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(11) | EP 0 282 081 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for increasing paper strength |
| (57) Paper having increased strength is made by adding aluminum sulfate and a paper strength
agent containing a copolymer comprising (a) 98 to 60 % by mole of repeating units
derived from (meth)acrylamide, (b) 1 to 20 % by mole of repeating units derived from
at least one compound selected from the group consisting of α,β-unsaturated monocarboxylic
acids and their salts and α,β-unsaturated dicarboxylic acids and their salts and (c)
1 to 20 % by mole of repeating units derived from a diallylamine derivative of the
formula:
wherein R₁ and R₂ are the same or different and hydrogen or methyl, R₃ and R₄ are the same or different and hydrogen or C₁-C₆ alkyl, and X⁻ is an anion of an organic acid or an inorganic acid as an effective component to a pulp slurry and then making a sheet of paper from said slurry. |
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a method for increasing paper strength comprising adding a certain paper strength agent to a pulp slurry during paper making. More particularly, it relates to a method for increasing paper strength comprising adding aluminum sulfate and a specific amphoteric copolymer as a paper strength agent to a pulp slurry.
DESCRIPTION OF THE RELATED ART
[0002] It is widely known and practiced in the paper making industry to increase paper strength by the addition of an acrylamide based polymer to a pulp slurry. In such case, aluminum sulfate is widely used as a retentin agent for the acrylamide based polymer.
[0003] Recently, in view of energy saving and anti-pollution, a neutral paper making method which does not use aluminum sulfate has been developed and increasingly employed. However, the neutral paper making method has several drawbacks such that a cheap rosin type sizing agent cannot be used, fixing of a filler onto the pulp is unsatisfactory, and increase of an amount of calcium carbonate decreases paper strength, and also it has some problems such as stain of a wire and a blanket and formation of slime. Therefore, aluminum sulfate is still widely used in paper making.
[0004] As the acrylamide based copolymer, an amphoteric water-soluble copolymer having a cationic functional group and an anionic functional group in one molecule (hereinafter referred to as "amphoteric copolymer") is known. Since the amphoteric copolymer can very effectively increase paper strength and decreases pollution of wastewater, it is intensively studied. For example, Japanese Patent Kokai Publication Nos. 30913/1979, 60095/1983, 91897/1983 and 94697/1985 disclose methods for increasing paper strength which uses amphoteric copolymers comprising acrylamide, an α,β-unsaturated carboxylic acid (e.g. acrylic acid) and dialkylaminoalkyl acrylate and the like.
[0005] However, the use of the conventional amphoteric copolymers in the paper making which uses aluminum sulfate does not increase paper strength satisfactorily.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a method for increasing paper strength which can overcome the drawbacks and problems of the conventional methods using the amphoteric copolymer together with aluminum sulfate.
[0007] Accordingly, the present invention provides a method for increasing paper strength comprising adding aluminum sulfate and a paper strength-agent containing a copolymer comprising (a) 98 to 60 % by mole of repeating units derived from (meth)acrylamide, (b) 1 to 20 % by mole of repeating units derived from at least one compound selected from the group consisting of α,β-unsaturated monocarboxylic acids and their salts and α,β-unsaturated dicarboxylic acids and their salts and (c) 1 to 20 % by mole of repeating units derived from a diallylamine derivative of the formula:
wherein R₁ and R₂ are the same or different and hydrogen or methyl, R₃ and R₄ are the same or different and hydrogen or C₁-C₆ alkyl, and X⁻ is an anion of an organic acid or an inorganic acid as an effective component to a pulp slurry and then making a sheet of paper from said slurry.
DETAILED DESCRIPTION OF THE INVENTION
[0008] As the (meth)acrylamide (a), acrylamide or methacrylamide is used as such or as a mixture thereof. Industrially, acrylamide is preferred.
[0009] Examples of the compound (b) are unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid; and their alkali metal salts such as sodium salt and potassium salt or ammonium salt. A mixture of two or more of them may be used.
[0010] Examples of the diallylamine derivative (I) as the component (c) are organic or inorganic salts of secondary amines such as diallylamine and dimethallylamine; organic or inorganic salts of tertiary amines such as diallylmethylamine, diallylethylamine and diallylbutylamine; quarternary ammonium salts such as diallyldimethylammonium chloride, diallyldimethylammonium bromide, diallyldiethylammonium chloride, diallyldibutylammonium chloride and diallylmethylethylammmonium chloride. A mixture of two or more of them may be used.
[0011] The amphoteric copolymer comprises 98 to 60 % by mole, preferably 96 to 70 % by mole of the (meth)acrylamide (a), 1 to 20 % by mole, preferably 2 to 15 % by mole of the compound (b) and 1 to 20 % by mole, preferably 2 to 15 % by mole of the diallylamine derivative (I) as the component (c). In addition to the above three essential components (a), (b) and (c), the amphoteric copolymer may comprise units derived from a comonomer which is copolymerizable with the three components (a), (b) and (c) in such an amount that the paper strength-increasing effect and water-solubility of the amphoteric copolymer are not deteriorated. Examples of such comonomer are nonionic monomers such as (meth)acrylonitrile, methyl (meth)acrylate, hydroxyethyl (meth)acrylate, styrene and vinyl acetate; cationic monomers such as dimethylaminoethyl (meth)acrylate, dimethylaminopropyl(meth)acrylamide and their quarternary derivatives; and bifunctional monomers such as ethyleneglycol di(meth)acrylate and methylene bis(meth)acrylamide; and the like.
[0012] The amphoteric copolymer used according to the present invention can be prepared by copolymerizing these essential components and the optional components by any of conventional polymerization methods. Preferably, the monomer components are copolymerized in water or a mixture of water and a water-soluble organic solvent in the presence of a polymerization initiator.
[0013] As the polymerization initiator, any of conventional ones may be used. Examples of such initiator are persulfates such as ammonium persulfate and potassium persulfate; azo compounds such as 2,2-diamidinyl-2,2-azopropane dihydrochloric acid and azobisisobutyronitrile; peroxides such as di-ter.-butylperoxide, cumene hydroperoxide and hydrogen peroxide; and the like. Further, a known redox initiator such as a combination of potassium persulfate and sodium hydrogen sulfite or a tertiary amine can be used.
[0014] If desired, a conventionally used chain transfer agent such as isopropanol and allylalcohol may be used.
[0015] The polymerization is carried out at a temperature of from 10 to 100°C, preferably from 40 to 90°C for 1 to 20 hours. Although the polymerization may be carried out in the presence of oxygen, it is preferably carried out in an atmosphere of an inert gas such as nitrogen.
[0016] The essential and optional monomer components may be added to a polymerization system all at once and then copolymerized, or one or more components are firstly added to the polymerization system and thereafter the rest of the components is added to the polymerization system continuously or by portions.
[0017] Among the amphoteric copolymers prepared as above, those having a viscosity of 10 to 1,000 poise, particularly 30 to 300 poise (in a 15 % by weight aqueous solution) at 25°C are preferred.
[0018] The viscosity of the amphoteric copolymer will influence the effects of the paper strength.
When the viscosity is too small, such effect is decreased, and when it is too high, texture of paper is worsened. Therefore, the amphoteric copolymer having a viscosity outside the range of from 10 to 1,000 poise are less preferred.
[0019] Aluminum sulfate to be used according to the present invention is usually called as "Alum" and Al₂(SO₄)₃ having 16 to 18 molecules of crystal water per molecule.
[0020] In the present invention, paper is made by a per se conventional method which uses aluminum sulfate. Namely, to an aqueous dispersion of pulp, the paper strength agent of the present invention is added in an amount of 0.05 to 3 % by weight based on a dry weight of pulp and a sheet of paper is made from the slurry in the presence of aluminum sulfate.
[0021] The amount of aluminum sulfate to be added is from 0.05 to 5 % by weight, preferably from 0.1 to 4 % by weight, more preferably from 0.2 to 1.5 % by weight based on the dry weight of pulp.
[0022] The paper slurry may contain a conventional internal sizing agent and/or a filler such as clay, talc and titanium oxide.
PREFERRED EMBODIMENTS OF THE INVENTION
[0023] Practical and presently preferred embodiments of the present invention are shown in the following Examples, in which "%" is by weight unless otherwise indicated.
Preparation Example 1
[0024] In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, diallylamine (2.9 g) as a component (c) was charged together with 36 % hydrochloric acid (3.0 g) and deionized water (178.2 g). pH of the mixture was adjusted to 4.5 with a 28 % aqueous solution of sodium hydroxide and air in the flask was purged by introducing nitrogen therein.
[0025] The interior temperature was raised to 70°C and ammonium persulfate (0.45 g) was added. Thereafter, a mixture of a 50 % aqueous solution of acrylamide as a component (a) (61.8 g) and a 80 % aqueous solution of acrylic acid as a component (b) (3.2 g) was dropwise added over 2 hours while keeping the interior temperature at 70°C. After completion of the addition of the mixture, the content in the flask was kept at 70°C for 4 hours.
[0026] After cooling the flask to a room temperature, a 15 % aqueous solution of an amphoteric copolymer having pH of 2.7 and a viscosity of 61 poise at 25°C (Amphoteric copolymer A) was recovered, properties of which are shown in Table 1.
Preparation Examples 2 to 10
[0027] In the same manner as in Example 1 but using the components (a), (b) and (c) in amounts shown in Table 1, a amphoteric copolymer was prepared. Properties of the amphoteric copolymers (Amphoteric copolymers B to J) prepared in Preparation Examples 2 to 10 are also shown in Table 1.
Preparation Example 11
[0028] In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, a 50 % aqueous solution of acrylamide as a component (a) (61.1 g), a 80 % aqueous solution of acrylic acid as a component (b) (3.6 g), dimethylaminoethyl methacrylate (4.7 g) as a component (c) and deionized water (184.5 g) were charged. Then, pH of the mixture was adjusted to 4.5 with a 20N aqueous solution of sulfuric acid and air in the flask was purged by introducing nitrogen therein.
[0029] The mixture was heated to 55°C, and then a mixture of ammonium persulfate (0.10 g) and sodium hydrogen sulfite (0.04 g) as polymerization initiators were added to the mixture. The resulting mixture was heated to 90°C over 60 minutes and kept at that temperature for 4 hours.
[0030] After cooling the flask to a room temperature, a 15 % aqueous solution of an amphoteric copolymer having pH of 4.0 and a viscosity of 56 poise at 25°C (Amphoteric copolymer a) was recovered, properties of which are shown in Table 1.
Preparation Examples 12 to 16
[0031] In the same manner as in Preparation Example 11 but using the components (a), (b) and (c) in amounts shown in Table 1, a amphoteric copolymer was prepared. Properties of the amphoteric copolymers (Amphoteric copolymers b to f) prepared in Preparation Examples 12 to 16 are also shown in Table 1.
[0032] Abbreviations used in Table 1 have following meanings:
AM: Acrylamide
MAM: Methacrylamide
DAA: Diallylamine
DAMA: Diallylmethylamine
DADMAC: Diallyldimethylammonium chloride
DMM: Dimethylaminoethyl methacrylate
Q-DM: Methacryloyloxyethyltrimethylammonium chloride
DP: Dimethylaminopropylmethacrylamide
AA: Acrylic acid
MAA: Methacrylic acid
MA: Maleic acid
IA: Itaconic acid
Examples 1 to 10 and Comparative Examples 1 to 6
[0033] To a 3 % slurry of pulp (Canadian Standard Freeness 400 ml; corrugated board waste paper), aluminum sulfate was added and mixed in an amount of 0.5 % by weight based on a dry weight of pulp (hereinafter, the same "weight percentage" being used). Then, each of the amphoteric copolymers A to J and a to f prepared in Preparation Examples 1 to 16 was added in an amount of 0.8 % by weight. After agitating for 1 minute, the pulp slurry was diluted to 1 % with water. From the diluted slurry, a sheet of paper was made by Tappi standard type hand paper making machine, dehydrated and pressed followed by drying at 110°C for 4 minutes to produce a sheet of hand made paper of 125 ± 2 g/m² of basis weight.
[0034] Bursting factor [(bursting strength/basis weight) × 100] and ring crush factor [(ring crush strength/basis weight) × 100] of each sheet of paper were measured according to JIS P-8112 and P-8126, respectively. The results are shown in Table 2.
Examples 11 to 13 and Comparative Examples 7 to 9
1. A method for increasing paper strength comprising adding aluminum sulfate and
a paper strength agent containing a copolymer comprising (a) 98 to 60 % by mole of
repeating units derived from (meth)acrylamide, (b) 1 to 20 % by mole of repeating
units derived from at least one compound selected from the group consisting of α,β-unsaturated
monocarboxylic acids and their salts and α,β-unsaturated dicarboxylic acids and their
salts and (c) 1 to 20 % by mole of repeating units derived from a diallylamine derivative
of the formula:
wherein R₁ and R₂ are the same or different and hydrogen or methyl, R₃ and R₄ are the same or different and hydrogen or C₁-C₆ alkyl, and X⁻ is an anion of an organic acid or an inorganic acid as an effective component to a pulp slurry and then making a sheet of paper from said slurry.
wherein R₁ and R₂ are the same or different and hydrogen or methyl, R₃ and R₄ are the same or different and hydrogen or C₁-C₆ alkyl, and X⁻ is an anion of an organic acid or an inorganic acid as an effective component to a pulp slurry and then making a sheet of paper from said slurry.
2. The method for increasing paper strength according to claim 1, wherein the compound
(b) is at least one compound selected from the group consisting of acrylic acid, methacrylic
acid, maleic acid, fumaric acid and itaconic acid and their sodium salt, potassium
salt and ammonium salt.
3. The method for increasing paper strength according to claim 1, wherein the diallylamine
derivative (I) as the component (c) is at least one compound selected from the group
consisting of diallylamine, dimethallylamine, diallylmethylamine, diallylethylamine,
diallylbutylamine, diallyldimethylammonium chloride, diallyldimethylammonium bromide,
diallyldiethylammonium chloride, diallyldibutylammonium chloride and diallylmethylethylammmonium
chloride.
4. The method for increasing paper strength according to claim 1, wherein the amphoteric
copolymer comprises 96 to 70 % by mole of the repeating units derived from the (meth)acrylamide
(a), 2 to 15 % by mole of the repeating units derived from the compound (b) and 2
to 15 % by mole of the repeating units derived from the diallylamine derivative (I)
as the component (c).