FI81644B - Paper laminate - Google Patents

Description

81 644

paper laminate

The invention relates to a paper laminate as set out in the preamble of claim 1.

At present, sulphate pulp-based paper chips are used, especially the so-called as sack paper for various types of packaging and wrapping purposes. There has been an increasing effort to add prints to packaging and wrapping papers containing different types of product information. Sulfate pulp-based paper grades 10 are of reasonable strength and, since they are most commonly unbleached kraft pulps, are inexpensive. However, the printing of these qualities in particular is problematic with current technology. The sulphate pulp-based paper forms a dark and rough background for the ink. Inks also tend to be absorbed through sack paper. From a printing point of view, it is only possible to apply FLEXO printing technology. In any case, the quality of the print is affected, the consumption of inks is relatively high and the contents of the packaging may show color defects caused by the inks.

On the other hand, alkaline sulfite-sulfide pulp-based papers are known, such as, for example, sulfite-based paper sold under the brand name SAP 25. A method of making this type of pulp and its cooking broth are disclosed in Finnish patent 67104. Sulphite pulp-based paper forms a good printing base, especially for printing. Paper made from this type of pulp 30 can be printed by four-color printing using known gravure printing methods. In addition, it should be noted that sulphite-sulphide pulp-based paper has very good tensile strength.

It is an object of the present invention to provide a paper laminate which can combine the advantages of sulphate pulp-based paper and alkaline sulphite-sulphide pulp-based paper so as to obtain a low-cost paper laminate for use in particular for packaging and wrapping purposes, said laminate having good or very good printing properties using gravure printing methods. With respect to the cost structure 10 of competing products, the paper laminate according to the invention provides cost savings of up to 10-20%.

To achieve this object, the paper laminate according to the invention is mainly characterized by what is stated in the characterizing part of the appended claim.

The laminate 20 provided by the sulphate pulp-based first layer and the alkaline sulphite-sulphide pulp-based second layer formed on at least the second surface thereof has in itself good gravure printing properties on the outer surface of the second layer.

The printing properties can be further improved by calendering the second layer. Further, the second layer may be coated with a coating prepared for gravure printing methods.

It is clear that the proportion of sulphate pulp-based first layer in the total weight of the paper laminate is to be maximized, of course taking into account the functional properties of the paper laminate. Thus, the first 30 layers account for 50-90% of the total weight (g / m2) of the paper laminate. In practice, a suitable range is probably 60-80%. Correspondingly, the proportion of the second layer (g / m *) is 5-10%. In practice, a suitable proportion is probably 40-20%.

3 81 644

It will be appreciated that the amount of coating applied to the outer surface of the second layer to achieve certain intaglio printing properties is significantly less than the amount of coating that would be required to provide the corresponding intaglio printing properties on the surface of the first layer. The amount of coating can be considered very reasonable, about 10-20 g / m2.

The paper laminate can be made using a conventional wet process technique with a double former, in which a web forming the first layer is fed from the first former to the wire. After the first former, at a suitable distance in the direction of travel of the web, there is a second former from which a web forming the second layer 15 is fed onto the web forming the first layer. Calendering follows the normal papermaking steps. The coating of the paper laminate can be performed with a separate coating unit. It will be appreciated that an additional former may be placed in front of the first former to feed a second layer of paper to the paper laminate to form sulphite-sulphide pulp-based second layers on either side of the first layer.

The manufacturing technique of the paper laminate will not be explained in more detail in this context, since the person skilled in the art can easily solve the problems encountered in the manufacturing technique with the available knowledge.

The following is a description of a series of experiments used to map the advantages of the paper laminate according to the invention.

4,81644

series of experiments,

1. Abbreviations

Sa = sulphate pulp of sack paper 5 SAP = semi-alkaline sulphite-sulphide pulp WEX = sack paper made from sa on a production scale paper machine WD = 2-ply sack paper:

base layer from sa and surface layer from SAP WDC = calendered WD

SAW = coated sa paper

WDW = coated WD

^ WWW = coated WDC

2. Paper test run

The test run was performed on a pilot plant paper machine (Keskusla-2Q boratorio).

3. Paper strength values

The purpose of the test run was not to optimize the strength values, nor can a pilot plant produce a paper with a strength equivalent to that of paper produced on a production scale paper machine. An example of this is shown in the following table in a test paper made of 3Q WEX series

Tensile index, see Nm / g 90 80 "ps" 60 35

Elongation, see% 5.5 2.0 M ps "7.0 4.0

Fractional index, see J / g 3.0 1.2 35 "ps" 2.8 1.0 5 81644 4. Coating

Dry matter (range) SPS Kaolin (1) 71.2% 60-80% 5 Alpatex Organic pigment 17.8% 10-25%

Dow-latex Binder (2) 9.8% 5-15% CMC 0.9% 0-2%

Glyoxal 0.3% 0-1% Ιΰ'ό ', ό * (1) can be replaced by eg talc (2) can be replaced by other latexes

Pasta 60% dry matter + 40% water 5. Test coating 15 Coating experiments were performed on a test coating machine (Central Laboratory).

The options were SAW, WDW, WWW.

With a coating volume of 10-12 g / m2, the following results were obtained:

SAW WDW WWW

Sileys, Bendtsen, ml / min 300 150 70

Kiilto, Kieser, ° 12 14 18 25 Brightness,% 45 70 75 6. Printing tests 30 WDC and WWW were printed with a 4-color offset printing machine (Hämeen Kirjapaino).

WDC was possible to print with offset, the coverage was good with normal ink amounts, but the luster of the trees-35 was due to the low gloss.

6 81644 The WWW gave a great print and according to professional printers the paper was very good on the press and the print was excellent.

7. WWW on paper machine 5 It is clear that the quality of coated paper improves when calendering and coating takes place in a production scale. This also applies and especially to the strength of the paper.

Claims (6)

1. Paper laminates manufactured by applying wetting process technology and intended to be used for packaging purposes such as sacking accessories, characterized in that it comprises as a combination: a sulfate pulp-based first layer and an alkaline sulfite-sulfide pulp-based second layer one surface of the first layer. Paper laminate according to Claim 1, characterized in that it is calendered with calendering directed to at least the second layer. Paper laminate according to claim 1, characterized in that the proportion of the first layer of the total weight (g / m) of the paper laminate is 50-90%, preferably 60-80%, and the proportion of the second layer in a corresponding manner ( g / m) 50-10%, preferably 40-20%. Paper laminate according to claim 1, characterized in that the second layer is coated. Paper laminate according to claims 1 and 4, characterized in that the amount of the coating is 10-15 g / m2. Paper laminate according to claims 1, 2 and 4, characterized in that the second layer exhibits color printing produced by gravure printing.