JPH043477B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for pre-bleaching wood pulp,
For more information, see mechanical pulp (MP), ground pulp (GP), refined ground pulp (RGP),
Prior to bleaching high-yield pulps such as thermomechanical pulp (TMP) and chemical mechanical pulp (CGP) using peroxide-based bleaches, specific water-soluble copolymers are used as pre-bleaching agents. The present invention relates to a bleaching pretreatment method characterized by: (Prior Art) Wood pulp High yield pulps such as mechanical pulp (MP), ground pulp (GP), refined ground pulp (RGP), thermomechanical pulp (TMP), chemical mechanical pulp (CGP), etc.
Bleached using peroxide bleaching agents such as hydrogen peroxide, sodium peroxide, and peracetic acid. However, these peroxide bleaches are wasted because they are eluted from the wood pulp during bleaching or are decomposed by the catalytic action of polyvalent metals such as Mn, Cu, Fe, Ni, and Co that are present in the water used. Because of its consumption, wood pulp is pretreated prior to bleaching to remove the harmful effects of these polyvalent metals. This pretreatment is generally performed by immersing the wood pulp in a pretreatment bath consisting of water and a pretreatment agent at a temperature of room temperature to 70° C. or less, and then dehydrating the wood pulp. Conventionally used pretreatment agents include, for example, ethylenediaminetetraacetic acid (EDTA), diethylenediaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA). Aminocarboxylate salts such as diethylenetriaminepentamethylene phosphate (DTPMPA) and condensed phosphate salts such as tripolyphosphate are used. However, aminocarboxylic acid-based bleaching pretreatment agents have low effectiveness, are expensive, and are relatively toxic, which severely limits their use. In addition, condensed phosphoric acid-based bleach pretreatment agents become a causative agent of red tide when they flow into the sea through rivers and the like as wastewater. (Problems to be Solved by the Invention) The present invention bleaches wood pulp using a peroxide bleaching agent such as hydrogen peroxide, sodium peroxide, percarbonate, perborate, peracetic acid, or ozone. It is possible to overcome the above-mentioned problems with conventional pre-treatment agents by using a specific pre-treatment agent that is inexpensive and has low toxicity and exhibits a remarkable pre-treatment effect even in relatively small amounts. A method for pre-bleaching pulp is provided. (Means and Effects for Solving the Problems) The present invention uses an inorganic acid selected from acrylic acid, methacrylic acid, and salts thereof as a bleaching pretreatment agent before bleaching wood pulp with a peroxide bleaching agent. Saturated monocarboxylic acid monomers 50 to 99.9 mol% and hydroxyl group-containing monomers (excluding monomers containing both hydroxyl groups and sulfonic acid groups) 0.1
A water-soluble polymer (I) having a molecular weight of 1,000 to 80,000 obtained by using a proportion in the range of ~50 mol% is used in an amount of 0.05 to 1% by weight based on the bone dry pulp. The present invention relates to a bleaching pretreatment method. Although the reason why the water-soluble copolymer (I) exhibits excellent pretreatment effects when used as a bleach pretreatment agent is not clear, it is speculated as follows. That is, when water-soluble copolymer (I) is used as a bleach pretreatment agent, Mn, Cu, and
This is probably due to the fact that polyvalent metals such as Fe, Ni, and Co can be removed by dehydration after being eluted or suspended in the pretreatment bath, which reduces the negative effects of polyvalent metals in the bleaching process that follows the pretreatment process. It is inferred. The unsaturated monocarboxylic acid monomer, which is one of the raw material monomers for obtaining the water-soluble copolymer (I) used in the present invention, includes acrylic acid, methacrylic acid, or monovalent metals thereof, Examples include partially neutralized products and completely neutralized products using divalent metals, ammonia, and organic amines. Monovalent metals include sodium, potassium, etc., and divalent metals include calcium, magnesium, zinc, etc. In addition, organic amines include alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, and triethylamine; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, and dimethylethanolamine; and pyridine. etc. can be given. Among them, sodium is the most preferred because it is inexpensive and industrially easily available. Further, as the other hydroxyl group-containing monomer of the raw material monomer for obtaining the water-soluble copolymer (I) used in the present invention, for example, 3-methyl-
3-buten-1-ol (isoprenol), 3
-Methyl-2-buten-1-ol (prenol), 2-methyl-3-buten-2-ol (isoprene alcohol), 2-hydroxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono (meth)acrylate, polyethylene glycol monoisoprenol ether, polypropylene glycol monoisoprenol ether, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, glycerol monoallyl ether, α-hydroxyacrylic acid, N-methylol (meth)acrylamide, Examples include glycerol mono(meth)acrylate and vinyl alcohol. In order to obtain the water-soluble copolymer (I) used in the present invention, these raw material unsaturated monocarboxylic acid monomers and hydroxyl group-containing monomers may be polymerized using known techniques. For example, in the case of aqueous polymerization, persulfates such as sodium persulfate and potassium persulfate; hydrogen peroxide, 2,2'-azobis(2-amidinopropane)
It can be produced by a conventional method using a hydrochloride, a water-soluble azo compound such as 4,4'-azobis-4-cyanovaleric acid, etc. as a polymerization catalyst. In addition, alcohols such as methanol and isopropyl alcohol,
In the case of polymerization in organic solvents such as ether systems such as tetrahydrofuran and dioxane, aromatic systems such as benzene, xylene, and toluene, or ketone systems such as methyl ethyl ketone and methyl isobutyl ketone, benzoyl peroxide, lauroyl peroxide, peracetic acid, etc. organic peroxide system; azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4
It can be produced by a conventional method using an oil-soluble azo compound such as -dimethylvaleronitrile) as a polymerization catalyst. In addition, when obtaining the water-soluble polymer (I), other monomers copolymerizable with the unsaturated monocarboxylic acid monomer and the hydroxyl group-containing monomer may be copolymerized within a range that does not impair the effects of the present invention. Polymerization is of course possible. Other copolymerizable monomers include (meth)acrylamide, t-butyl (meth)
Amide monomers such as acrylamide; (meth)
Hydrophobic monomers such as acrylic acid ester, styrene, 2-methylstyrene, vinyl acetate; cationic monomers such as dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide; (meth)acrylonitrile, etc. Nitrile monomers; phosphorus-containing monomers such as (meth)acrylamide methanephosphonic acid, (meth)acrylamide methanephosphonic acid methyl ester, 2-(meth)acrylamide-2-methylpropanephosphonic acid; ethylene, propylene, 1-butene, isobutylene, α-amylene, 2-methyl-
α-olefin monomers such as 1-butene, 3-methyl-1-butene (α-isoamylene), 1-hexene, 1-heptene; crotonic acid; maleic acid, fumaric acid, itaconic acid, citraconic acid, aconite Examples include unsaturated dicarboxylic acid monomers such as acids. The molecular weight of the water-soluble copolymer (I) is 1000
~80000 can be effectively used. If the molecular weight is outside this range, the pretreatment effect will not be sufficient. In the present invention, the water-soluble copolymer (I) is used in an amount of 0.05 to 1 weight percent based on the bone-dry pulp. If the amount used is less than the above range, a sufficient pretreatment effect will not be obtained. Furthermore, even if the amount used is larger than the above range, the pretreatment effect commensurate with the increased amount cannot be obtained, and on the contrary, the COD load of the wastewater increases, which is not preferable. In carrying out the present invention, the water-soluble copolymer (I) can of course be used in combination with conventionally used bleach pretreatment agents such as aminocarboxylic acid salts and condensed phosphates. In addition, the bleaching pretreatment method of the present invention is not only effective for high-yield pulp, but also for various wood pulps such as deinked pulp (DIP), kraft pulp (KP), and soda pulp (AP). It is also effective as a bleaching pretreatment method. (Examples) Hereinafter, the present invention will be specifically explained using Examples, but the present invention is not limited to these Examples. Note that parts and % in the examples indicate parts by weight and % by weight, respectively. Example 1 30 parts of unbleached ground pulp as bone dry weight in a beaker with a capacity of 5, 3000 parts of water at a temperature of 50°C, and acrylic acid/isoprenol (molar ratio 75/25) copolymer with an average molecular weight of 20000 as a pretreatment agent. Add 0.06 part of combined sodium salt (0.2% to pulp) and 50
Stir for 15 minutes at °C. The pulp is then separated from the pretreatment bath by passing it through No. 2 paper, and then water is added to the pulp.
After passing 1500 parts of the solution, it was dehydrated. The pulp obtained by pretreatment in this way has a volume of 500ml.
In a beaker, add the water, hydrogen peroxide, 4% (based on the pulp) needed to reach a final pulp concentration of 12%,
3% No. 3 sodium silicate (based on pulp) and sodium hydroxide were added to adjust the pH to 11.1. This was transferred to a polyethylene bag, the inlet was turned back to prevent moisture from evaporating, and then heat treated in a water bath pre-adjusted to 60°C for 3 hours to perform bleaching. The bleached pulp is passed through 420 mesh cloth.
Dehydrated. The residual hydrogen peroxide concentration in the liquid was measured to determine the hydrogen peroxide consumption rate, and the results are shown in Table 1. A portion of the bleached pulp was diluted to 3% and the pH was adjusted to 4.0 using sulfite water. Using the obtained pulp slurry, two handsheets were made using the TAPPI standard method, and after air-drying, Hunter Whiteness was measured using a whiteness meter. The results obtained are shown in Table 1. Examples 2 to 10 The same procedure was carried out except that the water-soluble copolymer (I) shown in Table 1 was used instead of the acrylic acid/isoprenol (molar ratio 75/25) copolymer sodium salt used in Example 1. In exactly the same manner as in Example 1, the hydrogen peroxide consumption rate and the whiteness of the handsheet were measured. The results obtained are shown in Table 1.

[Table] Comparative Examples 1 to 11 Examples except that the bleach pretreatment agent shown in Table 2 was used instead of the acrylic acid/isoprenol (molar ratio 75/25) copolymer sodium salt used in Example 1. The hydrogen peroxide consumption rate and the whiteness of the handsheet were measured in exactly the same manner as in Example 1. The results obtained are shown in Table 2.

【table】

Claims (1)

[Claims] 1. Before bleaching wood pulp with a peroxide bleach, acrylic acid and
50 to 99.9 mol% of unsaturated monocarboxylic acid monomers selected from methacrylic acid and their salts, and monomers containing hydroxyl groups (excluding monomers containing both hydroxyl groups and sulfonic acid groups) The molecular weight obtained by using a proportion in the range of 0.1 to 50 mol% is 1000 to
1. A method for pre-bleaching wood pulp, which comprises using a water-soluble copolymer (I) of 80,000 in an amount of 0.05 to 1 percent by weight based on bone dry pulp. 2. The bleaching pretreatment method according to claim 1, wherein the wood pulp is a high-yield pulp.