Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-12-21
2003-08-12
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S3550RA, C428S3550AC, C525S032100, C525S032200, C525S033000, C525S034000, C525S041000, C525S043000
Reexamination Certificate
active
06605347
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a polyester-based pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet prepared therefrom in the form of sheet or tape.
BACKGROUND OF THE INVENTION
Polyesters can be imparted a wide variety of excellent properties such as an excellent heat resistance, an excellent chemical resistance and an excellent mechanical strength by properly combining diol components, dicarboxylic acid components or hydroxycarboxylic acid components, and have find wide applications in films, fibers, paints, coating materials, adhesives, etc.
As polyester-based adhesives, there have been known, for example, hot-melt adhesives and thermosetting adhesives in which a curing agent is used to react by heating. In order to maintain or exhibit adhesive properties, these adhesives have a considerably higher melting point (softening point) than room temperature (23° C.), or are in a considerably highly crosslinked state, thus being in an extremely hard state at about room temperature.
Therefore, the above-described adhesives involve the problem that a heating apparatus is required or a working load such as a heating operation is required for obtaining the adhesive function, leading to an increase in cost. From this standpoint, application of a pressure-sensitive adhesive which can exhibit adhesive properties under a slight pressure in a short time has been demanded and, recently, there has been made an application as a pressure-sensitive adhesive as is disclosed in JP-A-11-21340 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”).
In general, as is disclosed in, for example, D. Satas, Adhesive Age, 31 (9), 28 (1988), pressure-sensitive adhesives are designed to have a storage elastic modulus at room temperature [G′] of about 1×10
5
Pa or lower than that and, in case where the storage elastic modulus at room temperature [G′] exceeds 5×10
5
Pa, a high tack required as a pressure-sensitive adhesive is not obtained, and sufficient adhesive performance can not be obtained in a short time (about 10 seconds) from its application.
Therefore, in the case of using a polyester in a pressure-sensitive adhesive, the polyester is required to have an enough flexibility as one of physical properties. Thus, it can be said to be effective to use an aliphatic polyester having a low glass transition temperature, which has a polyester structure of having hydrocarbon groups in the side chains, as disclosed in JP-A-11-21340. However, aliphatic polyesters having hydrocarbon groups in the side chains generally have a weak mechanical strength and is inferior in cohesive force which is another necessary function as a pressure-sensitive adhesive known by the definition in JIS that “adhesion can be completed by merely applying a slight pressure at room temperature for a short time without using water, solvents and heat and, due to enough cohesive force and enough elasticity, an adherend can be peeled off from a hard, smooth surface in spite of the strong adhesion”.
Thus, for the purpose of strengthen the mechanical strength, it is necessary to conduct crosslinking treatment using a crosslinking agent such as polyisocyanate and, in JP-A-11-21340, too, the crosslinking treatment using polyisocyanate is conducted. However, it is difficult to adjust the amount of a crosslinking agent so as to obtain both a good mechanical strength and a good flexibility at the same time. In case where the amount of the crosslinking agent is increased to preferentially obtain an increased mechanical strength, there results a poor flexibility, leading to poor adhesion properties to a rough surface. On the other hand, in case where the amount of the crosslinking agent is decreased to obtain an increased flexibility, there results a poor mechanical strength which is unsuitable for the use of fixing parts of electric products or fixing parts of automobiles, which use requires heat resistance and durability.
Under such circumstances, an object of the invention is to obtain a pressure-sensitive adhesive composition capable of finding wide applications and a pressure-sensitive adhesive sheet prepared therefrom by improving molecular structure of the polyester per se to attain both a good mechanical strength and a good flexibility at the same time.
SUMMARY OF THE INVENTION
As a result of intensive investigations to achieve the above object, the inventors have found that mechanical strength of a polyester is increased and heat resistance thereof is improved by using a specific aliphatic diol having a carbonate structure having a high molecular cohesive force as a starting material component of the polyester. In addition, the inventors have also found that, by using a polyhydric alcohol having three or more hydroxyl groups or a polycarboxylic acid having three or more carboxyl groups together with the above-described starting material component, there is obtained a polyester having branched chains and having a wide molecular weight distribution of 2.2 or more in degree of dispersion (weight average molecular weight
umber average molecular weight), which polyester has an improved flexibility, particularly without spoiling the mechanical strength in comparison with polyesters of less than 2.2 in degree of dispersion having a conventional structure formed by using only bi-functional components of a diol component and a dicarboxylic acid component.
As is described above, the inventors have found that polyesters having both a good mechanical strength and a good flexibility can be obtained by using, as starting components of the polyesters, a particular aliphatic diol having a carbonate structure in combination with a polyhydric alcohol having three or more hydroxyl groups or a polycarboxylic acid having three or more carboxyl groups, and that there are obtained a pressure-sensitive adhesive composition containing the polyester and a pressure-sensitive adhesive tape made therefrom having satisfactory heat resistance and adhesion properties to a rough surface, thus having achieved the invention based on the finding.
That is, the invention relates to a pressure-sensitive adhesive composition which comprises a polyester obtained from starting material components essentially comprising:
(A) an aliphatic diol having in the main chain a structural unit represented by the following formula (1):
wherein R represents a straight or branched hydrocarbon group having 2 to 20 carbon atoms; and
(B) at least one of a polyhydric alcohol having three or more hydroxyl groups and a polycarboxylic acid having three or more carboxyl groups, said polyester having a number average molecular weight of 5,000 or more and a degree of dispersion (weight average molecular weight
umber average molecular weight) of 2.2 or more. In particular, it relates to the pressure-sensitive adhesive composition having the above-described constitution, wherein the polyester has been subjected to a crosslinking treatment and the crosslinked polyester preferably comprises solvent-insoluble components in an amount of 10% by weight or more. In addition, it relates to the pressure-sensitive adhesive composition having the above-described constitution, which preferably has a glass transition temperature of −10° C. or lower and a storage elastic modulus at 23° C. of 5×10
5
Pa or lower.
In addition, the invention relates to a pressure-sensitive adhesive sheet comprising a substrate having provided on one side or both sides thereof a layer comprising the pressure-sensitive adhesive composition of the above-described constitution. Additionally, the term “pressure-sensitive adhesive sheet” usually includes pressure-sensitive adhesive tapes with a narrow width as well as pressure sensitive adhesive sheets with a wide width, and includes known various pressure-sensitive adhesive products such as pressure-sensitive adhesive labels.
DETAILED DESCRIPTION OF THE INVENTION
The polyester of the invention is a polyester obtained by using, as starting material compo
Amano Tatsumi
Ando Masahiko
Sakaitani Waka
Nitto Denko Corporation
Ribar Travis B
Seidleck James J.
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