Surface treatment agent for paper

Abstract: A surface treatment agent for paper comprising a quaternized product of a copolymer containing at least (a) styrene and/or a styrene derivative and (b) N,N-dialkylaminoalkyl(meth)acrylamide is disclosed. This surface treatment agent is excellent in slip prevention and sizing effect, the sizing effect not being impaired at a pH over 7.

Description: This invention relates to a surface treatment agent for paper, especially, to such an agent for anti-slipping treatment for paper. Paper is being put to increasingly diversed and specialized applications, and many attempts are made to improve paper quality by use of various kinds of quality-improving agents. However, use of such agents reduces, the friction coefficient of paper and has the disadvantage of making the paper more slippery. Recently, paper-making has shifted away from the conventional acid paper-making method to alkaline paper-making method in which alkylketene dimer compounds are used as internal sizing agents, and it has been found that these compounds make the resulting paper slippery. Slippery paper is troublesome to handle, since it often telescopically slips when rolled, and slides laterally when it is stacked. Therefore, application of inorganic materials such as alumina, silica and the like on the surface of paper has been widely employed in order to roughen the surface for the prevention of slipping. However, this method causes pronounced abrasion of calendar rolls and requires constant inspection and maintenance of the equipment. Also, this method inevitably degrades the paper quality, especially the sized effect. As surface treatment agents, an anti-slipping agent, a surface sizing agent, etc. are used as desired singly or in combination. However, when these agents are incompatible application, i.e., coating, must be carried out at different stations, which impairs efficiency of paper making. Therefore, there is a demand for a surface-treating agent which provides paper with both anti-slipping property and sized property. Previously, we proposed a method for providing paper with anti-slipping property in which a cationic copolymer obtained by quaternization of a copolymer of a styrene compound and an aminoalkyl ester of acrylic acid or methacrylic acid (JP-A-57-56598 (1982)). As surface sizing agents, property improvers, the following compounds are also disclosed in the following publications: a quaternized copolymer of styrene and nitrogen-containing vinyl monomer in US-A-2,964,445; a reaction product of epihalohydrin aqueous coating composition and a copolymer of a styrene compound and an aminoalkyl ester of (meth)acrylic acid in JP-A-48-11407 (1973); and a quaternized copolymer of N,N-dimethylaminoethyl(meth)acrylate, styrene and acrylonitrile in JP-A-56-118994(1981). However, these cationic copolymers have a defect in that they largely lose much of their sizing effect when the pH of the coating liquid is increased to 7-8 by any chemical reagent used in preparation of the coating liquid. Anionic surface-sizing agents commercially available today are not satisfactory in sizing and slip-prevention effects, either. "The US-A-3 170 901 relates to new monomeric and polymeric quaternary ammonium compounds and to their production, said monomeric compound having the formula where R is selected from the group consisting of hydrogen and methyl, Y is selected from the group consisting of 0, -CONR-, and -COO-, A is an alkylene group having 2 to 10 carbon atoms, at least two of the carbon atoms thereof being connected in a chain extending between the N atom and the Y group, R' and R² are selected from the group consisting of (1) separate groups selected individually from the group consisting of saturated and ethylenically unsaturated hydrocarbon groups of 1 to 4 carbon atoms, and (2) a composite group selected from the group consisting of the morpholino residue, the pyrrolidino residue, the piperidino residue, and an N-alkyl piperazino residue of the formula (C₂H₄)₂:NR⁴ where R⁴ is an alkyl group of 1 to 18 carbon atoms, X is a halogen atom, and R³ is an alkyl group having from 1 to 4 carbon atoms. The polymers obtained according to US-A-3 170 901 have a wide variety of uses and they are particularly useful as adjuvants to paper for imparting increased wet strength and as agents for impregnating or coating textiles for various purposes. Because of the fact that they are readily converted to insoluble condition after incorporation in the paper or textile, they may be rendered resistant to removal therefrom during subsequent wetting, washing or scouring operations." The purpose of the present invention is to provide a surface treatment agent for paper which has both sizing and slip-prevention effects, and are satisfactorily effective even when the pH of the coating liquid is 7 or higher. We conducted an intensive study in search of such surface treatment agents and found that a quaternized product of a styrene/N,N-dialkylaminoalkyl(meth)acrylamide copolymer overcomes the above mentioned problems. This invention provides a surface treatment agent for paper comprising a copolymer prepared by (I) polymerizing a mixture comprising (1) 95-50 mole % of at least one aromatic monomer selected from the group consisting of styrene and styrene derivatives; and (2) 5-50 mole % of at least one N,N-dialkylaminoalkyl(meth)acrylamide, and (II) quaternizing the polymerization product with a quaternizing agent selected from the group consisting of dimethyl sulfate, methyl chloride, allyl chloride, benzyl chloride, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, epibromohydrin, ethylene chlorohydrin and ethylene bromohydrin. It is preferred a surface treatment agent wherein the copolymer comprises (a) 94-50 mole % styrene and/or a styrene derivative, and (b) 5-50 mole % N,N-dialkylaminoalkyl(meth)acrylamide and (c) 1-20 mole % of another vinyl monomer copolymerizable with the above (a) and (b). The above-mentioned copolymers can be obtained by any known solution or block polymerization method. The quaternization can be effected by adding a quaternizing agent to a solution of the copolymer and heating the solution. Typical examples of the styrene derivative are α-methylstyrene, vinyltoluene, chlorostyrene, chloromethylstyrene, etc. Typical examples of the N,N-dialkylaminoalkyl(meth)acrylamide are N,N-dimethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, etc. and can be used singly or in combination. Typical examples of the other vinyl monomers used in addition to the above-described monomers are esters of acrylic or methacrylic acid such as methyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, 2-hydroxylethyl(meth)acrylate, lauryl(meth)acrylate, stearyl(meth)acrylate, etc.; esters of maleic or fumaric acid such as dibutyl maleate, dibutyl fumarate, dioctyl fumarate, etc.; vinyl acetate, acrylonitrile, etc. The quaternizing agents can be used singly or in combination. The invention will now be illustrated by way of working examples. Parts and percentages referred to hereinafter are by weight unless otherwise specifically defined. Example 1. In a four-necked flask equipped with a stirrer, a thermometer and a reflux condenser, 78 parts styrene, 39 parts N,N-dimethylaminopropylacrylamide and 50 parts toluene were placed and 3.3 parts azo-bis-isobutyronitrile as a polymerization catalyst was added. The reaction mixture was heated to 90°C and allowed to polymerize for 4 hours. Thereafter, 15 parts acetic acid and 558.6 parts water were added and toluene was removed by azeotropic distillation with water by heating the mixture to 90-100°C. To the thus obtained copolymer, 23.1 parts epichlorohydrin was added and quaternization reaction was carried out at 50°C for 2 hours. By adjusting the concentration, a surface treatment agent containing 20% non-volatile content was obtained. Example 2 The procedure of Example 1 was repeated using 88.4 parts styrene, 23.4 parts N,N-dimethylaminopropylacrylamide, 9.0 parts acetic acid and 13.9 parts epichlorohydrin as a quaternizer, and a surface treatment agent was obtained. Example 3 The procedure of Example 1 was repeated using 72.8 parts styrene, 31.2 parts N,N-dimethylaminopropylacrylamide, 11.8 parts vinyltoluene, 12 parts acetic acid and 18.5 parts epichlorohydrin as a quaternizer and a surface treatment agent was obtained. Example 4 The procedure of Example 1 was repeated using 72.8 parts styrene, 25.5 parts N,N-dimethylaminopropyl(meth)acrylamide, 21.3 parts isobutylmethacrylate, 9.0 parts acetic acid and 13.9 parts epichlorohydrin and a surface treatment agent was obtained. Example 5 The procedure of Example 1 was repeated using 78 parts styrene, 39 parts N,N-dimethylaminopropylacrylamide, 12 parts acetic acid and 18 parts butylene oxide as a quaternizer and a surface treatment agent was obtained. Example 6 The procedure of Example 1 was repeated using 83.2 parts styrene, 31.2 parts N,N-dimethylaminopropylacrylamide, 12 parts acetic acid and 25.2 parts dimethyl sulfate as a quaternizer and a surface treatment agent was obtained. Example 7 The following tests were carried out in order to evaluate the effects of the surface treatment agents obtained in Examples 1-6 and commercially available products as comparative agents. Evaluation 1 The surface of commercially available kraft liner test paper which was internally sized with an alkylketene dimer compound was coated with the surface treatment agents of Examples 1-6, a commercially available cationic sizing agent A (a reaction product of styrene/N,N-dialkylamino(meth)acrylate-epichlorohydrin) and a commercially available anionic sizing agent B (copolymer of styrene-acryl acid) under the condition of paper surface pH of 6.4 (neutral liner). The coating was carried out as follows. Coating liquids were prepared so that the resulting coating weight would be 0.05g/m² (solid content). The coating liquids were applied on the test paper by a laboratory scale size press (manufactured by Kumagaya Riki Kogyo K.K.) and dried by a drum drier at 100°C for 30 seconds. After conditioned in a chamber of constant temperature of 20°C and constant humidity of 65% for 24 hours, Cobb sizing degree and sliding angle of the surface treated paper were measured. The results are shown in Table 1. The Cobb sizing degree was measured in accordance with JIS P-8140. The lower the number, the better the effect. The sliding angle was measured in accordance with the inclination method stipulated in JIS P-8147. The sliding angles after paper had been slid 1 time, 5 times and 10 times, are shown in Table 1. The larger the numerical value, the better the effect. Evaluation 2 The procedure of Evaluation 1 was repeated using B-grade acidic liner test paper, with a surface pH of 4.2. The results are shown in Table 2. Evaluation 3 The procedure of Evaluation 2 was repeated using a coating liquid which had been kept at 50°C for 5 hours after the pH thereof was adjusted to 8.0. This test was carried out as a simulation of a practical commercial operation. That is, the surface treatment agent was tested with the pH of the coating liquid being raised by addition of another additive and the coating liquid being recirculated over a period of several hours. The results are shown in Table 3. The surface treatment agent for paper of the present invention has excellent slip prevention and sizing effects and its sizing effect is not impaired at a pH over 7.

Claims: A surface treatment agent for paper, comprising a copolymer prepared by (I) polymerizing a mixture comprising (1) 95-50 mole % of at least one aromatic monomer selected from the group consisting of styrene and styrene derivatives; and (2) 5-50 mole % of at least one N,N-dialkylaminoalkyl(meth)acrylamide, and (II) quaternizing the polymerization product with a quaternizing agent selected from the group consisting of dimethyl sulfate, methyl chloride, allyl chloride, benzyl chloride, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, epibromohydrin, ethylene chlorohydrin and ethylene bromohydrin. A surface treatment agent for paper as recited in Claim 1, wherein the copolymer comprises (a) 94-50 mole % styrene and/or a styrene derivative, and (b) 5-50 mole % N,N-dialkylaminoalkyl(meth)acrylamide and (c) 1-20 mole % of another vinyl monomer copolymerizable with the above (a) and (b).

Inventors: HAKATA TOSHIYUKI, IKEDA TSUYOSHI, IKEGAYA TSUGUMI, HAKATA, TOSHIYUKI, IKEDA, TSUYOSHI, IKEGAYA, TSUGUMI
Applicants: NIPPON PMC KK, JAPAN PMC CORPORATION
Application year: 1989
Main classification: D21H17
IPC codes: D21H17, D21H19