JP2017057517A - Base paper for press bonding postcard, application method thereof and selection method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base paper for press bonding postcard excellent in folding resistance and concealment property with generating paper breakage during wet at re-detachment.SOLUTION: There is provided a base paper for press bonding postcard consisting of a base paper having internal bond strength during wet of 100 mJ or more by an internal bond tester method defined in JAPAN TAPPI No.18-2. Absorption of water with contact time of 60 sec. by a Cobb method defined by JIS P 8140 of the base paper is preferably 3 g/mor more and 45 g/mor less.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive postcard base paper. Specifically, the present invention relates to a pressure-sensitive postcard base paper excellent in water resistance, and relates to a pressure-sensitive postcard base paper used in various postcard systems such as a two-fold postcard and a three-fold postcard.

  Along with the revision of the Postal Law, a postcard system with confidentiality in which a sheet on which necessary information is recorded is folded in half, folded in three, etc. has been put into practical use and has become widespread. A crimped postcard is known as such a confidential postcard, and a crimped postcard having a base material made of a base paper for a pressure-bonded postcard and a pseudo-adhesive layer made of pseudo-adhesive glue is used for the pressure-bonded postcard. . The pseudo-adhesive layer has no adhesiveness at normal temperature and normal pressure. For example, the pseudo-adhesive layer exhibits adhesiveness by being pressed or heated and pressed with the adhesive layers facing each other, and can be peeled again after bonding. Thereby, the recipient of the pressure-bonded postcard can peel the peelable adhesive portion and read the confidential communication information recorded inside.

  The pseudo adhesive layer is required to have stability over time under various environmental conditions. For this reason, the peeling force between the adhesive layers is adjusted so as not to be too strong to make re-peeling difficult, and to be too weak to peel off during postcard delivery.

  Crimp postcard base paper is required to have concealability and folding resistance. With regard to the concealment property, it is desirable that the secret part cannot be recognized at all from the outside. For this reason, it is conceivable to ensure the opacity by incorporating a filler into the base paper for the pressure-bonded postcard. However, the ash content in the base paper reduces the strength in the base paper layer and may destroy the substrate when it is peeled off again. Regarding folding resistance, it becomes a practical problem to cause paper breakage at a cut portion such as a perforation or a half cut in folding and crimping.

  In addition, when it is wetted with water due to rain, etc., and peels again in a damp state where drying is not sufficient, fluffing occurs on the surface of the base paper, and paper breaks when wet (base paper interlayer breakage) may occur. There is. In order to improve the re-peelability at the time of such wetness, a wet paper strength enhancer is internally added to the base paper to adjust the T-shaped peel strength (see Patent Document 1), and has a specific wet tensile strength. It has been proposed to increase the water resistance of the pseudo adhesive layer itself in a paper substrate (see Patent Document 2). However, in these proposals, it is said that the paper interlayer strength and peel strength measured by the T-shaped peel force, the wet tensile strength by tensile test, etc. were adjusted. Currently, satisfactory results are not always obtained.

JP 7-276858 A Japanese Patent Laid-Open No. 2008-24860

  The main object of the present invention is to provide a base sheet for a pressure-bonded postcard that has excellent folding resistance and concealment and does not cause tearing when wet.

  The base paper for pressure-bonded postcards of the present invention has the property that, when the beating of the pulp fiber used is advanced, the folding resistance of the base paper can be improved, but the concealment is significantly reduced, from the standard of weight as a postcard. There is. Further, when the ash content of the base paper is increased in order to improve the concealing property, the internal bond strength of the base paper is lowered, which causes the property that the folding resistance is lowered and the paper breaks easily.

  In order to achieve both the improvement of both folding resistance and concealment and the occurrence of paper tearing when wet when re-peeling, the present inventor has developed a pseudo-adhesive force and an internal bond when the base paper is wet. We focused on strength and studied. As a result, it was found that the pseudo-adhesive strength was unnecessarily increased when the pseudo-adhesive paste did not sufficiently penetrate into the base paper and remained on the surface of the base paper. The base paper JAPAN TAPPI No. Found that the internal bond strength when wet by the internal bond tester method stipulated in 18-2 is 100 mJ or more, while maintaining sufficient pseudo-adhesive strength and does not cause paper breakage when wet As a result, the present inventors have found that the paper is excellent in folding resistance and concealment and can be applied to a crimped postcard.

  The present invention has been completed based on such studies. That is, the present invention has the following configuration.

  Item 1: JAPAN TAPPI No. A base sheet for pressure-bonding postcards made of a base paper having an internal bond strength of 100 mJ or more when wet by the internal bond tester method defined in 18-2.

Item 2: The pressure bonding of Item 1, wherein the water absorption of the base paper is 3 g / m ² or more and 45 g / m ² or less when the contact time is 60 seconds according to the Cobb method defined in JIS P 8140. Postcard base paper.

  Item 3: The pressure bonding of Item 1 or 2, wherein the folding strength of the base paper measured according to JIS P 8115 is 100 times or more and the opacity measured according to JIS P 8149 is 90% or more. Postcard base paper.

  Item 4: The base paper contains pulp, and contains softwood bleached kraft pulp and hardwood bleached kraft pulp in a mass ratio (softwood bleached kraft pulp: hardwood bleached kraft pulp) in a range of 5:95 to 70:30. The base paper for pressure-bonding postcards of any one of -3.

  Item 5: The pressure-sensitive postcard base paper according to any one of Items 1 to 4, wherein the base paper contains pulp, and the Canadian standard freeness measured in accordance with JIS P 8121 of the pulp is in the range of 100 to 600 ml. .

  Item 6: The base paper for pressure-bonded postcards according to any one of Items 1 to 5, wherein the base paper contains pulp and further contains a wet paper strength enhancer in an amount of 0.1 to 2.0 parts per 100 parts by weight of the pulp. .

  Item 7: The item according to any one of Items 1 to 6, wherein the base paper contains at least one wet paper strength enhancer selected from the group consisting of a polyamide epichlorohydrin resin, a urea-formaldehyde resin, and a melamine-formaldehyde resin. Crimp postcard base paper.

  Item 8: The pressure-sensitive postcard base paper according to any one of Items 1 to 7, wherein the base paper contains talc or kaolin as a filler.

  Item 9: JAPAN TAPPI No. The internal bond strength when wet by the internal bond tester method specified in 18-2 is 180 mJ or more, and further provided with a pseudo adhesive layer having a pseudo adhesive force of 70 N / m or less on at least one side of the base paper, Item 10. A postcard for a pressure-bonded postcard according to any one of Items 1 to 8.

  Item 10: A method for using a base paper for a pressure-bonded postcard, wherein the base paper according to the above-mentioned items 1 to 9 is provided with a cut portion and / or a pseudo adhesive layer and applied to a pressure-bonded postcard.

  Item 11: A method for selecting a base paper for pressure-bonded postcards, which is a method of selecting a JAPAN TAPPI No. Measuring the internal bond strength when wet by the internal bond tester method defined in 18-2 and confirming whether the internal bond strength is 100 mJ or more, the internal bond strength is 100 mJ or more A sorting method including a step of selecting a base paper.

  The base paper for pressure-bonded postcards of the present invention is excellent in folding resistance and concealment, and does not cause paper breakage when wet when re-peeling. In addition, paper breakage at cuts such as perforations and half cuts can be suppressed, and the crimping process suitability is excellent.

  In this specification, the expression “comprising” includes the concepts of “comprising”, “consisting essentially of”, and “consisting solely”.

  The base paper for pressure-bonded postcards in the present invention is JAPAN TAPPI No. This is a pressure-sensitive postcard base paper made of a base paper having an internal bond strength of 100 mJ or more when wet by the internal bond tester method defined in 18-2. In the present invention, based on the fact that the tearing of the base paper for pressure-bonded postcards is caused by the interlaminar fracture of the base paper, JAPAN TAPPI No. It is defined from the relationship with the internal bond strength when wet by the internal bond tester method defined in 18-2. As a result, satisfactory results can be obtained that have not been obtained from the strength characteristics in the conventional state of T-peeling and drying. When the internal bond strength of the base paper when wet is less than 100 mJ, it wets with water due to rain or the like, and in the wet state where the dryness is not sufficient, the paper breaks when wet when re-peeling. In this case, there is a restriction that if the postcard is peeled off during delivery, it is not suitable for the base paper for the pressure-bonded postcard. Therefore, the pseudo adhesive force cannot be reduced more than necessary in order to suppress the occurrence of paper tearing. For this reason, the upper limit of the internal bond strength is not particularly limited, but is preferably about 500 mJ or less, more preferably about 400 mJ or less.

  JAPAN TAPPI No. The internal bond strength when wet by the internal bond tester method specified in 18-2 is, for example, the type and ratio of pulp used for the base paper, the freeness of the pulp, the type and content of the wet paper strength enhancer, It can be adjusted to 100 mJ or more by adjusting the type and content of filler, the type and amount of sizing agent, and the like. Here, the internal bond strength of the base paper when wet is measured by using an internal bond tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) after adjusting the wetness of the base paper based on JIS P 8135 by immersion in water for 1 hour. Can do.

In the present invention, the water absorption at a contact time of 60 seconds according to the Cobb method defined in JIS P 8140 of the base paper is preferably 3 g / m ² or more and 45 g / m ² or less. The water absorption is more preferably 5 g / m ² or more. On the other hand, the water absorption is more preferably 40 g / m ² or less. By making the water absorbency 3 g / m ² or more, the pseudo-adhesive paste is appropriately penetrated into the base paper and does not leave much on the surface of the base paper, thereby reducing the pseudo-adhesive force and suppressing paper tearing when wet during re-peeling Can be improved. On the other hand, by setting it to 45 g / m ² or less, it is possible to suppress the penetration of the pseudo adhesive paste into the base paper, to obtain a sufficient pseudo adhesive force, and to improve the effect of suppressing peeling during delivery of the postcard.

  In the present invention, the folding strength measured according to JIS P 8115 of the base paper is preferably 100 times or more, and the opacity measured according to JIS P 8149 is preferably 90% or more. By setting the folding strength to 100 times or more, there is no possibility of causing a paper break at a cut portion such as a perforation or a half cut in the folding and crimping processing such as V-folding and Z-folding. The folding strength is more preferably 150 times or more, still more preferably 200 times or more, and particularly preferably 400 times or more. The folding endurance can be increased by adjusting the pulp used for the base paper, for example, by lowering the freeness, increasing the content of softwood pulp, or reducing the ash content of the base paper. On the other hand, the opacity can be increased by adjusting the loosening of the pulp to increase the drainage, blending the base paper with a filler, and the like.

  In the present invention, the JAPAN TAPPI No. of the base paper is used. It is preferable that the internal bond strength when wet by the internal bond tester method defined in 18-2 is 180 mJ or more, and further, a pseudo adhesive layer having a pseudo adhesive force of 70 N / m or less is provided on at least one side of the base paper. . In this case, the internal bond strength is more preferably 200 mJ or more. On the other hand, the pseudo adhesive force is more preferably 60 N / m or less. Thereby, the effect of suppressing paper breakage when wet during re-peeling can be significantly improved. At this time, the pseudo-adhesive force is preferably 35 N / m or more, and more preferably 40 N / m or more so that the postcard is not too weak to be peeled off during delivery.

  In the present invention, the base paper preferably contains pulp. There are no particular limitations on the method and type of pulp. Examples of the pulp include chemical pulp such as kraft pulp (KP), mechanical pulp such as SGP, RGP, BCTMP and CTMP, wood pulp such as waste paper pulp such as deinked pulp, and kenaf, bamboo, straw, hemp, etc. Non-wood pulp. Further, organic synthetic fibers such as polyamide fibers and polyester fibers, recycled fibers such as polynosic fibers, and inorganic fibers such as glass fibers, ceramic fibers, and carbon fibers can also be used. It is preferable to use chlorine-free pulp such as ECF pulp or TCF pulp. Mechanical pulp is preferably removed in order to suppress yellowing of the base paper and improve the formation, but can be used as long as the effect of the present invention is not impaired.

  In the present invention, the base paper contains pulp, and preferably contains softwood bleached kraft pulp and hardwood bleached kraft pulp in a mass ratio (softwood bleached kraft pulp: hardwood bleached kraft pulp) of 5:95 to 70:30. . Here, the mass ratio is the mass ratio of absolutely dry pulp. By setting the mass ratio of the softwood bleached kraft pulp to 5 or more, the internal bond strength when the base paper is wet can be improved. In addition, the folding resistance can be increased to suppress paper breaks at the cuts such as perforations and half cuts, thereby further improving the suitability for crimping. The mass ratio of the softwood bleached kraft pulp is more preferably 10 or more, and still more preferably 20 or more. On the other hand, from the viewpoint of improving the formation of the base paper, the mass ratio of the hardwood bleached kraft pulp is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more.

  In the present invention, the base paper contains pulp, and the Canadian standard freeness (CSF) measured according to JIS P 8121: 2012 of the pulp is preferably in the range of 100 to 600 ml. By setting it to 100 ml or more, the opacity can be increased and the concealability can be improved. Moreover, drying in the paper making process can be promoted to improve operability. More preferably, it is 150 ml or more. On the other hand, from the viewpoint of improving the internal bond strength when the base paper is wet, it is preferably 600 ml or less, and more preferably 500 ml or less. Canadian standard freeness can be adjusted to the above range by mixing separately beaten pulp, or beaten premixed pulp when using two or more types of pulp. Also good.

  In the present invention, it is preferable that the base paper contains pulp and further contains a wet paper strength enhancer. Thereby, the internal bond strength when the base paper is wet can be improved. Also, the bending strength can be increased. The wet paper strength enhancer is not particularly limited, and examples thereof include polyamide polyamine epichlorohydrin resin, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide resin, and polyethyleneimine resin. As the wet paper strength enhancer, a cationic wet paper strength enhancer is preferable, and at least one selected from the group consisting of polyamide polyamine epichlorohydrin resin, urea-formaldehyde resin, and melamine-formaldehyde resin is more preferable.

  Although content of this wet paper strength enhancer is not specifically limited, 0.1-2.0 mass parts is preferable with respect to 100 mass parts of pulp, and 0.3-1.0 mass part is more preferable. By setting it as 0.1 mass part or more, the internal bond strength at the time of wetness of a base paper can be improved. On the other hand, by setting it as 2.0 mass parts or less, it is excellent in the effect of preventing the stain | pollution | contamination by the system internal rotation resulting from chemical excess, and can perform a continuous operation stably. In particular, the excessive amount of cationic chemicals easily generates agglomerated foreign matter in the paper machine system. Therefore, by setting the above range, it is possible to reduce the contamination of the product into the product and to exert the effects of the present invention without regret.

  In the present invention, the base paper preferably contains a filler. Various pigments can be used as fillers. Examples of fillers include talc, kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite and smectite. Examples include inorganic pigments and organic pigments such as polystyrene resin, urea resin, melamine resin, acrylic resin, and vinylidene chloride resin micro hollow particles, solid particles, and through-hole particles. These may be used alone or in combination of two or more. Among these, talc or kaolin is preferable from the viewpoint of improving the concealability and improving the internal bond strength when the base paper is wet. It is more preferable that talc is included from the viewpoint of improving folding resistance and suppressing paper breakage at the perforation.

  Although content of this filler is not specifically limited, 5-15 mass parts is preferable with respect to 100 mass parts of pulp completely dry, and 5-10 mass parts is more preferable. By setting it as 5 mass parts or more, opacity can be raised and concealment property can be improved. On the other hand, by setting the content to 15 parts by mass or less, it is possible to effectively suppress paper breakage at the time of re-peeling. Moreover, folding resistance can be improved. In the present invention, since sufficient opacity can be secured, it is preferable not to contain a colorant that may cause a decrease in whiteness or unevenness.

  The sizing degree of the base paper for the pressure-bonded postcard can be adjusted, for example, by an internal additive sizing agent contained in the base paper stock or a surface sizing agent applied or impregnated on the base paper by a size press device or the like. it can. The internal sizing agent is not particularly limited, and examples thereof include rosin sizing agents, synthetic sizing agents, petroleum resin sizing agents, alkyl ketene dimers, and alkenyl succinic anhydride neutral sizing agents. The internal sizing agent can be used in combination with a fixing agent such as a sulfuric acid band or cationized starch. The surface sizing agent is not particularly limited, and in addition to those listed as internally added sizes, oxidized starch, styrene-maleic acid copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, etc. It is done. By increasing the amount of the internal sizing agent added, it is possible to increase the internal bond strength when the base paper is wet, or to reduce the water absorption by the Cobb method defined in JIS P 8140 of the base paper. This makes it possible to adjust paper breakage when wet during re-peeling. Cobb water absorption can be adjusted by the type and amount of surface sizing agent. From the viewpoint of enhancing the stability of the pseudo adhesive force, it is preferable to include oxidized starch in the surface sizing agent, and it is more preferable to use a surface sizing agent made of oxidized starch.

  In the present invention, at the time of making a postcard paper for a pressure-bonded postcard, it is conventionally used in addition to pulp, a wet paper strength enhancer, a filler, and a sizing agent in the stock of the base paper as long as the effects of the present invention are not impaired. Various papermaking internal additives such as paper strength enhancers such as various anionic, nonionic, cationic or amphoteric polyacrylamide resins, yield improvers, drainage improvers, etc. Can be used. Furthermore, internal additives for papermaking such as colorants such as dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents and slime control agents can be added as necessary.

  There is no particular limitation on the papermaking method of the base paper for the pressure-bonded postcard. For example, the acidic papermaking method in which the papermaking pH is around 4.5, an alkaline filler such as calcium carbonate is used as a main component, and the papermaking pH is about 6 from weak acidity. All paper making methods such as a neutral paper making method with a weak alkalinity of about pH 9 can be applied. The paper machine is not particularly limited, and for example, a long net paper machine, a twin wire paper machine, a round net paper machine, a Yankee paper machine, an on-top multi-cylinder paper machine, and the like can be used as appropriate.

The basis weight of the base paper for the pressure-bonded postcard is not particularly limited, and can be appropriately selected so as to satisfy the weight standard as a postcard. In consideration of subsequent printing, pressure bonding, and the like, the basis weight of the base paper is preferably about 70 to 150 g / m ² . For example, the crimped postcard paper is preferably adjusted so as to be in the range of about 140 to 150 g / m ^{2 in} the case of two folds and in the range of about 120 to 130 g / m ^{2 in} the case of three folds.

  The pseudo adhesive layer in the present invention is formed using a pseudo adhesive paste. The pseudo-adhesive paste is not particularly limited as long as it has removability. For example, it contains a pseudo-adhesive generally used for pseudo-adhesion, an adhesive strength modifier, and other auxiliary agents if necessary. Can be used. The pseudo-adhesive is not particularly limited. For example, a rubber-based pressure-sensitive adhesive such as natural rubber or synthetic rubber; an acrylic pressure-sensitive adhesive containing acrylic acid and / or an acrylate ester as a main monomer component; a vinyl acetate polymer; Vinyl acetate pressure-sensitive adhesives containing vinyl acetate as the main monomer component such as ethylene-vinyl acetate copolymer (EVA); polysaccharide-based pressure-sensitive adhesives such as starch and sodium alginate, and water-soluble adhesives such as dextrin-based pressure-sensitive adhesives Is mentioned. In the present invention, it may be adjusted to the desired pseudo-adhesive force and is not particularly limited, but at least one selected from the group consisting of rubber-based, acrylic-based, vinyl acetate-based and dextrin-based pseudo-adhesive pastes may be used. It is preferable because the peeling force can be controlled arbitrarily and widely. The content ratio of the pseudo adhesive is preferably 10 to 100% by mass in the total solid content of the pseudo adhesive layer, and more preferably 20 to 80% by mass. Examples of the adhesion modifier include waxes such as polyethylene wax, inorganic pigments such as metal soap and silica, and organic pigments. As the pseudo-adhesive paste, for example, a pressure-sensitive adhesive, a pressure-sensitive adhesive paste, a UV pressure-sensitive varnish, and the like are also commercially available, and can be easily obtained and used.

The method of forming the pseudo-adhesive layer is not particularly limited, and any of a method of applying, a method of pressing a film-like pseudo adhesive paste, a method of applying in a UV varnish form, and curing by irradiating with ultraviolet rays is adopted. can do. The coating method is not particularly limited, and examples thereof include a reverse roll coater, a reverse gravure coater, a bario gravure coater, a knife coater, a bar coater, a die coater, and a curtain coater. The application amount of the pseudo-adhesive paste is not particularly limited as long as it can be adjusted to a desired pseudo-adhesive force, but is preferably about ² to 15 g / m ² after drying.

  The pseudo-adhesive force may be adjusted so that it is not too strong to cause re-peeling, particularly re-peeling when wet, and is too weak to be peeled off during postcard delivery. In the present invention, it is preferable that a pseudo adhesive layer having a pseudo adhesive force of 80 N / m or less is further provided on at least one side of the base paper. The pseudo adhesive force is more preferably 75 N / m or less, further preferably 70 N / m or less, and particularly preferably 60 N / m or less. Thereby, there is no possibility that peeling becomes difficult because the pseudo-adhesive force is too strong or the base paper is destroyed. On the other hand, the pseudo adhesive force is preferably 35 N / m or more, and more preferably 40 N / m or more. Thereby, there is no possibility that the pseudo adhesive force is too weak and the postcard is peeled off during delivery.

  As a method of using the base paper for the pressure-bonded postcard in the present invention, a cut portion and / or a pseudo adhesive layer can be provided on the base paper and applied to the pressure-bonded postcard. Examples of the cut portion include a dot-like or linear perforation, a half cut, a slit, and the like, but are not limited to these as long as they can be applied to the planned folding portion. In the present invention, since the interlayer strength between the base papers can be increased and the folding resistance can be improved, the effects of the present invention can be exerted undeniably in the perforation that penetrates the base paper among the types of cut portions. If it can be separated by the perforation of the cut section, for example, in addition to event notification, the postcard can have functions such as an admission ticket, a stub thereof, and a voucher.

  The method of applying the base paper for the pressure-bonded postcard of the present invention to the pressure-bonded postcard is not particularly limited. What is necessary is just to carry out the crimping | compression-bonding by the well-known method about what provided the layer and gave printing, and what provided the notch part. In addition, the crimping process is performed by appropriately setting the application surface of the pseudo-adhesive glue, and then, for example, the sheet is folded into two (V-fold) or three-fold (Z-fold) along the perforation by the folding device, and then the postcard is sized. Cutting can be performed using a roll calendar, a dedicated sealer, or the like without cutting.

  It is desirable to use a metal mirror roll for the high-pressure treatment during the crimping process, and the roll temperature is preferably 15 to 80 ° C, more preferably 20 to 60 ° C. By setting the roll temperature to 15 ° C. or higher, sufficient adhesive strength can be obtained. On the other hand, by setting the roll temperature to 80 ° C. or less, there is no possibility that the adhesive force becomes too large to be re-peeled.

  The method for selecting the base paper for the pressure-bonded postcard in the present invention is the same as the method of JAPAN TAPPI No. Measuring the internal bond strength when wet by the internal bond tester method defined in 18-2 and confirming whether the internal bond strength is 100 mJ or more, the internal bond strength is 100 mJ or more Including a step of selecting a base paper. As a result, it is possible to select a base sheet for pressure-bonding postcards that does not cause paper breakage when wet during re-peeling. The sorting method of the present invention can be sorted at the stage of producing a base paper, and can be used for sampling inspection before and after being processed into a crimped postcard, thereby exhibiting excellent productivity.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “parts” and “%” represent “parts by mass” and “mass%”, respectively.

Example 1
・ Preparation of base paper for crimped postcards As an internal sizing agent, a pulp slurry consisting of 70 parts by weight of hardwood bleached kraft pulp (Canadian standard freeness 350 ml) and 30 parts of softwood bleached kraft pulp (Canadian standard freeness 350 mL) Rosin sizing agent (trade name: Size Pine GF, manufactured by Arakawa Chemical Co., Ltd.) 0.3 parts by mass, polyacrylamide resin (trade name: Polystron 504, manufactured by Arakawa Chemical Co., Ltd.) 0.5 as a paper strength enhancer 0.5 parts by mass of polyamide polyamine epichlorohydrin-based resin (trade name: WS4024, manufactured by Seiko PMC) as a wet paper strength enhancer, 0.8 parts by mass of sulfate band, and talc (trade name: talc N80, Japan) as a filler 8 parts by mass of talc) is added in terms of solid content, and the mixture is diluted with white water to prepare a paper stock having a pH of 4.5 and a solid content concentration of 0.8%. did. This stock is subjected to an on-top multi-cylinder paper machine to make paper, and the resulting wet paper has a size press solution containing 100 parts by mass of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch) at a concentration of 10%. Is applied with a size press device so that the total coating weight on both sides is 5 g / m ² , dried, and further smoothed using a machine calendar to obtain a basis weight of 112.1 g. A base paper for pressure-bonding postcards made of / m ² base paper was prepared. The obtained base paper had an internal bond strength of 200 mJ, a Cobb water absorption of 20 g / m ² , an opacity of 95%, and a folding strength of 500 times when wet.

Example 2
In preparation of the base paper for pressure-bonded postcards of Example 1, instead of the size press solution containing 100 parts by mass of oxidized starch at a concentration of 10%, 50 parts by mass of oxidized starch, styrene-acrylic copolymer (trade name: POLYMALON E- 109, manufactured by Arakawa Chemical Co., Ltd.) A pressure-sensitive postcard base paper was prepared in the same manner as in Example 1 except that the size press solution contained 50 parts by mass at a concentration of 10%. The obtained base paper had an internal bond strength of 200 mJ when wet, a Cobb water absorption of 3 g / m ² , an opacity of 95%, and a folding strength of 500 times.

Example 3
In the preparation of the pressure-sensitive postcard base paper of Example 1, a pressure-bonded postcard base paper was prepared in the same manner as in Example 1 except that the amount of the internal addition size was changed to 0.05 part by mass instead of 0.3 part by mass. . The obtained base paper had an internal bond strength when wet of 180 mJ, a Cobb water absorption of 45 g / m ² , an opacity of 95%, and a folding strength of 500 times.

Example 4
In the production of the pressure-sensitive postcard base paper of Example 1, the pressure-sensitive postcard base paper was prepared in the same manner as in Example 1 except that the amount of the wet paper strength enhancer was changed to 1.5 parts by mass instead of 0.5 parts by mass. Produced. The obtained base paper had an internal bond strength of 300 mJ when wet, a Cobb water absorption of 20 g / m ² , an opacity of 95%, and a bending strength of 550 times.

Example 5
In the production of the pressure-sensitive postcard base paper of Example 1, the pressure-sensitive postcard base paper was prepared in the same manner as in Example 1 except that the amount of the wet paper strength enhancer was changed to 2.0 parts by mass instead of 0.5 parts by mass. Produced. The obtained base paper had a wet internal bond strength of 350 mJ, a Cobb water absorption of 20 g / m ² , an opacity of 95%, and a folding strength of 550 times.

Example 6
In preparation of the base paper for pressure-bonded postcards of Example 1, the amount of hardwood bleached kraft pulp was changed to 30 parts by weight instead of 70 parts by weight, and the amount of softwood bleached kraft pulp was changed to 70 parts by weight instead of 30 parts by weight. Produced a pressure-sensitive postcard paper in the same manner as in Example 1. The obtained base paper had a wet internal bond strength of 250 mJ, a Cobb water absorption of 20 g / m ² , an opacity of 96%, and a folding strength of 1000 times.

Example 7
In preparation of the base paper for pressure-bonded postcards of Example 1, the amount of hardwood bleached kraft pulp was changed to 90 parts by weight instead of 70 parts by weight, and the amount of softwood bleached kraft pulp was changed to 10 parts by weight instead of 30 parts by weight. Produced a pressure-sensitive postcard paper in the same manner as in Example 1. The obtained base paper had an internal bond strength of 150 mJ when wet, a Cobb water absorption of 20 g / m ² , an opacity of 97%, and a folding strength of 120 times.

Example 8
A base paper for pressure-bonded postcards was prepared in the same manner as in Example 1 except that the Canadian standard freeness of pulp was changed to 600 mL instead of 350 ml in the preparation of base paper for pressure-bonded postcards in Example 1. The obtained base paper had an internal bond strength of 120 mJ when wet, a Cobb water absorption of 20 g / m ² , an opacity of 96%, and a folding strength of 350 times.

Example 9
A base sheet for pressure-bonded postcards was prepared in the same manner as in Example 1, except that the Canadian standard freeness of pulp was changed to 100 ml instead of 350 ml in the preparation of base paper for pressure-bonded postcards in Example 1. The obtained base paper had an internal bond strength of 250 mJ when wet, a Cobb water absorption of 20 g / m ² , an opacity of 92%, and a folding strength of 400 times.

Example 10
In the production of the base paper for pressure-bonded postcards of Example 1, a base paper for pressure-bonded postcards was prepared in the same manner as in Example 1 except that kaolin (trade name: Milagros J, manufactured by BASF) was used as a filler instead of talc. . The obtained base paper had a wet internal bond strength of 120 mJ, a Cobb water absorption of 30 g / m ² , an opacity of 95%, and a folding strength of 150 times.

Comparative Example 1
In the production of the pressure-sensitive postcard base paper of Example 1, a pressure-sensitive postcard base paper was produced in the same manner as in Example 1 except that talc was not used. The obtained base paper had an internal bond strength of 220 mJ when wet, a Cobb water absorption of 18 g / m ² , an opacity of 88%, and a folding strength of 800 times.

Comparative Example 2
A base paper for pressure-bonded postcards was produced in the same manner as in Example 1 except that the wet paper strength enhancer was not used in the production of the base paper for pressure-bonded postcards of Example 1. The obtained base paper had an internal bond strength of 80 mJ, a Cobb water absorption of 22 g / m ² , an opacity of 95%, and a folding strength of 450 times when wet.

  The base paper for pressure-bonded postcards thus obtained was subjected to the following processing and evaluation. The results were as shown in Table 1.

(Preparation of crimped postcard)
Acrylic pseudo-adhesive glue was applied to the obtained pressure-sensitive postcard base paper with a Mayer bar so that the coating amount after drying was 3.5 g / m ^2, and dried at 110 ° C. for 1 minute with an air dryer. A pseudo adhesive layer was formed. After that, it is folded in half so that the pseudo-adhesive layers face each other and cut to the size of a postcard, and is crimped using a manual hydraulic roll calender set to a linear pressure between rolls of 20 kg / cm. Produced.

(Interlayer fracture after water immersion)
The pressure-bonded postcard obtained above was cut to a width of 25 mm, immersed in water for 1 hour, taken out from the water, excess water on the surface was removed with a filter paper, and then peeled off again. The peeled surface after peeling was visually observed, and the degree of base paper interlaminar fracture and the degree of fiber fluff on the surface were evaluated according to the following criteria as paper breakage when wet.
(Double-circle): It peels between pseudo-adhesion layers, and an external appearance is also satisfactory.
○: Slight fuzzing is observed, but peeling occurs between the pseudo-adhesive layers, and there is no practical problem.
(Triangle | delta): A base paper interlayer fracture generate | occur | produces partially and is a problem in practical use.
X: The base paper interlayer breakage occurred on the entire surface, which is a problem.

(Pseudo adhesion)
A pressure-bonded postcard produced by the same method as that for the above-mentioned pressure-bonded postcard was cut to a width of 25 mm, and the pseudo adhesive force was measured by T-shaped peeling (peeling speed 300 mm / min).

(Concealment)
After the obtained base paper was printed in monochrome with a commercially available inkjet printer (model: EP-302, manufactured by Epson Corporation), a pressure-bonded postcard prepared by the same method as the above-mentioned pressure-sensitive postcard was prepared so that the printed surface was inside. It observed visually from the outside and evaluated the recognizable level of a secret part on the following reference | standard.
A: The secret part cannot be recognized at all.
○: The secret part can be recognized a little, but it cannot be deciphered, and there is no practical problem.
(Triangle | delta): Since a secret part can be decoded a little, it is a problem in practical use.
X: It is a problem because the secret part can be completely deciphered.

(Paper cut at perforation)
The folding strength of the obtained base paper was measured with an MIT testing machine (described in JIS P 8115) and evaluated according to the following criteria.
(Double-circle): Folding strength is 500 times or more and there is no problem in the paper break at the perforation.
○: Folding strength is 150 times or more and less than 500 times, and there is no practical problem with paper breaks at perforations.
(Triangle | delta): Folding strength is 100 times or more and less than 150 times, and the paper break at a perforation can be adjusted by adjusting processing conditions.
X: Folding strength is less than 100 times, and paper breakage at the perforation is a problem.

Claims (11)

  JAPAN TAPPI No. A base sheet for pressure-bonding postcards made of a base paper having an internal bond strength of 100 mJ or more when wet by the internal bond tester method defined in 18-2. ^2. The pressure-sensitive postcard according to claim 1, wherein the water absorption of the base paper is 3 g / m ² or more and 45 g / m ² or less when the contact time is 60 seconds according to the Cobb method defined in JIS P 8140. Base paper.   The crimping postcard according to claim 1 or 2, wherein the folding strength of the base paper measured according to JIS P 8115 is 100 times or more and the opacity measured according to JIS P 8149 is 90% or more. Base paper.   The said base paper contains a pulp, and contains softwood bleached kraft pulp and hardwood bleached kraft pulp in the range of 5: 95-70: 30 by mass ratio (softwood bleached kraft pulp: hardwood bleached kraft pulp). The base paper for pressure-bonding postcards described in any one of the above.   The base paper for pressure-bonded postcards according to any one of claims 1 to 4, wherein the base paper contains pulp, and a Canadian standard freeness measured in accordance with JIS P 8121 of the pulp is in a range of 100 to 600 ml.   The base paper for pressure-bonded postcards according to any one of claims 1 to 5, wherein the base paper contains pulp and further contains a wet paper strength enhancer in an amount of 0.1 to 2.0 parts with respect to 100 parts by weight of the pulp.   The pressure-sensitive postcard according to any one of claims 1 to 6, wherein the base paper contains at least one wet paper strength enhancer selected from the group consisting of polyamide epichlorohydrin resin, urea-formaldehyde resin, and melamine-formaldehyde resin. Base paper.   The base paper for pressure-bonding postcards of any one of Claims 1-7 in which the said base paper contains a talc or a kaolin as a filler.   JAPAN TAPPI No. of the base paper. The internal bond strength when wet by the internal bond tester method specified in 18-2 is 180 mJ or more, and further provided with a pseudo adhesive layer having a pseudo adhesive force of 70 N / m or less on at least one side of the base paper, The base paper for pressure-bonding postcards of any one of Claims 1-8.   The use method of the base paper for pressure-bonding postcards which provides a notch part and / or a pseudo-adhesion layer in the base paper of Claims 1-9, and applies to a pressure-bonded postcard.   This is a method for sorting base sheets for pressure-bonded postcards, which is based on JAPAN TAPPI No. Measuring the internal bond strength when wet by the internal bond tester method defined in 18-2 and confirming whether the internal bond strength is 100 mJ or more, the internal bond strength is 100 mJ or more A sorting method including a step of selecting a base paper.