Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-03-29
2002-01-01
Ogden, Necholus (Department: 1751)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550RA, C428S356000
Reexamination Certificate
active
06335090
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pressure-sensitive adhesive and a surface protecting material which exhibit good initial adhesion, retention of the initial adhesion, and excellent weather resistance and can easily be removed after long-term adhesion.
BACKGROUND OF THE INVENTION
A surface protecting material comprising a substrate and a pressure-sensitive adhesive layer comprising an isobutylene polymer as a base polymer is known. Compared with acrylic or natural rubber-based pressure-sensitive adhesive layers, polyisobutylene-based pressure-sensitive adhesive layer hardly increases its adhesiveness with time even when exposed to sunlight so that it is easily removed from an adherend surface without leaving the adhesive, which is advantageous for use as a surface protecting material. On the other hand, the initial adhesive strength of the polyisobutylene-based pressure-sensitive layer is sacrificed to adhesion retention and weather resistance. Therefore, it has been difficult to secure adhesion retention and weather resistance in good balance with initial adhesion.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polyisobutylene-based pressure-sensitive adhesive and a surface protecting material comprising the same which exhibit satisfactory initial adhesion, retention of the initial adhesion, and weather resistance in good balance and is easily removable without leaving the adhesive on the adherend surface even after long-term adhesion.
The present invention provides a pressure-sensitive adhesive comprising 100 parts by weight of an isobutylene polymer and 0.001 to 5 parts by weight of at least one release control agent selected from the group consisting of an alcohol having a molecular weight of 90 to 300 and an oxygen atom content of 8.5% or more or a derivative thereof and a carboxylic acid having a molecular weight of 70 to 400 and an oxygen atom content of 11% or more or a derivative thereof.
The present invention also provides a surface protecting material comprising a substrate having thereon a pressure-sensitive adhesive layer comprising the above-described pressure-sensitive adhesive.
The release control agent used in the invention exhibits high polarity due to the existence of oxygen atoms having high electronegativity. It is localized in the vicinities of the adhesive layer interface based on its high polarity in a peculiar compatible state to form a layer having weak cohesion in the vicinities of the adhesive interface. By the action of this layer, there are provided a pressure-sensitive adhesive having well-balanced adhesion characteristics including initial adhesion, weather resistance, and retention of the initial adhesion and a removable surface protecting material which exhibits satisfactory adhesion, retains the initial adhesion for a long time and is easily removed without leaving the adhesive.
DETAILED DESCRIPTION OF THE INVENTION
The pressure-sensitive adhesive according to the invention essentially comprises 100 parts by weight of an isobutylene polymer and 0.001 to 5 parts by weight of a release control agent selected from the group consisting of an alcohol having a molecular weight of 90 to 300 and an oxygen atom content of 8.5% or more or a derivative thereof and a carboxylic acid having a molecular weight of 70 to 400 and an oxygen atom content of 11% or more or a derivative thereof. The surface protecting material according to the invention comprises a substrate having thereon a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive of the invention.
The isobutylene polymer which can be used as a base polymer of the pressure-sensitive adhesive includes an isobutylene homopolymer and an isobutylene-isoprene random copolymer (i.e., butyl rubber) or a vulcanized or modified product thereof, such as regular butyl rubber, halogenated (e.g., chlorinated or brominated) butyl rubber, and partially crosslinked butyl rubber.
The modified butyl rubber also includes one prepared by introducing a functional group, such as a hydroxyl group, a carboxyl group, an amino group or an epoxy group, into the random copolymer. Isobutylene polymers preferred for weather resistance, etc. include an isobutylene homopolymer, an isobutylene-isoprene random copolymer having an isoprene content of 0.5 to 3% by weight and its vulcanized or modified product. An isobutylene homopolymer is particularly preferred. These isobutylene polymers can be used either individually or as a combination of two or more thereof.
The release control agent which can be used in the invention comprises at least one of an alcohol having a molecular weight of 90 to 300 and an oxygen atom content of 8.5% or more or a derivative thereof and a carboxylic acid having a molecular weight of 70 to 400 and an oxygen atom content of 11% or more or a derivative thereof.
The release control agent having high polarity, which is assigned to the high electronegativity of oxygen, exhibits compatibility to the isobutylene base polymer and is localized, when formulated as a pressure-sensitive adhesive layer, in the adhesive interface in a peculiar compatible state.
From the viewpoint of compatibility (which assures that the release control agent be retained in the adhesive layer without bleeding and exhibit satisfactory properties in forming the above-mentioned peculiar compatible state), improved adhesion, and long-term retention of the adhesion characteristics, a preferred release control agent is selected from an alcohol having a molecular weight of 100 or more, particularly 110 or more, especially 120 or more, a derivative of such an alcohol, a carboxylic acid having a molecular weight of 80 or more, particularly 90 or more, especially 100 or more, and a derivative of such a carboxylic acid.
An alcohol whose molecular weight is smaller than 90 or a derivative thereof or a carboxylic acid whose molecular weight is smaller than 70 or a derivative thereof would be lost through vaporization, etc., and the amount of the release control agent localized in the vicinities of the adhesive interface would be insufficient. It follows that the adhesion retention properties are reduced to impair removability. Where an alcohol or a derivative thereof whose molecular weight exceeds 300 or a carboxylic acid or a derivative thereof whose molecular weight exceeds 400 is used as a release control agent, the layer formed - of the agent localized in the vicinities of the interface would have too high a cohesive force, which ruins the removability.
If the oxygen atom content of the alcohol or alcohol derivative is less than 8.5%, or if that of the carboxylic acid or carboxylic acid derivative is less than 11%, the polarity is insufficient for making a clear difference from the polarity of the isobutylene polymer. As a result, a peculiar compatible state of the release control agent is hardly manifested in the vicinities of the adhesive interface, failing to accomplish the object of the invention. The oxygen atom content as referred to herein is calculated from equation:
Oxygen atom content (%)=(16A/Mw)×100
wherein A is the number of oxygen atoms present per molecule of the alcohol or alcohol derivative or the carboxylic acid or carboxylic acid derivative; and Mw is the molecular weight of the alcohol or a derivative thereof or the carboxylic acid or a derivative thereof.
The alcohol having a molecular weight of 90 to 300 and an oxygen atom content of 8.5% or more includes 1,1-cyclohexanediol, 3,3,5-trimethyl-1,1-cyclohexanediol, 2-methyl-2-pentanol, 2-(4-isopropylphenyl)-2-propanol, 2-hexyl-2-propanol, and 2-phenyl-2-propanol. The alcohol derivative includes esters formed of the above-enumerated alcohol component.
The carboxylic acid having a molecular weight of 70 to 400 and an oxygen atom content of 11% or more includes isobutyric acid, caprylic acid, succinic acid, benzoic acid, toluylic acid, and isophthalic acid. Benzoic acid is particularly preferred for the ease in compounding. The carboxylic acid derivative includes salts and esters of the above-enum
Eda Takeshi
Hayashi Keiji
Horada Mitsuru
Inoue Tsuyoshi
Matsui Komaharu
Nitto Denko Corporation
Ogden Necholus
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