JP4356128B2 - Method for producing pressure-sensitive adhesive sheet that can be peeled off from the sticking surface by heat treatment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, plastic containers, a pressure-sensitive adhesive sheet suitable as an adhesive label to be affixed to a container such as a glass container, a manufacturing method of the pressure-sensitive adhesive sheet can be peeled off by heat treatment in view of such a vessel PSA sheet is attached It is about.
[0002]
[Prior art]
In order to collect and recycle containers such as plastic containers, it is necessary to peel off the labels attached to the containers. For this reason, conventionally, a pressure-sensitive adhesive label using a water-soluble or alkali-soluble pressure-sensitive adhesive is used for the pressure-sensitive adhesive layer, and cleaning and peeling is performed using water, warm water, an alkaline solution, or the like as a cleaning liquid in the recycling process, or A method of peeling by reducing the adhesive strength in the solution has been taken.
[0003]
In such a method, when the surface base material is paper, there is a gap between the paper and the container, and water penetrates into the paper layer, so that peeling is easy. Adhering without gaps and the base material does not penetrate water, so water, warm water or alkaline aqueous solution penetrates the adhesive layer and takes a long time to peel off, resulting in poor work efficiency. For this reason, for example, it has been proposed that the label be peeled off quickly by partially providing an adhesive layer in order to immediately infiltrate between the label substrate and the container surface (Japanese Utility Model Publication No. 2-107179). ing.
[0004]
However, in the case of a water-soluble adhesive label, when the label surface gets wet with water or the like, the label is displaced or easily peeled off from the container. Especially, a beverage bottle may be cooled in a refrigerator or ice water. Not suitable for adhesive labels. Moreover, as a method for peeling the label in this way, a method of immersing in a solution is taken, but in these methods, a large amount of water is consumed, and when an alkaline aqueous solution is used, a neutralization treatment is performed. Disposal after the purification process such as the above is necessary, and there are disadvantages such as an adverse effect on the environment and high cost for collecting plastic containers.
[0005]
On the other hand, labels using a plastic tick film having high heat shrinkability, which can be easily peeled off by heating, have been proposed (Japanese Utility Model Publication No. 63-138584, Japanese Utility Model Publication No. 5-22337, etc.). However, before recovery by heat treatment, the pressure-sensitive adhesive label may be rolled or peeled at a temperature lower than the heat treatment conditions at the time of recovery. The adhesive label that has been twisted or peeled off adheres to the container, the collection case, and the like, resulting in poor workability at the time of collection or deterioration of the plastic container depending on the heat treatment conditions. Or a base material may shrink | contract when processing an adhesive to the plastic film shrink | contracted with a heat | fever. Furthermore, depending on the type of the adhesive provided on the back surface of the plastic film, only the plastic film may shrink and the adhesive may remain in the container, that is, an adhesive residue phenomenon may occur.
[0006]
[Problems to be solved by the invention]
The present invention solves the drawbacks as described above, has no problem in normal handling, and can be easily peeled off without causing any adhesive residue only by heat treatment under specific conditions. It aims at providing the manufacturing method of a sheet | seat.
[0007]
[Means for Solving the Problems]
As a result of intensive studies in order to solve the above problems, the present inventor has found that this can be achieved only by combining a specific film and a specific pressure-sensitive adhesive.
[0008]
In the present invention, the pressure-sensitive adhesive sheet having a surface base material and the adhesive layer is at least one direction of the heat shrinkage ratio at the surface substrate is 70 to 120 ° C. is 40% or more, both the thermal shrinkage rate at 65 ° C. or less A pressure-sensitive adhesive sheet, characterized in that it is a film of 20% or less and the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is a crosslinking agent-reactive acrylic pressure-sensitive adhesive having an adhesive strength of 150 to 700 N / m according to JIS Z 0237 It is.
[0009]
The pressure-sensitive adhesive layer preferably has an adhesive strength of 150 to 700 N / m according to JIS Z 0237 to the container surface.
Moreover, it is preferable to use the adhesive which has the retention strength in 70 degreeC for 2 hours or more.
The surface substrate is preferably a polyester film.
The container is preferably polyethylene terephthalate (PET), which has a relatively high heat-resistant temperature and is unlikely to deteriorate.
[0010]
Moreover, after applying and drying the cross-linking agent reaction type acrylic pressure-sensitive adhesive on the release agent layer surface of the release sheet, the pressure-sensitive adhesive layer surface is at least at 70 to 120 ° C. with the surface of the pressure-sensitive adhesive layer being less than 70 ° C. A method for producing a pressure-sensitive adhesive sheet comprising laminating films having a heat shrinkage rate in one direction of 40% or more and 65 ° C or less and a heat shrinkage rate in both directions of 20% or less. It is more preferable to laminate the film in a state where the surface of the pressure-sensitive adhesive layer is 65 ° C. or lower.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention , the pressure-sensitive adhesive sheet having a surface base material and a pressure-sensitive adhesive layer has a heat shrinkage rate in both directions of 40% or more and 65 ° C. or less in at least one direction when the surface base material is 70 to 120 ° C. The pressure-sensitive adhesive sheet is a 20% or less film, and the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is a cross-linking agent-reactive acrylic pressure-sensitive adhesive having an adhesive strength of 150 to 700 N / m according to JIS Z 0237 . This pressure-sensitive adhesive sheet is affixed as a label to , for example, a plastic container or glass container, and is subjected to heat treatment at 70 ° C. or higher, preferably 70 to 120 ° C., more preferably 70 to 100 ° C. when collecting the container or the like. by, it can be peeled off KuHiroshi easily such that adhesive residue.
[0012]
The surface base material used in the present invention has a heat shrinkage rate in at least one direction at 70 to 120 ° C., preferably 70 to 100 ° C. of 40% or more, and a heat shrinkage rate in both directions at 65 ° C. or less of 20%. % Film or less.
Incidentally, when the heat shrinkage rate in both directions at 70 to 120 ° C. is less than 40%, the label is difficult to peel off and is not suitable for recycling. Further, when at least one of the heat shrinkage at 65 ° C. or less exceeds 20%, the heat shrinks or peels off by heat other than the recovery step. In addition, the heat shrinkage rate under conditions exceeding 120 ° C. is not particularly limited, but when it exceeds 120 ° C., the cohesive force of the pressure-sensitive adhesive of the pressure-sensitive adhesive sheet is too low, and the adhesive remains in the container. Since the container may be altered or the heat capacity may be high and the economy may be deteriorated, it is preferable to heat in the range of 70 to 120 ° C., preferably 70 to 100 ° C., in the recovery step.
In addition, the heat shrinkage rate of the film as used in the present invention is set in a hot air circulation dryer so that the film surface temperature becomes each temperature for a film having a length of 100 mm × 100 mm in the vertical direction × horizontal direction, and the vertical or horizontal direction. The value in the higher direction is taken out of the shrinkage rate.
[0013]
The film having such a heat shrinkage rate may be selected from films of polyester, polyolefin, polyvinyl chloride (PVC), etc., but hardly contracts particularly at a low temperature to less than 70 ° C. The use of a polyester film (for example, polyethylene terephthalate) is preferred.
[0014]
In the present invention, a cross-linking agent reaction type acrylic pressure-sensitive adhesive (two-component cross-linking pressure-sensitive adhesive) is used as the pressure-sensitive adhesive. Incidentally, in the case of other pressure-sensitive adhesives, the pressure-sensitive adhesive label is not sufficiently peeled off by heating, and the adhesive residue is likely to be generated in the container during peeling. The cross-linking agent-reactive acrylic pressure-sensitive adhesive contains an acrylic resin and a cross-linking agent, and additives such as tackifiers, UV absorbers, cross-linking agents, pigments, plasticizers, anti-aging agents are blended as necessary. The
[0015]
Examples of acrylic resins include ethyl acrylate (EA), butyl acrylate (BA), 2-ethylhexyl acrylate (2-EHA) as main monomers, vinyl acetate (VAc), acrylonitrile (AN), styrene (St) as comonomers, Methyl methacrylate (MMA), butyl methacrylate (BMA), methyl acrylate (MA), methacrylic acid (MAA), acrylic acid (AA), itaconic acid (IA), hydroxypropyl methacrylate (HPMA), dimethylamino as functional group-containing monomers A copolymer composed of ethyl methacrylate (DM), acrylic amide (AM), methylol acrylamide (N-MAN), glycidyl methacrylate (GMA), maleic anhydride and the like as a main component (preferably 80% by weight) Can be mentioned those as above), also as a crosslinking agent, a polyisocyanate, melamine resins, urea resins, epoxy resins, crosslinked acrylic adhesive reacted with a metal chelate and the like are preferable. Further, among the above-mentioned cross-linking agents, polyisocyanate-based cross-linking agents having good reactivity with an acid or acid anhydride group, hydroxyl group, amide group, etc. and suitable reaction progress are particularly preferred.
[0016]
Among the above-mentioned pressure-sensitive adhesives, the adhesive strength according to JIS Z 0237 on the container surface is preferably 150 to 700 N / m. Incidentally, it is not preferable that the adhesive strength with respect to the surface of the container is less than 150 N / m because the adhesive label is easily peeled off from the container before the adhesive label peeling and collecting step by heat treatment. It is not preferable because it may become difficult to peel off from the container at the time of label peeling and recovery, or adhesive residue may be generated.
[0017]
Among the pressure-sensitive adhesives, it is preferable that the holding power at 70 ° C. is 2 hours or more. Here, holding force means that a certain amount of adhesive is applied to one side of a 40 μm OPP film (manufactured by Oji Paper Co., Ltd., PU-112) as a base material, and the adhesive surface is affixed onto a stainless steel plate so that the area is 25 mm × 25 mm. It is obtained by sticking the pressure-sensitive adhesive label so that the pressure-sensitive adhesive label is dropped and then measuring the time until the pressure-sensitive adhesive label falls when a load of 1 kg is applied in an atmosphere at 70 ° C. It is. In this measurement, it is preferable that the holding force at 70 ° C. does not drop for 2 hours or more. By the way, it is not preferable because the adhesive container may remain in the container when the adhesive container using the adhesive that drops in less than 2 hours is heat-treated and the adhesive label is peeled off. . In addition, when 48 hours are exceeded, the cohesive force of the pressure-sensitive adhesive is too high, and the adhesive may remain without following the shrinkage of the film. Therefore, the holding force is preferably 2 to 48 hours.
[0018]
The application amount of the pressure-sensitive adhesive layer is appropriately selected depending on the thickness of the surface base material to be used, but is preferably about 3 to 50 g / m ² , more preferably 5 to 30 g / m ² . Is. Incidentally, when the coating amount is less than 3 g / m ^2, the adhesive strength when the adhesive sheet is attached to the container may be reduced, and when it exceeds 50 g / m ² , the anchoring property of the adhesive is deteriorated, and the adhesive label. There may be a problem that the adhesive sticks out from the edge or the like, or the adhesive remains on the container. The pressure-sensitive adhesive may be partially coated so that it can be easily peeled off.
[0019]
As a coating method, a known method can be adopted and is not particularly limited. For example, a comma coating method, a reverse coating method, a gravure coating method, a reverse gravure method, a kiss coating method, a knife coating method, a bar coating method, and a die coating. And a transfer method for transferring a material coated by these methods onto a process paper, a curtain coating method and a process paper.
[0020]
Since the pressure-sensitive adhesive sheet of the present invention uses a heat-shrinkable film as the surface substrate, it is not preferable to perform pressure-sensitive adhesive processing at a high temperature, and it is necessary to adjust the drying temperature and the like. In particular, the adhesive is applied to the release sheet and dried, and then the surface substrate is bonded, or the adhesive is applied to the process paper, dried, and then bonded to the surface substrate, and then the process paper is peeled off. The method of forming the pressure-sensitive adhesive layer is preferable because it is less affected by heat and easy to process. Further, it is particularly preferable to laminate in a state where the temperature of the pressure-sensitive adhesive layer surface when the surface base material is bonded is less than 70 ° C. Particularly preferred is a method of forming a release sheet by applying an adhesive.
[0021]
The release sheet and process paper are not particularly limited, and a known release sheet in which a release agent layer such as silicone is formed on paper, glassine paper, laminated paper, plastic film, or the like can be used. Among them, in order to maintain the transparency and gloss of the pressure-sensitive adhesive sheet, it is preferable that the adhesive sheet has high smoothness so that no adhesive marks are left on the pressure-sensitive adhesive surface when the pressure-sensitive adhesive sheet is peeled off from the release sheet. For example, a polyethylene-laminated release sheet or plastic film A release sheet using is preferably used.
[0022]
The pressure-sensitive adhesive sheet of the present invention may have a structure in which a release agent layer is provided on the surface opposite to the pressure-sensitive adhesive layer without using a release sheet. In this case, it is preferable to form a release agent layer after printing and then form an adhesive layer. In this case, the release agent layer is preferably formed by low-temperature processing or ultraviolet curing.
[0023]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, “parts” and “%” represent “parts by weight” and “% by weight” unless otherwise specified.
[0024]
Example 1
(Adhesive adjustment)
85 parts by weight of butyl acrylate, 10 parts by weight of butyl methacrylate and 5 parts by weight of acrylic acid are solution-polymerized in ethyl acetate using 1 part by weight of benzoyl peroxide as an initiator, and a pressure-sensitive adhesive having a solid content of 40% by weight The main agent was obtained. What added 2 weight part of crosslinking agents (Nihon Polyurethane Industry Co., Ltd. product, Coronate L) with respect to this adhesive main ingredient was used as the adhesive.
[0025]
(Manufacture of adhesive sheet)
A 45 μm polyester film (Toyobo Co., Ltd., S5630, heat shrinkage at 70 ° C .: 50%, heat shrinkage at 65 ° C .: 1.2%) was used as the surface substrate. On the release agent layer of a release sheet laminated with polyethylene (manufactured by Oji Paper Co., Ltd., fine-quality OKC), the adhesive is coated and dried to a solid content of 20 g / m ^2, and then the surface of the adhesive layer A surface base material and a pressure-sensitive adhesive sheet were obtained in a state where the temperature was less than 70 ° C.
[0026]
(Evaluation)
"Holding power of adhesive"
The obtained adhesive was applied to one side of a 40 μm OPP film (manufactured by Oji Paper Co., Ltd., PU-112) with a solid content of 20 g / m ^2, and the adhesive surface was pasted on a stainless steel plate with an area of After sticking the adhesive sheet to 25mm x 25mm and reciprocating once with a 2Kg pressure roll, the time it took for the adhesive sheet to drop when a 1kg heavy load was applied in an atmosphere at 70 ° C was measured. It did not fall for 2 hours.
[0027]
(Recyclability)
The obtained pressure-sensitive adhesive sheet was cut to 50 mm × 100 mm to form a pressure-sensitive adhesive label. A pressure-sensitive adhesive label was applied to a plastic container (a polyethylene terephthalate (PET) container for 2.7 liters, manufactured by Toyo Seikan Co., Ltd.) by reciprocating with a 2 kg pressure roller.
The container surface temperature was 71 ° C. when placed in a hot air circulation dryer at 80 ° C. for 60 seconds. When the degree of peeling of the pressure-sensitive adhesive label at this time was evaluated, the pressure-sensitive adhesive label was easily peeled off without leaving any adhesive residue on the plastic container.
The container surface temperature was 83 ° C. when placed in a hot air circulation dryer at 100 ° C. for 60 seconds. When the degree of peeling of the pressure-sensitive adhesive label at this time was evaluated, the pressure-sensitive adhesive label was easily peeled off without leaving any adhesive residue on the plastic container.
In addition, when the heating conditions were put into a hot air circulation dryer at 70 ° C. for 60 seconds, the container surface temperature was 65 ° C., and it was not easy to remove the adhesive label from the container. In addition, when the heating condition was put into a hot air circulating dryer at 180 ° C. for 60 seconds, the container surface temperature was 130 ° C. and it was easily peeled off from the container, but a part of the adhesive remained in the plastic container, It was sticky.
Further, even when left in a 65 ° C. environment, the adhesive label was not curled or peeled off.
[0028]
Example 2
The same as Example 1 except that a 40 μm PVC film (manufactured by Shin-Etsu Chemical Co., Ltd., HR, heat shrinkage at 70 ° C .: 40%, heat shrinkage at 65 ° C .: 15%) was used as the substrate. An adhesive sheet was obtained.
[0029]
(Evaluation)
Recyclability was evaluated in the same manner as in Example 1.
The container surface temperature was 71 ° C. when placed in a hot air circulation dryer at 80 ° C. for 60 seconds. When the degree of peeling of the pressure-sensitive adhesive label at this time was evaluated, the pressure-sensitive adhesive label was easily peeled off without leaving any adhesive residue on the plastic container.
Further, when the pressure-sensitive adhesive label was left in an environment of 65 ° C., the pressure-sensitive adhesive label was slightly shrunk, but the adhesive label was not curled or peeled off.
[0030]
Example 3
(Adhesive adjustment)
70 parts by weight of 2-ethylhexyl acrylate, 15 parts by weight of butyl acrylate, 10 parts by weight of butyl methacrylate, and 5 parts by weight of acrylic acid were solution-polymerized in ethyl acetate using 1 part by weight of benzoyl peroxide as an initiator to form a solid. A pressure-sensitive adhesive main agent having a partial concentration of 40% by weight was obtained. A pressure-sensitive adhesive obtained by adding 2 parts by weight of a crosslinking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., Coronate L) to this pressure-sensitive adhesive main agent was used.
(Manufacture of adhesive sheet)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the above pressure-sensitive adhesive was used.
[0031]
(Evaluation)
When the holding power of the pressure-sensitive adhesive was measured in the same manner as in Example 1, the holding power at 70 ° C. did not fall for 2 hours.
Further, the recyclability was evaluated in the same manner as in Example 1.
The container surface temperature was 71 ° C. when placed in a hot air circulation dryer at 80 ° C. for 60 seconds. When the degree of peeling of the pressure-sensitive adhesive label at this time was evaluated, the pressure-sensitive adhesive label was easily peeled off without leaving any adhesive residue on the plastic container.
Further, even when left in a 65 ° C. environment, the adhesive label was not curled or peeled off.
[0032]
Comparative Example 1
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that a 40 μm PVC film (manufactured by Gunze Co., Ltd., BYC, heat shrinkage at 70 ° C .: 20%, one direction) was used as the surface substrate.
(Evaluation)
Recyclability was evaluated in the same manner as in Example 1.
The container surface temperature was 71 ° C. when placed in a hot air circulation dryer at 80 ° C. for 60 seconds. When the degree of peeling of the pressure-sensitive adhesive label at this time was evaluated, it was not easily peeled off from the plastic container.
[0033]
Comparative Example 2
Example 1 except that a 40 μm PVC film (manufactured by Shin-Etsu Chemical Co., Ltd., TR, heat shrinkage at 70 ° C .: 48%, heat shrinkage at 65 ° C .: 35%) was used as the surface substrate. In the same manner, an adhesive sheet was obtained.
(Evaluation)
Recyclability was evaluated in the same manner as in Example 1.
The container surface temperature was 71 ° C. when placed in a hot air circulation dryer at 80 ° C. for 60 seconds. When the degree of peeling of the adhesive label at this time was evaluated, it was easily peeled off from the plastic container. However, when the plastic with the adhesive label attached was placed in an environment at 65 ° C., both end portions of the adhesive label were rolled up.
[0034]
As is clear from the above-mentioned examples and comparative examples, in each example, the adhesive label does not remain on the plastic container and easily peels off, and the adhesive label swells at a temperature lower than the heat treatment conditions when the plastic container is recovered. Or there was no peeling. That is, the adhesive label is not peeled off before the container is collected, and the container can be collected by the heat treatment which is the object of the present invention.
[0035]
Although the comparative example 1 contracted to some extent by the heat treatment, it was not easily peeled off. In Comparative Example 2, the pressure-sensitive adhesive label was easily peeled off by heat treatment. However, since the adhesive label was drowned before being collected and heat-treated, it would adhere to other things such as a collection case during the plastic collection. It can be difficult.
[0036]
【The invention's effect】
The pressure-sensitive adhesive sheet produced according to the present invention can be easily peeled off by heat treatment after being attached to the container, and is therefore suitable for recycling of the container. Also before the recovery, at a temperature below the heat treatment conditions or the adhesive label is rolled up during collecting, no to or is peeled off, an excellent pressure-sensitive adhesive sheet nor that the adhesive in the container remains.

Claims (2)

After applying a crosslinker reaction type acrylic pressure-sensitive adhesive on the surface of the release sheet of the release sheet and drying to form a pressure-sensitive adhesive layer having an adhesive strength of 150 to 700 N / m according to JIS Z 0237, the surface of the pressure-sensitive adhesive layer is In a state where the temperature is less than 70 ° C., a film having a heat shrinkage rate in at least one direction at 70 to 120 ° C. of 40% or more and a heat shrinkage rate in both directions at 65 ° C. or less of 20% or less is laminated on the pressure-sensitive adhesive layer surface. The manufacturing method of the adhesive sheet which can be peeled from the sticking surface by heat processing characterized by the above-mentioned. The adhesive layer is formed of an adhesive having a holding force at 70 ° C of 2 hours or more according to the following measurement method, and can be peeled off from the sticking surface by heat treatment. A method for producing an adhesive sheet.
<Pressure holding power>
An adhesive is applied to one side of an OPP film (manufactured by Oji Paper Co., Ltd., PU-112) with a solid content of 20 g / m. ² After applying, sticking the adhesive surface on the stainless steel plate, sticking the adhesive sheet so that the area is 25 mm x 25 mm, making one round trip with a 2 Kg pressure roll, and then applying a 1 kg weight load in an atmosphere at 70 ° C Measure the time until the adhesive sheet drops when it is applied.