JPH11100556A - Pressure-sensitive adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pressure-sensitive adhesive sheet effectively made proof against the separation of the constituent pigment in a printing step by adding a polyester resin having a specified glass transition point to a base comprising a natural rubber and a pigment. SOLUTION: This sheet has a coating film of a pressure-sensitive adhesive containing a base comprising a natural rubber and a pigment and a polyester resin having a glass transition point of below 25 deg.C. Preferably, the amount of the polyester resin used is generally in the range of 5-50 pts.wt. per 100 pts.wt. natural rubber, though it depends on the types and compositions of the pressure-sensitive adhesive component and pigment used. The polyester resin used may be selected among general commercially available ones. The polyester resin is added to a natural rubber emulsion as a base, so that it is used in the form of an aqueous dispersion. The pigment used may be an organic or inorganic pigment usually used in a pressure-sensitive adhesive for a pressure- sensitive adhesive sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of applying a pressure-sensitive adhesive of a type which does not exhibit adhesiveness in a non-pressurized state but exhibits adhesiveness only when pressurized to a predetermined paper. It relates to the formed pressure-sensitive adhesive sheet.

[0002]

2. Description of the Related Art A pressure-sensitive adhesive used for a pressure-sensitive adhesive sheet of this type does not exhibit tackiness when applied to the surface of the sheet and then dried, but exhibits an adhesive property when pressed at a high pressure. And has the property of not exhibiting tackiness even after being peeled off after bonding. Therefore, a two-sheet sheet in which arbitrary data is described is bonded to each other via a pressure-sensitive adhesive to form a postcard because of the advantage that data confidentiality is protected. .

[0003] Conventionally known pressure-sensitive adhesives are basically prepared by blending a filler composed of solid fine particles such as silica with an adhesive component mainly composed of a rubber component to prevent blocking. (For example, see Japanese Patent Application Laid-Open No.
No. 53). The adhesive layer formed by applying the pressure-sensitive adhesive to the surface of the sheet and then drying the sheet has a reduced surface tackiness in a normal state because the filler reduces the tackiness of the rubber component. Although not shown, when pressed with a high pressure, the rubber component exudes to the surface of the adhesive layer to exhibit adhesiveness, and adheres to the other surface.

As one means for solving the problem of character transfer, which is a drawback that such pressure-sensitive adhesives often have, for example, Japanese Patent Application Laid-Open No. 8-277383 discloses a method of adding a filler to the adhesive. A pressure-sensitive adhesive in which a specific self-dispersion type aqueous polyester resin emulsion is blended as an anti-transfer agent with a normal composition containing the same has been proposed.

[0005]

The above-mentioned conventional pressure-sensitive adhesives have a natural rubber latex as a main component, but the natural rubber has a holding force required to hold a pigment such as silica. In particular, there is a serious problem that the pigment is peeled or separated in the printing step, and the peeled pigment contaminates the printing unit.

[0006] The present invention relates to a pressure-sensitive adhesive sheet using a pressure-sensitive adhesive containing natural rubber as a main component, and particularly to an improved pressure-sensitive adhesive sheet capable of effectively preventing peeling and detachment of pigments in a printing process. It is intended to provide a pressure-bonded sheet.

[0007]

The pressure-sensitive adhesive sheet of the present invention is coated with a pressure-sensitive adhesive containing a natural rubber and a pigment as main components and a polyester resin having a glass transition point of less than 25 ° C. It is characterized by.

A pressure-sensitive adhesive sheet coated with a pressure-sensitive adhesive containing a polyester resin having a glass transition point of less than 25 ° C. containing natural rubber and a filler as main components greatly improves the pigment retention performance of the adhesive layer. As a result, it is possible to effectively prevent the occurrence of the above-mentioned trouble caused by the peeling of the pigment.

Further, since the glass transition point of the polyester resin is lower than 25 ° C., when a desired printing is performed on the pressure-sensitive adhesive sheet using a printer or a printing machine, the temperature of the polyester resin is lower than the glass transition point. In addition, the initial properties are maintained without causing a glass transition.
When such use conditions are close to 23 ° C., it is preferable to select a polyester resin having a glass transition point not higher than the temperature at the time of use as the polyester resin to be used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, any kind of natural rubber commonly used in the field of pressure-sensitive adhesive can be used as the pressure-sensitive adhesive component of the pressure-sensitive adhesive. is there. Usually, an emulsion of any natural rubber is used for preparing the pressure-sensitive adhesive, and the emulsion is mixed with a pigment and various additives as necessary. In the present invention, a polyester resin having a glass transition point of less than 25 ° C. is further added to this formulation in the form of an emulsion.

As the pigment, an organic or inorganic pigment usually used for a pressure-sensitive adhesive for a pressure-sensitive adhesive sheet can be used. Examples of such pigments include zinc oxide, titanium oxide, calcium carbonate, kaolin, activated clay, spherical alumina, silica, glass powder, shirasu balloon, micro talc, wheat starch and the like, alone or in combination of two or more. Can be Further, porous spherical inorganic pigments such as porous spherical silica having a particle size (several μm to several tens of μm), and porous spherical organic pigments made of an acrylic resin or the like can be advantageously used.

In the pressure-sensitive adhesive sheet of the present invention, the polyester resin having a glass transition point (Tg) of less than 25 ° C. is selected from generally marketed polyester resins having a glass transition point of less than 25 ° C. Can be selected and used. The polyester resin is used in the form of an aqueous dispersion because it is blended with the synthetic rubber emulsion as the main component. As the aqueous dispersion of the polyester resin,
For example, those described in JP-A-6-256437 can be advantageously used, and the product name “Vylonal MD1400” (trade name, manufactured by Toyobo Co., Ltd.) (Tg
= 23 ° C.), “Vylonal MD1930” (Tg = −
10 ° C.) and the like.

The amount of the polyester resin added is not particularly limited. However, if the amount is too small, the pigment is peeled or separated, while if it is too large, the adhesive force of the pressure-sensitive adhesive layer becomes insufficient. The preferred amount of addition varies depending on the type or compounding of the adhesive component and pigment used, but is generally preferably in the range of 5 to 50 parts by weight based on 100 parts by weight of natural rubber.

[0014]

EXAMPLES Examples of the present invention are shown below in comparison with comparative examples outside the scope of the present invention. In the examples and comparative examples, "parts" indicates parts by weight.

(Examples 1 to 4) Natural rubber latex (N.V. 50 wt%), water, silica and kaolin as pigments, and "Vironal MD1400 (N.V. 50 wt%, Tg =
Each component was mixed at a ratio shown in Table 1 below, and the mixture was dispersed with a homomixer for 10 minutes to prepare a pressure-sensitive adhesive. This pressure-sensitive adhesive is applied to a high-quality paper so as to have a thickness of 15 μm.
It dried at 1 degreeC for 1 minute, and produced the pressure-sensitive adhesive sheet.

For each of the obtained pressure-sensitive adhesive sheets, a tensile test (90 ° peeling) and the degree of adhesion of the pigment were measured. The results are shown in Table 1. In the table, “Polyester resin (parts by weight) / natural rubber (100 parts by weight)”
The column shows the parts by weight of the solid content of the polyester resin added to 100 parts by weight of the natural rubber.

The degree of adhesion of the pigment is measured by applying a commercially available pressure-sensitive adhesive tape (manufactured by Sumitomo 3M, trade name "Scotch Mending Tape") on the pressure-sensitive adhesive coated surface of the pressure-sensitive adhesive sheet.
Was adhered and immediately peeled off, and the adhesion of the pigment on the adhesive surface of the adhesive tape was observed by an electron microscope. The symbols indicating the degree of adhesion of the pigment in Table 1 have the following meanings.

×: Pigment adhered ○: Slightly pigment adhered ◎: Almost no pigment adhered The “paper discoloration” of the peel strength was measured when the peel strength was measured.
It means that the pressure-sensitive adhesive layer was peeled off from the base paper without being peeled off on the pressure-sensitive adhesive coated surface.

[0019]

[Table 1] (Examples 5 to 8) In Example 1, “Vironal MD1930 (N.V. 30 wt%, T
g = −10 ° C.) except that a pressure-sensitive adhesive having the same components was prepared and operated in the same manner to produce a pressure-sensitive adhesive sheet. For each of the obtained pressure-sensitive adhesive sheets, a tensile test (90 ° peeling) and the degree of adhesion of the pigment were measured in the same manner as in Example 1. Table 2 summarizes the composition of each pressure-sensitive adhesive and the measurement results.

[0020]

[Table 2] (Comparative Examples 1 to 5) In Example 1, "Vironal MD1200 (N.V. 34 wt%, T
g = 67 ° C. "), except that a pressure-sensitive adhesive having the same components was prepared and operated in the same manner to produce a pressure-sensitive adhesive sheet. For each of the obtained pressure-sensitive adhesive sheets, a tensile test (90 ° peeling) and the degree of adhesion of the pigment were measured in the same manner as in Example 1. Table 3 summarizes the composition of each pressure-sensitive adhesive and the measurement results.

[0021]

[Table 3] The pressure-sensitive adhesive sheet of Comparative Example 5 had a remarkably large peel strength as compared with the other Examples and Comparative Examples, but on the other hand, the stickiness unique to natural rubber was extremely remarkable, and It had no sex.

(Comparative Examples 6 to 9) In Example 1, "Vironal MD140" was used as a polyester resin dispersion.
0 ”instead of“ Vironal MD1110 (N.V.3).
4 wt%, Tg = 40 ° C.), and a pressure-sensitive adhesive sheet having the same components was prepared and operated in the same manner to produce a pressure-sensitive adhesive sheet. For each of the obtained pressure-sensitive adhesive sheets, a tensile test (90 ° peeling) and the degree of adhesion of the pigment were measured in the same manner as in Example 1. Table 4 summarizes the composition of each pressure-sensitive adhesive and the measurement results.

[0023]

[Table 4] FIG. 1 shows the relationship between the Tg of the polyester resin used and the amount thereof added and the peel strength of the pressure-sensitive adhesive sheet in the above pressure-sensitive adhesive composition.

As is apparent from the above Examples and Comparative Examples and FIG. 1, the peel strength tends to decrease as the amount of the polyester resin added increases.
When Tg is less than 25 ° C., a decrease in peel strength with an increase in the amount of the added polyester resin is effectively suppressed, and it has been confirmed that the resin has sufficient practicality.

[0025]

As described above, according to the present invention, the most disadvantage of the pressure-sensitive adhesive sheet using the pressure-sensitive adhesive containing natural rubber is that the pressure-sensitive adhesive sheet does not impair the adhesive performance. There is a remarkable effect that pigment peeling is greatly reduced and the problem that the pigment peeled during printing contaminates the printing unit can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of polyester resin added and the peel strength in Example 1 and Comparative Example 1.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09J 167: 02)

Claims (2)

[Claims] 1. A pressure-sensitive adhesive sheet characterized by being coated with a pressure-sensitive adhesive containing a natural rubber and a pigment as main components and a polyester resin having a glass transition point of less than 25 ° C. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the polyester resin is contained in an amount of 5 to 50 parts by weight based on 100 parts by weight of the natural rubber.