JPH06285006A - Method for production of wiping cloth and apparatus therefor - Google Patents

Abstract

PURPOSE:To provide the wiping cloth having an excellent grade free from a disturbance in formation on the front surface by disposing the suction port of a stagnating water suction device in the position of a specific range from the point where the water injected from a high-pressure water column flow treating device collides against the surface of a paper sheet. CONSTITUTION:A laminated sheet 3 which is a laminate composed of the paper sheet and a long fiber non-woven fabric is placed on a net conveyor 2 and is bonded by the high-pressure water column flow injected from a high-pressure water column flow injection device 1. The stagnating water suction device 10 sucks the stagnating water W stagnating near the collision point of the water column flow on a net conveyor 2 after injection from the high-pressure water column flow injection device 1 by a static pressure over the entire transverse direction of the laminated sheet 3. The static pressure for the suction is in a -50 to -350mmHg, more preferably -150 to -200mmHg range. A stagnating water suction port 12 is preferably installed generally at 3 to 6mm height from the plane of the laminated sheet 3. The distance L from the front end thereof to the collision point of the high-pressure water column flow on the laminated sheet is in a preferably 10 to 30mm, more preferably 15 to 20mm range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a disposable cloth such as a hand wipe, a wet tissue, a wiper and a disposable rag.

[0002]

2. Description of the Related Art Conventionally, as a wipe cloth such as a disposable hand wipe, a dry pulp sheet in which pulp fibers are bulky accumulated and which is soaked with water or chemicals is used. However, the dry pulp sheet has a drawback that it has a low wet strength after being impregnated with water, chemicals, etc., and is easily broken during use.

On the other hand, there is also used a non-woven fabric in which rayon fibers, which are hydrophilic fibers, are accumulated, and then the rayon fibers are bonded to each other with a rubber binder soaked with water or the like. This wiping cloth has a high wetting strength because the rayon fibers are bonded to each other, but it has a drawback that it has a strange odor because the wiping cloth contains a rubber-based binder. Further, since the rubber-based binder has a rough texture, the feeling of using the wiping cloth is not good.

Attempts have also been made to produce non-woven fabrics in which rayon fibers are entangled with each other without using a rubber-based binder. To entangle the rayon fibers with each other, it is possible to apply a high-pressure water column flow to the web in which the rayon fibers are accumulated. The wiping cloth thus obtained is preferable in that it does not give off a strange odor and does not have a rough texture. However, the wiping cloth made of rayon fiber,
There were fatal drawbacks as shown below. That is, since the rayon fiber is excellent in hydrophilicity, when used as a wiping cloth, it often absorbs water and swells, so that its rigidity may be extremely reduced. If the rigidity of the rayon fiber is lowered, the rigidity of the wiping cloth is also lowered, the repulsive force when the wiping cloth is held by the hand is lowered, and the fatal defect that it is difficult to use is caused.

Therefore, as a result of various researches aimed at solving the above-mentioned drawbacks, the present applicant basically decided to solve the above-mentioned drawbacks by obtaining a wiping cloth by the following method. Succeeded and filed a patent application first.
That is, after laminating a long-fiber non-woven fabric and a paper sheet made of pulp fiber, by applying a high-pressure water column flow from the paper sheet side of the laminate toward the long-fiber non-woven fabric side, the long-fiber and the pulp fiber are entangled. To obtain a wiping cloth (Japanese Patent Application No. 3-204875, Japanese Patent Application No. 4-89650, Japanese Patent Application No. 4-113048, etc.). This wipe is
Since long fibers, which are difficult to absorb water, mainly maintain the shape, there is no disadvantage that rigidity is lowered during use and it is difficult to grip with fingers. Further, since the long fibers are entangled with the pulp fibers, the absorbency of water does not decrease, and it can be suitably used as a wiping cloth.

However, the wiping cloth obtained by the above-mentioned method had a defect derived from its manufacturing method. This wipe is made by laminating a paper sheet on the surface of a long-fiber nonwoven fabric,
Since a high-pressure water column flow is applied toward the paper sheet side of the laminate, when the basis weight of the paper sheet increases, accumulated water that is not discharged near the collision point between the high-pressure water column flow and the paper sheet is generated, and the energy of the high-pressure water column flow is increased. However, since this is consumed to blow off the water, the high pressure water column flow treatment effect is weakened, and the action effect of the high pressure water column flow on the fiber web becomes non-uniform, which causes a fatal drawback. That is, as the basis weight of the paper sheet increases, the water permeability of the paper sheet decreases,
The discharge pressure of the water supplied by the high-pressure water column flow decreases, and stagnant water easily occurs.

In Japanese Patent Publication No. 4-34057, a high-pressure air injection nozzle is provided near the high-pressure water column flow collision point, and the accumulated water is discharged by high-pressure air injected from the high-pressure air injection nozzle. However, this method has problems of deterioration of work environment due to scattering of water containing pulp and poor formation (generation of surface roughness due to high-pressure air).

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks and jets high-pressure water from a nozzle by jetting high-pressure water in a state where the amount of accumulated water on the fibrous web is reduced to the extent that it does not hinder high-pressure water column flow treatment. By making the most of the energy of high-pressure water, the effect of high-pressure water column flow on the fiber web is made uniform, thus providing a method for producing a good-quality wiping cloth with no formation of disorder on the surface. is there.

[0009]

According to one aspect of the present invention, a paper sheet is laminated on the surface of a long fiber non-woven fabric, and the obtained laminate of long sheets is conveyed by a conveyor,
Manufacture of a wiping cloth in which pulp fibers forming a paper sheet and long fibers forming a long fiber non-woven fabric are entangled by applying a high pressure water column flow so as to penetrate from the paper sheet side of the laminate to the long fiber non-woven fabric side. In the method, the water accumulated on the paper sheet due to the high-pressure water column flow jetted onto the paper sheet is removed by suction at a static static pressure of -50 to -350 mmHg at a position of 10 to 30 mm from the high-pressure water column flow collision point on the sheet surface. A method for producing a wiping cloth is provided.

According to another aspect of the present invention, a conveyor for transferring a long sheet-like laminate having a paper sheet laminated on the surface of a long fiber non-woven fabric, and a long sheet-like laminate being transferred by the conveyor. In a manufacturing apparatus for a wiping cloth comprising a device for applying a high pressure water column flow so as to penetrate from the paper sheet side to the long fiber non-woven fabric side, a accumulated water suction device is provided in proximity to the high pressure water column flow treatment device, There is provided a wiping cloth manufacturing apparatus, wherein a suction port of the suction device is arranged at a position of 10 to 30 mm from a point where water jetted from the high-pressure water column flow treatment device collides with a paper sheet surface.

The method and apparatus for manufacturing a wiping cloth of the present invention will be described below step by step. First, in the present invention, a long fiber nonwoven fabric is prepared. Here, as the long fibers constituting the long fiber non-woven fabric, conventionally known long fibers can be used, for example, polyolefin long fibers, polyester long fibers, polyamide long fibers, polyacrylic acid ester long fibers, etc. Can be used. In the present invention, the reason for using the long fibers is that the long fiber non-woven fabric made of the long fibers is much improved in tensile strength and morphological stability when the fibers are entangled with each other, as compared with the short fiber web made of short fibers. Because it does. Furthermore, in the case of long fibers, even if a high pressure water column flow is applied, the fibers are less likely to be washed out together with the water column flow.

The fineness of the long fibers is preferably 1 to 4 denier. When the fineness of the long fibers exceeds 4 denier, the flexibility of the long fiber non-woven fabric tends to decrease, and the feeling of use when used as a wiping cloth tends to deteriorate. On the other hand, when the fineness of the long fibers is less than 1 denier, strict conditions are required for producing the long fibers, and it becomes difficult to industrially produce the long fibers and eventually the long fiber non-woven fabric at high speed.

The basis weight of the long fiber nonwoven fabric is 5 to 30 g / m ²
Is preferred. The basis weight of long-fiber non-woven fabric is 30 g /
If it exceeds m ² , even if a high-pressure water column flow is applied from the paper sheet to the long fiber non-woven fabric side to the laminate of the paper sheet and the long fiber non-woven fabric, the pulp fibers forming the paper sheet will have the back surface of the long fiber non-woven fabric. It becomes difficult to move to (the surface that is not in contact with the paper sheet), and the pulp fibers are unevenly distributed only on one surface of the obtained wiping cloth, and the water absorption tends to decrease on the surface having less pulp fibers. On the contrary, when the basis weight of the long fiber nonwoven fabric is less than 5 g / m ² , the morphological stability of the long fiber nonwoven fabric is lowered, and the wet strength of the obtained wiping cloth tends to be lowered. Furthermore, since the gap between the long fibers is large, when the high pressure water column flow is applied, the pulp fiber easily flows out from the gap, and when the high pressure water column flow after use is recovered, a large amount of pulp fiber is contained in it. There is a risk of mixing.

The long-fiber nonwoven fabric used in the present invention is
It may be a so-called long-fiber non-woven fabric in which long fibers are self-fused with each other, or may be a fleece-shaped long-fiber fleece in which long fibers are not bonded to each other. In particular, among the former long-fiber non-woven fabrics, it is preferable that a large number of point-welded areas in which long fibers are self-welded are distributed in a scattered manner. The reason for this is that since there is a point fusion area where the long fibers are self-fused to each other, the morphological stability is excellent, and in the areas other than the point fusion area, the long fibers are self-fused. Since it is accumulated in a free state, it has excellent flexibility and is easily bonded to pulp fibers well.

The basis weight of the paper sheet to be used is a matter that can be arbitrarily determined, but a paper sheet having a basis weight of 10 to 100 g / m ² measured by the method described in JIS P8124 is particularly preferable. When the basis weight of the paper sheet is less than 10 g / m ² , the absolute amount of pulp fibers is small, and it becomes difficult to give sufficient water absorption and water retention to the obtained wiping cloth. On the contrary, when the basis weight of the paper sheet exceeds 100 g / m ² , the absolute amount of pulp fibers is too large, and when the paper sheet is subjected to high pressure water column flow,
It becomes difficult to give momentum to the extent that each pulp fiber can be entangled with a long fiber. Furthermore, the absolute amount of pulp fibers is too high, which reduces the flexibility of the resulting wipe.

The pulp fibers constituting the paper sheet are unbleached pulp fibers or bleached pulp fibers obtained by cooking softwood and hardwood wood by the kraft method, sulfite method, soda method, polysulfide method, etc., or ground pulp fibers, chemi-mechanical pulp. Any of fibers and mechanical pulp fibers such as thermomechanical pulp fibers may be used, and these may be used alone or in combination. The weight mixing ratio of the softwood pulp fiber and the hardwood pulp fiber is preferably softwood pulp fiber / hardwood pulp fiber = 100 to 20/0.
80, most preferably 100-40 / 0-60. If the hardwood pulp fiber content exceeds 80%, not only the amount of pulp lost due to high-pressure water column flow increases but also the flexibility of the sheet after entanglement tends to decrease.

The density of the paper sheet used in the present invention (JI
Measured by the method described in S P 8118) is 0.6 g
/ Cm ³ or less, preferably 0.55 g / c
Most preferably, it is not more than m ³ . When the density of the paper sheet exceeds 0.6 g / cm ³ , when the high pressure water column flow is applied from above the paper sheet, the movement of the pulp fiber is suppressed and the amount of energy required for entanglement increases.

The paper sheet is laminated on the surface of the long-fiber nonwoven fabric prepared in advance. At this time, the ratio of the basis weight of the long fiber nonwoven fabric to the basis weight of the paper sheet is preferably set as follows. That is, the ratio of the basis weight of the long fiber nonwoven fabric to the basis weight of the paper sheet measured by the method described in JIS P8124 is preferably long fiber nonwoven fabric: paper sheet = 1: 1 to 19. When the long fiber non-woven fabric: paper sheet is less than 1: 1, the amount of pulp fibers is relatively small with respect to the amount of long fibers, and the water absorbency and water retention of the obtained wiping cloth are reduced. In addition, the amount of inexpensive pulp fibers is smaller than that of long fibers, so that the obtained wiping cloth itself becomes expensive. On the other hand, if the basis weight of the paper sheet increases beyond the long fiber non-woven fabric: paper sheet = 1: 19, it becomes difficult for all the pulp fibers constituting the paper sheet to be strongly entangled with the long fibers,
When the obtained wiping cloth is used after being moistened, the pulp fibers easily fall off.

After a paper sheet is laminated on one surface of the long fiber non-woven fabric, a high pressure water column flow is applied from the surface of the paper sheet toward the long fiber non-woven fabric side. That is, the high pressure water column flow is applied so that the high pressure water column flow penetrates from the paper sheet side of the laminate to the long fiber nonwoven fabric side. This high-pressure water column flow is obtained by ejecting water at high pressure through a nozzle hole having a fine diameter. For example, it is obtained by ejecting water at a pressure of about ²⁰ to 150 kg / cm ² through a nozzle hole having a hole diameter of about 0.01 to 0.3 mm.

When a high-pressure water column flow is applied to the laminate, the high-pressure water column flow collides with the paper sheet, so that the paper sheet first adheres to the long-fiber nonwoven fabric, and then, in this adherence state, the paper sheet is destroyed. The pulp fibers forming the paper sheet are isolated, the pulp fibers are deformed such as bent and twisted, and the pulp fibers are sufficiently given kinetic energy to cause random movement of the pulp fibers. as a result,
Due to these composite actions, the pulp fibers and the long fibers in the long fiber nonwoven fabric are entangled with each other, and the pulp fibers also entangle the long fibers with each other. As described above, a composite sheet in which pulp fibers and long fibers are entangled with each other is formed.

The main point of the present invention is to suck and remove the water accumulated near the sheet surface near the collision point of the high-pressure water column flow, thereby solving the problem of weakening the high-pressure water column flow treatment effect by the accumulated water, and The point is that it is possible to manufacture a cloth that has an excellent quality with no formation of texture on the surface.

The manufacturing method and apparatus of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the accumulated water suction device according to the present invention. In the figure, 1 is a high pressure water column flow injection device. A nozzle plate 5 is fixed to the high-pressure water column flow injection device 1, and the nozzle plate 5 is reinforced by a pressure plate 6. A large number of nozzle holes 4 are formed in the nozzle plate 5. The high pressure water column flow injection device 1 is connected to a high pressure water generation device (not shown). A laminated sheet 3, which is a laminate of a paper sheet and a long-fiber nonwoven fabric, is placed on the net conveyor 2 and entangled by a high-pressure water column flow injected from the high-pressure water column flow injection device 1.

Below the net conveyor 2, a support block 8 is provided for counteracting the pressing force of the high pressure water column flow jetted from the high pressure water column flow jetting device 1. Further, a drain port 9 for discharging the high pressure water column flow penetrating the laminated sheet 3 is also provided at the bottom of the net conveyor 2. The drainage port 9 is formed in a slit shape extending in the width direction of the laminated sheet.

On the other hand, the accumulated water suction device 10 keeps the accumulated water W, which is injected from the high pressure water column flow injection device 1 and then stays in the vicinity of the water column flow collision point on the net conveyor 2, over the entire width direction of the laminated sheet 3. It has a structure to suck by pressure. Water sucked from the suction port 12 of the suction device 10 is air pipe 11
Is discharged to the outside of the device.

The suction static pressure of the accumulated water suction device is from -50 to-
350 mmHg, preferably -150 to -200 mm
It is in the range of Hg. When the suction static pressure is higher than -350 mmHg and the degree of vacuum is high, the surface of the paper sheet is in a state of being dug up, and not only the smoothness of the surface of the wiping cloth is deteriorated but also the texture is apt to be deteriorated. Can be seen. On the other hand, if the static suction pressure is less than -50 mmHg, it is difficult to reduce the amount of accumulated water to the extent that it does not hinder the high-pressure water column flow treatment. The accumulated water suction device 10 is connected to an air pipe 11, a vacuum pump and a header (not shown).

The accumulated water suction port 12 has a higher suction effect when it is as close as possible to the sheet surface, but in general, it is preferably installed at a height of 3 to 6 mm from the laminated sheet 3 surface. Further, the distance L from the tip of the accumulated water suction port 12 (more specifically, the end of the suction port closest to the water column collision point) to the collision point of the high pressure water column flow on the laminated sheet is preferably 10 to 30 m.
m, most preferably 15-20 mm. When the distance L is less than 10 mm, the high pressure water column flow interferes with each other and the treatment effect tends to be weakened. On the contrary, when the distance L exceeds 30 mm, the suction effect of the accumulated water suction device 10 tends to decrease. Although FIG. 1 shows a mode in which the suction port is provided on the upstream side of the water column flow collision point, the suction port can be provided on the downstream side.

As described above, the long fibers and the pulp fibers are entangled with each other and integrated to obtain a wiping cloth. And, to this wiping cloth, if desired, a wetting agent such as water or propylene glycol, an antibacterial agent such as alcohols and parabenzoic acid, a mildew proofing agent, a chemical such as a fragrance, etc. is applied, and a disposable hand wipe,
It is used as a wet tissue, wiper, disposable rag, etc.

[0028]

Example A long-fiber nonwoven fabric was prepared in which polypropylene long-fibers were accumulated and which had a large number of spot-fused areas in which polypropylene long-fibers were self-fused to each other. The fineness of the long fibers constituting this long-fiber nonwoven fabric is 2.5 denier,
The basis weight of the long-fiber nonwoven fabric was 20 g / m ² . On the surface of this long-fiber nonwoven fabric, a paper sheet obtained by wet papermaking was laminated using bleached softwood kraft pulp fibers. The density of the paper sheet was 0.55 g / cm ³ , and the basis weight was 50 g / m ² . Then, the long laminated sheet was placed on a transfer conveyor formed of a wire mesh so that the paper sheet was positioned above and the long fiber non-woven fabric was positioned below.

While transporting this long laminated sheet at a speed of 30 m / min, a high-pressure water column flow injection apparatus equipped with nozzles each having a large number of nozzle holes having a hole diameter of 0.1 mm arranged at intervals of 1 mm in the transverse direction is provided. Then, a high pressure water column flow was jetted at a water pressure of 45 kg / cm ² , and the high pressure water column flow was applied to the surface of the paper sheet. Then, the accumulated water suction device provided with a suction port located 15 mm away from the collision point of the high-pressure water column flow on the laminated sheet and at a height of about 4 mm from the sheet surface was -200 m.
It was aspirated with a static pressure of mHg. As described above, the pulp fiber and the long fiber constituting the paper sheet were entangled with each other to obtain an integrated wiping cloth.

Example 2 A long fiber non-woven fabric was prepared in which polypropylene long fibers were accumulated and which had a large number of spot-fused areas in which polypropylene long fibers were self-fused to each other. The fineness of the long fibers constituting this long-fiber nonwoven fabric was 2.2 denier, and the basis weight of the long-fiber nonwoven fabric was 21 g / m ² . On the surface of this long-fiber nonwoven fabric, a paper sheet obtained by wet papermaking was laminated using bleached softwood kraft pulp fibers. The density of the paper sheet was 0.53 g / cm ³ , and the basis weight was 52 g / m ² . Then, the long laminated sheet was placed on a transfer conveyor formed of a wire mesh so that the paper sheet was positioned above and the long fiber non-woven fabric was positioned below.

While transporting this long laminated sheet at a speed of 30 m / min, a high-pressure water column flow injection apparatus equipped with nozzles having a large number of nozzle holes having a diameter of 0.1 mm arranged at intervals of 1 mm in the transverse direction was provided. Then, a high pressure water column flow was jetted at a water pressure of 40 kg / cm ² , and the high pressure water column flow was applied to the surface of the paper sheet. The accumulated water suction device provided with a suction port located 20 mm away from the collision point of the high-pressure water column flow on the laminated sheet and at a height of about 4 mm from the sheet surface was -150 m.
It was aspirated with a static pressure of mHg. As described above, the pulp fiber and the long fiber constituting the paper sheet were entangled with each other to obtain an integrated wiping cloth.

Comparative Example 1 A wiping cloth was obtained in the same manner as in Example 1 except that the accumulated water was sucked with a static pressure of -40 mmHg.

Comparative Example 2 A wiping cloth was obtained in the same manner as in Example 1 except that the accumulated water was sucked at a static pressure of -400 mmHg.

Comparative Example 3 A wiping cloth was obtained in the same manner as in Example 1 except that the accumulated water suction device was not used.

Comparative Example 4 A wiping cloth was obtained in the same manner as in Example 2 except that the suction nozzle was arranged so that the distance L from the collision point of the high-pressure water column flow to the suction port on the laminated sheet was 5 mm.

Comparative Example 5 A wiping cloth was obtained in the same manner as in Example 2 except that the suction nozzle was arranged so that the distance L from the collision point of the high pressure water column flow on the laminated sheet to the suction port was 35 mm. Examples 1-2,
And the wiping cloths obtained in Comparative Examples 1 to 4 were subjected to the following tests to evaluate their quality. The results are shown in Table 1.

[0037]

[Table 1]

The appearance (texture) and adhesive strength evaluation methods in Table 1 are as follows. (1) Appearance (texture): It was visually evaluated by 20 monitors. The appearance (texture) of the sample was evaluated on the basis of the five levels shown in Table 2 and the average value was obtained. (2) Adhesive strength: Adhesive strength was judged by a sensory test by 20 monitors. For the test, pick the sample from the side of the paper sheet with tweezers, and evaluate each in five stages shown in Table 2,
The average value was calculated.

[0039]

[Table 2]

When the wiping cloths obtained in Examples 1 and 2 are compared with the wiping cloths obtained in Comparative Examples 1, 3 and 5, it is clear that in the method according to Comparative Examples 1, 3 and 5, Was inferior in both appearance (texture) and adhesive strength because the suction of accumulated water was not sufficient, resulting in unevenness in the high pressure water column flow treatment and non-uniform entanglement of long fibers and pulp fibers. . The wiping cloth obtained in Comparative Example 2 had an excessively high suction static pressure of the accumulated water suction device, so that the surface of the wiping cloth was disturbed and the appearance (texture) was poor. The wiping cloth obtained in Comparative Example 4 interfered with the high pressure water column flow treatment because the distance between the accumulated water suction device and the collision point of the high pressure water column flow was too short, resulting in the same appearance (ground) as Comparative Examples 1 and 5. However, the adhesive strength was inferior.

[0041]

As described above, according to the present invention, when a high pressure water column flow is applied to a long laminated sheet obtained by laminating a paper sheet on the surface of a long fiber nonwoven fabric, a high pressure water column on the surface of the laminated sheet is applied. Since the accumulated water suction device having a suction port is provided near the collision point of the flow to suck and remove the accumulated water, the high pressure water column flow treatment becomes uneven due to the accumulated water,
It is possible to produce a wiping cloth of excellent quality in which the effect of the high pressure water column flow treatment is prevented from being deteriorated and the texture of the surface is not disturbed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing an example of an apparatus for manufacturing a wipe according to the present invention.

[Explanation of symbols]

 1 High Pressure Water Column Flow Treatment Device 2 Net Conveyor 3 Laminated Sheet 4 Nozzle Hole 5 Nozzle Plate 6 Pressure Plate 7 High Pressure Water Inlet 8 Support Block 9 Drainage Port 10 Retained Water Suction Device 11 Air Piping 12 Retained Water Suction Port

Claims (2)

[Claims] 1. A paper sheet is laminated on the surface of a long fiber non-woven fabric, and the obtained long sheet-like laminate is transferred by a conveyor while penetrating from the paper sheet side of the laminate to the long fiber non-woven fabric side. In the method for producing a wiping cloth in which the pulp fibers forming the paper sheet and the long fibers forming the long fiber non-woven fabric are entangled by applying a high pressure water column flow, the high pressure water column sprayed on the paper sheet. The accumulated water generated on the paper sheet due to the flow is sucked static pressure -50 to -3 at a position 10 to 30 mm from the high pressure water column flow collision point on the sheet surface.
A method for manufacturing a wiping cloth, which comprises suction-removing at 50 mmHg. 2. A conveyor for transferring a long sheet-like laminate having a paper sheet laminated on the surface of a long fiber non-woven fabric, and a long fiber from the paper sheet side of the long sheet-like laminate being transferred by the conveyor. In a manufacturing apparatus for a wiping cloth comprising a device for applying a high pressure water column flow so as to penetrate the nonwoven fabric side, a accumulated water suction device is provided in proximity to the high pressure water column flow treatment device,
A wiper manufacturing apparatus, wherein the suction port of the suction device is arranged at a position of 10 to 30 mm from the point where water jetted from the high-pressure water column flow treatment device collides with the surface of the paper sheet.