Paper coating

Paper making and fiber liberation – Processes and products – With coating after drying

Patent

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Details

Other Related Categories

427391, 428514, 428521, 101492, 524828, 162169, D21H 1936, D21H 1734, D21H 1958

Type

Patent

Status

active

Patent number

057593477

Description

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP95/0022400 filed on Jan. 23, 1995.


BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to binders for papercoating slips which permit uniform printability, containing a polymer prepared by the seed procedure and comprising temperature of from -80.degree. to +25.degree. C. and based on esters of acrylic acid or methacrylic acid, and to 100% by weight, based on B), of which monomers are butadiene, ethylenically unsaturated monomers.
The present invention furthermore relates to the use of these binders, aqueous dispersions thereof and paper coating slips containing such binders and papers coated therewith.
2. Discussion of the Background
In offset printing on coated papers, a frequently encountered problem specific to this printing process is nonuniformity of the print, which is referred to technically as mottling. It is to date one of the unsolved problems in this area and occupies both paper manufacturers and printers. This phenomenon is an effect which occurs especially in multicolor offset printing in halftones and appears as a type of cloudiness in the color effect. The nonuniformity in the print reproduction is quite evidently due to the fact that the printing ink is better accepted on some parts of the paper and less well accepted on other parts.
The causes of this nonuniform ink acceptance have not been clarified to date.
The reasons why a better understanding of this phenomenon has not been acquired to date in spite of intensive efforts relate on the one hand certainly to the complicated offset printing process and on the other hand to the no less complicated structure of the paper as printing material.
In addition to optimizing the properties of both the paper and the printing ink, these components must be tailored to one another as well as being adapted to the offset printing process.
From the point of view of the paper manufacturer, not only do process engineering parameters in the papercoating process have a major effect in the case of coated papers, but the physicochemical properties of the coating components also play a decisive role here. The binders used in the coating slips are particularly important.
In addition to natural products, such as starch, polymer emulsions based on styrene and butadiene or styrene and acrylates are predominantly used as binders for papercoating slips.
It is known that there is a substantially higher tendency to mottling when binders based on butadiene (co)polymers, eg. styrene/butadiene copolymers, are used for coated offset papers, in comparison with acrylate (co)polymers, eg. styrene/acrylate copolymers.
It is also known that emulsions based on styrene/butadiene can be mixed with acrylate emulsions.
Japanese Preliminary Published Application 90/169 800 describes latex mixtures for paper coating which comprise butadiene copolymers and acrylate copolymers and are said to result in homogeneous printing ink acceptance in the paper coat. The latex mixtures contain acrylate copolymers having an alkyl acrylate content of from 20 to 50% by weight and have a minimum film formation temperature of from 35.degree. to 80.degree. C.
Japanese Preliminary Published Application 82/191 392 discloses polymer mixtures for paper coating which consist of a butadiene copolymer and an acrylonitrile copolymer and impart high gloss to the print on coated paper.
Furthermore EP-A 099 792 discloses aqueous polymer emulsions containing a mixture of butadiene/styrene copolymers and acrylates of C.sub.1 -C.sub.8 -alkanols, and the use thereof in adhesives.
The unpublished European Application 93116834.8 (O.Z. 0050/44391) discloses the use of binder mixtures containing from 1 to 49% by weight of a polymer of (meth)acrylates and from 51 to 99% by weight of a polymer based on butadiene/styrene in papercoating slips.
The unpublished German Patent Application P 4325851.4 (O.Z. 0050/44029) discloses step polymers of (meth)acrylates (1st step) and styrene/butadiene (2nd step).


SUMMARY OF THE INVENTION

It is an object of the pres

REFERENCES:
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patent: 3875097 (1975-04-01), Sedlak
patent: 4064304 (1977-12-01), Fujita et al.
patent: 4336172 (1982-06-01), Marquardt et al.
patent: 5093405 (1992-03-01), Frankel et al.
patent: 5093449 (1992-03-01), Durney Cronin et al.
patent: 5354800 (1994-10-01), Suzuki et al.
patent: 5356683 (1994-10-01), Egolf et al.
patent: 5444118 (1995-08-01), Tsuruoka et al.

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