Transparent plastic writing sheet

Abstract: A writing sheet (1) includes a transparent plastic film (11) coated with a layer of transparent coating (112). The coating layer (112) is prepared from a mixture of a binder and at least one pigment. The weight ratio of the binder to the pigment ranges from 1:1 to 1:10 so as to render the coating (112) to possess a transparent characteristic with excellent writing quality.

Description: This invention relates to a writing sheet, more particularly to a transparent writing sheet coated with a layer of transparent coating that possesses excellent writing quality. Self-stick writing sheets have become popular in recent years since they can be attached on a surface of a table, a wall, a book or a document as desired. However, conventional self-stick writing sheets are normally made of paper, thereby suffering from the following drawbacks that (1) they are prone to break upon use due to the lack of tensile strength for paper, and (2) they are not waterproof. It is known that polypropylene can be used to fabricate synthetic paper with writing quality, printability, waterproof, and good tensile strength. However, since the writing quality of the synthetic paper is still poor in comparison with common papers, such as poor ink absorbability, there remains a need for improving the writing quality for the synthetic paper. In addition, synthetic paper is not transparent. Therefore, it is an object of the present invention to provide a writing sheet that has good tensile strength and excellent writing quality, and that is water-proof and transparent. EP-A-0 696 516 and US 5,888,635 disclose an ink jet recording medium which comprises: (i) a base substrate which can be a transparent, translucent or opaque plastic or a paper, (ii) an underlayer on one surface of the base substrate, wherein the underlayer comprises one or more polymeric materials, in which at least one polymeric material is a water-imbibing component, and (iii) a surface layer disposed of on a surface of the underlayer, wherein the surface layer comprises one or more inorganic particulates. According to the present invention, a writing sheet comprises a transparent plastic film directly coated with a layer of transparent coating, the coating layer being prepared from a mixture of a binder and at least one pigment, the binder being selected from the group consisting of polyvinyl alcohol, polyacrylate, polyvinyl acetate, and styrene butadiene rubber, the pigment being selected from the group consisting of titanium dioxide, calcium carbonate, clay, and mixtures thereof. The weight ratio of the binder to the pigment ranges from 1:1 to 1:10. In drawings which illustrate the preferred embodiment of the invention, Fig. 1 illustrates a side view of a self-stick writing sheet of a preferred embodiment of this invention; and Fig. 2 illustrates a plurality of the self-stick writing sheets of Fig. 1 arranged in a stack. Fig. 1 illustrates a side view of a writing sheet embodying this invention. The writing sheet 1 of the present invention includes a plastic film 11 coated with a layer of removable adhesive 111 on the bottom side of the writing sheet 1 and a layer of transparent coating 112 on the top side of the writing sheet 1. The coating 112 provides a mat writing face. A plurality of the writing sheets 1 are assembled to form a stack of self-stick notes 2 (see Fig. 2) by stacking the writing sheets 1 one above the other with the bottom side of each writing sheet 1 in contact with the top side of an adjacent sheet 1. The plastic film 11 is made from a material selected from the group consisting of polypropylene, polyethylene, polyvinyl chloride, polyethylene terephthalate, and Mylar RTM . The removable adhesive 111 may be any one of pressure sensitive adhesives known in the art. A typical example of the removable adhesive 111 is an acrylate-type adhesive. The coating 112 of the writing sheet 1 comprises a mixture of a binder and at least one pigment. The binder of the coating 112 is preferably selected from the group consisting of polyvinyl alcohol, polyacrylate, polyvinyl acetate, and styrene butadiene rubber. The pigment of the coating 112 is preferably selected from the group consisting of titanium dioxide, calcium carbonate, clay, and mixtures thereof. The weight ratio of the binder to the pigment preferably ranges from 1:1 to 1:10 so as to render the coating of the writing sheet 1 of this invention to possess a transparent characteristic with excellent writing quality. The coating of the writing sheet 1 can further include a dye so as to color the writing sheet 1. The dye may be added in an amount of more than 2% by weight based on the total weight of the pigment. The writing sheet 1 of this invention can further include a release paper (not shown) for covering and protecting the coating layer 112 of the plastic film 11. EXAMPLES Tests were done for investigating the writing quality of samples of the writing sheet of this invention. The writing quality of the writing sheet is classified into three rankings which are represented as excellent (e), good (g) , and fair (f) , and is determined based on the writability, anchorage ( a binding power of the pigment to the film ) , and ink absorbability. Polypropylene was used as a plastic film in each of the samples. The coatings on the samples were prepared from different combinations of binders and pigments with differing weight ratios of binder to pigment. The binders used in these tests were polyvinyl alcohol (PVA), polyvinyl acetate (PA), and styrene butadiene rubber (SBR). The pigments used in these tests were titanium dioxide(TiO 2 ), calcium carbonate (CaCO 3 ), and clay. The weight ratios of the binder to the pigment arranged in these tests ranged from 1 : 10 to 1 : 1 which are expressed in terms of grams of binder per 100 g of pigment in Tables 1-3. Sample # TiO 2 g Clay g CaCO 3 g PVA g Sample # TiO 2 g Clay g CaCO 3 g PVA g 1 100 - - 100 11 - 100 - 25 2 100 - - 75 12 - 100 - 20 3 100 - - 50 13 - 100 - 15 4 100 - - 25 14 - 100 - 10 5 100 - - 20 15 - 100 - 5 6 100 - - 15 16 - - 100 75 7 - 100 - 100 17 - - 100 50 8 - 100 - 75 18 - - 100 30 9 - 100 - 50 19 - - 100 20 10 - 100 - 30 - - - - - Sample # TiO 2 g Clay g CaCO 3 g PA g Sample # TiO 2 g Clay g CaCO 3 g PA g 20 - - 100 100 28 100 - - 25 21 - - 100 75 29 100 - - 5 22 - - 100 50 30 - 100 - 100 23 - - 100 25 31 - 100 - 75 24 - - 100 5 32 - 100 - 50 25 100 - - 100 33 - 100 - 25 26 100 - - 75 34 - 100 - 5 27 100 - - 50 - - - - - Sample # TiO 2 g Clay g CaCO 3 g SBR g Sample # TiO 2 g Clay g CaCO 3 g SBR g 35 100 - - 100 42 - 100 - 25 36 100 - - 75 43 - 100 - 5 37 100 - - 50 44 - - 100 100 38 100 - - 25 45 - - 100 75 39 - 100 - 100 46 - - 100 50 40 - 100 - 75 47 - - 100 25 41 - 100 - 50 48 - - 100 5 Samples #1-#19 are listed in Table 1, samples #20-#34 in Table 2, and samples #35-#48 in Table 3. The results of these tests were shown in Table 4. To summarize from the results shown in Table 4, samples #1-#2 which contain TiO 2 , samples #12-#14, #33-#34 and #42-#43 which contain clay, and samples #19, and #45-#47 which contain CaCO 3 exhibit good and/or excellent writability, anchorage, and as well as ink absorbability. Sample # Writability Anchorage Ink absorbability Sample # Writability Anchorage Ink absorbability 1 e g e 25 f e f 2 e g e 26 f e f 3 e f g 27 f g e 4 g f g 28 g g g 5 g g g 29 peeling - - 6 f f e 30 f g f 7 f f e 31 f e f 8 f f e 32 f e f 9 e f f 33 g e g 10 f f e 34 e e g 11 g f e 35 g e f 12 g g g 36 e e f 13 g g g 37 e e f 14 g e g 38 g f f 15 g e f 39 g e f 16 e f g 40 g e f 17 e f f 41 g e f 18 e f F 42 e e g 19 e g g 43 g g g 20 f e f 44 g e f 21 f g f 45 e e g 22 e g f 46 g e g 23 g g f 47 g g g 24 g g f 48 g f g It will be appreciated that the specific examples of writing sheets referred to herein include adhesive labels. Such adhesive labels encompass labels which may be permanently affixed to a substrate and labels which are readily removable or repositionable (c.f. Post-it RTM notes).

Claims: A writing sheet characterized by a transparent plastic film (11) directly coated with a layer of transparent coating (112), said coating layer (112) being prepared from a mixture of a binder and at least one pigment, said binder being selected from the group consisting of polyvinyl alcohol, polyacrylate, polyvinyl acetate, and styrene butadiene rubber, said pigment being selected from the group consisting of titanium dioxide, calcium carbonate, clay, and mixtures thereof, the weight ratio of said binder to said pigment ranges from 1:1 to 1:10. The writing sheet of Claim 1, characterized in that said plastic film (11) is made from a material selected from the group consisting of polypropylene, polyethylene, polyvinyl chloride and polyethylene terephthalate. The writing sheet of Claim 1 or Claim 2, further characterized by a layer of removable adhesive (111) applied to said plastic film (11) to provide said writing sheet (1) with a removable sticking characteristic. The writing sheet of any of Claims 1 to 3, further characterized by a release paper that covers said coating layer (112) of said plastic film (11). The writing sheet of Claim 1, characterized in that said binder is polyvinyl alcohol, and said pigment is titanium dioxide, wherein the weight ratio of polyvinyl alcohol to titanium dioxide is from 1:1 to 1:2. The writing sheet of Claim 1, characterized in that said binder is styrene butadiene rubber, and said pigment is calcium carbonate, wherein the weight ratio of styrene butadiene rubber to calcium carbonate is from 1:1 to 1:2. The writing sheet of Claim 1, characterized in that said coating further includes a dye.

Inventors: HSIEH HSIEH-CHANG, KUO TSUNG-TIEN, LIN BIN-TZER, LIN HO-TSAI, LIU JEN-RONG, HSIEH, HSIEH-CHANG, KUO, TSUNG-TIEN, LIN, BIN-TZER, LIN, HO-TSAI, LIU, JEN-RONG
Applicants: TAIWAN HOPAX CHEMICALS MFG CO, TAIWAN HOPAX CHEMICALS MFG., CO., LTD
Application year: 1999
Main classification: B41M5
IPC codes: B41M5