Water-dispersible adhesive composition and adhesive tape

Abstract

The present invention relates to a water-dispersible PSA composition comprising polymer particles, water in which the polymer particles are dispersed, and ammonium ions present in the water. The polymer particles are formed from a polymer containing monomer components of an alkyl (meth)acrylate and (meth)acrylic acid. The median particle size of the polymer particles is 0.10 μm or greater. The pH of the water-dispersible PSA composition is greater than 9.0.

Description

Technical Field

[0001] The present invention relates to a water-dispersible adhesive composition and an adhesive tape. Background Art

[0002] Aqueous-dispersible acrylic PSA compositions are known, in which acrylic polymer particles are dispersed in water (see, for example, Patent Document 1 below). The monomer components constituting the acrylic polymer particles include an alkyl (meth)acrylate and (meth)acrylic acid. Furthermore, in aqueous-dispersible acrylic PSA compositions, ammonia is added after polymerization of the polymer particles to neutralize the carboxyl groups derived from the (meth)acrylic acid.

[0003] In Patent Document 1, a water-dispersible acrylic PSA composition is continuously applied to a substrate using a coating machine to form a PSA layer. The coating machine includes, for example, rollers or a die. In the coating machine, the water-dispersible PSA composition is conveyed through the gap between rollers or ejected from the gap between the die.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-155462 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, the water-dispersible PSA composition described in Patent Document 1 is susceptible to agglomeration of acrylic polymer particles. This can lead to agglomeration of the polymer particles in the gaps between coaters. In areas where agglomeration occurs, transport and dispensing of the water-dispersible PSA composition stall. This can lead to undesirable streak-like defects in the PSA layer along the transport direction of the substrate.

[0009] The present invention provides a water-dispersible PSA composition and a PSA tape capable of suppressing the generation of streak-like defects in a PSA layer.

[0010] Solutions to the problem

[0011] The present invention (1) comprises a water-dispersible adhesive composition comprising polymer particles, water for dispersing the polymer particles, and ammonium ions present in the water, wherein the polymer particles are formed from a polymer containing monomer components of an alkyl (meth)acrylate and (meth)acrylic acid.

[0012] The median particle size of the polymer particles is 0.10 μm or more.

[0013] The pH of the water-dispersible PSA composition is greater than 9.0.

[0014] The present invention (2) includes a pressure-sensitive adhesive tape comprising a substrate layer and a pressure-sensitive adhesive layer disposed on one surface in the thickness direction of the substrate layer and formed from the water-dispersible pressure-sensitive adhesive composition described in (1).

[0015] The present invention (3) comprises the adhesive tape described in (2), wherein the thickness of the adhesive layer is 40 μm or less,

[0016] The present invention (4) comprises the adhesive tape described in (2) or (3), wherein:

[0017] The content of ammonium ions in the adhesive layer is 800 μg / g or more.

[0018] Effects of the Invention

[0019] The water-dispersible PSA composition and PSA tape of the present invention can suppress the generation of streak-like defects in the PSA layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cross-sectional view of one embodiment of the pressure-sensitive adhesive tape of the present invention.

[0021] Figure 2 This is a cross-sectional view of a modified example of the pressure-sensitive adhesive tape.

[0022] Explanation of symbols

[0023] 1 adhesive tape

[0024] 2. Base material layer

[0025] 3 Adhesive layer DETAILED DESCRIPTION

[0026] <Water-dispersible adhesive composition>

[0027] The water-dispersible PSA composition of the present invention contains polymer particles, water, and ammonium ions.

[0028] The polymer particles are formed from a polymer of monomer components. The monomer components include an alkyl (meth)acrylate and (meth)acrylic acid.

[0029] Alkyl (meth)acrylate is the main monomer or base monomer in the monomer component. Alkyl (meth)acrylate is alkyl methacrylate and / or alkyl acrylate. Hereinafter, the use and definition of (meth) are the same as above. Examples of alkyl (meth)acrylate include alkyl (meth)acrylates having an alkyl moiety with a carbon number of 2 or more and 14 or less. The carbon number of the alkyl moiety is preferably 4 or more and 12 or less. Specifically, examples of alkyl (meth)acrylate include ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, undecyl (meth)acrylate, tridecyl (meth)acrylate, and tetradecyl (meth)acrylate. Alkyl (meth)acrylates can be used alone or in combination. Preferred examples of the alkyl (meth)acrylate include butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. The proportion of the alkyl (meth)acrylate in the monomer component is, for example, 90% by mass or more, preferably 95% by mass or more, and, for example, 99% by mass or less, preferably 98% by mass or less.

[0030] (Meth)acrylic acid can copolymerize with alkyl (meth)acrylates. In order to suppress the formation of agglomerates in the water-dispersible adhesive composition, (meth)acrylic acid is included in the monomer component. Specific examples of (meth)acrylic acid include acrylic acid and methacrylic acid. (Meth)acrylic acid can be used alone or in combination. Preferred examples of (meth)acrylic acid include acrylic acid. The proportion of (meth)acrylic acid in the monomer component is, for example, 1% by mass or more, preferably 2% by mass or more, and, for example, 10% by mass or less, preferably 5% by mass or less. When the proportion of acrylic acid is above the lower limit and below the upper limit described above, the formation of agglomerates can be suppressed.

[0031] It should be noted that the monomer component may further contain a silicon-containing vinyl monomer. Examples of the silicon-containing vinyl monomer include 3-(meth)acryloxypropyltrimethoxysilane. The proportion of the silicon-containing vinyl monomer in the monomer component is, for example, 0.005% by mass or more, preferably 0.01% by mass or more, and, for example, 1% by mass or less, preferably 0.5% by mass or less.

[0032] The median particle size of the polymer particles is 0.10 μm or more, preferably 0.15 μm or more, and for example, 0.50 μm or less. When the median particle size of the polymer particles is less than the lower limit (0.10 μm) described above, streaky defects caused by agglomerates of the water-dispersible adhesive composition will form in the adhesive layer (described later). When the median particle size of the polymer particles is less than the upper limit (0.50 μm) described above, it is possible to suppress an excessive decrease in the viscosity of the water-dispersible adhesive composition and suppress depressions on one side of the substrate layer (described later), thereby stably coating the water-dispersible adhesive composition on the substrate layer. The median particle size of the polymer particles can be measured by a laser diffraction scattering method.

[0033] In a water-dispersible PSA composition, water disperses the polymer particles. For example, the water includes the water used in the emulsion polymerization of the monomer components. The proportion of water in the water-dispersible PSA composition is not particularly limited. The amount of water per 100 parts by mass of the polymer particles is, for example, 20 parts by mass or more, preferably 50 parts by mass or more, and, for example, 250 parts by mass or less, preferably 150 parts by mass or less.

[0034] Ammonium ion (NH4 + ) is present in water. Specifically, ammonium ions are ionized in water. It should be noted that the ammonium ions in this application do not include ammonium cations that form ionic bonds with the carboxyl groups of (meth)acrylic acid in the polymer particles. The proportion of ammonium ions in the water-dispersible adhesive composition can be appropriately adjusted to achieve the desired pH of the water-dispersible adhesive composition described below. The presence of ammonium ions in the water-dispersible adhesive composition is identified by ion chromatography.

[0035] The pH of the water-dispersible adhesive composition is greater than 9.0. The pH is preferably 9.5 or higher, and for example, 11.0 or lower. If the pH of the water-dispersible adhesive composition is below the lower limit (9.0), streak-like defects may form in the adhesive layer. On the other hand, if the pH of the water-dispersible adhesive composition is below the upper limit (11.0), ammonia odor can be mitigated. The pH of the water-dispersible adhesive composition can be measured using a pH meter.

[0036] The water-dispersible adhesive composition may also contain additives. Examples of additives include tackifying resins. Examples of tackifying resins include rosin resins, terpene resins, aliphatic petroleum resins, and aromatic petroleum resins. These resins may be used alone or in combination. Preferred examples include terpene resins. Terpene resins include, for example, terpene phenol resins. The amount of tackifying resin by mass relative to 100 parts by mass of the polymer particles is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and, for example, 50 parts by mass or less, preferably 40 parts by mass or less.

[0037] The solids concentration in the water-dispersible PSA composition is, for example, 30% by mass or more, preferably 40% by mass or more, and, for example, 70% by mass or less, preferably 60% by mass or less. When the solids concentration is above the lower limit, the formation of aggregates can be suppressed. When the solids concentration is below the upper limit, the thickness of the PSA layer can be reduced.

[0038] The method for producing a water-dispersible PSA composition is not particularly limited. For example, a method for producing a water-dispersible PSA composition involves first preparing monomer components. Next, the monomer components are dispersed in water to prepare an aqueous dispersion. Next, the monomer components in the aqueous dispersion are subjected to emulsion polymerization. During emulsion polymerization, the monomer components are heated in the presence of a polymerization initiator, an emulsifier, and, if necessary, a chain transfer agent. This produces an aqueous dispersion of polymer particles in which polymer particles are dispersed in water.

[0039] Then, ammonia water is added to the aqueous dispersion. At the same time, additives are added to the aqueous dispersion of polymer particles. Specifically, ammonia water is added to the aqueous dispersion of polymer particles until the total amount of carboxyl groups is neutralized, that is, until the pH reaches 7. Next, the additive is added to the aqueous dispersion of polymer particles, and then ammonia water is added to the aqueous dispersion of polymer particles. Ammonia water is added to the aqueous dispersion of polymer particles until the pH of the aqueous dispersion of polymer particles exceeds 9.0. The ammonia concentration in the ammonia water is, for example, 1% by mass or more, preferably 5% by mass or more, and for example, 30% by mass or less, preferably 20% by mass or less. It should be noted that after an excess amount of ammonia water is added to the aqueous dispersion of polymer particles, additives may be added to the aqueous dispersion of polymer particles as needed. Preferably, the aqueous dispersion of polymer particles is neutralized with ammonia water, and then the additive is added to the aqueous dispersion of polymer particles, and then ammonia is added to the aqueous dispersion of polymer particles until the pH exceeds 9.0. This suppresses the aggregation of the binder.

[0040] This allows the production of a basic water-dispersible PSA composition. The water-dispersible PSA composition contains polymer particles, water, and ammonium ions.

[0041] Next, refer to Figure 1 One embodiment of a pressure-sensitive adhesive tape including a pressure-sensitive adhesive layer formed from the above-described water-dispersible pressure-sensitive adhesive composition will be described.

[0042] like Figure 1 As shown, for example, an adhesive tape 1 can be prepared by winding a long strip of tape. It should be noted that in this application, the term "tape" is used interchangeably with "sheet" and "film." No distinction is made between tapes, sheets, and films. The adhesive tape 1 includes a base layer 2 and an adhesive layer 3 on one side in the thickness direction. The thickness direction is perpendicular to the strip direction.

[0043] The substrate layer 2 is a long film. Examples of the substrate layer 2 include plastic films, paper, cloth, non-woven fabrics, and metal foils. Examples of plastic films include polypropylene films, ethylene-propylene copolymer films, polyester films, and polyvinyl chloride films. Examples of paper include Japanese paper and kraft paper. Examples of cloth include cotton cloth and rayon cloth. Examples of non-woven fabrics include polyester non-woven fabrics and vinylon non-woven fabrics. Examples of metal foil include stainless steel foil. One side and the other side of the substrate layer 2 in the thickness direction may be subjected to a release treatment, for example. Examples of the release treatment include treatment using a silicone release agent. In this case, the substrate layer 2 functions as a release liner. The thickness of the substrate layer 2 is, for example, greater than 10 μm, and, for example, less than 500 μm.

[0044] The adhesive layer 3 is arranged on one side in the thickness direction of the base material layer 2. The adhesive layer 3 is formed from the above-mentioned water-dispersible adhesive composition. Specifically, the adhesive layer 3 is formed from a solid matter of the water-dispersible adhesive composition. The adhesive layer 3 is thin. Specifically, the thickness of the adhesive layer 3 is, for example, 40 μm or less, preferably 30 μm or less, more preferably 25 μm or less, and for example, 5 μm or more. When the thickness of the adhesive layer 3 is below the above-mentioned upper limit, the adhesive tape 1 can be made thin. On the other hand, when the thickness of the adhesive layer 3 is as thin as described above, it is easily affected by the coagulation of the application of the water-dispersible adhesive composition, and therefore, streak-like defects are easily formed in the adhesive layer 3. However, the water-dispersible adhesive composition of the present invention can suppress the formation of the above-mentioned streak-like defects because the pH exceeds 9.0 and the median particle size of the polymer particles is 0.10 μm or more.

[0045] The ammonium ion content in the adhesive layer 3 is, for example, 800 μg / g or greater, and 1500 μg / g or less. When the ammonium ion content in the adhesive layer 3 is 800 μg / g or greater, the formation of streak-like defects in the adhesive layer 3 is suppressed. When the ammonium ion content in the adhesive layer 3 is 1500 μg / g or less, ammonia odor can be mitigated.

[0046] Specifically, the ammonium ion content in the adhesive layer 3 was determined by collecting approximately 0.15 g of the adhesive layer 3 from the adhesive tape 1 to obtain a sample, which was then accurately weighed. The sample was immersed in pure water and boiled at 120°C for 1 hour for extraction. The ammonium ion (NH 4+ Specifically, the content of ammonium ions in the adhesive layer 3 can be measured according to the description in paragraph

[0013] of Japanese Patent Application Laid-Open No. 2003-155462.

[0047] Next, a method for producing the pressure-sensitive adhesive tape 1 will be described.

[0048] First, a substrate layer 2 is prepared. Next, a water-dispersible adhesive composition is applied to the substrate layer 2. A coating machine is used for applying the water-dispersible adhesive composition. The coating machine includes, for example, a mold and / or a roller. Specifically, a roll coater can be cited as a coating machine. Roll coaters include, for example, gravure roll coaters, reverse roll coaters, lick roll coaters, dip roll coaters, and blade coaters. In addition, the coating machine includes, for example, a slot die. The coating speed is not particularly limited.

[0049] The water-dispersible adhesive composition is then dried by heating. The heating conditions are not particularly limited. The water in the water-dispersible adhesive composition is removed by drying. Thus, an adhesive layer 3 is formed on one side of the substrate layer 2 in the thickness direction.

[0050] Then, if necessary, a second release liner 4 (imaginary line) is placed on one side in the thickness direction of the adhesive layer 3. The second release liner 4 protects one side in the thickness direction of the adhesive layer 3 before use of the adhesive tape 1 and is peeled off from the one side in the thickness direction of the adhesive layer 3 when the adhesive tape 1 is used. Examples of the second release liner 4 include the same materials as those for the base layer 2.

[0051] Effects

[0052] In the water-dispersible PSA composition, the median particle size of the polymer particles is 0.10 μm or greater, and the pH is greater than 9.0. Therefore, aggregation of the polymer particles is suppressed in the water-dispersible PSA composition. This prevents aggregation of polymer particles in the gaps of the coater. Consequently, the occurrence of streak-like defects in the PSA layer 3 caused by aggregation can be suppressed.

[0053] Furthermore, since the adhesive tape 1 includes the adhesive layer 3 described above, the adhesive reliability is high.

[0054] <Modifications of Adhesive Tape>

[0055] In the modification, the same reference numerals are used for the same components and processes as those in the embodiment, and detailed description thereof is omitted. In addition, unless otherwise specified, the modification can exert the same effects as those in the embodiment. Furthermore, the embodiment and its modification can be appropriately combined.

[0056] like Figure 2 As shown, two adhesive layers 3 may be arranged on one side and the other side in the thickness direction of the base layer 2. In this adhesive tape 1, the second release liner 4, the adhesive layer 3, the base layer 2, and the adhesive layer 3 are arranged in this order toward one side in the thickness direction.

[0057] Example

[0058] The specific numerical values ​​such as the mixing ratio (content ratio), physical property values, and parameters used in the following description can be replaced with the corresponding upper limit values ​​(defined as "less than" or "less than") or lower limit values ​​(defined as "more than" or "greater than") of the mixing ratio (content ratio), physical property values, and parameters described in the above-mentioned "Specific Embodiments". In addition, in the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0059] (Example 1)

[0060] Using a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirrer, 87 parts of butyl acrylate, 10 parts of 2-ethylhexyl acrylate, 4 parts of acrylic acid, 0.07 parts of 3-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Silicone Co., Ltd.), 0.05 parts of dodecylmercaptan (chain transfer agent), 0.1 parts of 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride (initiator), and 2 parts of sodium laureth sulfate (emulsifier) ​​were added to 100 parts of water to prepare an aqueous dispersion. Subsequently, the monomer components in the aqueous dispersion were emulsion polymerized to obtain a polymer particle dispersion in which polymer particles were dispersed in water.

[0061] 10% aqueous ammonia was added to the polymer particle dispersion to adjust (neutralize) the pH to 7. A terpene-phenol resin (Tamanol E-200NT, manufactured by Arakawa Chemical Industries, Ltd.) was added as a tackifier resin at a solid content of 30 parts per 100 parts solid content of the polymer particle dispersion. Ammonia (10% aqueous solution) was further added to the polymer particle dispersion until the pH reached 9.5, thereby obtaining a water-dispersible PSA composition.

[0062] The solid content concentration in the water-dispersible adhesive composition was 54%. The median particle size of the polymer particles was 0.15 μm. The median particle size was measured by laser diffraction scattering using a Beckman Coulter LS13 320 (laser diffraction particle size distribution analyzer, PIDS mode, refractive index of the dispersoid: 1.48, refractive index of the dispersion medium: 1.333).

[0063] Using a coating machine (slot die), the water-dispersible adhesive composition was applied to one side of a substrate layer 2 formed by a release liner (Mitsubishi Chemical Corporation, Diafoil MRF75) after one side in the thickness direction was subjected to a release treatment with a silicone release agent, so that the thickness after drying reached 25 μm. The coating speed was 20 m / min, and the coating distance in the longitudinal direction was 500 m. The width of the substrate layer 2 was 1250 mm. Thus, an adhesive tape 1 having a substrate layer 2 and an adhesive layer 3 was manufactured. The number of streak defects generated on the adhesive tape 1 was counted. The number of generated defects was 0.

[0064] The content of ammonium ions in the adhesive layer 3 is 800 μg / g or more.

[0065] (Example 2)

[0066] A water-dispersible PSA composition was obtained in the same manner as in Example 1. However, the amount of ammonia water (10% aqueous solution) added to the polymer particle dispersion was increased to adjust the pH to 10.0.

[0067] The solid content concentration in the dispersion type adhesive composition was 52% by mass. The ammonium ion content and the number of streak-like defects in the adhesive layer 3 are shown in Table 1. The ammonium ion content and the number of streak-like defects in the subsequent examples and comparative examples are also shown in Table 1.

[0068] (Example 3)

[0069] A water-dispersible PSA composition was obtained in the same manner as in Example 1. However, the amount of ammonia water (10% aqueous solution) added to the polymer particle dispersion was increased to adjust the pH to 11.0.

[0070] The solid content concentration in the dispersion-type pressure-sensitive adhesive composition was 50% by mass.

[0071] (Example 4)

[0072] A water-dispersible PSA composition was obtained in the same manner as in Example 1. The solid content concentration in the water-dispersible PSA composition was set to 40% by mass.

[0073] (Example 5)

[0074] A water-dispersible PSA composition was obtained in the same manner as in Example 1. The solid content concentration in the water-dispersible PSA composition was set to 60% by mass.

[0075] (Example 6)

[0076] A water-dispersible PSA composition was obtained in the same manner as in Example 1, except that the amount of acrylic acid added was changed from 4 parts to 5 parts.

[0077] (Example 7)

[0078] A water-dispersible PSA composition was obtained in the same manner as in Example 1, except that the amount of sodium lauryl polyoxyethylene ether sulfate (emulsifier) ​​was changed from 2 parts to 1.5 parts. The median particle size of the polymer particles was 0.30 μm.

[0079] (Comparative Example 1)

[0080] A water-dispersible PSA composition was obtained in the same manner as in Example 1. However, the amount of ammonia water (10% aqueous solution) added to the polymer particle dispersion was reduced, and the pH was changed to 8.0.

[0081] (Comparative Example 2)

[0082] A water-dispersible PSA composition was obtained in the same manner as in Example 1. However, acrylic acid was not blended.

[0083] (Comparative Example 3)

[0084] A water-dispersible PSA composition was obtained in the same manner as in Example 1, except that the amount of sodium lauryl polyoxyethylene ether sulfate (emulsifier) ​​added was changed from 2 parts to 3 parts. The median particle size of the polymer particles was 0.08 μm.

[0085] (Inspection of Examples and Comparative Examples)

[0086] <Comparison of Examples 1 to 3 and Comparative Example 1>

[0087] In Examples 1 to 3 and Comparative Example 1, the pH was varied by varying the amount of ammonia solution (10% aqueous solution). Furthermore, the effect of pH on the aqueous dispersion PSA composition was evaluated. No streak defects occurred in Examples 1 to 3, where the pH exceeded 9.0. However, streak defects occurred in Comparative Example 1, where the pH was less than 9.0.

[0088] <Comparison between Example 1 and Comparative Example 2>

[0089] In Example 1, acrylic acid was added to the monomer components, whereas in Comparative Example 2, acrylic acid was not added to the monomer components. Furthermore, the effect of the presence or absence of acrylic acid in the monomer components was evaluated. It is speculated that in Example 1, -COO - -NH 4+ On the other hand, it is inferred that in Comparative Example 1, there is no such repulsion, and thus the polymer particles are easily aggregated.

[0090] <Comparison of Example 1, Example 7, and Comparative Example 3>

[0091] In Examples 1, 7, and Comparative Example 3, the amount of emulsifier was varied to alter the median particle size of the polymer particles. Furthermore, the median particle size of the polymer particles was evaluated. In Examples 1 and 7, where the median particle size was 0.10 μm or greater, no streak-like defects occurred. On the other hand, in Comparative Example 3, where the median particle size was less than 0.10 μm, streak-like defects occurred.

[0092]

[0093] It should be noted that the above invention is provided in the form of exemplary embodiments of the present invention, but these are merely examples and are not to be construed as limiting. Modifications of the present invention that are obvious to those skilled in the art are included in the claims.

Claims

1. A water-dispersible PSA composition comprising polymer particles, water for dispersing the polymer particles, ammonium ions present in the water, and a terpene resin, wherein the polymer particles are formed from a polymer containing monomer components of an alkyl (meth)acrylate and (meth)acrylic acid. The median particle size of the polymer particles is 0.10 μm or more, The mass fraction of the terpene resin is 10 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the polymer particles. The pH of the water-dispersible adhesive composition is greater than 9.

0.

2. An adhesive tape comprising: substrate layer, and A PSA layer disposed on one surface in the thickness direction of the substrate layer and formed from the water-dispersible PSA composition according to claim 1.

3. The adhesive tape according to claim 2, wherein The thickness of the adhesive layer is 40 μm or less.

4. The adhesive tape according to claim 2 or 3, wherein The content of ammonium ions in the adhesive layer is 800 μg / g or more.

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