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Filler Pre-treatment for Strength Improvement in Highly Filled Paper

IP.com Disclosure Number: IPCOM000218117D
Publication Date: 2012-May-21
Document File: 3 page(s) / 86K

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William Davis: ATTORNEY

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Filler Pre-treatment for Strength Improvement in Highly Filled Paper

Author: Joseph M. Mahoney, Ashland Incorporated

Because of the difference in the cost between paper fillers, such as calcium carbonate, and wood pulp, it is very beneficial for paper manufacturers to produce highly filled sheets.  One of the main reasons why highly filled sheets are not the industry standard currently is that a great deal of the strength of the sheet is lost as filler loading increases. Filler loading is often called ash content. Filler can be increased while maintaining or increasing paper strength by pre-treating the filler with organic polymers (micro-particles) such as those described in patent US 7,250,448. When used in conjunction with an amphoteric polymer as described in US patent 8,163,134 even better strength and paper machine runnability can be attained.

The amphoteric polymer system described in US 8,163,134 provides for the maintenance of most of the sheet strength as the ash content of a sheet is increased. The amphoteric polymer system works equally well when used as a pre-treatment for the filler or when added directly to the thick stock. The amphoteric polymer system will be referred to as Hercobond™ HA5305 or HA5305 in the remainder of this document. In an effort to gain an extra boost in sheet strength, a polymer described in US 7,250,448 was used as a pre-treatment for the filler in the system. The polymer from US 7,250,448 is a water-soluble associative inverse emulsion anionic copolymer which is normally used as a treatment for the thin stock to improve retention and drainage. The water-soluble associative inverse emulsion anionic copolymer will be referred to as PerForm™ SP7200 or SP7200 in the remainder of the document. It is also believed that a composition comprising cross-linked anionic or amphoteric polymeric microparticles, such as that taught in US 5,171,808, would be effective as filler pretreatment.

A two-day pilot paper making trial was conducted. Paper was produced on a pilot paper machine using precipitated calcium carbonate (PCC) as the filler. There were three main trial conditions

1.    Pretreatment of filler with SP7200 while HA5305 was added to thick stock

2.    Pretreatment of filler with both HA5305 and SP7200

3.    HA5305 and SP7200 added to the thick stock

All trial conditions were compared to control sheets at a low ash and a high as content. The low ash target was 20% (condition 1) and the high ash target was 30% (condition 2). The results are summarized in figure 1 and table 1. All listed condition numbers refer to Table 1. Figure 1 shows only day 1 trial data for clarity. Table 1 summarizes and uses averages from both days.

Figure 1: Z-directional tensile data from pilot paper making - trial day 1

Filler pre-treatment meant that a stirred slurry of PCC at 20% solids was first treated with HA5305 then treated with diluted SP7200 if dual chemical pre-treatments were used. Filler pretreatment with SP7200 was done at d...