EP1395879A1

EP1395879A1 - Image-recording sheet

Info

Publication number: EP1395879A1
Application number: EP02725468A
Authority: EP
Inventors: Koji Kamiyama; Shigeaki Dohgoshi
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2001-04-27
Filing date: 2002-04-02
Publication date: 2004-03-10
Also published as: CN1505774A; WO2002088847A1; JP2002341580A

Abstract

The present invention provides an image-recording sheet capable of improving the gloss of a color image recorded thereon without being accompanied with hot-offset even if a toner is disposed in a high concentration on the image-receptive layer. In particular, the inventive image-recording sheet comprises a paper substrate and an image-receptive layer formed on at least one surface of the paper substrate. The image-receptive layer has a ten-point average surface roughness (Rz) of 0.1 to 3.0 mm and contains a thermoplastic resin having storage modulus of 1 x 103 to 1 x 106 Pa at 160°C. The image-recording sheet, if desired, may comprise a gloss layer disposed between the paper substrate and the image-receptive layer.

Description

IMAGE-RECORDING SHEET

Technical Field

The present invention relates to an image-recording sheet, more particularly to an

image-recording sheet suitable for image recording with an electrophotographic color

copying machine or a color printer.

Background

In general, a copying machine and a printer record images through electrography.

Illustrative images include letters, prints, lines and drawings or pictures on an

image-recording sheet provided in the form of a printing paper, an overhead projector

(OHP) film, and the like through electrophotography. Electrophotography, a general

term of photography, is used to obtain an image by photoelectric phenomena and static

electricity. Electrophotography is well known and can be generally carried out as

follows.

First, a photoconductive layer made of a photosemiconductor is pre-charged

with static electricity to make it photosensitive. Next, an image is projected onto the

photoconductive layer by exposure using a camera. Then, the electric charge in the

light parts of the image is eliminated to form an electrostatic latent image on the

photoconductive layer. After that, a coloring fine particle (that is, a toner) having an

electric charge opposite to that of the electrostatic latent image is adhered to the

photoconductive layer to develop the electrostatic latent image and form a toned image. The toned image is transferred to an image-recording sheet with a transfer

roll and fixed, for example, thermally with a fixing apparatus to record the image on

the image-recording sheet. For a color image, after latent images are formed for

respective color-separated light ray and the respective electrostatic latent images are

developed using color toners (e.g., cyan, magenta, yellow, etc.) to obtain toned

images, the color image is formed on the image-recording sheet.

Most of the image-recording sheets comprise an image-receptive layer formed

on a substrate and, usually, a toned image is fixed to the image-receptive layer. For

example, in image-recording sheets disclosed in JP-A-63-92965 and JP-A-11-160905,

an image-receptive layer of a transparent resin is formed on a prescribed paper

substrate, and the gloss of the color images on the image-recording sheet is improved

by decreasing the surface unevenness by burying the toner in the image-receptive

layer in the course of thermal fixing.

In the case where a toner is disposed on an image-receptive layer in a high

concentration, often a plurality of toner particles are disposed on top of one another.

In such a case, when the image-recording sheets disclosed in the above-described

patent applications are used, it is difficult to completely bury all of the toner particles

in the image-receptive layer. As a result, the toner particles protrude over the

image-receptive layer and scatter light thus reducing the gloss of the color images. When the thickness of the image-receptive layers are increased, all the toner

particles may be buried completely in the image-receptive layer. However, when the

image-recording sheet has a thick image-receptive layer, it is accompanied with

hot-offset possibly leading to image defect.

Hence, what is needed is an image-recording sheet capable of providing high

gloss of a color image recorded thereon without being accompanied with hot-offset

even if a toner is disposed in a high concentration on the image-receptive layer.

Summary

The present invention has been completed in order to solve the

above-described problems and provides an image-recording sheet comprising a paper

substrate and an image-receptive layer formed at least one surface of the paper

substrate, characterized in that the image-receptive layer has ten-point average surface

roughness (Rz) of about 0.1 to 3.0 μm and contains a thermoplastic resin having a

storage modulus of about 1 x 10³ to 1 x 10⁶ Pa at 160°C.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail with the reference to the

accompanying figure wherein: Fig. 1 shows a cross-section of an illustrative embodiment of the

image-recording sheet of the present invention comprising substrate 1,

image-receptive layer 2, and gloss layer 3.

This figure is idealized, not drawn to scale, and is intended for illustrative

purposes only.

DETAILED DESCRIPTION

In a first preferred embodiment, the image-recording sheet of the present

invention comprises substrate 1 and image-receptive layer 2 (without the gloss layer 3

in the first embodiment). In general, substrate 1 is a paper substrate and preferably at

least a surface of the substrate, the surface on which the image-receptive layer is to be

formed, is treated so as to have a ten-point average surface roughness (Rz) of about

0.1 to 3.0 μm. This treatment allows for smooth formation of the image-receptive

layer, which will be described later.

Such a paper substrate includes coated paper such as enamel paper, art paper,

synthetic paper, etc., and non-coated paper. The paper substrate basis weight is

preferably within a range of 60 to 230 kg. When the basis weight is less than 60 kg,

the stiffness of the paper substrate becomes weak and the transportability can be poor.

On the contrary, when the basis weight exceeds 230 kg, the heat quantity necessary to

sufficiently melt the toners becomes short and the gloss is lowered. The image-receptive layer has a ten-point average surface roughness (Rz) of

about 0.1 to 3.0 μm and is made glossy and supported while being adhered to at least

one surface of the paper substrate. The image-receptive layer may be formed on both

surfaces of the substrate.

In the present invention, the image-receptive layer is used for recording an

image including letters, printings, lines and drawings, pictures or the like through the

thermal fixing of a toned image.

In general, the image-receptive layer contains a thermoplastic resin. Suitable

thermoplastic resin has a storage modulus of about 1 x 10 to 1 x 10 Pa at 160°C, and

in the thermal fixation process around this temperature, the surface smootlmess is not

substantially reduced. Consequently, even with the thermal fixation process, the

image-receptive layer is kept substantially smooth and it is possible to produce the

image with good gloss.

When the thermoplastic resin has the storage modulus less than about 1 x 10³

at 160°C, the image-recording sheet tends to cause split of the toned image due to the

hot-offset in the thermal fixation process. This problem can lead to image default

and can cause contamination. On the contrary, when the thermoplastic resin has a

storage modulus higher than about 1 x 10⁶ Pa at 160°C, the image-recording sheet

cannot sufficiently closely fix the toned image on the image-receptive layer and thus tends to leave undesirable surface roughness on the toned image. Such unevenness

may deteriorate the image quality.

The kind of the thermoplastic resin is not particularly limited as long as its

storage modulus falls within the prescribed range. Preferably, acrylic resins, styrene

resin, styrene-acrylic resins, epoxy resins, styrene-butadiene resins, polyurethane

resins, or polyester resins are used. These resins have high transparency and are

capable of maintaining image color reproducibility. These resins also have high

compatibility with toners containing styrene resins, styrene-acrylic resins, polyester

resins, polyetherpolyol resins, or mixtures of these resins. Thus, the resins can

^"receive and hold almost all of the toner particles, even if the image-receptive layer is

relatively thin. Furthermore, the hot-offset can effectively be avoided by making the

image-receptive layer thin. Consequently, the image-recording sheet of the present

invention can effectively lower the image defect and contamination following the

defect.

The image-receptive transparent layer may further contain a compatibilizer.

Although the compatibilizer is not specifically limited, it preferably has a solubility

parameter (SP value) of about 8.0 to 10.0. When such a compatibilizer having a

solubility parameter in the above-defined range is used, the toner easily melts in the

thermal fixation process and becomes compatible with the thermoplastic resin to give

a smooth image, and thus light scattering can be prevented. Furthermore, the compatibility of the toner particles with other toner particles in the surrounding is

improved and, as a result, particularly in case of color toners, the color blending can

be effectively promoted. When the toner contains styrene resin, styrene-acrylic

resin, polyester resin, or their combination and is so designed as to record the image

having the printed characters (a character-printed image) with the low gloss, the gloss

of the image is improved and at the same time, the hue and the color reproducibility

of the image are also improved. Moreover, such is true, even when a fixing

apparatus is so designed as to record the image with the low gloss. Consequently,

the image-recording sheet of the present invention can provide the image with the

high gloss, hue, color reproducibility, and the like even in case of the color image

including the lines and drawings and pictures without requiring a toner and a fixing

apparatus to be specifically designed.

The above-described solubility parameter can be calculated according to the

disclosure of P. A. Small, J, Appl. Chem., 3, 71(1953).

The inventive image-recording sheet may contain an antistatic agent. The

antistatic agent controls the surface resistance of the image-receptive layer and

increases the transfer efficiency of the toner, and thus improves the quality and other

properties of the toned image. Preferable antistatic agents include nonionic antistatic

agent, cationic antistatic agent, anionic antistatic agent, fluorine-containing antistatic agent, a combination of these antistatic agents and a salt (such as lithium nitrate,

sodium nitrate, sodium chloride, etc.) and conductive polymers.

In another preferred embodiment of the present invention, the image-recording

sheet further comprises the gloss layer 3 interposed between the substrate 1 and the

image-receptive layer 2.

In the present invention, the gloss layer has a refractive index higher than that

of the thermoplastic resin of the image-receptive layer by at least 0.002 in terms of

absolute values. As a result, in the inventive image-recording sheet, even if light

passes through the image-receptive layer, it is effectively reflected at the interface

between the image-receptive layer 2 and the gloss layer 3 to improve the gloss of the

image like the above described first embodiment and, at the same time, to improve the

hue and color reproducibility of the image.

Such a gloss layer is made of a transparent optical material containing, for

example, acrylic resin, styrene resin, styrene-acrylic resin, epoxy resin,

styrene-butadiene resin, polyurethane resin, or polyester resin. Styrene-acrylic resin

and polyester resin are preferred because of the high adhesion strength between the

substrate and the image-receptive layer.

The above-described image-recording sheet can be produced by, for example,

a conventional method as described below. First, the thermoplastic resin and, if used, the compatibilizer are dissolved and

dispersed in water or a volatile solvent containing methyl ethyl ketone (MEK) to

obtain an over coating agent. A prescribed amount of the agent is applied to a

substrate. After that, together with the substrate, the over coating agent is heated and

dried to remove the solvent and to form an image-receptive layer with a desired dry

coating amount.

The dry coating amount is preferably from about 0.5 to 15 g/m . When the

dry coating amount is lower than about 0.5 g/m², a toned image tends to be difficult to

smooth. On the other hand, when the dry coating amount exceeds about 15 g/m², the

hot-offset of the image-receptive layer may be caused.

Furthermore, before the formation of the image-receptive transparent layer, if

desired, a glossy primer layer may be formed on the substrate. The primer can be

prepared by dissolving and dispersing an optical material containing the foregoing

thermoplastic resin in water or a volatile solvent containing methyl ethyl ketone

(MEK). The primer can then be applied to the substrate, and heated and dried

together with the substrate.

The dry coating amount of the gloss layer is preferably from about 0.1 to

5 g/m². When the dry coating amount is lower than about 0.1 g/m², it may be

difficult to evenly coat the layer and thus the thickness of the gloss layer may become less uniform. On the other hand, when the dry coating amount exceeds about 5 g/m²,

hot-offset is easily caused.

In the above, the image-recording sheet of the present invention is explained

with reference to the preferred embodiments. The present invention, however, is not

limited to those embodiments.

Also, the image-receptive layer may contain components other than those

described above unless they are beyond the scope of the purposes and the effects of

the present invention. For example, in order to adjust the whiteness of the

image-recording sheet, a loading filler comprising an inorganic pigment such as

calcium carbonate, clay, calcium sulfate, etc. or an acrylic type or a styrene-acrylic

type organic pigment may be used.

Furthermore, a wax such as paraffin wax, microcrystalline wax, carnauba wax,

etc. may be used. Such a wax is capable of efficiently separating the toner

protruding over the image-receptive layer from the fixing apparatus (e.g., the fixing

roll) in the thermal fixation process to prevent hot-offset. Furthermore, especially

when the wax adheres to the surface of the toned image, the gloss of the toned image

can further be improved. Examples

Hereinafter, the present invention will be illustrated by the following

examples. However, a person skilled in the art can readily understand that the

present invention is not limited to these examples.

Example 1

In this example, at first, an over coating composition was prepared by

mixing the respective components shown in Table 1.

Table 1

Next, a prescribed amount of the obtained over coating composition was

applied with a Mayer bar to one surface of a paper substrate (soft glossy paper,

C4179B, manufactured by Hewlett-Packard) having a ten-point average surface

roughness (Rz) of 0.146 μm. After that, together with the paper substrate, the over

coating composition was heated to 100°C and dried for 3 minutes to remove the

solvent and form an image-receptive transparent layer with the dry coating amount of 4.0 g/m² and produce an image-recording sheet. In this case, the image-receptive

layer was firmly adhered to the paper substrate.

The surface roughness of the image-receptive layer was measured with a

surface roughness meter (Surfcoder SE-30K manufactured by Kosaka Laboratory Co.,

Ltd.) and the surface roughness Rz was found to be 1.232 μm.

Next, an image was printed on the image-recording sheet using a laser printer

(Color Laser Shot LBP-2040 manufactured by Canon) to form a full color toned image

on the image-receptive transparent layer and after that, the gloss and the chromas (a ,

b ) of the image were measured to evaluate the quality of the image. The gloss was

measured by gloss-meter manufactured by Nippon Denshoku Kogyo Co., Ltd. The

measurement angle was set at 75°. The chromas were measured with a

colorimeter/color difference meter (SZ-Σ80 manufactured by Nippon Denshoku

Kogyo Co., Ltd.). The results are shown in Table 2.

Comparative Example 1

In this comparative example, an image was formed in the same manner as in

Example 1 except that the paper substrate itself was used as the image-recording sheet

and evaluation was carried out. The results are shown in Table 2.

Table 2

Example 1

According to the results shown in Table 2, it can be seen that the chromas in

the image-recording sheet of Example 1 were increased. Consequently, the inventive

image-recording sheet has excellent color reproducibility and can provide a toned

image with a high quality.

Example 2

In this example, an image-recording sheet was produced in the same manner as

in Example 1 except that an over coating composition was prepared by mixing the

respective components shown in Table 3 and used, and the evaluation was carried out

in the same manner as in Example 1 except the measurement of chroma.

Table 3

In this case, the image-receptive transparent layer was firmly adhered to the

paper substrate, and the image-receptive transparent layer had a surface roughness Rz

of 1.512 μm. Example 3

In this example, an image-recording sheet was produced in the same manner as

in Example 1 except that an over coating composition used was prepared by mixing

the respective components shown in Table 4 and a copy paper sheet (J coated paper;

Rz = 1.218 μm) manufactured by Fuji Xerox Co., Ltd. was used as the paper

substrate, and evaluation was carried out in the same manner as in Example 1 except

the measurement of chroma.

Table 4

In this case, the image-receptive transparent layer was firmly adhered to the

of 0.959 μm.

Comparative Example 2

In this comparative example, an image-recording sheet was produced in the

same manner as in Example 3 except that a copy paper sheet (Color Laser Copier

paper; Rz = 4.354 μm) manufactured by Canon Co., Ltd. was used in place of the copy paper manufactured by Fuji Xerox Co., Ltd. and the evaluation was carried out.

In this case, the image-receptive transparent layer was firmly adhered to the paper

substrate and the image-receptive transparent layer had a surface roughness Rz of

4.921 μm.

Comparative Example 3

An image-recording sheet was produced in the same manner as in Example 1

except that an image-receptive transparent layer with the dry coating amount of

2.5 g/m² was formed using an over coating composition prepared by mixing the

respective components shown in Table 5. In this case the surface roughness Rz of

the image-receptive layer was 1.218 μm. However, in the image-recording sheet of

this comparative example, hot-offset was caused at the time of forming a full color

image and therefore, the evaluation of image was impossible.

Table 5

Example 4 In this example, first, a primer composition was produced by mixing the

respective components shown in Table 6. Next, the prescribed amount of the

obtained primer composition was applied with a Mayer bar to one surface of a paper

substrate (Mirrorcoat manufactured by Oji Paper Mill, Ltd.; basis weight: 157.0 kg) having a ten-point average surface roughness (Rz) of 0.228 μm. After that, together

with the paper substrate, the primer composition was heated to 100°C and dried for

3 minutes to remove the solvent and form a gloss layer with a dry coating amount of

0.9 g/m². The refractive index of the gloss layer was 1.4952.

Table 6

Next, an over coating composition was prepared by mixing the respective

components shown in Table 7 and then the prescribed amount of the composition was

applied with a Mayer bar to the previously formed gloss layer. After that, together

with the paper substrate and the gloss layer, the over coating composition was heated

to 100°C and dried for 3 minutes to remove the solvent and form an image-receptive

transparent layer with a dry coating amount of 4.0 g/m² to yield an image-recording

sheet. The refractive index of the image-receptive layer was 1.4879.

Table 7

In this case, the image-receptive transparent layer and the gloss layer were

firmly adhered to each other and held on the paper substrate. The image-receptive

transparent layer had a surface roughness Rz of 0.231 μm when measured using the

same surface roughness meter as that used in Example 1.

Furthermore, a full color toned image was formed on the image-receptive

transparent layer of the image-recording sheet in the same manner as in Example 1

and the gloss was measured in the same manner as in Example 1.

The gloss of each image-recording sheet produced in Examples 1 to 4 and

Comparative Examples 1 to 2 is shown in Table 8.

According to the results in Table 8, it can be seen that all the image-recording

sheets of Examples 1 to 4 had a high gloss in comparison with those of Comparative

Examples 1 and 2. Consequently, the image-recording sheets of the present

invention can provide a high quality toned image.

Table 8

Example 5

In this example, an image-recording sheet was produced in the same manner as

in Example 4 except that a paper substrate (Pearlcoat produced by Mitsubishi Paper

Mills, Ltd.; basis weight: 127.9 kg) having a ten-point average surface roughness Rz

of 0.784 μm was used as the paper substrates and a gloss layer composition and an

image-receptive layer composition used were prepared by mixing the components

shown in Table 9 and Table 10, respectively and the evaluation was carried out in the

same manner as in Example 1. In this case, the image-receptive transparent layer and

the gloss layer were firmly adhered to one another and held on the paper substrate,

and the image-receptive transparent layer had a surface roughness Rz of 0.835 μm.

The refractive index of the image-receptive layer was 1.5044.

Table 9

Table 10

Comparative Example 3

In this comparative example, an image-recording sheet was produced in the

same manner as in Example 5 except that no gloss layer was formed, and then the

evaluation was carried out. In this case, the image-receptive transparent layer was

firmly adhered to the paper substrate, and the image-receptive transparent layer had a

surface roughness Rz of 0.770 μm.

The gloss of each image-recording sheet produced in Example 5 and

Comparative Example 3 is shown in Table 11.

Table 11

According to the results in the Table 11, it can be seen that the

image-recording sheets of Example 5 had a high gloss in comparison with that of

Comparative Example 3. Consequently, the image-recording sheet of the present

invention can provide a high quality toned image by forming the gloss layer.

Claims

1. An image-recording sheet comprising a paper substrate and an image-receptive

layer formed at least one surface of the paper substrate, characterized in that the

image-receptive layer has ten-point average surface roughness (Rz) of about 0.1 to 3.0

μm and contains a thermoplastic resin having a storage modulus of about 1 x 10 to

l x l0⁶ Pa at l60°C.

2. The image-recording sheet according to claim 1, characterized in that the

image-receptive layer is transparent.

3. The image-recording sheet according to claim 1 further comprising a gloss layer

disposed between the paper substrate and the image-receptive layer.

4. The image-recording sheet according to claim 3, characterized in that the gloss

layer has a refractive index higher than that of the thermoplastic resin of the

image-receptive layer by at least about 0.002 in terms of absolute values.

5. The image-recording sheet according to any one of claims 1 to 4, characterized in

that the image-receptive layer contains a compatibilizer having a solubility parameter of

about 8.0 to 10.0.