Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-03-29
2001-12-11
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C428S356000, C428S3550BL, C525S333800
Reexamination Certificate
active
06329049
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 having been masticated in an organic solvent with a radical generator 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. When the highly polar release control agent is formulated into a pressure-sensitive adhesive layer comprising an isobutylene polymer having its molecular weight reduced by mastication with a radical generator in an organic solvent, 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 having been masticated with a radical generator in an organic solvent 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 in preparation of the pressure-sensitive adhesive has been masticated in an organic solvent with a radical generator. The isobutylene polymer to be masticated 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.
From the viewpoint of the balance among initial adhesion, retention of initial adhesion, and weather resistance, it is preferred for the isobutylene polymer be masticated to such a degree that the weight average molecular weight is reduced to 90% or less, desirably 10 to 80%. More specifically, a preferred degree of mastication is such that the masticated isobutylene polymer may have a weight average molecular weight of 300,000 to 700,000 and/or a number average molecular weight of 100,000 to 400,000.
Accordingly, the average molecular weight of the isobutylene polymer to be masticated is decided appropriately based on the desired molecular weight after mastication. Polymers having a weight average molecular weight of 2,500,000 or smaller, particularly 330,000 to 2,000,000, especially 350,000 to 1,500,000 are generally used for their solubility in an organic solvent. The number average molecular weight of the polymer to be masticated is arbitrarily selected. The above-described isobutylene polymers can be used either individually or as a mixture of two or more thereof having different average molecular weights. The change in molecular weight of an isobutylene polymer by mastication can easily be seen through measurement by gel-permeation chromatography, etc.
The mastication of the isobutylene polymer is carried out with a radical generator in an organic solvent. Mastication of an isobutylene polymer having no isoprene unit (e.g., polyisobutylene) could be performed by a mastication operation applied to isoprene unit-containing rubber, such as natural rubber and butyl rubber, that is carried out by adding an organic peroxide as a peptizer to solid rubber followed by mastication in a pressure kneader, a roll mill or a Banbury mixer. It turned out, however, that an isobutylene polymer having been masticated by the mastication operation fails to achieve a satisfactory balance among weather resistance, adhesion retention and initial adhesion probably because of difference in molecular weight distribution.
The organic solvent which can be used for mastication of the isobutylene polymer is appropriately selected from those capable of dissolving the isobutylene polymer.
Examples of generally useful organic solvents include aliphatic hydrocarbons having 5 to 15 carbon atoms, such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, cyclohexane, methylcyclohexane, methylhexane, dimethylpentane, nonane, and decane; aromatic hydrocarbons having 6 to 12 carbon atoms, such as toluene, xylene, ethylbenzene, isopropylbenzene, diethylbenzene, triethylbenzene, and diisopropylbenzene; mixed hydrocarbons, such as gasoline, petroleum ether, petroleum benzine, ligroin, mineral spirit, and kerosine; alcohols; ketones; and ethers. These organic solvents can be used either individually or as a mixture of two or more thereof. Preferred organic solvents are those comprising 80% by weight or more of aliphatic hydrocarbons preferably having 6 to 8 carbon atoms.
The radical generator which can be used for mastication includes radical polymerization ini
Eda Takeshi
Matsui Komaharu
Mitsuda Hideki
Sano Kenji
Shirai Mitsuyoshi
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Zirker Daniel
LandOfFree
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