JP7173012B2 - TOTAL HEAT EXCHANGER SHEET, TOTAL HEAT EXCHANGER ELEMENT, AND TOTAL HEAT EXCHANGER - Google Patents

Description

TECHNICAL FIELD The present invention relates to a total heat exchanger sheet, a total heat exchanger element, and a total heat exchanger.

BACKGROUND ART Conventionally, a heat exchange ventilator (heat exchanger) that exchanges heat between supply air and exhaust air during ventilation has been proposed as a device that can ventilate without impairing the effects of cooling and heating. As this heat exchanger, a plurality of partition plates (liners) are laminated via spacers, and an air supply path for introducing outdoor air into the room and an exhaust path for discharging indoor air to the outside are separated, Total heat exchangers are widely used to exchange latent heat (humidity) at the same time as sensible heat (temperature).
Patent Document 1 discloses a fine cellulose fiber nonwoven fabric layer made of fine cellulose fibers for the purpose of providing a multilayer structure having high air permeability and high moisture permeability and which is highly suitable as a sheet for a total heat exchanger. A multilayer structure comprising at least one layer is described.

WO2014/014099

The present invention provides a total heat exchanger sheet having high moisture permeability and air permeability and excellent carbon dioxide barrier properties, a total heat exchanger element comprising the total heat exchanger sheet, and a total heat exchanger element comprising the total heat exchanger element. The object is to provide a heat exchanger.

The present inventors have found that a total heat exchanger sheet provided with a fiber layer containing fine cellulose fibers has high air permeability and moisture permeability and carbon dioxide barrier properties by setting the water content to a specific content. It was found that an excellent total heat exchanger sheet can be obtained.
That is, the present invention relates to the following <1> to <18>.
<1> It has a substrate layer and a fiber layer provided on the substrate layer, and the fiber layer contains fine cellulose fibers having a fiber width of 1,000 nm or less and has a water content of 8% by mass. A sheet for a total heat exchanger, which is the above.
<2> The total heat exchanger sheet according to <1>, further comprising a moisture absorbent.
<3> The moisture absorbent is at least one selected from metal halides, metal sulfates, metal acetates, amine salts, phosphoric acid compounds, guanidine salts, and metal hydroxides (preferably metal halide salts , more preferably alkali metal halides, alkaline earth metal halides, and still more preferably at least one selected from the group consisting of lithium chloride and calcium chloride).
<4> The sheet for a total heat exchanger according to <2> or <3>, wherein the content of the moisture absorbent is 100 parts by mass or more relative to 100 parts by mass of the fine cellulose fibers.
<5> The fine cellulose fibers contain an ionic group (preferably an anionic group, more preferably a phosphate group or a group derived from a phosphate group, a carboxy group or a group derived from a carboxy group, and a sulfonic acid group or a sulfonic acid group). at least one selected from groups derived from groups, more preferably at least one selected from a phosphate group or a group derived from a phosphate group, and a carboxy group or a group derived from a carboxy group, still more preferably The total heat exchanger sheet according to any one of <1> to <4>, having a phosphoric acid group or a group derived from a phosphoric acid group.
<6> The sheet for a total heat exchanger according to any one of <1> to <5>, wherein the surface on the fiber layer side has a water contact angle of 50° or more.
<7> D1/D2 is 0.25 or more and 4 or less, where D1 is the contact angle of water on one surface of the total heat exchanger sheet and D2 is the contact angle of water on the other surface, <1> The sheet for a total heat exchanger according to any one of <6>.
<8> The total heat exchanger sheet according to any one of <1> to <7>, wherein the fine cellulose fibers have a fiber width of 30 nm or less.
<9> The total heat exchanger sheet according to any one of <1> to <8>, wherein the fine cellulose fibers have a basis weight of 0.1 g/m ² or more and 3 g/m ² or less.
<10> The sheet for a total heat exchanger according to any one of <1> to <9>, comprising one substrate layer and one fiber layer provided on the substrate layer.
<11> The total heat exchanger sheet according to any one of <1> to <10>, which has a water content of 25% by mass or less.
<12> Further, it contains a moisture absorbent, and the basis weight of the moisture absorbent is 1 g/m ² or more and 20 g/m ² or less, preferably 3 g/m ² or more and 15 g/m ² or less, more preferably 5 g/m ² or more and 12 g/m 2 . The sheet for a total heat exchanger according to any one of <1> to <11>, which is m ² or less.
<13> The total heat exchanger sheet according to any one of <1> to <12>, wherein the base material layer and the fiber layer contain a moisture absorbent.
<14> Density is 0.65 g/cm ³ or more and 1.3 g/cm ³ or less (preferably 0.7 g/cm ³ or more and 1.3 g/cm ³ or less, more preferably 0.75 g/cm ³ or more and 1.0 g /cm ³ or less), the total heat exchanger sheet according to any one of <1> to <13>.
<15> The sheet for a total heat exchanger according to any one of <1> to <14>, having a thickness of 20 μm or more and 150 μm or less (preferably 20 μm or more and 120 μm or less, more preferably 30 μm or more and 100 μm or less).
<16> Basis weight is 10 g/m ² or more and 300 g/m ² or less (preferably 10 g/m ² or more and 200 g/m ² or less, more preferably 30 g/m ² or more and 100 g/m ² or less, still more preferably 30 g/m 2 or more) m ² or more and 80 g/m ² or less), the total heat exchanger sheet according to any one of <1> to <15>.
<17> A total heat exchanger element comprising the total heat exchanger sheet according to any one of <1> to <16>.
<18> A total heat exchanger comprising the element for a total heat exchanger according to <17>.

According to the present invention, a total heat exchanger sheet having high moisture permeability and air permeability and excellent carbon dioxide barrier properties, a total heat exchanger element having the total heat exchanger sheet, and the total heat exchanger element A total heat exchanger is provided comprising:

FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and electrical conductivity with respect to fiber raw materials having phosphate groups. FIG. 2 is a graph showing the relationship between the amount of NaOH dripped onto a fiber raw material having a carboxyl group and electrical conductivity.

[Total heat exchanger sheet]
The sheet for a total heat exchanger of the present invention has a substrate layer and a fiber layer provided on the substrate layer, the fiber layer containing fine cellulose fibers having a fiber width of 1,000 nm or less, Moisture content is 8% by mass or more.
A total enthalpy heat exchanger exchanges heat while supplying fresh outside air and exhausting dirty indoor air. At this time, from the viewpoint of improving the heat exchange efficiency, the sheet for the total heat exchanger is required to be able to transfer sensible heat (temperature) and also to transfer latent heat (humidity) by allowing moisture to pass through. be done. Therefore, moisture permeability and heat conductivity are required.
In addition, high gas barrier properties (mainly carbon dioxide barrier properties) are also required so that supply air and exhaust air do not mix through the total heat exchanger sheet.

Patent Document 1 describes that a multilayer structure having a high air resistance (air permeability) can be obtained by providing a fine cellulose fiber nonwoven fabric layer. has not been considered.
According to the present invention, by setting the water content of the total enthalpy heat exchanger sheet within a specific range, a total enthalpy heat exchanger sheet having high moisture and air permeability and excellent carbon dioxide barrier properties can be obtained. Although the detailed action mechanism by which the above effects are obtained is unknown, part of it is considered as follows.
That is, by providing a fiber layer containing fine cellulose fibers, high air permeability and carbon dioxide barrier properties can be obtained. It is thought that the humidity increased. This is because by setting the moisture content of the total heat exchanger sheet to 8% by mass or more, the total heat exchanger sheet becomes more hydrophilic than when the moisture content is less than 8% by mass, and the moisture permeability is improved. It is presumed that
The present invention will be described in more detail below.

<Base material layer>
The total heat exchanger sheet of the present invention has a substrate layer and a fiber layer provided on the substrate layer.
The base material constituting the base material layer is not particularly limited, and is preferably exemplified by a base material selected from nonwoven fabrics, porous membranes, and fabrics.
In the sheet for a total heat exchanger of the present invention, as described later, it is preferable to form a fiber layer containing fine cellulose on the base material and to further contain a hygroscopic agent. At this time, the "base material" means the base material itself that forms the base material layer before containing the moisture absorbent, and the "base material layer" means the support for the fiber layer in the total heat exchanger sheet. It means the entire support layer including the base material itself and the moisture absorbent.
Examples of nonwoven fabrics include nonwoven fabrics composed of at least one selected from natural cellulose fibers, nylon fibers, polyester fibers, and polyolefin fibers.
Examples of the porous membrane include olefin resins such as polyethylene and polypropylene; polysulfone; fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride and polyvinylidene fluoride; polycarbonate; nylon resins such as 6-nylon and 6,6-nylon. acrylic resins such as polymethyl methacrylate; polyketones such as poly(1-oxytrimethylene); and porous films composed of polyether ether ketones.
Examples of fabrics include cellulose fibers including cellulose derivative fibers, nylon fibers, polyurethane fibers, and fabrics (including union fabrics) made of blended yarns thereof.

Among these, the substrate is preferably a non-woven fabric, more preferably made of plant pulp fiber such as natural cellulose, which is classified as "paper" from the viewpoint of facilitating the formation of a fiber layer and obtaining a desired moisture content. It is a non-woven fabric.
The pulp used as the raw material for the base material may be softwood pulp or hardwood pulp, and the cooking method and bleaching method are not particularly limited. From the viewpoint of the strength of the base material and the carbon dioxide barrier properties, it is preferable to use bleached softwood kraft pulp (NBKP), and it is more preferable to use NBKP as the main raw material. In addition to wood pulp, non-wood pulp such as hemp pulp, kenaf, and bamboo may be used, and materials other than pulp fiber, such as rayon fiber, nylon fiber, and other heat-sealable fibers, may be used as secondary materials. May be blended.
The pulp content in the substrate is preferably 95% by mass or more, more preferably 98% by mass or more, from the viewpoint of facilitating the formation of the fiber layer and obtaining the desired moisture content, and is 100% by mass. good too.
As paper, non-coated printing paper such as fine paper and medium quality paper, information paper such as copy paper, high pressure treated glassine paper (measured by the Canadian Standard Freeness Test Method (CSF) specified in JIS P 8121) 40 to 80 ml, which is freeness), and semi-glassine paper having a pulp freeness lower than that of glassine paper (the above freeness is about 100 to 200 ml).
Among these, fine paper or semi-glassine paper is more preferable, and semi-glassine paper is even more preferable.

Although the air permeability of the substrate is not particularly limited, it is preferably 5 sec or more, more preferably 10 sec or more, and still more preferably 30 sec or more from the viewpoint of increasing the air permeability of the resulting total heat exchanger sheet. Also, from the viewpoint of economy, it is preferably 1,000 sec or less, more preferably 500 sec or less, and even more preferably 200 sec or less. Air permeability is measured by the method described in Examples.

Although the basis weight of the substrate is not particularly limited, it is preferably 5 g/m ² or more, more preferably 10 g/m ² or more, and still more preferably from the viewpoint of setting the basis weight of the resulting total heat exchanger sheet within the desired range. is 20 g/m ² or more, more preferably 25 g/m ² or more, still more preferably 30 g/m ² or more, still more preferably 35 g/m ² or more, and preferably 200 g/m ² or less, more It is preferably 150 g/m ² or less, more preferably 100 g/m ² or less, and even more preferably 70 g/m ² or less. Basis weight is measured by the method described in Examples.

The thickness of the substrate is not particularly limited, but is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of obtaining strength as a support, and from the viewpoint of reducing the thickness of the total heat exchanger sheet as a whole. , preferably 150 μm or less, more preferably 120 μm or less, still more preferably 100 μm or less, even more preferably 90 μm or less, and even more preferably 65 μm or less. The thickness is measured by the method described in Examples.

The density of the substrate is not particularly limited, but from the viewpoint of keeping the density of the total heat exchanger sheet within the desired range, it is preferably 0.3 g/cm ³ or more, more preferably 0.5 g/cm ³ or more, and even more preferably 0.5 g/cm 3 or more. 0.6 g/cm ³ or more, more preferably 0.65 g/cm ³ or more, and preferably 1.3 g from the viewpoint of availability, economy, and suppression of the mass of the total heat exchanger. /cm ³ or less, more preferably 1.0 g/cm ³ or less, still more preferably 0.85 g/cm ³ or less, still more preferably 0.80 g/cm ³ or less. Density is measured by the method described in Examples.

<Fiber layer>
The sheet for a total heat exchanger of the present invention has a fiber layer, and the fiber layer contains fine cellulose fibers having a fiber width of 1,000 nm or less. The fiber width of fine cellulose fibers can be read, for example, with an electron microscope.
The average fiber width of the fine cellulose fibers is preferably 1,000 nm or less, more preferably 100 nm or less, still more preferably 30 nm or less, and even more preferably, from the viewpoint of obtaining a total heat exchanger sheet having excellent air permeability and moisture permeability. is 10 nm or less, more preferably 8 nm or less. Also, the average fiber width of the fine cellulose fibers is preferably 2 nm or more, more preferably 3 nm or more. By setting the average fiber width of the fine cellulose fibers to 2 nm or more, dissolution of the cellulose molecules in water is suppressed, and the effect of improving air permeability and moisture permeability due to the fine cellulose fibers is likely to be exhibited. The fine cellulose fibers are, for example, monofilament-like cellulose.

The average fiber width of cellulose fibers is measured using electron microscopy as follows.
First, an aqueous suspension of cellulose fibers with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on a hydrophilized carbon film-coated grid to serve as a sample for TEM observation. do. SEM images of surfaces cast on glass may be observed if they contain wide fibers.
Then, an electron microscope image is observed at a magnification of 1,000, 5,000, 10,000, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification are adjusted so as to satisfy the following conditions.
(1) A single straight line X is drawn at an arbitrary point in the observed image, and 20 or more fibers intersect the straight line X.
(2) Draw a straight line Y that intersects the straight line perpendicularly in the same image, and 20 or more fibers intersect the straight line Y.
The width of the fiber crossing the straight line X and the straight line Y is visually read from the observed image satisfying the above conditions. In this way, at least three sets of observed images of surface portions that do not overlap each other are obtained. Next, for each image, the width of the fiber crossing the straight line X and the straight line Y is read. This gives at least 20 x 2 x 3 = 120 fiber width readings. And let the average value of the read fiber width be the average fiber width of a cellulose fiber.

Although the fiber length of the fine cellulose fibers is not particularly limited, it is preferably 0.1 μm or more, and preferably 1,000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. By setting the fiber length of the fine cellulose fibers within the above range, it is possible to suppress breakage of the crystalline regions of the fine cellulose fibers. In addition, it becomes possible to set the slurry viscosity of the fine cellulose fibers within an appropriate range, which facilitates the formation of the fiber layer.
The fiber length of the fine cellulose fibers can be determined by image analysis using TEM, SEM, or AFM, for example.

The fine cellulose fibers preferably have a Type I crystal structure. Here, the fact that the fine cellulose fibers have a type I crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by having typical peaks at two positions near 2θ=14° or more and 17° or less and 2θ=22° or more and 23° or less.
The proportion of the I-type crystal structure in the fine cellulose fibers is preferably 30% or more, more preferably 40% or more, still more preferably 50% or more. This is preferable because a fiber layer having excellent strength can be obtained. The degree of crystallinity is determined by a conventional method from the pattern of X-ray diffraction profiles (Seagal et al., Textile Research Journal, vol. 29, p. 786, 1959).

The axial ratio (fiber length/fiber width) of the fine cellulose fibers is not particularly limited, but is preferably 20 or more, more preferably 50 or more, and preferably 10,000 or less, more preferably 1,000 or less. be. By setting the axial ratio within the above range, a slurry viscosity suitable for forming a fiber layer can be obtained.

In the present invention, the basis weight (coating amount) of the fine cellulose fibers is preferably 0.1 g/m ² or more, more preferably 0.2 g/m ² or more, from the viewpoint of obtaining high air permeability and moisture permeability. It is preferably 0.3 g/m ² or more, and is preferably 20 g/m ² or less, more preferably 10 g, from the viewpoint of keeping the thickness of the total heat exchanger sheet within the desired range and from the viewpoint of economy. /m ² or less, more preferably 3 g/m ² or less, and even more preferably 1 g/m ² or less.

In the present invention, it is preferable that at least one group selected from ionic groups and nonionic groups is introduced into the fine cellulose fibers. Also, the ionic group and the nonionic group are preferably hydrophilic groups. From the viewpoint of improving the dispersibility of the fibers in the dispersion medium and enhancing the defibration efficiency in the fibrillation treatment, it is more preferable that the fine cellulose fibers have an ionic group. The ionic group can contain either one or both of an anionic group and a cationic group. In the present invention, it is particularly preferred to have an anionic group as the ionic group.
Examples of the anionic group include a phosphate group or a group derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxy group or a group derived from a carboxy group (sometimes simply referred to as a carboxy group), and a sulfonic acid group. or a group derived from a sulfonic acid group (sometimes referred to simply as a sulfonic acid group), and more preferably at least one selected from a phosphoric acid group and a carboxyl group. A phosphate group is particularly preferred.

A phosphate group is a group that functions as a dibasic acid, which corresponds to phosphoric acid with the hydroxyl group removed. Groups derived from a phosphate group include salts of phosphate groups, phosphate ester groups, and the like. The group derived from a phosphoric acid group may be contained in the fine cellulose fibers as a condensed group of the phosphoric acid group.
A phosphate group or a group derived from a phosphate group is, for example, a group represented by the following formula (1).

In formula (1), a, b and n are natural numbers (where a=b×m). At least one of α ^{1 , α 2} , . All of α ⁿ and α′ may be O ⁻ . When n is 2 or more and α' is R or OR, at least one of each α ⁿ is O ^- and the rest are R or OR. When n is 2 or more and α′ is O ⁻ , each α ⁿ may be all R or all may be OR, at least one may be O ⁻ and the rest may be R or It may be OR. Each R is independently a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched chain represents a hydrocarbon group, an aromatic hydrocarbon group, and a derivative group thereof.
Examples of the saturated straight-chain hydrocarbon group include, but are not limited to, methyl group, ethyl group, n-propyl group, n-butyl group, and the like. The saturated-branched hydrocarbon group includes i-propyl group, t-butyl group and the like, but is not particularly limited. The saturated cyclic hydrocarbon group includes, but is not particularly limited to, a cyclopentyl group, a cyclohexyl group, and the like. The unsaturated straight-chain hydrocarbon group includes, but is not particularly limited to, a vinyl group, an allyl group, and the like. The unsaturated-branched hydrocarbon group includes i-propenyl group, 3-butenyl group and the like, but is not particularly limited. The aromatic hydrocarbon group includes, but is not particularly limited to, a phenyl group, a naphthalene group, or the like.
Further, as the derivative of R, at least one functional group such as a carboxy group, a hydroxy group, or an amino group is added or substituted to the main chain or side chain of the various hydrocarbon groups. Examples include, but are not limited to, groups. Although the number of carbon atoms constituting the main chain of R is not particularly limited, it is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R to 20 or less, the molecule of the phosphorus oxoacid group containing R can be prevented from becoming too large, and good permeability into the fiber raw material can be maintained. It can contribute to the improvement of the yield of fine cellulose fibers.
β ^b+ is a b-valent cation composed of organic or inorganic matter. Examples of b-valent cations composed of organic substances include aliphatic ammonium and aromatic ammonium. Examples of b-valent cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, and lithium, calcium, Alternatively, a cation of a divalent metal such as magnesium, or a hydrogen ion may be used, but is not particularly limited. These may be applied singly or in combination of two or more. As the b-valent cation composed of an organic substance or an inorganic substance, sodium or potassium ions are preferable, but not particularly limited, because they are less likely to turn yellow when fiber raw materials containing β are heated, and are easy to use industrially.

The amount of the ionic group introduced into the fine cellulose fibers is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and still more preferably 0.50 mmol/g or more per 1 g (mass) of the fine cellulose fibers. Even more preferably, it is 1.00 mmol/g or more. The amount of the ionic group introduced into the fine cellulose fibers is preferably 3.65 mmol/g or less, more preferably 3.50 mmol/g or less, and even more preferably 3.00 mmol/g per 1 g (mass) of the fine cellulose fibers. It is below. By setting the amount of the ionic group to be introduced within the above range, the fiber raw material can be easily made finer, and the stability of the fine cellulose fibers can be enhanced. Further, by setting the amount of the ionic group to be introduced within the above range, defibration becomes easier.
The amount of ionic groups introduced into the fine cellulose fibers can be measured, for example, by conductivity titration. In the measurement by the conductivity titration method, the introduced amount is measured by determining the change in conductivity while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the fine cellulose fibers.

FIG. 1 is a graph showing the relationship between the amount of NaOH added to fine cellulose fibers having a phosphate group and the electrical conductivity.
The amount of phosphate groups introduced into cellulose fibers is measured as follows.
First, a slurry containing cellulose fibers is treated with an ion exchange resin. In addition, before the treatment with the ion-exchange resin, a defibration treatment similar to the fibrillation treatment step described below may be performed on the object to be measured, if necessary. Next, change in electrical conductivity is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in FIG.
As shown in FIG. 1, the electrical conductivity drops sharply at first (hereinafter referred to as "first region"). After that, the conductivity starts to rise slightly (hereinafter referred to as "second region"). Further thereafter, the increment of conductivity increases (hereinafter referred to as "third region"). The boundary point between the second region and the third region is defined as the point where the second derivative of the conductivity, that is, the amount of change in the increment (slope) of the conductivity is maximized. Thus, three regions appear in the titration curve. Among these, the amount of alkali required in the first region is equal to the amount of strong acid groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weak acid groups in the slurry used for titration. be equal. When the phosphate groups condense, the weakly acidic groups are apparently lost, and the amount of alkali required for the second region becomes smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Therefore, the amount of phosphate groups introduced (or the amount of phosphate groups) or the amount of substituents introduced (or the amount of substituents) means the amount of strongly acidic groups. Therefore, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve obtained above by the solid content (g) in the slurry to be titrated is the amount of phosphate group introduced (mmol/ g).

FIG. 2 is a graph showing the relationship between the amount of NaOH added to fine cellulose fibers having carboxyl groups and electrical conductivity.
The amount of carboxyl groups introduced into fine cellulose fibers is measured as follows.
First, change in electrical conductivity is observed while adding an aqueous sodium hydroxide solution to a slurry containing fine cellulose fibers to be measured, and a titration curve as shown in FIG. 2 is obtained. In addition, if necessary, a defibration treatment similar to the fibrillation treatment step to be described later may be performed on the object to be measured. As shown in FIG. 2, the titration curve has a first region where the increment (slope) of the conductivity becomes almost constant after the electrical conductivity decreases, and then the increment (slope) of the conductivity increases. It is divided into a second area. The boundary point between the first region and the second region is defined as the point where the second differential value of the conductivity, that is, the amount of change in the increment (slope) of the conductivity becomes maximum. Then, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the fine cellulose fiber-containing slurry to be titrated is the introduction amount of the carboxy group (mmol / g).

In addition, since the denominator "g" is the mass of the acid-form fine cellulose fibers, the amount of phosphate groups introduced (mmol/g) is "the amount of phosphate groups possessed by the acid-form cellulose fibers" (hereinafter referred to as The amount of phosphate groups (referred to as acid form) is shown. Here, when the proton of the phosphate group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator "g" is the mass of the cellulose fiber when the cation C is a counter ion. By converting, "the amount of phosphate groups possessed by the cellulose fibers whose counter ion is cation C" (hereinafter referred to as the amount of phosphate groups (C-type)) can be obtained.
That is, it is calculated by the following formula.
Phosphate group amount (C type) = phosphate group amount (acid form) / {1 + (W-1) × A / 1000}
here,
A [mmol/g]: total amount of anions derived from phosphate groups possessed by cellulose fibers (value obtained by adding the amount of strongly acidic groups and the amount of weakly acidic groups of the phosphate groups)
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)
is.

In addition, since the denominator "g" is the mass of the acid-type cellulose fiber, the amount of carboxyl groups introduced (mmol/g) is "the amount of carboxyl groups possessed by the acid-type cellulose fibers" (hereinafter referred to as "the amount of carboxyl groups (acid form)). Here, when the proton of the carboxy group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator "g" is converted to the mass of the cellulose fiber when the cation C is a counter ion. By doing so, it is possible to obtain the "amount of carboxyl groups possessed by the cellulose fibers whose counterions are the cations C" (hereinafter referred to as the amount of carboxyl groups (C type)).
That is, it is calculated by the following formula.
Carboxy group amount (C type) = carboxy group amount (acid form) / {1 + (W-1) × (carboxy group amount (acid form)) / 1000}
here,
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)
is.

In order to obtain fine cellulose fibers into which ionic groups are introduced as described above, an ionic group introduction step of introducing an ionic group into a fiber raw material, a washing step, an alkali treatment step (neutralization step), and a fibrillation treatment step. in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic group-introducing step include a phosphate group-introducing step and a carboxyl group-introducing step. Each step will be described below.
(Ionic group introduction step)
[Phosphate group introduction step]
The step of introducing a phosphate group into the cellulose fiber (phosphate group introduction step) will be described below.
In the phosphate group-introducing step, at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of reacting with hydroxyl groups possessed by fiber raw materials containing cellulose and capable of introducing phosphate groups is added to the fibers containing cellulose. This is the step of acting on the fiber raw material.
In the phosphate group-introducing step, the reaction between the fiber raw material containing cellulose and compound A may be carried out in the presence of at least one selected from urea and derivatives thereof (hereinafter also referred to as "compound B"). On the other hand, the reaction between the cellulose-containing fiber raw material and the compound A may be carried out in the absence of the compound B.

The efficiency of introduction of phosphate groups is high, the defibration efficiency is more likely to be improved in the fibrillation step described later, the cost is low, and the compound A is easy to apply industrially. sodium salt, potassium phosphate, or ammonium phosphate, and more preferably phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate.
The amount of compound A added to the fiber raw material is not particularly limited, but when the amount of compound A added is converted to the phosphorus atomic weight, the amount of phosphorus atoms added to 100 parts by mass of the fiber raw material (absolute dry mass) is preferably 0. .5 parts by mass or more, more preferably 1 part by mass or more, still more preferably 2 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 30 parts by mass or less . By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine cellulose fibers can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to be equal to or less than the above upper limit, it is possible to balance the effect of improving the yield and the cost.

Compound B used in this embodiment is at least one selected from urea and derivatives thereof as described above. Compound B includes urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.
From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. From the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.
The amount of compound B added to 100 parts by mass of the fiber raw material (absolute dry mass) is not particularly limited, but is preferably 1 part by mass or more, more preferably 10 parts by mass or more, still more preferably 100 parts by mass or more, and It is preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and still more preferably 350 parts by mass or less.

In the reaction between the fiber raw material containing cellulose and compound A, in addition to compound B, amides or amines may be included in the reaction system. Amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Among these, triethylamine in particular is known to work as a good reaction catalyst.

In the phosphate group-introducing step, it is preferable to heat-treat the fiber raw material after adding or mixing the compound A or the like to the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which the phosphate group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature is preferably 50° C. or higher, more preferably 100° C. or higher, still more preferably 130° C. or higher, and preferably 300° C. or lower, more preferably 250° C. or lower, further preferably 200° C. or lower. .
In addition, the heat treatment can be performed using equipment having various heat media, such as stirring drying equipment, rotary drying equipment, disk drying equipment, roll heating equipment, plate heating equipment, fluidized bed drying equipment, and flash drying equipment. , a vacuum drying device, an infrared heating device, a far infrared heating device, and a microwave heating device.
In the heat treatment, for example, a method of adding compound A to a thin sheet-like fiber raw material by a method such as impregnation and then heating, or a method of heating and drying while kneading or stirring the fiber raw material and compound A with a kneader or the like is adopted. can do. This makes it possible to suppress concentration unevenness of the compound A in the fiber raw material and to more uniformly introduce phosphate groups to the surface of the cellulose fibers contained in the fiber raw material. This is because when water molecules move to the surface of the fiber material during drying, the dissolved compound A is attracted to the water molecules by the surface tension and moves to the surface of the fiber material (that is, uneven concentration of the compound A occurs. It is thought that this is due to the fact that it is possible to suppress the

In addition, as a heating device used for the heat treatment, the moisture retained by the slurry and the moisture generated due to the dehydration condensation (phosphorylation) reaction between the compound A and the hydroxyl groups contained in the cellulose etc. in the fiber raw material are always kept in the equipment system. A device that can be discharged to the outside is preferable. As such a heating device, for example, an air-blowing oven can be used. By constantly draining the water in the device system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of phosphorylation, and to suppress the acid hydrolysis of the sugar chains in the fiber. can. Therefore, fine fibers having a desired axial ratio can be obtained.

The heat treatment time is preferably 1 second or more, more preferably 10 seconds or more, and preferably 300 minutes or less, more preferably 1,000 seconds or less, after water is substantially removed from the fiber raw material. , and more preferably 800 seconds or less. By setting the heating temperature and the heating time within appropriate ranges, the introduction amount of the phosphate group can be set within a preferable range.

The step of introducing a phosphate group may be performed at least once, but may be performed repeatedly two or more times. By performing the phosphate group-introducing step two or more times, many phosphate groups can be introduced into the fiber raw material. In the present invention, one example of a preferred embodiment includes the case where the step of introducing a phosphate group is performed twice.

The amount of phosphate groups introduced per 1 g (mass) of fine cellulose fibers is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, still more preferably 0.50 mmol/g or more, and even more preferably It is 1.00 mmol/g or more. The amount of phosphoric acid groups introduced per 1 g (mass) of fine cellulose fibers is preferably 5.20 mmol/g or less, more preferably 3.65 mmol/g or less, still more preferably 3.00 mmol/g or less. It is preferable to introduce phosphate groups into the fiber raw material so that the amount of phosphate groups introduced into the fine cellulose fibers is within the above range. By setting the amount of the phosphate group to be introduced within the above range, the fiber raw material can be easily made finer, and the stability of the fine cellulose fibers can be enhanced.

[Carboxy group introduction step]
The step of introducing carboxy groups into cellulose fibers (carboxy group introduction step) will be described below.
In the step of introducing a carboxy group, the fiber raw material containing cellulose is subjected to oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a carboxylic acid-derived group or a derivative thereof, or a carboxylic acid-derived group. This is done by treating the compound with an acid anhydride or a derivative thereof.
The compound having a carboxylic acid-derived group is not particularly limited, but dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid and itaconic acid, and tricarboxylic acids such as citric acid and aconitic acid. acid compounds. Derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but include imidized acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized acid anhydrides of compounds having a carboxy group include, but are not particularly limited to, imidized dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

In the step of introducing a carboxyl group, when the TEMPO oxidation treatment is performed, it is preferably carried out under the condition of pH 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH=6.8), pulp as a fiber raw material, and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst. This can be done by adding sodium hypochlorite as a nitroxy radical, sacrificial reagent. Furthermore, coexistence of sodium chlorite enables efficient oxidation of aldehydes generated in the process of oxidation to carboxyl groups.

When carboxyl groups are introduced by TEMPO oxidation, the amount of carboxyl groups introduced per 1 g (mass) of fine cellulose fibers is preferably 0.10 mmol/g or more, more preferably 0.20 mmol/g or more, and still more preferably 0.20 mmol/g or more. It is 50 mmol/g or more, and more preferably 0.90 mmol/g or more. Also, it is preferably 2.50 mmol/g or less, more preferably 2.20 mmol/g or less, still more preferably 2.00 mmol/g or less. In addition, when the substituent is a carboxymethyl group, the introduction amount per 1 g (mass) of fine cellulose fibers may be 5.8 mmol/g or less.
It is preferable to introduce carboxyl groups into the fiber raw material so that the amount of carboxyl groups introduced into the fine cellulose fibers is within the above range. By setting the amount of carboxyl groups to be introduced within the above range, the fiber raw material can be easily made finer, and the stability of fine cellulose fibers can be enhanced.

(Washing process)
In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic group-introduced fiber may be washed with water or an organic solvent after the ionic group-introducing step and before the alkaline treatment step. After the alkali treatment step and before the fibrillation treatment step, the alkali-treated ionic group-introduced fibers such as phosphate group-introduced fibers are washed with water or an organic solvent from the viewpoint of improving handleability. is preferred.
In the washing step, it is preferable to repeat the operation of dispersing the ionic group-introduced fiber in water or an organic solvent and then filtering it. can be done. The washing step is performed so that the electrical conductivity of the filtrate is preferably 10,000 μS/cm or less, more preferably 1,000 μS/cm or less, even more preferably 300 μS/cm or less, and even more preferably 150 μS/cm. is preferred.

(Alkali treatment process (neutralization process))
When producing fine cellulose fibers, an alkali treatment step (medium sum process). The method of alkali treatment is not particularly limited, but includes, for example, a method of immersing the ionic group-introduced fiber in an alkali solution.
The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. In the present invention, it is preferable to use sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. Moreover, the solvent contained in the alkaline solution may be either water or an organic solvent. The solvent contained in the alkaline solution is preferably water or a polar solvent containing a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5°C or higher, more preferably 10°C or higher, and preferably 80°C or lower, more preferably 60°C or lower. The immersion time of the ionic group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more, more preferably 10 minutes or more, and preferably 30 minutes or less, more preferably 20 minutes. minutes or less.
The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100 parts by mass or more, more preferably 1,000 parts by mass or more, relative to 100 parts by mass of the absolute dry mass of the ionic group-introduced fiber, And it is preferably 100,000 parts by mass or less, more preferably 10,000 parts by mass or less.

In the alkali treatment, for example, when a phosphoric acid group is introduced as an ionic group, an alkaline solution is gradually added to the dispersion in which the ionic group-introduced fiber is dispersed, and the pH in the system is adjusted to preferably 10 or more, or more. Preferably 11 or more, more preferably 12 or more, and preferably 14 or less, more preferably 13.5 or less, still more preferably 13 or less, the alkaline solution is added.
Further, when a carboxy group is introduced as an ionic group, the pH in the system is preferably 7 or higher, more preferably 8 or higher, still more preferably 9 or higher, still more preferably 10 or higher, and preferably 14 or lower. , more preferably 13.5 or less, still more preferably 13 or less, by adding the alkaline solution.
By setting the addition amount of the alkaline solution within the above range, the defibration treatment can be performed more easily, and fine cellulose fibers having a small fiber width can be easily obtained.

(Acid treatment step)
In the production of fine cellulose fibers, the ionic group-introduced fiber raw material may be subjected to an acid treatment between the ionic group-introducing step and the fibrillation treatment step described later. An example of a method for producing fine cellulose fibers includes a mode in which an ionic group introduction step, an acid treatment step, an alkali treatment step, and a fibrillation treatment step are performed in this order.
The method of acid treatment is not particularly limited, but a method of immersing the fiber raw material in an acidic liquid containing an acid can be mentioned. Although the concentration of the acid liquid used is not particularly limited, it is preferably 10% by mass or less, more preferably 5% by mass or less. The pH of the acidic liquid to be used is not particularly limited, but is preferably 0 or higher, more preferably 1 or higher, and preferably 4 or lower, more preferably 3 or lower.

Inorganic acid, sulfonic acid, carboxylic acid and the like are exemplified as the acid contained in the acidic liquid.
Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid.
Sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like.
Carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid and the like.
Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably 5°C or higher, more preferably 20°C or higher, and preferably 100°C or lower, more preferably 90°C or lower.
The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes or longer, more preferably 10 minutes or longer, and preferably 120 minutes or shorter, more preferably 60 minutes or shorter.
The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably 100 parts by mass or more, more preferably 1,000 parts by mass or more with respect to 100 parts by mass of the absolute dry mass (absolute dry mass) of the fiber raw material. Yes, and preferably 100,000 parts by mass or less, more preferably 10,000 parts by mass or less.

(Fibrillation treatment process)
Fine cellulose fibers can be obtained from the ionic group-introduced fibers by subjecting them to defibration treatment in the fibrillation treatment step.
A defibration treatment apparatus can be used in the defibration treatment step. The fibrillation processing equipment is not particularly limited, but includes a high-speed fibrillator, a grinder (stone mill type pulverizer), a high pressure homogenizer, an ultra-high pressure homogenizer, a high pressure impact pulverizer, a ball mill, a bead mill, a disc refiner, a conical refiner, and a twin-screw kneader. A machine, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or the like can be used, and the solid content concentration of the fine cellulose fibers during defibration can be appropriately set. Among the above fibrillation treatment apparatuses, it is more preferable to use a high-speed fibrillation machine, a high-pressure homogenizer, and an ultrahigh-pressure homogenizer, which are less affected by the grinding media and less likely to cause contamination.

In the fibrillation treatment step, the ionic group-introduced fibers are preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from organic solvents such as water and polar organic solvents can be used.
The polar organic solvent is not particularly limited, but is preferably exemplified by alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents and the like.
Alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol and the like. Polyhydric alcohols include ethylene glycol, propylene glycol, glycerin and the like. Ketones include acetone, methyl ethyl ketone (MEK), and the like. Ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether and the like. Examples of esters include ethyl acetate and butyl acetate. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.
Moreover, the slurry obtained by dispersing the ionic group-introduced fiber in the dispersion medium may contain solids other than the ionic group-introduced fiber, such as urea having hydrogen bonding properties.

(coarse cellulose fiber)
As described above, the step of obtaining fine cellulose fibers includes a step of refining fiber raw materials (coarse cellulose fibers). At this time, most of the coarse cellulose fibers are pulverized, but some of them may remain without being pulverized. In such a case, the fiber layer will contain coarse cellulose fibers.
In the present invention, the coarse cellulose fibers contained in the cellulose fiber-containing composition are obtained by adjusting the cellulose dispersion to a solid content concentration of 0.2% by mass, and using a cooling high-speed centrifuge (Kokusan Co., Ltd., H-2000B). is the cellulose fiber that sediments when centrifuged at 12,000 G for 10 minutes.
Less sedimentation means that the yield of the supernatant after centrifugation is high. The supernatant yield after this centrifugation is preferably 80% by mass or more with respect to the total mass of the cellulose fibers. The supernatant yield after centrifugation is more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 99% by mass or more. In this specification, the supernatant yield after centrifugation of the fine cellulose fiber dispersion can be measured by the following method.
The supernatant yield after centrifuging the fine cellulose fiber dispersion was measured by the method described below. The supernatant yield after centrifugation is an index of the yield of fine cellulose fibers, and the higher the supernatant yield, the higher the yield of fine cellulose fibers.
The fine cellulose fiber dispersion is adjusted to a solid content concentration of 0.2% by mass, and centrifuged at 12,000 G for 10 minutes using a cooling high-speed centrifuge (Kokusan Co., Ltd., H-2000B). The obtained supernatant was collected and the solid content concentration of the supernatant was measured. The yield of fine cellulose fibers is calculated based on the following formula.
Yield (%) of fine cellulose fibers = Solid content concentration (%) in supernatant/0.2 x 100

(Method for forming fiber layer)
In the present invention, the method of providing the fiber layer on the substrate is not particularly limited, and may be formed by a papermaking method. Alternatively, fine cellulose fibers may be applied onto the substrate by coating, spraying, or the like, and then dried. A fibrous layer may be formed.
The concentration of the fine cellulose fiber dispersion used for making paper or imparting fine cellulose fibers is not particularly limited, but from the viewpoint of suppressing an increase in viscosity, it is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably. 3% by mass or less, more preferably 1.5% by mass or less, still more preferably 1% by mass or less, and preferably 0.05% by mass or more from the viewpoint of efficiently imparting fine cellulose fibers to the substrate. , more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.
The concentration of the fine cellulose fiber dispersion and the amount applied to the substrate may be appropriately adjusted so that the basis weight (coating amount) of the fine cellulose fibers after drying falls within the desired range described above.

<Water content>
The total heat exchanger sheet of the present invention has a moisture content of 8% by mass or more. If the water content is less than 8% by mass, it is difficult to obtain high moisture permeability.
The moisture content can be adjusted by highly controlling the manufacturing process of the total heat exchanger sheet. According to the inventors of the present invention, it is presumed that, for example, the type, blending amount, addition method, etc. of the fine cellulose fibers and the moisture absorbent constituting the sheet affect the water content.
From the viewpoint of obtaining high moisture permeability, the moisture content of the total heat exchanger sheet is preferably 9% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass or more, and even more preferably 15% by mass or more. is. In addition, from the viewpoint of preventing dew condensation and increasing the strength of the total heat exchange sheet, the water content of the total heat exchanger sheet is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably It is 20% by mass or less.
The moisture content (moisture content) of the total heat exchanger sheet is measured by the method described in Examples.

(Moisture absorbent)
The total heat exchanger sheet of the present invention preferably contains a moisture absorbent in order to obtain a desired moisture content. The moisture absorbent may be contained in either one of the substrate layer and the fiber layer, or may be contained in both the substrate layer and the fiber layer. From the viewpoint of increasing the contact angle on the surface of , it is preferable that both the substrate layer and the fiber layer contain. In addition, as will be described later, the higher the contact angle, the better.
The moisture absorbent is not particularly limited as long as it is a conventionally known moisture absorbent, and may be appropriately selected and used. Specifically, at least one selected from metal halide salts, metal lactates, metal sulfates, metal acetates, amine salts, phosphoric acid compounds, guanidine salts, and metal hydroxides is preferred.
Examples of metal halide salts include lithium chloride, sodium chloride, calcium chloride, magnesium chloride, aluminum chloride, and zinc chloride. Examples of metal lactates include sodium lactate. Examples of metal sulfates include sodium sulfate. , calcium sulfate, magnesium sulfate, zinc sulfate and the like, and examples of metal acetates include potassium acetate and the like.
Examples of amine salts include dimethylamine hydrochloride, examples of phosphoric acid compounds include orthophosphoric acid, and examples of guanidine salts include guanidine hydrochloride, guanidine phosphate, and guanidine sulfamate. Furthermore, examples of metal hydroxides include potassium hydroxide, sodium hydroxide, magnesium hydroxide, and the like.
Furthermore, as a hygroscopic agent, a hygroscopic polymer such as a water-soluble polymer or a hydrophilic polymer having hydrogel-forming ability may be used.
Among these, the hygroscopic agent is preferably a metal salt, more preferably a metal halide salt, and an alkali metal halide from the viewpoint of excellent hygroscopicity and handleability and increasing the contact angle with water. , alkaline earth metal halides, and more preferably at least one selected from the group consisting of lithium chloride and calcium chloride.
The inventors of the present invention originally expected that the hydrophilicity of the total enthalpy heat exchanger sheet would be increased by adding a moisture absorbent to the total enthalpy heat exchanger sheet, and as a result, the contact angle of water would be reduced. However, when the moisture absorbent is a metal salt and the fine cellulose fibers have an ionic group, especially an anionic group, the contact angle of water on the surface of the fiber layer increases as an unexpected effect. Although the detailed reason is unknown, the anionic groups contained in the fine cellulose fibers and the metal atoms of the moisture absorbent form a pseudo-crosslinked structure, as a result of which the surface becomes hydrophobic and resistant to water. It is believed that the contact angle increases.
From the above point of view, a mode in which the fine cellulose fibers have a carboxyl group or a phosphate group, preferably a phosphate group as an anionic group, and the hygroscopic agent contains lithium chloride or calcium chloride is particularly suitable.

The content of the moisture absorbent in the total heat exchanger sheet is preferably 100 parts by mass or more, more preferably 100 parts by mass or more, based on 100 parts by mass of the fine cellulose fibers, from the viewpoint of keeping the moisture content of the total heat exchanger sheet within the desired range. is 300 parts by mass or more, more preferably 500 parts by mass or more, still more preferably 600 parts by mass or more, and preferably 10,000 parts by mass or less, more preferably 5,000 parts by mass or less, and still more preferably 2 , 500 parts by mass or less.
The basis weight (coating amount) of the moisture absorbent in the total heat exchanger sheet is preferably 1 g/m ² or more, more preferably 3 g/m ² or more, from the viewpoint of keeping the moisture content of the total heat exchanger sheet within a desired range. , more preferably 5 g/m ² or more, and preferably 20 g/m ² or less, more preferably 15 g/m ² or less, still more preferably 12 g/m ² or less.

The method for incorporating the moisture absorbent into the total heat exchanger sheet is not particularly limited, but from the viewpoint of increasing the contact angle of water on the surface of the fiber layer, it is preferable to incorporate the moisture absorbent after forming the fiber layer. Preferred examples include a method of spraying or coating an aqueous solution in which a moisture absorbent is dissolved after the layer is formed, and a method of immersing the layer in an aqueous solution in which a moisture absorbent is dissolved.
According to this method, the contact angle of water on the surface of the fiber layer can be further improved compared to the method of forming the fiber layer after applying the moisture absorbent to the base material layer in advance. In addition, aggregation of the fine cellulose fibers in the dispersion can be suppressed more effectively than in the method of adding a hygroscopic agent to the fine cellulose fiber dispersion and applying it to the base material.

<Sheet for total heat exchanger>
Preferred embodiments of the sheet for a total heat exchanger of the present invention are described below.
The sheet for a total heat exchanger of the present invention is not particularly limited as long as it has at least one substrate layer and at least one fiber layer. It may have a three-layer structure of material layer/fiber layer, or may have a two-layer structure of fiber layer/base material layer having a fiber layer on one side, and is not particularly limited.
Among these, a two-layer structure of a fiber layer/base material layer is preferred from the viewpoint of ease of production and sufficient moisture permeability, air permeability, and carbon dioxide barrier properties with a single fiber layer.

The density of the sheet for a total heat exchanger of the present invention is preferably 0.65 g/cm ³ or more, more preferably 0.7 g/cm ³ or more, and still more preferably 0.75 g/cm ³ from the viewpoint of improving heat transfer. That's it. Although the upper limit of the density is not particularly limited, it is preferably 1.3 g/cm ³ or less, more preferably 1.0 g/cm ³ or less from the viewpoint of suppressing the mass of the entire heat exchanger.
The density of the total heat exchanger sheet is measured by the method described in Examples.

The thickness of the sheet for a total heat exchanger of the present invention is preferably thinner from the viewpoint that many sheets can be arranged in a total heat exchanger, specifically, preferably 150 μm or less, more preferably 120 μm or less, and further. It is preferably 100 μm or less.
From the viewpoint of maintaining the strength required for a sheet for a total heat exchanger, the thickness is preferably 20 μm or more, more preferably 30 μm or more.

The basis weight of the sheet for a total heat exchanger of the present invention is preferably 10 g/m ² or more, more preferably 30 g/m ² or more, and preferably 300 g/m ² from the viewpoint of obtaining desired density and thickness. Below, more preferably 200 g/m ² or less, still more preferably 100 g/m ² or less, and even more preferably 80 g/m ² or less.

When the sheet for a total heat exchanger of the present invention has a fiber layer on at least one of its outer surfaces, the contact angle of water on the surface on the fiber layer side is preferably 50° or more. When the contact angle of water is 50° or more, when the spacer and liner are adhered and assembled as a total heat exchanger element, wetting and spreading of the adhesive is suppressed, and the effective area of the total heat exchanger sheet (liner) is reduced. The decrease is suppressed, and high moisture permeability and air permeability are maintained even after processing into a total heat exchanger element.
The contact angle of water on the fiber layer side surface is more preferably 55° or more, and still more preferably 60° or more.
Although the upper limit of the contact angle is not particularly limited, it is preferably 150° or less, more preferably 130° or less, and still more preferably 110° or less from the viewpoint of adhesive applicability.
The contact angle means the contact angle to water 0.1 second after dropping, and is measured by the method described in Examples.

When a fiber layer containing fine cellulose fibers is provided, the contact angle of water on the surface of the fiber layer is generally less than 50° unless a metal-containing compound such as a moisture absorbent is contained. This is probably because the contact angle of water decreases due to the capillary action of the fine cellulose fibers.
In order to make the contact angle of water on the surface of the fiber layer side within the above range, the fine cellulose fibers have ionic groups as described above, and the fiber layer has the ionic groups and a crosslinked structure (pseudo It is preferable to contain a moisture absorbent having a metal atom capable of forming a crosslinked structure.
As a result, a crosslinked structure (including a pseudo-crosslinked structure) is formed, which is presumed to make the surface hydrophobic and improve the contact angle.

Further, when the contact angle of water on one surface of the total heat exchanger sheet is D1 and the contact angle of water on the other surface is D2, the ratio of the two, D1/D2, is preferably 0.25 or more. Below, it is more preferably 0.3 or more and 3 or less, and still more preferably 0.5 or more and 2 or less.
When D1/D2 is within the above range, the difference in the contact angle of water between one surface and the other surface is small, which facilitates assembly of the total heat exchanger element, which is preferable.
When the total heat exchange sheet uses paper as the base material and has a two-layer structure of a base material layer and a fiber layer, the contact angle of the surface of the fiber layer side is generally small, and the base layer side The contact angle of the surface of is large.

The air permeability of the sheet for a total heat exchanger of the present invention is preferably high from the viewpoint of separating supply air and exhaust air, preferably 500 sec or more, more preferably 1,000 sec or more, and still more preferably 3,000 sec or more. , more preferably 10,000 sec or more, and even more preferably 25,000 sec or more.
Air permeability is measured by the method described in Examples.

The moisture permeability of the sheet for a total heat exchanger of the present invention is preferably high, preferably 2,800 g/(m ² ·24 hr) or more, more preferably 2,800 g/(m 2 ·24 hr) or more, from the viewpoint of promoting latent heat transfer and improving heat transferability. It is 3,000 g/(m ² ·24 hr) or more, more preferably 3,500 g/(m ² ·24 hr) or more.
The moisture permeability is measured by the method described in Examples.

The sheet for a total enthalpy heat exchanger of the present invention preferably has high carbon dioxide barrier properties ( _CO2 barrier properties) from the viewpoint of suppressing the mixing of carbon dioxide in the exhaust air into the supply air, which is described in the Examples. The carbon dioxide concentration reduction rate measured by the method of is preferably 1.3% or less, more preferably 1.0% or less, still more preferably 0.8% or less, even more preferably 0.5% or less, and more More preferably, it is 0.3% or less.

The sheet for a total enthalpy heat exchanger of the present invention may contain other components in the base material layer or the fiber layer, specifically, sizing agents, wet strength agents, surfactants, flame retardants. agents, antifungal agents, antirust agents, antiblocking agents, and the like.
The fiber layer may contain other components as described above, but the total content of the fine cellulose fibers, the moisture absorbent, and the moisture in the fiber layer is preferably It is 90% by mass or more, more preferably 95% by mass or more, still more preferably 97% by mass or more, and may be 100% by mass.

Surfactants include anionic surfactants such as alkyl sulfates, polyoxyethylene alkyl sulfates, alkylbenzene sulfonates, α-olefin sulfonates, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, benzalcochloride. amphoteric surfactants such as trimethylglycine, betaine alkyldimethylaminoacetate and betaine alkylamidodimethylaminoacetate, and nonionic surfactants such as alkylpolyoxyethylene ethers and fatty acid glycerol esters.
Flame retardants include halogen flame retardants, red phosphorus, melamine phosphate, ammonium polyphosphate, melamine polyphosphate, melamine pyrophosphate, piperazine polyphosphate, piperazine pyrophosphate, guanidine phosphate, guanidine sulfamate, (condensation) Phosphorus flame retardants such as phosphate compounds and phosphazene compounds, nitrogen flame retardants such as melamine cyanurate, metal hydroxides such as magnesium hydroxide and aluminum hydroxide, phosphinates and diphosphinates, and the like.

Examples of antifungal agents include benzimidazole-based compounds, pyrithione-based compounds, iodopropenylbutylcarbamate-based compounds, isothiazolone-based compounds, organic nitrogen-sulfur-based compounds, and the like.
As the rust preventive agent, a water-soluble rust preventive agent is preferable, and examples thereof include alkali metal salts of aliphatic carboxylic acids and piperazine derivatives such as monohydroxymonoethylpiperazine.
Examples of anti-blocking agents include waxes selected from polyethylene waxes, zinc stearate, polyethylene wax emulsions, polyethylene oxide waxes, paraffin waxes, etc., and metal soaps such as silicone resins and calcium salts of higher fatty acids. be done.

In the production of the sheet for a total heat exchanger of the present invention, if necessary, a post-processing such as a coating treatment or a chemical treatment, and a calendering step may be carried out for the purpose of adjusting the average thickness or thinning the sheet.
In the post-processing step, for example, a step of preparing a flame retardant coating solution and applying and drying the coating solution by a process such as spray coating, printing, or coating is exemplified.
In addition, the obtained total heat exchanger sheet can be subjected to a calendering process for smoothing or thinning with a calendering device, thereby adjusting the average thickness and further improving the density. Examples of the calendering device include a normal calendering device using a single press roll and a super calendering device having a multistage structure. It is preferable to select these devices and the materials (material hardness) and linear pressure on both sides during calendering according to the purpose. Specifically, the material of the roll may be appropriately selected from a combination of a metal roll and a high-hardness resin roll, a combination of a metal roll and a cotton roll, a combination of a metal roll and an amide roll, and the like.

[Total heat exchanger element and total heat exchanger]
The total heat exchanger element of the present invention has the above-described total heat exchanger sheet of the present invention, particularly as a liner of the total heat exchanger element.
More specifically, the total enthalpy heat exchanger element includes a plurality of total enthalpy heat exchanger sheets (liners), and a spacer constituting a flow path is sandwiched between each sheet, and the spacer and the sheet are sandwiched between the sheets. is attached with an adhesive or the like.
Further, a total heat exchanger of the present invention comprises the element for a total heat exchanger of the present invention. A static total heat exchanger is exemplified as a suitable total heat exchanger. The static total heat exchanger may be a cross-flow type or a counter-current type, and is not particularly limited. A static total heat exchanger is partitioned by the sheet (liner) for a total heat exchanger of the present invention, and a total heat exchanger element having a structure in which two mutually independent flow paths are alternately stacked is provided with an air supply fan and an exhaust air. It is configured by combining fans.
A supply gas, such as outside air, is sucked into the total heat exchanger element by the air supply fan and comes into contact with the total heat exchanger sheet incorporated in the total heat exchanger element. On the other hand, exhaust gas such as room air is sucked into the total heat exchanger element by the exhaust fan, and similarly contacts the total heat exchanger sheet.
The supply gas and the exhaust gas that are in contact with each other through the total heat exchanger sheet exchange heat through temperature and humidity. The heat-exchanged supply gas is blown into an air supply fan and taken into the room, for example. On the other hand, the heat-exchanged exhaust gas is blown into an exhaust fan and discharged to the outside, for example.
The total heat exchanger sheet of the present invention has high moisture permeability and air permeability, and further has excellent carbon dioxide barrier properties, so it is excellent in exchanging not only sensible heat but also latent heat, and has high heat conductivity. Furthermore, mixing of supply air and exhaust air is suppressed. Therefore, the total heat exchanger provided with the sheet for a total heat exchanger of the present invention is capable of efficient heat exchange. In other words, while suppressing the release of heat or cold energy in the building, it is possible to ventilate the air with increased carbon dioxide concentration, and further increase the efficiency of the total heat exchanger that maintains the thermal effect of air conditioning. be able to.

EXAMPLES The features of the present invention will be described more specifically below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below.

[Example 1]
<Production of fine cellulose fibers>
(Phosphate group introduction step)
As raw material pulp, Oji Paper Co., Ltd. softwood kraft pulp (solid content 93% by mass, basis weight 208 g / m ² sheet, disaggregated and Canadian standard freeness measured according to JIS P 8121: 2012 ( CSF) was 700 ml).
The raw material pulp was subjected to a phosphorylation treatment as follows.
First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to the raw material pulp, and 45 parts by mass of ammonium dihydrogen phosphate and 120 parts by mass of urea are added to 100 parts by mass (absolutely dry mass) of the raw material pulp. The amount of water was adjusted to 150 parts by mass to obtain chemical-impregnated pulp. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 200 seconds to introduce phosphoric acid groups into cellulose in the pulp to obtain phosphorylated pulp.

(Washing process)
Then, the obtained phosphorylated pulp was washed.
In the washing treatment, 10 L of ion-exchanged water is poured into 100 g (absolute dry mass) of phosphorylated pulp, stirred so that the pulp is uniformly dispersed to obtain a pulp dispersion, and then filtered and dehydrated are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

(alkali treatment step)
Next, the washed phosphorylated pulp was subjected to alkali treatment (neutralization treatment) as follows.
First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. . Next, the phosphorylated pulp slurry was dehydrated to obtain alkali-treated (neutralized) phosphorylated pulp.
Next, the washing treatment was performed on the phosphorylated pulp after alkali treatment.
An infrared absorption spectrum was measured using FT-IR for the phosphorylated pulp after alkali treatment thus obtained. As a result, absorption due to phosphate groups was observed near 1230 cm ⁻¹ , confirming that phosphate groups were added to the pulp. Moreover, the amount of phosphate groups (the amount of strongly acidic groups) measured by the above-described measuring method was 1.45 mmol/g.
In addition, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffraction device, it was found that the A peak typical of cellulose type I crystals was confirmed, confirming the presence of cellulose type I crystals.

(Fibrillation treatment process)
Ion-exchanged water was added to the phosphorylated pulp obtained through the alkali treatment step to prepare a slurry having a solid content concentration of 2% by mass. This slurry was treated twice at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine cellulose fiber dispersion containing fine cellulose fibers. X-ray diffraction confirmed that the fine cellulose fibers maintained cellulose type I crystals. Further, when the fiber width of the fine cellulose fibers was measured using a transmission electron microscope, it was 3 to 5 nm.
Furthermore, the yield of fine cellulose fibers obtained was measured according to the method described above, and the yield was 99.2%.

<Preparation of sheet for total heat exchanger>
Pulp blended with NBKP (Needle Bleached Kraft Pulp) and LBKP (Leaf Bleached Kraft Pulp) at a ratio of 65:35 (mass ratio) is beaten to 450 ml with Canadian Standard Freeness, and aluminum sulfate is added. 1.0 parts by mass, and 0.01 parts by mass of alkyl ketene dimer (Size Pine K-903-20, manufactured by Arakawa Chemical Industries, Ltd.) as a sizing agent were added to 100 parts by mass of pulp. Using this paper stock, fine paper having a basis weight of 60 g/m ² was made by a fourdrinier multi-cylinder paper machine.
Next, the fine paper obtained above is used as a base material, and on one side of the base material, the fine cellulose fiber dispersion obtained above is dried with a Meyer bar. The coating amount) was 0.4 g/m ² to form a fiber layer.
Next, lithium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) as a moisture absorbent was impregnated and dried with a mangle roll so that the basis weight (coating amount) after drying was 3.9 g / m ² . A sheet for a total heat exchanger was produced. The total heat exchanger sheet had a basis weight of 73 g/m ² and a moisture content of 10% by mass.

[Example 2]
In Example 1, except that instead of lithium chloride, calcium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was impregnated and dried so that the coating amount after drying was 4.9 g / m ² . A sheet for a total heat exchanger was produced in the same manner. The total heat exchanger sheet had a basis weight of 73 g/m ² and a moisture content of 10% by mass.

[Example 3]
In Example 1, the fine cellulose fiber dispersion was applied so that the coating amount of fine cellulose fibers (CNF) after drying was 0.8 g/m ² , and then lithium chloride (Wako Jun Yakukogyo Co., Ltd.) was impregnated and dried so that the mass after drying was 5.2 g/m ² . The total heat exchanger sheet had a basis weight of 78 g/m ² and a moisture content of 12% by mass.

[Example 4]
In Example 3, except that instead of lithium chloride, calcium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was impregnated and dried so that the coating amount after drying was 6.0 g / m ² . A sheet for a total heat exchanger was produced in the same manner. The total heat exchanger sheet had a basis weight of 76 g/m ² and a moisture content of 10% by mass.

[Example 5]
Pulp blended with NBKP and LBKP at a ratio of 50:50 (mass ratio) was beaten to 170 ml by Canadian Standard Freeness, and 1.0 part of aluminum sulfate and 0.01 part of alkyl ketene dimer as a sizing agent (Size Pine K-903- 20, manufactured by Arakawa Chemical Industries, Ltd.) and 0.15 parts of a wet strength agent (Arafix 255, manufactured by Arakawa Chemical Industries, Ltd.) were added to 100 parts by mass of pulp. Using this paper stock, semi-glassine paper having a basis weight of 40 g/m ² was made by a fourdrinier multi-cylinder paper machine.
Next, the semi-glassine paper obtained above is used as a base material, and on one side of the base material, in the same manner as in Example 1, a fine cellulose fiber dispersion is applied with a Meyer bar, and fine cellulose fibers (CNF) are dried. A fiber layer was formed by coating so that the coating amount was 0.4 g/m ² .
Next, lithium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) as a desiccant is impregnated and dried with a mangle roll so that the coating amount after drying is 5.6 g/m ² to prepare a total heat exchanger sheet. did. The total heat exchanger sheet had a basis weight of 60 g/m ² and a moisture content of 17% by mass.

[Example 6]
In Example 5, except that instead of lithium chloride, calcium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was impregnated and dried so that the coating amount after drying was 5.0 g / m ² . A sheet for a total heat exchanger was produced in the same manner. The total heat exchanger sheet had a basis weight of 58 g/m ² and a moisture content of 17% by mass.

[Comparative Example 1]
A total heat exchanger sheet was produced in the same manner as in Example 1, except that water was applied and impregnated instead of the fine cellulose fiber dispersion and the moisture absorbent. The total heat exchanger sheet had a basis weight of 60 g/m ² and a moisture content of 5% by mass.

[Comparative Example 2]
A total heat exchanger sheet was produced in the same manner as in Example 1, except that water was impregnated in place of the moisture absorbent. The total heat exchanger sheet had a basis weight of 63 g/m ² and a water content of 4% by mass.

[Comparative Example 3]
A total heat exchanger sheet was produced in the same manner as in Example 5, except that water was applied and impregnated instead of the fine cellulose fiber dispersion and the moisture absorbent. The total heat exchanger sheet had a basis weight of 40 g/m ² and a moisture content of 5% by mass.

[Comparative Example 4]
A total heat exchanger sheet was produced in the same manner as in Example 5, except that water was impregnated in place of the moisture absorbent. The total heat exchanger sheet had a basis weight of 41 g/m ² and a moisture content of 3% by mass.

[Evaluation and Analysis]
<Water content (moisture content)>
The water content (hereinafter also simply referred to as water content) of the base material and the obtained sheet for total heat exchanger was measured according to JIS P 8127:2010.

<Basis weight>
The basis weight of the total heat exchanger sheet was measured according to JIS P 8124:2011.

<Thickness>
The thickness of the total heat exchanger sheet was measured according to JIS P 8118:2014.

<Density>
The density of the total heat exchanger sheet was calculated from the basis weight and paper thickness obtained by the above-described measuring method.

<Water contact angle>
In accordance with JIS R 3257: 1999, using a dynamic water contact angle tester (manufactured by Fibro, 1100DAT), 4 μL of distilled water was dropped on the surface of the total heat exchanger sheet, and water was added 0.1 seconds after dropping. Contact angles were measured. The measurement was performed on each of the fiber layer side surface (CNF surface) and the substrate layer side surface (rear surface).

<Air Permeability>
JAPAN TAPPI paper pulp test method No. The air permeability of the total heat exchanger sheet was measured according to the Oken air permeability method of 5-2:2000.

<Carbon dioxide barrier>
A carbon dioxide (CO ₂ ) analyzer is installed inside an acrylic cubic container with a side of 1 m and a square window of 20 cm on each side in the center of each of the four side surfaces and the top surface. and
A 25 cm square total heat exchanger sheet was attached to _each window of the measuring device, and 5,000 ppm of carbon dioxide was sealed in the container. Measurements were taken four times every minute for a total of one hour.
From the measured values after 15 minutes, 30 minutes, 45 minutes, and 60 minutes, the rate of decrease in carbon dioxide concentration at each time point is obtained, and the average is determined as the rate of decrease in carbon dioxide concentration of the measured sample. . The lower the carbon dioxide concentration decrease rate, the more excellent the carbon dioxide (CO ₂ ) barrier property of the total heat exchanger sheet.
A sheet having a carbon dioxide concentration reduction rate of 1.3% or less is preferably used as a sheet for a total heat exchanger.

<Moisture permeability>
Measured in accordance with JIS Z 0208:1976 under conditions of 20°C and 65% RH.
However, the moisture permeability was calculated as follows.
Let A be the mass increment (g) after 1 hour from the start of the test, B be the mass increment (g) from 1 hour to 2 hours after the start of the test, and calculate the mass increment C per hour by the following formula (1). rice field. This value was converted into a value per 1 m ² of the moisture permeable sheet for 24 hours to obtain the moisture permeability (g/(m ² ·24 h)).
Mass increment per hour C=(A+B)/2 (1)
The results of Examples and Comparative Examples are shown in Table 1 below.

The sheet for a total heat exchanger of the present invention has high moisture permeability and air permeability, and is also excellent in carbon dioxide barrier properties. Therefore, a total heat exchanger that is suitably used as a liner for a total heat exchanger element and constructed using the above total heat exchanger element has high carbon dioxide barrier properties and heat exchange properties.

Claims (11)

a substrate layer;
and a fiber layer provided on the base material layer,
The fiber layer contains fine cellulose fibers with a fiber width of 1,000 nm or less and a moisture absorbent ,
In the fiber layer, the content of the moisture absorbent is 300 parts by mass or more with respect to 100 parts by mass of the fine cellulose fibers,
The water content is 8% by mass or more,
Sheet for total heat exchanger. 2. The whole of claim 1 , wherein the moisture absorbent comprises at least one selected from metal halide salts, metal sulfates, metal acetates, amine salts, phosphoric acid compounds, guanidine salts, and metal hydroxides. Sheet for heat exchanger. The sheet for a total heat exchanger according to claim 1 or 2, wherein the moisture absorbent is a metal halide salt. The sheet for a total heat exchanger according to any one of claims 1 to 3 , wherein said fine cellulose fibers have ionic groups. 5. The total heat exchanger sheet according to claim 4, wherein the ionic group is an anionic group. The sheet for a total heat exchanger according to any one of claims 1 to 5, wherein the surface on the fiber layer side has a water contact angle of 50° or more. Claims 1 to 6, wherein D1/D2 is 0.25 or more and 4 or less, where D1 is the contact angle of water on one surface of the total heat exchanger sheet and D2 is the contact angle of water on the other surface. The sheet for a total heat exchanger according to any one of the above. The sheet for a total heat exchanger according to any one of claims 1 to 7, wherein the fine cellulose fibers have a fiber width of 30 nm or less. 9. The sheet for a total heat exchanger according to claim 1, wherein said fine cellulose fibers have a basis weight of 0.1 g/m ² or more and 3 g/m ² or less. A total heat exchanger element comprising the total heat exchanger sheet according to any one of claims 1 to 9. A total heat exchanger comprising the element for a total heat exchanger according to claim 10.

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