality paper (base material) cut to 8 cm × 8 cm. After bonding for 3 minutes with a force of about 5 kgf, it was left to dry for 24 hours.
With respect to the adhesive, the adhesive strength and easy peelability were evaluated by the following methods.

<Evaluation method of adhesive strength>
Acrylic plates were attached to both sides of the adhesive with double-sided tape, and hooks were attached to the acrylic plates on the adhesive side. Only the acrylic plate on the base material side was fixed with screws with the hook down. The weight was gently suspended from the hook, and the weight of the weight when the adhesive surface was peeled was defined as the adhesive strength (kgf / cm ² ).

<Evaluation method of easy peelability>
The adhesive was gently peeled from one side, the state of the adhesive and the substrate was visually observed, and easy peelability was evaluated as follows.
++++: No adhesive or adhesive remains on the substrate, and the adhesive does not break.
++: Adhesive and adhesive remain slightly on the substrate, but the adhesive is hardly broken.
+: Adhesive body and adhesive remain on the substrate, and the adhesive body is slightly broken.
-: Many adhesive bodies and adhesives remain on the base material, and the adhesive body hardly retains its original shape.

[Example 2] to [Example 4]
It was prepared and evaluated in the same manner as in Example 1 except that the dilution concentration of the cellulose fiber A1 was 0.2 to 1.0%.

[Example 5], [Example 6]
Preparation and evaluation were performed in the same manner as in Example 2 except that wood and a glass plate were used instead of the fine paper.

[Example 7] to [Example 12]
Preparation and evaluation were performed in the same manner as in Examples 2, 5 and 6 except that A2 and A3 were used instead of cellulose fiber A1.

[Comparative Example 1] to [Comparative Example 4]
It was prepared and evaluated in the same manner as in Example 2 except that A′1, starch paste, polyvinylpyrrolidone (PVP), and carboxymethylcellulose (CMC) were used instead of cellulose fiber A1.

Table 2 shows the compositions and evaluation results of the above Examples and Comparative Examples.
Although all of the adhesives of the examples have sufficient adhesive strength in the direction perpendicular to the surface, they can be easily peeled off when a force is applied from one direction. Almost no residual adhesive was observed.

  On the other hand, when cellulose fiber A′1 was used, it could not be bonded. In addition, when starch glue, PVP, or CMC, which is generally used as an adhesive, was used, adhesion in the direction perpendicular to the surface was possible. It was impossible to peel off.

The easily peelable adhesive composition of the present invention is useful for attaching labels such as foods and cosmetics, and attaching posters to wall surfaces.

Claims (2)

Cellulose nanofibers having a cellulose I-type crystal structure, a number average fiber diameter of 2 nm to 500 nm, and a fiber aspect ratio of 50 or more ;
Consisting of water,
The cellulose nanofiber content is 0.01% by mass or more and 10.0% by mass or less.
Easy peelable adhesive composition for paper .   The easily peelable adhesive composition for paper according to claim 1, wherein the cellulose nanofiber is anion-modified.