JPH043476B2 - - 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 polycarboxylic acid-based (co-)based bleaching agents are used as pre-bleaching agents. The present invention relates to a bleach pretreatment method characterized by using a polymer. (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), diethylenediaminepetaneacetic 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. The above-mentioned problems of conventional pretreatment agents can be overcome by using a specific pretreatment agent that is inexpensive and has low toxicity and exhibits a remarkable pretreatment effect even in a relatively low amount. A method for pre-bleaching wood pulp is provided. (Means and effects for solving the problem) The present invention provides a bleaching pretreatment agent of the general formula (However, in the formula, A ¹ and A ² are each independently hydrogen,
Represents a methyl group or -COOX ² , and A ¹ and A ² cannot be -COOX ² at the same time, A ³ is hydrogen,
represents a methyl group or -CH ₂ COOX ³ and A ³ is -
In the case of CH ₂ COOX ³ , A ¹ and A ² each independently represent hydrogen or a methyl group, and X ¹ , X ² and X ³ each independently or together represent hydrogen, a monovalent metal, a divalent metal, or an ammonium group. or organic ammonium group. ) A polycarboxylic acid (co)polymer (I) having a repeating structural unit represented by
It relates to a method for pre-bleaching wood pulp, characterized in that an amount of ~1 weight percent is used. The reason why the excellent pretreatment effect is achieved when the polycarboxylic acid (co)polymer (I) is used as a bleach pretreatment agent is not clear, but it is speculated as follows. In other words, when polycarboxylic acid (co)polymer (I) is used as a bleach pretreatment agent, polyvalent metals such as Mn, Cu, Fe, Ni, and Co present in wood pulp are eluted into the pretreatment bath. Alternatively, it is speculated that this is because polyvalent metals can be removed by dehydration after suspension, which reduces the adverse effects of polyvalent metals in the bleaching step following the pretreatment step. The raw material unsaturated carboxylic acids for obtaining the polycarboxylic acid-based (co)polymer (I) used in the present invention include acrylic acid, methacrylic acid, crotonic acid, monovalent metals, divalent metals, and ammonia groups thereof. , partially or completely neutralized products with organic amines;
(anhydrous) maleic acid, itaconic acid, fumaric acid,
Examples include citraconic acid or partially or completely neutralized products thereof with monovalent metals, divalent metals, ammonia, or organic amines. Monovalent metals include sodium, potassium, etc.
Examples of valent metals include calcium, magnesium, and zinc. In addition, organic amines include alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, and triethylamine; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, and dimethylethanolamine;
Examples include pyridine. Among them, sodium is the most preferred because it is inexpensive and industrially easily available. In order to obtain the polycarboxylic acid (co)polymer (I) used in the present invention, these raw material unsaturated carboxylic acids 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) hydrochloride, 4,4'-azobis-4-cyanovaleric acid, etc. It can be produced by a conventional method using a water-soluble azo compound or the like as a polymerization catalyst. In addition, alcohols such as methanol and isopropyl alcohol, tetrahydrofuran,
When polymerizing in organic solvents such as ethers such as dioxane, aromatics such as benzene, xylene, toluene, or ketones such as methyl ethyl ketone and methyl isobutyl ketone, organic solvents such as benzoyl peroxide, lauroyl peroxide, peracetic acid, etc. It can be produced by a conventional method using a peroxide, an oil-soluble azo compound such as azobisisobutyronitrile/2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. as a polymerization catalyst. In addition, in obtaining the polycarboxylic acid (co)polymer (I), within the range not impairing the effects of the present invention,
It is of course possible to copolymerize other monomers that are copolymerizable with the unsaturated carboxylic acid. Examples of other copolymerizable monomers include amide monomers such as (meth)acrylamide and t-butyl (meth)acrylamide; (meth)acrylic acid esters, styrene, 2-methylstyrene, vinyl acetate, etc. Hydrophobic monomers; vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, sulfoethyl (meth) Acrylate, sulfopropyl (meth)acrylate, 2
-Hydroxysulfopropyl (meth)acrylate, sulfoethylmaleimide or one thereof
Unsaturated sulfonic acid monomers such as partially or completely neutralized products with valent metals, divalent metals, asimonia, and organic amines; 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, glycerol mono(meth)acrylate, vinyl alcohol, and other hydroxyl group-containing unsaturated monomers; dimethylaminoethyl (meth)acrylate, dimethylaminopropyl Cationic monomers such as (meth)acrylamide; Nitrile monomers such as (meth)acrylonitrile; (meth)acrylamide methanephosphonic acid, (meth)acrylamide methanephosphonic acid methyl ester, 2-(meth)acrylamide-2
- Phosphorous monomers such as methylpropanephosphonic acid; ethylene, propylene, 1-butene, isobutylene, α-amylene, 2-methyl-1-butene, 3-methyl-1-butene (α-isoamylene), 1- Examples include α-olefin monomers such as hexene and 1-heptene. As the molecular weight of the polycarboxylic acid (co)polymer (I), those in the range of 800 to 80,000 are effectively used. If the molecular weight is outside this range, the pretreatment effect will not be sufficient. In the present invention, the polycarboxylic acid (co)polymer (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. In addition, even if the amount used exceeds the above range, the pretreatment effect commensurate with the increase in amount cannot be obtained, and conversely, the COD of wastewater
This is not preferable because it increases the load. In carrying out the present invention, it is of course possible to use the polycarboxylic acid (co)polymer (I) in combination with conventionally used bleach pretreatment agents such as aminocarboxylic acid salts and condensed phosphates. It is. 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 In a beaker with a capacity of 5, 30 parts of unbleached ground pulp as an absolute dry weight, 3000 parts of water at a temperature of 50°C, and acrylic acid with an average molecular weight of 4000 as a pretreatment agent were added.
0.06 part (0.2% based on pulp) of maleic acid (mole ratio 20/80) copolymer sodium salt was added, and the mixture was stirred at 50°C for 15 minutes. Next, the pulp was separated from the pretreatment bath by passing it through No. 2 paper, and then 1500 parts of water was passed through the pulp, followed by dehydration. The pulp obtained by pretreatment in this way has a volume of 500ml.
In a beaker, add water, hydrogen peroxide 4% (based on pulp), necessary to make the final pulp concentration 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 8 In place of the acrylic acid/maleic acid (molar ratio 20/80) copolymer sodium salt used in Example 1,
Polycarboxylic acid-based (co)polymer (I) shown in the table
The hydrogen peroxide consumption rate and the whiteness of the handmade sheet were measured in exactly the same manner as in Example 1, except that the same procedure was used as in Example 1. The results obtained are shown in Table 1.

[Table] Comparative Examples 1 to 10 In place of the acrylic acid/maleic acid (mole ratio 20/80) copolymer sodium salt used in Example 1, the second
The hydrogen peroxide consumption rate and the whiteness of the handsheet were measured in exactly the same manner as in Example 1, except that the bleach pretreatment agent shown in the table was used. The obtained results are shown in the second
Shown in the table.

【table】

Claims (1)

[Claims] 1. Before bleaching wood pulp with a peroxide bleaching agent, as a bleaching pretreatment agent, the general formula (However, in the formula, A ¹ and A ² are each independently hydrogen,
Represents a methyl group or -COOX ² , and A ¹ and A ² cannot be -COOX ² at the same time, A ³ is hydrogen,
represents a methyl group or -CH ₂ COOX ³ and A ³ is -
In the case of CH ₂ COOX ³ , A ¹ and A ² each independently represent hydrogen or a methyl group, and X ¹ , X ² and X ³ each independently or together represent hydrogen, a monovalent metal, a divalent metal, or an ammonium group. or organic ammonium group. ) The polycarboxylic acid-based (co)polymer (I) having a repeating structural unit represented by the following as a main structural unit and having a molecular weight of 800 to 80,000 is used in an amount of 0.05 to 1% by weight based on the bone dry pulp. A method for pre-bleaching wood pulp. 2. The bleaching pretreatment method according to claim 1, wherein the wood pulp is a high-yield pulp. 3. The bleaching pretreatment method according to claim 1, wherein the polycarboxylic acid (co)polymer (I) is an acrylic acid/maleic acid copolymer (salt). 4. The bleaching pretreatment method according to claim 1, wherein the polycarboxylic acid (co)polymer (I) is an acrylic acid/itaconic acid copolymer (salt). 5. The bleaching pretreatment method according to claim 1, wherein the polycarboxylic acid (co)polymer (I) is a polymaleic acid (salt).