JP4241504B2 - Electrophotographic transfer paper and image forming method - Google Patents

Description

  The present invention relates to an electrophotographic transfer paper used for forming an image by an electrophotographic method applied to a color copying machine or a color printer, and an image forming method using the same.

  Conventionally, as a method of forming a color image by an electrophotographic method, an electrostatic latent image is formed for each color by irradiating color separation light on a photoconductor, and the electrostatic latent image for each color is converted into Y (yellow). ), M (magenta), C (cyan) and other color toners are sequentially developed to form a color toner image for each color, and each time a toner image of each color is formed, it is superimposed and transferred onto the transfer member. And a method of forming a color image by heat-melting and fixing the toner image.

  As another method, the color toner images for the respective colors are formed on the photosensitive member instead of the transfer member, and the superimposed color toner images are collectively transferred onto the transfer member and heated. There is a method of forming a color image by melting and fixing. Further, as another method, a toner image is transferred from the photosensitive member to the transfer member indirectly using an intermediate transfer member such as a belt; specifically, a color formed on the photosensitive member for each color. There is a method in which a toner image is superposed on an intermediate transfer member, and the superposed color toner image is batch-transferred onto the transfer member and heated and melted to fix.

  The color toner is constituted by dissolving or dispersing various dyes or pigments as a colorant in a binder resin, and the particle diameter thereof is about several μm to several tens μm. As the color toner receiver, a paper base such as plain paper, general printing paper, and coated paper is used, and the color toner superimposed on the paper base is heated and melted and fixed. Thus, a color image is formed (see Patent Document 1). Since the surface of the color image formed in this way has unevenness of, for example, about 10 to 100 μm, the unevenness of the color image surface causes unevenness in the gloss of the image.

In order to improve the above problems, various methods are known in which a thermoplastic transparent resin layer is provided as an image receiving layer on a substrate and a toner image is embedded in the transparent resin layer by a heat roller fixing device.
As such a method, for example, a toner image is transferred onto the surface of an image transfer sheet having a glass transition temperature of 40 to 70 ° C. and having a transparent resin layer made of a cross-linked resin soluble in tetrahydrofuran, and a belt-like fixing device And a method of embedding a toner image in a transparent resin layer (see Patent Document 2). Further, there is a method in which a toner image is transferred onto the surface of an image transfer sheet on which a thermoplastic resin is coated, and the toner is embedded in a transparent resin layer with a belt-like fixing device (see Patent Documents 3 and 4).

Further, in order to obtain a gloss-matching image free from gloss unevenness, the average molecular weight (Mwa) of the transparent resin provided on the transfer sheet surface and the average molecular weight (Mwb) of the binder resin of the color toner are Mwa−Mwb ≧ An image is obtained using an electrophotographic transfer paper (see Patent Document 5) having a relationship indicated by 10000 and having a melting inclination angle with respect to the binder resin of the color toner adjusted to 40 degrees or less at the fixing temperature of the transparent resin toner. The method of forming is mentioned.
Moreover, the electrophotographic transfer paper in which the number average molecular weight (Mn) of the transparent resin layer provided on the transfer sheet surface is in the range of 5000 to 20000 and the glass transition temperature is in the range of 30 to 85 ° C. (see Patent Document 6) ) To form an image. Furthermore, there is a method in which a plasticizer is blended in a thermoplastic resin layer, and a binder and solid components that form the layer at the time of fixing are softened and toner is embedded in the thermoplastic resin layer (see Patent Document 7).

In the techniques shown in the above documents, when a color toner image is fixed on a transfer body, the color toner image is heated and melted by pressurizing with a heat roller, and the transparent resin layer on the surface of the electrophotographic transfer paper. It is fixed so as to be embedded inside.
When forming an image using these methods, the toner image is embedded in the thermoplastic resin layer in the low image density region, and the smoothness of the entire image forming surface becomes high and gloss is developed. In this case, the toner image cannot be completely embedded in the thermoplastic resin layer, and the image portion in the image forming surface is raised as compared with the non-image portion, resulting in a step (hereinafter referred to as “image”). May be abbreviated as "step"). Such an image step causes a sense of incongruity when viewed visually, and the gloss decreases due to the presence of the image step, resulting in an image having a large gloss difference on the entire image forming surface.

As a method of eliminating such a difference in toner image height and overall gloss, a porous coating layer (thermoplastic foamed resin layer) is provided on the support and the toner is embedded in the voids on the surface of the porous coating layer. Have proposed a method of eliminating a sense of incongruity due to an image step and a difference in gloss between an image portion and a non-image portion (see Patent Documents 8 to 10).
When an image is formed using these techniques, the toner can be easily embedded in the voids on the surface of the porous coating layer at the time of fixing, so that the image level difference can be improved compared to a paper provided with a thermoplastic resin layer. A sense of incongruity and a difference in gloss caused by the step can be suppressed.
However, even when an image is formed using a paper having a thermoplastic foam resin layer as described above, there is a difference in gloss between the image area and the non-image area, or in the image area, and the overall gloss is sufficient. There was a case where the feeling was not obtained.

  An object of the present invention is to solve the above problems. That is, an object of the present invention is to provide an electrophotographic transfer paper on which the gloss on the surface of the image receiving layer is uniform and can form a glossy image as a whole, and an image forming method using them.

In order to achieve the above-mentioned problems, the present inventors diligently studied the problems in a paper provided with a conventional thermoplastic foamed resin layer as an image receiving layer.
Therefore, the present inventors examined the relationship between the occurrence of a gloss difference and the like and the thermoplastic foamed resin layer in a conventional paper provided with a thermoplastic foamed resin layer.
FIG. 4 is a schematic cross-sectional view showing an example of a cross-sectional structure of a transfer paper for electrophotography in which a thermoplastic foam resin layer (image receiving layer) is provided on a conventional base material, in which 100 is a thermoplastic foam resin layer. (Image receiving layer), 101 is a gap located on the surface of the thermoplastic foamed resin layer, 102 is a gap located inside the thermoplastic foamed resin layer, and 110 is a substrate. As shown in FIG. 4, the conventional electrophotographic transfer paper has a structure in which voids (voids 101 and 102) exist almost uniformly in the thickness direction from the surface of the thermoplastic foam resin layer 100 to the substrate 110 side. Have.

When an image is formed, the thermoplastic foamed resin layer 100 causes toner to enter the gap 101 on the surface of the thermoplastic foamed resin layer 100 at the time of transfer, and embeds the toner in the thermoplastic foamed resin layer 100 at the time of fixing. For this purpose, it is provided on the surface of the substrate.
On the other hand, the present inventors investigated the cross-sectional structure of the thermoplastic foamed resin layer when the gloss became non-uniform when an image was formed using a sheet as shown in FIG. As a result, it was found that voids tend to remain in the thermoplastic foamed resin layer after fixing as the gloss is non-uniform.

Such a paper has a void volume ratio (hereinafter referred to as “internal void volume ratio”) inside the thermoplastic foamed resin layer of 70% or more, and the void volume inside the thermoplastic foamed resin layer is very large. all right. The internal void volume ratio is a value calculated based on the following formula (1).
Formula (1) Internal void volume ratio (%) = [D / (ρ · t)] × 100
However, in Formula (1), D represents the coating amount (g / m < ² >, dry mass conversion value) of the solution for thermoplastic foam resin layer formation at the time of forming a thermoplastic foam resin layer, and (rho) is thermoplasticity. It represents the density (g / cm ³ ) of the resin component of the foamed resin layer, and t represents the thickness (μm) of the thermoplastic foamed resin layer.

  Accordingly, the present inventors have found that the voids 102 present inside the thermoplastic foam resin layer 100 before fixing increase the heat capacity of the thermoplastic foam resin layer 100 more than necessary, and melt the toner during fixing. I thought it was inadequate. That is, due to an increase in the heat capacity of the thermoplastic foam resin layer 100, the toner is insufficiently melted at the time of fixing, so that the toner is not uniformly embedded in the thermoplastic foam resin layer 100, and an image step is generated. It is considered that the in-plane gloss is uneven. Further, as a proof of such a phenomenon, as a result, it is considered that voids easily remain in the thermoplastic foamed resin layer after fixing.

Based on the above findings, the present inventors have found the following present invention. That is, the present invention
<1>
In an electrophotographic transfer paper comprising a substrate and an image receiving layer having a void provided on at least one side of the substrate,
The electrophotographic transfer paper is characterized in that the image receiving layer is a thermoplastic foamed resin layer containing bubbles and satisfies the following formula (2).
Formula (2) Sb <St
[In the formula (2), Sb represents the void area ratio (%) of the cross section corresponding to the thickness of 1/3 from the surface side of the image receiving layer in contact with the substrate, and St represents the surface of the image receiving layer. Represents a cross-sectional void area ratio (%) of a layer corresponding to a thickness of 2/3. ]

<2>
The electrophotographic transfer paper according to <1>, wherein the cross-sectional void area ratio Sb is 50% or less.

<3>
The electrophotographic transfer paper according to <1> or <2>, wherein the cross-sectional void area ratio St is in a range of 20% to 90%.

<4>
The electrophotographic transfer paper according to any one of <1> to <3>, wherein a surface void area ratio Ss of the image receiving layer is in a range of 20% to 70%.

<5>
The electrophotographic transfer paper according to any one of <1> to <4>, wherein an average diameter of voids present on the surface of the image receiving layer is in a range of 0.5 μm or more and 50 μm or less. .

<6>
When an image is formed by electrophotography so that an image portion and a non-image portion are mixed on the surface of the image receiving layer, the difference between the gloss before fixing and the gloss after fixing in the non-image portion is 10% or more. The electrophotographic transfer paper according to any one of <1> to <5>.

<7>
The electrophotographic transfer paper according to any one of <1> to <6>, wherein the image receiving layer has a thickness in the range of 5 μm to 100 μm.

<8>
Any one of <1> to <7>, wherein a coating amount (in terms of dry mass) of the image receiving layer per one side of the substrate is in a range of 3 g / m ^{2 to} 30 g / m ^2. The electrophotographic transfer paper described in 1.

<9>
The electrophotographic transfer paper according to any one of <1> to <8>, wherein the image receiving layer contains a release agent.

<10>
A latent image forming step of forming a latent image on the latent image carrier, a developing step of developing the latent image using an electrophotographic developer to form a toner image, and transferring the toner image to a transfer target A transfer step, and a fixing step of heat-pressing the toner image onto the surface of the transfer object,
An image forming method, wherein the transfer target is the electrophotographic transfer paper according to any one of <1> to <9>.

<11>
<10> The image forming method according to <10>, wherein the fixing step is oilless fixing.

  As described above, according to the present invention, it is possible to provide an electrophotographic transfer paper capable of forming a glossy image with uniform gloss on the surface of the image receiving layer and an image forming method using these. it can.

The electrophotographic transfer paper of the present invention is an electrophotographic transfer paper (hereinafter sometimes abbreviated as “transfer paper”) including a base material and an image receiving layer having a void provided on at least one side of the base material. The following expression (3) is satisfied.
Formula (3) Sb <St
However, in the formula (3), Sb is a cross-sectional void area ratio (%) of a layer corresponding to a thickness of 1/3 from the surface side of the image receiving layer in contact with the substrate (hereinafter sometimes abbreviated as “lower layer”). St represents the void area ratio (%) of the cross-section of a layer corresponding to a thickness of 2/3 from the surface of the image receiving layer (hereinafter sometimes abbreviated as “upper layer”).

  That is, the transfer paper of the present invention has a size and number of voids 102 in the thermoplastic foamed resin layer (image receiving layer) 100 of the conventional transfer paper shown in FIG. However, since the heat capacity of the image receiving layer is reduced by making the size relatively small, it is possible to prevent the toner from being poorly fused at the time of fixing. For this reason, it is possible to prevent the occurrence of an image level difference and a gloss difference due to toner melting failure.

FIG. 1 is a schematic cross-sectional view showing an example of the cross-sectional structure of the electrophotographic transfer paper of the present invention, in which 100 ′ corresponds to the image receiving layer and 103 corresponds to a thickness of 2/3 from the surface of the image receiving layer 100 ′. Layer (the layer that does not contact the substrate 110 (upper layer) of the two layers obtained by horizontally dividing the image receiving layer 100 ′ by a dotted line), 104 from the surface side that contacts the substrate 110 of the image receiving layer 100 ′ / 3 represents a layer corresponding to the thickness (the layer (lower layer) in contact with the substrate 110 out of the two layers obtained by horizontally dividing the image receiving layer 100 ′ by a dotted line), and other symbols are shown in FIG. It is the same as that shown.
As in the example shown in FIG. 1, in the transfer paper of the present invention, the number and size of the voids 102 present in the image receiving layer 100 ′ so as to satisfy the relationship of the expression (3) It is relatively less than For this reason, an increase in the heat capacity due to the void 102 existing inside the image receiving layer 100 ′ can be suppressed, and poor melting of the toner at the time of fixing can be prevented. And can have a uniform and glossy image.

  In addition, although the cross-sectional void area ratio Sb of the lower layer and the cross-sectional void area ratio St of the upper layer need to satisfy the relationship represented by the formula (3), more preferably Sb + 10% <St, and even more preferably Sb + 20%. <St. When the cross-sectional void area ratio Sb of the lower layer is equal to or greater than the cross-sectional void area ratio St of the upper layer, the lower layer voids remain after fixing, and the toner embedding deteriorates due to the cushioning effect of the remaining voids.

Further, the ratio of the upper layer cross-sectional void area ratio St to the lower layer cross-sectional void area ratio Sb is preferably within a range that satisfies the relationship of the expression (3). The lower layer cross-sectional void area ratio Sb may become too small, or the upper layer cross-sectional void area ratio St may become too large.
When the cross-sectional void area ratio Sb of the lower layer becomes too small, an embedding allowance for crushing voids existing in the image receiving layer by the toner at the time of fixing is sufficiently reduced, so that an image step is likely to occur. There is. In addition, if the upper layer cross-sectional void area ratio St is too large, the uneven portions on the surface of the image receiving layer are excessively large, so that the voids on the surface are not sufficiently blocked by the embedding of the toner even after fixing, and the non-image area or image The gloss of the part may be lowered.
For this reason, it is preferable that the cross-sectional void area ratio Sb of the lower layer and the cross-sectional void area ratio St of the upper layer satisfy the relationship of Sb + 40% ≧ St while satisfying the formula (3).

Further, the cross-sectional void area ratio Sb of the lower layer is preferably 50% or less, more preferably 30% or less, and particularly preferably 20% or less. When the upper limit value of the cross-sectional void area ratio Sb of the lower layer exceeds 50%, removal of voids existing in the image receiving layer at the time of fixing becomes insufficient, the heat capacity of the image receiving layer becomes high, and toner embedding becomes worse. There is.
However, when the cross-sectional void area ratio Sb of the lower layer is too small, the embedding margin of the image receiving layer is small, so that the toner cannot be sufficiently embedded in the image receiving layer at the time of fixing, and an image step may occur. is there. For this reason, the cross-sectional void area ratio Sb of the lower layer is preferably at least 0.1% or more, more preferably 1% or more.

On the other hand, the cross-sectional void area ratio St of the upper layer is preferably in the range of 20% to 90%, more preferably in the range of 25% to 85%, and in the range of 30% to 80%. More preferably, it is within.
If the cross-sectional void area ratio St of the upper layer is less than 20%, there are few voids inside the image receiving layer, and the toner embedding property may deteriorate. Further, when the cross-sectional void area ratio St of the upper layer exceeds 90%, the heat capacity of the image receiving layer increases, and the toner may be unevenly embedded.

The surface void area ratio Ss of the image receiving layer is preferably in the range of 20% to 70%, more preferably in the range of 20% to 65%, and in the range of 20% to 60%. More preferably, it is within.
When the surface void area ratio Ss is less than 20%, the toner may not be sufficiently embedded in the image receiving layer. Further, if the surface void area ratio Ss exceeds 70%, the uneven portions on the surface of the image receiving layer increase too much, so that the voids are not blocked even after fixing, and the gloss of the non-image area and the gloss of the image area may decrease. .

  Here, the values of the cross-sectional void area ratio Sb of the upper layer, the cross-sectional void area ratio St of the lower layer, and the surface void area ratio Ss were obtained by photographing the cross section and the surface of the image receiving layer using a scanning electron microscope or an optical microscope. Thereafter, the cross-section and the outline of the pores (voids) on the surface can be accurately drawn on a transparent film with a black pen or the like, and further measured using a drum scanner (trademark: Luzex III, manufactured by Nireco).

It is preferable that the average diameter of the voids existing on the surface of the image receiving layer (average void diameter) is 0.5 μm or more and 50 μm or less. When this average gap diameter is in the above range, the toner is embedded in the image portion, and the gap is filled in the non-image portion.
When the average gap diameter is less than 0.5 μm, the toner is less likely to be embedded in the gap at the time of transfer, and in particular, the toner in the high-density image area may be less likely to be embedded in the image receiving layer even after fixing. When the average gap diameter is larger than 50 μm, the toner can be buried in the gap at the time of transfer, but the gap is not completely blocked at the time of fixing and may remain as a void mark after fixing.
The average void diameter is more preferably 2 μm or more and 45 μm or less, and the average void diameter is further preferably 4 μm or more and 40 μm or less.

  In the non-image area, the gap is closed by the softening of the resin in the non-image area and the gloss increases. However, the gloss difference, that is, the gloss difference before and after fixing in the non-image area of the transfer paper needs to be 10% or more. . By setting the gloss difference before and after fixing to 10% or more, a uniform and good gloss feeling can be obtained. The difference in gloss before and after fixing is more preferably 20% or more, and further preferably 30% or more. However, the gloss difference means a gloss difference before and after fixing in the thick paper 2 mode by DocuCenter Color 500 (manufactured by Fuji Xerox Co., Ltd.). The gloss (gross) of the non-image area is also called white paper gloss.

  The thickness of the image receiving layer is preferably in the range of 5 μm to 100 μm. If the thickness of the image receiving layer is less than 5 μm, it may be insufficient to sufficiently embed the toner inside the image receiving layer. In addition, when the thickness of the image receiving layer exceeds 100 μm, the heat capacity of the image receiving layer increases, and the void on the surface of the image receiving layer may not be blocked after fixing. The thickness of the image receiving layer is more preferably 10 μm or more and 90 μm or less, and further preferably 15 μm or more and 80 μm or less.

The coating amount per one side of the substrate of the image receiving layer is preferably 3 g / m ² or more and 30 g / m ² or less in terms of dry mass. If the coating amount is less than 3 g / m ² , it may be difficult to completely embed the toner in the image receiving layer at the time of fixing. On the other hand, if the coating amount exceeds 30 g / m ² , the heat capacity of the resin itself constituting the image receiving layer increases, and the toner may become unevenly embedded. The coating amount is more preferably 5 g / m ² or more and 25 g / m ² or less, and further preferably 8 g / m ² or more and 20 g / m ² or less.

  The thermoplastic resin constituting the image receiving layer is not particularly limited as long as it is a known thermoplastic resin. For example, a resin having an ester bond; a polyurethane resin; a polyamide resin such as a urea resin; a polysulfone resin; Vinylidene chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl propionate copolymer resin; polyol resin such as polyvinyl butyral, cellulose resin such as ethyl cellulose resin and cellulose acetate resin; polycaprolactone resin, styrene-anhydrous Maleic acid resin, polyacrylonitrile resin, polyether resin, epoxy resin, phenol resin; polyolefin resin such as polyethylene resin and polypropylene resin, copolymer resin of olefin such as ethylene and propylene and other vinyl monomers, acrylic resin It can be exemplified a resin. These thermoplastic resins may be used as a mixture or copolymer in combination of two or more. The thermoplastic resin used preferably has a softening point in the range of 50 ° C. or higher and 120 ° C. or lower.

  The image receiving layer may contain a pigment. Examples of the pigment include inorganic pigments such as zinc oxide, titanium oxide, calcium carbonate, silicate, clay, talc, mica, calcined clay, aluminum hydroxide, barium sulfate, lithopone, silica, colloidal silica, polystyrene, polyethylene, polypropylene, epoxy Resin, organic pigments called plastic pigments such as spheres, hollow spheres, confetti, donuts and flats such as styrene / acrylic copolymers, starch powder, cellulose powder, etc. can be used. Is not to be done. In addition, these pigments can be used individually or in mixture of 2 or more types as needed.

  The image receiving layer preferably contains a release agent. By including a release agent, it is possible to prevent so-called oil-less fixing that prevents the transfer paper from being wrapped around a fixing member such as a fixing roller at the time of fixing, and performs fixing without supplying oil from the fixing device side to the surface of the fixing member. It can be easily realized.

As the release agent, waxes, higher fatty acids, higher alcohols, higher fatty acid amides and the like can be used. Examples of waxes include plant waxes such as carnauba wax and rice wax, petroleum waxes such as paraffin, microcrystalline, and petrolactam, and synthetic hydrocarbon waxes such as polyethylene wax.
Examples of higher fatty acids include stearic acid, oleic acid, palmitic acid, myristic acid, lauric acid, and examples of higher alcohols include lauryl alcohol, myristyl alcohol, stearyl alcohol, cetyl alcohol, and behenyl alcohol. Examples of the higher fatty acid amide include stearic acid amide, palmitic acid amide, methylene bisstearyl amide, and ethylene bisstearyl amide.

  The release agent is preferably blended in the image-receiving layer in an amount of 0.1% to 20% by weight. If the blending amount is less than 0.1%, the release effect by the release agent cannot be sufficiently exhibited, and the transfer paper may be wound around a fixing member such as a heat roller at the time of fixing. When the blending amount exceeds 20% by mass, the amount of the release agent oozing out to the surface of the image receiving layer increases, and the release agent bleed trace remains in the non-image area and image area after fixing. It may end up.

The “image receiving layer” provided on the transfer paper of the present invention means a layer having at least a void on the surface, and mechanically agitated and blown air into a resin coating solution containing a thermoplastic resin. It is formed through at least a process of forming a thermoplastic foamed resin layer by containing a large number of fine bubbles and applying and drying this on a substrate.
The voids on the surface of the image receiving layer are the traces of bubbles contained in the resin coating liquid subjected to mechanical stirring, and are different from fine scratches and dents on the surface of the image receiving layer.

  A method of generating and dispersing bubbles in the resin coating liquid (foaming method) is, for example, a stirrer having a stirring blade that rotates while performing planetary motion, such as a homomixer generally used for emulsification dispersion, a stirrer such as a cowless dissolver, , A device that can mechanically stir and continuously mix and mix air as fine bubbles while continuously feeding a mixture of air and coating liquid into a closed system, for example, Gaston County in the United States, Stoke in the Netherlands, etc. Although a foaming machine can be used, it is not limited to these.

A foam stabilizer or a foaming agent may be added to the resin coating solution. These are added in order to improve the stability of the bubbles in the resin coating liquid containing bubbles or the desired bubble-containing state cannot be obtained due to insufficient mechanical stirring ability.
Specifically, higher fatty acids such as stearic acid and palmitic acid, higher fatty acid salts such as sodium lauryl sulfate, ammonium stearate, ammonium palmitate, and higher fatty acid modified products such as alkyl alkanolamides, sorbitan fatty acid esters, etc. This is particularly suitable because it has a high effect of enhancing the foaming property of the resin coating solution and improving the dispersion stability of the bubbles.

  Although there is no restriction | limiting in the selection of these foam stabilizers and a foaming agent, It is better to avoid the thing which may inhibit the fluidity | liquidity of a resin coating liquid, or may impair coating workability | operativity. The blending amount of the foam stabilizer and the foaming agent is a solid content with respect to 100 parts by mass of a solid content (a thermoplastic resin, a pigment added if necessary) contained in the resin coating liquid. The range of 0-30 mass parts is preferable, and the range of 1-20 mass parts is more preferable.

  The coating method for forming the image receiving layer on the substrate is from a known method such as a Mayer bar method, a gravure roll method, a roll method, a reverse roll method, a blade method, a knife method, an air knife method, an extrusion method, or a casting method. It can be selected arbitrarily.

Further, the image receiving layer provided on the transfer paper of the present invention must satisfy the relationship represented by the formula (3). For example, as shown in FIG. 1, the number of the voids existing on the surface of the image receiving layer and the size thereof In comparison, the number and size of the voids in the image receiving layer are relatively small / small.
As a specific method for forming an image receiving layer having such a structure, for example, a thermoplastic foam formed by applying a resin coating liquid containing bubbles to a substrate and drying it in the same manner as in the past. Examples include a method (first method) in which an electrophotographic transfer paper having a resin layer is heated from the surface (back surface) opposite to the surface on which the thermoplastic foam resin layer is formed.

By such a backside heat treatment, an electrophotographic transfer paper having an image receiving layer in which the number and size of the voids existing inside is reduced / reduced while maintaining the number and size of the voids once formed on the surface is obtained. be able to.
Although it does not specifically limit as a method to heat from a back surface, For example, the method of pressing and rotating a back surface to the heated roll (for example, cast drum of a heating state), etc. are mentioned. The optimum heating time in this case varies depending on the resin constituting the image receiving layer, but it is preferable to heat at the softening point of the resin for 0.5 to 5 minutes.

  Further, as another method for forming an image receiving layer having a configuration satisfying the formula (3), there is a method (second method) in which two or more layers are stacked. For example, in the case where an image receiving layer is formed by laminating two layers, a thermoplastic resin layer (first layer) containing no voids using a non-foamed resin coating solution on a substrate. And then, a thermoplastic foamed resin layer (second layer) containing voids is formed on the first layer using a resin coating solution containing bubbles.

When this method is used, the types of thermoplastic resins used for forming the first layer and the second layer may be the same or different.
However, the second method is inferior in productivity as compared with the first method described above. Therefore, when importance is placed on the productivity, the first method is to heat-treat the single-layered thermoplastic foam resin layer once formed. Preferably, the method 1 is used.

  When the image receiving layer is formed by the above method, the image receiving layer satisfying the formula (3) can be formed. Further, the cross-sectional void area ratio Sb of the lower layer is adjusted to 50% or less, the cross-sectional void area ratio of the upper layer is adjusted to a range of 20% to 90%, and the surface void area ratio Ss is adjusted to a range of 20% to 70%. Is also easy. Further, the internal void volume ratio of the image receiving layer formed by the above method can be suppressed to less than 70%, and the proportion of voids that are likely to remain after fixing can be reduced from the beginning.

Examples of the base material for the electrophotographic transfer paper of the present invention include LBKP (hardwood bleached kraft pulp), NBKP (softwood bleached kraft pulp), LBSP (hardwood bleached sulfite pulp), NBSP (softwood bleached sulfite pulp), cotton pulp and the like. Any conventionally known pulp such as non-wood pulp, waste paper pulp, GP (ground pulp), and TMP (thermomechanical pulp) can be used.
As for the papermaking method, a general long-mesh multi-cylinder type, a round net single-cylinder type, a Yankee type or the like can be used as appropriate. In addition, the filler used for these is not particularly limited, and calcium carbonate such as heavy calcium carbonate, light calcium carbonate, chalk, and kaolin, calcined clay, biophyllite, sericite, talc, and other silicic acids. Inorganic fillers such as titanium dioxide and organic fillers such as urea resin and styrene can be used.

  The sizing agent is not particularly limited. Can use sizing agents such as rosin sizing agents, synthetic sizing agents, petroleum resin sizing agents, neutral sizing agents, etc., and use appropriate sizing agents such as sulfate bands and cationized starches in combination with fiber fixing agents. You can also In addition, a paper strength enhancer, a dye, a pH adjuster, etc. may be added.

  In order to adjust the electrical resistance value of these substrates, inorganic substances such as sodium chloride, potassium chloride, calcium chloride, sodium sulfate, zinc oxide, titanium dioxide, tin oxide, aluminum oxide, magnesium oxide, sodium carbonate, and alkylphosphoric acid are used. Organic materials such as ester salts, alkyl sulfate esters, sulfonic acid sodium salts, and quaternary ammonium salts can be used alone or in combination.

  When the base material is subjected to the smoothing process, it is performed using a smoothing processing apparatus such as a normal super calendar, gloss calendar, or soft calendar. Moreover, you may carry out suitably by an on-machine or an off-machine, and the form of a pressurization apparatus, the number of pressurization nips, heating, etc. are suitably adjusted according to a normal smoothing processing apparatus.

  When coated paper is used as the substrate, the base paper is not particularly limited. For example, acidic paper having a papermaking pH of around 4.5, weakly acidic papermaking pH of about 6 containing an alkaline filler such as calcium carbonate as a main component. A paper substrate such as neutral papermaking having a weak alkalinity of about 9 is used. The coated paper used as the substrate is a coated paper having a pigment coating layer obtained by coating a coating liquid mainly containing an adhesive and a pigment on at least one side.

As the adhesive for the pigment coating layer, a water-soluble and / or water-dispersible polymer compound is used. For example, cationic starch, amphoteric starch, oxidized starch, enzyme-modified starch, thermochemically-modified starch, esterified starch. , Starches such as etherified starch, cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose, natural or semi-synthetic polymer compounds such as gelatin, casein, soy protein, natural rubber, polyvinyl alcohol, isoprene, neoprene, polybutadiene, etc. Polyalkylenes such as polydienes, polybutene, polyisobutylene, polypropylene, and polyethylene, vinyl polymers such as vinyl halide, vinyl acetate, styrene, (meth) acrylic acid, (meth) acrylic acid ester, (meth) acrylamide, and methyl vinyl ether And copolymers, Len - butadiene, methyl methacrylate - synthetic rubber latex butadiene etc., polyurethane resins, polyester resins, polyamide resins, olefin - maleic acid resins, and synthetic polymer compounds such as melamine resin.
From these, one or more kinds are appropriately selected and used according to the desired quality required for the electrophotographic transfer paper.

  The blending ratio of the adhesive is preferably in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the pigment. When the blending ratio of the adhesive is less than 5 parts by mass, the surface of the base material is attacked by the resin liquid when the resin layer is applied onto the obtained coating layer, so that it is not possible to obtain good white paper glossiness. There is a case. Also, if the blending ratio of the adhesive exceeds 50 parts by mass, bubbles may be generated when the pigment coating layer is applied, and the coated surface may become rough, so that good white paper glossiness may not be obtained. is there.

  Examples of pigments include heavy calcium carbonate, light calcium carbonate, kaolin, calcined kaolin, structural kaolin, delaminated kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, and silica. , Magnesium aluminosilicate, particulate calcium silicate, particulate magnesium carbonate, particulate light calcium carbonate, mineral pigments such as white carbon, bentonite, zeolite, sericite, smectite, polystyrene resin, styrene-acrylic copolymer resin, urea Resins, melamine resins, acrylic resins, vinylidene chloride resins, benzoguanamine resins, fine hollow particles thereof, through-hole type organic pigments, and the like can be used, and one or more of these can be used.

  In the coating liquid for the pigment coating layer, in addition to the pigment and the adhesive, various auxiliary agents such as a surfactant, a pH regulator, a viscosity modifier, a softener, a gloss imparting agent, a dispersant, a flow modifier, Antistatic agent, stabilizer, antistatic agent, cross-linking agent, antioxidant, sizing agent, fluorescent brightener, colorant, ultraviolet absorber, antifoaming agent, water resistance agent, plasticizer, lubricant, preservative, A fragrance | flavor etc. can also be used suitably as needed.

The coating amount of the pigment coating layer is appropriately selected according to the purpose of use of the electrophotographic transfer paper of the present invention. And is preferably 8 to 40 g / m ² in terms of dry mass.
As a coating method for forming the pigment coating layer, generally known coating apparatuses such as blade coaters, air knife coaters, roller coaters, reverse roller coaters, bar coaters, curtain coaters, die coaters, gravure coaters, Champlex coaters, brush coaters, A two-roller or metering blade type size press coater, a bill blade coater, a short dwell coater, a gate roller coater, or the like is appropriately used.

  The pigment coating layer may be formed on one or both sides of the substrate, and the coating layer may have a multilayer structure by providing one layer or two or more intermediate layers as required. In the case of double-sided coating or a multilayer structure, the coating liquids do not have to be the same or the same coating amount, and may be appropriately adjusted according to a required quality level. In addition, when a coating layer is provided on one side of the substrate, a synthetic resin layer, a coating layer made of an adhesive and a pigment, or an antistatic layer is provided on the back side to prevent curling, impart printability, and supply / discharge It is also possible to impart paper suitability and the like. Furthermore, it is of course possible to add various application suitability to the back surface of the substrate by post-processing such as adhesion, magnetism, flame retardancy, heat resistance, water resistance, oil resistance, and anti-slip.

  The base material having the pigment coating layer used in the present invention is adjusted so that the water content is 3 to 10% by mass, preferably about 4 to 8% by mass, in a normal drying process or surface treatment process. And finished.

  Further, when a smoothing treatment is performed on a base material having a pigment coating layer, it is carried out using a smoothing treatment apparatus such as a normal super calender, gloss calender, or soft calender. Moreover, you may carry out suitably by an on-machine or an off-machine, and the form of a pressurization apparatus, the number of pressurization nips, heating, etc. are suitably adjusted according to a normal smoothing processing apparatus.

The transfer sheet for electrophotography of the present invention may be one in which an image receiving layer is simply formed on a substrate using the first method or the second method described above. The smoothness of the surface can be further improved by using a super calender constituted by appropriately combining a roll or a metal roll and a cotton roll.
Further, after the coating, the surface smoothness of the image receiving layer may be further improved by bringing the transfer paper in a semi-dry state or a dry state into contact with a heated or non-heated cast drum with a mirror finish. .

  However, if the above smooth finish treatment is performed under excessive pressure, the resin wall surrounding the bubbles in the image receiving layer is destroyed, the image receiving layer is densified to reduce heat insulation and cushioning properties, and the surface of the image receiving layer Since the pores may be destroyed and the excellent transfer performance of the image receiving layer may be lost, it is necessary to sufficiently consider the processing conditions in the smooth finishing process.

The electrophotographic transfer paper according to the present invention preferably has a composition adjusted so that its surface electrical resistance is 8.0 × 10 ⁸ Ω or more at a temperature of 28 ° C. and a relative humidity of 85%.

(Image forming method)
Hereinafter, the image forming method will be described in detail.
The image forming method of the present invention is an image forming method using a known electrophotographic system, and is characterized in that the electrophotographic transfer paper of the present invention is used as a transfer target. The process itself of the image forming method is not particularly limited, but specifically, the image forming method described below is preferable.

  That is, a latent image forming step of forming a latent image on the latent image carrier, a developing step of developing the latent image with an electrophotographic developer to form a toner image, and transferring the toner image to a transfer target. Preferably, the method includes a transfer step and a fixing step in which the toner image transferred onto the transfer target is heat-pressed onto the transfer target. The fixing step is preferably performed by oilless fixing.

The oilless fixing is a fixing method in which fixing is performed without fixing a release agent such as oil on the surface of the fixing member at the time of fixing, and generally a release agent is applied to the surface of the fixing member from a conventional fixing device. This is a fixing method performed using a fixing device in which a supplying means is omitted. Further, in the image forming method as described above, other steps may be included as necessary in addition to the four steps.
According to oilless fixing, since no oil is used, roughness of the obtained image surface is suppressed and writing on the image surface is facilitated.

Further, the developer for electrophotography may be either a two-component system composed of toner and carrier, or a one-component system composed only of toner, and known toners and carriers can be used. .
For the binder resin, colorant, release agent and other additives constituting the toner, known materials can be used in appropriate combination. For example, as the binder resin, polyester resin or styrene-acrylic resin can be used. Can be used mainly. The toner production method is not particularly limited, and any known toner production method such as a pulverization method or a polymerization method may be used.

  Next, the image forming method of the present invention will be specifically described with reference to the drawings. FIG. 2 is a schematic configuration diagram showing an example of an image forming apparatus preferably used in the image forming method of the present invention.

  In FIG. 2, 1 is a heat fixing roller, 2 is a pressure roller, 3 is a heat source, 11 is a photosensitive member (latent image carrier), 12 is a roller charger, 13 is an exposure device, and 14a is a developer (cyan). , 14b is a developer equipped with a developer (magenta), 14c is a developer equipped with a developer (yellow), 14d is a developer equipped with a developer (black), and 14a is a developing device. , 15 is an intermediate transfer member, 16 is a cleaner, 17 is a light static eliminator, 18a, 18b and 18c are spindle rollers, 19 is a transfer roller, and 20 is a transfer target (electrophotographic transfer paper of the present invention). .

The image forming apparatus shown in FIG. 2 has a roller-type charger 12, an exposure device 13, and cyan, magenta, yellow, and black developers in the clockwise direction around a photosensitive member 11 that can rotate in the direction of arrow R. The developing device 14 incorporating the developed devices 14a, 14b, 14c, and 14d, the belt-like intermediate transfer member 15, the cleaner 16, and the light neutralizer 17 are arranged in this order.
The intermediate transfer member 15 is stretched by support shaft rollers 18a, 18b, and 18c arranged on the inner peripheral surface thereof, and is rotatable in the direction of arrow P. The support roller 18 a is in pressure contact with the photoreceptor 11 via the intermediate transfer member 15. The support roller 18 c is in pressure contact with the transfer roller 19 via the intermediate transfer member 15.

  In addition, the contacted portion between the outer peripheral surface of the intermediate transfer member 15 and the transfer roller 19 allows the transfer target 20 to be inserted in the arrow Q direction. A heat roller fixing device including a heat fixing roller 1 and a pressure roller 2 in pressure contact with the outer peripheral surface of the intermediate transfer body 15 and the transfer roller 19 is disposed on the arrow Q direction side. The transferred body 20 that has passed through the contact portion between the heat transfer roller 1 and the pressure roller 2 and the contact portion between the outer peripheral surface of the intermediate transfer member 15 and the transfer roller 19 can be inserted in the arrow Q direction. .

  Image formation using the image forming apparatus shown in FIG. 2 is performed as follows. First, the surface of the photoconductor 11 rotating in the direction of arrow R is charged by the roller charger 12. A latent image is formed on the charged portion of the surface of the photoconductor 11 by exposing the surface of the photoconductor 11 with irradiation light L emitted from the exposure device 13 based on image information corresponding to each color of cyan, magenta, and yellow. The latent image formed on the surface of the photoconductor 11 is developed by developing units 14a, 14b, 14c, and 14d built in the developing device 14, and a toner image is formed for each color. The developed toner image is transferred onto the outer peripheral surface of the belt-like intermediate transfer member 15.

  The toner image transferred onto the outer peripheral surface of the intermediate transfer member 15 is transferred in contact with the support roller 18 c via the intermediate transfer member 15 as the intermediate transfer member 15 advances in the direction of arrow P. Move between and. When the toner image on the outer peripheral surface of the intermediate transfer member 15 passes through a contact portion (nip portion) between the support roller 18c and the transfer roller 19 that is in pressure contact with the intermediate transfer member 15, this nip. The portion is transferred onto the transfer target 20 inserted in the direction of arrow Q. The toner image transferred onto the transfer target 20 is fixed on the transfer target 20 when the transfer target 20 passes through the contact portion between the heat fixing roller 1 and the pressure roller 2 in the direction of arrow Q. An image is formed.

  The photosensitive member 11 transfers the toner image onto the outer peripheral surface of the intermediate transfer member 15 and then rotates in the direction of the arrow R. The toner remaining on the photosensitive member 11 is removed by the cleaner 16, and the photosensitive member 11 is moved onto the photosensitive member 11. The remaining residual charge is neutralized by the light neutralizer 17 to prepare for the next image formation.

  As the fixing device used in the image forming method of the present invention, a contact-type heat fixing device can be used, for example, a heat fixing roller having a rubber elastic layer on a cored bar and, if necessary, a fixing member surface layer, In addition to a heat roller fixing device comprising a pressure roller having a rubber elastic layer on a mandrel and optionally having a fixing member surface layer, and a combination of such a roller and a roller, two members Any of the above can use a combination of a roller and a belt having a heating and / or pressure function, or a combination of a belt and a belt.

  For the base material (core) of the fixing member, a material having excellent heat resistance, strong strength against deformation, and good thermal conductivity is selected. In the case of a roller type fixing device, for example, aluminum, iron, copper, etc. In the case of a belt-type fixing device, for example, a polyimide film, a stainless steel belt, or the like is selected. On the surface of the roller type substrate, an elastic rubber layer usually made of silicone rubber, fluorine rubber or the like is provided on the surface.

  The fixing member may contain various additives depending on the purpose. For example, the fixing member contains carbon black, metal oxide, ceramic particles such as SiC, etc. for the purpose of improving wear resistance and controlling resistance. May be.

  Next, the fixing process will be described in detail with reference to the drawings. FIG. 3 is a schematic configuration diagram showing an example of a fixing device used in the fixing step of the image forming method of the present invention. In FIG. 3, 1 is a heat fixing roller, 2 is a pressure roller, 3 is a heating source, 4 is a surface layer of a fixing member, 5 is an elastic layer, 6 is a toner image, and 7 is a transfer object (for electrophotography of the present invention). Transfer paper). Reference numerals 1 and 2 shown in FIG. 3 have basically the same functions as reference numerals 1 and 2 shown in FIG.

The fixing device shown in FIG. 3 is a device in which a fixing member has a roller shape, and the basic configuration thereof includes a heat fixing roller 1 and a pressure roller 2 disposed opposite thereto. The heat fixing roller 1 includes a heating source 3 for heating inside, and at least one layer such as an elastic layer 5 is provided so as to enclose the heating source 3, and the outer peripheral surface of the elastic layer 5. Is provided with the fixing member surface layer 4 located on the outermost periphery.
Further, the pressure roller 2 includes a heating source 3 for heating inside, and includes the heating source 3, and is provided with at least one layer such as an elastic layer 5 positioned at the outermost periphery. The heating source 3 may not be provided inside the pressure roller 2. The heating source 3 is controlled by a temperature control device (not shown) so that a desired heating temperature is obtained.

  The contact portion between the heat fixing roller 1 and the pressure roller 2 allows the transfer body 7 on which the toner image 6 is formed on the surface contacting the heat fixing roller 1 to be inserted in the arrow S direction. The toner image 6 is fixed by being heated and pressurized when the transfer body 7 passes through the portion, and an image is formed on the surface of the transfer body 7.

  Around the heat fixing roller 1, if necessary, a cleaning member for removing toner attached to the surface of the heat fixing roller 1, and a nail (finger) for peeling the transferred object 7 from the surface of the heat fixing roller 1. Etc. may be arranged.

  The heat fixing roller 1 and / or the pressure roller 2 are preferably provided with an elastic layer 5 having a single layer or a laminated structure, and the thickness of the elastic layer 5 is within a range of 0.1 to 3 mm. Is preferable, and it is more preferable that it is in the range of 0.5 to 2 mm. The elastic layer 5 is made of heat-resistant rubber such as silicone rubber or fluorine rubber, and the rubber hardness is preferably 60 or less. The fixing member having the elastic layer 5 is advantageous in that the fixing member is deformed following the unevenness of the toner image 6 on the transferred body 7 and the smoothness of the image surface after fixing can be improved. is there. When the thickness of the elastic layer 5 exceeds 3 mm, the heat capacity of the fixing member increases, and it takes a long time to heat the fixing member to a desired temperature, and energy consumption may increase. . If the thickness of the elastic layer is less than 0.1 mm, if the thickness is too thin, the deformation of the fixing member cannot follow the unevenness of the toner image, resulting in uneven melting, and distortion of the elastic layer effective for peeling. May not be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples, but of course, the scope of the present invention is not limited thereto. In the examples, “parts” and “%” indicate “parts by mass” and “% by mass” unless otherwise specified.

(Example 1)
A resin coating solution containing air bubbles having the following composition was prepared in commercially available coated paper with a basis weight of 157 g / m ² (JD Coat, Oji Paper Co., Ltd.), and immediately after foaming, the coated paper was coated using an applicator bar. Coating on one side (coating amount 15 g / m ² ) was performed to form a thermoplastic foam resin layer, and a paper having a basis weight of 172 g / m ² was obtained.
Subsequently, the cotton roll of TEST CALENDER (MODEL: 25FC, manufactured by Kumagaya Riki Kogyo Co., Ltd.) is removed, the temperature of the metal roll is set to 105 ° C., the speed is set to 4 cm / sec, and the paper image receiving layer is not provided. The surface void area ratio Ss46.2% and the cross-sectional void area ratio St48.3 of the upper layer are obtained by contacting the surface (back surface) with the metal roll and heating the thermoplastic foamed resin layer from the back surface. %, An electrophotographic transfer paper having a lower layer void area ratio Sb of 16.5% was obtained.

[Preparation of resin coating solution]
Thermoplastic resin A (styrene acrylic acid resin, John Crill 52, manufactured by Johnson Polymer Co., Ltd., softening point 105 ° C. by ring and ball method): 100 parts by mass Foam stabilizer (higher fatty acid type, DC100A, manufactured by San Nopco): 10 masses Part / Thickener (Carboxymethylcellulose, AG Gum SG, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 5 parts by mass Release agent (Polyether-modified silicone oil, KF-354L, manufactured by Shin-Etsu Chemical Co., Ltd.): 5 parts by mass Using a continuous foaming machine (trade name: Turbo Whip TW-70, manufactured by Aikosha Seisakusho Co., Ltd.), the resin coating liquid mixed with the components is mixed and stirred with air at a stirring speed of 1000 rpm, and the expansion ratio is 3 times. Foaming treatment was applied so that Here, the expansion ratio is a value obtained by dividing the mass of 100 ml of the resin coating solution (raw solution) before the foaming treatment by the mass of 100 ml of the resin coating solution containing bubbles after the foaming treatment.

(Example 2)
A thermoplastic foam resin layer on one side of the coated paper was used in the same manner as in Example 1 except that the resin coating liquid containing bubbles whose stirring speed was changed to 3000 rpm was used and the coating amount was changed to 18 g / m ^2. Was formed (basis weight: 175 g / m ² ).
Subsequently, this paper was subjected to a backside heat treatment in the same manner as in Example 1 to obtain a surface void area ratio Ss24.4%, an upper layer cross-sectional void area ratio St22.4%, and a lower layer cross-sectional void area ratio Sb8.6%. An electrophotographic transfer paper was obtained.

(Example 3)
A thermoplastic foam resin layer on one side of the coated paper was used in the same manner as in Example 1 except that a resin coating liquid containing bubbles with a stirring speed changed to 700 rpm was used and the coating amount was changed to 16 g / m ^2. Was formed (basis weight 173 g / m ² ).
Subsequently, this paper was subjected to a backside heat treatment in the same manner as in Example 1 to obtain a surface void area ratio Ss66.5%, an upper layer void area ratio St67.3%, and a lower layer void area ratio Sb43.6%. An electrophotographic transfer paper was obtained.

(Example 4)
A coating amount of 15 g / m ² and a basis weight of 172 g / s were used in the same manner as in Example 1 except that a resin coating solution containing bubbles having the following composition was used and the metal roll temperature used for the backside heat treatment was 50 ° C. An electrophotographic transfer paper having m ² , surface void area ratio Ss 45.2%, upper layer cross-sectional void area ratio St 43.3%, and lower layer cross-sectional void area ratio Sb 23.4% was obtained.

[Preparation of resin coating solution]
Thermoplastic resin B: ethylene acrylic resin (Zyxen AC, manufactured by Sumitomo Seika Co., Ltd., softening point 60 ° C. by ring and ball method): 100 parts by mass Foam stabilizer (higher fatty acid type, DC100A, manufactured by San Nopco): 10 parts by mass -Thickener (carboxymethylcellulose, AG gum SG, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 5 parts by mass-Release agent (polyether-modified silicone oil, KF-354L, manufactured by Shin-Etsu Chemical Co., Ltd.): 5 parts by mass Using a continuous foaming machine (trade name: Turbo Whip TW-70, manufactured by Aikosha Seisakusho Co., Ltd.), the resin coating liquid mixed with is mixed with air at a stirring speed of 1000 rpm and stirred to obtain a foaming ratio of 3 times. A foaming treatment was applied.

(Example 5)
It was produced in the same manner as in Example 1 except that the coating amount when forming the thermoplastic foamed resin layer was 5 g / m ^{2. The} basis weight was 162 / m ² , the surface void area ratio Ss was 45.3%, An electrophotographic transfer paper having a cross-sectional void area ratio of St. 41.3% and a lower layer cross-sectional void area ratio of Sb of 12.8% was obtained.

(Example 6)
It was produced in the same manner as in Example 1 except that the coating amount when forming the thermoplastic foamed resin layer was 28 g / m ^{2. The} basis weight was 185 g / m ² , the surface void area ratio Ss42.8%, An electrophotographic transfer paper having a cross-sectional void area ratio of 47.8% and a lower-layer void area ratio of Sb of 36.8% was obtained.

(Comparative Example 1)
Without foaming the resin coating solution prepared in Example 1, coating was performed on one side of a commercially available coated paper having a basis weight of 157 g / m ² (product name: JD Coat, manufactured by Oji Paper Co., Ltd.) (coating amount: 13 g / m ² ) to form a thermoplastic resin layer (image receiving layer), an electron having a basis weight of 170 g / m ² , a surface void area ratio Ss0%, an upper layer void area ratio St0%, and a lower layer void area ratio Sb0% Photographic transfer paper was obtained.

(Comparative Example 2)
The basis weight is 175 g / m ² , the surface void area ratio Ss is 18.6%, and the upper layer is the same as in Example 1 except that the stirring speed is 4000 rpm, the coating amount is changed to 18 g / m ² , and the backside heat treatment is not performed. An electrophotographic transfer paper having a cross-sectional void area ratio of St 19.4% and a lower-layer cross-sectional void area ratio Sb of 20.5% was obtained.

(Comparative Example 3)
The basis weight is 173 g / m ² , the surface void area ratio is Ss 8.1%, and the upper layer is the same as in Example 1 except that the stirring speed is 6000 rpm, the coating amount is changed to 16 g / m ² , and the backside heat treatment is not performed. An electrophotographic transfer paper having a cross-sectional void area ratio of St of 5.4% and a lower-layer cross-sectional void area ratio of Sb of 7.7% was obtained.

(Comparative Example 4)
The basis weight is 170 g / m ² , the surface void area ratio is Ss86.3%, the upper layer except that the stirring speed is changed to 500 rpm, the coating amount is changed to 13 g / m ² , and the back surface heat treatment is not performed. An electrophotographic transfer paper having a cross-sectional void area ratio of St. 83.3% and a lower-layer cross-sectional void area ratio of Sb of 86.0% was obtained.

(Comparative Example 5)
Remove the cotton roll of TEST CALENDER (MODEL: 25FC, manufactured by Kumagai Riki Kogyo Co., Ltd.) from the electrophotographic transfer paper before carrying out the backside heat treatment in Example 1, the temperature of the metal roll is 80 ° C., and the speed is 4 cm / set to sec, by heat-treating the surface (thermoplastic foamed resin layer side), the basis weight 172 g / m ² , the surface void area ratio Ss 10.5%, the cross-sectional void area ratio St 14.8% of the upper layer, An electrophotographic transfer paper having a cross-sectional void area ratio Sb of 40.7% was obtained.

(Comparative Example 6)
The basis weight is 159 g / m ² , the surface void area ratio is Ss 18.6%, and the upper layer is the same as in Example 1 except that the stirring speed is 4000 rpm, the coating amount is changed to ² g / m ² , and the backside heat treatment is not performed. An electrophotographic transfer paper having a cross-sectional void area ratio of St 19.7% and a lower-layer cross-sectional void area ratio Sb of 19.8% was obtained.

(Comparative Example 7)
The basis weight was 195 g / m ² , the surface void area ratio was Ss15.8%, and the upper layer was changed in the same manner as in Example 1 except that the stirring speed was changed to 4000 rpm, the coating amount was changed to 38 g / m ² , and the back surface heating treatment was not performed. An electrophotographic transfer paper having a cross-sectional void area ratio of St. 17.1% and a lower-layer void area ratio of Sb of 21.2% was obtained.

(Comparative Example 8)
A thermoplastic foam resin layer was formed on one side of the coated paper in the same manner as in Example 3 except that the coating amount was changed to 14 g / m ² using the resin coating solution containing bubbles used in Example 3. A formed paper (basis weight 171 g / m ² ) was produced.
Subsequently, this paper was subjected to a backside heat treatment in the same manner as in Example 1 to obtain a surface void area ratio Ss of 22.4%, an upper-layer cross-sectional void area ratio of St. 26.3%, and a lower-layer cross-sectional void area ratio of Sb of 37.6%. An electrophotographic transfer paper was obtained.

(Comparative Example 9)
On one side of the base material used in Example 1, 10 g / m ^{2 of} the resin coating solution containing the bubbles used in Example 1 was applied to form a first thermoplastic foamed resin layer, By applying 10 g / m ² of the resin coating solution containing the bubbles used in Example 4 on the surface of this layer to form a second thermoplastic foam resin layer, two layers of thermoplastic foam are formed. An image receiving layer provided with a resin layer is provided, and has an basis weight of 177 g / m ² , surface void area ratio Ss44.7%, upper layer void area ratio St43.3%, and lower layer void area ratio Sb48.6%. A transfer paper was obtained.

(Quality evaluation method)
Tables 1 and 2 show various evaluation results of the obtained electrophotographic transfer papers. The image forming conditions, the measurement methods for each evaluation, and the evaluation criteria for performing each evaluation shown in Tables 1 and 2 are as follows.

[Image formation]
Using the obtained electrophotographic transfer paper, an image was formed and evaluated by DocuCenterColor 500 (manufactured by Fuji Xerox Co., Ltd., provided with an oilless fixing mechanism similar to FIG. 3) having the same configuration as FIG. The image was output in the thick paper 2 mode of the DocuCenterColor500.

[Basis weight measurement method]
It was measured by the method of JIS P 8124.

[Method of measuring softening point by ring and ball method]
It measured according to JIS K 7234.

[Observation method of image receiving layer cross section]
A scanning electron microscope (Scanning Electron Microscope S-4200, manufactured by Hitachi, Ltd.) was used for observation of the cross section of the image receiving layer. As a sample preparation method for observing the cross section of the image-receiving layer, a sample for observing the cross section is prepared using a resin embedding method (embedded with epoxy resin and then processed into a thin piece with a microtome and a diamond cutter). did.

[Measurement method for air gap]
The surface void area ratio Ss of the image receiving layer, the cross-sectional void area ratio Sb of the lower layer, and the cross-sectional void area ratio St of the upper layer were measured using a scanning electron microscope (Scanning Electron Microscope S-4200, manufactured by Hitachi, Ltd.). After photographing the surface and cross section, the outlines of the pores (voids) in the surface and cross section are accurately drawn on a transparent film with a black pen or the like, and further, using a drum scanner (trademark: Luzex III, manufactured by Nireco) It was measured.
The surface void area ratio Ss, the lower-layer cross-sectional void area ratio Sb, and the upper-layer cross-sectional void area ratio St were obtained by preparing five observation samples from one transfer paper, measuring four locations per sample, It calculated | required from the average value of the measurement location (20 locations).

  Further, when measuring the cross-sectional void area ratio Sb of the lower layer and the cross-sectional void area ratio St of the upper layer, the thickness of the image receiving layer was measured at four locations in each sample, and the average value of all measurement locations (20 locations) was obtained. Then, a portion corresponding to 2/3 of the average thickness of the image receiving layer from the surface of the image receiving layer is an upper layer, and the remaining thickness (a portion corresponding to 1/3 of the average thickness of the image receiving layer from the base material side) is a lower layer. As a result, the measurement range was specified, and the cross-sectional void area ratios Sb and St were measured.

The surface void area ratio Ss and the cross-sectional void area ratios Sb and St were calculated based on the following equations (4) to (6).
Formula (4) Surface void area ratio Ss (%) = (total area of void portion on the surface of the image receiving layer) / (total surface area of the surface of the image receiving layer) × 100
Formula (5) Cross-sectional void area ratio Sb (%) = (total area of the void portion of the image-receiving layer lower layer section) / (total area of the image-receiving layer lower layer section) × 100
Formula (6) Cross-sectional void area ratio St (%) = (total area of void portion in cross section of upper layer of image receiving layer) / (total area of cross section of upper layer of image receiving layer) × 100

  Further, the average diameter of the voids existing on the surface of the image receiving layer (average void diameter) was also measured in the same manner as described above. Since the shape of the void formed on the surface of the image receiving layer is not necessarily a perfect circle, the average void diameter is a value converted to an equivalent circle diameter based on the area in the outline of the void obtained by the image analyzer. It was.

[Glossiness measurement method]
Based on the method of JIS Z 8741, a gloss measuring device (GM-26D type, manufactured by Murakami Color Research Co., Ltd.) was used, and the glossiness of the image portion after fixing was measured under the conditions of an incident angle and a light receiving angle of 60 degrees. .

[Evaluation of uniformity of gloss in image area]
A sample in which a color chart (S7) image of high-definition color digital standard image data (ISO / JIS-SCID JIS X 9201-1995 compliant, issued by the Japanese Standards Association) is formed on a transfer paper is prepared, and Δ The gloss uniformity was evaluated by determining the gloss. Here, Δ gloss is a value represented by the following expression (7).
Formula (7) Δ gloss (%) = maximum glossy part (%) − minimum glossy part (%)
The evaluations in Tables 1 and 2 are based on the following evaluation criteria.

-Δ gloss evaluation criteria-
◎: Δ gloss value is less than 5% ○: Δ gloss value is 5% or more and less than 10% △: Δ gloss value is 10% or more but less than 20% ×: Δ gloss value is 20% or more

[Evaluation of image step]
The height difference at the boundary between the non-image area and the image area was evaluated as an image step. The measurement method was an ultra-deep shape microscope (VK-8000, manufactured by Keyence Corporation), and the level difference between the image area and the non-image area was measured when an image was formed by fixing with a tertiary color of 100%. In addition, the value in a table | surface is an average value of the measured value of five places.

  As is apparent from the results in Tables 1 and 2, when an image is formed using the transfer paper of the present invention, a uniform and glossy color image can be formed without any image step, which is extremely useful in practice. I know that there is.

It is a schematic cross section showing an example of a cross-sectional structure of the electrophotographic transfer paper of the present invention. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus preferably used in an image forming method of the present invention. 1 is a schematic configuration diagram illustrating an example of a fixing device used in a fixing step of an image forming method of the present invention. It is a schematic cross-sectional view showing an example of a cross-sectional structure of a conventional electrophotographic transfer paper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal fixing roller 2 Pressure roller 3 Heat source 4 Fixing member surface layer 5 Elastic layer 6 Toner image 7 Transfer object (electrophotographic transfer paper)
DESCRIPTION OF SYMBOLS 11 Photoconductor 12 Roller-type charger 13 Exposure apparatus 14 Four-color developing device (14a, 14b, 14c, 14d)
15 Intermediate transfer member 16 Cleaner 17 Light neutralizer 18 Spindle roller (18a, 18b, 18c)
19 Transfer roller 20 Transfer object (electrophotographic transfer paper)
100 Thermoplastic foamed resin layer (image receiving layer)
100 'image receiving layer 101, 102 void 103 upper layer 104 lower layer 110 substrate

Claims (2)

In an electrophotographic transfer paper comprising a substrate and an image receiving layer provided on at least one side of the substrate and having a gap,
The electrophotographic transfer paper , wherein the image receiving layer is a thermoplastic foamed resin layer containing bubbles and satisfies the following formula (1).
Formula (1) Sb <St
[In the formula (1), Sb represents the void area ratio (%) of the cross section corresponding to the thickness of 1/3 from the surface side of the image receiving layer in contact with the substrate, and St represents the surface of the image receiving layer. Represents a cross-sectional void area ratio (%) of a layer corresponding to a thickness of 2/3. ] A latent image forming step of forming a latent image on the latent image carrier, a developing step of developing the latent image using an electrophotographic developer to form a toner image, and transferring the toner image to a transfer target A transfer step, and a fixing step of heat-pressing the toner image onto the surface of the transfer object,
The image forming method according to claim 1, wherein the transfer object is the electrophotographic transfer paper according to claim 1.

Images