Ink-jet recording material comprising pigment layers

Details Ink-jet recording material comprising pigment layers Ink-jet recording material comprising pigment layers

2000-04-28

2003-01-07

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Medium and processing means

C428S195100

Reexamination Certificate

active

06502935

ABSTRACT:

BACKGROUND, SUMMARY AND DESCRIPTION OF THE INVENTION
BACKGROUND of the INVENTION
The invention relates to a recording material for the ink-jet printing process.
The technology for producing color printouts has, in recent years, much increased in significance in conjunction with the overall expansion of the electronic media. The goal of this technology is the adaptation of the image quality of color printouts to the level of silver salt photography.
One important technology is the ink-jet printing method which has provided improved image quality in the last years. In the ink-jet printing method fine ink droplets are applied to a recording material. High demands are made of the ink-jet recording materials used in this technology. Such requirements are, for example, high resolution, high color density, no bleed, short drying time of the ink, light fastness as well as dimension stability. A further important requirement for commercial applications is the surface gloss. This is in particular important for the preparation of art graphics, but also for the creation of images which provide a photographic look.
EP 0 650 850 discloses a recording material which consists of a polyolefin coated base paper and a recording layer. This material allows the preparation of images with high resolution, color density and high gloss, which are comparable to common photographic images as far as their appearance is concerned. One disadvantage of this resin coated paper is the inferior ink absorption capacity which is due to the sealing action of the resin resulting in inferior drying properties of the recording material, which gives rise to ink bleed and poor overall image quality.
JP 10-119424 proposes a recording paper that comprises a hydrophobic support and two porous silica containing layers. The particle size of the silica in the upper layer is smaller than the particle size of the silica particles in the lower layer. A disadvantage of this recording material is the long drying time.
Glossy recording materials are known which are obtained by cast-coating the recording layer onto a support and treatment of the resulting product with an extremely smooth heated cylinder surface, whereby a recording material with a high glossy surface is achieved.
EP 0 450 540 B1 discloses an ink-jet recording material with a lower pigment layer on a support material and an upper pigment layer formed on the lower pigment layer. White aluminum oxide is the major pigment in both layers, aluminum oxide in the lower layer has a smaller specific surface area (<90m
2
/g) than Al
2
O
3
in the upper layer (90-170m
2
/g) . This recording material is described to provide a high color density and images with very slight indoor color changes.
SUMMARY of the INVENTION
The problem of the present invention is to provide a recording material for the ink-jet printing method with a high ink absorption capacity, a short drying time and good smear resistance properties. Moreover, this recording material shall allow the creation of images with high color density and gloss.
This problem is solved with a recording material that comprises a support material and pigment layers provided on the support material, wherein said pigment layers comprise a lower layer containing barium sulfate and an upper layer containing aluminum oxide as a main pigment. This problem is further solved by a recording material that comprises a support material and pigment layers provided on the support material, wherein said pigment layers comprise a lower layer containing barium sulfate and an upper layer containing a mixture of at least two pigments.
DETAILED DESCRIPTION of the INVENTION
The lower layer may contain besides barium sulfate as a major pigment, at least one further pigment. Particularly suited as a further pigment is aluminum oxide, silica and/or barium oxide. The aluminum oxide used in the invention is a so called active aluminum oxide which, for example, is obtained by calcination of aluminum hydroxide and which may have a specific surface area (BET) of 160 to 240 m
2
/g and an average particle size of 0.7 to 5 &mgr;m, preferably 1 to 3 &mgr;m. The silica which may be used according to the invention is preferably those which are obtained by precipitation and which may have a specific surface area (BET) of 30 to 800 m
2
/g. The silica obtained by precipitation may have an average particle size of 0.7 to 5 &mgr;m, preferably 3 to 5 &mgr;m.
The particle size of the barium sulfate which is used according to the invention may be 0.2 to 2.0 &mgr;m, preferably 0.7 to 1.2 &mgr;m. The mass ratio barium sulfate/aluminum oxide amounts to 4:1 to 1:1.
The use of an aluminum oxide or a silica in the lower layer improves the absorption capacity of this baryta containing layer. Accordingly, the applied coating weight of the upper layer may be reduced without impairing the absorption capacity of the recording material. With a reduction in the coating weight of the upper layer it is possible to eliminate the so-called “cracking-effect” which can occur during drying of the layer, especially at higher coat weights, and which impairs the image quality. Moreover, the modification of the baryta containing layer eliminates dusting problems and improves the adhesion to the support. In order to achieve these aims it is not required that the specific surfaces of the pigments used in the upper and the lower layer are different as, for example, disclosed in EP 0 450 540 B1.
The binder used in the lower layer may be selected from the group of hydrophilic colloidal and/or water soluble binding agents such as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, gelatin, starch, starch derivatives, casein, cellulosic esters, alginates, polyethylene glycols, polyacrylic acid or mixtures thereof. In particular suited as a binder in the lower layer is gelatin. Each kind of gelatin may be used. Preferably, a gelatin with a gel strength of 100 to 300 bloom, in particular 100 to 200 bloom (determined according to BIS 757, 1975) is used.
The mass ratio pigment to binder in the lower layer amounts from 1:1 to 10:1, in particular 1:1 to 8:1.
Further additives may be used in the lower layer such as crosslinking agents, dispersing agents, plasticizers and optical brighteners. The coating weight of the lower layer may be 5 to 30 g/m
2
, preferably 10 to 25 g/m
2
.
The pigment mixture of the upper layer consists of at least two finely divided pigments, the particle size of which shall not be larger than 500 nm. Particularly preferred is a mixture of aluminum oxide with a particle size of 50 to 150 nm and silica with a particle size of 200 to 300 nm. According to a particular preferred embodiment of the invention a mixture of a cationically modified aluminum oxide and a cationically modified silica is used. The mass ratio of aluminum oxide to silica may amount from 4:1 to 1:1.
According to the further embodiment of the invention the upper layer comprises barium sulfate and/or barium oxide in an amount of up to 50% by weight, relating to the dried layer.
The binder used in the upper layer may be selected from the group of hydrophilic colloidal and/or water soluble binding agents such as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, gelatin, starch, starch derivatives, casein, cellulosic esters, alginates, polyethylene glycols, polyacrylic acid or mixtures thereof. Particularly suited as a binding agent in the upper layer is polyvinyl alcohol, whereby a completely saponified polyvinyl alcohol with a high viscosity of 35 to 80 cP, in particular 50 to 75 cP, determined in aqueous solutions of a concentration of 4% by weight at 20° C. is particularly preferred. Also partially saponified polyvinyl alcohols or cationically modified polyvinyl alcohols may be used according to the invention.
The mass ratio pigment/binder in the upper layer amounts to 20:1 to 1:1, preferably 14:1 to 6:1 and more preferably 8:1 to 6:1.
The upper layer may contain further additives such as dye fixing agents, crosslinking agents, coloring pigments and optical brighteners. Examples of dye fixing

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