JP2855778B2 - Transfer paper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to transfer paper having reduced curl after thermal fixing by a copying machine, printer, or the like (hereinafter referred to as curl after thermal fixing).

(Prior art) When a toner image on paper is thermally fixed by a copier, a printer, or the like, heat is applied from one side of the paper. Troubles such as poor tray accommodation and poor sorter accommodation occur.
It can be said that the curl after thermal fixing is an important characteristic that greatly affects the paper running performance of a copying machine, a printer, and the like.

Conventionally, attempts to improve the curl after heat fixing have been made by various methods of each company, but since the mechanism of curl generation after heat fixing is unknown, effective measures could not be implemented, and papermaking conditions The fact is that some changes, pulp beating degree and dryer differential pressure are used. As for the improvement of transfer paper, for example, JP-A-48-96801, JP-A-51-102107, JP-A-54-96107, etc.
It is disclosed that inorganic fibers such as glass fibers and rock wool are mixed with wood pulp fibers, as disclosed in JP-A-57-204057.
Japanese Patent Application Laid-Open Publication No. H11-157, discloses that a large amount (18% or more) of an organic or inorganic filler is added.

(Problems to be Solved by the Invention) The present inventors have intensively studied the mechanism of curl generation after thermal fixing and have obtained the following knowledge. That is, when copying or printing a line drawing (low image density), which is generally used as a document, the toner layer has little effect on curl after heat fixing. It can be limited to characteristic values. After heat fixing, the curl is heated on one side of the paper,
The moisture evaporates from the backing layer and the paper shrinks accordingly. The difference in the amount of shrinkage between the surface layer and the back layer of the paper at this time appears as curl after thermal fixing. The curl after thermal fixing is represented by the following equation.

K: Curl curvature (reciprocal of the radius of _{curvature) (1 / mm) H 1} : moisture content change caused by the surface layer of the thermal fixing of paper (%) H _2: moisture content change caused by the surface layer of the thermal fixing of paper (%) beta ₁ : Dehumidifying shrinkage of paper surface layer (% / moisture 1% change) β ₂ : Dehumidifying shrinkage of paper back layer (% / moisture 1% change) t: Paper thickness (mm) In 1), factors that affect the curl after heat fixing are dehumidifying shrinkage, change in moisture content, thickness,
It is.

Incidentally, the above-mentioned JP-A-48-96801 and JP-A-51-1
No. 02107, Japanese Patent Application Laid-Open No. 54-96107, etc., reduce the change in the dehumidifying shrinkage and the moisture content, but when inorganic fibers are blended, the strength is large. To reduce the papermaking and quality problems,
When synthetic fibers are blended, heat resistance is reduced, and deformation (wrinkles, waving) and shrinkage during heat fixing become a problem. Further, since these inorganic fibers and synthetic fibers are more expensive than wood pulp fibers, they cause a cost increase. Also, Japanese Unexamined Patent Publication No.
In the case of Japanese Patent Application Laid-Open No. 204057, since a large amount of filler is blended, problems such as a reduction in stiffness and an increase in the amount of paper powder generated become problems.

On the other hand, measures to reduce the curl after thermal fixing by increasing the thickness of the paper increase the basis weight and increase the cost if the density is the same. Further, if the thickness is increased with the same basis weight, there is a problem that the smoothness is reduced.

The present inventors have previously proposed that the fiber orientation be randomized, that is, that the ratio of longitudinal wave propagation velocities of ultrasonic pulses be in the range of 1.00 to 1.25 (Japanese Patent Application No. 1-38402, Patent No. No. 2743435). The transfer paper is effective in reducing the curl after heat fixing, but has a drawback that the papermaking speed for production cannot be increased. That is, when the paper making speed is increased, there is a disadvantage that the fibers are easily arranged in the flow direction.

The present invention has been made in view of the above-described problems in the related art.

Accordingly, an object of the present invention is to provide a transfer sheet which can be easily manufactured and has a reduced curl after thermal fixing.

(Means for Solving the Problems) The present inventors have studied the improvement of the curl after thermal fixing from the viewpoint of the dehumidifying shrinkage ratio in the cross direction of the paper. As a result, the paper was dried while restricting the cross direction of the paper. As a result, it has been found that, regardless of the fiber orientation ratio, the dewetting shrinkage in the cross direction can be reduced, and the curl after heat fixing can be greatly improved, thereby completing the present invention.

The transfer paper of the present invention has a dehumidifying shrinkage rate of the cloth method of 0.
It is characterized by being 12% /% moisture or less. The transfer paper of the present invention is greatly characterized in that it can be applied to a range of 1.26 to 2.00 in which the ratio of longitudinal wave propagation velocity of ultrasonic pulse is larger than 1.25.

In the present specification, the “dehumidification shrinkage in the cross direction” means% dimensional change /% moisture change at the time of reversible dimensional change after repeated moisture absorption / desorption treatment at a humidity of 25 to 90% RH or less.

FIG. 1 shows the relationship between the content absorption rate and the dimensional change rate in the dehumidifying shrinkage treatment in the cross direction. The moisture absorption / desorption treatment is performed sequentially from reference numerals 1 to 12, and the% dimensional change /% dimensional change at the time of reaching a substantially constant relationship (reference numerals 6 to 12) at the time of reversible dimensional change is defined as the dehumidifying shrinkage rate. I do.

In this specification, the “longitudinal wave propagation velocity ratio of an ultrasonic pulse” means a value represented by the following equation.

The "machine direction (MD)" means the flow direction of the paper machine, and the "cross direction (CD)" means the direction perpendicular to the flow direction of the paper machine.

The longitudinal wave propagation velocity ratio of the ultrasonic pulse in the present invention can be obtained by the measuring method shown in FIG. That is, the sample was placed on a 10 mm thick bubble-containing rubber plate 21.
The transmitting oscillator 23 and the receiving oscillator 24 are brought into contact with each other at an interval of 150 mm, and the longitudinal wave of the ultrasonic pulse is transmitted from the transmitting unit 25, received by the receiving unit 26, and transmitted. The time from when the sample passes through the wave oscillator to when it is received by the receiving oscillator is measured and converted to the propagation velocity. For each sample, the propagation speed in both the MD and CD directions is measured, and the propagation speed ratio is determined. In the figure, reference numeral 27 denotes an arithmetic element, and 28 denotes a display element.

The transfer paper of the present invention is a paper (water content) after passing through the press part.
(40 to 80%) in a cross direction, while drying with a drier to a moisture content of 5% while suppressing the shrinkage of the paper in the cross direction during drying of the drier.

Since the shrinkage of the paper in the cross direction is suppressed during drying of the dryer, the expansion and contraction when the moisture of the paper changes after drying is smaller than that of free-dried paper that does not impose a binding force in the cross direction of the paper during drying of the dryer. , Become much smaller.

The method of applying a restraining force in the cross direction of the paper during the drying of the dryer is a restraint by vacuum (Japanese Patent Application Laid-Open No. 61-266693,
Nos. 58-70794 and 56-501732), restraint by air blow (Japanese Patent Application Laid-Open Nos. 61-501461 and 62-62993), single-side restraint of paper by felt, rolls and the like (Japanese Patent Publication No. 60-29800) No. 60-35477, No. 52-11786, No. 52
-11784 and JP-A-61-258094), double-sided binding of paper with felt, canvas, etc. (JP-A-49-50206)
And Japanese Patent Publication No. 51-35708), but it is important to apply an appropriate restraining force in the cross direction of the paper according to the fiber orientation ratio of the paper during drying of the dryer. . Transfer paper having a dehumidifying shrinkage of 0.12% /% water or less according to the present invention can be obtained by drying the paper by applying an appropriate restraining force in the cross direction of the paper according to the fiber orientation ratio, regardless of the restraining method during drying. Can be obtained.

Hereinafter, the present invention will be described with reference to examples.

Example 1 Hardwood bleached kraft pulp was prepared to a freeness of 480 cc, and 10% by weight of light calcium carbonate, 1% by weight of cationized starch, and 0.5% by weight of alkyl ketene dimer were added thereto. An oriented paper machine for experiments (Kumaya Riki Co., Ltd. )), The wire ejection speed was changed at a wire speed of 600 m / min, and 52.3 g /
Transfer paper of m ² , 64.0 g / m ² , and 81.4 g / m ² were prepared.

The transfer paper was pressed by a sheet press to a paper moisture of 40 to 60%, and then dried with hot air to a pure moisture of 4% while changing the restraining force in the cross direction. The machine direction restraining force during hot air drying was adjusted to a constant value of 100 g / mm ² .

Transfer paper obtained by the above method to B5 size
Twenty pieces were cut vertically and used as test samples.

Five samples were taken from the above test sample, and the longitudinal wave velocity ratio of the ultrasonic pulse was measured using a measuring instrument (SST-210 (Sonic Sheet Tester-
210) Nomura Trading Co., Ltd.). Table 1 shows the average value.

Further, five samples were collected from the test sample, and the dehumidifying shrinkage in the cross direction was measured by using an HK-type stretching tester (manufactured by Honshu Paper Co., Ltd.). Table 1 shows the average value.

The remaining 10 test samples were pre-processed in an appropriate chamber or the like so that five of the test samples had a moisture content of 5% and five of the test samples had a moisture content of 7%, and an electrostatic copying machine (9500B, Fuji Xerox Co., Ltd.) )), And measure the curl (curl curvature after thermal fixing) after heat-fixing to the wire side surface with horizontal paper passing (paper passing with the short side of the paper perpendicular to the heat fixing roll axis) did.

The curl curvature after heat fixing was measured as shown in FIG. 3, that is, the center of a piece perpendicular to the curl axis of the test sample 31 was fished with a 1 cm-width hanging tool 32, and the curl height ( h) is measured. The measured curl height is converted to curl curvature by the following equation.

h = γ {1-cos (7.75 / 2γ)} Curl curvature (K) = 1 / γ γ: radius of curvature Table 1 shows the measurement results of curl after heat fixing. The curl after thermal fixing is represented by an average value obtained by converting the curl height (h) of five test samples into a curl curvature.

Example 2 A hardwood bleached kraft pulp was prepared to have a freeness of 480 cc, and 10% by weight of light calcium carbonate, 1% by weight of cationized starch, and 0.5% by weight of alkyl ketene dimer were added thereto. An oriented paper machine for experiments (Kumaya Riki Co., Ltd. 5) g / m at the wire speed of 1200 m / min
² , 64.0 g / m ² and 81.4 g / m ² transfer paper were produced.

The transfer paper was pressed by a sheet press to a paper moisture of 40 to 60%, and then dried with hot air to a pure moisture of 4% while changing the restraining force in the cross direction. The machine direction restraining force during hot air drying was adjusted to a constant value of 100 g / mm ² .

Transfer paper obtained by the above method to B5 size
Twenty pieces were cut vertically and used as test samples.

With respect to the test sample, the longitudinal wave propagation velocity ratio of the ultrasonic pulse, the dewetting shrinkage in the cross direction, and the curl curvature after heat fixing were measured in the same manner as in Example 1. Table 2 shows the average value.

FIG. 4 shows the relationship between the dehumidifying shrinkage in the cross direction and the curl curvature after heat fixing of the samples of Examples 1 and 2.

As is clear from Tables 1, 2 and 4, an appropriate restraining force according to the fiber orientation ratio of the test sample is applied in the cross direction of the paper, and the paper after passing through the press (water content of 40 to 60%) Water 5
%, The cross-direction dehumidifying shrinkage becomes 0.12% /% moisture or less, and the curl curvature after heat fixing is significantly reduced.

The present invention provides a longitudinal wave velocity ratio of 1.26 to 2.00 that exceeds the effective range when the fiber orientation is random (the fiber propagation velocity ratio of the ultrasonic pulse is 1.00 to 1.25) to reduce the cross-direction dehumidifying shrinkage. It can be seen that the paper of the range is also effective. Further, even when the papermaking speed is as high as 1200 m / min, the curl after thermal fixing is small as in the case of low-speed papermaking.

(Effect of the Invention) The transfer paper of the present invention has a dehumidifying shrinkage in the cross direction of 0.12%.
/% Moisture, the curling after heat fixing is significantly smaller than that of conventional transfer paper. Especially, it is difficult to prevent curl after heat fixing, longitudinal wave propagation speed ratio 1.26 to 2.00
Is also effective for paper in the range of.

[Brief description of the drawings]

FIG. 1 is a graph showing a dimensional change in the cross direction due to moisture absorption / desorption processing, FIG. 2 is a block diagram of a method of measuring a longitudinal wave propagation velocity of an ultrasonic pulse, and FIG. 3 is a method of measuring curl after heat fixing. FIG. 4 is a graph showing the relationship between the dewetting shrinkage in the cross direction of paper and the curl curvature after heat fixing. 21: rubber plate with bubbles, 22: test sample, 23: transmitting oscillator, 24: receiving oscillator, 25: transmitting unit, 26: receiving unit, 27: computing element, 28 ... display element, 31 ... test sample, 32 ... suspension tool.

Claims (2)

(57) [Claims] 1. A transfer sheet having a dehumidifying shrinkage in the cross direction of 0.12% /% moisture or less. 2. A longitudinal wave propagation velocity ratio of an ultrasonic pulse is 1.26 to 2.
2. The transfer sheet according to claim 1, wherein the transfer sheet is 00.