JP2799194B2 - Method of manufacturing adhesive sheet - Google Patents

Description

The present invention relates to a method for manufacturing a composite sheet having a four-layer structure, and more particularly to a method for manufacturing a double-sided adhesive sheet that can be peeled between two central layers.

<< Conventional Technology >> Conventionally, a plastic film has been laminated on at least one surface of base paper for the purpose of imparting water resistance and weather resistance and enhancing paper strength.

Also, for the purpose of improving the appearance of the printed matter, or protecting the printed information, for example, a resin layer is provided on the surface after printing, but with the increase in the amount of information in recent years, From the viewpoint of privacy protection or the saving of postage, after covering the information recording surface with a plastic film, the plastic films are peeled and adhered to each other and folded, and the postcard size is twice or three times as large as the conventional one. There have been many proposals for confidential postcards that prevent the recipient from opening or opening the package except for the recipient. Among them, the ones in which heat-sensitive adhesive films are temporarily adhered to each other in a peelable manner are easy to use, easy to manufacture, and privacy. It can be said that it is particularly preferable from the viewpoint of protection and the like.

The postcard using such a heat-sensitive adhesive film is, for example, after thermocompression bonding the heat-sensitive adhesive film on the recording surface at a sufficiently high temperature and affixing it, then fold it and bring the heat-sensitive adhesive films into close contact with each other at a temperature lower than the above temperature. By pressure bonding, heat-sensitive adhesive films can be peeled off from each other, or a pressure-sensitive adhesive layer is provided on one side of the heat-sensitive adhesive film,
It is manufactured by a method in which a recording surface is pressed against the layer, folded, and heat-sealed.

However, in the case of the former method, peeling occurs on the recording surface contrary to the intention, and the recorded contents may become unclear or destroyed. In the latter case, although the above-mentioned inconveniences can be avoided, the conditions for heat sealing must be strictly controlled, and the conditions for heat sealing must be changed according to the type of recording paper, which is complicated. .

<< Problems to be Solved by the Invention >> The disadvantage is that a more adhesive layer is provided on both sides of a temporary adhesive sheet in which the heat-sensitive adhesive films are preliminarily releasably adhered to each other by a recording paper on which information has already been recorded. Although it can be solved by the method of sandwiching, the manufacturing process of such an adhesive sheet having a four-layer structure is not simple and has a disadvantage that it is disadvantageous in terms of cost.

The present inventors have conducted intensive studies to solve the above-mentioned drawbacks relating to the four-layered adhesive sheet. As a result, the co-extrusion molding of at least two adjacent layers can significantly simplify the manufacturing process. In addition, the inventors have found that the uniformity of product quality is improved, and have reached the present invention.

Accordingly, an object of the present invention is to provide a method in which the transparent heat-sensitive adhesive films are temporarily adhered to each other in a peelable manner, and are bonded to the recording surface and the transparent heat-sensitive adhesive film on both sides of the temporarily adhered film with an adhesive force larger than the temporary adhesive force. An object of the present invention is to provide a simple method for producing a four-layer adhesive sheet provided with a transparent adhesive layer to be obtained.

<< Means for Solving the Problems >> The object of the present invention is to produce a four-layer adhesive sheet having a transparent adhesive layer disposed on both sides of a temporary adhesive sheet composed of two transparent sheets which can be peeled off from each other. In the method, at least two adjacent layers among the four layers are manufactured by co-extrusion molding.

Each layer of the temporary adhesive transparent sheet in the present invention is made of a thermoplastic resin having a thickness of 10 to 30 μm.

The combination of the materials of the resin of each layer can be appropriately selected, but the resin of one layer is made of polyethylene terephthalate polymer, acetate polymer, 4-methylpentene-
1 polymer, polyethylene (a) and polypropylene, and the resin of the other layer is ethylene / ethyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / α-olefin copolymer, It is preferable to select from polyethylene (b) having a different density from (a), and in particular, a combination in which one layer is a 4-methylpentene-1 copolymer and the other layer is an ethylene / α-olefin copolymer. However, it is preferable because it is easy to adjust the adhesive strength at the time of temporary bonding and the adhesive strength with the adhesive layers provided on both sides of the temporary adhesive transparent sheet.

The adhesive layers provided on both sides of the temporary adhesive transparent sheet may be of a hot melt type, a solvent application type or an emulsion application type, but preferably have a thickness of 10 to 40 μm. In the case of solvent coating type or emulsion type,
After co-extrusion of the two-layer temporary adhesive transparent sheet, a predetermined amount of a known adhesive capable of bonding to each layer and the recording surface is applied and dried by a known method on both surfaces of the temporary adhesive. good.

When using a hot-melt adhesive layer, it can be co-extruded with the layer constituting the temporary adhesive transparent sheet,
The co-extrusion molding of the temporary adhesive transparent sheet may be followed by thermocompression bonding. Therefore, in the method for producing an adhesive sheet of the present invention when only one of the adhesive layers is of a hot melt type (see FIG. 1), a temporary adhesive transparent sheet composed of an A layer and a B layer is produced by coextrusion molding. After hot-melt type adhesive layer (D layer) is thermocompression-bonded or directly melt-extruded on layer B, the adhesive layer (C layer) on layer A of the temporary adhesive transparent sheet
After the co-extrusion molding of one layer (layer B) constituting the temporary adhesive sheet and the hot melt type adhesive layer (layer D), the other layer (A) constituting the temporary adhesive sheet
Layer) by hot pressing or direct melt extrusion to form a temporary adhesive sheet, then applying an adhesive layer (C layer) on the other surface of the layer and co-extrusion molding the above A, B, D3 layers Then, there is a method of applying an adhesive layer (C layer) on the A layer.

When using a hot-melt type for both adhesive layers, instead of applying the adhesive layer (C layer) in the above (1), a method of thermocompression bonding or melt extrusion ('-
') And one layer (A) constituting the temporary adhesive sheet.
Layer) and one adhesive layer (C layer) and the other layer (B layer) and the other adhesive layer (D layer) are co-extruded, respectively, so that the adhesive layers are both disposed outside. A method in which layer A and layer B are overlapped and thermocompression-bonded, on layer A of a sheet obtained by coextrusion molding one layer (layer A) and one adhesive layer (layer C) constituting a temporary adhesive sheet The other layer (Layer B) and the other adhesive layer (Layer D) are directly co-extruded into
A method of obtaining an adhesive sheet having a layer structure and a method of co-extrusion of four layers at a time become possible.

Therefore, from the viewpoint of simplifying the process by co-extrusion,
It is preferable that at least one of the adhesive layers is of a hot melt type, and it is particularly preferable that both of them are of a hot melt type.

The adhesive layer may be a heat-sensitive adhesive layer or a pressure-sensitive adhesive layer.

Specific examples of the hot-melt type heat-sensitive adhesive include, for example, ethylene-vinyl acetate copolymer, ethylene / acrylic acid copolymer, acrylic, styrene / butadiene / styrene copolymer, and styrene / isoprene / styrene copolymer. And styrene / ethylene butylene / styrene copolymer adhesives. These may be used alone or as a mixture having good compatibility. Further, a known adhesion-imparting agent may be appropriately added.

Specific examples of the hot-melt type pressure-sensitive adhesive include styrene / isoprene / styrene copolymer, styrene / butadiene / styrene copolymer, styrene / ethylenebutylene / styrene copolymer, and acrylic adhesive. it can.

These may be used alone, or a mixture of those having good compatibility may be used, or a known adhesion promoter may be appropriately added.

If a pressure-sensitive adhesive is used, the surface of the adhesive layer is sticky, so it is necessary to further provide a release paper on it. Therefore, not only is it economical, but also the number of adhesive sheet manufacturing steps can be reduced. Therefore, an embodiment using a heat-sensitive adhesive layer is a preferred embodiment of the present invention.

The coextrusion method used in the present invention is already known as a method of simultaneously extruding two or more different resins through a single die as a single molten film ("Coating method by Yuji Harazaki"). , 1979, published by Maki Shoten, 21
2 pages).

In this case, by controlling the extrusion temperature and designing the difference in the chemical properties and thermal rheology of the resin used,
The adhesive strength between the layers can be controlled.

In particular, the adhesive force at the interface of the temporary adhesive sheet (the interface between the A layer and the B layer) is determined by the interface between the temporary adhesive sheet and the adhesive layer (that is, the interface between the A layer and the C layer and the interface between the B layer and the D layer) and In order to make the adhesive strength at the interface between the layer and the recording surface weaker and to make the layer peelable, combinations of the resins of the layers A and B include polypropylene and polyethylene, polypropylene and ethylene / vinyl acetate copolymer, polyethylene terephthalate. And polyethylene, polyethylene terephthalate and ethylene / α-olefin copolymer, polyethylene terephthalate and ethylene / ethyl acrylate copolymer, 4-methylpentene-1 and polyethylene, 4-methylpentene-1 and ethylene / ethyl acrylate copolymer, 4-methylpentene-1 and ethylene / α-olefin copolymer, 4-methylpentene-1 and ethylene A combination of styrene / vinyl acetate copolymer, acetate and polyethylene is preferred, and a combination using 4-methylpentene-1 is particularly preferred.

Since it is not necessary to peel off the adhesive interface between the A layer and the C layer and between the B layer and the D layer, a combination having similar chemical properties and thermal rheology is appropriately selected, and the temperature difference during coextrusion is particularly large. do not have to. However, since the A layer and the B layer need to be peelable temporary adhesives, it is necessary to select a combination of resins to be used as described above, and the co-extrusion temperature of the A layer and the B layer is set within a range in which extruding is possible. It is preferable that the difference between the extrusion temperature of A and the extrusion temperature of B be as large as possible.

When co-extrusion of layers A and C and co-extrusion of layers B and D on layer A, particularly by keeping the extrusion temperature on the B side low, the adhesion of layers A and B can be easily achieved. The strength can be controlled to a peelable strength.

The co-extrusion conditions for co-extrusion of three or more layers are as follows:
After setting the layer to a condition capable of peeling, the type and extrusion of the resin adhesive used so that the adhesive strength between the adhesive layer and the A layer and / or the B layer becomes stronger than the adhesive strength between the A layer and the B layer. The temperature and the like may be set as appropriate.

<< Effects of the Invention >> According to the method of the present invention, the conventional laminating step to be performed sequentially can be reduced or omitted altogether, so that the homogeneity and reliability of the product are remarkably improved. That is, not only the uniformity of the temporary adhesive force is good, but also the adhesive force between the other layers can be surely made larger than the temporary adhesive force, so that the adhesive sheet of the present invention is sandwiched between the recording surfaces. Documents can be securely peeled off with a temporary adhesive surface, and not only do not cause damage to the documents, but also are difficult to re-attach after peeling, so they are suitable for mailing documents belonging to secrets at low cost. .

<< Examples >> Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1. A 4-methylpentene-1 polymer and low-density polyethylene were used as resins for each layer constituting a temporary adhesive sheet, and a hot-melt type ethylene / ethyl acrylate copolymer-based heat-sensitive adhesive was used as an adhesive layer. These resins were co-extruded in four layers at a time to obtain the adhesive sheet of the present invention. At the time of co-extrusion, the extrusion temperature was set to 290 ° C., the thickness of the 4-methylpentene-1 polymer and the low-density polyethylene was set to 20 μm, and the thickness of the adhesive layers on both the upper and lower sides was set to 25 μm. The conditions were adjusted.

The adhesive sheet thus obtained was able to be peeled cleanly between the 4-methylpentene-1 polymer and the low-density polyethylene, but the adhesive force between these layers and the adhesive layer was large. However, it was difficult to peel without destruction between them.

Example 2 A polypropylene resin and an ethylene / ethyl acrylate copolymer-based heat-sensitive adhesive were used, the former being 20 μm and the latter being 25 μm.
After co-extrusion molding at 310 ° C., a low-density polyethylene and ethylene / ethyl acrylate copolymer-based heat-sensitive adhesive are applied to the polypropylene resin side so that the former has a thickness of 20 μm, the latter has a thickness of 25 μm, and the polypropylene resin has a low thermal conductivity. It was co-extruded at 250 ° C. so as to adhere to the high density polyethylene to obtain an adhesive sheet of the present invention.

The resulting adhesive sheet has sufficient adhesion between the polypropylene resin and the low-density polyethylene resin and the ethylene / ethyl acrylate copolymer-based heat-sensitive adhesive, while the polypropylene resin and the low-density polyethylene are peeled off by an appropriate force. We were able to.

Example 3 Extrusion temperature of 4-methylpentene-1 polymer was 290 ° C.
The extrusion temperature of high-density polyethylene was 270 ° C, and the former was co-extruded so that the thickness was 15 μm and the latter was 25 μm, and then a hot-melt acrylic pressure-sensitive adhesive was applied to both sides of the obtained sheet. Were laminated at 150 ° C. so as to have a thickness of 25 μm each to obtain an adhesive sheet of the present invention. After cutting the obtained adhesive sheet into postcard size, sandwiching it with 80 kg of high-quality paper slightly larger than twice the postcard size and crimping it, the paper was gently pulled up and down so that the paper was not broken,
Peeling occurred at the interface between the 4-methylpentene-1 polymer and the high density polyethylene.

 The surface after peeling was not broken at all.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a document in which an adhesive sheet of the present invention is sandwiched between recording surfaces, with a part of the document being peeled off. In the figure, reference numerals A and B denote releasable temporary adhesive sheets, and C and D denote adhesive layers provided on both surfaces of the temporary adhesive sheet.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-55197 (JP, A) JP-A-1-214485 (JP, A) JP-A-64-36490 (JP, A) 22874 (JP, U) JP-A 2-126877 (JP, U) JP-A 1-67075 (JP, U) JP-A 63-11863 (JP, U) JP-A 1-174170 (JP, U) Actual Opening Hei 2-25546 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09J 7/00-7/04 B42D 15/00-15/10

Claims (6)

(57) [Claims] 1. A method of manufacturing a four-layer adhesive sheet comprising a temporary adhesive sheet composed of two transparent sheets that can be peeled off from each other and a transparent adhesive layer disposed on both sides of the temporary adhesive sheet. A method for producing an adhesive sheet, comprising producing two layers by coextrusion molding. 2. The resin constituting one layer of the temporary adhesive sheet is one selected from the group consisting of polyethylene terephthalate, acetate, 4-methylpentene-1 polymer, polypropylene and polyethylene (a). The resin constituting the other layer is composed of an ethylene / ethyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / α-olefin copolymer and polyethylene (b) while being composed of a mixed resin of two or more types. The method for producing an adhesive sheet according to claim 1, comprising one or more mixed resins selected from the group (provided that the densities of polyethylene (a) and polyethylene (b) are different). 3. The transparent adhesive layer is a hot-melt type heat-sensitive adhesive or a hot-melt type pressure-sensitive adhesive.
Or the manufacturing method of the adhesive sheet of 2. 4. After co-extrusion of one layer of the temporary adhesive sheet and an adhesive layer bonded to the layer, the other layer of the temporary adhesive sheet and the adhesive layer bonded to the layer are The method for producing an adhesive sheet according to any one of claims 1 to 3, wherein the adhesive sheet is formed by co-extrusion so as to constitute the four-layer adhesive sheet. 5. The temporary adhesive sheet is formed by co-extrusion of two transparent sheets, and then an adhesive layer is laminated on both surfaces of the temporary adhesive sheet. The method for producing an adhesive sheet according to any one of the above items. 6. A composite sheet having a four-layer structure in one step by co-extrusion of all four layers.
4. The method for producing an adhesive sheet according to any one of claims 1 to 3.