JP2000351949A - Production of kraft adhesive tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To gain a method for producing a kraft adhesive tape excellent in curability of a releasing layer, enabling a pressure sensitive adhesive layer to be formed immediately after the formation of the releasing layer and excellent in a releasing performance. SOLUTION: This method for producing a kraft adhesive tape comprises forming a releasing layer made of a silicone mainly comprising a branched organopolysiloxane having alkenyl groups combined with silicon atoms located at the ends of the organopolysiloxane which is expressed by the formula, wherein R1s are each a monovalent substituent selected from the group consisting of H, a 1-4C lower alkyl group and phenyl group; R2 is a 2-10C alkenyl group; (a1)+(a2)+(a3) is 30-1000; and (b) is an integer of 1-5 and being crosslinked with an organohydrogenpolysiloxane on one side of kraft paper, and then forming an adhesive layer made of a rubber-based pressure sensitive adhesive on the other side of the kraft paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a kraft pressure-sensitive adhesive tape used for packaging and the like, and more particularly, to a method for producing a kraft pressure-sensitive adhesive tape capable of forming a pressure-sensitive adhesive layer immediately after forming a release layer. .

[0002]

2. Description of the Related Art An adhesive tape including a kraft adhesive tape is generally prepared as a wound body, and is unwound from the wound body when used. Therefore, it is required that the pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape has good releasability from the back surface of the pressure-sensitive adhesive tape on the inner peripheral side. Therefore, a release layer is formed on the surface of the base of the pressure-sensitive adhesive tape opposite to the surface on which the pressure-sensitive adhesive layer is formed.

Usually, in a kraft pressure-sensitive adhesive tape based on kraft paper, a release layer made of a silicone resin is often used. However, in order to apply a solventless silicone resin at a high speed so as to form a thin film, its molecular weight is required to be small. In addition, since the reaction proceeds even after film formation, aging had to be performed until the peeling performance was stabilized. If the aging is not sufficient, the adhesive performance changes, causing a problem of a decrease in the initial adhesive strength and heavy peeling of the tape over time due to aging.

Therefore, in order to stabilize the release layer, a step of applying and curing a silicone resin and a step of applying an adhesive to kraft paper have to be performed in separate steps. In addition, since the step of applying and curing the silicone resin is separated from the step of applying the pressure-sensitive adhesive layer, there is a problem that a space for storing a semi-finished product is required.

On the other hand, in a method of diluting a silicone resin in a solvent and coating it on one surface of kraft paper, a silicone resin thin film can be coated at a high speed even if the molecular weight of the silicone resin is increased. However, a solvent recovery device is required, and it goes against the flow of reducing the environmental load.

[0006] Emulsion-type release agents have also been studied, but it has been difficult to apply them stably and at high speed on kraft paper, and there has been a problem that the cost is high.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a kraft pressure-sensitive adhesive tape using a solvent-free silicone resin capable of achieving safety and a reduction in environmental load as a release layer constituting material. Therefore, it is an object of the present invention to provide a method for producing a kraft pressure-sensitive adhesive tape which is stable in a short time, and therefore can be coated with a pressure-sensitive adhesive in the same step immediately after formation of a release layer, and has excellent release performance.

[0008]

The process for producing a kraft pressure-sensitive adhesive tape according to the present invention comprises a alkenyl group-containing branch bonded directly or indirectly to a terminal silicon atom represented by the following general formula (1) on one surface of kraft paper. After forming a release layer comprising an organopolysiloxane as a main component and crosslinking with an organohydrogenpolysiloxane, a rubber-based pressure-sensitive adhesive layer is formed on the opposite surface of the kraft paper.

[0009]

Embedded image

In the general formula (1), R ¹ is a monovalent substituent selected from the group consisting of a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms and a phenyl group. Also,
A plurality of R ¹ in the general formula (1) may be the same or different. R ² is an alkenyl group having 2 to 10 carbon atoms and corresponds to the alkenyl group bonded to the terminal silicon atom. Also, a ¹ + a
² + a ³ is in the range of 30 to 1000, and b is 1 to 5
Is an integer.

In the method for producing a kraft pressure-sensitive adhesive tape according to the present invention, preferably, the equivalent ratio of the SiH group of the organohydrogenpolysiloxane to the alkenyl group of the alkenyl group-containing branched organopolysiloxane bonded to the terminal silicon atom is used. c = SiH / SiR ² satisfies 1 ≦ c ≦ 2.

[0012] More preferably, the formation of the release layer and the formation of the pressure-sensitive adhesive layer are performed in-line. Hereinafter, details of the present invention will be described.

In the method for producing a kraft pressure-sensitive adhesive tape according to the present invention, kraft paper is used as a base material. In this case, the kraft paper is subjected to clupak processing in order to increase the strength, and its basis weight is not particularly limited, but is usually 60 to 80 g / m ² .

In the present invention, a release layer is formed directly or indirectly on one side of kraft paper. "Indirectly"
This means that after forming another layer such as a filling layer on one side of the kraft paper, a release layer may be formed on the other layer.

The filling layer is provided before the release layer is formed, in order to reduce the amount of silicone resin applied and to increase the coating accuracy. Examples of such a filling layer include a laminate layer made of polyolefin or the like and a coating layer made of polyvinyl alcohol or the like.

Of course, a release layer may be formed directly on one side of kraft paper. As described above, the solvent-type silicone resin requires a solvent recovery device, and causes a problem of environmental pollution. Therefore, in the present invention, a solventless silicone resin is used as the silicone resin constituting the release layer.

In order to enable the pressure-sensitive adhesive layer to be formed immediately after the formation of the release layer, the base polymer constituting the release layer contains an alkenyl group having a specific terminal silicon atom bonded thereto. A branched organopolysiloxane is used.

The branched organopolysiloxane undergoes a crosslinking reaction with the organohydrogenpolysiloxane by using a platinum complex as a catalyst to form a cured film. In this case, a reaction control agent may be used if necessary. Examples of the reaction control agent include ethynylcyclohexanol, 2-methyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol, 1,1-dimethylpropynyloxytrimethylsilane, and the like. be able to.

As described above, the use of the alkenyl group-containing branched organopolysiloxane bonded to a terminal silicon atom represented by the general formula (1) is excellent in curability (reactivity), that is, excellent stability of peeling performance. And the cured film has good high-speed deployability for rubber-based adhesives,
This is because it has high-speed peelability.

On the other hand, when a linear alkenyl-terminated organopolysiloxane having the same degree of polymerization as that of the alkenyl-containing branched organopolysiloxane represented by the above formula (1) is used, the alkenyl terminal group Is the equation (1)
Since it is smaller than that of the alkenyl group-containing branched organopolysiloxane represented by the formula (1), the curability is inferior and the developing power in the high-speed region is increased, that is, the high-speed developing characteristics are impaired.

An alkenyl group is introduced into a side chain,
Even when a linear terminal side chain alkenyl group-containing organopolysiloxane having the same alkenyl group content as that of the terminal alkenyl group-containing branched organopolysiloxane is used, the side chain alkenyl group may be changed to a terminal alkenyl group due to steric hindrance. As a result, the curability is also inferior to that of the branched alkenyl group-containing organopolysiloxane containing alkenyl groups, and the deterioration of the developing performance with the passage of time increases.

The alkenyl group-containing branched organopolysiloxane bonded to a terminal silicon atom used in the present invention is represented by the following general formula (1).

[0023]

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In the general formula (1), b is an integer of 1 to 5. When b is 0, the content of the alkenyl group is small, good curability cannot be obtained, and the high-speed development characteristics are deteriorated. On the other hand, if b is larger than 5, the synthesis becomes difficult, and the desired organopolysiloxane cannot be stably obtained.

R ¹ is a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or a phenyl group. More specifically, R ¹ is a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group. And the like. A plurality of R ¹ in the general formula (1) may be the same or different.

R ² is bonded to a terminal silicon atom, and further has a double bond having 2 to 1 carbon atoms.
It is an alkenyl group of 0. In the case of an alkenyl group having more than 10 carbon atoms, synthesis of an organopolysiloxane is difficult and not practical. Examples of such an alkenyl group include, but are not particularly limited to, a vinyl group, an allyl group, a butynyl group, and a pentynyl group. A vinyl group is preferably used.

In the equation (1), a¹~ A^ThreeIs one or more
It is an integer. Also, a¹+ A^Two+ A ^ThreeIs 30 to 1000
It is. If this value is smaller than 30, the viscosity will be low.
To apply a thin film of silicone resin composition with high precision
Becomes difficult. To ensure high-speed coating,
Means that the viscosity of the silicone resin composition is 50 to 1000 cps
(25 ° C.)¹+ A^Two+ A^ThreeIf you adjust
Good.

If a ¹ + a ² + a ³ exceeds 1000, the viscosity of the organopolysiloxane becomes too high and is not practical for coating. In the present invention, the organohydrogenpolysiloxane for crosslinking the alkenyl group-containing branched organopolysiloxane includes:
A molecule containing at least three hydrogen atoms bonded to a silicon atom in one molecule is used. The organohydrogenpolysiloxane is catalyzed by the platinum complex and undergoes a hydrosilylation reaction with the alkenyl group-containing branched organopolysiloxane bonded to the terminal silicon atom to form a cured film.

Examples of the organohydrogenpolysiloxane include methylhydrogenpolysiloxane and a copolymer of methylhydrogenpolysiloxane and dimethylsiloxane, but are not limited thereto. Those containing an alkyl group other than a methyl group or a phenyl group, or those having a cyclic structure or a branched structure may be used.

In the present invention, preferably, the equivalent ratio of the SiH group of the organohydrogenpolysiloxane to the alkenyl group R ² of the organopolysiloxane represented by the general formula (1), c = SiH / SiR ^Two
Is desirably in the range of 1 to 2. Equivalent ratio c is 1
If it is smaller, the number of reactive residues of the alkenyl group R ² increases, and the curability may be impaired. If it is larger than 2, the developing power may increase over time.

In the production method according to the present invention, the release layer is formed on one side of the kraft paper or without forming the filler layer. In this case, in forming the silicone release layer, the hydrogen polysiloxane is blended with the alkenyl group-containing branched organopolysiloxane represented by the above formula (1), and if necessary, the reaction control agent described above. After mixing and mixing, a platinum-based complex is added as a catalyst and mixed to obtain a coating liquid for forming a silicone release layer composed of a silicone resin composition. This coating liquid is applied on one side of the kraft paper after forming the sealing layer or without forming the sealing layer. The coating method is not particularly limited, and examples thereof include a method using a multi-stage roll coater represented by a three-offset gravure coater or a five-roll coater.

The coating amount of the silicone resin composition for forming the release layer is not particularly limited, but it is preferable that the coating amount is small in consideration of economy, but the coating accuracy is considered. Then, generally, 0.1 to 2.0
g / m ^2, preferably it is preferably in the range of 0.3 to 1.0 g / m ^2.

In the production method according to the present invention, the pressure-sensitive adhesive layer is formed on the opposite side of the kraft paper immediately after the formation of the silicone release layer. In this case, since the curing of the silicone release layer proceeds rapidly, the pressure-sensitive adhesive layer can be formed immediately after the formation of the silicone release layer.

The rubber-based pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, and rubber-based pressure-sensitive adhesives widely used for kraft pressure-sensitive adhesive tapes can be used, but hot-melt-type rubber-based pressure-sensitive adhesives are more preferable. Is desirable. When a hot-melt type rubber-based pressure-sensitive adhesive is used, not only is it excellent in tackiness, but also because it does not use an organic solvent when forming the pressure-sensitive adhesive layer, it can improve safety and environmental resistance in the production process. it can. The hot-melt type rubber-based pressure-sensitive adhesive generally comprises a synthetic rubber containing styrene-isoprene-styrene (SIS) as a main component and a pressure-sensitive adhesive resin. Agent,
What mixed the extender etc. is used.

The thickness and coating method of the rubber-based pressure-sensitive adhesive layer are appropriately determined according to the type of the pressure-sensitive adhesive, required characteristics, and the like, and are not particularly limited.

[0036]

EXAMPLES The present invention will be clarified below by giving specific examples of the present invention. (Example 1) This corresponds to the case where b = 1 in the general formula (1), and is represented by the following formula (2), and the viscosity at 25 ° C. is 4
A linear hydrogen polysiloxane having a viscosity of 20 cps at 25 ° C. as a cross-linking agent was used as a crosslinking agent with respect to the alkenyl group-containing branched organopolysiloxane A bonded to a terminal silicon atom of 00 cps.
H / SiR ² was blended to 1.5, and 3 parts by weight of ethynylcyclohexanol was added as a reaction control agent to 100 parts by weight of the total polysiloxane and mixed.

[0037]

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[0038] A platinum-based catalyst was added to the obtained mixture at 200 p.
pm, and the mixture was stirred to prepare a silicone resin coating liquid. 15g of polyethylene laminated on one side of unbleached kraft paper processed by Clupak
/ M ^2, and the above-mentioned silicone resin coating solution was coated on the surface on which polyethylene was laminated so that the coating amount was 0.5 g / m ² .

Immediately after applying the above silicone coating liquid,
A hot-melt type rubber-based pressure-sensitive adhesive having the following composition containing SIS as a main component is heated to 150 ° C. and melted, coated on the opposite surface so as to have a coating amount of 50 g / m ² , wound, and kraft-coated. An adhesive tape was obtained.

Composition of Hot Melt Rubber Adhesive 100 parts by weight of styrene-isoprene-styrene copolymer (trade name: Clayton TR-1107, manufactured by Shell Chemical Co., Ltd.) Petroleum resin (trade name: Quinton A, manufactured by Zeon Corporation) −
100) 100 parts by weight Process oil (manufactured by Shell Chemical Company, trade name: Shellflex 702) 30 parts by weight Antioxidant (manufactured by Yoshitomi Pharmaceutical Co., Ltd., trade name: Yoshinox 4)
25) 1 part by weight (Example 2) Except that in Example 1, the branched organopolysiloxane A and the linear hydrogen polysiloxane were blended so that the equivalent ratio c was 1.8. In the same manner as in Example 1, a kraft pressure-sensitive adhesive tape was obtained.

(Example 3) In Example 1, instead of the branched organopolysiloxane A, b = 4 in the general formula (1) and 25 represented by the following formula (3):
A kraft pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that the branched organopolysiloxane B having a viscosity at 300C of 300 ° C was used.

[0042]

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Comparative Example 1 In Example 1, a linear organopolysiloxane C having a viscosity at 25 ° C. of 450 cps represented by the following formula (4) was used in place of the branched organopolysiloxane A. A kraft pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except for the presence of the adhesive.

[0044]

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(Comparative Example 2) In Comparative Example 1, after the silicone coating solution was applied, the pressure-sensitive adhesive was not immediately applied.
After aging at a temperature of 24 ° C. for 24 hours, a kraft pressure-sensitive adhesive tape was obtained in the same manner as in Comparative Example 1, except that a pressure-sensitive adhesive was applied.

Comparative Example 3 The procedure of Comparative Example 1 was repeated except that the linear organopolysiloxane C and the hydrogenpolysiloxane were blended such that the equivalent ratio c = SiH / SiR ² was 2.5. Then, a kraft adhesive tape was obtained in the same manner as in Example 1.

(Evaluation) With respect to each of the kraft adhesive tapes obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the developing power, the curability of the silicone release layer, and the tack were evaluated in the following manner. Regarding deployment power and tack, "Normal"
And "Accelerated aging". Evaluation for “normal” was made after obtaining a kraft adhesive tape.
This is a value measured after 2 days at ℃, and the evaluation by “accelerated aging” is a value measured after leaving the kraft adhesive tape in an oven at 40 ° C. for 1 month and further lapsed at 25 ° C. for 12 hours. This is the result when the change is promoted under the above conditions.

Developing force: A kraft adhesive tape having a width of 50 mm is applied to a JIS Z 0237 10 “High-speed rewinding force”.
The resistance at the time of rewinding at a speed of 30 m / min was measured according to the above, and the measured value was defined as the deployment force. The smaller the deployment force is, the more excellent the high-speed deployment is.

Curability of silicone release layer: Before obtaining each kraft pressure-sensitive adhesive tape, the silicone release layer was strongly rubbed with a finger five times before applying the pressure-sensitive adhesive and one day after the release layer was formed. Those that were confirmed to drop were marked with a cross, and those that were not recognized were marked with a circle.

Tack: JIS Z 0237-12
The tack value of each kraft pressure-sensitive adhesive tape was measured at a tilt angle of 30 ° by a “ball tack test”. The results are shown in Table 1 below.

[0051]

[Table 1]

As is clear from Table 1, in Comparative Example 1,
Immediately after the formation of the silicone release layer, the curability of the silicone release layer was not sufficient. Therefore, in the obtained kraft pressure-sensitive adhesive tape, the tack value of the pressure-sensitive adhesive layer was as low as 10 in both "normal state" and "accelerated aging", and the adhesiveness was impaired and the developing power was large.

In Comparative Example 2, since the pressure-sensitive adhesive layer was formed after aging for 24 hours after the formation of the silicone release layer, the tack value of the pressure-sensitive adhesive layer was sufficient and the developing force was small. However, since aging was required for 24 hours, productivity was low, and a storage space during that time was required.

In Comparative Example 3, when the linear organopolysiloxane C and hydrogen polysiloxane were mixed, a large amount of hydrogen polysiloxane was contained. Was raised. However, in the “accelerated aging” evaluation, the deploying power was large, and the high-speed deployability was not sufficient.

On the other hand, in Examples 1 to 3, the silicone release layer was quickly cured immediately after the application, and the adhesive layer was applied immediately after the formation of the silicone release layer. The performance and high speed deployment characteristics were shown. Also,
There was almost no deterioration in the development characteristics due to the accelerated aging.

[0056]

According to the method for producing a kraft pressure-sensitive adhesive tape according to the present invention, the branched alkenyl group-containing organosilicon bonded to the terminal silicon atom, represented by the above-mentioned general formula (1), is directly or indirectly attached to one side of kraft paper. A release layer containing polysiloxane as a main component and being crosslinked with an organohydrogenpolysiloxane is formed. Since this release layer has the above-described composition, it is quickly cured after coating. Therefore, after applying the release layer, the pressure-sensitive adhesive layer composed of the rubber-based pressure-sensitive adhesive can be immediately formed without requiring long aging. Therefore, the productivity of the kraft adhesive tape can be increased, and a storage space required for aging is not required.

Further, the release layer formed by crosslinking the branched organopolysiloxane represented by the general formula (1) with an organohydrogenpolysiloxane has a good release performance with respect to the rubber-based pressure-sensitive adhesive layer. Even when a wound body is formed after the production of the kraft pressure-sensitive adhesive tape, the pressure-sensitive adhesive performance of the pressure-sensitive adhesive layer is hardly deteriorated with time, and the high-speed deployability is also good. Therefore, when the kraft pressure-sensitive adhesive tape is paid out from the wound body of the kraft pressure-sensitive adhesive tape, the kraft pressure-sensitive adhesive tape can be fed quickly and stably.

In the production method according to the present invention, the equivalent ratio (c = SiH / SiR ² ) of the SiH group of the organohydrogenpolysiloxane to the alkenyl group R ² of the branched organopolysiloxane is in the range of 1-2. In some cases, the silicone release layer cures more quickly, and the increase in deployment force over time is more effectively suppressed.

In the production method according to the present invention, since the silicone release layer is rapidly cured as described above, the formation of the silicone release layer and the formation of the pressure-sensitive adhesive layer can be performed in-line. Can further improve the productivity of the kraft adhesive tape.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shinji Irifune 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture F-term (reference) 4E004 AA05 AA07 AB01 AB03 CA02 CB02 CC02 CC05 CD06 DA04 DB03 EA01 GA01

Claims (3)

[Claims] 1. An alkenyl group-containing branched organopolysiloxane bonded to a terminal silicon atom represented by the following general formula (1) directly or indirectly on one side of kraft paper as a main component, and crosslinked with an organohydrogenpolysiloxane. And forming a rubber-based pressure-sensitive adhesive layer on the opposite surface of the kraft paper. Embedded image However, in the formula (1), R ¹ is a hydrogen atom, carbon number 1
A monovalent substituent selected from the group consisting of an alkyl group and a phenyl group, which may be the same or different. R ² is an alkenyl group having 2 to 10 carbon atoms, a ^{1 to} a ³ are integers of 1 or more, and a ¹ + a ² + a ³
Is an integer between 30 and 1000, and b is an integer between 1 and 5. 2. The equivalent ratio c = SiH / SiR ^{2 of the} SiH group of the organohydrogenpolysiloxane to the alkenyl group of the alkenyl group-containing branched organopolysiloxane bonded to the terminal silicon atom is 1 ≦ c ≦ 2. The method for producing a kraft pressure-sensitive adhesive tape according to claim 1, wherein 3. The method for producing a kraft pressure-sensitive adhesive tape according to claim 1, wherein the formation of the release layer and the pressure-sensitive adhesive layer are performed in-line.