WO2023039743A1

WO2023039743A1 - Retroreflective sheeting for digital cutting

Info

Publication number: WO2023039743A1
Application number: PCT/CN2021/118464
Authority: WO
Inventors: Weiwei Gao; Fan GAO
Original assignee: 3M Innovative Properties Company
Priority date: 2021-09-15
Filing date: 2021-09-15
Publication date: 2023-03-23

Abstract

A retroreflective sheeting for signage in which the logo or message to be displayed is created using digital cutting operations. The retroreflective sheeting comprises in the following order immediately adjacent to each other: a retroreflective layer, a heat-sensitive release layer comprising both a urethane polymer and a methacrylic copolymer, a crosslinked acrylic pressure sensitive adhesive layer, a transparent, colored film layer.

Description

RETROREFLECTIVE SHEETING FOR DIGITAL CUTTING

The present application relates to a retroreflective sheeting useful for signage in which the logo or message to be displayed is created using digital cutting operations.

BACKGROUND

Reflective films are often used in the production of traffic signs because they reflect light in the direction of incidence, making them well-recognizable at night. Typically, traffic signs currently in use are made by applying film cut-outs of words or logos in different color on the surface of the base film. For example, for a road sign where a green reflective film is used as the base film, a white reflective film is used to create a desired pattern or text (words or characters) , which is then pasted on the green reflective film to obtain the final sign. In another example, the colors are reversed and the white reflective film may be used as the base film and the green transparent film may be used for the logo or text message. However, the method described is cumbersome, and requires high professional skills on operator who creates the logo or text and then applies them to the base film. For instance, when the logo or text cut-outs are applied to the base retroreflective film, if the operation is improper, the logo or text pieces may be deformed, wrinkled, or placed on a crooked manner, among other defects.

Additionally, the inventors have observed that certain existing retroreflective sheeting may delaminate at low temperatures and the outermost layer may scratch easily during handling and installation, leading to reduced retroreflectivity.

Accordingly, one goal of the present disclosure is to provide sign retroreflective film suitable for digital cutting with excellent reflective brightness, long service life, and maintaining suitable adhesive properties at low temperatures.

SUMMARY

According to an aspect of the disclosure, we provide retroreflective sheeting comprising, in the following order, a retroreflecting layer, a heat-sensitive release layer, a pressure sensitive adhesive (PSA) layer, and a colored transparent layer. Optionally, a reinforcing layer may be present in the PSA layer and the colored transparent layer. When the reinforcing layer is present, then an additional adhesive layer to bond the reinforcing layer to the colored transparent layer may be present. Throughout this disclosure, the terms retroreflective sheeting and retroreflective film are used interchangeably.

Specifically, in one embodiment, the disclosure is directed to a retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

b) a heat-sensitive release layer comprising both a urethane polymer and a methacrylic copolymer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

i. an acrylic adhesive having a number average molecular weight from 20,000 to 100,000,

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker, and

d) a transparent, colored film layer.

In another embodiment, the disclosure is directed to a retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker,

d) a reinforcing layer,

e) a polyurethane layer, and

f) a transparent, colored acrylic layer.

All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently in this application and are not meant to exclude a reasonable interpretation of those terms in the context of the present disclosure.

Unless otherwise indicated, all numbers in the description and the claims expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about. ” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviations found in their respective testing measurements.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. a range from 1 to 5 includes, for instance, 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singular forms “a” , “an” , and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

The term “polymer” will be understood to include polymers, copolymers (e.g., polymers formed using two or more different monomers) , oligomers and combinations thereof, as well as polymers, oligomers, or copolymers that can be formed in a miscible blend. Polymers referred to in this disclosure include those polymerized in-situ from monomers as well as those materials that exist in a polymeric form independent of the processes used to create them herein.

The term “adjacent” refers to the relative position of two elements, such as, for example, two layers, that are close to each other and may or may not be necessarily in contact with each other or that may have one or more layers separating the two elements as understood by the context in which “adjacent” appears.

The term “immediately adjacent” refers to the relative position of two elements, such as, for example, two layers, that are next to each other and in contact with each other and have no intermediate layers separating the two elements. The term “immediately adjacent, ” however, encompasses situations where one or both elements (e.g., layers) have been treated with a primer, or whose surface has been modified to affect the properties thereof, such as etching, embossing, etc., or has been modified by surface treatments, such as corona or plasma treatment, etc. for example, to improve adhesion.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic cross-sectional view of a retroreflective film according to an embodiment of the present disclosure.

Element	Description
1	Reflective layer
2	Heat-sensitive release layer
3	Pressure sensitive adhesive layer
4	Optional reinforcing layer
5	Optional adhesive layer
6	Colored film layer

Figure 2 is a schematic cross-sectional view of a retroreflective film according to an embodiment of the present disclosure, which shows how the heat sensitive release layer aids in removing the colored film layer (transparent in preferred embodiments) .

In Figure 1,

layers

4 and 5 are optional. Additionally, layer 5 (reinforcing layer) may be present with or without the adhesive layer 4.

Figure 1 illustrates an embodiment of the present disclosure. However, that embodiment is not intended to limit the scope in any way.

DETAILED DESCRIPTION

In one embodiment the retroreflective film comprises a base film (e.g., a retroreflecting layer) and a transparent, colored acrylic layer in which the colored acrylic layer is weakly adhered to the base layer via a heat-sensitive release layer and a pressure sensitive adhesive (PSA) layer. In this embodiment, typically, a logo or text is cut on the colored acrylic layer. Once the logo or text are removed from the sheeting, because of the low adhesion of the colored acrylic layer to the base layer, the base layer is exposed creating a sign in which the logo or text are shown in the color of the base layer. Afterwards, the adhesion between the colored acrylic layer and the base film is enhanced by heating, so that the colored acrylic layer is permanently bonded to the base film.

In one embodiment, the disclosure is directed to a retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

iv. an acrylic adhesive having a number average molecular weight from 20,000 to 100,000,

v. at least one plasticizer comprising an ester moiety,

vi. a crosslinker, and

d) a transparent, colored film layer.

In another embodiment, the retroreflective sheeting further comprises a reinforcing layer immediate adjacent both the pressure sensitive adhesive layer and the transparent, colored film layer. In other embodiments, when the reinforcing layer is present, the retroreflective sheeting further comprises an adhesive layer immediate adjacent both the reinforcing layer and the transparent, colored film layer.

Heat-Sensitive Release Layer

Typically, the heat-sensitive release layer has low adhesion (low peel force) towards the PSA layer before the logo or text is scored on the colored film layer. However, once the scored logo or text is peeled off and the retroreflective sheeting is subjected to a heat treatment, the bond between the colored film layer and the retroreflective layer is strong and stable.

The scoring of the logo or text on the colored film layer may be accomplished by using an engraving method. For example, a laser engraving instrument may engrave characters or patterns on the colored film layer as needed. Subsequently, the undesired portion of the engraved logo or text is completely peeled off due to the low peel force on the heat-sensitive release layer. Finally, the retroreflective sheeting is heated to eliminate the release effect of the heat-sensitive release layer, and pressure sensitive adhesive layer is crosslinked and cured to enhance the adhesion between the colored film layer and the retroreflective layer.

According to some preferred embodiments, the heat-sensitive release layer comprises both a polyurethane-type heat-sensitive release component and a methacrylic copolymer. The heat-sensitive release layer is typically obtained by coating a solution having the polyurethane-type heat-sensitive release agent and the methacrylic copolymer on the retroreflective layer, followed by subsequent drying. In certain preferred embodiments, the polyurethane type heat-sensitive release layer is formed from the reaction product of partially hydrolyzed polyvinyl alcohol and octadecyl isocyanate.

According to certain preferred embodiments, the reaction product of the partially hydrolyzed polyvinyl alcohol and octadecyl isocyanate has a glass transition temperature in the range of from 30 ℃ to 70℃. According to certain preferred embodiments, the partially hydrolyzed polyvinyl alcohol has a degree of hydrolysis in the range of from 30%to 99%. According to certain preferred embodiments, the partially hydrolyzed polyvinyl alcohol has a number average degree of polymerization in the range from 500 to 2,500 (for example about 500, about 1700, about 2500, and ranges in between each of these values) .

According to certain preferred embodiments, in the preparation of the reaction product of the partially hydrolyzed polyvinyl alcohol with octadecyl isocyanate, the molar ratio of partially hydrolyzed polyvinyl alcohol to octadecyl isocyanate is in the range of 1 to 1: 0.3.

According to some embodiments, the methacrylic copolymer comprises homopolymers of methyl methacrylate (MMA) , ethyl methacrylate (EMA) , butyl methacrylate (BMA) , styrene, their copolymers with other acrylic monomers, and combinations thereof. The other acrylic monomers include both acrylate and methacrylate monomers. In certain preferred embodiments, the methacrylic copolymer comprises MMA/BMA polymers, EMA homopolymers, styrene/BMA polymers, and combinations thereof, preferably chosen from MMA/BMA polymers and EMA homopolymers, and more preferably chosen from MMA/BMA polymers.

In other embodiments, the ratio of the urethane polymer to the methacrylic copolymer is from 1: 4 to 4: 1 on a dry basis, preferably from 2: 3 to 3: 2 on a dry basis.

In some embodiments, the methacrylic copolymer has a glass transition temperature greater than 60℃, for instance from 60℃ to 110℃. In other embodiments, the methacrylic copolymer a molecular weight of greater than 10,000 Da, for example from 10,000 Da to 200,000 Da. In certain preferred embodiments, the methacrylic copolymer has a glass transition temperature from 60℃ to 110℃ and a molecular weight from 10,000 Da to 200,000 Da.

The presence of the methacrylic copolymer improves the abrasion resistance of the heat-sensitive release layer, which remains exposed when the logo or text have been peeled off. The inventors observed that the exposed heat-sensitive release layer was easily scratched or lost clarity, becoming hazy and reducing retroreflectivity. The inventors surprisingly determined that the addition of the methacrylic copolymer as described above improved the abrasion resistance of the heat-sensitive release layer, while at the same time maintaining its low adhesion properties before heat treatment and being compatible without affecting its heat response.

Accordingly, in some embodiments, the reflectance of the retroreflective sheeting retained after the abrasion resistance test described in the Examples section is greater than 80%, for example from 80%to 100%. In other embodiments, the reflectance retained after the abrasion resistance test is greater than 85%, for example from 85%to 100%, or from 85%to 95%. In other embodiments, the reflectance retained after the abrasion resistance test is greater than 90%, for example from 90%to 100%, or from 90%to 95%.

According to some preferred embodiments, the thickness of the heat-sensitive release layer is in the range of 0.2 to 5 μm. In other embodiments, the thickness of the heat-sensitive release layer is from 0.5 to 5 μm, from 0.5 to 4 μm, from 1 to 4 μm, from 1 to 3 μm, and preferably from 1 to 2 μm.

By using the above process with the polyurethane-type thermosensitive release agent mentioned previously and controlling the thickness thereof within a suitable range as described above, the release effect of the heat-sensitive release layer is eliminated under a relatively low-temperature heat treatment, such as, for example, below 120 ℃ for a short period of time (for example, 10 seconds to 10 minutes) or by placing the construction into a 70℃ oven for 30 min.

Pressure Sensitive Adhesive Layer (PSA layer)

The pressure sensitive adhesive layer bonds the colored film layer to the heat-sensitive release layer. However, when an optional reinforcing layer is present, then the pressure sensitive adhesive layer bonds the reinforcing layer to the heat sensitive release layer. In a preferred embodiment, the pressure sensitive adhesive layer comprises an acrylic pressure sensitive adhesive.

In some embodiments, the acrylic pressure sensitive adhesive is selected from one or more of 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer and isooctyl acrylate/acrylic acid copolymer. According to some embodiments, the 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer and the isooctyl acrylate/acrylic acid copolymer have a number average molecular weight of from 200,000 to 1,000,000, preferably from 400,000 to 600,000.

According to some embodiments, the 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer and the isooctyl acrylate make up to 100%by weight of the pressure sensitive adhesive layer, based on the total weight of the pressure sensitive adhesive layer. The weight percentage of the acrylic polymer unit in the acrylic copolymer is in the range of from 3%by weight to 15%by weight, more preferably from 8%by weight to 12%by weight.

In other embodiments, the acrylic pressure-sensitive adhesive has a glass transition temperature in the range from -30 ℃ to -60 ℃, more preferably from -40 ℃ to -50 ℃. According to some embodiments, the pressure sensitive adhesive layer has a thickness in the range from 5 to 100 μm, preferably from 15 to 50 μm, and more preferably 25 to 30 μm.

In some embodiments, the acrylic pressure-sensitive adhesive comprises a plasticizer and a crosslinker, wherein the plasticizer and the crosslinker are different from each other. In certain embodiments, the plasticizer is an ester. In other embodiments, the plasticizer ranges from 5-20%by weight considering the total weight of the acrylic pressure sensitive adhesive layer to be 100%.

In some embodiments, the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl adipate, PEG ester, and combinations thereof. In certain preferred embodiments, the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl hexanedioate, polyethylene glycol ethyl ester, and combinations thereof. In other embodiments, the plasticizer comprises a cyclic moiety.

In some embodiments, the crosslinker is chosen from multi-functional aziridines, multi-functional isocyanate, a metal salt, and combinations thereof. In certain preferred embodiments, the crosslinker is chosen from multi-functional aziridines. The crosslinker may be present in a range from 0 %to 0.5 %on a weight basis, where the total weight of the pressure sensitive adhesive layer is 100%. In some preferred embodiments, crosslinker is present in a range from 0.05 %to 0.2 %by weight.

Specific examples of the acrylic pressure-sensitive adhesive according to the present invention include 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer having a copolymerization ratio of 25: 70: 5 and isooctyl acrylate at a copolymerization ratio of 90: 10.

Colored Film Layer

The retroreflective sheeting comprises a transparent colored film layer, which in some preferred embodiments this layer is an acrylic layer and comprises a polymethyl methacrylate component. However, the colored film layer may also be made of polyethylene terephthalate, polyvinyl chloride, and polyurethane. Preferably, the colored film layer has excellent transparency to allow light to be retroreflected by the retroreflective layer.

Typically, the colored film layer has a color different from the color of the base layer (retroreflective layer) so that the pattern (logo or text) cutout on the colored film layer contrasts with the color of the retroreflective layer, which is now visible on the cutout portions. Accordingly, the colored film layer may comprise one or more pigments or dyes of different colors commonly employed in the art. The specific type of pigment or dye is not particularly limited as long as it enables the colored film layer to be effectively colored and does not significantly impair its transparency.

The colored film layer has a thickness in the range of 10μm to 150μm, preferably 50μm to 100μm, more preferably 50μm to 75μm. A non-limiting specific example of a colored film layer is a green polymethyl methacrylate film having a thickness of 75μm.

In some preferred embodiments, the colored film layer is the outermost layer of the retroreflective sheeting. Accordingly, the colored film layer has good weatherability and may comprise additives known in the art to aid against UV radiation, such as UV absorbers and hindered amine light stabilizers (HALS) .

Reinforcing Layer

A colored film layer made of polymethyl methacrylate may be brittle and relatively easy to tear. Therefore, depending on the use or specific application, the retroreflective sheeting of this disclosure may comprise a reinforcing layer to provide stability to the sheeting. Therefore, the reinforcing layer is optional and may be used when the requirements of the use of the retroreflective sheeting demand it.

The reinforcing layer may be immediately adjacent to the colored film layer or it may be bonded to the colored film layer by a separate adhesive layer, as shown in Figure 1.

The material of the reinforcing layer is not particularly limited as long as it can exert a sufficient reinforcing effect and is sufficiently transparent. Preferably, the reinforcing layer is chosen from polyethylene terephthalate layers, polyvinyl chloride layers, and polyurethane layers. In certain preferred embodiments, the reinforcing layer is a polyethylene terephthalate layer.

According to some embodiments, the reinforcing layer has a thickness in the range of 5μm to 100μm, preferably 10μm to 50μm, more preferably 25μm to 40μm.

Adhesive layer (e.g., polyurethane layer)

When the reinforcing layer is present in the retroreflective sheeting of this disclosure, an adhesive layer may be present between the reinforcing layer and the colored film layer. The specific type of adhesive is not particularly limited as long as the adhesive can firmly bond the reinforcing layer and the colored polymethyl methacrylate transparent layer. In some embodiments, the adhesive layer is a structural adhesive layer or a pressure sensitive adhesive layer. In certain preferred embodiments, the adhesive is preferably a two-component polyurethane adhesive such as Dow Chemical's ADCOTETM 811A + Catalyst 811B or ADCOTETM 545-80 + Catalyst F.

The thickness of the adhesive layer is in the range of 1μm to 20μm. When a structural adhesive layer is employed, the thickness of the structural adhesive layer is preferably in the range of 1μm to 3μm. If a pressure-sensitive adhesive is used, it is preferably an acrylic pressure-sensitive adhesive. Examples of the acrylic pressure-sensitive adhesive for adhering the reinforcing layer to the colored film layer include any of the PSA adhesives described above under the section “Pressure Sensitive Adhesive Layer. ”

When a pressure-sensitive adhesive is used, the thickness of the pressure-sensitive adhesive layer is preferably in the range of 5μm to 20μm.

Retroreflective Layer

The retroreflecting sheeting comprises a retroreflective layer bonded to the heat-sensitive release layer. There is no limitation on the specific type of the retroreflective layer, which may be a prism type or a glass bead type. In certain preferred embodiments, the retroreflective layer is a prismatic retroreflective layer. Non-limiting examples of the retroreflective layer include 3930 series retroreflective film and 4090 series retroreflective film, both produced by 3M Company.

The invention will now be described in greater detail with reference to the embodiments. It is to be understood that the description and examples are intended to be illustrative and not restrictive. The scope of the invention is defined by the appended claims.

EXEMPLARY EMBODIMENTS

The following embodiments are shown to further illustrate the retroreflective sheeting of the present disclosure, but should not be considered limiting the claimed subject matter.

1. A retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker,

d) a transparent, colored film layer.

2. A retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker,

d) a reinforcing layer,

e) a polyurethane layer, and

f) a transparent, colored acrylic layer.

3. The retroreflective sheeting according to any of the preceding claims, wherein the methacrylic copolymer has a glass transition temperature greater than 60C.

4. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer has a glass transition temperature from 60C to 110C.

5. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer a molecular weight of greater than 10,000 Da.

6. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer has a molecular weight from 10,000 Da to 200,000 Da.

7. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer has a glass transition temperature greater than 60C and a molecular weight of greater than 10,000 Da.

8. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer has a glass transition temperature from 60C to 110C and a molecular weight from 10,000 Da to200,000 Da.

9. The retroreflective sheeting according to any of the preceding embodiments, wherein the reflectance retained after the abrasion resistance test is greater than 80%.

10. The retroreflective sheeting according to any of the preceding embodiments, wherein the reflectance retained after the abrasion resistance test is from 80%to 100%.

11. The retroreflective sheeting according to any of the preceding embodiments, wherein the reflectance retained after the abrasion resistance test is greater than 90%.

12. The retroreflective sheeting according to any of the preceding embodiments, wherein the reflectance retained after the abrasion resistance test is from 90%to 100%.

13. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer comprises one or more types of methacrylic homopolymers and combinations thereof.

14. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer comprises homopolymers of methyl methacrylate (MMA) , ethyl methacrylate (EMA) , butyl methacrylate (BMA) , or their copolymers with other acrylic monomers.

15. The retroreflective sheeting according to claim 6, wherein the other acrylic monomers include acrylate or methacrylate monomers.

16. The retroreflective sheeting according to claim 6, wherein the methacrylic copolymer comprises MMA/BMA polymers, EMA homopolymers, styrene/BMA polymers, and combinations thereof.

17. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer is chosen from MMA/BMA polymers and EMA homopolymers, and combinations thereof.

18. The retroreflective sheeting according to any of the preceding embodiments, wherein the methacrylic copolymer is chosen from MMA/BMA polymers.

19. The retroreflective sheeting according to any of the preceding embodiments, wherein the ratio of the urethane polymer to the methacrylic copolymer is from 1: 4 to 4: 1 on a dry basis.

20. The retroreflective sheeting according to any of the preceding embodiments, wherein the ratio of the urethane polymer to the methacrylic copolymer is 2: 3 to 3: 2 on a dry basis.

21. The retroreflective sheeting according to any of the preceding embodiments, wherein the thickness of the heat-sensitive release layer is in the range from 0.2 to 5 μm.

22. The retroreflective sheeting according to any of the preceding embodiments, wherein the polyurethane of the heat-sensitive release layer comprises the reaction product of a partially hydrolyzed polyvinyl alcohol and octadecyl isocyanate and has a glass transition temperature in the range of 30℃ to 70℃.

23. The retroreflective sheeting according to any of the preceding embodiments, wherein the acrylic adhesive is chosen from one or more of 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer and isooctyl acrylate/acrylic acid copolymer.

24. The retroreflective sheeting according to claim Error! Reference source not found., wherein the weight percentage of acrylic acid block in 2-ethylhexyl acrylate/butyl acrylate/acrylic acid copolymer and isooctyl acrylate/acrylic acid copolymer ranges from 3%to 15%by weight when the total weight of the acrylic pressure sensitive adhesive layer is 100%.

25. The retroreflective sheeting according to any of the preceding embodiments, wherein the glass transition temperature of the acrylic pressure-sensitive adhesive is in the range of -30 ℃ to -60℃.

26. The retroreflective sheeting according to any of the preceding embodiments, wherein the plasticizer is an ester.

27. The retroreflective sheeting according to any of the preceding embodiments, wherein the plasticizer ranges from 5-20%by weight when the total weight of the acrylic pressure sensitive adhesive layer is 100%.

28. The retroreflective sheeting according to any of the preceding embodiments, wherein the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl adipate, polyethylene glycol ethyl ester, and combinations thereof.

29. The retroreflective sheeting according to any of the preceding embodiments, wherein the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl hexanedioate, and polyethylene glycol ethyl ester, and combinations thereof.

30. The retroreflective sheeting according to any of the preceding embodiments, wherein the crosslinker is chosen from multi-functional aziridines, multi-functional isocyanate, and a metal salt.

31. The retroreflective sheeting according to claim 8, wherein the thickness of the colored transparent layer is in the range from 10 to 150 μm.

32. The retroreflective sheeting according to any of the preceding embodiments, wherein the reinforcing layer is chosen from polyethylene terephthalate layers, polyvinyl chloride layers, and polyurethane layers.

33. The retroreflective sheeting according to any of the preceding embodiments, wherein the reinforcing layer has a thickness in the range from 10μm to 50μm.

34. A retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

b) a heat-sensitive release layer comprising the reaction product of partially hydrolyzed polyvinyl alcohol and octadecyl isocyanate and, copolymer of MMA and BMA

c) an acrylic pressure sensitive adhesive layer comprising:

ii. diisononyl cyclohexane-1-2-dicarboxylate,

iii. a plasticizer chosen from diisononyl hexanedioate and polyethylene glycol ethyl ester

iv. two-functional aziridine,

d) a reinforcing layer,

e) an adhesive layer, and

f) a transparent, colored acrylic layer.

35. A retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker,

d) a polyethylene terephthalate layer,

e) a polyurethane layer, and

f) a transparent, colored PMMA film.

EXAMPLES

Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

Materials Used in the Examples

Abbreviation	Description and Source
RD1543	Urethane LAB	5%Solid, 3M (St. Paul, USA)
NeoCryl B-890	MMA/BMA polymer, DSM (Shanghai, China)
NeoCryl B-813	EMA polymer, DSM (Shanghai, China)
NeoCryl B-851	BMA/Styrene, DSM (Shanghai, China)
NeoCryl B-842	BMA polymer, DSM (Shanghai, China)
B60H	PVB, Kurary (Toyko, Japan)
CAB381-0.1	CAB Eastman (Shanghai, China)
CSA2918	IOA/AA=90/10 adhesive, 3M (Shanghai, China)
RD1054	Crosslinker, 3M (St. Paul, USA)
DINCH	Diisononyl cyclohexane-1, 2-dicarboxylate plasticizer, BASF (Shanghai, China)

Abbreviation	Description and Source
DINA	Diisononyl adipate plasticizer, Kangjian (Shanghai, China)
UN610	Adipic acid polyester plasticizer, Liancheng, (Zhenjiang, China)
TegMeR 809	PEG 400 ester plasticizer, Hallstar (Shanghai, China)
BA	Butyl Acetate, Sinopharm (Shanghai, China)
EA	Ethyl Acetate, Sinopharm (Shanghai, China)
HIP3930	Reflective sheeting, 3M (Singapore)

Test Methods

Two types of tests were conducted on exemplary and comparative examples, they include an abrasion resistance test and a 180 degree peel strength test. Examples tested were 20cm by 8 cm and included a retroreflective layer, a pressure sensitive adhesive layer, a heat-sensitive release layer and a transparent film layer.

Abrasion Resistance Test

The purpose of the abrasion resistance test is to simulate abrasion that may occur on the heat-sensitive release layer, exposed because the transparent film and PSA layers were removed, during installation. The abrasion may be because of felted squeegees or other installation tools. Reflectance retention after installation of the invention is important.

The transparent film layer of each example was peeled away along with the PSA layer to expose the heat-sensitive release layer. Each example was then exposed to 70C for 2 hours followed by 25C, a hot temperature profile. Then a first reflectivity measurement was taken of each example using a 933 retroreflectance meter (Road Vista, California, USA) at 0.2/-4 degree angle. The examples were then abraded with a 3M wet abrasion scrub tester where a 3M 4100 super polish pad was placed atop and in contact with the heat-sensitive release layer and a 1 kg weight was placed on the pad to apply consistent pressure from the pad to the example surface. The pad was then pulled back and forth across the example for a total of 25 cycles. After the 25 cycles a second reflectivity measurement was taken at 0.2/-4 degree angle. The percent retained retroreflection is calculated by taking the absolute difference of the two reflectivity measurements divided by the first reflectivity measurement and multiplied by 100.

180 Degree Peel Strength Test

The purpose of the Peel Strength Test is to assess the peel strength required to remove waste transparent film layer material when weeding the invention and prior to heat treating the example which will bind the PSA layer to the heat-sensitive release layer, to assess the peel strength required to remove the transparent film layer after heat treating and under different environmental conditions, and potentially portions of the heat-sensitive release and PSA layers from the retroreflective layer. The peel strength prior to heat treating the example is representative of a sign being weeded as part of a sign installation. The peel strength after heat treating the example and under different conditions is representative of the example to survive certain environmental conditions.

Peel tests were conducted at three different temperature profiles: 25C, 70C, and –10C. Examples were placed in an environmental chamber at a specified temperature profile. After environmental conditioning the examples were peel tested in room temperature environment. The peel test conducted was a 180 degree peel test where the transparent film layer was peeled at a 30.48 cm/min rate on an

machine (Norwood, Massachusetts, USA) from which an average peel strength was calculated. Specified temperature profiles include: 25C for 24 hours (room temperature profile) , 70C for 2 hours followed by 25C for 2 hours (hot temperature profile) , and 70C for2 hours followed by –10C for 2 hours (cold temperature profile) . Cold temperature profile examples were tested on an I-Mass machine at a peel rate of 30.48cm/min in a –10C room environment. The peel strength is reported for each of the three temperature profiles in units of N/mm.

Preparatory Examples

Reflective sheeting with LAB coating preparation

A coating solution is made according to the formulation below table 1 by dissolving the resin BA to make a 20%solid solution. Seven samples representative of the invention and six comparative samples were prepared using the formulation, by weight, in Table 1. Each sample is approximately 20cm by 8cm. The prepared coating solution was coated with a 10um Mayer bar onto a retroreflective sheeting and a transparent colored layer placed on top of the coating layer. The sheeting with coating was then dried at 90C for 5 minutes. The coating layer corresponds to the heat release layer, element 2. These samples help test the effectiveness of the heat release layer before and after the release layer is heat treated. The transparent color layer needs to be able to be peeled and weeded from the retroreflective sheeting by sign installers before the sheeting is heat treated. Also, the transparent color layer needs to have a high peel strength after heat treating for sign durability.

Table 1. LAB coating Formulation by dry-weight (unit: g) coated on reflective sheeting

Examples

Samples	RD1543	B-890	B-813	B-851
#1	50	50	0	0
#2	60	40	0	0
#3	40	60	0	0
#4	20	80	0	0
#5	80	20	0	0
#6	50	0	50	0
#7	50	0	0	50

Comparative Examples

Samples	RD1543	B-890	B-842	B60H	CAB381-0.1
#C1	20	0	0	0	0
#C2	10	90	0	0	0
#C3	90	10	0	0	0
#C4	50	0	50	0	0
#C5	50	0	0	50	0
#C6	50	0	0	0	50

Topfilm preparation (Clear colored layer with reinforcing layer bonded with adhesive layer)

A 3M 100um PMMA film is laminated to a 25um PET a two-component polyurethane adhesive, Dow Chemical's ADCOTETM 811A + Catalyst 811B.

Topfilm with PSA layer preparation

Mixing adhesive, crosslinker and plasticizer together and adding EA to make a 40%solid solution.

Coating solution is made according to the formulation below.

The top film includes an adhesive layer (CSA2918 based, 40%solid in EA) . The adhesive was coated on the backside of the top film from the adhesive formulation in Table 2 by comma coater and then dried at 85C for 5min to form a 30um thickness adhesive layer.

Table 2. Adhesive Formulation by dry-weight (unit: g) coated on topfilm

Examples

Sample	CSA2918	RD1054	DINCH	DINA	TegMeR 809
#8	100	0.1	5	0	0
#9	100	0.1	10	0	0
#10	100	0.1	20	0	0
#11	100	0.1	0	10	0

Sample	CSA2918	RD1054	DINCH	DINA	TegMeR 809
#12	100	0.1	0	0	10
#13	100	0.1	5	5	0

Comparative Examples

Samples	CSA2918	RD1054	DINCH	UN610
#C7	100	0.1	0	0
#C8	100	0.1	40	0
#C9	100	0.1	0	20

Sheeting composite preparation

The PSA side of top film with PSA layer is laminated to the LAB side of reflective sheeting with LAB layer.

To prepare example #14-26 and #C10-18, applied adhesive formulation examples as shown in table 3, PSA layer column to PMMA/PET lamination film by comma coater and then dried at 85C for 5min to form a 30um thickness adhesive layer. And then laminated with examples as shown in table 3, heat-sensitive release layer column.

To prepare example #27, applied adhesive formulation used in sample #8 to PET film by comma coater and then dried at 85C for 5min to form a 30um thickness adhesive layer. And then laminated with example #1.

To prepare example #28, applied adhesive formulation used in sample #8 to PVC film by comma coater and then dried at 85C for 5min to form a 30um thickness adhesive layer. And then laminated with example #1.

Table 3. Example Construction by relative layers.

Application

After weeding off the letters, the image goes through a hot roller of 110C at the speed of 0.75m/min or staying a 70C oven for 30 mins.

The letters from example #14-28 can be easily weeded off before heat treatment. And the letters were firmly adhered to the reflective sheeting after heat treatment.

Results

1. LAB anti-abrasion performance

Examples #14-#20 and #C10-#C15 included a reflective sheeting with LAB coating which was then tested for LAB abrasion resistance test.

Table 4. Abrasion Resistance Test Results

2. Peel test performance

Examples #14-20 and #C10-18 included applied adhesive formulation example #11 to PMMA/PET lamination film by comma coater which was then dried at 85C for 5 minutes to form a 30um thickness adhesive layer. The resulting was then laminated with examples #1-7 and #C1-C6 to form the Examples for conducting the 180 Peel Strength Test.

Table 5. 180 degree Peel Strength Test Results: #14-#20 and #C10-#C15

The peel strength should be lower than 0.1N/mm at room temperature profile and more than 1N/mm at high temperature profile. The peel strength at room temperature profile should be lower than 0.1N/mm for ease of sheeting preparation when removing the waste, weeding, top film. The ideal reflectance retain percentage is more than 80%. Examples #14-20 showed good results in reflectance remain and peeling strength. The comparative example #C10 did not contain any hardening resin. Comparative example #C12 does not contain enough hardening resin (<20%) . Comparative example #C13 consisted hardening resin which Tg was lower than 60C. Comparative example #C14 and #C15 used the other kinds of hardening resins. As a result, #C10, 12, 13, 14, 15 showed lower retained reflectance. Comparative example #C11 contains too much hardening resin and contains too little LAB, resulting in a relative high release force at 25C.

3. Adhesive layer performance

To get example #21-26 and #C16-18, applied adhesive formulation examples #8-13 and #C7-9 to PMMA/PET lamination film by comma coater and then dried at 85C for 5min to form a 30um thickness adhesive layer. And then laminated with example #1.

Table 6. 180 Degree Peel Strength Test Results: Examples #21-#26 and #C16-#C18

The adhesive between the top film and reflective sheeting was expected to maintain bonding strength at low temperatures. The peel strength should be more than 0.5N/mm for cold temperature profile. Examples #21-26 showed strong adhesion performance. The comparative example #C16 did not contain any plasticizer which resulted in low adhesion. The content of plasticizer in comparative example #C17 was out of 5-20%, which showed a lower peel strength performance. Comparative example #C9 used polyester plasticizer, which resulted in poor peel strength performance as well.

Two additional examples were prepared where the top layer is single layer without a reinforcing layer or adhesive. The peel strength performance at both room and high temperature profiles for examples#27 and 28 is acceptable. The peel strength performance of PVC and PET is higher that PMMA.

Table 7. 180 Degree Peel Strength Test Results: #27-#28

Claims

A retroreflective sheeting comprising, in the following order immediately adjacent to each other:

a) a retroreflective layer,

b) a heat-sensitive release layer comprising both a urethane polymer and a methacrylic copolymer,

c) a crosslinked acrylic pressure sensitive adhesive layer comprising:

i.an acrylic adhesive having a number average molecular weight from 20,000 to 100,000,

ii. at least one plasticizer comprising an ester moiety,

iii. a crosslinker,

d) a transparent, colored film layer.
The retroreflective sheeting according to claim 1, wherein the methacrylic copolymer has a glass transition temperature from 60C to 110C.
The retroreflective sheeting according to claim 1, wherein the methacrylic copolymer has a molecular weight from 10,000 Da to 200,000 Da.
The retroreflective sheeting according to claim 1, wherein the reflectance retained after the abrasion resistance test is from 80%to 100%.
The retroreflective sheeting according to claim 1, wherein the methacrylic copolymer comprises one or more types of methacrylic homopolymers and combinations thereof.
The retroreflective sheeting according to claim 1, wherein the methacrylic copolymer comprises homopolymers of methyl methacrylate (MMA) , ethyl methacrylate (EMA) , butyl methacrylate (BMA) , or their copolymers with other acrylic monomers.
The retroreflective sheeting according to claim 6, wherein the other acrylic monomers include acrylate or methacrylate monomers.
The retroreflective sheeting according to claim 1, wherein the ratio of the urethane polymer to the methacrylic copolymer is from 1: 4 to 4: 1 on a dry basis.
The retroreflective sheeting according to claim 1, wherein the plasticizer is an ester.
The retroreflective sheeting according to claim 1, wherein the plasticizer ranges from 5-20%by weight when the total weight of the acrylic pressure sensitive adhesive layer is 100%.
The retroreflective sheeting according to claim 1, wherein the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl adipate, polyethylene glycol ethyl ester, and combinations thereof.
The retroreflective sheeting according to claim 1, wherein the plasticizer is chosen from diisononyl cyclohexane-1-2-dicarboxylate, diisononyl hexanedioate, and polyethylene glycol ethyl ester, and combinations thereof.
The retroreflective sheeting according to claim 1, wherein the crosslinker is chosen from multi-functional aziridines, multi-functional isocyanate, and a metal salt.