Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2002-06-21
2004-08-31
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C525S227000, C525S228000, C524S523000, C524S526000
Reexamination Certificate
active
06783850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acrylic polymer composition wherein substantially no solvent is contained, an acrylic pressure sensitive adhesive tape prepared with the use thereof and processes for producing these.
2. Description of the Prior Art
Acrylic monomers have excellent polymerizability, and can be polymerized by various reaction systems including the solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization techniques.
For example, the following processes have been proposed for production of acrylic polymers. One process comprises heating a mixture of an acrylic monomer and a mercaptan at a temperature ranging from 20 to 200° C. in the presence of oxygen to there by effect a bulk polymerization thereof (see Japanese Patent Publication No. 50(1975)-401). Another process comprises polymerizing a mixture of an acrylic monomer and a mercaptan wherein substantially no initiator is contained in a nitrogen atmosphere (see Japanese Patent No. 258,251). A further process comprises carrying out polymerization with the use of an extrusion type barrel apparatus, in place of a batch reaction vessel, at high temperatures (near 150° C.) (see Japanese Patent Publication No. 2(1990)-55448). Still a further process comprises irradiating a batch reaction vessel with UV light through an optical fiber and carrying out polymerization by pulse irradiation of UV light (see Japanese Patent Laid-open Publication No. 7(1995)-330815). Yet still a further process comprises carrying out a UV bulk polymerization by stepwise changing the reaction temperature while irradiating a batch reaction vessel with UV light (see Japanese Patent Laid-open Publication No. 11(1999)-49811).
However, when it is intended to react acrylic monomers in the presence of a heat decomposable polymerization initiator in conventional batch reaction vessels of industrial scale, because of the high reactivity of acrylic monomers, the heat generation in the reactor (reaction vessels) is so intense that it is difficult to expel the heat of reaction toward outside of the reaction system. Therefore, it has been impracticable to accomplish a bulk polymerization of acrylic monomer in the presence of a heat decomposable polymerization initiator in reaction vessels while effectively controlling the reaction.
The reaction using a barrel apparatus has a drawback in that it is needed to set the reaction temperature so as to fall within a high temperature region with the result that, in accordance with the lowering of precision of temperature control, the molecular weight distribution of obtained polymer will be broadened and the molecular weight of obtained polymer will become polydisperse.
With respect to the barrel apparatus including UV irradiation means, temperature control is difficult, so that a reaction control of high precision cannot be effected. Further, with respect to the batch reaction vessel equipped with UV irradiation means, the cost on cooling facilities for controlling the heat generation accompanied with scale increase is so large that it is not suitable for mass production of an acrylic polymer by the use of existing facilities.
On the other hand, as aforementioned, the bulk polymerization technique is known as a method of polymerizing an acrylic monomer. In the bulk polymerization, the produced polymer does not contain solvents and does not contain surfactants and the like. Thus, in the bulk polymerization, an operation of separating solvents from the produced polymer is not needed. The produced polymer does not contain surfactants and other matters which are likely to cause deterioration of water resistance and other properties. For these reasons, the bulk polymerization, when assessed only from the viewpoint of reaction mode, provides a preferable reaction mode.
However, in the bulk polymerization wherein use is made of a thermal polymerization initiator, it is extremely difficult to control the thermal polymerization reaction because of the high reactivity of monomers used, so that the runaway of polymerization reaction is likely to occur. The runaway reaction means a phenomenon such that the reaction can no longer be controlled to thereby cause violent advance of the reaction. That is, the runaway reaction is extremely dangerous because of a rapid change of the state of components charged in the reactor, for example, a rapid rise of the reaction temperature. Moreover, the molecular weight distribution of produced polymer tends to be broad, and the molecular weight of obtained polymer tends to be low.
With respect to the bulk polymerization technique wherein an acrylic monomer is used, Japanese Patent Laid-open Publication No. 53(1978)-2589 discloses a process for producing a thermosetting acrylic resin, comprising polymerizing a mixture or syrup of a (meth)acrylic ester and a crosslinking monomer, wherein first a prepolymer with a polymerization degree of 60% or more is produced at 150° C. or below in a vessel type reactor, the prepolymer is taken out from the vessel type reactor, and further polymerization of the prepolymer is conducted through multi-stage polymerization steps set for 10 to 60% polymerization degree differences. In the Example section of the published specification, azobisisobutyronitrile, tert-butyl peroxylaurate or the like is used in an amount of about 0.01 to 0.3 part by weight per 100 parts by weight of monomer. The 10-hr half-life temperature of azobisisobutyronitrile is 66° C. The 10-hr half-life temperature of tert-butyl peroxylaurate is 98.3° C. If these thermal polymerization initiators of high 10-hr half-life temperatures are used for the above monomers in an amount of about 0.01 to 0.3 part by weight, the temperature of reaction system would rapidly rise simultaneously with the initiation of reaction. Thus, the reaction would run away unless a cooling unit of high performance is provided. Therefore, in the invention described in the published specification, it is inevitably needed to advance multi-stage polymerization reaction while effecting satisfactory cooling so as to prevent the runaway of reaction at each stage with the use of a reactor equipped with a cooling unit of satisfactory cooling capacity. Consequently, in the process described in the published specification, a high-performance equipment must be installed for cooling the reaction system.
Furthermore, Japanese Patent Laid-open Publication No. 58(1983)-87171 discloses a process for producing an acrylic pressure sensitive adhesive of 100 thousand to 600 thousand of weight average molecular weight, which comprises the first stage wherein 0.00005 to 0.5 part by weight of a thermal polymerization initiator whose half-life period is in the range of 0.1 to 1000 hr at 70° C. and in the range of 0.1 to 5 hr at the polymerization initiation temperature is mixed with 100 parts by weight of an acrylic monomer and the acrylic monomer is polymerized at 40 to 120° C., and the second stage wherein 0.0001 to 1 part by weight of a thermal polymerization initiator whose half-life period is longer than 1000 hr at 70° C. and 2 hr or longer at the polymerization initiation temperature is added and polymerization is carried out at a temperature which is higher than that of the first stage but in the range of 100 to 200° C. In the published specification, as examples of polymerization initiators used in the invention described therein, there are mentioned organic peroxides such as acetyl peroxide, lauroyl peroxide, benzoyl peroxide, diisopropyl peroxide, di-2-ethylhexyl peroxydicarbonate, tert-butyl peroxy(2-ethyl hexanoate), tert-butyl peroxylaurate and tert-butyl peroxyacetate; and azo compounds such as azobisisobutyronitrile and 2,2′-azobis(2,4-dimethylvaleronitrile).
The polymerization initiators used in the invention described in this published specification are thermal polymerization initiators, and the 10-hr half-life temperatures thereof are in the range of 43 to 102° C. Upon reviewing the thermal polymerization initiators used i
Nakazawa Mitsuhiko
Takizawa Youichi
Buttner David J.
Keehan Christopher
Soken Chemical & Engineering Co., Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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