JPH02240659A - Electrophotographic planographic printing plate material - Google Patents

Abstract

PURPOSE:To form an image having superior quality without causing damage by friction or scumming by printing by dispersing and incorporating a prescribed average particle size into an electrophotographic sensitive layer. CONSTITUTION:An electrophotographic sensitive layer 3 based on a mixture of zinc oxide particles 6 with an insulating resin binder 7 is formed on a sub strate 1a and particles 4 of benzoquanamine-formaldehyde condensation resin having 4-30mum average particle size are further dispersed and incorporated into the layer 3 to form many projections 5 on the surface of the layer 3. Since the projections 5 are formed by the dispersed hard particles 4, the mechanical wear of the electrophotographic sensitive layer itself can be prevented. The scumming of printed matter is prevented and a fine image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrophotographic lithographic printing plate material. More specifically, the present invention relates to an electrophotographic lithographic printing plate material that does not cause or has little occurrence of printing background staining caused by friction.

[Conventional technology]

Printing plate materials for direct plate making using electrophotography are disclosed, for example, in Japanese Patent Publication No. 47-47610 and Japanese Patent Publication No. 47-4.
No. 0002, Special Publication No. 18325, Special Publication No. 18325, Special Publication No. 18325, Special Publication No. 1971-
These are disclosed in Japanese Patent Publication No. 15766, Japanese Patent Publication No. 51-25761, etc., and these have an electrophotographic photosensitive layer of a photoconductive zinc oxide-resin dispersion system. Such printing plates have the advantages of being inexpensive, having relatively high sensitivity, and having a simple plate-making process, and are widely used in practical use.

To produce an electrophotographic printing plate, the printing plate material is submitted to a plate making machine and subjected to a corona charging, exposure, development and fixing process in the desired pattern, thereby forming the desired pattern on the photoconductive layer. A commonly used method is to form a patterned toner image.

The above development process can be classified into a dry development method using a mixture of toner and a carrier such as iron powder, and a wet development method using a developer in which toner is dispersed in an organic solvent such as Isopar.

When plate making is carried out using the above-mentioned wet development method, the resulting printed matter has advantages such as good halftone reproducibility, excellent resolution, and short plate making time.

Therefore, electrophotographic lithographic printing plates based on this wet development method are widely used.

Such an electrophotographic lithographic printing material needs to have various properties required as a lithographic printing material in addition to the image characteristics generally required as an electrophotographic material.

For example, as a plate material for offset printing, it is possible to make non-image areas hydrophilic by treating the surface of the electrophotographic photosensitive layer with an etchant, and in addition, a large amount of dampening water is used during printing. However, it is necessary to have excellent water resistance.

The electrophotographic photosensitive layer of the printing plate material is made by applying a paint consisting of a photoconductive pigment such as zinc oxide or titanium oxide, an insulating resin binder, a sensitizing dye, and a solvent to a support. It dries and forms.

Insulating resin binders used in electrophotographic photosensitive layers generally include highly hydrophilic acrylic ester copolymers, methacrylic ester copolymers, and vinyl acetate copolymers to prevent scumming during printing. Polymers, silicone resins, butyral resins, etc. are used. Additionally, for the purpose of improving image quality, paint physical properties, and mechanical strength of coating films, it is common practice to copolymerize functional groups such as acrylic acid, methacrylic acid, and ≠maleic acid to the above resins. There is.

However, the electrophotographic photosensitive layer using the resin binder as described above has a problem of insufficient surface strength and easy wear. For this reason, the electrophotographic photosensitive layer is easily damaged by pressure and friction during the manufacturing process of electrophotographic lithographic printing plate materials, during transportation, or during feeding in a plate-making machine, and toner adheres to the damaged areas. Therefore, when printing plates manufactured from such plate materials are used, printing background stains often occur.

In order to solve the second problem, attempts have been made to increase the pressure resistance of the electrophotographic photosensitive layer by using polystyrene resin or polymethyl methacrylate resin, which have a high glass transition temperature, as an insulating resin binder. However, when such a resin binder is used, the resulting photosensitive layer has low flexibility and flexibility, which tends to cause cranking when used as a printing plate, resulting in a decrease in stiffness resistance. This causes problems.

In addition, one way to increase the strength of the coating film is to increase the blending ratio of the insulating resin binder contained in the photosensitive layer forming material, but if the resin binder ratio is increased, the amount of zinc oxide As the compounding ratio decreases, the photoconductivity of the resulting photosensitive layer decreases, good image quality is not obtained, and the etching effect becomes insufficient, resulting in the resulting prints being smudged and unsatisfactory. Become something.

As a method for preventing printing stains caused by mechanical friction of the electrophotographic photosensitive layer, JP-A-59-40654 discloses a zinc oxide photosensitive material for offset printing in which particle sizes of 20 to 20 are added to the electrophotographic photosensitive layer. To form a large number of protrusions on the surface of a photosensitive layer by dispersing zinc oxide particles coated with an acrylic-butadiene copolymer and thereby to reduce the occurrence of printing stains caused by mechanical friction. is listed. However, zinc oxide particles coated with this acrylic-butadiene copolymer have a problem in that the resin has too high flexibility and is difficult to crush. In addition, printing plates using acrylic-butadiene copolymer-coated zinc oxide particles have poor electrophotographic properties, tend to cause fogging during platemaking, and tend to cause background stains on printed matter. Furthermore, the protrusions formed by the acrylic-butadiene copolymer-coated zinc oxide particles do not have sufficient hardness against mechanical wear.

The present inventors dispersed and contained zinc oxide aggregate particles obtained by bonding a plurality of zinc oxide fine particles with a styrene-butadiene copolymer in an electrophotographic photosensitive layer, thereby creating a large number of particles on the surface of the photosensitive layer. We considered forming protrusions. In this case, it was possible to eliminate the occurrence of printing stains caused by friction, but it was desirable to further improve the strength and hardness against mechanical wear.

Furthermore, both the method using the acrylic-butadiene copolymer coated zinc oxide particles and the method using the zinc oxide bound particles made of the styrene-butadiene copolymer include mixing and dispersing the resin and zinc oxide, drying, pulverizing, There is a problem in that it requires many steps such as classification.

Furthermore, the present inventors dispersed resin particles containing a benzoguanamine-formaldehyde condensation reaction product as a main component and having an average particle diameter of 10 to 60 in the electrophotographic photosensitive layer, thereby reducing the electron A method of forming a large number of protrusions on the surface of a photographic photosensitive layer was investigated. As a result, it was possible to eliminate the occurrence of printing stains caused by friction.

However, in order to eliminate printing stains caused by friction,
It is preferable that the particle size of the resin particles is 30- or more. However, when the content of resin particles with a particle size of 30- or more becomes high, there is a problem that the images of printing plates and printed matter become rough. .

In addition to the normal light source, H
There is also a strong desire to develop printing plate materials that can use light beams of various wavelengths such as e-Ne laser light and semiconductor laser light.

[Problems to be Solved by the Invention] The problems to be solved by the present invention are to solve the above-mentioned problems of lithographic printing materials using conventional electrophotographic methods, and to eliminate the occurrence of printing surface stains due to friction; An object of the present invention is to provide an electrophotographic printing plate material that has a small amount of image roughness and does not have rough images.

Furthermore, another problem to be solved by the present invention is that He-N
An object of the present invention is to provide an electrophotographic lithographic printing plate material having a spectral sensitivity recordable with light beams of various wavelengths such as e-laser light or semiconductor laser light.

[Means and actions to solve the problem]

The electrophotographic lithographic printing plate material of the present invention includes a conductive and water-resistant support, and an electrophotographic photosensitive layer formed over one surface of the support and containing a mixture of zinc oxide particles and a resin binder as main components. and a metal layer is formed on the electrophotographic photosensitive layer forming side of the support, and the electrophotographic photosensitive layer further contains a benzoguanamine-formaldehyde condensation reaction product as a main component. , and 4-30
It is characterized in that a large number of resin particles having a trending average particle diameter are dispersed and contained, thereby forming a large number of protrusions on the surface of the electrophotographic photosensitive layer.

The electrophotographic lithographic printing plate material of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory cross-sectional view showing the basic structure of the lithographic printing plate of the present invention.

In FIG. 1, the electrophotographic photosensitive layer side of a substrate 1 is coated with a layer 2 made of metal such as aluminum, thereby forming an electrically conductive and water-resistant support 1a. On this support la.

An electrophotographic photosensitive layer 3 containing as a main component a mixture of zinc oxide particles 6 (indicated by many dots) and an insulating resin binder 7 (forming a matrix) is formed. Further, particles 4 made of a benzoguanamine-formaldehyde condensation reaction product having an average particle size of 4 to 30 nm are dispersed therein, and thereby a large number of protrusions 5 are formed on the surface of the electrophotographic photosensitive layer 3. There is no particular limitation on the thickness of the electrophotographic photosensitive layer, but it is generally 20 to 30 mm.
It is a trend.

As the substrate used in the present invention, paper, a laminate of paper and a plastic resin film, or synthetic paper can be used. Although there is no particular limitation on the thickness of the substrate, it is generally preferable to use a sheet-like material with a thickness of about 100 to 170 mm.

The metal layer formed on the substrate is not particularly limited in type as long as it can impart conductivity to the support, such as aluminum, gold, silver, tin, lead, platinum, and brass. However, it is generally preferable to use aluminum in consideration of price and ease of handling.Although there is no particular limitation on the thickness of the metal layer, it is generally 5 to 50J! Im is preferable, and when it is too thin, the surface of the resulting support (photosensitive layer forming side)
If it is difficult to make it sufficiently smooth and is excessively thick, not only will the cost be high and it will be economically disadvantageous, but the resulting support and printing plate will be too rigid and difficult to handle. It will be inconvenient.

There are no particular limitations on the method of forming the metal layer, but generally,
It can be formed by adhering a metal foil having the above thickness onto the base. Furthermore, an anchor layer, such as a layer consisting of a polyacrylic resin emulsion alone or a mixture of a polyacrylic resin emulsion and casein, may be provided on the surface of the metal layer for the purpose of surface protection and enhancement of adhesion to the photosensitive layer. It is preferable that the surface of the metal layer to be adhered to the photosensitive layer has as high a smoothness as possible.

Zinc oxide photosensitive materials for lithographic printing plates generally contain a soft resin as a binder, so their surfaces are soft and are therefore susceptible to wear and damage. When such a soft surface is mechanically abraded, the electrophotographic sensitivity of the abraded area decreases, and when this area is exposed, the potential attenuation is less, so that it is less susceptible to abrasion during the development process. Toner adheres to the exposed areas, which often causes printing stains on printed matter and causes image deterioration.

However, since the electrophotographic photosensitive layer of the present invention has hard particles of a specific size scattered on its surface to form protrusions, mechanical abrasion of the electrophotographic photosensitive layer itself is prevented. This makes it possible to prevent background stains from occurring on printed matter.

Furthermore, by disposing a metal layer such as aluminum on the side of the electrophotographic photosensitive layer of the support, the surface of the electrophotographic photosensitive layer other than the protrusions formed by the resin particles can be made extremely smooth.
The particle size of the protrusion-forming resin particles used is also relatively small, making it possible to form a surface of the photosensitive layer having sufficient strength against friction.

The average particle diameter of the benzoguanamine-formaldehyde condensation resin particles in the present invention is 4 to 30 nm, and 10 to 20 nm.
It is preferable to use one classified as -. When the average particle size of the resin particles is larger than 30 pm, images on printing plates and printed matter tend to become rough. Also, it is 4
- If the particle size is smaller, the anti-wear effect will be reduced and printed matter will be more likely to be smeared.

The benzoguanamine-formaldehyde condensation resin particles are
Since it is not dissolved in the solvent of the electrophotographic photosensitive layer coating solution (generally an aromatic solvent such as toluene), it does not adversely affect the electrophotographic properties of the electrophotographic photosensitive layer.

In the electrophotographic photosensitive layer of the present invention, other organic pigments such as urea resin pigments, polymethyl methacrylate resin particles, etc. are used instead of the benzoguanamine-formaldehyde condensation resin particles.
High-density polyethylene fine powder, starch, and polyester resin particles, etc., and inorganic pigments such as aluminum hydroxide, alumina, spherical silica balloons, spherical aluminosilicate particles, calcium metasilicate, and titanium oxide, etc., can cause friction-induced Regardless of the presence or absence of printing background stains, electrophotographic characteristics deteriorate,
In addition, plate making fog and printing background staining occur, which are thought to be due to deterioration of desensitization properties, and therefore, a practically usable electrophotographic printing plate material cannot be obtained.

In the electrophotographic photosensitive layer of the present invention, the benzoguanamine-formaldehyde condensation resin particles having an average particle size of 4 to 30 are added to an ordinary photoconductive zinc oxide-insulating resin binder coating solution for electrophotographic photosensitive layers. It is formed by mixing and dispersing, coating this coating solution on a conductive and water-resistant support so that the film thickness becomes 20 to 30 kon (after drying), and drying.

In this electrophotographic photosensitive layer, the resin particles form a large number of protrusions on the surface of the photosensitive layer. The height of this protrusion is preferably 4 to 20 mm. Further, the amount of the resin particles added is 0.00% of the solid weight of the electrophotographic photosensitive layer coating liquid.
It is preferably 1 to 1.0% by weight, and 0.2 to 0.
More preferably, it is 6% by weight.

The insulating resin binder used in the electrophotographic photosensitive layer of the present invention may be composed of a single type of resin (or two types of resin).
A mixture of more than one type of resin binder may also be used. Examples of such resin binders include polyester resins, acrylic resins, epoxy resins, polycarbonate resins, melamine resins, butyral resins, silicone resins, polyurethane resins, polyamide resins, alkyd resins, polystyrene resins, xylene resins, and phenoxy resins. Resin etc. are used.

The electrophotographic photosensitive layer of the present invention includes 1. In addition to zinc oxide, mainly
For the purpose of improving electrophotographic properties such as sensitivity, various sensitizers and additives such as conventionally used photosensitive dyes and electron-accepting substances may be appropriately contained. In addition, in order to have sensitivity to the light beam of the wavelength of the semiconductor laser, in the photosensitive layer,
Compounds represented by the following formulas (1) and (II) having maximum sensitivity to light in the wavelength range of 700 to 1000 nts may be included as a sensitizer.

and [However, in the above formula, R1, Rz and R1 each independently represent C)Is, CJs, and C)l
x represents one member selected from CH=CHz group, preferably -CIlz C)l=cH! group, and X is B
r.

Cj! and! Atoms and C7! O, and preferably (/!04) To make a lithographic printing plate from the printing plate material of the present invention, first, in a dark place, corona is applied to the entire surface of the photosensitive layer of the printing plate material according to a normal electrophotographic method. The image is uniformly charged using a charger, and then reflected image exposure is performed using a light source such as a tungsten lamp, halogen lamp, xenon lamp, or fluorescent lamp, contact exposure is performed through a transparent positive film, or H
An electrostatic latent image is formed on the electrophotographic photosensitive layer by scanning exposure with a laser beam such as an e-Ne laser, an argon laser, or a semiconductor laser, and this electrostatic latent image is developed with toner by a conventional method. , this is heated and fixed to form a toner image on the plate.

The non-image area of the printing plate having the image thus obtained is subjected to desensitization treatment using a normal desensitization treatment liquid. Next, this printing plate is mounted on an offset printing machine and used for printing.

〔Example〕

Next, the present invention will be explained in more detail with reference to examples, but these do not limit the content of the present invention. In the examples, "parts" and "%" are used unless otherwise specified. , "parts by weight", and "% by weight".

Jitsushin LfLL The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., trademark: 5AZEX #2000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., trademark: LR-188)
Part 25 Rose Bengal 0.0
2 parts toluene 120
A mixture is prepared by dispersing the mixture of 1. parts with a sand grinder, and then 1. Add 0.4 parts of benzoguanamine-formaldehyde condensation resin particles (manufactured by Nippon Shokubai Co., Ltd.,
Trademark: Epostor (average particle size: 164) was added thereto, and the mixture was stirred and dispersed using a stirrer to prepare a coating solution for forming an electrophotographic photosensitive layer.

As a support, a composite sheet obtained by laminating a 10-thick aluminum foil on one side of a base paper having a basis weight of 80 g/rrf was used. An anchor layer was applied to the surface of this aluminum foil at the same time as the lamination to protect the surface.

This anchor layer was composed of a mixture of 60 parts of a polyacrylic resin emulsion (manufactured by Saiden Chemical Co., Ltd., trademark: Cypinol X-19) and 40 parts of casein.

The coating solution was applied onto the support and dried to form an electrophotographic photosensitive layer. The thickness of this photosensitive layer was 25 m (dry). The height of the many protrusions formed on the surface of the photosensitive layer is 15I! It was about m or less.

In order to evaluate the scratch resistance of the photosensitive layer of the obtained electrophotographic printing plate material, test pieces of the printing plate material were heated at 25°C and 250°C.
%RH and conditioned for 24 hours.Next, another printing plate material was placed on the surface of the electrophotographic photosensitive layer of this printing plate material test piece so that its back surface was in contact with the other printing plate material. A 3 kg weight (diameter 7 cm) was placed on the plate 1, and the upper plate material was pulled once by about 20 cm to damage the surface of the photosensitive layer of the lower plate material. Thereafter, plate making and printing were performed using this printing plate material test piece, and the degree of printing soiling in damaged areas (especially non-image areas) was sensory evaluated.

Plate making and printing were performed as follows.

That is, a plate was made using a 235 model plate making machine manufactured by Itek, and after being subjected to a desensitization treatment using an etchant (product of Itek), an offset printing machine (2800 manufactured by Ryobi) was used.
The image quality of the resulting printed matter was evaluated by observing and evaluating the image quality of the resulting printed matter, especially the scumming caused by friction.

The results are shown in Table 1.

Jitsuki fl The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., trademark: 5AZEX #2000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., trademark: LR-188)
25 parts sensitizer: the above-mentioned formula (■) [However, in the formula, R1 represents a CL CH=CHz group, and X is! 0.02 parts of toluene
A mixed solution was prepared by dispersing 120 parts of the mixed solution using a sand grinder.

Next, 0.2 parts of benzoguanamine-formaldehyde condensation resin particles (average particle size 16 m) similar to those in Example 1 were added to the mixed solution to prepare a coating solution for forming an electrophotographic photosensitive layer.

Next, using this coating liquid, an electrophotographic lithographic printing material was prepared in the same manner as in Example 1.

A test piece of the obtained electrophotographic printing plate material was heated at 25°C.
After conditioning for 24 hours in a dark place in a 50% RH atmosphere, the surface of the photosensitive layer was damaged in the same manner as in Example 1, uniformly charged with a corona charger, and then charged according to a predetermined pattern. Semiconductor laser light (5 mW, wavelength 780 nsi) was irradiated and scanned. Next, positively charged toner (manufactured by Itek) was applied to the electrophotographic photosensitive layer irradiated with laser light.
Development processing was performed using. After development, apply an etchant (I t
After desensitizing the specimen using an offset printing machine (Ryobi 2800CD, Synflo type)
The image quality of the resulting printed matter was observed and evaluated, especially for scumming caused by friction.

The results are shown in Table 1.

This] L [Discharge 1 The following composition: Zinc oxide (manufactured by Sakai Chemical Co., Ltd., trademark: 5AZEX #2000)
90 parts polyacrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., trademark: LR-188)
Part 25 Rose Bengal 0.1
A mixed solution containing 120 parts of toluene was dispersed using a sand grinder to prepare a mixed solution. This mixed solution was used as it was as a coating solution for an electrophotographic photosensitive layer without mixing resin particles, and was coated on the same support as in Example 1 to produce an electrophotographic lithographic printing material. Using the obtained electrophotographic lithographic printing material, plate making and printing were carried out in the same manner as in Example 1, and the printing background stain was evaluated.

The results are shown in Table 1.

Comparison 1 flLi An electrophotographic lithographic printing material was produced in the same manner as in Example 1, except that paper treated with electrical conductivity and water resistance was used as the support. Using the obtained electrophotographic lithographic printing material, plate making and printing were carried out in the same manner as in Example 1, and the printing background stain was evaluated.

The results are shown in Table 1.

In addition, instead of benzoguanamine-formaldehyde condensation resin particles (manufactured by Nippon Shokubai Co., Ltd.) with an average particle diameter of IEzm, particles with an average particle diameter of 32. An electrophotographic lithographic printing material was produced in the same manner as in Example 1 except that 0.1 part of OIn@ resin particles were used. Using the obtained electrophotographic lithographic printing material, plate making and printing were carried out in the same manner as in Example 1, and the printing background stain was evaluated.

The results are shown in Table 1.

Comparison (2) An electrophotographic lithographic printing material was produced in the same manner as in Comparative Example 3, except that paper treated with electrical conductivity and water resistance was used as the soil support. Using the obtained electrophotographic lithographic printing material, plate making and printing were carried out in the same manner as in Example 1, and the printing background stain was evaluated.

The results are shown in Table 1.

This 124 juice i As a sensitizer for the electrophotographic photosensitive layer coating solution, the above-mentioned formula (■
) [wherein R3 represents a CL CII= C11g group and X represents an I atom] was used, but an electrophotographic lithographic printing material was produced in the same manner as in Comparative Example 1. Using the obtained electrophotographic lithographic printing material, plate making and printing were carried out in the same manner as in Example 2, and printing background staining was evaluated.

The results are shown in Table 1.

Remaining days below Table 1 Evaluation results 1) Plate making and printing were performed without applying mechanical friction.

2) Evaluation of resolution and image reproducibility.

O: Good △; Slightly poor ×: Poor As Table 1 clearly shows, the electrophotographic photosensitive layers of the printing plate materials of Examples 1 and 2 according to the present invention are resistant to forced friction. It was possible to produce printed matter without background stains.

However, in Comparative Example 1.5, since no protrusions were formed on the surface of the photosensitive layer, the surface of the electrophotographic photosensitive layer was easily damaged by friction, resulting in a large number of stains on the printed surface.

In Comparative Example 2, the smoothness of the support was lower than that of a support with a metal layer such as aluminum, that is, the surface of the support was rough, so the anti-friction effect of the small-sized benzoguanamine-formaldehyde condensation resin particles was eliminated. It is thought that the

In Comparative Example 3, it was possible to obtain a printed matter that was resistant to forced friction and free from scumming during printing, but since it contained resin particles with a large particle size of 30 or more,
Image deterioration occurred, such as flickering in solid areas of the image and blurring in fine line images.

In Comparative Example 4, unlike Comparative Example 2, the effect of the benzoguanamine-formaldehyde condensation resin particles was not erased, and a printed matter was able to be obtained that was resistant to forced FJW and free from scumming during printing. Similar to Comparative Example 3, the problem of image deterioration occurred.

〔Effect of the invention〕

In the electrophotographic lithographic printing plate material of the present invention, a support having a metal layer such as aluminum on the side surface of the electrophotographic photosensitive layer is used, and benzoguanamine having an average particle size of 4 to 30 is contained in the electrophotographic photosensitive layer. - By dispersing and containing formaldehyde condensation resin particles, there is no or little damage to the electrophotographic photosensitive layer due to friction, etc. Therefore, it is possible to form images with excellent quality without or little staining on the printing surface. An electrophotographic printing plate material can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing the structure of the lithographic printing plate of the present invention. 1... Base body, 1a... Support body, 2...
...metal layer, 3...electrophotographic photosensitive layer, 4
... Resin particles containing a benzoguanamine-formaldehyde condensation reaction product 5 ... Protrusions, 6 ... Zinc oxide particles (indicated by dots), 7 ... Resin binder (forming a matrix).

Claims (1)

[Scope of Claims] 1. A conductive and durable support; zinc oxide particles formed on one side of the support;
an electrophotographic photosensitive layer containing a mixture with a resin binder as a main component, a metal layer is formed on the electrophotographic photosensitive layer forming side of the support, and a metal layer is formed on the electrophotographic photosensitive layer on the electrophotographic photosensitive layer forming side of the support. teeth,
Further, a large number of resin particles containing a benzoguanamine-formaldehyde condensation reaction product as a main component and having an average particle size of 4 to 30 μm are dispersed, thereby forming a large number of protrusions on the surface of the electrophotographic photosensitive layer. An electrophotographic printing plate material comprising: