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EP-4108732-B1 - HOT-MELT PRESSURE-SENSITIVE ADHESIVE COMPOSITION AND HOT-MELT PRESSURE-SENSITIVE ADHESIVE SHEET

EP4108732B1EP 4108732 B1EP4108732 B1EP 4108732B1EP-4108732-B1

Inventors

  • NEGISHI, NOBUKAZU
  • HATANAKA, ITSUHIRO
  • TAKAHASHI, HIROAKI

Dates

Publication Date
20260506
Application Date
20210217

Claims (6)

  1. A hot-melt pressure-sensitive adhesive composition which is solvent-free, comprising: a base polymer; an isocyanate crosslinking agent; and a tackifier A which is represented by the following general formula (1): R-[(CH 3 ) 2 C 6 H 2 -(CH 2 O) n -CH 2 ] m -OH (1); (in the general formula (1), R is a hydrogen atom or a hydroxyl group, m is 9 to 16, and n is 0 to 3), wherein a content of the tackifier A with respect to 100 parts by weight of the base polymer is 1 part by weight to 10 parts by weight.
  2. The hot-melt pressure-sensitive adhesive composition according to Claim 1, comprising an acrylic polymer as the base polymer.
  3. The hot-melt pressure-sensitive adhesive composition according to Claim 2, wherein in the acrylic polymer, an alkyl (meth)acrylate having an alkyl group with 4 or more and 12 or less carbon atoms at its ester terminus is polymerized in a proportion of 50% by weight or greater.
  4. The hot-melt pressure-sensitive adhesive composition according to Claim 2 or 3, wherein a degree of dispersion (Mw / Mn) of the acrylic polymer is 3.0 to 9.0, wherein the weight average molecular weight Mw and the number average molecular weight Mn are determined referring to polystyrene equivalent values obtained on the basis of gel permeation chromatography measurement.
  5. The hot-melt pressure-sensitive adhesive composition according to any one of Claims 1 to 4, wherein a content of the isocyanate crosslinking agent is 2 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the base polymer.
  6. A pressure-sensitive adhesive sheet, comprising: a pressure-sensitive adhesive layer which is formed of a hot-melt pressure-sensitive adhesive composition according to any one of Claims 1 to 5.

Description

[Technical Field] The present invention relates to a hot-melt pressure sensitive adhesive composition. The present invention, in particular, relates to a pressure-sensitive adhesive sheet which includes a pressure-sensitive adhesive layer formed of the hot-melt pressure-sensitive adhesive composition. This application claims priority to Japanese Patent Application No. 2020-26123 filed on February 19, 2020; and the entire content thereof is herein incorporated by reference. [Background Art] In general, pressure-sensitive adhesive (hereinafter, referred to as PSA) exists as a soft solid (viscoelastic material) in a room temperature range and has a property to adhere easily to an adherend with pressure. With such property, PSA is widely used in various industrial fields from home electric appliances to automobiles and OA equipment as a highly reliable bonding means having a favorable workability. PSA is typically formed in the form of a film by using a PSA composition, and is used in the form of a PSA sheet which includes the PSA in the form of a film (a PSA layer). For manufacturing the PSA sheet having such configuration, generally, a PSA composition of a solvent solution such as toluene solution is used, and the PSA layer is formed by the solvent solution being coated on a suitable surface. However, in recent years, restraining of the use of solvents has been sought for preservation of the environment, and even in the formation of the PSA layer, use of a solvent-free hot-melt PSA composition has been reviewed. Technical literature related to this type of PSA include Patent document 1 and Patent document 2. Patent document 2 discloses a hot-melt pressure-sensitive adhesive composition which is solvent-free, comprising: an acrylic rubber including a copolymer of 95 parts of butyl acrylate and 5 parts of hydroxyethyl acrylate; an isocyanate crosslinking agent; and a xylene-based tackifier, wherein a content of the tackifier with respect to 100 parts by weight of the base polymer is 10 parts by weight. [Citation List] [Patent Literature] [Patent Document 1] Japanese Patent Application Publication No. 2013-147655[Patent document 2] US2010040777A1 [Summary of Invention] [Technical Problem] A crosslinking agent may be added to a PSA composition with the purpose of improving the adhesive performance of the PSA layer. In a case of forming a PSA layer by using a PSA composition used in a conventional solution form, by heating the PSA composition containing the crosslinking agent after being formed as a film by coating, the PSA layer may be formed by the crosslinking reaction and drying progressing simultaneously. Whereas, in a case of forming a PSA layer by using a solvent-free hot-melt PSA composition, the hot-melt PSA composition is formed as a film in a state of being melted by heating. However, when the holt-melt PSA composition having a crosslinking agent added thereto is heated until attaining a melted state in which the composition has an adequate fluidity, a reaction of the crosslinking agent added to the composition progresses, and sometimes a gelled substance is generated rapidly in the PSA composition. Thus, when gelling progresses at a stage of melting by heating the PSA composition, it may be a factor contributing to a trouble developing in a process of forming the film thereafter, a degradation of uniformity of thickness of the PSA layer and even the PSA sheet, and a poor appearance. The present invention has been made in view of the abovementioned circumstances with an objective to provide a hot-melt PSA composition that enables formation a PSA layer without the gelling progressing rapidly at the time of being melted by heating. Other related objective of the present invention is to provide a PSA sheet obtained by using the hot-melt PSA composition. [Solution to Problem] According to this description, there is provided a hot-melt PSA composition which is solvent-free. The hot-melt PSA composition includes a base polymer, an isocyanate crosslinking agent, and a tackifier A. Here, the tackifier A is represented by the following general formula (1):         R-[(CH3)2C6H2-(CH2O)n-CH2]m-OH     (1); (in the general formula (1), R is a hydrogen atom or a hydroxyl group, m is 9 to 16, and n is 0 to 3). A content of the tackifier A with respect to 100 parts by weight of the base polymer, is 1 part by weight to 10 parts by weight. In the hot-melt PSA composition, the progression of rapid gelling at the time of being melted by heating may be suppressed. When such hot-melt PSA composition is used, a defect in formation at the time of molding the composition in the film form is suppressed, and moreover, the uniformity in thickness is improved, and there is a tendency that a PSA layer having a favorable appearance is achieved. Moreover, when this hot-melt PSA composition is used, it is easy to achieve a PSA layer showing a favorable adhesive performance. In a preferable embodiment of the art disclosed herein, the