CS196479B1 - Starch composition for finishing paper and cardboard - Google Patents

Description

The invention relates to a starch composition for refining paper and cardboard, in particular by spraying it onto a paper sheet.

Various types of modified starches, such as starches hydrolyzed, oxidized, etherified or esterified, have hitherto been used for the surface treatment of paper and board to improve the mechanical properties and flatness of the paper surface. These starches are applied to the paper and board in the form of a homogeneous solution, usually prepared by boiling starch in water, and applied by various coating systems located at or near the end of the paper machine. Said modified starches are not suitable for the paper surface treatment technology by spraying into the paper sheet in the screen section of the machine. This technology requires a heterogeneous aqueous suspension of non-lubricated starch, which only becomes colloidal upon heating in the first stage of drying the paper sheet, so starch does not act as a colloid in this process but as a mechanical particle filling the paper sheet. The use of individual modified starches results in an uneven distribution of the starch particles into the pores of the pulp, thereby producing paper that does not have the necessary mechanical properties and exhibits an uneven surface. This is because these starches do not correspond to their particle size ratio, the behavior of the particles in an aqueous suspension, and the overall behavior of the aqueous suspension, particularly with regard to sedimentation,

196 479

47β 478 spray technology requirements.

These disadvantages are solved by the starch composition according to the invention, which comprises 88 to 92% by weight native or bleached cereal starch, 2 to 5% by weight swelling starch having a particle size of 50 to 100 microns and 3 to 8% by weight swelling starch having a particle size of 100 to 400 microns. It may further comprise a hydrophilic hydrocolloid in an amount of up to 5% by weight. Most preferred is the use of corn and wheat starches.

The starch mixture according to the invention forms, after mixing in cold water, a heterogeneous suspension with sufficient sedimentation stability and a polydispersible particle which satisfies the pore size distribution in the paper sheet. As a special purpose suspension stabilizer, a water-soluble hydrocolloid, such as carboxymethylcellulose, carboxymethyl starch, thermally modified starches, and the like, may be used in the mixture. This starch mixture fills perfectly all pores of the paper stock after the spraying and allows the paper and the uniform surface to have sufficient strength and stiffness.

Example 1

For the preparation of 100 kg of starch mixture:

kg of unprocessed commercial starch 2 kg of swelling corn starch with a particle size of 50 to 100 microns 8 kg of swelling corn starch with a particle size of 100 to 400 microns

The swelling starch is prepared by gelatinizing a maize starch suspension on a drying cylinder and by specific sieving to obtain the necessary fractions. The mixture is prepared by dry mixing all ingredients. This starch composition is suitable for treating cartons and printing papers.

Example 2

For the preparation of 100 kg starch mixture ee will use the same amount of raw materials as in Example 1 except that ββ will use wheat starch powder instead of corn starch, the starch composition produced according to this example is suitable for treating technical papers.

Example 3

For the preparation of 100 kg of starch mixture:

kg of corn starch alkaline deproteinized

2.5 kg of swelling corn starch with a particle size of 50 to 100 microns

7.5 kg of swellable corn starch having a particle size of 100-400 microns are starved by stirring in 0.4% sodium hydroxide solution at 40 ° C for 4 hours, then neutralized and dried. All components of the composition are ee dry blended at the indicated ratio. This starch mixture is particularly suitable for treating packaging cartons.

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Example 4

For the preparation of 100 kg starch mixture ee shall use:

kg of bleached maize starch kg of swelling maize starch with a particle size of 50 to 100 microns kg of swelling maize starch with a particle size of 100 to 400 microns 5 kg of carbamymethylcellulose

Bleached starch is prepared by bleaching corn starch with a slightly alkaline solution of 1 to 6% sodium hypochlorite. This starch mixture is particularly suitable for finishing white fine paper.

Claims (2)

1. Starch blend for paper and board upgrading, characterized in that it contains 88 to 92% by weight of native or bleached cereal starch, 2 to 5% by weight of swelling starch having a particle size of 50 to 100 microns and 3 to 8% by weight of swelling starch having a particle size of 100 to 400 microns. 2. The starch composition of claim 1, further comprising a hydrophilic hydrocolloid, e.g., carboxymethyloellulose in an amount of up to 5% by weight.