JP2888940B2 - Transfer paper for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a transfer paper for electrophotography, particularly for a dry PC.

[Prior art]

2. Description of the Related Art In an image forming apparatus using electrophotography or electrostatic printing, an electrostatic latent image formed on an image support is generally developed using a dry type developer (toner), and a transfer paper is supported in a transfer process. The transfer paper is separated from the image support after being superimposed on the body and charged from the transfer paper side by a corona discharger to transfer the developed toner image to the transfer paper. In order to perform this transfer favorably, it is necessary that the image support and the transfer paper be in close contact with each other during this charging. In order to fix the transferred toner on the transfer paper, a method of applying heat is generally used. In recent years, multi-color transfer to transfer paper or transfer printing to both sides has been increasing. JP-A-62-198875, JP-A-62-198875
Coated papers such as those described in JP-A-198876 and JP-A-62-198877 are used.

[Problems to be solved by the invention]

As described above, in an image forming apparatus using electrophotography or electrostatic printing, heat is applied to the transfer paper to fix the toner transferred on the transfer paper. At this time, moisture evaporates from the fibers constituting the transfer paper, and contraction occurs. Such shrinkage appears as "wrinkles" on the surface of the transfer paper, and the appearance after printing is often significantly impaired. In addition, there is a drawback that, in double-sided printing or multicolor printing, streak-like wrinkles generated in the first printing hinder good transfer of toner to transfer paper from the second printing. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic transfer paper which has a good appearance after printing and can obtain a good image with a low defect rate even when the image area ratio is high in multicolor transfer printing / double-sided transfer printing. It is in.

[Means for Solving the Problems]

In order to achieve the above object, the present inventors have intensively studied a mechanism for generating streaky irregularities generated on transfer paper during printing and an improvement thereof. In an image forming apparatus using electrophotography or electrostatic printing, when the toner is transferred to a transfer sheet and then passes through a hot roll or an oven-type fixing device, the transfer sheet and the toner are transferred.
Since the transfer paper is heated to about 120 to 220 ° C., the moisture in the transfer paper evaporates instantaneously and the transfer paper shrinks. At this time, streaky irregularities are generated on the transfer paper surface in the flow direction. Such irregularities are
It not only impairs the appearance of the printed matter, but also reduces the adhesion between the transfer paper and the image support during continuous printing in multicolor printing and double-sided printing, preventing complete transfer of toner. The present inventors have conducted intensive studies on what factors determine the appearance of such irregularities, and have found that the following two points are important. That is, (1) the magnitude of the contraction of the paper in the vertical and horizontal directions, and (2) the anisotropy of the contraction of the paper in the vertical and horizontal directions. As long as cellulose fiber is used as a constituent fiber of paper, it is a well-known fact that shrinkage occurs with evaporation of water, and in the case of machine-made paper,
It is also known that there is anisotropy. However, even if there is shrinkage due to heat and the anisotropy of the shrinkage as long as it satisfies the following ranges at the same time, the unit of the streaky irregularities on the paper surface even after the heat is applied by the fixing device. It has been found that a transfer paper which can be used practically with a small number of undulations per length and a small amplitude of unevenness can be obtained. r (MD) · r (CD) ≦ 0.20 r (CD) · r (MD) ≦ 2.2 To evaluate the appearance of such irregularities, actual printing was performed using a PPC type copier Xerox 5055. Height h of streaky irregularities when placed on a horizontal table as shown in FIG.
And the number n of irregularities per unit length was evaluated.
In addition, visual judgment was also made at the same time. The heat shrinkage of the paper was determined by measuring the length of shrinkage dL in the longitudinal direction of a test piece of 15 mm width and 100 mm length, which was conditioned for 2 hours at a temperature of 20 ° C and a relative humidity of 65% RH, at 105 ° C. It was measured and calculated based on the following equation. Heat shrinkage r = dL / L × 100 dL: Shrinkage L: Length of the first test piece This measurement is performed in the machine direction and the cross machine direction of the paper. In order to adjust the width of the electrophotographic transfer paper having a heat shrinkage in the range of the present invention in the width direction, there are a method of suppressing the shrinkage product in the vertical and horizontal directions and a method of suppressing the shrinkage ratio in the vertical and horizontal directions. It becomes possible by using them in combination. Methods for suppressing the shrinkage product of paper include increasing the water removal rate in the press part, setting a higher tension in the dryer canvas in the dry part, and using a method that has recently been reported (paper paper technology). (Journal Vol.42 No.10, p940-p946) Control using a sheet-run method that eliminates free-run spots as much as possible and a known method that dries the wet paper on the wet side of the dry part in a manner that suppresses shrinkage. Is also achieved. If necessary, the transfer paper may contain starch,
Although surface treatment with polyvinyl alcohol, polyacrylamide, gelatin, etc. can be performed, the amount of shrinkage can be suppressed by using a method that can be impregnated into the paper layer of the paper as a coating method. is there. On the other hand, the method of suppressing the shrinkage ratio of the paper is achieved by adjusting the J / W ratio in the wire part to an appropriate value and by controlling the draw of the wet paper from the press part as much as possible. The electrophotographic transfer paper having the characteristics of the present invention can be provided by using the methods described above alone or in combination. In the electrophotographic transfer paper of the present invention, fillers, dyes, sizing agents, dry paper strength enhancers, wet paper strength enhancers, fixing agents, retention aids, and other additives usually used in papermaking are optionally used. Shall be included.

【Example】

Hereinafter, the present invention will be described in detail with reference to Examples. The present invention is not limited to the embodiments. In the following, all parts and percentages are by weight.
In each of Examples and Comparative Examples, 100 parts of a 7: 3 weight ratio mixture of LBK and NBKP beaten to a freeness of 350 ml csf was mixed with 100 parts of a precipitated calcium carbonate having a content in paper of 7%. 0.1 part of alkyl ketene dimer sizing agent, 0.7 part of cationic starch
Part of the slurry, making width 2500mm, netting speed 500m / min
With a fourdrinier paper machine. Examples 1 and 2 and Comparative Examples 1 to 3 Each sample was weighed at 64 g / m ^2, and paper was produced under the papermaking conditions shown in Table 1. Paper having different drying shrinkage rates as shown in Table 2 was produced by adjusting the draw of wet paper and the tension of the dryer canvas during operation. Table 3 shows the results of evaluating the appearance of the transfer paper manufactured under these conditions. In Example 1, the draw between the press outlet and the group of dryers was suppressed compared to the comparative example, and the canvas tension in the dryer was increased. In Example 2, a single-stage dryer system was used on the dry part wet side. By adopting, as shown in Table 3, as compared with the comparative example, it was possible to obtain transfer paper having less irregularities per unit length (21 cm) and smaller wave height (amplitude of irregularities). *: Papermaking was performed using the "single-stage dryer method" described in the Paper and Paper Technical Association, Vol. 42, No. 10, p. 940-p946.・ Drawing is between the press outlet and the group of dryers, and the unit is%. ・ Canvas tension is about the dryer canvas, and the unit is kg / cm. Heat shrinkage product: Product of heat shrinkage r (MD) in the machine direction and heat shrinkage r (CD) in the cross machine direction r (MD) · r (CD) Heat shrinkage ratio: Heat shrinkage in the cross machine direction Ratio of r (CD) to heat shrinkage r (MD) in machine direction r (CD) / r (MD) Wave number: The wave number is the number of irregularities between the lengths of 21 cm. Wave height: Indicates the average height of the wave from the reference plane. Visual: Evaluated on a scale of 1 to 1 (bad) to 5 (best). Examples 3 to 5 and Comparative Examples 4 to 6 Except for Example 5, the weight and surface size of each sample were changed as shown in Table 4 under constant conditions of 1.2% draw and dryer canvas tension of 1.4 kg / cm. Paper-made. In addition, a cation-modified starch was used as the surface size liquid. Table 5 shows the product of the heat shrinkage and the ratio of the heat shrinkage of each sample prepared under the conditions of Table 4, and Table 6 shows the results of the appearance evaluation. As shown in Examples 3 and 4, the size liquid is impregnated into the paper layer by setting the surface size coating method to the in-size press method, thereby suppressing the heat shrinkage of the transfer paper. Also,
As shown in the fifth embodiment, good results can be obtained by adjusting the amount of shrinkage of the wet paper during drying, as in the first embodiment, even on the transfer paper surface-treated by the gate roll size method. It is possible. GRC: Gate roll coater system ISP: In-size press system * In Example 5, a single-stage dryer system was adopted on the wet side of the dryer part.

【The invention's effect】

As is clear from the above, the heat shrinkage ratio r (MD) in the machine direction of paper and the heat shrinkage ratio r (CD) in the cross machine direction are as follows: r (MD) · r (CD) ≦ 0.20 r By adjusting the manufacturing conditions so that (CD) / r (MD) ≦ 2.2, it is possible to obtain an electrophotographic transfer paper having excellent appearance after printing.

[Brief description of the drawings]

 FIG. 1 is a view showing a state of streaky irregularities. 1: Sample 2: Reference plane h: Wave height, n: Wave number,

Claims (1)

(57) [Claims] 1. Heat shrinkage ratio r (MD) in the machine direction and heat shrinkage ratio in the cross machine direction when humidity is controlled at a temperature of 20 ° C. and a relative humidity of 65% RH for 24 hours, and then dried at 105 ° C. The product of r (CD) is
Electrophotographic transfer paper with characteristics of r (CD) / r (MD) ratio of 2.2 or less at 0.20 or less.