Image carrying material for electrophotographic processes

The invention relates to an image carrier material for electrophotographic processes.

Electrophotographic processes produce a latent electrostatic image of an original on a semiconductor material, and this latent image can be made visible or developed through toners. The final product may be the semiconductor material itself (for example, zinc oxide paper) or an image carrier material on which the toner image is transferred to the semiconductor material (for example, a selenium drum). The second mentioned process currently represents the current state of the art as a copying process in the office equipment.

In recent years, the so-called color copiers have been increasingly accepted. They work based on the same process mentioned above, but with colored toners.

While the usual office copiers are predominantly used for text copying, for this reason it is satisfying to have a low-cost carrier material (eg plain paper), color copiers predominantly serve for the photocopying of images, and in this case, carrying materials are required. high quality.

US 5112717 describes an image-carrying material for electrophotographic processes, on the surface of which, the toner copying cup is printed a texture in order to give the image a surface similar to that of photographic paper. The image carrier material consists of a paper core provided with a front cover and one on the back, both made of plastics. The front cover is preferably of polystyrene and the back cover is preferably of a polyolefin.

The image-bearing material presented in the mentioned document has layers of plastic material on both sides and cannot give the user the sensation that the photographic paper offers. It also lacks other properties, such as superior white, antistatic qualities and the ability to write on the back.

The invention therefore aims to obtain an image carrier material for electrophotographic processes, which have the character of a photographic paper and ensure image quality that approximates that of a photograph.

Image carrier material for electrophotographic processes containing a base paper as a core material having applied on both sides of the base paper layers of thermoplastic resin and an antistatic layer applied on one of the thermoplastic layers, characterized in that on the layer of thermoplastic resin, not covered with the antistatic layer, there is a receiving layer for toner image, the receiving layer containing a polymer with an interface voltage> 32mN / m and a film forming temperature, according to DIN 53787, below 100 ° C.

In principle, any paper produced from bleached cellulose can be used as base paper.

The base papers may contain white pigments, such as titanium dioxide or calcium carbonate. They can be neutrally or basicly finished, for example, by means of reactive finishing agents such as alkyl-ketene dimers or succinic anhydride derivatives; they can be acid-finished, for example, with a resin finishing agent (copofonium) and aluminum sulfate; they can be treated to give them moisture resistance, for example, with melamine-formaldehyde resin or polyamide-amino-apichlorohydrin resins; and / or can additionally support faces by finishing finishing in the paper making machine serve, for example, to further strengthen the fibrous structure or to improve the properties of the paper surface, such as, increased gloss, by adding magnets. of optical gloss, for example, or of the antistatic properties by the addition of alkaline salts, for example, or an increased adhesion for the layers to be applied subsequently. Additives to increase adhesion or strengthen the structure are polymers such as, starch, cellulose derivatives, alginates, polyvinyl alcohol, polyacrylate dispersions, water soluble polyacrylic acids, styrene copolymers and other similar compounds.

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However, all the paper quality additives mentioned above are not absolutely necessary for the application of the invention.

The base paper described above is provided on both sides with layers of thermoplastic resin. The thermoplastic materials of the plastic layers, which are preferably deposited by a melt extrusion coating, are preferably 55 polyolefins such as polyethylene, polypropylene or clefine copolymers synthesized, for example, from ethylene together with other α-olefins or vinyl acetate or acrylic (meth) ester esters.

Polyethylene should be understood as low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). However, also compounds 60 with polystyrene, polycarbonate, polyvinyl and polyacrylics and polyurethanes are suitable for use as thermoplastic materials according to the invention.

The applied weight of the plastic coatings is approximately the same on both sides of the base paper if the thermoplastic materials used are the same. This ensures a smooth smoothness of the final product. When using different thermoplastic materials on the two sides, the different stresses must be balanced by applying weights that differ accordingly.

while the plastic layer applied on the back meets the requirements mentioned as such, the plastic layer on the front is adjusted to have good optical properties, ie to exhibit high light reflectance, high brightness and 70 degree high. white. It can also be adapted to the color requirements dictated by aesthetics or fashion by adding shades of color. High light reflectance and high brightness are obtained by adding white pigments, preferably titanium dioxide, and using optical gloss agents. Due to process technology, the amount of white pigments is usually between 10 and 25% by weight, but can reach up to 50% 75 by weight.

The receiving layer on the front, which is disposed of the plastic layer, contains as a vital component a polymer that ensures a good adhesion of the toner image to be transferred. The tests performed showed that the polymers having an interface voltage greater than 32 mN / m and a film-forming temperature, according to DIN 80 53787 below 100 ° C, correspond in particular. Such polymers are polystyrenes, polyacrylates, polyacrylate-methacrylates, ionomers, polyvinylidene chlorides, cellulose esters and copolymers of two or more butadiene monomers, styrene, acrylonitrile, an acrylic ester or an alkyl acrylic ester.

In addition, the receiving layers may advantageously contain finely divided silica, such as 85, silica modified with colloidal aluminum, as anti-adhesive agents, or may contain tinting paints, optical gloss agents, surface active agents or anti-adhesive agents. -spumanţi. However, these additives are not required for the functionality of the image carrier material.

The antistatic layer on the back, which is disposed on the plastic layer, contains 90 inorganic salts in a binder as an antistatic agent and preferably contains alkali salts, or organic sulfonic or carboxylic acids or alkaline salts thereof, or oxides. metal.

The antistatic effect, measured as surface resistance of the layer, should have values ​​between 10⁹ and 10¹³A / cm. in addition, good printing and writing properties can be conferred to this antistatic layer by choosing binders or other additives. In order to obtain good printing properties with non-aqueous or non-polar printing inks, the binder must be hydrophobic in nature; copolymers of two or more monomers comprising butadiene, styrene, acrylonitrile, acrylic acid esters and vinyl acetate correspond to this purpose. To give the material good properties compared to writing with pencil, silica is added which provides the necessary abrasion.

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All the usual systems that apply the coating material directly or indirectly to the roofing material through immersion drums, raster drums or nozzles and that measure this coating with scrapers, scrapers or sprayers, are suitable as coating installations for the receiving and antistatic layers. .

The individual layers of the image carrier material, according to the invention, have the following ranges of weights per unit area:

receptor layer - 0.1 +1 g / m² plastic layer -10 + 50 g / m² basic paper - 60 + 200 g / m² plastic layer -10 + 50 g / m² antistatic layer - 0.05 + 2 g / m².

The following properties are obtained or improved by forming the image carrier material according to the invention:

The receiving layer for receiving the toner material from the semiconductor material has a good temperature resistance and a high absorption capacity of the toner, so that only a small amount of residual toner remains on the semiconductor material. After fixation, a very good adhesion of the toner is obtained.

The plastic layer on the front ensures the image a good white background and brightness. It compensates for the irregularities of the base paper and gives a certain compressibility to the entire coverage on the front, which makes a more complete and better contact, between the transfer paper and the toner image, so that the toner transfer is more complete, not missing points appear in the image, and the elasticity of the image is improved.

The base paper represents the general support of the image carrier material; which provides the necessary strength and rigidity.

The back plastic layer gives the whole smoothness very good and clogs the pores of the base paper, so that the vacuum applied to the copier paper guide station between the transfer of the toner and the fixing of the toner retains its efficiency, thus ensuring the correct guide of the paper. , the optimal maintenance of the paper's smoothness and the intimate contact between the image carrier material and the preheating plates or the heated drum. In combination with the plastic layer on the front, this layer ensures the sealing of the base paper on both sides. As a consequence, the moisture content of the base paper remains relatively constant, even when the humidity of the environment varies considerably. The moisture content of a paper that is not coated with thermoplastic materials has a great influence on the electrical surface resistance and volume of the paper, so that the humidity variations of the environment lead in such a case to variations of the quality. image transmission.

The antistatic layer on the back improves the stacking capacity of the image-carrying material, which means that taking individual sheets of paper from one stack and placing individual sheets of paper on top of each other can be carried out smoothly, as it prevents the appearance of an electrostatic loads. However, the antistatic coating on the back of the image carrier should not be too pronounced, as it would perform toner transfer and toner adhesion on the front.

The additional ability to adjust print and write properties ensures the possibility of marking and entering information.

as a whole, the image carrier material thus made makes it possible to obtain high quality images and which the characteristics of a photographic paper.

In addition, this structure makes it possible to produce glazed images, by further processing the image, under pressure and temperature. For this purpose, for example, an over-limestone or a passage over a very shiny heated drum is sufficient, at a pressure 150 of about 10 bar and at a temperature of 180 ° C. This effect is not possible in the absence of a thermoplastic intermediate layer.

The following examples illustrate image carriers formed in this way.

EXAMPLE 155

A mixture of 70% by weight of cellulose-sulphate of whitewood was milled to a consistency of 4%, with a milling degree of 35 ° SR.

The following finishing agents were then added to the wood cellulose suspension:

0.5% by weight, cationic starch

1.0% by weight, amphoteric polyacrylamide 160

0.6% by weight, an alkyl ketene dimer

1.0% by weight, a polyamide-polyamide-epichlorohydrin resin

0.1% by weight, an epoxy fatty acid amide.

in a Fourdrinier machine with sanding rollers a basic paper was produced by

170 g / m². 165

This basic paper was coated in a tandem extruder with the following two layers of plastic, first on the back and then on the front, in each case after a crown pretreatment.

The composition of the back layer is:

70% by weight, HDPE (density = 0.950 g / cm²) 170

30% by weight, LDPE (density = 0.924 g / cm²)

The composition of the front layer is:

58.0% by weight, LDPE (density = 0.924 g / cm²)

27.73% by weight, LLDPE (density = 0.935 g / cm²)

17.73% by weight, titanium dioxide, rutile 175

0.2% by weight, ultramarine blue

0.2% by weight, antioxidant

0.07% by weight, metal stearate

0.07% by weight, cobalt violet.

The extrusion coating was made at a machine speed of 110m / min and at a melting temperature of 290 ° C. The deposited layers had the following weights:

g / m² for the back layer and

30g / m² for the front layer.

The following antistatic and receiving layers were produced in a dispersion machine, after prior corona treatment of the corresponding 185 plastic layer in each case. The respective aqueous coating materials were applied by means of an immersion roller, measured with a squeegee and dried in a hot air duct, at an air temperature of 90 ° C.

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<td>Antistatic layer A1</td><td>% by weight</td>

<td>Carboxylate styrene copolymer - acrylic ester</td><td> 43,5</td>

<td>Carboxylated styrene copolymer - acrylic butyl</td><td> 10,4</td>

<td>Metal oxide; acicular titanium dioxide, surface treated with zinc oxide and doped with antimony</td><td> 43,5</td>

<td>Surface active agent</td><td> 1,7</td>

<td>Trifunctional aziridine J</td><td> 0,9</td>

<td>Antistatic layer A2</td><td>% by weight</td>

<td>Styrene - butadiene copolymer</td><td> 64,6</td>

<td>silica; particle size of 3 + 6 pm</td><td> 7,8</td>

<td>Silica modified with colloidal aluminum</td><td> 20,7</td>

<td>Sodium polystyrene sulphonate</td><td> 5,2</td>

<td>Surface active agent</td><td> 1.7</td>

<td>E1 receptor layer</td><td>% by weight</td>

<td>Carboxylate styrene copolymer - butadiene</td><td> 100</td>

<td>E2 receptor layer</td><td>% by weight</td>

<td>Copolymer ester acrylic acid - vinyl acetate - vinyl chloride</td><td> 45,4</td>

<td>Silica modified with colloidal aluminum</td><td> 27,3</td>

<td>Pyrogenic silica</td><td> 27,3</td>

Different combinations of receiving and antistatic layers were applied to the paper coated with the two layers of plastic material, resulting in the following examples:

<td rowspan="2">Example</td><td colspan="2">Antistatic layer (g / m²)</td><td colspan="2">Receiving layer (g / m²)</td>

<td>A1</td><td>A2</td><td>E1</td><td>E2</td>

<td> 1</td><td> 0,2</td><td></td><td> 0,4</td><td></td>

<td> 2</td><td> 0,2</td><td></td><td></td><td> 0,9</td>

<td> 3</td><td></td><td> 0,7</td><td> 0,4</td><td></td>

<td> 4</td><td></td><td> 0,7</td><td></td><td> 0,9</td>

The following material was used as comparison examples:

V1 paper described above, coated on both sides with thermoplastic materials, but without receiving layer and without antistatic layer

V2 a simple commercial paper, that is a paper used for copying texts.

Testing methods

Photographic character: the final product, containing the image, has been evaluated, independently of the quality of the image, following whether it offers the sensation of holding a photographic image in the hand, according to the subjective sensation of the person performing the test, when it is reached, grasped or manipulated.

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Writing properties: The back side of the final product containing the image has been marked with a date stamp, a pen and an HB pencil. The evaluation was considered as the average value of the three individual results.

Image quality: The final image was evaluated visually, compared to the original.

Retrieval from a stack: retrieval of individual sheets from a copier stack was tracked to detect disturbances.

Scratch resistance: The final image was drawn under a jagged scraper whose six distinctive tips were disposed to the weight of different values ​​(up to a maximum of 100g). The image speed was 0.8 cm / s.

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235

All five test methods were evaluated by assessing them as. good. medium, weak.

<td>Examples</td><td>Photographic character</td><td>Writing properties</td><td>Image quality</td><td>Taking over from the stack</td><td>Scratch resistance</td>

<td> 1</td><td>good</td><td>good</td><td>Hi</td><td>Hi</td><td>Hi</td>

<td> 2</td><td>good</td><td>good</td><td>Hi</td><td>Hi</td><td>Hi</td>

<td> 3</td><td>good</td><td>good</td><td>Hi</td><td>Hi</td><td>Hi</td>

<td> 4</td><td>good</td><td>good</td><td>Hi</td><td>Hi</td><td>Hi</td>

<td colspan="6">Comparison</td>

<td>V1</td><td>environment</td><td>weak</td><td>average</td><td>weak</td><td>weak</td>

<td>V2</td><td>weak</td><td>good</td><td>weak</td><td>Hi</td><td>Hi</td>

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245

The good results of examples 1 + 4 were confirmed in other tests, according to the invention, in which the acid finishing of the base paper was selected, an additional finding of pressed finishing of the base paper, other thermoplastic materials mentioned in the text or other layers receivers or antistatic