Paper strength enhancing aid for interlayer spray starch, starch-based paper strength enhancing agent, and laminated paper

Abstract

The present invention pertains to a paper strength enhancing aid for an interlayer spray starch, the paper strength enhancing aid comprising a polymer (A) including, as essential components: a (meth)acrylamide (a1); an ethylenically unsaturated monomer (a2) having an amino group; an ethylenically unsaturated monomer (a3) having a carboxyl group; and an ethylenically unsaturated monomer (a4) having a sulfo group. The weight average molecular weight of (A)-component is 1,500,000-6,000,000. In a turbidity distribution of an aqueous solution of the polymer (A) having a nonvolatile matter concentration of 1% in a pH range of 3-9, two local maximum values exist. Of the local maximum values, the value of the turbidity on the low pH side is 50-3000 NTU.

Description

Interlayer spray starch paper strength enhancer assistant, starch-based paper strength agent and laminated paper

[0001] The present invention relates to an interlayer spray starch paper strength enhancer assistant, a starch-based paper strength agent and laminated paper.

[0002] Laminated paper is generally obtained by spraying starches onto the surface of wet paper webs and then bonding them together. However, when the wet paper webs are dewatered by pressing after lamination, the starches flow out together with water, which makes it difficult for the starches to be fixed on the surface of the wet paper webs (low retention), and as a result, there are problems that the laminated paper cannot exhibit sufficient interlayer strength, or the outflowed starches cause drainage load.

[0003] Therefore, in order to fix starches on wet paper webs, a measure of adding an assistant to starches for adsorption has been adopted. For example, the present applicant discloses a method for producing laminated paper using a mixture comprising ungelatinized starches, an ionic acrylamide copolymer, a water-soluble aluminum compound, and one or more water-soluble inorganic electrolytes selected from alkali metal salts, alkaline earth metal salts and quaternary ammonium salts (Patent Document 1). However, in this method, among the components compounded as assistants, the water-soluble aluminum compound excessively aggregates starches, which is prone to cause nozzle clogging during spraying, and the ionic acrylamide copolymer may lead to insufficient interlayer strength of the laminated paper depending on its ionic composition.

[0004] Japanese Patent Application Laid-Open No. 2018-003231

[0005] An object of the present invention is to provide an interlayer spray starch paper strength enhancer assistant that can be well adsorbed to starches, fixes starches on wet paper webs, does not cause nozzle clogging during spraying, and also provides high interlayer strength when formed into laminated paper.

[0006] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that an interlayer spray starch paper strength enhancer assistant having a specific weight average molecular weight and turbidity distribution can solve the above problems. That is, the present invention provides the following contents.

[0007] (Item 1) An interlayer spray starch paper strength enhancer comprising a polymer (A) whose essential components are (meth)acrylamide (a1), an ethylenically unsaturated monomer having an amino group (a2), an ethylenically unsaturated monomer having a carboxyl group (a3), and an ethylenically unsaturated monomer having a sulfo group (a4), wherein the weight-average molecular weight of component (A) is 1.5 million to 6 million, and the turbidity distribution of an aqueous solution of polymer (A) with a non-volatile content of 1% in the pH range of 3 to 9 has two maximum values, and of the maximum values, the turbidity value on the lower pH side is 50 to 3000 NTU. (Item 2) The paper strength enhancer according to item 1, wherein the components further comprise a crosslinkable monomer (a5). (Item 3) A starch-based paper strength enhancer comprising the paper strength enhancer according to item 1 or 2 and starches (B). (Item 4) Laminated paper comprising the starch-based paper strength enhancer according to item 3.

[0008] The interlayer spray starch paper strength enhancing agent of the present invention (hereinafter also simply referred to as "paper strength enhancing agent") adsorbs well to starches, fixes the starches to wet paper, does not cause nozzle clogging when sprayed, and exhibits high interlayer strength when used in laminated paper.

[0009] This is a turbidity chart for polymer (A-1) <Example 1>, polymer (A-2) <Example 2>, polymer (AC-1) <Comparative Example 1>, polymer (AC-2) <Comparative Example 2>, and polymer (AC-3) <Comparative Example 3>.

[0010] The interlayer spray starch paper strength enhancing aid of the present invention contains a polymer (A) whose essential components are (meth)acrylamide (a1) (hereinafter referred to as component (a1)), an ethylenically unsaturated monomer having an amino group (a2) (hereinafter referred to as component (a2)), an ethylenically unsaturated monomer having a carboxyl group (a3) ​​(hereinafter referred to as component (a3)), and an ethylenically unsaturated monomer having a sulfo group (a4) (hereinafter referred to as component (a4)). Hereinafter, (meth)acrylic means methacrylic or acrylic, (meth)acrylate means methacrylate or acrylate, and (meth)acryloyl means methacryloyl or acryloyl (the same applies hereinafter).

[0011] (a1) The components are methacrylamide and acrylamide. These may be used individually or in combination of two or more.

[0012] (a1) From the viewpoint of paper strength enhancement effect, the molar ratio of component is preferably 81 to 98.75 mol%, more preferably 85.7 to 97.4 mol%, and even more preferably 89.7 to 95.85 mol%, based on 100 mol% of the total constituent components.

[0013] (a2) Component is an ethylenically unsaturated monomer having an amino group. An ethylenically unsaturated monomer is one which has one or more carbon-carbon double bonds and / or one or more carbon-carbon triple bonds in the monomer (the same applies hereinafter).

[0014] (a2) Examples of components include ethylenically unsaturated monomers having a primary amino group, ethylenically unsaturated monomers having a secondary amino group, ethylenically unsaturated monomers having a tertiary amino group, and quaternary salts of these ethylenically unsaturated monomers. These may be used individually or in combination of two or more.

[0015] Examples of ethylenically unsaturated monomers having a primary amino group include vinylamines and allylamines. These may be used individually or in combination of two or more.

[0016] Examples of ethylenically unsaturated monomers having a secondary amino group include diallylamine. These may be used individually or in combination of two or more.

[0017] Examples of ethylenically unsaturated monomers having a tertiary amino group include (meth)acrylates having a tertiary amino group, such as N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate; and (meth)acrylamides having a tertiary amino group, such as N,N-dimethylaminopropyl (meth)acrylamide and N,N-diethylaminopropyl (meth)acrylamide. These may be used individually or in combination of two or more.

[0018] These quaternary salts of monomers refer to those obtained by reacting an ethylenically unsaturated monomer having a primary amino group, an ethylenically unsaturated monomer having a secondary amino group, or an ethylenically unsaturated monomer having a tertiary amino group with a quaternizing agent. The quaternary salt may be an inorganic acid salt such as a hydrochloride or sulfate, or an organic acid salt such as an acetate. Examples of quaternizing agents include methyl chloride, benzyl chloride, dimethyl sulfate, and epichlorohydrin. These may be used individually or in combination of two or more.

[0019] Among these (a2) components, it is preferable to include (meth)acrylate having a tertiary amino group and / or a quaternary salt of said (meth)acrylate, since the obtained paper strength enhancing aid is more easily adsorbed onto starches; it is more preferable to include one or more selected from the group consisting of (meth)acrylate having a tertiary amino group, inorganic salt of (meth)acrylate having a tertiary amino group, methyl chloride salt of (meth)acrylate having a tertiary amino group, and benzyl chloride salt of (meth)acrylate having a tertiary amino group; and it is even more preferable to include (meth)acrylate having a tertiary amino group and / or an inorganic salt of (meth)acrylate having a tertiary amino group.

[0020] (a2) The molar ratio of the component is preferably 1 to 10 mol%, more preferably 2 to 9 mol%, and even more preferably 3 to 7 mol%, with the total constituent components being 100 mol%, in order to facilitate the adsorption of the obtained paper strength enhancing agent to starches.

[0021] Component (a3) ​​is an ethylenically unsaturated monomer having a carboxyl group. Examples of component (a3) ​​include (meth)acrylic acid, acrylic anhydride, 2-(meth)acrylamide-N-glycolic acid, N-(meth)acryloylglycine, 3-(meth)acrylamidepropanoic acid, 4-(meth)acrylamidebutanoic acid, itaconic acid, itaconic anhydride, fumaric acid, maleic acid, and maleic anhydride. These (a3) ​​components may also be used as alkali metal salts such as sodium and potassium; ammonium salts such as ammonia; or organic amine salts such as trimethylamine, triethylamine, trimethanolamine, and triethanolamine. These may be used individually or in combination of two or more. In particular, it is preferable to include (meth)acrylic acid, acrylic anhydride, and itaconic acid, and more preferably itaconic acid, because the resulting polymer (A) tends to exhibit the turbidity distribution described later, and when used as a paper strength enhancing agent, it is adsorbed to starches (B) and tends to exhibit high interlayer strength.

[0022] (a3) The molar ratio of component (a3) ​​is preferably 0.2 to 6 mol%, more preferably 0.5 to 3 mol%, and even more preferably 1 to 2 mol%, based on the same considerations as above, with the total constituent components being 100 mol%.

[0023] Component (a4) is an ethylenically unsaturated monomer having a sulfo group. Examples of component (a4) include vinyl sulfonic acid, methallyl sulfonic acid, and p-styrene sulfonic acid. These components (a4) may also be used as alkali metal salts such as sodium and potassium, or ammonium salts. These may be used individually or in combination of two or more. In particular, it is preferable to include methallyl sulfonic acid or a salt of methallyl sulfonic acid, as this allows for easy adjustment of the weight-average molecular weight of polymer (A) to achieve an appropriate viscosity and facilitates the display of high interlaminar strength when used as a starch-based paper strength enhancer.

[0024] (a4) The molar ratio of component (a4) is preferably 0.05 to 2 mol%, more preferably 0.1 to 1.5 mol%, and even more preferably 0.15 to 0.8 mol%, based on the same considerations as above, with the total constituent components being 100 mol%.

[0025] The aforementioned components may further include a crosslinkable monomer (a5) (hereinafter also referred to as component (a5)).

[0026] (a5) Examples of components include N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and N-t-butyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N,N-diisopropyl(meth)acrylamide; N,N'-alkylenebis(meth)acrylamides such as N,N'-methylenebis(meth)acrylamide and N,N'-ethylenebis(meth)acrylamide; crosslinkable monomers having a trialyl group such as triallyl isocyanurate, triallyl trimellitate, triallylamine, and triallyl(meth)acrylamide; and triazines having a (meth)acryloyl group such as 1,3,5-triacryloyl-1,3,5-triazine and 1,3,5-triacryloylhexahydro-1,3,5-triazine. These can be used individually or in combination of two or more. In particular, it is preferable to include N,N-dialkyl(meth)acrylamide and triazine having a (meth)acryloyl group, as this increases the weight-average molecular weight of polymer (A) by introducing a cross-linking structure, making it easier to achieve high interlaminar strength when used as a starch-based paper strength enhancer.

[0027] (a5) The molar ratio of component (a5) is preferably 1.0 mol% or less, more preferably 0.8 mol% or less, and even more preferably 0.05 to 0.5 mol%, based on the same considerations as above, with the total constituent components being 100 mol%.

[0028] The aforementioned constituent components may further include monomers other than components (a1) to (a5), namely (a6) (hereinafter referred to as component (a6)).

[0029] (a6) Examples of components include: ethylenically unsaturated monomers having aromatic rings such as styrene, α-methylstyrene, and vinyltoluene; alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, n-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, and cyclohexyl(meth)acrylate; vinyl carboxylates such as vinyl acetate and vinyl propionate; nitriles such as acrylonitrile; mercaptans such as 2-mercaptoethanol and n-dodecylmercaptan; alcohols such as ethanol, isopropyl alcohol, and n-pentyl alcohol; aromatic compounds such as α-methylstyrene dimer, ethylbenzene, isopropylbenzene, and cumene; and carbon tetrachloride. These may be used individually or in combination of two or more.

[0030] (a6) The molar ratio of component is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less, with the total constituent components being 100 mol%.

[0031] In the production of polymer (A), organic acids such as acetic acid, propionic acid, butanoic acid, citric acid, succinic acid, oxalic acid, glycolic acid, and glyoxylic acid; inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; inorganic salts such as sodium sulfate, potassium sulfate, and ammonium sulfate; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; resins such as polyvinyl alcohol; and additives such as urea, defoamers, antioxidants, preservatives, and disinfectants may be added. These may be used individually or in combination of two or more.

[0032] The additive content is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of the total constituent components.

[0033] Polymer (A) is obtained by polymerizing components (a1), (a2), (a3), and (a4) in a solvent in the presence of a polymerization initiator, with components (a5), (a6), and the additives as needed.

[0034] Examples of the polymerization methods mentioned above include methods using only dropwise polymerization, methods using only simultaneous polymerization (where the monomer mixture is charged all at once), and methods combining simultaneous polymerization and dropwise polymerization.

[0035] Droplet polymerization is a method of adding a monomer mixture dropwise to a reaction system that has been pre-filled with a solvent such as water. Examples of methods using only this polymerization method include the following (1) to (3). The dropwise addition can be done continuously, or it can be stopped midway, polymerization can be allowed to proceed for a certain period of time, and then the addition can be resumed. (1) A method of adding a monomer mixture containing all monomer components dropwise. (2) A method of preparing two or more monomer mixtures separately and then adding them simultaneously dropwise. (3) A method of preparing two or more monomer mixtures separately and then adding them sequentially dropwise.

[0036] Furthermore, the following methods (4) to (7) are examples of methods that combine simultaneous polymerization and dropwise polymerization: (4) A method in which each monomer mixture is polymerized separately simultaneously and then each polymer is mixed. (5) A method in which the simultaneous polymerization of one or more monomer mixtures is completed, and then the remaining monomer mixture is added dropwise. (6) A method in which the remaining monomer mixture is added dropwise during the simultaneous polymerization of one or more monomer mixtures. (7) A method in which one or more monomer mixtures are polymerized dropwise, and then the remaining monomer mixture is added all at once, followed by simultaneous polymerization.

[0037] Of the above methods (1) to (7), methods (3) and (6) are preferred.

[0038] Examples of solvents include water and organic solvents, which may be used alone or in combination of two or more. Examples of water include tap water, pure water, ultrapure water, deionized water, and industrial water. Examples of organic solvents include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-octyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and diacetone alcohol; and ethers such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0039] The solvent content is adjusted so that the polymerization concentration is preferably 5 to 50% by weight, more preferably 10 to 35% by weight.

[0040] Examples of polymerization initiators include inorganic peroxides such as ammonium persulfate and potassium persulfate; organic peroxides such as benzoyl peroxide, dicumyl peroxide, and lauryl peroxide; azo compounds such as 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride, and 2,2'-azobis[2(2-imidazolin-2-yl)propane] hydrochloride; and hydrogen peroxide. These may be used individually or in combination of two or more. Among these, ammonium persulfate, potassium persulfate, and 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride are preferred, and 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride is more preferred, from the viewpoint of allowing solution polymerization to proceed sufficiently. Furthermore, the method of adding the polymerization initiator can be appropriately selected, such as adding it all at once, adding it in stages, or adding it continuously dropwise.

[0041] The polymerization initiator content is typically 0.01 to 1 part by weight, preferably 0.03 to 0.5 parts by weight, per 100 parts by weight of the total components.

[0042] As the polymerization conditions, for example, the reaction temperature is usually 50 to 100°C, preferably 60 to 90°C. Further, the reaction time is usually 1 to 10 hours, preferably 1 to 6 hours.

[0043] The obtained polymer (A) may further contain inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid; sulfates such as sodium sulfate, potassium sulfate and ammonium sulfate; metal hydroxides such as sodium hydroxide, potassium hydroxide and calcium hydroxide; resins such as polyvinyl alcohol; and additives such as urea, defoaming agents, antioxidants, preservatives and bactericides.

[0044] The weight average molecular weight of the polymer (A) of the present invention is 1,500,000 to 6,000,000. If the weight average molecular weight is less than 1,500,000, the adhesive strength of the paper strength reinforcing auxiliary in paper tends to be weakened, and the interlayer strength of the laminated paper tends to be deteriorated. On the other hand, if the weight average molecular weight exceeds 6,000,000, the viscosity increases during polymerization, and nozzle clogging tends to easily occur during spraying even when the paper strength reinforcing auxiliary is obtained. Further, from the same viewpoint, the weight average molecular weight of the component (A) is preferably 1,700,000 to 5,000,000, more preferably 2,000,000 to 4,500,000. The "weight average molecular weight" as used herein refers to a value obtained by gel permeation chromatography (GPC).

[0045] In the present invention, the turbidity distribution of an aqueous solution of the polymer (A) having a non-volatile content concentration of 1% is also one of the parameters. Turbidity will be described below.

[0046] Turbidity is the degree of cloudiness, and is a value obtained by measuring 180-degree scattered light using 900 nm infrared light with ANALITE NEPHELOMETER 152 (manufactured by McVan Instruments), and the measured value refers to a relative evaluation value with respect to a standard substance (formazine standard solution 400 NTU, manufactured by Wako Pure Chemical Industries, Ltd.).

[0047] In this invention, turbidity is measured in an aqueous solution of polymer (A) with a non-volatile content of 1%. The aqueous solution is prepared by diluting component (A) with water such as deionized water. The turbidity of polymer (A) correlates with the degree of polyion complex (hereinafter referred to as PIC) formation, and its value fluctuates with pH. In this invention, the turbidity distribution in the pH range of 3 to 9 has two maximum values. When polymer (A) begins to form PIC, turbidity occurs in the diluted solution. As the pH is changed, the turbidity value increases, reaching a first maximum value. If the pH is changed further, the turbidity value begins to decrease, reaching a minimum value, then turbidity occurs again, the turbidity value increases, reaching a second maximum value, and then begins to decrease again.

[0048] In the turbidity distribution of the present invention, there are two maximum values, and of these maximum values, the turbidity value on the lower pH side is 50 to 3000 NTU. By exhibiting such a distribution, the paper strength enhancing agent can be efficiently adsorbed to the starches (B) described later, allowing the starches to be fixed to the wet paper, and also preventing nozzle clogging when sprayed, and the resulting laminated paper has high interlayer strength. Similarly, for the turbidity value on the lower pH side, 150 to 2000 NTU is preferred, and 200 to 1500 NTU is more preferred. Furthermore, it is preferable that the paper strength enhancer of the present invention has a distribution as shown by polymers (A-1) and (A-2) in Figure 1, where the maximum turbidity value on the low pH side is within the range of 50 to 3000 NTU, and the turbidity is positive between the two pH regions where the maximum value is shown (the minimum value in that region is also positive). As a result, the formed PIC does not separate, and turbidity continues to be generated in the liquid, making it possible to apply it as the starch-based paper strength enhancer of the present invention described later in that pH region, and also making it easier to exhibit high interlayer strength.

[0049] Furthermore, the viscosity of polymer (A) is preferably 100 to 100,000 mPa·s, and more preferably 1,000 to 50,000 mPa·s. Here, "viscosity" refers to the value measured with a B-type viscometer of a solution with a solid content concentration of 20% by weight, which has been pre-adjusted to a temperature of 25°C.

[0050] The starch-based paper strength enhancer of the present invention comprises the aforementioned paper strength enhancer and starches (B).

[0051] Starches (B) are classified into unmodified starch and modified starch. The following unmodified and modified starches may be used individually or in combination of two or more types. Furthermore, it is preferable to use ungelatinized starches (B) to prevent nozzle clogging when the starch paper strength enhancer is sprayed.

[0052] Examples of unmodified starches include corn starch, waxy corn starch, potato starch, tapioca starch, wheat starch, rice starch, and sago starch.

[0053] Examples of modified starches include oxidized starch, esterified starch, etherified starch, amidated starch, cationized starch, amphoteric starch, cross-linked starch, and reduced-production starch.

[0054] Examples of oxidized starch include unmodified starch treated with an oxidizing agent. Examples of the oxidizing agent include halogens such as chlorine, bromine, hypochlorite, and hypobromite. Examples of salts include alkali metal salts such as potassium and sodium.

[0055] Examples of esterified starches include inorganic acid esterified starches such as nitrate esterified starch, sulfate esterified starch, phosphate esterified starch (including amphoteric starches having phosphate ester groups), and urea phosphate esterified starch; and organic acid esterified starches such as acetoacetate esterified starch, acetate esterified starch (acetylated starch), xanthogene acetate esterified starch, succinate esterified starch, maleic anhydride esterified starch, and fumarate anhydride esterified starch.

[0056] Examples of etherified starches include alkyl etherified starches such as methyl etherified starch, ethyl etherified starch, and propyl etherified starch; hydroxyalkylated starches such as hydroxymethyl etherified starch, hydroxyethyl etherified starch, hydroxypropyl etherified starch, and hydroxybutyl etherified starch; and carboxymethyl etherified starch and allyl etherified starch.

[0057] Examples of amidated starches include carbamoylethylated starch.

[0058] Cationic starch is obtained by treating the aforementioned unmodified starch with a compound having a cationic group. Examples of compounds having a cationic group include ammonium halides such as 2-diethylaminoethyl chloride and 2,3-epoxypropyltrimethylammonium chloride.

[0059] Amphoteric starch is obtained by treating the aforementioned unmodified starch with a compound having a cationic group and a compound having anionic properties, or a compound having both cationic and anionic groups; in other words, it means starch that has both cationic and anionic groups.

[0060] Examples of cross-linked starches include phosphate cross-linked starch, acetylated phosphate cross-linked starch, adipic acid cross-linked starch, acetylated adipic acid cross-linked starch, formaldehyde cross-linked starch, acrolein cross-linked starch, and epichlorohydrin cross-linked starch.

[0061] Reduced-modification starch is obtained by reducing the modification of unmodified starch or modified starch (excluding reduced-modification starch), by reacting these starches with a modification agent and heating and stirring them at 60 to 100°C for 30 to 60 minutes.

[0062] Examples of decontamination agents include hypochlorites, peroxodisulfates (ammonium persulfate, potassium persulfate, sodium persulfate, etc.), inorganic peroxides such as hydrogen peroxide, bacteria, enzymes such as α-amylase, etc. These may be used individually or in combination of two or more. When using hydrogen peroxide, at least one water-soluble metal salt from among iron sulfate and copper sulfate may be used in combination.

[0063] Furthermore, the reduced-quality starches obtained by the above method are defined according to the raw materials used, as shown in Table 1.

[0064]

[0065] Examples of commercially available starches (B) include "Corn Starch," "Ace A," "Ace P160," "Ace K100" (manufactured by Oji Corn Starch Co., Ltd.), "Nisshoku MS#4600" (manufactured by Nippon Shokuhin Kako Co., Ltd.), "Nutrastar RA-900" (manufactured by Sanwa Starch Industry Co., Ltd.), and "CS-2" (manufactured by Arakawa Chemical Industries, Ltd.). These can be used individually or in combination of two or more types.

[0066] Among these, it is preferable to include one or more selected from unmodified starch, oxidized starch, cationized starch, and esterified starch, as these readily adsorb the aforementioned paper strength enhancing agents. It is even more preferable to include one or more selected from corn starch, tapioca starch, potato starch, oxidized starch, cationized starch, acetate esterified starch (acetylated starch), and urea phosphate esterified starch.

[0067] In starch-based paper strength enhancers, the content of the paper strength enhancing aid is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, even more preferably 1 to 5 parts by weight, and particularly preferably 1.5 to 3.5 parts by weight, based on non-volatile content, per 100 parts by weight of starch (B), in order to facilitate the adsorption of the paper strength enhancing aid to starches (B).

[0068] The aforementioned solvent may be added to the starch-based paper strength enhancer. The solvent content is adjusted so that the non-volatile content of the starch-based paper strength enhancer is preferably 0.1 to 20% by weight, and more preferably 0.5 to 8% by weight.

[0069] Starch-based paper strength enhancers may also contain additives such as inorganic acids like hydrochloric acid, sulfuric acid, and phosphoric acid; sulfates like sodium sulfate, potassium sulfate, and ammonium sulfate; metal hydroxides like sodium hydroxide, potassium hydroxide, and calcium hydroxide; resins like polyvinyl alcohol; and urea, defoamers, antioxidants, preservatives, and disinfectants.

[0070] Starch-based paper strength enhancers can be obtained, for example, by mixing a paper strength enhancer and starches (B), and optionally an additive, at room temperature (e.g., 20°C, 23°C, etc.). There are no particular limitations on the mixing order or method. Heating or cooling can also be adjusted as appropriate.

[0071] The physical properties of the starch-based paper strength enhancer include, for example, a pH of 3 to 9, more preferably 4 to 8, at a temperature of 25°C. The pH value here is measured using a commercially available pH meter.

[0072] The laminated paper of the present invention contains a starch-based paper strength enhancer.

[0073] Laminated paper can be obtained, for example, by a manufacturing method in which a starch-based paper strength enhancer is sprayed onto the surface of one or more layers of wet paper obtained by papermaking from a pulp slurry, then the layers are laminated, dehydrated, and dried.

[0074] Examples of pulp include chemical pulps such as hardwood pulp (LBKP) and softwood pulp (NBKP); mechanical pulps such as wood pulp (GP), refiner ground pulp (RGP), and thermomechanical pulp (TMP); and recycled paper pulp such as corrugated cardboard. These may be used individually or in combination of two or more types. In addition, the pulp slurry may contain fixatives such as aluminum sulfate, pH adjusters such as sulfuric acid and sodium hydroxide; papermaking chemicals such as sizing agents and wet strength agents; and fillers such as talc, clay, kaolin, titanium dioxide, and calcium carbonate.

[0075] When spraying (aerosolizing) the starch-based paper strength enhancer onto the surface of wet paper, the non-volatile content concentration is preferably 0.1 to 20% by weight, and more preferably 0.5 to 8% by weight. Furthermore, the viscosity (non-volatile content concentration: 2% by weight) of the starch-based paper strength enhancer at a temperature of 25°C is preferably 1 to 20 mPa·s, and more preferably 1 to 10 mPa·s. The viscosity values ​​here are measured using a B-type viscometer.

[0076] Furthermore, the amount of starch-based paper strength enhancer used is preferably 0.01 to 5% by weight, and more preferably 0.1 to 2% by weight, based on the weight of nonvolatile content relative to 100% by weight of pulp.

[0077] The laminated paper of the present invention can be used in a variety of products, such as coated base paper, newsprint, liners, cores, paper tubes, printing and writing paper, form paper, PPC paper, cup base paper, inkjet paper, thermal paper, and the like.

[0078] The present invention will be described below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, "parts" and "%" are based on weight unless otherwise specified.

[0079] The following compounds are abbreviated as follows: AM: Acrylamide DM: N,N-dimethylaminoethyl methacrylate DML: N,N-dimethylaminoethyl methacrylate benzyl chloride DMC: N,N-dimethylaminoethyl methacrylate methyl chloride BQ: N,N-dimethylaminoethyl acrylate benzyl chloride IA: Itaconic acid AA: Acrylic acid SMAS: Sodium methallyl sulfonate DMAA: N,N-dimethylacrylamide TAF: 1,3,5-triacryloyl-1,3,5-triazine V-50: 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride APS: Ammonium persulfate

[0080] Example 1 A reaction apparatus equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet tube, and three dropping funnels was filled with 353.8 parts of deionized water. After removing oxygen from the reaction system by passing nitrogen gas through it, the mixture was heated to 90°C. Dropping funnel (1) was filled with 174.61 parts (22.88 mol%) of 50% AM aqueous solution, 22.27 parts of 62.5% sulfuric acid, 45.56 parts (5.40 mol%) of DM, 1.61 parts (0.23 mol%) of IA, 4.8380 parts (0.57 mol%) of SMAS, 0.69 parts (0.13 mol%) of DMAA, and 109.40 parts of deionized water. The pH was adjusted to around 3.0 with sulfuric acid (monomer mixture (I)). Next, 519.7 parts (67.82 mol%) of 50% AM aqueous solution, 2.47 parts of 62.5% sulfuric acid, 5.06 parts (0.60 mol%) of DM, 14.45 parts (2.07 mol%) of IA, 0.2546 parts (0.03 mol%) of SMAS, 1.44 parts (0.27 mol%) of DMAA, and 320.27 parts of deionized water were charged into dropping funnel (2), and the pH was adjusted to around 3.0 with sulfuric acid (monomer mixture (II)). 0.2940 parts of V-50 and 180 parts of deionized water were charged into dropping funnel (3). Then, the V-50 aqueous solution was added dropwise from dropping funnel (3) over 3 hours. In parallel, the monomer mixtures (I) and (II) from dropping funnels (1) and (2) were added dropwise in that order at a constant flow rate over 3 hours. After the dropwise addition was complete, the mixture was kept warm for 30 minutes, then a mixture of 0.42 parts APS and 10 parts deionized water was added, and after keeping it warm for 1 hour, deionized water was added to achieve a non-volatile content of 20% to obtain polymer (A-1). Table 2 shows the molar ratio of all monomer components and the molar ratio of the monomer components added to each monomer mixture.

[0081] Examples 2-5 and Comparative Examples 1-4 were synthesized in the same manner as in Production Example 1, using the monomer components and molar ratios shown in Table 2, to obtain polymers (A-2) to (A-5) and (AC-1) to (AC-4), respectively, with a non-volatile content of 20%.

[0082] Comparative Example 5: In the same method as in Production Example 1, except that after the dropwise addition was completed and the mixture was kept warm for 30 minutes, no APS aqueous solution was added afterward. 436.80 parts of ion-exchanged water were added to obtain a polymer (AC-5) with a non-volatile content of 20%.

[0083] <Turbidity> (Measurement conditions) ・Turbidimeter: ANALITE NEPHELOMETER 152 (McVan Instruments) ・Infrared wavelength: 900 nm ・Standard substance: Formazin standard solution (400 NTU, Wako Pure Chemical Industries, Ltd.) ・Sample concentration: 1% (non-volatile content concentration of polymer (A)) ・Solvent: Ion-exchanged water ・Sample temperature: 25°C

[0084] (Measurement Method) An aqueous solution of polymer (A) diluted to 1% non-volatile content with the above solvent was stirred at 500 rpm using a stirrer. To increase the pH, a 1% sodium hydroxide aqueous solution was added dropwise, and to decrease the pH, a 1% sulfuric acid aqueous solution was added dropwise, changing the pH by 0.1 increments. The turbidity value as a function of pH was measured. If the turbidity value was not stable, the user waited until it stabilized, and the value at which it stabilized was taken as the turbidity value. The maximum value was read from the turbidity distribution (peak) obtained from the measurement. Table 2 shows the maximum values ​​of turbidity. Figure 1 shows the turbidity charts for polymer (A-1) <Example 1>, polymer (A-2) <Example 2>, polymer (AC-1) <Comparative Example 1>, polymer (AC-2) <Comparative Example 2>, and polymer (AC-3) <Comparative Example 3>.

[0085] <Weight-average molecular weight> The weight-average molecular weight of component (A) was measured by gel permation chromatography (GPC) under the following measurement conditions. The results are shown in Table 2. Column: One Guard PWXL column and two GMPWXL columns manufactured by Tosoh Corporation Eluent: Phosphate buffer (0.05 mol / L phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) + 0.13 mol / L sodium dihydrogen phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution, pH approximately 2.5) Flow rate: 0.8 ml / min Temperature: 40°C RI detector: Shodex RI-101 manufactured by Showa Denko K.K. MALS detector: DAWN HELEOS-II manufactured by WYATT Measurement sample: The polymer (A) was diluted with the above eluent so that the non-volatile content concentration was 0.1% before measurement.

[0086]

[0087] The polymer (A) obtained above was used as a paper strength enhancer, and the following evaluation was performed.

[0088] Preparation Example 1 Two parts of the paper strength enhancer (polymer (A-1)) from Example 1 and 100 parts of corn starch (product name: "Corn Starch", manufactured by Oji Corn Starch Co., Ltd.) were added by weight of non-volatile content. Ion-exchanged water was added to achieve a non-volatile content concentration of 2%, and the mixture was stirred at room temperature for 10 minutes to obtain a starch-based paper strength enhancer (E-1).

[0089] Preparation Example 2 After obtaining starch-based paper strength enhancer (A-1) using the method of Example 1, sulfuric acid was added to adjust the pH to 6.0 to obtain starch-based paper strength enhancer (A-2).

[0090] Preparation Examples 3-15 and Comparative Preparation Examples 1-17 were prepared using the same method as in Preparation Example 1, with the components and amounts shown in Table 3 changed. Starch-based paper strength enhancers (E-3) to (E-15) and (EC-1) to (EC-17) were obtained, respectively. For the starch-based paper strength enhancers in Preparation Examples 3, 14, 15 and Comparative Preparation Examples 2 and 7, sulfuric acid was added to achieve the pH shown in Table 3.

[0091] <pH> After adjusting the temperature of each starch-based paper strength enhancer to 25°C, the pH was measured using a commercially available pH meter (manufactured by Shimadzu Corporation). The results are shown in Table 3 (the same applies below).

[0092] <Preparation of laminated paper> Corrugated cardboard waste is beaten in a Niagara-type beater, and tap water is added to a pulp slurry adjusted to 400 ml of Canadian Standard Freeness (C.S.F.) to a non-volatile content of 0.5%, and then paper is made using a TAPPI paper machine to produce wet paper A (moisture content: 86%, dry basis weight: 60 g / m²). ２ ) and wet paper B (moisture content: 96%, dry basis weight: 60 g / m²) ２ A solution was prepared. Each starch-based paper strength enhancer was sprayed onto one side of wet paper A at a concentration of 0.3% relative to the pulp (weight of non-volatile content) using a cap spray device (device name: "HV-380", manufactured by WAGNER). Then, wet paper B was placed on top of the sprayed surface of wet paper A, with wet paper B on top, and dewatered at 150 mmHg for 1 minute. After that, 5 kg / cm 2 Press for 2 minutes, then dry in a rotary dryer at 105°C for 4 minutes to form laminated paper (basis weight: 120 g / m²). ２ The laminated paper was conditioned for 24 hours under conditions of 23°C and 50% humidity.

[0093] (Adsorption rate of paper strength enhancer to starches (B)) The starch-based paper strength enhancer of Preparation Example 1 was filtered using filter paper (product name: "Quantitative Filter Paper No. 5A 70mm", manufactured by Advantec Toyo Co., Ltd.), and the residue was conditioned for 24 hours under conditions of 23°C and 50% humidity. Next, an appropriate amount of the residue was placed in a container and crushed in an agate mortar, and 2 mg of the powder was set in a trace total nitrogen analyzer (product name: "Trace Total Nitrogen Analyzer TN-2100H", manufactured by Nitto Seiko Analytech Co., Ltd.) to measure the nitrogen content (1) (unit: ppm). The same procedure was performed with corn starch alone to measure the nitrogen content (2) (unit: ppm). The nitrogen content obtained for each was substituted into (Equation 1) to calculate the adsorption rate. The adsorption rates of the starch-based paper strength enhancers of Preparation Examples 2 to 15 and Comparative Preparation Examples 1 to 17 were calculated in the same manner. (Equation 1) Adsorption rate (%) = [(Nitrogen content (1)) - (Nitrogen content (2)) ÷ 10000] ÷ (Percentage of paper strength enhancing agent in starch-based paper strength enhancer) (%) × (Nitrogen content in paper strength enhancing agent (%)) ÷ 100) × 100 [In Equation 1, nitrogen content (1) is the measured value for the starch-based paper strength enhancer, nitrogen content (2) is the measured value for starches (B) only, and the nitrogen content in the paper strength enhancing agent is the value calculated from the molar amount of each monomer that makes up the agent.]

[0094] (Yield) 500g of each starch-based paper strength enhancer was passed through 80mesh wire mesh (product name: "Plain Weave Wire Mesh 80mesh", manufactured by Nippon Kanaami Shoko Co., Ltd.) cut to a diameter of 4cm. Then, 50g of deionized water was passed through the 80mesh wire mesh twice, and it was air-dried for 24 hours under conditions of 23°C and 50% humidity. After that, the 80mesh wire mesh was visually inspected for any yield material and evaluated according to the following criteria. (Evaluation Criteria) ○: No yield material present ×: Yield material present

[0095] (Measurement of interlaminar strength) In accordance with J-TAPPI Paper Pulp Test Method No. 18-2, the internal bond strength (J / m²) of laminated paper was measured using an internal bond tester (manufactured by Kumagai Riki Kogyo Co., Ltd.). ２ The interlaminar strength was measured and that value was defined as the interlaminar strength.

[0096]

[0097] The symbols shown in Table 3 represent the following compounds. (Paper Strength Enhancers) ・A-1 to A-5: Polymers of Examples 1 to 5 (A-1) to (A-5) ・AC-1 to AC-5: Polymers of Comparative Examples 1 to 5 (AC-1) to (AC-5) (Starches) ・B-1: Corn starch, trade name: "Corn Starch", manufactured by Oji Corn Starch Co., Ltd. ・B-2: Urea phosphate esterified starch, trade name: "Oji Ace P340", manufactured by Oji Corn Starch Co., Ltd. ・B-3: Cationized starch, trade name: "Pillar Starch P-4", manufactured by Oji Corn Starch Co., Ltd. ・B-4: Potato starch, trade name: "Potato Starch Bihoro", manufactured by Bihoro Regional Agricultural Processing Cooperative Federation

Claims

1. An interlayer spray starch paper strength enhancer comprising a polymer (A) whose essential components are (meth)acrylamide (a1), an ethylenically unsaturated monomer having an amino group (a2), an ethylenically unsaturated monomer having a carboxyl group (a3), and an ethylenically unsaturated monomer having a sulfo group (a4), wherein the weight-average molecular weight of component (A) is 1.5 million to 6 million, and the turbidity distribution of an aqueous solution of polymer (A) with a non-volatile content of 1% in the pH range of 3 to 9 has two maximum values, and of the maximum values, the turbidity value on the lower pH side is 50 to 3000 NTU.

2. The paper strength enhancing agent according to claim 1, wherein the constituent component further comprises a crosslinkable monomer (a5).

3. A starch-based paper strength enhancer comprising the paper strength enhancer according to claim 1 or 2 and starches (B).

4. Laminated paper containing the starch-based paper strength enhancer described in claim 3.

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