Patent Application
20150119600
Not applicable.
Not applicable.
Chemical pulps (Kraft) have excellent strength properties and a high brightness value. These attributes, however, are obtained at the cost of low yields and the highly negative effect produced on the environment by the effluent from the bleaching process. Typically speaking, the brightness of the Kraft pulp is 88 in ISO standards.
Within the last few decades, there has been some intensive development work aimed at producing mechanical pulps in high yields to about 90% with high brightness values, and with strength properties approaching those of the chemical pulps while at the same time retaining the opacity and bulk properties unique to the mechanical pulps. The resulting pulps, while quite strong, are often highly colored mostly due to the colored chromophores present in lignin. Bleached mechanical pulps would usually achieve a brightness of 84 in ISO standards.
In recent years, the consumers' pursuit for ultra-bright paper has pushed the market demands for more products with a brightness of 90-110 in .ISO standards. In order to produce these ultra-high brightness products, optical brightener agents (OBA's) or fluorescent whitening agents (FWA's) must be utilized.
OBA's or FWA's have chemical properties that absorb light in the UV and violet region (340-370 nm) and then re-emitting it back into the visible spectrum, usually in the color blue (420-470 nm). The absorption and re-emission happen at a rapid pace unlike the slow phosphorescence behaviour. The newly added blue light combined with yellowness of paper products will have a net whitening effect.
There is an ongoing need for improved brightness with low cost and with greater stability of the optical properties, i.e. decreased reversion such as yellowing caused by overdosage, and photoyellowing.
One of the biggest hurdles to using conventional OBA is the limit on overdosing. This is especially prominent in lower brightness paper that has significant mechanical pulp present. As an increasing amount of excess conventional OBA has been input into the system, the paper materials coming off the machine would have more of a yellow tinge due to the natural appearance of the conventional OBA.
The new generation OBA 351 does not encounter this problem as it has a totally different molecular structure which exhibits an almost pure white appearance. There is a plateauing effect for brightness gain associated with injection (at which point the cost effectiveness decreases), but the paper products will no longer have a yellowish tinge. In short, the machine tender can inject as much OBA. as needed to increase the brightness, without the risking yellowing caused by overdosing.
Secondly, the retention rate has also been improved significantly. Due to the fact that OBA 351 is in a different chemical family, its large number of ethylene bonds allows better interactions with the fibres. This is a totally different case than the conventional OBA, which relies heavily on Van de Waals forces for charge binding. Instead of having a significant amount of conventional OBA left over in the white water system for a prolonged period of time after injection has ceased, a sharp decrease in concentration for the OBA 351 in white water can be observed.
Lastly, conventional OBA will cease to exist in the near future due to the nature of its scarce and toxic raw materials. This means a replacement for the conventional OBA is an urgent and top priority matter. OBA 351 is both biodegradable and environmentally friendly, which will allow a much simpler sewage treatment.
The present invention relates to a novel, low-cost method of producing high final brightness values in paper production not previously achieved, and reducing brightness reversion of paper material.
According to the present invention there is provided an OBA for making high brightness paper. The usage of the OBA comprises of approximately 0.01%-1.0% by weight OBA 351 based on dry weight at a temperature of 30° C.-80° C.
By using the inventive process, an ISO brightness value of at least 120 is preferably obtained, still more preferably an ISO brightness value of at least 130 is obtained.
The invention provides several advantages over conventional OBA's:
1. Lower cost benefits due to the decreased addition of OBA while still achieving the same, or greater, ISO brightness values.
2. Increased brightness values for paper materials over conventional OBA's. This increases the number and variety of applications for the product, significantly expanding its marketability.
3. Environmental benefits from switching from conventional OBA's.
The invention and its advantages will be illustrated in more detail by the examples below which however, are only intended to illustrate the invention without limiting the same. The percentage and parts stated in the description, claims and examples refer to percent by weight and parts by weight, respectively, unless otherwise stated.
The invention will be further described with reference to the following non-limiting examples:
Pulp brightness (ISO brightness) is measured with a brightness meter, which determines the brightness of a split sheet at a wavelength of 457 nm (ISO D65 Standard Method).
The OBA's described in this invention are the following:
1. OBA 351 has a chemical name of 4,4″-B s(2-sulfostyryl)biphenyl disodium salt (100% purity), and a CAS number of 27344-41-8.
2. Disulfo-stilbene based OBA has a chemical name of Disodium 4,4′-bis[(4-anilino-6-hdroxyethylamino-1,3,5-triazin-2-yl)amino]stilbene-2,2′-disulphonate] (100% purity), and a CAS number of 12224-06-5.
3. Tetrasulfo-stilbene based OBA has a chemical name of Tetrasodium 4,4′-bis[[4-[bis(2-hydroxyethyl)amino]-6-(4-sulphonatoanilino)-1,3,5-triazin-2-yl]amino]stilbene-2,2′-disulphonate] (100% purity), and a CAS number of 16470-24-9.
The incoming samples of 30% Kraft and 70% mechanical pulp mixture (from a pulp mill in British Columbia, Canada) with a brightness of 78 ISO and a concentration of 0.7%, was treated with three different OBA's 40° C. and 5 minutes of retention time.
From the results shown in TABLE 1, it is evident that under the same dosage, OBA 351 can obtain a significantly higher brightness value compared to the conventional OBA's when used on production that requires more mechanical pulp than Kraft pulp.
The incoming paper samples (from a paper mill in British Columbia, Canada) with brightness of 84 ISO were coated with coating color and two different OBA's.
From the results shown in TABLE 2, it is evident that under the same dosage, OBA 351 can obtain a significantly higher brightness compared to the conventional OBA's when used on production that requires coating materials.
The incoming samples of 100% Kraft pulp (from a pulp mill in British Columbia, Canada) with a brightness of 88 ISO and a concentration of 1.0%, was treated with three different OBA's at 40° C. and 5 minutes of retention time.
From the results shown in TABLE 3, it is evident that OBA 351 has a plateauing effect with whiteness as the dosage is increased, whereas the two conventional OBA's causes yellowing once overdosing occurs.
A plant test was performed at a pulp and paper mill in British, Columbia, Canada, Incoming pulp with 86 ISO brightness and a concentration of 0.7% was used to make paper products.
From the results shown in TABLE 4, it is evident that the new OBA 351 was able to obtain an additional 16 points of ISO brightness. Therefore, it is clear that OBA 351 is effective in stabilizing paper and has a high affinity for paper essential.
In the following references of related patents, optical brighteners, optical brightening agents (OBA's) and fluorescent whitening agents (FWA's) refer to the same type of specialty chemical. The brightening, chemicals present in these patents do not solve the problem of yellowing caused by overdosage of OBA/FWA. In addition, none of the patents below discuss the use of OBA 351 on the application of wet-end and coating, papermaking process. U.S. Pat. No. 7,812,156 proposes a modified OBA which maintains the high solubility and strong fluorescent whitening effects of previous OBA's while decreases the anionic load that stresses the papermaking system. U.S. Pat. No. 7,566,349 explores the use of a new FWA of amphoteric bis-triazinylaminostilbene derivative on the process of whitening synthetic or natural organic materials such as paper. This new type of FWA is not usually suppressed in performance when put in the cationic papermaking environment or when combined with residual anionic FWA's. U.S. Pat. No. 3,790,443 presents a technique of utilizing a water-soluble hydroxymethylaminonitrile salt in the form of dry powder on papermaking materials to quench the fluorescence of optical brightening agents present in the papermaking materials. By adding an acid along with the quencher, some undesirable whitening effects of the OBA's could be neutralized. US20120211188 discloses the preparation techniques for a specific concentrated aqueous disulfo-stilbene based FWA for optically whitening paper. U.S. Pat. No. 8,475,630 introduces an aromatic ring based additive that can increase the retention rate of OBA's on paper materials, By using the aromatic ring on the additive to associate with the OBA molecules chemically, capacity for retention is improved. U.S. Pat. No. 7,789,917 reveals the composition of an amphoteric stilbene OBA, which consists of a substrate and the associated stilbene (one of 4,4′-diamino-2,2′-stilbene disulfonic acid, biarylsulfonate-4,4′-diamino-2,2′-stilbene disulfonic acid, biaryldisultbriate4,4′-diamino-2,2′-stilbene disulfonic acid, derivatives thereof, salts thereof, and mixtures thereof). U.S. Pat. No. 7,497,971 describes the use of a mixture of FAA's based on dicyano-1,4-bis-styrylbenzenes and bisbenzoxazoles, Such mixtures of two or more components may exhibit a higher degree of whiteness than that of the sum of the individual components alone. U.S. Pat. No. 8,262,858 and U.S. Pat. No. 7,9146,46 identify the use of oxidative agents for the paper process which enhances the performance of OBA's and chelants. By analyzing various stages of the papermaking process that involve oxidative compositions and processes that preserve and enhance the brightness and improve color of pulp or paper, it was found that the use of an oxidative agent could also reduce the photoyellowing of aged, bleached pulp materials. U.S. Pat. No. 7,638,016 proposes a method of brightening pulp fibres with at least one stilbene-based OBA after the last bleaching/extraction stage with a chlorine based bleaching agent. US20120199302 presents a new composition using at least two specific disulfo-stilbene based FWA for optically whitening paper or board. U.S. Pat. No. 5,064,570 introduces a new preparation method for fluorescent brightener that involves the use of specific water-insoluble aromatic or carbon-substituted fatty alcohol auxiliaries.
