technical field:
the invention relates to supporting materials used in photographic and non-photographic imaging technology by using base paper and at least one thermoplastic layer arranged on the front surface of the base paper.
The principle of refining paper for photographic and non-photographic imaging technology is that at least one polyolefin layer is used for surface bonding through extrusion, compound extrusion or lamination. Its purpose is to improve the appearance and performance of the base material. Coating with polyolefin is an important step.
low density polyethylene (LDPE) is often used to coat the front of paper for imaging technology. The advantages of this polymer are mainly that it is cheap and easy to handle. Therefore, it turns out that a film with uniform thickness can be extruded without any problem. Photographic paper coated with polyethylene can be further processed without any problem, that is, a photosensitive emulsion layer can be coated on it. Good adhesion between gelatin of photographic latex and coated paper can be achieved by corona treatment of polyethylene (PE) paper. However, compared with other polymer coatings, polyethylene coatings have a series of disadvantages. During heat treatment, LDPE molecules are prone to cross-linking reaction, which will significantly increase the melt viscosity. This mechanism leads to the unevenness of the paper substrate to be coated, which is caused by the fiber structure, and can only be compensated to an unsatisfactory degree in the extrusion coating process. This will lead to a decrease in gloss and smoothness of the coated paper. In addition, the thickness fluctuation in the tone of the intermediate image can be observed, which is called mottle on the paper coated with photographic emulsion.
polypropylene does not have these problems in thermoplastic treatment technology. During the treatment, the sharp decrease of melt viscosity was observed, which can be explained by the local fracture of polymer chain without subsequent crosslinking reaction. Therefore, polypropylene is obviously more suitable than LDPE to balance the flatness of the paper substrate to be coated, so as to obtain the optical smooth surface of extruded paper.
However, a series of problems occurred during the coating and further treatment of polypropylene. In the extrusion coating process, it is extremely difficult to obtain a uniform coating thickness of the extruded film with polypropylene, because the unsuitable film stability of the film extruded from the extrusion nozzle leads to, for example, shrinkage, which leads to great fluctuation of the coating amount in the range of several g/m2. Paper coated with polypropylene homopolymer or polypropylene/polyethylene * * * polymer shows a sharp deterioration in the adhesion between photographic latex and carrier layer when coated with photographic latex. This problem can't be compensated even with enhanced coronal light treatment. In addition, when polypropylene/polyethylene * * * polymer is used, the unique properties of polypropylene are partially lost.
EP 8865A discloses a photographic carrier material, which is characterized by a very smooth surface and high rigidity. This carrier material consists of a paper support and a multilayer film on the front of the paper. The film consists of at least three layers, which are oriented in two directions. Preferably, the polypropylene film is extruded. The paper support and the film are connected by an extruded polyethylene layer. The disadvantages of this document are high manufacturing cost and insufficient adhesion of photographic latex. In order to improve the adhesion, an additional adhesive layer must be applied.
similarly, EP8866A discloses a photographic carrier material on paper support and multilayer polypropylene film. This film is extrusion coated with polyethylene. As a result, the adhesive force required for the photographic layer is obtained, and the surface is good, but this increases the cost related to the standard photographic support material. There is also a disadvantage that there is an adhesion problem between the polypropylene film and the extruded polyethylene layer.
JP 79267A discloses a photographic carrier material coated with polyethylene with high gloss and good adhesion. The single polyethylene layer contains, as its main component, a polyethylene produced by means of a metallocene catalyst. The Mw/Mn ratio of this polyethylene is greater than 5. The disadvantage of this paper is that it is easy to form stripes. Stiffness cannot be increased with this support material.
JP 727969A discloses a photographic carrier material that can be coated on the front of a polyethylene layer and a polypropylene layer. In this document, a polypropylene layer can be used as an upper layer. This results in a supporting material with good luster. However, the adhesion between the material with this structure and the emulsion is not enough, and the adhesion between polymer layers is not satisfactory.
in addition to the surface properties, the strength value of the supporting material is also very important. Good surface quality and high stiffness can be obtained by using thin films or materials similar to thin films. Properties such as breaking strength are generally weakened. Generally speaking, when thermoplastic coated paper is coated with only one resin layer, the strength properties such as breaking strength are good.
The purpose of the present invention is to provide a supporting material for photographic or non-photographic imaging technology. This supporting material has a smooth surface, which is similar to film. On the one hand, it allows good adhesion of photographic emulsion or receiving layer, on the other hand, it also has good adhesion between different thermoplastic polymer coatings, as well as good speckle performance, high rigidity and breaking strength, and at the same time, the production cost is low.
the above object is achieved by a support material consisting of a base paper with a thermoplastic layer on the front, which has at least one polyolefin layer and at least one polyethylene layer arranged on the base paper, and at least one of these layers contains polyethylene obtained by means of a metallocene catalyst.