JP6250334B2 - Confidential postcard - Google Patents

Description

  The present invention relates to a confidential postcard that protects information written on a pressure-bonded surface by pressure-bonding at least a base material and a protective material with a pressure-sensitive adhesive, and in particular, covers and protects the information-written surface even when wet. The present invention relates to a water-resistant confidential postcard in which the protective material is easily peeled off.

  In recent years, “confidential postcards” have been used as means for notifying individual individuals of their deposit status, balance information, pension information, etc. from banks, credit companies, government offices, and the like. In such a confidential postcard, a pressure-sensitive adhesive is applied to the surface of a base material on which information is described, and the information description surface is formed by covering the information description surface with a protective material and pressing it with a predetermined pressure. Mailed to recipient in a protected state. The recipient can read the protected information by peeling off the protective material.

  Patent Document 1 discloses a pressure-sensitive adhesive containing a rubber latex, a cationic water-soluble polymer or a cationic oligomer, and a nonionic or cationic aqueous urethane resin as a pressure-sensitive adhesive suitable for inkjet printing. Agents are disclosed. Patent Document 2 discloses a natural rubber-based adhesive as a pressure-sensitive adhesive having adhesion to a base sheet of an adhesive layer suitable for a high-speed conveyance printer and adhesion to a protective material on an information description surface. A pressure-sensitive adhesive containing latex and an ionomer type water-based urethane resin is disclosed. Further, Patent Document 3 discloses a pressure-sensitive adhesive containing a cold sealant, fine mineral powder, and a cationic urethane resin as a pressure-sensitive adhesive suitable for ink jet printing.

JP 2003-336023 A Japanese Patent Laid-Open No. 2004-359887 JP-A-11-58940

  A confidential postcard may get wet by rain or snow when mailing or in a mailbox. The pressure-sensitive adhesive used in conventional confidential postcards has a significant increase in peel strength due to water wetting. Therefore, in confidential postcards using such pressure-sensitive adhesives, protective materials remain wet in water. However, there is a problem that the peel strength is too strong to be easily peeled off, or the base material or the protective material is peeled off due to delamination.

  An object of the present invention is to provide a water-resistant confidential postcard in which a protective material can be easily peeled off even in a wet state.

The present invention is a confidential postcard that protects information written on at least one of the pressure-bonding surfaces of the base material and the protective material by pressure-bonding the base material and the protective material via the pressure-sensitive adhesive composition, The base material and the protective material are water-resistant paper having a wet delamination strength of 1.18 g / mm ( 30 g / inch ) or more and a static contact angle of 115 degrees or more , and at least one of the base material and the protective material A pressure sensitive adhesive composition containing a rubber latex and a nonionic water-based urethane resin as a resin component and having an ink fixing agent less than the solid content of the rubber latex is applied to the pressure-bonding surface.

In the present invention,
The wet delamination strength of the water-resistant paper is 4.53 g / mm ( 115 g / inch ) or more ,
When the solid content of solids and nonionic water-borne urethane resin before Symbol rubber latex is 100 mass%, solid rubber latex content of 65 wt% to 97 wt% and a solid content of the nonionic water-based urethane resin is 3 wt% Ri 35% by mass, substantially contains no ink fixing agent,
The pressure-sensitive adhesive composition further contains an antiblocking agent, and the total solid content of the rubber latex and the nonionic water-based urethane resin is 50 to 80 parts by mass with respect to 90 parts by mass of the antiblocking agent. Being
The antiblocking agent is starch and silica;
Is included as a preferred form.

  The confidential postcard of the present invention uses a pressure-sensitive adhesive composition having a specific composition as a pressure-sensitive adhesive for press-bonding a base material and a protective material, thereby improving the water resistance of the base material and the protective material made of water-resistant paper. Get higher. Further, the pressure-sensitive adhesive composition can stably maintain the peel strength immediately after pressure bonding even when wet. Therefore, the confidential postcard of the present invention has no significant increase in peel strength even if water wetting occurs after the base material and the protective material are pressure-bonded, and is compatible with the improvement of the water resistance of the base material and the protective material. Thus, paper breakage of the base material and the protective material when peeling the protective material is prevented. Therefore, in the confidential postcard of the present invention, the information is protected until the recipient peels off the protective material, and when reading the information, not only the dried state but also the wet state for a short time and for a long time. However, it is possible to easily peel off the protective material and read the written information.

  The confidential postcard of the present invention will be described in detail below.

  First, the pressure-sensitive adhesive composition used in the present invention will be described.

  The pressure-sensitive adhesive composition used in the present invention uses, as resin components, rubber latex and nonionic water-based urethane resin as main components, and when blended with an ink fixing agent, it is less than the solid content of rubber latex. It is characterized by blending.

  As the rubber latex used in the present invention, natural rubber latex, modified natural rubber latex and synthetic rubber latex are preferably used. Specific examples of the modified natural rubber latex include acrylic-modified natural rubber latex, pre-peroxide vulcanized latex, and the like. Specific examples of the synthetic rubber latex include styrene-butadiene rubber and acrylonitrile-butadiene rubber.

  The nonionic water-based urethane resin used in the present invention is a solution in which a urethane resin is dissolved or dispersed in an aqueous medium. For example, an emulsion type nonionic water-based urethane in which urethane resin fine particles are dispersed in an aqueous medium using an emulsifier. Resin.

  In the present invention, the rubber latex is a component that develops an adhesive force when the base material and the protective material are pressure-bonded to each other. By adding a nonionic water-based urethane resin to this, the surface of the base material and the protective material is pressure sensitive. It takes the state coated with the adhesive composition. As a result, even when the base material or the protective material is wetted with water, the nonionic surfactant has a low HLB (Hydrophile-Lipophile Balance) value at the time of emulsion polymerization of the nonionic water-based urethane resin, so that the hydrophilicity is low. Low, and peel strength immediately after press bonding is almost maintained. Therefore, even if the protective material is peeled off while being wet, the risk of causing the paper torn of the protective material and the substrate is reduced.

  Since cationic water-based urethane resins have the property of agglomerating, when combined with a rubber latex to form a pressure-sensitive adhesive composition, the cationic water-based urethane resin aggregates and solidifies with the rubber latex, producing particles in the composition. End up. For this reason, the pressure-sensitive adhesive composition is not suitable as a pressure-sensitive adhesive for confidential postcards because the pressure-bonding force causes unevenness and a sufficient pressure-bonding force cannot be obtained.

  In addition, an anionic water-based urethane resin has a property of being easily soluble in water or wettable due to the hydrophilicity of the anionic surfactant included in the urethane resin, so that a pressure-sensitive adhesive composition using an anionic water-based urethane resin is used. As for the thing, a dry film tends to take in moisture. Therefore, when a pressure-sensitive adhesive composition using an anionic water-based urethane resin is used in a confidential postcard, the interface of the pressure-sensitive adhesive composition elutes when wet with water, and the pressure-sensitive adhesive composition and the substrate It is considered that an increase in peel strength is manifested by strengthening the adhesion with the protective material. Therefore, when an anionic water-based urethane resin is combined with a rubber latex to form a pressure-sensitive adhesive composition and used in a confidential postcard, the peel strength increases rapidly due to water wetting, and the base material tries to peel off when wet. And there is a risk of tearing the protective material. Therefore, an anionic water-based urethane resin is not suitable as a pressure-sensitive adhesive for confidential postcards.

  Furthermore, since ionomer-type water-based urethane resin has a small amount of hydrophilic ionic groups in the hydrophobic main chain, it is used as a pressure-sensitive adhesive composition in combination with rubber latex. The ionic group captures water and the pressure-sensitive adhesive composition expands, and the peel strength increases rapidly, so if you try to peel it while wet, there is a risk of paper breakage of the base material or protective material. Not suitable for pressure sensitive adhesives for confidential postcards.

  Conventionally, a pressure-sensitive adhesive composition for a confidential postcard has used a cationic water-soluble polymer or a cationic oligomer as an ink fixing agent. However, since the ink fixing agent affects water resistance, the present invention In the present invention, the rubber latex and nonionic water-based urethane resin described above are used as the main components, and the ink fixing agent made of a resin material is used in an amount less than the solid content of the rubber latex so as to reduce the influence. Preferably, no ink fixing agent is blended in the present invention.

  In the present invention, the compounding amount of the rubber latex and the nonionic water-based urethane resin contained in the pressure-sensitive adhesive composition is 100% by weight as the sum of the solid content of the rubber latex and the solid content of the nonionic water-based urethane resin. It is preferable to blend so that the solid content is 65 mass% to 97 mass% and the solid content of the nonionic water-based urethane resin is 3 mass% to 35 mass%. When the solid content of the rubber latex is less than 65% by mass, that is, when the solid content of the nonionic water-based urethane resin exceeds 35% by mass, the peel strength when the protective material and the substrate are pressed against each other is weak. Therefore, the protective material may be easily peeled off, which is not preferable. In addition, when the solid content of the nonionic water-based urethane resin is less than 3% by mass, it is difficult to obtain the effect using the urethane resin, and when the protective material is peeled off, the peel strength is greatly increased by water wetting. The base material and the protective material easily break the paper.

  In the present invention, it is preferable to add an anti-blocking agent in order to prevent the adhesive surfaces coated with the pressure-sensitive adhesive composition from adhering to each other during storage. Examples of the antiblocking agent used in the present invention include calcium bicarbonate, light calcium carbonate, talc, metal stearate soap, starch, silica and the like. Among these, it is preferable to contain silica in order to improve heat resistance by a laser printer or the like after application of the pressure-sensitive adhesive composition. Moreover, it is preferable to contain starch as a pressure sensitive adhesive composition.

  The antiblocking agent has a total of 50 to 80 parts by mass of the solid content of the rubber latex and the solid content of the nonionic water-based urethane resin in the pressure-sensitive adhesive composition with respect to 90 parts by mass of the antiblocking agent. It is preferable to add so that it becomes.

  The pressure-sensitive adhesive composition used in the present invention can be obtained by adding an ink fixing agent and an antiblocking agent to rubber latex and a nonionic water-based urethane resin, if necessary, and mixing them. An appropriate amount of water may be added as necessary to facilitate coating.

  Next, the base material and protective material used in the present invention will be described.

In the present invention, by using a water-resistant paper having a wet delamination strength of 1.18 g / mm ( 30 g / inch ) or more as a base material and a protective material, sufficient water resistance can be obtained even for a long period of water wetting. It is done. Preferably, the water-resistant paper has a wet delamination strength of 4.53 g / mm ( 115 g / inch ) or more. The water-resistant paper preferably has a water repellency with a static contact angle of 115 degrees or more.

  The wet delamination strength is obtained by attaching a cellophane adhesive tape (manufactured by Kyowa Co., Ltd.) to the sample, applying a pressure of 2 kilograms, adhering the cellophane adhesive tape to the sample, cutting to 1 inch width, and immersing in water. . After 3 hours, the sample was taken out, wiped with water on the surface, and allowed to stand for 3 minutes. Using “FGP-2” (manufactured by Nidec Sympo Co., Ltd.) as a vessel, the peel strength is measured at an angle of 90 degrees and a peel speed of 264 mm / min. The peel strength of 20 mm from the start position is ignored, the peel strength of 20 mm to 130 mm is measured for five samples, and the average value is taken as the wet delamination strength.

  The static contact angle indicates the wettability of pure water droplets. When the static contact angle is 0 degree, the wettability of pure water is high and the pure water droplets adhere to the sample without being repelled. On the other hand, when the static contact angle is 180 degrees, the wettability of pure water is low, and pure water droplets are repelled by the sample and do not adhere at all. The static contact angle can be easily measured using a known contact angle measuring device (for example, automatic contact angle measuring device CA-V type: manufactured by Kyowa Interface Chemical Co., Ltd.). In the present invention, 40 μL of pure water was dropped, and the contact angle was measured 5 times after 1 second, 2 seconds, 3 seconds, 4 seconds, and 5 seconds, and the average value was taken.

  The confidential postcard of the present invention is obtained by applying the above-mentioned specific pressure-sensitive adhesive composition to at least one of the above-mentioned base material made of water-resistant paper and a protective material by coating means such as a gravure coater, flexo, air knife coater, and bar coater. Coated. The information to be protected is described in at least one of the base material and the protective material.

  In the confidential postcard of the present invention, the base material and the protective material are pressure-bonded via the pressure-sensitive adhesive composition with the coated surface of the pressure-sensitive adhesive composition facing inside. Therefore, the base material and the protective material may be prepared separately, or a continuous sheet of water-resistant paper may be folded into two or three. In the case where the base material and the protective material are prepared separately, it is also possible to use different water-resistant paper. The confidential postcard of the present invention is mailed in a state in which the base material and the protective material are bonded to each other via the pressure-sensitive adhesive composition to protect the information.

  In addition, when printing is performed on the coated surface of the pressure sensitive adhesive composition of the confidential postcard of the present invention, the pressure sensitive adhesive composition has a low content of the ink fixing agent or does not contain the ink fixing agent. In some cases, the ink fixing property is not good. Therefore, it is desirable that the pressure-sensitive adhesive composition is applied to the coated surface of the base material or the protective material and then applied to form the confidential postcard of the present invention.

  Hereinafter, the present invention will be described in detail by way of examples.

  In addition, the raw material used in the Example and the evaluation method in an Example are as follows. In the examples, “%” and “part” are both “% by mass” and “part by mass”.

[Base materials and protective materials]
・ Waterproof paper “OK Rainguard (registered trademark)” (manufactured by Oji F-Tex Co., Ltd.)
・ Waterproof paper “Poem N” (Hokuetsu Kishu Paper Co., Ltd.)
・ Waterproof paper “NPi Foam (registered trademark) NEXT-IJ” (manufactured by Nippon Paper Industries Co., Ltd.)
[Pressure-sensitive adhesive composition raw material]
(1) Rubber Latex Acrylic modified natural rubber latex “Q. ADHESIVES QY-25MG · C” (manufactured by Qu Yu Kasei Co., Ltd.), solid content: 50%

(2) Water-based urethane resin / nonion type: "Superflex (registered trademark) E-2000" (Daiichi Kogyo Seiyaku Co., Ltd.)
Solid content: 50%
・ Cation type: “Superflex 620” (Daiichi Kogyo Seiyaku Co., Ltd.)
Solid content: 30%
Anion type: “Superflex 820” (Daiichi Kogyo Seiyaku Co., Ltd.)
Solid content: 30%
・ Ionomer type: “Hydran APX-101H” (Dainippon Ink Chemical Co., Ltd.)
Solid content: 45%

(3) Starch Cationized tapioca starch “Mermaid C-50” (Shikishima Starch Co., Ltd.)
(4) Silica Hydrous amorphous silicon dioxide “Nipgel (registered trademark) AZ-600” (manufactured by Tosoh Silica Co., Ltd.)
(5) Ink fixing agent Polyamine polymer cation "MORIN FIX 6P" (Morin Chemical Industry Co., Ltd.)

(Experimental example 1)
With respect to the three types of waterproof paper prepared as the base material and the protective material, the wet delamination strength and the static contact angle were measured by the measurement method described above. The results of wet delamination strength are shown in Table 1, and the results of static contact angles are shown in Tables 2 to 5. The unit of numerical values in Table 1 is g / inch, and the unit of numerical values in Tables 2 to 5 is degrees.

  As shown in Tables 1 to 4, “OK Rainguard” has a wet delamination strength of 127 g / inch, a static contact angle of 120 degrees, and a sufficiently high value in both water resistance and water repellency. And was found to be suitable for the confidential postcard of the present invention. In addition, it was found that “Poem N” and “NPi Foam NEXT-IJ” have low wet delamination strength and are easily delaminated when wet for a long time.

(Examples 1-5, Comparative Examples 1-5)
An appropriate amount of water is added to the composition shown in Table 5 to prepare a pressure-sensitive adhesive composition, and each is applied to a base material and a protective material using a bar coater so that the film thickness at the time of coating is 16 μm. The coated surfaces were overlapped so that the coated surfaces face each other, and pressure was applied by a pressure roller with a mail sealer “MS-9500” (Dai Nippon Printing Co., Ltd.). Here, in order to compare the increase in peel strength due to water wetting, in Examples 1 to 5 and Comparative Examples 1 to 4, the roller gap of the pressure roller was adjusted so that the peel strength immediately after pressure bonding was 80 g / inch. . For Comparative Example 5, the roller gap of the pressure roller was adjusted so that the peel strength immediately after pressure bonding was 50 g / inch. Then, it cut | disconnected to 1 inch width, was set as the sample for a measurement, and peel strength was measured. "OK rain guard" was used for the base material and the protective material.

  For the peel strength measurement test, “FGS-50VB-400-DM” (manufactured by Nidec Sympo Co., Ltd.) is used as a load measuring tester, and “FGP-2” (Nidec Sympo Co., Ltd.) is used as a measuring instrument. The peel strength is measured at an angle of 90 degrees and a peel speed of 264 mm / min. The peel strength of 20 mm from the start position is ignored, the peel strength of 20 mm to 130 mm is measured for five samples, and the average value is taken as the peel strength.

  The sample for measurement was immersed in water, taken out after 5 seconds and wiped with water on the surface, and then the peel strength was measured. Similarly, the measurement sample was immersed in water, taken out after 3 hours, wiped with water on the surface, and allowed to stand for 3 minutes to measure the peel strength.

  As described above, the peel strength was measured immediately after pressing for 5 seconds and after 3 hours. In addition, it was observed whether or not a paper break occurred in the base material or the protective material during peeling. The results are shown in Table 5.

  An example in which the peel strength immediately after the pressing was less than 80 g / inch was an example in which the value reached only that value even if the pressure condition was maximized by adjusting the roller gap of the pressing roller. Further, even if the roller gap of the pressure roller is adjusted so that the peel strength immediately after the pressure bonding is 80 g / inch, the control is not easy, and there is an example that exceeds 100 g / inch.

  Moreover, in Table 5, in the case where the value of the peel strength after 5 seconds of wetness (after wet for 5 seconds / immediately after the press fit) with respect to the peel strength immediately after the pressurization exceeds 1.5, the peel strength was significantly increased by water wetting. This shows that even when the paper is not torn during peeling, the base material and the protective material are easily broken.

  As shown in Table 5, in Examples 1 to 4, a stable and appropriate peel strength was exhibited immediately after pressure bonding, and no significant increase in peel strength was observed even after wetting. Therefore, the risk of the protective material peeling off even when wet or when wet is reduced. Further, it is less likely that the protective material is difficult to peel off due to water wetting, and the base material and the protective material are torn. In Example 5, since the content of rubber latex in the resin component is small, the peel strength immediately after the compression is low, but the peel strength does not increase significantly even when wet, and the nonionic water-based urethane resin. The effect using was seen.

  In Comparative Example 1, since a nonionic water-based urethane resin was not used, the peel strength significantly increased due to water wetting, and paper breakage occurred after wetting for 5 seconds.

  Since Comparative Example 2 uses a cationic water-based urethane resin, particles were formed in the pressure-sensitive adhesive composition, the pressure bonding force was uneven, the pressure bonding force itself was weak, and sufficient pressure bonding was not possible.

  In Comparative Examples 3 and 4, since ionomer type or anion type water-based urethane resin was used, the peel strength after 5 seconds of wettability significantly increased due to water wetting.

  In Comparative Example 5, although the composition is close to that of Example 2, since the ink fixing agent is added more than the solid content of the rubber latex, the pressure-sensitive adhesive has the effect of adsorbing the moisture of the ink that the ink fixing agent has. The composition easily absorbs moisture, and as a result, the pressure-sensitive adhesive composition becomes flexible, the cohesive force between the pressure-sensitive adhesive compositions facing each other at the time of pressure bonding is improved, and the pressure-sensitive adhesive composition An increase in peel strength was manifested by the action of tight adhesion between the substrate and the protective material. In addition, due to the positive water absorption action of the ink fixing agent, the absorbed water penetrates the base material and the protective material through the pressure-sensitive adhesive composition, and the strength of the base material and the protective material decreases, resulting in paper breakage. It becomes easy. In Comparative Example 5, the roller gap of the press roller is adjusted so that the peel strength immediately after press bonding is 50 g / inch. Therefore, the peel strength immediately after press bonding is lower than that in Example 2.

(Example 6, Comparative Examples 6 and 7)
Samples prepared in the same manner using the pressure-sensitive adhesive composition of Example 2 in Table 2 using “OK Rainguard” and “Poem N” as the base material and protective material (Example 6, Comparative Example 6). ), Using “OK rain guard” as the base material and the protective material, and using the pressure-sensitive adhesive composition of Comparative Example 1 shown in Table 5 in the same manner (Comparative Example 7) was wetted for 3 hours, respectively. The surface water was wiped off and dried for 2 minutes, and then the protective material was peeled off to observe paper breakage. The results are shown in Table 6.

  As shown in Table 6, the sample composed of “OK rain guard” and the pressure-sensitive adhesive composition of Example 2 did not break paper, but “Poem” was coated with the same pressure-sensitive adhesive composition. “N” caused paper breakage on all five samples. The reason why the sample was dried for 2 minutes was that the pressure sensitive adhesive composition was dried faster than the base material and the protective material, and therefore the pressure sensitive adhesive was lower than the base material and the protective material whose delamination strength was lowered. This is because the tendency for paper breakage to develop as the adhesive strength of the composition increases.

  Further, in the sample in which the pressure-sensitive adhesive composition of Comparative Example 1 was applied to “OK rain guard”, paper tearing occurred in one of the five samples. Note that when the pressure-sensitive adhesive composition of Comparative Example 1 was applied to “Poem N”, paper tearing can be expected, and no experiment was conducted.

  Therefore, as the physical properties of the substrate and the protective material used in the present invention, those having a wet delamination strength of 30 g / inch or more can be used, and preferably the wet delamination strength is 115 g / inch or more. preferable. The static contact angle is preferably 115 degrees or more.

  By using a base material and a protective material satisfying these physical property values in combination with a pressure-sensitive adhesive composition having a specific composition according to the present invention, when the protective material is peeled off after a short period of water wetting, It was found that a confidential postcard having sufficient water resistance against paper breakage can be obtained in any case where the protective material is peeled off after being wet.

  The same experiment was not conducted for “NPi Foam NEXT-IJ”, but the wet delamination strength was even lower than “Poem N”. It is thought to occur easily.

Claims (5)

A confidential postcard that protects information written on at least one of the pressure-bonding surfaces of the base material and the protective material by pressure-bonding the base material and the protective material through the pressure-sensitive adhesive composition, The protective material is a water-resistant paper having a wet delamination strength of 1.18 g / mm ( 30 g / inch ) or more and a static contact angle of 115 degrees or more , and on the pressure-bonding surface of at least one of the base material and the protective material, A confidential postcard comprising a rubber latex and a nonionic water-based urethane resin as a resin component, and a pressure-sensitive adhesive composition having an ink fixing agent less than the solid content of the rubber latex. The confidential postcard according to claim 1, wherein the water-resistant paper has a wet delamination strength of 4.53 g / mm ( 115 g / inch ) or more. When the solid content of the rubber latex and the solid content of the nonionic aqueous urethane resin is 100% by mass, the solid content of the rubber latex is 65% by mass to 97% by mass, and the solid content of the nonionic aqueous urethane resin is 3% by mass to 3% by mass. 35% by mass is, the confidential postcard according to claim 1 or 2, characterized in that substantially no ink fixing agent. The pressure-sensitive adhesive composition further contains an antiblocking agent, and the total solid content of the rubber latex and the nonionic water-based urethane resin is 50 to 80 parts by mass with respect to 90 parts by mass of the antiblocking agent. The confidential postcard according to claim 1, wherein the confidential postcard is any one of claims 1 to 3 . The confidential postcard according to claim 4 , wherein the antiblocking agent is starch and silica.