Support material

Details Support material Support material

2001-02-27

2003-12-02

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S098000, C430S348000, C430S357000

Reexamination Certificate

active

06656572

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a support material for photographic and non-photographic imaging processes with a raw paper and at least one thermoplastic layer arranged on the front of the raw paper.
The principle is known of refining papers for photographic and non-photographic imaging processes by surface combination with at least one polyolefin layer by extrusion, co-extrusion, or lamination. The purpose of this is to improve the appearance and properties of the base material. Coating with polyethylene plays a major part in this.
For coating the front side of papers for imaging processes, low-density polyethylene (LDPE) is usually used. The advantages of this polymer lie mainly in the price and in the largely trouble-free processing. Thus, in particular, the extrusion of a film with uniform thickness is manifested without any problem. Photographic papers coated with polyethylene can undergo further processing without any problem; i.e. they can be coated with light sensitive emulsion layers. Very good adhesion between the gelatines of the photoemulsion and the coated paper can be achieved by corona treatment of the PE paper. Polyethylene coatings also feature a range of disadvantages in comparison with coatings with other polymers, however. Under thermal treatment, the LDPE molecules are inclined to cross-linking reactions, which substantially increases the melt viscosity. This mechanism leads to unevenness of the paper base layer which is to be coated, which result from the fibre structure, and which can only be compensated for to an unsatisfactory degree during the extrusion coating. This results in a reduction of gloss and smoothness of the coated paper. In addition, an increase may be observed in the thickness fluctuations in the middle image tones and what is referred to as mottle on the papers coated with photographic emulsions and developed.
Polypropylene does not feature these problems in thermoplastic processing. During processing, a drastic reduction in melt viscosity is observed, which can be explained by partial breaking of the polymer chains without subsequent cross-linking reactions. Polypropylene is accordingly clearly better suited than LDPE to equalize unevenness in the paper base layer which is to be coated, and so leads to an optically smoother surface of the extruded paper.
However, a series of problems arise at the coating of the polypropylene and during further processing. With polypropylene, a uniform coating thickness of the extruded film can only be applied with great difficulty during the extrusion coating, because the inadequate film stability of the film extruded from the nozzle leads, for example, to constrictions and therefore to considerable application fluctuations in the range of several g/m
2
. Papers which were coated with a polypropylene homopolymer or also with a polypropylene/polyethylene copolymer show, at the application of a photographic emulsion, a drastic deterioration in the adherence of the photographic emulsion to the carrier. This problem cannot be compensated for even by a stronger corona treatment. In addition to this, with the use of polypropylene/polyethylene copolymers, the polypropylene-specific properties are in part lost.
EP 0 880 065 A describes a photo carrier material which is characterised by an especially smooth surface and high rigidity. This carrier material consists of a paper support and a multi-layered film on the front side. The film is composed of at least three layers, and is biaxially oriented. For preference polypropylene films are extruded. Paper support and film are joined by means of an extruded polyethylene layer. Disadvantageous in this context are the high production costs and the inadequate adherence of the photographic emulsion. To improve the adherence, an additional adherence layer must be applied.
EP 0 880 066 A likewise describes a photo carrier material on a paper support and a multilayer polypropylene film. This film is extrusion-coated with a polyethylene. As a result, a readily-attainable adherence of the photographic layer is achieved, with a good surface, but this again increases the costs in relation to a standard photo support material. Disadvantages are again the adherence problems which arise between the polypropylene film and the extruded polyethylene layer.
JP 7 092 607 A describes a photographic carrier material coated with polyethylene with high gloss and good adherence. The single polyethylene layer contains, as its main constituent, a polyethylene manufactured by means of metallocene catalysts. The Mw/Mn ratio with this polyethylene is greater than 5. Disadvantageous with this paper is the inclination to mottle. No increase in rigidity can be achieved by means of this support material.
JP 7 270 969 A describes a photo carrier material which can be coated on the front side of a polyethylene layer and a polypropylene layer. In this situation the polypropylene layer can be applied as the upper layer. This results in a support material with a high gloss. The emulsion adherence with this formulation, however, is inadequate; adherence between the polymer layers is not satisfactory either.
In addition to the surface properties, the strength values of the support material play an important part. With the use of films on materials similar to films, good surface qualities and high rigidity values can be achieved. Properties such as resistance to tearing are in general impaired. With thermoplastic coated papers, with only one resin layer, strength properties such as resistance to tearing are, as a rule, good.
SUMMARY OF THE INVENTION
The object of the invention is to provide a support material for photographic and non-photographic imaging processes with a smooth surface, similar to a film, which on the one hand allows for good adherence of the photographic emulsion or the recipient layer, and, on the other, good adherence between the different thermoplastic polymer coatings, with good mottle behaviour, high rigidity and tearing resistance with, at the same time, low production costs.
The problem is solved by a support material comprising a raw paper provided with a thermoplastic layer on the front side, whereby the thermoplastic layer contains at least one polyolefin layer arranged on the raw paper and at least one polyethylene layer, and at least one of these layers contains a polyethylene obtained by means of metallocene catalysts. For preference, the polyethylene layer contains the metallocene polyethylene.
Metallocene polyethylenes are copolymers of the ethene with &agr;-olefins such as butene-1, hexene-1, or octene-1, manufactured with the aid of metallocene catalysts. These polyethylenes and there manufacture are known.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A polyethylene layer is applied onto the surface of a raw paper by means of (co) extrusion of at least one polyolefin layer and at least one polyethylene layer. The polyolefin layer is in this case located on the raw paper. The polyethylene layer is arranged above the polyolefin layer. For the polyolefin layer, a variety of different polyethylene types can be used, such as HDPE, MDPE, or LDPE. These polyolefins can be manufactured by means of Ziegler or also metallocene catalysts. The use of polypropylenes, polybutylenes, and other polyolefins is also possible.
For preference, the lower layer is a polypropylene layer. By means of this layer arrangement, the positive properties of the lower layer, such as uniform coating of the raw paper and high gloss, can be combined with the good adherence properties of the polyethylene.
The application weight of the polyolefin layer can be 10 to 35 g/m
2
, for preference 15 to 25 g/m
2
. The application weight of the polyethylene layer is 2 to 30 g/m
2
, for preference 10 to 20 g/m
2
. All known polypropylene types are suitable for the polypropylene coating. Propylene homopolymers and/or propylene copolymers can be used. Mixtures of polypropylene with other polyolefins can be used. Especially preferred are polypropylene types with long-chain branches (HMS type

Affiliated with

Also associated with

Rating

Support material does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Support material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Support material will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3111110