Diffractive microstructure and a method of producing the same

Abstract

Diffractive microstructure comprising micro-protrusions or microgrooves or a combination thereof and method of producing the same. The microstructure is formed in a layer of a thermoplastic carbohydrate polymer or a polymer derived from a carbohydrate material, said polymer having a glass transition point of less than 210 C. The thermoplastic polymer is preferably selected from the group of native starch, dextrin, native hemicellulose, native cellulose, poly(lactic acid), polylactides, polycaprolactone, starch derivatives, dextrin derivatives, hemicellulose derivatives, cellulose derivatives, and mixtures thereof. The invention provides an inexpensive and reliable way of incorporating into the products safety markings, which allow for visual inspection or detection, such as holograms and barcodes.

Claims

1. A diffractive microstructure consisting of micro-protrusions or microgrooves or a combination thereof formed in a layer, wherein said layer consists of a thermoplastic carbohydrate polymer, said polymer having a glass transition point of less than 210 C., wherein the thermoplastic carbohydrate polymer is a hydrophobic starch ester having a degree of substitution of at least 1.7, and wherein the thermoplastic carbohydrate polymer is plasticized with a hydroxyl compound selected from the group of C2 to C4 alcohols having 1-5 hydroxyl groups, sorbitol and mixtures thereof, wherein said layer is a self-supporting layer or film having a thickness of from 0.1 to less than 12 micrometers.

2. The microstructure according to claim 1, wherein the micro-protrusions or microgrooves or the combination thereof form a detectable pattern.

3. The microstructure according to claim 1, which is capable of diffracting monochromatic or polychromatic light.

4. The microstructure according to claim 3, which is capable of diffracting light in the visual range, in the ultraviolet range, in the infrared range or in a broad wave length range comprising visual, ultraviolet and/or infrared light.

5. The microstructure according to claim 1, comprising a barcode tag or a safety marking or an identification label or a combination thereof.

6. The microstructure according to claim 1, comprising a cinegram, an exelgram or a hologram.

7. The microstructure of claim 1, wherein the thermoplastic carbohydrate polymer is a hydrophobic starch ester having a degree of substitution of at least 2.0.

8. The microstructure of claim 1, wherein the thermoplastic carbohydrate polymer is plasticized with a glycerol or sorbitol or mixtures thereof.

Description

EXAMPLE 1

Coating of Base Paper with Coating Colour Containing Modified Starch Pigments

(1) LWCbase paper was coated with a one side laboratory coater (CLC-600) with following coating colour formulations presented in table 1. The coating pigments used in the formulations were clay, ground calcium carbonate and experimental modified starch based pigment developed at VTT.

(2) TABLE-US-00001 TABLE 1 Coating color formulations for coating trials Coating Color CLC13 CLC13B CLC14 CLC14B CLC15 CLC16 CLC17 CLC18 Clay 50 50 0 0 25 0 100 0 GCC 0 0 50 50 25 0 0 100 AP (New pigment) 50 50 50 50 50 100 0 0 Latex 12 12 12 12 12 12 12 12 CMC 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Viscosity, cP 4230 1480 5700 1920 5560 3000 1440 5110 Density, g/l 1104 1166 1170 976 1430 1512 A-GWR, g/m.sup.2 0.09313 0.1715 0.09838 0.17975 0.0545 0.09938 PH 7.6 7.6 8.2 8.2 8.2 6.8 7.6 8.4 Solids, % 50 45 50 45 50 40 60 65

(3) The samples were calandered three passes at 500 kN/m.sup.2 with a laboratory calander, tested for paper technical and surface properties and printed with a four-color offset press. The uncalandered sample of coating color 16 was not printed and it is marked with ctg #16.

(4) Selected calandered and printed samples and uncalandered sample ctg #16 were hot-embossed.

EXAMPLE 2

(5) The aim of this task was to the test embossability of the paper samples, which were coated with coatings containing different amounts of starch based pigment. The amount of coating was about 7 g/m2 for each sample. Sample ctg #16 was uncalendared.

(6) Procedure

(7) Coated paper samples containing 100, 50 or 0 parts of modified starch pigments in the conting (Example 1) were embossed using a static embosser. During these embossing tests only the hot-embossing temperature was varied from 70 to 145 C. The hot-embossing pressure and stamping time were kept constant; stamping time was 5 seconds and pressure 6 bars. The suitable temperature for good embossing quality is shown in Table 2.

(8) TABLE-US-00002 TABLE 2 Suitable temperatures for paper samples coated with coating colors containing modifified starch based pigments and hot embossed using static embosser. Sample Stamping time, s Temperature, C. Pressure, bar 13b 5 90-105 6 14 5 90-120 6 15 5 90-100 6 16 5 90-140 6 17 5 90-100 6 ctg#16 5 90-145 6 18 5 90-120 6

(9) The hot-embossing temperature scale for all samples, are relatively large. Based on the above date, a person skilled in the art can easily adapt the static process to continuous embossing using, e.g., a roll-to-roll embossing machine:

(10) According to the tests the best sample based on visual estimation was calandered sample 16. The best results were obtained when the temperature of 130 C. and pressure of 5 bars for 5 s of embossing was used.

(11) The results with noncalendared sample (ctg #16) were also surprisingly good, almost at the same level as for the calendered sample. It was noticed that the brightness of the noncalendared sample became better when higher embossing temperature was used.

(12) The suitable hot-embossing temperature range with sample 13b, and 15 were narrower than for the other samples. This was maybe caused by the lower content of the starch pigment amount in the coating and combination of effects of starch based and mineral pigments.

(13) The weakest embossing effects could be seen on samples 17 and 18 which were coated with coating colors containing only mineral pigments.