Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-28
2003-02-11
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S271000, C524S272000
Reexamination Certificate
active
06518342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an emulsion for pressure-sensitive adhesive which exhibits high adhesive strength to hard-to-adhere adherend such as polyolefin, high resistance to water, and high cohesive strength.
2. Description of the Related Art
In consideration of various factors such as environmental protection, safety in the working environment, resource saving, cost etc. there has been a large trend in recent years away from supplying solvent based adhesives (using an organic solvent as solvent medium) and more to supplying non-solvent adhesives (which do not use organic solvents). Amongst these non-solvent adhesives, pressure-sensitive adhesives emulsion have been favored in consideration of their general-purpose properties and workability. However, with these emulsion for pressure-sensitive adhesives, it is necessary to have a dispersant such as emulsifier in order to disperse the non-soluble pressure-sensitive adhesive polymer into the aqueous medium. Such a dispersant is water-soluble material, and there has been a problem that the resultant pressure-sensitive adhesive coating exhibits poor water-resistance.
The International Publication WO96/29373, filed by the present inventors, discloses an emulsion for pressure-sensitive adhesive which exhibits high water resistance. In the preparation of the emulsion, a compound which can chemically bond to the dispersant is added to the emulsion. After the emulsion is formed into a film, the carboxyl groups in the dispersant react with the compound, thereby nullifying the hydrophilic nature of the dispersant. The pressure-sensitive adhesive products produced using the emulsion has high water resistance.
It is true that the emulsion for the pressure-sensitive adhesive disclosed in the International Publication WO96/29373 can give high water resistance to the pressure-sensitive adhesive products. However, in recent years, there is an increasing demand for the pressure-sensitive adhesive products with superior adhesive properties including high adhesive strength, adhesion to polyolefin, and cohesive strength at high temperature, on top of high water resistance. In order to meet the demand, further studies have been conducted. As a method for providing such a pressure-sensitive adhesive products, it has been suggested to change the composition of the monomers for the pressure-sensitive adhesive polymer which is a component of the emulsion. As another method, it has been suggested that an adhesive strength modifier such as tackifier is added to the pressure-sensitive adhesive emulsion. However, most of tackifier are oil-soluble compound. When they are added to the pressure-sensitive adhesive emulsion, they require a large amount of emulsifier to be dispersed in water. The use of a large amount of emulsifier causes the deterioration in the water resistance of the pressure-sensitive adhesive products.
SUMMARY OF THE INVENTION
It is an object of the aspect of the present invention to provide an emulsion for pressure-sensitive adhesive which is capable of producing pressure-sensitive adhesive products having high resistance to water, and excellent adhesive properties such as high adhesive strength, adhesion to polyolefin, and high cohesive strength at high temperature.
In an aspect of the present invention, an emulsion for pressure-sensitive adhesive includes as essential components: a pressure-sensitive adhesive polymer (A) having a glass-transition temperature of −80 to −20° C., a weight-average molecular weight of 150,000 or larger, and a carboxylic acid value of 30 or smaller; a rosin derivative (B) having a weight-average molecular weight of 100,000 or smaller, and containing at least part of the carboxyl groups being alkali salt with a carboxylic acid value of 190 or larger before alkalization; and a compound (C) having a weight-average molecular weight of 100,000 or smaller, and having no carboxyl group but having at least one functional group reactive with a carboxyl group in its molecule. The amount of the rosin derivative (B) is 2 to 30 mass percent when the total amount of the pressure-sensitive adhesive polymer (A) and the rosin derivative (B) in the emulsion is defined as 100 mass percent, and the compound (C) is contained in the emulsion so that the functional group of the compound (C) is in an amount of 0.05 to 10 equivalent with respect to one equivalent of the carboxyl groups of the rosin derivative (B) before alkalization.
DETAILED DESCRIPTION OF THE INVENTION
The emulsion for pressure-sensitive adhesive of the present invention contains, as essential components, a pressure-sensitive adhesive polymer (A), a rosin derivative (B) and a compound (C). The most outstanding feature of the present invention resides in that the rosin derivative (B) having carboxyl groups is stabilized in the form of alkali salt in the emulsion without no need of much help of an emulsifier, and after the emulsion forms a pressure-sensitive adhesive layer, the carboxyl groups in the rosin derivative (B) (substantially, the carboxyl groups in the rosin derivative (B′), as will be described later) are chemically reacted with the compound (C) to nullify the hydrophilic nature of the rosin derivative (B). The rosin derivative (B) can sufficiently show its ability of improving adhesive strength while the layer keeps its water resistance high. Hereinafter, the present invention will be described in detail. In the description, the term “polymer” includes not only homopolymer but also multi-polymer including copolymers and terpolymers. It should be appreciated that the pressure-sensitive adhesive polymer (A), the rosin derivative (B) and the compound (C) are compounds different to one another.
First, the pressure-sensitive adhesive polymer (A) which is the first essential component will be described. The pressure-sensitive adhesive polymer (A) is a polymer which can display pressure-sensitive adhesiveness in the range of temperatures at which pressure-sensitive adhesive products are generally used. There are two types of polymer as the pressure-sensitive adhesive polymer (A): one type does not dissolve in water and alkali aqueous solution but can be emulsified by water-soluble emulsifier other than the polymer (A) and be made into a water dispersion and the other type can emulsify in itself. The latter type is obtained by using an emulsifier having reactivity with a monomer for the polymer (A). By use of the reactive emulsifier such as emulsifier having an ethylenically unsaturated double bond in the emulsion polymerization, the reactive emulsifier chemically bonds to the molecular chains of the pressure-sensitive adhesive polymer by polymerization. As a result, the polymer incorporated with the reactive emulsifier is obtained, and the polymer can emulsify in itself. In this invention the latter type is preferably used as well as the former type as the pressure-sensitive adhesive polymer (A).
A glass-transition temperature (Tg) of the pressure-sensitive adhesive polymer (A) is in the range of −80 to −20° C. The pressure-sensitive adhesive polymer (A) having the Tg of −20° C or higher may not exhibit its pressure-sensitive adhesiveness at a room temperature in some cases. To avoid this trouble, the upper limit of the Tg is determined to −20° C. Contrary to this, the Tg of lower than −80° C. is not preferable because the cohesive strength at high temperature tends to deteriorate. The glass-transition temperature Tg (K) can be easily obtained b the calculation from the following Formula using the Tg (K) of each homopolymer described in “POLYMER HANDBOOK, the third edition (issued by John Wiley & Sons, Inc.)”, or can be obtained using a differential scanning calorimetry apparatus (DSC) or a differential thermal analysis apparatus (DTA).
W
Tg
=
W
1
Tg
1
+
W
2
Tg
2
+
…
+
W
n
Tg
n
wherein Wn is a mass fraction of each monomer; and
Tg
n
is the Tg (K) of the homopolymer of each monomer.
The pressure-sensitive adhesive polymer (A) has a weight-average
Konosu Osamu
Tanaka Yasumasa
Tsunemine Naoki
Nippon Shokubai Co. , Ltd.
Reddick Judy M.
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