JP6523772B2 - Surface coated paper strength agent and paper coated with the same - Google Patents

Description

  The present invention relates to a paper strengthening agent using a slurry containing a pulverized material of a material containing cellulose.

  At present, paper is used in various applications, and among them, there are many products that require high strength, including paperboard used for packaging materials such as cardboard. To make high strength paper, use high quality wood pulp that is easy to exert strength, or to improve the strength of paper, such as polyacrylamide (PAM), starch, polyvinyl alcohol (PVA), etc. It is conceivable to use a paper strengthening agent. In terms of cost, it is difficult to use high quality wood pulp and in many cases high strength papers are made by the addition of paper strength agents. In particular, when manufacturing corrugated paper made from used paper as a raw material, a paper strengthening agent is used.

  However, the use of large amounts of these paper strengthening agents also increases the cost of producing paper. Also, among paper strengthening agents, those derived from natural products such as starch and synthetic polymers such as PVA and PAM are roughly classified into two types, but those derived from natural products are more environmentally friendly Considering the load of For this reason, a paper strengthening agent with low impact on the environment at low cost is desired.

  By the way, although paper mainly consists of cellulose, utilization in various forms is considered by making cellulose into a ground material until now. Specific applications include food additives, filter aids, resin fillers, feeds and the like.

  In the field of papermaking, for example, Patent Document 1 describes coated paper prepared by mixing pulp as a raw material of paper and fine fibrous cellulose and making (internal addition) paper, and this coated paper has high rigidity. It is written that it becomes. Moreover, the example which utilizes what grind | pulverized the ground material of cellulose containing raw material mixed with an inorganic substance for a filler is proposed (patent document 2).

JP-A-6-341094 Unexamined-Japanese-Patent No. 2014-19830

  As in Patent Document 1, a method of increasing stiffness by mixing a pulverized material containing cellulose with a raw material pulp for papermaking has been reported, but the cellulose pulverized material is coated on the paper after paper making (external addition) There is no example of increased strength. On the other hand, Patent Document 2 also contributes to whiteness and smoothness, but the effect as a paper strengthening agent is limited even if it is mixed and papermaking, and it is sufficiently compressed even when applied in large amounts. There was a problem that strength did not go up. As described above, the study of specific utilization as a paper strengthening agent, which has been conventionally studied, is limited to the use form mixed at the time of paper making, and the concrete examination of the utilization method as a coated paper strength agent is I was not going forward.

  Then, this invention makes it possible to use suitably the material containing a cellulose as a paper strengthening agent for coating, and it aims at obtaining a paper strengthening paper which is easy to handle.

  In the present invention, a slurry obtained by dispersing a material obtained by pulverizing a material containing cellulose so that the fiber diameter is 1 μm or less and the mode diameter of the longest part is 5 μm or more and 100 μm or less in water is a coated paper strength agent The above-mentioned problem was solved by doing.

  In the present invention, first, the size of the pulverized material has to be optimally prepared so as to fall within the above range. Simply applying a slurry of a material containing cellulose as a paper strengthening agent to paper does not have the effect of improving the paper strength. In the present invention, it has been found that the slurry containing the pulverized material pulverized into the size of the above range particularly improves the paper strength improvement effect as compared with the pulverized material having the size of the range before and after that.

  The principle is probably considered as the following mechanism. First, by setting the fiber diameter to 1 μm or less, the fibers become thin, and when coated on paper, they enter between the fibers on the surface and strengthen the bond between the fibers of the paper, which is considered to improve the paper strength. Furthermore, when the above-mentioned optimum size crushed material is coated on the paper, it is considered that the crushed material is formed in a nearly uniform state on the surface of the paper and this greatly improves the paper strength. If the above-mentioned cellulose pulverized material is too long in the longitudinal direction, the viscosity of the slurry becomes high and tends to be uneven, and the coated surface becomes uneven due to the length of the cellulose pulverized material itself. In addition, when the pulverized material is too long, the pulverized materials are entangled with each other, so that they are not uniformly dispersed on the surface of the paper, and a sufficient paper strength enhancing effect can not be obtained, resulting in a mere coating agent. On the other hand, if the above-mentioned pulverized material is too short, the interaction between the pulverized materials becomes weak, so the paper strengthening effect becomes limited. The present invention takes full advantage of the unique behavior which occurs only when the grind on the surface of the paper is within the above specified length range.

  The effect of the above-mentioned pulverized material can be exhibited not only by pure cellulose-derived pulverized material. That is, in addition to cellulose, an organic substance such as hemicellulose or lignin, or a plant-derived or additive-derived inorganic substance may be contained. However, if the amount of the inorganic substance is too large, it has the effect of preventing the paper reinforcing effect by the pulverized material, and therefore, when the inorganic substance is mixed, the amount is desirably less than 50% by mass in the solid content. If the material contains 50% by mass or more of inorganic matter, adjust it to less than 50% by mass by mixing with other materials with high cellulose content or removing some of the inorganic matter in any way Can be used in the present invention.

  By using the coating paper power enhancing agent according to the present invention, not only filter paper and waste paper but also various types of cellulose such as plant biomass such as rice straw, paper powder, waste generated during paper making (scum and excess sludge) The material can be suitably used as a paper strengthening agent. Thereby, the necessary paper strength can be effectively imparted to the paper, and a paper strength-enhancing paper can be suitably obtained.

Photomicrograph of the deflocculating paper used in the examples (A) An enlarged photograph of the filter paper after crushing (pretreatment) to a 0.08 mm pass in Example 2, (b) An enlarged photograph after dry crushing in Example 2, (c) An enlarged photograph before the main crushing after preliminary crushing, (D) Enlarged photo after this crushing (A) An enlarged surface photograph of core base paper used in the examples, (b) An enlarged photograph of a surface of a paper strength-enriched paper coated with the paper strength enhancer according to Example 2, a sectional enlarged photograph of (c) (b) (A) A polarized light micrograph of microcrystalline cellulose before grinding, (b) A polarized light micrograph after grinding of (a) (A) Electron micrograph (1000 ×) of microcrystalline cellulose before grinding, electron micrograph (5500 ×) of (b) (a) after grinding

  Hereinafter, the present invention will be described in detail. The present invention relates to a coated paper strength agent comprising a slurry containing a pulverized material of a material containing cellulose, a paper strength paper coated with the same, and a method for producing the same.

  The material containing the cellulose used as the raw material of the said ground material is not specifically limited. For example, materials containing cellulose such as filter paper, waste paper, microcrystalline cellulose, plant biomass such as rice bran, rice husk, wood powder, paper powder, scum generated during paper making, excess sludge, etc. can be used. In particular, it is preferable to use scum and excess sludge, which are wastes generated during papermaking, because the strength of the obtained paper can be improved while reducing the wastes in the whole papermaking process. That is, the material does not need to be pure cellulose, and may contain other organic substances such as hemicellulose and lignin, inorganic substances, and the like. Therefore, the slurry of the ground material obtained by grinding the material containing cellulose may contain the water-insoluble organic matter and inorganic matter. However, if the content of cellulose is too low, the weight will increase unnecessarily when coating, and it may be necessary to remove impurities once, so it is a material containing at least 10% by mass of cellulose or more. Is preferred. The content of cellulose is that of α-cellulose.

  In the above pulverized material, the mode diameter (particle diameter corresponding to the mode value) of the longest part needs to be 5 μm or more, and preferably 10 μm or more. If the mode diameter is less than 5 μm, the ground material will crack even when coated on paper, and the effect of the present invention on the paper can not exhibit a particularly high strength enhancing effect on the paper, but merely the additives It is because it is easy to stay at the effect grade. On the other hand, the mode diameter needs to be 100 μm or less, preferably 80 μm or less. When the mode diameter exceeds 100 μm, the viscosity of the slurry becomes too high, and the thickness of the ground product on the surface becomes uneven, or the fibers of the ground product become too long and become entangled and become lumps. The ground matter formed on the surface is not sufficiently uniform. In addition, when a plurality of the above-mentioned pulverized materials are collected, there is a possibility that the unevenness can not be neglected depending on the size of itself. Because these effects overlap, if there is a large amount of pulverized material that is too large, it will not be able to exert a unique paper-strengthening effect on paper, and will remain only to the extent that the additive is merely placed. In the following description, the term “particle diameter” refers to the length of the longest part of the pulverized material.

  In addition, even when an inorganic substance is contained in the above-mentioned material as described later, the value of this mode diameter is basically based on a product obtained by grinding a component derived from cellulose (hereinafter referred to as "a pulverized product derived from cellulose"). It is determined. Since the inorganic substances contained in the above-mentioned materials are generally smaller than the fibrous component derived from cellulose, what appears as the mode value is the value of the component derived from cellulose.

  In addition, since the component derived from cellulose among the said pulverized materials is what grind | pulverized the cellulose which is fibrous originally, the shape where a fiber length is longer than a fiber diameter is often maintained also after a grinding | pulverization . The above-mentioned mode diameter defined in the present invention is a value for the fiber length corresponding to the maximum diameter as particles.

  When preparing the above-mentioned pulverized material, the particle size distribution differs depending on the above-mentioned material and the method of pulverization. For this reason, it is more preferable not only to satisfy the condition of the above-mentioned mode diameter but also to meet other distribution conditions.

  The above-mentioned pulverized material preferably has a median diameter (d50) of 5 μm or more, and preferably 10 μm or more. When the median diameter is 5 μm or more, in addition to the mode diameter satisfying the above range, it is possible to secure a sufficient number of particles having a size capable of suitably exhibiting the paper strength enhancing effect. On the other hand, the median diameter is preferably 50 μm or less, and more preferably 40 μm or less. The viscosity of the slurry is easily suppressed as a whole, and the uniformity of the pulverized material formed on the surface is enhanced, so that the paper strength improvement effect is likely to be enhanced. In the case where the above material contains an inorganic substance, the inorganic substance tends to be smaller than the cellulose-derived pulverized substance, so the pulverized substance having a large content of the inorganic substance has a median diameter smaller than the value of only the cellulose-derived component. It may be a value.

  Furthermore, the above-mentioned pulverized material has a diameter (hereinafter referred to as "fiber diameter") which is the shortest part of the pulverized material in the form of fibers, not the longitudinal direction of fibers, of the above-mentioned pulverized material derived from cellulose If it does not, the paper strength improvement effect can not be seen. For this reason, it is necessary to include particles crushed to at least a fiber diameter of 1 μm or less. It is considered that substantially no improvement in paper strength can be obtained unless particles of 10% or more are 1 μm or less. More specifically, it is preferable that 50% or more of the fiber diameter of the cellulose-derived pulverized material constituting the pulverized material is 1 μm or less. Furthermore, it is more preferable that the fiber diameter of the above-mentioned pulverized material derived from cellulose of 90% or more is 1 μm or less.

  The above-mentioned pulverized material is preferably contained in an amount of 0.5% by mass or more, more preferably 1% by mass or more, in the above-mentioned slurry when used as a surface-coated paper strength agent according to the present invention. If it is too thin, it takes time to put a sufficient amount of the above-mentioned pulverized material on paper, and it takes too long to dry after coating. On the other hand, the content of the pulverized material contained in the slurry is preferably 7% by mass or less, and more preferably 5% by mass or less. If it is too thick, the viscosity of the above-mentioned slurry becomes too high, and it becomes difficult to apply uniformly on paper.

  In the above slurry, the proportion of the above-mentioned pulverized material in solid content which is a component remaining without being dissolved in water is preferably 15% by mass or more, more preferably 30% by mass or more, and 50 It is further preferable that it is mass% or more. If the amount is too small, the efficiency of the paper strengthening effect obtained by placing the above-mentioned slurry may be poor, and the paper may be unnecessarily heavy.

  In order to disperse the above-mentioned pulverized material in water in the above-mentioned slurry, the above-mentioned cellulose material as a raw material of the above-mentioned pulverized material is dropped into water, and a method of carrying out pulverization treatment for wet grinding for suitable time is mentioned. Moreover, before dropping the above-mentioned cellulose material into water, the fibers may be loosened in advance by a disintegrator, or dry-pulverized by a stirring mill or the like. Furthermore, after wet grinding, wet grinding may be performed in multiple stages. Other than these methods, the method is not particularly limited as long as the slurry satisfying the above-described diameter condition can be obtained.

  The slurry may contain an inorganic substance. However, when an inorganic substance is contained, the content of the inorganic substance in the slurry is preferably less than 50% by mass in the solid content. The content is more preferably 25% by mass or less, still more preferably 15% by mass or less, and the less the better in terms of the paper reinforcing effect. The particularly excellent paper-strengthening effect exerted by the coated pulverized material having an appropriate size is suppressed or not exerted when the amount of the inorganic substance contained in the slurry is too large. It is considered that this is because the integrity of the crushed material is disturbed by the inorganic matter. For this reason, when the above-mentioned original material has an inorganic substance of 50% by mass or more, it is mixed with another material having a high cellulose content, or the inorganic substance is removed by some method to reduce the proportion of the inorganic substance contained. Above, used as a material. However, it is not necessary to exclude it to the limit, and if it is less than 10% by mass, the suppressing effect on the paper strengthening effect is hardly exerted.

  Here, the above-mentioned inorganic substance means a particle of a metal element or a compound which is poorly soluble or insoluble in water and contains a metal element. Specifically, calcium carbonate, titanium oxide, talc, mica, silica, kaolin and the like can be mentioned. These above-mentioned inorganic substances are not dissolved in water but are dispersed as fine particles, and they remain on the surface of the paper even after being coated on the paper.

  As a form in which these above-mentioned inorganic substances are mixed in the above-mentioned slurry, for example, when the material is papermaking scum or paper powder, calcium carbonate, titanium oxide, talc, mica mixed as pigments or additives contained in the original paper Etc. Moreover, when materials are plants, such as rice straw, the inorganic substance etc. which these plants originally contain are also mentioned. In addition to this, components for intentionally mixing for the purpose of other effects may be included.

  In addition, when the above-mentioned inorganic substance is intentionally added, various compounds other than the above examples may be included. However, the merit of intentionally mixing the above-mentioned inorganic substance in the above-mentioned slurry is mainly the improvement of whiteness, fluorescence degree, and smoothness, and it is thought that there is little to overcome the demerit that the paper strengthening effect of the present invention declines.

  The above-mentioned slurry may contain other additives soluble in water, in addition to the above-mentioned ground matter and the above-mentioned intentionally added inorganic substance. Specifically, pH adjusters, retention improvers, wet strength improvers, drainage improvers, polyaluminum chloride, PAM, starch, sodium acrylate, sulfuric acid bands, etc. may be mentioned.

  The above-mentioned slurry can be used as a coated paper strength agent to be coated on the paper after paper making. The method for coating is not particularly limited, and for example, the coating can be performed by a general method such as immersion, spraying, and application.

In using the slurry as coated paper strength agent, the coating amount of the paper is preferable to be 2 g / m ² or more, and more preferably 4g / m ² or more. If it is less than 2 g / m ² , the paper strength improvement effect is insufficient. The coated paper strength agent of the present invention is advantageous over the conventional coated paper strength agent in terms of cost of procuring materials, so there is almost no merit of overcutting the coated amount. On the other hand, the coating amount of the paper is preferable to be 10 g / ^{m 2} or less, more preferably 8 g / ^{m 2} or less. Even if it is too large, the amount of the above-mentioned pulverized material which contributes to the paper strength in contact with the surface of the paper is physically limited, and the paper strength enhancing effect can not be obtained for the coating weight.

  The coating paper strength agent according to the present invention can exert beneficial effects even with the above-mentioned cellulose material treated as waste, and can reduce the cost and labor for waste treatment. In addition, not only the effect by simple bulkiness, but by making the crushed product of appropriate size, it is possible to exert a particularly excellent paper strengthening effect and to make the strength of the coated paper reinforced paper excellent. .

Hereinafter, the contents of the invention will be more specifically described by way of examples in which the present invention is actually practiced.
First, the materials and raw materials used will be described.

<Material containing cellulose>
-Filter paper (Advantec: qualitative filter paper No. 1)
-Rice straw (the ash is mainly plant-derived silica)
・ Paper waste (Scum collected at Rengo Co., Ltd. Paper mill. Ash is mainly derived from additives added during papermaking; calcium carbonate or inorganic substances such as titanium oxide and kaolin)
・ Waste paper (used as a general-purpose papermaking material. Ash is mainly an inorganic material such as calcium carbonate or titanium oxide derived from additives added at the time of paper making)
Paper powder (cut powder produced at Corrugated Cardboard Factory, Rengo Co., Ltd. Ash is an inorganic substance such as calcium carbonate or titanium oxide derived mainly from additives added during papermaking)
<Additional inorganic substances>
-Calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd .: Softon # 3200)

  The analyzed mass content on dry weight of the material containing cellulose used is shown in Table 1. The component analysis method was performed based on the method of TAPPI standard, and the holocellulose content was measured by the Wise method. Here, the holocellulose is the combined content of alpha cellulose and hemicellulose. Further, the ash content is the weight of ash remaining after combustion, and corresponds to an inorganic substance. Note that the total value does not reach 100% because other components are included.

<Study on length of pulverized material of material containing cellulose>
First, using a filter paper as a material containing cellulose, the particle size distribution of the pulverized material slurry prepared by changing the degree of pulverization was measured. In addition, tests of compressive strength (ring crush test) were conducted on paper-strengthened papers coated with the respective slurries.

(Reference Example 1)
First, in accordance with JIS P 8220, a 5 mm square filter paper was fibrillated in water to obtain a deflocculated paper. The results of particle size distribution measurement of this deflocculated paper are shown in Table 2 as Reference Example 1. Also, Table 3 shows the difference between the raw materials and procedures of each example.

(Comparative example 1)
First, as a pretreatment, a 5 mm square of filter paper was cut to a 0.08 mm pass with a Fritsch dry crusher rotor speed mill P-14. This pretreated material is described as "0.08 mm pass" in Table 3. Next, this pretreated material was treated by wet grinding in a stirring mill for 1 hour. Specifically, about 15.3 g of a 0.08 mm path raw material is put in a 900 cc pot, 1 mm diameter zirconia beads are introduced up to 450 cc (50 volume%), and the solid content is 5.14 mass%. Water was added as it became and stirred at 900 rpm for 1 hour. The particle size distribution measurement results of this pulverized material are shown in Table 2 as Comparative Example 1.

  In addition, in the measurement of particle size distribution, a laser diffraction type particle size distribution measuring apparatus (manufactured by Shimadzu Corporation: Shimadzu-SALD 2100) was used. The refractive index was 1.80 to 0.20 i, the measurement method was a flow cell, and the measurement range was 0.01 to 1000 μm. The sample for measurement of particle size distribution using the pulverized material was a slurry of 0.1 to 0.5%, and a dispersant to which 1% by mass of sodium 1.25% sodium CMC was added as a liquid amount was used as a dispersant. The “mode diameter” is the particle diameter that is the highest frequency. "D10" is the particle size when integrated from fine particle size and reaching 10% of the whole. “D50” is the particle size when integrated from fine particle size and reaching 50% of the whole. "D90" is the particle size when integrated from fine particle size and reaching 90% of the whole.

(Comparative example 2)
The wet-grinding process was carried out seven times using muscoroider (a stone mill attrition mill, manufactured by Masuko Sangyo Co., Ltd .: Super Mascoloider MKCA-6-2R) using a deflocculated paper as a raw material. The particle size distribution measurement results of this ground material are shown in Table 2 as Comparative Example 2.

Example 1
In the same manner as Comparative Example 1, a filter paper cut into 5 mm square was crushed to a 0.08 mm pass by a Fritsch dry crusher rotor speed mill. The 0.08 mm pass raw material was dry-pulverized using the stirring bead mill of Comparative Example 1 for 30 minutes. In the dry pulverization treatment, zirconia beads were similarly placed in the same pot used for wet pulverization in Comparative Example 1, and the pulverization treatment was performed without adding water. Next, water was added so that the solid content was 5.14% by mass, and wet pulverization treatment was performed at 1000 rpm for 90 minutes. The particle size distribution measurement results of this pulverized material are shown in Table 2 as Example 1.

(Example 2)
In the slurry of the pulverized material obtained in Example 1, the pulverization treatment up to that point was pre-crushing, and further, wet pulverization to be main pulverization was further performed in the same pot at 750 rpm for 5 hours. The particle size distribution measurement results of this pulverized material are shown in Table 2 as Example 2.

(Comparative example 3)
In Example 2, the grinding process was performed according to the same procedure except that the main grinding was increased from 5 hours to 24 hours. The results are shown in Table 2.

(Comparative example 4)
In Example 2, the grinding treatment was performed according to the same procedure except that the main grinding was increased from 5 hours to 48 hours. The results are shown in Table 2.

<On the tendency of crushing>
From the measurement results, it can be seen that in the process of grinding, the fibers are ground in order from large fibers. First, it was found that particles of 400 μm or more in Reference Example 1 before grinding were almost crushed in Comparative Example 1. In Comparative Example 1, the peaks of the distribution were at two points of 50 to 70 μm and 100 to 200 μm, but the mode diameter was 138 μm. In Example 1 in which wet grinding was performed after dry grinding, any of these two peaks decreased and the mode diameter decreased to 48.8 μm. When grinding was further performed for a long time, the mode diameter was less than 5 μm, and after 48 hours, the mode diameter was less than 1 μm.

<Production of coated paper>
A dispersion of each of the ground products of each example having a solid content adjusted to 3.0 to 7.0% on a 25 cm square Rengo Co. core base paper (120 g / m ² ), a bar coater It coated on both sides so that it might become about 10 g of one side by (Yasuda Seiki Mfg. Co., Ltd. make: No. 16). The coated paper was sandwiched with water absorbing filter paper, and squeezed for 5 cycles (20 seconds) with a squeeze roll. Then, it was dried for 2 minutes with a drum dryer at 120 ° C., conditioned at room temperature 23 ° C., humidity 50% for 24 hours or more, and subjected to the next paper strength test.

<Measurement of compressive strength>
According to JIS P 8126, a test piece of 152.4 mm in length and 12.7 mm in width is cut out from the coated paper, and it is 13 mm per minute until it is crushed by a compression tester (manufactured by Japan TMC Co., Ltd .: ring crush tester TMC-R-200) The load was applied at the speed of and the maximum load when crushing was recorded. The number of N was 6 for one type of sample, and the average value was determined. The values are shown in Table 4.

Comparative Examples 1 and 2 showed a slight increase in compressive strength as compared to Reference Example 2 in which only water was added. However, in each case, the increase is less than 20 N at maximum with respect to Reference Example 2. Particularly in Comparative Example 1, despite the addition of 8 g / m ² , the compressive strength was inferior to that of Comparative Example 2-2. These are considered to be due to the fact that the ground material is not uniformly applied because the fibers are too large. Next, in Examples 1 and 2, an increase in compressive strength near 20 N was observed at a coating weight of ² g / m ² , and a large improvement in compressive strength was observed in proportion to the increase in the coating weight. However, in Comparative Examples 3 and 4 in which crushing was further progressed, the increase in compressive strength appeared to the same extent as Comparative Examples 1 and 2. This confirms that a specific increase in compressive strength is observed only in a specific mode diameter range including the range of the example.

<Fiber condition verification>
A photomicrograph of the disaggregated paper used in Reference Example 1 is shown in FIG. The displayed scale is 10 μm on one scale. The majority of the fiber length is 1 mm (1000 μm) or more, and the fiber diameter is about 10 to 20 μm.

  Next, for the series of procedures in Example 2, a magnified photograph after pretreatment (grind to a 0.08 mm pass) is shown in FIG. 2 (a), and a magnified photograph after dry pulverization is shown in FIG. 2 (b). The enlarged photograph of (corresponding to Example 1) is shown in FIG. 2 (c), and the enlarged photograph after the main crushing for 5 hours is shown in FIG. 2 (d). However, the magnification is different only in FIG. In each case, one scale of the scale is 10 μm. The mode diameter in FIG. 2D at the final stage is 17.2 μm.

  The surface photograph of the core base paper before coating is shown in FIG. 3 (a). The magnification is 150 times. The surface photograph (150 times) after applying the paper strengthening agent concerning Example 2 in FIG.3 (b) is shown the cross-sectional photograph (1000 times) in FIG.3 (c). Although unevenness due to fibers is clearly observed in the original core base paper, most of the unevenness is evened out in FIG. 3 (b) after the addition of the paper strength agent. Looking at the cross section, it was confirmed that a layer of cellulose was formed on the surface with a substantially uniform thickness, and this layer was the main factor to enhance the paper strength.

<Verification of differences in cellulose materials>
(Examples 3 to 7, Reference Example 2)
The ground material slurry was prepared such that the mode diameter falls within the range of 5 to 100 μm for materials other than filter paper. About rice straw, the ground material was obtained by the same procedure as Example 2. Other than papermaking waste, waste paper, and paper powder, ground materials were obtained by the same procedure as in Example 2 except that dry grinding was not performed. However, the time required for the main crushing in each example was adjusted as appropriate. Although paper waste contains 48% of ash content per dry weight, it has been confirmed that particles of ash content have d90 of 20 μm or less and do not overlap with fine fibers including cellulose. However, since the effect of ash appears in the median diameter, it is not the particle size distribution of only the pulverized material derived from fine fibers containing cellulose (crushed material derived from cellulose). On the other hand, with regard to the mode diameter, the measured value can be considered as a value for a pulverized material derived from fine fibers containing cellulose (crushed product derived from cellulose) for the reason described later. The slurry of each example was coated on a core base paper by the same procedure as in Example 2, and the compressive strength was measured. The results are shown in Table 5. The content rate is a rate in solid content.

  Regardless of the type of material containing cellulose, a high increase in compressive strength was observed in all cases. For this reason, it was confirmed that the present invention is practicable regardless of the type of material. However, among these, only Example 4 had a lower value than the other Examples although the compressive strength exceeded 170N. This is considered to be due to the fact that the amount of the inorganic substance contained in the material was particularly high only in Example 4. It is considered that lignin and hemicellulose other than inorganic substances do not inhibit the paper strength improvement effect. This is because rice straw containing 16% lignin and 30% hemicellulose is equivalent in strength to waste paper and paper powder containing 8% lignin and 24% hemicellulose.

<Verification of the influence of inorganic substances>
(Comparative example 5)
The solid content concentration of the filter paper pulverized to the same size as in Example 2 and the calcium carbonate (manufactured by Shiroishi Calcium Co., Ltd .: Softon # 3200, average particle size 0.7 μm) both become 5.0 mass% A mixed slurry was prepared. That is, it is the slurry used as the content rate of the inorganic substance in solid content will be 50 mass%. When this slurry was applied according to the same procedure as in Example 2, the compressive strength remained at 165 N, although the coating amount was 8.2 g / m ² . For this reason, it has been confirmed that when the inorganic matter of 50% by mass or more is contained in the solid content, the unique paper strength improvement effect exhibited by the present invention can not be sufficiently exhibited.

<Verification of fiber diameter>
(Comparative example 6)
Using microcrystalline cellulose (mode diameter 17.2 μm, median diameter 10.5 μm, cellulose microcrystal manufactured by Merck Ltd.), compressive strength was measured by applying as it was without pulverization (Comparative Example 6). The results are shown in Table 6. Although the mode diameter was 17.2 μm, the compressive strength was hardly increased.

  The electron micrograph of the microcrystalline cellulose according to this Comparative Example 6 was taken by JSM-6010PLUS / LA scanning electron microscope (SEM) manufactured by JEOL. The photograph is shown to Fig.5 (a). The fiber diameter was confirmed in the measurement mode which SEM has about 50 fibers observed. The results are shown in Table 6 together. The fiber diameter when integrated from a short fiber diameter reaches 10% of the whole is set to d10, and the fiber diameter when integrated from a short one reaches 90% of the whole is set to d90. The fiber diameter was 1 μm at the minimum, and no particles with a fiber diameter of 1 μm or less were found. Thus, it is considered that the strength increasing effect was not exhibited because the particles having a thin fiber diameter were insufficient.

(Example 8)
The microcrystalline cellulose of Comparative Example 6 was pulverized so as to have a distribution as shown in Table 6 above. The polarized light micrograph is shown in FIG. 4 (b). When a paper strengthening agent was similarly prepared for this material and the compressive strength was measured, high compressive strength improvement was observed. An electron micrograph was taken in the same manner as Comparative Example 6. The photograph is shown in FIG. 5 (b), and the fiber diameter measured in the measurement mode is shown in Table 6. Although the particle diameter was only about half as a whole, the fiber diameter was finely ground to 0.39 μm at maximum. Thus, it has been confirmed that a high strength improvement effect is exhibited by pulverizing the particles to a sufficiently thin particle having a fiber diameter of 1 μm or less.

<Verification of mode diameter when containing inorganic substance>
A test was conducted to confirm that the mode diameter to be measured is the value for the cellulose pulverized material, for the pulverized papermaking waste having a large content of inorganic substance. First, the particle size distribution of the paper waste before grinding was measured. This value is shown in Table 7 as Reference Example 3. Next, this papermaking waste was incinerated at 600 ° C. for 2 hours, and the particle size distribution was measured. This value is shown in Table 7 as Reference Example 4. This reference example 4 is considered to be substantially the same as the value measured by extracting only the inorganic substance contained in the scum.

  Although the mode diameter of Reference Example 3 which is a scum before grinding is 138.2 μm, the mode diameter of the ash contained in this is 7.5 μm as in Reference Example 4. Therefore, it was confirmed that the mode diameter before the above grinding was hardly affected by the inorganic substances which contained a large amount of ash. Further, since the mode diameter after grinding is also 60.1 μm, which is a value higher than the mode diameter of the ash content, it is confirmed that there is no particular influence by the grinding of the inorganic ash content. For this reason, the reason why the mode diameter is reduced from 138.2 μm of Reference Example 3 to 60.1 μm of Example 4 is also the ground material of cellulose fine fibers (ground material derived from cellulose) etc. regardless of the ash content. It was confirmed that the particle diameter of

Claims (4)

A surface-coated paper-strengthening agent comprising a slurry in which a pulverized material of cellulose having a fiber diameter of 1 μm or less, a mode diameter of 5 μm to 60 μm , and a median diameter of 10 μm to 40 μm is dispersed in water.   The surface coating paper strength agent according to claim 1, wherein when the solid content of the slurry contains an inorganic substance, the content of the inorganic substance in the solid content is less than 50% by mass.   A paper with paper strength coated with the paper strength agent according to claim 1 or 2. A method for producing paper-strengthened paper, wherein the paper-strengthening agent according to claim 1 is applied to paper after paper making.