Paper towels

Abstract

To provide a paper towel having low basis weight and excellent water absorption.SOLUTION: The invention provides a paper towel produced by wet type paper-making of a fiber raw material, wherein the paper towel has a basis weight per 1 ply of 23-27 g / m, a specific volume of 4.5-7.0 cm / g, and a ratio of a conifer kraft pulp in the fiber of 40 mass% or over, containing an enzymic paper strengthening agent, having a wet crepe, having mesh marks of bulky wires of 10-26 line / inch, and having irregularity difference of the paper surface under dry condition of 0.0400 mm or over and the rate of change of irregularity difference of the paper surface between a dry condition and a wet condition of 120-140%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a paper towel used for wiping off liquids or stains attached to living bodies or objects, and a method for manufacturing the same. [Background technology]

[0002] Paper towels are generally disposable and therefore must be inexpensive. In particular, in food service industries, supermarkets, and other places that handle food, where safety and a sense of security are important, there is a high demand for paper towels that are made from 100% virgin pulp fiber and do not contain recycled paper. However, paper towels that do not contain recycled paper are more expensive than those that contain recycled paper, so there is a demand for technology to make them cheaper.

[0003] One way to make paper towels cheaper is to reduce the amount of fiber raw material used and reduce the basis weight, but simply reducing the basis weight makes the paper more likely to tear, resulting in lower user satisfaction. Reducing the crepe rate and freeness is known as a method for making paper less likely to tear, but simply reducing the crepe rate and freeness makes the paper thinner and denser, which tends to reduce water absorption, reducing user satisfaction when wiping off liquids, which is the main use of paper towels. Another method is to increase the paper thickness by reducing the crepe rate and the thickness of the base paper and then embossing it, but this also reduces the strength and makes the paper more likely to tear.

[0004] Another method for making paper towels less likely to tear is to increase the amount of chemicals such as strength agents added. Conventionally, in paper towel manufacturing methods, in order to facilitate fixation of the strength agent to the fiber raw material, a wet strength agent is supplied to a seed box, and then a dry strength agent is supplied at a later stage of the seed box, such as when the paper material is transferred to a papermaking facility using a fan pump or the like. However, in the case of inexpensive, low-basis-weight paper towels, the yield of chemicals and raw materials is poor, and even if the amount of additive is increased, the effect is not fully achieved.

[0005] In this way, in order to improve the tear resistance caused by the low basis weight, it is possible to consider a method of increasing the amount of chemicals such as paper strength agents and softeners added. However, since the yield of the chemicals decreases when the basis weight is reduced, it has been difficult to fully demonstrate the effects of conventional paper strength agents and their usage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5570714 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above problems, a primary object of the present invention is to provide a paper towel that is tear-resistant and has excellent water absorbency even though it has a low basis weight, and a method for producing the same. [Means for solving the problem]

[0008] The means for solving the above problems are as follows.

[0009] The first means is, A paper towel made by wet-processing a fiber raw material, The ratio of softwood kraft pulp in the fiber is 40% by mass or more, Basis weight per ply: 23-27g / m 2 and Specific volume is 4.5 to 7.0 cm 3 / g, Contains enzyme-based paper strengthening agent, The paper surface is uneven when dry. The height difference of the unevenness of the paper surface when dry is 0.0400 mm or more, and the rate of change of the height difference of the unevenness of the paper surface when dry and when wet is 120% to 140%. The paper towel is characterized by the above.

[0010] The second method is In the paper towel according to the first aspect, the unevenness on the paper surface is at least one of wet crepe and bulky wire mesh marks.

[0011] The third method is The paper towel according to the above second means, wherein the bulky wire mesh marks are 10 to 26 lines / inch.

[0012] The fourth measure is The paper towel according to any one of the first to third means, wherein the wet tensile strength in the longitudinal direction is 400 to 1000 cN / 25 mm and the wet tensile strength in the transverse direction is 300 to 800 cN / 25 mm.

[0013] The fifth measure is: The paper towel according to any one of the first to fourth means contains no recycled paper pulp in its fibers.

[0014] The sixth method is: In a papermaking raw material preparation process prior to a process of discharging the papermaking raw material from a stock inlet to form a wet paper, This method for producing paper towels is characterized in that an enzyme-based paper strength agent is added to the paper stock at a position where the residence time until the stock inlet can be ensured to be at least 30 minutes, and the paper stock is kept at a temperature of 40°C or less for at least 30 minutes from the time of addition.

[0015] The seventh measure is: The method for producing paper towels according to the sixth means, wherein the amount of the enzyme-based paper strength agent added to the pulp is 0.1 kg / t to 5.0 kg / t.

[0016] The eighth method is: A step of forming a wet paper from a papermaking raw material containing 40% by mass or more of softwood kraft pulp as a fiber raw material; A step of forming irregularities on the wet paper; and a step of drying the wet paper having the irregularities with a dryer. The method for producing a paper towel according to the sixth or seventh aspect of the present invention has the following features.

[0017] The ninth measure is: The step of forming the unevenness on the wet paper is a method for manufacturing paper towels of the above-mentioned eighth means, which includes the steps of wet creping, transferring the wet creped wet paper onto a bulky wire, and forming bulky wire mesh marks on the wet paper on the bulky wire.

[0018] The tenth measure is: The method for producing paper towels according to the ninth aspect, wherein the bulky wire is a bulky wire of 10 to 26 lines / inch.

[0019] The eleventh measure is: The base paper is dried in a dryer to obtain a basis weight of 23 to 27 g / m 2 The sixth to eleventh aspects of the present invention are methods for producing paper towels.

[0020] The twelfth measure is: A first dry strength agent adding step of adding an amphoteric dry strength agent to at least one of the machine tank and the mixing tank; A wet strength agent addition step of adding a cationic wet strength agent to the stock that has been subjected to the first dry strength agent addition step in a seed box downstream of the mixing tank; A second dry strength agent addition step of adding at least one of an amphoteric dry strength agent and a cationic dry strength agent to the stock that has undergone the wet strength agent addition step; The method for producing paper towels according to any one of the sixth to eleventh aspects of the present invention comprises the steps of: Effect of the Invention

[0021] The present invention provides a paper towel that is tear-resistant and has excellent water absorbency despite its low basis weight, and a method for producing the same. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is an enlarged view of the paper surface of the paper towel according to the present invention. [Diagram 2] 1 is a planar profile image for measuring unevenness of a paper towel according to the present invention. [Diagram 3] 1 is a depth profile image for measuring unevenness of a paper towel according to the present invention. [Figure 4] FIG. 2 is a diagram for explaining a papermaking raw material preparation process in the example of a paper towel manufacturing method according to the embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram for explaining a papermaking process in an example of a method for producing a paper towel according to an embodiment of the present invention. [Figure 6] FIG. 2 is a plan view of a paper towel according to an embodiment of the present invention, processed for measuring the difference in unevenness between when the paper towel is dry and when the paper towel is wet. [Figure 7] FIG. 2 is a plan view of a paper towel according to a comparative example of the present invention, processed for measuring the difference in unevenness between when the paper towel is dry and when the paper towel is wet. [Figure 8] FIG. 13 is a plan view of a paper towel according to another comparative example of the present invention, processed for measuring the difference in unevenness between a dry state and a wet state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] The paper towel according to the present invention is so-called "paper" made by a wet papermaking method, and does not include nonwoven fabric. The paper towel according to the present invention is made of pulp fibers at least 98% by mass of the constituent fibers, and particularly 100% by mass of pulp fibers. When the pulp fibers are 100% by mass, it becomes easy to make the paper by a normal wet papermaking method, and the effects of the present invention can be exhibited. However, chemical fibers and the like can be contained as long as the amount is less than about 2% by mass within the range where wet papermaking is possible.

[0025] In the paper towel according to the present invention, 40% by mass or more of the constituent fibers is softwood pulp. Softwood pulp includes softwood kraft pulp (NBKP), softwood unbleached pulp (NUKP), etc. In particular, when softwood unbleached pulp (NUKP) is used, it is preferable to use hardwood unbleached pulp (LUKP), and when softwood kraft pulp (NBKP) is used, it is preferable to use hardwood kraft pulp (LBKP). In addition, when the pulp fibers are composed of softwood kraft pulp (NBKP) and hardwood kraft pulp (LBKP), it is preferable to set the ratio of softwood kraft pulp (NBKP):hardwood kraft pulp (LBKP) to 40:60 to 60:40. Here, softwood pulp has long fiber length, which easily develops stiffness, and easily diffuses and absorbs moisture quickly along the fiber. In the paper towel of the present invention, the ratio of coniferous pulp in the constituent fibers is 40% by mass or more, and the paper towel has excellent water absorption properties, particularly when wiping off water after hand washing, and exhibits appropriate stiffness that does not become floppy even after absorbing water. It is preferable that the fibers in the paper towel of the present invention are made only of virgin pulp, particularly without containing recycled paper pulp.

[0026] The paper towel according to the present invention has a basis weight per ply of 23 to 27 g / m 2 The use of one ply can reduce costs. Although the number of plies in the paper towel of the present invention is not limited, one or two plies are preferred, and one ply is particularly preferred, since the paper towel can be made inexpensively and sufficient strength and water absorbency can be ensured even with a low number of plies. The basis weight of the paper towel is 30 g / m per ply. 2 Generally, the basis weight per ply of the paper towel of the present invention is 23 to 27 g / m. 2 This low basis weight allows the cost of the fiber raw material to be reduced. The basis weight according to the present invention is a value measured based on JIS P 8124 (1998).

[0027] On the other hand, the paper towel according to the present invention has a specific volume of 4.5 to 7.0 cm 3 / g. The larger the specific volume, the larger the gaps between the fibers. If the specific volume is within this range, the paper will be adequately dense and stiff. The specific volume is calculated by multiplying the paper thickness (μm) by the basis weight (g / m 2 ] divided by [cm 3 / g]. The paper thickness may be adjusted as appropriate within the range in which the specific volume can be achieved in relation to the basis weight. The paper thickness here is the value measured using a dial thickness gauge (thickness measuring device) "PEACOCK G type" (Ozaki Manufacturing Co., Ltd.) under the conditions of JIS P 8118 (1998). Specifically, after making sure that there is no dirt or dust between the plunger and the measurement table, the plunger is lowered onto the measurement table, the dial thickness gauge's scale is moved to set the zero point, the plunger is then raised and the sample is placed on the test table, the plunger is slowly lowered perpendicular to the paper surface, and the gauge value at that time is read. At this time, the plunger is simply placed on the test table. The plunger terminal is made of metal, and the plane with a diameter of 10 mm is made to contact perpendicularly to the paper surface, and the load during this paper thickness measurement is approximately 70 gf. The paper thickness is the average value obtained by performing 10 measurements.

[0028] On the other hand, the paper towel according to the present invention characteristically contains an enzyme-based paper strength agent. The enzyme-based paper strength agent contains an enzyme that decomposes polysaccharides and acts to fluff the fiber surface and inside of the fiber. By the action of the enzyme-based paper strength agent, entanglement between fibers, especially on the surface, is generated, increasing the paper strength, and the above-mentioned high specific volume is achieved despite the low basis weight. Furthermore, it is believed that the characteristics of the fiber surface are modified, resulting in excellent water absorption. Here, examples of the enzyme-based paper strength agent according to the present invention include those containing at least one of cellulase, hemicellulase, and xylanase. These enzymes decompose polysaccharides. In addition, as paper strength agents containing such enzymes, Hercobond 8922 (manufactured by Riken Green Co., Ltd.), Hercobond EZ4423 (manufactured by Riken Green Co., Ltd.), etc. can be used.

[0029] The paper towel according to the present invention further has unevenness on the paper surface. The unevenness can be formed by unevenness forming means such as embossing. However, it is preferable that the unevenness is caused by unevenness applied in a wet paper state. The unevenness is difficult to collapse in a wet state such as when absorbing water. In particular, the unevenness is preferably a wet crepe. A wet crepe is a crepe formed by a wet crepe method, and is a crepe formed in a wet paper state. A wet crepe has a property that the crepe is difficult to stretch even when it absorbs liquid. By forming unevenness by wet creping, the crepe is difficult to stretch even when it absorbs water, and the unevenness due to the fine crepe is maintained on the surface. Therefore, it is excellent in wiping off liquids and dirt attached to living organisms and objects, etc., especially when wiping after hand washing or wiping off moisture from objects.

[0030] Furthermore, the unevenness of the paper surface of the paper towel according to the present invention is preferably a bulky wire mesh mark. The bulky wire is one aspect of a papermaking net used to transfer a wet paper in wet papermaking. The bulky wire mesh mark is formed in response to the surface unevenness caused by the regular weaving of the wire, as shown in the enlarged view of the paper surface in FIG. 1(A). In particular, recesses that look like holes with sparse fibers are regularly formed at positions corresponding to the parts that appear as protrusions on the surface of the woven wire. The bulky wire mesh mark is also an unevenness given in the state of a wet paper, and the mesh mark is maintained and becomes more prominent even in a wet state, as shown in the enlarged view of the paper surface when water is absorbed in FIG. 1(B) (in the figure, one of the recesses corresponding to the wire protrusions that constitute the mesh mark is indicated by the symbol 40), and the unevenness is unlikely to collapse or be crushed in a wet state such as when water is absorbed.

[0031] Furthermore, the bulky wire mesh marks are preferably 10 to 26 wires / inch bulky wire mesh marks. More preferably, they are 15 to 21 wires / inch bulky wire mesh marks. Bulky wires of 10 to 26 wires / inch are relatively sparse. Such mesh marks are relatively large irregularities on the paper surface, but are difficult to stretch.

[0032] A particularly preferred embodiment of the paper towel according to the present invention has both the unevenness of the wet crepe and the mesh marks of the bulky wire (note that FIG. 1 is a diagram of an embodiment having the wet crepe as well). By forming mesh marks by the bulky wire on the paper in addition to the wet crepe, the unevenness of the paper surface is maintained when liquid is absorbed, and the contact area does not expand excessively when wiping hands or objects, and the unevenness is maintained, and this, combined with the high water absorbency, makes it excellent in wiping off dirt and the like. In other words, the wet crepe and mesh marks make the paper surface less likely to collapse and the unevenness of the paper surface is easily maintained, and the mesh marks are maintained even after sufficient liquid is absorbed, so that the effect of excellent wiping performance as a paper towel even at a low basis weight is even more remarkable.

[0033] On the other hand, the paper towel according to the present invention has a height difference of 0.0400 mm or more when dried. When the height difference of the unevenness of the paper surface is 0.0400 mm or more, the effect of the unevenness is fully exhibited. The height difference of the unevenness of the paper surface when dried according to the present invention is measured using a one-shot 3D measuring macroscope VR-3200 manufactured by Keyence Corporation or an equivalent machine (hereinafter simply referred to as one-shot 3D measuring macroscope) and image analysis software "VR-H1A" or an equivalent software. The measurement is performed with a sample size of about 11 cm square, a magnification of 12 times, and a field of view area of ​​24 mm x 18 mm, and the surface side that was in contact with the bulky wire surface is measured. However, the magnification and field of view area can be appropriately changed depending on the size of the recess. The specific measurement procedure is as follows: First, a planar profile image 100 is obtained by using the one-shot 3D measuring macroscope and image analysis software to display the XY plane of the sample in color by color coding according to height. In this planar profile image 100, as shown in FIG. 2, the height of the surface irregularities caused by the individual mesh marks etc. formed by the bulky wire are clearly displayed in different colors (note that the actual planar profile image is obtained as a color image. FIG. 2 is a grayscale version of this image. The same is true for FIGS. 6 to 8). FIG. 2 is a planar profile image 100 of a paper towel according to the present invention, and the mesh marks in which recesses 40 are arranged alternately vertically and horizontally are clearly displayed. Next, as shown in FIG. 2, a recess depth (measured cross-sectional curve) profile image is obtained at line segment Q1 that crosses the longest part X of the periphery of any one recess 40A of the mesh marks in the planar image profile 100. From the cross-sectional curve of this recess depth profile, surface roughness components with wavelengths shorter than λc:800 μm (where λc is the "filter that defines the boundary between roughness components and waviness components" described in JIS-B0601, "3.1.1.2") are removed using a low-pass filter, and the "contour curve Q2" of the depth direction profile image 200 (Figure 3) shown from the cross-sectional viewpoint is obtained. Of the two upwardly convex apexes P1, P2 and the minimum value between these apexes P1, P2, this is determined as the minimum depth value Min.Furthermore, the average value of the depth values ​​of the apexes P1 and P2 is set as the maximum depth value Max (note that the actual depth profile image is obtained as a color image. In FIG. 3, this is shown in grayscale).

[0034] From the maximum value Max and minimum value Min, the height difference of the unevenness on the paper surface is calculated as the height difference of the unevenness on the paper surface = maximum value Max - minimum value Min. The apexes P1 and P2 are selected visually. The selection is made with reference to the outline E in the planar profile image (Fig. 1) of the recess 40A being measured from the planar viewpoint. Similarly, the unevenness difference is also measured for the shortest part Y in the direction perpendicular to the longest part X, and the larger value is adopted as the height difference of the unevenness. The above measurements are performed for any seven recesses of the bulky wire mesh marks on the sample surface, and the average value is taken as the final height difference of the unevenness.

[0035] Furthermore, the paper towel according to the present invention has a change rate of the height difference of the unevenness of the paper surface when dry and when wet of 120% to 140%. In other words, the unevenness is clearer when wet than when dry, and the unevenness does not expand when wiping off moisture and dirt together with moisture, so that it can be wiped off suitably. The height difference of the unevenness of the paper surface when wet is measured in the same procedure as the height difference of the unevenness of the paper surface when dry, with the sample in a wet state. The wet state is measured by placing a metal frame with outer frame dimensions of about 99 mm wide x 59 mm deep x 5 mm high, inner frame dimensions of about 70 mm wide x 40 mm deep x 5 mm high, weighing about 133 g, on the sample placed on the measurement table of the one-shot 3D measurement macroscope, and pouring 1.5 cc of tap water (about 20°C) using a pipette so that the entire part of the sample inside the frame is sufficiently wet, and leaving it to stand for 1 minute. If the sample swells due to water absorption and wrinkles or the like are formed, the wrinkles may be smoothed out to an extent that allows measurement.

[0036] On the other hand, the paper towel according to the present invention preferably has a wet tensile strength in the longitudinal direction of 400 to 1000 cN / 25 mm and a wet tensile strength in the transverse direction of 300 to 800 cN / 25 mm. The wet tensile strength according to the present invention refers to a value measured based on JIS P 8135 (1998). The test piece was cut into a strip shape with a longitudinal length of 150 mm and a transverse length of 25 mm. The wet tensile strength of the paper towel according to the present invention is very high compared to conventional dry crepe products, and has extremely high strength even when absorbed. The paper towel according to the present invention has excellent workability even when handled with wet hands. The wet tensile strength can be sufficiently adjusted by a wet strength agent, etc., as long as it is within the basis weight range according to the present invention.

[0037] Next, an example of a method for manufacturing paper towels according to the present invention will be described with reference to Figures 4 and 5. In the method for manufacturing paper towels according to the present invention, in a papermaking raw material preparation process P1, the fiber raw material is slurried and prepared to produce papermaking raw material S4, and the papermaking raw material S4 is sent to a papermaking process, where a sample is discharged from a stock inlet 24 of the papermaking equipment 2 in the papermaking process and paper-made to produce paper towel base paper D1. The paper towel base paper D1 is then processed to produce individual paper towels. For example, it may be processed into a roll to produce a roll-shaped paper towel, or it may be folded and processed with an interfolder to produce a product having a pop-up paper towel bundle. The process for processing the paper towel base paper into paper towels as products is performed using known techniques.

[0038] 4, the papermaking raw material preparation process P1 is a process in which a fiber raw material such as pulp is prepared by supplying additives and stirring the raw material in each of the equipments of the raw material tank 11, the mixing tank 12, the machine tank 13, the seed box 14, and the screen 16, and the raw material is prepared for papermaking in the papermaking equipment 2. In this embodiment, the addition of a paper strength agent is uniquely performed in this papermaking raw material preparation process.

[0039] The raw material tank 11 is a tank for storing the fiber raw material produced in the pulp process, and may be simply called a chest. The raw material tank supplies the pulp material S1 to the mixing tank 12 or the machine tank 13.

[0040] The mixing tank 12 is also called a mixing box, and is one of the devices that mixes chemicals and fiber raw materials by stirring. A typical papermaking raw material preparation facility 1 attached to a papermaking facility 2 has a mixing tank 12, but some do not have this mixing tank 12. When the mixing tank 12 is not provided, the fiber raw material is supplied from the raw material tank 11 to the machine tank 13.

[0041] The machine tank 13 is a device that agitates the raw materials to keep the concentration in the tank constant and stores the paper stock, and is capable of mixing chemicals and fiber raw materials by agitating the tank. The machine tank is also called a finishing tank or machine chest.

[0042] The seed box is a device that stores and adjusts the concentration of fibers and chemicals in the paper stock, and mixes the chemicals by utilizing the convection of the paper stock. It also makes the paper stock flow down to the rear stage at a certain pressure.

[0043] The pulp adjusted through the seed box is transferred to the papermaking equipment as papermaking raw material S4 by a fluid transfer device such as a fan pump. In the illustrated example, the pulp is transferred to the papermaking equipment as papermaking raw material S4 through a screen.

[0044] In the paper towel manufacturing method of the present embodiment, characteristically, after preparing a stock S1 containing 40% by mass or more of softwood pulp as a fiber raw material, the enzyme-based paper strength agent is added to the stock at a position where the residence time up to the stock inlet 24 can be secured for at least 30 minutes or more during the period from the stock S4 containing softwood pulp as a fiber raw material to the stock inlet 24 of the papermaking equipment 2 until the wet paper is formed. The specific addition position is not necessarily limited and depends on the scale of the equipment, the line length, the flow rate of the papermaking raw material, etc. The enzyme-based paper strength agent is added at a position where the residence time can be secured. This is because the action of the enzyme-based paper strength agent mainly acts on the fiber surface to decompose the fiber surface and fluff it, and it is necessary to secure sufficient time for this. Furthermore, the paper stock is kept at a temperature of 40°C or less for at least 30 minutes from the time of addition of the enzyme-based paper strength agent. This is because the enzyme action of the enzyme, which is the active ingredient, of the enzyme-based paper strength agent becomes inactivated when the temperature of the enzyme-based paper strength agent is 40°C or higher.

[0045] The amount of enzyme-based paper strength agent added to pulp is preferably 0.1 kg / t to 5.0 kg / t. Within this range, the enzyme-based paper strength agent can fully exert its effect.

[0046] Furthermore, in the method for producing paper towels according to the present invention, it is preferable to add the dry strength agent and the wet strength agent as follows. That is, a first dry strength agent addition step is performed in which an amphoteric dry strength agent is added to the stock S1 in at least one of the mixing tank 12 and the machine tank 13. If the papermaking raw material preparation equipment 1 does not have a mixing tank 12, the dry strength agent is added in the machine tank 13. The dry strength agent may be added separately to the mixing tank 12 and the machine tank 13, or to either one of them. However, it is preferable to add the dry strength agent all at once in the machine tank 13, which is located at the rear. Adding the dry strength agent to one tank is easier to manage than adding the dry strength agent to two tanks. Next, a wet strength agent addition step is performed in which a cationic wet strength agent is added to the stock S2 that has undergone the first dry strength agent addition step in the seed box 14 located at the rear of the machine tank 13. Furthermore, a second dry strength agent addition process is performed in which at least one of an amphoteric dry strength agent and a cationic dry strength agent is added to the stock S3 that has been subjected to the wet strength agent addition process. This second dry strength agent addition process is preferably performed at the position of a fluid transfer device 15 such as a fan pump for transferring the stock S3 adjusted in the seed box 14. In particular, in the case of a fan pump, the stock is also stirred, so it is preferable to use the fan pump as the fluid transfer device and add the agent using the fan pump. If the first dry strength agent addition process, the wet strength agent addition process, and the second dry strength agent addition process are performed in this order at each position, and the dry strength agent is divided and added before and after the addition of the wet strength agent, the yield of both the dry strength agent and the wet strength agent is increased, and the resistance to tearing is easily improved without increasing the amount of strength agent added. In addition, the fixation rate of the strength agent is improved, and the dirt of the equipment in the papermaking raw material adjustment process can be reduced. This is believed to be because flocs are formed by adding the dry strength agent to the mixing tank 12 or the machine tank 13, and the flocs capture the wet strength agent, thereby increasing the wet strength agent retention rate. As for the type of dry strength agent, an amphoteric polyacrylamide compound can be used in the first dry strength agent addition process performed in at least one of the mixing tank 12 and the machine tank 13.As those used in the second dry papermaking agent addition step performed by a fan pump or the like in the process of transferring the paper stock from the seed box, examples include amphoteric polyacrylamide compounds, cationic polyacrylamide compounds, cationic starches, and the like. Further, as the wet papermaking agent used in the wet papermaking agent addition step performed in the seed box 14, examples include polyamide epichlorohydrin resin, urea formaldehyde resin, melamine formaldehyde resin, polyamide polyamine epichlorohydrin (PAE), and polyvinylamine (PVAm). Furthermore, as a combination of the dry papermaking agent and the wet papermaking agent, it is desirable that the dry papermaking agent in the first dry papermaking agent addition step be an amphoteric polyacrylamide compound, the dry papermaking agent in the second dry papermaking agent addition step be an amphoteric polyacrylamide compound, and the wet papermaking agent in the wet papermaking agent addition step be a polyamide epichlorohydrin resin. In this case, the addition amounts of the dry papermaking agent and the wet papermaking agent are 5 to 30 kg per ton of raw material pulp for the dry papermaking agent and 10 to 40 kg per ton of raw material pulp for the wet papermaking agent. The dry papermaking agent is added by dividing the above addition amount between the first dry papermaking agent addition step and the second dry papermaking agent addition step. The distribution of the addition amounts in the first dry papermaking agent addition step and the second dry papermaking agent addition step (first dry papermaking agent addition step: second dry papermaking agent addition step) is 30:70 to 70:30. Preferably, it is 40:60 to 60:40. Note that the addition amount is adjusted according to the desired basis weight, paper thickness, and strength.

[0047] The papermaking raw material S4 adjusted in the papermaking raw material adjustment step as described above is supplied to the papermaking equipment and is made into a paper towel base paper through the papermaking process. In particular, it is desirable that the slurry concentration of the papermaking raw material S4 be 0.10 to 0.20 mass%. Further, it is desirable that the freeness (CSF) of the papermaking raw material be 400 ± 150 cc.

[0048] Next, the papermaking process according to this embodiment will be described. As shown in FIG. 5, the papermaking equipment 2 according to this embodiment has a wire part P2, a press part P3, and a dryer part P4, and may be either a round wire type or a fourdrinier type. However, the round wire type, which has a shorter press part distance, is preferable. The type of the stock inlet (former) of the papermaking equipment 2 is not particularly limited. The strict boundaries of the wire part P2, the press part P3, and the dryer part P4 differ depending on the papermaking equipment 2. In this embodiment, the process of forming and stabilizing the wet paper W1 is called the wire part P2, the process of dehydrating the wet paper W1 to a moisture content sufficient to transfer it to the dryer part is called the press part P3, and the process of drying the wet paper W3 in the dryer to make it into a dry paper is called the dryer part P4.

[0049] In the former section 21 of the wire part P2, the papermaking raw material prepared in the papermaking raw material preparation process is formed on a felt 23 or wire from a stock inlet 24 also called a head box. 2 The raw material concentration and discharge rate are adjusted so that the basis weight is 100%. Note that the papermaking equipment 2 is not limited to equipment that transports the wet paper web using only a wire or a felt. It may be equipment that combines a process of transporting the wet paper web using a wire and a process of transporting the wet paper web using a felt.

[0050] The wet paper web W1 thus formed in the former section 21 of the wire part P2 is transferred by the felt 23 or wire to the rear stage of the wire part, and then to the press part P3. In the rear stage of the wire part P2 and in the press part P3, the same manufacturing method as known paper towels can be performed. In the press part P3, the water in the wet paper web W2 can be squeezed out by the suction action of a suction roll or suction box (not shown) located on the opposite side of the felt 23 or wire to the wet paper contact surface, or by the press roll 54. A plurality of suction rolls, suction boxes, and press rolls 54 can be provided. The suction force of the suction roll or suction box and the pressing pressure of the press roll 54 are adjusted by known methods taking into account the physical properties of the paper towel to be manufactured, such as the thickness of the paper towel.

[0051] In this embodiment, the wet crepe process 3 includes a step of applying a wet crepe to the wet paper W2 whose moisture content has been reduced by dewatering in the press part P3. The moisture content of the wet paper W2 when the wet crepe is applied is preferably 40 to 60%. That is, the moisture content of the wet paper W2 is reduced to 40 to 60% in the press part P3 and then transferred to the dryer 60. The crepe rate here is preferably 5 to 25%. By applying a wet crepe and setting the crepe rate to 5 to 15%, it becomes easier to improve the water absorption rate and softness and achieve sufficient strength. In particular, it may have a favorable effect on improving the water absorption rate due to the development of strength and bulkiness in a wet state. The crepe rate is calculated from the difference in the transport speed of the wet paper before and after the scraping device such as a creping doctor. For example, when the wet paper on the press roll 54 is scraped by the creping doctor 55 and transferred to the bulky wire 26 in the subsequent stage as in the illustrated example, the crepe rate is calculated by the following formula. Crepe rate: {(peripheral speed of Yankee dryer (60 in FIG. 5))-(peripheral speed of roll (54 in FIG. 5))} / (peripheral speed of Yankee dryer)×100.

[0052] The wet paper web W3 to which the wet crepe is applied in the wet crepe application process 3 is dried in the dryer part. In the dryer part P4, the wet paper web W3 on the bulky wire 26 is transferred to the Yankee dryer 60 via the touch roll 56 or the like and dried. After the wet crepe is applied, the wet paper web is transferred to the bulky wire 26 and transferred to the dryer part P4, whereby mesh marks of the bulky wire 26 are formed on the surface of the wet paper web to which the wet crepe is applied. Here, the bulky wire 26 used in the present invention is 10 to 26 mesh (lines / inch). In addition, the wire constituting the bulky wire 26 is preferably about 0.5 mmφ in diameter. In this way, mesh marks are formed by transferring the wet paper web W4 to the Yankee dryer 60 via the bulky wire 26.

[0053] The drying process in the dryer part P4 can be performed in the same manner as a known drying process for paper towels. After being dried in the dryer 60 of the dryer part P4 to turn the wet paper W3 into dry paper D1, the wet paper W3 is transferred to an appropriate winding process and wound into a raw paper roll 70 for the paper towel. Note that a dry crepe application process 4 may be performed in which a dry crepe is applied when the dry paper is peeled off from the dryer 60, or the speed of the Yankee dryer and the winding means downstream of the dry crepe may be intentionally adjusted so that the dry crepe is not applied.

[0054] The raw paper roll 70, onto which the dry paper D1, which is the base paper for the paper towels thus produced, is wound up, is turned into a paper towel product through subsequent known paper towel manufacturing processes (not shown), such as an embossing process and a folding process using an interfolder. EXAMPLES

[0055] A sensory evaluation test was carried out on the paper towels according to the present invention (Examples 1 to 5) and Comparative Examples 1 to 3 for "thickness", "absorbency" and "firmness". The physical properties and measurements of each example and the test results are shown in Table 1 below. The sensory evaluation test was carried out on 10 subjects. The sensory evaluation test was carried out by assigning scores to each sample according to how it was evaluated in comparison with the reference sample (Comparative Example 1). The samples were scored as follows: "quite superior" was given 5 points, "slightly superior" was given 4 points, "same" was given 3 points, "slightly inferior" was given 2 points, and "inferior" was given 1 point. The average scores of each Example and Comparative Example (except Comparative Example 1) were calculated. In the table, the average scores of 3.5 or more are indicated as "◎", those of 3.5 to 3.0 are indicated as "◯", those of 3.0 to 2.5 are indicated as "△", and those of 2.0 or less are indicated as "×". Comparative Example 1 does not contain an enzyme-based paper strength agent, and the change rate of the unevenness difference of the paper surface between dry and wet is less than 120%. Comparative Example 2 is a paper towel with a general dry crepe that does not have wet crepe or bulky wire mesh marks, and Comparative Example 3 is a paper towel with unevenness formed by embossing.

[0056] The physical properties in the table were measured as described above, and the water absorption was measured as follows.

[0057] [Water absorption] The test specimen is prepared by cutting it to 100mm length x 100mm width (length and width error ±1mm each) and measuring its weight. Distilled water is poured into a pan to a depth of 20mm, and the cut test specimen is immersed in the distilled water up to the top of the paper surface, then pulled out of the distilled water and its weight is measured 30 seconds later. Five measurements are made for one test specimen, and the average value is taken as the measured value. Water absorption = [(weight after water absorption) - (weight before water absorption)] x 100 (unit: g / m 2 )

[0058] [Table 1]

[0059] As shown in Table 1, the examples of the present invention have better results in the sensory evaluation test, despite having a lower basis weight than Comparative Examples 1 and 3. In addition, the results of the sensory evaluation test are far superior to those of Comparative Example 2, which is a dry crepe having a large amount of wet strength agent and dry strength agent.

[0060] Moreover, Example 4 has a lower basis weight than Comparative Example 1 and contains enzyme-based strength. Looking at these evaluations, Example 4 had higher results in all evaluations than the benchmark Comparative Example 1. It can be seen that the enzyme-based strength makes the paper less likely to tear even at a low basis weight and has excellent water absorbency.

[0061] Furthermore, looking at the tensile strength when wet (wet tensile strength), the basis weight is 23.3 g / m 2 Even in Example 1, which has the lowest basis weight and crepe rate of 10%, the crepe strength is sufficient at 440 cN in the longitudinal direction and 322 cN in the transverse direction, which is significantly higher than that of Comparative Example 3, which is a commercially available dry crepe product. Although the numerical values ​​themselves are lower than those of Comparative Example 1, the basis weight is 4 g / m 2 Considering that the crepe rate is also low, this result can be said to be satisfactory.

[0062] For reference, planar profile images of the one-shot 3D measuring microscope in Example 4, Comparative Example 1, and Comparative Example 3 are shown in Fig. 6 to Fig. 8. Fig. 6 is for Example 4, Fig. 7 is for Comparative Example 1, and Fig. 8 is for Comparative Example 3, with (A) being the image in a dry state and (B) being the image in a wet state.

[0063] Comparing the planar profile image of Example 4 in FIG. 6 with the planar profile image of Comparative Example 1 in FIG. 7, the clarity of the depressions 45 in Comparative Example 1 does not change much overall when dry or wet. When wet, the depressions 40 are more clearly visible in Example 4, and the unevenness is more pronounced. The enzyme-based paper strength improves the maintenance of the unevenness imparted when wet. Also, it can be seen that the depressions 47 and protrusions 48 due to the embossing that can be seen when dry are almost completely lost when wet in the embossed product of Comparative Example 3.

[0064] As described above, according to the present invention, a paper towel that is tear-resistant and has excellent water absorbency despite its low basis weight and a method for producing the same can be obtained. [Explanation of symbols]

[0065] 1...Papermaking raw material preparation equipment, 2...Cylinder papermaking equipment, 3...Wet crepe application process, 4...Dry crepe application process, 11...Raw material tank, 12...Mixing tank, 13...Machine tank, 14...Seed box, 15...Fluid transfer device (fan pump), 16...Screen, S1 to S3...Paper material, S4...Papermaking raw material, 21...Former section, 23...Felt (wire), 24...Former (inlet), 26...Bulky wire, 54...Press roll, 55...C Reping doctor, 56...touch roll, 60...yankee dryer, 70...base roll, W1~W3...wet paper, D1...dry paper (paper towel base paper), P1...papermaking raw material preparation process, P2...wire part, P3...press part, P4...dryer part, 40, 40A, 45...one of the recesses of the bulky wire mesh marks, 47...embossed recess, 48...embossed convex part, 100...planar profile image, 200...depth profile image.

Claims

1. A paper towel made by wet-processing a fiber raw material, In a papermaking raw material preparation process prior to a process of discharging the papermaking raw material from a stock inlet to form a wet paper, The paper is produced through a process of adding an enzyme-based paper strength agent containing cellulase as an enzyme that decomposes polysaccharides and fluffs the fiber surface and inside of the fiber to the paper stock at an amount of 0.1 kg / t to 5.0 kg / t of pulp at a position where a residence time to the stock inlet can be ensured for at least 30 minutes, and maintaining the paper stock at a temperature of 40° C. or less for at least 30 minutes from the time of addition, The fiber does not contain recycled paper pulp, and the ratio of softwood kraft pulp in the fiber is 40% by mass or more. Basis weight per ply: 23-27g / m ２ and Specific volume is 4.5 to 7.0 cm ３ / g, The enzyme-based paper strength agent is contained, The paper surface is uneven when dry. The height difference of the unevenness of the paper surface when dry is 0.0400 mm or more, and the rate of change of the height difference of the unevenness of the paper surface when dry and when wet is 120% to 140%. A paper towel characterized by:

2. 2. The paper towel according to claim 1, wherein the unevenness on the paper surface is at least one of wet crepe and bulky wire mesh marks.

3. 3. The paper towel according to claim 2, wherein the bulky wire mesh marks are 10 to 26 lines / inch.

4. 4. The paper towel according to claim 1, wherein the wet tensile strength in the machine direction is 400 to 1000 cN / 25 mm and the wet tensile strength in the cross direction is 300 to 800 cN / 25 mm.

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