JP7731753B2 - Process film and method for recycling process film substrate - Google Patents

Description

The present invention relates to a process film and a method for recycling the substrate of the process film.

In the process of manufacturing electronic devices, etc., there is sometimes a process in which components are temporarily fixed to an adhesive film, and after performing predetermined processing such as punching, the components are peeled off from the adhesive film. Such adhesive films are called process films.

In addition, optical films such as diffusion films, prism sheets, polarizing films, retardation films, hard coat films, and transparent conductive films may have adhesive films applied to their surfaces to prevent scratches during manufacturing, distribution, storage, etc. Such adhesive films are also called process films.

Processing films have a structure in which a pressure-sensitive adhesive layer is formed on a substrate such as a plastic film. Examples of processing films are proposed in Patent Documents 1 to 3.

JP 2009-292959 A JP 2010-254789 A Japanese Patent Application Publication No. 11-129401

After a predetermined process and time has passed, the process film is peeled off from the part, etc. In order to reduce the burden on the environment, it is desirable to recycle the substrate of used process film.
However, as in Patent Documents 1 and 2, general process films do not take into consideration the recycling of the substrate.

In the process film of Patent Document 3, the adhesive constituting the adhesive layer is a water-dispersible adhesive, so that the adhesive can be removed from the substrate by washing with water, and the substrate can be recycled.
However, the process film of Patent Document 3 is limited to adhesives that are water-dispersible, and therefore, depending on the materials of the substrate and the adherend, it is not possible to improve the adhesion between the substrate and the adhesive layer, or between the adhesive layer and the adherend, and the process film lacks versatility.

An objective of the present invention is to provide a process film that allows the plastic film substrate to be easily recycled. Another objective of the present invention is to provide a method for easily recycling the plastic film substrate of the process film.

In order to solve the above problems, the present invention provides the following [1] and [2].
[1] A process film having a pressure-sensitive adhesive layer on a substrate,
the substrate is a plastic film,
The process film has a peel strength according to Method 1 of JIS Z0237:2009 of 0.001 N/10 mm or more and 0.500 N/10 mm or less,
A process film having a water-soluble resin layer between the plastic film and the pressure-sensitive adhesive layer.
[2] A method for recycling a substrate of a process film, comprising the following steps 1 to 4:
Step 1: A step of recovering the process film described in [1] above.
Step 2: A step of immersing the recovered film in water to dissolve the water-soluble resin layer in the water.
Step 3: A step of recovering the plastic film substrate.
Step 4: Recycle the collected plastic film.

The process film of the present invention allows the plastic film substrate to be easily recycled. Furthermore, the recycling method of the present invention allows the plastic film substrate of the process film to be easily recycled.

1 is a cross-sectional view showing one embodiment of the process film of the present invention.

The following describes an embodiment of the process film of the present invention and an embodiment of a method for recycling the substrate of the process film of the present invention.

[Process film]
The process film of the present invention is
A process film having a pressure-sensitive adhesive layer on a substrate,
the substrate is a plastic film,
The process film has a peel strength according to Method 1 of JIS Z0237:2009 of 0.001 N/10 mm or more and 0.500 N/10 mm or less,
A water-soluble resin layer is provided between the plastic film and the pressure-sensitive adhesive layer.

Fig. 1 is a cross-sectional view showing one embodiment of the process film of the present invention. The process film 100 of Fig. 1 has a pressure-sensitive adhesive layer 30 on a plastic film 10 as a substrate. The process film 100 of Fig. 1 has a water-soluble resin layer 20 between the plastic film 10 and the pressure-sensitive adhesive layer 30. The process film 100 of Fig. 1 has a release sheet 40 on the side of the pressure-sensitive adhesive layer 30 opposite the plastic film.
The process film may be in the form of a roll or a sheet.

<Plastic film (substrate)>
The process film of the present disclosure uses a plastic film as a substrate.
The water-soluble resin layer and the pressure-sensitive adhesive layer do not easily penetrate into the plastic film. Therefore, using a plastic film as the substrate makes it easier to recycle the substrate. On the other hand, if the substrate is paper or fiber, the pressure-sensitive adhesive layer and the like easily penetrate into the paper or fiber, making it difficult to recycle the substrate.
Furthermore, by using a plastic film as the substrate, the process film can be made easier to handle and more durable.

Resins constituting the plastic film include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polycarbonate; polyolefins such as polyethylene and polypropylene; polystyrene; triacetyl cellulose; poly(meth)acrylate; polyvinyl chloride; and the like. Among these resins, polyester is preferred. That is, polyester film is preferred as the plastic film. Polyester film is preferred because it has excellent mechanical strength, dimensional stability, and transparency. Furthermore, among polyester films, biaxially oriented polyester film is preferred, and biaxially oriented polyethylene terephthalate film is more preferred.
The surface of the plastic film may be corona discharge treated.

From the standpoint of ease of handling and strength, the thickness of the plastic film is preferably 10 μm or more and 500 μm or less, more preferably 15 μm or more and 250 μm or less, and even more preferably 20 μm or more and 100 μm or less.

<Peel strength>
The process film of the present invention is required to have a peel strength according to Method 1 of JIS Z0237:2009 of 0.001 N/10 mm or more and 0.500 N/10 mm or less.
If the peel strength is less than 0.001 N/10 mm, the adhesion between the process film and the adherend cannot be made good.
If the peel strength exceeds 0.500 N/10 mm, a force is applied when peeling the process film from the adherend, which reduces the workability of peeling.
In addition, used process films are sometimes collected by being wound up into rolls. When recycling the substrate of a used process film wound up into a roll, it is necessary to unwind the used process film from the roll. If the peel strength exceeds 0.500 N/10 mm, the aforementioned unwinding becomes difficult, resulting in a decrease in the workability of recycling.

Method 1 of JIS Z0237:2009 refers to the peel strength of 180° peeling from a stainless steel test plate. The peel strength can be measured, for example, as follows (1) to (2).
(1) The process film is cut into a test sample having a width of 25 mm and a length of 100 mm.
(2) The pressure-sensitive adhesive layer side of the sample is attached to a stainless steel test plate, and the sample is peeled off in a direction of 180° using a peel strength measuring device. The peeling speed during the peel test is preferably 300 mm/min.

The stainless steel test plate is preferably one that has a BA surface finish as specified in JIS G4305:2021. Furthermore, the stainless steel test plate preferably has a surface profile with an arithmetic mean roughness of 50 nm ± 25 nm as specified in JIS B0601:2013. Furthermore, the stainless steel test plate is preferably a SUS304 stainless steel plate.

Peel strength can be adjusted by the composition of the adhesive layer, etc. For example, increasing the degree of crosslinking of the base agent tends to decrease peel strength, while decreasing the degree of crosslinking of the base agent tends to increase peel strength. Also, increasing the amount of tackifier tends to increase peel strength, while decreasing the amount of tackifier tends to decrease peel strength.

<Adhesive Layer>
The pressure-sensitive adhesive layer is preferably formed from a pressure-sensitive adhesive composition containing a base agent and a curing agent. By using such a configuration, the peel strength of the process film can be easily adjusted to the above range by adjusting the blending ratio of the base agent and the curing agent.

The base resin can be a resin used in general-purpose adhesives, and specific examples include acrylic resins, polyester resins, urethane resins, rubber resins, and silicone resins. Of these, acrylic resins are preferred from the standpoints of heat resistance, non-contamination, and cost.

General-purpose curing agents can be used, including isocyanate-based curing agents and amine-based curing agents.

The adhesive composition may contain a tackifier. However, adhesive layers formed from adhesive compositions containing a tackifier tend to have high peel strength. For this reason, the tackifier must be carefully blended into the adhesive composition so that the peel strength falls within the above range.

The pressure-sensitive adhesive layer is preferably water-insoluble.
By making the pressure-sensitive adhesive layer water-insoluble, it is possible to prevent the pressure-sensitive adhesive layer from dissolving in water along with the water-soluble resin layer when recycling the processing film, thereby preventing multiple resins from being mixed into the waste liquid and facilitating waste liquid disposal. Furthermore, by making the pressure-sensitive adhesive layer water-insoluble, it is possible to recover the film-like pressure-sensitive adhesive layer peeled off from the plastic film when recycling the processing film, thereby reducing the environmental impact. Furthermore, by making the pressure-sensitive adhesive layer water-insoluble, it is possible to prevent the cohesive strength of the pressure-sensitive adhesive layer from decreasing due to moisture, and it is possible to easily prevent the pressure-sensitive adhesive layer from undergoing cohesive failure when peeling off the processing film. Furthermore, by making the pressure-sensitive adhesive layer water-insoluble, it is possible to easily improve the interlayer adhesion of the processing film. Furthermore, since many adherends are water-insoluble, making the pressure-sensitive adhesive layer water-insoluble can easily improve adhesion to the adherend. Furthermore, by making the pressure-sensitive adhesive layer water-insoluble, it is possible to prevent the pressure-sensitive adhesive layer from becoming sticky due to moisture.

In this specification, a water-insoluble adhesive layer means one in which the amount of the adhesive layer that dissolves in water when immersed in water at 23°C for 120 minutes is less than 1.0% by mass. The amount of dissolution is preferably less than 0.5% by mass, and more preferably less than 0.1% by mass.

The thickness of the pressure-sensitive adhesive layer is preferably from 1 μm to 50 μm, more preferably from 2 μm to 20 μm, and even more preferably from 3 μm to 10 μm.
By making the thickness of the adhesive layer 1 μm or more, it is possible to easily make the peel strength 0.001 N/10 mm or more. By making the thickness of the adhesive layer 50 μm or less, it is possible to reduce costs.

The pressure-sensitive adhesive layer may contain additives such as an ultraviolet absorber and an antioxidant.
The pressure-sensitive adhesive layer can be formed, for example, by applying a pressure-sensitive adhesive composition onto a water-soluble resin layer and drying the applied composition. A general-purpose application method can be used as the application method.

<Release sheet>
A release sheet may be provided on the side of the pressure-sensitive adhesive layer opposite the plastic film. By providing a release sheet, the process film can be easily handled during storage and distribution.
When the process film is used, the release sheet is peeled off.

Examples of release sheets include plastic film and paper. To improve release properties, the surface of the plastic film, paper, etc. may be treated with a release agent such as silicone.

<Water-soluble resin layer>
The processing film of the present invention has a water-soluble resin layer between the plastic film and the pressure-sensitive adhesive layer. The water-soluble resin layer dissolves in water when the processing film is immersed in water. When the water-soluble resin layer dissolves in water, separation of the plastic film from the water-soluble resin layer and the pressure-sensitive adhesive layer progresses, allowing the plastic film to be recovered from the processing film. In this way, the processing film of the present invention can be easily separated from the processing film by immersing it in water after use, allowing the plastic film to be recovered.

The water-soluble resin layer preferably contains a water-soluble resin.
The water-soluble resin may be a general-purpose water-soluble resin. Examples of the water-soluble resin include polyester, polyurethane, acrylic resin, epoxy resin, polyvinyl alcohol, and polyvinylpyrrolidone. Among these, water-soluble polyester is preferred because it easily provides good adhesion to the polyester film. Furthermore, among water-soluble polyester resins, water-soluble polyester resins having a highly polar functional group such as a polycarboxylic acid residue, a polyhydric alcohol residue, and a polyamine residue are preferred.

In this specification, a water-soluble resin layer refers to a resin layer in which 50% or more by mass of a 3 g sample is dissolved when the sample is taken from the water-soluble resin layer, placed in 97 g of water at 23°C, and stirred for 60 minutes at 300 rpm using a magnetic stirrer. An example of a magnetic stirrer that can be used is Yamato Scientific's "Mag Mixer MG600H" product name.

The thickness of the water-soluble resin layer is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.3 μm or more and 5.0 μm or less, and even more preferably 0.5 μm or more and 3.0 μm or less.
By making the thickness of the water-soluble resin layer 0.1 μm or more, the plastic film can be easily separated from the processing film when the processing film is immersed in water, and by making the thickness of the water-soluble resin layer 10.0 μm or less, costs can be reduced.

The water-soluble resin layer may contain additives such as an ultraviolet absorber and an antioxidant.
The water-soluble resin layer can be formed, for example, by applying a coating liquid containing components constituting the water-soluble resin layer onto a plastic film, followed by drying. As the coating method, a general-purpose coating method can be used.

[Method for recycling substrate of process film]
The method for recycling the substrate of a process film of the present invention includes the following steps 1 to 4.
Step 1: A step of recovering the process film of the present invention described above.
Step 2: A step of immersing the recovered film in water to dissolve the water-soluble resin layer in the water.
Step 3: A step of recovering the plastic film substrate.
Step 4: Recycle the collected plastic film.

<Step 1>
Step 1 is a step of recovering the process film of the present invention described above. The process film to be recovered is a used process film. Therefore, the recovered process film does not have a release film. It is preferable to recycle the release film via a separate route.

The process film collected in step 1 may be in the form of a roll or sheets.

<Step 2>
Step 2 is a step of immersing the recovered process film in water to dissolve the water-soluble resin layer in water.

In step 2, by dissolving the water-soluble resin layer in water, the plastic film can be easily recovered in step 3.
The more the water-soluble resin layer dissolves in water, the more the plastic film separates from the water-soluble resin layer and the pressure-sensitive adhesive layer, making it easier to recover the plastic film from the processing film. Therefore, in step 2, it is preferable to allow the water-soluble resin layer to dissolve in water. However, the plastic film can be separated from the water-soluble resin layer and the pressure-sensitive adhesive layer even if the water-soluble resin layer is not completely dissolved in water. Therefore, it is not necessary to completely dissolve the water-soluble resin layer in water in step 2. However, if the water-soluble resin layer is not completely dissolved in water in step 2, there is a possibility that part of the water-soluble resin layer will adhere to the plastic film. Therefore, if the water-soluble resin layer is not completely dissolved in water in step 2, it is preferable to include a water-washing step in the recycling process.

If the pressure-sensitive adhesive layer is water-insoluble, the pressure-sensitive adhesive layer will gradually peel off from the water-soluble resin layer while remaining in film form during step 2. For this reason, the method for recycling the substrate of a process film of the present invention may include a step of recovering the pressure-sensitive adhesive layer in film form. Including a step of recovering the pressure-sensitive adhesive layer can further reduce the environmental impact.

The process film may be in roll form and immersed in water while being unwound from the roll. Alternatively, the process film may be immersed in water in sheet form.

The temperature of the water in which the casting film is immersed is preferably 20°C or higher and 90°C or lower, and more preferably 20°C or higher and 60°C or lower.
By setting the water temperature to 20°C or higher, the water-soluble resin layer can be dissolved in water more quickly, improving the workability of recycling. By setting the water temperature to 90°C or lower, excessive power consumption can be suppressed, reducing the environmental load.

The time for which the process film is immersed in water cannot be generalized, as it varies depending on the water temperature and the degree of water solubility of the water-soluble resin layer. If the water temperature is 23°C, an immersion time of 60 to 240 minutes is preferable. If the water temperature is 60°C, an immersion time of 10 to 40 minutes is preferable.

The pH of the water is preferably between 5.8 and 8.6, which is the water quality standard for tap water, and more preferably between 6.8 and 8.1. Using water with a pH within this range can further reduce the environmental impact.

<Step 3>
Step 3 is a step of recovering the plastic film substrate.
Since a part of the water-soluble resin layer and the pressure-sensitive adhesive layer may remain on the plastic film, step 3 may include a water washing step.

In order to improve the workability of recycling, it is preferable to carry out steps 1 to 3 in the form of a roll as follows.
In step 1, the process film is collected in the form of a roll.
In step 2, the rolled process film is immersed in water while being fed from the roll, to dissolve the water-soluble resin layer in water.
In step 3, the plastic film is collected in the form of a roll.

<Step 4>
Step 4 is a step of recycling the collected plastic film.

Recycling methods include material recycling, chemical recycling, and thermal recycling. Of these, material recycling is preferred.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

1. Measurement and Evaluation 1-1. Peel Strength The release film was peeled from the process film of each of the Examples and Comparative Examples, and test samples were prepared by cutting the film to a width of 25 mm and a length of 150 mm. Using the test samples, peel strength was measured according to Method 1 of JIS Z0237:2009, as described in the specification. The measurement device used was Shimadzu Corporation's Autograph AGS-5NJ. Stainless steel test plates were used that had a BA surface finish as specified in JIS G4305:2021. The measurement environment was a temperature of 23°C ± 5°C and a relative humidity of 40 to 65%.

1-2. Water Immersion Test (1) The release film was peeled off from the process films of the Examples and Comparative Examples. Next, the process films from which the release film had been peeled off were immersed in water at 23°C for 120 minutes. Next, the process films were removed from the water, and the state of the coating film was visually evaluated.
(2) The release film was peeled off from the process films of the Examples and Comparative Examples. The process films from which the release film had been peeled off were then immersed in water at 60°C for 20 minutes. The process films were then removed from the water, and the state of the coating film was visually evaluated.

2. Preparation of Process Film [Example 1]
The following water-soluble resin layer coating liquid was applied to one surface of a 25 μm-thick transparent polyester film (Lumirror 25S10, manufactured by Toray Industries, Inc.), and dried at 100° C. for 120 seconds to form a 1 μm-thick water-soluble resin layer. Next, the following pressure-sensitive adhesive layer coating liquid was applied to the water-soluble resin layer, and dried at 100° C. for 120 seconds to form a 5 μm-thick pressure-sensitive adhesive layer, thereby obtaining the process film of Example 1.
<Coating liquid for water-soluble resin layer>
100 parts by mass of water-soluble polyester (Goo Chemical Industry Co., Ltd., product name: Plus Coat, solid content 20% by mass)
・Dilution solvent (appropriate amount)

<Coating liquid for adhesive layer>
Base agent 100 parts by mass (acrylic resin)
(Soken Chemical & Engineering Co., Ltd., product name: SK Dyne 1499M, solid content 30% by mass)
Curing agent: 1 part by mass (isocyanate compound)
(Soken Chemical & Engineering Co., Ltd., product name: Curing Agent D-90, solid content 90% by mass)
・Dilution solvent (appropriate amount)

[Comparative Example 1]
The above-mentioned pressure-sensitive adhesive layer coating liquid was applied to one side of a 25 μm thick transparent polyester film (Lumirror 25S10, manufactured by Toray Industries, Inc.), and dried at 100° C. for 120 seconds to form a 5 μm thick pressure-sensitive adhesive layer, thereby obtaining a process film of Comparative Example 1.

The results in Table 1 confirm that the process films of the examples have excellent recyclability, allowing the plastic film substrate to be easily recovered.

10: Plastic film 20: Water-soluble resin layer 30: Pressure-sensitive adhesive layer 40: Release sheet 100: Process film

Claims (7)

A process film having a pressure-sensitive adhesive layer on a substrate,
the substrate is a plastic film,
The process film has a peel strength according to Method 1 of JIS Z0237:2009 of 0.001 N/10 mm or more and 0.500 N/10 mm or less,
A process film having a water-soluble resin layer between the plastic film and the pressure-sensitive adhesive layer. The process film according to claim 1, wherein the water-soluble resin layer has a thickness of 0.1 μm or more and 10.0 μm or less. The process film according to claim 1 or 2, wherein the pressure-sensitive adhesive layer is water-insoluble. The process film according to any one of claims 1 to 3, wherein the plastic film is a polyester film. The process film according to any one of claims 1 to 4, which has a release sheet on the side of the adhesive layer opposite the plastic film. A method for recycling a substrate of a process film, comprising the following steps 1 to 4:
Step 1: A step of recovering the process film according to any one of claims 1 to 5.
Step 2: A step of immersing the recovered film in water to dissolve the water-soluble resin layer in the water.
Step 3: A step of recovering the plastic film substrate.
Step 4: Recycle the collected plastic film. 7. The method for recycling a substrate of a processing film according to claim 6, wherein in step 2, the temperature of the water in which the processing film is immersed is 20°C or higher and 90°C or lower.