Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-12-06
2003-11-11
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S050000, C525S081000, C525S085000, C525S191000, C525S192000, C525S217000, C525S218000
Reexamination Certificate
active
06646046
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-soluble pressure-sensitive adhesive composition and to a method for producing it. The present invention also relates to a pressure-sensitive adhesive tape with a water-soluble pressure-sensitive adhesive for use in papermaking processes or paper splicing in printing processes.
2. Description of Related Art
Paper manufacturers and print manufacturers use a pressure-sensitive adhesive tape containing a water-soluble pressure-sensitive adhesive when splicing two or more sheets of paper together in a processing step. The spliced portion is disintegrated to material pulp by means of a pulp disintegrator and reused. For this reason, the pressure-sensitive adhesive used in the splicing has to be dissolved in water and removed.
Usually, this completely water-soluble type pressure-sensitive adhesive comprises a highly polar polymer that contains significant amount of acrylic acid. However, such a pressure-sensitive adhesive by itself does not exhibit sufficient tack at ambient temperature and a large amount of a plasticizer is blended in order to decrease the modulus of elasticity so that sufficient tack can be developed. Blending a large amount of plasticizer causes various disadvantages. For example, although it has tack, it exhibits low shear resistance. After a pressure-sensitive adhesive tape is applied to a thin paper and stored for a certain period of time, the plasticizer component bleeds out from the adhesive into paper. Further, the plasticizer is subjected to a drastic change in water content and as a result, deformations such as so-called “telescoping” or “gapping” occur when the pressure-sensitive adhesive tape is stored in the form of a roll.
To avoid these problems, redispersible aqueous emulsion type acrylic pressure-sensitive adhesives have been proposed and are commercially available. The pressure-sensitive adhesive of this type is made hydrophilic by comprising high polar monomers and a surfactant. After the coating and drying, the emulsion particles bond to each other to form a film and they will not be redispersed in water unless a mechanical destructive force is applied to the pressure-sensitive adhesive. As a result, upon the disintegration of the spliced portion, the part where no mechanical destructive force has been applied remains as it is as an agglomeration or globule. In addition, the pressure-sensitive adhesive is not water-soluble in the strict sense, so that in the case where the pressure-sensitive adhesive is colored, the remaining pressure-sensitive adhesive, if any, makes paper recovered from the pulp unacceptable. The coloring of pressure-sensitive adhesive is often necessary in order to detect the spliced portion by means of a photomultiplier. Furthermore, the redispersible aqueous emulsion type acrylic type pressure-sensitive adhesives will hardly exhibit sufficient shear resistance at high temperatures encountered when they are used as a splice in a paper manufacturing process or in a printing process. This is because the polymers used therein have relatively small molecular weights and the crosslinking between the particles is difficult to achieve. U.S. Pat. No. 6,136,903 (Su, et al.) teaches blending a water-insoluble (non-redispersible) emulsified polymer to a water-soluble (redispersible) emulsion polymer as defined according to Technical Association of The Pulp and Paper Industry Useful Method 213 (TAPPI UM 213, incorporated herein by reference) so as to increase the adhesive properties. However, the shear resistance of this pressure-sensitive adhesive when it is used as a splice in a paper manufacturing process or in a printing process is insufficient.
A further problem of pressure-sensitive adhesives of the completely water-soluble type is that the adhesive property imparted is in a limited range. No water-soluble tackifier that is compatible with water-soluble polymers has been found yet. The definition of tackifier used herein is it gives tackiness to the polymer although its Tg is higher than room temperature. When conventional emulsified tackifiers are added, they are dispersed in the polymer but they exhibit insufficient effect as a tackifier. In most cases, the addition of an emulsified tackifier alone results in a loss of stability and formation of granular structures and it becomes a mass. In the case of ordinary water-insoluble pressure-sensitive adhesives, addition of a tackifier or alteration of the composition of the polymer may provide the necessary properties of the pressure sensitive adhesive. For example, addition of a selected tackifier or alteration of polymer composition to lower the polarity of the polymer results in an increased adhesion to a nonpolar substrate such as polypropylene or polyethylene.
Thus, currently available water-soluble pressure-sensitive adhesives can hardly bond to polyethylene-coated paper or base paper that has a rough surface and contains a lot of paper powder. However, there is no room to further improve the pressure-sensitive adhesive and there has been available no appropriate product yet.
Furthermore, the conventional water-soluble pressure-sensitive adhesives must be blended with a plasticizer in a large amount when it is intended to obtain high adhesion and high tack and this causes the problems of oozing and change of properties due to humidity. The definition of plasticizer used herein is Tg is lower than room temperature and it is liquid state at room temperature. Attempts have been made to use polymers having as low a Tg as possible in order to maintain the blending amount of a plasticizer to a low level as in U.S. Pat. No. 5,439,748 to Nakamura et al. However, no sufficient effect was obtained. As disclosed in U.S. patent application Ser. No. 09/385,946 (Contrada), improvements in humidity stability and in adhesion have been tried by addition of 2-alkyl-2-oxazoline, or the like. This is also insufficient to achieve high adhesion to non polar substrate.
Naturally, further improvements of pressure-sensitive adhesive compositions and methods for producing them are keenly demanded.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to solve the above problems and provide a water-soluble pressure-sensitive adhesive composition having balanced adhesive properties.
Another object of the present invention is to provide a method for producing such a water-soluble pressure-sensitive adhesive composition.
Still another object of the present invention is to provide a pressure-sensitive adhesive tape with such a water-soluble pressure-sensitive adhesive composition.
With a view to achieving the above-mentioned objects, the present inventors have made extensive studies. As a result they discovered that the above objects are attained by providing a water-soluble pressure-sensitive adhesive composition having blended therein a water-soluble polymer, a water-insoluble component, a water-incompatible solvent that dissolves the water-insoluble component, a water-soluble plasticizer, and an optional water-soluble component other than the water-soluble polymer and water-soluble plasticizer. Further, use of such a water-soluble pressure-sensitive adhesive gives rise to a pressure-sensitive tape with a water-soluble pressure-sensitive adhesive having balanced adhesive properties that could not be obtained by the conventional pressure-sensitive adhesive tapes.
Accordingly, the present invention provides the following:
(1) A pressure-sensitive adhesive composition comprising a water-soluble polymer A, a water-insoluble component B, a water-incompatible solvent C that dissolves the water-insoluble component B and is incompatible with water, a water-soluble plasticizer D, and water, wherein the pressure-sensitive adhesive composition in a dry state has water solubility according to Technical Association of The Pulp and Paper Industry Useful Method 213 (TAPPI UM 213). As used herein, the phrase “in a dry state” means that the composition has been dried so that water and solvent are essentially e
Contrada Svetlana I.
Hamblin, Jr. David R.
Nakamura Koichi
Permachel
Ribar Travis B
Seidleck James J.
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