WO2007105897A1

WO2007105897A1 - Reflective sheet for printing

Info

Publication number: WO2007105897A1
Application number: PCT/KR2007/001210
Authority: WO
Inventors: Kwan-Seung Ko; Eung-Kee Lee; Won-Seop Jin
Original assignee: Lg Chem, Ltd.
Priority date: 2006-03-14
Filing date: 2007-03-13
Publication date: 2007-09-20

Abstract

Disclosed is a reflective sheet for printing, which can be subjected to solvent digital printing. The reflective sheet includes an uppermost surface layer which is subjected to printing, a retroreflective element layer formed beneath the uppermost surface layer, and a base layer formed beneath the retroreflective element layer. The uppermost surface layer includes a polyvinylchloride layer, and the base layer includes a polyester film. The uppermost surface layer has the polyvinylchloride layer and thus can receive ink, and a swelling phenomenon can be prevented by the base layer, formed beneath the retroreflective element layer, thereby making possible a solvent digital printing process and exhibiting superior properties and constructability.

Description

REFLECTIVE SHEET FOR PRINTING

Technical Field

[1] The present invention relates, in general, to a reflective sheet for printing and, more particularly, to a reflective sheet for printing, which can be subjected to solvent digital printing, has superior properties and constructability, andean be easily manufactured.

[2]

Background Art

[3] Generally, advertising boards, tour guide boards, information posters, no accident notification boards, construction site guide boards, construction safety informing boards, androad signs for use in displaying advertisements or promoting safety have a reflectivesheet attached thereto so as to have superior visibility. In such a reflective sheet, fine lenses (glass beads) are embedded, thus leading to high visibility. Further, a design for depicting an advertisement or promoting safety is formed on the surface of the reflective sheet. To this end, a printing process is particularly usefully applied. The present invention pertains to such a reflective sheet for printing.

[4] The reflective sheet for printing has an uppermost surface layer and a retroreflective element layer which is formed beneath the uppermost surface layer and has lenses (glass beads) embedded therein. As such, the uppermost surface layer is printed with a design for depicting an advertisement or promoting safety.

[5] However, conventional reflective sheetsfor printing have problems such that they are incapable of being subjected to printing using a solvent plotter. The solvent digital printing process is advantageous that it results in a clearer print image and a higher plotting speed, compared to those of heat transfer printing or aqueous digital printing. As well, good durability, applicability to outdoor use, and large-format printing may result.

[6] Korean Unexamined Patent Publication No. 1998-702074 (WO 96/024867) discloses a retroreflective product including a retroreflective element layer and an upper layer, in which heat transfer is performed on the surface of the upper layer. According to the above parent, the process of depicting the design on the surface of the reflective sheet is conducted through heat transfer, but the procedure thereof is complicated. Specifically, such a heat transfer process is carried out by printing an additional film with a design, attaching the film to a reflective sheet, and performing heat transfer to thus transfer the printing design to the surface of the reflective sheet. However, the heat transfer process suffers because it is very complicated and is unsuitable for use in large-format printing, compared to a digital printing process. [7] As in the Unexamined Patent Publication mentioned above, although the conventional reflective sheet is subjected to heat transfer or aqueous digital printing, it is impossible to perform a solvent digital printing process using a solvent. Specifically, in the case where the conventional reflective sheet for printing is subjected to solvent digital printing, a swelling phenomenon is caused by the solvent included in the ink, and thus the sheet may sag or expand when attached to an advertising board or a road sign, consequently making it impossible to construct it.

[8] In addition, Korean Unexamined Patent Publication No. 2005-0002261 discloses a method of printing an advertising board having an ink-receiving layer for solvent digital printing, comprising a base film formation step, an ink-receiving layer formation step, a design formation step, and a protective film formation step, but suffers because the process thereof is complicated, undesirably resulting in a high manufacturing cost.

[9]

Disclosure of Invention Technical Problem

[10] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a reflective sheet for printing, which includes a base layer for preventing a swelling phenomenon, and which therefore can be subjected to a solvent digital printing process, can have superior properties and constructability, and can be easily manufactured.

[H] [12]

Technical Solution

[13] In order to accomplish the above object, the present invention provides a reflective sheet for printing, comprising an uppermost surface layer which may be subjected to printing, a retroreflective element layer formed beneath the uppermost surface layer, and a base layer formed beneath the retroreflective element layer.

[14] According to the present invention, the uppermost surface layer may comprise a polyvinylchloride layer, and the base layer may comprise a polyester film. The retroreflective element layer may have a structure in which a lens-bonding binder resin layer, a lens layer, a focusing resin layer, anda metal reflective layer are sequentially formed beneath the uppermost surface layer.

[15]

Advantageous Effects

[16] As described above, the present invention provides a reflective sheet for printing. In the reflective sheet according to the present invention, an uppermost surface layer is composed of a polyvinylchloride layer and thus can receive ink, and a base layer is formed beneath a retroreflective element layer to thus prevent a swelling phenomenon, consequently realizing a solvent digital printing process and exhibitingsuperior properties and constructability.

[17] Further, compared to conventional manufacturing techniques including steps of forming an ink-receiving layer and a film required to conduct solvent digital printing, the reflective sheet of the invention has a simple layer structure, and therefore can be easily manufactured, and can also be provided at a low price.

[18]

Brief Description of the Drawings

[19] FIG. 1 is a sectional view illustrating the reflective sheet for printing, according to the present invention and

[20] FIG. 2 is a photograph showing the image of the surface of the reflective sheet printed using a solvent plotter.

[21]

Best Mode for Carrying Out the Invention

[22] Hereinafter, a detailed description will be given of the present invention with reference to the appendeddrawings. The appended drawings illustrate the preferred embodiment of the present invention, which is set forth to illustrate, but is not to be construed as the limit of the present invention.

[23] FIG. 1 is a sectional view illustrating the reflective sheet for printing, according to the present invention, and FIG. 2 is a photograph showing the image of the surface of the reflective sheet printed using a solvent plotter.

[24] As illustrated in FIG. 1, the reflective sheet for printing according to the present invention essentially comprises an uppermost surface layer 10, a retroreflective element layer 20 formed beneath the uppermost surface layer 10, and a base layer 40 formed beneath the retroreflective element layer 20. Further, the reflective sheet of the invention may have a structure in which an adhesive layer 30 is formed between the retroreflective element layer 20 and the base layer 40 for adhesion therebetween. Furthermore, the reflective sheet may have a structure which includes an adhesive layer 50 formed beneath the base layer 40, and a release paper layer 60 attached beneath the adhesive layer 50 so that release paper is removed from the reflective sheet and then the reflective sheet is directly attached at the construction site.

[25] The uppermost surface layer 10 constitutes the outermost portion of the reflective sheet and functions to protect the retroreflective element layer 20 from the external environment, and the surface thereof is printed with a design for depicting an ad- vertisement or promoting safety. Any such uppermost surface layer lOis included in the present invention as long as it can be subjected to a printing process, and preferably comprises a polyvinylchloride layer. The uppermost surface layer 10 has a thickness of 25-60 D. According to the present invention, the polyvinylchloride layer functions to protect the surface of the sheet, and also enables the efficient absorption or adsorption of printing ink to thus exhibit optimal printability.

[26] The polyvinylchloride layer is essentially formed of a sol composition comprising polyvinylchloride and a plasticizer. As such, polyvinylchloride has a degree of polymerization of 800-1,500, and furthermore, has a viscosity of 2,000 cps or less after being mixed with the plasticizer. As the plasticizer, one or more selected from among dioctylphthalate (DOP), dioctyladipate (DOA), and polyester may be used. Preferably useful is a polyester-based plasticizer, such as adipic acid polyester, which has good migration and thus does not flow out when mixing with polyvinylchloride. Such a plasticizer is used in an amount of 20-50 parts by weight, based on 100 parts by weight of polyvinylchloride.

[27] Further, the polyvinylchloride layer is preferably formed of a sol composition comprising polyvinylchloride, a plasticizer, a stabilizer for attainting surface weatherability and durability, and a diluent for controlling viscosity. The stabilizer is preferably used in the form of a mixture of a light stabilizer and a heat stabilizer, in which the light stabilizer includes an ester-based liquid UV absorbent, for example, Tinuvin 123, and the heat stabilizer includes an inorganic metal-based heat resistant stabilizer, for example, a barium-zinc organic complex or a calcium-zinc organic complex. Examples of the diluent include toluene, ethylacetate, xylene, butyleneglycol, etc. The composition for forming the polyvinylchloride layer comprises 100 parts by weight of polyvinylchloride, 20-50 parts by weight of the plasticizer, 0.2-10 parts by weight of the light stabilizer, and 0.2-10 parts by weight of the heat stabilizer, mixed together. As such, the diluent is added to attain a viscosity of 2,000 cps or less.

[28] Any retroreflective element layer 20 can be included in the invention as long as it has lenses embedded therein to thus exhibit a retroreflective function. As seen in FIG. 1, beneath the uppermost surface layer 10, a lens-bonding binder resin Iayer22, a lens layer, 24, a focusing resin layer 26, and a metal reflective layer 28 are sequentially formed. In this case, the lenses are embedded between the lens-bonding binder resin layer 22 and the focusing resin layer 26.

[29] The lens-bonding binder resin layer 22 is used to embed portions of the lenses therein to thus hold them, and is formed by applying a binder resin on the uppermost surface layer 10. As the binder resin, particularly useful is a two-component thermosetting resin, which is composed mainly of polyester urethane resin, comprising polyester polyol cross-synthesized with polyisocyanate, and is mixed with a curing agent upon a coating process. Specifically, the lens-bonding binder resin layer 22 is preferably formed in such a manner that the polyester urethane resin is applied on the uppermost surface layer 10 (preferably, the polyvinylchloride layer) immediately after being mixed with the curing agent. In the case where the above-mentioned two- component thermosetting resin, composed mainly of polyester urethane resin, is used as the binder resin, the lenses are efficiently held andthe tensile strength of the reflective sheet is increased. The lens-bonding binder resin layer 22 preferably has a thickness of 20-35 D.

[30] The lens layer 24 is preferably provided in the form of a single layer, in which a plurality of lenses is arranged in a line. Further, it is preferred that the lens be transparent and have the form of fine spheres or cubes. In FIG. 1, fine spherical glass beads are exemplary. The lens has a diameter of 40-70 D, and 30-70% of the diameter thereof is preferably embedded in the lens-bonding binder resin layer 22.

[31] The focusing resin layer 26 is formed by applying a focusing resin on the lens layer

24. The focusing resin is exemplified by a two-component thermosetting resin, composed mainly of polyester urethane resin comprising polyester polyol cross- synthesized with polyisocyanate, or polyacryl urethane resin, comprising acrylic polyol cross-synthesized with polyfunctional polyisocyanate. Polyacryl urethane resin is particularly useful. As such, the acrylic polyol preferably includes a copolymer obtained by synthesizing a compound having an OH group, such as glycol or vinyl acetate, with an acrylic compound, such as acrylate, methylmethacrylate, butylacrylate, or ethy- lacrylate. In the case where the polyacryl urethane resin, comprising acrylic polyol cross-synthesized with polyfunctional polyisocyanate, is used as the focusing resin, luminance and tensile strength are increased.

[32] The focusing resin layer 26 should have a thickness corresponding to the focal distance of light refracted through the lenses (fine glass beads) in order to manifest superior retroreflective luminance. In particular, the thickness thereof is preferably 10-20 D, corresponding to 10-30% of the diameter of the lens (fine glass bead).

[33] The metal reflective layer 28 functions to reflect light, which is refracted by the focusing resin layer 26 to thus be focused, in the original light source direction, and is formed by depositing one or more metals, selected from among gold, silver, aluminum, platinum, nickel, and chromium, on the focusing resin Iayer26. As such, examples of the deposition process include vacuum deposition, sputtering deposition, electron beam deposition, etc.

[34] The base layer 40 is attached beneath the retroreflective element layer 20 so as not to disturb the visibility of the retroreflective element layer 20. In this case, the base layer 40 is attached by an adhesive layer 30. Such a base layer 40 functions to prevent a swelling phenomenon that may be caused by the solvent, so that the sheet does not sag or expand.

[35] The base layer 40 may be a polyvinylchloride film or a polycarbonate film, and- preferably includes a polyester film in the interest of low cost and high tensile strength. Further, the thickness thereof preferably falls in the range of 10-50 D. The adhesive layer 30 used to attach the base layer 40 is formed by applying a polyacryl adhesive or a polyester adhesive on the base layer 40, and has a thickness of 15-60 D after drying.

[36] The adhesive layer 50 is formed beneath the base layer 40 through a coating process using a urethane adhesive or an acrylic adhesive, andhas a thickness of 20-80 D.

[37] The release paper layer 60 is formed in a manner such that polyethylene is applied on either or both surfaces of paper, one surface of which is treated with a releasing agent, such as silicone, to thus prepare 50-150 g/m of release paper.

[38] The reflective sheet for printing thus manufactured is usefully applied to an advertising board, a tour guide board, an information poster, no accident notifica- tionboard, a construction site guide board, a construction safety information board, and a road sign, can be subjected to solvent digital printing, and has high tensile strength and constructability. Specifically, since the uppermost surface layer 10 of the reflective sheet of the invention is composed of a polyvinylchloride layer, printing ink can be absorbed or adsorbed therein or thereon, and thus it is possible to conduct a printing process using a solvent plotter. As such, the base layer 40 acts to prevent a swelling phenomenon, attributable to the solvent included in the printing ink. In this way, a solvent digital printing process can be realized, therefore resulting in a clear print image, a fast plotting speed, and good durability. Furthermore, superior visibility is achieved by the retroreflective element layer 20. Moreover, since the tensile strength is increased by the base layer 40, the sheet does not sag even when manufactured at a large size, and thus the constructability thereof becomes high.

[39] Below, the specific example and comparative examples of the present invention are described.

[40] [Example 1]

[41] 100 parts by weight of polyvinylchloride having a degree of polymerization of

1,200 was mixed with 40 parts by weight of adipic acid polyester as a plasticizer, 7.5 parts by weight of a barium-zinc organic complex (LTX-630J, available from Korea Daehyup) as a heat stabilizer, and 0.5 parts by weight of liquid Tinuvin 123 as a light stabilizer (UV absorbent), after which a solvent mixture of xylene and butyleneglycol, as a diluent, was added thereto, thus obtaining a PVC sol composition having a viscosity of 1,500 cps. The PVC sol composition was applied on a polyester carrier film having a thickness of 100 D, and was then dried at 150C, thus preparing a laminate in which the polyvinylchloride layer 50 D thick was formed on the carrier film (preparation of an uppermost surface layer). [42] Subsequently, polyester urethane resin (glass transition temperature: -20C, MW:

30,000) comprising polyester polyol cross-synthesized with polyisocyanate was mixed with a curing agent to thus prepare a lens-bonding binder resin, which was then applied on the uppermost surface layer (polyvinylchloride layer). Further, fine glass beads having an average diameter of 50 D were arranged on the lens-bonding binder resin, dried in an oven at 150C for 3 min, and then aged at 50C for 24 hours. As such, the dried lens-bonding binder resin layer was 20 D thick.

[43] Subsequently, polyacryl urethane resin (glass transition temperature: -20C, MW:

25,000) comprising acrylic polyol cross-synthesized with polyisocyanate was mixed with a curing agent to thus prepare a focusingresin, which was then applied on the glass beads, and was thereafter dried in an oven at 150C for 3 min, thereby forming a focusing resin layer 18 D thick.

[44] Subsequently, an aluminum film was deposited on the focusing resin layer using a vacuum deposition process, thereby manufacturing a semi-finished product in which the uppermost surface layer (polyvinylchloride layer), the lens-bonding binder resin layer, the lens layer, the focusing resin layer, and the metal reflective layer were sequentially formed on the carrier film.

[45] Separately, as a base layer, a polyester film 36 D thick was prepared, and an acrylic resin adhesive having a molecularweight of 80,000 was applied thereon using a roll coating process.

[46] The polyester film coated with the adhesive was attached to the metal reflective layer of the semi-finished product and was then dried, thereby completing a test piece for a reflective sheet. Thereafter, the carrier film was removed. As such, the dried adhesive layer had a thickness of 30 D.

[47] The printability of the test piece thus manufactured (60 cm width x 90 cm length) was measured using a solvent plotter. Further, using a universal test machine, tensile strength and elongation were measured and compared before and after the printing process. Furthermore, an adhesive acrylic resin was applied on the surface opposite the printed surface of the test piece, after which the test piece was attached to an acrylic sheet to thus measure constructability.

[48] The results are shown in Table 1 below.

[49]

[50] [Comparative Example 1]

[51] A reflective sheet was manufacturedin the same manner as in Example 1, with the exception that the base layer (polyester film) was not attached. The results are shown in Table 1 below.

[52]

[53] [Comparative Example 2] [54] A reflective sheet was manufacturedin the same manner as in Example 1, with the exception that the uppermost surface layer (polyvinylchloride layer) was not formed. The results are shown in Table 1 below.

[55] [56] Table 1

[57] [58] As is apparent from Table 1, the reflective sheet manufactured in the example of the present invention could be subjected to printing using a solvent plotter, and had superior tensile strength and elongation. Furthermore, after the printing process, there was almost no decrease in the properties thereof. However, in the case of Comparative Example 1, having no base layer (polyester film), although a printingprocess could be conducted using a solvent plotter, after the printing process, the tensile strength thereof was drastically decreased due to a swelling phenomenon,and elongation was increased, and consequently, it was very difficult to construct the sheet due to sagging or expansion. In the case of Comparative Example 2, having no polyvinylchloride layer, it was difficult to adsorb ink upon a solvent digital printing process, and thus it was impossible to perform the printing process. However, in Comparative Example 2, due to the presence of the base layer (polyester film), tensile strength and elongation were relatively good.

[59] Industrial Applicability

[60] As described above, the present invention provides a reflective sheet for printing. In the reflective sheet according to the present invention, an uppermost surface layer is composed of a polyvinylchloride layer and thus can receive ink, and a base layer is formed beneath a retroreflective element layer to thus prevent a swelling phenomenon, consequently realizing a solvent digital printing process and exhibitingsuperior properties and constructability.

[61] Further, compared to conventional manufacturing techniques including steps of forming an ink-receiving layer and a film required to conduct solvent digital printing, the reflective sheet of the invention has a simple layer structure, and therefore can be easily manufactured, and can also be provided at a low price.

[62]

[63]

[64]

Claims

[I] A reflective sheet for printing, comprising an uppermost surface layer which is able to be subjected to printing, a retroreflective element layerformed beneath the uppermost surface layer, and a base layer formed beneath the retroreflective element layer.

[2] The reflective sheet of claim 1, wherein the uppermost surface layer comprises a polyvinylchloride layer. [3] The reflective sheet of claim 1, wherein the retroreflective element layer comprises a lens-bonding binder resin layer, a lens layer, a focusing resin layer, and a metal reflective layer, which are sequentially formed. [4] The reflective sheet of claim 2, wherein the polyvinylchloride layer comprises

100 parts by weight of polyvinylchloride, 20-50 parts by weight of a plasticizer,

0.2-10 parts by weight of a light stabilizer, and 0.2-10 parts by weight of a heat stabilizer. [5] The reflective sheet of claim 2, wherein the polyvinylchloride layer is 25-60 D thick. [6] The reflective sheet of any one of claims 1 to 5, wherein the base layer comprises a polyester film. [7] The reflective sheet of any one of claims 1 to 5, wherein the base layer is coated with a polyacryl adhesive or a polyester adhesive layer 10-60 D thick to thus be attached beneath the retroreflective element layer. [8] The reflective sheet of any one claim 1 to 5, wherein the base layer is 10-50 D thick. [9] The reflective sheet of claim 3, wherein the lens-bonding binder resin layer is formed by curing polyester urethane resin. [10] The reflective sheet of claim 3, wherein the lens-bonding binder resin layer is

20-35 D thick.

[II] The reflective sheet of claim 3, wherein lenses of the lens layer comprise glass beads having a diameter of 40-70 D, 30-70% of the diameter thereof being embedded in the lens-bonding binder resin layer.

[12] The reflective sheet of claim 3, wherein the focusing resin layer is formed by curing polyacryl urethane resin.

[13] The reflective sheet of claim 3, wherein the focusing resin layer is 10-20 D thick.

[14] The reflective sheet of claim 4, wherein the polyvinylchloride has a degree of polymerization of 800-1,500. [15] The reflective sheet of claim 4, wherein the plasticizer comprises polyester.