JP5429807B2 - Water-based emulsion adhesive - Google Patents

Description

  The present invention relates to an aqueous emulsion adhesive for information carrying sheets. More specifically, the present invention relates to a water-based emulsion adhesive for postcard paper that can be bonded with a force of folding.

  The information-carrying sheet has such a specification that once it is peeled off, it cannot be bonded twice, so that personal information can be safely handled even with a postcard whose shipping cost is lower than that of a sealed letter while protecting personal privacy. For this reason, it is used in various situations such as direct mail, tax / pension notices, confidential postcards such as bank statements, and delivery slips.

  Laminated postcard paper, which is a type of information-carrying sheet, is attached so that it can be re-peeled by a pseudo-adhesive layer provided on the base material by folding it with the information printing surface inside and then applying predetermined pressure and heat. It is to be combined. In this bonded postcard paper, the method of forming the pseudo-adhesive layer on the base material is classified into a front paste type and a back paste type. The pre-glue method refers to a method in which after a pseudo adhesive layer is provided on a substrate such as paper, information such as characters and figures is printed / printed on the surface of the pseudo adhesive layer. On the other hand, the post-glue method refers to a method in which a pseudo adhesive layer is provided on the information printing surface after printing information such as characters and figures on a substrate.

  The pressure-sensitive adhesive and heat-sensitive adhesive used in the pre-glue method must be bonded by a mechanical post-treatment, and it is difficult to bond them at ordinary households. In addition, the adhesive force changes over time after bonding, and printed characters appear on the peeled side, so-called show-through, re-peeling is impossible, or peeling occurs on the contrary. There is a point. On the other hand, the water-based emulsion adhesive used in the post-glue system requires non-ink transferability and releasability because it often requires drying after coating, and often uses wax in the adhesive. There is a problem that it is inferior or the appearance of the printed paper after peeling tends to deteriorate.

  In addition, when bonding by pseudo-adhesion using the above-mentioned adhesive, a film or the like must be pasted on the surface of the base material such as paper, or after being processed such as a release treatment. Therefore, it takes time and money. Furthermore, paper that has been processed to attach a film or the like cannot often be used as recycled paper.

  Patent Document 1 discloses that a vinyl acetate-polyolefin copolymer resin is used as a heat-sensitive removable adhesive that can be bonded at home. Patent Document 2 discloses one using an acrylic emulsion as a pressure-sensitive removable adhesive with little change over time. However, these adhesives are pressure-sensitive or heat-sensitive removable adhesives, and require some kind of post-treatment such as heat and large pressure during bonding.

  Patent Document 3 discloses a water-based adhesive for information-carrying sheets containing an acrylic resin emulsion, a vinyl acetate resin emulsion, a wax emulsion, and a silicon oil emulsion as essential components. However, since the above-mentioned adhesive has a wax emulsion or silicone oil emulsion as an essential component, it is inferior in the writing property of the adhesive coating surface after peeling, for example, when it is used as a reply postcard, it needs writing property on the peeling surface. There is a problem that it cannot be used for various purposes.

JP-A-8-258467 JP 2001-303007 A JP 2007-99797 A

  Accordingly, an object of the present invention is an aqueous emulsion adhesive for information carrying sheets, which can be bonded with a force of folding without applying heat or a large pressure, and also has excellent removability. Another object of the present invention is to provide an aqueous emulsion adhesive for information-carrying sheets in which printed matter does not show through during peeling.

  The above object is achieved by the present invention described below. That is, the present invention relates to a copolymer comprising 100 parts by mass of a hydrophobic monomer (a) mainly composed of (meth) acrylic acid alkyl ester and 1 to 40 parts by mass of a crosslinkable monomer (b) ( A water-based emulsion adhesive in which 10 to 80 parts by mass of polyethylene oxide (B) is blended with 100 parts by mass of solid content of A), and the glass transition temperature of the copolymer (A) is -10 ° C to 50 ° C. Provided is an aqueous emulsion adhesive characterized in that it is at ° C. In the present invention, the copolymer (A) is preferably obtained by emulsion polymerization in the presence of at least water, a surfactant, and a polymerization initiator.

  According to the present invention, it is an aqueous emulsion adhesive for information-carrying sheets, which can be bonded with a force of folding without applying heat or a large pressure, and also has excellent removability, It is possible to provide an aqueous emulsion adhesive for an information carrying sheet in which a printed matter does not show through during peeling.

  Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention. The term “(meth) acryl” in the claims and the specification of the present invention means both “acryl” and “methacryl”, and the term “(meth) acrylate” ”And“ methacrylate ”.

  The aqueous emulsion adhesive of the present invention comprises a co-polymer consisting of 100 parts by mass of a hydrophobic monomer (a) mainly composed of (meth) acrylic acid alkyl ester and 1 to 40 parts by mass of a crosslinkable monomer (b). It is characterized by blending 10 to 80 parts by mass of polyethylene oxide (B) with respect to 100 parts by mass of the solid content of the polymer (A).

  The monomer (a) used in the present invention is a hydrophobic monomer mainly composed of (meth) acrylic acid alkyl ester. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) ) Acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate or lauryl (meth) acrylate Examples include acrylic monomers, aromatic monomers such as styrene and α-methylstyrene, and nitrile monomers such as (meth) acrylonitrile. These can be used alone or in combination of two or more. Furthermore, these monomers (a) can be used in combination with other hydrophilic monomers (c), for example, carboxyl group-containing monomers such as acrylic acid and methacrylic acid.

  The crosslinkable monomer (b) used in the present invention is a monomer having at least divalent polymerizability, such as diethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate. Diacrylate such as, triacrylate such as trimethylolpropane tri (meth) acrylate, trimethylolmethane tri (meth) acrylate, acrylamide such as N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, divinylbenzene, etc. Preferably, a monomer having a trivalent or higher valence is good, and trimethylolpropane tri (meth) acrylate and the like can be mentioned. These can be used alone or in combination of two or more.

The usage-amount of the said crosslinking | crosslinked monomer (b) is 1-40 mass parts when it is 100 mass parts of monomers (a). Preferably it is 10-30 mass parts, More preferably, it is 15-25 mass parts. When the amount of the crosslinkable monomer (b) used is less than 1 part by mass, the non-ink transferability is insufficient. On the other hand, when the amount of the monomer (b) used exceeds 40 parts by mass, The stability of the adhesive becomes insufficient.
Note that “non-ink transferability” means that a printed character or the like appears on the peeled side, ie, no so-called show-through.

  The copolymer (A) obtained by copolymerizing the monomers (a) and (b) preferably has a weight average molecular weight (GPC measurement, standard polystyrene conversion) of 50,000 or more. A weight average molecular weight of less than 50,000 is not preferable because non-ink transferability is insufficient.

  Moreover, the glass transition temperature of the copolymer (A) used by this invention is -10 degreeC-50 degreeC. Preferably, it is 0 degreeC-30 degreeC. When the glass transition temperature of the copolymer (A) is less than −10 ° C., the non-ink transfer property becomes insufficient. On the other hand, when the glass transition temperature exceeds 50 ° C., film formation does not occur and the adhesive is not used. The coated surface will be whitened. The said glass transition temperature can be adjusted to said range by the usage-ratio of each monomer.

  Although the manufacturing method of the said copolymer (A) is not specifically limited, It is preferable to manufacture by emulsion polymerization. In particular, it is preferable to produce the copolymer (A) by emulsion polymerization in the presence of at least water, a surfactant, and a polymerization initiator. Thereby, the copolymer (A) excellent in mechanical stability and storage stability can be manufactured, and the aqueous emulsion adhesive excellent in removability is obtained. The content of the copolymer (A) is preferably 30 to 73% by mass of the aqueous emulsion adhesive.

  Examples of the reaction method for the emulsion polymerization include a normal one-stage continuous monomer uniform dropping method, a core-shell polymerization method that is a multi-stage monomer feed method, and a power feed polymerization method that continuously changes the monomer composition to be fed during the polymerization. The polymerization method can also be used.

  As the surfactant used in the emulsion polymerization, known non-reactive surfactants and reactive surfactants which are usually used such as nonionic, anionic, cationic or amphoteric surfactants can be used. One type or a combination of two or more types can be used.

  In particular, examples of anionic surfactants include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, polyoxyethylene alkylaryl sulfonates, polyoxyethylene alkylaryl ether sulfates, and the like. Examples of the surfactant include polyoxyethylene alkyl ester type, alkylphenyl ether type or alkyl ether type, and acetylene alcohol type. Examples of the cationic surfactant include aliphatic amine salts and their Examples of amphoteric surfactants such as quaternary ammonium salts and aromatic quaternary ammonium salts include carboxybetaine, sulfobetaine, aminocarboxylate, and imidazoline derivatives. These surfactants can be used alone or in combination of two or more.

  As for the usage-amount of the said surfactant, 0.1-10 mass parts is preferable with respect to 100 mass parts of solid content of a copolymer (A). When the amount of the surfactant used is less than 0.1 parts by mass, the resulting emulsion is inferior in chemical stability. On the other hand, when the amount used exceeds 10 parts by mass, the obtained emulsion is loaded with information. Since it is inferior to non-ink transferability when used as an aqueous emulsion adhesive for sheets, it is not preferred.

  Moreover, as a polymerization initiator used for the emulsion polymerization, a known polymerization initiator usually used in emulsion polymerization of acrylic resins can be used. For example, as a water-soluble polymerization initiator, potassium persulfate, sodium persulfate, Examples include persulfates such as ammonium persulfate and hydrogen peroxide. Examples of oil-soluble polymerization initiators include peroxides such as benzoyl peroxide and lauroyl peroxide, azobisisobutyronitrile, and azobisvaleronitrile. These azobis compounds and polymer azo polymerization initiators can be used, and these can be used alone or in combination of two or more. A redox polymerization initiator composed of a combination of these oxidizing agents and a reducing agent such as sodium bisulfite, sodium thiosulfate, Rongalite, and ascorbic acid can also be used.

  In the emulsion polymerization, a mercaptan compound such as n-dodecyl mercaptan or a chain transfer agent such as alcohol can be used for the purpose of adjusting the molecular weight of the resulting copolymer (A). Furthermore, a monomer having two or more polymerizable double bonds such as diallyl phthalate or a silane coupling agent having a polymerizable double bond such as γ- (meth) acryloxypropyltrimethoxysilane is also used. be able to.

  The emulsion polymerization can be carried out by reacting the copolymer (A) containing the monomers (a) and (b) in the presence of at least water, a polymerization initiator and a surfactant. The reaction temperature is preferably about 30 to 100 ° C., for example, and the reaction time is preferably about 1 to 10 hours, for example. Specifically, in a reaction vessel charged with water and a polymerization initiator, the monomer mixture, or a mixture obtained by emulsifying the monomer mixture, is reacted by batch addition or dropwise addition for a while, as appropriate. It reacts for a certain time while adjusting the temperature.

  By blending 10 to 80 parts by mass of polyethylene oxide (B) with respect to 100 parts by mass of the solid content of the copolymer (A) produced as described above, the aqueous emulsion adhesive for information-carrying sheets of the present invention is obtained. Can be obtained. Since the polyethylene oxide used in the present invention is easily dissolved in water, it has good compatibility with the emulsion obtained by emulsion polymerization, and by using the polyethylene oxide, it is suitable for the aqueous emulsion adhesive of the present invention. Adhesiveness and good removability can be imparted. Furthermore, it becomes possible to control the peel strength of the aqueous emulsion adhesive depending on the degree of polymerization of the polyethylene oxide used.

  The polyethylene oxide (B) used in the present invention is a general polyethylene oxide having a weight average molecular weight of 50,000 to 8,000,000, preferably 70,000 to 4,000,000, more preferably about 100,000 to 1,000,000. The polyethylene oxide (B) can be dissolved in water and then blended in the emulsion. Examples of the polyethylene oxide (B) include PEO-1 (manufactured by Sumitomo Seika: molecular weight 150,000 to 400,000), Alcox R-150 (manufactured by Meisei Chemical Industry: molecular weight 100,000 to 170,000), and the like. . These can be used alone or in combination of two or more different weight average molecular weights.

  As above-mentioned, the usage-amount of the said polyethylene oxide (B) is 10-80 mass parts with respect to 100 mass parts of solid content of a copolymer (A). When the amount of polyethylene oxide (B) used is less than 10 parts by mass, the removability is inferior or non-ink transferability is insufficient. Bends, the viscosity becomes too high, causing poor coating, and the stability of the adhesive becomes insufficient. In addition, the said polyethylene oxide (B) can also be made to exist during the copolymerization reaction of the said monomer (a) and a monomer (b) in the range which does not impair the effect of this invention.

  Moreover, the water-based emulsion adhesive of this invention can contain a water-soluble high molecular compound as needed. Examples of the water-soluble polymer compound include vinyl alcohol polymers such as polyvinyl alcohol and various modified products thereof, cellulose derivatives such as alkyl cellulose, hydroxyalkyl cellulose, alkyl hydroxyalkyl cellulose, and carboxymethyl cellulose, polyalkylene glycol, anhydrous A maleic acid / styrene copolymer, a maleic anhydride / methyl vinyl ether copolymer, or the like can be used, and other known water-soluble polymer compounds can also be used. These water-soluble polymer compounds can also be present during the copolymerization reaction of the monomer (a) and the monomer (b) as long as the effects of the present invention are not impaired.

  Moreover, the aqueous | water-based emulsion adhesive agent of this invention can contain the neutralizing agent which neutralizes the acid group, when the said copolymer (A) has acid groups, such as a carboxyl group. The neutralizing agent may be any of a basic organic compound and a basic inorganic compound. For example, an amine such as trimethylamine, diethanolamine, triethanolamine, 2-aminomethylpropanol, sodium hydroxide, water Examples thereof include alkali metal hydroxides such as potassium oxide, ammonia and the like, and other known neutralizing agents can also be used. In addition, these neutralizing agents can also be made to exist in the copolymerization reaction of the said monomer (a) and a monomer (b) in the range which does not impair the effect of this invention.

  Furthermore, the aqueous emulsion adhesive of the present invention may contain various additives as long as the effects of the invention are not impaired. For example, use additives such as dispersants, antifoaming agents, thickeners, leveling agents, anti-gelling agents, light stabilizers, antioxidants, heat resistance improvers, lubricants, antistatic agents, and crosslinking agents. Can do.

The adhesive of the present invention can be applied to a postcard paper by a coating method using a conventionally known coating machine. The said coating machine is not specifically limited, For example, it can coat using an air knife coater, a blade coater, a curtain coater, and a roll coater. The amount of adhesive applied by the above method is preferably 3 to 40 g / m ² . When the coating amount is less than 3 g / m ^2, it is difficult to obtain a desired adhesive strength, and when it exceeds 40 g / m ² , the adhesive strength becomes too strong and it may be difficult to peel again. Immediately after applying the adhesive under the above conditions, it is desirable to bond them using a folding machine. If it takes a long time from the adhesive coating to the bonding, it is difficult to obtain a desired adhesive strength, which is not preferable.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not restrict | limited at all by these. In the examples, “%” and “part” represent “% by mass” and “part by mass”, respectively, unless otherwise specified.

<Preparation of adhesive>
[Example 1]
51 parts of ion-exchanged water, 16 parts of polyoxyethylene alkyl ether sulfate sodium salt (trade name: Latemul E-118B, manufactured by Kao Corporation), 50.0 parts of butyl acrylate, 50.0 parts of methyl methacrylate, 3 acrylic acid 0.0 part, 1.0 part of methacrylic acid and 20.0 parts of trimethylolpropane triacrylate were weighed and stirred to prepare an emulsified mixture.

  Next, 60.0 parts of ion exchange water was charged into a reactor equipped with a stirrer, a reflux condenser, a thermometer, a dropping device and a nitrogen gas introduction tube, and the air in the device was replaced with nitrogen gas, followed by stirring. However, the internal temperature of the said apparatus was heated at 80 degreeC. After the internal temperature reached 80 ° C., 1.0 part of a 10% ammonium persulfate aqueous solution was added, and immediately the emulsion mixture and 4.0 parts of a 5% ammonium persulfate aqueous solution were added dropwise over 3 hours. After completion of the dropwise addition, the reaction was further carried out for 3 hours while maintaining the internal temperature of the apparatus at 80 ° C., and then the internal temperature was cooled to room temperature to obtain an emulsion containing the copolymer 1. The glass transition temperature of the copolymer 1 was calculated from the monomers used. The results are shown in Table 1.

  With respect to 100 parts of solid content of the emulsion containing the copolymer 1 after cooling, 0.3 part of 25% aqueous ammonia and polyethylene oxide (trade name: PEO-1, manufactured by Sumitomo Seika, molecular weight: 150,000- 400,000) is dissolved in water, 340 parts of a polyethylene oxide aqueous solution prepared so that the concentration of polyethylene oxide becomes 10% is added, and further, 64 parts of water is prepared so that the solid content becomes 20.0%. Thus, an aqueous emulsion adhesive of Example 1 was obtained. As a result of analysis, this aqueous emulsion adhesive had a viscosity of 500 mPa · s / 25 ° C., a solid content of 20.0%, and a pH of 7.5. The results are shown in Table 2.

[Examples 2-14, Comparative Examples 1-5]
An emulsion composition containing copolymers 2 to 19 and Examples 2 to 14 under the same conditions as in Example 1 except that the monomer components and blending amounts in Example 1 are changed to those shown in Table 1. The adhesives of Comparative Examples 1 to 5 were prepared. Table 2 shows the monomer constituents, blending amounts, and analysis results of the obtained adhesives of Examples 2 to 14 and Comparative Examples 1 to 5.

BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate EA: ethyl acrylate MA: methyl acrylate MMA: methyl methacrylate BMA: butyl methacrylate St: styrene AAc: acrylic acid MAAc: methacrylic acid (* 1): diethylene glycol diacrylate (* 2): Divinylbenzene (* 3): Trimethylolpropane triacrylate

<Test methods and evaluation criteria>
About the adhesive agent of the said Example and a comparative example, it tested by the following test method and the result shown in Table 3 was obtained.
[Sample preparation]
Prepare two sheets of high-quality paper <70> printed with a laser printer, apply the adhesives of Examples and Comparative Examples on one printed surface with Mayer Bar # 18 (coating amount of about 30 g / wet), and immediately apply the other Paste the print side of the paper. After bonding, the sample was left for 24 hours in an atmosphere of 23 ° C. and 50% RH.

[Peel adhesion strength test]
The sample prepared by the above method is cut into a width of 100 mm, and the peel adhesive strength is measured with an autograph (Shimadzu Corporation AUTOGRAPH AGS-1000B) at a pulling speed of 300 mm / min.

[Adhesiveness]
The sample prepared by the above method is bent by hand to evaluate the bending resistance. Also, the sample is peeled off by hand to evaluate the peelability, non-ink transferability (printing show-through condition), and white residue. The evaluation criteria are shown below.
<Evaluation criteria>
(1) Bending resistance ○: No peeling even when bent ×: Peeling when bent (2) Peelability ◎: Peelable with moderate force ○: Peelable but slightly peeled surface Fluffy x: Non-peelable (3) Non-ink transferability (print show-through)
◎: Characters do not appear at all on the opposite side ○: A part of the characters appear on the opposite side ×: The characters appear darker on the opposite side (4) White residue ◎: The density of the printed characters is peeled off ○: The printed characters are slightly white after peeling. ×: The printed characters are almost invisible after peeling.

[Writing]
After the sample prepared by the above method is peeled off by hand, a character is written on the peeled surface with an HB pencil, a water-based ballpoint pen, and an oil-based ballpoint pen, and the writing property is evaluated.
<Evaluation criteria>
◎: Writable with all writing tools ○: Water-based and oil-based ballpoint pens can be written, but HB pencils cannot be written ×: Items that cannot be written with all writing tools

  As can be seen from Table 3, the adhesives of Examples 1 to 14 of the present invention have moderate peel adhesive strength, excellent re-peelability, and do not cause print-through or white residue. There is no. On the other hand, the adhesives of Comparative Examples 1 to 5 show print-through and white residue even when the peel strength is insufficient or the strength is too strong to be peeled off or the peel strength is good. .

  According to the present invention, it is an aqueous emulsion adhesive for information-carrying sheets, which can be bonded with a force of folding without applying heat or a large pressure, and also has excellent removability, It is possible to provide an aqueous emulsion adhesive for an information carrying sheet in which a printed matter does not show through during peeling.

Claims (2)

  Solid content 100 of copolymer (A) consisting of 100 parts by mass of hydrophobic monomer (a) mainly composed of (meth) acrylic acid alkyl ester and 1 to 40 parts by mass of crosslinkable monomer (b). An aqueous emulsion adhesive comprising 10 to 80 parts by mass of polyethylene oxide (B) with respect to parts by mass, wherein the glass transition temperature of the copolymer (A) is from -10 ° C to 50 ° C. A water-based emulsion adhesive.   The aqueous emulsion adhesive according to claim 1, wherein the copolymer (A) is emulsion-polymerized in the presence of at least water, a surfactant, and a polymerization initiator.