Laser marking additive

Abstract

A laser marking additive including a bismuth compound and a polyol. The laser marking additive can be directly added to a matrix polymer to prepare a laser markable composition, or the laser marking additive can be added to a polymer to prepare a masterbatch, which can be added to a matrix polymer. Preferred polyols are PEG, and polyols having at least 3 hydroxy groups.

Claims

1. A laser marking additive comprising: a bismuth compound and an alcohol, wherein Bi.sub.2O.sub.3 is used as the bismuth compound and wherein the alcohol has a melting temperature of at least 40 C., and wherein the weight ratio between Bi.sub.2O.sub.3 and the alcohol having a melting temperature of at least 40 C. is between 3:1 and 1.5:1.

2. The laser marking additive according to claim 1, wherein the alcohol has a melting temperature (Tm) of at least 100 C.

3. The laser markable composition according to claim 2, wherein the alcohol has a melting temperature (Tm) of at least 200 C.

4. The laser markable composition according to claim 3, wherein the alcohol has a melting temperature (Tm) of at least 240 C.

5. The laser marking additive according to claim 1, wherein the melting temperature of the alcohol is between 0 and 50 C. above a processing temperature of a matrix polymer in a step of making a laser markable composition.

6. The laser marking additive according to claim 1, wherein the alcohol is a polyol is chosen from the group consisting of pentaerythritol, dipentaerythritol, 1,1,1-tris(hydroxymethyl) ethane (or 2-Hydroxymethyl-2-methyl-1,3-propanediol), 2,2,2,2,tetrakis(hydroxymethyl)-3,3oxydipropan-1-ol, and di(trimethylolpropane).

7. The laser marking additive according to claim 1, wherein further a carrier material is present.

8. The laser marking additive according to claim 7, wherein the carrier material is an oil, a fatty acid or a polymeric material.

9. The laser marking additive according to claim 8, wherein the polymeric material is selected from polyethylenemethylacrylate (EMA) or polyethylenevinylacetate (EVA).

10. A masterbatch, comprising: the laser marking additive according to claim 1, wherein the amount of laser marking additive ranges between 0.01 and 70 wt. % and wherein the weight ratio between the Bi.sub.2O.sub.3 and alcohol ranges between 3:1 and 0.5:1.

11. A laser markable composition, comprising: 95-99.9 wt. % of a matrix polymer and 0.1-5 wt. % of the laser marking additive according to claim 1, based on the total weight of the laser markable composition.

12. The laser markable composition according to claim 11, wherein the amount of the Bi.sub.2O.sub.3 in the laser markable composition ranges between 0.01 wt. % to 5 wt. %.

13. The laser markable composition according to claim 12, wherein the amount of the Bi.sub.2O.sub.3 in the laser markable composition ranges between 0.05 wt. % to 3 wt. %.

14. The laser markable composition according to claim 13, wherein the amount of the Bi.sub.2O.sub.3 in the laser markable composition ranges between 0.1 and 1 wt. %.

15. An article or part of an article, comprising: the laser markable composition according to claim 11.

16. Use of a laser markable composition according to claim 11 for the preparation of articles that can be marked by treating the article with laser light.

17. Use of the laser marking additive according to claim 1, for the preparation a masterbatch or laser markable composition for the preparation of articles that can be marked by treating the article with laser light.

18. The laser marking additive according to claim 1, wherein the alcohol has a melting temperature (Tm) of at least 80 C.

19. A masterbatch, comprising: a laser marking additive comprising a bismuth compound and an alcohol, wherein Bi.sub.2O.sub.3 is used as the bismuth compound and wherein the alcohol has a melting temperature of at least 40 C., wherein the amount of laser marking additive ranges between 0.01 and 70 wt. % and wherein the weight ratio between the Bi.sub.2O.sub.3 and alcohol ranges between 3:1 and 0.5:1.

20. A laser markable composition, comprising: 95-99.9 wt. % of a matrix polymer and 0.1-5 wt. % of a laser marking additive comprising a bismuth compound and an alcohol, wherein Bi.sub.2O.sub.3 is used as the bismuth compound and wherein the alcohol has a melting temperature of at least 40 C., based on the total weight of the laser markable composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention relates to the laser marking additive, to the use of the laser marking additive, to masterbatches containing the laser marking additive and to polymer blends containing the masterbatch or the laser marking additive.

(2) Bismuth Compound

(3) The bismuth compound should be able to absorb laser light. Examples of suitable bismuth compounds are oxides, hydroxides, sulphides, sulphates and phosphates of bismuth. Examples of bismuth compounds are BiONO.sub.3, Bi.sub.2O.sub.2CO.sub.3, BiOOH, Bi.sub.2O.sub.3, BiOC.sub.3H.sub.5O.sub.7, Bi(C.sub.7H.sub.5O.sub.2).sub.3, BiPO.sub.4, Bi.sub.2(SO.sub.4).sub.3 and Bi-citrate. Preferably Bi.sub.2O.sub.3 is used as bismuth compound, because Bi.sub.2O.sub.3 is halogen-free, has a light color and gives a high contrast at the highest marking speed compared to other bismuth compounds.

(4) The amount of Bi-compound in the laser marking additive ranges between 0.01 wt % and 99.99 wt. %, preferably between 1 and 99 wt. % of the laser marking additive. Preferably the amount of Bismuth ranges between 25 and 75 wt. % in the laser marking additive.

(5) Alcohol

(6) The lasermarking additive comprises an alcohol. Preferably the alcohol is a polyol.

(7) Preferably the alcohol is a solid at room temperature, more preferably having a melting temperature of at least 40 C., or preferably at least 80 C. More preferably the alcohol has a melting temperature (Tm) of at least 100 C., 150 C. or at least 200 C., 220 or 240 C. In a most preferred embodiment, the melting temperature of the alcohol is preferably between 0 and 50 C. above the processing temperature of the matrix polymer in the step of making a laser markable composition.

(8) Without wanting to be bound by any theory, it is believed that the alcohol carbonizes during irradiation of the laser marking additive and improves the laser marking of a matrix material. A polyol is a compound comprising two or more hydroxyl (OH) groups. Examples of alcohols are tetradecanol, hexadecanol, (also called cetyl and lauryl alcohol). Examples of polyols are butyl ethyl propanediol, hexanediol, methyl propanediol, neopentyl glycol, trimethylpentanediol, trimethylolpropane, glycerine, di-trimethylolpropane, pentaerythritol, di-pentaerythritol, difunctional propoxylated polyol, trifunctional ethoxylated polyol, tetrafunctional ethoxylated polyol, dimethylolpropionic acid, trimethyolpropane monoallyl ether, monoethylene glycol, diethyleneglycol and polyethylene glycol.

(9) Preferably, the polyol is chosen from the group consisting of pentaerythritol, dipentaerythritol, 1,1,1-tris(hydroxymethyl) ethane (or 2-Hydroxymethyl-2-methyl-1,3-propanediol), 2,2,2,2,tetrakis(hydroxymethyl)-3,3oxydipropan-1-ol, di(trimethylolpropane).

(10) The amount of polyol in the laser marking additive ranges between 99.99 and 0.01 wt. %, relative to the total of the laser marking additive, preferably between 99 and 1 wt. %.

(11) In the laser marking additive the weight ratio of the light-absorbing bismuth compound and the polyol preferably is between 1000:1 and 1:1000, more preferably between 10:1 and 1:10. To choose a suitable weight ratio the person skilled in the art will be guided by the desired amount of the additive composition in the matrix polymer.

(12) In a preferred embodiment, the weight ratio between Bi.sub.2O.sub.3 and the alcohol having a melting temperature Tm of at least 40 C., preferably at least 80 C. is between 3:1 and 1.5:1.

(13) In a preferred embodiment, the Bi.sub.2O.sub.3 and the alcohol are mixed as a physical blend of two individual components.

(14) The laser marking additive, comprising a bismuth compound (preferably bismuth oxide) and an alcohol (preferably a polyol), can be added directly to a matrix polymer, or can be formed into a master batch. The masterbatch can be added to a matrix polymer. The combination of the matrix polymer with the laser marking additive is a laser markable composition.

(15) Carrier Material

(16) The laser marking additive may comprise a carrier material. The carrier material disperses and dilutes the additive composition and facilitates the dispersion of the additive composition in a matrix polymer.

(17) The carrier material is a liquid or a polymeric material.

(18) In principle any liquid can be applied that can disperse the Bi-compound. Preferably the boiling point of the liquid is higher than the extrusion temperature of the matrix polymer. Examples of liquids are oils, fatty acids, monomers like for example MMA, dispersants and the like.

(19) According to an embodiment the carrier material is an oil, preferably a natural oil is applied. For example, the oil is linseed oil, olive oil, or a paraffinic oil.

(20) According to an embodiment the carrier material is a fatty acid. A fatty acid is a carboxylic acid with a long aliphatic chain, which can be either saturated or unsaturated. The fatty acids preferably have 4-28 carbon atoms in the aliphatic chain. Examples of fatty acids are palmitoleic acid, oleic acid, -linoleic acid, arachidonic acid, lauric acid, palmitic acid, stearic acid and the like.

(21) According to a further embodiment the carrier material is a polymeric material. Preferably, the polymeric material is polyethylenemethylacrylate (EMA) or polyethylenevinylacetate (EVA).

(22) In an embodiment the Bi-compound and the polyol are encapsulated in the carrier material in order to be dispersed as particles in the matrix polymer.

(23) The invention also relates to a masterbatch comprising between 0.01 and 70 wt. % of the laser marking additive, wherein preferably the weight ratio between bismuth oxide and alcohol ranges between 3:1 and 0.5:1. The master batch can further contain between 30 and 99.99 wt. % of a liquid or polymer.

(24) Example of the liquid can be for example a liquid colorant, wherein a masterbatch is obtained which is a colorant and which can be a laser marking additive at the same time.

(25) Example of the polymer which can be present in the masterbatch can be any polymer, like a polyolefin, a polyester, a polycarbonate, an elastomeric material, a polystyrene, ABS and the like.

(26) Mixing of the laser marking additive and a matrix polymer can be performed in different ways. A preferred way is to extrude the matrix polymer with the laser marking additive.

(27) Both the bismuth compound and polyol can be added directly (and independently) to the extruder while also feeding the matrix polymer to the extruder, and together be extruded into an article.

(28) The bismuth compound and polyol can also first be mixed together and as a mixture be added to a matrix polymer in (for example) an extruder.

(29) Also the bismuth compound and polyol can be added to a carrier polymer in an extruder to make a masterbatch which can be blended in a next step with a matrix material to make a laser markable composition.

(30) It is possible that the amount of light absorbing bismuth compound is as low as 500 ppm in the laser-markable composition to obtain good resolution, or even as low as 250 ppm. Especially in transparent carrier polymers, the amount of laser marking additive ranges preferably between 0.02 and 0.2 wt. %, or between 0.03 and 0.1 wt. %.

(31) Preferably, the amount of light absorbing bismuth compound in an opaque laser-markable composition is between 0.05 to 2 wt. %, based on the total weight of the composition. This gives good laser-marking performance while retaining the mechanical properties of the lasermarking composition.

(32) Composition

(33) The invention is further directed to a laser markable composition comprising 95-99.9 wt. % of a matrix polymer and 0.1-5 wt. % of the laser marking additive, based on the total weight of the laser markable composition. The laser markable composition can be prepared by mixing the laser marking composition with the matrix polymer, for example, in an extruder.

(34) The matrix polymer can be any type of polymer such as plastics, binders and resins. Suitable matrix polymers are thermoplastic and thermosetting plastics such as polyethylene (PE), polypropylene (PP), polyester, polyether, polyphenylene ether, polyacrylate, polyurethane (PU), polyoxymethylene (POM), polymethacrylate, polymethylmethacrylate (PMMA), polyvinyl acetate (PVAC), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), ABS graft polymer, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polycarbonate (PC), polyether sulfones, polyether ketone, thermoplastic polyurethane (TPU), thermoplastic elastomers (TPE), epoxy resin (EP), silicon resin (SI), unsaturated polyester resin (UP), phenolic formaldehyde resin (PF), urea formaldehyde resin (UF), melamine resin (MF) and copolymers thereof and/or mixtures thereof. The polymer can also be a copolymer or block copolymer.

(35) Preferably, the matrix polymer is a polyolefin, more preferably ethylene or propylene homo- or copolymers.

(36) Conventional and suitable additives may be present in the matrix polymer.

(37) In the laser markable composition 95-99.9 wt. % of a matrix polymer based on the total weight of the laser markable composition, can be present, preferably, 96-99 wt. %, more preferably 97-98 wt. %.

(38) In the laser markable composition 0.1-5 wt. % of the laser marking additive, based on the total weight of the laser markable composition, can be present, preferably, 0.3-4 wt. %, more preferably 0.5-3 wt. %.

(39) The amount of Bi-compound in the laser markable composition preferably ranges between 0.01 wt. % to 5 wt. %, more preferably between 0.02 wt. % to 3 wt. %, or between 0.3 and 1 wt. %.

(40) Use

(41) The invention is further directed to the use of a laser markable composition for the preparation of articles that can be marked by treating the article with laser light.

(42) Article

(43) The invention is further directed to an article or part of an article comprising a laser markable composition. The laser markable compositions according to the present invention can, for example, be used in any sector where conventional printing processes have hitherto been used to inscribe or mark matrix polymers. Almost any plastic article or part of an article can be obtained in a laser markable or laser writable form. Any kind of article made of a matrix polymer can be provided with functional data, barcodes, logos, graphics, pictures and identification codes. Furthermore, they can find application in the medical equipment such as tubes, containers for tissue samples or fluids, syringes, pots, covers, catheters, automotive business such as fluid containers, cabling, components, telecom and E&E fields such as GSM fronts, keyboards, micro circuit breakers, security and identification applications such as credit cards, identification cards, animal identification tags, labels, security straps, advertising applications such as logos, decoration on corks, golf balls, promotional articles, packaging such as mono- and multilayer films, bottles, caps and closures including but not limited to screw caps for bottles, tamper proof caps and synthetic corks.

(44) For example, articles made from the laser markable composition of the invention may be used in the electrical industry, electronic industry or motor vehicle industry. With the aid of laser light, it is possible to produce identification markings or inscription markings even at locations to which it is difficult to gain access, for example, on cables, lines, decorative strips, or functional parts in the heating, ventilation or cooling sector, or on switches, plugs, levers or handles which consist of the plastics of the invention. It is also possible for the polymer system of the invention to be used for packaging in the food and drinks sector, or in the toy sector. The markings on the packaging are wipe- and scratch-resistant, resistant to downstream sterilization processes, and can be applied by the marking process in a manner which is hygienically clean. Complete label motifs can be applied durably to the packaging for a reusable system. Another important application sector for laser inscription is that of the marking of plastics to produce individual identification marking for animals, known as cattle tags or ear tags. The information specifically associated with the animal is stored via a barcode system. It can be called up again when required with the aid of a scanner. The inscription must be highly durable since some tags remain on the animals for a number of years.

(45) The invention further relates to a process for making a laser markable masterbatch comprising the steps of

(46) Providing Bi.sub.2O.sub.3 and an alcohol (preferably polyol) in powder form

(47) Providing a Polymer

(48) Extruding the polymer while adding the Bi.sub.2O.sub.3 and polyol to obtain a laser markable composition.

(49) In this process Bi.sub.2O.sub.3 can be present as such or as a Bi.sub.2O.sub.3 masterbatch. Also the polyol can be added as pure compound or as a polyol masterbatch.

(50) Use can be made of the masterbatch for preparing the laser markable composition.

(51) The laser markable composition can be prepared in different ways.

(52) The polymer and solid Bi.sub.2O.sub.3 with solid alcohol can be directly added to an extruder to make the laser markable composition.

(53) Alternatively, a liquid masterbatch can be prepared by mixing a liquid (like for example a coloring masterbatch) with the Bi.sub.2O.sub.3 and polyol, which mixture can be added to a polymer in an extrusion step.

(54) In yet another embodiment, the masterbatch containing Bi.sub.2O.sub.3 with a polyol can be added to a polymer in an extrusion step.

(55) Lasermarking

(56) The invention is further directed to the lasermarking of an article comprising the laser markable composition as described above, wherein parts of the laser markable composition are treated with light from a laser.

(57) The laser marking additive is capable of absorbing laser light of a certain wavelength. In practice this wavelength lies between 157 nm and 10600 nm, the customary wavelength range of lasers. If lasers with larger or smaller wavelengths become available, other absorbers may also be considered for application in the additive according to the invention. Examples of such lasers working in the said area are CO.sub.2 lasers (10.6 micrometer), Nd:YAG lasers, vanadate (1064, 532, 355, 266 nm), and excimer lasers of the following wavelengths: F.sub.2 (157 nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm) and XeF (351 nm), FAYb fiber lasers, diode lasers and diode array lasers. Preferably Nd:YAG, vanadate or fiber (1064 or 532 nm) lasers and CO.sub.2 lasers are used since these types work in a wavelength range which is very suitable for the induction of thermal processes that are applied for marking purposes.

(58) The energy densities of the lasers used are generally within the range from 0.3 mJ/cm.sup.2 to 50 J/cm.sup.2, preferably from 0.3 mJ/cm.sup.2 to 10 J/cm.sup.2.

(59) When pulsed lasers are used, the pulse frequency is generally within the range from 1 to 150 kHz. Corresponding lasers which can be used in the process of the invention are commercially available. The inscription with the laser is preferably carried out by introducing the article into the ray path of a CO.sub.2 laser (10.6 m) or a pulsed laser, preferably of an Nd, YAG, vanadat or fiber laser.

(60) It is noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

(61) It is further noted that the term comprising does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

(62) The invention is now elucidated by way of the following examples, without however being limited thereto.

EXAMPLES

(63) Materials:

(64) Bismuth Compound

(65) Bismuth oxide (Bi.sub.2O.sub.3)Varistor grade

(66) Polyol

(67) P1: Dipentaerythritol of Sigma Aldrich

(68) P2: Pentaerythritol of Sigma Aldrich

(69) P3: 1,1,1-tris(hydroxymethyl)ethane of Sigma Aldrich

(70) P4: PEG: Pluriol E600 NF of BASF

(71) Carrier Material

(72) EMA: Elvaloy AC 12024S of DuPont

(73) Matrix Polymers

(74) MP1: Queo 0203 of Borealis

(75) MP2: TPU 795 of BASF

(76) MP3: Plurell GA 7760 Borealis (MDPE)

(77) Production Process:

(78) Bi2O3 and EMA have been added to an extruder to prepare a blend. The Bi-EMA blend has been added together with a polyol and matrix polymer to an extruder and extruded at a temperature of 160 C. After extrusion, a testpiece has been prepared (at 220 C.) that has been used for laser writing. Laser writing has been performed with a Nd:YAG laser (1064 nm), with a frequency of 28 kHz and a velocity of 2190 mm/sec

(79) The distance between the lines (hatch) was 0.076 mm.

(80) Color measurement. The L value of the color after laser writing has been determined in the La/b color space, with the aid of a Konica Minolta spectrometer CM-3600A, against a black and white background. L values are indicative for the amount of color development after laser marking: a high L value indicates a rather weak reaction to laser light, a low value indicates a dark reaction and more response to the laser.

(81) Lasermarking Results:

(82) Lasermarking result judged by visual inspection of the samples. =very poor lasermarking, contrast very low =poor lasermarking, contrast low +=lasermarking possible, contrast low ++=lasermarking possible, contrast reasonable +++=lasermarking good, contrast reasonable ++++=lasermarking good, contrast good +++++=lasermarking excellent dark, contrast excellent

(83) Stability results:_(when exposed to ambient light at room temperature)_ =very fast grey/black coloring =fast grey/black coloring ++=almost no grey coloring +++=stable color, after months no color change

(84) Test Results:

(85) TABLE-US-00001 TABLE 1 Light MP1 Bi2O3 EMA P1 P2 P3 P4 P5 P6 Laser- Stability Experiment (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) marking L* Marking 20 C. A (ref) 99.7 0.18 0.12 67.1 ++ +++ B (ref) 99.1 0.54 0.36 63 +++ +++ 1 99.7 0.2 0 0.1 50.1 ++++ +++ 2 99.4 0.2 0 0.1 0.3 47.3 +++++ 3 99.01 0.54 0.36 0.09 58 ++++ +++ 4 99.01 0.54 0.36 0.09 48 +++++ 5 99.01 0.54 0.36 0.09 44 +++++ 6 99.01 0.54 0.36 0.09 <50 +++++ 7 99.01 0.54 0.36 0.09 <60 ++++ ++ P1: dipentaerythritol Mp = 215-218 C. P2: pentaerythritol Mp = 253-258 C. P3: 1,1,1-tris(hydroxymethyl)ethane, (2-Hydroxymethyl-2-methyl-1,3-propanediol) Mp 190-200 C. P4: PEG 600 (liquid at room temperature) P5: 1,2 propylene glycol (liquid at room temperature) P6: di(trimethylolpropane) Mp 108-111 C.

(86) It can be seen from table 1 that a Bi.sub.2O.sub.3/EMA mixture shows some laser marking activity. This activity is however increased by polyols P1-P4, or combinations of polyols (example 2). The stability against discoloration (from a white resin to a grey or black resin over time, due to exposure of the sample to ambient light at room temperature) of the liquid alcohols (PEG, MEG) is insufficient.

(87) TABLE-US-00002 TABLE 2 Laser Titaan Eartag mark- Exper- MP2 MP3 Bi.sub.2O.sub.3 P1 dioxide yellow ing iment wt. % wt. % wt. % wt. % wt. % wt. % result C (ref) 100.00 6 98.70 0.20 0.10 1.00 +++++ D (ref) 100.00 7 98.90 0.20 0.10 0.80 +++++

(88) Table 2 shows that other matrix polymers like MP2 and MP3 also can be activated by the new bismuth laser writing additive, while the polymers without additive do not show any response to a laser.