Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-09-13
2002-12-31
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S3550RA, C428S352000, C428S353000, C428S354000
Reexamination Certificate
active
06500536
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heat activatable adhesive composition and to an adhesive sheet or tape having an heat activatable adhesive layer.
Conventional adhesive sheets generally have a pressure-sensitive adhesive layer provided on a support with a liner (i.e., disposable backing sheet) being attached to the adhesive layer. In use, such a liner is removed and discarded. In view of problems caused by the use of liners, there are proposed adhesive sheets having a heat activatable adhesive layer but having no liner, that is, liner-free adhesive sheets.
The heat activatable adhesive layer is of a type which is not adhesive at room temperature but becomes adhesive when heated at an elevated temperature. The adhesive composition for use in the heat activatable adhesive layer is generally composed of a thermoplastic resin, a plasticizer and, optionally, a tackifier. The thermoplastic resin exhibits adhesiveness when plasticized. The plasticizer assumes a solid state at room temperature but is melted by the application of heat thereto to plasticize or swell the thermoplastic resin and to actualize the adhesiveness of the resin. The tackifier is used for improving the tackiness of the thermoplastic resin.
The heat activatable adhesive sheets are utilized in a wide variety of fields, for example, in the system of Point of Sales (POS) in which a heat activatable adhesive label is attached onto a wrapping film covering food. As the wrapping film, polyolefin films are substituted for conventional polyvinyl chloride films which cause environmental problems. Known heat activatable adhesive sheets, however, have a problem because its adhesion to polyolefin surfaces is not satisfactory.
JP-A-H09-265260 discloses an adhesive sheet including a substrate, an undercoat (heat insulation) layer provided on the substrate and containing hollow fine particles, a heat-sensitive recording layer provide on the undercoat layer, and a heat activatable layer provided on the substrate opposite the recording layer and containing dicyclohexyl phthalate as a plasticizer.
The conventional heat activatable adhesive sheet has another drawback that blocking phenomenon occurs when the sheet is stored in rolled form for a long period of time at a temperature of, for example, 40° C. There is a demand for a heat activatable adhesive sheet which does not cause blocking at a temperature of 50° C.
Known heat activatable adhesive sheets have a further problem because of the use of a phthalate as a plasticizer. The phthalate compounds are likely to adversely affect reproduction function through a food cycle.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a heat activatable adhesive composition which can exhibit strong adhesiveness and excellent anti-blocking properties.
Another object of the present invention is to provide a heat activatable adhesive composition which can exhibit strong adhesiveness to polymer surfaces such as polyolefin surfaces.
It is a further object of the present invention to provide a heat activatable adhesive composition which does not contain a phthalate compound.
It is yet a further object of the present invention to provide a sheet having a heat activatable adhesive layer.
It is a further object of the present invention to provide sheet having (a) a heat activatable adhesive layer and (b) a heat-sensitive recording layer or an image receiving layer adapted for receiving an ink image transferred from an ink ribbon.
In accordance with the present invention there is provided a heat activatable adhesive composition comprising a thermoplastic resin, and a plasticizer including a hindered phenol compound which is solid at 20° C. and which is fusible at an elevated temperature.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A heat activatable adhesive composition according to the present invention comprises a thermoplastic resin, a specific plasticizer and, optionally, a tackifier.
The thermoplastic resin is not particularly limited in the present invention, but the following polymeric resins can be preferably employed: a latex of natural rubber to which a vinyl monomer is graft-copolymerized, a natural rubber latex, polyvinyl acetate, polymethacrylate such as polybutyl methacrylate, synthetic rubber, vinyl acetate-2-ethylhexyl acrylate copolymer, vinyl acetate-ethylene copolymer, vinyl pyrrolidone-styrene copolymer, vinyl pyrrolidone-acrylate copolymer such as vinyl pyrrolidone-ethyl acrylate copolymer and styrene-acrylate compolymer. The amount of the thermoplastic resin in the adhesive composition is generally 10-70% by weight, preferably 20-60% by weight, for reasons of adhesiveness.
As the plasticizer, a hindered phenol compound which is solid at 20° C. and which is fusible at an elevated temperature is used. The melting point of the hindered phenol compound is preferably at least 50° C., more preferably at least 60° C., for reasons of satisfactory anti-blocking property of an adhesive layer of the heat activatable adhesive composition. The upper limit of the melting point of the hindered phenol compound is preferably 150° C. for reasons of heat sensitivity of the heat activatable adhesive layer.
The hindered phenol compound is preferably at least one compound selected from those represented by the following formulas (I) through (IV):
wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
9
, and R
10
independently stand for an alkyl group, and R
8
and R
11
each stand for a divalent hydrocarbyl group.
The alkyl groups R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
9
and R
10
each have preferably 1-20 carbon atoms, more preferably 1-12 carbon atoms. Most preferably, R
1
, R
2
, R
4
, R
5
, R
6
, R
7
, R
9
and R
10
are each —CH
3
or —CH
2
H
5
or an &agr;-branched alkyl group having 3-10 carbon atoms, such as tert-butyl, while R
3
is a lower alkyl having 1-8 carbon atoms. Preferably, the divalent hydrocarbyl groups R
8
and R
11
are each an alkylene group having 1-12 carbon atoms.
The amount of the hindered phenol compound in the adhesive -composition is preferably 30-70% by weight, more preferably 35-65% by weight, for reasons of satisfactory adhesiveness.
In addition to the hindered phenol compound, the plasticizer can contain one or more conventional plasticizers, if desired. Examples of such conventional plasticizers include diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dihydroabietyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene glycol dibenzoate, trimethylolethane tribenzoate, glyceride tribenzoate, pentaerythritol tetrabenzoate, sucrose octacetate, tricyclohexyl citrate and N-cyclohexyl-p-toluene-sulfonamide. The amount of the plasticizer in the adhesive composition is preferably in the range of 30 to 70% by weight, more preferably in the range of 35 to 65 wt % by weight, of the total weight of the adhesive composition for reasons of satisfactory adhesiveness of the adhesive composition.
It is preferred that the adhesive composition contain a tackifier for reasons of improved adhesiveness of thereof. The tackifier preferably has a melting point or softening point of at least 70° C., more preferably 70-200° C. for reasons of satisfactory anti-blocking property of a heat activatable adhesive layer formed of the adhesive composition. Examples of suitable tackifier include rosins and derivatives thereof (such as polymerized rosin, hydrogenated rosin, esters of the above-mentioned rosins with polyhydric alcohols such as glycerin and pentaerythritol, and diners of resin acid); terpene resins; petroleum resins; phenolic resins; and xylene resins. The tackifier is used in an amount of 3 to 30% by weight, more preferably 5 to 25% by weight based on the total weight of the adhesive composition.
In one embodiment of the present invention, the heat activatable adhesive composition is used for a label or
Ichikawa Akira
Nagamoto Masanaka
Yamada Hiroshi
Ribar Travis B
Ricoh & Company, Ltd.
Seidleck James J.
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